RSITY OF A BERTA LIBRARY 0 0004 8739 643 EDITION '• W r_. - ill "' MW 11 1 0X UBBIS Digitized by the Internet Archive in 2019 with funding from University of Alberta Libraries https://archive.org/details/exploringbiology00smit_0 HARCOURT, BRACE SCIENCE PROGRAM [ZE| Ui± Under the General Editorship of Paul F. Brandwein JUNIOR HIGH SCHOOL Science for Better Li ving Series YOU AND YOUR WORLD • Teacher’s Manual • Teaching Tests YOU AND YOUR INHERITANCE • Teacher’s Manual • Teaching Tests YOU AND SCIENCE • Experiences in Science (Workbook) • Teacher’s Manual • Teaching Tests, Forms A and B • Harbrace Science Filmstrips SCIENCE FOR BETTER LIVING: complete course • Teaching Tests • Film Guide • Workbook SENIOR HIGH SCHOOL EXPLORING BIOLOGY: the science of living things • Experiences in Biology (Workbook plus Laboratory Manual) • Teacher’s Manual • Teaching Tests, Forms A and B YOUR BIOLOGY • Teacher’s Manual (Including Unit Tests) YOUR HEALTH AND SAFETY • Teacher’s Manual • Teaching Tests LIFE GOES ON THE PHYSICAL WORLD: a course in physical science • Teacher’s Manual • Teaching Tests EXPLORING CHEMISTRY • Laboratory Manual in Chemistry • Experiences in Chemistry (Workbook plus Laboratory Manual) • Teacher’s Manual • Teaching Tests (In Preparation) EXPLORING PHYSICS • Laboratory Manual in Physics • Experiences in Physics (Workbook plus Laboratory Manual) • Teacher’s Manual • Teaching Tests, Forms A and B A SPECIAL BOOK FOR THE STUDENT HOW TO DO AN EXPERIMENT BOOKS FOR THE TEACHER TEACHING HIGH SCHOOL SCIENCE: a book of methods TEACHING HIGH SCHOOL SCIENCE: a sourcebook for the biological sciences TEACHING HIGH SCHOOL SCIENCE: a sourcebook for the physical sciences (In Preparation) THE GIFTED STUDENT AS FUTURE SCIENTIST /?'■ ■ y.fi: Fifth Edition The Science of Living Things Ella Thea Smith Under the General Editorship of Paul F. Brandwein Artwork by Helen Speiden and the staff of CARU Studios HARCOURT, BRACE AND COMPANY New York Chicago ABOUT THE AUTHOR ELLA THEA SMITH is a veteran teacher of high school biology from Salem, Ohio. She is the author of four previous editions of Exploring Biology and co-author of Your Biology, a textbook for the science-shy student. Her experience in teaching and textbook writing covers a span of more than twenty- five years. Currently she is serving as a member of the Biological Sciences Curriculum Study Group, a part of the Committee on Education and Professional Recruitment, American Institute of Biological Sciences. ABOUT THE GENERAL EDITOR PAUL F. BRANDWEIN is Science Consultant and General Editor for the Harcourt, Brace Science Program. For many years he was a teacher and Chairman of the Science Department at Forest Hills High School, Forest Hills, New York. More recently he has taught classes for science teachers at Columbia, Harvard, and Colorado College, and he has conducted science teaching seminars throughout the country. He is the author of several scientific papers and co-author of several films and textbooks, including three textbooks covering teaching methods and procedures in science. © 1959, by Harcourt, Brace and Company, Inc. All rights reserved. No part of this book may be reproduced in any form, by mimeograph or any other means, without permission in writing from the publisher. Acknowledgments for permissions and illustrations are covered by the present copyright for this edition as well as copyrights for i the 1938, 1942, 1943, 1949, 1952, and 1954 editions of Exploring Biology. [b • 5 ■ 59] Printed in the United States of America ACKNOWLEDGMENTS In the preparation of a complete introductory course in biology— a course rigorous in breadth, depth, and accuracy of content, yet easily paced in progression from one level of understanding to another— 1 have depended heavily upon the co-operation and constructive criticism of many leading teachers, professors, and research scientists. To the following I owe much more than a general statement of gratitude: Dr. George Gaylord Simpson, eminent paleontologist at the American Museum of Natural History and Professor at Columbia University, who read and criticized the third and fourth editions of Exploring Biology, thus giving me the benefit of his own unique ideas for a course in high school biology. Dr. Jerome Metzner, Chairman of the Department of Biological Sciences at Bronx High School of Science, New York City, who edited the entire manuscript for this textbook and suggested many valuable modifications in approach and subject matter. Dr. Claude E. Buxton, Professor of Psychology at Yale University, who read the first draft of Chapter 15 in this textbook and contributed valuable comments and ideas that were most helpful to me in revising the manuscript. Dr. Paul F. Brandwein, formerly Chairman of the Science Department at Forest Hills High School, Forest Hills, New York, and Instructor at Columbia University (now General Editor of science textbooks for Harcourt, Brace and Company), who worked with me closely throughout all stages in the preparation of this book. Teachers in many public school systems throughout the United States, and especially those in Detroit, Michigan, who have been most generous of their time in making helpful suggestions based upon use of the fourth edition of Exploring Biology. Dr. C. W. Mattison, U.S. Forest Service, who contributed valuable information on ecology, forestry, and conservation. When a new biology textbook is designed to reflect increasingly higher standards of teaching, the problem of securing increasingly finer illustrations— both artwork and photographs— proves understandably difficidt. In most cases, new research has been necessary, in conjunction with use of the best of existing primary references. In this connection, I owe much to the following people: Mrs. Helen Speiden, formerly a medical artist for the College of Physicians and Surgeons, Columbia University, who with Charles Halgren and his staff at CARU Studios prepared the carefully executed drawings for this textbook. The distinguished few authorities in their fields— such as the late Dr. Libbie Henrietta Hyman of the American Museum of Natural History— who have compiled in their published works a treasury of detailed artwork and technical information based upon life studies and deserving of consideration in correcting many errors and misconceptions that have persisted for years in biology textbooks. Mr. John Limbach of Triarch Botanical Products, Ripon, Wisconsin, who gave generously of both time and money to prepare slides ( from which photographs could be made ) of plant preparations not available commercially. Several research scientists, such as Dr. Don W. Fawcett at The Cornell University Medical College and Dr. H. J. Muller, Nobel prize-winning geneticist at the University of Indiana, who gave the necessary time to help locate unusual and unpublicized photographs to illustrate material not considered possible to illustrate successfully heretofore. Mr. Marion A. Cox, who provided many photographs and original drawings, some of which were used as source work for other drawings, and some of which appear as he prepared them. There is yet another task with which I received assistance. It is a pleasure to express my thanks to Mrs. Virginia Long of Phoenix, Arizona, for her hard work and co-operation in typing and retyping the manuscript of this book. E. T . S. Photo facing page by Ylla from Rapho Guillumette. Front cover photo: courtesy of Upjohn Company, Kala¬ mazoo, Michigan; back cover photo: T. C. Hsu, courtesy of C. M. Pomerat, University of Texas, Medical Branch; title page photo: Merrim from Monkmeyer; contents opening and closing photos: Herman Eisenbeiss, Munchen ; contents Unit cuts: 2, A. W. Schoof ; 3, New \ ork Zoological Society; 4, U.S.D.A.; 5. Donald C. Shoop; 6, Chas. Pfizer & Co., Inc.; 7, J. H. Tjio and T. T. Puck, “The Somatic Chromosomes of Man.’’ 1958, proceedings of the National Academy of Sciences (in the press); 8, Hal H. Harrison, frpn) National AucUibon Society. CHAPTER 1 CELLS-THE BUILDING UNITS 26 CELLS-Their Discovery-Examining Onionskin, Cheek Cells, and Frog’s Blood-Comparing Parts of Cells-Leaf Cells, Cork and Wood Cells, Human Blood Cells— TWO CELLS FROM ONE-The Nucleus and Its Parts- Mitosis and Mitotic Cell Division— TISSUES AND ORGANS— From Cells to Tissues-Tissues to Organs-Organs to Organisms-Organization: A Key¬ note of Life CHAPTER 2 CHEMICALS-THE BUILDING MATERIALS 50 PROTOPLASM— Interchangeable Parts-Substances Most Abundant in Pro- toplasm— COMPOSITION OF MATTER-What Is MatterP-Atoms and Their Make-up— Isotopes— Radioisotopes— CHEMICAL COMBINATIONS —Compounds in Protoplasm— Molecules— Chemical and Physical Changes -THE NATURE OF PROTOPLASM-Colloids: Sols and Gels-Nutrients in Protoplasm— Chemical Make-up of Nutrients— Oxidation in Living Cells —Chemical Changes in Protoplasm 6 CONTEXTS CHAPTER 3 LIFE PROCESSES-THE BASIC ACTIVITIES 74 MICROSCOPIC ANIMALS AT WORK-Life in a Drop of Water-Observ¬ ing What One-celled Animals Do— Kinds of One-celled Animals— Life Proc¬ esses in Ameba and Paramecium— MICROSCOPIC PLANTS AT WORK- Life Processes in Spirogyra— Pleurococcus— Diatoms— LARGER PLANTS AND ANIMALS AT WORK— A Flowering Plant— A Fish and How It Lives -ORGANIZATION AND LIFE-No Life Without Complex Organization —Viruses: Living or Nonliving?— Levels of Organization Variety Among Living Things -Plants CHAPTER 4 THE LOWLIER PLANTS 102 HOW BIOLOGISTS SORT AND CLASSIFY ORGANISMS-Classifying Plants— Scientific Names— Who Names New Species?— The Need for Scien¬ tific Names-THE FIRST PLANT PHYLUM— Thallophytes— LOWLY PLANTS WITH CHLOROPHYLL— Subphylum Algae-Blue-green Algae -Grass-green Algae — Organic Puzzles: Flagellates — Seaweeds: Red and Brown Algae— Importance of Algae to Man— LOWLY PLANTS WITHOUT CHLOROPHYLL— Subphylum Fungi— Molds— Mushrooms and Puffballs— Rusts, Smuts, and Mildews— Yeasts and Bacteria— Double Plants: Lichens— Importance of Fungi to Man-PLANT PHYLUM TWO: MOSSES AND LIVERWORTS— The Bryophytes— Mosses—' The Moss Plant Body— Repro¬ duction in Mosses— Importance of Mosses to Man— Liverworts CHAPTER 5 FERNS AND SEED PLANTS 132 FERNS— The Pteridophytes— Vascular Tissue in Fern Stems— Life Cycle of Ferns— The Fern Class— FERN RELATIVES— Club Mosses— Life Cycle of Club Mosses— Horsetails— Primitive Fern Relatives— Importance of Pterido¬ phytes to Man— SEED PLANTS— The Spermatophytes— Variety Among the Seed Plants— Two Common Subphyla: Gymnosperms and Angiosperms— Two Classes of Angiosperms— Importance of Seed Plants to Man CONTENTS 7 Variety Among Living Things -Animals CHAPTER 6 THE LOWLIER ANIMALS 158 PHYLA ONE AND TWO: PROTOZOA AND SPONGES-Phylum One: Protozoa— Classes of Protozoa— Phylum Two: Sponges— Kinds of Sponges— A Step Ahead in Organization-PHYLA THREE AND FOUR: ANIMALS WITH TWO AND THREE CELL LAYERS-Phylum Three: Coelenterates —Hydra and Its Two Cell Layers— Jellyfish— Corals and Other Forms— Increasing Levels of Organization— Phylum Four: Flatworms— Body Plan of a Planarian— Life Processes in Planarians— Other Flatworms— PHYLA FIVE, SIX, AND SEVEN: ROUNDWORMS, ROTIFERS, AND MOSS ANIMALS — Phylum Five: Roundworms — Ascaris— Trichinas— Hookworms —Phyla Six and Seven: Rotifers and Moss Animals— Greater and Greater Complexity CHAPTER 7 CLAMS, EARTHWORMS, STARFISH, AND THEIR RELATIVES 183 PHYLUM EIGHT: SOFT-BODIED ANIMALS-Mollusks-Body Plans of Mollusks— Clams— Importance of Mollusks to Man— PHYLUM NINE: EARTHWORMS AND THEIR RELATIVES— Annelids— The Earthworm and How It Lives-Other Annelids-PHYLUM TEN: STARFISH AND THEIR RELATIVES— Echinoderms— The Starfish and How It Lives- Other Echinoderms CHAPTER 8 ANIMALS WITH JOINTED LEGS 205 IDENTIFYING ARTHROPODS— Similarities in Arthropod Body Plans— Similarities in Reproduction— Level of Organization in Arthropods— Biologi¬ cal Success— Variety Among Arthropods— CENTIPEDES AND MILLI— PEDES— “Many Legs”-SPIDERS AND THEIR RELATIVES— Spiders— Scorpions— Mites and Ticks-CRAYFISH AND THEIR RELATIVES— Variety Among Crustaceans— The Lobster— Body Plan of a Lobster— Repro¬ duction in Lobsters— Level of Organization in Crustaceans— INSECTS— Insect Characteristics— The Grasshopper— Variety Among Insects— Butter¬ flies and Moths— Beetles— Bees, Wasps, and Ants— Termites— Other Insect Orders 8 CONTENTS CHAPTER 9 ANIMALS WITH BACKBONES 232 THE PHYLUM OF THE VERTEBRATES— Puzzling Features-Lancelets —Vertebrates— Level of Organization in the Vertebrates— BONY FISH— The Habitat of Fish— Oddities Among the Fish— Level of Organization in Bony Fish-FROGS AND THEIR RELATIVES-Frogs-Toads-Supersti- tions About Amphibians— Variety Among the Amphibians— Level of Organi¬ zation— REPTILES— Characteristics of Reptiles— How to Know the Snakes —Our Poisonous Snakes— Level of Organization in the Reptiles— BIRDS— Common Features— Variety Among Birds— Identifying Birds— Reproduction —Level of Organization in Birds— Birds and Human Welfare— MAMMALS —The Mammalian Body Plan— Reproduction— Variety Among Mammals— Egg-laying Mammals— Pouched Mammals: Marsupials — Rodents— Hoofed Mammals— Carnivores— Primates— Man: The Dominant Organism Specialization in Higher Organisms CHAPTER 10 SEED PLANTS AND HOW THEY LIVE 266 THE SEED PLANT AS A WHOLE— Bean and Corn Seedlings— Variations in Roots, Stems, and Leaves— New Growth— Food-storage in Seed Plants— LEAVES— Leaf Structure— The Work of the Leaf— How Leaves Make Glu¬ cose-Recent Discoveries About Photosynthesis— Cane Sugar— Starch-making —Fats and Oils— Protein-making— Plants That Fix Nitrogen— Strange Labo¬ ratories— Further Steps in Protein-making— Photosynthesis and Respiration —Transpiration— Relationship of Leaves to Other Plant Organs— STEMS— Monocot Stems— Dicot Stems— Functions of Stem Tissue— ROOTS— Variety Among Roots— Structure of Roots— Functions of Roots— THE FLOW OF MATERIALS— Diffusion— Osmosis— Root Hairs and Osmosis— Other. Exam¬ ples of Diffusion in Seed Plants-SENSITIVITY AND BEHAVIOR— What Is Behavior?— Plant Reactions— The Basis of Plant Behavior— Types of Plant Behavior CHARTS: Seed Plants following page 288 CONTENTS 9 CHAPTER 11 VERTEBRATES AND HOW THEY LIVE 295 ORGANIZATION IN THE VERTEBRATE BODY-From Fish to Mammal —Vertebrate Organ Systems— The Circulatory System— The Vertebrate Nervous System— Other Organ Systems— THE FISH— Food-getting and Respiration— The Food Canal— The Circulatory System— Central Co-ordina¬ tion— THE FROG— Its Mouth— How Does a Frog Breathe?— The Lungs— The Food Tube— The Circulatory System— Organs of Excretion— The Nerv¬ ous System— Locomotion— WARM-BLOODED VERTEBRATES— Circula¬ tory Systems— Oxidation and Warm-bloodedness— Respiratory Enzymes— Digestive Enzymes— Other Factors in Warm-bloodedness— BEHAVIOR IN VERTEBRATES— Pathways Through the Nervous System— Reflex Arcs —Inborn and Modified Reflexes— The Cerebrum and Learning CHARTS: The Leopard Frog following page 304 The Human Body CHAPTER 12 THE BODY AT WORK 330 THE DIGESTIVE SYSTEM— The Alimentary Canal— Digestive Glands— Action of Saliva— Digestion in the Stomach and Intestine— How Digested Foods Enter the Blood— THE RESPIRATORY SYSTEM-How Oxygen Enters the Blood— How Do You Breathe?— Your Windpipe and Voice Box -THE CIRCULATORY SYSTEM-Circulation of the Blood-Lymph and Lymph Circulation— Food and Oxygen in the Cells— MUSCLES AND BONES— Skeletal Muscles— Bones As Levers— Energy Use in Muscle Cells -ORGANS OF EXCRETION— The Lungs-The Kidneys-Skin CHARTS: The Human Body following page 336 CHAPTER 13 FOODS AND NUTRITION 351 ESSENTIAL RAW MATERIALS— What Elements Make Up the Human Body?— Classes of Nutrients— Indispensable Building Foods— Energy Foods —THE BODY’S ENERGY NEEDS— Measuring the Energy Stored in Foods —Calories— Weight— Calories and Food Values— PROTEIN AND MIN¬ ERAL NEEDS— Body Proteins— Essential Amino Acids— Minerals— VITA¬ MIN NEEDS— The History of Vitamin Discovery— B Complex Vitamins— B Vitamins and the Respiratory Enzymes— Vitamin A— Vitamin C— Vitamin D— Vitamin K— A New Fat-soluble Vitamin— How Cooking Affects Vitamins —Daily Vitamin Needs— Planning a Diet— Food and Drug Laws 10 CONTENTS CHAPTER 14 INTERNAL REGULATION AND CO-ORDINATION 373 THE DUCTLESS GLANDS— Hormones: Chemical Messengers— The Pi¬ tuitary or “Master Gland ’— The Pancreas and Its Hormone— The Thyroid Gland— The Parathyroid Glands— The Adrenal Glands— Selye’s Theory of Stress Reactions— The Reproductive Glands— Other Endocrine Glands— THE STABILITY OF THE BLOOD-Composition of the Blood-Formed Elements— Hemoglobin— Stability of Cell Counts— Clotting— Blood Types— THE NERVOUS SYSTEM— Co-ordination of the Human Body— Parts of the Nervous System— Forty-three Pairs of Nerves— The Central Nervous System— The Cerebrum— The Autonomic Nervous System— Autonomic Gan¬ glia and Nerves— The Nature of an Autonomic Impulse— Functions of the Autonomic System— The Autonomic System and Body Stability CHAPTER 15 HUMAN BEHAVIOR AND THE NERVOUS SYSTEM 400 THE SENSE ORGANS— The Human Eye— The Ear— Balance Organs— Chemical Senses: Taste and Smell— Receptors in the Skin— INBORN AND CONDITIONED RESPONSES— Inborn Responses— Conditioning— Pavlov’s Experiments and Conclusions— Conditioned Responses in Man— General¬ ized Responses— Emotional Behavior— Nerve Pathways and Conditioned Responses— Reaction Time— Habits and Skills— MOTIVATION IN HUMAN BEHAVIOR— Organic Needs and Behavior— Blood-sugar Levels and Be¬ havior-Needs and Motivation: Organic and Psychological Factors — LEARNING PROCESSES AND PROBLEM-SOLVIN G— Animal Experi¬ ments— Human Learning— Solving Problems— Control Over Environment The Fight for Health CHAPTER 16 DISEASES AND THEIR CAUSES 428 MICROORGANISMS AND DISEASE— “The Good Old Days”?-Discovery of Specific Germs— Types of Disease-causing Microorganisms— Germs and Their Toxins— Germs and Tissue Damage— Is Inheritance a Factor in Germ Diseases?— Infection and Contagion— HOW GERMS ARE SPREAD— Air — Water and Food — Insects — Direct Contact — Soil — Human “Carriers’ — OTHER CAUSES OF DISEASES— Noninfectious Diseases— Allergies— De¬ ficiency Diseases— Pernicious Anemia— Alcohol and Disease— Does Smoking Cause Disease?— Drugs and Disease— BODY STABILITY AND DISEASE —Older Theories of Disease— Specific Causes— The Newer Point of View CONTENTS 11 CHAPTER 17 IMPROVED CONTROLS OVER DISEASES 448 DEFENSES AGAINST GERMS— Lines of Defense: Skin, Lymph Nodes, and Phagocytes— Chemical Defenses: Control over Smallpox, Diphtheria, Rabies, and Polio— The Nature of Chemical Defenses— Immunization- Types of Immunity— NEW MEDICINES— Sulfa Drugs— Antibiotics— Better Control over Tuberculosis— Decrease in Effectiveness of New Medicines— Better Antimalarial Drugs— Tranquilizers— IMPROVED METHODS OF DIAGNOSIS— Tools and Laboratory Tests— X rays— The Need for Modera¬ tion in Use of X rays— Radioactive Tracers— MODERN SURGERY— Partial Conquest of Pain— Prevention of Infection— Partial Conquest of Appendi- citis— PREVENTION OF INFECTIONS AND OTHER SERIOUS RE¬ SULTS OF INJURIES— Treatment of Minor Wounds— Bone Fractures— Control of Bleeding— Care of Unconscious Patients— IMPORTANCE OF PREVENTION— Habits, Attitude, and Health— Public Health Agencies— Control of Narcotics— Extent of Addiction— Mental Health and Narcotics CHAPTER 18 HEALTH PROBLEMS YET TO BE SOLVED 472 CANCER AND ITS CONTROL— Cancer in Human Beings— Malignant and Benign Tumors— How Cancer Spreads— Importance of Early Diagnosis- Danger Signals— Precancerous Conditions— Radiations and Cancer— Heredity and Cancer— Leukemia and Hodgkin’s Disease— Treatments— HEART AND CIRCULATORY DISEASES AND THEIR CONTROL-What Is Blood Pressure?— Blood Pressure and the Heart— Hardening of the Arteries— Coro¬ nary Heart Disease— Symptoms of Heart and Circulatory Diseases The Continuity of Life CHAPTER 19 REPRODUCTION IN HIGHER ORGANISMS 486 REPRODUCTION IN FLOWERING PLANTS-Asexual Reproduction- Sexual Reproduction— Pollination and Fertilization— Fruits and Seeds— Com¬ plete and Incomplete Flowers— Perfect and Imperfect Flowers— Types of Pollination-Growth of Seeds-REPRODUCTION IN EARTHWORMS- Two Parents-How Offspring Are Produced-REPRODUCTION IN FROGS— Eggs and Sperms— Growth of Frog Eggs— Behavior of Chromo¬ somes— Maturation of Sperms and Eggs— Mitotic and Meiotic Cell Division -Haploid and Diploid Numbers— REPRODUCTION IN MAMMALS- Rabbits— Fertilization Effects— Mammal Embryos and Their Development- Advantages of Mammalian Reproduction over Other Kinds— Human Repro¬ duction-Care of Mother and Baby— The Rh Factor and Pregnancy— Boy or Girl? 12 CONTEXTS CHAPTER 20 HOW TRAITS ARE INHERITED 514 DISCOVERY OF THE PRINCIPLES OF GENETICS-Mistaken Beliefs About Heredity— Inheritance of Single Traits— Mendel’s Experiments— Homozygous and Heterozygous Organisms— Phenotypes and Genotypes— Dominance: Complete and Incomplete— Gene Interaction— Segregation and Independent Assortment— Linkage— EXPLANATIONS AND APPLICA¬ TIONS OF GENETIC PRINCIPLES-Determining Whether an Organism Is Homozygous or Heterozygous for a Given Trait— Inheritance of More Than One Trait— Multiple Alleles— Studies of Human Traits— Sex-linked Traits-NATURE OF CHROMOSOMES AND GENES-Research into the Chemical Nature of Genes— Genetic Accidents— Causes of Mutations— Gene Transduction— Polyploidy— Crossing Over— The Role of Plasma Genes and Cytoplasm in Heredity— General Applications of Genetics CHAPTER 21 HOW NEW VARIETIES MAY ARISE 546 MUTATIONS AND NEW VARIETIES— Mutations and Selection-Arti¬ ficial and Natural Selection— Mutation Rates in Fruit Flies— Mutation Rates in Man— Gene Pools of Populations— New Varieties— NEW COMBINA¬ TIONS AND VARIETY AMONG THE OFFSPRING-Each Fertilization a New Combination— New Combinations from Crossing Over— Gene Trans¬ duction and New Varieties— Polyploidy and New Varieties— Variety Through Natural Selection-VARIETY AMONG LIVING PEOPLES- American Indians— Racial Stocks— Blood Groups and Racial Stocks— Living Peoples Today CHAPTER 22 INHERITANCE THROUGH THE AGES 559 MODERN HORSES AND THEIR ANCESTORS-Fossils-Fossil Ancestors of the Horse— Horses in America— Other Ancestral Lines— THE EARTH AND ITS HISTORY— The Haddonfield Giant— The Changing Earth— Life in the Time of Hadrosaurus— How Old Is the Earth?— Formation of Rock Layers— How Fossils Get into Rocks— How Undersea Fossils Are Exposed- Earth History-AN OUTLINE HISTORY OF LIVING THINGS-The Paleozoic Era— Cambrian Period— Ordovician Period— Silurian Period— De¬ vonian Period— Carboniferous Period— Permian Period— End of the Paleozoic Era— The Mesozoic Era: Age of Reptiles— Rise of Birds, Mammals, and Flowering Plants— The Cenozoic Era: Completing the Earth’s Timetable- Changes in Living Things: The Genetic Record CHAPTER 23 INHERITANCE IN PLANT AND ANIMAL BREEDING 586 ARTIFICIAL SELECTION FOR A SINGLE TRAIT-Disease-resistant Clover— Selection for Larger Eggs— Selection for Increased Milk Production —Causes of Failure in Selecting for One Trait— HYBRIDIZATION AND SELECTION FOR SEVERAL TRAITS-Solving a Cotton Problem-Im¬ proving Other Plants— Hybrid Vigor— LIMITATION S AND VALUES OF PURE-LINE BREEDING— Pure-line Breeding in Corn— Pure-line Breed¬ ing in Cattle— OTHER FACTORS IN PLANT AND ANIMAL BREEDING —Mutations and Breeding— Radiation Genetics— Selection for Polyploidy CONTENTS 13 Living Populations and Their Interdependence CHAPTER 24 THE BIOLOGY OF GROUP INTERACTIONS 602 WILDLIFE POPULATIONS AND THEIR HISTORY— Balance and Im¬ balance in Wildlife Populations: A Disastrous Lesson— Demes— Biomes— M an-made Disturbances— Natural Successions— Biography of a Biome— Interrupted Successions— EXCHANGES OF MATERIALS— Food Chains —Complexity of Food Chains— Producers and Consumers: Maintaining the Balance— Exchanges of Materials with the Nonliving Environment— Inter¬ dependence of Living Things CHAPTER 25 MAN AND CONSERVATION 620 A FAMOUS FOREST FIRE— Reclaiming the Burn— Conservation— SOIL AND WATER CONSERVATION— The Nature of Soil-Soil Conservation Districts— How Is Soil Conserved?— Crop Rotation— Contour Cultivation and Strip Cropping— Soil-binding Plants— Restoring Organic Matter— Organic Matter and the Plow— Restoring Minerals— Wiser Use of the Land— Why Do We Have Water Shortages?— Water Conservation— FOREST CONSERVA¬ TION— Forests as Continuing Crops— Forests and Animals— Forest Conser¬ vation Today— WILDLIFE CONSERVATION- Wildlife Conservation Agencies— Wildlife Refuges— Artificial Breeding and Restocking— Control of Enemies— Harvesting— Protection of Birds and Wild Flowers— What Can Each of Us Do to Help? BIOLOGY AND SPACE TRAVEL 642 GLOSSARY 653 INDEX • 684 CONTENTS w ' 0 m A Guide to the Study of T^IOEOGY is the study of life. The word biology was invented in 1802 in Germany by combining two ancient Greek words, bios meaning “life” and logos meaning “the study of.” Different living things, say for exam¬ ple, onions, frogs, and people, may hardly seem alike at all. And yet all of them are living, so that biology by defi¬ nition must be about onions, frogs, and people. Biology is about all living things, not only plants and animals on the earth today but also those that have lived and died in past ages. Perhaps a better definition of biology, then, would be the science of living things. How many different kinds of plants and animals do you suppose there are? Biologists have described and named almost one and a half million kinds of living plants and animals. And they have described and named almost a million kinds that lived and died out long ago. Biology is about all these kinds of living things— over two million of them. Though widely different in many ways, living things also are alike in many ways. Bits of them examined un¬ der a microscope even look alike in many ways. And living things do many things in common, such as taking in or making food, digesting it, getting rid of waste materials, growing, and so on. Bi¬ ology is about all the ways in which living things are alike and all the ways in which they are different. Study of the very stuff of life— living matter— is an ever-growing part of bi¬ ology. What makes one tiny blob of matter alive, but another, say, a grain of sand or a snowflake, not alive? And how can living things produce new liv¬ ing things? Even more important, why ( continued on page 18) MICROSCOPIC VIEW OF FROCKS BLOOD ► do horses give birth to young horses rather than to cows or clams or pigeons or altogether new kinds of living things? New kinds of living things do arise, as a study of life in past ages reveals. But how? Does it happen overnight? Biology is about this, too. Biology is also about the relation¬ ships between each living thing and all others. Are deer, for example, best pro¬ tected by killins; off mountain lions? It would seem so, and yet if too many mountain lions were killed off, deer would multiply too rapidly, overgraze the land, and eventually die of starva- tion, killing much valuable vegetation in the process. As a matter of fact, most of the mountain lions have been killed off— but replaced by deer hunting sea¬ sons for men. You might say that we have destroyed the old balance in life and created a new one. Take another kind of relationship be¬ tween living things— bacteria that live in the human body. Are they helpful or harmful? When are living things of benefit to one another, and when do they bring only disease or death to each other? By now you will have guessed that biology is also about you— your life, your behavior, your health, and even your future. An ever-increasing knowl¬ edge of yourself and other living things, and of ways in which to conserve the living resources in the world, is of vital importance to you. Biology thus emerges as a vast field of inquiry, one in which you may some¬ day choose to work, and certainly one in which you are likely to choose a hob¬ by, if you are hobby-minded at all. Gar¬ dening, life photography, bird watch¬ ing, raising and training pets— the list of biological hobbies is virtually endless. As for occupations and professions— doctors, dentists, druggists, farmers or ranchers, plant and animal breeders, nurses, laboratory technicians, teachers, botanists, zoologists, forest rangers, game wardens, commercial fishermen, geologists, psychologists— these are but a few of the people whose specialized interests are partly or wholly biological. Here is an interesting thought: not knowing some basic biology may well be a bigger handicap today than not knowing how to read and write was a hundred years ago. TOOLS AND TECHNIQUES FOR THE BIOLOGY STUDENT Your textbook will give you help and guidance in every possible way. It cov¬ ers the broad field of biology both com¬ prehensively and logically. You have only to start with Chapter 1 and take the remaining chapters in sequence to have a logical, understandable ap¬ proach to biology (reinforced by the grouping of the twenty-five chapters in¬ to eight units). Within each chapter, topic headings, topic summaries, and experimental activities give you the guidance you need. At the end of each chapter, a chapter summary, review ac¬ tivities, questions for further thought, and projects and book listings for fur¬ ther investigation help you to review and to carry on further inquiries of your own. One of the most valuable features of your course in biology is the opportu¬ nity to acquire hundreds of important new terms for your permanent vocabu¬ lary. Learning these new words as they are used— words you will run across throughout life as you read magazines and newspapers, listen to radio, watch television, or talk with friends— is not at all difficult. First of all, each new term 18 A GUIDE TO THE STUDY OF BIOLOGY to# ■■ Stanley Rice and Helen Faye 8 Some of the glassware and equipment you will use in your biology course are: A. beakers, B. a tripod, C. flasks, and D. a funnel. is printed in bold type, pronounced phonetically with the accented syllable printed in capital letters, and defined in context at the point at which it is intro¬ duced. [Example: “In higher animals, the body cavity is completely lined with covering tissue and is called the coelom ( see lum ) to distinguish it from the unlined body cavities of, say, round¬ worms.] Where possible, a drawing or photograph is also used to illustrate the meaning of the new term. Then the most important of the new terms are re¬ viewed in chapter-end activities, and all new terms are listed, pronounced, and defined in the Glossary at the end of the book. Learning these new terms is easy when you are given their pronuncia¬ tions and meanings along with the terms themselves. Books and words are tools of discov¬ ery, and so are many other things you will learn to use as you study biology. For example, you will probably do a number of chemical tests and investiga¬ tions. For these you will use glassware and equipment, such as beakers, a tri¬ pod, flasks, and funnels (Figure 8); wire gauze coated with asbestos, a Bun¬ sen burner, a ring stand with ring clamps, Petri ( pay tree ) dishes and covers, and test tubes and a test tube rack (Figure 9). You will also use quite a few chemi¬ cal reagents ( ree ay j’nts ) —among oth¬ ers, iodine (2 per cent), ethyl alcohol, and acid indicators such as litmus pa¬ per (which turns from blue to red in color when immersed in an acid). In some of your studies you may be asked to dissect ( dih sekt ) an onion, a corn stalk, a flower, an earthworm, an insect, or other animals and parts of plants. For this work you will need dis- A GUIDE TO THE STUDY OF BIOLOGY 19 9 You will also use: A. asbestos-coated wire gauze, B. a Bunsen burner, C. a ring stand, D. ring clamps . . . . . . E. Petri dishes and covers, and F. test tubes and a test tube rack. Photos by Marion A. Cox secting tools— a scalpel (sKALp’l), dis¬ secting scissors, dissecting tweezers, some dissecting needles, and a dissect¬ ing pan (Figure 10). Perhaps the tools you will need most often are those that magnify images of objects or parts of living things and make them look many times their actu¬ al size. A hand lens may be used for some of your studies, but a compound microscope (Figure 11) will be used far more often. Thus you will need to J know how to use this instrument cor¬ rectly (refer often to Figure 11 as you read on). The compound microscope is some¬ times called a light microscope, because it uses light, reflected by the mirror up through the objective, tube, and eye¬ piece to your eye. Where would you put whatever you wish to examine? You would have to place it over the bole in the center of the stage. And yet you could not place the end of your finger there and look at it through the eye¬ piece, because your finger tip would keep the light reflected by the mirror from reaching your eye. But you could place the wing of a fly at the center of the stage and look at it through the eye¬ piece. A fly’s wing is so thin that light passes through it. Before trying to study, say, a fly’s wing under the microscope, it is wise to mount the wing on a glass microscope slide and cover it with a glass cover slip. To do this, you would need a clean slide and cover slip, tweezers, a medi¬ cine dropper, and a little water. Here are the steps: 1. Use the medicine dropper to place a small drop of water near the middle of the clean slide. 2. With the tweezers place the fly’s wing on the drop of water. 20 A GUIDE TO THE STUDY OF BIOLOGY 3. With your fingers ( or the tweezers if you are light enough of touch and steady enough not to break the cov¬ er slip) place one edge of the cover slip on the drop of water, then lower the cover slip gently, so that it cov¬ ers the fly’s wing. Thus you would “make a slide.” The light would pass through the glass slide, the fly’s wing, and the glass cover slip. You can make slides of some things without using water or a cover slip. But those things, too, must be thin enough so that light will pass through them ( or small enough so that light reflected from the mirror will pass around them ) and on through the tube and eyepiece to your eye. Before placing your slide on the mi¬ croscope stage and looking through the eyepiece, you would have to know how to focus your microscope on the slide, even as you focus the image of another kind of slide (or film) on a screen. Otherwise, you probably wouldn’t see anything even if you looked through the eyepiece at the fly’s wing. Here are the steps in focusing your microscope (refer again to Figure 11): 1. Before placing your slide on the stage, be sure that the low power objective is in line with the tube and eyepiece. If it is not, rotate the nose- piece until it clicks into place with the low power objective in the line of sight through the eyepiece. 2. Look through the eyepiece and turn the mirror toward a window (or to¬ ward your microscope lamp, if you are using one). Keep adjusting the mirror until you see a circle of bright light through the eyepiece. 3. Use the coarse adjustment to raise the tube upward so that the low power objective is about one-fourth inch from the stage. 4. Now place your slide on the stage with the fly’s wing over the hole in the center of the stage. 5. Watch the objective from one side 10 For dissecting plant parts or animals, you will need: A. a dissecting pan, B. dissect¬ ing needles, C. a scalpel, D. dissecting tweezers, and E. dissecting scissors. Marion A. Cox Eyepiece Clips Low power objective High power 'ective Stage Tube 1 1 Almost any microscope you will use has the parts shown here. Some also have a diaphragm to adjust the size of the center hole in the stage. Others have a third objec¬ tive, the oil immersion objective, and a scanning mechanism rather than clips. while you carefully lower it by turn¬ ing the coarse adjustment until the end of the objective is about one- eighth inch from the cover slip. 6. Look through the eyepiece and start turning the coarse adjustment slow¬ ly to raise the objective. ( Be sure to raise the objective. If you lower it, you may break the cover slip and slide, or scratch the lens.) As soon as you see something rather clearly, use the fine adjustment to bring the fly’s wing into sharp focus. You may be surprised that you would not see all of the fly’s wing at one time. 22 A GUIDE TO THE STUDY OF BIOLOGY ■ Stanley Rice 12 The numbers on the objectives of the microscope (usually 10 X for low power and 43 X for high power) are multiplied by the number on the eyepiece (usually 5x or 10 X ) to get the magnification , obtainable with each objective. Even the low power objective enlarges the image of the wing too much for it to be seen in its entirety. Look for a num¬ ber on or near the top of the eyepiece of your microscope. It may read 5x. Next look for a number on the low power objective. It may read 10 X. Now multiply 5 X 10 and you will know how much the image of the fly’s wing would be enlarged. We say that your low pow¬ er objective has obtained a magnifica¬ tion of 50 X. Your microscope also has a high pow¬ er objective (your teacher will show you how to use it). You can find a num¬ ber on this objective, too. It may read 43 X. If your eyepiece is 5x, the high power objective gives you a magnifica¬ tion of 215 X. The eyepiece on your microscope may bear the number 10 X rather than 5X. What difference would this make? GETTING OFF TO A GOOD START Why fight unnecessary obstacles to learning? Instead, you should follow a plan when you are ready to study. It is no more wise to waste study time by thinking of other things than it is to waste relaxation time by worrying about your studies. Here are some tips: 1. Get paper, pencils, your textbook, and reference books together before you start studying. 2. Turn off the radio or television set, and retire to a quiet place which has a good supply of light ( without glare) falling over your shoulder on your study area. 3. Sit down and study, keeping your rest breaks 45 minutes or so apart. a. Scan your study assignment first, reading headings and summaries. b. After getting the general idea of the assignment, start again at the be¬ ginning. Read carefully and take notes. Write down an outline of the important ideas, and note any points you don’t understand. c. When you have finished your as¬ signment, review your notes. d. Sometime before class the next day, go over your notes again. Be ready to discuss the assignment and to raise any questions you have. And so you are ready to start your course in biology. On your way to or from school tomorrow, take a new look around you. What living things do you see? How do they appear to be alike? In what ways do they seem to differ from one another? A GUIDE TO THE STUDY OF BIOLOGY 23 JLhe largest living things on earth are the giant redwoods of California, one of which is pictured on the opposite page. One of these trees may weigh nearly a thousand tons— almost two million pounds. To put it another way, it would take 10,000 people, each weighing nearly 200 pounds, to match the weight of one giant redwood. The smallest known particles that show some evidence of life are the viruses ( vy rus ez ) that we know to be agents of such diseases as chicken pox, influenza, and polio. Viruses are much too small to be seen under the compound microscope, even with the use of the high power objective. Those shown at the bottom of this page were photographed under a special microscope that magnifies images of particles tens of thousands of times their actual size. How many viruses do you think it would take to match the weight of a giant redwood? Start by writing the number 10, then add 24 zeros. If you can read this number— 10,000,000,000,- 000,000,000,000,000— you will know the answer, the number of viruses that a single giant redwood offsets in weight. The range of sizes among living things is tremendous. Even among similar living things, sizes vary almost unbelievably. One kind of jellyfish, for example, may weigh only a few ounces, while another kind found in Arctic SIMILARITIES AMONG LIVING THINGS waters may weigh 1,000 pounds— half a ton. The ecptfnvorms you know are only a few inches long, but earthworms in Australia may be as much as twelve feet long! One kind of frog is the smallest known animal with a backbone; another kind is as large as a fox terrier. Most frogs, however, like the one pictured at the top of the opposite page, range from six inches to a foot in length with their legs extended. Among dissimilar living things, the range in sizes is even more extreme. Some kinds of one-celled life measure less than 1/10,000 of an inch in length or width. Other living things reach lengths or heights that are almost equally difficult to imagine; for example, the blue whale may reach a length of 90 feet, and redwood trees of California a height of 300 feet or more. In spite of what may be almost unimaginable differences in size or appearance or both, all living things are strikingly similar in a number of basic ways. This unit is about all these basic similarities. Chapters 1. Cells— the Building Units 2. Chemicals— the Building Materials 3. Life Processes— the Basic Activities Living building blocks Cells are very old, almost as old as life, but our knowledge of cells began only about 300 years ago. To the best of our knowledge, the first crude com¬ pound microscope was “invented” about 1590 in Holland. The inventors, the Janssen brothers, probably never used their microscope to look at any¬ thing alive. Other men did that, for the first time, during the last part of the 1600’s. These were the first men to see the building units— we now call them cells— in living things. Today biologists are still learning new facts about cells. Even now not all biologists agree as to exactly what a cell is. But all of them do agree that all cells are alike in some basic ways. They agree also that all living cells today come from other living cells (although obviously the first living cell did not). Dr. Philip Siehevitz In this chapter you will explore the facts that led biologists to the idea that cells are the building units of living things. You will use your microscope to look at living cells in onionskin. You will even get to see some of your own cells. All of your investigations will help you to understand the idea that all plants and animals are made of cells. CELLS Discovering a new world is always a great adventure. Columbus and his men sailed westward into the unknown, in 1492. This was a great adventure. Some 200 years later, Robert Hooke and oth¬ er men looked at things through com¬ pound microscopes. This, too, was the beginning of a great adventure into a new and unknown world, a world of invisible but living cells. 26 SIMILARITIES AMONG LIVING THINGS How did cells get their name? Robert Hooke had used his micro¬ scope to look at all sorts of small ob¬ jects. One day his gaze fell on a piece of cork. He wondered what it would look like under the microscope. He cut the thinnest possible slice off the cork and looked at it. To his utter amazement, the cork was full of holes. He tried slice after slice. Every slice looked like neatly arranged rows of holes. In England in 1665, a now-famous book was published. Robert Hooke was its author. In that book is his drawing of a bit of cork as it looked to him under the microscope (Figure 1-1). In his de¬ scription, he called the holes cells, be¬ cause they made him think of the cells of a honeycomb, in which bees store nectar and honey is made. That seems to have been the first time the word cell was ever used in print to mean a microscopic part of a plant. At about the same time in England another man was making history with the microscope. Nehemiah (nee eh my uh * ) Grew looked at many parts of plants under his microscope. His four- volume work was published in 1682. In one of those volumes, this sentence appears: “The microscope . . . shows that these pores are all, in a manner, spherical (round), in most plants; and this part an infinite mass of little cells. . . ” The word cell was gradual¬ ly coming to have a new meaning. As the years went by, more and more men looked at more and more parts of more and more plants and animals with * Accent the my, and pronounce the word just the way it looks. All pronunciations in this book are given in this form, with capital letters to show you which syllable to accent. This easy pronunciation system is based on that used in Words: The New Dictionary, published by Grosset & Dunlap, N. Y. better and better microscopes. By 1809, a Frenchman named Lamarck (lah mahrk) was writing, “. . . without cellular tissue, no living body would be able to exist. . . .” In 1824, anoth¬ er Frenchman, Dutrochet (dootroh shay), was saying, “All the organic tis¬ sues of animals are actually globular (roundish) cells of exceeding small¬ ness.” Finally in 1838 and 1839 came the publications of two Germans, Schleiden (sHLYden) and Schwann (shvon), saying that all plants and all animals are made of cells. More than a century and a half of in¬ vestigation by many men in several countries had finally shown that the cell is the building block of all living things. By then, biology was on its way. Now in a few hours, or at most a few days, you can learn what it took man¬ kind nearly two centuries to find out. One good way to begin is to look at some cells. 1-1 CORK CELLS The care with which Robert Hooke first investigated the cellular structure of cork nearly three hundred years ago is still evident in his drawing of two slices of cork as he saw them under his microscope. Note that he found differences between slices taken lengthwise and cross¬ wise. The Bettmann Archive CELLS— THE BUILDING UNITS 27 1-2 MOUNTING ONIONSKIN FOR MICRO¬ SCOPIC STUDY A. Add a drop of water to a clean slide. B. Cut a bit of onion. C. Remove the outer skin tissue. D. Place the skin on the slide. E. Add a cover slip. Stanley Rice Getting ready to look at cells Before you can look at cells under the microscope, you will need to learn how to get them ready to examine. You can’t put the end of your finger under the microscope and see the cells in it. Your finger is much too thick. Robert Hooke made thin slices of cork, but you certainly do not want to cut a thin slice of a finger. And yet you must have thin material. It must be thin enough to let the light shine right through it, if you want to see the cells well. So you will need to make a slide of something very thin, such as a bit of onionskin. PREPARING ONIONSKIN FOR EXAMINA¬ TION. You will need microscope slides and cover slips, a medicine dropper, a little water, some cleansing tissues, a little dilute iodine (one part of two-per-cent iodine in two parts of water), a knife, tweezers, and part of an onion. First clean a slide and cover slip with a paper tissue. Then with the medicine dropper put a small drop of water near the center of the slide. Loosen an inner layer of onion and cut off a piece of the layer about !4 inch square. With the tweezers, pull the skin off one side of the small piece of onion. Lay the onionskin in the drop of water on the slide and cover it with the cover slip (Figure 1-2). You have now prepared a slide of onionskin. You could look at it as it is. But you will be able to see the cells better if you stain them with iodine. Place a small drop of dilute iodine at the edge of the cover slip. It will run under the cover slip and stain the onionskin. The iodine will run under the cover slip faster if you touch one corner of a blotter to the water at the op¬ posite edge of the cover slip. 28 SIMILARITIES AMONG LIVING THINGS You have just made and stained a slide of onionskin. Biologists call this kind of slide a wet mount, because the specimen is placed in a drop of water on the slide. You can use this wet mount until the water dries up, per¬ haps for half an hour. Biologists make slides in other ways. They may put a specimen in a drop of some fluid that will not dry up. These slides last for years. So we shall call them permanent slides. You will soon be looking at some slides of this type. Biologists call the making of a slide mounting a specimen for microscopic examination. Cells of onionskin You have just mounted a specimen of onionskin in water, making a wet mount. Now you are ready to look at it through your microscope. Look at your slide of onionskin un¬ der the low power of your microscope. Move the slide until you find one place where the cells look quite clear. Do they make you think of anything you have ever seen before? Try to see how they fit together. Turn to high power. Focus with the fine adjustment as you look at one cell. Do you see anything inside it? If not, look at another cell. Keep on looking till you find a cell with something visible inside it. Then draw that one cell on scratch paper, exactly as it looks to you, and show all the parts you can see. Does your drawing look somewhat like the cells in Figure 1-3? Save this drawing and your wet mount to use a little later. The microscope shows that an onion¬ skin cell is long and wide. But it does not show that the cell also has thick¬ ness. To get the idea, you must use your imagination. Each cell in the onionskin is something like a room. It has a “floor'’ and a “ceiling’’ as well as four “walls.’’ You saw the four “walls,” 1-3 ONIONSKIN Under the microscope, it appears as an orderly arrangement of cells. Not apparent is its three-dimensional nature, shown for a single cell above. but not the “floor” and “ceiling.” You were looking right through them. When light is shining through them, they are too thin to see. But the cell does have thickness, as well as length and breadth, even though that thickness did not show. Using your imagination, try to construct a drawing of a cell to show that it has three dimensions. Compare your drawing with the one in Figure 1-3. Cells from the lining of your mouth Scrape the inside of your cheek gently with a toothpick. Make a wet mount of the scrapings and stain with dilute iodine, just as you did with the onionskin. Look at the slide under low power. When you have located some cells, turn to high power. You may see single cells or two or three or more that CELLS— THE BUILDING UNITS 29 1-4 CHEEK CELLS How do these cells, taken from the mouth, resemble onionskin cells? are still joined together. Of course, in the lining of your cheek, the cells are all joined together, but they are likely to come apart as you make a slide. Do your cheek cells look at all like those of onionskin? They are certainly not the same shape (Figure 1-4). But look inside the cells. Do you see any¬ thing that looks like anything you saw in the onionskin cells? Sketch a few cheek cells on scratch paper. Save your slide and your sketch. Cells of frog's blood For this study, use a permanent slide of frog’s blood. Activity 4 on page 47 tells you how permanent slides of hu¬ man blood or frog’s blood are made. Under high power, look at frog’s blood that has been stained to make the cells show well. Most of the cells you see are red blood cells. Can you see any resemblance between these red blood cells (Figure 1-5) and your cheek cells or those of onionskin? Look around for a smaller cell with a larger dark center. This will be a white blood cell. Sketch six or eight red blood cells and one white blood cell. If you wish, use fresh blood from a living frog to make your sketch. WET MOUNT OF FROG'S BLOOD. First thoroughly mix 1 teaspoonful of table salt in 6 cups of water. Chemists call this salt water normal saline (say leen). It is about the same as the salt water in the blood. Pour the mixture into a clean bottle and label the bottle Normal Saline. You will use it often in biology. Put a drop of normal saline on a slide. With a sharp needle, draw a little blood from the membrane between the frog's toes. With a toothpick, pick up a little blood and stir it into the normal saline on the slide. Add a cover slip. Examine the wet mount first under low power, then under high power. You will see many red blood cells, and it is pos¬ sible that you may see one or more white blood cells (although they may not show up unless stained). Sketch what you see. Comparing cells Compare the three kinds of cells you have now seen. Use your sketches. Look for ways in which all three kinds 1-5 FROG BLOOD CELLS The cells were stained, then photographed under the high power of the microscope. General Biological Supply House, Inc., Chicago White blood cell Red blood cell 30 SIMILARITIES AMONG LIVING THINGS Nucleus Cell membrane : Cytoplasm Nucleus 1-6 ANIMAL AND PLANT CELLS COMPARED These two kinds of cells (shown greatly en¬ larged) have several parts in common, but there are differences. Which cell is which? of cells are alike. If you have trouble finding any likeness, look again at all the wet mounts you have made, to make sure your sketches really show what is in the cells. Remember that it took the early observers more than a century to discover the basic similari¬ ties in all cells. Do not be discouraged if you do not find them readily. What are the main parts of a cell? Without a doubt you noticed that each kind of cell has a boundary around it. This was the first thing bi¬ ologists noticed in cells, too. They called it the cell wall. But you may have noticed that the onionskin cell wall is thicker and more definite than the boundaries of the cheek and blood cells. Onions are plants. Plant cells usu¬ ally have thick, firm cell walls. Cheek and blood cells are animal cells. The boundaries of animal cells are usually thinner and less firm than the cell walls of plant cells. So today we call the boundaries of animal cells cell mem¬ branes. Plant cells have cell mem¬ branes, as well as cell walls. But their cell membranes are hard to see because they are close inside the cell walls. The cell membrane is one of the three main parts of any cell. Go back now to your drawings. Draw a guide line out from the cell wall of an onion¬ skin cell. At the end of the guide line, print the name cell wall. Draw guide lines out from the cell membrane of one cell of each kind you have drawn and print the name cell membrane. (You may have to revise your sketch of onionskin cells to indicate the loca¬ tion of the cell membrane.) Now go on with the comparison of the three kinds of cells. Inside of each cell there is a rounded body. It takes on more of the iodine stain than anv other part of the cell. It is called the nucleus (noo klee us— plural, nuclei , noo klee eye). The space between the nucleus and the cell membrane is more or less filled with cytoplasm ( sy toh plazm). Study Figure 1-6. Then add the labels nucleus and cytoplasm to your drawings of the three kinds of cells. Save the drawings. Now you know from your own ob¬ servations that at least some of the cells of onions, frogs, and people are alike. Their cells have the same three basic parts: nucleus, cytoplasm, and cell membrane. (The onion cells also have cell walls.) The cells are alike in an¬ other way. All of them have thickness as well as length and breadth. Even your cheek cells have a little thickness, although they appear flat. The three kinds of cells are alike in still another way. They are alive, or CELLS— THE BUILDING UNITS 31 Science Service Photo, from the University of California 1-7 CELLULOSE FIBERS IN A PLANT CELL WALL The first such photograph ever made, it shows cellulose fibers enlarged 57,500 times by an electron microscope (Figure 1-8). they were alive as long as they were in the plant or animal. Where is the life in a cell? In a living cell, the nucleus, cyto¬ plasm, and the cell membrane are all alive. It is customary among biologists to lump all these living constituents of a cell together and to call them proto¬ plasm ( proh toh plazm ) . One biologist has put it this way, “Protoplasm is the stuff life is made of.” Another has said, “Protoplasm is the physical basis of life.” Biologists today realize that the word protoplasm is useful but mislead¬ ing in some ways. As George Gaylord Simpson has pointed out, to say that all living things are made of protoplasm is a bit like saying that all radios are made of radioplasm.* A radio is a com¬ plex of many highly specialized parts. So is protoplasm. Protoplasm is not a single substance, as water is. It is a complex living system, as you will learn later. With these things in mind, we may still call all the living constituents (cell membrane, cytoplasm, and nucle¬ us ) of a cell protoplasm. ° Life by George Gaylord Simpson et al., Ilarcourt, Brace, 1957, p. 46. 32 Some parts of most plants and ani¬ mals are not alive. Much of the mate¬ rial in your bones is not alive. Much of the wood in the inside of a tree is not alive. The cell walls of plant cells are 1-8 ELECTRON MICROSCOPE Electrons (Chapter 2) are used to get magnifications far beyond a compound microscope's range. Bell Telephone Laboratories not alive. Plant cell walls are largely cellulose (sELyuhlohs) fibers (Figure 1-7 ) , the same fibers your cotton dresses or shirts are made of. Cellulose fibers, like much material in your bones, are not alive. They are not protoplasm. Both plant and animal cells are much alike. Go back and read over your list of the ways in which the cells of onion¬ skin, cheek lining, and blood are alike. Correct your list if it needs it. Then go on to examine other kinds of cells. Green leaf cells EXAMINING CELLS OF A GREEN LEAF. Most leaves are too thick to examine whole under a microscope. Tear a leaf in two. Place the torn edge in a drop of water on a slide. With a dissecting needle pick loose a few bits of green tissue into the drop of water. Or you may mount whole a few moss leaves or leaves of the com¬ mon aquarium plant called elodea (el uh DEE uh). These leaves are thin enough to let the light through easily. Leaf cells may not look like cells at all when you first focus on them. They are so full of green bodies that you can hardly see the other cell parts. But look more close¬ ly. The cell walls are there, as you can soon see. The nucleus and cytoplasm are there, too, although they may be hidden by the green bodies. Sketch a few leaf cells on scratch paper. Read the following paragraph, then label the green bodies and any other parts you see. Save the sketch. The green bodies that seem to fill the cell are the chloroplasts ( klor uh plasts). (See Figure 1-9.) It is the chloroplasts that make a leaf look green. What makes the chloroplasts green? They contain a green coloring matter, chlorophyll ( klor uh fil ) . You will Cell membrane Cell wall Cytoplasm Nucleus Vacuole (filled with cell sap) Chloroplast 1-9 A GREEN LEAF CELL One type of leaf cell is shown much as it would appear un¬ der the high power of a microscope. learn a little later that your very life depends, indirectly, upon chlorophyll. The clear, oval-like spaces you may see in the cytoplasm of the cell are probably vacuoles ( vak yoo ohlz ) filled with cell sap and bounded by thin membranes. Cork and wood cells Mount and examine a thin slice of cork. Or look at permanent slides that show cork or wood cells. You will see “holes” just as Robert Hooke did, long ago. Which part of the cells do you see? Which parts are missing? Cork cells and wood cells are dead. The living protoplasm is gone. Only the cell walls remain. Cork and wood cells once had cytoplasm and nuclei, like any other living cells. But gradually the walls grew thick and the living contents disappeared, leaving only the empty cell walls. Their very emptiness makes them useful in the life of the plant, as you will see later. CELLS— THE BUILDING UNITS 33 Your own blood cells EXAMINING FRESH CELLS OF HUMAN BLOOD. You may want to make a wet mount of your own blood. You will need to prick your finger.* If no one wants to do that, skip this activity and go on to the next topic. To make a slide of your own blood cells, you will need several things from the drug¬ store. You will need sterile (germ-free) gauze pads, 70-per-cent ethyl alcohol, and some normal saline. (Refer to page 30, if you have not yet made any normal saline.) First put a drop of normal saline on a slide. Next soak a gauze pad with alcohol and scrub the end of your finger with it. Then use the same gauze to clean thor¬ oughly the end of a sharp needle. Now, prick your finger with the needle. Squeeze out a small drop of blood. Dip the end of the needle into the drop of blood and then into the drop of normal saline on the slide. Repeat two or three times, but be careful not to add too much blood to the saline. Add a cover slip. Before you look at your slide, turn to Activity 4 on page 47 and make a stained slide as directed there. Save the stained slide for use in the next topic. Examine your saline slide under low power, then high. At first you will see only red blood cells. You have about a J thousand times as many red blood cells J as white. So naturally there are a thou¬ sand times as many red cells on your slide. But why aren’t the cells red, you ask? They are. They do not look red because they are so thin the light shines right through them and makes them look pale. But the red color is there just the same. It is scattered all through the ° Since there is some slight risk of infec¬ tion in a finger prick, it should be done only in the presence of your teacher or parents, and all directions should be followed to the letter. cytoplasm of the red blood cells. The name of the red coloring matter in the red cells is hemoglobin ( hee moh gloh bin). Hemoglobin makes your blood look red, much as chlorophyll makes leaves look green. You have probably noticed that your red blood cells do not have nuclei. They did have nuclei when they were young. But that was before they came out of the red marrow of your bones into your blood stream. New red cells are being made in the red marrow of the bones all the time. They are made rapidly, too. Several million new red cells are made every second. Their nuclei dis¬ appear before the cells move out into your blood stream. On your wet mount, you may pos¬ sibly see an occasional cell that looks different from the red blood cells. If you do, it is probably a white blood cell. If you do find a different looking cell, watch it closely under high power. You may see it move slowly along the slide. Then you will know it is a white blood cell, because red blood cells can¬ not move along in this fashion. Stained blood cells Examine a slide of human blood that has been stained. But first read Activ¬ ity 4, page 47, to learn how such slides are made. Then you will understand the slide better. Look over the stained blood smear under low power. Look for a place where there are several tiny, dark blue or purple spots. These are probably white blood cells. When you have found such a place, turn to high power. Your white blood cells (Figure 1-10) have nuclei. Some have a large single nucleus. Others have a compound nu¬ cleus that may look like several nuclei in the same cell. 34 SIMILARITIES AMONG LIVING THINGS White blood cell Red blood cell Clay -Adams 1-10 HUMAN BLOOD CELLS The cells have been stained, then magnified about 1600 times (usually noted as “l,600x”). How do the red blood cells differ from those of a frog (shown in Figure 1-5)? You will notice that the red cells (Figure 1-10) have pale centers. These are not nuclei. They are thin places where nuclei used to be but no longer are. Sketch several red cells and at least one white one. Save the sketch. Summing up: what is a cell? You have now seen several kinds of cells. If you could go on looking at more and more cells from more and more parts of more and more plants and animals, as biologists have done, you would eventually come up with a generalized understanding that would fit all cells. When scientists reach the point where they arrive at a general¬ ized understanding, say, of a whole set of observations, they call that under¬ standing a generalization. Enough ob¬ servations of cells would lead you to this generalization: A cell is the unit of life. It is the building unit of plants and animals. A living cell has three liv¬ ing parts: cell membrane , cytoplasm , and nucleus. All the living parts of a cell make up its protoplasm. Cells from different forms of life or different parts of one plant or animal differ in some ways , but all are basically alike. For your biology record book 1. Title page. Set aside a loose-leaf notebook for recording your activities in biology. Use the first page in your biology record book as a title page, writing something like this on it: BIOLOGY RECORD BOOK School Year . Class Period . My Name . Address . 2. Cell sketches. On a fresh page of unruled paper in your record book, copy the sketches you have now made of different cells. Name each type of cell and label its main parts. Beside each sketch, note how much the cells were enlarged, writing either low pow¬ er or high power, or 50 x or 430 X ( see pages 22 and 23). 3. Listing cell parts. On a fresh page of ruled paper, make two lists with these headings: Parts Present Parts Present Only in All Cells in Plant Cells TWO CELLS FROM ONE A giant redwood tree was once a sin¬ gle cell. So was an elephant. And so were you. A full-grown redwood or an elephant or a human being is built of many, many billions of cells. How can they all come from one original cell? The original cell, in each case, was an egg. Yes, redwoods, elephants, and people begin life as single-celled eggs. CELLS— THE BUILDING UNITS 35 CELL DIVISION IN A WHITEFISH EGG mmm fm-zi- 1-11 Cell division is a continu¬ ous process, not separate “steps.” The best understanding of the process is gained by watching it occur in a living cell studied under a microscope. Since this is difficult to arrange, a movie may accomplish much the same result. Or, on this page, the idea may be gained by beginning with the top photograph and glancing rapidly at each photo¬ graph in clockwise order. Cell division is explained in Figure 1-13 and in the text on pages 38 and 39. Here it is important only to note that the original cell’s nucleus breaks up, and that a separation of nuclear materials occurs, until two new nuclei exist and the cell begins to cleave in two between these nuclei. (560x) General Biological Supply House, Inc., Chicago 36 SIMILARITIES AMONG LIVING THINGS just as many other plants and animals do. The original egg cell changed into two cells, the two into four cells, the four into eight cells, and on and on, until many, many billions of cells had been produced. A full-grown human being weighs something like a thou¬ sand million times as much as the egg that produced him. The whole story of how one cell changes into two cells is full of complex details. At this point we are not con¬ cerned with these details, but as you explore biology further, you will find them in this text. How does one cell make two cells? In recent years, biologists have dis¬ covered a way to take movies through a microscope. They have made movies of the changing of one cell into two cells. In Figure 1-11, you see several pictures selected from one of those movies. One cell divides into two cells. This is the shortest possible answer to the question, “How does one cell make two cells?” The answer is correct, but it tells you almost nothing about a compli¬ cated process. Before you can follow that process, you need to learn the names of some of the parts of the nu¬ cleus of a cell. Parts of a nucleus You have seen the nucleus in each of several cells. Did you see its parts? You are not likely to see anything in the nucleus of a living cell. But you can see some of its parts in cells that have been killed and stained. Look at Figures 1-12 and 1-13 now and refer to them often as you read on. The outside edge of the nucleus is a thin membrane, called the nuclear membrane. It holds the nucleus togeth¬ er and regulates the passage of mate¬ rials into and out of the nucleus. Inside the nucleus, there is usually at least one small, dark-staining, round¬ ish body called the nucleolus ( noo klee oh lus). Scattered throughout the nu¬ cleus are long, fine, slightly coiled threads which also take on a dark color when stained. These threads are the chromosomes ( kroh muh sohmz ) . The chromosomes are so intertwined, when a cell is not dividing, that they make what looks like a network of threads inside the nucleus. The chro¬ mosomes play the most important part in the dividing of one cell into two. Keep them in mind as you read on. Just outside the nucleus of many cells (those of higher animals and of lower plants), there is a structure biologists call the centrosome ( sen truh sohm ) , 1-12 LIVING HUMAN CELL The cell is a young red blood cell, with parts important in cell division identified. (3,000x) Dr. P. H. Ralph, from Roy O. Greep, Histol- ogij, 1954, Blakiston Div., McGraw-Hill Book Co. Nuclear membrane Nucleus Nucleolus Chromosome materia Centrosome ■ shown in Figure 1-12. When present, this centrosome plays a part in the di¬ viding of one cell into two. Cell division Now you are ready to look at some of the main events in the division of one cell into two cells. For the sake of con¬ venience, biologists usually break this story down into some four “steps.” We shall do that here. But remember, to get the full story, you would need to see the whole continuous process, not just four isolated “steps” selected from that process. With that in mind, let s look at the four main “steps” in cell division. Step one. The first event in cell divi¬ sion takes place inside the nucleus. There, each chromosome builds an¬ other exactly like itself. Read that again. Inside the nucleus, each chromo¬ some builds an exact duplicate of itself. It builds its “twin” chromosome out of the nuclear materials around it. You have just read one of the most basic of all known facts in biology. What would you think if a friend told you this story? “Last night at that steak fry, I lost my diamond ring. I went back to hunt for it as soon as it was light this morning. I found it in that box of charcoal we had left over. And what do you think? That diamond had 1-13 The four parts of this drawing might be considered “stills” from a movie of mitotic cell division. A theoretical animal cell having only four chromosomes is shown. If this were a human cell, it would have 46 or 48 chromosomes. The artist avoided using a hu¬ man cell for obvious reasons: 46 or 48 chromosomes would not show clearly in a draw¬ ing. (See text on this and the following pages for details of the process of cell division.) MITOTIC CELL DIVISION Centrosomes _ Spindle forming Duplicate chromosomes r Spindle disappeari Nucleolus Centrosome forming Centrosome Single chromosome Nucleus New cells Nuclear membrane breaking down built another diamond exactly like it¬ self. It must have built its ‘twin’ out of the carbon in that charcoal.” You would know right away that your friend was “handing you a line.” A diamond can’t make another diamond like itself. But a chromosome can make another chro¬ mosome like itself. Certain other kinds of living particles can also duplicate themselves. Now go back and read again the amazing fact stated in the last paragraph. The “twin” chromosomes lie close beside each other. Next they coil up into short, tight coils. At this stage, in a stained cell, the chromosomes are easy to see under the high power objective of your microscope (Figure l-13a). And you can see what looks like a split down the length of what may look like one chromosome, but is actually two— the original and its newly built “dou¬ ble.” For a long time, this “split look” led biologists to believe that one chro¬ mosome had split into two. Careful re¬ search has now shown that what looked like splitting is actually self-duplica¬ tion. In the meantime, the centrosome (if present) divides, and the two centro- somes move apart, as in Figure l-13a. The spindle begins to form and the nu¬ clear membrane breaks down and dis¬ appears. Step two. In due time, the spindle completes itself across the central part of the cell. The double-looking chromo¬ somes now lie along the “equator” of the spindle, shown in Figure l-13b. Then something— biologists are not quite sure what— seems to pull each two duplicate chromosomes apart, as you see them beginning to be pulled apart in Figure l-13b. Step three. The pulling apart of du¬ plicate chromosomes goes on until one complete set of chromosomes is moved toward one end of the cell and another, identical set toward the other end, as in Figure l-13c. Step four. One set of chromosomes is finally located at one end of the orig¬ inal cell and the other set at the other end. A nuclear membrane forms around each chromosome set. Then each chro¬ mosome inside each new nucleus un¬ coils and lengthens out. Now there are two nuclei! Finally a new cell mem¬ brane (and in plant cells, also a new cell wall) forms between the two new nuclei (Figure l-13d). And one cell has made two cells. Each cell now has a duplicate set of chromosomes in its nu¬ cleus and has all other cell parts that the parent cell had. The whole process of cell division usually takes about an hour to an hour and a half. It is a continuous process, not a series of four distinct steps, as here described. Cell division of this type is often called mitosis (myTOHsiss), but in strictly technical language, mitosis means the series of changes inside the nucleus, changes that result in dupli¬ cate sets of chromosomes. The actual division of the cytoplasm and the for¬ mation of the new cell membrane be¬ tween the two new cells are not in¬ cluded in mitosis, in this strict sense. In this book, we shall use the term mi¬ totic cell division to mean a cell divi¬ sion which follows mitosis and results in duplicate sets of chromosomes in each daughter cell. There is another type of cell division which results in daughter cells each having only half as many chromosomes as the cell that produced them. It is called reduction division. You will learn more about reduction division later. For now, remember that mitotic CELLS— THE BUILDING UNITS 39 cell division results in two new cells with duplicate sets of chromosomes. At the end of cell division, each cell is smaller than the original cell. It starts to crow and grows to full size. Then it may divide again. This goes on and on, say, in the growth of an elephant or a redwood tree or a human being, until one original egg cell has produced the billions of cells that are the building units of these large living things. Summing up: two cells from one One cell divides into two cells. This process is a complicated one. The most important feature of mitotic cell divi¬ sion is the self -da plication of each chromosome and the equal division of the duplicates between the two new cells. Later you will learn in some de¬ tail why this is important. Right now, just remember that the chromosomes have a good deal of control over the whole cell, and consequently over the whole body of any plant or animal. TISSUES AND ORGANS Cells as building units of tissues Some cells live alone. As you may al¬ ready know, there are one-celled ani¬ mals and plants. But most plants and animals are made of many cells. In your own body there are many, many billions of cells. If you have permanent slides of liver cells, bone cells, muscle cells, skin cells, or gland cells from the human body, examine them. Or exam¬ ine slides of various parts of a plant: root, stem, leaf, flower. These slides show cells in each part of your body or in each part of a plant. You soon notice that all wood cells, say, or all muscle cells or all bone cells are much alike in all ways: shape, size, etc. In other words, your body is built of many billions of cells, but not many billions of different kinds of cells. On the contrary, your body is built of only a limited number of different kinds of cells. You could name several: muscle cells, bone cells, nerve cells, skin cells, and a few others. The bodies of many-celled plants and animals are also made of only a limited number of different kinds of cells. In a tree, there are wood cells, bark and cork cells, leaf-skin cells, and a few more. All the cells of one kind do the same kind of work. In an animal, mus¬ cle cells move, skin cells protect, nerve cells carry “messages.” All the cells of one kind that do the same kind of work in the body of a plant or animal are called a tissue. The main tissues in the human body are: 1. Covering tissue. The cheek cells you examined earlier in this chapter came from the lining of your mouth. This lining covers the inside of the mouth. It is a covering tissue. The outer layers of the skin cover the out¬ side of the body. Layers of cells that form covering tissues are usually called epithelium ( ep ih thee lih um ) . (See Figure 1-14.) Epithelium covers both the outside and inside surfaces of the body. The nose and the ear canals are lined with epithelium. So are the stomach and in¬ testine and windpipe and other internal surfaces. 2. Muscle tissue. All the muscles of the body are made up largely of muscle tissue. You have three kinds of muscles: (1) heart muscle, (2) muscles of the food tube and blood vessels, and (3) muscles that are attached to your bones, such as the ones that move your arms and legs. Under the microscope, it is easy to tell the three types of mus- 40 SIMILARITIES AMONG LIVING THINGS TISSUES IN THE HUMAN BODY 1-14 COVERING TISSUE The epithelium shown here is from inside the nose. The clear area at the top represents the nasal passage. The cells forming the epithelium are long columnar cells extending from the nasal passage almost to the bottom of the photograph. The black spots are the cell nuclei. Many nuclei are visible because the photograph shows a depth-of-view of sev¬ eral cells. All photos from General Biological Supply House, Inc., Chicago 1-15 MUSCLE TISSUE Left. Heart muscle is striped and has disks that take stain readily, producing occasional heavy cross lines. The disks are not held to be cell boundaries, for tiny fibers pass through un¬ interrupted. Below left. Smooth muscle (the vertical fibers in the photograph) is found in the walls of most internal organs and blood vessels. Below right. Skeletal muscle also is striped. It is usually attached to bones, hence its name. All three photo¬ graphs include nuclei— but only parts of the long cell bodies. I 1-16 CONNECTING AND SUPPORTING TIS¬ SUES Above left. Connective tissue fibers bind other tissues together. Above right. Droplets of fat in these fat-storage cells obscure other cell parts. Right. The irregu¬ lar-appearing bone tissue shown here is be¬ ing produced by the cartilage below it. 1-17 NERVE TISSUE Below left. These nerve cells are found in the spinal cord. To show the entire length of their fibers at this degree of magnification would require a photograph more than 1000 feet long. Below right. The nerve cells shown here are from the brain. Note the complex branch¬ ing of the fibers. / / All photos from General Biological Supply House, Inc., Chicago, except Figure 1-16, bone tissue, by Carl Striiwe, from Monkmeyer cle tissue apart. Figure 1-15 shows the difference. It also shows why one type is called striped muscle and another smooth muscle. The muscles in the walls of blood vessels and the food tube are smooth muscles. The ones that are fastened to bones are striped. Heart muscle is striped but in a class by itself. 3. Connecting and supporting tis¬ sues. Under this heading come all the tissues (Figure 1-16) that support the body and bind its cells and tissues to¬ gether. Chief of these are: (a) Connective tissue proper, which binds the cells together in each part of the body. The cells of connective tissue produce long threads that spread be¬ tween the other cells of a muscle, say, and bind them together. ( b ) Fat tissue, which is specialized in storing fat. Each cell is virtually filled with a droplet of fat or oil. ( c ) Bone and cartilage tissues, or the supporting tissues. Their cells are remarkable for their ability to fill up the spaces around them with lime and other hard materials. In this way they build bones, teeth, and cartilage. 4. Nerve tissue. This tissue makes up the brain, spinal cord, nerves, and parts of the eyes, ears, and other sense or¬ gans. Its cells produce long branches of cytoplasm (Figure 1-17). Nerve tis¬ sue is the conducting tissue of the body. Over it, “messages’’ are conducted from one part of the body to another. 5. Blood is usually listed as a tissue, in spite of the fact that its cells (Fig¬ ure (1-10) are not knit together. Tissues as parts of organs Tissues are organized groups of cells that work together. But no one tissue works alone. Take the heart as an ex¬ ample. Heart-muscle tissue makes up most of the heart, but not all of it. The 1-18 ORGANS IN A FLOWERING PLANT Each major part of this begonia is an or¬ gan, just as your hand or ear is an organ. The roots, for example, are organs made up of several tissues, including covering tissue, food-storage tissue, and water- and food¬ conducting tissues. muscle cells are bound together by con¬ nective tissue. Running through all parts of the heart are blood vessels and nerves. Covering tissue lines the inside and covers the outside of the heart. The heart is made up of several tissues that work together in pumping the blood. Biologists say that these tissues are organized into an organ. The heart, then, is an organ— a closely knit group of tissues working together at a task. The leaf of a green plant is an organ made of several tissues, including: (1) covering tissue, usually called the epidermis ( ep ih der mis ) , ( 2 ) con¬ ducting tissues through which water and sap circulate, and (3) a spongy CELLS— THE BUILDING UNITS 43 tissue whose cells have chloroplasts in them. All these tissues work together in making food. A leaf is a highly organ¬ ized group of tissues that work to¬ gether at one task. The body of any large plant or ani¬ mal has several organs. A begonia or any other seed plant has roots, stems, leaves, and flowers. All these are organs (Figure 1-18). A dog has eyes, ears, feet and legs, a heart, a brain, two lungs, two kidneys, and several more closely knit groups of tissues. All these are organs. Systems of organs A dog has a brain, a spinal cord, long nerves, and several sense organs (eyes, ears, tongue, nostrils, etc.). All of these organs work together. They enable the dog to see, hear, smell, taste, and feel things outside its body and to do something about these things. To¬ gether, all these organs make up a dog’s nervous system. Other organs make up a dog’s diges¬ tive system; still others, its breathing (or respiratory) system; and yet others, its circulatory system. Each system of organs does its specialized part in keep¬ ing the dog alive. You, too, have several systems of or¬ gans, as you know. So does a robin or a grasshopper or an elephant. Even an earthworm (fishing worm, in everyday language), an oyster, and a starfish have systems of organs. A whole animal is a highly organized living system . Its cells are organized into tissues, its tissues into organs, its or¬ gans into systems, and its systems into a living system— the whole animal. So a whole, living animal is an organism. If you would like to get a brief picture of the human organism and some of its tissues and organs, turn to the Human Body Charts following page 336 and scan them briefly. You will study them in detail later. Organisms A dog is an organism. So is a grass¬ hopper, an earthworm, a robin, and an elephant. Each one is a highly organ¬ ized living system. Every living animal, even a one- celled animal, is an organism. You probably know that an ameba ( uh mee buh) is a microscopic animal. It is a single cell (see Figure 3-2, page 77). While it cannot be thought of in terms of tissues and organs, an ameba is still a highly organized living system. You will learn many of the details of its organ¬ ization later. Right now, just remember that it is an organism. So are the 15,000 or so other known kinds of one-celled animals. A rosebush is also a highly organized living system. It is an organism. So is a grapevine or a blackberry bush or a redwood tree. So are ferns and mosses and the green pond scums so often seen on quiet pools of water. Even the mi¬ croscopic plants like yeasts and germs are organisms. We can now say that an organism is a highly organized living system. Every plant and every animal on earth is an organism. Organization— a keynote of life What is life? People have argued about that question for centuries. No one yet has been able to answer it cor¬ rectly in a few words. In a way, all biology is an ever-growing answer to that question. So we cannot define life for you, in a short sentence. But we can point out that being alive means being highly organized. A cell itself is highly organ- 44 SIMILARITIES AMONG LIVING THINGS izecl internally. In most many-celled plants and animals, cells are organized into tissues, tissues into organs, organs into systems, and systems of organs into the whole organism. Protoplasm, our word for all the liv¬ ing constituents of a cell, is a highly organized system of many complex parts. Protoplasm differs from organism to organism. Dog protoplasm differs from robin protoplasm. Protoplasm differs from organ to or¬ gan. A dogs liver protoplasm differs from its brain protoplasm. Protoplasm differs from tissue to tis¬ sue. Muscle-tissue protoplasm isn’t ex¬ actly like nerve-tissue protoplasm, even in the same dog. Protoplasm differs from cell to cell and from nucleus to cytoplasm. The protoplasm in one muscle cell isn’t ex¬ actly like the protoplasm in the next muscle cell. Even in the same cell, the nuclear protoplasm differs from the cy¬ toplasm. All in all, protoplasm is merely a con¬ venient word for any living matter. It is not the name of a single substance. Even so, all protoplasm is somewhat alike in several ways. One of the most important likenesses is its highly organ¬ ized complexity. As you go on exploring biology, you will build more and more meaning into the idea that organization is a keynote of life. In a way, it is the theme of bi¬ ology— or at least one main theme. CHAPTER ONE: SUMMING UP Cells are the building units of living things. The number of cells in any given organism may vary from a single cell in the one-celled plants and ani¬ mals to many, many billions of cells in the larger plants and animals. These cells, at least when young, have the same three main parts: nucleus, cyto¬ plasm, and cell membrane. Most plant cells also have cellulose cell walls. In many-celled plants and animals, all the cells are the offspring of a single egg cell. The cells are organized into tissues, the tissues into organs, and the organs into systems. Any living plant or animal is a highly organized living system, an organism. Your Biology Vocabulary Here is a list of important new terms used in this chapter. You will be using these words again and again in biology. All your life, you will be hearing and seeing and using some of these terms— in your conversation, in your reading, and in television and radio programs. It will pay you to make sure that you understand and can use each term correctly. The way to learn to use new words is to use them. Use them in talking with each other in and out of the classroom. Use them in conversation at home. Use CELLS— THE BUILDING UNITS 45 them in writing. Do not try to memorize the new terms and recite them. Learn them by using them and by continuing to use them. Soon they will seem to belong to you. Here are the important biological terms used in this chapter. wet mount permanent slide cell cell membrane cell wall nucleus nuclear membrane nucleolus cytoplasm protoplasm mitosis mitotic cell division tissue organ organism chloroplast chlorophyll chromosome centrosome spindle hemoglobin epithelium cellulose epidermis normal saline Testing Your Conclusions The purpose of this section at the end of each chapter in Exploring Biology is to help you review and organize what you have learned and to check your mastery of the im¬ portant facts and ideas. 1 . Let one student draw on the chalkboard a group of each of the four different kinds of cells you have studied. Draw guide lines from the essential parts of one cell in each drawing. Place a number at the end of each guide line. Each of you may then write down each number and beside it write the name of the part of the cell to which that guide line is connected. Repeat until you can identify the cell parts correctly. 2. On a fresh sheet of paper, sketch in order the four main “steps” in mitotic cell divi¬ sion. If you aren’t sure how to make these sketches, turn back to pages 36-38 and study the illustrations. Then close your book and try to make your own sketches. Label the main parts in each sketch. Beneath your sketches, answer these questions. Use complete sentences. a. Why is it easier to see the chromosomes when a cell is getting ready to divide? b. Biologists used to say that each chromosome split in half lengthwise during cell division. How do biologists now explain the “double look” of a chromosome at an early stage of cell division? c. Which part of a nucleus disappears during cell division and then reappears later? d. After one cell has divided into two cells, the two into four, the four into eight, and so on, until there are 128 cells, all of the 128 cells have duplicate sets of chromosomes. Can you explain how mitotic cell divisions give these results? 3. Copy the letter of each statement below. Beside the number write the word or ex¬ pression that correctly completes that statement, do not mark this book. a. One part that is present in an onionskin cell but not in a cheek cell is the . . . . b. Parts that are present in many leaf cells of green plants but not in onionskin cells are .... c. In a living cell, the nucleus is enclosed by the . . . membrane. d. The tissue that holds other cells and tissues together in an organ of a higher ani¬ mal is called .... e. The substance that makes red blood cells red is ... . f. The substance that makes green leaves green is ... . g. The tissue that carries “messages” in the bodies of larger animals is ... . 46 SIMILARITIES AMONG LIVING THINGS h. The human blood cells that do not have nuclei are the .... i. The ... of a cell lies between the nucleus and the cell membrane. j. Early in mitosis, each . . . builds a duplicate of itself. k. Mitotic cell division results in two cells with duplicate sets of ... . l. . . . are organized into tissues, and tissues are organized into organs. m. Every living thing, plant or animal, is a highly organized whole. That is why biologists call any living thing an ... . n. The growth of an egg into a baby chick is due partly to cell division and partly to the enlargement of . . . following cell division. More Explorations L Other cell investigations. Bring to class other materials you think may show cells. Make slides and examine them. Of course any part of any organism will show cells, if you can make thin enough slices. Make whatever records you wish of these ob¬ servations. 2. Looking for tissues. An onion is an organ of the onion plant. You have already seen one of its tissues. Make wet mounts and use your microscope to find other tissues in the onion. Apples have several tissues in them. See how many you can find with the help of your microscope. Look for tissues in an orange, a potato, a cucumber, or any other plant organ. There are several tissues in a frog’s foot. See how many you can find. Or try to find tissues in the leg of a grasshopper or fly. Make as many examinations for tissues as you care to. Be sure to make records of your observations in your record book. 3. A long-range project. Soak some dry beans overnight. Then plant them in moist saw¬ dust. When the first green leaves appear, pull up one whole plant. Snip off the tip of one root and lay it in a little water in a Petri dish or other small dish. With a sharp knife, slit the root tip lengthwise. Use two dissecting needles to pick bits of tissue out of the root tip. Mount a bit of this tissue in a drop of dilute iodine, add a cover slip and examine this wet mount under the high power of your microscope. You may be able to see cells that were dividing when killed. How do you recognize a dividing cell? In your biology record book, explain what you did and what you saw. You may prefer to record what you saw in sketches. 4. Staining human blood. (To be demonstrated by one student.) Clean two microscope slides. Scrub and prick your finger as directed on page 34, or in Figure 1-19. Refer often to Figure 1-19 as you proceed. Squeeze out a small drop of blood. To get that drop on a slide, touch the drop with one side of a clean slide. Lay the slide down so that the drop of blood is on the upper side of the slide. Next, touch that drop of blood with the end of a second slide. In a few seconds, the drop of blood will spread across the end of the second or top slide. Then, by moving the top slide quickly toward one end of the lower slide, spread the blood along the surface of the lower slide, making what hospital laboratory technicians call a blood smear. Now you are ready to stain the blood smear with Wright’s stain, available at many drugstores and biological supply houses. To stain the smear, lay the slide across the top of a small bottle or medicine glass. Pour enough Wright’s stain over the smear to cover it well. Wait one to two minutes, then add enough water (preferably dis- CELLS— THE BUILDING UNITS 47 All photos by Stanley Rice 1-19 PREPARING A STAINED BLOOD SMEAR A. An automatic device for pricking a fin¬ ger is shown in use. The needle is first retracted, then the end of the barrel is set against the finger and the trigger pulled. The needle shoots forward and pricks the finger. B. Squeezing the finger forces a drop of blood out through the punctured skin. C. A clean glass slide is used to pick up the drop of blood. ( continued on facing page) tilled water) to flood the whole surface of the slide. Wait two to three more minutes, then hold the slide under running water to rinse it, and lean it up to dry. When it is dry, it is ready to examine under your microscope. Thought Problems 1 . How could you tell stained frog’s blood from human blood under the microscope? 2. Why is it impossible for a one-celled organism to have tissues? 3. How can you distinguish between anything at all that is or has been alive, and all other things? 4. You have looked at blood cells, onionskin cells, leaf cells, and several other kinds of cells. You did not see any of the cells undergoing mitosis. But if you examined cells from the growing tip of a root, you did see several cells that were in one or another stage of dividing. Why is a growing root tip a better place to look for dividing cells than a leaf or an onion or blood? 5. Your body is made of many billions of cells. All of them came from one original egg cell, by repeated mitotic cell divisions. Do the nuclei in your liver cells and in your skin cells have duplicate sets of chromosomes? ° 6. The word protoplasm is a convenient one. Why is it somewhat misleading? Further Reading 1. Would you like to know more about cells? You will be learning more about them as you go on with this course. But you may want to read more about them now. If so, * Accidents do sometimes happen even to chromosomes, as you will learn later. Right now, assume that no accidents have happened to any of your chromosomes. 48 SIMILARITIES AMONG LIVING THINGS D. The end of a second slide, moved along the surface of the first, spreads the blood thinly over the surface of the first slide. E. Wright’s stain is applied liberally to the blood smear. Without such staining the blood cells would be almost invisible under the micro¬ scope. F. A minute or so after the stain has been added, water is added. After several more minutes, the slide is rinsed with running water. use any recent college textbook of biology, zoology (about animals), or botany (about plants). Here are a few references. Do not worry about the many technical terms in these references. You will be learning those you need when you need them. Life by George Gaylord Simpson et al., Harcourt, Brace, 1957. See pages 39-48. Principles of Zoology by John A. Moore, Oxford Univ. Press, 1957. See “The Cellular Nature of Organisms,” pages 32-45. Note particularly the discussion of “Levels of Organization,” pages 43—45. Botany, An Introduction to Plant Science, Second Edition, by Wilfred W. Robbins and T. Eliot Weier, Wiley & Sons, 1957. See “The Plant Cell,” pages 50—80. Looking Ahead In Chapter 3, you will be studying some of the one-celled organisms that may live in a drop of water. To have plenty of them to examine, start growing some now. To grow microscopic organisms rapidly, set up several bottles of water, preferably pond water. If you can’t get pond water, use tap water that has been left standing over¬ night. (Tap water, as you probably know, usually has chlorine in it to kill “germs.” The chlorine passes out of the water into the air when the water stands several hours in an open pan. Then microscopic organisms will grow in it. ) Fill each of several bottles half full of pond water (or tap water that has been stand¬ ing overnight). Number the bottles. To bottle No. 1, add a few dry leaves or some dry grass. To No. 2, add some garden soil and some leaves. To No. 3, add some of the green scum from a pond. To No. 4, add some sediment from the bottom of a shallow pond and then a water plant, such as elodea. These bottles we call cultures, because we culture (grow) one-celled plants and ani¬ mals in them. Keep these cultures in a warm place in the classroom until you are ready to use them. CELLS— THE BUILDING UNITS 49 2 Chemicals— the Building Materials other. \ et Doth these organ and all other plants and ani require many of the same substances in order to live . Ho w if - is it that living things have so o many similar needs P ■ HHHHH Roche Interchangeable parts All living things are so much alike in their chemical make-up that they can exchange many substances. A noted biologist has compared this situation to the “interchangeable parts” of many automobiles; for example, the clutch of one automobile is interchangeable with that of several others. However, it is substances in living things that are widely interchangeable, rather than whole parts like lungs or kidneys or hearts. It is true that a kidney has been sue- cessfully transplanted from one twin to another. And sometimes a certain part of the human eye can be transplanted from one human being to another. It is also true that blood from one human being can be transferred (by a blood transfusion ) to another person with the same type of blood. But all these are transfers from one human being to an¬ other, not from one kind of organism to another kind. On the whole, the tissues and organs of different organisms are not interchangeable, but many of the substances in one organism are inter¬ changeable with substances in many other kinds of organisms. You use many substances in your body that come from other types of organisms. For example, your cells use vitamin C from an orange and grape sugar from grapes and other plants. A child who has diphtheria may be cured by a substance taken from the blood of a horse that has previously been in¬ fected with diphtheria germs. All living cells contain some inter¬ changeable substances. Among them are water, oxygen, a large number of vitamins, grape sugar, salt, and other 50 SIMILARITIES AMONG LIVING THINGS substances that you will learn more about as you read this chapter. PROTOPLASM In a general way, the protoplasm in the cells of different kinds of living things has much the same chemical make-up. For example, the protoplasm in the cells of a redwood tree has much in common with the protoplasm in the cells of a whale. This is not to say that the protoplasm is identical in both kinds of cells. As you already know, the protoplasm in the cells of your liver isn’t identical to that in the cells of your heart. But all kinds of protoplasm have some identical substances and also have some features of physical make¬ up that are at least closely similar. What substance is most abundant in protoplasm? You might expect protoplasm to be made of something special, something found nowhere else, or at least some¬ thing rare. It isn’t. Protoplasm is made of common, ordinary substances, all of which are plentiful outside of living things. Not a single one of the really rare substances has been found essen¬ tial to the make-up of protoplasm. Protoplasm is largely water, common ordinary water. From 60 to 99 per cent of all protoplasm is water. For exam¬ ple, a common jellyfish (Figure 2-1) is about 99 per cent water. A thousand- pound jellyfish would have some 990 pounds of water in its body. In each 100 pounds of living tissues in your own body, there are some 68 pounds of wa¬ ter. Whether you are thinking of the protoplasm in the cells of onionskin or frog’s blood or your own brain, think of it as largely water plus lesser amounts of a number of other substances. What is protoplasm made of? Protoplasm is not all water. It in¬ cludes salt and other substances. MIXING SALT AND WATER. To help you understand more about the make-up of protoplasm, hold a glass of water up to a window and look through it while you drop into the water a teaspoonful of table salt. Where does the salt go? Stir the water for several minutes. Then hold the glass up to the window again. Can you still see grains of salt? Do you have any idea why? Mount and examine a drop of the salt water under your microscope. Can you see any grains of salt? We say that salt dissolves in water and makes a solution. 2-1 JELLYFISH Only one per cent of the materials in its protoplasm are substances other than water. Robert C. Hermes Dissolved salts make up almost ex¬ actly the same fraction,0 by weight, of the water in all protoplasm, whether it is that of an onion, a frog, or man. This fraction is much the same as that in sea water. Of course protoplasm isn't all salt wa¬ ter. Sugar and oxygen and other mate¬ rials are dissolved in the water, too. In addition, there are particles of several ° In case you want to know, the fraction is a little less than one per cent (0.9 per cent). Table salt alone makes up about 0.6 per cent of the weight of the salt water in protoplasm. In other words, 100 pounds of salt water in the living tissues of your body would contain six-tenths of a pound of table salt. The normal saline used in the last chap¬ ter was 0.9 per cent table salt, with no other salts in it. kinds scattered all through the water solution. You probably saw some par¬ ticles in the cytoplasm of some of the cells you have already looked at. You can't see particles in a solution, even under the high power objective of your microscope. So the particles in proto¬ plasm that are visible under the micro¬ scope (Figure 2-2) must be made of something other than the substances in solution. To understand the make-up of those particles and the things that happen to them, you must turn to chem¬ istry and physics. For now, think of vour cells as little sacks filled with a substance that is largely salt water but is so thickened by the presence of other microscopic and submicroscopic parti- 2-2 LIVING PROTOPLASM Under the high power of the microscope (using dark-field illumination), a one-celled ameba is revealed as a naked bit of protoplasm. The visible particles are but the larger ones; many times this number are too small to be visible. Roman Vishniac, from Scientific American cles that it has about the consistency of raw egg white or thick glue. Chemistry is the study of the sub¬ stances that make up everything in or on or above this earth and the changes that may take place in those substances. Biochemistry ( by oh kem iss tree ) is the study of the chemistry of living things. Physics is the study of matter and motion. Biophysics (byohnziks) is the study of matter and motion in plants and animals. The very names biochemistry and biophysics show that biology is no longer looked upon as something separate and apart from chemistry and physics. Many of the great biological discov¬ eries of recent years have come from biochemistry and biophysics. The ever¬ growing list of new medicines such as sulfa drugs and antibiotics ( an tih by ot iks ) is an example. Biochemists are learning more and more about cell chemistry. They have found out exactly what some of the vitamins do in living cells. They can now make in the test tube many of the substances once made onlv by plants or animals. They can make in the test tube virtually all the known vitamins, penicillin and other anti¬ biotics, synthetic rubber, and hundreds of other substances. All these man-made drugs and other materials are known as synthetics. Obviously, the student of up-to-date biology must know some chemistry and physics. The next section will review a few basic facts from these two sci¬ ences. Summing up: make-up of protoplasm Protoplasm is made up largely of wa¬ ter with several salts, sugar, and other substances dissolved in it. Scattered through the water are larger particles of various kinds. You will learn more about the other substances in proto¬ plasm as you read on. COMPOSITION OF MATTER What is matter made of? Anything that takes up space and has weight is matter. Protoplasm takes up space and has weight. So of course it is matter. To understand the make-up of protoplasm you need to know some¬ thing about the make-up of matter. All matter is made of atoms. You know that. Ever since the atom bomb burst on Hiroshima on August 6, 1945, the word atom has been on the lips of people all over the world. But this doesn’t mean that many people know what an atom is. What is an atom? Unfortunately, you can’t put a single atom on a slide and look at it under your microscope. The smallest speck you can see with the best lens of the best compound microscope contains millions of atoms. Atoms are exceedingly small particles of matter. You probably learned that in general science. The smallest atoms are those of hydrogen. Hydrogen atoms are so small that to reach an inch it would take 250 million of them, far more than there are people in the whole United States. The smallest particles that can be seen under a compound microscope must be big enough so that 125 thou¬ sand of them will reach an inch. Even the largest atoms are only five or six times as large as a hydrogen atom. So it would take some 50 million of the largest ones to reach an inch. Even the biggest atoms are far, far too small to look at under your microscope (Fig¬ ure 2-3). CHEMICALS— THE BUILDING MATERIALS 53 Dr. Martin J. Buerger 2-3 ATOMS UNDER THE ELECTRON MICRO¬ SCOPE Above. An atom of iron and two of sulfur combine to form a molecule of iron pyrite, often called “fool s gold.” Many iron pyrite molecules are visible here; that is, the enlarged images of these molecules are visible, as cast on a screen by a “beam” of electrons. The larger black dots represent the iron atoms, the smaller dots the sulfur atoms. ( 2, 000, 000 x) Below. In the com¬ plex structure of a crystal of tungsten, each atom is represented by an individual light spot. ( 800, 000 X) Dr. Erwin Muller Until comparatively recently, many chemists and physicists thought atoms were the smallest particles of matter. They thought atoms were solid, like marbles. And they thought atoms could not be divided or broken into smaller pieces. The very word atom was coined from a Greek word that means “that which cannot be cut or divided.” Today nearly everybody knows that atoms can be divided or split and that splitting them sets loose atomic energy. The atom bomb proved that to the world, but physicists knew it long be¬ fore 1945. Some 50 years ago, physicists had discovered that atoms were not solid particles. They were certain that atoms were made of still smaller par¬ ticles with plenty of space between them. What are atoms made of? Atoms are made of three main kinds of smaller particles: electrons, pro¬ tons, and neutrons.* Small as atoms are, some kinds have large numbers of these particles in them. An atom of or¬ dinary uranium, for instance, has 330 separate particles in it: 92 electrons, 92 protons, and 146 neutrons. And that is not all— there is plenty of room be¬ tween the electrons. Atoms are small, but electrons, pro¬ tons, and neutrons are far smaller. And yet by 1917 the weight of a single elec¬ tron had actually been calculated by the noted physicist and Nobel Prize winner, Dr. Robert A. Millikan, then of the University of Chicago. Millikan also estimated how many electrons pass through the carbon fila- * Several other kinds of particles have now been found in atoms. Some of these exist only for a fraction of a second. The research in this field goes on rapidly, but as yet it doesn’t seem necessary to discuss any other atomic particles here. ment of a 16-candle power lamp in one second. His estimated number looks fantastic— 883,000,000,000,000,000 or 883 thousand million millions— but that is about the number of electrons that pass through the fine carbon filament of a 16-candle power lamp in one second. Think of it! In the modern light bulbs in your home today, many more times that many electrons pass through the filament every second. Electrons are not only fantastically small. They are also fantastically fast-moving particles. Everything is made of electrons, pro¬ tons, and neutrons, plus other atomic particles. This book and the print in it, the air and the clouds, the sun and the stars, and the protoplasm in your cells —all these are made of electrons, pro¬ tons, and neutrons. How can things as different as protoplasm and the sun be made of the same fantastically small particles? You shall see. The smallest atom, hydrogen, is made of one proton and one electron (Figure 2-4). The next larger atom, helium, has two protons and two electrons. Next in size comes the lithium atom with three protons and three electrons. The larg- 2-4 DIAGRAM OF ATOMS OF TWO ISOTOPES OF HYDROGEN p indicates a proton, n a neutron. The drawings are not to scale, for if the nucleus were the size shown, the electron would be many, many miles away. Nucl eus (lp) i | # ( 1 P ) \ /V Electron ^ - ^ Atom of Atom of ordinary isotope of hydrogen hydrogen TABLE 2 -A ATOMS OF THE TEN SIMPLEST ELEMENTS Element No. of electrons No. of protons Usual no. of neutrons 1. Hydrogen 1 1 0 2. Helium 2 2 2 3. Lithium 3 3 4 4. Beryllium 4 4 5 5. Boron 5 5 6 6. Carbon 6 6 6 7. Nitrogen 7 7 7 8. Oxygen 8 8 8 9. Fluorine 9 9 10 10. Neon 10 10 10 est atom commonly found in nature is uranium. It is 92nd in size and has 92 protons and 92 electrons. Any substance that contains just one kind of atom is an element. So hydrogen, helium, lith¬ ium, and uranium are elements. Every element has an atomic num¬ ber. That number tells you how many protons and electrons that element has in its atoms. For example, the atomic number of hydrogen is 1, that of helium is 2, and so on, to uranium whose atomic number is 92. Table 2- A lists the ten elements with atomic numbers from 1 through 10. Look at the table and you will see, for example, that carbon has 6 protons and 6 electrons in each atom, so the atomic number of carbon is 6. Scientists have long since listed 92 elements known to occur in nature, starting with hydrogen with atomic number 1 and running through urani¬ um with atomic number 92. In recent years, scientists have made several more kinds of atoms in their labora¬ tories, so that now a complete list would have over 100 kinds of atoms and hence over 100 kinds of elements. The one with the atomic number 100 has 100 protons and 100 electrons in each of its atoms. Elements with 93 or CHEMICALS— THE BUILDING MATERIALS 55 more protons and electrons in each atom may or may not occur in nature. There is some indication that traces of some of these elements do occur natu¬ rally, but too little evidence is available at the present time. Table 2- A also shows you that every atom of a particular element like hy¬ drogen has the same number of pro¬ tons and electrons as every other atom of that element; one of each in the case of hydrogen. But some atoms of an ele¬ ment have more neutrons than other atoms of the same element. For exam¬ ple, each atom of the most common form of hydrogen has no neutrons at all. Each atom of a second form of hy¬ drogen has one neutron and each atom of still a third form has two neutrons. These three forms of hydrogen are called isotopes ( eye suh tohps ) of each other. The only difference in the make¬ up of any two isotopes is that one has more neutrons in its atoms than the other one has. Isotopes You have just read about the three hydrogen isotopes. There are two or more isotopes of all the known ele¬ ments. Take carbon, for example. The most common form of carbon has six neu¬ trons in each atom. This form of carbon is often called carbon 12 (Figure 2-5). The 12 is the sum of the number of neutrons ( 6 ) and protons ( 6 ) . One iso¬ tope of common carbon has seven neu¬ trons, and it is called carbon 13. The 13 is the sum of the number of neu¬ trons (7) and protons (6). Carbon 14 is a third isotope of carbon. Can you tell how many neutrons an atom of car¬ bon 14 has in its nucleus? (Remember, the number of protons in an atom of any element is always the same, six in carbon carbon 2-5 DIAGRAM OF ATOMS OF TWO ISOTOPES OF CARBON Carbon 12 (6p, 6n) is the common form. Carbon 14 is radioactive. the carbon atom.) There are several other isotopes of carbon, too. The uranium used in the atom bomb is an isotope of the most common form of uranium. The common form of ura¬ nium is uranium 238 (each of its atoms has 146 neutrons and 92 protons in it). The uranium isotope used in the atom bomb is uranium 235. Can you tell how many neutrons each of its atoms has? Two other isotopes are uranium 232 and 233. Radium is an element. You have probably heard or read about it, since it is sometimes used in treating cancer. The most common isotope of radium is radium 226. Its atoms have 138 neu¬ trons and 88 protons. As you probably know, radium and uranium make a Geiger counter tick. This is because some of their atoms are constantly breaking down or shooting off particles and/or rays. The particles shot off by the disintegrating atoms hit the Geiger counter and make it tick. These parti¬ cles also affect photographic negatives if they strike them. And they may kill cancer cells if they hit them. Uranium and radium are radioactive elements. Some of the isotopes of many other elements are likewise radioactive; that 56 SIMILARITIES AMONG LIVING THINGS is, some of their atoms are always breaking down and giving off particles and/or rays. Carbon 14 is radioactive. So is hydrogen 3. Two isotopes of iron and all isotopes of uranium are radio¬ active. Radioactive isotopes are usu¬ ally called radioisotopes, for short. Radioisotopes Many radioisotopes are what you might call by-products of the making of atom bombs. The United States Atomic Energy Commission ships out these radioiso¬ topes to research scientists at univer¬ sities and other institutions for use in many kinds of chemical and biological research. Some radioisotopes are also available to doctors for use in treating patients with certain types of disease. For the first time in history, trained investigators can now follow some atoms (those of radioisotopes) wher¬ ever they go. To do this, investigators use a Geiger counter or the even more sensitive scintillator ( sin tuh lay ter ) . For example, a radioisotope may be placed in the soil, traced into meadow grass, then into a cow and its milk, and finally into the body of the person who drinks the milk. It was research with radioisotopes which showed that only about two per cent of the atoms now in your body are the same ones that were there a year ago. Much of our newest knowledge of protoplasm and of what goes on in liv¬ ing cells has come from research done with radioisotopes. On page 465, Spec- tor’s Handbook of Biological Data, Saunders, 1956, lists 55 radioisotopes which are used in biological research. Each radioisotope has what scientists call a half life. The half life of radium is 1,620 years. That means that it takes 1,620 years for half of the atoms in any given bit of radium to disintegrate. So, if a given piece of pitchblende had one million atoms of radium in it 1,620 years ago, it now has just half a mil¬ lion atoms of radium left. The other half-million atoms of radium have bro¬ ken down, or disintegrated, as physi¬ cists say. In another 1,620 years, only one quarter of a million atoms of ra¬ dium will be left in that bit of pitch¬ blende. The half life of hydrogen 3 is 12.4 years while that of carbon 14 is 5,570 years. Both hydrogen and carbon enter into the make-up of all protoplasm. Ra¬ dioisotopes of both these elements may also enter into the make-up of proto¬ plasm, where they can be traced with a scintillator. Internal organization of atoms As most scientists now picture an atom, the neutrons and protons are lo¬ cated somewhere near the center, in an area called the nucleus. The electrons are thought to speed around the nu¬ cleus through orbits (Figure 2-6), in somewhat the way our earth and the other planets move through orbits around the sun. If the nucleus of a hy¬ drogen atom were as large as the pe¬ riod at the end of this sentence, the orbit of its electron would be some fifty miles away. This shows how mistaken men were when they thought an atom was solid. Actually, an atom seems to be largely emptiness, because its particles take up so little of the room in it. As of now, we think of electrons and protons as indivisible. However, we know that neutrons, under certain con¬ ditions, disintegrate, and that a disin¬ tegrating neutron may give off an elec¬ tron, leaving a proton. Perhaps next year or a hundred years from now, some scientist will have discovered that even CHEMICALS— THE BUILDING MATERIALS 57 2-6 ARTIST'S CONCEPTION OF ORBITING ELECTRONS In this representation of a carbon atom (not drawn to scale), note the exact orbits in which the electrons surrounding the nucleus are supposed to be. Whether the orbits are usually this exact or are so irregular that the electrons should be thought of as making up a “cloud” around the nucleus is a point not all scientists agree upon. electrons and protons are made up of still smaller particles. Summing up: atoms To sum up, atoms are not solid. They are made of protons, electrons, and neutrons, plus other particles, with plenty of room between the particles (specifically, between the electrons and the particles in the nuclei). There are 92 natural kinds of atoms and ten or so more man-made kinds. Each kind of atom has the same number of protons and electrons. Dif¬ ferent forms of the same kind of atoms are isotopes. Isotopes differ in the num¬ ber of neutrons in each atom, and many isotopes are radioactive. Everything is made up of atoms. CHEMICAL COMBINATIONS Water, like everything else, is made up of atoms— but not just one kind of atom. Water is made of hydrogen and oxygen atoms. These two kinds of atoms are not mixed together in a glass of water the way you might mix red and white beads in a glass. The atoms in a glass of water are bound together in “sets” of three, with two hydrogen atoms and one oxygen atom in each “set.” Each “set” of three bound atoms in water is a molecule. If you were to let a gray bead stand for an atom of hydrogen and a green bead for an atom of oxygen, then you might tie two gray beads and one green bead together with a little fine wire and let the whole stand for a molecule of water, although this 58 SIMILARITIES AMONG LIVING THINGS model would be quite imperfect. For one thing, the atoms in a molecule of water are joined by chemical bonds, not by fine wire. The smallest unit of water is the molecule (Figure 2-7, page 60). If the hydrogen and oxygen atoms in water molecules are separated, say, by a cur¬ rent of electricity, you no longer have water, but two elements, hydrogen and oxygen. Obviously water is not an element. Its molecules contain two kinds of atoms, not just one kind as do the mole¬ cules of elements. Water is a com¬ pound. Carbon dioxide is another com¬ pound, important in biology. Each of its molecules contains one atom of car¬ bon and two atoms of oxygen (Figure 2-7). There are hundreds of thousands of known compounds. The molecules of every compound are made of two or more kinds of atoms chemically bound together. Chemists use a kind of shorthand to indicate atoms and molecules. They use H as a symbol for an atom of hy¬ drogen, O for one of oxygen, C for one of carbon, N for one of nitrogen, Cl for one of chlorine, and so on. The short¬ hand for a molecule of water is FLO, pronounced H-two-O. It tells you that a molecule of water contains two atoms of hydrogen chemically bound to one of oxygen. The symbol for a molecule of carbon dioxide is C02. What does it tell you? There are molecules of elements, too, but these contain only one kind of atom. H2 is the symbol for a molecule of the element hydrogen. It tells you that a hydrogen molecule contains two chemi¬ cally bound hydrogen atoms. 02 is the symbol for a molecule of oxygen, and N2 stands for a molecule of nitrogen. What does each symbol tell you? Compounds in protoplasm Most of the substances in living pro¬ toplasm are compounds. One of these is grape sugar. The symbol for a mole¬ cule of grape sugar is CgH12Og, pro¬ nounced C-six-H-twelve-O-six. This symbol tells you that a molecule of grape sugar consists of six atoms of car¬ bon, 12 of hydrogen, and six of oxygen (Figure 2-8, page 60), all bound to¬ gether chemically. Table 2-B lists sev¬ eral kinds of molecules and their sym¬ bols. What does each one tell you? The symbol CgH12Og has something else to tell you. It not only shows that grape sugar is a compound. The carbon atoms in its molecules also indicate that grape sugar is a special kind of com¬ pound. Grape sugar is an organic com- TABLE 2-B FAMILIAR COMPOUNDS Compounds Elements present Formula of one molecule Water Hydrogen, oxygen H20 Table salt Sodium, chlorine NaCl Grape sugar Carbon, hydrogen, oxygen CeH^Oe Cane sugar Carbon, hydrogen, oxygen C12H22O11 Egg albumin Carbon, hydrogen, oxygen, nitrogen, sulfur C696H1125O220N175S8 Milk casein Carbon, hydrogen, oxygen, nitrogen, sulfur, phosphorus C708H1130O224N 108S4P 4 Human hemoglobin Carbon, hydrogen, oxygen, nitrogen, sulfur, iron C3032H48160872N78oSsFe4 CHEMICALS— THE BUILDING MATERIALS 59 pound. The word organic comes from organism. An organism, as you know, is any living thing, plant or animal. So organic refers to plants and animals. Nearly all compounds made by organ¬ isms are known to contain carbon. Organic chemistry is the chemistry of the carbon compounds. Compounds that are not organic are inorganic. Water (FLO) is one exam¬ ple. Inorganic compounds are the ones that do not contain carbon. Look over the compounds in Table 2-B and pick out the organic and inorganic com¬ pounds. Close to a million kinds (800,000) of compounds are known. Some two- thirds of these are organic. For some reason it takes living things to make most carbon compounds, with a few exceptions such as carbon dioxide. Car¬ bon dioxide is produced outside of liv¬ ing things as well as inside them. And chemists today make many carbon com- 2-7 STICK MODELS OF CARBON DIOXIDE AND WATER MOLECULES The carbon di¬ oxide (C02) model is above, the water (HoO) below. Each ball represents an atom, and each stick a chemical combina¬ tion. Try to locate each kind of atom. 2-8 STICK MODEL OF A GRAPE SUGAR MOLECULE Not only the count of types of atoms but their arrangement in mole¬ cules helps to determine the nature of compounds. The molecular “plan” of grape sugar (C6H1206) is recorded in this stick model. pounds in test tubes. But in nature, car¬ bon compounds are made only by living things, with a few exceptions. Molecules Most molecules are bigger than atoms, but still exceedingly small. For example, if each molecule in a glass of water were suddenly to change into a grain of sand, there would be enough O 7 O sand to cover our whole nation a hun¬ dred feet deep. Of course, water mole- cules are quite small as molecules go. Sugar molecules are larger, but still are pygmies compared to certain protein (proh tee in ) molecules. Protein mole¬ cules contain many smaller molecules chemically bound together. They may have hundreds or even thousands of atoms in them. No wonder they are called “giant molecules.” Some of the giant protein molecules are eight mil¬ lion times as big as a hydrogen atom. Even so, they are way below the range of the compound microscope. It took a different kind of microscope to get the pictures of molecules shown in Figure 2-3 on page 54. Molecules are never still. Even in a solid rock the molecules are always on the move. They dart this way and that, run into each other, bounce off, and move on in another direction (Figure 2-9). You must have seen the dance of dust particles in a beam of light shining into an otherwise dark room. No, those dust particles are not single molecules. But their movements do show, in a way, what the constant movement of molecules is like. What is more, it is partly the motion of the air molecules around the dust particles that keeps those particles in motion. Of course, air currents in the room also make dust particles move. But even without air currents, the moving air molecules keep hitting the particles of dust and push¬ ing them this way and that, until the dust finally settles. Think of the way a group of children might push a huge ball around and you will get some idea of the way moving air molecules push dust particles about. Molecules of air (and of all other substances ) are al¬ ways on the go. The particles in the cytoplasm of an onionskin cell do not lie perfectly still. They, too, are kept in motion in some¬ what the way dust particles in air are. The molecules in the water in cells are always moving. They bump into the particles in the cytoplasm and help keep them moving, too. The constant motion of molecules explains why salt dissolves in water. When you put salt in water, the salt molecules move out among the water molecules. Soon they are scattered all through the water and you have a so¬ lution. The same thing happens to sugar molecules in tea. A solution, then, is a liquid with single molecules of another 2-9 MOLECULAR MOTION All molecules are in motion, frequently hitting one an¬ other and taking a new direction. Many scientists believe that the energy of mo¬ lecular motion is what we know as heat. page 61 kind scattered all through it. The con¬ stant motion of the molecules explains why some substances dissolve in water or in some other liquid. The motion of the molecules also ex¬ plains many other things. For example, you hang wet clothes on the line. The water molecules move out into the air and in due time the clothes are dry. See if you can explain why potatoes may boil dry, why your feet seem to sweat more than your hands, and why your breath has moisture in it. All these have to do with moving molecules. Molecules are forever changing Not only are molecules forever on the move, but under suitable conditions, many of them change rapidly, too. Think of a candle on your birthday cake. When you set up suitable condi¬ tions by holding a match to the wick, the molecules change rapidly. You say the candle burns. This is due to rapid changes in the molecules. The molecules of fat in the candle contain atoms of carbon, hydrogen, and oxygen. About a fifth of the air around the candle is oxygen. At room tempera¬ ture, the molecules in the candle and in the air stay much the same. But apply¬ ing a match to the wick changes that. Oxygen from the air combines chemi¬ cally with hydrogen from the candle molecules, forming molecules of water. Taking the hydrogen atoms out of the candle molecules leaves only carbon and oxygen atoms. These form carbon dioxide. Both the water and the carbon dioxide pass off into the surrounding air. At the same time, heat and light energy are set free. You start out with molecules of fat (candle) and oxygen. You end up with molecules of water and carbon dioxide. In the meantime, heat and light are given off. ACTION OF YEAST ON STARCH. Stir a teaspoonful of cornstarch into a pint of warm water. Take out a spoonful of the mixture and add a little dilute iodine. The iodine will turn the mixture blue. This shows there is starch present. Now crumble a yeast cake into the mixture of starch and water. Keep the mixture warm but not hot. Every ten minutes, take out a spoonful and add iodine to test for starch. As time goes on, the test shows less and less starch and finally none at all. The yeast has changed all the starch into sugar. (In case you want to know, the yeast then changes most of the sugar into alcohol and carbon dioxide.) Chemical and physical changes In the burning of a candle and the changing of starch to sugar, the mole¬ cules change. New kinds of molecules appear. A change of this kind is natu¬ rally called a chemical change, since the make-up of the molecules changes. Any change in chemical make-up is a chemical change (Figure 2-10). 2-10 CHEMICAL CHANGE Burning changes the make-up of the molecules in candle wax. Marion A. Cox 62 SIMILARITIES AMONG LIVING THINGS Marion A. Cox 2-11 PHYSICAL CHANGE Crushing chalk does not change the molecular make-up. There are changes that are not chemi¬ cal. For example, crush a piece of chalk. The chalk has changed in ap¬ pearance, but it is still chalk. Its mole¬ cules have not been changed. Freeze some ice cubes. The water has changed from liquid to solid, but it is still water and its molecules are still water mole¬ cules. Such a change is called a physi¬ cal change (Figure 2-11). Can you think of more examples? Summing up: the composition of matter The following statements summarize the important points in this section. 1. All matter is made of atoms. 2. Molecules are made of atoms and are always on the move. 3. Atoms are made of electrons, pro¬ tons, and neutrons, plus some other kinds of particles. 4. More than 100 kinds of atoms are known; at least 92 occur in nature. Each kind of atom has an atomic num¬ ber. The atomic numbers of known kinds of atoms run from 1 to over 100. The atomic number of an atom is the same as the number of protons in that kind of atom. 5. All of the atoms with the same atomic number have the same number of protons and electrons, but certain of them may have a few more or a few less neutrons than others. Atoms that differ only in the number of neutrons are isotopes. 6. Any substance all of whose atoms have the same atomic number is an ele¬ ment. Two or more isotopes of every element are known. 7. Some isotopes of many elements are radioactive and are called radio¬ isotopes for short. 8. Compounds have two or more kinds of atoms chemically bound to¬ gether in their molecules. 9. Nearly all compounds that have carbon atoms in their molecules are or¬ ganic compounds. All other compounds are inorganic. 10. Salts and many other substances dissolve in water, forming solutions. 11. All of these facts are useful in understanding the nature of proto¬ plasm. THE NATURE OF PROTOPLASM You already know that protoplasm is largely water that has several salts, sugar, and other substances dissolved in it, and that contains still other parti¬ cles large enough to be seen under your microscope. The particles in protoplasm that are visible under your microscope are made of millions of molecules clumped together, as in the nucleolus, or strung together, as in the chromosomes. In other words, the molecules in the visi¬ ble parts of a living cell are not in solu¬ tion. CHEMICALS— THE BUILDING MATERIALS 63 MIXING OIL AND WATER. It is easy to get some idea of how small even the larg¬ est particles in protoplasm are. Label two test tubes 1 and 2. Fill each one half full of tap water. To No. 1, add one teaspoonful of salad oil. To No. 2, add one teaspoonful of salad oil plus one tea¬ spoonful of soap powder. Shake each test tube until the contents are well mixed, then stand them in a test-tube rack for several minutes. Examine each test tube. Where is the oil now located in tube No. 1? Can you see where the oil is in tube No. 2? Mount and examine under your micro¬ scope a drop from tube No. 2. Sketch what you see. Suspensions As you probably learned in general science, the three most obvious states in which matter may exist are gases, liquids, and solids. The same substance may exist in all three states. Water, for example, may exist as an invisible va¬ por in steam before it condenses on dust particles, or as a liquid in a glass of water, or as a solid in an ice cube. But a solution— a salt solution, for ex¬ ample— isn’t entirely liquid water. Mole¬ cules of salt in the solution are scat¬ tered all through the water. The salt molecules are so small that gravity ex¬ erts almost no pull at all upon them. On the other hand, they are also so small that they are at the mercy, so to speak, of the always-moving water molecules which keep bumping and pushing the salt molecules about. Oil mixed with water is not a solu¬ tion. The oil droplets are many, many times bigger than the salt molecules in a solution. They are so big that gravity does affect them. Since they are lighter than water, they rise to the top of the water (Figure 2-12). Parti¬ 2-12 USING SOAP TO SUSPEND OIL IN WATER How does the soap affect the oil? cles of fine sand mixed with water may stay scattered through the water for a while. As long as they do, we say they are suspended in the water and form a suspension. But even the smallest sand particles are so big that gravity affects them. Since they are heavier than wa¬ ter, they settle to the bottom. So we say that a fine sand and water suspension is an unstable suspension. There are a number of unstable suspensions. Fresh milk is one. Its cream droplets rise to the top. Homogenized milk acts differ¬ ently. It has been treated to break up the ordinary cream droplets into very much smaller droplets. The cream drop¬ lets in homogenized milk are so small that the effect of gravity is more than counterbalanced by the moving water molecules around them. The cream does not rise to the top of homogenized milk because its particles are so small that they are not affected by gravity. On the other hand, the cream particles in homogenized milk are much, much 64 SIMILARITIES AMONG LIVING THINGS larger than single salt molecules. So homogenized milk is not a simple solu¬ tion. It is a stable suspension. Its drop¬ lets stay suspended in the milk. Would you say that the oil-soap- water suspension you made (Figure 2-12) is a stable or an unstable sus¬ pension? Why? We can now define a stable suspen¬ sion as any mixture in which the larg¬ est particles are big enough but not too big to remain scattered throughout the liquid (or other substance). There is another name for a stable suspension. Any stable suspension is a colloid (kol oyd ) . The three types of mixtures just dis¬ cussed are solutions, unstable suspen¬ sions, and stable suspensions or col¬ loids. The differences between true so¬ lutions, unstable suspensions, and col¬ loids are due to differences in the sizes of the particles of the substances mixed with water (or with some other sol¬ vent similar to water). In true solu¬ tions, the mixed-in substance breaks up into separate molecules (of submicro- scopic size) that scatter through the water (or other solvent) and remain scattered through it. In unstable sus¬ pensions, the mixed-in substance breaks up into comparatively large droplets (or other particles) easily visible under the low power objective of your mi¬ croscope. In colloids, the mixed-in sub¬ stances exist in particles of sizes in be¬ tween the size of molecules scattered through a solution and the size of drop¬ lets or other particles scattered for a while through an unstable suspension. The particles scattered through a col¬ loid may be visible under the high power objective of your microscope. There is no hard-and-fast dividing line between the size of the smallest particles suspended in an unstable sus¬ pension and the largest ones suspended in a colloid. Hence, no exact mathe¬ matical definition of a colloid can be formulated. Examples of colloids are glue, raw egg white, and homogenized milk. By the way, suspensions of one liquid in another, like cream drops in the water in milk, are called emulsions. The oil-water-soap suspension is an emulsion. So is milk. As you will learn later, all the butter and cream and oth¬ er oils you eat have to be changed into emulsions before you can digest them. What has all this to do with proto¬ plasm? It lays a basis for an under¬ standing of the physical nature of pro¬ toplasm. The physical make-up of protoplasm In one way, protoplasm is like raw egg white or homogenized milk. Its largest particles do not rise to the top nor fall to the bottom of a cell. In other ways, protoplasm is not like raw egg white or homogenized milk. Protoplasm is alive. They are not. But the sizes of the particles in protoplasm make it a colloid, or, better, a living colloidal system. As one biologist put it, the particles in protoplasm are “just the right size'’ to make life possible. Protoplasm is a living colloidal sys¬ tem, made up largely of water with various salts and other substances in solution, and with larger particles of several kinds held in stable suspension in it. All the living constituents in a cell make up its protoplasm. It must now be obvious to you that protoplasm is a highly complex living system, but none¬ theless one made up of atoms and molecules. How many molecules do you suppose there are in one living cell in your body? The biochemist Hoff- CHEMICALS — THE BUILDING MATERIALS 65 meister ° lias estimated the number of molecules that are found in a single liver cell of a human being. Here are his estimates: 225,000,000,000,000 53,000,000,000 166,000,000,000 2,900,000,000,000 molecules of water molecules of proteins molecules of fats and oils molecules of smaller size You would be wasting your time to try to memorize Hoffmeister’s estimates. | ust look at them and try to realize how impossible it is to understand the com¬ plexity of protoplasm. Colloids may be semiliquids or semisolids Raw egg white is a colloid. So is the white of a boiled or fried egg. In the raw egg white, the water solution car¬ ries separate particles. So raw egg white is a semiliquid. In the cooked egg white, the particles join up and make a sort of network that enmeshes the wa¬ ter. So cooked egg white is a semi¬ solid. Raw eiis; white is a colloid in the sol state. Cooked egg white is a colloid in the gel state. Heat changed the sol into a gel. This gel (egg white) can¬ not change back into the sol state, but some gels can. The protoplasm of all your cells, and of the cells of any other living thing, is J O o? a colloidal svstem. The cell membranes J and nuclear membranes of your living cells are colloids in the gel state. With¬ out these gels, the contents of your cells would run out, and you couldn’t live. Most of the cytoplasm and some of * Professor Donald Frederick Hoff meister, University of Illinois. the nuclear protoplasm in your living cells are in the sol state. You will learn why that is important as you proceed. When the colloidal particles in sol protoplasm concentrate enough to form a network enmeshing the rest of the protoplasm around these particles, then the protoplasm becomes gel. You have read that colloidal particles may be vis¬ ible under the high power objective of your microscope. This is true of the larger particles in protoplasm, but in a living cell, by far the majority of col¬ loidal particles are too small to be visi¬ ble in this way. Even under the elec¬ tron microscope, which magnifies the image of a cell tens of thousands of times, special techniques are required to bring out the detail you see in Fig¬ ure 2-13. The main components of protoplasm Protoplasm is made up largely of six main classes of substances. They are: (1) starches and sugars, (2) fats and oils, (3) proteins, (4) vitamins, (5) wa¬ ter, and (6) minerals— salts, phos¬ phorus, etc. These six classes of sub¬ stances are necessary in all living cells. There is a constant flow of materials into and out of living cells. The foods you eat must supply all the materials your cells need. All organisms use about the same food materials, the six classes named above. These six classes of foodstuffs necessary for living things are often called nutrients. Chemical make-up of nutrients A molecule of starch or sugar is made up of atoms of carbon, hydrogen, and oxygen. So is a molecule of fat or oil. For example, a molecule of grape sugar, as you know, is C0H12O6. A molecule of the fatty acid that gives rancid butter its foul odor is C4H8(X. How, then, can 66 SIMILARITIES AMONG LIVING THINGS Dr. Don W. Fawcett, Cornell University Medical College 2-13 PARTICLES IN THE PROTOPLASM OF AN ANIMAL CELL Colloidal particles may be fibrillar or granular or both. In the part of a cell visible here, fibrillar particles that appear to be colloidal in nature are easy to see. The photograph shows part of a cell from a re¬ productive gland of an adult man. Extending up and down on the right is the edge of - the cell, or the cell membrane. To the left are certain bodies found in the cytoplasm. The nucleus is not visible; at this magnification, it would be perhaps two feet to the left. The fibrillar particles shown are thus all near the edge of the cell. It is not unlikely that they take part in sol-gel transformations. CHEMICALS— THE BUILDING MATERIALS 67 chemists so easily distinguish starches and sugars from fats and oils? In all starches and sugars, each molecule has twice as many atoms of hydrogen as it has of oxygen. This is never true of a molecule of any fat or oil. Look at the formulas on page 66, one for grape sugar with H120(, or 6H0O in it, and one for a fatty acid with Hs02 in it. You can see why chem¬ ists class starches and sugars as carbo¬ hydrates ( kahr boh hy drayts— made up of carbon and water ) . F ats and oils are not carbohydrates. Can you explain why? Proteins also contain carbon, hydro¬ gen, and oxygen, but these are not all. In addition, proteins always contain atoms of nitrogen, while sugars, starches, fats, and oils never do. It may help you to remember this fact if you notice that there is an n in the words nitrogen and proteins, while there is no n in the words starches, sugars, fats, and oils, all of which substances lack nitrogen. Usually proteins contain a few sulfur and phosphorus atoms in ad¬ dition to those of carbon, hydrogen, oxygen, and nitrogen. Most vitamins have carbon, hydro¬ gen, oxygen, and nitrogen in their mole¬ cules, but some kinds have only carbon, hydrogen, and oxygen. In a later unit, you will study your vitamin needs in some detail. Read through the list of nutrients in Table 2-C and make a list of the ele¬ ments they contain. How many ele¬ ments are there on your list? It should show six (not counting the minerals): carbon, oxygen, hydrogen, nitrogen, sulfur, and phosphorus. Take the ini¬ tials of those six elements and you get cohn, s. p. That might stand for a man’s name in a telephone book. Learn the name and you will find it easy to re¬ member the six elements most common in protoplasm. Small amounts of other elements do occur in living things. There is a little iron in hemoglobin and a little mag¬ nesium in chlorophyll. There is cal¬ cium in bones and teeth. Tomato seeds have some zinc in them. Several other elements also enter into the make-up of living things. Altogether some 20 ele¬ ments have been found in the bodies of virtually all plants and animals. Some biochemists report that as many as 40 elements have been proved to TABLE 2-C CLASSES OF NUTRIENTS Nutrient Elements it contains Sugars and starches Carbon, hydrogen, oxygen (The number of hydrogen atoms is double that of oxygen atoms.) Fats and oils Carbon, hydrogen, oxygen (The number of hydrogen atoms is more than double that of oxygen atoms.) Proteins Carbon, hydrogen, oxygen, nitrogen, and usually sulfur and phosphorus Vitamins Carbon, hydrogen, oxygen, and usually nitrogen Water Minerals: Hydrogen, oxygen Table salt Sodium, chlorine Calcium Calcium Phosphorus Phosphorus Iodine and several others Iodine 68 SIMILARITIES AMONG LINING THINGS take part in some processes in some organisms.* But all of them are com¬ mon elements. Protoplasm is made of elements that are common outside of living things as well as inside them. Oxidation in living cells In the burning of the candle, you will remember, oxygen combines with hy¬ drogen from the candle fat. The chemi¬ cal combination of oxygen with any other element is called oxidation. And oxidation is one of the most common chemical changes in living cells. Oxidation is going on right now in some of the cells in your eve as you read these words. Oxidation is also go¬ ing on in the nerve cells that are carry¬ ing “messages” from your eyes to your brain and in those brain cells that are getting the “messages.” For that matter, oxidation goes on in all your living cells all the time. It takes two kinds of molecules for oxidation to occur. It takes oxygen and fat molecules in the case of the burning candle. In your cells, it takes oxygen molecules and molecules of one of the organic compounds, say, grape sugar. A molecule of grape sugar is CGH1206. An oxygen molecule is 02. During oxi¬ dation, oxygen atoms from the oxygen molecules in the air vou breathe com- J bine chemically with hydrogen atoms from the grape sugar molecules. As oxidation goes on, energy is set free. A cell starts with grape sugar and oxygen molecules and ends up with water, car¬ bon dioxide molecules, and energy. Chemists say it this way: Grape Carbon sugar Oxygen Water dioxide Energy C6Hi206 + 602 — ► 6H20 + 0CO2 + energy * For a complete list, see page 19, Human Biochemistry by Israel S. Kleiner, C. V. Mosby Co., 1954. This formula is a short way of saying that one molecule of grape sugar plus six molecules of oxygen produce six molecules of water, six molecules of carbon dioxide, and energy. And this is what the oxidation of grape sugar in a living cell comes to, when it is fin¬ ished. The oxidation of grape sugar in a liv¬ ing cell isn’t finished in a single step, however. Between the start and the finish, some 20 steps are known to bio¬ chemists. What is more, not just one but several chemical changes occur be¬ tween the start and the finish. Some of these chemical changes are not oxida¬ tions. But they are necessary steps in the complete oxidation of grape sugar in a living cell. And they, too, or some of them, release energy. All 20 steps are included in the complete oxidation of grape sugar in a living cell. Fats and proteins also supply energy, but only after a number of chemical changes take place. First the molecules of fats and proteins are broken down into simpler molecules. Then some of the resulting molecules undergo still further chemical changes, one of which may be complete oxidation. Some of these chemical changes, including oxi¬ dation, release energy. From the chemical changes in the nutrients, all living cells get all their energy. Energy from your food not only keeps you warm, but it also en¬ ables you to do everything you do. You will learn more about some of the chemical changes that take place in your body in a later unit. Respiration (oxidation in living cells ) is one of them and always supplies energy. Chemical changes in protoplasm The only way protoplasm can stay the same is to keep changing. Read that CHEMICALS— THE BUILDING MATERIALS 69 sentence again. The only way proto¬ plasm can stay the same is to keep changing. It doesn’t make sense, does it? Now read the sentence again, but this time read “whirlpool ' in place of “protoplasm.” The only way a whirl¬ pool can stay the same is to keep chang¬ ing. Does that make sense? Of course. The water in a whirlpool today isn’t the same water that was there yester¬ day. If it were, it would be a pool, not a whirlpool. So the only way a whirl¬ pool can stay the same is to keep changing. Of course a cell isn’t a whirlpool. Its protoplasm doesn’t whirl around. Not at all. But some of the molecules in pro¬ toplasm this minute aren’t the same ones that were there a minute ago. Some molecules will change in the next minute. This applies both to the mole¬ cules in solution and to those that cling together in the suspended particles. The molecules in protoplasm keep changing all the time. That’s why we say that the only way protoplasm can stay the same (alive and active) is to keep changing. The molecules in protoplasm are for¬ ever changing. Chemical changes in living cells keep the cells alive. You have just read about some examples of oxidation in living cells. These are among the most common chemical changes in protoplasm, but there are many more. You will be learning about the chemical changes in cells all through this course. Of course, there is a word for it. The sum total of all the chemical changes that take place in any organism is called metabolism ( muh tab uh liz’m ) . Res¬ piration is metabolism. So is digestion. All the life processes are metabolism. So it is a useful word to know. You may already have heard it used in the phrase "basal metabolism test.” You will find out later what this test is and whv doctors have it made in certain cases. CHAPTER TWO: SUMMING UP Plants and animals are made of cells. Cells are made of protoplasm. And pro¬ toplasm is made of elements that are common outside living things as well as inside them. The six most abundant elements in protoplasm are carbon, oxv- gen, hydrogen, nitrogen, sulfur, and phosphorus. Several other elements, such as iron, zinc, and magnesium, do occur in living cells, but in small amounts. Nearly all the building materials of living cells are compounds. These in¬ clude starches and sugars, fats and oils, proteins, vitamins, water, and salts and other minerals. Protoplasm is largely water with salts and other substances dissolved in it. Scattered through it are particles large enough to be seen under a compound microscope. In physical make-up, protoplasm is a colloid. Its colloidal nature plays an important role in life processes. The only way protoplasm can stay the same is to keep changing. Many of the changes in protoplasm are chemical changes. Of these, respiration is one of the most common and important. Res¬ piration is the oxidation of substances in living cells. From it, cells get enersv that enables them to do everything they do. Protoplasm is the most complex sub¬ stance known. You may think chem¬ ists have learned all there is to know about it. They have not. Probably they have barely made a good beginning. But the more they learn, the better we can understand ourselves and other liv¬ ing things. 70 SIMILARITIES AMONG LIVING THINGS Your Biology Vocabulary Here is a list of the important new terms introduced in Chapter 2. Make sure you understand and can use each term correctly. electron proton neutron atom molecule radioactive elements elements compounds isotopes radioisotopes half life solution unstable suspension atomic number emulsion colloid or stable suspension gel state sol state organic compounds inorganic compounds chemical change physical change carbohydrates proteins oxidation respiration nutrients synthetics metabolism Testing Your Conclusions Match the items in Column B with those not be used, do not mark this book. Column A 1 . atomic number a. 2. C0H12Ofl and 02 b. 3. colloids 4. H.,0 and CO., c. 5. metabolism 6. neutrons d. 7. organic compounds 8. proteins e. f. g- h. i. i- in Column A. Two items in Column B will Column B have the smallest known molecules, always have atoms of nitrogen in their mole¬ cules. include such typical examples as egg white, homogenized milk, and protoplasm, signify the molecules of two substances that result from complete oxidation of grape sugar. signify the molecules of a carbohydrate and an element. includes oxidation, respiration, and other processes. have carbon atoms but may or may not have nitrogen atoms in their molecules, traces radioactive materials from one or¬ ganism to another. indicates the number of protons in each atom of an element. vary in number in isotopes of the same ele¬ ment. CHEMICALS— THE BUILDING MATERIALS 71 More Explorations 1. Examining, carbon. Burn a wooden match and save what is left. Then, with tweezers, hold a small piece of bread in the flame and let it burn. Do the same thing with a bit of lean meat, then with a bit of fat bacon. The “black” on what you have left, in each case, is largely carbon, even as the “black” in coal is largely carbon. A diamond is almost pure carbon. In your biology record book, explain what you did, and answer these questions. a. Did all the substances you burned have organic compounds in them? How do yon know? b. Would you guess, to look at it, that lean meat has carbon in it? Why would you expect to find carbon in an apple? c. How would you explain the differences in appearance between carbon and carbon compounds? 2. Examining sulfur and phosphorus. You may borrow a bottle of sulfur and one of phos¬ phorus from the chemistry department. Do not take the phosphorus out of the bottle, as it sometimes “catches fire” when exposed to the air. It is safe to take the sulfur out of the bottle. Look again at the carbon you already have, and at the sulfur and phosphorus speci¬ mens. Then look at your hand. Is it any wonder that it took mankind a long time to find out that protoplasm contains these elements? 3. Setting up a demonstration. On a table in your classroom, set out the items listed below: a glass of water a salt shaker of salt a bowl of sugar a box of cornstarch a bottle of salad oil a plate of butter a shelled, hard-boiled egg a bottle of vitamin capsules On a cardboard of poster size, print neatly in large letters: examples of types of substances in protoplasm. Place the poster on the table with the items. 4. Preparing oxygen. It is easy, but slightly dangerous, to demonstrate the preparation of oxygen. Consult your teacher if you wish to try it. 5. Chemical and physical change. Demonstration. a. Examine a piece of magnesium ribbon. It is made of magnesium atoms alone. Hold the piece of ribbon with tweezers and light it in a flame. The white ash that results is made by the union of atoms of oxygen with atoms of magnesium. b. Crush a piece of chalk and look at the white powder. In both cases you get a white powder. How do you know one of the changes was a physical and the other a chemical change? 6. Protoplasm on the move. Make a slide of a young elodea leaf. Place the slide in a good light for ten minutes. Then examine the slide under high power. Can you see anything moving in the cells? If so, make a drawing and indicate the motion with arrows. (Parts of the protoplasm that you will not be able to see are also moving.) Then examine under high power a living ameba from a drop of pond water and watch the streaming of particles in its cytoplasm. Make a sketch of the ameba and use arrows to show the motion of particles in its cytoplasm. 72 similarities among living things Thought Problems 1. Finish this sentence: “The only way protoplasm can stay the same is to . . . Now give an example, to show that you really understand this sentence. 2. You may have looked at the chromosomes in cells that were dividing. How do you know that a chromosome is not a single molecule? 3. You burned magnesium and got a white, powdery ash. Is the ash heavier or lighter than the original bit of magnesium ribbon was? Why? 4. Respiration goes on all the time inside your cells. Does it involve the destruction of anv atoms? In other words, does respiration reduce the number of atoms in the cell? What makes you think one way or the other? Further Reading 1. If you found the make-up of protoplasm interesting, you may enjoy reading Chap¬ ters 1 and 2 in Unresting Cells by R. W. Gerard, Harper & Bros., 1949. On page 38 in this book you will find these words: “Now what is a man worth; an average man, one hundred and fifty pounds of him? Simple enough: thirty pounds of carbon, fifteen cents’ worth of coal; . . . .” Wouldn’t you like to read the rest of it? 2. For excellent and detailed discussions of the nature of protoplasm, refer to any recent college text. Here are three specific references. Life, George Gaylord Simpson, et al., Harcourt, Brace, 1957, pages 48-51. Principles of Zoology, John A. Moore, Oxford Univ. Press, 1957, pages 12-30. Botany, An Introduction to Plant Science, Second Edition, Wilfred W. Robbins and T. Eliot Weier, Wiley & Sons, 1957, pages 52-53. CHEMICALS— THE BUILDING MATERIALS 73 CHAPTER Life Processes— the Basic Activities A definition of life found in a dictionary begins: “Life is that which . . ” ( But what is “that”? ) No one knows what life is. Biologists still seek the answer in many ways, but mainly through a study of life processes— the basic activities of living things . Life in a drop of water Less than 200 years after Columbus discovered America, Antony van Leeu¬ wenhoek ( lay ven hook ) discovered another new world, the world of life that can exist in a drop of water. Leeu¬ wenhoek was born in Delft, Holland, in 1632, and lived most of his 90 years in that town. He was an unusual man, and a busy man. A linen merchant and a surveyor, he also served more than 50 years as ‘ chamberlain to the sheriffs of Delft,” a job similar to that of jani¬ tor today. In spite of all these occupa¬ tions, Leeuwenhoek found time to per¬ fect the art of grinding bits of glass into lenses. These lenses he built into sim¬ ple, one-lens microscopes. Some of his microscopes magnified 150 times and more. It was with his microscopes that he discovered what he later called “ani¬ malcules” (little animals) in a drop of rain water that he had kept in a dark closet for some time, and in drops of water that he had collected from many other places. In the beginning, Leeuwenhoek nev¬ er dreamed that there might be plants and animals small enough to live by the thousands in a few drops of water. Nor did anyone else imagine such a micro¬ scopic world might exist. Leeuwen¬ hoek’s first glimpse of his new world seems to have been in the late summer of 1674. He had gone fishing in a lake some two miles from his home, and happened to notice what he called “green clouds” floating in the water. He collected a bottle of water with some of the “green cloud” in it and carried the bottle home. 74 SIMILARITIES AMONG LIVING THINGS Next clay Leeuwenhoek examined a drop of that water with one of his mi¬ croscopes. Here is part of a letter he wrote to the Royal Society in England, describing what he saw. ‘1 found float¬ ing therein . . . some green streaks, spirally wound serpent-wise— and or¬ derly arranged— and there were very many small green globules as well. Among these, there were, besides, very many little animalcules— some round¬ ish, others a bit bigger and oval. And the motion of these animalcules in the water was so swift, and so various, up¬ wards, downwards, and round about, that ’twas wonderful to see.” * In these words, Leeuwenhoek described his first glimpse of the living things no one had even seen or even imagined before. Today they are still “wonderful to see. MICROSCOPIC ANIMALS AT WORK Leeuwenhoek’s “little animals” were busy doing a number of things. Each little animal was a single cell. With its single cell, each one-celled animal does everything it must do to stay alive. YOUR FIRST OBSERVATIONS. On page 49, directions for starting cultures were given. Use those cultures. Do what Leeu¬ wenhoek did. Examine a drop of water from one of the cultures under the microscope. You should see "very many little animal¬ cules" darting "upwards, downwards, and round about," just as Leeuwenhoek did. If you do not, make another slide from an¬ other culture. When you find what seem to be hundreds of little animals, watch them under low power. * From Antony van Leeuwenhoek and His “ Little Animals ” by Clifford Dobell, reprinted bv permission of Harcourt, Brace & Company. You will enjoy reading other sections of this book. Most, and possibly all, of the animals on your slide are one-celled.00 What are they doing? At first, you may think they aren't doing anything except darting here and there. But keep on watching them. What do they do when they run into something? Now place three or four grains of salt in the water at the edge of the cover slip. What do the animals do now? Make a new slide and place a drop or two of dilute vinegar at the edge of the cover slip. What do they do this time? Make another siide. Watch the animals for some time. Hunt for one that looks as if it were being pinched in two. If you watch it long enough, you will see the two halves break apart. Then each one will go its own way, a complete one-celled animal. What do one-celled animals do? From what you have now seen on your slide, you know that one-celled animals move about and that they are sensitive and react to such things as salt or vinegar. And they sometimes divide into two cells, each a complete one- celled animal, which soon grows as large as the original animal. In other words, one-celled animals may multi¬ ply by dividing. When they do, they are reproducing. By this time you will probably find that most of the animals on your slide have collected around an air bubble or around the edge of the cover slip (Figure 3-1). What makes them do this? They need air, or better, the oxy¬ gen in the air. Air dissolves in water, wherever the two are in contact. But the cover slip shuts the air out of most of the water on the slide. The animals * * You may also see a water flea or a worm or a rotifer ( roh tih fer ) on the slide. All these are more than one-celled and will be discussed later. But most of the animals in your cultures are one-celled. LIFE PROCESSES— THE BASIC ACTIVITIES 75 have used up the oxygen from the air that was in the water when the slide was made. Now they are driven to places where air is still dissolving into the water— around an air bubble or at the edge of the cover slip. As long as there is plenty of air in the water around these animals, mole¬ cules of oxygen keep moving through their cell membranes into the cyto¬ plasm. There the air takes part in the oxidation of food molecules. The oxida¬ tion of food molecules in a living cell is respiration, as you know. So respiration must be added to the list of things the one-celled animals are doing. The list of basic life processes you have now observed in these animals in¬ cludes movement, respiration, sensitiv¬ ity and reaction, growth, and reproduc- 3-1 OBSERVING ONE-CELLED ANIMALS UN¬ DER THE MICROSCOPE After a time these tiny animals move toward and collect at J the edge of the cover slip. Why? General Biological Supply House, Inc., Chicago tion. The one-celled animals also do several other things. They take in food, so food-getting is a basic life process. They change their food into substances that can either be readily oxidized or built into their protoplasm. Changing foods into substances of these kinds is digestion. They also produce waste ma¬ terials and get rid of them, often through their cell membranes. Getting rid of these wastes that are produced is excretion ( eks kree sh’n ) . So what do one-celled animals do? They do these basic things: (1) they move about, (2) they take in food, (3) they digest food, (4) they take in oxygen and carry on respiration, (5) they excrete wastes, (6) they grow, (7) they are sensitive and react to many things, and (8) they reproduce. Kinds of one-celled animals How many different kinds of one- celled animals did you see? There are thousands of kinds. Biologists have de¬ scribed and named over 15,000 kinds*/ And they have one name for the w hole group. They call all of them, together, the protozoa ( proh toh zoh uh ), proto meaning “first" and zoa meaning “ani¬ mals.” Probably the “first animals” on earth were one-celled. Two common kinds of protozoa are the ameba and the slipper animal. Let’s see how they carry out the basic proc¬ esses of living. O The ameba Your teacher will help you find an ameba (Figure 3-2) under vour micro- scope. Watch the animal under high power. At first you may find it hard to believe you are looking at an animal. At first sight an ameba looks more like a blob of jelly than a living organism. But keep watching. Soon you will see BLUEPRINT OF A RROTOZOON -AMEBA Pseudopod Contracting uole Nucleus Food vacuoles Photo from General Biological Supply House, Inc., Chicago 3-2 The ameba is an organism famous for what it isn’t— complex in make-up. This tiny blob of protoplasm has no fixed shape, no top or bottom, no front or back, and no spe¬ cialized parts within it other than a nucleus and vacuoles. Yet it carries on the same basic life functions as, say, man. (Photograph and drawing of a living ameba under the high power of a microscope.) the cell membrane bulge out at one or more places. Then the cytoplasm will How into a bulge and keep flowing un¬ til the whole animal has moved into the bulge. Then another bulge will appear and the ameba will flow into it. This will happen over and over again. You might say an ameba uses its bulges in somewhat the way a larger animal uses its feet. So those bulges are often called false feet. Biologists call them pseudopods ( soo doh podz ) , pseudo meaning “false’ and pods mean¬ ing “feet.” Figure 3-2 shows you what a pseudopod looks like. Some kinds of amebas put out several pseudopods at once; others usually put out only one at a time. Keep watching the ameba. You may see it “flow” up to a particle of food, perhaps a microscopic animal or a bit of pond scum. Then the next thing you know, that food will be inside the ameba. The ameba takes in food by flowing up to and around it. Biologists say that the ameba ingests its food, and therefore they call this method of tak¬ ing in food ingestion. Keep your eye LIFE PROCESSES— THE BASIC ACTIVITIES 77 msaamm on the bit of ingested food inside the ameba. Soon a clear area will appear around it. The clear area is filled with liquid. It is the only “stomach” an ame¬ ba has. Of course it is not a stomach. It is a digestive food vacuole. Sub¬ stances in the liquid within the vacuole attack the ingested bit of food. If it is a bit of pond scum, the contents of the pond scum cells disappear. Only its cell walls are left. What has happened? The ameba has digested its food. Substances formed in the ameba’s protoplasm pass into the vacuole and break down the laro;e food molecules in each bit of food. The smaller mole¬ cules that are left dissolve in the fluid and then move out into the ameba’s cytoplasm, where they may be oxidized to supply energy or built into the proto¬ plasm. Building molecules from food into living protoplasm is assimilation (uh sim uh lay shun ) . In this way, the ameba digests and assimilates its food. When the ameba has digested its meal, it will flow slowly away, leaving behind the empty cell walls of the plant cells. Why didn't it digest the plant cell walls? It can’t. It can't change the cellulose molecules into smaller ones. Neither can you. The ameba gets rid of, or eliminates, this solid waste simply by moving on and leaving it behind. (We do not say, in this case, that the ameba excretes the wastes. Ex¬ cretion refers only to the elimination of wastes produced by an organism, not to indigestible parts of its food. You may have noticed what looks like a rather large bubble in the ameba. This bubble is another kind of vacuole. Watch it closely. Suddenly it will seem to disappear. Then it will show up again, enlarge, then disappear again. This vacuole is very important. Water molecules are always entering the ame¬ ba through its cell membrane. That water would soon make the ameba swell up and burst, if it were not for this bubble-like vacuole. First the vac¬ uole fills up with water. Then it con¬ tracts and “squirts’’ the water out of the ameba’s body. So we call this vacuole a contracting vacuole. It eliminates the 3-3 The offspring of this ameba (shown reproducing by mitotic cell division) will truly be “chips off the old block,” unless an accident should somehow alter a chromosome. Each of the two offspring will have a set of chromosomes like those of its parent; thus it will have its parent’s characteristics— and no others. (In one kind of ameba, sexual re¬ production [involving two parents] may occur. Would it be possible for the resulting off¬ spring to be “chips” off either “old block”?) TABLE 3-A LIFE PROCESSES IN PROTOZOA Life process A meba Paramecium Food-getting Ingestion (flows around its food) Oral groove and cilia Digestion Digestive food vacuole Digestive food vacuole Movement Pseudopods Cilia Respiration Oxygen enters through the cell membrane and respiration takes place throughout the cell. Excretion Contracting vacuole and cell membrane Contracting vacuole, cell membrane, and anal pore Sensitivity and reaction Whole cell Whole cell Reproduction * Cell division, controlled by nucleus Cell division, controlled by nucleus Growth Whole cell Whole cell * Both animals may also reproduce in another way. Figure 3-5 illustrates two methods of repro¬ duction for paramecia. excess water and some cell wastes. Most of the cell wastes, like carbon dioxide from oxidation of foods, are not eliminated by the contracting vacuole, but are excreted directly through the cell membrane. Like other protozoa, the ameba mul¬ tiplies by mitotic cell division. The nu¬ cleus of one ameba undergoes mitosis, during which duplicate sets of chromo¬ somes are produced. Then the ameba divides into two new amebas, each with a duplicate set of chromosomes. This is reproduction (Figure 3-3). See Table 3-A for a brief summary of the way an ameba carries on its basic life processes. The slipper animal This unusually large protozoon, bare¬ ly visible to your naked eye, gets its name from its shape. When you ex¬ amine it under the microscope, you can see that the slipper animal is shaped somethin 2; like the sole of a shoe or a ‘ slipper.” Biologists call the slipper ani¬ mal a paramecium ( pair uh mee see um —plural, paramecia) . The paramecium is a single cell, even as the ameba is. But the paramecium has several more parts in its body than the ameba has, as you can see in Figure 3-4. For one thing, a paramecium has a kind of “mouth” and “gullet.” The “mouth” is an opening in the cell mem¬ brane, and it leads down the “gullet” into the inside of the cell. Like you, a paramecium takes in food through its “mouth” and passes the food down through its “gullet.” Biologists do not call the opening in the cell membrane the “mouth.” Instead they call this en¬ trance passage the oral groove (Fig¬ ure 3-4). For another thing, a paramecium is covered all over with tiny hairlike things. These are not “hairs” at all, but simply fine projections of the cell mem¬ brane. Paramecia use these hairlike projections in swimming, somewhat as you might use oars to row a boat. They also use the projections around the oral groove to sweep bits of food (mostly bacteria ) into the body. These hair¬ like projections all over the parame- LIFE PROCESSES— THE BASIC ACTIVITIES 79 BLUEPRINT OF A PROTOZOON —PARAMECIUM Food vacuoles Contractin vacuole Cilia Contracting vacuole Small nucleus Large nucleus Cilia Oral groove Gullet Food vacuole forming Anal pore Photo by Roman Vishniac 3-4 Unlike an ameba (Figure 3-2), a paramecium has a definite shape, two nuclei, and several well-developed organelles in addition to its food vacuoles and contracting vac¬ uoles. It has, for example, an oral groove, cilia, and an anal pore. And yet both organisms —ameba and paramecium, dissimilar as they are— are one-celled animals (some biologists prefer to call them acellular or “not-celled”) . (Photograph and drawing of a living para¬ mecium under the high power of a microscope.) cium are called cilia ( sil ee uh— singu¬ lar, cilium). The cilia are used both in food-getting and in locomotion (mov¬ ing from place to place). Paramecia, like amebas, have diges¬ tive food vacuoles, in which bits of food are digested. They also have con¬ tracting vacuoles. Each slipper animal has two contracting vacuoles, one at either end, which eliminate excess wa¬ ter. Most of the other cell wastes are excreted through the cell membrane. A paramecium excretes some wastes and eliminates any solid particles that cannot be digested, through an open¬ ing in its cell membrane, the anal (ay n’l ) pore ( Figure 3-4 ) . All together, a paramecium has a good many special parts in its single cell. These special parts are not true organs. Can you explain why? But they do special work, even as the organs of larger animals do. So we call them organelles ( or gan elz— little organs ) . 80 SIMILARITIES AMONG LIVING THINGS Cilia, the oral groove, the digestive and contracting vacuoles, the anal pore- all these are organelles. What organ¬ elles does an ameba have? Paramecia grow and they reproduce by mitotic cell division, or sometimes by a process called conjugation (kon jooGAYsh’n). (See Figure 3-5.) They are also sensitive and react to many things. See Table 3- A for a brief sum¬ mary of the way paramecia carry out the basic life processes. 3-5 A. Like an ameba, a paramecium usually reproduces by mitotic cell division. The offspring are like the parent, unless an accident should occur to a chromosome. B. At times paramecia reproduce by conjugation. Here there is an exchange of nuclear material before reproduction, after which many nuclear changes take place in each parent. The two parents divide to become four intermediate offspring, which in turn divide to become eight new paramecia, none of which is exactly like either of the original two. Summing up: microscopic animals at work Protozoa have to do about the same things any other organism has to do to stay alive. They (1) take in food, (2) di¬ gest and assimilate food, (3) move about, (4) take in oxygen and carry on respiration, (5) excrete wastes, (6) re¬ produce, (7) are sensitive and react to many things, and (8) grow. So their basic life processes are: food-getting digestion movement respiration excretion reproduction sensitivity and reaction growth The one-celled animals seem very simple as compared with rosebushes, oak trees, robins, elephants, or people. Actually, as you now know, even the protozoa are highly organized bits of protoplasm with several specialized parts, or organelles. MICROSCOPIC PLANTS AT WORK your microscope. Try to find one filament that is lying apart from the others, so that you can see this single plant well. What do you notice first in one of these plants? Probably the green chloroplasts. Next try to see how the cells are put to¬ gether. Each filament of pond scum is one plant of several cells. Its cells are attached end to end. Turn to high power and focus carefully. Can you see where one cell ends and the next one starts? Now look for some "green streaks, spiral¬ ly wound serpent-wise," as Leeuwenhoek put it. When you find them (or you may already have them), you will be looking at one of the most common kinds of pond scum. It has been named for its spiral chlo¬ roplasts. It is called spirogyra (spy ruh JY ruh). Examine one spirogyra cell carefully under high power. Sketch a spirogyra as it looks to you under low power, then under high power (Figure 3-6). Then mount a few spirogyras in a drop of strong salt water and watch what happens. You probably ran across some little green plants on some of your slides. You are most likely to find little plants shaped like long threads. These are pond scums. A single pond scum plant is a long “thread’’ of cells, end to end. So one plant is a filament, which means a “thread.’’ A filament is not one-celled, but you may also have found some one- celled green plants on your slides. Most of these microscopic plants lie still. So they are not as exciting to watch as the protozoa are. Even so, you can learn a little about the way they carry on their basic life processes by watching them. EXAMINING POND SCUMS. Mount sev¬ eral filaments of pond scum and look at them under the low power objective of Life processes in spirogyra Watch as long as you please, but you will not see a spirogyra dart about the way protozoa do. Spirogyras lack loco¬ motion. However, inside each cell, par¬ ticles in the cytoplasm do move about. So there is motion inside the plant. Another thing you’ll never see a spi¬ rogyra do is take in food. Pond scums have no “mouths.” They do not take in solid food as protozoa do. Why? Be¬ cause they make their own food. The green chloroplasts make sugar out of carbon dioxide and water. Then the plant makes starch and other foods out of the sugar. So food-making is a life process of spirogyra. If you mount a bit of spirogyra in dilute iodine and examine a chloroplast closely under high power, you may be 82 SIMILARITIES AMONG LIVING THINGS Photo from General Biological Supply House, Inc., Chicago 3-6 A. These microscopic plants were first seen by Leeuwenhoek ('‘green streaks, spirally wound . . B. Spirogyra cells photograph clearly under the high power of a microscope. C. Note the two chloroplasts per cell. Some spirogyras have several in each cell, others only one. able to see bits of blue color strung along the chloroplast. The iodine stain turns starch grains blue. So the bits of blue color strung along the chloroplasts show where the starch grains are lo¬ cated. Certain organelles in the chloro¬ plasts seem to be the centers where sugar is changed to starch. These or¬ ganelles are the pyrenoids ( py ruh noyds). Maybe you can see pyrenoids on your fresh slide. If not, you can cer¬ tainly see them on a permanent stained slide of spirogyra, such as the one in Figure 3-6b. You may or may not be able to see the vacuoles in a spirogyra cell, but they are there (Figure 3-6c). These vacuoles contain water with many sub- LIFE PROCESSES— THE BASIC ACTIVITIES 83 stances dissolved in it. This water solu¬ tion in a vacuole is often called cell sap. Out of materials in the cell sap, the liv¬ ing;; cell gets its food materials and its oxygen. A vacuole in a plant cell does not digest foods or eliminate water, as a vacuole in a protozoon does. Rather it stores necessary substances and sup¬ plies them to the rest of the cell, as needed. Spirogyra mounted in strong salt wa¬ ter changes in appearance. The cell contents pull away from the cell walls. That is because water has passed out of the cytoplasm through the cell mem¬ brane and cell wall into the salt water. Loss of water makes the spirogyra cells shrink and pull away from the cell walls. Why don't the cell walls shrink? Water molecules are not the only ones that can pass through cell mem¬ branes. There is a steady flow of mate¬ rials into and out of the spirogyra cell through its cell membrane and cell walls. Molecules of water, oxygen, and certain minerals are always passing into the cell. Molecules of carbon dioxide and other cell wastes are always pass¬ ing out of the cell. The cell membrane helps to regulate this flow of materials. Inside the spirogyra cell, foods are digested and assimilated into the pro¬ toplasm, or oxidized (respiration) . Movement of particles in the cytoplasm occurs. Even though you can’t see their re¬ actions, spirogyras are sensitive to such things as light and do react to things around them. And spirogyras grow. When one cell divides into two cells, the thread¬ shaped plant grows longer. Sometimes a spirogyra filament (thread) breaks in two. Then each piece 3-7 Reproduction by conjugation is sexual, resulting in offspring that differ in some ways from either parent cell. Two cells from two spirogyra filaments grow a connecting tube, and the contents of the two cells fuse forming a spore, which in turn produces a new plant. Five stages in this process of reproduction are shown below. A COMMON METHOD OF REPRODUCTION IN SPIROGYRA grows longer by cell division and you have two spirogyras, where before you had one. This is reproduction. Usually, however, it takes two spirogyra plants to produce young. Figure 3-7 shows, in simplified form, how the two “parents” produce one-celled spores which later grow into new plants. You will learn more about these spores later. Tree green: pleurococcus There are many kinds of one-celled plants. Several kinds of one-celled green plants (containing chlorophyll) live in water. You may have seen some. The one-celled plants that make thin, green patches on tree bark or on flower¬ pots in a greenhouse also contain chlo¬ rophyll. EXAMINING TREE GREEN. You can prob¬ ably find patches of green on the bark of any tree that grows in a moist place. Or you may find similar green growths on a damp flowerpot. Mount and examine a bit of "tree green" under your microscope. Then ex¬ amine a permanent stained slide showing this plant. It is called pleurococcus (ploor uh KOK us) in some books and protococ¬ cus (proh toh KOK us) in other books. The label on your permanent slide will bear one name or the other. Sketch one or two of the single-celled plants, and a cluster of two or more cells (Figure 3-8). Use a green pencil to color the green part of the cell. Pleurococcus (call it “tree green,” if you wish) is a one-celled plant with a cell wall, cell membrane, nucleus, a vacuole, and cytoplasm with one large plate-like chloropast in it. But the cell is so small that you may not have been able to distinguish all these parts under your microscope. BLUEPRINT OF AN ALGA PLEUROCOCCUS Chloroplast Cell wail Cell membra Cytoplasm Vacuole 3-8 Under the microscope, the cell mem¬ brane and the chloroplast in pleurococcus may not show. The cell may appear to have chlorophyll distributed throughout its cyto¬ plasm, but this is not true. With these cell parts, this micro¬ scopic plant does all the things a spiro¬ gyra does to stay alive. It makes food and digests it. It excretes cell wastes. It carries on respiration. It is sensitive to and reacts to light and other things. There is motion within the cell. It re¬ produces by dividing, and each new cell grows to full size. Diatoms Diatoms ( dy uh toms ) are one-celled plants, too. They usually do not look green (Figure 3-9), but they do con¬ tain chlorophyll. EXAMINING DIATOMS. On the glass sides of some of your culture bottles, you may find some diatoms. Often you can find them sticking to pond scums or water plants in an aquarium. Mount and examine some living diatoms. LIFE PROCESSES— THE BASIC ACTIVITIES 85 If you can't find any, examine a perma¬ nent slide of diatoms. If you find living diatoms, watch one "slide" along the glass of your slide. These odd, one-celled plants do move (but very slowly) from place to place. Sketch any diatoms you see and show any parts you are able to make out. Diatoms are one of the surprises among plants. These little one-celled plants move about, as most plants do not. And they have shells. A diatom is a single cell. It is covered with a shell. That shell is double and the two halves fit together, somewhat as the two halves of a pillbox fit together. Diatoms have lived in the oceans and in fresh water for many, many millions of years. When they die, their shells settle to the bottom of the ocean or lake. Deposits of diatom shells, hun- 3-9 DIATOMS Under the microscope, they may appear colorless, but they con¬ tain chlorophyll. They are also free-moving. General Biological Supply House. Inc., Chicago TABLE 3-B BASIC LIFE PROCESSES Green plants Animals and most nongreen plants Food-making Digestion Movement * Respiration Excretion Sensitivity and reaction Reproduction Growth Food-getting Digestion Movement * Respiration Excretion Sensitivity and reaction Reproduction Growth * See text for differences in plant and animal movement. dreds of feet thick, have been un¬ earthed. One near Lompoc, California, is 1,400 feet thick. Each vear we mine about 100,000 tons of diatom shells, called diatomaceous ( dy uh toh may situs) earth. We use diatomaceous earth in several commercial processes. Its biggest use is for filtering impurities out of sugar solutions in refining white sugar. Obviously, diatoms are successful plants, to have survived in large quan¬ tities for millions upon millions of years. Obviously, they carry on all the basic life processes. They make and digest food. Can you name the other processes they must carry on? Table 3-B summa- J J rizes these processes. The group name of these plants Biologists have a group name for all the simplest green plants, such as pond scums, pleurococcus, and diatoms. All of them together are called algae (al jee— singular, alga, ALguh). About 150,000 different kinds of algae have already been described and named. New kinds are discovered every year. You will learn more about algae in the next chapter. Summing up: microscopic plants at work Discuss these questions in class: 1. In what two ways are the one- celled algae called diatoms different from most plants? 2. What is our most important use of diatomaceous earth? 3. One of the similarities in all or¬ ganisms is that they all do about the same things; that is, they all carry on about the same life processes. What is one life process of the algae and all other green plants, but not of protozoa and other animals? 4. Some biologists today think it would be more accurate to stop calling the protozoa animals and the micro¬ scopic algae plants. They recommend that we group most one-celled organ¬ isms and call them protists (PROH tists). Then we would have three king¬ doms of living things: (1) the plant kingdom, (2) the animal kingdom, and (3) the protist kingdom. Can you see any reasons for this suggestion? 5. What does each of the following organelles do? a. chloroplast b. vacuole in a spirogyra cell c. cell membrane LARGER PLANTS AND ANIMALS AT WORK You now know the main life proc¬ esses, and you know something about the way in which protozoa and algae carry them out. You could take up one plant after an¬ other and one animal after another to find out how each one carries out its life processes. But, in your whole life¬ time, you couldn’t study a million kinds of organisms. And it wouldn’t be worth your while, even if you could. It is worthwhile to examine, now, any common flowering plant and any common higher animal, to see how each one carries out its life processes. EXAMINING A FLOWERING PLANT. You could use any available plant with flowers on it for this study: a weed pulled out of your lawn, a rosebush, an orange tree, or a geranium. These directions are for the examination of a rosebush, but you would make about the same study of any flower¬ ing plant. Look at the rosebush. If it is in bloom, you can see three of its main organs: the flower, the green leaf, and the stem (Fig¬ ure 3-1 Oa). The roots are the other organs, and they are underground. Sketch one whole leaf. Roses have sub¬ divided leaves, as shown in Figure 3-1 Ob. Draw the veins in each leaflet. Label leaf¬ let, vein, and leaf stem. Tear apart one blossom. You should find four different structures, as outlined in Figure 3-10c. Sketch one sepal (SEE pi), one petal, one stamen (STAY men), and the compound pistil. The base of the pistil is made up of the ovary. Inside the ovary are the ovules (OH vyoolz) which contain eggs. Cut a twig off the rosebush and examine the cut end. Compare it with Figure 3-11. Look for the tissues in the stem, using Fig¬ ure 3-1 1 as a guide. Under your micro¬ scope, examine a permanent stained slide showing a cross section of any woody twig and try to find each tissue. Draw a map of a woody twig and show where each tissue is located. Examine a permanent stained slide showing a cross section of a young root. Use Figure 3-1 1 to help you locate the main tissues. Draw a map of a young root and show where each tissue is located. LIFE PROCESSES— TILE BASIC ACTIVITIES 87 3-10 The specialized organs of this many-celled wild rose enable it to carry out its life processes. The leaves are food-makers. Respiration and excretion also are functions of the leaves— and the rest of the plant. All plant parts digest food, grow, and react to things (involving some kind of movement) . And the flowers are organs of reproduction. A flowering plant at work With its roots, stems, leaves, and flowers, a rosebush carries on its life processes. Take food-making first. The green leaves make the sugar from which the plant makes all its foods. To make su¬ gar, the green leaf must have two sub¬ stances: carbon dioxide and water. It gets the carbon dioxide out of the air. It gets the water out of the ground. The leaves are not on the ground, so they can’t get water directly. But the roots are underground. Water mole¬ cules from soil water enter the under¬ ground roots through the root hairs (Figure 3-11). The water passes from cell to cell through the root cortex (kor teks) and into the wood cells in the middle of the root ( Figure 3-11). Wood cells are long, slender, hollow cells, ar¬ ranged end to end. These hollow wood cells run up through the plant stems into the leaf stems and out into the veins of the leaves. The cells in a green leaf get their water through the veins. So the woody tissue of root, stem, and leaf make up the water-vessel system of the rosebush. Through this system soil water reaches the green leaves. Respiration goes on all the time in every living cell in a rosebush. Respira¬ tion calls for food and oxygen. Food made in the leaves dissolves in water and circulates through the food vessels (Figure 3-11) to all the living cells. 88 SIMILARITIES AMONG LIVING THINGS Oxygen from the air enters the leaves through thousands of tiny openings in the leaf’s covering tissue (epidermis). More oxygen enters the stems through tiny openings in the bark. And still more oxygen enters root cells through root hairs and the other epidermal cells. So each cell gets food and oxy¬ gen and carries on respiration. The tips of the roots and twigs of the rosebush grow by means of mitotic cell division. So do new buds and flowers. Growing tips of twigs “turn” toward the light. Root tips grow downward or toward water. So roses are sensitive and react to light, gravity, and water. All living cells digest foods and pro¬ duce cell wastes. Rosebushes excrete cell wastes through the same openings and root hairs through which they get oxygen. Roses do not move from place to place. But there is movement. Leaves grow toward light, roots grow down, and flower buds open. The rose blossom is the organ of re¬ production. It produces a fruit with seeds in it. Those seeds will grow into a new rosebush, if they are planted and watered. This process is reproduc¬ tion. Perhaps you should also know now that it takes both pollen from the stamens and eggs within the base of the pistil to make seeds. The pollen supplies the male cell, or sperm, that must fertilize the egg to make it grow into a seed inside a fruit. Figure 3-12 summarizes briefly how a flower makes fruit and seeds. A rosebush carries out all of the main life processes. Table 3-C summarizes briefly how it does so. A fish and how it lives Fish are many-celled organisms with tissues, organs, and systems of organs. With these, a fish carries on all its life processes, much the same processes you studied in protozoa, algae, and flower¬ ing plants. 3-1 1 CROSS SECTIONS OF A ROOT AND A WOODY TWIG Left. In this enlarged cross sec¬ tion of the root of a seed plant, two young secondary roots are seen. Also visible are sev¬ eral root hairs, through which water (bearing oxygen and minerals) enters the root from the soil. Once the water gets to woody tissue, it travels upward to the stem and leaves. Right. The age of this five-year twig (stem) is found by counting the annual rings in the wood. The tissues are much the same as in the root, but arranged differently. General Biological Supply House, Inc., Chicago Bark Wood Root hair Epidermis Cortex Food vessels Pith SEED-MAKING IN A FLOWERING PLANT 3-12 The two most important flower parts are the stamen and pistil. The stamen (up¬ per left) is the male reproductive organ, producing pollen grains. Pollen grains which reach the pistil sprout, and the sprouts become pollen tubes that grow downward through the stigma and style of the pistil until they reach the ovule in the ovary. Sperms from the pollen grains then travel through the pollen tubes and ferti¬ lize the eggs in the ovules. The fertilized eggs and the ovules subsequently grow and ripen into seeds. And as the seeds mature, the ovary ripens into a fruit, the rest of the flower usually having withered and died. Later, the fruit may split open or rot away, setting the seeds free. STUDYING A LIVING FISH. Watch a goldfish in a fish bowl or an aquarium. Which organs does it use in swimming? Drop a bit of fish food on top of the wa¬ ter. What does the fish do? Watch the fish's mouth. As you can see, it opens its mouth many times a minute. Work with a partner and use a watch with a second hand to find how many times the fish opens its mouth in one minute. Stain some bits of fish food with red ink and let the fish eat the food. Watch the sides of its head just afterwards. What do you see? Have you any idea which life process de¬ pends on that frequent opening of the mouth? Does the fish seem to be able to see the same object with both eyes? How did you find out? Which life processes are you sure you have now observed in the living fish? Food-getting and digestion in the fish You have seen a fish take a bit of fish food into its mouth, but do you know how that food gets to the fish’s stom¬ ach? You saw red-colored water come out of the sides of its head after it ate stained fish food. But the food didn’t come out with the reddened water. Why? In the back of a fish’s mouth, there are four slits on each side. The water comes in the mouth and goes out the slits, but the food doesn’t go out be¬ cause “teeth” on the edges of each slit fit together and form a “sieve.” The sieve strains the food out of the water and the fish then swallows the food. Actually the sieve isn’t formed of teeth, but of gill rakers, as shown in Figure 3-13. The food goes through a short gullet into the stomach. In the stomach and 90 SIMILARITIES AMONG LIVING THINGS TABLE 3-C LIFE PROCESSES IN HIGHER ORGANISMS KB Life process Rosebush Fish F ood-making Green leaves (substances needed in food-making obtained by roots and leaves) Food-getting Mouth and gill rakers Digestion All living cells Stomach and intestine Movement Opening of buds; growth of roots downward and toward water; growth of stem and leaves to¬ ward light. Muscles, bones, fins Respiration Oxygen enters through openings in epidermis and through root hairs; respiration in all living cells Oxygen enters blood in the gills; respiration in all living cells Excretion Openings in epidermis; root hairs Gills; kidneys Sensitivity and reaction Reaction to heat, light, gravity, and water Seeing, smelling, feeling, reacting, etc. Reproduction Flower * Glands that make sperms in male, eggs in female Growth Cell division in stem and in buds and fruits Cell division in many tissues * Some roses may also be reproduced bjr planting cut twigs from a plant in moist soil. later in the intestine, digestive juices change the food molecules into smaller molecules that can enter the blood stream. Anything left over finally leaves the body of the fish through the anus (ay nus ) . ( See Figure 3-13. ) Circulation and excretion Every time a fish opens its mouth, water passes through the mouth and through slits in the back of the mouth into a space at each side of the head. If you have ever caught fish and strung them on a line, you know that there are red organs in the space at each side of the head. Those red organs are gills, and the space in which you find them is the gill chamber. The blood in the gills makes them look red. Water with air dissolved in it runs out over the gills in the gill chamber. Oxy¬ gen molecules from the air in the water pass into the fish’s blood in the gills. At the same time, molecules of carbon di¬ oxide pass out of the blood into the water. So the gills are organs of breath¬ ing (taking in oxygen) and of excre¬ tion (getting rid of wastes). The fish’s heart pumps the blood to the gills, then on to the rest of the body. The blood stream carries digested food and oxygen to all the cells in the body. The blood then flows back to the heart again, to be pumped on to the gills once more. So the fish’s system of circulation is a closed one. The blood goes round and round through the heart and blood ves¬ sels several times a minute, as long as the fish is alive. The blood vessel that carries blood away from the heart to the gills is an artery. Arteries carry blood away from the heart. The blood vessels that carry LIFE PROCESSES— THE BASIC ACTIVITIES 9T . RESPIRATION AND FOOD-GETTING IN A GOLDFISH 3-13 From ameba to goldfish (as from pleurococcus to flowering plant) is a jump of al¬ most the entire range of complexity in living things. A goldfish has highly specialized organs. Its mouth is used in food-getting. Also, water taken in by the mouth flows over the gills, where oxygen from air dissolved in the water passes into the fish’s blood, and carbon dioxide passes from the blood to the water. The gills, then, are organs both of respiration and excretion (there are also other organs of excretion). The fins are used in movement. Try to name four other life processes the fish carries on. blood back toward the heart are veins. To get from the smallest arteries into the smallest veins, the blood passes through microscopic blood vessels called capillaries (kap 1 air eez). WATCHING CIRCULATION. Wrap moist cotton around the body of a goldfish. Lay its tail on a glass square and examine the tail under the low power objective of your microscope. You will be able to see the red blood cells passing along, probably in single file, through a capillary. In your record book, make notes on what you did and what you saw. 92 SIMILARITIES AMONG LIVING THINGS Capillaries spread among all living cells in the fish. Molecules of digested foods, water, and oxygen pass out of the capillaries into cells, say, in the brain or the muscles. Respiration goes on all the time in every living cell. Molecules of cell wastes pass out of the cells into blood in the capillaries. In the kidneys, some cell wastes and water are excreted from the blood. So both kidneys and gills are organs of excretion. Feeling and reacting A highly specialized nervous system plays the major role in enabling a fish to feel or smell or see things and react to them in the ways that it does. A fish has a brain, a spinal cord, sev¬ eral pairs of nerves, and several sense organs (eyes, for example). In a later chapter, you will learn more about the nervous system and how it works. Reproduction It takes two fish, a male and a fe¬ male, to produce young. In the male’s body, two glands produce male cells or sperms. Two glands in the female’s body produce eggs. In most kinds of fish, the female lays her eggs, called roe, in the water. Then the male deposits sperms, called milt, over the eggs. A sperm fertilizes an egg by uniting with it, forming a single cell, the fertilized egg. That egg grows into a young fish. Most fish reproduce in the manner just described. A few fish, like the guppies, give birth to their young. In the guppies, the eggs are fertilized while still inside the mother’s body. The fertilized eggs then grow into young which are born alive. As you can see, fish, like protozoa, algae, and rosebushes, carry on certain basic life functions. Table 3-C sum¬ marizes these processes in fish and rose¬ bushes. Summing up: larger plants and animals at work 1. Which organ of a rosebush makes the plant’s food? 2. Which organ of a rosebush pro¬ duces the fruit and seeds? 3. What other life processes does a rosebush carry out? 4. Which organs of a fish are used in food-getting? in breathing? in diges¬ tion? in feeling and reacting? in excre¬ tion? in swimming? in circulation? in reproduction? ORGANIZATION AND LIFE You have now reviewed the main similarities in living things. You know that cells are the building units. You know that all organisms contain about the same elements and use about the same nutrients. And you know that all plants and animals carry on about the same life processes. Because all living things are so much alike in those ways, they are studied together in one science —biology. You are now ready for a quick pre¬ view of the organization levels among living things. No life without complex organization Electrons are the smallest of the three commonly known particles of matter. Protons and neutrons are next in size. Hydrogen atoms are larger than a sin¬ gle electron or proton or neutron, be¬ cause an atom of hydrogen has both a proton and an electron in it. The hydrogen atom is the first step in the organization of matter out of electrons, protons, and neutrons. A hy¬ drogen atom is organized, but only in the simplest manner. The atoms of all the elements have simple organizations. You might say that the simplest atoms, like hydrogen, represent the first or lowest level of organization. The next step in organization is the molecule. A molecule of hydrogen con¬ sists of two hydrogen atoms, chemical¬ ly bound together. A molecule of water is a bit more complex, with its two hy¬ drogen atoms chemically bound to an oxygen atom. A molecule of grape sugar is still more complex, with its six carbon atoms, twelve hydrogen atoms, and six oxygen atoms, all chemically bound together. As you move on up the scale of or¬ ganization of molecules, you come to LIFE PROCESSES— THE BASIC ACTIVITIES 93 cane sugar, egg-albumin protein, and human hemoglobin. Turn to Table 2-B on page 59 to see how many atoms these molecules of organic compounds may contain. From electrons, protons, and neu¬ trons to human hemoglobin, the degree of organization increases, but still none of the molecules is large enough to be seen under a compound microscope, and none is alive. There is no life without highly or¬ ganized materials— more highly organ¬ ized than any of the ones mentioned so far in this discussion of levels of or¬ ganization. The first molecules that are at least partially alive are those of viruses. What are viruses? People have been hearing and read¬ ing a lot about virus diseases in recent years. “Virus pneumonia” is a common expression today. The polio a virus has been in the news often in connec¬ tion with the Salk vaccine. Other virus diseases are chicken pox, smallpox, mumps, cold sores, and several more. A well-known virus disease of plants is tobacco mosaic ( moh zay ik ) disease. Just what is a virus? ° Polio is short for poliomyelitis ( poh lee oh mv eh ly tiss ) , the doctor’s name for in- fantile paralysis. Dr. Wendell M. Stanley, now head of the large virus research laboratory at the University of California in Berke- ley, heads the list of those scientists who have helped to find out what a virus is. Nearly 25 years ago, Dr. Stan¬ ley isolated a pure virus of tobacco mo¬ saic disease. This virus was proved to consist of a small needle-shaped crys¬ tal. This crystal and others of its kind do not seem to be any more alive than salt crystals in a salt shaker. But these J same crystals can be dissolved and ap¬ plied to a healthy tobacco plant. That plant develops mosaic disease. Inside the living cells of the tobacco plant, each particle of the virus is able to build a duplicate of itself. In other words, inside of living cells, viruses re¬ produce. That makes them seem to be partially alive, since reproduction is a life process. Dr. Stanley found out, years ago, that a single virus is a giant molecule. At one time, it seemed to be a giant protein molecule. Later research has shown that it is a giant molecule of nucleic ( noo klee ik ) acid with a thin coat of protein. A nucleic acid mole¬ cule is a giant among molecules, but even it is invisible under a compound microscope. It takes an electron micro¬ scope to get pictures, such as Figure 3-14, of viruses. 3-14 VIRUSES As seen here (photographed under an electron microscope) viruses are inert, but in a living cell they can reproduce. Are they alive? (31,800x) Virus Laboratory, University of California, Berkeley So viruses are molecules of nucleic acid coated with protein. Inside of liv¬ ing cells, they may shed the protein coat and reproduce. When they do, they may cause cold sores, mumps, chicken pox, smallpox, or, in some ani¬ mals at least, cancer. A virus molecule is one of the more (but not the most) highly organized molecules known. It at least borders on being alive. Is it, or something similar to it, the connecting link between non¬ living matter and protoplasm? Today most biologists think so. At any rate, virus particles and certain other parti¬ cles you will learn about later seem to represent the simplest kind of highly organized materials that show at least one life process, reproduction. Further organization A virus is a complex thing when compared with an electron or proton or neutron. And a single-celled ameba is highly complex when compared with a virus. But even an ameba is compara¬ tively simple when compared with a tree or a robin or a human being. A tree or a robin or a human being has billions of highly organized cells built into tissues, its tissues are built into organs, and its organs into sys¬ tems. Increasing organization is one basic story in biology. You might even go further. Individ¬ ual organisms are often organized into groups: trees into a forest, bees into a hive colony, robins into pairs at nesting time or into flocks at migration time. Human beings have built up highly complex groups: states, nations, clubs, schools, churches, and many more. To how many groups do you belong? One theme of Unit 1 is that what we call life depends on a highly complex organization of materials. It is a theme that runs through all biology. Table 3-D summarizes some of the levels of organization of matter, non¬ living and living. TABLE 3-D LEVELS OF ORGANIZATION Level Examples Subatomic particles Electrons, protons, neutrons, and several more subatomic particles Atoms Hydrogen, helium ... to uranium, plus ten or more man¬ made elements Molecules Water, carbon dioxide ... up to the most complex giant molecules, such as nucleic acids and proteins Viruses and similar particles Giant nucleic acid particles, coated with protein, and able to reproduce inside living cells Simplest cells Bacteria More complex single-celled organisms- Protozoa, some of the algae, and yeasts; organisms many of which have organelles Simplest many-celled organisms Spirogyra and other pond scums, sponges; organisms hav¬ ing no true tissues More complex organisms Plants and animals with true tissues; mosses and hydras, with their relatives Most complex organisms Plants and animals with true organs and organ systems; ferns, seed plants, and the higher animals beginning with flatworms LIFE PROCESSES— THE BASIC ACTIVITIES 95 CHAPTER THREE: SUMMING UP All living things, from a one-celled ameba to the most complex animal, or from a one-celled pleurococcus to the most complex plant, carry on roughly the same basic life processes. These life processes are: food-making or sensitivity and food-getting reaction digestion movement respiration There is no life without complex or¬ ganization. Beginning with subatomic particles and with atoms, and working up to the complexity of living matter, increasing organization is a major theme. excretion reproduction growth Your Biology Vocabulary Below are the essential new terms that have been introduced in Chapter 3. Make sure that you understand and can use each one correctly. protozoa water vessels anus ameba food vessels life processes paramecium root hairs ingestion pseudopods sepals digestion cilia petals excretion digestive food vacuole root cortex assimilation contracting vacuole stamens respiration anal pore pistils reproduction oral groove pollen eggs organelles gills sperms algae gill chamber spores spirogyra gill rakers viruses pyrenoids arteries pollen tube diatoms veins ovule pleurococcus capillaries ovary Testing Your Conclusions 1 . At the top of the next page is a list of the basic life processes. On a fresh page in your record book, copy the list. After each item, mention something you have seen in protozoa, algae, flowering plants, or in fish that is an example of that life process. Example: “Food-making— I saw starch grains, stained blue, lying close to the pyre- noids in the chloroplasts of spirogyra.” 96 SIMILARITIES AMONG LIVING THINGS movement breathing and respiration sensitivity and reaction excretion food-getting or food-making growth digestion reproduction 2. Each statement below is true. In a sentence or two, explain how you know it is true. a. Amebas and paramecia are protozoa. b. Spirogyras, diatoms, and pleurococcus (tree green) are algae. c. The flower of a rose is an organ of reproduction. d. One kind of vacuole in amebas and paramecia gets rid of excess water by con¬ tracting. e. Algae do not take in solid food. f. A fish uses its mouth in breathing. g. The pistil of a flower makes the fruit and seeds. h. Mitotic cell division in a cell of spirogyra results in lengthening the filament, not in reproduction of the plant. i. Protozoa and fish can live only in water that has air dissolved in it. j. Some algae can move about. More Explorations 1. An experiment with one-celled animals. Make two slides of one-celled animals in this way: (a) On one slide put a ring of Vaseline about the size of a cover slip. Then put a drop of water from one of the cultures inside the ring of Vaseline. Lay the cover slip on the Vaseline and press it down, (b) Make another slide from the same cul¬ ture without the Vaseline. Note the time when the slides are completed. Keep comparing the two slides. What differences in the actions of the animals on the two slides do you notice after a while? How do you explain this? Which animals die first? Why? Which of the life functions have you been testing? Save your cultures of microscopic organisms. You will need them again later. 2. Experimenting with beans. Soak some lima beans overnight. Line a drinking glass with part of a paper towel. Fill the glass with sawdust and moisten the sawdust. Place several soaked beans between the paper towel and the glass. Keep the sawdust moist for two or three days, while you examine the beans from day to day. What has happened? Which one of the life functions is illustrated by the sprouting of the seeds? 3. Study of a pet. Make a list of everything one of your pets does for half an hour. Then relate each thing to one of the life processes. Example: A dog barks at a stranger. This refers to “sensitivity and reaction.” Compare your list with those of your class¬ mates. Thought Problems 1. You mounted some spirogyra filaments in dilute iodine. What did you see on your slide that proved that iodine molecules had passed through the cell membrane into the spirogyra cell? 2. Carmine powder is bright red, and it does not dissolve freely in water. A biology student mounted a drop of water with paramecia in it, then added a little carmine LIFE PROCESSES— THE BASIC ACTIVITIES 97 powder and a cover slip. When he examined the slide under high power, he saw carmine powder in the digestive vacuoles of the paramecia. How did the carmine powder get inside the paramecia? How would the carmine powder get outside again? 3. People sometimes start roses from slips. They cut rose twigs and plant them in moist soil. Does this type of reproduction in roses involve eggs and sperms? Does it involve cell divisions? Why did you answer as you did? 4. Air enters your lungs through your nose and windpipe. A goldfish has no windpipe. Why doesn’t it need one? Further Reading 1. This is a good time to start planning an exciting science project, one that may make you a winner in a science talent search, like the boy in Figure 3-15. There are lit¬ erally thousands of projects to choose from. Your text will raise many questions. Your extra reading outside your text will raise others. Consult Science Clubs of America and Thousands of Science Projects, pamphlets published by Science Service, 1719 N Street, N.W. Washington 6, D.C. When you run across a question or a problem that intrigues you, plan how you might go about solving it. Discuss your plans with your teacher. If both of you feel that your investigation is worthwhile, make more detailed plans. If your investigation is to involve experiments, consult How to Do an Experi¬ ment by Philip Goldstein, Harcourt, Brace, 1957, for suggestions as to how to set up scientific experiments so that they will give you reliable results. A successful science project may run for two or three years, so plan it that way. 3-15 COMPETING FOR A SCIENCE SCHOLARSHIP A biological investigation gave George Chaniot, Jr., of Decatur, Illinois, a chance to compete for a Westinghouse Science Schol¬ arship. Westinghouse Photo 2. You are almost sure to enjoy some of Leewenhoek's letters as printed in Antony van Leeuwenhoek and His “ Little Animals ” by Clifford Dobell, Harcourt, Brace, 1932 (or Russell and Russell, N.Y., 1958). For example, on page 125, Leeuwenhoek describes what he found in rainwater that had stood for 24 hours. He ends with these words: . . and in narrowly scrutinizing 3 or 4 drops I may do such a deal of work, that I put myself in a sweat.” 3. Read the life story of an ameba in Chapter 2 of Unresting Cells by R. W. Gerard, Harper & Bros., 1949. You are sure to enjoy the illustrations, one of which shows an ameba “stepping over an obstacle.” 4. You can learn many more things about arnebas and paramecia and algae in any college biology text. See Further Reading, page 73. 5. If you enjoy using your microscope, you will get real help from Exploring with Your Microscope by Julian D. Corrington, McGraw-Hill, 1957. This book was written for people who want to make a hobby of studies with the microscope. 6. A few biologists today object to our calling the ameba and the paramecium one-celled animals. These biologists think it would be better to call them protists, not cells. To them, a cell is part of a many-celled organism. No single-celled organism, such as an ameba, is a cell, they say. They adopt the view that all “one-celled” organisms are noncellular, or acellular (ay sel yoo ler) , organisms. Would you like to learn one biologist’s outlook on this idea? Read the article “Are There Anv ‘Acellular Organisms’?” bv Alan Boyden, on pages 155-56 of Science mag¬ azine for January 25, 1957. You will find many words that you may not know (one of them is Metazoa and means “many-celled animals”) but you can understand enough to see where Dr. Boyden stands on this matter. Watch the science magazines for more new items on the cell theory, and report on what you read. LIFE PROCESSES— THE BASIC ACTIVITIES 99 Mo one knows when some primitive man first named a plant, or how he came to name it, or what the name was and what it meant. We cannot hope ever to find out. We do know, however, that plants later were grouped under certain names. For example, the word corn was in print in England as early as a.d. 888. In early English, as well as in German and other languages, corn meant any grain except what Americans know as corn today. It meant rye or barley or even wheat, the plant pictured on this page. The American plant that came to be called corn, pictured on the opposite page (with the ears of corn field-stripped ) , was unknown in Europe until after the discovery of America. A confusion of terms came to exist because variety among plants far exceeded the number of names that had been invented to identify them. In the case of corn, most of the confusion was eventually eliminated; separate names have been assigned to other grain plants. But if the confusion has been eliminated, or almost so, among the grain plants, it still exists with respect to many other plants ( as well as animals), any two or more of which may be called by the same name in different countries— or even in different parts of the same country. A more recent cause of confusion is VARIETY AMONG LIVING . H, THINGS-PLANTS m the result of several names having been invented for the same plant (or animal). For example, in parts of the southwestern United States, one variety of tree is known to different people by at least three common names— “scrub oak,” “gnarled oak,” and “blackjack.” Furthermore, this variety of tree is not at all the same tree that is called “scrub oak” by residents of other parts of the southwestern states. And this is but one example in one small area of the world. To eliminate confusion among names, biologists have invented a scientific name for each known plant in the world ( and for each known animal ) . The name for American corn is Zea (zee uh ) mays . Zea mays means the same thing all over the world. Here is one advantage in using a scientific name for each known kind of plant ( or animal ) . In Unit 2, we shall examine the main kinds of living plants to get an idea of the great variety among them. As we go along, we shall learn how biologists make use of the similarities and differences among plants in sorting them into their main groups and in assigning names to them. Chapters 4. The Lowlier Plants 5. Ferns and Seed Plants CHAPTER JjL The Lowlier Plants Roche Plants without transport systems Every living cell must constantly take on some materials from outside itself and give off other materials ( cell wastes). In a single-celled plant like pleurococcus or a many-eelled filament like spirogyra, each living cell is in di¬ rect contact with the outside world, 'file exchange of materials goes on eon- stantlv through the cell membranes. Even in a many-eelled plant like the seaweed called “sea lettuce,” the cells take on materials directly from the out¬ side and give off materials directly into the surrounding water. In a manv-celled organism of much J O size, such as a rosebush or a human be¬ ing, the inner cells are too deeply bur¬ ied to exchange materials directlv with the outside world. In these larger or- ganisms, some system of transporting materials to and from the inner cells is necessary. In your own body, your blood vessels are the main transport system. In a rosebush, the transport svstem consists mainly of long, hollow J J wood cells— the water vessels— and cer¬ tain other elongated cells— the food vessels. The water and food vessels of the higher plants do for these plants about what your blood vessels do for you. They transport necessary materi¬ als to and from all the living cells. The lowly plants are the ones that do not have any food or water vessels at all, or have onlv beginnings of such vessels.* In this chapter, you will learn about the lowly plants and how biolo- * Some seaweeds have primitive food ves¬ sels. A few mosses have primitive food and water vessels. But these are the exceptions. 102 VARIETY AMONG LIVING THINGS— PLANTS gists have sorted them into groups. But first you need to understand how bi¬ ologists go about sorting and classify¬ ing organisms. HOW BIOLOGISTS SORT AND CLASSIFY ORGANISMS Sorting and classifying How would you sort all the plants and animals you know? You might sort them in a number of ways. You might divide them into two groups— useful and harmful. Or you might divide them into three groups— large, medium, and small. Sorting organisms into groups isn’t easy for the beginner. You wouldn’t have any trouble in sorting a box of money. First you would separate the paper money from the coins. Next you would probably sort all the paper money into piles of one- dollar, five-dollar, and ten-dollar bills. You would sort the coins into piles of pennies, nickels, dimes, quarters, half- dollars, and silver dollars. If you mere¬ ly wanted to count the money, you would stop sorting at this point. A coin collector would go on sorting, probably first according to the dates on the coins, then according to the metal they are made of, their value, and what “heads” the coins bear (say, Lincoln pennies, Indian-head pennies, buffalo nickels, and so on). A complete classification of coins would give you a “class” in which to put every coin you come across. Suppose you worked in a library. How would you sort all the books (Figure 4-1)? You would certainly need a system of some kind. But the question of more importance to biology is this: How would you go about finding a “class” for every plant and animal you come across? To do that, you need to know about the system biologists have worked out for sorting organisms. Biologists have worked out a more- or-less complete system of classification for all known plants and animals. This is a specialized field of biology. The science of classification is called taxon¬ omy ( taks on uh mee ) and those who specialize in it are taxonomists. Biology is not finished. Neither is any special field of biology. Taxonomy is not static; that is, it is not the same “yesterday, today, and forever.” Like all biology, taxonomy changes and is developed into a more complete sys¬ tem as new facts are discovered. Right now, taxonomists are revising the system of classification for the algae and their relatives. Ten years from now, they may have reached agree¬ ment as to the most accurate and useful way to set up that revision. As yet, they have not done so. So we shall follow the established system here. How are plants classified? Until recently, nearly everybody agreed that there are two main kinds of organisms— plants and animals. So taxonomists sorted all living things into two kingdoms— the plant kingdom and the animal kingdom. All plants from the smallest one-celled ones to the larg¬ est redwoods were placed in the plant kingdom. We shall follow this classifica¬ tion. In a way, sorting organisms into two kingdoms is like sorting a day’s business receipts into checks and money. Plant taxonomists recognize four main divisions of the plant kingdom: (1) algae and their relatives, (2) mosses and their relatives, (3) ferns and their relatives, and (4) seed plants. Each of these main divisions of the plant king¬ dom we shall call a phylum (fyIuiu— Tin. LOWLIER PLANTS 103 Phil Palmer, from Monkmeyer 4-1 CLASSIFICATION OF BOOKS Knowing the classification system used by libraries saves much time in searching for particular books. What do the numbers mean? plural, phyla). Sorting the plant king¬ dom into phyla is somewhat like sort¬ ing money into coins and bills. Each phylum of plants breaks down into subphyla, and each subphylum in¬ to classes. Classes are sorted into or¬ ders, orders into families, families into genera (jen uh ruh— singular, genus, jEEnus), and genera into species (spee sheez ) . Think of sorting money again. Each larger pile gets sorted into two or more smaller piles. In the plant kingdom, each larger group is sorted into smaller groups. In classifying almost anything, large related groups are sorted into smaller and smaller groups until, in some cases, even single things within groups are classified. For example, Ta¬ ble 4-A shows the idea behind classifi¬ cation by comparing the standard classi¬ fication of one kind of spirogyra with one possible classification of a certain American man. Examine the table care¬ fully to get the idea, but do not try to memorize everything in it. After examining Table 4-A, you should be aware of one major differ¬ ence between classifying plants or ani¬ mals and classifying people. We recog¬ nize and classify individual people, but we do not do so for other organisms (except for pet animals). In other words, once we have classified, say, a plant in its species ( and perhaps its sub¬ species), we are often not interested in distinguishing it from others of its kind. Scientific names You would call the man classified in Table 4-A White Eagle ( or Chief White Eagle). In somewhat the same way, biologists call one kind of spirogyra Spirogyra protecta (proh tek tuh). The scientific name of any plant or animal has two parts. The first part names its genus, the second part its species. It is customary to capitalize the genus but not the species name. Spirogyra pro¬ tecta is one species of the genus Spiro¬ gyra. Spirogyra punctata (punkTAY tuh ) is another species. This two-name system is known among biologists as the binomial (by noh mee ill ) system. Carolus Linnaeus (lih nee us ) , a Swedish botanist, in¬ vented the binomial system about 1753. Both botanists and zoologists have been using this system ever since. Every organism on earth is supposed to fit somewhere in this system of clas¬ sification. But the system is man-made. 104 VARIETY AMONG LIVING THINGS— PLANTS TABLE 4-A EXAMPLES OF CLASSIFICATION Spirogyra A certain American man Kingdom: Plant (1) American Indian Phylum: Thallophyta (thuh lof ih tuh) (2) North American Indian Subphylum: Algae (3) Sioux nation Class: Grass-green algae (4) Western Sioux tribes Order: Zygnematales (zig nee muh tay leez) (5) Omaha-Ponca tribal community Family: Zygnemataceae (zig nee muh tay sih ee) (6) Ponca tribe Genus: Spirogyra (7) Eagle family Species (and name) : Spirogyra protecta (8) [Chief] White Eagle It is convenient and helpful to use the system, but today biologists know that no system can be devised into which every organism fits perfectly. You will study organisms that show both plant and animal traits. These organisms don’t seem to fit well into either of the two kingdoms. You will also study oth¬ er organisms— for instance, the seed ferns— that do not fit exactly into one phylum to the exclusion of another. Lit¬ erally thousands of kinds of plants and animals do not fit exactly into our sys¬ tem of classification. But most plants and animals do fit into the system. Who names new species? Who gives plants and animals their names? The first person to describe a plant or animal in print has the privi¬ lege of naming it. For example, Lin¬ naeus was the first to publish a descrip¬ tion of our mountain laurel, state flower of Connecticut and Pennsylvania. In his published description, he named this plant Kalmia latifolia ( kal mee uh lah tih foh lee uh ) . The name still stands and will probably continue to do so, because no one is likely ever to find a published description and name that predates that of Linnaeus. Would you like to know the name of your own species? The scientific name of the human species is Homo sapiens (hoh moh say pee enz ) . It comes from the Latin words meaning “man, the wise.” Linnaeus named and classified the human species some 200 years ago (Table 4-B ) . Why did taxonomists use so much Latin and Greek in making scientific names? For one thing, Linnaeus and all other scholarly men of his day knew Latin and Greek well. Linnaeus wrote nothing but Latin, so that scholarly men all over the world could read and understand his letters and his published books. Our own John Bartram, first American botanist of real standing, taught himself Latin so he could corre¬ spond with Linnaeus. Taxonomists still draw heavily on Latin in naming new species. There are TABLE 4-B CLASSIFICATION OF MAN (HOMO SAPIENS ) Kingdom: Animal Phylum: Chordata (kor day tuh) Subphylum: Vertebrata (ver tuh bray tuh) Class: Mammalia (muh may lee uh) Order: Primates (pry may teez) Family: Hominidae (hoh min ih dee) Genus: Homo (hoh moh) Species: Homo sapiens (hoh moh say pee enz) THE LOWLIER PLANTS 105 A. W. Schoof 4-2 TWO GIANT CACTUS PLANTS OF ARIZONA Using a book on the classification of American flowers, a botanist anywhere in the world would be able to find an exact description of these cactus plants, if given the plant’s scientific name, Cereus giganteus. This is one of many advantages of the binomial system of nomenclature. several advantages. For one thing, Latin names are not likely to change, since no peoples speak Latin today. Spoken languages are always changing. For another, Latin names are usually descriptive, once you know some com¬ mon Latin roots. For example, in Kalmia latifolia (mountain laurel), the word latifolia comes from the Latin words meaning “broad leaves.” Kalmia latifolia is the broad-leaved laurel. The need for scientific names To biologists all over the world, sci¬ entific names are useful, because they mean the same thing to everybody who knows them. Common names do not. For example, right here in the United States, the common flicker has some 80 different common names: vellowham- J mer, golden-winged woodpecker, high- holder, yellow-shafted flicker, and many more. All over the world, the yellow- shafted flicker is known to biologists by the one scientific name, Colaptes aura - tus ( koh lap teez aw ray tus ) . The scientific names of species are useful in other ways, too. But they are useful primarily to those who specialize in botany or zoology or in some special field of these sciences. Florists, garden¬ ers, nurserymen, and directors of zoo- 306 VARIETY AMONG LIVING THINGS— PLANTS logical gardens make good use of scien¬ tific names. For you, in high school biology, understanding the ideas that underlie classification is more impor¬ tant than memorizing such species names as Kalmia Icitifolici or Colaptes auratus. It will pay you, however, to learn the names of the main plant and animal phyla, as you come to them. The first plant phylum You are about to examine plants of the first plant phylum. The plants of this phylum are sometimes spoken of as lowly plants, because their bodies are not highly organized. These lowly plants have no roots or stems or leaves. Most of them haven’t even any special¬ ized tissues. Many of them are single- celled plants. The name of this phylum is Thal- lophyta ( thuh lof ill tuh ) or the thal- lophytes (thal oh fytes). Note that the name ends in phyta or phytes, from a Greek word meaning “plants.” The names of all four plant phyla have the same ending. This makes it much easier to remember the names of the plant phyla. Summing up: how biologists classify organisms To see if you get the idea that under¬ lies taxonomy (classifying and naming organisms), try this. Heading the next column is a list of groups to which the giant cactus of Arizona belongs. The groups are not in order, from kingdom down to species. Use Table 4-A as a guide. Arrange the following list so that each group is a subdivision of the one above it. Then copy the correct list in your record book. What is the scientific name of the giant cactus (Figure 4-2)? Species: Cereus giganteus Class: Dicotyledonae Subphylum: Angiospermae (the flow¬ ering plants) Family: Cactaceae Genus: Cereus Phylum: Spermatophyta (the seed plants) Kingdom: Plant Order: Opuntiales LOWLY PLANTS WITH CHLOROPHYLL Thallophytes are lowly plants. They do not have roots, stems, or leaves. They do not have highly developed tis¬ sues, either; they have no water-trans¬ port tissue, and, with a few exceptions, no food-transport tissue. The thallophytes are divided into two groups, those that have chlorophyll (or a similar substance) and those that do not. These two groups make up the two subphyla of the first phylum of the plant kingdom. Subphylum algae The algae make up one subphylum of the thallophytes, the one in which the plants have chlorophyll (or a sim¬ ilar substance that plays a part in food¬ making). In Table 4-A on page 105, you will find one member of this sub¬ phylum fully classified. You have already studied three kinds of algae: the pond scums (including spirogyra), pleurococcus (tree green), and diatoms. You will agree that these plants are built on simple lines as com¬ pared with an apple or lemon tree or even a house fern. Diatoms and pleu¬ rococcus are one-celled plants with chlorophyll. Some of the pond scums are long threads ( filaments ) of cells with chlorophyll. In pleurococcus and THE LOWLIER PLANTS 107 Partridge berry Wintergreen plant Frog Fern Toad Woodland mosses Liverwort General Biological Supply House, Inc., Chicago 4-3 MAINTAINING PLANTS FOR CLASSROOM STUDY Setting up a terrarium requires that conditions of growth in nature be duplicated (as nearly as possible) in the classroom. For lowlier plants such as algae and mosses (the liverwort and woodland mosses shown here are lowlier plants), greater freedom in choice of specimens accompanies a choice of moist, rich soil and a partly shaded location for the terrarium. pond scums, the chlorophyll is usually in chloroplasts inside each cell. Some algae are more complex. True seaweeds are algae, even though some may grow to lengths of 200 feet. The longest ones have primitive food-trans- port tissues. None of the algae, how¬ ever, have specialized water-conducting vessels, or true roots, stems, or leaves. The algae are a varied lot. They differ in size, form, and color. They live in all sorts of places— the oceans, fresh- wa¬ ter lakes and streams, mud puddles, moist rock walls, on the hark of trees, and even on the undersides of white, semiclear rocks on the hot deserts. A COLLECTING TRIP. Plan a field trip to collect algae and other lowly plants, such as mushrooms and mosses. Even if you live in a large city, you. may be able to visit a park where there is a stream or small pond or lake. If you live near the ocean, per¬ haps you can go to a beach. You will need clean jars about the size of mayonnaise jars, a few boxes about the size of shoe boxes, some tweezers, a knife, and perhaps a dip net. On your trip, look especially for differ¬ ent kinds of algae, such as pleurococcus on tree bark, patches of "green felt" on moist or wet earth, bluish-green patches on damp soil or on muddy banks or in shal¬ low rain puddles, growths of algae at¬ tached to rocks under water, and different- looking floating masses of pond scums. Collect a little of each kind, and put them in the jars. For pond scums, fill a jar about 108 VARIETY AMONG LIVING THINGS— PLANTS two-thirds full of pond water and then add just a little pond scum, about what you can pick up with a pair of tweezers or on the end of a small stick. For other speci¬ mens, moisten the inside of the jar but do not cover the specimens with water. If you visit an ocean beach, look for seaweeds. You may use a dip net to collect them. Put each kind in a jar of sea water. Also watch for mushrooms and similar nongreen plants, and for mosses. Carry these specimens in your shoe boxes. Take all your specimens back to your classroom or laboratory. Transfer the mosses to a glass terrarium (teh rair ee urn), if you have one. (See Figure 4-3.) If not, plant them in an open box or dish. Keep all the green plants in a well-lighted place but not in direct sunlight. You will have discovered from your col¬ lecting trip that algae vary in many ways. They are sorted into several classes, as you will see. Blue-green algae This class of algae gets its name from the color'of the plants that are grouped here. They have a bluish-green color, not the grass-green of many other algae. You may have collected some blue- green algae from a puddle or pool. If so, make slides and examine them. The blue-green alga you are most likely to find is Oscillatoria ( oss uh luh tohr ee uh ) , the waving blue-green alga (Figure 4-4). This alga is able to thrive in places where other algae can¬ not live, such as muddy, stagnant wa¬ ter. About 30 species have been de¬ scribed and named. Not all species look bluish-green. One species, Oscilla¬ toria prolifica ( proh lif ih kuh ) , has a reddish color. This species sometimes becomes so plentiful in some lakes that the water takes on a red coloration. 4-4 WAVING BLUE-GREEN ALGA The cells in a filament of this alga contain chlo¬ rophyll and a blue pigment, plus colorless central bodies that are nuclear in nature but not well defined. Filaments grow bv cell division and reproduce by breaking apart. (At what points would the filaments seen here be most likely to break apart?) If you find other blue-green algae, use the classification summary on pages 120 and 121 and the directions and ref¬ erence books found under Further Reading at the end of this chapter to help you identify them. Grass-green algae The most plentiful algae in our fresh water streams and lakes are grass-green in color. All 65 species of spirogyras belong to the class of grass-green algae. So do many other pond scums. So does pleurococcus. These are the algae which biologists describe as the “grass of many waters.” Why? Because they are the forage crops used by fresh-wa¬ ter animals, even as grass itself is a forage crop used by cattle and deer and other land animals. Try to see how many different kinds of grass-green algae you can find in your recently collected cultures. You may find some spirogyra plants that look somewhat like those in Figure 3-7 on page 84. If so, you will know they THE LOWLIER PLANTS 109 are reproducing. As you learned in Chapter Three, it usually takes two spirogyra plants (filaments) to produce the spores. The cell contents from a cell in one filament (the male parent) move over through the connecting tube and fuse with the cell contents of the eell in the other filament. The two fused cells become one cell, which forms a thick cell wall and is the spore. Each spore, in time, may grow into a new spirogyra. So the new plant has two parents. Use the classification summary on pages 120 and 121 and the references listed under Further Reading at the end of this chapter to help you identify other grass-green algae you may find. 4-5 This microscopic organism moves about freely and has a flagellum, mouth, and eyespot. In all these ways it is ani¬ mal-like. Why, then, is it a “puzzle”? EUGLENA— AN ORGANIC PUZZLE Organic puzzles Some lowly organisms are puzzling because they are like plants in some ways and like animals in other wavs. The ones discussed here are sometimes classified as algae by botanists, but as protozoa by zoologists. We shall classify them in both places. You will soon un¬ derstand why. Several species of organisms which botanists call algae can swim. These algae have long, whiplike organelles. With these they whip the water, as thev move freely about. A whiplike organ¬ elle is called a flagellum ( fluh jel urn- plural, flagella). So all these organisms are called flagellates ( flaj uh layts ) . EXAMINING FLAGELLATES. In some of your jars of pond water or even in an aquarium, you should be able to find a flagellate like the one in Figure 4-5. Make slides and hunt for such organisms. The one-celled algae of this type belong to the genus Euglena (yoo GLEE nuh). Try to find out all you can from living specimens. Then study prepared slides of Euglena. In your biology record book, title a fresh page Flagellates. On it, sketch and label a Euglena. Then answer these questions: 1. What does Euglena have in its body that makes it look like a plant? 2. What features make it seem like an animal? Leeuwenhoek discovered and de¬ scribed the Euglena. He called these organisms “green globules. To this day, biologists are not in agreement as to where to classify these and similar swimming, green organisms. CV O O Take Euglena as an example. Were you surprised to see an organism full of chloroplasts like a plant cell, and yet swimming around freely like a one- celled animal? It swims by whipping BLUEPRINT OF AN ALGA -VOLVOX Photo by Carl Striiwe, from Monkmeyer 4-6 Like Euglena, this miscroscopic colonial organism is something of a puzzle, with both plantlike and animal-like features (see text). Thus there appear to be limitations to a classification system based only upon “plants” and “animals.” Some biologists suggest that the first living things on earth— and the lowliest organisms today— are “protists,” and that only more highly specialized organisms are plants or animals. (Photograph of five young Volvox emerging from parent; drawing of one of the young.) Flagella Cells Protoplasm connecting cells with one another the water with its long flagellum. It has chloroplasts, but no cellulose cell wall. It has a mouth and a red eye spot. Volvox is another puzzle. It is a many-celled flagellate, shaped some¬ what like a ball, as you can see in Fig¬ ure 4-6. The 500 or more cells cover the outside of the “ball” in a single layer. Each cell has an eye spot, two flagella, and two or more contractile vacuoles, as well as a good-sized chloroplast with one pyrenoid in it. The whole, hollow ball of similar cells is a single organism. The 500 or more cells work together in using their flagella in swimming. And only certain specialized cells can pro¬ duce young. And yet each single cell in a Volvox carries on most of the life processes itself. On the whole, Volvox is a “colony” of cells, each carrying on most of its own life processes. Some biologists prefer to list three kingdoms— plant, animal, and protist. They put the flagellates in the protist kingdom. Do you remember the vi¬ ruses? Some biologists also call them protists. They are on the borderline be¬ tween nonliving matter and living cells. THE LOWLIER PLANTS 1 1 1 The flagellates are on another border- O line, between the lowly plants and low¬ ly animals. Red algae and brown algae So far, you have been studying large¬ ly the fresh-water algae. Another whole host of algae lives in the oceans and in salt marshes. These algae are the true seaweeds. Many seaweeds are highly branched, feathery plants, red in color. People sometimes call them “sea mosses,” but they are not mosses. They are algae of the class called red algae. The largest seaweeds are olive-green to brown in color. They make up the class called brown algae (Figure 4-7). Some seaweeds are of the grass-green class. Sea lettuce is a common example. EXAMINING SEAWEEDS. Study any sea¬ weeds available, either living specimens collected at the seashore or preserved specimens. You can often get dead sea¬ weeds from a sea-food restaurant. The one most often displayed in their windows, along with a lobster, is a brown, leathery seaweed often called a rockweed. Try to find the names of any seaweeds you collect. Use the classification sum¬ mary on pages 120 and 121 and the refer¬ ences listed under Further Reading at the end of this chapter to help you. Keep a record of those you are able to identify. You may have collected some pond- weeds along with the pond scums. People often call fresh-water pondweeds "sea¬ weeds." But these fresh-water plants are not seaweeds at all. Examine some and try to find out why pondweeds are not clas¬ sified among the algae. Discuss the mat¬ ter in class. The true seaweeds live only in the oceans. They are all algae, but most of 4-7 BROWN ALGA This giant kelp grows in cold waters near the Pacific Coast. In spite of its size, it has only crudely developed food-transport tissue— and no water-transport tissue. It survives successfully because it grows entirely submerged in water. Myron R. Kirsch them are neither blue-green nor grass- green algae. Most of them are brown or red algae. The biggest of all the algae belong to the brown algae class (Figure 4-7). Rockweeds grow attached to rocks along shores in part of the Arctic as well as in temperate seas. The air blad¬ ders at the ends of their branches help keep the rockweeds afloat in shallow water. The somewhat ribbonlike branches are leathery and covered with mucilage. On the Pacific Coast the brown seaweeds called kelps are com¬ mon. There are bladder kelps, elk kelps (also called “sea oranges”), the devil’s apron, and the giant kelps. These giant kelps sometimes reach a length of 200 feet. They have at least the beginnings of a food-conducting system, but no true roots, stems, or leaves. They are algae, in spite of their size. Remember the diatoms with their tiny shells? They are not seaweeds, but they do live in the seas as well as in fresh water. In fact, they are the only plants in the far-northern Arctic sea, or far from shore in any sea. They were once classed as brown algae, because of their color, but now they are placed in a separate class (see page 120). Chlorophyll and other pigments Although we speak of the algae as lowly plants with chlorophyll, not all of them actually contain chlorophyll. Some algae contain other pigments (either in addition to or in place of chlorophyll ) which are the cause of their differences in color. However, the important point is that whatever pig¬ ment is responsible, all of the algae make their own food. The algae with¬ out chlorophyll contain another pig¬ ment which, like chlorophyll, enables these algae to make their own food. Are algae important to man? Perhaps you are asking the question, “What good are the algae?” Of course, you mean to ask, “Are algae useful to human beings?” Algae are here and we do make use of them, just as we make use of many other organisms, but you should under¬ stand that the algae were in the seas hundreds of millions of years before there were any people on earth. We use diatomaceous earth in refin¬ ing white sugar, in filtering water for our swimming pools, and in other ways. We extract from certain seaweeds a substance that acts much like gelatin. We call this seaweed extract agar-agar (ah gahr ah gahr). We use it in prepar¬ ing culture tubes and culture plates on which we grow bacteria. We are now growing huge tanks of certain algae, hoping to be able to use them as food for cattle. We get food indirectly from the algae. Sea-food animals like salmon, cod, shrimp, and lobster feed upon smaller animals that in turn feed upon algae. Every time you eat salmon or shrimp or any other sea food, you are getting food substances that came origi¬ nally from seaweeds or from diatoms. Summing up: lowly plants with chlorophyll 1. In what places do algae live? 2. Why is it that you can see pleu- rococcus on tree bark, when it is a mi¬ croscopic, one-celled plant? 3. What algae have shells and how do we use the shells? 4. How can you tell Spirogyra and Oscillatoria apart? 5. Why are seaweeds classified as algae? 6. Why are flagellates classified both as algae and as protozoa? THE LOWLIER PLANTS 113 LOWLY PLANTS WITHOUT CHLOROPHYLL Some 75,000 species of thallophytes without chlorophyll have been de¬ scribed and named. This subphylum includes molds, mushrooms, puffballs, rusts, mildews, and smuts. Here we are including also the bacteria and the yeasts, although some taxonomists put them in a phylum by themselves. The bacteria and the yeasts are one-celled organisms. The others are many-celled plants, but none of them has highly developed organs. In some molds, the threads are not divided into separate cells. GROWING BREAD MOLD. Moisten a slice of bread, cover it, and place it in a warm, dark place. Examine it each day for mold. When the mold first appears, it looks like a mass of white cobweb. Examine a bit of the white mass under the microscope and you will find that mold is a mass of threads. The threads may make you think of the pond scums except that they do not have chloroplasts in their cells. Also, the mold threads usually branch, while those of many pond scums do not. When greenish or bluish or black patches appear on the mold, make a slide of one small patch and examine it under low power. In your record book, sketch a bit of what you see. Molds Molds come from spores, not seeds. As you already know, spores are single cells, microscopic in size. Mold spores float in the air almost everywhere. It was mold spores from the air that started the growth on your slice of bread. After a day or two, you will see 4-8 The true plant body of this mold is its mycelium, the parts of which serve one of three purposes: (1) as rootlike structures (not true roots), (2) as stalks supporting the sporangia, or (3) as runners connecting upright parts of the plant. (Photograph and drawing of Rhizopus nigricans, the most common bread mold, greatly enlarged.) Photo from DuPont Magazine BLUEPRINT OF A FUNGUS - BREAD MOLD 4-9 TWO FUNGI Left. When collecting mushrooms for study, avoid the deadly Amanita. Right. Like the Amanita on the left, the corn smut seen here consists of spore-producing organs. Where is the body of the plant? some green or black patches on the white mold (Figure 4-8a). This means the mold is reproducing; that is, form¬ ing spores. The real mold plant is a mass of white threads. The green or black patches are clusters of spore-making organs. The green in these patches is not chlorophyll (molds do not produce their own food). The mass of fine white threads makes up the body of the mold plant. Biolo¬ gists call the branching threads the mycelium ( my see lee um ) of the mold (Figure 4-8b). In some cases, the myce¬ lium resembles a filament of pond scum with its cells end to end. In other cases, there are no cell walls across a thread of mycelium. The spore-making organs of the molds are sporangia ( spoil ran jee uh— singular, sporangium). (See Figure 4-8b.) So are the spore-making organs of ferns and many other plants. Molds are lowly plants without chlo¬ rophyll. Their bodies are threadlike, and they produce spores. Mushrooms and puffballs Nongreen plants of the mushroom type are numerous. They include puff¬ balls, coral mushrooms, hedgehog mushrooms, truffles, and many more (Figure 4-9, left-hand photograph). The real mushroom plant or puffball plant is not the part you see above ground. The real plant body is myce¬ lium: a mass of threads much like that of the molds. The mushroom or the puffball is a specialized organ that pro¬ duces spores. The mushroom or puffball does not grow overnight. It grows underground for weeks. Then suddenly, perhaps dur¬ ing the night, its cells absorb water and enlarge so much that the mushroom or puffball “comes up, as we say. THE LOWLIER PLANTS 115 BLUEPRINT OF A FUNGUS — MUSHROOM Photo from Hugh Spencer, from National Audubon Society 4-10 The mushroom proper is a reproductive organ; the body of the plant is mycelium, located underground. A mushroom of the type shown here has 300 to 600 gills, and on the sides of each gill are many spore-producing organs. EXAMINING MUSHROOMS. First, com¬ pare any specimens you collected earlier with the one in Figure 4-9 (left-hand photo¬ graph) and throw away any that look like deadly Amanitas (am uh NEE tuhs). Examine any other mushrooms you have. Try to find the mycelium. Cut out a tiny bit of one gill (see Figure 4-9) and crush it in a drop of dilute iodine or acetocarmine on a slide. Add a cover slip and examine under your microscope. In your record book, sketch what you see. Rusts, smuts, and mildews Figure 4-9 (right-hand photograph) shows corn smut, but only the spore¬ making part. The real plant body— the mycelium— grew inside the corn. The plant body of wheat rust and other rusts and of mildews like those you may see on lilac or clover leaves in the fall is also mycelium. Only the spore¬ making parts of these smuts and rusts are visible; the mycelium grows inside the infected plant. All of the lowly nongreen plants ex¬ cept the yeasts and bacteria have threadlike plant bodies of mycelium. Yeasts and bacteria The one-celled nongreen plants are common everywhere. A cake of yeast is a mass of yeast cells mixed with starch grains. There are yeast cells or yeast spores on the skins of apples and grapes and other fruits. Yeast spores even float in the air. 116 VARIETY AMONG LIVING THINGS— PLANTS Most bacteria are many times smaller than yeasts, as Figure 4-11 shows. Bac¬ teria are the smallest organisms visible under a compound microscope. EXAMINING YEASTS. Into a glass beaker put a cup of water and !4 teaspoonful of dextrose. Crumble half a yeast cake into the sugar solution. Let it stand for 24 hours in a warm, dark place. Next day, make slides (one without a stain, and one stained with dilute iodine) and examine the yeast plants on both slides under high power. Use the unstained slide to look for yeasts linked together in chains like those appearing in Figure 4-11. A yeast plant is just one cell. That cell pro¬ duces a bud, a smaller cell. Then the small cell produces a still smaller one, and so on, until a chain is formed. In due time, the cells break apart. This is one type of re¬ production. We call this type of reproduc¬ tion budding. Yeasts also make spores, but you are not likely to find any spores on your slide. In your record book, draw sketches of a single yeast plant and of budding yeasts in a chain. Then answer these questions. 1. What is the most noticeable differ¬ ence between a yeast plant and a one- celled alga, such as pleurococcus? 2. Did you see any starch grains on your slide? (In dilute iodine, they would be dark blue.) A yeast cake has starch grains in it. If you didn't find any starch grains, try to explain what you think might have happened to them. 3. Did you see "bubbles" in the yeast culture in your flask? Where did the carbon dioxide in these bubbles come from? 4. How do yeasts make bread dough rise? What are nongreen thallophytes called? The nongreen thallophytes make up the second subphylum of the first plant phylum. We call this subphylum the fungi ( fun jy— singular, fungus, fung gus). Molds are fungi. So are mush¬ rooms and puffballs and other similar plants. Here, for convenience, we are also including the yeasts and bacteria. Double plants You may have read that reindeer paw away the snow to get at the so-called reindeer moss underneath. Reindeer moss is not a moss at all. Reindeer moss is a plant community, inhabited by two kinds of plants— algae and fungi. The algae may be either blue-green or green. Usually they are one-celled. The 4-1 1 BACTERIA AND YEASTS Left. These rod-shaped bacteria cause milk to sour. Right. Enlarged the same amount as the much smaller bacteria on the left, these yeasts are bud¬ ding. The chains of cells will grow longer, then eventually break apart. Left: U.S.D.A. ; right: Dr. Carl Lindegren, Southern Illinois University, from Anheuser-Busch, Inc. LICHEN— TWO THALLOPHYTES LIVING AS ONE Photo by Marion A. Cox 4-12 When an alga and a fungus live as a single organism, the association is somewhat at the expense of the alga (the chlorophyll-bearing, food-making member of the “team”). Yet often it is the fungus that on rock, desert, or Arctic wasteland absorbs and holds the moisture needed by the alga for food-making. Thus there is mutual benefit. algae are enmeshed in the mycelium of a fungus, as in Figure 4-12. Such "double plants ’ are called lichens (ly kenz ) . Lichens are common all over the world. They are of three types: (1) crusty lichens, (2) “leafy’’ lichens (not true leaves, of course), and (3) cushionlike lichens. They play an important part in soil-making. Lichens are the only plants that can grow on a bare rock surface. They can actually dissolve a bit of the rock surface. In so doing, they start the formation of a thin layer of soil. After that, mosses may be able to get a start, then ferns. And that bare rock surface is then on its way toward the formation of good soil that one day will support large plants including trees. On the desert, lichens are to be seen everywhere on the rock surfaces, in spite of the fact that these rocks may reach a temperature of 150° F. or more on a hot August day. On the other hand, the lichens called reindeer moss grow under the snow in the Arctic. Some¬ thing about the alga-fungus combina¬ tion in these lichens enables them to grow in conditions where most other O plants do not succeed. Are fungi important to man? You can think of many uses people make of fungi. We use yeasts to make bread dough rise. Yeasts also ferment fruit juices like apple cider and grape juice. And they ferment great vats of grain mashes, in the making of beer and whiskey. J 118 VARIETY AMONG LIVING THINGS— PLANTS Some kinds of bacteria cause dis¬ eases, such as pneumonia, typhoid fe¬ ver, boils, appendicitis, and many oth¬ ers. Far more kinds of bacteria are use¬ ful. For one thing, certain kinds of bacteria help cause dead plants and animals to decay. This not only gets these dead bodies out of the way, but also restores to the water or soil organic compounds and minerals that new plants can use again. Still other kinds of bacteria take free nitrogen out of the air and build it into simple compounds that other plants can use. You can’t use free nitrogen. Neither can most other organisms. Without these nitrogen¬ combining bacteria or some other kinds of organisms with the same ability, you could not live. People eat a number of kinds of mushrooms. But some mushrooms are deadly. Commercially grown mush¬ rooms are safe. Only experts in recog¬ nizing the edible species of mushrooms can safely gather wild ones for food. Large puffballs are good to eat, if gath¬ ered soon after they “come up.” Molds add flavor to a number of foods, such as blue cheese. We get penicillin and several other antibiotics from certain molds. On the other hand, molds do sometimes spoil our foods. And they do sometimes grow on our skin ( athlete’s foot is caused by a mold¬ like fungus) or even in our lungs (val¬ ley fever is caused by a fungus growth in the lungs). Rusts— especially wheat rust— and smuts do heavy damage to our grain crops every year. Mildews sometimes grow on clothes dampened for ironing and allowed to stand too long in hot weather. Lichens are soil builders, and so are the bacteria and other fungi that rot leaves, logs, and the bodies of dead ani¬ mals. All in all, fungi are important plants, useful in many ways to man. Phylum one: the algae and the fungi You now know the two main sub¬ phyla of the first plant phylum— the algae and the fungi (lichens are part alga and part fungus). The chief dif¬ ference between the two subphyla is that algae have chlorophyll (or a simi¬ lar substance), and fungi do not. Oth¬ erwise, the two classes of plants are much alike. So they are grouped to¬ gether in the first plant phylum, the one botanists call Thallophyta. After you have summed up your knowledge of the fungi, as directed be¬ low, turn the page. You will find on the next two pages an illustrated summary of the plants that make up Phylum Thallophyta. Use this summary and the reference books listed under Further Reading on pages 130 and 131 to help you identify specimens that you find. (You will notice that Latin names and their pronunciations are given in the illustrated summary. If your interest in biology is a serious one, you will want to become familiar with these names.) Summing up: lowly plants without chlorophyll 1. What are the smallest plants vis¬ ible under the highest power of the compound microscope? o 1 1 2. How do yeasts reproduce? V, 3 What is meant by mold myce¬ lium? A fold sporangia? 4. Where do the gill mushrooms bear their spores? 5. Why are lichens called double plants? 6. Why are the algae and fungi clas¬ sified in two different subphyla? 7. What is the name of Phylum One of the plant kingdom? TJIE LOWLIER PLANTS 119 4-17 4-16 4-15 4-14 4-13 PHYLUM THALLOPHYTA The thallophytes (thal oh fytes) are the simplest plants— one-celled or many-celled, with or without chlorophyll, but all with¬ out roots, stems, leaves, or well-developed food- and water-conducting tissues. The number of species is estimated at about 107,000, with thousands of new species discovered each year. J SUBPHYLUM I. ALGAE Algae (ALjee) are thallophytes that con¬ tain chlorophyll or a chemically similar substance. They are found mainly in water (both fresh and salt water), although nu¬ merous species exist on land, growing on trees, earth, and even the undersides of rocks. Class 1. Cyanophyceae (sy an oh fy sell ee). Blue-green algae. Example: Oscillatoria (Figure 4-13) . Class 2. Chlorophyceae ( klor oh fy sell ee ) . Grass-green algae. Examples: Pleurococcus (Figure 3-8), Spirogyrci (Figure 4-14). Class 3. Chrysophyceae (kris oh fy sell ee). Diatoms and yellow-green and golden- brown algae. Example: diatoms (Figure 4-15). Class 4. Phaeophyceae (fee oh fy seh ee) . Brown algae. Examples: giant kelps (Fig¬ ure 4-7), rockweeds such as Fucus (Figure 4-16). Class 5. Rhodophyceae (roll doh fy sell ee) . Red algae. Example: Chondrus (Figure 4-17). j Organic Puzzles. Flagellates ( FLAJ uh layts) . Organisms having both plantlike and ani¬ mal-like features. Examples: Euglena (Fig¬ ure 4-5), Volvox (Figure 4-6). Photos top to bottom: Hugh Spencer; Carl Striiwe, from Monkmeyer; General Biological Supply House, Inc., Chicago; Hugh Spencer; Hugh Spencer 120 VARIETY AMONG LIVING THINGS— PLANTS SUBPHYLUM II. FUNGI Fungi (FUNjy) are thallophytes that do not contain chlorophyll or a chemically similar substance. Usually they are white in appearance, although some species are colored by pigments unlike chlorophyll (that is, not of use in food-making). Fungi, then, depend on other organisms for their food; they do not make their own food as most plants do. Class 6. Schizomycetes (skiz oh my SEE teez). Bacteria. Examples: coccus-type bacteria, such as Streptococcus (Figure 4-18), bacillus-type bacteria (Figure 4- 11), spirillum-type bacteria. Class 7. Myxomycetes (mix oh my see teez). Slime molds. Example: Fuglio (Figure 4-19). Class 8. Phycomycetes (fy koh my see teez). Fungi in which the plant body is usually mycelium, but in which a single distinctive type of spore is not found. Examples: bread mold (Figure 4-20), potato blight. Class 9. Ascomycetes (as koh my see teez) . Yeastlike fungi. Examples: yeasts (Figure 4-11), cup fungi, blue and green molds such as Penicillium (Figure 4-21 ) . Class 10. Basidiomycetes (buh sih dee oh my see teez). Club fungi, in which the plant body is usually mycelium, and in which a single distinctive type of spore is usually found. Examples: mushrooms (Fig¬ ures 4-9, 4-10, 4-22), puffballs, rusts, smuts (Figure 4-9) . Lichens, being two organisms in one (Fig¬ ure 4-12), are not classified here either as algae or fungi. In many recent books on classification, the ten classes of thallophytes given here are listed as separate phyla ( Cyanophyta, Chlorophyta, etc. ) . Photos top to bottom: E. R. Squibb & Sons; Roche; DuPont Magazine; Merck & Co.; Roche THE LOWLIER PLANTS 121 4-22 4-21 4-20 4-19 4-18 PLANT PHYLUM TWO: MOSSES AND LIVERWORTS Have you ever walked out upon a quaking bog? If so, you know it felt as if the whole earth were “quaking” under your feet. Of course, it was not the whole earth that seemed to rise and fall beneath your feet. It was only the floating mass of plants that rose and fell (quaked) as you walked. Walking over a quaking bog, also called a peat bog, is a surprising and somewhat un¬ nerving experience to people who are used to feeling the solid earth beneath their feet. On a bog, you are not walk¬ ing on solid earth but on a floating mat of plants, perhaps two to four feet thick. Most of the plants in the floating mat of a bog are moss plants of the kind we call peat moss ( genus Sphagnum— sf ag num). These mosses are enmeshed in a vine that creeps over the top of the water somewhat as strawberry or dew¬ berry vines creep over the ground. Peat is harvested from old bogs and used in greenhouses, nurseries, and in many flower gardens. Peat moss and all other mosses are classified in the second phylum of the plant kingdom. So are the liverworts. Botanists call this phylum Bryophyta (bry off ih tub ) or the bryophytes ( bry ohfytes). The bryophytes include low¬ ly plants with simple leaves only two cell layers thick and with rootlike parts and crude stems, but with no well- developed food or water vessels. The rootlike parts are not true roots, but they serve somewhat similarly. Al- though mosses and liverworts are lowly plants (lacking in highly complex or¬ ganization), they are considerably more complex than the thallophytes, as you will see. The mosses You may never have paid enough at¬ tention to mosses to discover the vari¬ ety among them. If you will take the trouble to examine and compare the mosses you find in several different places, you will soon discover that there are different kinds of mosses, just as there are different kinds of flowers. Botanists recognize 14,000 different species. They grow in nearly every type of habitat (hab ih tat) or “home” where plenty of moisture is available. Mosses grow in abundance in the Arctic and in high mountain regions. Many kinds grow in fresh water. One kind has been found 180 feet below the surface of a Swiss lake. In almost any J woods you can find fallen tree trunks covered with mosses of many kinds. Even on the desert, some kinds of mosses grow. You can find them in shady spots after a period of good rain. One of the larger and more commonly seen mosses is the pigeon-wheat moss. It grows in dense patches in moist spots in open fields or woods. It may attain a height of two or more inches. The pigeon-wheat moss is one of the few mosses with primitive woody tissue (water vessels ) . EXAMINING MOSSES. Examine the mosses you collected recently. If you did not collect any, try to find some now. Even in a city, you may find a patch of moss growing along the edge of a sidewalk, in a shady spot in a flower garden, or in a park. Separate one single moss plant from the mass you have collected and lay it in a shallow dish of water. Study it with a hand lens or under a “dissecting micro¬ scope/7 Look for rootlike and stemlike structures, 122 VARIETY AMONG LIVING THINGS — PLANTS BLUEPRINT OF A MOSS— mnium Photo by Hugh Spence 4-23 Two generations of a moss of the genus Mnium i w uni ) are shown here. The "bristle” with its spore ease is a plant apart from the leafv green moss. The spores that are released from the spore case will give rise to new' leafy moss plants. Mnium has true leaves and a true stem, although both are crude as compared with, say, the leaves and stems of flowering plants. The rhizoids are not true roots. and for leaves. Mount and examine the rootlike growths and a leaf under your mi¬ croscope. You will find that each rootlike structure is a thread of single cells, end to end. Crush a bit of the stem in a drop of water on a slide, then tear it apart with needles. Examine it under your microscope. Look for any specialized tissues, such as wood (water-conducting tissue) and epi¬ dermis (covering tissue). Pigeon-wheat moss and a few other mosses do have primitive food and water vessels (and thus true stems), but most mosses do not. Some of your mosses may have "bris¬ tles" (Figure 4-23) on them. If so, examine one moss bristle under a hand lens, then crush the spore case (Figure 4-23) and ex¬ amine part of it under the low power ob¬ jective of your microscope. Title a fresh page in your record book Mosses. On it, sketch one moss plant. Be sure to show the bristle, if your plant showed one. Sketch one rootlike structure as it looked under your microscope. Sketch one leaf. Then answer these questions. 1. Is the rootlike structure an organ with several specialized tissues in it? 2. Did you find woody tissue or any other highly specialized tissues in the bit of crushed stem? 3. Did you find veins of woody tissue spreading throughout each leaf? 4. What did you find in the bit of v,. crushed spore case you looked at? 5. Would you say that mosses are more highly organized living systems than algae and fungi? Why? The moss plant body A moss plant has what look like “roots.” a “stem/ and leaves. But these THE LOWLIER PLANTS 123 organs are not made of several highly specialized tissues. The roots, stems, and leaves of ferns and seed plants— the higher plants— are made of highly specialized tissues, one of which is woody tissue, the water-conducting tis¬ sue. The moss “roots” are mere fila¬ ments (threads) of cells, end to end. “Roots” like these are called rhizoids (RYzoydz). (See Figure 4-23.) Even the moss leaf is only one or two cell layers thick ( except at its midrib, where most species have several layers of cells), and it has no veins like those in the leaves of higher plants. Mosses do not have well-developed food and water vessels, but a few do have primitive ones. In nearly all mosses, water and dissolved food mate¬ rials pass through cell membranes from one cell to another, not through food and water vessels. Materials enter and leave moss plants through the cell walls and cell membranes of the cells. Moss¬ es are more complex than algae and fungi, but much less complex than ferns and seed plants. That is why bry- ophytes are classed as lowly plants. Mosses are the pygmies among land plants. They do not grow very tall. Even so, they are successful plants in moist habitats. How do mosses reproduce? The bristles you may have seen on some of your mosses are really sepa¬ rate plants. Each bristle grows from a fertilized egg, usually located in the top of the green moss plant. The bristle usually gets its food and water from the green moss plant beneath it. In the spore case on the top of a bristle, repeated cell divisions result in spores. If a spore falls in a moist spot, it will grow— not into a bristle, but into a green, leafy moss plant. The leafy moss plant may produce both sperms and eggs. Or one leafy plant (in some genera) may produce only sperms, and another leafy plant may produce only eggs. Moss sperms look somewhat like one-celled flagel¬ lates and can swim. To reach an egg, a sperm must have a little water in which to swim. Dew or moisture after a rain may supply the necessary water. You may want to know how a sperm finds an egg. Figure 4-24 shows you that a moss egg is at the bottom of an organ that is shaped somewhat like a glass flask. The sperm has to find the mouth of the “flask” and swim down the neck to the egg. How does the sperm find its way? The flask-shaped egg-making organ and the egg itself release sugar into the water from a drop of dew or rain. Sugar water “attracts” sperms, so they swim toward the spot where the sugar solu¬ tion is most concentrated— and there is the egg! Remember how an ameba moved toward vinegar water? A moss sperm swims toward sugar in solution in much the same way, not by “choice,” but just because it can’t help it. The sperm and egg fuse into one cell, the fertilized egg. Then the fertilized egg grows into the bristle, and the bristle’s spore case makes spores. A spore then grows into a leafy moss plant. Figure 4-24 gives you a more complete picture, but you need to know four new terms in order to understand the illustration. Here they are. Anv plant that produces spores is a sporo- phyte (spoh roh fyte), sporo meaning “spore” and phyte meaning “plant.” The moss bristle is a sporophyte. The eggs and sperms of any organism are called gametes ( gam eets ) , from the ancient Greek gamein, meaning “to marry.” So any plant that produces 124 VARIETY AMONG LIVING THINGS— PLANTS gametes (eggs and/or sperms) is a gametophyte ( guh mee toh fyte ) . A leafy moss plant is a gametophyte. In Figure 4-23 is a drawing of a moss ga¬ metophyte with the next-generation sporophyte; the “bristle" is the sporo- phyte. Study Figures 4-23 and 4-24 carefully to get the idea. Among many plants (including mosses), sporophytes as well as game- 4-24 The life cycle of a moss is traced here, beginning with a fertilized egg that grows into a sporophyte (bristle) atop the gametophyte (leafy, green plant). As the sporophyte matures, it forms a spore case. Spores from the spore case sprout into algalike green fila¬ ments that bud and become young gametophytes. The gametophytes mature as new leafy green moss plants, male and female. Male gametes (sperms) reach female gametophytes and fertilize female gametes (eggs). The fertilized eggs grow into new sporophytes, starting the cycle again ( from sporophytes to spores to gametophytes to gametes). Do sporophytes grow atop both male and female gametophytes? Adapted from Sinnott and Wilson, Botany — Principles and Problems, 1955, McGraw-Hill Book Co. MOSS— LIFE CYCLE START HERE Sperms ® Mature sporophyte Young sporophyte Egg Spore case of sporophyte Mature female gametophyte Mature male gametophyte Young gametophyte tophytes are common. In these plants, each life cycle is double; in each com¬ plete cycle, there are two plants, one a gametophyte and the other a sporo- phyte. So the life cycle is like this: spore^gametophyte— >gametes— >sporo- phyte. Sporophyte and gametophyte al¬ ternate with each other (Figure 4-24). Biologists refer to this situation as an alternation of generations. For most of you, memorizing these terms probably isn't important, fust getting the idea is enough. But for those of you who plan to go on into college biology, these terms are worth learning. What are mosses called? The mosses make up one class of the bryophytes. The biologists name for this class is Musci ( muss eye ) , from the Latin muscus, meaning “moss.” Would you like to learn the names of some of the mosses you find? Use page 127 and the reference books listed under Further Reading at the end of this chapter. Are mosses important to man? Mosses are not nearly so important to people as the algae and fungi are. And yet, peat mosses are widely used in gardening. Also, many mosses add the second step to the process of soil forma¬ tion. After the lichens dissolve a bit of a rock surface, these mosses move in, and when they die and decay, tliev en- rich the soil. Liverworts You may have seen a patch of fork¬ ing, ribbonlike green plants growing on the moist walls of a rockv canyon or J J ravine. Figures 4-25 and 4-26 may help you to recognize a liverwort the next time you see one. Some 4,800 species of liverworts have been described. Liverworts make up another class of the bryophytes. Like mosses, they never grow tall. They grow out Hat on moist rocks, logs, or on damp, shady soil. Liverworts have single-celled rhi- zoids. They also have alternation of J generations, but the sporophyte is small. The class name of the liverworts is Hepaticae ( heh pat ih see ) , from the ancient Greek hepar, meaning “liver,” so named because of the imagined re¬ semblance to a liver. Summing up: the bryophytes The mosses (Musci) and the liver¬ worts (Hepaticae), plus one other class of now-rare plants, make up the second plant phylum, the one botanists call Bryophyta. They are more complex plants than the thallophytes, but less complex than the ferns and seed plants, which will be discussed in the next chapter. On the following page you will find an illustrated summary of Phylum Bry¬ ophyta. Use it to help you identify spec¬ imens that you collect. If you find a specimen of a plant you think is a bryophyte, compare it with the pictures on the next page, and note the class description for the illustrated specimen that looks most like yours. Then turn to page 130 and carefully read the in¬ structions given there for using refer¬ ence books to identify specimens. You will find reference books listed imme¬ diately following the instructions. Also use the summary of bryophytes on the next page for review. After you have studied the information given there, turn back to pages 120 and 121 and take note of the differences be¬ tween thallophytes and bryophytes. 126 VARIETY AMONG LIVING THINGS— PLANTS PHYLUM BRYOPHYTA The bryophytes (bry oh fytes) are small, many-celled, mostly land-inhabiting plants, numbering about 24,000 speeies. They have rhizoids but no true roots; their rhizoids are made up of undifferentiated eells at¬ tached end to end (in mosses) or of sin¬ gle cells (in liverworts). They have stems and leaves, although both are primitive as compared with stems and leaves of flower¬ ing plants. Most of them do not have spe¬ cialized tissues that conduct food and water from one part of the plant to another, but some species do have a primitive form of food and water vessels. Most (but not all) species undergo alternation of generations. The leafy, green plants most commonly seen are the gametophytes, which produce male and female gametes (sperms and eggs). The fertilized eggs grow into sporo- phytes, and the sporophytes, in turn, pro¬ duce spores that give rise to the next game- tophyte generation. Class 1. Hepaticae (heh pat ih see) . Liver¬ worts. Examples: Riccia (Figure 4-25), Marchantia (Figure 4-26). Class 2. Musci ( muss eye). Mosses. Ex¬ amples: Catharinea (Figure 4-27), Pin¬ cushion moss (Figure 4-28), Mnium (Fig¬ ure 4-23). Photos top to bottom: Hugh Spencer; Hugh Spencer; Roche ; Roche THE LOWLIER PLANTS 127 4-28 4-27 4-26 4-25 Your Biology Vocabulary Here is a list of the important new terms introduced in this chapter. Make sure that you understand and can use each term correctly. binomial system grass-green algae lichens phylum red algae thallophytes subphylum brown algae Sphagnum class flagellates habitat order flagellum moss bristle family Oscillatoria rhizoids genus Volvox gametes species Euglena sporophyte taxonomy agar-agar gametophyte taxonomist sporangium alternation of generations Homo sapiens mycelium Musci fungi Amanita Hepaticae blue-green algae budding bryophytes Testing Your Conclusions Rule off two columns on a fresh page of your record book. Title the first column Thallophijtes and the second column Bryophytes. Next rule off two columns under each title. Title the two columns under thallophytes Algae and Fungi. Title the two columns under bryophytes Musci and Hepaticae. Copy each item below into the correct column. Oscillatoria mushroom corn smut puffball wheat rust Volvox bread mold pneumonia germ Amanita spirogyra liverwort bacteria pigeon-wheat moss rockweed yeasts diatom sea orange seaweeds sea lettuce Sphagnum mildew Thought Problems Sugar-making thallophytes. Some thallophytes (those which contain chlorophyll) make their own food. Others do not. Plants that make sugar make it out of the carbon atoms, hydrogen atoms, and some but not all of the oxygen atoms in carbon dioxide (CO.,) and water (H..O). Some of the oxygen atoms that are left over from sugar-making pass out of the plant into the nearby air or water. Which of the following plants give off oxygen and why is this process important to you? Talk it over in class. 128 VARIETY AMONG LIVING THINGS— PLANTS bacteria pleurococcus mushrooms yeasts spn-ogyra sea lettuce diatoms molds More Explorations 1. A class contest: Who can find the most kinds of fungi? Pick a week end, perhaps from Friday at the close of school until the opening of school on Monday. Go out into the yard or a park or into a woods or meadow and look for fungi. Try to see who can collect the most different kinds during this time. One biology student once collected over a hundred kinds of fungi over a week end. Bring your specimens to class, then refer to paragraph 4 under Further Reading. 2. Another class contest: Who can find the most kinds of mosses and liverworts? Proceed as in 1, above. 3. Mushroom prints. To make a mushroom print, lay a gill mushroom, gill side down, on a piece of white cardboard. Put it in a dry, warm place and leave it there until the mushroom looks rather dry. Then lift off the mushroom carefully. You should have a “print” on the cardboard. What made the “print?” If you can’t guess, make a slide and examine it under your microscope. Then see page 4 and Figure 1 in Field Book of Common Mushrooms, listed in the following section. Further Reading 1. News items on algae. Science magazines and newspapers often carry news items re¬ porting new researches on the algae, especially the cultivation of algae as possible food for cattle and other food animals. The Science News Letter, published weekly by Science Service, 1719 N Street, N.W., Washington 6, D.C., is one of the best places to look for such news, as well as for other biological news. Clip newspaper items concerning algae and bring them to class. Take notes on news items in Science News Letter or other science magazines and report in class. Or read the “Introduction,” pages 5-10, in the book The Culturing of Algae, edited by jules Brunei, Gerald W. Prescott, and Lewis H. Tiffany, published by The Charles F. Kettering Foundation, 1950. 2. A look at the algae. Here is part of the opening paragraph of a book on the algae: “My first experience with algae— though heaven knows I did not know such a word then— was a suggestion from my father regarding swimming during the ‘dog days of August in southern Illinois. “Father’s words were few: ‘When there’s green scum on the water, that is a sign of dog days; don’t go swimming.’ ” Wouldn’t you like to read more in this book? The book is Algae: The Grass of Many Waters by Lewis H. Tiffany, published by Charles C. Thomas, 1938. You can probably borrow a copy at your school or public library. 3. Mushroom culture. Use an encyclopedia or any available book on the commercial growing of mushrooms to find out how and where mushrooms are raised. Handbook of Mushroom Culture by Albert M. Kligman, published by J. B. Swayne, Kennett Square, Pennsylvania, 1942, tells all about the culture of mushrooms. This booklet THE LOWLIER PLANTS 129 has a number of interesting illustrations, too. Kennett Square, Pennsylvania, is a center for the commercial growing of mushrooms. 4. Identifying thallophytes and bryophytes. Collecting specimens to identify is a good way to get started on a biological hobby. It is also an excellent way to further your understanding of the system used by biologists to classify plants and animals. Are you collecting specimens of thallophytes and bryophytes? Here’s what you do to identify them. J Look through the illustrated summaries for these two phyla (pages 120, 121, and 127) and find the picture that looks most like your specimen. (Of course, you must first be sure that what you have is a thallophyte or bryophyte, and not a fern or seed plant.) Read the class description given for the illustration that looks most like your specimen, and make a note of the class name and other examples of that class. Then locate one or more reference books and use the index of each book you choose to find the pages dealing with the phylum and class in which you are interested. If you fail to find the class name listed in the index, look instead for the genus of one or more of your known examples of that class (these genus names you will find on pages 120, 121, and 127 in this book). One or the other of these methods should lead you to the reference pages that may help you to identify your specimen. If the first book you try doesn’t help you, try another. Ask your teacher for help if you need it. The reason you may not be able to find the class name you are looking for listed in certain reference books is that not all authorities agree with the system of classifica¬ tion used in this text. For instance, some biologists now sort organisms into three king¬ doms in place of two. The three are: (1) Protista (some, but not all, of the one-celled organisms, plus viruses, etc.); (2) the Plant Kingdom; and (3) the Animal King¬ dom. Another example has to do with plant phyla. Biologists are now classifying as plant phyla what this text lists as classes of thallophytes. Do not worry about this. It doesn’t matter to you whether the grass-green algae constitute a phylum or a class. They have been a class ( Chlorophyceae ) for a long time. Some day biologists may all agree to call them a phylum (Chlorophyta) , but as yet, we stick with the older usage, which seems simpler for you to use. Remember— if you cannot find the class name you are interested in listed in the index of a reference book, look instead for listings of the genera of other examples of that class. Nearly all reference books use the same genus names, and related speci¬ mens from the same class usually are discussed within a few pages of each other in a reference book. When you have located the pages dealing with the class you are in¬ terested in, thumb through them and study all the illustrations carefully. The chances are that you will be able to identify many of your specimens without having to look in more than two or three reference books. Remember that to identify your specimen you need at least the name of its genus, and preferably also the name of its species. HOOKS FOR GENERAL USE: Botany by Ronald D. Gibbs, Blakiston Division, McGraw-Hill, 1950. Botany: Principles and Problems, Fifth Edition, by Edmund W. Sinnott and Kath¬ erine S. Wilson, McGraw-Hill, 1955. Life by George Gaylord Simpson et ah, Harcourt, Brace, 1957. Plant Families, IIow to Know Them by Harry E. Jaques, Wm. C. Brown, 1948. 130 VARIETY AMONG LIVING THINGS— PLANTS BOOKS OX ALGAE: Algae of the Western Great Lakes Area by Gerald W. Prescott, Cranbrook Institute of Science, 1951. The Fresh-Water Algae of the United States, Second Edition, by Gilbert M. Smith, McGraw-Hill, 1950. books on fungi: Common Edible Mushrooms by Clyde M. Christensen, Univ. of Minnesota Press, 1943. Field Book of Common Mushrooms, New Revised Edition, by William S. Thomas, Putnam, 1948. Fundamentals of Microbiology, Sixth Edition, by Martin Frobisher, Saunders, 1957. books on mosses: How to Know the Mosses by Henry S. Conard, edited by Harry E. Jaques, Wm. C. Brown, 1944. Mosses by E. T. Bodenberg, Burgess, 1954. THE LOWLIER PLANTS 131 CHAPTER Ferns and Seed Plants Forty million years ago , this hollow-celled and at that time woody tissue was part of the stem of a living fern Even today , it serves to identify that fern as a higher plant. But in what respect higher ? The higher plants You have just reviewed the lowly plants, those of the first two plant phyla. You come now to the higher plants, those of the third and fourth plant phyla. The higher plants include all the ferns and their relatives and all the plants that produce seeds. They are called higher plants because they are considerably more highly organized in most respects than the thallophytes and bryophytes. All of the higher plants have true roots, stems, and leaves, each with sev¬ eral highly specialized tissues, includ¬ ing the tissues that make up the food and water vessels of the transport sys¬ tem. Botanists call all these plants to¬ gether vascular ( vass kyoo ler ) plants, from the Latin word vcisculum, mean¬ ing a “small vessel.” Vascular plants have “small vessels” that transport food and water to all the living cells in their bodies. You will learn more about these food and water vessels later. For now, Dr. Chester A. Arnold, Curator of Plant Fossils, Museum of Paleontology, University of Michigan think of them as bundles of micro¬ scopic tubes that do for the vascular plants about what your blood vessels do for you— they transport necessary materials to and from internal living cells. The vascular plants of Phylum Three are the ferns and their relatives. Those of Phylum Four are the plants that produce seeds. The chief difference be¬ tween plants of these two phyla is that the ferns and their relatives do not pro¬ duce seeds, while the plants of the fourth phylum do. Botanists call the third plant phylum (composed of the ferns and their rela¬ tives ) Pteridophyta ( tehr ih doff ih tuh ) or the pteridophytes ( tehr ih doh fytes), from pteris meaning “fern” and phijtes meaning “plants.” They call the fourth phylum Spermatophyta (sper muh toff ih tuh ) or the spermato- phytes ( sper muh toh fytes ) , from sper- mato meaning “seed” and, again, phijtes meaning “plants.” 132 VARIETY AMONG LIVING THINGS— PLANTS The living pteridophytes have been sorted into three main classes— the ferns, the club mosses (not mosses, of course), and the horsetails. Let’s look first at the ferns. FERNS The ferns make up the most numer¬ ous class of pteridophytes. If you go out to look for ferns, you will probably recognize them by their leaves. Most ferns have leaves that are divided and that may be subdivided into many leaflets. (The walking fern has a leaf that is not subdivided at all, however, and there are other ferns like it in this respect.) The whole leaf with its leaf¬ lets is called a frond. Fern fronds grow at the tip and uncurl as they grow (Fig¬ ure 5-1 ). In addition to true leaves with vascular tissues in their veins, ferns also have true roots and stems with several specialized tissues, including vascular tissue (Figure 5-2). 5-1 GROWTH OF FERN FRONDS From right to left are five stages in the growth of fern fronds. As they grow, they unroll at the tip. American Museum of Natural History People often grow ferns as house plants. Look at a potted fern plant. The fronds ( leaves ) are all you can see above ground. The fern stem is under¬ ground with the roots. The same thing is true of all the ferns you are likely to find in woods and rocky ravines, such as the maidenhair fern, cinnamon fern, sensitive fern, brake fern, and many more. In the tropics, some ferns grow like trees and are called tree ferns. Their stems are above ground and form the “trunks’ of the tree ferns. There are many flowering plants that have subdivided leaves which are often mistaken for fern leaves. Yarrow leaves and asparagus leaves are often collected by biology students as examples of fern leaves. Yarrow and asparagus produce flowers and seeds; therefore, they are not ferns. How, then, can you tell a fern? Any plant you find that has fronds similar to those in Figure 5-1 is likely to be a fern. Fern fronds unroll at the tip as they grow. Ferns have true roots, stems, and leaves, all with several specialized tissues, including vascular tissue. But a fern never blooms. It never makes seeds. Ferns produce spores, usually on the undersides of the frond leaflets. So a plant with unrolling fronds and vascular tissue, but no flowers or seeds at any time, is a fern. Vascular tissue in fern stems The ferns you examined surely do not look much like the trees you may see on your way to school, the flowers in a city park, or the tomatoes, beans, and peppers your family may raise in a garden. And yet ferns are like these familiar plants in several ways. For one thing, they have true transport systems. So do trees, flowers, and vegetable FERNS AND SEED PLANTS 133 BLUEPRINT OF A FERN— SWORD FERN Leaf Roofs Epidermis Phloem Fibrovascular bundle Left : Myron R. Kirscli 5-2 Two types of underground stems— short and upright, or long and horizontal— are common among ferns. From one, fronds and roots grow in a cluster, as in this sword fern. Along the length of the other, fronds and roots emerge at intervals. Endodermis Xylem Cortex EXAMINING FERNS. You may be able to collect ferns in your area. If so, examine them. If not, use a potted fern for study. Remove a frond. Sketch it. Then put the frond stem in a jar of water reddened with a little red ink. Next day, hold a leaflet of this frond to the light and examine it with a hand lens. The reddened water reaches the leaflets through water vessels (woody tissue). Can you see the red in the veins of the leaflet? If so, sketch the leaflet, much enlarged, and show the veins in red. Remove a whole fern plant from the soil and shake loose the soil particles. Locate the roots and the underground stem. Sketch and label root, stem, and leaf or frond. Find out for yourself just where the wa¬ ter vessels are located in root and stem by putting them in reddened water. Crush and examine the root and stem after 24 hours and record what you find out. Figure 5-2 shows a stained cross sec¬ tion of a fern stem. You may want to J examine a slide showing the same thing. The covering tissue of a fern stem is the epidermis (Figure 5-2). Most of the tissue inside the epidermis is rather soft. Like the similar tissue of a root, it is called cortex. Food is stored in the stem cortex. Scattered through the cor¬ tex, you will see bundles of vascular tissue. These bundles vary in size and shape, but each one has both food and water vessels in it. The covering tissue that surrounds each bundle is endo¬ dermis ( en doh der mis ) . Each bundle is called a fibrovascular ( fy broh vass kyoo ler ) bundle, because these bundles of food and water vessels make up the fibers in the stem. (The fibers in a stalk of celery, a seed plant, are also fibro¬ vascular bundles.) 134 VARIETY AMONG LIVING THINGS— PI. ANTS The water vessels in vascular plants are usually stained red (or purple, or pink) on slides. They are long, hollow wood cells, end to end, running from roots through the stems to the leaves. The reddened veins you saw in a leaf¬ let of a fern frond showed where the woody tissue was located. Biologists call woody tissue xylem ( zy I’m ) . ( See Figure 5-2.) The food vessels in a fibrovascular bundle may be stained blue or green on a slide. They lie close to the xylem cells. Biologists call the cells that make up the food vessels phloem ( floii ’m ) . (See Figure 5-2.) These names of fern-stem tissues would not be important to you, if ferns were the only plants that had them. But they aren’t. All fern relatives and all seed plants have these tissues in their stems. You will be reading and talking about these tissues often in biol¬ ogy. So it will pay you to start making use of these terms now. Remember, don’t just memorize and recite these new words. Learn them by using them, in written work, in class discussions, and even in conversation. For example, if you eat some celery for lunch today, mention its fibrovascidar bundles (fi¬ bers) to a friend. The life cycle of ferns Ferns do not bloom. They do not make seeds. Ferns produce spores. So the fern is a sporophyte (spore-making plant ) . At certain times of the year, you can find green or brown patches on the undersides of the leaflets of many fern fronds. Examine any available fronds for such patches. Each patch is a clus¬ ter of sporangia (spore-making or¬ gans). You can often tell the genus of a fern by the arrangement and appear¬ ance of its sporangia (Figure 5-3). Fern spores do not grow into leafy ferns. (You will remember that moss spores do grow into leafy moss plants ) . Fern spores grow into small, flat, green plants called fern prothallia (proh thal ee uh— singular, prothallium) . (See Figure 5-4.) You may never have seen fern prothallia, but you can find them if you search well. A fern prothallium grows flat. It is usually much smaller than your little fingernail. It has rhizoids, not true roots. Fern prothallia usually grow in patches on moist, shady logs or rocks. 5-3 FERN SPORANGIA Left. This cluster of sporangia (much enlarged) is one of many that line the undersides of Christmas fern fronds. Right. In a polypody fern, the clusters of sporangia also line the undersides of the fronds, but in details of appearance and arrange¬ ment they differ somewhat from sporangia of other ferns. Hugh Spencer American Museum of Natural History 5-4 FERN PROTHALLIA The inconspicuous fern gametophyte has rhizoids, not true roots. Both it and the sporophyte grow as independent plants (unlike the sporophyte generation of mosses). They look a little like certain liver¬ worts. You may be able to raise some fern prothallia in class. Ask your teacher for directions. A fern prothallium (Figure 5-4) is a gametophyte. It produces gametes (eggs and sperms). The sperms swim, in a drop of dew or other moisture, from the sperm-making organs to the egg-making organs. One sperm ferti¬ lizes one egg. The fertilized egg then grows into the leafy fern plant. So the life cycle of a fern is similar to that of a moss. Both undergo alter- nation of generations. Sporophytes pro¬ duce spores that grow into gameto- phytes that produce fertilized eggs that grow into sporophytes. But in mosses, the leafy plant is the gametophyte, as you can see in Figure 4-24, page 125. In ferns, the leafy plant is the sporo- 136 phyte, and the small prothallium (Fig¬ ure 5-4) is the gametophyte. The fern class The ferns make up one class of the third plant phylum. The botanical name of the class is Filicineae (filihsiNuh ee). If you are interested in identify¬ ing some of your specimens, or in know¬ ing more about them, use the illustrated summary on page 141 and the section Further Reading at the end of this chapter to help you find reference books. Ferns are the most numerous living descendants of the first known vascu¬ lar plants. Ferns are more successful in moist, tropical conditions than any¬ where else on earth. In the tropical forests, some ferns grow like trees, oth¬ ers climb like vines, and still others 5-5 STAGHORN FERN This tropical fern is so-called because most of its fronds are shaped somewhat like a stag’s horn. Hugh Spencer 5-6 CINNAMON FERN A species found in the Eastern United States, its fronds closely resemble the “print” of an ancient frond shown in Figure 5-7. Do the similarities be¬ tween the two justify any conclusions regarding a close relationship? resemble “staghorns” (Figure 5-5) and grow attached to forest trees. Some of you may have found prints of what looked like fern leaves in the coal used to heat your home. That coal came from the great coal forests of many millions of years ago. Early stu¬ dents of the leaf prints in coal thought they were all prints of the fronds of ancient tree ferns. Today, microscopic studies have proved that many of these leaf prints are not of fern fronds at all, because they bore tiny seeds, not spores. Today botanists call these seed-bearing fernlike plants of the great coal forests seed ferns, or Pteridospermae ( tehr ih doh sper mee ) . So the next time you find a leaf print in coal, remember that it may be a print of a true fern frond (Figure 5-6) or of a seed fern frond (Figure 5-7), since both kinds of plants My ron R. Kirsch FERNS AND SEED PLANTS 137 Marion A. Cox 5-7 SEED FERN FROND This “print” of an ancient seed fern was found in a shale deposit in Ohio. Its appearance as com¬ pared with true ferns (Figure 5-6) is somewhat misleading, for it bore seeds, not spores. were abundant in the great coal forests. Ferns are still successful plants, but not as abundant as they once were. Seed ferns have disappeared entirely. Summing up: ferns List the numbers (1-10) of the blanks in the following statements. Beside each number, write the word or term you would use to fill that blank. Pteridophytes is the name of the (1) ... in which ferns are classified. Filicineae is the name of the (2) in which ferns are classified. Fibro vascular bundles contain water vessels, called wood tissue or (3) . . . , and food vessels, called (4) .... The leaves of most ferns are divided into many leaflets and are called (5) You can tell a young, growing fern leaf by the fact that it (6) ... at the tip. Most ferns bear clusters of (7) ... on the backs of their leaves. To find fern prothallia, you must look for tiny, flat, green plants on moist, shady (8) ... or (9) .... Ferns are most plentiful and various in the hot, moist (10) . . . forests. FERN RELATIVES Two other classes of vascular plants are included along with the fern class in the third plant phylum. These are the club mosses and the horsetails. These plants are the sole living survivors of plant lines that were quite successful more than 250 million years ago, when the great coal forests were living. Club mosses You have probably seen at least one kind of club moss, without knowing what it was. Where? In a Christmas wreath. One of the club mosses, Lyco¬ podium clavatum ( ly koh poh dee um kluh vay turn), is widely used in wreaths at Christmas time. In Figure 5-8 (left), you see a club moss, one people often call the “ground pine.” Club mosses are not mosses. They are not pines, either. The ones you are most likelv to see be- long to the genus Lycopodium (Figure 5-8, left). This and three other living genera make up one class of pterido¬ phytes.* The botanical name of this class is Lycopodineae ( ly koh poh din uh ee ) . See the illustrated summary on page 141 for further information. The club mosses of today are not numerous. Their day of glory came long ago in the great coal forests. Then, some lycopods were huge trees, as * Some modern taxonomists call the pteri¬ dophytes a subphylm, some a phylum, and still others call them a family. 138 VARIETY AMONG LIVING THINGS— PLANTS much as 30 or even 40 feet high. Today most of the club mosses are small plants, although certain ones may trail over the ground for as far as 20 feet. The life cycle of club mosses Club mosses undergo alternation of O generations. The green, leafy plant is the sporophyte. It produces spores, usually in conelike organs (Figure 5-8, left). The spores are of two kinds, small and not-so-small spores. The small spores grow into male gameto- phytes, the larger ones into females. These gametophytes are hard to find, but those that scientists have studied are always living in close association with a fungus, reminding one of the lichens. Male gametophytes produce sperms with two cilia. Sperms swim to the eggs inside the egg-making organs of the fe¬ male gametophyte. Then the fertilized egg grows into a leafy sporophyte. Horsetails You may have seen “scouring rushes" like those in Figure 5-8 (right). They usually grow in sandy soil near bogs or 5-8 CLUB MOSS AND HORSETAIL Left. In conelike organs like the one growing from “scouring rush” ( Equisetum hiemale ), the pans. streams. Scouring rushes feel scratchy when you handle them, because their stems contain gritty, sandlike silica (siLuhkuh). American pioneers used horsetails to scour their pots and pans, hence the name “scouring rushes.” O You may have seen another species of horsetail growing along a railroad track. Figure 5-11 in the classification summary on page 141 shows what this species looks like. The horsetails make up the remain¬ ing class of living pteridophytes, a class called Equisetineae ( eh kwuh see tin uh ee ) . Only one genus of this class survives today, the one called Equisetum (eh kwuh see turn ) , with some two dozen species known. Most of these are small plants. Like the club mosses, the horse¬ tails had their golden age in the great coal forests. In that far off time, some of them were large trees. Where did ferns and their relatives come from? Scientists have found fossils of very primitive vascular plants, dating back over 300 million years. Figure 5-9 shows club mosses, spores often are produced by the top of this Li/copodium. Right. This is a horsetail used by pioneers to scour pots and Hugh Spencer a drawing of one of the few surviving examples of those ancient vascular plants. It is known as a psilopsid (sy lop sid). Two genera of psilopsids survive today. But once they were a varied lot. The psilopsids were the first vascular plants on earth, or at least the first of which we have found fossils. From the psilopsids came the horse¬ tails, the club mosses, and the ferns, or so biologists now interpret the evi¬ dence. Study the drawing in Figure 5-9. As you see, the psilopsids of old had no true roots and no true leaves. Why do you suppose the ferns and their relatives soon crowded out most of the psilopsids? Do you think their roots and leaves gave them an advantage over their “forebears”? 5-9 PSILOPSID Only two genera of this ancient line of plants survive. The sporo- phyte of one of them is shown here. Its gametophyte (it undergoes alternation of generations) grows underground. Pteridophytes today The three main classes of living pteridophytes are the ferns, the club mosses, and the horsetails. All of these have true roots, stems, leaves, and spores. All three show alternation of generations. Some 8,000 species of living pterido¬ phytes have been named and. described. Over 3,000 more species are known to have lived in the past. Are pteridophytes important to man? Do you know of any ways in which people make use of ferns and their rela¬ tives today? Of course, you know that many people grow and enjoy house ferns. You also know that a club moss is often used in Christmas wreaths. And people use coal, much of which came from pteridophytes. Can you think of any more uses? Here’s an odd one. Lycopodium powder is made of the spores of club mosses. It is used in fireworks, because it is highly inflammable. And doctors sometimes use it in treating skin sores, because it absorbs moisture readilv. J After you have summed up your knowledge of club mosses and horse- tails (as directed below), go on to the next page and study the illustrated summary of the pteridophytes. Summing up: fern relatives Discuss these questions in class: 1. At what time of year are you like¬ ly to see club mosses used as a decora¬ tion in someone’s home? 2. In what kind of place might you find “scouring rushes”? 3. How did “scouring rushes” get their name? 4. Which probably came first— horse¬ tails, ferns, psilopsids, or club mosses? 5. Why are pteridophytes called vas¬ cular plants? PHYLUM PTERIDOPHYTA n mHa The pteridophytes (tehr ih doh fytes) are vascular land-inhabiting plants, numbering about 11,000 species. They have true roots, * stems, and leaves, with highly developed vascular tissue (food and water vessels). Because much of the vascular tissue is woody in nature, it serves as a good sup¬ porting tissue for stems and leaf stems; thus, pteridophytes have grown taller, on the average, than the lowlier plants. Like most of the bryophytes (liverworts and mosses), pteridophytes undergo alterna¬ tion of generations: from sporophyte to spores to gametophyte to gametes (eggs and sperms) to sporophyte again. One generation is more primitive in most re¬ spects than the other (fern gametophytes, for example, do not have true roots, but the sporophytes do). Class 1. Filicineae (hi ih sin uh ee) . Ferns. Examples: Polystichum (Christmas fern, Figure 5-10), sword fern (Figure 5-2), Platycerium (staghorn fern, Figure 5-5), Osmunda cinnamomea (cinnamon fern, Figure 5-6). Class 2. Equisetineae ( eh kwuh see TIN uh ee). Horsetails. Examples: Equisetum arvense (Figure 5-11), Equisetum hiemale (“scouring rush,” Figure 5-8). Class 3. Lycopodineae (ly koh poll din uh ee). Club mosses. Examples: Selaginella (Figure 5-12), Lycopodium (Figure 5-8). Photos top to bottom : Hugh Spencer ; Hugh Spencer ; Brooklyn Botanic Garden FERNS AND SEED PLANTS 141 5-12 5-11 5-10 SEED PLANTS Most of the plants you have been seeing all your life are spermatophytes (seed plants). In the woods and mead¬ ows, in the deserts and along the road¬ sides, in city parks and in flower and vegetable gardens, it is seed plants that you see, in abundance. You will study in detail the plant body and life processes of the sperma¬ tophytes in a later unit. Here, we shall briefly survev the entire phylum. Variety among the seed plants Seed plants may be huge trees as high as 300 feet and as much as 25 or even 50 feet around the trunk. They may be climbing or trailing vines of great length. Or they may be only a few feet or a few inches tall. One kind, called duckweed, is a bare fraction of an inch in diameter. You have prob¬ ably seen masses of tiny leaves floating on quiet water somewhere in your re¬ gion. These were probablv the leaves of the duckweed. Some seed plants live and die in one season. They are called annuals. Others live two seasons, flowering and forming seeds during the second summer before they die. They are called biennials. Others live on vear after year. These are called perennials. All trees are per¬ ennials, and among them are found the oldest living things on earth. A big cypress tree in Mexico and some of the giant sequoias of our West are more than 3,000 years old. It would be a mistake to think that seed plants grow only on the land. Many kinds, such as cattails and cran¬ berries, grow in watery habitats, such as swamps and bogs. Other kinds, like duckweed, grow on the surface of the water; still others, like pondweeds, grow under water. Some kinds grow in the salt marshes along the ocean shore, but none grow in the open seas. Taxonomists have described and named over 200,000 species of seed plants. Of these, some 25,000 species lived and died out long ago. How can you identify a seed plant? Seed plants are vascular plants that have roots, stems, leaves, and seeds (Figures 5-13 and 5-14). Pteridophytes also have roots, stems, and leaves, but no seeds. What is a seed? Most seeds are small plants encased in a seed coat. A lima bean or a shelled peanut is a good ex¬ ample. Remove the brown skin from a shelled peanut, or soak a bean and re¬ move the “skin. In each case, what vou have left is a little plant that grew 5-13 ANATOMY OF A BEAN The production of seeds— beans, for one example— is the chief characteristic of spermatophytes. A. Here is a common bean, familiar to everyone. B. The shape is the same, but the seed coat has been removed, exposing the seed leaves. C. When the two seed leaves are pulled apart, the entire embryo bean plant is revealed. Seed leaves BLUEPRINT OF TWO SEED PLANTS— CORN AND BEAN Compound leaf Seed leaves Leaf Roofs Stem Leaf Brace roots Fibrous roots Photos by Myron R. Kirsch 5-14 Angiosperms make up the largest subphylum of seed plants. They are of two types— monocots and dicots (mono meaning "one.” di meaning "two,” and cot or cott/lc- don meaning “seed leaf ). Corn is a monocot, the bean plant a dicot. Why? from a fertilized egg. Biologists call the young plant inside a seed an embryo (em bree oh ) . The embryo inside an orchid seed is merely a short filament, but in most seeds, the embryo is obvi¬ ously a little plant, with a little root, one or more seed leaves (Figures 5-13 and 5-14), and a shoot (often with one or more small leaves already formed at its tip). FERNS AND SEED PLANTS 143 Photo by Hugh Spencer 5-15 Pines bear naked seeds— that is, seeds that are not enclosed in fruits. And yet pine seeds are not formed under exposed conditions. While seeds are maturing in a female cone, the scales of the cone are closed against one another. It is onlv as the seeds become mature that the scales of the cone separate, exposing the seeds. Naked seed Scale of cone Seed wing PINE — CONE AND SEEDS COMPARING CONES AND FRUITS. You will need a fruit, such as an apple, and some of the larger cones from a pine tree. (The larger pine cone is the female and produces the seeds.) Take a female pine cone that has not yet opened up and shed its seeds. Pry open the cone and look for seeds between the woody scales of the cone. Examine a seed with a hand lens. You will find that it is a dry, naked seed. It was protected in the cone only as long as the scales of the cone remained closed (Figure 5-15). Cut an apple in cross section and look for the seeds inside the core. Apple seeds are surrounded by a fruit. They are not naked. Sketch a cone and a naked seed. Also sketch a cross section of an apple and label fruit and seed. Two common subphyla of seed plants A number of evergreen trees and shrubs bear naked seeds in cones (Fig¬ ure 5-15). They bear no flowers. Sev¬ eral other seed plants also bear naked seeds, not always in cones, but not inside fruits. The cycads (sYkads) and the maidenhair tree, or Ginkgo (gink goh), 144 VARIETY AMONG LIVING THINGS— PLANTS are examples. (See Figure 5-16.) All the plants that bear naked seeds make up one subphylum of the seed plants. We call them Gymnospermae (jimno sper mee ) or the gymnosperms ( jim noh spermz), from gymno meaning “naked" and sperm meaning “seed." About 665 species of gymnosperms have been de¬ scribed and named. Of these, only about 500 are still living. The rest are extinct. Among the extinct species is the entire class of seed ferns. The overwhelming majority of the spermatophytes produce seeds that are enclosed in some kind of covering, usu¬ ally called the fruit. Apple, peach, and tomato seeds are familiar examples. Nut shells, grains, and milkweed pods contain enclosed seeds, though you may not be used to calling them fruits. Enclosed seeds are produced by flow¬ ers. Consequently plants that bear them are often referred to as fioivering plants. The name of this subphylum is Angiospermae ( an jee oh sper mee ) or the angiosperms ( an jee oh spermz ) . Some 200,000 species of angiosperms have been described and named. You can tell an angiosperm by its Mowers and fruits. Usually this is easy to do. But some angiosperms produce Mowers that may not look like Mowers to you. The tassels and voung ears of corn are Mowers. So are pussy willows and poplar catkins. Their Mowers lack sepals and petals, but they have sta¬ mens and pistils. (Refer to page 88, if you have forgotten what sepals, petals, stamens, and pistils are. ) The pistils produce the fruits and seeds. Yes. in biologv a grain of corn or wheat is a fruit with an embryo inside of it. The embryo of wheat is made into wheat germ, which you may use on your breakfast cereal every morning, if you wish to enrich the cereal. Two classes of angiosperms Botanists recognize two classes of angiosperms. You are familiar with the two halves of a peanut, a walnut, or a lima bean. These two halves are the seed leaves. When the seed starts to grow, the two seed leaves come above ground and turn green. There is a whole host of angiosperms whose seeds have two seed leaves similar to those of the bean or nut. The seeds of nearly all crop plants except the grains have two seed leaves (Figure 5-14). Such plants are called dicots ( dy kots ) . Their correct class name is Dicotyle- donae ( dy kot ih lee dun ee ) . There are other seeds, such as those of corn, that have only one seed leaf instead of two. Plants that produce seeds having only one seed leaf (Fig¬ ure 5-14) are called monocots (mon oh kots ) . Their correct class name is Monocotyledonae ( mon oh kot ih lee dun ee ) . All the grains are of this type. Lilies, grasses, irises, and orchids also are monocots. 5-16 CYCAD This “sago palm” ( Cijcas revoluta) is no palm, but a gymnosperm. It bears naked seeds in cones. The stubby, primitive stem has no branches and curi¬ ously little woody tissue. Myron R. Kirsch Monocots differ from dicots in still other ways. Compare the leaf of a corn plant with that of a bean. Notice par¬ ticularly the arrangement of the fine lines (veins) in each. The veins of the corn leaf are more or less parallel; those of the bean form a network in the leaf. Most monocots have parallel-veined leaves and most dicots have netted- veined leaves (Figure 5-14). EXAMINING LEAVES OF ANGIOSPERMS. Examine the leaves of any ten angiosperms you can find. (Refer to the illustrated sum¬ mary on pages 148-150 for help in iden¬ tifying your specimens.) Look at the ar¬ rangement of the leaf veins. List the names of the plants under one of two headings: Monocots or Dicots. Later you will study monocots and dicots in some detail. Right now, try to learn to tell them apart by their leaves. Importance of seed plants For many reasons, the seed plants are far and away the most important plant phylum to you. All of the lumber that man uses comes from trees. Soft woods like pine and spruce come from gymnosperms. Hard woods like oak and maple come from angiosperms. Most of the foods you eat come either directly from angiosperms or indirect¬ ly from animals that eat angiosperms. About 60 per cent of all man’s food comes directly or indirectly from grains, and grains are angiosperms of the monocot class. Coconuts and dates and useful fibers come from palms, and palms are mono- cots. People get cotton fibers from the dicot plant, cotton. They get linen from flax, another dicot. The three basic needs of man are food, shelter, and clothing. For all three, he depends largely upon the spermatophytes. Summing up: the seed plants The seed plants are the spermato¬ phytes. All of them have vascular sys¬ tems in their roots, stems, leaves, and reproductive structures. The first seed plants were probably the seed ferns. Their leaves were like fronds, but the seed ferns bore seeds, not spores. They are long since extinct. The seed ferns, cycads, maidenhair trees, and the conifers (KON ih ferz— cone-bearers, such as pines) make up the subphylum of gymnosperms. All of them bear naked seeds. The angiosperms are flowering plants. They bear their seeds inside of fruits. They divide naturally into two classes: monocots (such as lilies, corn, wheat) and dicots (such as beans, pea¬ nuts, buttercups, violets, sunflowers). Human life as you know it could not go on without the spermatophytes, on which you depend heavily for food, clothing, and shelter. On the next four pages you will find an illustrated summary of Phylum Spermatophyta. Use it (and the refer¬ ences listed under Further Reading at the end of the chapter) to help you identify seed plants you find. You have already studied illustrated summaries J for the other three plant phyla (Phylum Thallophyta, pages 120 and 121, Phy¬ lum Bryophyta, page 127; and Phylum Pteridophyta, page 141). Review these summaries now and establish to your satisfaction the similarities and differ¬ ences between plants of different phyla. Notice especially the increasing levels of organization from thallophvtes to spermatoph v t e s . 146 VARIETY AMONG LIVING THINGS— PI. ANTS I PHYLUM SPERMATOPHYTA Spermatophytes (sper muh toh fytes) are vascular, seed-bearing plants, numbering over 200,000 species, that inhabit both land and water. By far the majority are land-in¬ habiting; those found in water usualh grow in inland lakes and streams or in marshes along the seashore, but never in the open seas. Spermatophytes are dis¬ tinguished from other vascular plants (pteridophytes ) by the fact that they bear seeds. Also, their vascular tissue is usualh more highly developed than similar tissue in other vascular plants. Thus, since much of this tissue is woody and serves as good supporting tissue, some seed plants are en¬ abled to grow taller than any other plants. The spermatophytes, like bryophytes and pteridophytes, undergo alternation of gen¬ erations; however, the gametophvte gen¬ eration is microscopic in size and short¬ lived (it exists in cones or flowers with few exceptions, and it produces male and female gametes ) . Adult plants and embryo plants in seeds are the alternate sporophyte generations. SUBPHYLUM I. GYMNOSPERMS Gymnosperms (jim noh spermz) are plants that bear naked seeds, usually in cones. Ex¬ amples: Ginkgo (maidenhair tree. Figure 5-17), cycad (Figure 5-15), Pinus (pine. Figure 5-18), fir, spruce, sequoia, juniper. (continued on next page) Photos top to bottom: U.S. Forest Service; Hugh Spencer FERNS AND SEED PLANTS 147 5-18 5-17 ¥ SUBPHYLUM II. ANGIOSPERMS Angiosperms ( an jee oh spermz) are flowering plants that bear seeds enclosed in fruits. Class 1. Monocotyledonae (mon oh kot ih lee dun ee). Plants whose seeds have one seed leaf. Some common families * are: Grass Family. Examples: corn (Fig¬ ure 5-19), wheat, oats, barley, sugar cane, bamboo, rice, blue grass. Lily Family. Examples: lily (sand lily, Figure 5-20), onion, tulip, hyacinth, asparagus, yucca. Amaryllis Family. Examples: daffodil, jonquil, narcissus, sisal. Palm Family. Example: palm (Queen palm. Figure 5-21). Orchid Family. Examples: lady’s slip¬ per (Figure 5-22), orchid. 0 The Porifera (poh rif er uh) are sponges, numbering about 5,000 species. They are water-inhabiting animals that are attached by the base of their bodies to one spot. Most of them live in salt water, although a few species are found in fresh water. Their bodies are porous; the pores open into canals lined by flagellated cells, and the canals in turn open into a central cavity. The flagellated cells in sponges represent a primitive, partial bodv tissue and form an incomplete second layer of body cells. Sponges reproduce by budding or by the production of eggs and sperms. Class 1. Calcispongiae (kal sih SPUNj ih ee). Sponges that have limelike “skeletons.” Ex¬ amples: Scypha (Figures 6-7 and 6-2), Grantia. Class 2. Hyalospongiae (hy uh loh SPUNJ ih ee). Sponges that have glasslike “skele¬ tons.” Example: Venuss-flower-basket (skeleton only, Figure 6-8). Class 3. Demospongiae ( de moh SPUNJ ih ee). Sponges that have horny (or a com¬ bination of horny and glasslike) “skele¬ tons.” Examples: bath sponge (Figure 6-9 ) , boring sponge. Photos top to bottom : General Biological Supply House, Inc., Chicago; American Museum of Natural History; Douglas P. Wilson 164 VARIETY AMONG LIVING THINGS— ANIMALS PHYLA THREE AND FOUR: ANIMALS WITH TWO AND THREE CELL LAYERS The first animals with true tissues be¬ longed to the same phylum as our mod¬ ern jellyfish and corals. The bodies of these animals might be said to consist of a “stomach” surrounded by two com¬ plete layers of cells. Within these two cell layers, certain cells make up one tissue and other cells another tissue, as you are about to discover. These animals make up Phylum Three of the animal kingdom. This phylum is called Coe- lenterata ( see len ter ay tuh ) or the coelenterates ( see len ter ayts ) . The first animals with true organs and organ systems are the flatworms. They belong to Phylum Four, which is called Platyhelminthes ( plat ee hel min theez), from pJatij meaning “flat” and helminthos meaning “worm.” The body of a flatworm might be said to consist of a food tube surrounded by three layers of cells. Phylum Three: the coelenterates First let’s examine a fresh- water rel¬ ative of the jellyfish, the one called hy¬ dra ( hy druh ) . Its body consists of two layers of cells. It is a coelenterate. COLLECTING AND EXAMINING HYDRAS. Hydras grow attached to the leaves and stems of pondweeds in fresh-water lakes and ponds, and even on elodea and other plants in an outdoor goldfish pool or water lily pond. You will need glass jars and perhaps a dip net. Put pond water in the jars. Then add a sprig of pondweed, elodea, or an¬ other water plant from the pond. Bring your cultures to the classroom and let them stand quietly for a half-hour or so. (Or you can examine living hydras purchased from a biology supply house.) With the naked eye, look for hydras on the leaves or stem of the plant. You will have to look closely to see hydras. When at rest, they are only about as big around as a coarse thread and about Vs inch long. They look like a short piece of white thread with the ends frayed out. When you find a hydra, try to remove it to a Petri dish, so that you can examine it with a hand lens or under the low power objective of the microscope. If your teacher has a culture of water fleas, add a few to the Petri dish. Try to see how a hydra eats a water flea. In your record book, sketch the hydra as it now looks to you. Hydra and its two cell layers The body of the hydra is shaped somewhat like one finger of a glove, with a fringe around the open end. Of course, it is the merest fraction of the size of a glove finger, since to the naked eye it looks like a short piece of thread with the ends frayed out. The frayed appearance is due to the half- dozen arms that project from the region around the animal’s mouth (Figure 6-10a and b). Each arm is a tentacle (ten tuh k’l ) . The hydra can stretch out its tenta¬ cles and its hollow body to great lengths, as you know if you examined living specimens with a hand lens. When a water flea or worm or some other small water animal brushes a tentacle, certain stinging cells in the tentacle sting and numb the prey. Then the ten¬ tacles push the water flea in toward the hydra’s mouth. The animal takes the bit of food into its body through the mouth; that is, it swallows the food. The long, slender body of the hydra is hollow, but it is not empty. The space inside the body has food parti- THE LOWLIER ANIMALS 165 BLUEPRINT OF A COELENTERATE— HYDRA Mouth Food cavity Ectoderm Endoderm Ectoderm Endoderm Stinging ceii Sensory ceil Flagella Pseudopods Contractile fibers Food vacuole Gland cell Nerve cell Photo by Roman Vishniac 6-10 The base of a hydra’s body produces a sticky substance and “glues” itself to water plants or rocks. At times the animal breaks loose and “turns handsprings” to a new loca¬ tion. Hydras are much more complex than sponges (Figure 6-2). They have two com¬ plete cell layers and true nerve, gland, and epithelial tissues. Their tentacles are true organs. (Photograph of living hydra, 7X; drawings, 50 X and 300 X.) cles, water, and digestive juices in it. That space is the food cavity. It does for the hydra about what your food tube does for you. A hydra takes in food through its mouth, an opening that lies at one end of the body, be- tween the bases of the tentacles (Fisc- ure 6-10b). In the food cavity, the food is partially or wholly digested. Then the digested food passes through the cell membranes of the cells that line the body cavity and on into all the liv¬ ing cells. Any indigestible food parti¬ cles are ejected through the mouth. The hydra’s hollow body is covered with two layers of cells. Even the ten- tacles are hollow and covered with two layers of cells. The outside layer of cells is the ectoderm (ek toll derm), meaning “outside skin” (Figure 6-10b). 166 VARIETY AMONG LIVING THINGS— ANIMALS The inside layer of cells is the endo- derm (ENdohderm), or “inside skin.” But the cells in the ectoderm are not all alike. Neither are the cells in the endo- derm. Some cells make up one tissue, other cells make up another. Look at Figure 6-10c. It shows the various kinds of cells. In both ectoderm and endoderm, most of the cells are epithelial tissue with contractile fibers projecting into the jellylike layer be¬ tween the two cell layers. Hydras do not have a specialized muscle tissue but use the contractile fibers of their epithelial tissue in movement. In the endoderm, the epithelial cells not only have contractile fibers, but also take care of the digestion of food. Some of them are gland cells that se¬ crete digestive juices into the food cav¬ ity. Some have flagella that keep the contents of the food cavity moving. These flagellated cells make you think of those that line the canals in sponges. Some endoderm cells take in bits of partly digested food and digest these bits in food vacuoles. These cells (Fig¬ ure 6-10c) make you think of an ameba. The epithelial cells in the ectoderm (outer skin ) also have contractile fibers, and they protect the body in somewhat the way your skin protects your body. So you might call all these ectoderm cells protective-muscular tissue and the cells in the endoderm (inside skin) di¬ gestive-muscular tissue (Figure 6-10c). Scattered through both layers of cells in the hydra are long, slender nerve cells that are the animal’s “sense cells,” or better, sensory cells. The sensory cells are sensitive to touch, food mate¬ rials, etc., much as your sense organs are. When stimulated, the sensory cells transfer “messages” to the network of nerve cells that runs through the whole body. The sensory cells and the nerve network make up the nerve tissue of the hydra. As you can see in Figure 6-10c, there is no close-knit cluster of nerve cells at any one point. So there is nothing that you could call a “brain” or a “central nervous system.” The nerve “messages” spread out from any one point in all directions. That’s why the whole hydra reacts when a water flea touches the end of one tentacle. In the ectoderm are the stinging cells. They are especially numerous in the tentacles. Each stinging cell con¬ tains a sharp-pointed, coiled hair and a little poison fluid. When the tentacles grab a water flea, the hairs uncoil and sting; they inject poison into the water flea, thus numbing it. The stinging cells of the hydra cannot prick human skin, but those of certain jellyfish can, as bathers at ocean beaches sometimes find out to their discomfort. Finally, in both layers of cells there are groups of small cells which can grow into any of the other kinds of cells in the hydra. For example, some of them turn into stinging cells and re¬ place those used in numbing prey. Hydras may reproduce by budding or by means of eggs and sperms. Study Figure 6-11 to get a general idea of how they reproduce by these methods. You can see now why hydras and other coelenterates are a step above the sponges in complexity, or level of organization. Sponges show the begin¬ nings of tissue organization in having a rather loosely organized covering tis¬ sue lining their canals. But the coelen¬ terates have not only epithelial tissue but also nerve and gland tissues. The coelenterates illustrate the tissue level of organization. The hydra and its relatives make up Class One, Hydrozoa ( hy droll zoh uh), in Phylum Coelenterata. THE LOWLIER ANIMALS 167 TWO METHODS OF REPRODUCTION IN HYDRA 6-1 1 Hydras reproduce in two ways, sometimes in both at once. A. Here a hydra is bud¬ ding, producing a young hydra that will soon break away. B. These hydras are reproduc¬ ing sexually. Sperms fertilize eggs, and the fertilized eggs begin to develop. Soon a heavy membrane or “shell” will form around each egg, and the eggs will (probably) drop away from the parent. In time, young hydras will emerge from the eggs. Jellyfish In the water, a jellyfish looks some¬ what like an inverted cup with a fringe of tentacles hanging from the rim (Fig¬ ure 6-12). The outer layer of the cup¬ shaped body is the ectoderm, the inner layer is the endoderm. The tentacles 6-12 JELLYFISH This species of jellyfish is common along the Pacific Coast. At the bottom of the whitish stalk within each animal is the mouth. Around the mouth stalk are stringlike reproductive organs, either male or female. Trailing beneath the body are the tentacles. Photo by Ralph Buchsbaum, Animals Without Back¬ bones, University of Chicago Press, 1938. also have the two complete cell layers. There are many different kinds of jellyfish. Some of them are as large as washtubs. Even these have the same two layers of cells. Most of the mass of the body is water. Many jellyfish give off a sort of golden light, much like that of the firefly. They swim slow¬ ly, close to the surface of the sea, by means of a kind of body pulsation. Many of the animals of the jellyfish class reproduce in two ways by alterna¬ tion of generations. If you are especial¬ ly interested, use the information in the classification summary on page 174 and reference books listed at the end of this chapter to help you find out more about this class, called the Scyphozoa (sy foil zoh uh ) . Corals and other forms You may have seen a string of beads J O made of bits of coral. You have un¬ doubtedly studied in geography about the coral reefs of the South Seas. You are probably wondering how animals that can form coral reefs or produce the materials used in making coral beads can be classed in the same phy¬ lum with hydras and jellyfish. What you call coral is only a hard limy secretion of the coral colony. The living corals take calcium carbonate (a compound also used commercially to make lime) out of sea water and use it in making the hard secretion. The liv¬ ing tissue is supported by the hard se¬ cretion. In each “cup” in the coral skele¬ ton, there once lived a little animal, with tentacles and stinging cells and a hollow body very similar to those of the hydra and the jellyfish. There are still other animals in this phylum. Sea anemones, sea fans, sea pens, and the Portuguese man-of-war belong here. ( Refer to the classification summary on page 174. ) Increasing levels of organization Altogether, the animals of the third phylum are an interesting, colorful lot. The bodies of the coelenterates are real cell communities in which some cells are specialized in one function, others in another. Coelenterates have sensory cells and nerve tissue. They have musclelike fibers and gland cells. They have flagellated cells in the lin¬ ing of the food cavity and stinging cells all over the surface, particularly on the tentacles. Hydras, jellyfish, and their relatives are the first animals with true tissues (Table 6-A). They are also the first animals with true organs— their tentacles. Phylum Four: the flatworms Have you ever seen a flat worm? Phylum Platyhelminthes has nothing but flatworms in it. Probably you haven’t seen one, unless you have seen a tapeworm, perhaps from a dog. And TABLE 6-A TISSUES IN HYDRA Ectoderm tissues Endoderm tissues Protective-muscular Digestive-muscular without flagella with flagella Nerve Nerve Stinging cells Gland yet the flatworms we call planarians (pluh nair ee uns ) are common in small streams, pools, and ponds. One reason most people never see planari¬ ans is that they are so small. A planar- ian is only about /2 inch long. It is flat and shaped a little like a small, long leaf (Figure 6- 13a and b). You may have planarians in the hy¬ dra cultures you have already col¬ lected. To find out, pour one hydra cul¬ ture into a white dish or pan. Lay a piece of raw liver in the water where you can see it well. After a while, you may see one or more small, dark-colored worms on the surface of the liver. These are planarians. They are feeding on the liver. If you can’t find planarians in your hydra cultures, some of you may be able to collect them as directed below. Or you may use specimens from a bi¬ ological supply house. COLLECTING PLANARIANS. One way to find planarians is to throw a piece of raw liver into a spring or small stream or pool. Any planarians nearby will move to the liver and feed on it. In a few hours, you may find hundreds of planarians feeding on the liver. Dip up the liver and put it into a jar of pond water. Add some stones and water plants from the pool. When the planarians finish feeding on the liver, they will move away and "hide" under the stones or among the leaves or roots of water plants. Then remove the liver, so it won't foul up the water. THE LOWLIER ANIMALS 169 EXAMINING PLANARIANS. Transfer a planarian to water in a Petri dish. Examine it under a hand lens or the low power ob¬ jective of a microscope. If it has not fed recently, add a bit of liver. From your observations, answer as many of these questions as you can. 1. How does a planarian move about? Does it swim freely, or glide, or crawl, or move by means of feet or fins? 2. Does one end go first? In other words, does this flatworm have a head? 3. Is it usually the same side up? In other words, does it have an upper and a lower side? 4. Where is the mouth located? 5. Does it have eyes? 6. What does it do that shows that the planarian "senses" the liver from some dis¬ tance away? 7. Cover half of the Petri dish with dark paper to put that part of the water in the shade. Does a well-fed planarian seem to prefer a dark place? 8. Cut a planarian in two pieces. Exam¬ ine each day. What happens? The body plan of a planarian Planarians (Figure 6-13) show a body plan that is on a higher level of organization than that of any animals in the first three phyla. Protozoa (Phylum One) have orga¬ nelles in their single-celled bodies, but no tissues. Porifera (Phylum Two) have loosely organized epithelial cells, but no true tissues. Coelenterates (hy¬ dras, jellyfish, etc., of Phylum Three) have true tissues, and their tentacles are true organs. Planarians have true tissues that are also organized into nu¬ merous true organs (eyes, for exam¬ ple), and they have true organ sys¬ tems (digestive, nervous, muscular, and excretory systems, for example). Planarians also show another feature not present in animals of the first three phyla. As the embryo grows inside the egg, it develops three layers of cells: endoderm, ectoderm, and a layer be¬ tween called the mesoderm ( mess uh derm ), or “middle skin” ( Figure 6-13c ) . The mesoderm, or middle layer of cells, gives rise to the muscles and to parts of other organ systems. The ectoderm gives rise to the epithelial or covering tissue and the nervous system. The en¬ doderm mves rise to the inner lining of the food tube and to other inner tissues. From these three cell layers of the em¬ bryo come all the tissues, organs, and organ systems of the adult. Still another feature of the body plan of planarians is worth attention here. These worms have a right and left side, an upper and lower side, and an end that goes first. Biologists use accurate terms for this body plan. You may want to learn these terms now, because you will be using them often in the rest of your biology course. Here they are: 1. Anterior (anTEER ee er) end— the end that goes first, the head (Figure 6- 13a) 2. Posterior ( poss teer ee er ) end— the end that goes last, the tail (Figure 6- 13a) 3. Dorsal ( dor s’l ) side— the upper side (Figure 6-13a and c) 4. Ventral (vENtr’l) side— the lower side (Figure 6-13c) 5. Bilateral symmetry ( by lat er ul sim uh tree ) —the two sides ( right and left) are “mirror images” of each other, just as yours are. To sum up, the planarians are built on a higher level of organization than any of the animals in the first three phyla. They have reached the organ- system level, as you will see by study¬ ing Figure 6-13b, c, and d, and Table 170 VARIETY AMONG LIVING THINGS— ANIMALS BLUEPRINT OF A FLATWORM —FRESHWATER PLANARIAN Excretory canal omitted from near side of body) Excretory pores Anterior intestine Mouth Lateral intestines Pharynx Mesoderm Ectoderm Longitudina muscles ircuiar luscle jgngsssa 333$^ Diagonal muscle fibers Ventral surface Anterior intestinal cavity i Anterior end Dorsal surface Posterior end iscsstiasBOwMi Photo by A. M. Winchester, Stetson University, Deland, Florida 6-13 In planarians— unlike protozoa, sponges, or hydras and jellyfish— certain animal features familiar to everyone are found. Planarians have a head with eyes; they also have nervous, digestive, and "muscular systems, among others (see text). (Photograph of liv¬ ing planarian, 8 X ; drawings of planarian stained to show body structure, with cross sec¬ tion of body and diagram of body wall.) TABLE 6-6 LEVELS OF ORGANIZATION IN THE FIRST FOUR ANIMAL PHYLA Phylum Level of organization l. Protozoa Mostly one-celled, with organelles 2. Porifera (sponges) Many-celled, with begin¬ nings of a tissue in flagellated cells that line the canals 3. Coelenterata Many-celled, with true tissues in the two cell layers; tentacles are true organs 1. Platyhelminthes (flatworms) Many-celled, with true tissues, organs, and organ systems, all com¬ ing from the three cell layers of the embryo 6-B. In the embryo stage, they develop three layers of cells. These three cell layers give rise to all the tissues, or¬ gans and organ systems of the adidts. You will find that the animals in all the rest of the animal phyla also start out with three cell layers, and all of them have organ systems. All of the animals from planarians to man are built on the organ-system level of or¬ ganization. Life processes in planarians Planarians feed in an odd way. A pla- narian projects its pharynx (FAmingks) out through its mouth (Figure 6-13b) and into the liver or other food, such as a small water animal or the dead bodv J of an animal. By means of sucking mus¬ cular movements, the pharynx “tears” the food to bits and swallows it. When swallowed, the food goes into the much-branched food tube. From the food tube, endoderm cells take in the chewed bits of food, ameba fash¬ ion, and digest them in digestive vacu¬ oles. From these endoderm cells, mole¬ cules of digested food pass through cell membranes from cell to cell and reach all the living cells. A planarian gets along very well without a specialized circulatory system, partly because it is so small and partly because its much- branched food tube reaches into all parts of its body. Planarians do have a complex excre¬ tory system that excretes excess water and wastes. Plowever, most of the cell wastes and all indigestible bits of ma¬ terial from the food are ejected through the pharynx and mouth. These animals, like the hydras, have no anus. Planarians have eyes on the head (Figure 6-13a and b). These are made of sensory cells, sensitive to light. The two “knobs” on the head are sensory lobes, especially sensitive to water cur¬ rents and touch and probably to near- bv food and other chemicals. Sensorv y y cells are scattered through the ecto¬ derm all over the body. These sensory cells carry “messages” from outside into the nervous system. M any of the ectoderm cells have cilia. Other ectoderm cells secrete a slimy material that covers the body of the animal. The cilia beat against the slime and push the animal forward in a gliding motion. So the ciliated ecto¬ derm cells are used in moving about; that is, in locomotion. The planarians have three layers of muscles, one layer running lengthwise, one diagonally, and the third around the body (Figure 6-13d). With these muscles, the planarians move rather quickly by waves of muscular contrac¬ tion. Did you see both types of locomo¬ tion in the planarians you observed? The living cells of a planarian get their oxygen from air that is dissolved in the water. These worms do not have a respiratory system. Can you explain how they get along without one? 172 VARIETY AMONG LIVING THINGS— ANIMALS The reproductive system of planari- ans is complex and is not shown in Figure 6-13b. Some planarians repro¬ duce by simply pinching in two. But they usually reproduce by means of eggs and sperms. Other flatworms Several thousand species of animals belong to Phylum Four, Platyhelmin- thes. A good many of these live inside the bodies of other animals, but others, like the planarians, are free-living (do not live inside other organisms). A number of free-living species are found in the seas. The classification summary on page 175 will give you further in¬ formation. Tapeworms belong to the flatworm phylum. So do liver flukes and lung flukes. These members of Phylum Platyhelminthes are not free-living. They live inside other animals and get their food from them. (A tapeworm does not even have a digestive system. ) These animals are parasites, and the animals they live upon are the hosts. Flukes and tapeworms (Figures 6-18 and 6-19) are parasites. They are com¬ mon in many animals (hosts). Dogs and other animals often “get tapeworms.” People sometimes do. If an animal, such as a pig or a cow in the case of the commonest tape¬ worms that are sometimes found in hu¬ mans, happens to eat the tapeworm eggs, the young hatch and bore into the animal’s muscles and enclose them¬ selves within hard coats called cysts (sists). If a person eats pork or beef that has not been cooked long enough to kill any tapeworm cysts it contains, he runs the risk of getting a tapeworm. It is usually possible to kill such a worm with the correct medicine given under a doctor’s directions. However, it often happens that the medicine fails to kill the head of the worm. In such cases, the head grows new sections and soon the worm is as long as ever. Summing up: animals with two and three cell layers The animals of Phyla Three and Four show an increasing degree of or¬ ganization over the animals of Phyla One and Two (protozoa and sponges), as Table 6-B shows. The hydras, jelly- fish, corals, and their relatives of Phy¬ lum Coelenterata are the first animals to show two complete cell layers. They are also the first animals having what we might call true organs— tentacles. The flatworms of Phylum Platyhel¬ minthes are the first animals having nu¬ merous different organs that are organ¬ ized into true organ systems. They also are the first animals with three cell layers. All the rest of the animals you will study, in Phyla Five through Twelve, also form three cell layers in a stage of growth of their embryos. Perhaps flatworms are not very pleas¬ ant, but knowing about them is very important. To be sure you never get a tapeworm or certain other worm para¬ sites, make certain that all the meat you eat, especially pork, is thoroughly cooked, so that no pink color is left in the meat. On the next two pages, you will find illustrated summaries of Phylum Coe¬ lenterata and Phylum Platyhelminthes. Study the summaries until you are sat¬ isfied that you understand the similari¬ ties and differences among the animals of these two phyla. Also use these pages, along with the reference books listed under Further Reading at the end of this chapter, to help you iden¬ tify any animals of these two phyla that you may come across. THE LOWLIER ANIMALS 173 6-16 6-15 6-14 PHYLUM COELENTERATA nom ■ , _ The coelenterates (see len ter ayts) are water-inhabiting animals whose bodies consist of two complete layers of cells (ectoderm and endoderm) surrounding a saclike food cavity that has an external opening. Most species inhabit salt water; a few, fresh water. Coelenterates have true body tissues, and their tentacles (which very few of the 10,000 or so species are without) are true organs; in these respects they are advanced in body organization over the lower two animal phyla. Some coelenterates exist individually, others in colonies. They reproduce mainly by bud¬ ding or by means of eggs and sperms. Cer¬ tain species show alternation of generations (one generation is a colony attached to one spot; the other, free-swimming individ¬ uals) . Class 1. Hydrozoa ( hy droh zoh uh ) . Coe¬ lenterates whose reproductive organs are in the ectoderm.* Includes both fresh-wa¬ ter and salt-water forms, some hydralike and some jellyfishlike. Examples: Physalia (Portuguese man-of-war, Figure 6-14), Hydra (Figures 6-10 and 6-11), Obelia. Class 2. Scyphozoa (sy foh zoh uh ) . Salt¬ water, jellyfishlike coelenterates whose re¬ productive organs are in the endoderm.* Includes most of the common jellyfish. Examples: Chrysaora (Figure 6-15), Poly¬ orchis (Figure 6-12). Class 3. Anthozoa (an thoh zoh uh) . Salt¬ water, hydralike coelenterates in which there is no alternation of generations and whose reproductive organs are in the endo¬ derm.* Examples: coral (living coral, Fig¬ ure 6-16), sea anemones (photograph, page 158), sea pens. * The reproductive organs are but one of the characteristics bv which these animals are J divided into classes. Details of the structure of the endoderm, of the nature of the food cavity, and of the nature of the space between the ectoderm and endoderm are others. Photos top to bottom: Douglas P. Wilson; Douglas P. Wilson ; American Museum of Natural History 174 VARIETY AMONG LIVING THINGS— ANIMALS PHYLUM PLATYHELMINTHES Photos top to bottom : Carolina Biological Supply Co. ; Armed Forces Institute of Pathology; U.S.D.A. Class 3. Cestoda (sess toh duh ) . Parasitic flatworms having no digestive system- tapeworms. Example: Taenia (human-host tapeworm, Figure 6-19). Platyhelminthes (plat ee hel min theez) is a phylum of flatworms, numbering more than 6,000 species. The flatworms have numerous true organs organized into organ systems (in planarians, these are the diges¬ tive, nervous, muscular, excretory, and re¬ productive systems ) ; thus, they represent an advance in body structure and organiza¬ tion over the animals of the lower three phyla (protozoa, sponges, and coelenter- ates). Many of the flatworms have heads with eyes; there is a definite front and rear to these animals, but no true body seg¬ ments. They reproduce mainly by produc¬ ing eggs and sperms, but some species also reproduce by pinching in two or by grow¬ ing into two or more individuals after hav¬ ing been torn into pieces. Class 1. Turbellaria (ter beh lay ree uh) . Free-living flatworms found in water or O soil. Example: Dugesia (planarian, Figures 6-17 and 6-13). Class 2. Trematoda (tree muh toh duh) . Parasitic flatworms known as flukes. Ex¬ amples: Clonorchis (Chinese liver fluke, Figure 6-18), Schistosoma (blood fluke). THE LOWLIER ANIMALS 175 6-19 6-18 6-17 PHYLA FIVE, SIX, AND SEVEN: ROUNDWORMS, ROTIFERS, AND “MOSS ANIMALS" As you carry on your study of the animal phyla to learn about the animals we are now going to consider, you will discover an ever-increasing amount of specialization in body plans, organs, and organ systems. And yet we are still a long way from fish, birds, dogs, and the other animals that we think of as the “higher” animals! Phylum Five: roundworms Worms of Phylum Five are so plenti¬ ful that a spadeful of garden soil may contain millions of them. And yet the chances are that you probably never saw a roundworm. Most roundworms are no bigger around than fine sewing thread. Some are so small they can crawl through a breathing pore in a green leaf. A few kinds are of some size, even several inches to a foot or more in length. But the name “threadworms” is a descrip¬ tive one. The name of Phylum Five is Nemathelminthes ( nem uh thel min theez), from nematos meaning “thread” and helminthos meaning “worm.” EXAMINING VINEGAR EELS. Pour the dregs from a jug of vinegar into a dish. With a hand lens, look for threadlike, squirming worms. These are the round- worms commonly called vinegar eels. What shape have they? How do they move? What else can you discover about them? 6-20 Ascaris is in several ways more complex than animals of the four lower phyla (protozoa, sponges, coelenterates, and flatworms). It not only has several organ systems (nervous, digestive, muscular, reproductive, and excretory), but two features not found even in flatworms: an anus, or second opening in the food tube, and a primitive body cavity between the food tube and body wall. (Photograph of female Ascaris, one-third to one-half actual size, in body tissue of host; drawing of female Ascaris in the position shown in photograph.) Photo by Roman Vishniac Primitive body cavity (not a true coelom) Anus Dorsal nerve Pharynx Nerve ring Mouth Ventral nerve cord Lateral nerves i Many roundworms are parasites. People may be hosts to one or more of fifty different species. Some are harm¬ less. Others cause mild illnesses, and still others cause serious diseases in man, other animals, and in plants. Ascaris The so-called stomach worms (actu¬ ally intestinal) that people sometimes get belong to the genus Ascaris (ass kuhriss). This genus of roundworms is often studied as being typical of the Nemathelminthes. Refer often to Figure 6-20 as you read on. Ascaris has a digestive tube with two openings— a mouth where food enters and an anus where waste leaves the tube. The animals of Phylum Five are the first to have an anus. As¬ caris also has a cavity between the food tube and the body wall ( Figure 6-20b ) . In higher animals, this cavity is called the body cavity, or coelom (see lum), but in Ascaris and other roundworms, this cavity has no lining of its own. So it is not considered a true body cavity or coelom. In any case, Ascaris has the beginnings of a body cavity. This fea¬ ture and the anus show that the animals in Phylum Five are ahead of those of all previous phyla in complexity— in level of organization. Figure 6-20b also shows the main nervous system of Ascaris: a nerve ring and a well-developed ventral nerve cord and a less well-developed dorsal nerve cord. The food tube consists of the mouth, pharynx, intestine, and anus. Ascaris does not have a respiratory or a circulatory system. Ascaris is not a pleasant animal, but from it you learn a little more about increasing complexity. Ascaris infection of the human food tube is not usually serious and is easily Carl Striiwe, from Monkmeyer 6-21 TRICHINA CYST These cysts become embedded in muscle tissue, where they may cause painful inflammation. The usual treatment for trichinosis in man is obser¬ vation alone. Except in severe cases, the young trichinas will eventually die. (100 x) cured. Certain other threadworm infec¬ tions are more serious, especially tri¬ china ( trill ky null) and hookworm in¬ fections. Trichinas Trichinas are parasitic roundworms. A trichina lives one part of its life in one animal host and another part in another animal host. It alternates be¬ tween the two hosts. Adult trichinas may live by the millions in the intes¬ tine of some animal such as a pig. Oc¬ casionally, female trichinas bore into the wall of the pig s intestine and there produce young. The young spread through the body and lodge in muscles and form cysts (Figure 6-21), which lie there, inactive, until the host dies. If the muscle of a pig containing tri¬ china cysts (usually called “measly” THE LOWLIER ANIMALS 177 pork) is thoroughly cooked, the young trichinas will be killed, but if a person eats measly pork which is not thor¬ oughly cooked, the young trichinas will emerge from the cysts when they reach the human intestine. There they grow into adults. After mating, the males die, but the females bore into the walls of the intestine, where they lay eggs. The young that hatch from the eggs are carried all over the body through the circulation. Eventually they reach the person s muscles, where they pro¬ duce inflammation. A single ounce of measly pork may contain from 50,000 to 100,000 trichina cysts and yet look all right to the naked eye. Anyone who eats pork that is not thoroughly cooked is running the risk of eating thousands of trichina cysts in every mouthful. It has been estimated that as many as 100 million trichina cysts may occupy the muscles of a person suffering from this disease, called trichinosis ( trik uh noh sis). Trichinosis may be serious, though rarely fatal. Hookworms These small worms (Figure 6-22) may live in the human intestine. They bite into its lining and suck the blood of the human host. When they let go, the wounds in the human intestine do not heal at once. Thus, a slow but con¬ tinued loss of blood makes persons in¬ fected with hookworms pale and list¬ less. The hookworm is a roundworm that spends its early youth as a free-living organism in moist soil. Men, women, and children who go barefooted to work in the fields in the warm southern states are likely to develop “ground itch” or “dew sores” on their feet. A “dew sore” marks the spot where a young hookworm is entering the body. The worm gets into the blood vessels, is carried to the lungs, climbs the wind¬ pipe with the help of the hairlike cilia on the lining of the windpipe, and is then swallowed. Once in the intestine, the hookworm lives at the expense of its host. Hookworms can be killed and eliminated from the human intestine with the proper medicines given under a physician’s direction. Roundworms— a successful group The roundworms are a highly suc¬ cessful phylum. They live virtually everywhere, both inside and outside of other organisms. As one biologist put it, if all the rest of the materials and organisms on earth except the threcid- worms were swept away, the shape and form of the outer shell of our earth would still be traceable in the pattern made by these worms; the hills and mountains and lakes and seas and even the cities and highways, marked by ghostly worm-infested tree forms and other organisms, would remain in out¬ line. Two side lines: Phyla Six and Seven Among the protozoa, you may have found small, many-celled “wheel ani¬ mals,” that looked like the animal in Figure 6-23. They are rotifers (ROHtih ferz); the name of this sixth animal phylum is Rotifera (roh tif er uh). Use the classification summary on page 180 if you want to find out more about the rotifers, or wheel animals. At the seashore, people often mistake certain “moss animals” for seaweeds. They are not seaweeds at all but ani¬ mals that grow in colonies and look a little like underwater mosses (Figure 6-24). The name of this seventh ani¬ mal phylum is Bryozoa ( bry oh zoh uh), from bryum meaning a “moss,” and 178 VARIETY AMONG LIVING THINGS— ANIMALS zoa meaning “animals.” Refer to the classification summary on page 180 and to the references listed under Further Reading at the end of this chapter for further information on the moss ani¬ mals. The rotifers and moss animals are not very important to you. Dr. Ralph Buchsbaum, a prominent American zo¬ ologist, calls them “lesser lights” in the animal kingdom. They are mentioned here only because you may see some of them and want to know what they are. You should know only that the second of these two phyla marks the appear¬ ance of animals with true body cavities. What was a beginning of a body cav- itv in the roundworms is a true coelom J in the moss animals. Summing up: greater and greater complexity You have now met animals of several phyla that show more and more organ¬ ization of tissues, organs, and organ systems. From hydra (Phylum Three) to As- caris (Phylum Five), animals pass from forms with two cell layers and true tis¬ sues (hydra) to highly organized forms with three cell layers in embryos from which tissues, organs, and organ sys¬ tems of adults develop. The animals of Phylum Five are more highly organized than those of any previous phylum, in that their food tubes have two open¬ ings (mouth and anus) and their bodies have primitive body cavities. The roti¬ fers (Phylum Six) also have primitive body cavities. But it is the moss ani¬ mals (Phylum Seven) in which a true coelom first appears. From ameba (Phylum One) to As- caris (Phylum Five), there is an in¬ creasing complexity, from a single cell with organelles to highly organized ani¬ mals with tissues, organs, and systems of organs. The animals in all the rest of the animal phyla also are highly organ¬ ized units, as you will soon see. Go on now to the next page, and re¬ view the animals of Phyla Five, Six, and Seven in the classification summary presented there. Then turn back to pages 163-164 and 174-175, and review the animals of the first four phyla. Your Biology Vocabulary Below is a list of the essential new terms introduced in Chapter 6. Make sure that you understand and can use these terms correctly. vorticella ciliates Porifera coelenterates Platyhelminthes flatworms hydra tentacle ectoderm endoderm mesoderm sensory cells stinging cells planarians anterior posterior dorsal ventral THE LOWLIER ANIMALS 179 PHYLUM NEMATHELMINTHES CN cs I o Nemathelminthes (nern uh thel min theez) is a phylum of about 5,000 species of roundworms, some parasitic, others not. Nearly all have two features not found in lower animals: a second opening (anus) in the digestive tract, and a primitive body cavity. Class Nematoda ( nem uh toh duh ) . Ex¬ amples: hookworm (Figure 6-22), Ascaris (Figure 6-20). PHYLUM ROTIFERA U.S. Public Health Service Hugh Spencer The 2,000 or so species of rotifers (non tih ferz) are microscopic, many-celled ani¬ mals ( in adults, cell boundaries usually dis¬ appear). Rotifer means “wheel-bearer”; the rhythmic motion of the cilia on a roti¬ fer’s head suggests the rotation of a wheel. Females (Figure 6-23) have well-devel¬ oped organ systems and a body cavity; males often do not (in some species, males appear only at mating season, then die). Most rotifers inhabit fresh water. PHYLUM BRYOZOA Douglas P. Wilson There are some 3,000 species of bryozoans (bry oh zoh unz) , often called “moss ani¬ mals” because their eilia-bearing tentacles give them a plantlike appearance (Figure 6-24). They have well-developed organ systems, including a U-shaped digestive tract that in many species has both mouth and anus within the circle formed bv the J tentacles. One of two major groups of bryozoans has a body cavity that is a true coelom, lined with mesoderm-derived covering tissue. Bryozoans are both salt- and fresh-water inhabiting; most live in colonies. Colonies grow by budding; new colonies arise sexually (fertilized eggs pro¬ duce “creeping” or free-swimming young each of which attaches itself, then buds). 180 VARIETY AMONG LIVING THINGS— ANIMALS bilateral symmetry pharynx cysts Nemathelminthes roundworms Ascaris Testing Your Conclusions coelom ventral nerve cord nerve ring dorsal nerve cord trichinas trichinosis host parasite free-living organism rotifers moss animals Of the four possible ways to complete each statement, pick the one that completes it most correctly. 1. Animals having organelles but no tissues belong to Phylum: (a) Coelenterata, (b) Platyhelminthes, (c) Porifera, (d) Protozoa. 2. The first animals having true body tissues belong to Phylum: (a) Coelenterata, (b) Platyhelminthes, (c) Porifera, (d) Protozoa. 3. The first animals with true organ systems belong to Phylum: (a) Nemathelminthes, (b) Platyhelminthes, (c) Porifera, (d) Protozoa. 4. The first animals with a food tube having two openings (mouth and anus) belong to Phylum: (a) Coelenterata, (b) Nemathelminthes, (c) Platyhelminthes, (d) Po¬ rifera. 5. An animal that has both ectoderm and endoderm but no mesoderm is: (a) Ascaris, (b) hydra, (c) hookworm, (d) planarian. 6. Parasites known to alternate between two host animals are: (a) Ascaris, (b) hook¬ worms, (c) tapeworms, (d) vinegar eels. 7. Coelenterates have: (a) eyes, (b) brains, (c) centralized nervous systems, (d) sen¬ sory cells and a nerve network. More Explorations 1. Does cutting planarians in pieces kill them? Transfer several planarians from the cul¬ ture you already have to a shallow pan or dish in which you can see them well. With a sharp knife, cut one planarian in two lengthwise. Cut another in three pieces cross¬ wise. Slit one planarian from the tip of the head back to the mouth region. Slit the posterior end of another planarian. Keep the culture in a dark place. Examine the specimens every day with a hand lens. Title a fresh page in your record book Regrowth of Severed Planarians. On it sketch each worm you cut, and show how it was cut. When you finish your studies, show with sketches what happened to the worm parts after cutting. Tell the class about your results. 2. A class poster. On a large piece of cardboard make a chart of the seven animal phyla studied so far. First, either cut pictures of animals from papers or magazines or draw animals, so that you have at least one illustration of each of the seven phyla. Arrange your pictures on the cardboard in the order in which you studied them. Under each illustration, print neatly the name of the animal and its phylum. Name also its sub¬ phylum and class, if you can. Use the classification summaries in this chapter to help you. Display your poster in class. 3. Identifying specimens. Go on identifying the phyla of any animals you collect or see, or use magazine or newspaper photos as specimens and identify the phyla of the animals. You may carry this activity on all year, if you are especially interested. THE LOWLIER ANIMALS 181 Thought Problems 1. Errors in print. Almost all printed publications contain errors of one kind or another. Can you find the error in classification in each of the following sentences? If so, point each of them out in class. Keep watching for similar errors in your reading. example: A recent newspaper article said, “The fall-out of radioactive materials from bomb tests threatens the whole human race" To be scientifically correct, it should have said the whole human species. Can you find the errors that follow? “Scientists are carrying on experiments on the worm species, Planaria .” “Scientists have discovered that trichinosis is much more common than it was formerly thought to be. Trichinosis is caused by parasitic flatworms.” 2. Animal puzzles. Can you name an animal that has: a. its “arms” attached around its mouth? b. both ciliary and muscular locomotion? c. a food tube with only one opening to the outside of its body? Further Reading Listed below are some reference books which will help you to identify animals that you come across. This list of books covers the seven animal phyla that you have studied in this chapter. Before you attempt to use the references, turn back to page 130 and reread the precautions and directions given there for using reference books to identify plants. The same precautions apply also to your reference reading on animals. Remem¬ ber that all authorities do not use exactly the same classification system. BOOKS FOR GENERAL USE: Animal Kingdom by George G. Goodwin et al., 3 volumes, (Greystone) Hawthorn, 1954. Animals Without Backbones by Ralph Buchsbaum, Univ. of Chicago Press, 1948. General Zoology by David F. Miller and James G. Haub, Holt, 1956. Life by George Gaylord Simpson et al., Harcourt, Brace, 1957. Parade of the Animal Kingdom, Imperial Edition, by Robert W. Hegner, Macmillan, 1953. The Story of Animal Life, Vol. I, by Maurice Burton, Bentley, 1951. books on protozoa: Foraminifera: Their Classification and Economic Use, Fourth Edition, by Joseph A. Cushman, Harvard Univ. Press, 1948. Protozoology, Fourth Edition, by Richard R. Kudo, Charles C. Thomas, 1954. BOOKS ON ANIMALS LIVING IN WATER: Beginners Guide to Fresh-Water Life by Leon A. Hausman, Putnam, 1950. Beginners Guide to Seashore Life by Leon A. Hausman, Putnam, 1949. Field Book of Ponds and Streams by Ann H. Morgan, Putnam, 1930. Field Book of Seashore Life by Roy Waldo Miner, Putnam, 1950. Fresh-Water Invertebrates of the United States by R. W. Pennak, Ronald, 1953. Introduction to Parasitology, Ninth Edition, by A. C. Chandler, Wiley & Sons, 1955. 182 VARIETY AMONG LIVING THINGS— ANIMALS L : H A P T E R , 7 Clams, Earthworms, Starfish, and Their Relatives Three snails— where are they going that they must take their “homes’ with them? And what is it that sets them apart as more highly organized animals than \ bryozoanSy rotifers , and roundworms? Strange company Probably you have never before seen so many different kinds of animals grouped together, as they are here. They are grouped in one chapter be¬ cause all of them have two body fea¬ tures not found in any of the animals you have thus far studied in some de¬ tail. ( Bryozoans— moss animals— do have one of these body features, but you have not studied them in detail.) Clams, earthworms, starfish, and their relatives have ( 1 ) a specialized circulatory system, and ( 2 ) a true body cavity, or coelom, with a lining of epi¬ thelial tissue (mesoderm). These two body features place these animals ahead of those in Phyla One through Seven in complexity, or level of organi¬ zation. The clams and their relatives make up Phylum Eight of the animal king¬ dom; earthworms and their relatives, Phylum Nine; and starfish and their Hugh Spencer relatives, Phylum Ten. Let’s take a look at each phylum.* PHYLUM EIGHT: THE SOFT-BODIED ANIMALS Clams, oysters, snails, and their rela¬ tives are called mollusks ( mol usks ) , from the Latin word mollis, meaning “soft.” These animals do have soft bodies ( think of a raw oyster out of its shell), but so do the animals of many other phyla. Furthermore, nearly all mollusks have shells; but so do certain protozoa. Nevertheless, if you have ever gathered sea shells, vou were collecting the shells of mollusks. No matter * The numbers assigned to the 12 phyla discussed in this text are arbitrary, used here for your convenience. Numbering the phyla in the order in which they are discussed should help you to keep them straight. But you will not find these same numbers used in the more technical reference books, where some 21 or more phyla of animals are listed, not always in the same order. CLAMS, EARTHWORMS, STARFISH, AND THEIR RELATIVES 183 whether or not the name fits these ani¬ mals better than others, this phylum is and will continue to be known as Mol- lusca ( muh lus kuh ), or the soft-bodied animals. EXAMINING SEA SHELLS. You probably have access to a collection of sea shells in your school museum. You may even have a box of sea shells at home. Or you may be able to visit a museum where sea shells are on display. Sea shells sort into four groups. If you have a box of unsorted shells, try to sort * them into the four groups listed in Table 7-A. If you want to find the names of some of your shells, use the classification summary on page 189 and the reference books listed at the end of this chapter to help you. Mollusks are a highly successful and varied lot, and they have been for a long, long time. Biologists have de¬ scribed and named more species of mol¬ lusks than of any other phylum except the one to which insects belong. If the number of species is a mark of success, then the phylum of the insects (Phy¬ lum Eleven) ranks first with over 750.000 known species. The mollusks rank second with some 70,000 known species. In third place comes the phy¬ lum to which the vertebrates belong (Phylum Twelve), with an estimated 60,000 species. Body plans of mollusks Taxonomists have sorted the 70,000 or more species of mollusks into five main classes. In each class, the bodv plan differs in several ways from that of the other classes. So the description of the body plan of a mollusk of the clam class, for example, will not fit the animals of the octopus class. But some things can be said of the body plan of nearly all mollusks. All mollusks have a mouth, a food tube, and an anus. All of them have a true body cavity or coelom between the food tube and bodv wall, most often confined to the area around the heart. It is a true coelom because a covering!; tissue lines the body cavity. In case you want to know, this epithelial or cover¬ ing tissue that lines a true coelom is called the peritoneum ( pehr ih tuh nee um), in man as well as in mollusks and other animals that have true coeloms. * All mollusks have practically all the or¬ gan systems you have, including a di¬ gestive system, a respiratory system, a circulatory system with a heart, a nerv¬ ous system (usually with a “brain” of sorts), an excretorv svstem with “kid- In man, the chest and abdominal cavities are divided, and the lining of the chest cavity is called the pleura ( floor uh ) . TABLE 7-A MAIN TYPES OF SEA SHELLS Several Coiled Bivalves, or Tusk-shaped cross plates shells two hinged shells shells Example: Example: Example: Example: Chiton Snail Clam Tooth shell Photos from American Museum of Natural History and (far right) from Myron R. Kirsch Dl I IEDDIMT At A UAIIIICI/ Pharynx Muscular foot Nerve ring Stomach Mantle Intestine (part cut away) Coelom (pericardial cavity) olivary gland sad Heart Kidney tubules Anus Photo from Roman Vishniac 7-1 The chiton is a sluggish animal, usually two to three inches long, found on algae- encrusted rocks in shallow water at the seashore. It “rasps” off bits of algae for food. Its shell is eight separate plates, secreted by the mantle immediately beneath them. Its ven¬ tral side consists of its long, muscular foot and its head, surrounded by the wide lower part of the mantle (not shown). The chiton breathes by means of two rows of gills (also not shown) /one on either side of the body inside the space between mantle and foot. Note that in addition to other organ systems a chiton has a true circulatory system— a heart (within a coelom) and blood vessels. Animals of lower phyla are without circula¬ tory systems. J j neys,” muscular and skeletal systems, and a reproductive system. Mollusks also have a specialized tis¬ sue called the mantle (Figure 7-1). It 1 ines the inside of the shell and its cells secrete the shell. It is the mantle that, in certain mollusks, makes real pearls. It secretes mother-of-pearl around some minute parasite lodged between the mantle and the shell. One of the features found in nearly all mollusks is the muscular organ called CLAMS, EARTHWORMS, STARFISH, AND THEIR RELATIVES 185 the foot. This single foot lies just be¬ hind the mouth. You must have watched a snail crawl along the glass in your aquarium or on a plant in your yard or garden, leaving its trail of slime behind. The snail crawls with its mus¬ cular foot. Most other mollusks have a similar foot. Maybe it would be more descriptive to call the mollusks the one¬ footed animals. But then the name wouldn’t seem to fit the octopus with its tentacles. Yes, the octopus, squid, and land slug are mollusks, even though the outside shells are missing. The embryos (young) of these nonshelled mollusks start to grow a shell, then stop. So the adults do not have external shells. The body plan of one class of mol¬ lusks differs in several ways from that of the other classes. Of all the classes, the chitons ( ky t ns ) are least complex. If you are interested, study Figure 7-1 to get the general idea of the chiton’s body. As you can see, the chiton’s heart is in its “tail’ (not a true tail, of course, but the posterior end of the animal ) . The clams Some of you have probably gathered fresh-water clams (Figure 7-2a), usu¬ ally called mussels. At least, you may have seen them. They have two shells hinged together. That’s why people call them bivalves ( by valvs ) . Some of you may have watched someone open live oysters to serve them “on the half-shell.” If so, you know it takes a sharp knife to cut the two strong muscles that hold the two half-shells together. On the inside of a clam shell, you can usually see the spots to which the two large muscles were attached (Figure 7-2b and c). The food tube, heart, “kidneys,” and other internal organs of the clam lie between the two halves of the mantle (Figure 7-2b). In the space between the mantle and the internal organs is the mantle chamber. The respiratory system consists of specialized breathing organs, called gills (Figure 7-2b), which lie in the mantle chamber. Clams get their oxygen from air in the water that circulates through the gill cham¬ bers and over the blood-filled gills. Yes, clams do have blood, but not red blood, like yours. Their blood is colorless. The water that circulates through the gill chambers carries bits of food. Cil¬ iary action (the cilia are on a pair of movable appendages near the mouth) siphons out the food particles, which are then swallowed. See Figure 7-2b, if you are interested in the parts that a clam’s food tube has. 7-2 Unlike animals of the lower phyla, clams and most other mollusks have all the organ systems found in vertebrates, the highest of animals. The clam’s skeletal system (A and C ) consists of its hinged half-shells. Its muscular system ( B and C ) includes its foot, two muscles that hold its half-shells together, and other muscles (not shown). Its circulatory system (B) consists of a heart, blood vessels, and blood sinuses. The respiratory system (B) includes two folds of gills on either side of the animal (water that washes over and into the gills enters and leaves the shell through two openings at the rear). The clam’s digestive system (B) is made up of the mouth, stomach, digestive gland, intestine, and anus (the two appendages near the mouth remove particles of food from water on the gills and “channel the food to the mouth). The nervous system (B) includes three pairs of ganglia (gang leeuh), or clumps of nerve cells, connected by nerves (one of each pair of ganglia is shown). The other two organ systems, excretory and reproductive (B), are represented by an excretory organ (kidney) and a reproductive gland (either male or female). 186 VARIETY AMONG LIVING THINGS— ANIMALS BLUEPRINT OF A MOLLUSK-FRESH-WATER CLAM Shell Foot Lines of growth Digestive gland Stomach Muscle Coelom (pericardial cavity) Vein Kidney Muscle Anus Gills Excretory Artery pore Heart Mouth Blood sinus of foot Nerve ganglion Nerve tissue Mantle Reproductive organ c Anterior adductor muscle Inside of shell Posterior adductor muscle A clam has a heart with three cham¬ bers in it— two receiving chambers into which the blood flows from the general circulation, and one discharging cham¬ ber out of which the blood flows to the general circulation. The heart lies in the clam’s body cavity, or coelom. Be¬ cause this body cavity surrounds the heart onlv— not the food tube and other J organs— it is called the pericardial (pehr ih kahr dee ul— meaning “around the heart”) cavity (Figure 7-2b). The discharging chamber of the heart pumps the blood out through arteries (true blood vessels) into open spaces in the tissues. These open spaces have no lining tissue— so they are not blood vessels, as the arteries are. These open spaces in the circulatory system are called blood sinuses ( sy nus ez ) . From the blood sinuses the blood flows back to the receiving chambers through veins (also true blood vessels). This kind of circulatory system is called an open circulatory system, because of the sinus openings in it. The squids and some other mollusks have closed circu¬ latory systems; that is, the blood stays within true blood vessels all the way. You will learn more about closed cir¬ culatory systems a little later. The clam is obviously considerably above, say, Ascaris or even rotifers and bryozoans in complexity, or level of organization. Can you mention the one or more body features that illustrate this point? If you want to know more about clams and other mollusks, refer to the classification summary on the facing page. Are mollusks useful to man? Mollusks play a part in human life, and have for a long time. Here are just a few examples: Many American Indians used shells as money (wampum). People make buttons of mother-of- pearl. People have used a number of mol¬ lusks for food for a long time. Today, the French serve “snails” as a delicacy. People eat oysters, clams, and octopus and abalone meat. Shells are used in making jewelry. The “ink” from squids is used in making a photographic paper called sepia. The studv of mollusk shells is con- J chology ( kon kol uh jee ) . Quite a number of people take up conchologv either as a specialized profession or as a hobby. If you are interested, you can get help from the little paperback book entitled Seashores, A Guide to Animals and Plants Along the Beaches, by Herbert S. Zim and Lester Ingle, Simon & Schuster, 1955. Summing up: the mollusks Look ahead at the classification sum¬ mary on the opposite page. Then, with everything you have read in mind, dis¬ cuss these questions in class. 1. What body feature of most mol¬ lusks makes the term “soft-bodied ani¬ mals” seem inappropriate? 2. Which mollusks are not “one¬ footed animals”? 3. How does a true body cavity or coelom differ from the primitive body cavity of Ascaris? 4. Why is the coelom of a clam called the pericardial cavity? 5. Why is the clam’s circulatory sys¬ tem said to be an open one? What is a closed circulatory system? 6. What one soft body tissue of mol¬ lusks would you guess sets them apart not only from lower animals, but per¬ haps from higher ones as well? 188 VARIETY AMONG LIVING THINGS— ANIMALS PHYLUM MOLLUSCA s Mollusks (MOLusks) are found on land and in both fresh and salt water. They may be large or small, and they may or may not have shells and a muscular foot or tentacles. Yet they are similar enough in many ways. All of them have a soft tissue called the mantle, which usually (but not always) secretes a shell. They are set apart from all lower animals except bryozoans by having a true coelom— a body cavity lined with covering tissue. And they are set apart even from bryozoans by having a true circulatory system, not found in any of the lower animals. Mollusks number about 70,000 species, many of which lived and died out long ago. Class 1. Amphineura ( am fill NYOO ruh ) . Mollusks with and without shells or a muscular foot, but with a head not dis¬ tinctly separated from the body, no ten¬ tacles, and no bivalve or tusk-shaped shells. Example: Chiton (Figures 7-3 and 7-1). Class 2. Pelecypoda (pel eh sip oh duh) . Wed^e-footed mollusks with bivalve shells, no distinct head, and no tentacles. Ex¬ amples: clam (Figure 7-4), Onodonta (fresh-water clam or mussel, Figure 7-2), oyster. Class 3. Gastropoda (gas trop oil duh ) . Flatfooted mollusks with distinct eyes and tentacles, and many with coiled shells. Ex- amples: whelk (Figure 7-5), snail (photo¬ graph, page 183), Triton, slug. Class 4. Scaphopoda (ska fop oh dull) . Salt-water mollusks with elongated bodies, tusk-shaped or tube-shaped shells, and a foot. Example: Dentalium (Figure 7-6). Class 5. Cephalopoda (sef uh lop oh duh) . Salt-water mollusks with and without shells, but with a distinct head, eyes, and a foot modified into long arms or tentacles. Examples: cuttlefish (Figure 7-7), Octo¬ pus, squid, nautilus. Photos top to bottom: no credit; Harrison, from , Monkmeyer ; Douglas P. Wilson; Myron R. Kirsch ; Douglas P. Wilson „ CLAMS, EARTHWORMS, STARFISH, AND THEIR RELATIVES 189 PHYLUM NINE: EARTHWORMS AND THEIR RELATIVES You have probably seen earthworms, especially in the morning after a rain, but you may call them night crawlers or fishing worms (Figure 7-8a). You see them in gardens, on lawns, and even along city sidewalks. Earthworms are the first segmented animals you have studied. What is a segmented animal? Look at the series of rings on an earthworm. Each ring is a segment (Figure 7-8). Count the segments and you will find that the common earthworm has 100 or more segments in its body. Inside the worm, there is a thin “partition’’ between each segment and the next one. The body of the tapeworm (Phylum Four) is made of sections, but these the tapeworm produces constantly, and they are all identical. They are not considered true body segments. Earthworms belong to the ninth phy¬ lum of the animal kingdom. This phy¬ lum gets its name from the “rings,” or segments. The name of the phylum is Annelida ( uh nel ih duh ), commonly called the annelids ( an eh lidz ) , or segmented worms. On page 155, you found directions for collecting earthworms ( and for pre¬ serving some of them). Use the living and preserved specimens you have col¬ lected for the activities which follow. Or use specimens from a biological supply house. WHAT CAN YOU SEE IN A LIVING WORM? Watch a living earthworm in a shallow pan that has moist sandpaper in the bottom. From your observations, an¬ swer as many of these questions as you can. Talk over the questions in class, then record answers in your record book. 1. Does one end of the earthworm go first? 2. Does the worm have a dorsal (top) side? a ventral side? 3. Does it have a right and left side? In other words, does it have bilateral (two- sided) symmetry? 4. Does it have a distinct head, with a "neck"? 5. Shade one end of the pan. Does the worm move to the lighted or shaded end? Does it seem to be able to "sense" light? Does it have eyes? 6. Can the worm crawl backwards? 7. Look for a red blood vessel running lengthwise along the dorsal side of the worm. Watch the blood vessel through a hand lens. What happens again and again to that blood vessel? Can you guess what these changes in the blood vessel mean? 8. Can you see anything that looks like breathing movements in the worm? 9. Lay the worm on a smooth surface, such as a piece of glass. Does it crawl as easily as it does on the sandpaper? 10. Can you see any organs that serve as "feet"? 1 1 . Put the worm on top of some slightly moist soil in a can. See if you can find out how it digs its hole into the soil. 7-8 In some ways, an earthworm seems less complex than a clam (Figure 7-2). For ex¬ ample, a clam has a skeletal system (its bivalve shell), but an earthworm (B) has none. Also, a clam has a respiratory system, but an earthworm (B and C) has none (oxygen passes through its moist skin into its blood vessels). On the other hand, an earthworm’s coelom (C) extends the length of its body; a clam’s is restricted to the area around its heart. Moreover, an earthworm’s circulatory system (B) is a closed system; a clam’s is open. And an earthworm’s nervous system (B) has many ganglia (two dorsal ganglia, plus up to a hundred or more ventral ganglia); a clam’s nervous system has few. 190 VARIETY AMONG LIVING THINGS— ANIMALS BLUEPRINT OF A SEGMENTED WORM:— EARTHWORM A Girdle Ventral blood vessel Ventral Zrop Gizzard nerve cord Reproductive glands Aortic arches Mouth retory tubule Ventral nerve cord Ventral blood vessel Dorsal blood vessel Gullet (esophagus) Intestine Dorsal ganglia Nerve collar Dorsal blood vessel Circular muscles Lengthwise muscles Intestine Setae Coelom How does an earthworm crawl? You can see that a crawling earth¬ worm gets smaller around and longer, as it pushes its anterior end (head) forward. Then it gets larger around and shorter, as it pulls its posterior end (tail) forward. It does these two things over and over again as it crawls either forward or backward. There are two sets of muscles in the earthworm’s body wall. One set runs lengthwise, the other set around the body (Figure 7-8c). When the length¬ wise muscles contract (shorten), the worm gets shorter and larger around. When the circular muscles contract, they “squeeze” the body and make it longer. (You will get the idea if you think of the way you can close your hand again and again around a piece of bread dough or homemade taffy, and squeeze it out into a long piece.) The muscular system of the earthworm is used in locomotion. But what keeps the posterior end from sliding backwards when the worm lengthens? And what keeps the anterior end from sliding backwards when the worm shortens? Run your finger along the underside of a preserved worm and you can feel a roughness. The rough¬ ness is due to the four rows of “bristles,” or “hairs,” on the ventral side of the body. These bristles are the setae (see tee— singular, seta). (See Figure 7-8c.) There are 4 pairs of setae in each seg¬ ment. The worm can move the setae so that they point either forward or backward. When crawling forward, it keeps the setae pointed backward. This keeps the tail from sliding backward when the worm lengthens, and the head from sliding backward when the worm shortens. To crawl backwards, a worm reverses the setae and points them for¬ ward. How does a worm dig its hole? A worm digs its burrow into the ground with its mouth. It swallows the dirt as it goes. So it literally eats dirt. At night, it comes out of its burrow and eats grass, cabbage, lettuce, or other available plants. But it also uses organic matter in the soil (like decay¬ ing leaves ) as food. Eventually, the dirt and indigestible materials are deposited on top of the ground as “castings.” Charles Darwin, one of the great bi¬ ologists of a century ago, used another descriptive name for the earthworm. He called it “nature’s plow.” In a way, earthworms do slowly “plow up” the soil by digging holes in it and adding their castings to the top of the soil around their burrows. It has been esti¬ mated that the earthworms in an undis¬ turbed field would bring enough soil to the surface in ten years to cover it to a depth of some two inches. Digestion in the earthworm An earthworm eats dirt and leaves and other plant materials. It digests the organic matter in the soil it swal¬ lows, as well as the leaves it gets above ground at night. All the living cells in the worm’s body must have food,^but they can’t get their food directly, as an ameba can. So the food taken into the food tube must be digested— changed into smaller molecules— before it can be shipped through the blood stream to all the living cells. To help gain an un¬ derstanding of digestion in the earth¬ worm, you need to dissect one. DISSECTING AN EARTHWORM. Follow these directions to dissect (cut open) a pre¬ served earthworm. 1. Starting at the enlarged "ring" about 30 segments back of the head, cut a length¬ wise slit all the way to the tip of the head 192 VARIETY AMONG LIVING THINGS— ANIMALS through the dorsal (top) body wall. Be care¬ ful not to cut too deeply. 2. With tweezers and scalpel (knife), loosen the body wall from the internal or¬ gans by cutting the membranes ("parti¬ tions") between the segments. Pin the flaps to the wax in the dissecting pan (Figure 7-9). 3. Trace the food tube from mouth to intestine, using Figure 7-9 to help you. Then save your specimen for later use. The food tube lies exposed, once you have opened the worm’s body. At the anterior end, just back of the mouth, is the pharynx (Figures 7-8b and 7-9). The pharynx is hollow and has strong muscles in its wall. These muscles help the mouth eat its way through the ground. The dirt is swallowed by the pharynx and so passed on into the gul¬ let, also called the esophagus ( uh sof uh gus). You may have trouble finding the esophagus in your specimen. It is covered with some white organs. These white organs (Figure 7-9) are part of the reproductive system and will be studied later. Push them aside to find the esophagus. The esophagus opens into a soft- walled, whitish pouch, called the crop, which in turn opens into a strong- walled, brownish gizzard. Extending from the gizzard back to the posterior end is the intestine. The food tube con¬ sists of the mouth, pharynx, gullet or esophagus, crop, gizzard, and the long intestine (Figures 7-8b and 7-9). The pharynx swallows the food and dirt, which pass back through the esophagus into the crop. Cells in the wall of the crop secrete digestive juices over its contents. These juices soften leaves and bits of organic matter in the dirt swallowed. The crop’s contents then pass into the muscular gizzard and are there ground to bits. The giz¬ zard uses the tiny stones in the dirt as a substitute for teeth. Then the food passes on into the intestine. In the intestine, digestion is com¬ pleted. Digested foods pass into the blood vessels in the wall of the intes¬ tine. Indigestible materials leave the body through the anus. The earthworm's circulatory system You already know that earthworms have true circulatory systems. And they have red blood, as you know if you have ever put a live one on a fishhook. Hemoglobin makes the blood red. There are no red blood cells in the earthworm’s blood— the hemoglobin (red coloring matter) is dissolved in the blood fluid. The worm’s blood circu¬ lates round and round the body through true blood vessels all the way. In other words, the earthworm has a closed circulatory system, in contrast to the open system with blood sinuses in a clam. You have a closed circula¬ tory system, and so do all other verte¬ brates. OBSERVING BLOOD VESSELS IN AN EARTHWORM. Use the preserved speci¬ men you have already partly dissected. Look for the blood vessel that lies dorsal to the food tube. See if you can locate the five pairs of "hearts" among the reproduc¬ tive glands in front of the crop (Figures 7-8b and 7-9). Again, save your specimen for later use. If you examined a living earthworm earlier, you saw the dorsal blood ves¬ sel contract and then fill up again with blood, over and over again. This sug¬ gests a “beating heart.” The dorsal blood vessel does serve the same pur- CLAMS, EARTHWORMS, STARFISH, AND THEIR RELATIVES 193 EARTHWORM —DISSECTED 7-9 Here is an earthworm as it looks when dissected (see text for directions), with one difference. The excretory tubules in each segment (except the first three and the last) have been removed, along with the membranes that separate the segments. (See Figure 7-8c.) pose as a beating heart— it helps to push the blood through the blood ves¬ sels all over the body. In addition to the “beating” dorsal blood vessel, an earthworm also has five pairs of “beating hearts,” so to speak. Toward the anterior end of the worm, there are five pairs of blood ves¬ sels that branch off from the dorsal vessel, encircle the gullet, and join the ventral blood vessel beneath it. These blood vessels beat like hearts, but they are called aortic ( ay or tik ) arches be¬ cause, strictly speaking, they are not true hearts. Nevertheless, these aortic arches, along with the dorsal blood ves¬ sel, pump the blood around the body (Figure 7-8b) after the fashion of a true heart. The blood flows forward through the dorsal blood vessel and down through the aortic arches to the ventral blood vessel, through which it flows backward through the body. From the ventral vessel, the blood flows out through branching blood vessels that end in small capillaries which spread through all parts of the body. The blood then returns to the dorsal vessel. In the walls of the intestine, mole¬ cules of digested foods diffuse into the blood in the capillaries and are carried to every living cell. There are many capillaries in the skin of an earthworm. As long as the skin is moist, oxygen molecules from the air pass into the blood in the capil¬ laries. In other words, earthworms “breathe” through the skin. They have no specialized breathing organs like the gills of clams or the lungs of human beings. They do not show any breath¬ ing movements, as we do. The hemoglobin in the blood carries oxygen to every living cell. Have you ever wondered why worms come out of the ground when it rains? Ordinarily, air fills the spaces between soil par¬ ticles in the ground, but when rain water fills the air spaces in the ground, the worms can no longer breathe freely. It is the lack of air in rain-soaked soil that stimulates the nervous system and through it, the muscles and setae, 194 VARIETY AMONG LIVING THINGS— ANIMALS which “react’ with movements that bring the earthworms to the surface. This makes you think of the movements of protozoa to air bubbles or to the edge of a cover slip on a slide, doesn’t it? In each living cell, some of the food is changed into living protoplasm. Some of the food is oxidized, releasing the energy which the cell uses in doing its work. Cell wastes are carried away from each living cell by the blood stream. Carbon dioxide leaves the blood through the skin. Other cell wastes are eliminated from the blood by a pair of tiny excretory tubules ( too byoolz) in each segment (Figure 7-8c). These tubules do for earthworms about what human kidneys do for people. In case you want to know, biologists call these tubules nephridia ( neh frid ee uh), from a Greek word meaning “kid¬ ney.’’ In the earthworm, only the first three and the last body segments are without nephridia. A worm's guiding and controlling system One more system of organs functions in the daily living of the earthworm. This is the nervous system. It enables the worm to react to such things as light, moisture, and other things around it. The nervous system also co-ordinates the worm’s movements. Earthworms usually come out only at night. Daylight sends them back un¬ derground. Put some live worms in a moist pan. Cover one end of the pan to keep out the light. Notice what the worms in each part of the pan do. Or use a flashlight to hunt night crawlers. You must grab a worm quickly after the light strikes it, or it will withdraw into its burrow. So worms must be able to tell when light is shining on them. And yet they have no eyes. Certain cells in the skin on the dorsal side are sensitive to light. These light-sensitive cells take the place of eyes. They do not “see’’ as we do. Perhaps they just “feel” light. The light-sensitive cells are connected by nerves to the internal nervous system. “Messages” travel in¬ ward and spread through the nervous system to the muscles, which then move the animal out of the light. Earthworms are also sensitive to moisture and to touch. Invent and carry out experiments of your own to test the effects of moisture and touch on living worms. Earthworms select some kinds of food in preference to others. These and many other reactions are con¬ trolled by their nervous systems. EXAMINING THE NERVOUS SYSTEM OF AN EARTHWORM. Push aside the inter¬ nal organs in your dissected earthworm. Look for a white nerve cord running the full length of the body. That nerve cord is on the ventral (under) side of the food tube. To find it, push the gizzard aside and look for a white cord about the size of a coarse thread. This is the ventral nerve cord (Figure 7-8b). See if you are skillful enough with scissors and scalpel to remove intact the "brain/' collar, and a part of the ventral nerve cord. Just back of the mouth, the nerve cord branches. The two branches en¬ circle the pharynx and join the “brain” on the upper (dorsal) side. This is not a true brain; it consists of two small clusters of nerve cells. Such a clump of nerve cells is called a ganglion (gang lee un— plural, ganglia). So the “brain” is actually just two small dorsal ganglia, together not much larger— if at all — than the head of a pin. CLAMS, EARTHWORMS, STARFISH, AND THEIR RELATIVES 195 On the ventral nerve cord there is a ganglion in each segment of the worm. Branching out from these ventral gan¬ glia are tiny nerves which run to the muscles and skin and other parts of the body. “Messages” come into the nerve J O cord and its ganglia and are sent on to the muscles and other structures that react in one way or another. The nervous system seems simple when compared with your own. But the whole body of the earthworm is much less complex than the human body. The worm’s nervous system is well suited to play its part in the animal’s life. That nervous system helps to keep the animal out of danger in the dav- time. It helps the worm find food at night. It controls the crawling move- O O ments. In brief, it plays somewhat the same part in the total life of the organ¬ ism as the nervous system of a verte¬ brate does. Reproduction in the earthworm Earthworms reproduce by means of eggs and sperms produced by repro¬ ductive glands. The reproductive sys¬ tem is a complicated one and will be studied in a later unit. If you especially want to study it now, turn to pages 496-97 and do so. Other annelids Earthworms are not the only seg¬ mented worms. Leeches belong to this phylum. So do many worms that live in the sea. Of the marine worms, the sand- worm Nereis ( neer ee us ) is one of the most interesting. On each segment, this sandworm has a pair of fleshy “feet” with setae at the outer ends. Nereis uses these “side feet” both in locomo¬ tion and as respiratory organs. Many of the marine worms are handsome or¬ ganisms with many-colored plumes. One strange annelid (belonging to the same class as Nereis ) has a very delicate body and never moves around. It spends its life in the mud or sand in shallow water along the Atlantic Coast, living in a U-shaped tube which it secretes. Both ends of the tube open above the mud or sand, and a steady current of water passes down one open¬ ing, through the tube, and up again to the other opening. The worm just lies in its tube, never emerging, feeding on whatever small organisms are brought into the tube by the current of water. Certain other annelids, also of the same class as Nereis, live in upright tubes which they build in the sand in shallow water. The heads of these fan worms bear a whole circle of long feathery gills, and only the heads and the “fans” of gills emerge from the up¬ right tube. At first glance they look more like plants than animals. To learn more about the annelids, studv first the classification summary J J on the facing page, then refer to books listed under Further Reading at the end of this chapter. Summing up: earthworms and their relatives Title a fresh page in your record book Organ Systems in an Earthworm. Down the left-hand side of the page, list the items given below. To the right of each item on the list, name all the parts of that system you can. Digestive system— Name six parts. Excretory system— Name the tissue that excretes CO., and the organs that ex¬ crete liquid wastes. Circulatory system— Name three parts. Nervous system— Name three parts. Organs of locomotion— Name three parts. 196 VARIETY AMONG LIVING THINGS— ANIMALS PHYLUM ANNELIDA The annelids (an eh lidz) are segmented worms, numbering about 6,500 species. • They have well-developed organ systems and a true coelom extending the lengths of their bodies (in leeches, the coelom is ° crow ded out by connective tissue that fills 8 the body cavity). Oddly enough, annelids have fewer organ systems than many mol- * lusks of the next lower phylum, but most • of the organ systems they have are more highly developed than in mollusks. The annelid coelom is also more extensive than * in mollusks (wEere it usually is restricted , to the cavity around the heart ) . Annelids are found on land, in fresh and salt water, and as parasites on or in other organisms. ® • Class 1. Polychaeta (pol ih KEE tuh) . Salt- a water inhabiting worms with many promi¬ nent bristlelike structures along both sides of the body. Example: Arabellidae (Figure • 7-10), Nereis, fan worm. • Class 2. Archiannelida (ark ih un nel ih duh) . Salt-water inhabiting w^orms without * bristlelike structures and with little or no • external evidence of their segmentation. Example: Polygordius (Figure 7-11). • Class 3. Oligochaeta ( ol ih goh kee tuh ) . • Earthworms and fresh-water inhabiting , worms. Example: Lumbricus (common earthworm, Figures 7-12 and 7-8). Class 4. Hirudinea (hihr uh DIN ee uh) . • Leeches, some free-living, others parasitic. . Examples: Hirudo (medicinal leech, Fig¬ ure 7-13), pond leech. Photos top to bottom : Myron R. Kirsch ; no credit ; Lynwood M. Chase, from National Audubon Society; Carolina Biological Supply Co. CLAMS, EARTHWORMS, STARFISH, AND THEIR RELATIVES 197 PHYLUM TEN: STARFISH AND THEIR RELATIVES Now you come to the tenth phylum of the animal kingdom, that to which the starfish and their relatives belong. Examine a dead and dried-up star¬ fish. The most noticeable features are the shape and the spines all over the dorsal side. This phylum gets its name from those spines. The animals are called echinoderms (ee ky noh dermz), from echinus meaning “spine” and derm meaning “skin.” The technical phylum name is Echinodermata ( ee ky noh der muh tuh ) . The starfish and many, but not all, of their relatives are spiny-skinned animals. 7-14 STARFISH AT LUNCH A starfish has no teeth, yet it can eat its weight in fish! It turns its stomach inside out through its mouth and partially digests the fish (as it is doing here). Later, it takes its food— and its stomach— inside its body. This method of feeding is very efficient in a way; few in¬ digestible materials are taken in with the food. Robert S. Bailey Starfish Like oysters and earthworms, starfish start out as embryos (young, unhatched animals) with three cell layers. They have open, not closed, circulatory sys¬ tems, and true body cavities. And they have a respiratory system. They have about the same systems of organs as people have. Starfish have no right and left sides. They are built around a central point somewhat as a wheel is. Much as the spokes of a wheel radiate out from the center, so the parts of the starfish’s body radiate out from a central point. So they have radial, not bilateral, sym¬ metry. They have a dorsal and a ven¬ tral side, but no anterior or posterior ends (Figures 7-14 and 7-15). Anyone who studies a starfish and the way it lives is in for several sur¬ prises. For one thing, it turns its stom¬ ach inside out through its mouth and digests food (say, an oyster, clam, or fish) that is too big to swallow (Fig¬ ure 7-14). Are you wondering how a starfish gets at the soft body of the oyster? That is another one of the surprises. A starfish folds itself around the oyster in its shell, takes hold of the two half¬ shells, and then begins to pull. The starfish pulls by means of the suction pads on the ends of its hundreds of “feet.” At first the much stronger mus¬ cles of the oyster hold tight and noth¬ ing happens, but the starfish’s “feet” keep on pulling. After a while, perhaps 20 minutes or so, the oyster’s muscles get tired, much as your hand muscles would get tired if you clenched your fist for 20 minutes. Then the oyster shell opens and the starfish turns its stomach inside out over the oyster’s soft body. In this way, the starfish presses its stom¬ ach lining over the oyster, partly di- 198 VARIETY AMONG LIVING THINGS— ANIMALS Stomach Digestive glands Spines Skin gills Ectoderm Ring canal Coelom Reproductive glands Sieve plate Cilia Tube feet Photo by Douglas P Wilson 7-15 One arm and the central portion of a starfish are shown cut open here. The mouth is on the underside of the body; the anus and sieve (siv) plate on the upper side. The water that fills the tube feet is taken in through the sieve plate and distributed to each arm from the ring canal around the mouth. The starfish’s coelom is lined with ciliated tissue, parts of which have been cut away to reveal the inner “bulbs” on the tube feet. ( Actually, cilia would not be visible without magnification.) Spines embedded in the flesh are the starfish’s skeletal system; its muscular system includes muscles in the tube feet. The nervous system (not shown) includes a ring of nerve tissue around the mouth, from which five nerves (one to each arm) branch off; there are also other nerve tissues. The liquid-filled coelom serves as a simple circulatory system; the skin gills (and tube feet) as a respiratory system. The digestive system is easily traced, and there is no specialized ex¬ cretory system (most wastes are excreted by the skin gills). The reproductive system consists of either ovaries or testes. gests it, and then takes in the already partly digested food. Why do we call the organs used to pull open the oyster the “feet”? Because the starfish uses them in locomotion. Along the ventral side of each arm of the starfish are rows of “feet,” more correctly called tube feet (Figure 7-15b). These tube feet are like small rubber tubes, closed at the outer end and connected toward the inner end to water vessels inside the starfish. CLAMS, EARTHWORMS, STARFISH, AND THEIR RELATIVES 199 These water vessels are always kept full of sea water. When the starfish moves about, it forces some of the water out into the tube feet, causing them to lengthen out. On the end of each foot is a little suction pad with which the starfish sticks to objects. The respiratory system of a starfish is still another surprise. The starfish breathes partly through its tube feet, but chiefly through the skin gills that lie between its spines (Figure 7-15b). The circulatory system is also a sur- prise. It is not a well-organized system. The coelom (body cavity) is filled with fluid (“blood”) which bathes all the living tissues and delivers digested O O food and oxygen to them, and also car¬ ries away cell wastes. There are no blood vessels and no closed circulatory system. There is no heart. The cells in the lining (peritoneum) of the coelom are ciliated (Figure 7-15b). These cilia keep the blood moving. A starfish has either egg-making or¬ gans (ovaries) or sperm-making organs (testes— tess teez ) . The female sheds the eggs, and the male the sperms, into the surrounding sea water, where fer¬ tilization occurs. The embrvos in the J early stages show certain features which make it seem likely that the star¬ fish and the vertebrates are more close- lv related than anvone would think to * J look at the adult starfish and any back¬ boned animal. If you are especially in¬ terested, look up the term trochophore (trok oh fohr ) in any college textbook of biology or zoology. Maybe you will want to report in class on reproduction in the starfish. Figure 7-15 will give you more in¬ formation, if you are interested. So will the classification summary on the fac¬ ing page and some of the books listed at the end of this chapter. Other echinoderms Some 5,000 species of echinoderms have been named and described. They are divided into five classes— the star¬ fish class, the brittle stars, the sea ur¬ chins and sand dollars, the sea cucum¬ bers, and the sea lilies. As their name implies, sea lilies look much like plants; they are stalked echinoderms ( the stalks upright) with a crown of much- branched arms. Sea lilies live in deep water and thus are seldom seen by people. Altogether, the echinoderms are more interesting as a side line than they are important to man. They do cause a lot of damage to oyster beds, but otherwise they do not affect peo¬ ple’s lives much, although some peo¬ ples do eat sea cucumbers. Summing up: the first ten animal phyla You have now become acquainted with ten animal phyla. Two of these (rotifers and bryozoans) were merely mentioned, but the other eight have been presented in some detail. Table 7-B on page 202 summarizes all ten of these phyla briefly. The theme of Chapters Six and Seven has been the increasing level of organization, from the single-celled animals to the highly complex, many- celled ones with well-developed organ systems. Turn back to Table 3-D on page 95 and read through it again. It should mean more to you now. You will study two more animal phyla. These are Phylum Eleven, ani¬ mals with jointed legs, and Phylum Twelve, the one to which the verte¬ brates belong. Because the animals of these two phyla are the most successful and most familiar animals on land, each one will be treated in a chapter by it¬ self. (See Chapters Eight and Nine.) 200 VARIETY AMONG LIVING THINGS— ANIMALS PHYLUM ECHINODERMATA Class 2. Ophiuroidea ( off ill yoo roy dee uh ) . Brittle stars, with five to eight arms (sometimes branched) that are not grooved ventrally. Example: five-armed brittle star (Figure 7-17) . Class 3. Echinoidea ( ee ky NOY dee uh ) . Spherical or disc-shaped echinoderms with¬ out arms. Examples: sea urchin (Figure 7-18), sand dollar. Class 4. Holothuroidea (hoi oh thyoo ROY deeuh). Elongated echinoderms without arms, but with tentacles around the mouth; also without spiny skin, but with micro¬ scopic skeletal particles embedded in the flesh. Example: sea cucumber (Figure 7- 19). Class 5. Crinoidea (kry noy dee uh). Echi¬ noderms with a plantlike appearance, long arms (often much branched), and usually a stalk with fixed base. Examples: feather star (Figure 7-20), sea lilies. Photos top to bottom : General Biological Supply House, Inc., Chicago; American Museum of Natural History ; Douglas P. Wilson ; American Museum of Natural History ; Douglas P. Wilson The echinoderms (ee ky noh dermz) are exclusively salt-water inhabiting animals with radially symmetrical body forms and spiny skeletons (sometimes made of plates) embedded in the body wall. They have true organ systems, some highly developed, others (including the circulatory, respira¬ tory, and excretory systems) usually not highly developed. They have a true coe¬ lom, often with ciliated lining, and most species have tube feet. The total number of species is about 5,000, many of which lived and died out long ago. Class 1. Asteroidea (as ter oy dee uh) . Starfish, usually with five, six, or ten ven¬ trally grooved arms (rarely, four to more than twenty arms ) . Example : five-armed starfish (Figures 7-16 and 7-15). 7 CLAMS, EARTHWORMS, STARFISH, AND THEIR RELATIVES 201 7-20 7-19 7-18 7-17 7-16 TABLE 7-B THE FIRST TEN ANIMAL PHYLA Phyl um Some important features Examples Protozoa One-celled animals with organelles Ameba, paramecium, vorticella Porifera Loosely organized, many-celled ani¬ mals with “pores” and incomplete inner layer of flagellated cells. No true tissues Scypha, Venus’s-flower-basket, other sponges Coelenterata Two complete cell layers; true tissues. Tentacles are true organs. No other organs or organ systems Hydras, jellyfish, corals, sea anem¬ ones J Platyhelminthes Three cell layers; true tissues, numer¬ ous organs, and organ systems. No body cavity or anus Planarians, tapeworms, liver flukes, many parasites, other flatworms Nemathelminthes Beginnings of a body cavity (but not a true coelom). Digestive tract with second opening (anus) Ascaris, vinegar eels, hookworms, tri¬ chinas, many parasites of both plants and animals, other round- worms Rotifera Also beginnings of a body cavity (but not a true coelom). Mouth and anus Rotifers (microscopic, many-celled animals abundant in pools and ponds) Bryozoa Mouth and anus; true coelom sepa¬ rates digestive tract from other body parts. No true circulatory system “Moss animals” (a little-known group, largely marine) Mollusca Soft-bodied, with true circulatory system (usually open circulatory system) Oysters, clams, snails, tooth shells, chitons, octopus, squid Annelida Segmented bodies, usually with closed circulatory systems Earthworms, leeches, sandworms Echinodermata Built around a central point, with tube feet, water-vascular system, and skin gills. Body cavity useful in circulation Starfish, sea urchins and sand dollars, sea cucumbers, sea lilies Your Biology Vocabulary Here are the important new terms that have been introduced in Chapter 7. You will find it worthwhile to make sure that you understand and can use them correctly. mollusks chitons bivalves mantle mantle chamber gills pericardial cavity blood sinuses open circulatory system closed circulatory system segmented worms annelids 202 VARIETY AMONG LIVING THINGS— ANIMALS dorsal blood vessel Nereis aortic arches echinoderms ventral blood vessel radial symmetry excretory tubules of earthworm skin gills ganglion tube feet O O dorsal ganglia Testing Your Conclusions Some of the following statements are true. Others are false but can be made true by replacing the italicized word or phrase with another word or phrase. In your record book, copy all the true statements. Also copy the false ones, but change the italicized word or phrase so that each statement is true. 1. Earthworm embryos have a mesoderm layer. 2. Starfish have bilateral symmetry. 3. Echinoderms have ciliated cells in the lining of the body cavity. 4. Mollusks secrete mother-of-pearl. 5. Earthworms have a dorsal nerve cord and a pair of ventral ganglia that might be called a “brain.” 6. Of the eight animal phyla you have studied in some detail, the first one with a true circulatory system is that called Annelida. 7. There are more known species of annelids than of any of the other animal phyla so far studied. 8. A sandworm has tube feet and skin gills. 9. A snail uses its setae in crawling. 1 0. When an earthworm’s lengthwise muscles contract, the body of the worm is length¬ ened. More Explorations 1. Dissecting a clam. If you want to examine some of the organ systems of a clam (or oyster), use preserved specimens. First insert a dissecting knife and cut the two muscles (Figure 7-2c) that hold the shells together. Open the shells. Using Figure 7-2b, try to find the parts shown in that illustration. In your record book, draw a map of the body plan of a clam and label the parts you saw. 2. Examining a starfish. Examine preserved specimens. Look for the spines, skin gills, tube feet, and sieve plate (Figure 7-15). (Water enters the water- vessel system through the sieve plate.) The mouth lies at the center of the ventral side of the starfish. Try to find it. Make a dorsal slit the full length of one arm of the starfish, and cut away enough dorsal body wall from the arm and the central disk of the body to enable you to see inside. Use Figure 7-15 to help you find the digestive glands, stomach, anus, coelom or body cavity, and the internal parts of the water-vessel system. In your record book, draw a map of the body plan of a starfish and label the parts you saw. Thought Problems 1. Earthworms can crawl backwards. How do they do that? In your answer, mention the lengthwise muscles, circular muscles, and setae. setae gullet esophagus crop gizzard intestine CLAMS, EARTHWORMS, STARFISH, AND THEIR RELATIVES 203 2. The mouth of a starfish is not very large, and yet, for its size, a starfish can eat some sizable bits of food. How can it do this? What limits the size of a meal it can take? (Remember that starfish also have no teeth; they cannot chew.) Further Reading To learn more about oysters, earthworms, starfish, and their relatives, turn to the end of the preceding chapter (page 182) and choose as references books from the first and third groups listed there. Two of the most readable books from this list are Animals Without Backbones by Ralph Buchsbaum and Parade of the Animal King¬ dom by Robert W. Hegner. Below are a few more titles. Vegetable Mould by Charles Darwin has interested many biology students, but it has long been out of print. Even so, your library may have a copy. This book deals with Darwin’s reasons for calling earthworms “nature’s plows.” This Fascinating Animal World by Alan Devoe, McGraw-Hill, 1953. Undersea Adventure by Phillip Diole, Messner, 1953. Between Pacific Tides by Edward F. Ricketts and Jack Calvin, Stanford Univ, Press, 1952, will be useful to those living on or near our West Coast. Looking Ah IMHiflHi 1. Start now to collect insects for study in the next chapter. Most books on insects tell you how to make an insect collection. Refer to pages 227-228 for help in identifying insects and to page 231 for a listing of books on insects. 2. In Chapter 10, you will need young pea or bean plants and corn plants. In one box of earth, plant some beans and peas. In another, plant corn. Water these plants regularly, but not too much. It will probably take about three weeks for them to be ready to study. Choose the time to plant them so that you will have good-sized young plants by the time you reach page 266. 204 VARIETY AMONG LIVING THINGS— ANIMALS CHAPTER Animals with Jointed Legs Flying saucers? People living in the foothills of the Sierra Nevada mountains in California saw strange objects in the sky on the morning of October 11, 1950. One ob¬ server, Mr. W. H. Hutchinson, reported in Natural History Magazine for Janu¬ ary, 1951, that he and his wife and two sons saw hundreds of shining white balls in the sky above their home on that morning. Other people in and around Paradise, California, reported that they saw a flight of ten or twelve such balls about nine o’clock the same morning. The observers agreed that the silvery balls looked like small, white, toy bal¬ loons and had long tails. They agreed, too, that the strange objects were noise¬ less and had no visible means of flying, except the waving of the tails. The peo¬ ple in and around Paradise thought the objects were some 2,000 feet high, but those seen by the Hutchinsons varied in height, the lowest ones being no more than 100 feet off the ground. The Hutchinson family ran to capture one that came down almost to the ground, but it took off and disappeared before they could reach it. The problem solved All observers saw one or more of the balls disintegrate in thin air without a sound, leaving only a trail of what looked like “light blue smoke” behind. On the morning after the flight, the Hutchinsons found what seemed to be a fragment of one of the sky objects caught on a twig of a fir tree. The par¬ ticle looked like a bit of spiderweb. Mr. Hutchinson sent his fragment to the American Museum of Natural History in New York City for identification. Dr. Willis J. Gertsch of the Museum’s De- Roche ANIMALS WITH JOINTED LEGS 205 partment of Insects and Spiders iden¬ tified the fragment as indeed spider¬ web and explained the “flying saucers” as spider “balloons.” In this case, what some people thought might be flying saucers turned out to be spiderwebs. Dr. Gertsch and many other students of spiders report that many species of spiders, especially while “babies,” do go “ballooning” through the sky. To do that, they climb to the top of some ob¬ ject, face into the wind, stretch out their legs, spin threads of cobweb, and then take off. The webs make the “bal¬ loons,” and the wind blows them along. They may be carried for only short dis¬ tances. Or they may travel a long way. The noted English naturalist, Charles Darwin, on his five-year-trip around the world in the ship Beagle, reported that huge numbers of tiny spiders arrived one day on the ship when it was 60 miles off the coast of South America. Spiders have jointed legs. So do all the other animals in Phylum Eleven. They are called arthropods ( ar throh podz ) , from two ancient Greek words— arthron meaning “joint” and podos meaning “foot.” The technical name of this phylum is Arthropoda ( ar throp oh duh ) . In this chapter you will ex¬ amine some of the arthropods and learn how biologists classify them. IDENTIFYING ARTHROPODS Spiders have four pairs of legs with movable joints. Count them in the fe¬ male black widow spider in Figure 8-1. All arthropods have several pairs of jointed legs. This phylum includes the spiders, mites, and ticks; the crayfish and lobsters; the centipedes (sENtih peedz ) and the millipedes ( mil ih peedz); and all the insects. People often call these animals “crawly things,” probably because so many of them have so many legs. All of them have at least three pairs of legs, and some of them have as many as 173 pairs. And these legs have joints, so that movement is easy and often fast. The arthropods outnumber all the rest of the animals put together. Some 750,000 species are known. Of these, some 650,000 are species of insects. If we may judge by numbers, variety, and wide distribution, the arthropods are by far the most successful animal phy¬ lum on earth. The insects give human beings severe competition. In parts of the tropics, certain insects like the ma¬ larial mosquito make it almost impos¬ sible for people to live there. Similarities in arthropods A butterfly doesn’t look at all like a lobster or a spider. And a centipede, 8-1 BLACK WIDOW SPIDER The only really dangerous spider in the United States is the female black widow. About one-half inch long, and solid black except for a red “hour¬ glass” mark on its ventral side, it inflicts a painful and poisonous bite. (The male of the species is harmless. It is much smaller and has a slender body. ) John H. Gerard, from National Audubon Society at first glance, makes you think of a worm. Yet butterflies, lobsters, spiders, and centipedes are all classified to¬ gether in the same phylum. Why? COMPARING ARTHROPODS. Compare a crayfish or lobster with a grasshopper. Then compare them both with a spider, and with a centipede or millipede. If you do not have all these animals, compare pic¬ tures of them, shown on pages 211, 212, 215, and 219. In what ways are all four animals alike? Before you read about them, write down the similarities you can discover. Check your list with the similarities de¬ scribed in the following paragraphs. How are these animals alike? For one thing, each of them has several pairs of legs with movable joints. For an¬ other, each has a head with sense or¬ gans on it, especially eyes and “feel¬ ers,” better called antennae (an ten ee— singular, antenna). Besides a head, most arthropods have a middle body region, the thorax ( thoh raks ) , and a posterior body region, the abdomen (ab duh m’n ) . (See Figure 8-2. ) Arthropods are alike in another way. They wear their skeletons on the out¬ side. Sea-food restaurants usually fur¬ nish a nutcracker with broiled lobster, so the diner can crack the “shell” to eat the meat inside the claws. Even a spi¬ der has an outside skeleton, although the body, especially the large abdomen, lacks a hard covering. Arthropods, then, have exoskeletons ( ek soh skel eht’ns), meaning “outside skeletons.” One more similarity among arthro¬ pods is easy to see in centipedes, but not so obvious in the others. It is the segmented body (Figure 8-2). Look for the segments in the abdomens of the lobster and the grasshopper. Do U.S.D.A. 8-2 ARTHROPOD BODY PARTS Strictly speaking, these are insect body parts (the insect is the praying mantis). Most other arthropods have about the same body parts, except that some have no antennae, or no externally visible segments in the abdomen, or less definite division into head, thorax, and abdomen. they remind you of the segments in the body of an earthworm? Similarities in reproduction You will not see the similarities in reproduction by examining the full- grown animals. But there are similari¬ ties. All arthropods lay small eggs. At hatching time, the young are naturally small and must eat, grow, and change in several ways to become adults. Most young arthropods are called larvae (lahr vee— singular, larva). In¬ cidentally, you should know that the young of many other animals, such as oysters and earthworms, are also called larvae, but you will find this term most often applied to arthropod young, and especially to insect young. Mosquito wrigglers, caterpillars, and apple “worms” are all larvae of insects. The points to remember just now are that most young arthropods are larvae ANIMALS WITH JOINTED LEGS 207 Left: Harold V. Green; right: Roche 8-3 ARTHROPOD LARVAE Some larvae are easily identifiable because of their resem¬ blance to adults of their species. This is true of the larva of a brine shrimp (left), but not of the larva of a black swallowtail butterfly (right). and that larvae must change to become adults. The larvae of many arthropods, including the lobsters and crabs, have hard exoskeletons which do not grow. But everv so often these larvae molt— J shed their exoskeletons— and then grow rapidly before the new exoskeleton hardens. Have you ever eaten soft- shelled crabs? They are crab larvae J which are collected just after molting. Arthropods come from eggs. The young may molt several times before becoming adults. The life cycles of most arthropods include several changes in form from egg through lar¬ val stages to adult. The word for this process of changing form several times in a lifetime is metamorphosis (metuh MORfuhsiss). You will build more meaning into this word as you proceed. Similarities in arthropod reproduc¬ tion are: (1) the eggs hatch into lar¬ vae* and (2) the larvae (Figure 8-3) 0 Dr. Willis J. Gertsch, Curator of Insects and Spiders at the American Museum of Natu¬ ral History in New York City, questions the use of the word larvae for spider voung. See page 40 in his book, American Spiders, Van Nostrand, 1949. undergo metamorphosis in growing up. Many larvae molt time after time. Level of organization Centipedes and millipedes make you think of the annelids with their seg¬ mented bodies. But what features of centipedes and crayfish and insects seem to you to show an increase in J complexity among arthropods as com¬ pared with annelids? For one thing, the annelid body is covered with a soft, thin cuticle (kyoo till k 1 ) , or outside layer over the epi¬ dermis. The outside layer of most ar¬ thropods, on the other hand, is a hard, thick cuticle, the exoskeleton. Cells in the epidermis secrete the cuticle in both annelids and arthropods, but in arthropods, these cells secrete several different substances, some of which harden the cuticle, or exoskeleton. One of these secretions is a horny substance called chitin (KYtin).** Chitin, with 00 The name chitin is similar to, but not to be confused with, the mollusks known as chitons, which you read about in the previous chapter. 208 VARIETY AMONG LIN ING THINGS— ANIMALS some other substances added, makes up the exoskeletons of arthropods, as well as their biting jaws, piercing “beaks,” lenses of the eyes, sense or¬ gans of touch, legs, and wings. Many other animals secrete chitin, but in none of them is this material so highly organized as in the arthropods. This organization includes joints— in the legs, jaws, etc. Try to imagine what a grasshopper would be like if its whole exoskeleton were one continuous layer of hard chitin. The grasshopper couldn’t “hop” or fly or chew. Examine the joints in a grasshopper’s hind leg and you will find that the cuticle over a joint is a thin, flexible membrane. This lets the joints move. It takes muscles to move joints. The muscles of an arthropod are fastened to the inside layer of the exoskeleton. Each arthropod muscle is a separate bundle of muscle fibers. If you could compare an arthropod’s muscles with an earthworm’s muscle layers ( discussed on page 192) you would see that the arthropod’s muscular system is more highly specialized. Arthropod bodies are more highly specialized than annelid bodies in many more ways— in the eyes and other sense organs, to mention one. You will dis¬ cover some of the increased specializa¬ tion as you study some individual ar¬ thropods, later in this chapter. Right now, the point to remember is that arthropods have reached a consid¬ erably higher level of organization than the animals in any other phylum except the one to which vertebrates belong, which you will study in Chapter Nine. Biological success How do people usually judge suc¬ cess? Often by the money a person makes, or the kind of car he drives, or the fame he has achieved. Biological success is another matter entirely. Biological success is measured in bio¬ logical terms. The most successful ani- mal groups, biologically speaking, are the ones with the most living individ¬ uals and species, the ones that occupy the widest territory, the ones that eat the most of the greatest number of dif¬ ferent kinds of food, and the ones that are best able to defend themselves against natural enemies. By all these marks of success, the arthropods out¬ rank all other phyla, including that of the vertebrates. That does not make them more important than people, but it does make them man’s greatest com¬ petitors on earth. Variety among arthropods You have learned that all arthropods are alike in these wavs: 1. They have segmented bodies. 2. They have jointed exoskeletons. 3. They have three or more pairs of jointed legs. 4. They usually have three body re¬ gions— head, thorax, and abdomen— al¬ though in some the thorax is not set off from the head. 5. All except those of the spider class have antennae and compound eyes. 6. Those that start life as larvae un¬ dergo metamorphosis. Arthropods also differ a great deal among themselves. For example, they differ in number of pairs of legs and in manner of breathing. On the basis of these and other differences, taxonomists sort them into several classes. Four main classes which you will study sepa¬ rately are: 1. Centipedes and millipedes 2. Crayfish and their relatives j 3. Spiders and their relatives 4. Insects ANIMALS WITH JOINTED LEGS 209 Summing up: identifying arthropods You have had a brief, over-all view of arthropods in general. Test your un¬ derstanding with these questions: 1. Many people think of certain ar¬ thropods as ‘‘crawly things.” What ar¬ thropod body parts probably lead peo¬ ple to think this? 2. Why is the arthropod phylum ranked first in biological success? 3. As of now, what does the word metamorphosis mean to you? Would you say that dogs undergo metamor¬ phosis? Why? 4. In what ways is the chitinous cov¬ ering of the arthropod body more high¬ ly specialized than the cuticle of an¬ nelids? 5. What are the basic similarities in all arthropods? 6. Is the animal shown in Figure 8-4 an arthropod? What features make you think so, or think not? CENTIPEDES AND MILLIPEDES Centipedes and millipedes are often called thousand-legged worms. But they are not worms, and they do not have a thousand legs. You must have seen both centipedes (Figure 8-5) and milli¬ pedes at one time or another. Centi¬ pedes live in moist places— under rocks or beneath the bark of rotting logs or in damp places in our homes. Millipedes are common among dead leaves or other decaying plant materials. "Many legs" Both a centipede and a millipede look somewhat like a segmented worm with many legs and an exoskeleton. Both have a head and one pair of antennae. One way to tell centipedes and milli¬ pedes apart is to see how many legs each has on one segment. Centipedes have one pair of legs to a segment; millipedes have two pairs on each seg¬ ment. One species of centipede has 173 pairs of legs; another has only 15 pairs. A common millipede has 115 pairs of legs, but most have fewer pairs. Centipedes move fast. They are al¬ most never still unless both the upper and lower sides of the animal are touch¬ ing something. Under the bark of a dead log, the bark touches one side of a centipede and the wood the other. There, a centipede may lie still all day, coming out at night to feed. It eats only animal food, such as cockroaches, plant lice, or earthworms. It poisons its prey 8-4 IDENTIFICATION? Consider this animal’s body features— eyes (Is there a head?), antennae, jointed legs, and so on. Is it an arthropod or not? (diuuqs v si }j) American Museum of Natural History Hal H. Harrison, from National Audubon Society 8-5 GIANT DESERT CENTIPEDE The segmented body of a centipede somewhat resembles that of an earthworm, but there are many differences. A centipede has a distinct head with eyes and antennae, and a pair of jointed legs on each body segment. with the two poison claws on a pair of legs near the head. Some centipedes can inflict a painful but not dangerous wound on human skin. Millipedes move more slowly than centipedes. They are vegetarians. For the most part their food is decaying plant tissues, but sometimes they do eat roots of garden plants, doing some dam¬ age to our gardens in this way. Name of the class The centipedes and millipedes make up one class of arthropods, called the myriapods * ( mihr ee uh podz ) , mean¬ ing “many feet.” As far as most people are concerned, the myriapods are not very important. SPIDERS AND THEIR RELATIVES This class of arthropods is usually ranked third in this phylum, but we are going to discuss it here, because you will want to study the crayfish class and the insect class in more detail. Spiders and their relatives make up a class of arthropods that is hard to de- Some taxonomists put the centipedes in one class and the millipedes in another. scribe, because its members differ in so many ways. But all of them do have four pairs of ivalking legs. None of them have antennae or compound eyes. None of them have a movable joint (“neck”) between the head and thorax. If you find an arthropod with four pairs of walking legs, but without antennae, compound eyes, or a “neck,” you will know it belongs to the spider class. The name of this class is Arachnida ( uh rak nih duh ) or the arachnids ( uh rak nidz), from arachne meaning “spider.” The arachnids include the spiders, scorpions, “daddy longlegs” or harvest- men, and the mites and ticks. (See Fig¬ ures 8-1, 8-6, and 8-7. ) The spiders Are you one of the many people who fear spiders? With the exception of one or two kinds, spiders are harmless. Most of them in our country can’t bite a per¬ son, because they can’t even puncture human skin. True, the bite of a black widow spider may be painful and should have the attention of a physi¬ cian. If you live in an area where black widows are common, learn to know one when you see it. Look at the picture in ANIMALS WITH JOINTED LEGS 211 Figure 8-1. Black widow spiders go out of their way to let people alone, unless someone happens to squeeze the spider against his skin. Then the spider may bite, in self-defense. Spiders are not only harmless, but are useful to man. They eat houseflies and other harmful insects. One black widow in captivity ate 250 houseflies during its lifetime. The tarantulas ( tuh ran tvoo lulls ) , often called “banana spiders,’’ are our largest spiders, but they are not “dread¬ ful creatures,” as so many people think. Tarantulas (Figure 8-6) are sluggish creatures. Like the black widows, they will not even try to bite a human being unless goaded to it, in self-defense. Ac¬ tually, they make good pets, if a per¬ son knows how to take care of them. Spiders are a colorful lot. Leaf through Gertsch’s American Spiders (cited in the footnote on page 208 ) and look at the pictures. Then read the chapter on “Economic and Medical Im¬ portance,” starting on page 236. You may get interested enough to want to make a special study of spiders. 8-6 TARANTULA A fully grown tarantula of the southwestern United States is two to three inches long. It can inflict a painful but not dangerous bite. A few tropical ta¬ rantulas reach seven inches in length. O Gordon S. Smith, from National Audubon Society Scorpions The scorpions of today come from a long line of ancestors. Sea scorpions lived in the oceans close to half a bil¬ lion years ago. They were able to breathe under water. Our modern scorpions are lung-breathers. Those of you who live in the South¬ west will know that the sting of the scorpion is poisonous. To human be¬ ings, the sting of most scorpions is pain¬ ful, though rarely dangerous. In the Southwest, the sting of only two spe¬ cies is serious and may prove fatal, es¬ pecially to small children. (See Figure 8-7.) Recently, Dr. Herbert L. Stahnke of Arizona State University at Tempe, Arizona, developed a serum treatment for the sting of the two deadly species of scorpions. His serum was first used successfully on a child in Tucson on June 29, 1951. * Mites and ticks Mites and ticks are unpleasant little animals, especially when they invade the human skin as parasites or suck our blood. Ticks are common parasites of sheep and other domestic animals. But on the whole, they live without ever coming to the attention of most of us. Summing up: arachnids Arachnids include spiders, scorpions, harvestmen, and mites and ticks. These animals have four pairs of walking legs, no antennae, no compound eyes, and no movable joint between head and thorax. Except for two species of scor¬ pions, the mites and ticks, and possibly an occasional black widow spider, they are not only harmless, but usually use¬ ful to man. * See Arizona Highways for February, 1954, p. 28, for a fine article on the subject. Also see the pamphlet Scorpions by Dr. Stahnke, Arizona State University, Tempe, Arizona, 1949. 212 VARIETY AMONG LIVING THINGS— ANIMALS Left: Robert C. Hermes; right: Dacle Thornton : both from National Audubon Society 8-7 POISONOUS OR NONPOISONOUS? Only one of these animals, the one with the coiled abdomen, is a true scorpion, and its sting is poisonous. The other animal is a harmless “whip scorpion.” CRAYFISH AND THEIR RELATIVES You must have seen the arthropods commonly called crayfish or crawfish, in some stream or shallow pond. They swim backwards. You might call them animals with “crusts." If you have ever picked up a crayfish, you probably grabbed his body just back of the claws, so he could not pinch you. If so, you were holding him near where the neck would be, if he had one. But he doesn’t. Instead, his head is joined right to his thorax, and a single “shell" covers them both. Lobsters are like the crayfish in this respect. Neither animal has a neck. You will remember that the head of a spider is also fused to the thorax. These fused body regions form the cephalothorax (sef uh loh thor aks), from cephalo meaning “head” and thorax. The exoskeleton and the class name The crayfish and lobsters and their relatives have hard, shell-like exoskele¬ tons. Epidermal cells secrete lime salts into the outer layer of cuticle. The lime salts make the exoskeleton hard, even as lime salts make your cndoskeleton (“inside” bones) hard. This class of ar¬ thropods gets its name from its body covering. The class name is Crustacea (krus tay shih uh), from crusta mean¬ ing “shell.” The name is an easy one to remember, too. Arthropods with crush) shells are crustaceans. Variety among crustaceans The crustaceans are the only arthro¬ pods with two pairs of antennae. Al¬ though most of them live in the oceans, a number of species besides the cray¬ fish live in fresh water, and a few spe¬ cies, like the sow bug, live in moist places on land. The crayfish and espe¬ cially the lobsters are giants among crustaceans. An occasional lobster at¬ tains a weight of over 30 pounds. But most of the 25,000 known species of crustaceans are a mere half-inch long or less. The crustaceans include water fleas, sow bugs, shrimps, and crabs. Barna¬ cles are crustaceans, too, although full- grown ones look more like mollusks. You have to see the young larvae of barnacles, before they have settled down on the keel of some ship or on the underwater parts of an ocean pier (or on a fellow crustacean— an old lobster) to recognize them as crustaceans. ANIMALS WITH JOINTED LEGS 213 The lobster The crayfish is so much like the lob¬ ster that you may study either animal, whichever is available. The lobster s body has 21 segments, but you cannot see those in the cephalo- thorax when you look at its dorsal ( up¬ per) side, as you can tell by looking at the upper side of the lobster in Figure 8-8a. You can see the seven segments in the abdomen distinctly, from above. You can see some of the 14 segments that are fused in the cephalothorax if you look at the ventral (lower) side, especially the eight segments of the thorax body region. On all but one of its body segments, a lobster has a pair of appendages; that is, a pair of legs or sense organs or chewing organs or swimming organs. The lobster’s appendages show how or¬ gans as different as antennae, jawlike mandibles ( man duh b’ls ), pincers, walking legs, and swimmerets (Figure 8-8a and b) can develop from append¬ ages that look much alike in the lobster larva. Refer often to Figure 8-8 as you do the following activities. EXAMINING THE LOBSTER (OR CRAYFISH). If you have a living crayfish, put a specimen in a shallow pan of water where you can watch it. Which parts of the body seem to "push" the animal backward? forward? Touch one eye with your pencil. What hap¬ pens? Take hold of the animal just back of the pincers and pick it up. With a tooth¬ pick or tweezers, place a bit of ground beef near the mouth appendages and watch what happens. Examine a preserved specimen of a lob¬ ster or crayfish. Look for the different kinds of appendages. Are the appendages on the ventral or dorsal side? Remove and sketch one of each pair, if you wish. Iden¬ tify the antennae, pincers, walking legs, and swimmerets. (You may identify other appendages, if you wish, by referring to pages 573 and 574 in Life by George Gay¬ lord Simpson et a/., Harcourt, Brace, 1957 —or any college zoology textbook.) Carefully remove the "shell," called the carapace (KAIR uh payss), from the cepha¬ lothorax. Then examine the exposed gills. Next lay the gills aside by rotating them downward to the ventral part of the body. Then make a careful incision immediately above the gills, into the side wall of the cephalothorax. Pull the side wall upward from the line of incision and finish cutting it away. Try to locate as many internal organs as you can, using Figure 8-8 as a guide. Look especially for the heart, stom¬ ach, liverlike digestive glands, and green glands. Remove the stomach and cut it open. Inside, look for the sharp, chitinous teeth that finish the chewing begun by the jaw appendages. Make a dorsal slit through the shell over the abdomen. Then trace the intestine back through the abdomen to the anus. In your record book, draw a map of the body plan of a lobster (or crayfish), as it would look cut open lengthwise and viewed from the side. Locate and label as many parts as you can. Body plan of a lobster The lobster’s body is like an anne¬ lid’s, in some ways. As in the earth¬ worm, the “brain” is dorsal (the dorsal ganglion), and the nerve collar joins it to the ventral nerve cord. But the lob¬ ster has eyes— compound eyes (Figure 8-9). The eyes are on stalks and can be raised and lowered, a bit like a peri¬ scope. The lobster also has two pairs of antennae. In these and other ways, the nervous system is an improvement over that of an earthworm. 214 VARIETY AMONG LIVING THINGS— ANIMALS I *- Pericardia! cavity Dorsal ganglion c . Stomach Heart Testis Carapace Muscles Intestine Mouth Ventral nerve cord Arteries BLUEPRINT OF A CRUSTACEAN -LOBSTER Photo from American Museum of Natural History 8-8 It is the lobster’s muscular system that people sometimes eat. And the “lobster tail” that restaurants serve is not a tail at all, but the lobster’s abdomen! Muscles virtually fill the abdomen as well as the pincers, legs, and swimmerets; the body wall is also muscu¬ lar. Both the muscular and skeletal systems are far more complex than those of lowlier animals; the jointed skeleton can be moved in many ways by the muscles attached to its inner surfaces. Lobsters and other arthropods have jointed exoskeletons, just as verte¬ brates have jointed endoskeletons. In general, the lobster’s other organ systems are easily traced here (except for the respiratory system). Parts of its body that have been cut away are its shell, gills, body wall, one of the two excretory green glands, one of the two digestive glands, and one of the two testes. (The gills lie on either side of the body, be¬ neath the carapace but outside the body wall.) One question remains: where is the lob¬ ster’s coelom? Surprisingly enough, it is almost nonexistent— restricted chiefly to small cavities of the testes (or, in a female lobster, the ovaries). Neither pericardial cavity nor body cavity is a true coelom (parts of the body cavity not otherwise occupied serve as blood sinuses) . 8-9 COMPOUND EYE OF A LOBSTER The lobster’s two compound eyes are in reality rounded clusters of many thousands of tiny eyes, each with a very narrow field of view. When the lobster looks at something, it takes many thousands of fragmentary “looks' at once. Compound eyes do not get as clear a total image as, say, the rounded individual eyes of man. But since movements are recorded successively in every unit of each of the lobster’s eyes, the slightest motion of enemy or prey is detected. The lobster has a heart and blood vessels (Figure 8-8b). Its blood vessels carry blood away from the heart, but not back to it. The ends of the smallest arteries open into cavities in the tissues. These cavities serve as blood sinuses and make you think of the blood sinuses of a clam. From the blood sinuses, the blood works its way to the 20 pairs of gills, where it picks up a new supply of oxygen. Through several channels leading from the gills, the blood passes back to the pericardial cavity (a cavity around the heart). From the pericar¬ dial cavity (Figure 8-8b), the blood enters the heart through three pairs of slits. The lobster has an open, not closed, circulatory svstem. 7 J J The lobster’s stomach lies in its head, right above its mouth (Figure 8-8b). Its single pair of “kidneys’’ is in its head, too. The kidneys are not highly specialized organs and are better called the green glands. Reproduction in lobsters A lobster is either a male or a female. A female has a pair of ovaries, which are the egg-making organs. A male has a pair of testes, which are the sperm¬ making organs (Figure 8-8b). When a male and female mate, the male depos¬ its sperms near the openings through which the female lays the eggs. Just after it emerges from the female’s body, each egg is fertilized by a sperm. The eggs hatch into larvae that look a good deal like adults except for the appendages. The larvae go through a series of changes (the process of meta¬ morphosis) as they grow up. Level of organization in the lobster Lobsters have a highly protective, “crusty” exoskeleton, hardened with lime salts. They have much the same J general body plan as the annelids: bi¬ lateral svmmetrv, dorsal and ventral sides, and anterior and posterior ends; 216 VARIETY AMONG LIVING THINGS— ANIMALS a ventral nerve cord and a dorsal gan¬ glion (the “brain”); and a food tube running from mouth to anus. Their coe¬ lom, however, is almost nonexistent. (See the caption for Figure 8-8.) In many ways, the body of a lobster is more highly specialized than that of an annelid, and much more specialized than that of animals that are below annelids in complexity. A lobster has specialized sense organs (compound eyes and two pairs of antennae ) , a jointed exoskeleton, many pairs of ap¬ pendages, including antennae, “jaws,” pincers, walking legs, and swimmerets. More specialized parts include a respir¬ atory system of 20 pairs of gills, sepa¬ rate muscles attached to the inside surfaces of the exoskeleton, grinding “teeth” in the stomach, an excretory system with a pair of green glands or “kidneys,” an open circulatory system with a heart, specialized digestive glands, and male and female glands (ovaries and testes ) in separate indi¬ viduals. Summing up: crustaceans List the numbers of the following statements. Beside each number, write the letter of the phrase that best com¬ pletes that statement. 1. The only arthropods with two pairs of antennae are the: (a) arach¬ nids, (b) crustaceans, (c) insects, (d) myriapods. 2. The lobster’s green glands are used primarily in: (a) circulation, (h) digestion, (c) excretion, (d) respira¬ tion. 3. The lobster’s stomach lies: (a) dorsal to its mouth, (b) on the left side of its mouth, (c) on the right side of its mouth, (d) ventral to its mouth. 4. The lobster’s blood takes on a fresh supply of oxygen while passing through the: (a) blood sinuses, (b) gills, (c) swimmerets, (d) veins. 5. The lobster’s blood enters the heart through: (a) arteries, (b) capil¬ laries, (c) three pairs of slits, (d) veins. THE INSECTS Last but far from least comes the in¬ sect class of arthropods, Insecta ( in sek tuh). As you already know, the insects far outnumber all the rest of the ani¬ mals in the world, both in the number of individuals and species. You can find one or more species of insects suited to live in almost every conceivable place, from the hide of a cow or the stomach of a horse to the wooden beams of a barn or the rain barrel under a spout, or even in a can of flour. Most insects are not bugs Most people who have not studied biology call all insects “bugs.” They call spiders “bugs,” too. You already know that spiders are not “bugs.” Nei¬ ther are most insects. All bugs are in¬ sects, but not all insects are bugs. Far from it. Actually, the true bugs make up only a fraction of the insect popula¬ tion. You may never have seen a true bug in your life. You will learn, how¬ ever, to tell an insect from other arthro¬ pods, and a true bug from other in¬ sects. What is an insect? A grasshopper is a common insect, easy to collect and easy to study. From a grasshopper, you can learn how to identify an insect when you see one. It will help if you have a grasshopper to look at as you read on. Refer also to Figure 8-10. A grasshopper has a movable head. You can see its three body regions— ANIMALS WITH JOINTED LEGS 217 head, thorax, and abdomen. It has th ree pairs of jointed legs. It has one pair of antennae. All insects have these three body features. A grasshopper also has wings, at¬ tached to its thorax. So do nearly all other insects. A grasshopper breathes through sev¬ eral pairs of small holes, one pair in each segment of its abdomen. These O holes are spiracles ( spy ruh k’lz ) . ( See Figure 8-10a. ) Air enters through the spiracles and is “piped” all over the body through air tubes, or tracheal (tray kee ul ) tubes (Figure 8-10c), if you prefer the technical name. Most insects breathe through spiracles and tracheal tubes. EXAMINING A GRASSHOPPER. Look first for the three body regions— head, thorax, and abdomen. Examine the thorax. How many segments can you count? The wings and legs are at¬ tached to the thorax. How many of each do you find? Examine the wings. Remove the wings and look for the oval "eardrum" on the first segment of the abdomen. Look for the two spiracles on each segment of the abdomen. Loosen one spiracle and pull it out. Part of the tra¬ cheal tube should come with the spiracle. Mount and examine under low power. What holds the tracheal tubes open? Use a hand lens to examine one of the two compound eyes, and to locate the three simple eyes of the grasshopper (Figure 8-10a). If you wish examine a prepared slide showing a bit of the surface cut from a compound eye, or make a slide of your own and examine it. Study Figure 8-1 Ob. Then carefully make a ventral slit through the body wall of a preserved grasshopper and spread the body open. Using Figure 8-1 Ob as a guide, try to trace the food tube from mouth to anus, and the central nervous system from the dorsal ganglia ("brain") to the abdo¬ men. Refer to Figure 8-10c. Can you find internal parts of your specimen's respiratory system? In your record book, draw a map of the body of a grasshopper as seen from one side. Indicate on this map the location of these parts: compound eye, head, thorax, abdomen, leg and wing attachments to the thorax, mouth, anus, segments of ab¬ domen. Sketch also a spiracle and part of a tracheal tube. Grasshoppers come from eggs, fer¬ tilized by sperms from the male and laid in the ground by the female. New¬ ly hatched young grasshoppers look somewhat like small adults with al¬ most no wings (Figure 8-11). They are called nymphs. The nymphs eat. Then they molt ( shed the exoskeleton ) , grow rapidly, and form a new exoskeleton. Now the wings are visible but small. These nymphs eat and grow rapidly; then they shed the exoskeleton again. Then more growth follows. When the new exoskeleton forms, the wings are longer than before, but not yet full length. Grasshopper nymphs molt five times. After the fifth molt, the adult emerges with full-length wings. A goodly number of insects besides the grasshopper also undergo meta¬ morphosis with three stages— egg, nymph, and adult. Among them are the crickets, walking sticks, dobson flies, all true bugs, scale insects, plant lice, and cicadas ( sih kay duhz ) , often wrongly called seventeen-year “lo¬ custs.” Most insects, however, pass through four stages in their metamor¬ phosis. Moths and butterflies are good examples. So are flies, mosquitoes, wasps, ants, bees, and beetles. You will learn about these four stages later. 218 VARIETY AMONG LIVING THINGS— ANIMALS Photo by Charles Halgren Head Thorax Abdomen Excretory tubules Eggs in reproductive glands Anus Antennae Simple eyes (Hearing organ- Gullet Nerve collar Chewing mouth parts v enirai nerve cord Muscle intestine Small intestine Dorsal ganglia Crop Air sacs Dorsal I tube Spiracles Appendages to stomach (digestive Pericardial cavity - entral tracheal tube 8-10 Like the lobster (Figure 8-8), the grasshopper has a jointed exoskeleton to which muscles are attached from the inside. But its muscular, skeletal, and nervous systems are even better developed than those of the lobster; for example, it can jump fast and far. Two other of its features are shared by many insects: oxygen is delivered to body cells mostly by tracheal tubes, very little by blood; and the excretory tubules excrete their wastes (picked up from blood in the body cavity) through the intestine and anus, not through a separate passage. The point to remember now is that almost all insects undergo metamor¬ phosis. So what is an insect? It is an arthro¬ pod showing these features: 1. Three pairs of jointed legs 2. Three distinct body regions— head, thorax, and abdomen 3. One pair of antennae 4. Eyes ( usually both compound and simple ) 5. Wings (with a few exceptions) 6. Spiracles and tracheal tubes (with some exceptions ) 7. Metamorphosis (with a few rare exceptions ) Variety among the insects Insects are alike in several general ways, but they differ in nearly every 8-11 GRASSHOPPER NYMPHS Unlike the young of many other insects, a grasshopper is a grasshopper, whatever its age. detail. Some insects, like the beetles, have hard, shell-like top wings. Some, like the moths and butterflies, have large, beautifully colored wings. Some, like the Hies and bees and wasps, have clear, membrane-like wings. A few, like certain female roaches, have almost no wings at all. Insects vary in many other features besides their wings, but the type of wings an insect has helps to classifv it in its correct order. (You may remember that classes are divided into orders in our system of classification. ) Taxonomists list some 20 orders of insects. If you learn to recognize in¬ sects of eight or nine orders, you will be able to classify in their correct or¬ ders nearly all the insects you are likely to find. Here we shall discuss briefly nine of the orders of insects. These nine orders include most of the insects you are likelv to find and want to identify. The J J technical names of these nine orders are included here for your convenience. By using the classification summary on pages 227-228, in addition to the text description of these orders, you can usually identify the order of an insect. Then you can turn to a technical refer¬ ence book on insects ( several are listed at the end of this chapter), look up the name of the order in that book’s index, and leaf through the pages devoted to that order. Often vou will be able to J identify the genus or even the species of your specimen from the illustrations in your reference book. Butterflies and moths Butterflies and moths make up one of the many orders of the insect class. You can tell them by their wings. Examine one of their wings under a hand lens or under the low power of your micro¬ scope. You will see why they are called 220 VARIETY AMONG LIVING THINGS— ANIMALS George A. Smith 8-12 METAMORPHOSIS OF A BUTTERFLY The monarch butterfly begins life as a lightly striped egg (shown greatly enlarged), but soon hatches into a wormlike larva. Under¬ neath its larval skin, the larva begins secreting a tough pupa case, then one day hangs from a leaf or twig and sheds its skin to become a pupa. Later still, the pupa case is broken open from within, and the butterfly emerges. the scaly-winged order. The technical name of this order is Lepidoptera (leh pih dop ter uh), meaning “scaly wings.” The mouth parts of a moth or but¬ terfly are elongated into a hollow tube. With this mouth tube, one of these in¬ sects may suck nectar from flowers in somewhat the same way you suck a soda through a straw. When the tube is not in use, it is carried in a coil under the head. In some of the species in this order, the mouth tube is never used. Some moths and butterflies never eat a thing, O7 but live just long enough to mate and lay eggs, perhaps a day or two. Then they die. The eggs of a moth or butterflv do not hatch into moths or butterflies. They hatch into little animals that look like segmented worms with feet and spiracles. Of course they are not worms, but larvae. The larvae eat almost stead¬ ily and grow rapidly. When full size, the larvae of many moths spin cocoons. Inside its cocoon, each larva then en- ANIMALS WITH JOINTED LEGS 221 cases itself in a tough coat and becomes a pupa (pYOopuh). In due time, the adult moth emerges from its pupa case and cocoon. The larvae of butterflies (Figure 8-12) and some moths do not spin cocoons, but simply make pupa cases, from which the adult emerges later. So the stages in the life history of these insects are: (1) the egg, (2) the larva, ( 3 ) the pupa, and ( 4 ) the adult moth or butterfly. It would be hard to believe that a larva like the one in Figure 8-12 could possibly turn into the butterfly in the same picture, if you did not know that it does. The change is complete, or looks to be. So we call this a complete metamorphosis, in coqtrast to the in¬ complete ( or three-stage ) metamor¬ phosis in grasshoppers and some other insects. Adult moths and butterflies are harmless, short-lived insects. Some are useful, for they carry pollen from flower to flower as they sip nectar. In many plants, this transfer is necessary if fruits and seeds are to form. But the larvae of many of these in¬ sects are injurious, some in one way, others in another. The larvae of clothes moths eat holes in woolen garments. The “worm” in an apple is the larva of the codling moth. The larvae of both gypsy moths and tent caterpillar moths eat the leaves off trees. “Army worms’ and corn borers are larvae of moths. And these are only a few of many ex¬ amples. The larva stage in the meta¬ morphosis of the scaly-winged insects is the destructive one. You won't have any trouble in recog¬ nizing most adult moths and butterflies, but their larvae are often hard to iden¬ tify. Beetles You can tell most beetles by their wings (Figure 8-13), although a few are wingless. In a typical beetle, the top or front pair of wings forms what looks like a hard shell or sheath that fits down over part of the thorax and all of the abdomen. The second pair of wings is folded underneath the “shell” or sheath wings. Beetles have chewing mouth parts. In the weevils or snout beetles, these mouth parts are on the end of the snout. The technical name of this order is Coleoptera ( koh lee op teruh), meaning “sheath wings.” Two out of every five species of in¬ sects are beetles. That makes some 260,000 species. Of these, a great num¬ ber are injurious. Nearly everything useful to man, from leather and car¬ pets to solid wood, is attacked by some 8-13 BEETLES Body shapes of beetles vary. Left. The ladybird beetle is short and squat. Note the curved sheath wings. Right. The ground beetle is long and slender, but it, too, has curved sheath wings. Nearly all beetles have distinctive outer wings. Roche kind of beetle. The mere names of a few of the many destructive beetles will give you some idea of the ways in which they interfere with human ac¬ tivities and welfare: carpet beetles, wood borers, bark beetles, rose beetles (not “bugs”), leaf beetles, cotton boll weevils, bean weevils, alfalfa weevils, potato beetles, and blister beetles. Some beetles are useful. The lady¬ bird beetles (Figure 8-13) are one ex¬ ample. They are natural enemies of the insect pests known as mealy “bugs,” scale insects, and plant lice. If you have done any gardening or helped take care of the shrubbery and trees around your home, you know that plant lice and scale insects attack almost any kind of plant. Ladybird beetles feed on these harmful insects, helping in this way to keep their numbers down. About 1868 the cottony-cushion scale insect was accidentally imported into California from Australia. It attacked the orange trees. By 1890 hundreds of thousands of trees were dead, and it looked as though every orange grove in the state would be wiped out. In Cali¬ fornia this scale insect had no natural enemies. The native ladybird beetles let it strictly alone. Workers from the United States Department of Agricul¬ ture were sent to Australia to look for its natural enemies there. They found that an Australian ladybird beetle kept the scale insects in check there. So the scientists imported some of these bee¬ tles and turned them loose on a few infested orange trees in California. In a comparatively short time, those im¬ ported beetles had spread over the whole state and saved the orange¬ growing industry. In this case, man deliberately used a natural enemy to control a pest. This is called biological control. Today some 24 insect pests in various countries have been brought under at least par¬ tial control by this method. Some beetles are scavengers; that is, they eat dead and decaying materials. Water scavenger beetles and carrion beetles are examples. The “fireflies” are not flies but beetles, and the “glow worms” are larvae of beetles. No other order of living organisms, plant or animal, is so numerous or varied as that of the Coleoptera. Bees, wasps, and ants These insects are perhaps best known by their stings. But biologists know them as the membrane-winged order. Look at their wings and you will see why. The technical name of this order is Hymenoptera ( hy men op ter uh ) , meaning “membrane wings.” The Hy¬ menoptera have chewing mouth parts, or chewing and lapping mouth parts. They undergo a complete metamor¬ phosis. Many of them live in colonies (beehives are an example) and are called social insects. Others are soli¬ tary; that is, they live alone. Of all the many orders of insects, the Hymenoptera are probably the most useful to man, although there are harm¬ ful species in this order, too. Bees are especially useful. For one thing, they make honey. For another, they carry pollen from flower to flower. Apples and many other fruits would be scarce indeed, if bees did not carry the pollen from blossom to blossom. Red clover forms almost no seeds at all unless bees visit its flowers. It has been estimated that pollination by bees is some 20 times more valuable to man than their honey-making is. Other insects carry pollen, too, but bees are especially useful in this re¬ spect. As the late Dr. Frank Lutz, then ANIMALS WITH JOINTED LEGS 223 of the American Museum of Natural History, put it, you would have almost no fruits and very few vegetables for your table and no cotton or linen “shirts for your back,” if it were not for pol¬ lination by bees and other insects. Among the Hymenoptera, too, there are many natural enemies of insect pests. The ichneumon (ik nyoo m’n) wasps, often mistakenly called “flies,” and several other wasps lay their eggs in the skin of the larvae of insect pests. The wasp larvae eat out the insides of the host larvae and then form pupas, often with cocoons, on the skin of their hosts (Figure 8-14). These wasp lar¬ vae are useful parasites. Bees and ants and some wasps are social insects. For example, thousands of bees live together in a colony. The work is divided amonc; various indi- viduals. In a bee hive, there is one queen. She mates once with a drone (a male bee). From then on, the drones are useless. The queen does just one 8-14 INSECT AGAINST INSECT The small cocoons on this dying larva of a sphinx moth contain wasp pupas that a short time before were themselves larvae— parasitic ones that fed on the body tissues of the sphinx moth larva. There will be wasps, but no sphinx moth. Tom Eberwein thing— she lays eggs. Most of the bees in the hive are workers (females that never grow up). Some of the workers feed the larvae in the cells of the comb. Others collect nectar and pollen from flowers. With their wings, still other workers fan the water out of the nectar placed in the comb, changing that nec¬ tar slowly into honey. This is something like boiling the water out of a sugar mixture to make fudge. In these and other ways, the work of the colony is divided among its members. A similar set-up is found in the colonies of the other social insects. Termites Not so many years ago on a farm in Pennsylvania, the kitchen stove fell through the floor. The farmer examined the floor boards. He found that ter¬ mites had tunneled through the insides of the boards until they were no longer strong enough to support the weight of the stove. That family had a difficult problem on its hands. Termites are hard to get rid of, as you may know. Termites belong to the order called Isoptera (eye sop ter uh), meaning “equal wings.” They are interesting in¬ sects, in spite of their destructiveness. In our country, there are some 57 spe¬ cies of them, but they reallij thrive in the tropics. There, some species build termite nests as high as 12 feet. Like ants and bees, they are social insects. They live in colonies. Often there are a million or more termites in a eolonv. J And all of them are the offspring of the same mother, the queen. Within the termite colony, there are several kinds of individuals (Figure 8-15): kings and queens, workers, and soldiers. Only one king and one queen are functional. The others are reserves. The queen is huge compared to the Drawings: a, b after Herms; c, d after Snyder; winged termite after Herms, from College Zoology, by R. W. Hegner, The Macmillan Co. Photo from E. L. Bruce Co., Memphis 8-15 TERMITES These insects live in colonies and are highly specialized within a species. (The unusual woodcut is no thing of art; it was done by workers and soldiers.) other termites. The king is smaller than the queen. The workers and soldiers are still smaller and are colorless (you can tell the soldiers by their huge jaws). The king and queen do nothing except take care of reproduction. They can’t even feed themselves or digest their own food. The queen is just an egg¬ making machine. After mating, she lays eggs at the rate of one a second. In some species, she keeps this up for as long as 30 years. All the while an army of workers keeps stuffing predigested food into her mouth. Another army of workers carries away the eggs as they are laid. The eggs are placed in cham¬ bers in the nest, where they hatch into nymphs. The workers feed the nymphs until they are mature enough to take their place in the colony. Termite workers and soldiers eat wood and paper, but they can’t digest them. At least, some species can’t. How¬ ever, living in the food tubes of these termites are certain flagellates. These flagellates can digest the cellulose in wood and paper. They break down its molecules into simpler ones that can be used as food both by themselves and their termite hosts. So the termites help the flagellates by serving as their home and bringing them a supply of wood. The flagellates help the termites by di¬ gesting cellulose. This makes it incor¬ rect to call the flagellate a parasite. Parasites do not benefit the host. The termites and flagellates help each other. They are called symbionts (sim bee onts ). The relationship of the two organisms is called symbiosis (sim bee oh sis), from a word meaning “liv¬ ing together.” Symbiosis is quite widespread among the living things of the world. Many different species live together intimate¬ ly and help each other. Look up ants and their “cows” (plant lice), or ter¬ mites and the way they grow a crop of fungus, and report in class. You will find these and other examples discussed under “symbiosis” in encyclopedias and in college biology and zoology texts. ANIMALS WITH JOINTED LEGS 225 Other insect orders The grasshoppers ( also correctly called locusts), crickets, katydids, walking sticks, and praying mantises belong to an order called the Orthop- tera ( or thop ter uh ) , meaning “straight wings.’’ The cicadas, mealy “bugs” (not true bugs), scale insects, and plant lice belong to an order called Homoptera (hoh mop ter uh ), meaning “similar wings.” The true bugs can be told by their wings and sucking mouths. The front half of a bug’s top pair of wings is hardened, giving them the effect of be¬ ing only “half-wings.” The sucking mouth of a true bug is prolonged. When not in use, the bug carries this pro¬ longed, sucking mouth folded back be¬ tween the two front legs. The name of the order of the true bugs is Hemiptera (heh mip ter uh), meaning “half-wings.” The order called Odonata ( oh doh nay tuh ) contains the dragonflies and the damsel flies. These are not true flies. True flies, gnats, and mosquitoes make up the order called Diptera (dip teruh), meaning “two wings.” Insects of the Diptera order have only two wings (one pair) or, in some species, no wings at all. Some species of the Diptera are notorious for carrying dis¬ ease germs. For instance, certain mos¬ quitoes carry malaria germs, and others carry yellow fever virus. An African fly carries the protozoon that causes Afri¬ can sleeping sickness. And house flies carry any number of germs. The war¬ bles of cattle and the bots of cattle and sheep are larvae of flies. Summing up: the insects You can tell an insect from other ar¬ thropods by its three pairs of legs, its three distinct body regions, and by its one pair of antennae. You can tell the orders of most in¬ sects by their wings, although this is sometimes difficult to do. Insects live virtually everywhere. They are the most successful animal class on earth, if judged by their num¬ bers and wide range. Insects are our greatest natural ene¬ mies; they compete with us for food, for forests and their products, for cot¬ ton and the hides of animals, and for virtually every other useful thing around us. And yet our life, as we live it, couldn’t go on without the useful in¬ sects, those that pollinate flowers and those that help us in the biological con¬ trol of harmful insects and other pests. Insects illustrate metamorphosis more fully than any other animals. Most insects pass through four stages: egg, larva, pupa, and adult. These four stages constitute a complete metamor¬ phosis. Other insects undergo an in¬ complete metamorphosis, having only three stages: egg, nymph, and adult. CHAPTER EIGHT: SUMMING UP To get a brief review of all the ar¬ thropods you have studied in this chap¬ ter, and to see all the main classes ( and the orders of insects) in their proper perspective, read through the illustrated classification summary on the next two pages. Here, too, you will get a chance to see all the technical names in a sum¬ marized list that will help you distin¬ guish them. Do not bother to try memorizing the technical names of the orders of insects unless you plan to go further in biology or, perhaps, make an insect collection. But do use the classification summary and the reference books listed at the end of the chapter to help you identify the insects you have already collected for your classroom work. 226 VARIETY AMONG LIVING THINGS— ANIMALS PHYLUM ARTHROPODA - ■ .v. >■;. > s-~y The arthropods (ar throh podz) are ani- • mals with segmented bodies, three or more . pairs of jointed legs, and jointed exoskele¬ tons to which highly specialized muscles are attached from the inside. Nearly all of • J the arthropod body systems are more complex than those of any animals of lower phyla ( an exception is the open circulatory * system). Arthropods number about 750,- • 000 species (many no longer living), and they are found on land, in the air. and in fresh and salt water. • • Class 1. Myriapoda ( mihr ee AH poll duh ) . Elongated, many-segmented arthropods with one or two pairs of legs per segment; • respiration by means of tracheal tubes. Ex¬ amples: millipede (Figure 8-16), centi¬ pede (Figure 8-5). • Class 2. Crustacea ( krus TAY shih uh ) . • Arthropods with two pairs of antennae and a hardened exoskeleton; respiration usually by means of gills. Examples: true crabs * (spiny spider crab, Figure 8-17), lobster . (Figure 8-8), shrimp (Figure 8-4), cray¬ fish, barnacle, water flea. Class 3. Arachnida ( uh RAK nih duh ) . * Arthropods with no antennae and four • pairs of legs; respiration by means of tracheal tubes or “book lungs.” Examples: spider ( Pholcus , 8-18; black widow. Fig- • ure 8-1; tarantula, Figure 8-6), scorpion # (Figure 8-7), king crab, tick, mite. Class 4. Insecta (inSEKtuh). Arthropods with one pair of antennae and three pairs • of legs; respiration by means of tracheal # tubes. The insects. Some common orders and their usual characteristics are: Order Orthoptera (or THOP ter uh ) . Two • pairs of wings, the outer pair straight and thickened; chewing mouth parts; incom¬ plete metamorphosis. Examples: cricket • (Figure 8-19), grasshopper (Figure 8-10), . praying mantis (Figure 8-2), cockroach. Order Isoptera (eye sop ter uh ) . No wings or two pairs of long, narrow wings, equal « in size, lying flat on back; chewing mouth parts; incomplete metamorphosis. Ex¬ ample: termite (Figures 8-20 and 8-15). • (continued on next page) Photos top to bottom: Hugh Spencer : Douglas P Wilson: Hugh Spencer : Hugh Spencer; Hugh Spencer 8-20 8-19 8-18 8-17 8-16 8-25 8-24 8-23 8-22 8-21 Order Odonata ( oh doh NAY tuh ) . Two similar pairs of wings; chewing mouth parts; incomplete metamorphosis. Exam¬ ples: dragonfly (Figure 8-21), damsel fly. Order Hemiptera (hell mip ter uh) . No wings or two pairs of wings with outer pair half hardened; piercing and sucking mouth parts; incomplete metamorphosis. Ex¬ ample: bugs (squash bug, Figure 8-22). Order Homoptera (hoh mop ter uh). No wings or two pairs of wings held arched together; piercing and sucking mouth parts; incomplete metamorphosis. Exam¬ ples: cicada (Figure 8-23), aphid. Order Coleoptera (koh lee OP ter uh ) . No wings or two pairs of wings, the outer pair a hard sheath; chewing mouth parts; com¬ plete metamorphosis. Example: beetles (rhinoceros beetle, Figure 8-24; ladybird and ground beetles, Figure 8-13). Order Lepidoptera (leh pill DOP ter uh). Two pairs of scaly wings; coiled sucking tube; complete metamorphosis. Examples: moth (hummingbird moth, Figure 8-25), butter¬ fly (monarch butterfly, Figure 8-12). Order Diptera (dip ter uh) . No wings or one pair of wings; piercing and sucking mouth parts; complete metamorphosis. Examples: housefly (Figure 8-26), mosquito. Order Hymenoptera (hy men OP ter uh). No wings or two pairs of wings, hooked to¬ gether; chewing and sucking mouth parts; complete metamorphosis. Examples: bee (bumblebee, Figure 8-27), ant, wasp. I hot os top to bottom, left: Roche; Hugh Spencer; George A. Smith; Maslowski and Goodpaster, from Na¬ tional Audubon Society; Roche; right: Hugh Spencer; Roche 8-27 8-26 Your Biology Vocabulary You have met many new terms in this chapter. Most of them will be repeatedly useful to you. Those printed below are the ones you are most likely to use often. arthropods chitin spiracles antennae biological success tracheal tubes thorax biological control nymph abdomen myriapods pupa exoskeleton insects cicadas endoskeleton arachnids locusts larva crustaceans true bugs complete metamorphosis cephalothorax symbiosis incomplete metamorphosis green glands symbionts cuticle compound eyes testes Testing Your Conclusions 1. Make a list of five arthropods that may live in our homes. Then name the class of arthropods to which each one belongs. 2. Here is a list of arthropods that are used as food by one people or another. Name the class of arthropods to which each belongs. grasshoppers shrimp spiders large ants lobsters termites 3. Name several insects that help in the biological control of insect pests. 4. Many persons refer to the common insect enemy of potatoes as the potato bug. What should one call it? What is the order of this insect? 5. List four similarities in all insects. Then explain how to tell spiders and insects apart. 6. Here is a list of arthropods that have a cephalothorax. To which class does each one belong? black widow spider scorpion barnacle larva tarantula water flea tick or mite 7. In what way is each of the following names descriptive of the animals to which it refers? myriapods crustaceans centipedes scale insects arthropods grasshoppers More Explorations 1. Studying a centipede. If you can catch a centipede, place it in a glass jar and cover the jar with cheesecloth or a wire screen. Keep all parts of the jar evenly lighted ANIMALS WITH JOINTED LEGS 229 (why?) while you watch the animal. Is it ever still? After fifteen or more minutes, put a piece of glass tubing into the jar. The tubing should be of such a size that the centipede can just crawl into it. Now what happens? Explain the results. 2. Studying living grasshoppers. You can keep living grasshoppers in a wire cage. First plant some grass in a shallow pan and set the pan in the cage. Sprinkle the grass with water and repeat each day. Add two or three grasshoppers. You can learn much about the way they live by watching them. Try to find out how they drink. 3. Reporting on harmful insects. Choose any harmful insect that interests you. A list of suggestions below may help you, but choose one of your local insect pests, if pos¬ sible. Look up the insect in a government bulletin or in Insects: The Yearbook of Agriculture, 1952, U.S. Dept, of Agriculture, or in any other available reference book. Include in your report the life history of the insect, how to recognize the adult, and especially the ways in which it is harmful and the methods of control. cotton boll weevil codling moth gypsy moth Hessian fly potato beetle termites corn borer “armv worm housefly bean weevil silverfish ants Thought Problems 1. Many arthropods, including lobsters and grasshopper nymphs, can't grow without molting. Why? 2. A housefly lays about 150 eggs. About half of them (75) will have produced females in about two weeks. Assume that a female, soon after coming out of the pupa, lays 150 fertile eggs on June 1. Assume, too, that every egg hatches and that half pro¬ duce females on June 15, and that all these females lay 150 eggs (all of which are fertilized and hatch on July 1 ) . If this continues until September 15, how many flies will be produced on that date by the descendants of that one original pair of flies? 3. Specialists in insect control report that they often have letters asking how to kill off the ladybird beetles in gardens. What kind of reply would you make to such a letter? 4. A family that had recentlv moved into a new home found a large number of a certain organism in the kitchen. Two specimens were presented to a biology teacher for identification. The organism was a little over an inch long and dark brown in color. It had six jointed legs and four wings— all membranous. It had compound eyes and long antennae. What clues identify its phylum and class? 5. In the Southwest, little animals called solpugids (sol pyoo jids) are fairly common. A biology student caught one, put it in a glass jar, tied mosquito netting over the top, and brought it to class. The student took down a book on insects and leafed through it, looking at the illustrations. He found nothing that looked like his solpugid. Next he discovered that his animal had no antennae. Then he knew its class. What was the class, and how do you know? Further Reading 1. Poisonous spiders. Some of you may have access to Science Magazine, at home or in a library. If so, you may want to look up the article “Possible Cause of Necrotic 230 VARIETY AMONG LIVING THINGS— ANIMALS [tissue-killing] Spider Bite in the Midwest” on page 73 in Science, July 12, 1957, Volume 126, Number 3263. A few of the technical terms in the article may give you a little trouble, but an unabridged dictionary will help. You can get the general idea, in any case. 2. Can honeybees read ? In Frank E. Lutz’s book A Lot of Insects, Putnam, 1941, you will find a fascinating account of how Dr. Lutz made it look as if honeybees could read, with an explanation of how it was done. See also the diagram on page 189 in Life by George Gaylord Simpson et al., Harcourt, Brace, 1957. 3. Spiders. Gertsch’s American Spiders has already been mentioned (footnote page 208) and is listed under number 5 below, but it is worth further notice. Read these quotations and you may want to read more of this best-of-all books (for the general reader) on spiders. Page 1. “The spider can spin a line one-millionth of an inch in thickness.” Page 9. “It is rather generally believed that many cobwebs on the grass in the morning foretell clear weather.” Page 236. “In 1907, W. L. McAtee found approximately 11,000 spiders per acre in woodland and 64,000 per acre in a meadow near Washington, D.C.” 4. Insect oddities. One of the best short discussions of oddities among the insects is found on pages 8-14 of Insects: The Yearbook of Agriculture, 1952, U.S. Dept, of Agriculture. Here is one sentence: “If the mercury rises to 80°, the ice bug seems to suffer heat prostration.” Wouldn’t you like to read more? 5. Identifying arthropods. Here are some books to help you identify the arthropods that you see or collect. BOOKS FOR GENERAL USE: Animal Kingdom by George G. Goodwin et al., 3 volumes, (Greystone) Hawthorn, 1954. Life by George Gaylord Simpson et al., Harcourt, Brace, 1957. Parade of the Animal Kingdom, Imperial Edition, by Robert W. Hegner, Macmillan, 1953. General Zoology by David F. Miller and James G. Haub, Holt, 1956. General Zoology, Second Edition, by Tracy I. Storer, McGraw-Hill, 1951. BOOKS ON MARINE LIFE ( FOR CRUSTACEANS AND MARINE ARACHNIDS): Fieldbook of Seashore Life, by Roy W. Miner, Putnam, 1950. Seashores, by Herbert S. Zim and Lester Ingle, Simon & Schuster, 1955. books on insects: Collecting Cocoons by Lois J. Hussey and Catherine Pessino, Crowell, 1953. Field Guide to the Butterflies by Alexander B. Klots, Houghton Mifflin, 1951. The Insect Guide by Ralph B. Swain, Doubleday, 1948. Insects by Herbert S. Zim and Clarence A. Cottam, Simon & Schuster, 1956. Field Book of Insects, Third Revised Edition, by Frank E. Lutz, Putnam, 1935. book on spiders: American Spiders by Willis J. Gertsch, Van Nostrand, 1949. antmals with jointed legs 231 9 Animals with Backbones mart ij pe snakes ' are not A :: , are con ~ at al A rays reveal a skulk a jointed backbone , ribs, and even Y,--r-V T: 'ClY ./ -AbY ' _ lit plumes. Snakes are one group of the most complex of ail anirt mi Leake, from Natural History Magazine The most familiar animals You come now to the phylum in which the animals you know best are classified. In Phylum Twelve, taxono¬ mists classify all the animals that have backbones: trout, salmon, and other fish; frogs and toads; lizards, snakes, and turtles; birds; and last but by far the most complex, the animals with fur or hair and with milk for the young, like horses, cows, and dogs. For pur¬ poses of classification, man places him¬ self in the last, most complex group of animals. You will probably find this phylum the most interesting one of all. In this chapter, you will learn about the way the animals in Phylum Twelve are classified. At a later point, Chapter Eleven will discuss in some detail the complex body plans of the backboned animals, and how these animals carry out the basic life processes. Not all of the animals in Phylum Twelve have backbones. In other words, not all of them are vertebrates. Before we discuss the classification of the ver¬ tebrates proper, let’s look at the phy¬ lum as a whole, to learn the main char¬ acteristics of the animals of Phylum Twelve. THE PHYLUM OF THE VERTEBRATES Have you ever seen an acorn worm or a sea squirt or a lancelet? Probably not, since all of these animals live in the sea. They are neither very impor¬ tant to man nor very numerous. But they are interesting to biologists be¬ cause all of them have certain features that make it impossible to classify these little sea animals in any of the phyla of invertebrates ( animals without back¬ bones). At the same time, they lack 232 VARIETY AMONG LIVING THINGS— ANIMALS certain features found in vertebrates. For one thing, they do not have verte¬ brae (bones of the backbone). Actu¬ ally they have no bony tissue at all. So they can’t be classified as vertebrates. Puzzling features The acorn worms, sea squirts, and lancelets have two puzzling features: (1) they have a dorsal nerve cord, and (2) just below the nerve cord but still dorsal to the food tube, they have an elastic rod of tissue that supports the nerve cord and is the axis of the whole body. This supporting rod of tissue (Figure 9-1) is called the notochord (noh toll kord), from noto meaning “the back” or “dorsal” and chord mean¬ ing a “cord.” A notochord is a dorsal rod of supporting tissue. None of the animals in any of the phyla of invertebrates have notochords. In an embryo stage, all vertebrates have notochords, which are replaced in a later stage of growth by backbones made up of vertebrae. All vertebrates also have dorsal nerve cords, usually called spinal cords. Because of these two and some other features, biologists have classified the 9-1 Not all chordates are vertebrates. This little lancelet, for example, has no backbone, but a notochord— a dorsal rod of supporting tissue. (Notochords are probably primitive forerunners of backbones; vertebrate embryos have notochords that give way to bony vertebrae.) The lancelets gill slits are openings in the sides of its pharynx. Water is taken in by mouth and passed into the pharynx, where food particles are removed before the water washes out through the gill slits. Photo by Robert S. Bailey, Virginia Fisheries Laboratory BLUEPRINT OF A PRIMITIVE CHORDATE -LANCELET Segmented Tail fin Dorsal fin Notochord Dorsal nerve cord Dorsal fin rays Ar'fry Coel om Segmented muscles Tail fin Anus Mouth Pharynx Gill slits digestive gland Intestine Reproductive Vein glands Ventral fin Anterior end acorn worms, sea squirts, and lancelets in the same phylum as the vertebrates. The name of this phylum is Chordata (kor day tuh ) or the chordates ( kor dayts), from chord, as in the word noto¬ chord. You may recall that some 60,000 species of chordates are known. If you want to know more about the three groups of chordates without backbones, refer to the classification summary on pages 257-260, where you will find these three groups classified as the first three subphyla. Here we shall take a brief look only at the lance¬ lets ( the third subphylum ) . The lancelets Lancelets live near shore in the seas. The adults are never more than a few inches long (Figure 9-la). They can swim, but they spend most of their time buried in sand at the bottom of the water along seashores. These little animals get their name from their shape, which is somewhat like that of a doctor’s lance. Lancelets have many gill slits (Figure 9-lb); eye spots, but no true eyes; a hollow nerve cord that runs the full length of the dorsal side of the body, but no true brain (Figure 9-lb); a food tube with mouth and anus, and a true coelom. You may want to examine stained slides of a lancelet. You can also get an idea of their external features by exam¬ ining one mounted in plastic. Use Fig¬ ure 9-1 to help you. The vertebrates The fourth subphylum of chordates is that of the vertebrates. This subphy¬ lum is called Vertebrata (ver tuh bray tuh ) . You have been seeing vertebrates all your life. Not only that. The fish and meat you eat, the milk and other dairy products you use, the wool and leather used in your clothing, all these and many more useful things you get from vertebrates of one kind or another. Most important of all, you yourself are a vertebrate. So vertebrates call for special attention in your first course in biology. Classes of vertebrates Vertebrates vary a great deal among themselves, so much so that biologists have sorted this subphylum into seven or more classes. The lampreys (Figure 9-2) make up the first class, Cyclosto¬ mata ( sy kloh stoh muh tuh ) , or the jawless fish. Sharks and dogfish (Fig¬ ure 9-3) belong to the second class, Elasmobranchii ( uh las moh brang kee eye ) , or the cartilaginous ( kahr tih laj ill nus ) fish, so called because they have cartilage in place of hard, limy 9-2 LAMPREY The first class of vertebrates includes this so-called jawless fish. It is not only without jaws (it has a sucking mouth disc), but without true vertebrae. Its skeleton, including an incomplete cranium, is made up of cartilage. Lampreys are parasites; they attach themselves to, and suck blood from, the true fish. Robert S. Bailey, Virginia Fisheries Laboratory Douglas P. Wilson 9-3 DOGFISH A member of the second class of vertebrates, along with sharks, skates, and rays, the dogfish (actually any of certain small sharks that frequent shallow waters) has true bony vertebrae. The rest of its skeleton is mostly cartilaginous. bones. These two classes will not be discussed in detail, but are included in the classification summary on pages 257-260. Fish like salmon and cod and trout belong to the third class of vertebrates, the bony fish, so called because they do have limy bones. The technical name is Osteichthyes ( os teh ik thih eez ) . The frogs and toads and their relatives make up the fourth class, the Amphibia (am fib ee uh), or amphibians, so called because they live in water as tadpoles and on land as adults. Lizards, turtles, and snakes make up the fifth class, called the reptiles. The technical name of this class is Reptilia ( rep til ee 11I1 ) . The birds make up the sixth class of vertebrates. The technical name of this class is Aves ( ay veez ) . The seventh and last class is that of the mammals, or Mammalia ( muh may lee uh ) , in which all vertebrates with hair or fur and with milk for the young are classified. People are mammals. As you already know, you will study in some detail the body plans and the life functions of some vertebrates in a later chapter. Right now, make sure that you know the five classes of verte¬ brates that will be discussed. They are (1) the bony fish, (2) the amphibians, (3) the reptiles, (4) the birds, and (5) the mammals. In this chapter, vou will learn something about how animals are classified in these five classes. Level of organization in the vertebrates The vertebrate bodv shows the high- est level of organization in the whole animal kingdom, not because verte¬ brates have more organ systems than, say, the arthropods, but because they have far greater specialization within each organ system than do the animals in any invertebrate phylum. No other animals’ bodies come close to the com¬ plexity of the vertebrate body in such respects as, say, the nervous system or the circulatory system, to mention onlv two. Vertebrates have a large and well- developed central nervous system, con- ANIMALS WITH BACKBONES 235 sisting of the spinal cord and brain. No mere pair of large ganglia makes up the vertebrate brain, as it does that of an insect. On the contrary, the verte¬ brate brain is a large one with several specialized parts, as you will learn in a later chapter. And this brain is en¬ cased in a skull. Vertebrates also have well-developed and highly specialized sense organs, such as eyes that see ob¬ jects distinctly. The circulatory system is also com¬ plex, with a heart of two, three, or four chambers, arteries, capillaries, and veins— miles and miles of these blood vessels, in some vertebrates like man perhaps miles enough to reach around the earth several times. The muscular system is highly complex, too. So is the respiratory system and every other sys¬ tem, as you will learn in more detail in Chapter Eleven. For now, let’s get ready to take a look at each of the five common classes of vertebrates. Summing up: animals of Phylum Chordata Animals of Phylum Chordata have two characteristic features: (1) a noto¬ chord, at least in the embryo, and (2) a dorsal nerve cord. Three of the four chordate subphyla are interesting to biologists chiefly as possible links with the highest inverte¬ brate phyla. The fourth subphylum is that of the vertebrates, characterized mainly by having a backbone made of vertebrae, a skull containing a brain made up of several parts, and a high level of organization within each organ system. Vertebrates are sorted into seven classes, only five of which we shall dis¬ cuss in some detail. These five are the bony fish, the amphibians, the reptiles, the birds, and the mammals. THE BONY FISH Most of what you call fish belong to the class of the bony fish. Goldfish be¬ long here. So do carp, catfish, cod, mackerel, blue gills, salmon, and all trout. All these and many more are true fish, with bony skeletons. More than 3,000 species live in the lakes and streams of North America. This figure does not include our marine species. Altogether, some 40,000 species of bony fish are known. The habitat of fish Water is the home of the fish. They not only move and eat and grow and excrete wastes and lay eggs in the wa¬ ter, but they also breathe underwater. No other vertebrates can breathe un¬ derwater except the frogs and their rel¬ atives, and even they develop into lung- breathers when they become adults. (There are a few relatives of the frog that never leave the water, but these are exceptions. Other vertebrates, like whales, or some snakes and turtles that live in the water, must come to the sur¬ face to breathe. ) The pressure of water, even shallow water, is much greater per square inch than that of air. For this reason, water offers greater resistance than air does to any object that is moving through it. Even so, a fish seems to glide through the water with as much ease as a bird flies through the air. Watch a goldfish in a bowl. Its swimming looks almost effortless. You can see why. Its whole body is streamlined; this in itself re¬ duces resistance to a minimum. The fins and the tail are excellent means of loco¬ motion in the water. When you dive to the bottom of a pool, you have diffi¬ culty in staying down because your body weighs less than the amount of water you displace. Not so with your 236 VARIETY AMONG LIVING THINGS— ANIMALS £ goldfish. It can, almost automatically, raise or lower itself or remain station¬ ary, simply by increasing, decreasing, or keeping constant the size of the air bladder inside its body. In this way, the goldfish may weigh less than, more than, or an amount just equal to the weight of the volume of water it dis¬ places. Most fish are covered with scales. If you have ever caught fish and cleaned them, you know that the scales overlap toward the posterior end, in somewhat the way shingles overlap toward the eaves of a roof. This scale arrangement makes it easy to glide through the wa¬ ter. The scales also help to keep out the water; in other words, they keep the fish from getting “waterlogged.” You may remember that the contractile vacuoles of protozoa excrete extra wa¬ ter that gets into these one-celled ani¬ mals; the scales of fish help to keep water out of their bodies. Fish have no legs. But they do have fins. And their fins are their “oars.” Skin divers attach artificial “fins” to their feet and use them to push themselves through the water, much as fish use their fins. EXAMINING THE FINS OF A FISH. Watch a goldfish as it swims around in a bowl or aquarium. Try to find out which fins seem to propel it forward and which ones help it to guide and balance itself in the water. In your record book, draw the goldfish with its different kinds of fins and tell what each kind seems to do, in swiming. The gills of fish are excellently suited to underwater breathing, as you already know. Is it correct to say that fish “breathe water”? Do they get their oxy¬ gen from the water molecules ( FLO ) ? Douglas P. Wilson 9-4 SEA HORSES These strange little ani¬ mals are true bony fish of the third class of vertebrates. Their dorsal fins are not visible here, and the small fins at the sides of their “necks” are barely visible against their body coloration. Fish are highly successful water ani¬ mals, both in numbers and wide range of distribution in the earth’s waters. Oddities among the fish Among the queerest animals in the world are those which inhabit the deep sea. Many of the fish that live half a mile or more below the surface are equipped with lights and have huge eyes and dangerous-looking teeth. Sea horses are also most unusual ani¬ mals. Yes, they are fish— a mere five inches in length. The fins are fan¬ shaped and are moved much as a fan is. If you live near a city that has a large aquarium, it is worth a trip to the aquarium just to see the living sea horses (Figure 9-4). Perhaps the queerest fish of all are those called lungfish (Figure 9-5). ANIMALS WITH BACKBONES 237 Australian News and Information Bureau 9-5 LUNGFISH A few species of this once widespread type of fish survive today in South America, Africa, and Australia. They have gills, much as other fish do, but they also are able to breathe air, when out of water, using their air bladders as lungs. Only five species are now alive, a mere hangover of numerous species that “had their day” millions of years ago. The strange thing about a lungfish is that it can breathe air, using its air bladder as a lung. It also has gills and can breathe under water. The paired fins are of no use in swimming, but observ¬ ers report that the fins can be used in creeping over the mud. If a lake should begin to dry up, a lungfish buries itself in the mud, keeping a hole open to breathe through: Encased in this “co¬ coon of mud,” the lungfish passes the dry season, living on fat stored in its body. When the lake refills, the lungfish comes forth again into the water. Level of organization in bony fish The body of a bony fish shows great¬ er specialization— a higher level of or¬ ganization— than that of an acorn worm, a sea squirt, or a lancelet, but these fish are less specialized in several ways than amphibians, reptiles, birds, and mam¬ mals. You will learn more about the levels of organization among verte¬ brates in the next unit. Summing up: the bony fish The bony fish (Osteichthyes) are plentiful and varied in both fresh and salt water. Their bodies are well suited to life in the water. They are stream¬ lined. Their scales protect the inner tis¬ sues both from injury and from excess water absorption. The arrangement of the scales lets the animals swim easily J through the water. Other features that help fish to live in water are air bladders, fins, and gills. FROGS AND THEIR RELATIVES There are many kinds of frogs, even though vou may never have noticed the differences in them. As you probably know, frogs are tadpoles grown up. Tadpoles breathe under water by means of gills. Frogs breathe by means of lungs. In other words, frogs undergo a metamorphosis, from egg to tadpole to adult. Because they live part of their lives under water and part on the land, they are often said to live double lives. As you already know, that is why they are called Amphibia or amphibians, meaning “two lives.” You will study the body plan and life functions of a frog in Chapter Eleven. For now, all you need to remember is that true frogs (Figure 9-6) make up one large genus of amphibians and tree frogs another. 238 VARIETY AMONG LIVING THINGS— ANIMALS Relatives of frogs Toads make up still another large ge¬ nus of amphibians. They lay their eggs in water, as frogs do. The male fertilizes the eggs, just as they are laid. Toads also pass through a tadpole stage; that is, they undergo a metamorphosis. Two other kinds of amphibians, the newts (nyoots ) and the salamanders ( sal uh manderz), are common but may be less familiar to you (Figure 9-7). How¬ ever, you may have seen some of these creatures either in the water or under overturned logs or stones in the woods. If so, you may have called them lizards. This was a mistake, for lizards have scales and toenails, whereas newts and salamanders (and frogs and toads and all other amphibians ) have smooth, moist skins and no toenails. Superstitions about amphibians In the past, many people believed that handling toads would give you warts. This is not true. 9-6 WOOD FROG True frogs, such as this one (found in moist forests and woodland pools), several species of bullfrog, and the leopard frog, make up one genus of am¬ phibians, the fourth class of vertebrates. Hugh Spencer Many people still believe toads are poisonous to handle. In modern times, biologists have found that there are glands in a toad’s skin which secrete substances that are poisonous to ene¬ mies. The huge Colorado River toad, common in the Southwest, is an exam¬ ple of a toad having these glands. If a dog mouths one of these toads, the dog may become quite ill. But the secre¬ tions from a toad’s skin are not usually poisonous to human skin. Sometimes fishermen catch a water dog, also called a mud puppy, on their lines. It used to be their custom just to cut the line and discard hook, water dog, and all. The superstition was that these large salamanders were poison¬ ous, even to handle, but that isn’t true. Today, water dogs are sold to fisher¬ men as bait. If you have time in class, talk about some of the superstitions you have heard that have to do with frogs, toads, newts, and salamanders. Variety among the amphibians Less than 3,000 living species of am¬ phibians are known. But there is quite a bit of variety among; them. You can get an idea of the variety among the salamanders by leafing through the Handbook of Salamanders by Sherman C. Bishop, Comstock Pub¬ lishing Company, 1942. Dr. Bishop listed and described 126 species and subspecies of salamanders, all that were then known to occur in the United States, Canada, and Lower California. You will find pictures of water dogs, Congo eels, and hellbenders, all large and rather ugly salamanders, but all harmless to man. How many different kinds of frogs have you seen? Probablv the most com- mon one is the leopard frog, so called ANTMALS WITH BACKBONES 239 Hugh Spencer 9-7 NEWT AND SALAMANDER Actually, the newts, too, are salamanders— specifically, small salamanders that spend much of their time in water. Which is which above? from its spots. There are also wood frogs, bullfrogs, and tree frogs. The bullfrog is the one that supplies the fros; Ws served in our sea-food restau- rants. We eat some 125 tons of frog legs a year. Frog's are useful in another and much more important way. They eat many insects and help to keep down the insect population. OBSERVING A LIVING FROG. Try to bring a frog to the classroom. Also bring some flies and other insects for food for the frog. Set up two containers for the frog —a fairly small one in which you can put it and the insects, and a large one filled with water. Find the answers to these ques¬ tions: 1. How does a frog catch an insect? 2. Does the frog chew its food? 3. Which feet seem to be used most in hopping? in swimming? 4. Which parts of the body remain above water when the frog "floats"? 5. Watch the throat and try to see how the frog gets air into and out of its lungs. Record what you find. 6. How far can the frog jump? Toads, too, are more varied than most people realize. There is the com¬ mon garden toad, which may live to be 20 years old. Its skin is rough and rather dry. Some of the glands in the toad’s skin secrete a milky fluid that is poisonous, but not to our skin. One of the oddest of the toads is the Surinam (soor ih nahm ) toad of South America. It lives in the water. Its eggs and tad¬ poles develop in holes in the skin on the back of the mother; in due time, tiny toads burst forth and swim away. Even on our hot, dry deserts there are quite a few toads and frogs. One, the barking frog, sounds somewhat like a small dog barking. It lays its eggs in rain puddles or even in damp places among rocks. Unlike most other am¬ phibians, the barking frog does not produce swimming tadpoles. The eggs hatch into frogs. Keeping live frogs in the classroom You can keep living tadpoles in an aquarium or even in a battery jar. You can keep live frogs in a moist terrarium with a pan of water in it. You can learn a great deal about frogs and how they live, and you will enjoy doing it. You will find complete directions on pages 193-217 in Home-Made Zoo by Sylvia S. Greenberg and Edith L. Ras¬ kin, David McKay, 1952. Level of organization in amphibians The amphibians are ahead of the fish in some features. They are lung-breath- 240 VARIETY AMONG LIVING THINGS— ANIMALS ers, when full grown. And they have “voices ’—or at least some of them do. The heart is more specialized than a fish’s. So is the brain. All these and more complexities you will learn about later. Refer to the classification sum¬ mary on pages 257-260 if you want to learn more about the classification of the amphibians. Summing up: the amphibians Answer these questions about the amphibians. 1. Do tree frogs belong to the same genus as leopard frogs? 2. Where do most adult amphibians lay their eggs? 3. Name three stages in the meta¬ morphosis of most amphibians. 4. How can you tell a newt or sala¬ mander from a lizard? 5. With a few exceptions, adult am¬ phibians live rather close to streams, lakes, ponds, or other bodies of fresh water. Why is this an advantage? THE REPTILES Snakes, turtles, alligators, crocodiles, and lizards are reptiles. The dinosaurs of a former age were reptiles, too. Reptiles were once much more numer¬ ous and varied than they are today. A. W. Schoof 9-8 SNAKE SCALES Scales are one mark of the reptiles. The ones seen here are from the back of a diamondback rattlesnake. What are the reptiles like? Reptiles are lung-breathers all through their lives. Those that have feet have toenails. Their bodies are covered with scales. Even the turtle’s shell is formed from these scales. The scales of a snake’s or an alligator’s skin (Figure 9-8) are familiar to anyone 9-9 GILA MONSTER AND HORNED LIZARD Both these lizards are members of the fifth class of vertebrates— the reptiles. The Gila monster (left) inflicts a bite that is poisonous to man. The horned lizard (right) is often mistakenly called a horned “toad.” Photo left: William Bridges, from New York Zoological Society; right: Marion A. Cox who has examined a lady’s handbag or a pair of shoes made of them. In our country we have only a few hundred species of reptiles, which include snakes, lizards, turtles, alligators, and crocodiles. Most of the living species inhabit the warm tropics. Some reptiles are brilliantly colored. There are green snakes (both green garter snakes and green rattlesnakes); red snakes ( red racers and red dia- mondback rattlesnakes); bluish-black snakes; and even yellow, black, and red banded snakes (coral snakes and some others ) . One chameleon ( kuh meel yun ) is a little green and white lizard with a brilliant red throat. It can change color rapidly, but does not always match its surroundings in color, as many persons wrongly believe. Its color changes run from green through shades of yellow to gray. The Gila ( hee luh ) monster (Fig¬ ure 9-9), common in the Southwest, is brilliantly colored with orange and black, varying to pink and brown. It is the only lizard in our country that can inflict a bite poisonous to man. There are many fascinating books on reptiles. Some of them are listed at the end of this chapter. How to know the snakes There are more than 2,000 known kinds of snakes in the world, only 100 of which occur in the United States. In the United States, there are onlv four kinds of snakes that are poisonous to man: rattlesnakes, copperheads, wa¬ ter moccasins, and coral snakes. All other kinds of snakes in our country are not only harmless, but manv of them are extremely useful to mankind. Thev J J feed on rats and gophers and mice and insects and other destructive animals. Anyone who kills everv snake he finds is doing a definite disservice to human welfare. Most snakes are our allies, and it is to our interest to let them live un¬ harmed. Wise farmers let a black snake or two live about the barn, because this snake eats rats and mice, which destroy stored grain. If you are not afraid of snakes, you may develop a very exciting hobby in learning to know them. Some of the books listed at the end of this chapter will be useful in their study. Our poisonous snakes The water moccasin (Figure 9-10a) is common in the swamps of the south¬ eastern states. It is found westward as far as Texas and northward along the Mississippi to southern Illinois. It is often called the cottonmouth, because the lining of its mouth, which it opens when alarmed, is white in color. Usu¬ ally the water moccasin is only three or four feet long, but it may be more. It is sometimes dull brown or olive in color, with darker crossbands. However, it often is almost uniformly dark, as in Figure 9- 10a. Rattlesnakes (Figure 9-10b) mav be found in virtually every state in our country. More than a dozen species of rattlers inhabit the country, and these kinds differ considerably. The pygmy rattler is as small as the common gar¬ ter snake, whereas the southern dia- mondback rattler may grow to eight feet in length and measure 12 inches around. This huge snake occurs in southern North Carolina, south to the Gulf, and west to the Mississippi. From Texas to California, the somewhat smaller western diamondback occurs. Except for one small species in western New York State, the only rattlesnake found in the northeastern states is the timber rattlesnake. All rattlesnakes have 242 VARIETY VMONG I.IVIXG THINGS— ANIMALS New York Zoological Society 9-1 Oa WATER MOCCASIN Because the lining of its mouth is white, the water moccasin is often called a cottonmouth. When alarmed by man, as here, it may strike and deliver its poisonous venom, but much more often it tries to escape instead. 9-1 Ob DIAMONDBACK RATTLESNAKE Right. The “whirr-rr-rr” of a diamondback’s rat¬ tles is not a loud sound, but to people who have heard it before, it serves as an adequate warning. 9-1 Oc COPPERHEAD Below. The name is descriptive of this venomous snake’s color (apart from its dark, irregular crossbands). Humble Oil Co. 9-1 Od CORAL SNAKE Below. This deadly snake bites only if stepped on or touched. Humble Oil Co. rattles which make an easy identifica¬ tion mark, but the small rattle of the pygmy rattler might pass without no¬ tice unless one looked carefully for it. The buzz of the rattle is made by vi¬ brating the tail. The copperhead (Figure 9-10c) ranges from Massachusetts to northern Florida, and westward to Illinois, Mis¬ souri, and Oklahoma, and into Texas. The body color is pale brown or pink¬ ish brown with a series of rich brown Y-shaped blotches on the sides. These blotches are joined by bands of the same color across the back. The belly is a pale pinkish brown, with a row of dark spots on each side. The largest copperheads are only three or four feet long, and most specimens are even shorter. All specimens are thick and ap¬ pear to have stubby tails. Copperheads are usually found in wooded hills that have rocky ledges and that border wild moist meadows, where the snakes cap¬ ture small rodents, frogs, and birds. Copperheads and water moccasins be¬ long to the same genus but to different species. Coral snakes (Figure 9-10d) are found only in the South, from Florida to New Mexico and Arizona. They are small, slender snakes, and have smooth, glossy scales. The head is not distinct from the neck as it is in the other poi¬ sonous kinds. The colors consist of bril¬ liant red, yellow, and black, and appear in circular bands. Several nonpoisonous serpents resemble the coral snake in color, but in the coral snake the black band is bordered by two narrow yellow bands, whereas in the harmless forms the vellow is bordered by two black bands. The coral snake does not strike, but bites directly if stepped on or touched. Its bite is verv dangerous, but it rarely bites a human being. It is a Rattlesnake (pit viper) Red rat snake (constrictor) 9-1 1 SNAKE HEADS The pit of a pit viper (above) sets it apart from harmless snakes (below), but its vertical pupils are an iden¬ tifying feature only in bright light. In dim light, the pupils may enlarge until they ap¬ pear round. relative of the Old World cobra. Rattlers, water moccasins, and cop¬ perheads are all pit vipers. This name is used because these snakes have a deep pit in the skin between each eye and the nostril. The head is shaped some¬ what like an arrowhead (Figure 9-11). The body is usually thick and the tail blunt. The bites of all three pit vipers are serious, and the victim should get to a doctor as quickly as possible. The most 244 VARIETY AMONG LIVING THINGS— ANIMALS effective treatment now known is the hypodermic injection of antivenin (an tih ven in ) , which counteracts the ef¬ fects of the snake poison, or venom. Would you like to know more about rattlesnakes? For instance, would you like to read some of the “tall stories” told about them? Or the Indian customs relating to them? Or how to avoid be¬ ing bitten, if you live where they are plentiful? You will find all these and virtually everything else known about these reptiles in the two-volume set of books, Rattlesnakes, Their Habits, Life Histories, and Influence on Mankind by Lawrence M. Klauber, University of California Press, Berkeley and Los An¬ geles, 1956. Any city library is likely to have this set of books. Report in class on one topic that interests you. Level of organization in the reptiles The animals of Class Reptilia are vertebrates with scaly skins. Those with feet have toenails. Reptiles are lung-breathers throughout their lives. The living ones include turtles, lizards, snakes, alligators, and crocodiles. Most reptiles lay eggs that have shells. Obviously the males must fer¬ tilize the eggs before they develop shells; that is, within the female’s body. Some reptiles like the rattlesnake give birth to living young, but this does not make them mammals. Mammals have fur or hair, and milk for the young. Rattlesnakes and other reptiles whose young are born alive do not have these or other mammalian features. Reptiles have some advantages over amphibians. For one thing, the shelled eggs they lay can develop on land; thus, reptiles do not have to lay their eggs in the water, as most amphibians do. For another thing, the scales all over the body help to keep a reptile’s body from drying out in the air. These two features enable reptiles to live away from the water. In the far-distant past, reptiles were the first animals that were able to spread widely over the land. And they are still a widely dis¬ tributed group. Summing up: the reptiles 1. What are the main traits of rep¬ tiles? 2. Are reptiles in general beneficial or harmful to man? What are the ex¬ ceptions to this general truth? 3. What are the main kinds of living reptiles? 4. What adaptations to life on dry land do reptiles show over amphibians? THE BIRDS You can tell the birds, Class Aves, by their feathers. No other vertebrates— in fact, no other animals at all— have feathers of the type birds have. A bird’s feathers grow from its skin in some¬ what the way your hair grows. You can learn to recognize many kinds of birds by the colors of their feathers. But to the bird, the feathers are useful not so much for their color as for their light¬ ness and strength, and the streamlined outline the feathers give to the body. Common names of birds Many birds get their names from their colors. Cardinals are red, blue¬ birds are blue, vermilion flycatchers are vermilion, and blackbirds are black. Other birds get their names from other features. Flycatchers catch in¬ sects on the wing. Woodpeckers peck wood, and kingfishers catch fish. How many common names of birds can you mention that describe some¬ thing about the birds? ANIMALS WITH BACKBONES 245 Other bird features Birds, like reptiles, breathe air all their lives. Their claws and scaly feet and legs also make you think of rep¬ tiles. Most birds have four toes, three pointing forward and one backward. Birds are the only flying vertebrates, with the exception of bats. ( Flying fish and flying squirrels do not actually fly.) Birds fly amazingly well. Some kinds make long nonstop flights when they are migrating. The golden plover flies over 2,000 miles from the Arctic to South America, mostly over the ocean. One kind of hummingbird crosses the Gulf of Mexico— some 500 miles— non¬ stop. It takes a lot of energy to do that. They get the energy from their food, even as you do. Birds are warm-blooded animals, in contrast to fishes, amphibians, and rep¬ tiles— all of which are cold-blooded. In cold-blooded animals, the body tem¬ perature rises or falls as the surround¬ ing temperature goes up or down. In warm-blooded animals, the bodv tem¬ perature remains about the same, no matter whether the outside tempera¬ ture is high or low. The normal temper¬ ature of many species of birds is 102° F. or above. In some species the normal temperature is as high as 110° F. Variety among the birds Birds differ in many ways. Some kinds, like the ostriches and the kiwis (kee weez), have mere remnants of wings. Chickens, ducks, geese, and tur¬ keys, when raised in captivity, are not good fliers, either. You can often tell what a bird eats by looking at its bill (beak) and feet (Figure 9-12). Look at the beak and talons (toenails) of a hawk or owl. Both these body parts are useful in cap¬ turing and killing prey, such as field mice, and in tearing the kill apart to eat it. The long, pointed bills of wood¬ peckers enable these birds to “drill' into tree bark and get insect larvae from underneath the bark. Wading birds, such as the flamingos, have long legs. Wild ducks have webbed feet, useful as paddles, and bills, useful in picking up and straining food out of the water. The feet of perching birds are different from those of wading birds or of running birds like the sand- O pipers. Seed-eaters like the sparrows have short, strong bills. Hummingbirds have long hollow bills, useful in collecting nectar from flowers. Birds vary in every detail. Close to 800 species are known to nest in the United States. Identifying birds Many people enjoy learning to know the names of birds they see about them. You may want to start a hobby or even a profession of bird study now. A good way to begin is to spend some time looking at the pictures in a bird guide for your region. Chester A. Reed’s Pocket Bird Guide (Doubleday, Doran ) for your area is a handy one to carry on a field trip. Richard H. Pough’s Audubon Bird Guides (Doubleday), 3 volumes— one on Eastern Land Birds , 1946; one on Water, Game, and Large Land Birds, 1951; and a third on West¬ ern Land, Water, and Game Birds, 1957 —are especially helpful, because all the color illustrations are grouped together and easv to look through. After you have made yourself fa¬ miliar with color illustrations, start watching the birds. Early-morning field trips are usually most successful, but you can see birds of some kinds almost anvwhere— even on citv streets. Often J J 246 VARIETY AMONG LIVING THINGS— ANIMALS 9-12 BIRD BEAKS AND FEET Birds make up the sixth class of vertebrates. Most of them fly, and even among themselves they are highly specialized, as their beaks and feet show. A Cooper s hawk pounces on its prey and tears the flesh apart. A woodpecker perches on a tree trunk and bores into the bark for insect larvae. A sparrow perches anywhere and eats seeds. And a duck wades and swims, straining food out of the water. you will see a bird that looks like one j of the illustrations in a bird guide, and you can look it up that way. If you get really interested, and many biology students all over the country do, join a local bird club, or organize one. Set up a feeding board in your yard. Members of bird clubs are help¬ ing to advance our knowledge of birds and are having fun doing so. Reproduction in birds Birds lay fertile eggs with shells, as you know. The story of the activities that go with raising the young is inter¬ esting and often exciting. In birds, for the first time, you meet animals that spend much time and en¬ ergy looking after the young. (There are exceptions among other classes of animals— stickleback fish build nests, for example. But parental care is almost universal among birds.) Birds do not produce thousands or even hundreds of eggs at a time, as fish and many invertebrates do. Humming¬ birds lay one or two eggs. Quail lay more— maybe 20 or so. But even a few eggs are enough to keep a bird species going, partly because parental care lets more young survive and grow up. Among fish, most eggs never hatch. Fish that do hatch from the eggs have only a small chance of growing up. Not so with birds. A goodly percentage of bird nestlings usually survive. ANIMALS WITH BACKBONES 247 Refer to the end of this chapter for a listing of reference books on birds and their nesting habits. Level of organization in birds In several respects, birds are more highly specialized than fish, amphibi¬ ans, and reptiles. You already know that birds are warm-blooded— the only warm-blooded animals you have stud¬ ied so far. Their ability to keep their body temperature constant in widely varying weather conditions allows them wider range in habitats. Birds care for their young; this also you have learned. And surely this prac¬ tice indicates a higher level of speciali¬ zation than you have encountered in other animals, so far. Birds fly. Think of the specialization of body parts that must be involved! In fact, it may be that birds have the most highly specialized bones of any animals, including the mammals. In this one respect, they may be the most highly specialized animals of all. In other respects, birds are more com¬ plex, in general, than fish, amphibians, and reptiles. Their nervous system is more highly developed, as are their di¬ gestive and circulatory systems. For example, a bird’s heart is divided into four separate chambers, much like the mammal heart. Birds and human welfare Birds are as popular with people as “bugs," snakes, toads, and spiders are unpopular. They deserve their popular¬ ity. It is doubtful whether man could continue to lead the race with his in¬ sect competitors without the help of the birds. No one knows how much birds are worth to us as eaters of weed seeds and insects. State laws protect the song birds and many of the game birds, but some states still pay bounties for certain hawks. Some states have open season on crows all the time. Bounties on hawks do not pay off, because the cost in grain losses to field mice far outweighs the value of the comparatively few chickens saved. And crows are useful, too. People who know “which side their bread is buttered on" do not kill birds, except certain game birds, such as wild ducks and geese, and then only during a limited hunting season. Summing up: the birds The vertebrates with wings and feathers make up Class Aves. They are warm-blooded, air-breathing animals with bodies suited in many ways to fly¬ ing. The birds and the insects are the only animal classes able to “take to the air" on the wing. Birds play an important part in your life, even though you usually aren’t aware of the ways in which they are helpful. People have more to eat be¬ cause birds help to keep down the num¬ bers of weeds, insect pests, and other animals like field mice. Birds also give people pleasures of different kinds. Their musical songs, their attractive coloring, and their odd and interesting actions add to the joy of living for those who listen and look. MAMMALS There remains one more class of ver¬ tebrates to be discussed. This is the class of backboned animals that have hair or fur, and milk for the young— the class called mammals, or more tech¬ nically, Mammalia. Some 4,000 species of living mammals are known. Like the birds, mammals are warm-blooded, air- breathing vertebrates. They live in all 248 VARIETY AMONG LIVING THINGS— ANIMALS John H. Gerard, from National Audubon Society 9-13 SHORT-TAILED SHREW Mammals— the highest class of vertebrates— vary widely in size. This shrew is less than four inches long (and one other species is even smaller). kinds of places. Some kinds, like mon¬ keys and squirrels, live in trees. Some kinds, like whales and seals, live in the water, but they always come to the sur¬ face to breathe. Some kinds, like the mole and the muskrat, burrow under¬ ground. Bats have wings and fly at night, and they hang suspended from supports in caves or other dark places by day. Most mammals, however, live on the surface of the land. The mammals of today differ widely in many respects, including size (Fig¬ ure 9-13). The smallest is a little shrew only three inches long, tail and all. The largest (and the largest animal in the whole animal kingdom ) is the blue whale, which may grow to more than 30 yards in length and 150 tons (300,- 000 pounds ) in weight. The mammals include the most suc¬ cessful animal of all, biologically speak¬ ing— the human species, Homo sapiens. You will study in detail the machin¬ ery of the human body in a later chap¬ ter. But here it will pay to consider briefly the mammalian body plan in general. Body plan Mammals are built like other verte¬ brates. They have a dorsal nerve cord (spinal cord ) running through the bony canal inside the backbone, whose ver¬ tebrae have replaced the notochord found in one stage of the growth of the embryo. Mammals have a large brain with several parts, all encased in a skull. So do all vertebrates. But the mammalian brain is far more complex than that of any other vertebrate, as you will learn later. All vertebrates have a body cavity (coelom), but in mammals, a muscular diaphragm ( dy uh fram ) divides the body cavity into two cavities— an ante¬ rior one, often called the chest, and a posterior one, often called the abdo- ANIMALS WITH BACKBONES 249 men. Both cavities are lined with epi¬ thelial tissue, but only the lining of the abdomen is called peritoneum. The lin¬ ing of the chest cavity is called the pleura (PLOORuh). Mammals are the only animals that have a pleura. Like other vertebrates (or most of them— snakes are an exception), most mammals have two pairs of limbs— legs, legs and wings, or legs and arms. Like birds (Aves), mammals are warm-blooded and have a more highly specialized heart than that of fish, am¬ phibians, and reptiles. Unlike birds (and fish and reptiles), mammals have no scales or feathers, but have fur or hair. Unlike all other vertebrates, mam¬ mals have milk for their young. Reproduction in mammals Mammals get their name from the mammary (milk-producing) glands of the females. This is the only class of animals that nurse their young on milk from the mother’s milk glands. Most mammals produce only a few young in a litter, and many usually have only 9-14 PLATYPUS This little mammal is, in a way, a survivor of an age long past— it lays eggs. Note the “duckbill,” the webbed feet, and the powerful tail. What way of life do these features suggest? New York Zoological Society one “baby” at a time. Can you explain why mother’s milk gives the young a better chance to survive? Mammals come from eggs, like most other animals. But most mammals do not lay eggs. The fertilized eggs grow into embryos within special organs in¬ side the mother's abdominal cavity. In due time, living (but often quite help¬ less) young are born. Can you explain why the development of embryos in¬ ternal lv gives the fertilized eggs a bet- ter chance to develop and survive? Mammals usually take care of their J young for some time. Human babies re- J O quire parental care for a longer time than other mammal young. All in all, mammalian young stand a better chance of surviving and growing up than the young of any other animal class. You will study mammalian re¬ production in detail in a later unit. Variety in mammals The only organisms some people call animals are mammals. You are now used to calling many other organisms animals, too. And yet you probably know more kinds of mammals than members of any other animal class. Mammals vary in many ways, so much so that taxonomists sort them in¬ to three subclasses: (1) the egg-layers, (2) the pouched mammals like our opossum, and (3) the rest of the mam¬ mals— those whose voting are born rath- er well developed, like cats, rabbits, deer, horses, and many more. The three subclasses sort into orders —one order of egg layers, one order of pouched mammals, and some eighteen orders of the third subclass. Here we shall discuss only the main orders of living mammals. Refer often to the clas¬ sification summary on pages 257-260 as you read on. Egg-layers Egg-laying mammals were once nu¬ merous and widespread, but today only three genera remain, and these are lim¬ ited to Australia and some other near¬ by islands. The duckbills and two gen- J O era of spiny anteaters are the only living members of this order of mammals. The duckbill is correctly called a platypus ( plat ih pus ) . It is a little brown animal less than 1/2 feet long (Figure 9-14). It has a bill like a duck s, webbed feet useful in swimming, and long toenails useful in digging. It digs a burrow many feet in length into the bank of a stream. At the end of the bur¬ row a nest of grass is built. In this nest, the female lays from one to three eggs. Milk is secreted by glands on the un¬ der surface of the female’s body. After the young have hatched, they lap the milk off the mother s fur. The adults eat insects, worms, and other small ani¬ mals which they dig out of the muddy stream bottom with their bills. Spinv anteaters also have bills. Their eggs have tough, leatherv shells, much like those of turtles and snakes. Their internal structure resembles that of rep¬ tiles, too. Their long claws are used for digging and for breaking into ants’ nests. They lap the ants up with their long sticky tongues. This order of mammals is interesting chiefly because the egg-layers help to show what the first mammals may have been like. Pouched mammals A second order of mammals of spe¬ cial interest is that of the pouched mam¬ mals, the marsupials ( mahr soo pih ills). Perhaps you are familiar with the American opossum. You may even have seen a female with young in the pouch on her abdomen (Figure 9-15). The Dr. Fred Crowgey, Salem, Ohio. Shoop Photos 9-15 OPOSSUM The familiar “possum is the only pouched mammal native to the United States. Top. This mother has nine young in her pouch. Middle. The pouch is opened to expose three of the young. Bot¬ tom. The same three young, removed from the pouch, climb onto the mother’s back. At birth, the offspring were smaller than shelled peanuts. ANIMALS WITH BACK HON ES 251 F. E. Westlake, from National Audubon Society 9-16 PRAIRIE DOG This little rodent has a personality that delights observers. He dashes into his hole and digs furiously, suddenly reverses himself and pops out again, sits up, barks, and rushes off to frolic with other members of the prairie dog colony. opossum is the only pouched mammal in our country. It is in Australia that pouched mammals are numerous and varied. There, kangaroos, phalangers (fay lan jerz), wombats, and wallabies flourish; there are also ratlike, molelike, and small bearlike pouched mammals. The koala (koliAHluh) looks for all the world like a child’s teddy bear. Aus¬ tralia even has pouched mammals much like our flying squirrels except for the pouch. Pouched mammals are a step ahead of the egg-layers in that the young are born alive. They are a step behind the rest of the mammals in that the young are born while they are still very small and almost completely helpless. A baby opossum is born when it is still so small that several of them can be placed in a teaspoon, and a kangaroo at birth is no bigger than your little finger. The entirely helpless and immature young are carried in the mother’s pouch from the time they are born until they are old enough to look after themselves. In the pouch, the young are nourished with milk from the mammary glands. J O In Australia, marsupials are still rather important, but, in general, they are interesting to biologists because they represent a higher level of organi¬ zation than that of the egg-laying mam¬ mals but a lower level than that of the mammals whose young are born rather fully developed. In other words, to a biologist, marsupials seem to be a con¬ necting link between egg-layers and the rest of the mammals. All the rest of the orders of mammals give birth to rather well-developed young and then to an “afterbirth.” Bi- 252 VARIETY AMONG LIVING THINGS— ANIMALS ologists call the “afterbirth” the pla¬ centa ( pluh sen tuh ) and the subclass, the placentals. Most of the animals you know best are placentals. Of the pla¬ centals, the orders you are most like¬ ly to want to know about are the gnaw¬ ing mammals, the hoofed mammals , the flesh-eating mammals, and the “first- rank” mammals, of which you are one. Gnawing mammals One order of placental mammals consists of those which have teeth es¬ pecially suited for gnawing. The front teeth continue to grow throughout the life of the animal. The edges of the teeth are worn down and sharpened by constant gnawing. If for any reason the animal gives up gnawing, as some¬ times happens when pet chipmunks or squirrels are fed only cracked nuts, the front teeth continue to grow until the mouth is locked shut by the long teeth. Since the animal can no longer eat, it dies. Mammals with gnawing teeth of this kind are called rodents. Rodents, like other mammals except egg-layers and marsupials, are well de¬ veloped at birth. Like all mammals, they are nourished with mother’s milk. The largest rodent in North America is the beaver, which actually is able to gnaw down trees. The capybara (kap ih bah ruh ) of South America is the largest rodent in the world. It may weigh as much as 75 pounds. Other rodents are rather small animals. Rab¬ bits, squirrels, all of the many species of rats and mice, chipmunks, prairie dogs (Figure 9-16), chinchillas (highly prized for their fur), and porcupines are a few of the many species in this order. Although some of these animals supply us with useful furs, the order must be recognized as the most de¬ structive among the mammals. Hoofed mammals Still another order of mammals is that of the hoofed mammals. As the name implies, these mammals have hoofs ( Figure 9-17 ) . A hoof is simply an 9-17 CUD-CHEWING HOOFED MAMMAL A grazing cow swallows food unchewed, and the food collects in the first compartment of the stomach. Later, while the cow lies in the shade, small balls of food (cuds) return to the mouth, are chewed and reswallowed, and this time pass through the other compartments of the stomach, toward the intestine. enlarged toenail; cows and horses and pigs walk on the ends of their toes. Be¬ sides cows, horses, and pigs, there are camels, deer, giraffes, zebras, antelopes, sheep, goats, oxen, bison (often called buffalo), moose, elk, gazelles, tapirs, rhinoceroses, and hippopotamuses. The name for animals of this class is the ungulates ( ung gyoo layts ) . The animals of certain families of un¬ gulates chew their cuds (Figure 9-17). Cows, sheep, goats, deer, camels, and giraffes are among the end chewers. Flesh-eaters The mammals known as flesh-eaters belong to the order called the carni¬ vores ( kahr nih vorz ) . These mammals can be recognized by their teeth. Ex¬ amine a dog s teeth and you will know what the teeth of a carnivore look like. The teeth at the very front of the mouth are small. The four canines, next to the front teeth and also at the front of the mouth, are long and sharp, well suited to tearing flesh to pieces. For this rea¬ son, a carnivore’s canines are often called fangs. The back teeth have sharp points and cutting edges that are use- fid in chewing raw meat and breaking bones, as you know if you have ever watched a dog eat a bone. There are a great many species of carnivores, most of which are probably familiar to you. They include dogs and cats, wolves, coyotes (xyohts), foxes, hyenas, otters, minks, weasels, skunks, leopards, lions, tigers, and jaguars. Mammals of first rank The final order of mammals to be studied here is that called the primates (pRYmayts), which means “first in rank. Man himself is a primate. Since man named all the orders, perhaps his own conceit led him to consider his or¬ der “first in rank. Primates are first in rank in intelligence and in well-devel¬ oped hands. In other features they are inferior to some of the other orders. However, the name “primates” stands. Man has not classified himself as the only primate. In this class he has also placed lemurs, monkeys, gorillas, ba¬ boons, and chimpanzees. The features in which primates are alike are: ( 1 ) five toes or fingers, with the great toe or thumb so situated that the foot or the hand can be used for grasping, ( 2 ) toe¬ nails and fingernails, (3) eyes so lo¬ cated that both can look at the same object at once, (4) a large skull and brain, and (5) two mammary glands on the chest. There are exceptions, but these five traits are common to most primates. Lemurs If you wanted to see the little pri¬ mates known as lemurs at home, you would have to travel to Madagascar. Only about the size of a cat, they live in small troops in the trees. They walk on all four feet and climb along the branches of trees or jump from limb to limb with great ease. They have long bushy tails and soft woolly fur, even on the lower part of the face. They eat fruits, insects, eggs, and small birds. The lemurs are interesting but primi¬ tive relatives of monkeys and apes. Monkeys Monkeys are of two kinds— the Old World and the New World monkeys. The Old World monkeys include the baboons and mandrills and others. The New World monkeys include such kinds as the howling monkeys, the spi¬ der monkeys, and the night monkeys, among others. Of these, the howlers are the largest. 254 VARIETY AMONG LIVING THINGS— ANIMALS The great apes The apes are the largest of the pri¬ mates. They include orangutans, goril¬ las, chimpanzees, and one or two other kinds. Of these, the chimpanzees are most familiar, since they live and thrive in captivity. A “chimp” is one of the most popular exhibits in a zoo. In the wild, chimpanzees live in troops. A family consists of one male, one female, and their children. In captivity, chimps have been taught to roller skate, eat at a table with dishes and silver, ride bi¬ cycles, and do many other things. Man differs from all other organisms The human species, Homo sapiens, is classified as follows: kingdom: Animalia phylum: Chordata subphylum: Vertebrata class: Mammalia order: Primates family: Hominidae genus: Homo species: Homo sapiens The species Homo sapiens is differ¬ ent from every other species in certain 9-18 HUMAN BACKBONE The way the backbone is curved not only at the shoulders (as in other primates), but also at the small of the back, helps man to stand erect. Chest vertebrae < Lumbar vertebrae (small of back) Sacrum Coccyx respects. Of course, this statement is true of any other species, for a species is a group of organisms that are very much alike, and at the same time dif¬ ferent from all other species. It isn’t the fact that man differs from all other species, but rather the ways in which he differs, that give him an unusual place in the world of living things. In the build of our bodies, we have several features that belong only to hu¬ man beings: ( 1 ) Our backbones are curved in two directions (Figure 9-18). The structure of our hipbones, thighbones, and backbones enables us to stand more fully erect than other primates do. (2) We have human hands. Human hands are better suited to handling ob¬ jects than are any others. Our thumbs are stronger and much better suited for helping the fingers take hold of an ob¬ ject than are the thumbs of other pri¬ mates. Besides, our fingers and wrists can be moved much more freely in several directions than can those of any other primate. Without hands like ours, it would have been impossible to de¬ velop and use our many kinds of tools. (3) Man has a better-developed forebrain than any other animal. With man’s better-developed brain comes the intelligence to see the need for and the way in which to make tools. With the hand comes the ability to make and use these tools. With tools man has been able to change the world around him so that many things are made to serve his purposes. Man is the only species that has invented a spoken and written language. With language comes the ability to teach each new generation what has already been learned. Thus human knowledge can be increased from generation to gener¬ ation. Gradually man has achieved more and more control over his environment. Today he harnesses the forces of nature to do much of his work for him. He sows, cultivates, and harvests crops on a huge scale. He travels over water and land and through the air at phenomenal speeds. He goes down into the ocean, drills into the land, and ascends into the stratosphere. He even talks of trav¬ eling to the moon or to the nearest planets in rocket ships. Only man— no other species— can change his environ¬ ment on an extensive scale. Man is the knowing animal; Homo sapiens is a good name for him. Summing up: the mammals Mammals are the most highly devel¬ oped animals. They are vertebrates that have fur or hair, and milk for the young. Their two body cavities are separated by a diaphragm. They are warm-blooded, like birds. They have comparatively large brains encased in a skull. The only living mammals that lay eggs are the duckbill and the spiny ant- eaters. The marsupials like our opossum carry their young in pouches. All the rest of our living mammals are pla¬ cental mammals. CHAPTER NINE: SUMMING UP On the next four pages, you will find an illustrated summary of the classifi¬ cation of all the animals of Phylum Chordata. In addition to the animals studied in this chapter, you will find the first two subphyla, the first two classes of vertebrates, and several or¬ ders of mammals that were not dis¬ cussed in the text. Use this summary for review and for learning more about the chordates. Helpful reference books are listed at the end of this chapter. 256 VARIETY AMONG LIVING THINGS— ANIMALS PHYLUM CHORDATA The chordates (kor dayts) are animals with a notochord, or dorsal supporting rod. It appears only in the embryos of many species and is replaced in most cases by a back¬ bone made up of true bony vertebrae. In other cases it is replaced by a cartilaginous skeleton or is absorbed without being replaced. The highest specialization in all organ systems is found among the chordates, and especially among many of the vertebrates— complexly jointed endoskeletons, intricate nervous systems with complex brains, repro¬ ductive systems better adapted than those of lower animals to survival of the young, closed circulatory systems with two-, three-, or four-chambered hearts, and other ex¬ amples. The largest land-inhabiting and water-inhabiting organisms ever to exist in the animal kingdom— the dinosaurs of ancient times and certain whales of today— are among the chordates of the vertebrate subphylum. One type of dinosaur and one type of whale have reached over-all lengths of up to 90 feet. At the other end of the scale of size among chordates are shrews, lancelets, and other organisms measuring only a few inches in length. There are some 60,000 species of chordates, many of which are no longer liv¬ ing. Living species are found on land, in the air, and in fresh and salt water. SUBPHYLUM I. HEMICHORDA (hem ih kor duh). Mostly wormlike animals with noto- * chord onlv in anterior end: no other evi- • J 7 dence of endoskeleton. Example: acorn worm (Figure 9-19). SUBPHYLUM II. UROCHORDA (yoo roh kor duh ) . Salt-water animals in which noto¬ chord is present in embryo and larva * stages, but usually is absorbed and disap- • pears in the adults; no other evidence of endoskeleton. Adults have saclike bodies and usually attach to submerged objects, • although some are free-swimmers. Ex- # ample: Cionci (sea squirt. Figure 9-20). SUBPHYLUM III. CEPHALOCHORDA (sefuh • loh kor duh). Salt-water animals with prominent notochord extending from head to tail; no other evidence of endoskeleton. * Example: Arnphioxus (lancelet, Figures m 9-21 and 9-1). (continued on next page) Photos top to bottom: American Museum of Natural History; Douglas P. Wilson; Carolina Biological Supply Co. 9-21 9-20 9-19 9-27 9-26 9-25 9-24 9-23 9-22 Photos top to bottom: Robert S. Bailey, Virginia Fisheries Laboratory; Robert S. Bailey, Virginia Fish¬ eries Laboratory ; Douglas P. Wilson ; Harold V. Green; American Museum of Natural History; Aus- ting and Koehler, from National Audubon Society. SUBPHYLUM IV. VERTEBRATA (ver teh bray tuh ) . Animals in most of which an embry¬ onic notochord is replaced by a backbone of true vertebrae. Classes of vertebrates are: Class 1. Cyclostomata (sy kloh STOH mull tuh). Eel-like animals without jaws but with sucking mouth discs. Cartilaginous skeleton; no true vertebrae. Cold-blooded; usually with two-chambered heart. Ex¬ amples: lamprey (Figure 9-22), hagfish. Class 2. Elasmobranchii (uh las moh BRANG kee eye). Fish with jaws and with skele¬ tons mostly of cartilage, but usually with bony vertebrae. Cold-blooded; most species with two-chambered heart. Ex¬ amples: Sphijrna (hammerhead shark, Fig¬ ure 9-23), dogfish (Figure 9-3), skate, ray. Class 3. Osteichthyes (os teh ik thih eez) . Fish with jaws and true bony skeletons. Cold-blooded; most species with two- chambered heart (one order has three- chambered heart). Examples: whiting Figure 9-24), sea horse (Figure 9-4), lungfish (Figure 9-5), perch, bass, salmon, coelacanth. Class 4. Amphibia (am fib ee uh). Animals most of which undergo metamorphosis from gill-breathing young to lung-breath¬ ing adults. True bony skeleton. Cold-blood¬ ed; three-chambered heart (adults). Moist, smooth, scaleless skin. Usually with two pairs of limbs. Examples: salamander (Figure 9-25), Rana (wood frog, Figure 9-6; other true frogs), toad. Class 5. Reptilia ( rep til ee uh ) . Lung¬ breathing animals most of which have scaly skin. True bony skeleton. Cold-blooded; four-chambered heart (usually with ven¬ tricles incompletely separated). With or without two pairs of appendages. Exam¬ ples; turtle (Figure 9-26), lizard (Figure 9-9), snake (Figure 9-10), crocodile. Class 6. Aves (ay veez). Animals whose bodies are covered with feathers and whose feet are covered with scalv skin. True bonv ✓ J skeleton with hollow bones and front pair of limbs modified into wings. Warm¬ blooded; four-chambered heart. Examples: birds (bluebird, Figure 9-27; hawk, spar¬ row, woodpecker, and duck. Figure 9-12). page 258 9-29 9-28 Class 7. Mammalia ( muh MAY lee llh ) . Lung-breathing animals with body hair. True bony skeletons, usually with two pairs of appendages. Warm-blooded; four-cham¬ bered heart. Females with mammary glands. Young are live-born (except for one order). Some common orders are: Order Monotremata (moil oh TREE muh tuh). Egg-laying mammals. Examples: platypus (Figure 9-28), spiny anteater. Order Marsupialia (mahr soo pih ay lih uh) . Mammals whose young are born immature and carried in abdominal pouches. Ex¬ amples: kangaroo (Figure 9-29), opossum (Figure 9-15). Order Insectivora (in sek tiv oh ruh). In¬ sect-eating mammals with teeth. Exam¬ ples: mole (Figure 9-30), shrew (Figure 9-13). Order Chiroptera (ky rop ter uh ) . Flying mammals. Example: bat (Figure 9-31). Order Edentata (ee den tay tuh) . Tooth¬ less, or nearly toothless, mammals. Exam¬ ples: giant anteater (Figure 9-32). Order Rodentia (roll den shih uh) . Gnawing mammals with specialized incisor teeth. Examples: woodchuck (Figure 9-33), prairie dog (Figure 9-16), rat, squirrel. (continued on next page) Photos top to bottom, left: Australian News and In¬ formation Bureau; Australian News and Information Bureau; right: John H. Gerard, from National Audu¬ bon Society; George A. Smith; American Museum of Natural History; U.S. Forest Service Order Lagomorpha ( lag oh MOHR full ) . Mammals similar to rodents but with hind legs suited to jumping. Example: rabbit (Figure 9-34). Order Carnivora (kahr Niv oh ruh ) . Flesh¬ eating mammals, usually with claws on the four limbs. Examples: puma (Figure 9-35), lion, wolf, bear, dog, cat, seal. Order Ungulata (ung gvoo lay tuh ) . Her¬ bivorous, hoofed mammals. Examples: ze¬ bra (Figure 9-36), cow (Figure 9-17), goat, pig, camel, sheep, deer, rhinoceros. Order Proboscidea (proh bah SID ee uh). Mammals with trunks and tusks. Example: elephant (Figure 9-37) . Order Cetacea (see tay shee uh ) . Salt¬ water mammals with flippers; no hind limbs. Tail fin not vertical as in fish. Exam¬ ples: dolphin (Figure 9-38), whale. Order Primates (pry may teez) . Mammals some of which stand erect, and most of which have an opposing thumb, at least on the front limbs. Examples: gibbon (Figure 9-39), chimpanzee, gorilla, man. Photos top to bottom, left: Hugh Spencer; American Museum of Natural History; Union of South Africa Government Information Oflice; Sabena World Airlines; right: City of Miami News Bureau; New \ ork Zoological Society Your Biology Vocabulary Here is a list of the important new terms introduced in this chapter. Make sure that you understand and can use these terms correctly. lancelet birds diaphragm lamprey mammals mammary "lands J O notochord platypus marsupials chordates air bladder of fish placenta cartilaginous fish salamander placentals jawless fish chameleon rodents bony fish Gila monster carnivores amphibians pleura ungulates reptiles pit vipers primates Testing Your Conclusions 1. Copy the numbers of the blanks in the following outline. Beside each number, write the correct word which fills that blank, do not mark this book. I. If an animal has a notochord and gill arches, at least in an early stage of the embryo, it belongs to the phylum called (1). . . . A. Animals of the first three subphyla of this phylum include acorn worms, sea squirts, and (2). . . . B. Animals of the fourth subphylum have backbones and are called (3). . . . 1 . Lampreys belong to the class of backboned animals called ( 4 ) . . . . 2. Dogfish and sharks belong to the class ( 5 ) . . . . 3. Backboned animals with hard bones, scales, and gills are of the class called (6). . . . 4. Backboned animals with smooth skins, no toenails, gills while young, and lungs when grown up are of the class called ( 7 ) . . . . 5. Backboned animals with scales and lungs and toenails (if legs are present) are of the class called (8). . . . 6. Backboned animals with feathers are of the class called (9). . . . 7. Backboned animals with fur or hair and milk glands are called (10). . . . 2. Four orders of mammals are listed at the left. Copy the list. Beside the name of each order, list the animals from the right-hand list (1-15) that belong to that order. Rodents Carnivores Ungulates Primates 1 . lemurs 2. squirrels 3. bears 4. seals 5. monkeys 6. cats 7. mice 8. beavers 9. man 10. deer 11. dogs 12. cattle 13. prairie dogs 14. horses 15. zebras ANIMALS WITH BACKBONES 261 More Explorations 1. Comparing external features. Compare a fish with a frog. Then compare the frog with any reptile, such as a lizard or snake. How do the outer body coverings differ? How do the toes of a lizard differ from those of a frog? Now examine a newt or salamander. Explain why it is an amphibian rather than a reptile. See if you can find the two pairs of fins on the fish that correspond to the legs of a newt. Which part of a chicken has a covering similar to that of reptiles? Have you ever seen anything on a dressed fowl that resembles the hair of mammals? 2. Study of a backbone. If you have the skeleton of any vertebrate, examine the spinal column. Some plaster-of-Paris and plastic models of the human torso have removable vertebrae that show their structure. If you have such a model, examine the vertebrae. Why is it an advantage to have movable vertebrae rather than a single long bone in the spinal column? You can prepare and mount a mammal skeleton, if you wish. Ask your teacher for directions. 3. Reporis on chor dates. Choose one of the following chordates: acorn worm, sea squirt, lancelet. Look it up in any college zoology textbook or in an encyclopedia and pre¬ pare a report on it. Try to make your report interesting to your class. Include answers to questions such as these: Where does it live? How does it eat? What does it eat? How old are the oldest known fossils of its subphylum? 4. Finding the age of a fish. You may know that you can find out how old a tree was, when cut, if you count the growth rings in the top of the stump. Fish scales have growth rings, too. Each scale grows new rings all the time, but the winter growth rings are few and close together while for the rest of the year the rings are more numerous and farther apart. On page 573 of Tracy I. Storer’s General Zoology, McGraw-Hill, 1951, you can see pictures of fish scales and their growth rings. At a fish market, get some fish scales and examine them. Put sketches on the chalkboard and explain in class how you can tell the age of a fish. 5. How many young? Try to find out how many young some mammals usually have at a time. Report in class. Here is a list of some mammals to choose from, unless you prefer to choose others. opossum cow horse bear Thought Problems 1. Homo sapiens cannot run as fast as a deer. But he has invented the automobile and train. With these he can outrun any animal. Make a list of other ways in which man has been able to outstrip other animals by means of tools or machines. 2. Here are two paragraphs from page 272 of William Beebe’s The Log of the Sun. Read the paragraphs carefully. Then list each animal mentioned and try to give its phylum, subphylum, class, and order. “Some of the names of the commonest animals are lost in the dimness of antiquity, such as fox, weasel, sheep, dog, and baboon. Of the origin of these we have forever whale seal muskrat deer cat (a special breed) dog (a special breed) mouse bat 262 VARIETY AMONG LIVING THINGS— ANIMALS lost the clew [sic]. With camel we can go no farther back than the Latin word camelus, and elephant balks us with the old Hindoo elep, which means an ox. The old root of the word wolf meant one who tears or rends, and the application to this animal is obvious. “Lynx is from the same Latin word as the word lux (light) and probably was given to these wildcats on account of the brightness of their eyes. Lion is, of course, from the Latin leo, which word, in turn, is lost far back in the Egyptian tongue, where the word for the king of beasts was labu. The compound word leopard is first found in the Persian language, where pars stands for panther. Seal . . . was once a word meaning ‘of the sea/ close to Latin sal, the sea.” * Further Reading Here is a list of books that are helpful in identifying animals of Phylum Chordata. BOOKS FOR GENERAL USE: Animal Kingdom by George G. Goodwin et al., 3 volumes, Hawthorn, 1954. Life by George Gaylord Simpson et al., Harcourt, Brace, 1957. Parade of the Animal Kingdom by Robert W. Hegner, Macmillan, 1953. General Zoology by David F. Miller and James G. Haub, Holt, 1956. General Zoology, Second Edition, by Tracy I. Storer, McGraw-Hill, 1951. The Story of Animal Life, Vol. II, by Maurice Burton, Bentley, 1951. books on fishes: Field Book of Seashore Life, by Roy W. Miner, Putnam, 1950. Field Book of Marine Fishes of the Atlantic Coast by Charles M. Breder, Jr., Putnam, 1929. Tropical Fishes as Pets, Revised Edition, by C. W. Coates, Liveright, 1950. BOOKS ON AMPHIBIANS AND REPTILES: Reptiles and Amphibians by Herbert S. Zim and Hobart M. Smith, Simon & Schuster, 1953. Natural History of North American Amphibians and Reptiles by James A. Oliver, Van Nostrand, 1955. The Reptiles of North America, Revised Edition, by Raymond L. Ditmars, Double¬ day, 1936. Snakes of the World, Imperial Edition, by Raymond L. Ditmars, Macmillan, 1951. books on birds: Audubon s Birds of America by Ludlow Griscom, Macmillan, 1950. Audubon Guides, All the Birds of Eastern and Central America by Richard H. Pough, Doubleday, 1953. Audubon Water Bird Guide by Richard H. Pough, Doubleday, 1951. Audubon Western Bird Guide by Richard H. Pough, Doubleday, 1957. Birds’ Nests: A Field Guide by B. Richard Headstrom, Ives Washburn, 1949. How to Know the Birds by Roger Tory Peterson, Houghton Mifflin, 1949. BOOKS ON MAMMALS: A Field Guide to the Mammals by W. H. Burt and R. P. Grossenheider, Houghton Mifflin, 1952. Mammals by Herbert S. Zim and Donald F. Hoffmeister, Simon & Schuster, 1955. * Reprinted with permission from The Log of the Sun by William Beebe, Henry Holt and Co., 1906. ANIMALS WITH BACKBONES 263 Specialization among seed plants and vertebrate animals mav take many y J forms. In the desert of the southwestern United States, century plants such as the one in bloom pictured on this page live and grow for sixteen to eighteen years or more, bloom only once, then die. The pelican seen on the opposite page is specialized in several ways— it flies, it swims, and it dives under water to scoop up fish for a meal. Discovering characteristics peculiar to each plant or animal species, or to several species, could occupy many years of study. In general, the kinds of specialization we are concerned with in this unit are those that are common to many or most seed plants, or to most vertebrates. Consider, for example, the rose plant, part of which is shown in an X-ray photograph on the opposite page. It and most other seed plants (and many of the lowlier plants as well ) make their own food— sugar first, then starch, and on and on until highly complex proteins have been built up. Not only the plants themselves but the animals of the world depend upon the food-making process of green plants. Biochemists have for years been trying to discover laboratory processes for doing what the food-making plants do— make sugars, starches, and proteins, starting with inorganic materials. In 1947 two biochemists at Harvard SPECIALIZATION University synthesized a protein that looked something like the fibers of lean meat. It was not lean meat, but it was a protein. And in 1953 two other scientists (one a Canadian and one a Swiss), working together, synthesized cane sugar, starting with products of simpler sugars. But to date no one has yet synthesized grape sugar, the simple sugar that is the first of the foods that green plants manufacture. It takes some knowledge of biochemistry to understand what is known about how plants make food, or how both plants and animals use food and grow. You will learn something of the biochemistry of seed plants and vertebrates as you study this unit. You J J will also learn something of their behavior— how they react to things around them, and what kinds of things they react to. It may seem strange to you to think of plants as “behaving,” but thev as well as animals do behave J in predictable ways in response to certain stimulating factors in their environment. Chapters 10. Seed Plants and How They Live 11. Vertebrates and How They Live CHAPTER Seed Plants and How They Live How do green plants make their food , and where do they get the necessary raw materials? Suppose that a plant— a rosebush— is grown in a tub of soil. As the rosebush grows and gains in weight , does the soil lose weight accordingly? Experiment with a willow tree Almost three hundred fifty years ago, Jan Baptista van Helmont, a Belgian doctor and chemist, set up an experi¬ ment to test the belief that plants use soil for food. According to Van Hel- mont’s account, exactly 200 pounds of soil were placed in a tub. Then a young willow tree that weighed five pounds was planted in that soil. The tree was watered with rain water and allowed to grow for five years. Then the soil and the tree were weighed again. The tree had gained 164 pounds. The soil had lost less than three ounces. Van Hel¬ mont concluded that the tree had built 164 pounds of new tissues out of the rain water used in watering it. He was only partly right, as you will learn in this chapter. Even so, this experiment seemed to disprove the age-old con¬ clusion that plant food was mainly soil, Boyce Thompson Institute of Plant Research, Inc. and today, biologists have gone much further with the researches started by Van Helmont, as you will see. THE SEED PLANT AS A WHOLE You have already learned something about the seed plant and its organs, in¬ cluding its food- and water-conducting tissues. You know that the main organs are the root, stem, leaf, and flower. Of these, the root, stem, and leaf do the things it takes to keep the plant alive and growing. The flower is an organ of reproduction and will be studied in de¬ tail in Chapter 19. Bean and corn seedlings Young bean and corn plants are ex¬ cellent for the study of a whole seed plant. For the following studies, use 266 SPECIALIZATION IN HIGHER ORGANISMS the ones you planted some time ago (see page 204). Put the roots of several bean and corn seedlings in a glass of water to which you have added a few drops of red ink. Leave the seedlings standing in the stained water for a day. Then, before you read on, leaf quickly through the color charts on Seed Plants (following page 288), so that you will know what charts are there. As you read on, refer often to these charts. STUDYING A BEAN SEEDLING. Compare some of the bean seedlings you have grown (see page 204) with Figure 10-1. Look for the two seed leaves on your speci¬ mens. If they are still there, describe in your record book how they look, as com¬ pared with the seed leaves in a bean em¬ bryo. (Remember that the embryo of a bean is the part left after you remove the seed covering.) Next, examine the leaves of your seed¬ ling. Identify the leaf stem, or petiole (PET ee ohl), the leaflets, and their blades and veins (Figure 10-1). Do you find a bud at the base of each leaf stem? Compare the root system of your seed¬ ling with the diagram in Figure 10-1. Try to identify the primary (first) root and the secondary roots that branch out from the primary root. Mount one root tip with its root hairs and examine it under the low power of your microscope. Try to find out how many cells are in one root hair. What bryophytes have rhizoids much like the bean's root hairs? Refer to page 123, if you have forgotten. In your record book, sketch your bean seedling and label the parts you have identified. Finally, with a hand lens examine a seed¬ ling from the glass of reddened water. With a red pencil, add red lines to your sketch to show where you saw the lines in your plant. With arrows, show which way you think the water flowed through the water vessels in the plant. 10-1 A bean contains an embryo plant (see Figure 5-13, page 142), ready to grow. A. The roots grow first, and the stem begins to develop. B. Stem now erect, the seedling exposes its partly consumed (why?) seed leaves. C. Note that the first true leaves are simple leaves. These were present in the seed. D. All other leaves will be compound. GROWTH OF A BEAN SEEDLING First true leaves Seed Secondary roots A Seed leaves Primary root > Petiole First true leaves First compound leaves Leaflets Blade of leaflet Veins of leaflet CORN SEEDLINGS. Make similar studies of your corn seedlings. Compare them with the drawings of corn in Plant Chart 2 (following page 288). Note particularly the differences between corn and bean plants as to: (1) arrangement of leaf veins, (2) arrangement of water vessels in the stem (or corn stalk), and (3) attach¬ ment of leaves to stem. Variations in roots, stems, and leaves Bean leaves are compound and have petioles (Figure 10-1). Corn leaves are simple and sheathe the plant stems at their bases (Plant Chart 2). You will remember that beans are dicots and corn is a monocot. The fibrovascular bundles (water and food vessels) in a bean stem are arranged in a ring. In a corn stalk they are scattered throughout the stem. Corn and bean roots are prettv much alike, but radishes and carrots are roots of a different kind. Some kinds of seed plants even have green roots. In beans and corn, the stems and leaves are green, but in most trees, the trunks and older twigs (stems) show no visible green color. The leaves and stem of the Indian pipe are white. Like several other seed plants, Indian pipe has no chlorophyll. Stems usually grow above ground, and roots underground. But there are seed plants with underground stems, and there are seed plants with roots above ground. Roots, stems, and leaves varv widelv J J among seed plants, but in most species, each plays about the same part in the life of the plant. New growth Roots grow mainly at their tips. The growing root tip is protected by a root cap as it “pushes” downward through the soil. Stems grow longer by repeated cell divisions, mainly at the ends of their branches.. Dicot stems (like those of beans ) grow bigger around by re¬ peated cell divisions in a special inside layer. STUDYING ROOT ELONGATION. With a pen, put marks about Vs inch apart on the last inch or so of a young, growing bean root. Record these markings in a sketch. Examine 24 hours later. With a new sketch, show any changes. Repeat each day until you find out where most of the growth occurs. Food storage in seed plants Seed plants store food in various or¬ gans. You can often tell where, by the part of the plant people use as food. Here are a few examples. How many others can you mention? Food Part of plant people eat Celery Petioles of leaves Cabbage and lettuce Leaves White potato Specialized underground stem, called a tuber Radishes, beets, turnips, and carrots Roots Tapioca Made from underground stems of cassava plants Table sugar Refined from sugar beets (roots) or sugar cane (stems) Tea Made of leaves of tea plant Beans Seeds 268 SPECIALIZATION IN HIGHER ORGANISMS Food storage plays an important part in the lives of nearly all seed plants. Food stored in the fall in the roots and steins of trees or shrubs is used the fol¬ lowing spring, when the new growth starts. Plants like the dandelion and ear- rot get their new start each spring from food stored in their roots. Food stored in the seed leaves of a bean supplies the growing seedling un¬ til it can make its own food. All seeds contain some stored food, usually enough for the seedling to get well started. Summing up: the seed plant as a whole The main organs of a seed plant are the roots, stems, and leaves. Many leaves have petioles; others do not. Many leaves are simple; others are compound with leaflets. Monocot leaves are usually parallel-veined; dicot leaves are usually netted-veined. The fibrovascular bundles in dicot stems are arranged in one or more rings; in monocot stems they are scat¬ tered rather hit or miss. Roots, stems, and leaves vary from species to species, but in most seed plants each organ plays about the same part in the life of the plant. LEAVES Leaves vary a great deal in size and shape. The leaves of spermatophytes may be very small, as those of the duck¬ weed, whose leaves are less than an eighth of an inch across. Or they may be very large, as those of some palm trees, whose leaves are as much as 20 feet long. The leaves of our common iris, or sweet flag, are pointed, sword¬ shaped organs, as are those of the cat¬ tail. The leaves of pine trees are more or less needle-shaped (Plant Chart 1, following page 288). One of the most amazing leaves in the world is that of the largest water lily ( Victoria cruzi- ana ), which grows wild in the Amazon River. Its floating leaf blade with turned-up edges may be as much as five feet across, and the leaf stem may be as much as 20 feet long, thus enabling the water lily to grow in water 20 feet deep. The end leaflets of the pea vine serve as tendrils, with which the plant may cling to supports. The two spines at the base of the leaf of black locust and the spines on barberry are modified leaves. Asparagus and most cactuses have no green leaves at all. The great variety among leaves makes it impossible to give one description of leaf structure that will fit all leaves. The following description fits the leaves of many angiosperms. You should re¬ member, however, that it is only gen¬ eral. The leaves of any particular plant mav vary in one or more details. LEAF STRUCTURE. Refer often to the Seed Plant Charts as you continue. A green leaf might be called a food fac¬ tory. How is this food factory built? Exter¬ nally, a leaf is a flattened organ which is attached to the plant stem by a petiole in some plants, but not in others. It may be hard for you to realize that a leaf blade is thick enough to contain several layers of different tissues. However, examine care¬ fully a leaf of a dandelion or a lily or a buttercup or an elm or almost any available angiosperm. You will be able to discover layers in the blade. Tear the leaf blade and examine the torn edges. Look for a thin, colorless skin showing along the torn edge. This is the epidermis. With a pair of tweezers, tear a bit of the epidermis off the leaf blade, mount it, and examine it first under low power of the microscope, then under high power. SEED PLANTS AND HOW THEY LIVE 269 10-2 EPIDERMIS OF A GREEN LEAF From one kind of leaf to another, cells in the epider¬ mis vary in shape. Few cells in the epidermis contain chloroplasts; the leaf’s color comes mainly from chloroplasts in cells beneath the epidermis. The epidermis of a leaf Under the microscope, the epidermis is seen to be composed of a single layer of flat cells. Their shape varies in differ¬ ent kinds of leaves (Figure 10-2). In every leaf, the cells of the epidermis fit together and form the outer covering of the leaf blade. The epidermis is the covering tissue of a leaf. Air enters the leaf through many tiny holes in the epidermis. Each hole or opening is called a stomate ( stoh mayt). (See Figure 10-2.) On your slide, the somewhat doughnut-shaped structures that are scattered all through the epidermis will show you where to look for stomates. Look at one of these structures closely under high power. Can you see the long, slender opening in the center? This is the stomate. It might be compared to the hole in a doughnut. Then the doughnut-shaped part should show up as two long cells, each one forming half the “doughnut” (Figure 10-2). These two cells are called the guard cells. The guard cells contain chloroplasts. Guard cells get their name from the fact that they “guard” the size of the stomates. Under certain conditions— bright light, for one— water from the surrounding cells diffuses into the guard cells. This makes them swell out in such a way that the stomate is opened wider. Under certain other con¬ ditions— darkness, for one— water dif¬ fuses out of the guard cells into nearby cells. This makes the guard cells shrink O back to their former size, thus partially closing the stomate. Usually, the guard cells open the stomates shortly after sunrise and partially close them as night comes on. But this is not always true. For example, on hot, dry days, the stomates may remain partially closed all day. Can you explain why these changes in the size of the stomates are an advantage to the plant? In many leaves, there are far more stomates on the under surface than on the upper; but in a leaf like that of the water lily, most of them are on the up¬ per surface. The stomates are exceed¬ ingly small. An ordinary pinhole is some two thousand times the size of an aver¬ age stomate. It is only because there are so many stomates in the epidermis that the inner leaf tissues are able to 270 SPECIALIZATION IN HIGHER ORGANISMS get enough air. On the average, a square millimeter (this size: ■) of the under surface of a leaf contains any¬ where from 100 to 600 stomates. Meas¬ ure in millimeters ( one inch equals 25.4 millimeters) the length and width of any leaf you have, and estimate how many stomates the under surface might contain. Internal structure of leaves Between the upper and lower epi¬ dermis of a leaf blade, there are sev¬ eral layers of cells which contain chloro- plasts. Next to the upper epidermis there is a layer ( in many leaves, two or more layers) of elongated cells. This layer is called the palisade layer (see Plant Charts). Between the palisade layer and the lower epidermis, there are a large number of rather round cells that fit loosely together, with air spaces between them. These cells make up the spongy layer of the leaf. The cells of the palisade and spongy layers contain many chloroplasts, as you can see in the Seed Plant Charts. Branching through the leaf blade there are many veins (Figure 10-3). These veins are composed of three kinds of cells. Around each vein is a layer of cells which make up the sheath. Within this sheath there are elongated cells of two types: (1) wood cells or xylem, and (2) phloem cells. Together, the sheath and its enclosed xylem and phloem cells make up the leaf vein. The veins are extensions of the fibrovascular bundles in the plant stem. The main work of the leaf The main work of a green leaf is food-making. Green leaves make glu¬ cose (grape sugar) out of water and carbon dioxide. Then they make other sugars and starch out of the glucose. They may even make oils from glucose. And they make proteins out of glucose plus other substances, as you will soon learn. For now, the important thing is to learn to think of green leaves as food¬ making organs of seed plants. 10-3 LEAF VEINS The “skeleton” of a cot¬ tonwood poplar leaf, or of any other leaf, is its network of leaf veins. Marion A. Cox How leaves make glucose Green leaves make glucose out of carbon dioxide and water, but not all in one step. They make glucose by a series of some 20 steps. Each step involves chemical changes. We shall not go into the whole series of chemical changes involved, except to say that there are two main phases in the process of mak¬ ing glucose. One phase requires light. The other may and usually does take place in darkness. Each phase involves a number of chemical changes, but only the start and the finish of this impor¬ tant process will be discussed here. The process starts with carbon diox¬ ide (CO.) and water (H20). After a series of chemical changes, glucose (C6H1206) is formed. 271 Formerly, it was thought that the re¬ action could be summarized as follows: GC02 + GH20 -> c6h12o6 + C02 This equation is read: six molecules of carbon dioxide plus six molecules of water form one molecule of glucose plus six molecules of oxygen. Do you see how this equation balances? On each side of the arrow we find the same number of atoms of carbon (6), oxy¬ gen ( 18 ) , and hydrogen ( 12 ) . However, the equation is inadequate, for many reasons. First, it does not in¬ dicate that a green leaf cannot work without energy. The energy the leaf needs is the energy of sunlight,* and this energy is stored in the glucose that is made. For another thing, the equation does not indicate the role chlorophyll plays in the process. In general, glu¬ cose is made only in those cells that contain chlorophyll. There are a few ex¬ ceptions. Certain purple bacteria make glucose without benefit of chlorophyll; the purple coloring matter seems to take its place. And certain sulfur bacteria actually synthesize sugars without bene¬ fit of either chorophyll or light. But in general, chlorophyll seems to be neces¬ sary in glucose manufacture. A third reason the equation above is inadequate is the recent discovery that the oxygen set free in the glucose-mak¬ ing process comes from the water mole¬ cules, not the carbon dioxide molecules. (Notice that in the equation, 12 atoms of oxygen are contained in the 6 oxygen molecules that are given off, but that only 6 atoms of oxygen are contained in the 6 water molecules from which the oxygen that is set free is supposed to come.) To deal with the three problems * Artificial light of the proper kind will en¬ able leaves to make glucose 24 hours a clay and is sometimes used in greenhouses. discussed, a new equation has been pro¬ posed, as follows: Light energy CC02 + 12IL20 -* c6h12o6 + gh2o + go2 In the presence of chlorophyll What you should remember, however, is that no simple equation is adequate to represent a process so complex that we do not yet fully understand it. The process of glucose manufacture in plants is called photosynthesis (fob toh sin thuh siss ) , from two Greek words —photos meaning “light’’ and synthesis, “putting together.” In photo¬ synthesis, certain raw materials are put together in the presence of light. Recent discoveries Teams of research workers at several institutions are adding to our knowledge of photosynthesis, bit by bit. One of the interesting recent discov¬ eries has to do with the speed of photo¬ synthesis. A radioactive carbon was used in the experiments. Carbon diox¬ ide was prepared from oxygen and this radioactive carbon. The leaves of green plants were then exposed to this car¬ bon dioxide with its radioactive atoms. Within 30 seconds, radioactive carbon showed up in a new compound made within the leaf. Within an hour, it showed up in sugars and in other com¬ pounds made from sugar. When one leaf of an eleven-foot sugar cane was exposed to this “tagged” carbon diox¬ ide, compounds containing radioactive carbon were found in every part of the plant within three days. In another ex¬ periment, radioactive phosphorus added to the soil near the roots of a plant spread quickly through the roots and stem of the plant and into its leaves. In Figure 10-4, you see the “auto¬ graph,” or more properly, the radio- 272 SPECIALIZATION IN HIGHER ORGANISMS iven National Laboratory 10-4 RADIOAUTOGRAPH OF A LEAF This photograph was taken using only light given off by radioactive phosphorus that had spread from the roots to the leaves of the plant through its fibro vascular system. autograph, of the radioactive phos¬ phorus in one of the plant leaves. Research with an oxygen isotope has now shown that all the oxygen set free by green plants comes from the water molecules, not from the carbon dioxide. Scientists had thought that the oxygen set free during photosynthesis came from the carbon dioxide, not the water. And they thought the water molecules went into the sugar molecules whole. They now know that the first step in photosynthesis is the separation of the hydrogen atoms from the oxygen atoms in water molecules. Then the oxygen goes free and may pass into the air. After this start, the hydrogen atoms are passed along through a series of steps until they are finally combined with carbon and oxygen atoms from carbon dioxide, forming glucose. New evi¬ dence makes it necessary for scientists to revise their ideas. Photosynthesis and you Photosynthesis is important to you. Without glucose, you could not live. About one tenth of one per cent of your blood is glucose. There is glucose in every living cell in your body. And yet you can’t make glucose for your cells. You could sit all day blowing your breath through a bowl of water with¬ out producing a single molecule of glu¬ cose in that bowl. The raw materials are there : carbon dioxide in your breath and water in the bowl. But vou can't J make them combine. Neither can a chemist. In spite of all their achieve¬ ments in synthesizing one organic com¬ pound after another, biochemists still (1958) can’t make glucose in the test tube out of carbon dioxide and water. They may do so soon. But until they do, you and all other animals will have to remain dependent on the green plants of the world. Cane sugar Once a supply of glucose has been made by a green leaf, the plant can make other foods from it. For instance, some of the glucose is changed to fruc¬ tose (fruk tolls), another sugar. Then a molecule of glucose unites with one of fructose to form a molecule of cane sugar, called sucrose ( soo krohs ) . The sugar cane and the sugar beet are not the only plants that make sucrose. Green plants generally make it. Sugar canes, however, are about 18 per cent sucrose. Other plants contain far less. For instance, bean leaves are less than 5 per cent sucrose. All gr een plants make surprising amounts of sugar. It has been estimated that an average corn plant makes about two pounds of sugar during its grow¬ ing season. An average acre of corn makes some ten tons, and an average SEED PLANTS AND IIOW THEY LIVE 273 acre of apple trees some eight or nine tons, during a summer. Starch-making Starch can also be made from glu¬ cose. It is made in many plant cells, merely by removing a water molecule from each of several glucose molecules, then linking together what is left into a giant molecule of starch. Fats and oils Like sugars and starches, fats and oils can be made from glucose. This is done by a series of complex changes. First, by means of a process in which some oxygen molecules are set free, sugar is changed to glycerol ( gliss er ohl ) and fatty acids. Three molecules of fatty acid then unite with one of glycerol to make a molecule of fat or oil. There are many kinds of fatty acids and many kinds of fats and oils. You may have noticed how peanut oil stains a paper bag. Time was when all chil¬ dren were familiar with castor oil from the castor bean (it was used as a laxa¬ tive ) , but happily such is no longer the case. Try to list ten different kinds of fats and oils with which vou are famil- J iar— and remember that all of them were made from glucose. Protein-making Plants also make proteins— and cer¬ tain other compounds containing nitro¬ gen— out of sugar. Sulfur and, usually, phosphorus atoms, which plants get from the soil, may also be used in pro¬ tein manufacture. Even a giant protein molecule is made largely from glucose plus nitrogen, sulfur, and phosphorus. Where does the nitrogen come from? The nitrogen molecules come from the air, but not directly. A green leaf is surrounded by air, four fifths of which is free (uncombined) nitrogen, but strange as it may seem, the green leaf is not able to use free nitrogen. It can¬ not take molecules of free nitrogen out of the air and combine them chemically with glucose to make proteins. The green leaf can use only certain com¬ pounds of nitrogen. In nature, these compounds of nitrogen are made by certain kinds of nongreen plants. ( Since the turn of the century, man has been able to make certain nitrogen com¬ pounds by an electrical process.) Plants that fix nitrogen Fortunately for plants and animals, including you, there are certain non¬ green plants which can use free nitro¬ gen molecules. These plants are certain kinds of bacteria and a few other fungi. These particular bacteria are called nitrogen-fixing bacteria, because they fix ( fasten ) free nitrogen atoms in com¬ pounds. In other words, they build the element nitrogen into certain com¬ pounds. EXAMINING NITROGEN-FIXING BAC¬ TERIA. Would you like to see some nitro¬ gen-fixing bacteria? To do so, you will need the roots of a bean, soybean, clover plant, pea vine, peanut, or similar plant. Such plants belong to the family called legumes (leg yooms). Wash the roots of any legume and look for little lumps on them, like those in Figure 10-5 (left). Nitro¬ gen-fixing bacteria live inside those little lumps, better called nodules (nod yoolz). The bacteria in these nodules make nitro¬ gen compounds (fix nitrogen). With a sharp knife, slice open a nodule. Scrape out a little of its contents, mount in water, and examine under high power. You should be able to see hundreds of nitro¬ gen-fixing bacteria (Figure 10-5, right). 274 SPECIALIZATION IN HIGHER ORGANISMS Hugh Spencer 10-5 NITROGEN-FIXING BACTERIA On the roots of this legume (left) are many nodules containing nitrogen-fixing bacteria. When a thin slice of one of the nodules is examined under the microscope (right), hundreds of the bacteria are visible as small black dots. What is the importance of the work these bacteria do? These useful bacteria are always present in the soil. When beans or peas or the seeds of any other legume are planted, they send roots down into the earth. The nitrogen-fixing bacteria soon invade certain cells on the outside of the roots and live there. This invasion by bacteria causes the roots to grow the nodules which may be called “the chemical laboratories” of the nitrogen¬ fixing bacteria. Strange laboratories The nodules on the roots of legumes are strange laboratories indeed. The bacteria in these laboratories take free nitrogen molecules from the air that is in the soil. Next, by means of a com¬ plicated process, they join atoms of this nitrogen to atoms of oxygen and sodium, thus making a compound called sodium nitrate. Or they may use potas¬ sium instead of sodium, forming potas¬ sium nitrate. These nitrates are then used by both the bacteria and the leg¬ ume. The bacteria use some of the nitrates in building up their own proteins. But they make more nitrates than they use. The legume gets some of the extra nitrates from the bacteria, and the bac¬ teria get their glucose from the legume. So the legume (clover, bean, pea, or peanut plant, for example ) and the bac¬ teria are symbionts. (Remember the termites and their protozoa symbionts?) Each one benefits by their close associ¬ ation. And still some nitrates are left over. These remain in the soil after the legume crop is harvested. The next crop on the field then gets nitrates left in the soil by the legume crop. That’s why legume crops are said to enrich the soil. Actually, it is the nitrogen-fixing bacteria that add nitrates to the soil, thus enriching it. SEED PLANTS AND HOW THEY LIVE 275 Not all the nitrates in the soil come directly from nitrogen-fixing bacteria. Some come from man-made nitrates added in fertilizers. Others are released by the action of the bacteria of decay. These bacteria of decay are constantly breaking down dead organic matter, such as leaves, plowed-under rye, ma¬ nure, and dead organisms in the soil. In doing so, they set free the nitrates from the organic matter. Further steps in protein-making The bean plant gets nitrates from its root nodules. Non-leguminous plants get nitrates from the soil. These nitrates circulate up into the leaf and into all other living cells in a plant’s body. Within a living cell, nitrates and sugar are used to build amino ( uh mee noh) acids. In case you are interested, the proteins you eat are digested into amino acids that your body cells re¬ build into other proteins. Amino acids are the building blocks of which proteins are made. There are some 24 different known kinds of amino acids, but all of them contain atoms of carbon, hydrogen, oxygen, and nitro¬ gen. Some of them also contain atoms of sulfur. Out of these amino acids, plants build what chemists call peptide chains. Peptide chains are combinations of amino-acid molecules linked together chemically in long chains. The peptide chains then are also linked chemically to form proteins. A hundred or more molecules of amino acids are linked to¬ gether in a protein molecule. Indeed, in some cases, thousands or even tens of thousands of molecules of amino acids may be linked together in giant J O O protein molecules. Although we can now svnthesize ni- O J trates and even a protein, we and all other living things still depend largely on the nitrogen-fixing bacteria to make the nitrates that go into the proteins that go into all protoplasm (Figure 10-6). Out of the food materials just stud¬ ied, plus water and minerals, the whole plant body is built. In the seed plant, the leaf is the chief food-maker. Its main function is photosynthesis. Photo¬ synthesis is the first step in that phase of the plant’s metabolism ( chemical changes) that has to do with building up its organic compounds. (In addition to the compounds mentioned, each plant makes some compounds peculiar to itself. Think of the odor of onions, for example, or the turpentine of the pine, or raw rubber, or coloring matter in flowers.) Photosynthesis and respiration Photosynthesis serves the plant :n still another way. It furnishes at least part of the oxygen used in respiration. You will remember that respiration is the oxidation of foods in living cells. Of course, plant cells oxidize foods. That calls for oxygen. The living cells in the leaf get at least part of their oxygen from photosynthesis during the day¬ time. At night, they get it from the air. But most of the oxygen in the air came from photosynthesis. So photosynthesis not only supplies food— it also supplies oxygen. You may remember that oxygen com¬ bines with some of the hydrogen in food molecules during respiration, and that this is called oxidation. The equa¬ tion for the complete oxidation of glu¬ cose reads as follows: G02 -f- CeH^Oe — * GH2O -j- GCO2 T Energy In other words, oxidation of glucose is the reverse of photosynthesis. Table 10-A compares the two processes. 276 SPECIALIZATION IN HIGHER ORGANISMS THE NITROGEN CYCLE MAN gets nitrogen in the plant and animal protein he eats PEAS, CLOVER, AND OTHER LEGUMES get nitrogen in nitrates made by nitrogen-Pixing bacteria on the plant roots plant proteins it eats NITROGEN-FIXING BACTERIA bind nitrogen into nitrates on a scale sufficient to supply legumes and many other plants PLANTS OTHER THAN LEGUMES absorb nitrates from soil BACTERIA release nitrogen into air, and nitrates etc., into soil, from dead plants and animals 10-6 All living organisms get nitrogen directly or indirectly from nitrates built up by nitrogen-fixing bacteria. Today man synthesizes nitrates and adds them to the soil to help keep up the supply, but by far most of the nitrates are still furnished by nitrogen¬ fixing bacteria. Other kinds of bacteria help, too, by releasing to the cycle nitrogen and nitrates from dead organisms. Without nitrogen-fixing bacteria and the bacteria that work on dead organisms, life as we know it would not have been possible; none of the higher plants or animals can take its nitrogen directly from the air. SEED PLANTS AND HOW THEY LIVE 277 The equation just given seems to in¬ dicate that living cells oxidize glucose in one step, but they do not. Biochemists now know that many chemical changes occur, one after another, in the com¬ plete oxidation of glucose. Some of these chemical changes are oxidations; others are not. The formula given above mere¬ ly shows the raw materials and the end products. If you are ambitious and want to know more about how living cells get energy out of foods, read “The Mecha¬ nism of Energy Release and Expendi¬ ture,” starting on page 100, in Life by Simpson et ah, Harcourt, Brace, 1957. The important thing to remember is that oxidations are involved in all en- ergy-production in living cells. There are two phases in the metab¬ olism of all plants. In one phase, com¬ plex organic molecules are built up. Photosynthesis is one example. In the other, complex molecules are broken down. Respiration is one example. There are many other examples of both phases of metabolism in all plants ( and in animals, too, as you will see later). TABLE 10- A COMPARISON OF PHOTOSYNTHESIS AND RESPIRATION Photosynthesis Respiration Materials Carbon dioxide, Glucose, other used water foods, oxy¬ gen End products Glucose, oxygen Carbon diox¬ ide, water, energy Nature of the Building up of Tearing down chemical organic com- of organic change pounds compounds When it oc¬ curs Completed only in daylight hours All the time Where it oc- In cells that In every liv- curs contain chlo¬ rophyll ing cell Loss of water from leaves It is inevitable that some water from the moist inner tissues of a green leaf will evaporate into the air through the stomates. In fact, great quantities of water are lost from leaves in this way. It has been estimated that a single corn plant may lose a gallon of water through its leaves on a hot summer day. An ordinary tomato plant loses 30 gallons of water in this way during its brief lifetime, and an average full-grown apple tree loses nearly 2,000 gallons during a summer. This loss of water from the leaves is called transpiration. Transpiration of water from leaves is unavoidable, but is it beneficial to the plant? The consensus today seems to be that it is. As you know, water enters a plant’s roots and travels through the continuous xylem tubes into the leaf. The evaporation of water in transpira¬ tion is said to help keep water coming up from the roots. Transpiration also helps to keep leaves cooler on a hot day, even as the evaporation of perspi¬ ration cools your body. Relationship of leaves to other plant organs Leaves are essentially the food-mak¬ ing organs of the plant. In most plants they are supported and spread out into the air and light by the plant stem, which may or may not branch out into many parts. There are a few plants, such as the dandelion and celery, whose stems are short and under¬ ground. The plant stem serves as a kind of connecting organ between the leaves, which are above ground, and the roots, which are usually underground. Through the stem, various liquids are transported between the roots and leaves, or to and from the flowers and the fruits. 278 SPECIALIZATION IN HIGHER ORGANISMS Summing up: leaves The leaves of most seed plants make glucose out of carbon dioxide and wa¬ ter in the presence of sunlight. They then make starch out of glucose. Seed plants also make fats and oils out of glucose and amino acids out of glucose plus nitrates. They combine amino acids into peptide chains and finally into proteins. The leaf of a seed plant has several specialized tissues: epidermis with guard cells and stomates in it, palisade and spongy layers, and veins of fibro- vascular bundles. All of these tissues work together in making sugar and other foods. The living cells in a leaf use oxygen all the time. They get their oxygen either from the air that enters through the stomates, or from the oxygen set free during photosynthesis. Leaves get nitrates along with water through the xylem in the plant’s fibro- vascular bundles. Legumes get their nitrates from the nitrogen-fixing bac¬ teria in the root nodules. Most other seed plants take in nitrates along with ground water from the soil. Transpiration removes surprisingly large amounts of water from the leaves of seed plants. This is said to help keep the water coming up from the roots and to cool the leaves on a hot day. STEMS Just as leaves of various plants differ, so do their stems. A cornstalk is differ¬ ent from the trunk of a tree, and the stem of an ivy vine is different from either. As you already know, the stems of a number of seed plants are underground. Additional examples are Canadian this¬ tles, many grasses, onions (Figure 10- 10-7 ONION STEM Not all stems are found above ground. The onion stem is the small structure found between the roots and the fleshy scale leaves of the plant. 7), and Solomon’s seal. But most stems are above ground. In spite of many differences, stems are alike in certain features. They usu¬ ally bear buds and leaves. They all con¬ tain fibrovascular bundles and certain other tissues. If you were to cut a cornstalk across with a sharp knife and look at the end of it, you would easily discover its dif¬ ferent tissues. Covering the outside of the stalk is a tough rind (epidermis), which is to the cornstalk what bark is to the tree. Most of the inside of the cornstalk is filled with a soft tissue called pith (Figure 10-8). Sticking out of the pith here and there are the cut ends of tough fibrovascular bundles. SEED PLANTS AND HOW THEY LIVE 279 Tissues in a monocot stem If you now examine microscopically a stained cross section of a cornstalk or any other monocot stem, you will be able to see that the cell walls of the epidermis are thickened. The cells of the pith look much alike. In each fibro- vascular bundle you will see the cut ends of xylem and phloem cells (Plant Chart 2, following page 288). These ends look much like those in the veins of a leaf. As you know, these xylem and phloem cells extend end to end up into the leaf veins and down into the root. Water moves through the root xylem and passes up through the stem xylem into the leaves; dissolved food moves down from the leaves through the stem phloem into the root. 10-8 CORN STEM Unlike the onion stem (Figure 10-7), the corn stem and the stems of most other seed plants are found above ground. The black spots seen in the cross section of the stem are the irregularly spaced fibro vascular bundles. Left, Myron R. Kirsch; right. Hugh Spencer Structure of a dicot stem EXAMINING TWIGS. The best way to begin your study of a dicot stem is to ex¬ amine tree twigs or sections sawed off the stumps of such trees as elm, ash, maple, oak, and cottonwood. Twigs of elderberries are also excellent for these studies. Get such a twig, cut it across, and compare the cut end with Figure 10-9. Try to locate each part of the twig. In the center of the twig is the soft tissue called the pith. Around the pith there are one or more rings of wood, depending on the age of the twig. Each ring of wood is made of xylem cells. Outside the rings of wood there is a ring of living cells called cambium (KAXibeeum), which is not found in monocot stems. Outside the cambium layer there are phloem cells. Next out¬ side the phloem is a living tissue called the cortex, which is usually green. Fi¬ nally there is a layer of bark, in which there is usually some cork. If you exam¬ ine the bark of a twig, you will see that there are dots shattered over its surface. These dots are the openings through which air enters the stem and supplies oxygen to the living cambium cells and to the pith and cortex cells. These openings are called lenticels (len tih sels ) . (See Figure^ 10-9. ) Manv of the dicots are not trees or shrubs. Such plants as beans, gerani¬ ums, daisies, and buttercups are called herbs. These dicot herbs have the same tissues in their stems that trees and shrubs have, and these tissues have the same general arrangement. The chief difference is that the herbs have only one ring of wood, or xylem. (In the buttercup stem in Plant Chart 3, the pith surrounds the hollow center. The pith is surrounded by a ring of fibro- Hugh Spencer 10-9 CHERRY TWIG The arrangement of stem tissues in a cherry tree differs consider¬ ably from that of a corn plant (corn is a monocot, the cherry tree a dicot). Another dif¬ ference between the two is the amount of xylem (wood) and of pith that each contains. The greater part of a cherry stem is made up of xylem, that of a corn stem of pith (the corn’s xylem is in its fibrovascular bundles). vascular bundles, in which are xylem, then cambium, and then phloem tis¬ sues. On the outside of the fibrovas¬ cular bundles are cortex and then the stem epidermis, which encloses the en¬ tire buttercup stem. ) What is the function of the cambium? All dicot stems have a layer of cam¬ bium lying between the xylem and phloem, as you know. Cambium cells are young cells that continue to grow and divide as long as the plant remains alive. When one of the cambium cells divides, the new cell wall always comes in along the length of the cell, dividing it from side to side. When the new cell so formed is on the inside of the cam¬ bium layer, that cell becomes a xylem cell. When the new cell is on the out¬ side, it becomes a phloem cell. In a tree, the new xylem cells formed from the inside of the cambium in autumn months (or in the dry season in the tropics ) are small. Those formed in the spring and summer (or in the wet sea¬ son in the tropics) are larger. The suc¬ cessive layers of large and small xylem SEED PLANTS AND HOW THEY LIVE 281 cells in a tree trunk or a twig are called the annual rings. Usually only one an¬ nual ring is formed each year, but some¬ times two or more rings may be formed if there are two or more successive wet and dry seasons in a year. Functions of other tissues in stems The chief function of most stems is conducting water and dissolved foods and minerals up and down the plant. The fibrovascular bundles make up the conducting system. A second function of most stems is support. Stems hold up the leaves and help spread them to the air and light. The bark or rind and the woody tissue provide most of the sup¬ port. Stems also store food, in the pith in monocots and in both pith and cor¬ tex in dicots. The epidermis or covering tissue of stems protects the softer, living tissues just under it, both from injury and from too much loss of water into the air. Summing up: stems In your record book, answer the fol¬ lowing questions. 1. A white potato is a specialized type of dicot stem called a tuber. Does a white potato contain a layer of xylem and one of phloem? Why did you an¬ swer as you did? 2. Palm trees are monocots. Do their trunks have a layer of cambium? 3. In a maple sugar camp, people bore holes into the trunks of sugar maple trees and insert “tubes” through which the tree sap drains into buckets. Through which stem tissue does this tree sap travel? 4. People sometimes cut out a ring of bark and the underlying tissues around the trunk of a tree to kill it, say, if it is growing so near a city water line that its roots get into the line and stop the water. This removal of a ring of tis¬ sues is called “girdling” a tree. How does girdling kill a tree? 5. Most cactuses have no leaves at all. They do have green stems. What function do cactus stems carry on that is not carried on, at least not to a large extent, by the stems of most trees? EXAMINING PINE TWIGS. Pine trees are gymnosperms, not angiosperms, as you know. Cut a pine twig and examine the cut end. Compare it with the illustration in Plant Chart 1, following page 288. Try to locate in the twig all the tissues shown in the illustration. In your record book, sketch and label the cut end of the twig. Would you say the pine twig is more like the stem of a mono¬ cot or of a dicot? Why? ROOTS There are many different kinds of roots, just as there are many kinds of stems and leaves. The first main root to appear as a seed sprouts is, of course, the primary root. New roots branch out from the primary root, and these may branch again and again to form the complete root system. In the dandelion and some plantains, the primary root is large and strong, as you may have dis¬ covered when trying to dig these plants out of your lawn. Such roots are called taproots. Systems of roots such as those of grasses are called fibrous roots; those of the beet, radish, or carrot are called fleshy roots. All of these kinds of roots are found underground. Some plants have roots or parts of roots above ground. You may be famil¬ iar with the roots that grow out from the lower joints of a cornstalk and ex¬ tend down into the soil below. These 282 SPECIALIZATION IN HIGHER ORGANISMS roots help to brace the cornstalk and are often called brace roots (Plant Chart 2). Several tropical trees, such as man¬ grove, fig, and banyan, produce roots from the trunk or lower branches of the tree. These roots grow down into the soil and thus serve as brace roots much as those of corn do. Some vines, such as ivy and Virginia creeper, climb by means of air roots which attach them¬ selves to the bark of a tree or the wall of a building. Two fairly common parasitic angio- sperms, mistletoe and dodder, have still another kind of root. A dodder clings by means of its short suckerlike roots to the stem of a host plant, such as wheat. These small roots grow right into the xylem and phloem tissues in the wheat stalk. There the dodder roots absorb water, mineral salts in solution, and food made by the wheat. Dodder contains no chlorophyll; it cannot make its own food. It takes some of its host’s food by means of these odd little roots. INTERNAL STRUCTURE OF ROOTS. Ex¬ amine the roots of young bean and corn plants. Slice one of the roots lengthwise and examine it with a hand lens. You will find three regions in a young root, or in any small roots such as those of grasses. The inner core is called the central cylinder and contains xylem and phloem. The outer layer is called epidermis. The tissue that lies between the central cylinder and the epidermis is the cortex. The xylem and phloem are conducting tissues, just as they are in stems and leaves. The cortex and epidermis also have the same functions as they have in stems. Compare your speci¬ men with those in the Seed Plant Charts. Locate each of the three regions. Use a prepared slide of the cross section of a small root for examination under the microscope. Compare your slide with the photographs of root sections in the Plant Charts. Note the kinds of cells in each area of the root. There may be no root hairs on your prepared slide, for root hairs normally occur only near the growing tip of a root. The carrot as a root A carrot has long been studied as a typical root, but recent studies indicate that a carrot, like any root that enlarges by continued growth, differs consider¬ ably from a typical young or small root. As the carrot enlarges, the original epi¬ dermis and cortex are almost entirely lost. A cambium layer appears between the xylem and phloem of the central cylinder and adds new phloem cells on the outside. The edible carrot seems to be chiefly an enlarged central cylinder, with a core of xylem surrounded by secondary phloem (Figure 10-10). 10-10 CARROT ROOT The enlarged pri¬ mary root is the edible part of the plant. What are the functions of roots? Usually a plant’s root system helps to hold (anchor) it firmly in the ground. In other words, anchorage is one func¬ tion of roots. Roots often serve as organs in which O surplus supplies of various foods may be stored. Fleshy roots and the roots of trees are good examples. Storage of foods is thus a function of many roots. Probably the most important func¬ tion of roots is absorbing ( taking in) water and certain necessan/ mineral salts from the soil. These necessary minerals include compounds of nitro¬ gen, phosphorus, potassium, magne¬ sium, iron, manganese, sulfur, calcium, boron, and probably other elements as well. Absorption, anchorage, and stor¬ age are functions of most roots. Roots take in surprising quantities of water. If an ordinarv tomato vine loses J 30 gallons of water by transpiration during its short lifetime, of course the roots must take in far more than 30 gal¬ lons. This is plain, because water is used in making sugar and also is the sub¬ stance in which dissolved foods are transported through the plant’s body. Besides, every living cell in the plant’s body always contains water. There is a constant flow of materials into roots and into and out of all living cells in a seed plant. Summing up: roots In your record book, copy the list of root tissues below. Opposite the name of each tissue, copy that item from the list of functions that best matches it. Root Tissues epidermis cortex xylem phloem cambium (in some roots) Tissue Functions conducts water conducts dissolved foods protects inner tissues produces new xylem stores food THE FLOW OF MATERIALS Just how does water get into a root hair and on through the cortex into the xylem? How does carbon dioxide get into the cells inside a leaf, and how does oxygen get out of them? How does dissolved food get into and out of cells? To answer these questions, you need to understand a common process. The spread of an odor, like that of pepper¬ mint, illustrates that process. How does the smell of peppermint spread? Pour a little oil of peppermint in a dish at the side of a room. Soon a per¬ son clear across the room will smell the peppermint. How can the odor of pep¬ permint oil spread all over a room? Peppermint oil, like everything else, consists of molecules in constant mo¬ tion. As long as the peppermint oil is corked in a bottle, its moving molecules cannot get out. As soon as the oil is poured into a dish, its molecules begin moving out into the air. More and more molecules move farther and farther out into the air. They move on and on until they hit something that stops them, such as the walls of the room. The molecules of peppermint oil move across the room and enter the nostrils of anyone there. It is this spreading of the molecules through the air that ex¬ plains the spread of the odor of pepper¬ mint oil, or of any other odor. The spreading of the molecules of peppermint oil through the air of the 284 SPECIALIZATION* IX HIGHER ORGANISMS room is an example of a common proc¬ ess. You will think of many other exam¬ ples at once. The process is called dif¬ fusion ( dif yoo zh’n ) . Diffusion is the scattering of molecules in all directions by the constant motion of the mole¬ cules themselves. Substances which spread by diffusion are said to diffuse. Liquids may evaporate into the air; this is diffusion. Air may dissolve in water; this also is diffusion. Even solids may diffuse. When you put sugar into a cup of tea, the sugar disappears. You say it dissolves. The sugar molecules scatter out (diffuse) among the molecules of liquid in your teacup. Salt and many other solids also dissolve in water. In diffusion, the molecules of any one substance would seem to move toward the place where there are the fewest molecules of the same kind. Of course, molecules move in all directions. To be strictly accurate, we must say that in diffusion, the greater movement of molecules is toward the place where there are the fewest molecules of the same kind; that is, from the place of the greatest to that of the least concentra- tion of the same kind of molecules. Substances may diffuse through a membrane As you probably know, a hen’s egg has a thin skin just inside the shell. This skin is a membrane. You can use an egg membrane in an experiment to demonstrate diffusion of molecules through a membrane. EXPERIMENT WITH AN EGG. Dilute hy¬ drochloric acid reacts with the limy shell of a hen's egg, so that the shell gradually dis¬ appears. Lay a raw hen's egg in a beaker, cover it with dilute hydrochloric acid, and leave it there until the shell is gone, leaving only the thin inner membrane over the out¬ side of the egg. Then pour out the acid, wash the egg thoroughly, and lay it in a pan of water. Let it stand in water over¬ night. Examine the egg next day. In your record book, tell what you did and what happened. A raw hen’s egg with its shell re¬ moved by acid swells slowly but stead¬ ily when soaked in fresh water. The water molecules diffuse through the membrane of the egg into the inside of the egg faster than any other kinds of molecules from within the egg diffuse out into the water. We say that the egg membrane is much more permeable (per mee uh b’l ) to water molecules than to other molecules. This and other membranes like it are called semiper- meable membranes. There are many membranes through which some molecules will diffuse much more easily than will other molecules. Parchment paper, the skin that lines an egg shell, and the thin layer of cyto¬ plasm (cell membrane) that lines the cell wall of a plant cell are examples. The cell membrane is much more per¬ meable to water than it is to substances dissolved in water; the cell membrane is a semipermeable membrane. The diffusion of water molecules through a semipermeable membrane is called osmosis ( os moh sis ) . Osmosis is a special type of the general process, diffusion. DEMONSTRATING OSMOSIS. Dissolve a teaspoonful of cane sugar in a cup of water. Cap the end of a thistle tube (Figure 10-11) with your finger and fill the tube portion and three-fourths of the enlarged top with the sugar solution. SEED PLANTS AND HOW THEY LIVE 285 Tie a piece of parchment paper or of frog's skin or of pig's bladder tightly over the mouth of the thistle tube. Invert the this¬ tle tube to make sure it is not leaking. Set the inverted thistle tube in a jar of water, and then fasten its upper end to a ring stand so that the bulb of the tube is held well up from the bottom of the jar. You now have sugar water and plain water on the oppo¬ site sides of a semipermeable membrane, the parchment paper or frog's skin or pig's bladder, whichever you used. Mark this this¬ tle tube No. 1. With another thistle tube, marked No. 2, do the same thing, but fill it with plain water instead of sugar solu¬ tion. Suspend the second thistle tube in a second jar of water. With a red crayon or a rubber band, mark the level of the sugar water in No. 1 and the level of the plain water in No. 2. Note and mark the levels after 30 minutes and again after 24 hours. In your record book, tell what you did and what happened. After you read the next paragraph, explain in your record book why you got the results you did. Explanation of osmosis in the thistle tube Sugar dissolves in water. That means that the molecules of sugar move out among the water molecules. Any cubic inch of sugar water has both sugar molecules and water molecules in it. So a cubic inch of sugar water has fewer water molecules in it than a cubic inch of plain water has. Think of it this way. You have two boxes filled with beads. Each box holds just one cubic inch. In one box, some of the beads are black and the rest are white. In the other box, all the beads are white. All the white beads in both boxes are the same size. Naturally there are fewer white beads (water molecules) in the box of mixed beads (sugar water) than in the box of white beads (plain water). 286 Molecules of a given kind diffuse away from the place where they are most plentiful toward places where they are less plentiful. In thistle tube No. 1, water mole¬ cules are most plentiful outside the membrane. So water molecules diffuse into the thistle tube faster than they diffuse out of it. In thistle tube No. 2, water molecules are equally plentiful on both sides of the membrane. So they diffuse in equal numbers into and out of the thistle tube. A few sugar mole¬ cules may diffuse out of thistle tube No. 1, but so few in comparison to the number of water molecules that diffuse inward as to make no noticeable dif¬ ference in the result. Theoretically, osmosis involves only the diffusion of the water through the membrane, so 10-11 DEMONSTRATING OSMOSIS The thistle tube contains a sugar solution of water, separated by an animal membrane from plain water in the beaker. What will happen? Photo by Hugh Spencer 10-12 An experiment with osmosis (Figure 10-11 and text) helps explain how root hairs on plant roots “absorb” water. It is actually osmosis that takes place. The water outside the plant roots contains fewer dissolved materials than the water inside the roots; therefore, water molecules diffuse into the roots from the outside. that if sugar molecules also diffuse to a slight extent, the experiment is no longer one of osmosis but of diffusion in general. Can you explain the distinc¬ tion in your own words? J Turn back now to your record book and explain why you got the results you did in the osmosis demonstration. Root hairs and osmosis A root hair on a root is part of a sin¬ gle plant cell (Figure 10-12). It is lined with a cell membrane, and its vacuoles are filled with water that con¬ tains much dissolved material. Outside the root hair is the soil water that con¬ tains less dissolved material. Therefore, the water molecules in the water inside a root hair are less numerous in a given volume than are those in the soil water outside the root hair. Hence molecules of soil water diffuse through the semi- permeable cell membrane into the root hair. From the root hair the water dif¬ fuses from cell to cell in the cortex until it reaches the central cylinder. This diffusion of soil water into the cells of a root is an example of osmosis. Can you explain why most plants in soil containing salt water die? Digestion and diffusion Plants digest foods, even as animals do. For example, the starch in a grain of corn is digested when the grain starts to sprout. In a grain of corn there is one tissue that contains an abundance of starch. When the grain sprouts, food is needed in the growing root and shoot. Some of this food comes from the starch. The starch grains are located inside the cells of the storage tissue. And starch grains cannot diffuse through a cell membrane. How, then, does the starch in the stor¬ age tissue get to the root and shoot? The giant starch molecule is broken down into sugar molecules. The sugar SEED PLANTS AND HOW THEY LIVE 287 molecules in solution can and do dif¬ fuse through cell membranes; therefore, they diffuse into the growing root and shoot of the young corn plant. This changing of starch to sugar in the corn grain is an example of digestion. Digestion changes complex food molecules into the smaller ones that can diffuse through cell membranes. Without digestion, the starch and other foods which a green leaf builds up could not diffuse out into the phlo¬ em tissue in leaf veins. Glucose in the leaf is an exception. Can you explain why? Other examples of diffusion in seed plants You can probably think of several more examples of diffusion in seed plants. Oxygen diffuses into the air in soil, then into the root hairs and epi¬ dermal cells and on into the cortex. The living cells all over the plant’s body get their oxygen because it diffuses into them. Transpiration is the result of diffu¬ sion of water molecules out of leaf cells and on out through the stomates. (This diffusion of water out of the leaf cells is another example of osmosis. Why?) Carbon dioxide diffuses out of root cells into the air in the soil and out of stem and leaf cells, at least at night. Certain substances in flowers diffuse out into the air. When you breathe in air containing molecules of one of these substances, you say you smell the flower, or that the flower has an odor. Sugar molecules in solution diffuse out of the phloem tissue into living cells in a fruit or root or tree trunk. Nitrates diffuse into root cells from the soil in most plants, but in legumes nitrates dif¬ fuse out of the nodules on the roots into root cells. Diffusion goes on all the time nearly everywhere. Without it, life could not exist. Summing up: the flow of materials Keep in mind the fact that molecules diffuse away from the point of greatest concentration toward points of lesser concentration, as you answer these questions. 1. Why do water molecules and soil- mineral molecules diffuse from a root hair into one cortex cell after another? 2. Why do sugar molecules diffuse out of an old potato into a sprout grow¬ ing from an eye of that potato? 3. Carbon dioxide molecules from the air diffuse into cells in a green leaf during daylight hours. Carbon dioxide molecules diffuse out of leaf cells into the air at night. Why is it that these molecules diffuse in opposite directions at different times during every 24 hours? Before going on to the study of plant sensitivity and behavior, turn now through the Seed Plant Charts. Three types of seed plants are included— a gvmnosperm ( pine ) and two angio- sperms (corn, a monocot; and butter¬ cup, a dieot). Basic structure, plant or¬ gans, and plant tissues are illustrated in full color. Use these charts first to review what you have studied about seed plants. Compare the structure of each part of one plant with that of the corresponding parts of the other two plants. After you have reviewed the basic workings of each plant, study the illustrations of the reproductive process of each of them. This topic will not be discussed until a later unit, but vou may wish to scan it now. 288 SPECIALIZATION IN HIGHER ORGANISMS White Pine Monocot Corn Dicot Buttercup All artwork by CARU Studios, Inc., New York City. Photomicrographs by Triarch Botanical Products, Ripon, Wisconsin; General Biological Supply House, Inc., Chicago, Illinois; Carolina Biological Supply Company, E Ion College, North Carolina. Special acknowledgment is made to Mr. John Limbach of Triarch Botanical Products, Ripon, Wisconsin, who prepared most of the microscopic material for the buttercup (Ranunculus acris) especially for this textbook. All rights reserved. No part of “Seed Plants” may be reproduced in any form, by mimeograph or any other means, without permission in writing from the publisher. © 1959, BY HARCOURT, BRACE AND COMPANY, INC. PRINTED IN THE UNITED STATES OF AMERICA PLANT CHART 1-WHITE PINE Stomates Cambium A. Tip of Branch with Male Cones B. Tip of Branch with Third-year Female Cone Epidermis Phloem Branches Spongy layer Xylem Needles (leaves) C. Stained Cross Section of a Needle (much enlarged) Trunk D. Stained Cross Section of Part of a Five-year-old Stem (much enlarged) Roots Cambium Epidermis Cortex Xylem Phloem E. Stained Cross Section of Part of a Young Root (much enlarged) Bark Cortex Phloem (Photomicrographs of leaf, stem, and root copyrighted by General Biological Supply House. Inc., Chicago, Illinois) PLANT CHART 1-WHITE PINE Pollen sacs Pollen F. Stained Lengthwise Section of Male Cone Bearing Pollen Sacs (enlarged) Scales Pollen coat H. Stained Lengthwise Section of First-year Female Cone after Pollination (enlarged) Nuclei Wings Forerunner of egg cell I. Single Scale of Mid-second-year Female Cone after Pollination but before Fertilization (enlarged) Seed wing J. Mature Seed Released by Third-year Female Cone (top view) Seed leaves K. Young Seedling G. Pollen (enlarged) WHAT IT IS A white pine tree and de¬ tails of each of its four main kinds of organs (leaves, stems, roots, and reproductive or¬ gans) are shown on these pages. The main body of the plant is made up of the roots, stems (trunk, branches, and twigs) , and leaves. Note the extensive root system, the general shape of the tree due to the straightness of the trunk and the arrangement of the branch¬ es, and the five leaves or needles in each cluster (A and B). Compare the tissues in a leaf (C), stem (D), and root ( E ) with tissues in corresponding organs of corn and butter¬ cup plants, shown on the next two charts. Also compare reproductive structures in the three plants. WHAT IT DOES The pine’s roots anchor the tree, absorb and transmit soil water (bearing minerals) to the trunk, and store food. The trunk and branches support the tree, transmit water to the leaves and food to the roots, and also store food. The leaves make the food, using water and carbon diox¬ ide (in the presence of sunlight and chloro¬ phyll) to build simple sugars. The male cones (A and F) and female cones ( B and H) are reproductive organs. Pollen (G) from male cones is wind-borne to first-year female cones. Pollination takes place (/) but fertilization does not occur until a year or so later. The seeds ( J ) mature dur¬ ing the third year. (Photomicrographs of male and female cones copyrighted by General Biological Supply House, Inc., Chicago, Illinois) PLANT CHART 2-CORN i Phloem Guard cell Stomate Guard cell Upper epidermis Staminate flowers (tassels) Lower epidermis A. Stained Cross Section of Part of a Leaf (much enlarged) Fibrovascular bundles ^ Pistillate flower (young ear) Phloem Epidermis (rind) B. Stained Cross Section of Part of a Stem (much enlarged) Leaves Epidermis Cortex Central cylinder Phloem C. Stained Cross Section of Part of a Root (much enlarged) Fibrous roots (Photomicrographs of leaf and stem copyrighted by General Biological Supply House, Inc., Chi¬ cago. Illinois; photomicrograph of root, Caro¬ lina Biological Supply Company, Elon College, North Carolina) PLANT CHART 2-CORN Filament Anther D. Stamens on a Tassel (much enlarged) Silks (styles) E. Pistillate Flower (young ear) WHAT IT IS A com plant, like other seed plants, has four main organs— roots, stem, leaves, and reproductive organs (flowers). The tissues in its leaves (A), stem ( B ), and roots (C) are similar to those in other seed plants, but the arrangement of these tissues (scattered fibrovascular bundles in the stem, parallel veins in the leaves, one seed leaf in the seed, and other features) sets a corn plant apart from many other seed plants. For example, a corn plant produces flowers— tassels {D) and young ears (F)— unlike a pine tree, which produces cones. Corn is an angiosperm (flowering plant) and a monocot (producing one seed leaf per seed). The buttercup on the plant chart following this one is also an angiosperm, but a dicot (producing two seed leaves per seed). WHAT IT DOES The corn plant’s roots anchor the plant. They also absorb soil water (bearing minerals) and transmit it through xylem tissue to the stem. The stem supports the plant, transmits water (through xylem) to the leaves and food (through phloem) to the roots, and stores food (in the pith). The leaves make the plant’s food and transmit it to the stem. The tassels are the male or staminate flowers. They produce pollen, which is windblown to the silks ( F ) of the female or pistillate flowers— the young ears. Pollen tubes grow through the length of the silks, and fertilization then takes place, after which the ovaries mature (G) into ripe kernels of corn. F. Pollen on Silks (enlarged) G. Ovaries, with Silks Shoot Remnant of grain Roots H. Seedling (Photomicrographs of stamens, on tassel and pollen on silks copyrighted by General Bio¬ logical Supply House, Inc., Chicago, Illinois; photograpli of young ear, Carolina Biological Supply Company, Elon College, North Car¬ olina) PLANT CHART 4-METHODS OF POLLINATION A. Self-pollination (garden pea) Staminate flowers B. Pollination by Insects (clover) WHAT IT IS— WHAT IT MEANS Three common methods of pollination are shown here. The garden pea (A) and certain other plants are normally self-pollinating. Their flowers have both stamens and pistils, and the flowers’ parts are so arranged that the stamens and pistils are completely enclosed. Clover blossoms are commonly insect- pollinated. The bumblebee shown here on a clover blossom {B) is covered with pollen. As the bee travels from flower to flower, it takes pollen with it. Corn is commonly wind-pollinated. Pol¬ len from stamens on a tassel falls or is blown onto silks of young ears on the same or a different plant. Part of flower cut away to reveal stamens and pistil Pistillate flower C. Pollination by Wind or by Pollen Falling from Stamens (corn) SENSITIVITY AND BEHAVIOR You already know that all living things are sensitive and react to things around them. Seed plants are no excep¬ tion. They are sensitive to a number of things and react to them. But it may seem strange to you to talk about the behavior of seed plants. What is behavior? Such expressions as “Behave your¬ self, Johnny,” or “Johnny has behaved very badly today” are common in the American home. The word “behavior” is popularly used to refer to human ac¬ tions of which we approve or disap¬ prove. Biologists use the word “be¬ havior” in a different sense. In biology, all the reactions of any organism make up its behavior. When you look at it that way, you can see that “behavior of seed plants” is a meaning¬ ful expression, because they do react to light and a number of other things. A house plant in a room with only one window turns toward the window (Figure 10-13). This is a reaction to light. The light stimulates the plant, and the plant then turns toward the light. The light is the stimulus and the turning is the reaction, or response. All the responses of a seed plant to stimuli make up its behavior. No one ever tells a plant to “behave itself.” What would you think of any¬ one who set a plant on a table before a window and then said to the plant, “Behave yourself; don’t turn toward 10-13 PLANT RESPONSES To test their reactions to light as a stimulus, these three plants were placed in different positions with respect to a source of light on the right. After some days had passed, all three plants had made an obvious response. (Two of the plants also had reacted to gravity; their stems turned upward.) Boyce Thompson Institute for Plant Research the window.” As you know, in a few days at the most, the plant would have turned its leaves toward the window just the same. In other words, plants are not sensitive to spoken words, so they cannot react to them. Light is a stimulus to green plants. The spoken word is not. Plants react to only a few stimuli in comparison with the number that cause reactions in the higher animals. Plant behavior is on a lower level of organiza¬ tion than animal behavior, but its reac¬ tions are behavior, as biologists use the word. DEMONSTRATING PLANT BEHAVIOR. You will need beans or peas that have been soaked overnight, radish seeds, paper towels, sawdust (loose soil will do), water glasses, a sponge, and some string. 1. Line several water glasses with paper towel, then fill the space inside the towel with sawdust. Add enough water to the sawdust to make the paper towel moist but not wet. Keep the sawdust moist as you proceed. 2. Place soaked beans or peas between the towel and the glass in each of your glasses. Then place the glasses in good light. 3. Examine the glasses each day. As soon as the roots and shoots are an inch or so long, note which way they point, up or down. Then lay each glass on its side. After a day or two, note the direction the roots and shoots now point. Finally set the glasses wrong side up and note what hap¬ pens to the roots and shoots in a few days. 4. Tie a long string to a sponge. Moisten the sponge well. Then sprinkle radish seeds all over it. Hang the sponge up and keep it moist from day to day. Examine the radish plants on all sides of the sponge as soon as they show growth. 5. In your record book, tell whether the roots and shoots turn up or down. What stimulus do you think caused these turn¬ ings? Also describe differences in the turnings of the radish seedlings on the top and those on the bottom of the sponge. Which stimu¬ lus, water or gravity, seems to have the stronger effect on the radish roots? Plant reactions Plant reactions consist largely of turnings. Leaves turn toward the light. Roots turn toward gravity. Roots turn toward moisture. The growing tip of a stem turns away from gravity. Biol¬ ogists call all such turnings tropisms (troh pizmz ) . A turning toward a stim¬ ulus is called a positive tropism; a turn¬ ing away from a stimulus, a negative tropism. Each tropism gets a special name from the stimulus that produces it. When water is the stimulus, the re¬ sponse is hydrotropism ( hy drot roh pizm). Responses to gravity are geotro- pisms ( jee ot roh pizmz ) , from geo¬ meaning “earth.” Then there are chem- otropisms (responses to chemicals), phototropisms (responses to light), and thermotropisms (responses to heat). What is the basis of plant behavior? You have seen nerve cords and sense organs in several animals. But you haven’t seen anything even remotely resembling nerve cords or sense or¬ gans in plants. Plants do not have nerv¬ ous systems. Plants do not have any organ system specialized in being sensi¬ tive and reacting to things. Plant behavior is based at least part¬ ly on its body chemistry. In the growing tips and in other parts of the plant, the cells produce chemicals that affect the plants behavior. These chemicals dif¬ fuse from cell to cell and cause changes 290 SPECIALIZATION IN HIGHER ORGANISMS in cells at some distance from the cells that make the chemicals. We call all of these chemicals plant hormones (hor mohnz ) . Biochemists have discovered a num¬ ber of hormones in seed plants. Best known of these are the auxins (awk sinz ) . Auxins play the main part in phototropisms and in several other tro- pisms. Let’s see how they work. The cells in the growing tip of a stem, say, produce an auxin. The auxin travels down through the plant stem and stimulates growth of the cells in the stem. For some unknown reason the auxin diffuses in greater quantities into those cells on the dark side of the stem, the side away from the window or away from the light in other situa¬ tions. As a result the cells on the dark side of the stem elongate faster than those on the light side of the stem. This naturally bends the stem toward the light (Figure 10-13). So phototropism in the stem and leaves is due to the growth of longer cells on the dark side than on the light side of the stem. So it would be more correct to sav that J stems grow rather than tarn toward the light. Another auxin plays a part in geotro- pism, both positive and negative. This auxin works in a way opposite to that described in the preceding paragraph. When a root points to one side (as in the water-glass “gardens’’ you laid on their sides), more of this auxin moves from the growing tip into the epidermal cells on the underside of the root than into those on the upper side. Concen¬ trations of this auxin inhibit or deter growth. So the upper cells containing less of the auxin elongate faster and the root tip grows downward ( positive geotropism). In a stem on its side, an auxin concentrates in the cells on the underside of the stem, and the stem grows upward (negative geotropism). In this case, does the auxin promote or inhibit growth in the cells it affects? Auxins and probably other plant hor¬ mones play a part in plant behavior. So body chemistry seems to do for plants at least some of the things that nervous systems and animal hormones do for animals. Other types of plant behavior Plants may wilt on a hot, dry day. This results in drooping leaves, a re¬ sponse to dry air, apparently. How does it work? On a hot, dry day, plants may lose water faster by transpiration than they can replace it with ground water. A cell that has its usual amount of wa¬ ter in it is firm— we say it is turgid ( ter jid). But a cell that is losing water molecules faster than it is taking them in becomes limp, in somewhat the way a toy balloon does when you let most of the air out of it. We say the cell loses its turgor ( ter ger ) . When the cells in leaf petioles lose their turgor, the leaf droops. That’s why some plants wilt on a hot, dry day. As far as we know, plant hormones have nothing to do with this kind of plant behavior. Do you remember that light usually makes guard cells swell, which in turn causes the stomates to open wider? Can you explain this in terms of turgor? Apply heat to or touch the tip of the leaf of a sensitive plant ( Mimosa pu- dica, Figure 10-14) and the leaf droops, almost at once. If you want to see this rather unusual type of plant behavior, get some seeds of a sensitive plant from a nursery and raise some plants. In this case, applying heat to the tip of a leaf causes cells at the base of the petiole to lose their turgor rather quickly. Why, we still do not know. SEED PLANTS AND HOW THEY LIVE 291 ' pH mm? 'turn# ■ > • >'X 'i't *}.;&<' 'i» I > {*' <; >>>• < >;* hi ; ss? sp — Pr;S® >« : : > • ■ < : <•:■: oxws \>v<*>v:>;:<:; >tt*wW :;>>:<•»:<<<<• >:< PlllPi'® >>v.. -N- • !»">"«'( "> • '> •••••' tsilg-k Hi ?*p>.<5 ; *« >:< > j > • iZi-X. 4 ;.-a > i \ H \ii I MM & ■•■■■■ - > - i 'aw<£> < ; wii Hi. •''} x ; ?i « ;? ;««£$£•& < jx- •. < . |fl$w • ■ ■ Ki?j^ox;,x5h JL! K$ $i*5 'i:-'.' $gf§ «>■ «>' : <> L' :;::rlil^ ♦♦. - .. •-. . . >y.< IlIPi I 'ill iilB , : iffiK*! r-iSt -fl#! f!" $bj »<<'{<><< it .*?»«* 5 'w”*‘ ill USXSaXSaJ tT** <{ j < ; lWi|^atu:rr>r :.: KH%. ji.; j • .* ;'j rjt,., , , .<».«♦.<•<-'• :? H 1 3 5 i\m ■ 3; £3a;!Ht » w.»v» 'i-*'' *<»►» <'•,'<* ' h » «5 > - A -A ')» AAV !v/Ay(?wJ*A'< 'X < ;'i , i uHifii; o ’{< >< •; - ' ii'uX'V t? »•? :<: Hvi i • • ...; " . ,.: i.iiiQiiii;!:.-; - . ;»*<»<***'« ,<,« ,»V,A.. *• A> A. «.»< >» <*}< »<♦>'< k ' ' ' m , .. , -»-w* - //..*- a. m N»»i Si; ! m§m itffSHir.siiiii Git' tvuiwy. Myron R. Kirsch 10-14 SENSITIVITY TO HEAT Top. Heat from a burning match is applied to a leaf of Mimosa pudica. Middle. Immediately the leaves begin to lose their turgor. Bottom. Minutes later, the reaction is at its extreme. Still other stimuli affect plant be¬ havior. Some plants won’t bloom unless they get ten or more hours of light. J O O Chrysanthemums are an example. In greenhouses, keeping chrysanthemums in the dark all but eight hours a day de¬ lays their blooming. Can you think of other stimuli that affect plants? CHAPTER TEN: SUMMING UP You should now be able to look at the plant as a whole and see the parts played by leaves, stem, and roots in maintaining the life of the plant. Glu¬ cose is made in the leaves. It may be transported through the phloem direct¬ ly to all parts of the plant. Or it may be built into other sugars or into starches and oils— or into proteins, if nitrogen and perhaps sulfur or phosphorus are added. The leaves are essentially food¬ making organs. The stem transports water and foods in solution. The roots absorb water and minerals in solution. Each plant organ has other functions: roots anchor the plant, the stem sup¬ ports it, and any plant organ may serve as a food storage place. Oxygen enters leaves through the stomates, enters stems through sto- mates or lenticels, and enters roots through the root hairs. Of course, some of the oxygen used by leaf cells comes from photosynthesis during daylight hours. Auxins play a part in the tropisms that make up most of the seed plant’s behavior. Light, gravity, water, and some other stimuli produce responses, usually growth responses in certain cells, so that plant organs seem to turn toward or away from a given stimulus. The plant as a whole is a well-co¬ ordinated organism with each part carrying on its particular functions in maintaining the individual. The plant makes and digests food, respires, ex¬ cretes, grows, and is sensitive and re¬ acts. Bv these life processes, a seed plant maintains its own life. 292 SPECIALIZATION IN HIGHER ORGANISMS Your Biology Vocabulary You have met a number of new terms in this chapter. It will pay you to make sure you understand and can use the following terms correctly. petiole primary root secondary root root cap stomate guard cells palisade layer spongy layer photosynthesis nitrogen-fixing bacteria legumes amino acids peptide chains transpiration pith rind of cornstalk cortex lenticels cambium taproots fibrous roots air roots diffusion permeable membrane semipermeable membrane osmosis behavior stimulus response plant hormones auxins negative tropism positive tropism turgor Testing Your Conclusions Copy the numbers of the items in Column A and beside each, write the letter of the term from Column B that is most closely associated with it. do not mark this book. Column A 1. nodules on legume roots a. 2. digestion b. 3. auxins c. 4. loss of turgor d. 5. amino acids e. 6. stomates f. 7. transpiration g. 8. photosynthesis h. 9. chloroplasts 10. cell membrane i. j- k. l. More Explorations Column B wilting of a plant openings in leaf epidermis xylem and phloem glucose manufacture nitrogen-fixing bacteria normal diffusion of water out of leaves building blocks of proteins process by which molecules of water en¬ ter a living cell tropisms semipermeable membrane glucose-making structures breaking down complex food molecules into simpler ones 1 . A study of annual rings. If you can find a wood lot or forest where trees are being cut, examine some of the stumps for annual rings. Estimate the age of some of the SEED PLANTS AND HOW THEY LIVE 293 trees by counting the rings in the cut top of the stump. Compare the diameters of some of the trees still standing with that of a stump, and try to estimate the age of several of the standing trees. 2. Osmosis in spirogyra. Prepare three sugar solutions: (1) a 1-per-cent solution, (2) a 5-per-cent solution, and (3) a 20-per-cent solution. On one microscope slide place a small drop of the 1 -per-cent solution, on a second slide a small drop of the 5-per¬ cent solution, and on a third slide a drop of the 20-per-cent solution. With a wax pencil, number the slides 1, 2, and 3. Place a few short threads of spirogyra or some other pond scum in each drop, and add cover slips. After ten minutes, examine each slide under high power. On a page of drawing paper, sketch one cell of the pond scum in each sugar solution. Be sure to note beside the drawing the solution in which that cell was. Below your drawings explain briefly the results observed. 3. Experiment with an auxin. You can get an auxin at a seed store or nursery. Cut slips from a number of plants and apply the auxin (growth substance) as directed on the package. Also cut a growing tip off a plant, apply the auxin, and see what happens. In your record book, tell what you did and what happened. Also explain the results of removing the growing tip from a plant. Thought Problems 1. Botanists estimate that nine tenths of all the photosynthesis in the world takes place in algae that live in the seas. How does their photosynthesis benefit human beings? 2. Leaves can be dried and then crushed into fine bits. These bits of dead leaves, when mixed with water and exposed to sunlight, give off oxygen for a short time, but they do not make glucose. In other words, even dead leaves seem to be able to carry out the first step in photosynthesis— the separation of the hydrogen atoms from the oxygen atom in a water molecule. Is this oxidation? 3. Sap is collected from sugar maple trees and boiled down into maple syrup, usually in February and March. There are no green leaves on the tree at this time. Where did the sugar in the maple sap come from? 4. Lawn grass may turn yellowish when there isn’t enough nitrate in the soil. What is the stimulus and what is the response, when this happens? Is this a tropism? Why? Further Reading L Food and Life, Yearbook of Agriculture, 1939, U.S. Dept, of Agriculture, and many other U.S.D.A. Yearbooks are full of reports on experiments that have to do with the way our crop plants maintain themselves. Read up on one experiment and report in class. 2. To find out more about plant behavior, read about it in a college text. “The Plant as a Living Mechanism, ” pages 256-81 in Botany, Second Edition, by Wilfred W. Rob¬ bins and T. Eliot Weier, Wiley & Sons, 1957, discusses plant hormones and other fac¬ tors that affect behavior. 3. Another good book for further reading about plants, their behavior, and how they maintain themselves is Botany: Principles and Problems, Fifth Edition, by Sinnott and Wilson, McGraw-Hill, 1955. 294 SPECIALIZATION IN HIGHER ORGANISMS CHAPTER Vertebrates and How They Live The vertebrate body is almost unimaginably complex , yet all its parts work together with a precision unmatched by any engineering feat of man. How much do we know of the intricate machinery that enables vertebrates to live? "The motion of the heart and blood" Right now, you know a good deal more about the machinery of the verte¬ brate body and how it works than any¬ one in the whole world knew, say, in 1607, when the settlers were founding Jamestown, Virginia. When you finish this and the next unit, you will know quite a few things about the vertebrate body in general, and the human body in particular, that no one in the whole world knew, say, on December 17, 1903, when the Wright brothers launched the first airplane at Kitty Hawk. You know that the heart pumps blood and that the blood circulates through a closed system of blood vessels all over the body and back to the heart again. In 1607, no one, not even the doctors, knew these things. As far as we know, no one anywhere was even doing experiments to find out what the Carolina Biological Supply Co. beating heart does or where the blood goes when it leaves the heart. But by 1620, when the Pilgrims landed on Plymouth Rock, one man was deep in his researches into these problems. This man was William Harvey (1578-1657), a London physician and lecturer at a medical college there. Like his contemporary, Van Helmont of willow-tree fame, Harvey (Figure 11-1) dared to question the widely ac¬ cepted teachings of the ancients. He questioned in particular their teachings about what the beating heart does and where the blood goes. Plaving raised these questions in his own mind, Har¬ vey set about trying to find the answers by means of animal dissections, weigh¬ ings of blood, and by counting pulses. In other words, Harvey employed methods now in common use among scientists, but almost nonexistent then. VERTEBRATES AND HOW THEY LIVE 295 National Library of Medicine 11-1 WILLIAM HARVEY Over three hun¬ dred years ago, Harvey concluded that blood circulates again and again through¬ out the human body in a closed system of vessels. One of the careful drawings he made to illustrate his findings is repro¬ duced here. the heart could pump 34 pounds of blood an hour with less than 15 pounds of blood in the whole bodv. He did J some hard, straight thinking and came up with the answer. The only way the heart could pump 34 pounds of blood an hour was to pump the same blood over and over again. So the blood must flow out of the heart through arteries and back into the heart through veins. And he was right, as you know. The vertebrate heart does indeed pump the blood out through the arteries. And that blood does circulate through a closed system of blood vessels and back to the heart again. By 1628, Harvey was ready with his answers. In that year, his treatise, titled and written in Latin, was published. Translated, the title is Anatomical Studies on the Motion of the Heart and Blood of Animals. You can read a mod¬ ern translation of that treatise, if you wish. See Further Reading at the end of this chapter. ORGANIZATION IN THE VERTEBRATE BODY Harvey once had the chance to weigh the blood left in a human heart after death. He also measured the size of the openings out of the heart into the arteries. Then he estimated how much blood goes out of the heart each time it beats. By counting the pulse of a number of healthy people, Harvey then estimated how much blood leaves the human heart every hour and arrived at the figure of 34 pounds. (We now know that the heart of a human adult pumps, on the average, some 600 pounds or more of blood every hour.) Harvey knew that the whole body of a human adult has less than 15 pounds of blood in it. So he asked himself how You are a vertebrate of the mammal class. You will remember that the com¬ mon classes of vertebrates are: (1) fish, (2) amphibians, (3) reptiles, (4) birds, and (5) mammals. You will remember, too, that biologists rank vertebrates as the “highest animals” because there is greater specialization within some of their organ systems than is found in the animals in any other animal group. The vertebrate body shows the highest level of organization in the animal kingdom. From fish to mammal Certain organ systems of the fish show less specialization than do these same systems in birds and mammals. 296 SPECIALIZATION IN HIGHER ORGANISMS This is particularly true of the circula¬ tory system and the nervous system. Frogs (amphibians) rank above the fish but below the birds and mammals in the degree of specialization in these two systems. Reptiles rank somewhat above the amphibians, but still below the birds and mammals. So there is an increasing level of body organization, especially within the circulatory and nervous systems, rang¬ ing upward from fish to the birds and mammals. Nevertheless, even these sys¬ tems are enough alike in all vertebrates to be discussed together in a general way. Vertebrate organ systems Vertebrates have about the same organ systems that arthropods and mol- lusks and echinoderms have. How many can you name? List all you can think of, then check your list with this one. Vertebrates have the following organ svstems: J digestive system circulatory system locomotion system (or muscular and skeletal systems) respiratory system excretory system nervous system reproductive system Arthropods, mollusks, and echino¬ derms have these same systems, but without as much specialization within each system as in vertebrates. Let’s take a quick look at the circulatory sys¬ tem of a vertebrate, as one example of the higher level of organization. The circulatory system Since the time of Harvey, scientists have learned more and more about the circulatory systems of vertebrates. But first let’s review what Harvey proved. Harvey proved that the vertebrate heart is a pump. And he proved that the blood travels away from the heart through arteries and back to the heart through veins. ONE OF HARVEY'S DEMONSTRATIONS. You can repeat one of Harvey's demonstra¬ tions. Pick out a vein in your forearm, or on the back of your hand. With the tip of one finger of the other hand, push the blood in that vein toward your fingers and hold it there a few seconds. Now push the blood in that same vein in the other direc¬ tion. How does this indicate that the blood in that vein is flowing toward your heart? Harvey never was able to demon¬ strate how the blood gets out of the ends of the smallest arteries and into the ends of the smallest veins to flow back to the heart. Doubters used to ask Harvey this very question. Harvey said he was sure that some very small blood vessels must connect the ends of the arteries and veins. And he was right. But it took a microscope to prove it. Harvey had been dead four years when an Italian doctor discovered those small blood vessels with a microscope in 1661. That Italian was Marcello Malpighi (mahl pee gee ), the founder of the study of animal tissues under the microscope. This special field of biology is now called histology (hiss tol uh jee). Mal¬ pighi discovered the small blood ves¬ sels in the lungs and in the bladder of frogs. In this way, he forged the final link in the chain of evidence showing that a vertebrate’s blood circulates through a closed system of blood ves¬ sels. Today we call these small con¬ necting blood vessels capillaries, as you already know. VERTEBRATES AND HOW THEY LIVE 297 Today we know further that a verte- 1 Hate’s heart is more highly specialized and more efficient in pumping blood than the heart of any other animal. For one thing, it is divided into at least two chambers, even in fish— a receiving chamber into which the blood flows from the veins and a discharging cham¬ ber which pumps blood out into the arteries. For another, there are valves in a vertebrate’s heart that keep the blood from flowing backward. You will learn more about these valves later. Today we also know that the largest arteries in a vertebrate’s body “beat.’’ The muscles in the artery walls con¬ tract just after the heart pumps blood into them. This helps to push the blood forward. It is this “beating” of an artery that you feel when you count your pulse. We know further that the veins of higher vertebrates ( mammals, for example) have valves in them which keep the blood from flowing backward (away from the heart) through the veins (Figure 11-2). LOCATING A VALVE IN A VEIN. Hold your right hand tightly around your left wrist for a few seconds and watch the veins 11-2 VALVE IN A VEIN A. With each heartbeat, blood in a vein is pumped to¬ ward the heart. B. Between heartbeats, each valve closes, keeping the blood from backing up. on the back of your left hand. You should be able to see one or two little lumps or swellings in at least one vein. Each lump marks the location of a valve in that vein. Study Figure 11-2 to understand how these valves work. Then, in your record book, make a sketch of your own to show how a valve keeps the blood from flowing back¬ ward in a vein. Think back now to what you learned about the circulatory system of the earthworm with its aortic arches, or of the lobster with its blood sinuses. You can see that the circulatory system of a vertebrate is considerably more high¬ ly specialized. The same thing is true of other systems. The vertebrate nervous system Any way you look at it, a vertebrate’s nervous system is many times more complex than that of an earthworm, a clam, or even a lobster. In those ani¬ mals, as you know, the “brain” is a mere pair of ganglia (in the lobster, these are fused into one large ganglion) and the nerve cord ( or cords ) is a rather simple chain of ganglia. The brain and nerve cord of any animal make up its central nervous system. Now take a quick look at the central nervous system of a vertebrate, such as a frog. Refer often to Frog Chart 3, fol¬ lowing page 304, as you read on. A frog's central nervous system con¬ sists of a brain and a nerve cord, usuallv called the spinal cord. But the brain is no mere pair of ganglia, as you can see in Figure 11-11, page 319. The frog's brain has several parts. It has a pair of olfactory ( ol fak tuh ree) lobes at its anterior end, then the cere¬ brum ( seh ruh brum ) , then a pair of optic lobes, then a cerebellum ( ser uh BELum), and at the posterior end a medulla ( meh duhl uh ) . Each of these parts is specialized as a center of a par¬ ticular class of reactions, as you will learn later. The point now is that here is a brain that is highly developed and specialized. The frog’s spinal or nerve cord is also highly specialized. The sense organs of a vertebrate also rank above those even of a lobster in the degree of specialization they reveal. Other organ systems Other organ systems of vertebrates also show greater specialization than those of any animals in other phyla. You will learn about this increase in specialization as you proceed. But first, it will be better to study in some detail the organ systems of a fish and a frog. This will lay the founda¬ tion for further explorations of the way the higher vertebrates and especially human beings carry out the basic life functions. Summing up: organization in the vertebrate body Pick out the two true statements in the following list. 1. Vertebrates have several more or¬ gan systems than arthropods have. 2. William Harvey proved that a vertebrate’s blood circulates through a closed system of blood vessels. 3. William Harvey guessed that what we call capillaries are present in higher animals, but he never saw any capillaries. 4. The organ systems of fish and mammals are about equally specialized. THE FISH People go fishing all over the world. And they have been going fishing for thousands of years. Fish live in streams and rivers, ponds and lakes, and in all the oceans. Wherever you find a body of water, even in underground streams in a cave, you are likely to find fish of some kind. The bony fish have moved into and occupied water habitats every¬ where. The story of fish and how they live is a story of a highly successful and varied underwater life. Food-getting among the fish HOW DOES THE YELLOW PERCH GET ITS FOOD? You already know that fish strain food out of the water with a device in the back of the mouth. Now examine the "strainer" in the back of the mouth of a preserved yellow perch. Cut the corners of the perch's mouth so you can open its mouth wide. Look inside for the eight gill slits, four on each side of the throat. Every time the perch gulps water (a good many times a minute), that water passes out through the gill slits into the gill chamber. What keeps the food from going out, too? With a dissecting needle, pry apart the two sides of one gill slit. The "teeth" along each side are gill rakers. (If you have for¬ gotten what gill rakers are, refer back to Figure 3-13, page 92.) Open another gill slit the same way and look for the gill rakers. In your record book, draw a map of the "strainer" in the back of a perch's mouth and show how the gill rakers fit together and serve as a device that strains food out of the water. Fish eat many kinds of food. Many large fish eat smaller fish, as well as other organisms, such as small crus¬ taceans, which they strain out of the water. There are areas in the Antarctic and the Arctic, too, where diatoms (microscopic plants ) are the only plants VERTEBRATES AND HOW THEY LIVE 299 in the water. There all the fish and oth¬ er water animals depend directly or indirectly on the diatoms for food. J Lack of space here makes it impos¬ sible to discuss the many varieties of food used by fish and the methods used to capture the food. The main point is to understand how the gill rakers work. How do fish get oxygen? EXAMINING THE GILLS. Use the pre¬ served yellow perch. Better yet, use a fresh-caught fish, if you can get one. Cut away the gill cover on the side of the head. This exposes the gill chamber, with the gills in it. In a freshly caught fish, the gills are red, but in a preserved fish, they are not. Count the gills. In a preserved specimen, you will have to separate one gill after another to count them. How many gills do you count? With scissors, cut one gill and its rakers loose at each end and remove it from the gill chamber. Compare it with Figure 3-13, page 92. Locate each labeled part, in¬ cluding the gill filaments. Does the gill arch (the U-shaped bend at the top of the gill) seem to have bone in it? In your record book, sketch a gill. Label the gill rakers, gill arch, and a gill fila¬ ment. Record how many pairs of gills the fish has. Anyone who has caught fish and strung them on a line knows that the gill filaments are red. That is because these hollow filaments are filled with blood. The blood comes directly from the heart, after having circulated through the whole body. So the blood that enters the gill filaments is low in oxygen and high in carbon dioxide. Can you explain why? The blood gets its new load of oxygen in the gills. As you already know, water comes into the fish’s mouth and passes through the gill slits into the gill chambers many times a minute. Here oxygen molecules from the air that is dissolved in the water diffuse into the blood, and carbon dioxide molecules diffuse out from the blood into the water. Then the water escapes from the body through the openings on each side of the head. Can you explain why oxygen molecules diffuse into the blood and carbon dioxide molecules diffuse out of it? The blood with its fresh oxygen sup¬ ply flows on into the general circula¬ tion. All bony fish get their oxygen in this way. In addition, the few surviving lung fish may also get oxygen into their lungs directly from the air. But they are the rare exception. The food canal of a yellow perch DISSECTING A YELLOW PERCH. Use the preserved yellow perch you have already been examining. With dissecting scissors, make a ventral incision from the anus (Fig¬ ure 11 -3a) forward. Take hold of the two pectoral fins and pull. This will open the 1 1-3 In vertebrates, a degree of specialization not found in invertebrates is immediately evident. The vertebrate brain (C) is subdivided into a cerebrum, cerebellum, medulla, and other parts. The spinal cord and the many specialized nerves also reflect greater complexity than found in invertebrates. The closed circulatory system (C) includes a two- to four-chambered heart and a much-branched system of blood vessels. And other body systems, among them the skeletal and muscular systems (B), are even better de¬ veloped than the complex body systems of insects and other arthropods. All in all, the vertebrates— from fish to mammal— are the most complex animals on earth. 300 SPECIALIZATION IN HIGHER ORGANISMS Anterior dorsal fin Lateral line Pectoral fin (in motion) Caudal fin Pelvic fin (in motion) Anal fin Muscles Vertebrae Air bladder Stomach Dorsal aorta Gullet Pericardial cavity Heart Liver | Gall bladder and bile duct Intestine A v Reproductive gland Spleen Olfactory lobes Optic lobes Cerebrum Cerebellum jr — Medulla Olfactory nerves nerves Dorsal .aorta Ventral aorta Ventricle Portal vein Arterial bulb Auricle BLUEPRINT OF A VERTEBRATE — YELLOW PERCH body cavity. With scissors, cut away the two sides of the body wall. Refer often to Figure 11-3, as you pro¬ ceed. Look first for the heart. Lift it out and save it, to draw later. Next cut the intestine loose from the anus. Then lift up the whole food tube and cut it loose from the back of the mouth. Remove the liver and save it to draw later. Carefully straighten out the food tube and look for the gullet, stomach, pyloric caeca (py LOR ik SEE kuh), and intestine. About how long is the food tube? The two kidneys and the roe (eggs), in a female, or the milt (sperms), in a male, are dorsal to the food tube and lie close to the backbone. Look for these organs. Examine and sketch the heart, liver, and food tube. Label as many parts in each as you can. Then, after reading more about the fish, label other parts. The yellow perch does not chew its food, but swallows it whole. From the mouth, the food goes through a short, wide gullet into the stomach. In the back of the mouth of your specimen, look for the opening into the gullet. Special cells in the lining of the stomach secrete strong juices that can dissolve even the scales of a newly swallowed smaller fish. Digestion be¬ gins in the stomach. From the stomach, the partly digested food passes on into the intestine, where other digestive juices finish the job. Then the digested foods diffuse into the blood in the capillaries of the intestine wall. Near the place where the stomach empties into the intestine, there are three hollow, fingerlike projections from the intestine. They are “dead-end” or “blind” passageways out of the intes¬ tine, even as your appendix is. Any blind passageway out of the food tube is a caecum ( see kum ) . The yellow perch has three caeca (Figure ll-3b). Because of their location, they are called pyloric caeca, from pylorus, the opening from the stomach into the in¬ testine. Some of the food mass enters the pyloric caeca, and digested foods diffuse out of them into the capillaries in their walls. So they are useful in that they provide extra lining area through which foods enter the blood stream. Near the stomach there is a large liver, which secretes bile. The bile is stored in a little sac or pouch attached to the liver. The sac is called the gall bladder (Figure ll-3b). In the gall bladder, bile is stored until it is needed in the intestine. Then it is delivered through a small tube, the common bile duct, to the upper portion of the in¬ testine. Solid wastes are eliminated through the anus at the posterior end of the intestine. The primary function of the food tube is digestion. In it all foods under¬ go chemical changes which result in simpler molecules. These molecules dif¬ fuse into blood capillaries in the walls of the intestine. The fish's circulatory system You have learned how oxygen enters the blood through the gills. Digested food is picked up in the lining of the small intestine. The heart pumps the blood through the body. The blood de¬ livers oxygen and food to every living cell, and carries the cell wastes away. That sounds easy. But you will want to know more about the circulatory sys¬ tem than this brief summary reveals. So let’s study the heart and the course the blood travels in more detail. The fish’s heart is almost literally “in its throat.” Now at last you will see a 302 SPECIALIZATION IN HIGHER ORGANISMS heart that is more like what you have always called a heart. As you already know, the fish’s heart has two main chambers in it with a valve between, a one-way valve. The two chambers are the auricle and the ventricle (Figure ll-3c). Blood from the general body circulation flows into the auricle. Then the muscular wall of the auricle contracts, pushing the blood through the valve into the ven¬ tricle. Then the valve closes. The mus¬ cular ventricle contracts and pushes the blood into the arterial bulb (Figure ll-3c) and on into an artery to the gills. Near the gills, the artery branches, and the branches lead into the gill filaments, where the blood gets a new supply of oxygen and excretes carbon dioxide. From the gills the blood moves on through arteries to all the other parts of the body, then into capillaries and finally into veins that lead back again to the auricle. How many times does the blood go through the heart, in one complete round trip? Use Figure 11 -3c to help you answer that question. Central co-ordination All the body systems of the fish work together. The muscles and fins and jointed skeleton, together, enable the fish to swim. The digestive system pre¬ pares the food for distribution. The cir¬ culatory system carries food from the food tube, and oxygen from the gills, to living cells all over the body. The blood also carries cell wastes to gills and kidneys, which excrete them. All these systems do their part in keeping the fish alive. All the parts of the body work together in close co-ordination. The nervous system plays the main role in co-ordination. You have already taken a quick look at a frog’s central nervous system— the brain and the spinal cord. The fish’s central nervous system is quite similar and has the same parts in the brain (Figure ll-3c). Like all vertebrates, a fish has a long spinal cord running through the hollow centers of the vertebrae of the back¬ bone. In the head, the fish’s spinal cord joins the medulla of the brain. The spinal cord is connected by sev¬ eral pairs of spinal nerves to the mus¬ cles, fins, and other body parts back of the fish’s head. This means that nerve impulses to and from these body parts must pass through the spinal cord. In this sense, you might say that the spi¬ nal cord is the central co-ordinator of all reactions of the fish that involve its body muscles, fins, and some other body parts back of the head. In another sense, the brain inside the fish’s skull is the main central co-ordi¬ nator of all the fish’s reactions, because nerve impulses, say, from the fins, can and do reach the brain through the spinal cord and may be further co¬ ordinated in the brain itself. The brain is connected by several pairs of cranial ( kray nee ul ) nerves to various parts of the head. For example, the first pair of cranial nerves connects the nostrils (organs of smell) with the olfactory lobes. The optic nerves con¬ nect the eyes and the optic lobes. Other cranial nerves connect other parts of the fish’s head with other brain parts. You may have guessed already that the olfactory lobes are the centers of smell and that the optic lobes are the centers of sight. If so, you have guessed correctly. The cerebellum is the center of balance. The medulla is the center of such vital processes as the heartbeat and breathing movements. To us, the cerebrum is far and away the most interesting part of the brain. VERTEBRATES AND HOW THEY LIVE 303 In mammals, the cerebrum is the cen¬ ter of conscious activity; it is the center of what people usually call intelligence and memory. Even more important, the cerebrum is involved when a mammal or any other vertebrate learns anvthing new. It is easy to prove that goldfish do “learn” to come to the top of the wa¬ ter when someone approaches. Just drop flakes of fish food onto the surface of the water in your aquarium once a dav for a few weeks. In due time, the goldfish will come to the surface when you approach the aquarium. We say they have “learned” that your approach is a sign that food is coming. Goldfish certainly do “learn” some things. So do other fish. This ability to “learn” is centered in the fish’s cerebrum. You will learn much more about the cerebrum later. For now, it is enough to remember that the cerebrum is the nerve center of whatever ability to learn a fish may possess. REMOVING THE BRAIN (Optional). Care¬ fully pare away the top of the perch's skull. Just underneath the skull lies the brain. See if you can remove the brain and part of the spinal cord intact. If you succeed, sketch and label the brain. Then save your sketch for comparison with draw¬ ings of the brains of other vertebrates, which you will find a part of your study later in this chapter. The fish’s sense organs include eyes, nostrils, and part of an inner ear (the organ of balance that makes it possible for the fish to sense its position in the water). Fish also have what we often call a sense of touch. Your sense organs of touch are in your skin, but the scales that cover a fish’s body make it impos¬ sible for them to have sense organs of touch in the skin all over their bodies. Look for a moment at Figure ll-3a and locate the lateral line. In that lateral line there are nerve endings that are be¬ lieved to serve as touch sense organs in fish. Summing up: the fish How clear a picture do you now have of the make-up of a fish’s body? Check up in the following ways. 1. Name in order the organs through which food passes from mouth to anus. 2. In a brief paragraph, explain how a fish gets food out of the water that enters its mouth. 3. Can a fish live in water that has no air dissolved in it? Why? 4. Name the main sense organs in the fish. 5. Trace a drop of blood from the auricle around the body of the fish and back to the auricle. 6. List the parts of the brain and tell what the chief function of each part is. Now you are ready to go from fish to frog in your study of vertebrate bodies and how they work. On the next eight pages is a full-color body plan of a common frog (the leopard frog, Rana pipiens— ray nuh pip ee enz). Scan the Frog Charts now, so that you will be ready to study the frog in detail in the next section of text (page 305, fol¬ lowing the Frog Charts). Reproduction of frogs will be studied in a later unit. However, a brief sum¬ mary of the process appears on the last Frog Chart, and you may wish to familiarize yourself with it at this time. When you have finished examining the Frog Charts, go on to page 305. 304 SPECIALIZATION IN HIGHER ORGANISMS ^nvnfat Wwi C^t^U Studios> Tunc > Nfew York City* based uP°n dissected female specimen of Rana pipiens at time Bio^ogica^Supply1 House^^ic.^Chica^go, Illinois?*^ ^ P“r~ of ** tissues copyrighted by General © 1959, BY HARCOURT, BRACE AND COMPANY, INC. mIlnc8htSfvfSered' 1\Io.par.t of “The Le°Pard Fr°g” may be reproduced in any form, by mimeograph or any other means, without permission in writing from the publisher. y PRINTED IN THE UNITED STATES OF AMERICA FROG CHART 1-THE SKELETAL SYSTEM \ . \\ Femur Knee Tibio-fibula Ankle bones Bones of Cranium Shoulder blade (scapula) Collarbone (clavicle) _ _ Humerus ^Radio-ulna Vertebrae Breastbone (sternum) Tail pillar — u Pelvic girdle C atCKA) WHAT IT IS— WHAT IT DOES The # bony framework of the frog’s body is its skeleton, viewed here from be¬ neath the body (left) and as it would look if the frog were in a normal sitting position (below). The cranium (or skull), vertebral column, collarbones, shoulder blades, breastbone, and pelvic girdle help to protect from injury such organs as the brain, spinal cord, heart, lungs, and digestive organs. In addition, these skeletal parts, as acted upon by skeletal muscles (see facing page), give rigidity to the head and trunk of the body without making them immovable. Complete rigidity or im¬ mobility would be disastrous to the frog; movable joints are the out¬ standing feature of its skeleton. The leg and foot bones, along with the pelvic girdle and the bones of the shoulder, are the parts of the skele¬ ton having most to do with the frog’s locomotion (the jointed vertebral column also moves, but very little in proportion to the movement of the four legs). The bones function par¬ tially as levers upon which the skel¬ etal muscles act in producing the frog’s leaping movements on land. The frog’s backbone, unlike that of other vertebrates, has only a few vertebrae, nine in all. In this and in other respects the frog’s skeleton is specialized— that is, different from the skeletons of other vertebrates with other ways of life. FROG CHART 2-THE MUSCULAR SYSTEM WHAT IT IS— WHAT IT DOES The muscular system illustrated here is the skeletal muscular system— mus¬ cles nearly all of which are attached to bones. The muscles that would be visible from beneath the frog’s body when the skin is removed are shown at the right; those that would be vis¬ ible if the same frog were in a sitting position are shown below. The skeletal muscles are also called voluntary muscles because they are used for movements over which the frog normally has control. Usually these muscles work in pairs. When one muscle of a pair (the flexor ) con¬ tracts, a leg or another part of the body is bent. When the other muscle of the pair (the extensor ) contracts, the leg or other part of the body is straightened again. Other muscle pairs are responsible for twisting or rotating movements, first in one di¬ rection, then back in the other. Skeletal muscles normally are at¬ tached to bones by tendons, and the two ends of each muscle are attached to different bones. The tendon at one end of a muscle usually runs across a joint— for example, the knee— and is attached to the bone on the other side of that joint. When a muscle contracts, one bone to which it is at¬ tached serves as an anchor, and the other bone (sometimes more than one) is made to move. In this way, skeletal muscles and the bones of the skeleton work together. ds foot at wrist Straighten foot at wrist Bend leg at elbow Straightens leg at elbow Flattens stomach Rotates leg at hip Pull leg toward underside of body ightens leg at knee Bends leg at knee ightens foot at ankie Bends foot at ankle Tendon of Achilles Pulls leg forward (toward head) Pulls leg toward chest Pulls leg toward underside of body Move toes Move toes FROG CHART 3-THE NERVOUS SYSTEM WHAT IT IS— WHAT IT DOES The frog’s nervous system, viewed here from beneath the body, consists of the brain and spinal cord (Central nervous sys¬ tem), the cranial and spinal nerves, and the autonomic system (chains of ganglia near the spinal cord, and certain other ganglia and nerves). Like other parts of the body, the nervous system is built up of cells — specialized nerve cells of sev¬ eral types, characterized by nerve fibers extending from the cell bodies. The nervous system, along with the eyes, ears, and other sense organs, puts the frog “in touch” with its surround¬ ings. The central nervous system co¬ ordinates and regulates all of the frog’s activities except certain vital activities of which the frog is unconscious- breathing, heartbeat, digestive activities, and so on, all of which are regulated by the autonomic system. The brain and the spinal cord (A) consist mainly of gray and white matter. The gray matter is mostly cell bodies of nerve cells; the white matter, fatty sheaths surrounding nerve fibers of nerve cells. A nerve (B) consists of many nerve fibers, each with its own sheath of white matter, and all bound together in the nerve sheath. White matter Gray matter ■ Brain - Cranial nerves Spinal nerves Spinal cord Chains of autonomic ganglia Nerve sheath A. Stained Cross Section of Spinal Cord (32 X ) B. Stained Cross Section of Nerve (250 X) (Photomicrographs of spinal cord and nerve copyrighted by General Biological Supply House, Inc., Chicago, Illinois) FROG CHART 4-THi CIRCULATORY SYSTEM WHAT IT IS -WHAT IT DOES The frog’s circulatory system consists of its three-chambered heart ( B ), arteries which carry blood from the heart to the lungs and the rest of the body, micro¬ scopic capillaries (not shown) which carry blood from the arteries into all the body tissues, and veins which carry blood from the capillaries back to the heart. The beating of the muscular walls of the heart and arteries pumps the blood along in the circulatory system. Each time the blood circulates throughout the body, it passes through the heart twice— once as it returns from the body and is pumped to the lungs, and once as it returns from the lungs and is pumped to the rest of the body. Oxygen picked up in the lungs is car¬ ried by red blood cells (A). Newly oxygenated blood from the lungs enters the left auricle (B) of the heart; deoxygenated blood from the body, the right auricle (B). When the two auricles contract, blood from both is pumped into the common ventricle, where some mixing of oxygenated and deoxygenated blood occurs. In this re¬ spect, the frog’s three-chambered heart is less efficient than the four-chambered heart of man. Vein head and front legs Right au Valves White blood cell Ventricle Left auricle Vein from trunk and hind legs Vein from head Artery to head Pulmonary vein Pulmonary arteries Heart Liver (left lobe) Stomach Lung Kidney Arteries to leg Veins from leg A. Stained Blood Cells (400X) B. Interior of the C. Heart Heart (enlarged (ventral view) ventral view) FROG CHART 5-THE RESPIRATORY SYSTEM Internal openings of nostril Roof of mouth Upper jaw Glottis Voice box (larynx) Lower jaw (pulled down) Cut body wall Right lung _ Left lung — Spongy lung tissue A. Stained Cross Section of a Lung (7X ) Surface of skin Mucus- 1 ' „ glands WHAT IT IS -WHAT IT DOES The frog’s respiratory system, viewed at the left as it would appear from be¬ low the frog, consists of the nostrils, mouth, glottis, voice box or larynx, and the two lungs. When the frog lowers the floor of its mouth (its jaws are closed during breathing), air rushes through the nostrils and into the mouth. The frog then closes ex¬ ternal flaps over the nostrils and raises the floor of its mouth, pump¬ ing the air through the glottis and into the lungs. When the floor of the mouth is again lowered (the nostril flaps are still closed), air rushes from the lungs back into the mouth. Then the nostril flaps are opened as once again the floor of the mouth is raised, and the air is pumped out through the nostrils. In this manner, the frog breathes, over and over again. In the lungs, carbon dioxide is given off to the air by the blood, and oxygen is picked up from the air by red blood cells in the blood. Since the carbon dioxide is a waste prod¬ uct of cell activity in the frog, the lungs are organs of excretion as well as organs of respiration. In appear¬ ance, the lungs are spongy-walled organs (A) heavily infiltrated with blood capillaries and containing many air spaces. The frog’s skin ( B ) is a somewhat secondary part of its respiratory sys¬ tem. As long as the skin is moist (and it is kept moist by mucus-producing glands within it), a certain amount of oxygen from the air passes directly through the skin and into blood cap¬ illaries. At the same time, carbon dioxide leaves the blood and passes through the skin to the air. Thus, the skin, too, is both an organ of respira¬ tion and excretion. B. Stained Cross Section Through the Skin (much enlarged) (Photomicrographs of lung and skin copyrighted by General Biological Supply House, Inc., Chicago, Illinois) FROG CHART 6-THE DIGESTIVE SYSTEM WHAT IT IS— WHAT IT DOES The frog’s digestive system includes the mouth, gullet, stomach, small and large intestines, and the liver and pancreas. The large intestine opens into the cloaca (which receives — and eliminates from the body— material from the digestive, excretory, and reproductive systems). Food swallowed by the frog is passed along from gullet to stomach to intes¬ tines by peristalsis — the rhythmic con¬ traction of circular and longitudinal muscles (A and B) in the walls of the digestive organs. In the stomach and small intestine, microscopic glands ( B ) in the folded inner lining (A and B) secrete digestive juices that work on the food mass. Also in the small intes¬ tine, bile (from the liver) breaks fats up into tiny droplets, and digestive juices from the pancreas work further on the food mass. The end result is the break¬ ing down of foods into molecules small enough to be absorbed by the frog’s blood through the lining of the intes¬ tine (and to some extent, the stomach). Indigestible materials are eliminated through the cloaca. Opening of gullet Glottis Lower jaw (pulled down) Gullet Liver Gall bladder Stomach Pancreas Common bile duct Small intestine Large intestine rine bladder Cloaca (partly behind urine bladder) Longitudinal smooth muscle Circular smooth muscle Folded inner lining Inside of intestine A. Stained Cross Section of the Small Intestine (30 X ) Gastric pits < Inside of stomach Glands Circular smooth muscle gitudinal smooth muscle B. Stained Cross Section Through the Stomach Lining (much enlarged) (Photomicrographs of stomach lining and small intestine copyrighted by General Biological Supply House, Inc., Chicago, Illinois) FROG CHART 7-THE REPRODUCTIVE SYSTEM Male Enlarged thumb Dark coloration Fat bodies Testes Kidneys Nonfunctioning oviducts Cloaca - Female Light colo Fat bodies Ovary - Egg mass' Oviducts Uteri — Cloaca THE MALE REPRODUCTIVE SYSTEM The two testes of a male frog produce sperms that pass through sperm ducts to the kidneys. From the kidneys, the sperms travel through the excretory tubules (or ureters) through which urine passes from the kidneys to the cloaca. (In the drawing at the left, the ureters are hidden from view by the nonfunctioning oviducts that are found in male frogs.) Just short of the clo¬ aca, at an enlarged point in each of the two ureters, the sperms collect. There they remain until the male frog finds a female that is ready to shed its eggs. The male clasps the female, and as the female sheds its eggs (in shallow water) the male depos¬ its sperms over them. Both frogs then dis¬ regard the newly shed eggs. THE FEMALE REPRODUCTIVE SYSTEM In the female frog shown at the left, one of the two ovaries (the left one) is shown, and on the other side of the body the egg mass produced by the right ovary is shown. Ordinarily an egg mass would be produced by both ovaries, but the egg mass produced by the left ovary was omitted here in order to show the ovary itself (which otherwise would not be visible, as on the right-hand side of the body). The egg masses appear in the body cav¬ ity usually in the spring of each year, fol¬ lowing their rupture from the ovaries. The eggs then enter the oviducts, in which they receive a jellylike coating as they proceed to the two uteri (one uterus lies at the lower end of each oviduct, near the cloaca). From the uteri, the eggs are shed through the cloaca into shallow water, and sperms from a male frog are shed over them. Fertilized eggs develop into tadpoles (see the cover for these frog charts), and the gill-breathing tadpoles later mature as frogs. Openings into nostrils Openings of Eustachian tubes Opening of vocal sac Opening of Glottis Tongue Nostril External eardrum Photo by Charles Halgren 11-4 ORGANIZATION OF A FROG'S MOUTH A frog’s tongue, in contrast to that of a mammal, is attached near the front of the mouth and has its free end farther back to¬ ward the throat. The usefulness of this arrangement is evident from the manner in which the frog’s tongue is flipped out to capture an insect. The insect is captured, crushed against the teeth in the roof of the frog’s mouth, and swallowed— all so quickly that an observer does not get a clear picture of exactly what happened. THE FROG You are ready now to explore the organ systems of a frog. As you do so, watch for any increase in specializa¬ tion within each organ system as com¬ pared with the fish. If you are like other biology students, you will enjoy learning about the ma¬ chinery of the frog’s body. At the same time you will be laying a foundation for your studies of the machinery of the human body. The common leopard frog ( Rana pipiens) is the one most often studied. You can get either living or preserved specimens, or both, from any biologi¬ cal supply house. Or some of you may be able to collect and bring to class some live frogs from your own area. Bullfrogs or wood frogs will be just as suitable as leopard frogs. The mouth of a frog As you already know, a frog can catch an insect so quickly that you can’t see how it happens. The frog’s tongue is fastened in the mouth by the front end, and the back end is loose (Figure 11- 4). When a fly comes within range, the back end of the tongue flips out, catches the fly, pokes it into the mouth, crushes it against the two teeth in the middle of the roof of the mouth, and then pokes it down the throat to be swallowed. The whole thing is over in a flash, so quick¬ ly that an onlooker cannot see exactly what happens. Frogs will eat earthworms, too. Two frogs in an aquarium began at opposite ends of a worm, and each swallowed more and more until they came face to face in the middle of the worm. Both frogs struggled and tugged and pulled. VERTEBRATES AND HOW THEY LIVE 305 Finally one frog pulled the worm free of the other and, in a leisurely way, finished swallowing it. Refer to the Frog Charts as you read on. The gullet leads out of the back of the mouth and into the stomach (Frog Chart 6). Just in front of the gullet on the floor of the mouth is the glottis, a slit that opens into the windpipe (Frog Chart 5 ) . On the roof of the mouth are two pairs of openings, the openings into the nostrils and the openings into the tubes that run from the throat to the ear. These tubes are called the Eusta¬ chian ( yoo stay kee un ) tubes. The frog uses its mouth, especially its tongue, in capturing insects, ft uses its mouth in breathing, too, as you will learn. EXAMINING A FROG'S MOUTH. Use a preserved frog. Cut the corners of its mouth so that you can pin the lower jaw down to the body. Use a needle to locate the gullet, glottis, Eustachian tubes, nostrils, and, in males, openings into the vocal sacs 11-5 REMOVING SKIN FROM A FROG'S LEG to expose leg muscles involves only turning (Figure 11-4). Examine the tongue. In your record book, map the frog's mouth and locate the openings and other mouth parts on your map. Locomotion of frogs On the land, frogs have a peculiar way of getting from one place to an¬ other. They jump or hop instead of walking or running or flying as most land animals do. It is the hind legs that enable them to leap. To appreciate the strength of the muscles of these legs, just compare a high school boy’s broad¬ jumping ability with that of a frog. A frog can jump as much as 15 times the length of its body; a broad jumper does well if he jumps twice his own length (height). The world’s record broad jump is only a little over four times the height of the man who holds the record. In the water, frogs are good swim¬ mers. They are smooth-skinned, with a tapering body and no neck. The hind feet are webbed and make good oars with which the frog pushes against the water. The muscles of the legs are no Once the leg is severed, removing the skin the skin wrong side out and pulling it off. Shoop Photo 306 SPECIALIZATION IN HIGHER ORGANISMS less powerful in water than on land. Each muscle in a frog’s leg ends in a long, tough string of fibers, called a tendon, which extends across at least one joint and attaches to a separate bone. For example, the tendon of a muscle of the thigh runs down over the knee and is fastened to the bone of the lower leg. (This is true also in human beings— see Human Body Chart 3, fol¬ lowing page 336.) Muscles from the lower leg and the ankle end in long tendons that attach to the bones in the toes. The frog’s muscles work in pairs, as your muscles do. The muscle that bends your elbow joint cannot straighten it again. The straightening is done by a muscle on the other side of your arm. Feel your upper arm as you bend and straighten the arm, and you will see how true this is. A frog’s muscles work in the same way. One muscle bends the knee and another straightens it. You can demonstrate this fact by pulling muscles on opposite sides of the frog’s thighbone. Where the frog’s thighbone is jointed into the bone of the back (Frog Chart 1 ) , you will find a ball-and-socket joint which you may find interesting to open. The ends of two bones that work against each other in a joint are cov¬ ered with a special membrane that makes smooth surfaces. EXAMINING LEG MUSCLES AND BONES. Remove one of the hind legs of your pre¬ served frog, being careful not to damage the part closest to the abdomen. Pull the skin off the leg much as you might pull off a kid glove wrong side out (Figure 11-5). Look for the fine blood vessels in the skin just removed. Examine and try to count the muscles in the leg (Frog Chart 2). Pull the largest muscle in the lower leg and watch the toes. Remove the leg muscles, one at a time. Try to separate each single muscle with its tendon or tendons still attached. How many muscles do you count? Remove all the muscles from the foot. Examine the leg and toe bones. Examine, too, the joints where the ends of two bones meet. One (at the hip) is a ball-and-socket joint; others are hinge joints, much like those between the bones in your arms or legs. Study Frog Chart 1 and Human Body Chart 1. Sketch the bones of the frog's leg. Label: hip joint, knee joint, and toe joints. Then sketch the whole leg with the skin still on and label the hip, the knee, and the ankle. How do frogs breathe? Frog tadpoles breath by means of gills, much as fish do, but frogs breathe by means of lungs, as you do. Even so, your breathing differs from that of a frog. For one thing, you can breathe with your mouth open. A frog can’t. Here’s why. You will remember that you (and all mammals ) have a muscular diaphragm. You use your diaphragm in pumping air into your lungs (see Human Body Charts 6 and 7). A frog has no dia¬ phragm. It uses the floor of its mouth in pumping air into and out of its lungs. A frog, like you, has two lungs. The lungs are connected by a short ‘‘wind¬ pipe” to the mouth (Frog Chart 5). The windpipe is actually the voice box, or larynx (lair inks). Rings of cartilage keep the larynx open, making it an air passage. The nostrils of both frogs and people are passageways from outside into the mouth ( in frogs ) or the throat ( in peo¬ ple). Small flaps can close the outside VERTEBRATES AND HOW THEY LIVE 307 ends of a frog’s nostrils. ( People have no nostril flaps. ) A frog opens its nostril flaps and low¬ ers the floor of its mouth. Then air rushes into the mouth. Next the frog closes the nostril flaps and raises the mouth floor. This pushes the air through the glottis and larynx into the lungs. In a few seconds, with its nostril flaps still closed, the frog lowers the floor of its mouth and air rushes from the lungs into its mouth. Finally the frog opens its nostril flaps and raises the floor of the mouth. This pushes the air outside again. Now can you explain why a frog can’t breathe with its lungs, when the mouth is open? (Note: Frogs also get oxygen through the skin and the lining of the mouth, as long as these are moist.* ) Frogs have voices. They sing, espe¬ cially in the spring. In singing, they use the vocal cords in the voice box (larynx). Male frogs usually have vocal sacs, too. Frogs use the floor of the mouth to pump air into and out of the lungs— that is, back and forth across the vocal cords. In males, the vocal sacs fill, empty, and refill during singing. The tree frog in Figure 11-6 was sing¬ ing and its vocal sacs were full when the picture was taken. The frog's lungs The lungs of a frog are somewhat like hollow sacks with a thin layer of lung tissue over the outside (see Frog Chart 5). The lung tissue is full of microscopic capillaries. Oxygen mole¬ cules from the air diffuse into the blood in the capillaries. Carbon dioxide mole¬ cules diffuse out of the blood into the air inside the lungs. Can you explain ° This may be a good time to find out just how you get air into and out of your lungs. You will find the explanation on pages 337- 38, if you want to read about it now. why, in terms of what you have learned about diffusion? In insects, you saw that air was piped all over the body through air tubes. For a small animal, this has proved an efficient way to get oxygen to all the living cells. But no large animal today gets its oxygen in the way insects get theirs. In the larger, air-breathing ver¬ tebrates, most or all of the oxygen en¬ ters the blood in the lungs. Then the blood delivers the oxygen to the mil¬ lions or billions of living cells all over the body. In frogs, some oxygen also enters the blood in the capillaries in the skin, but most of it gets into the blood in the lungs. The frog's food tube The frog’s food tube is a good deal like that of a fish, but the frog’s intes¬ tine is longer than a fish’s. A fish has no large intestine, but a frog has one (Frog Chart 6). In addition, the frog’s food tube ends posteriorly in a channel called the cloaca ( kloh ay kuh— plural, cloacae, kloh ay see ) . This channel is a passageway through which wastes pass from the kidnevs as well as from the J large intestine. Even the eggs of the female and the sperms of the male pass out of the body through this same pas¬ sage. The anus is the exit from the cloaca. Birds, reptiles, amphibians, and some fish have cloacae.** The frog’s liver is three-lobed, too, in contrast with the fish’s one-lobed liver. The liver produces bile which is stored in the sail bladder and reaches the O small intestine through the common bile duct. The pancreas (Frog Chart 6) lies along the bile duct and secretes 00 As a matter of technical usage, ani¬ mals with cloacae are said to have a cloacal opening rather than an anus, since urine and eggs or sperms also exit through it. The dis¬ tinction, however, is unnecessary here. 308 SPECIALIZATION IN HIGHER ORGANISMS pancreatic juice into a duct which joins the bile duct. So bile and the pancreatic digestive juice reach the small intestine through the same duct. The frogs food tube digests foods much as yours does. You will learn more details in the next unit. The frog's circulatory system The blood stream is the transporta¬ tion system in frogs, as it is in fish, but in the frog it is an improved one. The frog’s heart has three chambers; the fish’s, only two. In the frog’s heart there are two auricles and one ven¬ tricle. The auricles are the receiving chambers, and the ventricle is the send¬ ing chamber. When the blood comes back to the heart from the general body circulation, it enters the right auricle (Figure 11-7 and Frog Chart 4). Then the blood is pumped into the ventricle , which in turn pumps most of it out through an artery to the lungs, where the blood spreads out in fine capillaries. The hemoglobin in the red corpuscles takes on a new oxygen supply, and car¬ bon dioxide is given off by the blood. The newly oxygenated blood is bright red. This is not to say that all of the carbon dioxide diffuses out of the blood, but only that much of it does. In other words, there is no such thing as “pure blood’’ or “impure blood,” as people used to say. A frog’s blood al¬ ways contains some oxygen and jome carbon dioxide. Newly oxygenated blood simply has much more oxygen and much less carbon dioxide than it had when it entered the lungs. The newly oxygenated blood then re¬ turns through veins to the left auricle, which pumps it into the ventricle again. Here there is a little but not much mix¬ ing of the blood from both auricles; most of that from the left auricle (the George A. Smith 11-6 SINGING TREE FROG Not a meal he can’t swallow, but his spring song, is re¬ sponsible for this tree frog’s appearance. newly oxygenated blood ) flows into the artery that delivers it to the general body circulation. In the tissues, food and oxygen leave the blood and enter the living cells, while carbon dioxide and other cell wastes enter the blood. This deoxygenated blood returns through veins to the right auricle. Valves keep blood from flowing back from the ventricle into the auricles. Study Figure 11-7 carefully. How many times does the blood go through the heart in one complete trip, say, from the right auricle back to the right auricle again? The chief advantage in this three-chambered heart is that it makes possible a rapid delivery of food and oxygen to cells all over the body. Can you explain why the slight mix¬ ing of the blood from both auricles in the single ventricle is a disadvantage? The blood from the right auricle carries a heavy load of carbon dioxide and a small load of oxygen. The blood from VERTEBRATES AND HOW THEY LIVE 309 OPERATION OF A THREE-CHAMBERED HEART (FROG) Right auricle (blood from • body) Blood to body Blood to lungs Left auricle (blood from lungs) Ventricle Ventricle Blood to body Blood to lungs 1 1 -7 Blood from the frog’s body and from its lungs is pumped by the two auricles into the ventricle. The ventricle then contracts and pumps the blood out of the heart into subdivided blood vessels. Obviously there is some mixing of the blood from the two auricles in the ventricle. Why might this affect the efficiency of the circulatory system? the left auricle carries only a little car¬ bon dioxide and a heavy load of oxy¬ gen. So even a little mixing of the new¬ ly oxygenated blood with blood having a heavy load of carbon dioxide and lit- tie oxvgen reduces to some extent the j O load of oxygen in the blood that goes out to the body. Frogs are cold-blooded animals. One reason (but probably not a major one) is that the single ventricle allows some mixing of blood and hence slows down a bit the rate of oxygen delivery to all the living cells. It takes a faster rate of delivery to enable animals to be warm¬ blooded, as birds and mammals are. Later, you will learn more about what makes warm-bloodedness possible. The frog's organs of excretion Besides the lungs and skin, which excrete carbon dioxide, and the anus, through which solid wastes are elimi¬ nated from the intestine, the frog has a well-formed pair of kidneys. Urea (yoo ree uh ) is a waste product of one step in the oxidation of protein foods. This compound was the first organic com¬ pound to be synthesized in the test tube. The kidneys excrete urine (yoo rin). Urine contains urea. It passes through tubes to the cloaca (Frog Chart 6), and thence to the bladder, where it is stored for a time. Later it passes into the cloaca once more and is finally eliminated through the anus. EXAMINING THE INTERNAL ORGANS. Use a preserved frog. From anus to chin, make a ventral incision, first through the skin, then through the body wall (Figure 11-8, left). Take hold of the two front legs and pull them apart. This will expose the internal organs much as they are in Figure 11-8 (right) and on the cover (first page) of the Frog Charts, following page 304. If you have a female frog, you will probably find masses of eggs. Remove them. Use Frog Charts 3-7 and the illustrations in this section, as you look in your specimen for the heart, lungs, liver, stomach, and other organs. Then cut the tissue around the posterior end of the cloaca so that you 310 SPECIALIZATION IN HIGHER ORGANISMS can loosen the cloaca from the anus. Lift up the food tube and the organs attached to it, and cut the anterior end loose from the mouth. Separate the heart from other organs, and examine and sketch it. Loosen the two lungs and larynx from the rest of the or¬ gans. Examine and sketch them. Cut open the larynx and see what it is like inside. Carefully stretch out the small and large intestine and cloaca. How long is the food tube? Look for the gall bladder, pancreas, and spleen. Sketch and label the food tube. Show the urine bladder, attached to the cloaca. The kidneys are along the ventral side of the backbone. Attached to the kidneys or close to them are the testes, in a male, or the ovaries, in a female. Locate these or¬ gans. The nearby elongated fat bodies (Frog Chart 7) will help you to find them. The egg tubes may be seen plainly in a female, but the tubes in the male that carry sperms and urine to the cloaca are not easily found. The frog's nervous system The central nervous system of the frog consists of the spinal cord and the brain, much like those of the fish. The brain contains the same parts: medulla, cerebellum, optic lobes, cerebrum, and olfactory lobes. However, in the frog the cerebrum makes up a much larger portion of the total brain than it does in the fish. If the cerebrum is directly re¬ lated to learning ability, frogs ought to be able to learn more than fishes. And they are. | Eleven pairs of~neTVes from \ the brain and ten pairs from the spinal ^cord extend to sense organs, muscles, skin, alimentary canal, and all other parts of the body. - - - Externally a frog shows three sense organs: eyes, ears, and nostrils. The eyes are much like those of a fish, but a frog has eyelids. If you try to touch the eye of a live frog, you can see a semiclear skin come up over the eye. You may have watched a similar eye¬ lid come up over the eye of a chicken. It is common among amphibians and birds and seems to be useful in pro¬ tecting the eye while allowing some light to enter it. The frog’s ear is not like your own. For example, its eardrum is on the out¬ side of the head. You will discover it as a dark ring just back of the eye. The frog’s ear is connected with the mouth 1 1-8 DISSECTING A FROG Left. A ventral opening is made from anus to chin with a pair of dissecting scissors. (If the cut is made too deeply, internal organs will be damaged.) Right. The incision completed, the two front legs are grasped and pulled apart to open the body and expose the internal organs. Even at this point, a blackish mass may ob¬ scure the organs from view. If so, the frog is a female with eggs, and the egg mass can be removed easily without further damage to the frog. Shoop Photos by the Eustachian tube. Air enters this tube through the mouth and thus keeps the air pressure equal on both sides of the eardrum. The organ of balance is near the organ of hearing in the inner ear, even as your own is. The frog’s skin has many nerve end¬ ings in it, making it sensitive to several kinds of stimuli, especially touch and pain. If you care to, you can find out which parts of a live frog’s skin are most sensitive. Try touching various spots— near the mouth, on the back of the head, etc. EXAMINING THE FROG'S NERVOUS SYS¬ TEM. In the body cavity of your partly dis¬ sected specimen, look for the spinal nerves that run to the hind legs. They lie at the sides of the backbone and are visible in¬ side the body cavity. Remove both eyes. Open one and re¬ move the lens, whitened by the preserving fluid. Pare off the external eardrum and look into the space beneath it. You may be able to find the single small bone that is located there. This single bone does for the frog what three little bones in your middle ear do for you. It carries vibrations from the drum to the inner ear, buried in the skull bone. Pare off the skull until you expose the brain. With skill, you can pare away enough of the skull and backbone to re¬ move the brain and cord intact. Sketch and label them, using Frog Chart 3 to iden¬ tify parts of the brain. Summing up: the frog The frog carries out its main life proc¬ esses with the organ systems you have been studying. Because, in a general way, its organ systems are much like those of a human being, the frog is especially interesting. As vertebrates go, the frog’s body plan is a bit ahead of that of a fish but quite a bit behind that of a mammal. The three-chambered heart is an ad¬ vance over a two-chambered one, but not as efficient as the four-chambered hearts of birds and mammals. The increased size of the cerebrum, as related to that of a fish, is an advan¬ tage, or so it seems. In the mature frog’s lungs and skin, oxygen from the air diffuses quickly into the blood in the capillaries. The blood stream then delivers oxygen to all the living cells. Can you think of more ways in which a frog’s body is more highly specialized than a fish’s? THE WARM-BLOODED VERTEBRATES Birds and mammals are warm-blood¬ ed vertebrates. Fish, amphibians, and reptiles are cold-blooded vertebrates. That doesn’t mean that the blood of a bird or mammal is warmer than the rest of its body or that the blood of a fish, frog, or reptile is colder than the rest of its body. What does it mean? The temperature of the body of a fish, for example, goes up and down with that of the surrounding water. Usually the body temperature of a fish is only about one degree more than that of the water around it. If the tempera¬ ture of the water is 60° F., that of the fish’s body is about 61° F. Most of the time, a fish or a frog or a lizard “feels cold'’ when you touch it. That is prob¬ ably why people started calling these animals “cold-blooded animals.” People thought it was the blood that was cold. Biologists still use the term “cold¬ blooded animals,” but they use it to 312 SPECIALIZATION IN HIGHER ORGANISMS mean “animals that can't maintain a constant body temperature.” You can probably explain now what biologists mean when they speak of “warm-blooded animals’ — the birds and mammals. Take your own body, for example. As long as you are in good health, your body temperature stays about the same, day and night, summer and winter. The normal temperature of the human body is usually given as 98.6° F. This is a reading taken in the mouth. One taken under the arm pit is usually about 97.6° F., while a reading taken by rectum is about 99.6° F. But the point is that your body temperature stays about the same all the time (un¬ less you are ill ) . Mammals usually are warm-blooded; that is, their body temperatures stay about the same all the time. There are exceptions. For example, when bears hibernate ( hy ber nayt ) , or “go to sleep” in the winter, their body tem¬ peratures fall several degrees. But in general, mammals are warm-blooded. Birds are warm-blooded, too. The normal body temperature of some spe¬ cies of birds is about 110° F. In other species, it is a little less than 110° F. Being warm-blooded plays an impor¬ tant part in the way birds and mammals live. Let’s take a look at some of the organ systems and some other factors that enable birds and mammals to live the way they do. Circulatory systems in warm-blooded vertebrates Like other vertebrates, birds and mammals have a heart that pumps blood out through arteries. That blood circulates through a closed system of blood vessels back to the heart and on again, many, many times an hour. Nothing new in that, is there? But look for a moment at the drawing of the heart of a warm-blooded verte¬ brate (Figure 11-9). Right away you should see something new— a wall be¬ tween two ventricles. This is a four- chambered heart. In this heart, there is 11-9 A four-chambered heart works much more efficiently than a three-chambered one (Figure 11-7). In reality, the four-chambered heart is a double pump serving two cir¬ culatory systems— one to the lungs and one to the rest of the body. There is no mixing of the blood from the two systems at any point within the heart; the blood travels first through one system, then the other, in alternating fashion. OPERATION OF A FOUR-CHAMBERED HEART (MAN) Blood from body Right ventricle Blood from body Blood from lungs Blood to body Blood to lungs Right auricle Left ventricle Left auricle no mixing of the newly oxygenated blood from the lungs and the deoxyge- nated blood with its heavy load of car¬ bon dioxide from the general body circulation. The left ventricle pumps to all parts of the body other than the lungs only blood with a maximum load of oxygen and a minimum load of car- J O bon dioxide. You will learn more about the four- chambered heart when you study the human body in the next unit. The point now is that all warm-blooded verte¬ brates have a four-chambered heart, while most cold-blooded vertebrates have either a two-chambered heart (fish ) or a three-chambered heart ( am¬ phibians). Reptiles do have a four- chambered heart with two auricles and two ventricles, but the wall between the two ventricles is incomplete. This lets some blood leak through the open¬ ings in the wall in both directions and mix with the blood in the other ven¬ tricle. (The reptiles we call crocodiles and alligators do have a complete wall between the two ventricles, but they are the exception. ) You can probably explain why a com¬ pletely four-chambered heart is an im¬ portant feature of the warm-blooded vertebrates. It enables the heart to de¬ liver only well-oxygenated blood into the arteries that supply the body. So oxygen reaches all the living cells faster and in larger quantities than it does in a cold-blooded vertebrate. Oxidation and warm-bloodedness What keeps your body warm? What keeps the body of any animal warm? You know the answer. The heat set free by the oxidation of glucose and other food substances inside living cells keeps you and other mammals, and indeed all other vertebrates, warm. The more rap¬ idly glucose is oxidized in living cells, the more heat is set free. So it takes rapid and continual oxidations in the cells of birds and mammals to enable them to “keep warm,” or, better, to maintain a constant body temperature in a wide range of outside temperatures. Rapid delivery of a plentiful supply of oxygen to all living cells makes rapid oxidation possible. That’s one reason why animals that have four-chambered hearts are the only ones that are warm¬ blooded. You will remember that oxidation of food within a living cell is cell respira¬ tion. Have you ever wondered what keeps cell respiration going? Take the oxidation of glucose as an example. If you wanted to burn (oxidize) com¬ pletely an ounce of glucose outside your body, you would first have to ap¬ ply enough heat, in an electric furnace, perhaps, to raise the temperature of the glucose to 1000° F. Then oxygen from the air would start combining rapidly with the glucose, and the glucose would “burn up”— be completely oxidized quickly. Glucose won’t burn in air at lower temperatures, not even in the hot sunlight on a desert in midsummer. But inside the living cells of your body, glucose is completely oxidized at body temperature, about 98.6° F. Even in a fish or a frog, glucose may be complete¬ ly oxidized, at temperatures consider¬ ably lower, 50° F. or even less. How is this possible? Chemicals that speed up cell respiration The complete oxidation of glucose in living cells is possible because of the presence of certain organic com¬ pounds, which start oxidation and keep it going. In other words, they bring about chemical changes that result in 314 SPECIALIZATION IN HIGHER ORGANISMS the complete oxidation of glucose. These compounds belong to a special class of organic compounds called en¬ zymes ( en zymez ) . The enzymes that keep the oxidations going in living cells are called the respiratory enzymes. You will remember that, broadly speaking, respiration includes all the steps ( some 20, in the case of the oxida¬ tion of glucose) in the complete oxida¬ tion of food molecules in living cells. One respiratory enzyme acts in one step, another in another, until the final end products, carbon dioxide and wa¬ ter, are produced. These enzymes keep respiration go¬ ing in all living cells. And yet they themselves are not used up (at least, not to any extent ) in the chemical changes involved in respiration. As soon as they cause the oxidation of one molecule, they move on to an¬ other and then another, causing the oxidation of each, in turn. In this re¬ spect, you might compare them to the workmen who build houses. They build one house, then move on and build another and another. The men them¬ selves are not built into the houses. Neither are enzymes built into the com¬ pounds produced by oxidation. That is why they are able to move on, from molecule to molecule, and so keep oxi¬ dation going in the cells. The respiratory enzymes are fast workers, too. A single molecule of one of your respiratory enzymes can play its part in the oxidation of 100,000 molecules each second. No team of workers could build even part of one house in a second, let alone 100,000 houses. But enzymes can work that fast, and keep it up, minute after min¬ ute, and still be ready to go on work¬ ing. No wonder Ralph W. Gerard calls them “Master Craftsmen" in his book, Unresting Cells, already cited on page 73. You can see now that the respiratory enzymes play an important role in en¬ abling birds and mammals to maintain a constant body temperature. These enzymes are plentiful and work rapidly in the cells of birds and mammals. Digestive enzymes It takes more than a rapid delivery of abundant oxygen to your cells to keep you warm. It also takes a rapid delivery of plenty of glucose and other food molecules. And that means rapid digestion as well as rapid circulation. Digestive enzymes make rapid diges¬ tion possible. One digestive enzyme you already know by name is pepsin. It is present in the digestive juice in your stomach and helps to activate the change of protein food molecules into simpler molecules. You have an enzyme in the saliva in your mouth. It speeds up the changing of starch into sugar. The pancreatic juice and the digestive juice in the small intestine contain a number of enzymes, some that speed up the completion of the digestion of all classes of foods. You will learn more about your own digestive enzymes in the next unit. The important point now is that digestive enzymes speed up di¬ gestion in the warm-blooded vertebrates and in doing so, help to get digested foods into the blood rapidly. Other enzymes There are many other enzymes be¬ sides the respiratory and digestive en¬ zymes. You may have watched the action of one of your own enzymes, without knowing it. Have you ever poured a few drops of hydrogen perox¬ ide on a cut finger? If so, you know VERTEBRATES AND HOW THEY LIVE 315 William J. L. Sladen, from Falkland Islands Dependencies Survey 11-10 WARM-BLOODED VERTEBRATES IN A COLD CLIMATE Not only do penguins main¬ tain their body temperature in spite of their Antarctic home, but they also lay and hatch eggs in this climate (one egg is shown within the white circle). Are penguins birds or mammals? how it bubbles. Those bubbles are the product of an enzyme in your blood. That enzyme changes hydrogen perox¬ ide (H202) into water (TLO). That sets oxygen free. The free oxygen forms the bubbles you see when you put hy¬ drogen peroxide on a cut. How could you find out whether a frog has the same enzyme in its blood? J Without enzymes, there would be no J photosynthesis in green leaves. Chloro¬ phyll itself acts as an enzyme. Several other enzymes play a part in the series of chemical changes that occur in pho¬ tosynthesis. Even these enzymes in green plants are indirectly important to warm-blooded vertebrates. Can you explain why? While we are talking about enzymes, here is a side light of interest. Recently, an enzyme extracted from certain parts of a fig tree was tried out in treating deep burns in the human skin. In 1957, most encouraging results were pub¬ lished. The enzyme cleaned away the tissues killed by the burns in five or six days; then skin grafting could begin. Now researchers are trying to find an enzyme that will make the burn wound clean in less time, maybe in 24 hours. Read your Science News Letter or sci¬ ence news columns in your newspapers to keep up with researches on enzymes. You will learn more about enzvmes J and their importance in the next unit. Other factors in warm-bloodedness You have learned that a four-cham¬ bered heart is one feature of all warm¬ blooded vertebrates. Rapid cell respira¬ tion and rapid digestion, activated by enzvmes, are others. But crocodiles J 7 have four-chambered hearts and are not warm-blooded. And all organisms, 316 SPECIALIZATION IN HIGHER ORGANISMS even the algae and protozoa, make respiratory, digestive, and many more enzymes. So why are birds and mam¬ mals warm-blooded? Obviously some¬ thing else is involved. Think a minute of a bird or rabbit, then of a fish or frog. The bird has feathers. The rabbit has fur. Feathers and fur are excellent insulation. They help to keep the heat set free by cell respiration from being lost rapidly to the surrounding air. A fish’s scales and a frog’s smooth skin are not good in¬ sulation. These and other cold-blooded animals lose heat rather rapidly to their surroundings. Some type of body cover¬ ing that prevents a rapid loss of heat is a feature of the warm-blooded verte¬ brates (Figure 11-10). Even your skin and the layer of fat underneath it are excellent insulation, although you may not think so on cold days. Birds and mammals have still another feature that is related to warm-blooded¬ ness. This feature is some means of cooling the body in very hot weather or during strenuous exercise. This cool¬ ing device involves a rapid evaporation of moisture. In birds, dogs, and in many mammals, the moisture is evaporated rapidly from the linings of the mouth, nose, throat, and lungs. You must have seen a dog pant after exercise or on a hot day. Panting speeds up the passage of air over the moist linings of the mouth, throat, and lungs. This speeds up evaporation. It takes heat to evapo¬ rate water. In warm-blooded verte¬ brates, body heat is used up when wa¬ ter in or on moist surfaces evaporates. That’s why this evaporation cools the body. In the next unit, you will learn more about how the evaporation of sweat helps to keep your temperature normal on a hot day or during strenu¬ ous exercise. Another feature of warm-blooded animals is what you might call a built- in thermostat. Of course it isn’t like the thermostat on the wall that regulates the temperature of a house by turning the furnace on and off as the tempera¬ ture falls or rises. The center of temper¬ ature regulation in man, at least, and probably in other mammals and in birds, too, is in a part of the brain- more specifically, in the midbrain, which is not properly a part of the cerebrum, cerebellum, or medulla. In man, this “thermostat’’ is connected with a nerve center in the medulla, which in turn is connected through nerves with the smallest arteries and the sweat glands in the skin. On a hot day, nerve impulses from the brain cause the blood vessels in the skin to enlarge and the sweat glands to pro¬ duce more sweat. Both the enlarged blood vessels and the increased amount of sweat result in a more rapid loss of heat from the body and help to keep the body temperature at 98.6° F. This tem¬ perature control in the central nervous system plays an important part in your life, and it brings us to the role of the rest of the nervous system in the lives of the vertebrates. But first let’s sum up this section on the warm-blooded verte¬ brates. Summing up: the warm-blooded vertebrates Birds and mammals are warm¬ blooded vertebrates. Several body fea¬ tures enable these animals to maintain a constant body temperature. In these and in other features, birds and mam¬ mals are more specialized than fish, amphibians, and reptiles. Biologists probably do not yet know all the factors in warm-blooded verte¬ brates that make this condition possi- VERTEBRATES AND HOW THEY LIVE 317 ble. Among the important factors are these: 1. A four-chambered heart 2. Rapid digestion in the food tube, activated by digestive enzymes 3. Rapid delivery of blood, heavily loaded with oxygen and digested food, to all living cells 4. Rapid cell respiration, activated by respiratory enzymes 5. An insulating body covering, such as feathers or fur and a layer of fat under the skin 6. A cooling device involving the evaporation of water from moist sur¬ faces within the body or from the skin 7. A “temperature-control’’ center in the midbrain, known to be present at least in man BEHAVIOR IN VERTEBRATES You already know that all the reac¬ tions of an organism make up its be¬ havior. The behavior of vertebrates is more varied and more effective than that of any other organisms. Let’s take a look, first, at a particular example of behavior in two mammals. A dog and a possum A fox terrier dog, named Spot, smelled out an opossum in the bottom of a hollow tree. After much growling and snapping, Spot finally dragged the fighting opossum into the open. There he grabbed it by the back and shook it as hard as he could, though the opos¬ sum was almost as big as he was. Then suddenly the opossum went limp. It lay as if dead, even while Spot growled and sniffed and poked it with his nose. In other words, the wild beast sudden¬ ly “stopped reacting” to the dog. Before long Spot abandoned his seemingly dead prey. But the opossum wasn’t dead. It was only “playing possum.” In due time, it slowly arose, looked all around, and then quickly scrambled back into its hole. It had saved its life by “playing dead.” This sudden stopping of outward action is part of the natural behavior of an opossum ( and some other animals ) —one way of reacting to changes around it. All of its reactions make up its total behavior. So do those of a doe;. O Muscles and nerves Spot’s behavior in attacking the opos¬ sum was possible largely because of three organ systems— the muscle sys¬ tem, the bone ( or skeletal ) system, and the nervous system. He saw the opos¬ sum with his eyes and smelled it with his nose. Eyes and nose are sense or¬ gans, part of the nervous system. He dug the opossum out with his feet, bit it with his mouth, and shook it with his head. These reactions involved the use of his leg and neck and head muscles. Spot’s reactions to the opossum were effected largely through his nervous, muscle, and bone systems. Usually, it takes both muscles and bones to move a part of the body. Without his jaw¬ bone, for example, Spot’s neck and face muscles could not “sink his teeth” into his prey. Most of the behavior you can see in dogs or in any other vertebrates in¬ volves movements. It takes muscles and bones to move your arm to catch a ball, or to enable you to jump out of the way of a truck or to eat your dinner. The same thino; is true of most of vour visi- ble responses. You can undoubtedly think of exceptions. For example, you see a picture of a roast ham and your mouth waters. Here the response is not a movement, but a flow of saliva into your mouth. There are other exceptions, 318 SPECIALIZATION IN HIGHER ORGANISMS like the flow of digestive juices into your stomach and intestine. But on the whole, the behavior of vertebrates is possible partly because of their muscle and bone svstems. J As mentioned early in this chapter, the vertebrate nervous system is on a much higher level of organization than that of any invertebrate. You have al¬ ready studied the central nervous sys¬ tem and some of the sense organs of the fish and the frog. You know that these animals have comparatively large brains (think of the dorsal ganglia of an earth¬ worm or an insect ) with several special¬ ized parts. Birds and mammals have still larger brains with much more high¬ ly developed cerebrums ( Figure 11-11 ) . Vertebrates learn more things faster than any invertebrates do. In verte¬ brates, the cerebrum is the nerve cen¬ ter of learning. No invertebrate has a cerebrum. Why is the cerebrum an ad¬ vantage when it comes to learning things rapidly? To answer that, you need to know about nerve cells. Nervous systems are made of cells'1'. Like any other part of the body, the nervous system is built of cells. Nerve cells are found in the brain, in the spi¬ nal cord, in the nerves, and in the sense organs of animals. Because they differ from all other kinds of cells in the body, nerve cells are given a special name. Nerve cells are called neurons (nyoo ronz). A neuron is too small to be seen without a microscope, even though some of the neurons in man have 11-11 A comparison of these four verte¬ brate brains reveals the increasing com¬ plexity, from fish to mammal, of the cere¬ brum and cerebellum. The degree of development of the brain is even more pronounced when considered in terms of the dorsal ganglia of, say, arthropods. VERTEBRATE BRAINS CODFISH FROG PIGEON HORSE Optic nerves Cerebrum Cerebellum Olfactory lobes Cerebrum Cerebellum Optic nerves Medulla Olfactory lobes Optic lobes Medulla Cerebellum Cerebrum Optic obes Medulla Olfactory Optic lobes nerves Cerebrum Optic lobe (s) Cerebellum Olfactory Optic lobe(s) nerve(s) Medulla 11-12 NEURONS Left. Sensory neurons enable a vertebrate to receive ‘‘messages’’ from outside the body. The sensory end¬ ings may be in the skin, the eye, or else¬ where. Right. Motor neurons enable a ver¬ tebrate to react to stimuli. They connect the brain or spinal cord with the muscles of the body. branches several feet long. In the com¬ plete nervous system, man has billions of neurons ( some 12 billion in the cere¬ brum alone), all of which are believed to be present at birth and to remain constant in number during his lifetime, O 7 unless injury or disease destroys some of them. Neurons have projections (fine threads) of cytoplasm that spread out in two or more directions from the main body of the cell (Figure 11-12). The threads, bound together in nerves like wires in a telephone cable, spread out to all parts of the body. You have often heard people say that your nerves carry “messages.’’ They do not, as we usually use the word mes¬ sage. They do carry nerve impulses that are at least something like electrical im¬ pulses. It is over the long branches of the neurons that nerve impulses travel to and from various parts of the body. A thread that carries an impulse away from the cell body is called the axon ( ak son ) , and those which carry impulses toward the cell body are called dendrites ( den drytes ) . Den¬ drites may be either short or long, and they are usually much branched. A sin¬ gle neuron may have only one dendrite or it may have several. In vertebrates, the cell bodies of neurons usually lie in the central nervous system. Only the axons and dendrites (Figure 11-12) run to the head and feet and body. The axons and dendrites that extend to dis¬ tant parts of the body are located with¬ in the nerves to these body parts. For example, the leg nerves you saw in the frog are bundles of axons and dendrites. The cell bodies of these neurons are in or very close to the spinal cord. So those nerves might be compared to telephone cables (Figure 11-13) and the whole vertebrate nervous system to 320 SPECIALIZATION IN HIGHER ORGANISMS General Riological Supply House. Inc., Chicago 11-13 CROSS SECTION OF A NERVE The black spots are axons or dendrites of neu¬ rons; the lighter areas, fatty sheaths. a telephone system, with central “op¬ erators” in the brain and spinal cord and millions or billions of “wires” in the cablelike nerves. A single neuron does not make up a complete “telephone” line through the nervous system of a vertebrate. Three or more neurons are necessary. In such a “telephone” line there are points where the end of a dendrite of one neu¬ ron “joins” the end of an axon of an¬ other neuron. That word “joins” is en¬ closed in quotation marks because it must be used with caution. To this dav, experts in the study of neurons are not sure whether the end of the dendrite of one neuron actually touches the end of the axon of another neuron or not. At any rate, the point at which the end of the dendrite “touches” or “nearly touches” the end of an axon is called a synapse ( sih naps ) . A synapse may be defined as the point at which a nerve impulse passes from an axon of one neuron into a dendrite of another. Pathways through the nervous system In the complex nervous system of a vertebrate with its millions or billions of cells, many pathways are present even at birth. Many more pathways are developed during the animal’s life¬ time. These pathways are courses over which impulses travel. A pathway through the nervous system of a verte¬ brate consists of three parts. First, there is an incoming line over which impulses travel from the sense organs or other points of stimulation into the spinal cord or the brain. Second, there is a line within the cord or the brain, over which impulses from incoming lines are transferred to outgoing lines. Third, there are the outgoing lines over which impulses travel out to muscles, glands, or other organs where the responses occur. These pathways are made of neu¬ rons. In its simplest form, a pathway through a vertebrate nervous system consists of at least three neurons: an incoming neuron, a central neuron, and an outgoing neuron. Since the incoming neuron receives impulses from a sense organ, it is called a sensory neuron. Bundles of dendrites of sensory neu- rons make up the sensory nerve fibers. Since most of the outgoing neurons carry impulses to muscles ( the im¬ pulses result in motion), they are called motor neurons. Their axons make up the motor fibers. Central neurons are called associative neurons. The outer end of a sensory neuron mav lie in the skin or the eve or in some j J other place where stimulation can be received from outside. The impulse travels in along the dendrite to the cell body, which is located in the brain or in the ganglion on one root of a spinal nerve (Figure 11-14). The impulse travels from the cell body through an VERTEBRATES AND HOW THEY LIVE 321 axon to one or more associative neu¬ rons in the brain or the cord (in the brain, many associative neurons often are involved) and is transferred from there to a motor neuron, which carries the impulse to a muscle or a gland where the response occurs. You see many one-way streets in cities these days. Neuron pathways are like one-way streets. All impulses travel only one way over them. The simplest pathways through the nervous system are called reflex arcs. A reflex arc is a pathway over which impulses that result in reflex acts pass. It consists of, in vertebrates, at least three neurons: a sensory, an associative, and a motor neuron (Figure 11-14). Let us now consider more exactly what reflex acts and reflex arcs are. Complexity of vertebrate reflex arcs It isn't likelv that anv vertebrate re- J J flex arc really has only three neurons in it. The axon of a sensory neuron has several endings. The nerve impulse may pass through these several synapses in¬ to several associative neurons. Associa¬ tive neurons may transfer the impulses to other associative neurons and so on. Finally, the nerve impulse may reach several motor neurons. Probably every neuron in a vertebrate’s bodv is in J touch, indirectly, with every other neu¬ ron. So any nerve impulse entering the central nervous system could probably travel into any motor neuron in the ani¬ mal's body. Think again of Spot’s attack upon the opossum. Impulses from his eyes and nose traveled over many sensory neu¬ rons into his brain, then over many as- sociative neurons, and out into many motor neurons. The nerve impulses reached muscles all over his bodv. He J barked and growled and dug a hole. He pulled out the opossum and strug¬ gled with it until it “played possum.” The nerve impulses traveled over many nerve pathways, some of which were reflex arcs. For example, nerve impulses traveled from eyes to brain to jaw mus¬ cles over reflex arcs, and these impulses caused the jaw muscles to contract and close the jaw in a bite. This act of biting is an example of a reflex act, or reflex, for short. Spot didn’t “decide” to bite at the opossum; he just bit. So at least some of Spot’s reactions were reflex acts, due to the functioning of reflex arcs. 11-14 DIAGRAM OF A SIMPLE REFLEX ARC On the left is the spinal cord, shown in cross section. Note the two roots, one containing sensory fibers and one containing motor fibers. Although the essential neurons are shown— one sensory, one associative, one mo¬ tor— it is doubtful whether many, if any, vertebrate reflex arcs are this simple. (The drawing is not to scale; neurons are much longer in relation to their breadth.) 322 SPECIALIZATION IN HIGHER ORGANISMS Many of your actions are reflexes. Pulling your finger back from a very hot object is a reflex; so is an involun¬ tary flow of tears, when in severe pain. Unfortunately for the sake of easy understanding, but fortunately for be¬ havior, vertebrate reflex arcs are com¬ plex beyond our imagination. Billions of neurons, with each one in possible contact with every other one, are like billions of telephones over the nation, with each one in possible contact through its wires with every other one. We cannot even conceive the physical complexity of a frog’s nervous system, to say nothing of Spot’s. Nevertheless, in all this complexity there are many direct lines always “plugged in,” as a telephone operator would say. A reflex arc is somewhat like a direct line that is always “plugged in.” Take down the receiver at one end of a direct-line tele¬ phone and you will get the other end directly. Stimulate the sensory end of a reflex arc and a reflex act occurs. Inborn and modified reflexes All vertebrates have some reflexes “hooked up” and ready to work as soon as they are hatched or born (Figure 11-15). Newly hatched fish have inborn swimming reflexes. So do young tad¬ poles. A frog, just matured from a tad¬ pole, has breathing, hopping, and feed¬ ing reflexes. How many inborn reflexes of puppies or kittens or bird nestlings can you think of? Almost as soon as they are born, ver¬ tebrates begin to “learn,” as we say. Very young chicks peck at any and all “specks,” even each other’s eyes. These peckings are due to inborn reflex arcs and are called inborn reflex acts, or just inborn reflexes. Soon their inborn re¬ flex actions change and they peck fewer and fewer worthless “specks” and more 11-15 INBORN BEHAVIOR These three baby squirrels, their eyes not yet open, were taken from their nest and placed on the bark of a tree. Immediately they be¬ gan climbing upward, an inborn response. and more bits of food. In time, they usually peck only at food ( and perhaps at each other ) . These modified peckings are often called conditioned reflexes. We usually say that the chick learns to peck at food. At least part of that “learning” is the result of conditioned reflexes that have been built upon in¬ born reflexes. Most of the reading you will find in reference books includes the use of the terms inborn reflex and conditioned re¬ flex. However, today many biologists prefer the terms inborn response and conditioned response, so from now on, we shall use the new terms. Both inborn and conditioned re¬ sponses play a role in the behavior of many invertebrates. But vertebrates have much greater ability to develop conditioned responses than any inver¬ tebrates have. That is just one reason A. Smith VERTEBRATES AND HOW THEY LIVE 323 why they learn more things faster than any invertebrate. Another and more im¬ portant reason involves the make-up of the cerebrum. The cerebrum and learning You can begin to see now why verte¬ brates can learn so much more than other animals. All the researches on the behavior of vertebrates show that the cerebrum is the nerve center of virtu¬ ally all learning. Invertebrates have no cerebrum at all. Think of the two small dorsal ganglia that serve as a “brain” in insects. Then think of the brain of the fish or frog or mammal with several specialized parts, including the cere¬ brum. Learning involves building neurons into new pathways in the nervous sys¬ tem. The simple ganglia and nerves of an earthworm or an arthropod have only a comparatively few neurons in them, as compared with the brain, cord, and nerves of a vertebrate. Nearly all of the neurons of an earthworm or an ar¬ thropod are tied up in inborn reflex arcs. This leaves very few neurons free J to be built into new pathways. No won¬ der these animals learn very little and very slowly. You can see that even the cerebrum of a fish, along with the rest of its nerv¬ ous system, must contain many, many more times as many neurons as does the nervous system of any invertebrate. As you move up to the frog, you find that the cerebrum makes up a much bigger fraction of the total brain than it does in the fish. In birds and mam¬ mals, the cerebrum makes up most of the brain. In general, the larger the cerebrum, the more neurons there are in it. (There are a few exceptions, of course.) Vertebrates are born with a goodlv number of their neurons already tied up in reflex arcs. But in all vertebrates, even in a fish or a frog, a goodly num¬ ber of the neurons in the cerebrum are not tied into inborn reflex arcs but are free to be built into new nerve path¬ ways. In other words, the comparative¬ ly large number of neurons in a verte¬ brate’s nervous system and especially in its cerebrum is a vital factor in the ability of vertebrates to learn so many more things and to learn them so much faster than any invertebrate can. You can begin to see now how the greatly increased specialization within the vertebrate’s nervous system and particularly in its highly specialized brain enter into the whole picture of how vertebrates live. You will go fur¬ ther in these studies in the next unit on the human body. CHAPTER ELEVEN: SUMMING UP In Chapter Eleven you have been learning about the vertebrates and how thev live. J First you explored the increased spe¬ cialization within the organ systems of vertebrates, particularly the circulatory system. Next you studied in some de¬ tail the main organ systems of a fish and a frog. After that you learned a little about the warm-blooded verte¬ brates, the birds and mammals, and some of the features of their bodies that enable them to maintain a constant body temperature. Finally you began your explorations into the role of the nervous svstem in the ability of verte- brates to learn many things rapidly. All these explorations have set the stage for your study of the human body, including human behavior. 324 SPECIALIZATION IN HIGHER ORGANISMS Your Biology Vocabulary The new terms introduced in this chapter are likely to be especially useful to you. Make sure that you understand and can use each one of the following terms correctly. pyloric caeca lateral line of fish neuron gall bladder Eustachian tubes axon auricle tendon dendrite ventricle larynx reflex arc arterial bulb cloaca inborn responses (inborn reflexes) olfactory lobes vocal sacs conditioned responses (conditioned cerebrum heart valves reflexes) optic lobes pancreas sensory neuron cerebellum pancreatic juice motor neuron medulla urine associative neuron spinal cord urine bladder warm-blooded animal central nervous enzymes ✓ cold-blooded animal svstem pepsin temperature control in midbrain Testing Your Conclusions All of the statements listed below are true. Some are true only of fish. Others are true only of frogs. Still others are true of both fish and frogs. Read all the statements. Copy only the ones that are true of both fish and frogs. 1. The blood goes through the heart twice in one complete circulation. 2. Some of the digested foods enter the blood stream in capillaries in the walls of the pyloric caeca. 3. Oxygen enters the blood stream and carbon dioxide leaves it in the lungs. 4. The brain is made up of olfactory lobes, cerebrum, optic lobes, cerebellum, and medulla. 5. The eardrums are external. 6. Inborn and conditioned responses play a part in their behavior. 7. They have arteries, veins, and capillaries. 8. They have several sense organs. 9. They have a larynx and vocal cords. 10. They excrete urea in the kidneys. 1 1. They can learn manv more things much faster than any invertebrate. 12. The cell bodies of the neurons that make up their nerves lie in or near the central nervous system. 13. They are cold-blooded. 14. They use their mouths in breathing. 15. Their cells produce respiratory enzymes. VERTEBRATES AND HOW THEY LIVE 325 More Explorations 1. Do fish have red blood cells? Get a freshly killed fish, perhaps from a fish market. From a gill filament, take a drop of blood and mount it in water, or, better yet, in normal saline (see page 30). Look for blood cells. Record what you did and what you learned. 2. What makes frogs hibernate? Frogs and a number of other vertebrates “sleep all winter,” as people say. Biologists say they hibernate. What stimulus produces the hibernation behavior? To find out, do these things. Put a live frog in a small glass jar. Put in a thermometer beside the frog. Set the jar in a large pan. Pack ice cubes around the jar. Keep reading the thermometer and watching the frog. At what temperature does the frog try to “dig in,” as it would in a pond in the fall? Record what you did and what you learned. 3. Behavior in a spinal frog. Ask your teacher to show you how to destroy a frog's brain painlessly, or almost so. It is done by inserting a needle at the base of the skull and pushing it into the skull with a combined pressing and stirring movement. A frog with its brain thus destroyed is called a spinal frog. Study the behavior of a spinal frog. Find out if it can see, by dangling a fly in front of its eyes. Touch various parts of the skin— on the head, on the legs, and on the dorsal and ventral sides of the body. Dip a toothpick into a weak acid solution and apply it to the skin on the side of the frog’s body. The only part of the spinal frog's central nervous system still intact is the spinal cord. In the light of that fact, try to explain the types of behavior still present in a spinal frog. Thought Problems L Fish have been found half a mile down in the ocean. There are no green plants down there, because light does not go down that far into the sea. Where do you suppose the food of these fish comes from? 2. In the late fall, frogs bury themselves at the bottom of a pond or stream and hibernate all winter. During hibernation, they are inactive, but the heart keeps on beating slowly. Where do the heart cells get the food and oxygen required to keep the heart beating? 3. As you know, yeasts ferment cider and grape juice. They ferment any sugar solu¬ tion. In doing so, they change sugar into alcohol and carbon dioxide. The compound zymase (zy mays) activates the change. To what class of organic compounds does zymase belong? Why do you place it in that class? 4. A frog got out of an aquarium one evening and couldn’t find its way back. Next day, a student found the dead frog, badly dried out, in one corner of the laboratory. What do you think caused the frog to die? Which life process probably stopped first? Further Reading 1. William Harvey’s Anatomical Studies on the Motion of the Heart and Blood is avail¬ able in a modern paperback edition, published by Charles C. Thomas, Springfield. Illinois. Even today, reading about the researches Harvey made 350 years ago is an exciting venture. 326 SPECIALIZATION IN HIGHER ORGANISMS 2. How many functioning lungs do snakes have? How many functioning egg tubes do hens have? How many heart chambers do the many different vertebrates have? How do bats find their way at night without bumping into things? Do any fish use the swim bladder as a breathing organ? Some of you may look up the answer to one of the above questions, others to an¬ other. Use any college zoology textbook, such as those already listed on page 263. Report these and any other interesting side lights on vertebrates in class. Under the title, Odd Facts About Some Vertebrates, record the information you and your class¬ mates uncover. 3. Look up pictures of the skeletons of several vertebrates and compare the bones in the forelimbs (wings in bats, legs or arms in many other vertebrates). See Brenda Putnam’s Animal X Rays, A Skeleton Key to Comparative Anatomy, Putnam, 1947, or any college zoology textbook. VERTEBRATES AND HOW THEY LIVE 327 T he boy shown in the photograph at the right is examining a model of a man, made of carved panels that are hinged at the back to allow the model to be opened or closed like a book. In a matter of a few hours, this boy can learn more about the human body than the most learned doctors knew one hundred and fifty years ago. Although it was already known by 1800 or so that certain diseases which took many lives could be cured simply by eating— eating the right foods— no one knew how many diseases could be cured so easily, or whv. No one knew J 7 J how the body made use of foods— what it could and could not do with or without certain nutrients. One hundred and fifty years ago, doctors did have a fairly good knowledge of how some of the parts of the body worked together— muscles and bones, or heart and lungs, for example. And they knew what the body looked like on the inside, for they had done post-mortem examinations. But their knowledge of what each organ in the body did (or controlled) was very primitive as compared with what we know todav. Thev knew that a J J certain gland in the head seemed to have something to do with how tall a person grew to be, but they did not know why. They knew that blood was J J circulated to all parts of the body lypi'J'' Pi, %'v!. ' through arteries and microscopic capillaries, then back to the heart through veins, but they did not know all the reasons why it was so important for a supply of blood to reach every part of the body. Do you know why, even today? One hundred and fifty years ago, doctors also knew that certain juices in the stomach acted upon foods that were eaten, but they did not know all that you will learn about foods and the digestive system when you read the first two chapters in this unit. Our knowledge of our bodies and how they work has had much added to it in the last hundred and fiftv years— or even in the last ten or twenty years. You will learn something of all that has been discovered as you study this J J unit. You will learn, too. that our knowledge of ourselves is far from complete, and that one hundred and fifty years in the future, much of what today is yet to be discovered will have become a factual part of every boy’s and girl’s education. Chapters 12. The Body at Work 13. Foods and Nutrition 14. internal Regulation and Co-ordination 15. Human Behavior and the Nervous System CHAPTER The Body at Work Research into the workings of body tissues newer ends . Here a medical scientist is studying the role of oxygen in the functioning of muscle cells. The muscle cells , still alive , are in glass flasks in the white circular basin . . A man and a kite Over 200 years ago, a Frenchman named Reaumur ( ray oh mer ) had a pet bird, a kite. Why is that fact re¬ membered? Because Reaumur used an odd trait of his pet s to get a substance for a series of experiments. These ex¬ periments led to a discovery that made biological history. The kite is one of the hawks, and it lives largely on field mice. It swallows its prey whole— fur, bones, and all. After some time, the indigestible parts, such as the fur, are discharged through the mouth. Reaumur fed the bird small sponges. In due time, these sponges were ejected from the bird’s stomach through its mouth. But before they were ejected from the stomach, the sponges had absorbed some of the stom¬ ach juice, called gastric juice. Reaumur pressed some of the gastric juice out of the sponges into dishes. Then he crushed some meat and mixed it with the gastric juice. He let the mix- Brookhaven National Laboratory tures stand for several days in a warm place. Slowly the meat “dissolved," as he put it. The gastric juice was digest¬ ing the proteins in the meat. This was one of the first studies of digestion. In this chapter, you will studv the human digestive system and several other organ systems in the body, all of which work in close co-operation in getting food and oxygen into the body and to all the living cells. Turn now to the Human Body Charts following page 336 and leaf through them. Refer to them often as you study the human body. J THE DIGESTIVE SYSTEM The chief parts of the digestive sys¬ tem are: 1. The food tube (alimentary canal). 2. The glands that secrete digestive juices and deliver them into the food tube at various points. 330 THE HUMAN BODY The food tube The human food tube consists of about the same parts as that of a fish or frog. In man, these parts are the mouth, gullet, stomach, small intestine, large intestine, rectum, and anus (Hu¬ man Body Chart 7). The appendix is attached to one part of the large intes¬ tine but plays no known part in the work of the food tube. Throughout its length, the walls of the food tube are composed of similar layers of tissue. The inner layer is called the mucous membrane, because some of its cells secrete a thick, sticky, lubri¬ cating fluid called mucus. In the stom¬ ach and intestine, the mucous mem¬ brane is not smooth— or perhaps we should say it is not flat— as it is in the mouth, but rather is folded or wrinkled (Figure 12-1 and Body Chart 7). This folding increases the inner surface of the stomach as much as fifteen times. In 1925, Gordon H. Scott * estimated that an adult’s stomach surface, if spread out completely flat, would cover * Now professor of anatomy and dean of the College of Medicine at Wayne University, Detroit, Mich. 12-1 CLOSE-UP OF LINING OF HUMAN STOMACH Folds greatly increase the in¬ ner surface area, enabling the stomach to work as quickly and efficiently as a smoothly lined organ many times its size. J O J William C. Stoddard a surface some three yards square. In both the stomach and small intestine, certain digestive glands lie in the mu¬ cous membrane. The second layer of the food-tube wall is smooth muscle. Along most of its length, the food tube has both lengthwise and circular muscles in this muscle layer. At several points, the cir¬ cular muscles form valvelike structures which can close the food tube. These are called sphincter ( sfink ter ) mus¬ cles. There is a sphincter muscle at the opening of the gullet into the stomach, another at the opening of the stomach into the small intestine, another where the small intestine joins the large intes¬ tine, and another around the anus. The outer layer of the wall of the food tube is a tough, elastic layer made up primarily of connective tissue. This tissue spreads through and binds to¬ gether all three layers of the food tube. All the layers are richly supplied with blood vessels, as well as nerves. Digestive glands Glands that secrete digestive juices are found along or near the food tube at many places. First come the salivary glands, three pairs of them. One pair of salivary glands lies just below the ears. The other two pairs lie farther forward under the jaw and the tongue. These glands make saliva out of mate¬ rials from the blood. The saliva flows out of each gland (Figure 12-2) into the mouth through a little duct ( tube ) . In the mucous membrane of the stomach lie the gastric glands, some 15 million of them, according to Gor¬ don H. Scott. From the gastric and other glands come the substances that make up gastric juice, which contains pepsin, very dilute hydrochloric acid, mucus, and water. THE BODY AT WORK 331 Jawbone 1 (cut away) Salivary glands 12-2 HUMAN SALIVARY GLANDS Shown in color here are the three salivary glands on one side of the head. How does saliva from these glands (and the three on the other side of the head) get into the mouth? The liver secretes bile, which may be stored in the gall bladder. The pan¬ creas secretes pancreatic juice. Both bile and pancreatic juice reach the small intestine through ducts. Finally, glands in the mucous membrane of the small intestine secrete intestinal juice, which flows into the small intestine through tiny openings in the epithelial lining. Action of saliva Digestion begins in the mouth. A dry soda cracker is mostly starch with no J sugar, but when you chew a cracker a little while, it begins to taste sweet. The saliva contains ptyalin ( ty uh lin ) , an enzyme which changes starch to a sugar called maltose, which tastes sweet. MAKING A SUGAR TEST. With a wax pencil, label three test tubes 1, 2, and 3. In No. 1 put some saliva, in No. 2 a few bits of dry soda cracker, and in No. 3 a little thoroughly chewed soda cracker. To each test tube add enough Benedict's solu¬ tion to cover the contents about % inch deep, then boil the contents of each tube a minute or so. A color change to yellow or red shows that sugar is present. Record the experiment and its results in your rec¬ ord book. Of help to you in breaking up food in your mouth are your four kinds of teeth. If you do not already know them and their names, learn them from Fig¬ ure 12-3. Most of you probably have 28 teeth, but a few of you may already have your wisdom teeth, which would bring the number to 32. Food, thoroughly chewed and mixed with saliva, is swallowed through the gullet. Wave after wave of muscular contractions of the walls of the gullet push the food mass into the stomach. This will happen even if a person is standing on his head. Digestion in the stomach and intestine When food enters the stomach, gas¬ tric juice begins to flow. Contractions of the stomach walls also begin to churn the food, mixing the digestive juices with the food mass. As soon as the hydrochloric acid is mixed with the food mass, the action of ptyalin on starch stops, since ptyalin acts only in an alkaline medium such as saliva. DEMONSTRATING THE ACTION OF PEP¬ SIN. Your teacher will be able to supply you with a solution of pepsin and a solu¬ tion of about four-per-cent hydrochloric acid. Label three test tubes 1, 2, and 3. Into each test tube, put some bits of cooked 332 THE HUMAN BODY American Dental Association 12-3 TEETH IN THE LOWER JAW Left. The four kinds of teeth labeled here are also found in the upper jaw. Dentists often call the canines cuspids. Right. Proper care of the teeth requires (among other things) periodic X-ray photographs such as this one. Both of these molars are developing hidden cavities at the common point circled in red. egg white and cover this with water. Leave No. 1 as it is. To Nos. 2 and 3, add a few drops of the pepsin solution. To No. 3, add also a dozen drops of dilute hydrochloric acid. Keep the test tubes in a warm place. Examine each one after half an hour, after 24 hours, and after 48 hours. In your record book, tell what you did and what hap¬ pened to the bits of egg white (largely pro¬ tein) in each test tube. In the presence of hydrochloric acid, pepsin digests protein foods rather rap¬ idly, changing them into proteoses (proh tee oh ses ) and peptones (pep tolmz ) . The sphincter muscle at the outlet of the stomach contracts when food enters the stomach, and thus keeps the food mass in the stomach for varying lengths of time. The waves of muscle contrac¬ tions of the stomach walls keep churn¬ ing the food mass, as the X ray in Fig¬ ure 12-4 indicates. In due time, perhaps two to five hours, the stomach digestion is finished. Then the food mass moves on into the small intestine. The first section of the small intes¬ tine is the duodenum ( doo oh dee num). As soon as the food mass from the stomach enters the duodenum, bile from the liver and pancreatic juice from the pancreas pour into the duo¬ denum through ducts ( Human Body Chart 7, bottom of right-hand page ) . Bile does to fats and oils about what soap does to them— it emulsifies them. Then an enzyme called lipase (ly pays), found both in pancreatic juice and in intestinal juice, changes the emulsified fats and oils into fatty acids 12-4 X-RAY PHOTOGRAPH OF THE STOM¬ ACH Two waves of contraction are shown passing over the stomach. The white mass is barium sulfate, a substance taken by J mouth to make the stomach show clearly J when X-rayed. and glycerol. ( You may remember from page 274 that plants synthesize fats by combining three molecules of fatty acids with one of glycerol. When you digest fats, you reverse this process. ) Other enzymes in pancreatic and in¬ testinal juice complete the digestion of the already partly digested carbohy¬ drates and proteins. When digestion is completed, carbohydrates have been changed into glucose, proteins into amino acids, and fats and oils into fatty acids and glycerol. (Table 12-A lists digestive glands and enzymes that play a part in human digestion.) From the small intestine, the digested foods make their way into the blood stream. The large intestine The indigestible parts of the food mass, along with considerable amounts of water, move on from the small intes¬ tine into the large intestine, or colon (Human Body Chart 7). Mixed with this mass are some bacteria that were on the food when it was eaten or that were present in the mouth. In the colon, there are always millions upon millions of bacteria. These bacteria re¬ produce all the time and live in the remnants of the food mass in the colon. Some kinds of bacteria in the colon are human symbionts (turn back to page 225, if you have forgotten what sym¬ bionts are). They are useful in one way or another. One kind, for example, makes a vitamin and another kind an amino acid that we need but cannot make in our own cells. While the mass remains in the colon, most of the water in it diffuses into the blood, while excess calcium salts and other heavy salts diffuse out of the blood into the colon. Finally, the mass J 7 of indigestible material is eliminated O from the body through the anus. The circular muscles in the walls of the food tube contract again and again, sometimes rapidly as in the stomach during digestion, and sometimes slow¬ ly, but the contractions go on to some extent all the time. Wave after wave of these contractions pass downward along the food tube— from gullet to stomach to small intestine to large intestine— pushing the food mass on toward the rectum. These waves of contractions we call peristalsis (pehr ih stahl sis ). TABLE 12-A DIGESTIVE GLANDS AND THEIR ENZYMES Glands Secretions Enzymes Foods affected Products of changes Salivary Saliva Ptyalin Starch Maltose Gastric Gastric juice containing hydrochloric acid Pepsin Protein Proteoses, peptones Pancreatic Pancreatic juice Lipase (in presence of bile) Amylase T rypsin Erepsin Fats Starch Protein, proteoses Peptones Fatty acids, glycerol Maltose Amino acids Amino acids Intestinal Intestinal juice Erepsin Maltase Lactase Invertase Peptones Maltose Milk sugar Table sugar Amino acids Glucose Glucose Glucose 334 THE HUMAN BODY On the end of the colon just below the place where the small intestine joins it is a pouchlike caecum to which the appendix (Human Body Chart 7) is attached. The appendix is a small tube, closed at the unattached end. It is normally about three inches long and considerably smaller in diameter than an ordinary lead pencil. So far as anyone knows, the appendix is of no use to us (but if it becomes infected it can do a great deal of harm, a topic that will be discussed in the next unit ) . How digested foods enter the blood You will recall that the mucous mem¬ brane that lines the intestine is wrin¬ kled into many folds ( Human Body Chart 7). On the surface of these folds there are thousands of little projections called villi ( vil eye— singular, villus ) . These villi (Figure 12-5) absorb much of the liquid that surrounds them in the intestine. Just beneath the surface of each vil¬ lus there are capillaries (Figure 12-5). Molecules of glucose and amino acids, along with water and salts and other necessary substances, diffuse into the blood that is passing through the capil¬ laries of the villi. We do not yet know in exactly what form fats and oils enter the circulatory system. Apparently they do not diffuse directly into the capillaries of the villi. They do diffuse into the little tubes in the centers of the villi. The little tube inside each villus is called a lacteal (Figure 12-5). The digested fats enter these lacteals. From the lacteals they are delivered into larger and larger tubes and finally into one big tube, or duct. That duct carries them to a large vein that comes from the left arm (Fig¬ ure 12-6). Thus digested fats enter the blood. of the small intestine increase the inner surface of the intestine many times over. This means that absorption of foods oc¬ curs much faster than it otherwise would. Summing up: the digestive system The human digestive system consists of the food tube and the glands that secrete juices useful in digestion. Digestion begins in the mouth, where ptyalin in the saliva activates the change of starch into maltose. Gastric juice in the stomach starts the digestion of proteins by breaking their molecules down into proteoses and peptones. In the small intestine, pancreatic juice and intestinal juice complete the digestion of carbohydrates and proteins. These juices change carbohydrates finally into glucose. They change proteins, prote¬ oses, and peptones into amino acids. Glucose and amino acids diffuse into the blood in the capillaries of the villi in the lining of the intestine. THE BODY AT WORK 335 Bile emulsifies fats. Then lipase ac¬ tivates their change into fattv acids and O J glycerol. Digested fats diffuse into the lacteals of the villi and finally reach the blood stream through a large duct that enters a vein in the upper left chest. 12-6 The lymph that bathes all the liv¬ ing cells in your body circulates back through lymph ducts and lymph nodes, toward veins near the heart. Into which vein does the duct that carries digested fats from the small intestine empty? CIRCULATION OF THE LYMPH Indigestible food materials, mixed with a good deal of water and millions upon millions of bacteria, pass into the colon, where most of the water diffuses into the blood. Here, too, certain bene¬ ficial bacteria synthesize a vitamin, and others an amino acid, that diffuse into the blood. Finally, the solid wastes that remain in the colon are eliminated through the rectum and anus. - > On the next sixteen pages a complete blueprint of the human body appears in full color. Before going on to the text discussion of the remaining organ sys¬ tems in the human body ( page 337, fol¬ lowing the sixteen pages in color), you may wish to thumb through these Hu¬ man Body Charts. Or, if you prefer, go on to the text on page 337 and com¬ plete the chapter, using the Human Body Charts for reference when so di¬ rected from points within the text. After completing this chapter, you will want to examine the Human Bodv J Charts again for review. At that time, re-examine the Frog Charts (following page 288 ) and compare the body struc¬ tures of these two vertebrates. If you wish to go even further, turn back through the text to Chapters 6-9 and 11, and compare man as a vertebrate with other vertebrates and invertebrates (use the animal blueprints, such as that for a yellow perch on page 301, or that for a fresh-water clam on page 187). Keep in mind not only body structures, but also different wavs of life. Look for ✓ modifications in the structure of each animal that enable it to live as it does. These comparisons will help you to better understand both vourself and J the lower animals. 336 THE HUMAN BODY All artwork by Caru Studios, Inc., New York City. Research by the editors, Harcourt, Brace, and Company, Inc., in collaboration with the artists. Critical review by Arthur M. Crosman, Ph.D., Assoc. Professor of Biology, New York University. Photomicrographs copyrighted by General Biological Supply House, Inc., Chicago, Illinois, made by Department of Anatomy, University of Illinois. COPYRIGHT, © 1957, BY HARCOURT, BRACE AND COMPANY, INC. All rights reserved. No part of “The Human Body” may be reproduced in any form, by mimeograph or any other means, without permission in writing from the publisher. PRINTED IN THE UNITED STATES OF AMERICA BODY CHART 1-THE SKELETAL SYSTEM WHAT IT IS Your skeleton con¬ sists of 206 bones. Some of these bones have grown together, as in your cranium and the lower part of your spinal column. Most of your bones, however, remain separate, yet are connected by some means. Your ribs and most of your verte¬ brae are connected by tough, stiff cartilage, which greatly restricts movement. Other bones are jointed and held together by tough but flex¬ ible ligaments (shown on one side of the skeleton), which do not restrict freedom of movement. Your skele¬ ton has freely movable joints that make it possible for you to do such things as turn your head, raise and bend your arms, bend at the hips and knees, and move your hands, feet, fingers, and toes. Cranium _ Upper jawbone Lower jawbone Collarbone (clavicle) _ Breastbone (sternum) _ Rib _ Cartilage of ribs _ Ligaments of wrist and hand Tendons of upper leg muscles _ Kneecap - (patella) Vertebrae (bones of spinal column) Hipbones Ligament enclosing hip joint . Sutures HOW IT WORKS The rigid framework of your skeleton is very important to you in three ways. 1. It gives shape and support to your body. Also, your spinal col¬ umn, with its double curve, and your freely movable joints enable you to stand erect. 2. It protects your vital organs. Your skull and spinal column pro¬ tect your brain and spinal cord. Your rib cage protects your heart and lungs, and your ribs and hipbones help protect your other vital organs. 3. It helps make it possible for you to move. Your entire skeleton, with its many movable joints, can be made to move in countless ways by your muscles. Even your ribs can be moved enough to let you expand your chest when you breathe. Ligament joining skull to vertebrae Ligament enclosing shoulder joint Shoulder blade (scapula) Upper arm bone (humerus) Lower arm bones - (radius and - ulna) Sacrum (part of spinal column) Ligament binding sacrum to hipbone Wrist bones Upper leg bone (femur) Tendons of lower leg muscles Lower leg bones - (tibia and - fibula) Ankle bones BODY CHART 2-THE MUSCULAR SYSTEM Moves jaw Turns head Pulls arm — toward chest Lift ribs - Ribs - Bends elbow - (biceps) Flattens - abdomen Lifts upper leg Rotates thigh Straightens lower leg Tendons at knee Raises forward part of foot Leg bones - Tendon of Achilles WHAT IT IS About one half of your body is muscle. The muscular system, as seen in these two views, consists of skeletal muscles— mus¬ cles that are attached to bones by tendons and other means. Since you cannot see the skeleton beneath sev¬ eral layers of muscle, certain mus¬ cles on one side of the body, front and back, have been stripped away. By studying the portions cut away, you may observe different layers of muscles and find a few points of attachment to the bones of the skeleton. Muscles have curious names. Since their names do not mean as much as the work they do, the muscles have been labeled here in terms of their work. BODY CHART 2-THE MUSCULAR SYSTEM ■ ■' • . : HOW IT WORKS Your muscles work in only one way — they con¬ tract. When they contract, your mus¬ cles become shorter and thicker; thus, they exert a pull on the bones to which they are attached and cause certain of these bones to move. Most muscles work in pairs. For instance, the biceps muscle causes your arm to bend at the elbow, while the triceps muscle causes it to straighten again. When one muscle of a pair contracts, the other relaxes. Otherwise, paired muscles would pull against each other without caus¬ ing movement. A few muscles are not attached to bones. An example is the ring of muscle that lets you purse your lips to whistle. Raises head Raises shoulder Lifts arm (deltoid) Straightens arm at elbow (triceps) Move ribs Move wrist, hands, and fingers Tendons from forearm muscles to fingers Bends leg at knee Raises heel (permits standing on toes) Tendon of Achilles Leg bones Tendons to toes BODY CHART 3-THE BONE-MUSCLE RELATIONSHIP Ligaments Collarbone Upper arm bone (humerus) Lower arm bones (radius) (ulna) - Lower tendon of biceps Ligaments Tendon Ligaments Cartilage Tendons Muscle used for raising heel and standing on tiptoe Tendon of Achilles Ligaments Bones of foot Upper leg bone (femur) Kneecap (patella) Lower leg bones (fibula) — (tibia) — WHAT IT IS The basic structure of an arm and leg (the left arm and leg, viewed from the inner side) helps clarify how your bones and muscles work together. The ends of the arm and leg bones are enlarged to form heads. Where the heads of two bones come together (as in the knee joint), they are padded by cartilage and bound together by flexible ligaments. Notice that for body movement to be possible, the tendons at the opposite ends of each muscle must be attached to differ¬ ent bones. For example, observe that the lower tendon of the biceps is attached to a bone of the forearm. Since the elbow is a freely movable joint, contraction of the biceps will cause the arm to bend. By studying the muscle in the drawing of the lower leg, you can observe that a similar relationship exists. BODY CHART 4-THE NERVOUS SYSTEM 1 1 *1 Cranium Cerebrum Cerebellum Medulla Spinal cord Vertebra Meninges A. The Brain and Spinal Cord (cut in two lengthwise) Convolutions Meninges Pineal body Pituitary body Cardiac plexus B. Cross Section of the Spinal Cord C. The of the Heart Nerve sheath Nerve fibers D. Stained Cross Section of a Nerve (as seen under the microscope) HOW IT WORKS Your central nervous system (A. above), controls chiefly your reactions to the world around you. Nerve impulses enter and leave your brain and spinal cord all the time. Incoming impulses make you aware of things around you and of your own actions. Out¬ going impulses rouse parts of your body to such actions as blinking, walking, and writing. Your autonomic nervous system controls chiefly such vital activities as heartbeat (C. above), breathing and gland action. Its nerves also carry impulses to and from its gan¬ glia and the lower part of the brain —but these impulses usually do not reach your cerebrum and make you aware of what is happening. Nucleus E. Stained Cell Body of a Motor Neuron (as seen under the microscope) Nerve fibers Cytoplasm (Microscopic views of nerve in cross section and motor neuron copyrighted by General Biological Supply House, Inc., Chicago, Illinois; made by Department of Anatomy, University of Illinois) BODY CHART 5-THE CIRCULATORY SYSTEM Artery to leg WHAT IT IS Your heart and ap¬ proximately 100,000 miles of blood vessels make up your circulatory sys¬ tem— your body’s inside transporta¬ tion system. Blood carries the sup¬ plies that your muscles, bones, brain, nerves, skin, and all other parts of you need to stay alive and work effi¬ ciently. Only the arteries and veins, your larger vessels, can be illus¬ trated, since the capillaries which connect them are too small and too numerous to be shown. Your heart pumps all your blood through your body in less than a minute— the equivalent of more than 2,800 gallons in one day. Yet this powerful “pump” is not more than twice as large as your closed fist! Artery walls three layers thick ( B . opposite) withstand the pressure of blood surging from the heart. Artery to head Artery to arm Aorta Pulmonary artery Heart Surface circulation (omitted from far side of body to reveal part of circulation to body organs) Veins from head Vein from leg Vein from arm Pulmonary veins Large vein — from lower part of body Large vein - from upper part of body BODY CHART 5-THE CIRCULATORY SYSTEM A. The Heart D. Stained Blood Cells (as seen under the microscope) Right auricle Valve Left ventricle Muscular wall between ventricles Right ventricle of the Heart Red blood cells Right ventricle Left ventricle Artery Aorta Pulmonary artery Large vein from upper part of body Right auricle Left auricle Coronary artery Cardiac vein Vein Aorta Valve B. Structure of an Artery and a Vein (enlarged) E. Blood Cells (greatly enlarged) HOW IT WORKS Blood with digested cells ( D . and E. above) carry the oxygen, foodstuffs from your digestive system, (White blood cells destroy germs.) From along with blood from all other parts of the lungs, your blood returns to the heart, your body, flows through veins to the right It enters the left auricle, is pumped to the auricle of your heart (A. and C. above). left ventricle, and surges out through the Then it is pumped to the right ventricle aorta, carrying the food and oxygen and out through the pulmonary artery to through your arteries to all parts of your your lungs, where it gets rid of carbon body— even to the walls of the heart itself dioxide and picks up oxygen. Red blood (A. above). (Microscopic view of stained blood cells copyrighted by General Biological Supply House. Chicago, Illinois; made by Depart¬ ment of Anatomy, University of Illinois) BODY CHART 6-THE RESPIRATORY SYSTEM # Windpipe Bronchi Sinuses Nasal passages Diaphragm Nostril Tongue Throat cavity Epiglottis Vocal cords Voice box (larynx) WHAT IT IS Your respiratory system extends from your nostrils all the way to tiny air sacs within your lungs. Both air and food pass through your throat. Fort¬ unately, you have a living trap door, the epiglottis, which closes the top of your windpipe whenever you swallow, prevent¬ ing what you swallow from entering your windpipe. Immediately beneath the epiglottis is a box-like structure made of cartilage— your voice box, or larynx. Inside your voice box are your vocal cords, which produce vibra¬ tions that result in sounds whenever you speak. Your rib muscles and diaphragm are responsible for your breathing move¬ ments. When your rib muscles and dia¬ phragm contract, air rushes into your lungs. When your rib muscles and dia¬ phragm relax, air is forced out by the elastic contraction of your lungs. BODY CHART 6-THi RESPIRATORY SYSTEM Windpipe (trachea) Bronchi Appearance of Right Lung (cut open lengthwise) Bronchial, tubes , Pulmonary ' artery Pulmonary veins Air Passages in a Lung Circulation in a Lung , Clusters of air sacs (greatly enlarged) ned Lung Tissue seen under microscope) Air sacs - (alveoli) HOW IT WORKS The air you breathe is filtered, moistened, and warmed in your nasal passages, throat, and windpipe. It passes through your windpipe into the bronchi, bronchial tubes, and tiny clusters of air sacs. Study the microscopic view of lung tissue above. You will see that the walls of air sacs and the walls of capillaries carrying blood to the air sacs are so thin that even under the microscope you can¬ not tell one from the other. Oxygen and carbon dioxide penetrate these walls easily. The blood in the capillaries gives up car¬ bon dioxide from your body to the air sacs and takes in the oxygen that the cells of your bodv use. (Microscopic view of lung tissue copyrighted by General Biological Supply House, Inc., Chicago, Illinois; made by Department of Anatomy, University of Illinois) BODY CHART 7-THE DIGESTIVE SYSTEM Spinal column Windpipe Lung (rotated to rear- heart and other lung removed) Gullet (esophagus) Small intestine Large intestine Stomach Gall bladder Diaphragm Liver WHAT IT IS Above, you see the body cavity with all the digestive organs in place. The gullet, stomach, small intestine, and large intestine form a long, continuous food tube. About 20 feet of small intestine are looped irregularly in the abdomen, and 5 or 6 feet of large intestine are located across the top and down both sides of the abdomen. The liver, the pancreas, and tiny digestive glands in the inside wall of the stomach and small intestine furnish juices that help you digest your food. Undigested food passes out of your body through the large intestine. On the opposite page you see separate views of the organs relating to digestion. Note the location of the appendix, fre¬ quently a troublemaker. BODY CHART 7-THE DIGESTIVE SYSTEM Stained Cross Section of Inner Wall of Small Intestine (as seen under the microscope) Stomach _ (cut open lengthwise) Several coils of small intestine Inner wall of small intestine Large intestine Inner wall of large intestine Small intestine Stained Cross Section of Inner Wall of Stomach (as seen under the microscope) Appendix Gall bladder HOW IT WORKS The food you swallow passes through your gullet and enters your stomach. The mus¬ cular outer wall of the stomach squeezes and churns the food, while digestive juices from millions of tiny glands inside the stomach act upon the food. Next, the partially digested food flows into the small intestine, where digestive juices from millions of other tiny glands, along with bile from the liver and pancreatic juice, complete the digestive process. Digested food in the small intes- Pancreatic duct Pancreas Opening of common duct in small intestine Relationship Between Liver, tine is absorbed by countless tiny projections on its inner wall. The absorbed foodstuffs then make their way into your blood stream and are carried to all parts of your body. Gall Bladder, Pancreas, and Small Intestine (Microscopic views of stomach wall and small in¬ testinal wall copyrighted by General Biological Supply House, Inc., Chicago, Illinois; made by Department of Anatomy, University of Illinois) BODY CHART 8-REGULATION IN THE BODY Hypothalamus Medulla Lung intestine Pineal body Pituitary body Parathyroid glands Thyroid gland Thymus gland Adrenal glands Pancreas v y Kidneys Ureters > Endocrine Glands (pineal body and thymus gland included though nature and work unknown) Excretory System WHAT IT IS— HOW IT WORKS Many organs help regulate the work done by your body. The endocrine glands produce hormones that affect growth, amount of sugar in the blood, sex characteristics, and other vital matters. The medulla of your brain controls breathing and many other activities, and your hypothalamus keeps your nerves and endocrine glands working together smoothly. Your skin and lungs help regulate body temperature by giving off excess heat. The liver destroys harmful substances in your blood stream, and the excretory system removes these and other wastes from your body. The large intestine removes undigested food. Because the many kinds of work done by your body are so well regulated, your major systems of organs work together in harmony. THE RESPIRATORY SYSTEM The main parts of the respiratory system are the nostrils, the throat, the windpipe with its branches, called bronchi ( bronk eye ) and bronchial tubes, and the lungs. The whole respir¬ atory system functions in such a way that air from outside the body is brought into close contact with the blood capillaries in the lungs. How does oxygen enter man's blood? Unlike the fish and the frogs, mam¬ mals have a double body cavity. The anterior (upper) one is called the tho¬ rax (chest) and the posterior (lower) one, the abdominal cavity. The muscu¬ lar diaphragm is the partition between the two ( Human Body Charts 6 and 7 ) . Above the diaphragm in man lie the two lungs and the heart, which fill the thorax. It is in the lungs that oxygen from the air enters the blood. Every time you inhale (breathe in), a mass of air moves into your lungs. The air enters through your nostrils, throat, windpipe, bronchi, and bronchial tubes. The bronchial tubes branch again and again and again and finally end in mi¬ croscopic air sacs ( Human Body Chart 6). With each inhalation, the air in¬ flates the air sacs like millions of small balloons. Oxygen molecules from the air dif¬ fuse into the blood in the capillaries in the thin walls of the air sacs, and car¬ bon dioxide molecules diffuse out of the blood into the air in the air sacs. Then you exhale (breathe out) and ex¬ pel air. How do you breathe? Your diaphragm arches upward when at rest (Figure 12-7 and Human Body Chart 6). When this sheet of muscle contracts, it pulls down toward a flat position. This and the contraction of certain chest muscles make the chest cavity bigger, with the result that the air pressure within the lungs is low¬ ered. The air pressure outside the body is now greater than that in the lungs. As a result, air rushes through the nos¬ trils, windpipe, bronchi, and bronchial tubes into the air sacs in the lungs ( Fig¬ ure 12-7a). Your lungs are very elastic. When you breathe in, they increase as much in size as the expanded chest will per¬ mit. When you breathe out, the dia¬ phragm and chest muscles relax, the 12-7 RESPIRATORY MOTION The chest cavity enlarges when the diaphragm contracts and decreases in size when the diaphragm is relaxed. Note the space between the two horizontal dashed lines from view A to view B. Also note that the larger size of the en¬ tire chest cavity in view A is shown in dotted lines around view B. Lungs (expanded) Lungs (contracted) mm diaphragm moving upward and the lower ribs downward. This reduces the size of the chest. Then the lungs con¬ tract and force the air out through the same passageways through which it entered (Figure 12-7b). But it is not the same air, for it contains less oxygen and more carbon dioxide and water. EXERCISE AND CARBON DIOXIDE EXCRE¬ TION. You may do this demonstration in front of the class. Get some phenolphthal- ein (fee nohl THAL een) and a bottle of one-per-cent sodium hydroxide from the chemistry department. Fill a half-pint bottle half full of water and add exactly five drops of the sodium hydroxide. Add enough phenolphthalein, drop by drop, to make the solution turn red. Record the exact time, to the second, and at once begin blowing your breath through a glass tube into the solution. Keep this up until the solution becomes colorless and record the time again. The carbon dioxide in your breath turns the solution colorless. How long did it take? Set up another bottle of the red solu¬ tion, again with exactly five drops of the sodium hydroxide. Then exercise by touch¬ ing the floor 15 times in quick succession, and repeat the test. How long did it take this time to turn the solution colorless? Explain in your record book how you know that exercise increased the rate of oxidation in your body. Your windpipe and voice box In the throat, the opening into the windpipe lies just in front of that into the gullet. The top of the windpipe forms the larynx (voice box). So every bite of food you swallow must pass over the top of the larynx. When you swal¬ low, a flap of tissue called the epiglottis (ep ih glot is ) normally folds down Mucus- producing cells I Roy M. Allen, from New York Biological Supply Co. 12-8 LINING OF THE WINDPIPE Ciliated epithelial cells line the windpipe and bronchial tubes. During a chest cold, the ciliated cells and the mucus-producing gland cells are especially active. (400x) over the top of the voice box and keeps food from “going down the wrong way,” as people say. Can you explain what happens when you “choke”? The windpipe, bronchi, and bron¬ chial tubes are lined with epithelial cells. These cells have cilia that wave upward all the time (Figure 12-8). Their motion forces dust and other ir¬ ritating particles up toward the throat, where “clearing the throat” then re¬ moves them. Summing up: the respiratory system Contraction of the diaphragm and certain chest muscles causes air to rush through the nostrils, throat, windpipe, bronchi, and bronchial tubes into the millions of air sacs in the lungs. There, oxygen molecules diffuse into, and car¬ bon dioxide and water molecules dif¬ fuse out of, the blood in the capillaries in the walls of the air sacs. Then the diaphragm and chest muscles relax, and the elastic lungs shrink. This makes the air go out of the lungs again, taking 338 THE HUMAN BODY with it the new load of carbon dioxide and water vapor. At the top of your windpipe is your larynx. The epiglottis covers the open¬ ing into the larynx when you swallow food. Both digested foods and oxygen are delivered to the blood stream. What happens then is part of the story of the circulatory system. THE CIRCULATORY SYSTEM The main parts of the circulatory sys¬ tem of the human body are the heart, arteries, veins, capillaries, lymph ves¬ sels, and the blood and lymph. This sys¬ tem of organs might be compared to the nation’s transportation system. Ma¬ terials may be picked up at any point and “shipped” to any other point. Circulation of the blood Refer frequently to Figures 12-9, 12-10, and to Human Body Chart 5 as you study these paragraphs. Let us start with the blood in the tiny capil¬ laries of the villi in the small intestine. Here the blood has absorbed its sup¬ ply of all digested foods except fats. The blood flows from these capillaries into larger and larger veins that lead into one very large vein which enters the liver (Figure 12-9). This vein di¬ vides into many capillaries among the liver cells. In the liver, some of the glucose diffuses out of the blood into the liver cells. There it is changed to glycogen and stored. The blood leaves the liver through a vein. This vein soon joins an¬ other large vein from the trunk and legs. The large vein carries the blood to the heart. Another large vein brings blood to the heart from the head and arms. The human heart (Figure 12-10) is a double pump. The right side pumps blood to the lungs and back to the left side. The left side of the heart pumps blood all over the body (except to the lungs ) and back to the right side. This double pump consists of four cham¬ bers— two auricles and two ventricles. The auricles are the receiving rooms. The ventricles are the shipping rooms, or, better, the main pumping rooms. The muscular walls of the ventricles are much thicker than those of the auricles (Human Body Chart 5). They need to be thicker and stronger, because they pump the blood through the lungs and body. The blood from the general body circulation enters the right auricle through the two large veins already mentioned. The auricle contracts. This pushes the blood into the right ventri¬ cle. Then the ventricle contracts and pushes the blood into an artery, which soon branches, one branch going to each lung. When the blood enters the lungs, it is a deep, dark red (never blue). As new oxygen from the air in the lungs enters the blood, it turns bright red or scarlet. From the lungs, the blood returns to the left auricle of the heart through veins (four, in most people). Then the left auricle pumps the blood into the left ventricle, which pumps it out into the large artery, called the aorta (ay or tuh ) . Through the aorta and its branches, the blood reaches all parts of the body except the lungs. The first arteries to branch off from the aorta carry blood to the heart, the arms, and to the head and brain. Those that supply the heart itself are called the coronary arteries (Human Body Chart 5 and Figure 12-10). A common cause of “heart attacks” is the block- THE BODY AT WORK 339 CIRCULATION OF THE BLOOD Vein from head and arms Aorta Heart Lung Vein from trunk and legs Portal vein ( leading from stomach and small intestine to liver) Liver Kidney Artery to lungs Veins from lungs Artery to trunk and legs Stomach Intestine 12-9 Bright red here indicates well-oxvgenated blood, dark red de-oxygenated blood. Most veins carry dark red blood, and most arteries bright red blood. But between the heart and lungs, the situation is reversed. Why? One organ— the liver— receives blood both from an artery and a vein. How is this explained in terms of liver function? ing of a coronary artery by a blood clot (Figure 12-11); the blocking of an artery in the brain causes what people usually call a “stroke.” All branches of the aorta branch again and again. Their smallest branches are the arterioles ( ahr teer eeohls), which lead finally into the 340 THE HUMAN BODY Large vein from head and arms •Arteries to lungs Right auricle Aorta Veins from lungs Left auricle Left ventricle Large vein from trunk and legs Coronary artery A. F. Jacques, Photographic Department, Rhode Island Hospital 12-10 HUMAN HEART A normal heart is shown here as seen from the front (left) and from above (right). In the right-hand view, the front of the heart is toward the top of the page. Hearts differ in several ways from person to person; these include not only size and shape, but also the number of pulmonary veins. Most people have four pulmonary veins, but some have only three, while others have as many as seven. microscopic capillaries that run be¬ tween all the living cells. Food and oxygen diffuse out of the blood of the capillaries and thus reach the cells. Car¬ bon dioxide and other cell wastes enter the blood, which passes on into larger and larger veins. The veins carry the blood back to the right auricle of the heart, to start its round trip again. Valves keep the blood from flowing backward when the heart contracts, or “beats,” as we usually say. There is a valve where each vein enters an auri¬ cle. There is a valve between each au¬ ricle and its corresponding ventricle. And there is a valve where each ar¬ tery leaves a ventricle (Human Body Chart 5). These valves work somewhat 12-11 CROSS SECTIONS OF CORONARY ARTERIES If a normal artery (left) picks up heavy deposits on its inner wall (middle), it may become blocked completely if a blood clot forms (right). Recovery from this kind of “heart attack” depends in part on the forma¬ tion of new branches of the artery to replace damaged ones. Dr. Timothy Leary, Boston as a valve in an automobile tire works. A tire valve lets air into but not out of a tire. The heart valves let blood through in one direction, but not in the other. Muscles in the walls of the arteries help to push the blood along toward the capillaries. In the larger arteries, like those in vour neck and wrist, the contractions of these artery muscles can be felt as the pulse. Altogether, you probably have be¬ tween five and six quarts of blood in vour body. That blood is always on the move. Round and round it goes, pick¬ ing up materials here and delivering them there, throughout all the years of vour life. Lymph Your blood is composed of several parts. The red color comes from the hemoglobin in the red blood cells, which float in a colorless liquid called plasma ( plaz muh ) . When some of this plasma passes out of the capillaries into spaces between the body cells, it is called lymph. (Actually, certain larger protein molecules in plasma do not pass out of the capillaries, so that lymph, strictly speaking, is plasma minus cer¬ tain of its protein molecules. ) There is space between your living cells, because most of the cells of your body do not fit tightly together like bricks in a wall, but loosely, like pota¬ toes in a basket. If you set a basket of potatoes in a tub of water, the spaces between the potatoes will fill with wa¬ ter. In much the same wav, the spaces between your cells are filled with lymph. Molecules of food and oxygen diffuse from the lymph through the cell membrane into the cell, and cell wastes diffuse out of the cell into the lymph and thence back into the blood stream (Figure 12-12). Clay- Adams 12-12 BLOOD, LYMPH, AND BODY TISSUE Note the capillary containing red blood cells in single file (most of them stacked like pancakes). Where the capillary seems to disappear (near the top of the photo¬ graph), a large lymph space can be seen between the body cells. Diffusion of oxy¬ gen and food substances from blood to O lymph to body cells, and of cell wastes back to the lymph and blood, occurs con¬ stantly. (l,200x) Lymph circulation The lymph that surrounds the cells is collected into tiny lymph capillaries (not blood capillaries ) that are present between the cells. The lymph capil¬ laries unite to form larger and larger lymph vessels (Figure 12-6). Along the course of the lymph ves¬ sels are lymph nodes, often called glands. They act like filters. If you have ever had a vaccination or an infected cut on vour hand, you must know where some of the lymph nodes are lo¬ cated, for they swell and become sore J 342 THE HUMAN BODY when they filter poisons and bacteria out of the lymph as it passes through them. The lump you may have had un¬ der your arm when you were vaccinated was a swollen lymph node. These nodes hold back and help destroy the poisons and bacteria. The smaller lymph vessels unite again and again until they finally form two lymph ducts. The larger duct empties its lymph into the vein from the left arm; the other into the vein from the right arm. The larger duct also carries digested fats from the lacteals in the villi of the intestine. This is a one-way circulation; lymph leaves the blood stream through the walls of the capil¬ laries and flows slowly back through the lymph vessels into the lymph ducts and thence into veins that lead into the right auricle. Your blood and lymph carry food and oxygen to every living cell in your body. So the final step in the story of these materials has to do with what happens to them in the cells. Food and oxygen in the cells Within the cells, many food mole- cules are built into molecules of other organic compounds. Amino acids from the proteins in beefsteak, say, are again built into proteins, but not beef pro¬ teins. They are synthesized into human proteins. Glucose may be changed into glycogen and stored, particularly in liver and muscle cells. Fatty acids and glycerol may be changed into fats and oils and stored in fat tissues. Or any of these food molecules may be built into the living protoplasm of a cell, or used to build new cells. The various food molecules, in these cases, build up and repair your body. All this is one phase of your body metabolism, the “build¬ ing-up” phase. You get all your energy from another phase of your body metabolism. In this phase, oxidations and other chemical changes break down complex organic molecules, like glucose, into simple molecules, like carbon dioxide and wa¬ ter. Oxidation always releases energy. So do some other chemical changes that break down complex molecules. This phase of your body metabolism— the “tearing-down” phase, you might say- supplies all the energy your cells use. It supplies the heat energy that keeps you warm and the energy that does all the work of your cells. Without the energy from the break¬ down of complex molecules, your heart couldn’t beat, peristalsis couldn’t push food along your food tube, your nerves couldn’t carry impulses, your hands couldn’t write, your eyes couldn’t see, your arms and legs couldn’t move, and your diaphragm and rib muscles couldn’t keep you breathing. In other words, your cells have to break down some of their organic molecules all the time to keep you alive. The only way protoplasm can stay the same is to keep changing. Do you remember this statement from Chapter Two, page 69? It is more meaningful now, isn’t it? Your living cells are al¬ ways building new organic molecules into their protoplasm and, at the same time, breaking down other organic molecules and getting energy out of them. Protoplasm is forever “burning itself up” and “replenishing itself,” as long as you live. The only way proto¬ plasm can stay the same is to keep changing. Summing up: the circulatory system Blood from the general body circula¬ tion enters the right side of the heart and is pumped from there to the lungs. THE BODY AT WORK 343 Bloocl from the lungs enters the left side of the heart and is pumped out through the aorta and its branches to all parts of the body except the lungs. The heart muscles, with some help from muscles in artery walls, keep your five to six quarts of blood circulating rapidly. In the capillaries of the villi in the intestine, the blood stream picks up glucose and amino acids. In the lungs, it picks up oxygen. Digested fats are absorbed bv the lacteals of the villi in J the small intestine and pass through lymph vessels to a vein in the upper left chest. The blood stream delivers the necessary materials rapidly to all the living cells in the body. And it car¬ ries away waste materials and delivers them to the organs that excrete them. The lymph around your living cells is a sort of ‘‘middle man” between the blood and the cells. Lymph delivers materials from the blood to the cells and transmits cell wastes back to the blood, either directly or through lymph vessels that empty into veins from the head and arms. Massachusetts General Hospital 12-13 X-RAY PHOTOGRAPH OF A BROKEN FEMUR This photograph was one of two taken to enable the doctor to “set” the broken bone. often these days, when so many auto¬ mobile accidents result in so many J broken femurs ( fee merz ) or scapulas (skap yoo luhz ) or clavicles ( klav ih k’lz). (See Figure 12-13.) For the rest, try to get the idea of how the bones and muscles function. YOUR MUSCLES AND BONES There was a time when people thought all students should memorize the names of all their bones and study J the muscles in some detail. Today, the emphasis is on understanding what part your muscles and bones play in the highly organized human body. Turn now to Human Body Charts 1, 2, and 3 (following page 336). Look over the muscles and bones pictured there and read what is said about them and how they work. You may want to learn the names, say, of the main bones in the arms and legs, because their names do get into conversation fairly Skeletal muscles You may remember the three types of muscle cells: heart, smooth, and striped. There are also two main classifications of muscles. The heart, the muscles in the food tube wall and artery walls, and certain others work automatically without your thinking about them. For this reason, they are usually called in¬ voluntary muscles. The so-called volun¬ tary muscles are the second type. They are the muscles which are at least part¬ ly under the control of your thinking. Most but not quite all of your volun¬ tary muscles are attached to bones. For example, the muscles you use in writing 344 THE HUMAN BODY are attached to bones in the hand and arm, those used in walking or kicking a football are attached to bones in the feet, legs, and hips. Some of the mus¬ cles you use in smiling are attached to face bones, others are not. But in gen¬ eral, the voluntary muscles are attached to bones of the skeleton. That is why they are often called skeletal muscles. J Bones as levers Bones are useful in protecting soft, inner tissues. They are also useful in movement, in which they serve as levers. Refer to Human Body Chart 3 to see how the bones of the upper arm and of the thigh serve as stationary levers, useful in bending your elbow or standing on tiptoe. DEMONSTRATION OF BONE LEVERAGE. Close your hand around your upper arm, bend your elbow, then straighten it. Re¬ peat several times (and refer to Human Body Chart 3), until you understand how the bone in your upper arm acts as a sta¬ tionary lever when the biceps (BY seps) muscle contracts, and thus bends your elbow. Without the leverage of bones (and without movable joints ) , you could not bend your elbow or the other joints in your skeleton. Energy used in muscle cells Biochemists have learned that the en¬ ergy used by muscle cells does not come directly from the oxidation of glucose, but rather from the constant building up and breaking down of certain or¬ ganic compounds called phosphates. The chemistry involved is complex. To understand it, you would need to have studied chemistry. It would not benefit you greatly to understand it now, any¬ way. If you are especially interested, refer to pages 378-84 in The Machinery of the Body, Fourth Edition, by An¬ ton J. Carlson and Victor Johnson, Uni¬ versity of Chicago Press, 1953. Summing up: muscles and bones Your muscles and bones are useful organ systems, as you know. For exam¬ ple, without them you couldn’t move about to find food. You couldn’t even chew food if it were put into your mouth. In these and many other ways, your muscles and bones are essential to you. THE ORGANS OF EXCRETION The chief organs of excretion are the lungs, kidneys, and, to some extent, the skin. The colon is often included, but, strictly speaking, it is not mainly an organ of excretion. Excretion, in a strict sense, means the removal of cell wastes from the blood. The colon eliminates chiefly indigestible materials from the food tube. You already know that the lungs ex¬ crete carbon dioxide from the blood. Both carbon dioxide and water vapor are exhaled in the breath. Here you need to examine only the kidneys and the skin as organs of excretion. The kid¬ neys excrete most of the urea and other nitrogenous wastes, but the skin also secretes small amounts of these wastes. Where does urea come from? Urea has nitrogen in its molecules. You will remember that proteins in your foods also have nitrogen in their molecules, but carbohvdrates and fats do not. The poisonous waste product, urea, comes from the breakdown of protein molecules. THE BODY AT WORK 345 You will remember that your cells can get energy from their protein foods, as well as from carbohydrates and fats. But first your digestive system has to break the proteins down into amino acids. Then your liver must remove all the nitrogen from the amino acids. You will also remember that plants make amino acids out of glucose and nitrates. Taking all nitrogen atoms out of a molecule of amino acid leaves glu¬ cose. Then your body cells can oxidize the glucose and get energy. But what becomes of the nitrogen? The cells in your liver remove the nitrogen group, NHL, from amino acids. NH2 is called the amino group. The re¬ moval of all amino groups from amino acid molecules is called deaminization (dee am ih nuh zay shun ) of amino acids. So your liver cells deaminize some of your amino acids and return glucose to the blood stream. The amino group then reacts with carbon dioxide and forms urea— CO(NH2)2. Urea leaves the liver cells and enters the blood 12-14 X-RAY PHOTOGRAPH OF KIDNEYS The flower-shaped collecting area of each kidney and the ureters leading to the blad¬ der show clearly. The bladder does not show. Eastman Kodak Company collecting area of kidney) Collecting area of kidney Ureter 12-15 KIDNEY AND ENLARGED COLLECTING TUBULE The collecting tubule is one of hundreds of thousands that each kidney contains. Why is its work so important? stream. The kidneys remove the urea from the blood stream, alorn* with some uric acid and ammonia— all waste prod¬ ucts of deaminization. So urea and other products of deam¬ inization c;et into the blood stream from the cells in the liver. The kidneys and their work You could not live without your kid- neys any more than you could live without your lungs or heart. True, one kidney may be removed if it is diseased, but not both. Without at least one kid¬ ney, urea and other wastes from deam¬ inization would soon poison your cells. The two kidneys are located high in the abdomen, more or less back of the liver and stomach. Each one is con¬ nected to the urinary bladder by a long, hoselike tube called a ureter ( yoo ree ter). (See Human Body Chart 8 and Figure 12-14.) The kidneys excrete urine. The urine trickles down through the ureter into the bladder. There it is stored until it is eliminated from the body through an¬ other tube, the urethra (yoo ree thruh). Most adults excrete something like a quart and a half of urine a day, on the average. Urine is largely water with some solids dissolved in it. Urea makes up most of the dissolved material, but there is also some table salt. Other salts, uric acid, and traces of some other sub¬ stances make up the rest of the solids. Altogether the kidneys excrete only a little over one ounce of urea and anoth¬ er ounce of other solids each day. Two ounces may not seem like much in a quart and a half of urine, but it makes the difference between life and death. A kidney is largely a mass of micro¬ scopic tubes, some coiled and some not. Figure 12-15 shows one excreting unit, somewhat as a microscope would re¬ veal it. Notice that a coiled tubule (little tube) ends in a cup-shaped cap¬ sule. Inside the capsule are blood capil¬ laries. Blood plasma minus its dissolved proteins diffuses out of the blood into the capsule. Then it flows into the coiled tubule. From there, much of the water and usually all of the glucose and other nutrients diffuse back into the blood. What is left in the tubule is urine. From the tubule, urine flows on and on until it reaches the ureter. The kidney is largely a collection of these excreting units. The kidneys do more than excrete wastes. They also help to keep the com- page 347 position of the blood the same from hour to hour and day to day. For ex¬ ample, you may drink more water than usual. This would increase the amount of water in your blood, if it weren’t for your kidneys. But they quickly excrete the extra water. In “sugar” diabetes, the blood sugar rises. Then the kidneys excrete some of the extra sugar. In these and other ways, the kidneys help maintain the normal composition of the blood. The chief work of the kidneys is the excretion of urine. In most people, most of the time, they do their work well. The skin The sweat glands in the skin (Figure 12-16) excrete a little urea and quite a bit of salt, along with surprisingly large amounts of water. Even on an ordinary day, more than a pint of water is ex¬ creted in sweat. And on a hot day, two or three quarts may be excreted. But the sweat glands are not primarily or- 12-16 ENLARGED DIAGRAM OF HUMAN SKIN The sweat glands excrete some wastes, but primarily they help control body temperature. Does sweating warm or cool the body? Capillaries Ends of nerve Oil gland Hair Nerve fibers Pore of sweat gland Sweat > gland ft Fat cell Artery PflC? Lobule of fat cells Duct of sweat gland Epidermis Dermis gans of excretion. At best, they excrete less than a tenth of an ounce of urea a day. Even so, that small amount of urea makes the daily bath important, for cleanliness if for no other reason. CHAPTER TWELVE: SUMMING UP In this chapter, you have been learn¬ ing something about what happens to food and oxygen in the human body. In the food tube, various digestive juices (saliva, gastric juice, bile, pan¬ creatic juice, and intestinal juice) bring about chemical changes in the food you eat. The enzymes in some of the diges¬ tive juices speed up these chemical changes in foods. The end results of digestion are simpler molecules (glu¬ cose, fatty acids, glycerol, and amino acids ) which diffuse either directly into the blood capillaries in the food-tube walls or reach the blood stream indi¬ rectly through the lacteals and lymph vessels. In the lungs, the blood picks up an almost full load of oxygen and gets rid of most of its load of carbon dioxide. The left side of the heart pumps the newly oxygenated blood with its heavy load of food molecules out into the aorta. Arteries carry this blood on into arterioles and then into capillaries all over the body (except in the lungs). Oxygen and food molecules diffuse out of the blood into the lymph and thence into living cells. In the living cells, food molecules may be built into protoplasm or they may be oxidized. Oxidation yields en¬ ergy. Complete oxidation of glucose re¬ sults in carbon dioxide and water. These cell wastes diffuse back into the lymph and reach the blood stream. In the liver, some amino acids are deam¬ inized, producing a substance (NHL) which then reacts with carbon dioxide and forms urea. Urea and certain other nitrogenous wastes from deaminization are carried by the blood stream to the kidneys and skin where they are ex¬ creted. The blood from the general body cir¬ culation returns to the right side of the heart, which pumps it to the lungs. From the lungs, the blood returns once more to the left side of the heart. This, in brief, is a general summary of what happens to food and oxygen in the human body. How many more de¬ tails can you add? Your Biology Vocabulary The new terms in this chapter, plus a few that you have already seen before, are especially important to you because all of them apply to the human body. Make sure von understand and can use correctly the terms on the following page. 348 THE HUMAN BODY glycogen intestinal juice lymph nodes gastric juice fatty acids deaminization saliva glycerol urine salivary glands peristalsis ureter maltose colon urethra ptyalin coronary arteries bronchi pepsin arterioles bronchial tubes lipase heart valves epiglottis mucous membrane aorta air sacs duodenum villi voluntary muscles sphincter muscles lacteals involuntarv muscles J bile plasma skeletal muscles pancreatic juice lymph biceps Testing Your Conclusions 1. On a fresh sheet of paper, copy the numbers of the blanks below. Beside each num¬ ber, write the word or words that correctly fill that blank, do not mark this book. a. The enzyme ptyalin is found in (1) . . . It changes (2) ... into (3) . . . . b. During digestion, carbohydrates are changed finally into (4) . . . , proteins into (5) . . . , and fats and oils into (6) ... and (7) .... c. In the (8) ... of the lungs, large numbers of (9) . . . molecules diffuse into the blood and large numbers of (10) ... molecules diffuse out of the blood. d. In the kidneys, urea, a product of (11) . . . , is excreted. Most persons excrete about a (12) ... of urine each day. e. (13) . . . keeps the food mass moving onward through the food tube. f. The (14) . . . side of the heart pumps the blood to the lungs; the (15) . . . side pumps it to the rest of the body. g. (16) ... keep the blood from flowing backwards when the heart beats. h. The blood in the (17) . . . side of the heart is dark red. i. (18) ... and (19) . . . diffuse out of the food tube into the capillaries in the villi. j. Blood from all over the body enters the (20) . . . auricle of the (21) . . . through two large (22) .... Blood from the lungs enters the (23) . . . auricle through a number (usually four) of veins. Is blood in these veins dark or light red? (24) . . . k. (25) ... of foods in your cells releases heat energy. 2. To see if you have a pretty good idea of where some of the parts of your body are, do these things. a. Lay your hand on your cranium. b. Lay your hand over the place where you think the gall bladder is, then the stomach, then the appendix. c. Arch your two hands and hold them to show where you think your diaphragm is, when arched upward. d. Double your fist and lay it over the place where you think your heart is. e. Point to your larynx. f. Use your hand to encircle both a biceps and triceps muscle at one time. g. Point to the part of your body where the organ with coronary arteries is located. h. Indicate on another person’s back where you think the vertebrae that are called THE BODY AT WORK 349 thoracic vertebrae are located. Since you have not encountered this term before, ex¬ plain how you reached your conclusion. More Explorations 1. Observing a mammalian heart. Get a beef or pig’s heart from a butcher shop. Be sure to ask the butcher not to trim the heart. (He usually trims away not only the large arteries and veins but also the auricles of a heart, before he offers it for sale.) Compare your specimen with Figure 12-10 and with Human Body Chart 5. Try to find the auricles and ventricles in your specimen. Slice the heart in half in such a way that you will be able to see the four chambers. Compare the thickness of the walls of the right and left ventricles. The stringy cords inside the heart are parts of the valves that keep the blood from flowing backward. Can you explain why this is an advantage? Explain in your record book. Thought Problems 1 . What is the fluid in skin blisters, such as those one gets when a shoe rubs a heel? 2. How were the terms respiration and respiratory used in this chapter? They have been used before (Chapters 3 and 11) with much broader meanings. Explain both the broad and the narrow sense in which these terms may be used, then check your ex¬ planation by referring to an unabridged dictionary. Do you find both meanings listed? Further Reading 1. Two highly readable books on the human body are The Machinery of the Body, Fourth Edition, by Anton J. Carlson and Victor Johnson, Univ. of Chicago Press, 1953, and The Body Functions by Ralph Gerard, Wiley & Sons, 1941. In either book, you may find advanced but thoroughly interesting discussions of digestion, respira¬ tion, circulation, and excretion, and of almost any special topic that interests you. 2. A recent book says, “There is literally a simmering and throbbing of the cytoplasm. It appears to be a boiling vortex of matter, even though it is known to be mostly water." A few ambitious readers among you may enjoy The Life and Death of Cells by a noted biophysicist, Joseph A. Hoffman, Hanover House, Garden City, N.Y., 1957. Soon you will have a chance to analyze your own daily diet in terms of your basic needs. To do that, you will need a complete record of everything you have eaten for several days. Start now to keep a list of everything you take by mouth, say, for two days near the middle of the week, then for two days over a week end, when people often eat a greater variety of foods. You may want to carry a pocket-size note pad so that you can jot down every¬ thing you eat or drink— soft drinks, candy, after-school snacks, and all food taken at meals. List every item and the approximate amount, like this: FIRST DAY, BREAKFAST: orange juice, 1 6-oz. glass toast, 1 slice butter, I2 pat egg, 1 soft-boiled Keep your lists to use in the next chapter. 350 THE HUMAN BODY CHAPTER Foods and Nutrition "Always changing yet always the same" People have the feeling that their bodies are the same bodies all their lives. And in a sense, they are. But, as you know, there is a constant flow of materials into and out of the human body. People have probably always known that. But it took modern re¬ search to get a fairly complete picture of this flow of materials. Research with radioisotopes has now proved not only that the only way your body can stay the same is to keep changing, but also that it must keep changing rapidly. For example, only about half of the water molecules in your body at this minute were there a week ago, and only some two per cent of the atoms in your body today are the same ones that were there a year ago. Obviously, the foods you eat, the liq¬ uids you drink, and the air you breathe must constantly supply all the kinds of atoms and molecules your body needs to replace those that are being lost all the time. This chapter is about your food and how you can make sure it supplies all the necessary raw materials your body needs. ESSENTIAL RAW MATERIALS Your intake of food, liquid, and air must constantly supply all the essential raw materials your body needs to re¬ place those that are constantly lost. That means you must take in raw ma¬ terials that supply 18 common ele¬ ments, and probably more— perhaps as many as 40 elements in all. Hays, from Monkmeyer FOODS AND NUTRITION 351 What elements make up the human body? You already know that your body, like that of any other living thing, is made primarily of six common ele¬ ments : oxygen, carbon, hydrogen, nitro¬ gen, calcium, and phosphorus. Table 13-A shows the relative amounts of these, and of the rest of the 18 elements known to be essential, in the body of a person who weighs 100 pounds. Some atoms of all these elements are constantly lost from the body. To re¬ place them, you can’t eat elements, as such. You can use the element oxygen from the air, but you must get the rest of the elements from compounds that contain them. You get these compounds in your foods, in the nutrients you take by mouth. Classes of nutrients Turn back now to Table 2-C on page 68 and review the elements in each class of nutrients: in carbohydrates, fats and oils, proteins, water, vitamins, and certain mineral salts. Nutrition experts list four of the six TABLE 13-A ELEMENTS BY AMOUNT IN THE BODY OF A PERSON WEIGHING 100 POUNDS Element Amount Oxygen 64 to 65 pounds Carbon 19 to 20 pounds Hydrogen 10 pounds Nitrogen 2% pounds Calcium 1 34 pounds Phosphorus 1 pound Sulfur 5 ounces Potassium 4 ounces Sodium 2 % ounces Chlorine 2% ounces Magnesium % ounce Iron 34 2 ounce Traces of manganese, iodine, fluorine, copper, zinc, cobalt classes of nutrients as indispensable building foods and the other two classes as energy foods. Indispensable building foods You can’t have a well-built body, or even live very long, without the spe¬ cific and indispensable raw materials from four classes of nutrients. These four indispensable nutrients are: 1. Water, which is built into proto¬ plasm and also serves as the fluid me¬ dium (in blood and lymph) through which other materials are transported to and from the living cells. 2. Proteins, which are built into pro¬ toplasm. 3. Certain minerals, some of which are built into the bony framework, others into the living cells in certain organs, and still others into specific substances, as iron is built into the hemoglobin in the blood. 4. Vitamins, which are essential in the building of enzymes. The enzymes activate the chemical changes involved in building raw materials into the body, as well as those involved in releasing energy. These four classes of nutrients you must have in your daily diet. They are indispensable in the construction, growth, and repair of the human body. Energy foods Your cells must have a constant sup¬ ply of energy to do their work or even to stay alive. Two classes of nutrients are the main sources of energy. They are: 1. The carbohydrates ( chiefly starch¬ es and sugars in the human body, since you cannot digest the carbohydrate called cellulose). 2. The hydrocarbons, usually called fats and oils. 352 THE HUMAN BODY You have already learned that you can and do get energy from protein foods. And you have also learned that both glucose and digested fats occur in the living colloid we call protoplasm. But in the over-all picture, you usually get most of your energy from carbohy¬ drates and hydrocarbons, while most of your proteins usually enter into processes of building and repair. At least, many biochemists and most nu¬ trition experts see it that way today. One more point about the main en¬ ergy foods is important. Your body does not have to have a specific one, say, potato starch or butter fat. Any starch or any digestible fat will do. In this sense, these so-called energy foods are interchangeable. Your body can handle any one food of these two classes of nutrients or of the protein class so that your cells get energy out of it. Obviously, then, specific carbohy¬ drates and fats are not indispensable in the way that proteins, vitamins, and minerals are indispensable for building and repair. But energy foods of some kind are indispensable. Carbohydrates are excellent energy foods. What is more, eating enough carbohydrates and fats to supply most of the body’s en¬ ergy needs is believed to allow most of the protein foods eaten to be used in building and repair. Summing up: essential raw materials Of the six classes of nutrients, four supply indispensable building mate¬ rials. These are: (1) water, (2) proteins, (3) minerals, and (4) vitamins. The other two classes of nutrients are usually called energy foods. These are: (1) car¬ bohydrates, and (2) fats and oils. The two classes of energy foods are largely interchangeable. The other four classes of nutrients are not. YOUR ENERGY NEEDS Your cells use energy all the time. They use more energy when you are active than when you are resting or asleep. The more active you are, the more energy your cells use. During strenuous exercise, like playing tennis or basketball, they use a great deal of energy. They get that energy from the foods you eat— from carbohydrates, fats, and oils, and to some extent, at least, from proteins. Measuring the energy stored in foods Are you counting your calories? If so, do you know what you are count¬ ing? You are counting units of heat energy that can be released from your food. What is a unit of heat? It is a calorie.* What is a calorie? It is a unit of heat. That doesn’t tell you anything, does it? Look at it this way. You can’t measure heat in inches or pounds or bushels. Heat is measured in calories. A calorie is just so much heat, even as an inch is just so much length and a pound is just so much weight. It isn’t important that you remember just how much heat a calorie is, but here is the definition, in case you are interested. A calorie ** is exactly the amount of heat energy it takes to raise the temperature of 1,000 cubic centi¬ meters (about a quart) of pure water one degree Centigrade. How do we know how many calories of heat can be released, say, from a slice of bread? Scientists burn a slice of * This is not to say that the calorie is the only unit we use in measuring heat, as an inch is not the only unit of length. But a calorie is the unit of heat used in measuring the heat energy that can be released from foods. ** The one defined is the great calorie. The great calorie is used in measuring the heat energy in foods. It equals 1,000 small calories. FOODS AND NUTRITION 353 Thermometer Source of electricity Partial vacuums From Brandwein ct al., Science for Better Living, Harcourt, Brace and Company, 1955 13-1 DIAGRAM OF A CALORIMETER As food is burned, the temperature of the water in the inside container goes up. Why are two thermometers used in finding calo¬ rie value? bread in a device called a calorimeter (kal er im uh ter). (See Figure 13-1.) The calorimeter measures the amount of heat set free. An average slice of white bread releases some 60 calories, a small chocolate bar some 250 calories of beat. Ounce for ounce, any fat or oil releases over twice as many calories as proteins or carbohydrates do. How many calories do you need? Of course, no one really eats calories. You eat foods capable of yielding so many calories of heat. What we are really asking is: How many calories of heat should your daily diet be able to release? There is no simple answer. You need more calories during the daytime, when you are active, than you do while resting and sleeping at night. According to Dr. Eric G. Ball of the Harvard Medical School, the body of an average adult, when resting quietly, is using about the same amount of en¬ ergy as a 100-watt light bulb— that is, about 85 calories an hour. That would be about 2,000 calories a day. But few people rest quietly 24 hours a day. So you probably need to eat food that will yield more than 2,000 calories a day. One column in Table 13-B shows about how many calories your daily diet should be able to yield, if you are about as active as most other high school girls or boys— some 2,400 cal¬ ories for girls and some 3,800 calories for boys. Boys usually need more cal¬ ories than girls, and men more than women. A very active person, such as a student who plays on the school basketball team, may need to eat enough food each day to supply 4,500 to 5,000 calories. ANALYZING YOUR CALORIE INTAKE. Use the record you have been keeping of everything you have taken by mouth for four days (see page 350, Looking Ahead). Refer to Table 13-C, pages 356-357, in one column of which you will find the num¬ ber of calories in average servings of a number of common foods. Or refer to any calorie table available to you, say, in your mother's cookbook or in one of the refer¬ ences listed at the end of this chapter. Determine how many calories the foods you have eaten over this four-day period would yield. Divide the total by four, to find the daily average. Then refer to Table 13-B. How does your daily average com¬ pare with that recommended in Table 13-B? Remember, you may need more calories a day than this table lists. You may even need fewer. In the light of your own estimate of how active you are, do you think now that your daily average is about right? Why? 354 THE HUMAN BODY TABLE 13-B AVERAGE DAILY DIETARY ALLOWANCES Minerals * Vitamins Co © ■ O © O 3 © o 5^ © © HO © ©, "© o pO S». © O © "© o Ci CO © © p~C S* CO © a, Ci © >-g se * fO Ci © © © * ci* -o o 'O CO KJ Boys 16-20 yrs. 3,800 100 1,400 2,000 15 5,000 1,900 2,500 19 100 400 Girls 16-20 yrs. 2,400 75 ? ** ? ** 1 ,300 1,800 15 5,000 1,200 1,900 12 80 400 * Potassium requirements have not been determined accurately, mainly because all diets are thought to supply adequate amounts of this mineral. ** Fat and carbohydrate requirements have not been successfully determined. However, in the United States, most diets are thought to contain adequate (if not excessive) amounts of both. Adapted with the permission of the authors from Food Values of Portions Commonly Used, Eighth Edition, by Anna de Planter Bowes and Charles F. Church, published by Anna de P. Bowes, N.E. corner 7th and Delancey Streets, Philadelphia 6, Pa. You and your weight A study of the life-insurance records of some 200,000 persons shows clearly that it is a handicap to be decidedly underweight while you are young, and a distinct disadvantage to be over¬ weight after you are 30. It has been estimated that for every pound added to its weight, the human body must build nearly a mile of new capillaries. Pumping blood through all these new capillaries puts an added burden on the heart. Among older persons, this is probably the chief disadvantage of be¬ ing overweight. No one can tell you just how much you should weigh. Perfectly healthy people of the same age, height, and sex have been found to vary considerably in weight. You have probably seen tables that give the so-called “normal’’ weight for persons of varying age and height. These tables are now looked upon as misleading. For one thing, they give only the average weight for a large number of individuals, not the “normal” weight. For another, they may seem to imply that anyone who weighs more or less than the average in the table for his age, sex, and height is likely to be in poor health. Actually there is no such thing as a “normal” weight. And a per¬ son may weigh considerably more or less than the average without suffering any discoverable disadvantages. For these reasons, no table of average weights is given here. No one knows exactly what you should weigh, but doctors can advise you about it. If you are in doubt about your own weight, consult your doctor. It is important not to be greatly over¬ weight or underweight, even though no one knows exactly what you should weigh, f f Physical Growth Record for Boys, and another, . . . for Girls, are available at only a few cents each from the American Medical Association, Bureau of Health Education, 535 North Dearborn Street, Chicago 10, Illinois. These records enable you to compare your rate of growth and gains in weight with those of other boys or girls your age. FOODS AND NUTBITION 355 I co CO 'O o c3 o o D a3 fcfl 3 O a o -H> O a o o C3 03 C c3 03 a a> a o a CO a ■ 03 a CO §; S d, S’ ‘ o o o o o c o o o c o O o o lO <=> 04 i 1 1 ® 40 o o Tt< rH X | o © © 1 © ftj CD T3 ’ ~ c 03 a? 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CO *0 O' 00 h 11CN O O 0*0 HI O M (N 00 h 50 N H 00 *o OOOO 90 H Cl Cl Cl CO CO W H o Cl 1-H o rH rH rH rH ©) rH CM CM rH X CM X <2 x 2 ft .2 § rH CIV* CM X © CM 73 0 73 G 0 0 © (72 - 0 +-> © £ G -0 © 3 t G jr 0 v~2 > & G G < 0 © © (72 -2 G o © G (72 0 £ o 0 0 -0 G G G 3 © G O 73 W bJO 3 P0 ^5 O s s o O o c5 ^ Oh 73 O O Ji O -0 G 0 .o *72 0 0 73 G 73 c FOODS AND NUTRITION 357 de P. Bowes, N.E. corner 7th and Delancey Streets, Philadelphia 6, Calories are not enough Merely eating enough food to yield your necessary calories each day will not meet the needs of your body. A pound and a half of table sugar (su¬ crose ) can yield 3,000 calories, but you would be exceedingly unwise to try to live on 1/2 pounds of sugar a day. In fact, you could not live very long on sugar alone. You would gradually weaken, become ill, and finally die on such a diet. You must have proteins and minerals and vitamins and water in sufficient amounts, in order to grow and to build and repair tissues; that is, to go on liv¬ ing an active healthy life. Your needs for these food materials will be dis¬ cussed next. Summing up: your energy needs Your daily diet must supply foods that can yield enough energy for your cells to do their work and to keep your body warm. The energy stored in foods is usually measured in terms of the calories the foods can yield when burned. Most high school girls seem to need a daily diet capable of yielding some 2,400 calories. Most high school boys require more, usually some 3,800 cal¬ ories. More active students require still larger yields of calories. The amount of food you eat bears a direct relation to what you weigh Sta¬ tistical studies seem to show that being distinctly overweight after age 30 is a handicap to a long life. No one knows just what you or anyone else should weigh, but your doctor can advise you, if you are in doubt. Certainly he can tell you whether you are distinctly overweight or underweight, or whether you fall within the range of weights to be expected in your age group. YOUR PROTEIN AND MINERAL NEEDS Proteins and certain minerals are building materials your body must have in about the right amounts each day. Let’s look first at proteins. Your body proteins Your bodv has many, many different kinds of protein molecules in it, per¬ haps as many as 100,000 different kinds, with billions upon billions of mole¬ cules of each kind. Your body cells have built up every last one of these protein molecules. And that isn’t all. Manv of J the protein molecules that were in your body an hour ago aren’t there now They have been broken down chem- ically in one process or another, and some of the end products of these chem¬ ical changes have left your body- some in the urine, some in sweat, and some in your breath. In the meantime, your cells have built new protein mole¬ cules which have replaced those lost. As you know, your cells build up their own proteins out of amino acids. So, as you can see, your cells need a con¬ stant supply of amino acids, the indis¬ pensable building materials of proteins. You already know that digestive juices in your food tube change protein foods into amino acids that pass into your blood stream. You also know that your blood carries the amino acids to your cells. But you need to know even more to understand the protein needs of) mu' body. Essential amino acids Biochemical research on the amino acids needed by the human bodv is still J J so new that no one yet knows for sure exactly how manv amino acids your protein foods must supply. To date, biochemists do seem to agree that your 358 THE HUMAN BODY protein foods must supply at least eight amino acids. They also seem to agree that there are times when the human body must get some other amino acids from the protein foods eaten, but they do not agree as to the exact number. The human body uses some 20 amino acids (perhaps more) in building its proteins. Of these, biochemists agree that your body cells can synthesize at least six in sufficient amounts to meet your needs, provided that all the rest of the 20 or so amino acids are avail¬ able. Under suitable conditions, your cells can also synthesize several more of these 20 amino acids, but not in suffi¬ cient quantities. (One amino acid is synthesized by bacteria in the colon and reaches your cells by way of the blood stream. ) In any case, the protein foods you eat must supply at least eight amino acids which your cells can’t get in any other way, and some other ones to supplement an inadequate supply al¬ ready present. Some protein foods, both plant and animal, supply all the eight or more essential amino acids. Others do not. Usually animal proteins (lean meat, fish, shellfish, cheese, etc. ) supply these indispensable amino acids in much greater abundance per unit of weight than do plant proteins, such as those in beans and peas and nuts. You can get all the amino acids you need from plant proteins, provided that you eat large enough amounts of plant foods and in¬ clude a wide variety of plant proteins in your diet. But you can get them more easily by making sure that you eat some meat, fish, cheese, eggs, or other animal proteins (Figure 13-2) every day. A recent discoverv about the amino J acids you get from your foods is espe¬ cially important. Your cells must have National Dairy Council 13-2 PROTEIN-RICH FOODS Of the foods shown, lean meats and eggs are richest in proteins. However, beans and nuts are also worthwhile for their protein content. all eight or more of the essential ones at the same time. If they do not have all of them at once, they can’t build the few available ones into human proteins. Your cells can’t store the few available amino acids to use later when the rest of the essentia] ones come along. Take milk and bread as an example. Milk proteins contain an amino acid called lysine (LYseen). Wheat proteins in bread do not. (Lvsine is one of the eight or more essential amino acids.) If you eat' a slice of bread that was made without milk at one meal, but eat no other protein foods, the amino acids from the bread can’t be used to build proteins, because of the lack of lysine. But if you eat the bread and drink milk at the same time, the amino acids from both can be used to build proteins, pro¬ vided that at about the same time you also eat foods containing the other es¬ sential amino acids. FOODS AND NUTRITION 359 So it is important to eat at the same meal each day protein foods you are sure will supply all the eight or more essential amino acids (and probably others) at the same time. Your protein foods will also supply some of your energy needs each day. For example, when one or more of the essential amino acids is absent from the protein foods you take at a given meal, those protein foods will be wasted as far as building new proteins is con¬ cerned, but they will not be wasted as food. On the contrary, the amino acids from these proteins will be deaminized in the liver, and the resulting glucose will be used as an energy food. Your mineral needs Your diet must supply certain min¬ erals, usually in the form of mineral salts. Some you need in only minute amounts, others in larger quantities. Table salt is one of the minerals you need in some quantity, since it occurs in solution in all the body fluids and in the protoplasm in all your cells. Your body needs calcium and phos¬ phorus salts in considerable quantities. These salts are used in building bones and teeth. Calcium salts also supply calcium ions ( eye unz— particles bear¬ ing electrical charges). Calcium ions are present in all body fluids and cells and play an essential part in the clotting of the blood and in the correct func¬ tioning of the nervous system, the mus¬ cle system, and of some enzymes. Your body needs only small amounts of a number of other minerals. Iron is needed in small quantities. It is neces¬ sary in the formation of hemoglobin, which carries the oxygen to all the cells. Strangely enough, a minute amount of copper is also necessary to enable the red blood cells to make use of iron. 13-3 HOT WEATHER AND PERSPIRATION On a hot day the body may lose two quarts or more of water in sweat. Much salt is also lost with the water. United Press Photo Small amounts of iodine are necessary in the building of an important sub¬ stance about which you will learn in the next chapter. Minute amounts of sodium, potassium, sulfur, magnesium, cobalt, and a few other elements are also known to be necessary. Doctors take advantage of modern knowledge of mineral needs in many ways. A baby’s diet is carefully planned to supply the proper minerals. Iodine tablets may be given to children who do not get enough iodine in their food. Iodized salt may be used for the same purpose. All sea foods contain iodine; they seem to supply the needs of the body more satisfactorily than do iodine tablets. Persons who work in the very hot sun or in bakeries, steel mills, or other places where heat is extreme may be “overcome by the heat.” It is usually the body’s loss of salt in perspiration that causes heat exhaustion. This can be prevented, even in extreme heat, by occasionally taking a little extra salt, from a quarter to a half teaspoonful in a full glass of water, especially when first exposed to such heat. If you use salt tablets, it is better in most cases to dissolve them in water. At least, drink a full glass of tap water, not ice water, with the tablet. (Ice water is so cold as to cause a degree of shock in many people suffering from extreme heat.) Loss of water in perspiration (Figure 13-3) is also a handicap. So drink plenty of water on hot days. Another mineral that is found in drinking water in some places is flu¬ orine. It occurs in the compound so¬ dium fluoride. It is now known that adding sodium fluoride to drinking wa¬ ter does help to prevent tooth decay. All in all, minerals do play an im¬ portant part in your diet. Table 13-D lists five of the minerals you need to get in your diet and some foods that sup¬ ply them. STUDYING YOUR MINERAL INTAKE. Use the list of foods you ate over a period of four days and Tables 13-C and 13-D. Title a fresh page in your record book Foods That Supplied Needed Minerals. Divide the page into six columns. Head the columns, in succession. Foods Eaten , Calcium, Phos¬ phorus , Copper, Iodine, and Iron. List each food you ate and enter a check mark for each element it contained. TABLE 13-D FIVE IMPORTANT MINERALS IN FOOD Mineral Uses . . . — MUll—— — ■ Foods that contain it Calcium Building bones and teeth; clotting of blood; prevention of rickets Milk, eggs, spinach, beans, celery, nuts, cheese Phosphorus Building bones, teeth, and other body tissues; prevention of rickets Milk, eggs, cheese, whole grains, peas and beans, carrots, spinach, peanuts, choco¬ late, liver Copper Enabling red blood cells to use iron Liver, oysters, nuts, leafy vegetables, whole grains, fowl Iodine Used by thyroid gland Sea foods, all foods grown on soil that contains a good supply of iodine, “iodized” salt Iron Making hemoglobin; enabling hemoglo¬ bin to carry oxygen; forming part of every living cell Liver, whole grains, prunes, spinach, oysters, lean meat, lettuce, egg yolk FOODS AND NUTRITION 361 Summing up: your protein and mineral needs You need to eat at the same time of day enough protein foods to supply all of the eight or more essential amino acids. Your cells need all of these amino acids to synthesize the rest of the neces¬ sary amino acids and to build those amino acids into the thousands upon thousands of kinds of proteins in your body. You need comparatively large amounts of some minerals, such as ta¬ ble salt and calcium and phosphorus. You need only small amounts of such minerals as iron and iodine, and mere traces of a number of others, such as copper. YOUR VITAMIN NEEDS You have been hearing about vita¬ mins for years. You know your body has to have them to keep healthy, but do you know what vitamins are or what they do? J One nutrition expert says, “Vitamins are the substances that make us ill if we don’t eat them. That is about the best definition we can give for vita¬ mins.” Even though no one can give an exact definition that fits all vitamins and no other food substances, biochem¬ ists have learned many things about them. Biochemists can and do synthe¬ size virtually all the vitamins you are known to need. They know the chemi¬ cal make-up of a large number of vita¬ mins. And thev have found out what J certain vitamins do in the body. Vitamins have one chemical trait in common. All of them are soluble. Some are soluble only in fat or oil, others in water. The former are often called the fat-soluble vitamins, the latter, the wa¬ ter-soluble vitamins. Perhaps the most unusual fact about the vitamins is that the body needs only small amounts of each, and yet that small amount makes the difference be¬ tween health and disease, yes, between life and death. Virtually all of our accurate knowl¬ edge of vitamins has been discovered since 1906, and the first vitamin to be synthesized was vitamin D in 1931. The second to be synthesized was vitamin C in 1932. Since that date, research has built up a vast amount of knowledge of vitamins. Among other things, it is now known that there are several forms of each vitamin— at least 14 of vitamin D, and several of each of the others. An¬ other important group of discoveries has to do with the actual work of cer¬ tain vitamins in the body. What you read here can be nothing more than a brief summary of some of the knowl¬ edge of vitamins and their importance to you. Early history People knew about the effects of the lack of vitamins for manv centuries be- J fore they even guessed that vitamins existed. This is evident from many his¬ torical accounts dating back as far as 100 a.d. One such storv has to do with J one of Columbus’s voyages to the New World in the earlv 1500’s. During the voyage, several sailors became ill with scurvy (sKERvee). Sailors on long voy¬ ages in those days dreaded scurvy more than the plague, and no wonder. Whole crews sickened and died of it. So, when an island was sighted, some of Colum¬ bus’s sailors asked permission to land so they could die in peace. They were landed and the ships sailed on. Some months later, the return voyage brought the ships once more within sight of the island. To their amazement, 362 THE HUMAN BODY the crew saw men waving from the island. They landed and found their fellow sailors in splendid health. To Columbus and his men, the island had wrought a miraculous cure. That is¬ lands name became Curasao ( kyoo ruh soh ) , from a Portuguese word for « r> cure. There was no miracle in the cure on Curagao. But it took the work of an English ship doctor, years later, to prove it. The whole crew of the ship on which Dr. Lind was “surgeon came down with scurvy. Dr. Lind set up an experiment. He divided the crew into groups. All groups got the regular ship’s fare, mainly salt pork and sea biscuits. In addition, each group got one extra food. The group given lime juice recov¬ ered from scurvy so rapidly that Dr. Lind ordered lime juice for all the crew. It cured them all. This was in 1593. So it became the custom to issue lime juice to British sailors every day. That’s why they are often called limeys. Dr. Lind’s experiment explains the cure of Columbus’s men. On Curagao, the sailors ate local fruits and other fresh foods. We now know that the vitamin C in those fresh foods cured them, as it cures scurvy today. History includes accounts of still an¬ other disease caused by a lack of some¬ thing in the diet. Beriberi ( behr ee behr ee ) once killed millions annually in the Ear East; even today it occurs. Its victims (Eigure 13-4) lose the abil¬ ity to use their muscles; in time they can’t walk; finally they die. The very name beriberi means “I can’t.” A Dutch doctor, Dr. Christiaan Eijkman (eyek mahn), first solved the riddle of this disease. He was stationed in the Dutch East Indies. Two thirds of the patients in the hospital where he worked had the disease. Those patients who could still walk often staggered and lost their balance. Dr. Eijkman happened to no¬ tice that some chickens in the yard were staggering and stumbling as if they, too, had beriberi. And they did have it. Did the chickens “catch” beriberi from the patients? If so, how? A little inquiry showed that the chickens were fed the leftovers from the table, chiefly polished rice. So Eijkman had rice cooked separately for the chickens, and still they came down with beriberi. Then Eijkman fed rice polishings (the outer layers in brown or unpolished rice) to chickens with beriberi. And in a matter of hours, they were better. Experiences with scurvy and beriberi pointed the way to the later discovery of vitamins. They suggested that hu¬ man beings need something besides 13-4 BERIBERI AND ITS CURE Left. This white rat has beriberi. It cannot use its muscles properly. Right. Following the addition of thiamin to its diet, the rat is cured. The Upjohn Company carbohydrates, fats, and proteins in their diet. In 1906 a feeding experi¬ ment with rats was set up to test the idea. One batch of rats was fed on a diet of pure synthetic foods that contained all the factors then known to be essen¬ tial. A second batch of rats was fed the same diet, but with one small differ¬ ence— a few drops of fresh milk were added to their daily diet. The results were amazing. The first batch of rats drooped, lost weight, and died. The second batch thrived and grew fat. That was in 1907. By 1911 Casimir Funk had produced cases of beriberi in chickens by feeding them polished rice. Then he cured the chickens by forcing them to swallow a brew made of the brown coverings that had been polished off the grains of rice. Next he extracted from these rice polishings a substance which, even in small doses, would cure beriberi in chickens. He proposed the name “vita- mine” for this beriberi-curing substance from rice polishings. By 1920 three different “somethings” in food had been recognized as neces¬ sary to prevent certain diseases. Since a name was needed for these “some¬ things,” it was decided to contract “vita- mine” to “vitamin,” and call them all vitamins. The one known to prevent one disease was called vitamin A, a second, vitamin B, and a third, vita¬ min C. Names of vitamins today There is a growing tendency to get away from the use of letters in naming vitamins, now that our knowledge of them has become extensive. The vita¬ min that prevents beriberi is called thiamin (thy uh min), instead of vita¬ min B as in the beginning. In many cases what was once sup¬ posed to be a single vitamin has turned out to be several. Thiamin is only one J of at least 12 vitamins in what was originally called vitamin B. It is cus¬ tomary today to call these the B com¬ plex vitamins. The B complex vitamins Thiamin is also called Br, because it was the first B complex vitamin named. B2 is riboflavin ( ry boh flay vin ) . Still another B complex vitamin is niacin (NYuhsin). You may already know all three names. You will find them on the wrappers of enriched bread and on the box tops of many breakfast cereals. All these B complex vitamins are water- soluble. Thiamin not only prevents and cures beriberi, but also plays several impor¬ tant roles in maintaining the health of the body. It is essential to healthy nerves, good appetite, good digestion, 13-5 RIBOFLAVIN DEFICIENCY AND ITS CURE Left. This white rat has unhealthy mouth, eye, and skin conditions, as well as nerve trouble. Right. After riboflavin has been added to its diet, the rat regains its health. The Upjohn Company and normal growth. Good sources of thiamin include whole grain breads and cereals, egg yolk, liver, oysters, yeast, milk, and certain fresh vegetables. Riboflavin helps to keep the eyes and skin healthy (Figure 13-5). Those who get some but not enough of this vitamin often develop sore, cracked lips, espe¬ cially at the corners of the mouth. Lean meats, liver, eggs, milk, yeast, and fresh vegetables are good sources of ribo¬ flavin. Niacin was first known as a cure for a serious disease called pellagra (peh LAYgruh), of which there were 400,- 000 known cases in the United States in 1937 (Figure 13-6). Of course, nia¬ cin (together with riboflavin and thia¬ min) keeps you from getting pellagra, but it also functions in other ways. It is found in the same foods as thiamin. At least three other B complex vita¬ mins are important in your body. These are Br>, B12, and folic acid. If your diet provides enough of the other B complex vitamins, you need not worry about B(„ B12, and folic acid. You will get enough of them in the foods that contain the other B complex vitamins. Doctors use B12 and folic acid in treating a serious blood disorder, about which you will learn in a later unit. B vitamins and the respiratory enzymes You will remember that the respira¬ tory enzymes make it possible for you to oxidize glucose at body temperature. Where do your cells get those enzymes? They make them. Among other things, your cells use niacin, riboflavin, and thiamin in the manufacture of some of the respiratory enzymes and enzyme¬ like substances. Without these sub¬ stances, the complete oxidation of glu¬ cose would be impossible in the hu¬ man body. The Upjohn Company 13-6 NIACIN DEFICIENCY AND BLACK TONGUE This animal has the black tongue of pellagra, caused by lack of niacin. Other vitamins Vitamins other than those of the B complex which are necessary for man include the fat-soluble ones, A, D, and K, and the other water-soluble ones, C, E, and probably others. Vitamin E is abundant in wheat germ, and will not be discussed further here, because its role in the human body has not been definitely demonstrated. Vitamin A Vitamin A is often called the vellow J vitamin, because such yellow vegeta¬ bles as carrots and yellow corn are known to be good sources. Actually, the fat-soluble vitamin A is only slightly yellow. The yellow in a carrot turns out not to be vitamin A, as was long sup¬ posed. Instead, that yellow color is due to carotene ( kair uh teen ) . Some or¬ gan, probably the liver in higher ani¬ mals, can change carotene into vita¬ min A. That is probably why liver is FOODS AND NUTRITION 365 K. Blakely Studio, from Squibb & Sons 13-7 VITAMIN A DEFICIENCY AND ITS CURE Left. This rat is suffering from a deficiency of vitamin A. Right. After the administration of vitamin A, the same rat is cured. one of the foods richest in vitamin A. Spinach and apricots are also rich sources of vitamin A, as are all leafy green vegetables. Watermelon, canta¬ loupe, cream, yellow butter, and en¬ riched margarine also contain consider¬ able amounts of vitamin A. We have known since 1935 that the eyes use vitamin A (Figure 13-7). With some, but not enough, of it people are likelv to develop what is called night blindness, a condition in which they have great difficulty in seeing in dim light. O Vitamin C This water-soluble vitamin is the one that cured Columbus’s men, without their knowing that it even existed. It is called ascorbic ( ay skor bik ) acid, meaning “the acid that prevents scurvy.” You would think that scurvy J J should have disappeared from our country long ago, but it hasn’t. Some severe cases still occur. And no one knows how many people in the nation are on the borderline of scurvy. Ascorbic acid is plentiful in all cit¬ rus fruits— oranges, lemons, grapefruit, limes— and tomatoes, and in their juices, either fresh or frozen. Most fruits and many fresh vegetables also supply this vitamin. TESTING FOODS FOR ASCORBIC ACID. In the presence of ascorbic acid, a solution of a substance called indophenol * (in doh FEE nohl) changes first from blue to pink and finally loses all color. Make a 0.01 -per-cent solution of indo¬ phenol in water, preferably distilled water. With a medicine dropper, put 25 drops of the solution in a test tube. To one table¬ spoon of fresh lemon juice, add four table¬ spoons of water and mix well. With a clean medicine dropper, add drop after drop of the diluted lemon juice to the test tube, counting the drops. Keep on until all color has disappeared. Make a note of the num¬ ber of drops used. Now boil the remainder of the diluted lemon juice, let it cool, and repeat the test, counting the drops. Make a note of your results. The more drops it takes to remove all color, the less ascorbic acid the fruit juice contains. Dilute other fruit juices one to four and test for ascorbic acid. Test fresh and canned orange juice, orange juice freshly made from frozen juice, and any others you wish. Title a fresh page in your record book "Ascorbic Acid Tests" and list your results and any conclusions you draw from them. * The indophenol you want is listed as so¬ dium 2, 6-diehlorobenzenone-indophenol. You can get it from Chemical Division of East¬ man Kodak Co., Rochester, N. Y., or from some biological supply houses. 366 THE HUMAN BODY Vitamin D Vitamin D is the so-called sunshine vitamin. It gets this name from the fact that sunlight causes your skin to make a substance which is then made into vitamin D. This vitamin is essential for building good teeth and bones, espe¬ cially during childhood. A serious lack of it causes bowlegs and the other de¬ fects that go with rickets. Teeth and bones are made largely of calcium and phosphorus compounds. For some rea¬ son not yet known, your body can’t use these minerals unless vitamin D is pres¬ ent. Fish-liver oils are the best natural food source of vitamin D. Homogenized milk usually has this vitamin added. But for the most part, foods do not supply this vitamin. People who can¬ not get into the sunshine should see to it that they get vitamin D in some other way. Sun lamps, properly used, fish- liver oils, and homogenized milk may supply it. There is evidence that a person can get too much vitamin D, with harmful results. If in doubt, consult your doctor as to how to get the right amount of the sunshine vitamin. Vitamin K Vitamin K is fat-soluble. It occurs in alfalfa, cheese, egg yolk, liver, spinach, and in other foods. Certain bacteria in the human colon also synthesize vita¬ min K. Your blood gets vitamin K either from these bacteria in the colon or from the foods you eat or from both. But first the fat or oil in which this vitamin is held in suspension must be digested. You will remember that bile must emulsify fats and oils before digestive enzymes can change them into fatty acids and glycerol, which can then en¬ ter the blood stream. When vitamin K (or A or D ) is present in a fat or oil, the vitamin can only get into the blood stream in solution in the fatty acids. The vitamins themselves do not have to be digested, but the fats or oils car¬ rying them do. The blood stream delivers vitamin K to the liver. That organ must have vita¬ min K to make a protein called pro¬ thrombin ( proh throm bin ) . The liver cells put prothrombin into the blood stream. That’s why it is called a blood protein. This blood protein is one of several substances that must be in the blood to enable the blood to clot after an injury. So getting enough vitamin K to the liver is vitally important, and most people get more than enough vita¬ min K into their blood streams, and thence to the liver. Newborn babies have few if any bac¬ teria in the colon and only a little vita¬ min K, picked up from the mother’s blood before birth. That is why young infants, under three to five days old, tend to hemorrhage (bleed) easily. After five to seven days, the bacteria taken in with food are active in the colon. Vitamin K is then available to the liver. Today many doctors give the mother extra vitamin K for several days before the baby is expected to be born, or they may give it directly to the in¬ fant after birth. Most people most of the time, or even all their lives after the first week of in¬ fancy, are in no danger of vitamin K deficiency. A new fat-soluble vitamin Have you ever heard someone say of a patient, "His legs are turning to stone”? Of course that isn’t true. But an occasional person does develop stiff ankles, wrists, or elbows, and streaks of calcium (lime) deposits in his mus- FOODS AND NUTRITION 367 cles. Biochemists have known for some time that people who take excessive amounts of vitamin D daily may devel¬ op calcium deposits— in muscles, or in kidneys ( kidney stones ) , or elsewhere. Not long ago, a vitamin that cures this condition was found in fresh kale, al¬ falfa, and in fresh cream. The vitamin has now been identified and named stigmasterol ( stig mass ter ohl ) . Soy¬ beans also contain stigmasterol. How does cooking affect the vitamins? Cooking has different effects on dif¬ ferent vitamins. Vitamin A is not de¬ stroyed in cooking. Also, it is not solu¬ ble in water; hence it does not dissolve out of the food into the water in which vegetables are cooked. It is destroyed by air, however. Therefore it is impor¬ tant for foods which contain vitamin A to be cooked in closed utensils. Like vitamin A, thiamin and ribo¬ flavin are not destroyed in cooking if the cooking utensils are tightly covered, but they are soluble in water. Vege¬ tables which contain thiamin and ribo¬ flavin should be cooked in small amounts of water, and the water should be used in gravy or soups or in any way you enjoy. You are wasting vitamins when you pour the water from green peas, string beans, and other green vegetables down the drain (Figure 13-8). Ascorbic acid is rapidly destroyed in cooking. Foods that contain this vita¬ min may be eaten raw. If cooked, they should be cooked as quickly as possi¬ ble. Like the B vitamins, ascorbic acid is soluble in water. Use as little water as possible for the cooking and do not throw the water away. Daily vitamin needs No one knows for sure how much of any single vitamin you or anyone else needs each day to be healthy. Table 13-B shows the minimum amounts needed daily, according to the 1953 re¬ port of the Food and Nutrition Board of the National Research Council. But no one knows how much more of each vitamin you may need to maintain your body at its best. Take ascorbic acid as an example. If you are a girl, according to the table you need 80 milligrams a day. It has 13-8 FOOD VALUES IN WATER IN WHICH VEGETABLES ARE COOKED Left. Pouring vege¬ table water down the drain wastes minerals and vitamins. Right. Using the vegetable water in soup or gravy saves these food materials and also makes a meal more tasty. Cleveland Health Museum Meat Group Vegetables and Fruits Bread and Cereals ESSENTIALS OF AN Dairy Foods Photos from National Dairy Council 13-9 Eating some foods from each group every day will probably supply all the mate¬ rials your body needs except water. Think of these food groups as you select your foods. been shown that 80 milligrams a day will keep most girls of your age from developing even borderline scurvy. But is it enough just to avoid borderline scurvy? Would more vitamin C make you feel better? And here is another difficulty. There is good evidence that the vitamin needs of one person may differ widely from those of another. So Table 13-B is not a sure guide. It should be used with this in mind. STUDYING YOUR DAILY VITAMIN INTAKE. Once more, use the list of foods you ate in four days. Use Table 13-C to estimate your daily intake of each vitamin listed in that table. Compare your daily average with the recommended minimum amounts in Table 1 3-B. Remembering that your estimates of daily intake are, at best, only rough approxima¬ tions, do you conclude that you are prob¬ ably getting enough or not enough of each vitamin listed? In your record book, record your find¬ ings. Then explain what changes, if any, you now seem to need to make in your daily diet, in order to make sure that you get enough of each essential vitamin. Our methods of refining and prepar¬ ing foods often reduce or almost de¬ stroy their vitamin and mineral con¬ tent. We remove the outer layers of grains, where the vitamins and minerals are, to make white flour. We refine the minerals out of sugar. Often we serious¬ ly injure a food by overcooking. Many of us avoid such vitamin-rich and min¬ eral-rich foods as liver, kidneys, brains, and bone marrow. We may let fruit juices stand so long that much of their vitamin C content is gone. All the evidence indicates that it is better to get our vitamins from our food than from “vitamin pills,” except when a doctor orders such “pills.” As you know, this calls for some raw foods every day, and for attention to the preparation of cooked foods and to a balanced diet. What shall we eat? Perhaps you are wondering just how you can remember all this newer knowl¬ edge of foods well enough to use it everv day. You can do it, but it isn’t J J necessary. The Institute of Home Eeo- nomics of the U.S. Department of FOODS AND NUTRITION 369 Agriculture has prepared a list of four food groups that are basic to the daily diet. Learn to use wisely what this agency terms the “Essentials of an Adequate Diet' (Figure 13-9): 1. Dairy foods. Drink four or more glasses of milk each day (two or more for adults). Cheese and ice cream can replace part of the milk. 2. Meat group. Eat two or more serv¬ ings, each day, of beef, veal, pork, lamb, poultry, fish, or eggs. Dry beans, peas, and nuts may also be used. 3. Vegetable and fruit group. Eat four or more servings daily, including: a. a green or yellow vegetable im¬ portant for vitamin A. b. a citrus fruit or other fruit or vegetable important for vitamin C. c. other fruits and vegetables in¬ cluding potatoes. 4. Bread and cereal group. Eat four or more servings daily of whole grain, enriched products. These essentials of an adequate diet should be supplemented with the fats and oils used in cooking, the butter used on bread, and unenriched grain products. Food and drug laws The United States government has two laws which help to protect the pub¬ lic from false claims regarding foods and medicines, and from certain other dangers. The first of these laws, passed in 1906, is called the Federal Food and Drug Act. Its provisions regard¬ ing the labeling of packages are as fol¬ lows : 1. Labels on packages of food must state: (a) the composition of the food, (b) its correct weight, and (c) what preservatives, if any, have been added. 2. Labels on drugs must state: (a) only those diseases for which the drug is a remedy, and ( b ) the amounts of certain listed drugs contained in the package. The second law, passed in 1938, went into effect in June, 1939. This law is called the Federal Food, Drug, and Cosmetics Act. These are its provisions: 1. Labels must tell the truth about the contents of the packages. 2. Any drug that may be habit-form¬ ing must bear the words “Warning— O O may be habit-forming.” 3. Labels must carrv directions for J the use of the drug and must warn of the dangers of using too much of it. 4. All medical devices sold as cures or treatments or preventives of disease must carry labels warning of any dan¬ gers in their use. Another recent law gives the United States government, through the Fed¬ eral Trade Commission, power to bring to trial in court any business or manu¬ facturing firm which falsely advertises any food, drug, medical device, or cos¬ metic. This applies to all forms of ad¬ vertising— by mail, in publications, or over the radio or on television. Many indictments and convictions have al¬ ready been obtained. These laws apply only to businesses which take part in interstate commerce or send out adver¬ tising through the mail. Even so, thev benefit us all. Food and people You have reviewed a little of what is now known about nutrition. A com¬ mittee of international experts reports that some 85 per cent of the people of the world suffer from malnutrition of some kind. Even in our own nation, it seems likely that many people suffer from some hidden hunger, even though they are not ill. Perhaps millions of Americans who suffer from unexplained 370 THE HUMAN BODY headaches, digestive upsets, or ‘nerv¬ ousness,” and who are below par for no apparent reason, need more of some of the known nutrients, or perhaps some still unknown ones. This may or may not be the case. But any wise person will do his best to see that his diet sup¬ plies his known needs. CHAPTER THIRTEEN: SUMMING UP The foods you eat, the fluids you drink, and the air you breathe must supply all the essential raw materials your cells need for growth, repair, and energy, if you are to be healthy and active. For growth and repair, you need four classes of nutrients : ( 1 ) proteins that will supply enough of all the amino acids your body either cannot make at all or cannot make all the time or in sufficient quantities, (2) water, (3) a number of mineral compounds, and (4) vitamins— the fat-soluble ones, A, D, and K; and the water-soluble ones, thiamin, riboflavin, niacin, ascorbic acid, and probably E and some others. For energy, you need: (1) carbohy¬ drates and ( 2 ) fats and oils, in addition to proteins which may also supply en¬ ergy, and vitamins which are essential to the making of respiratory enzymes. The easiest way to plan an adequate daily diet is to use the information about “Essentials of an Adequate Diet,” given on the preceding page (also see Figure 13-9). Your Biology Vocabulary Once more you have met a number of new terms you will want to make sure you understand and can use correctly. calorie thiamin riboflavin niacin ascorbic acid B complex vitamins folic acid carotene scurvy rickets beriberi essential amino acids pellagra prothrombin vitamin A vitamin D vitamin K fat-soluble vitamins water-soluble vitamins four essential food groups Testing Your Conclusions At the top of the next page are two lists: the first is a list of vitamins and minerals, and the second a list of foods. You are to pick out the foods in the second list which are good sources of each vitamin or mineral. Copy the list of vitamins and minerals. Beside each item write the number or numbers of the food or foods rich in that material. Use your book to check your opinions. FOODS AND NUTRITION 371 Vitamins and Minerals Foods 1. vitamin A a. turnip greens k. pork 2. vitamin C b. chocolate malted milk 1. beef 3. vitamin D c. liver m. lettuce 4. thiamin d. chicken n. milk 5. riboflavin e. cod-liver oil o. spinach 6. calcium f. tomatoes p. oysters 7. iron g- eggs q. carrots 8. phosphorus h. carrots r. snap green beans i. oranges s. American cheese j. sweet potatoes t. asparagus More Explorations 1. Is milk a perfect food? You have often heard people say that milk is a perfect food. Use indophenol to test diluted fresh milk for ascorbic acid. 2. Collecting food labels. Bread wrappers, milk containers, cereal boxes, and other food labels often list the vitamin and mineral contents of the foods. Collect and com¬ pare a number of such food labels. You can make an interesting classroom display of them. 3. A feeding experiment. Ask your teacher for suggestions as to how to carry out an animal feeding experiment, say, on a hamster or white rat. To some rats, feed a diet that lacks one essential vitamin or mineral. As a check, feed other rats a diet not lacking in any essential vitamins or minerals. Weigh the animals once a week. Note and record (and, if possible, photograph) any marked changes. Restore a complete diet as soon as some animals show signs of suffering from a vitamin or mineral de¬ ficiency. Thought Problems 1. Is your appetite a safe guide to correct eating? Why? Does craving a particular food always mean that you need it? For an interesting discussion of “hunger” as compared with “appetite,” see pages 78-79 in Food for Life, edited by Ralph W. Gerard, Univ. of Chicago Press, 1952. 2. Wild animals often develop vitamin deficiencies when kept in zoos, but in the wild they usually do not show such deficiencies. Why? Further Reading 1. An especially useful reference book for use in diet studies is Composition of Foods, Raw, Processed, Prepared, U.S.D.A. Agricultural Handbook No. 8, June, 1950. An¬ other is Food Values of Portions Commonly Used, Eighth Edition, by Anna de Planter Bowes and Charles F. Church, published by Anna de P. Bowes, N.E. corner 7th and Delancey Streets, Philadelphia 6, Pa. 2. Some of you are sure to enjoy some or all parts of the book Food for Life, cited un¬ der Thought Problem 1, above. 3. Chapter 5, “The Human Body,” in What Man May Be by George Russell Harrison, William Morrow, 1956, discusses many phases of nutrition in an interesting way. 372 THE HUMAN BODY M Internal Regu¬ lation and Co-ordination ou may nave seen wins tall or short people like these at a circus. Wide differences in height of the types pictured here are most often caused by too much or too secretion from an endocrine gland— a gland that is one of the hody s chief regulatory organs. Ewing Galloway Death of a giant Charles O’Brien was a giant. He was eight feet, four inches tall when he died at the age of 22, in England in 1783. Dr. John Hunter got permission to do a post-mortem on the young man’s body, to try to find out what had caused him to grow so tall. Hunter found a greatly enlarged gland in O'Brien’s head, a gland called the pituitary (pih tyoo ih ter ee ) gland, or pituitary body. In most people, the pituitary gland is about as large as a marble. The giant’s pituitary gland was as large as a hen’s egg. Hunter suggested that this huge gland might have caused O’Brien to grow unusually tall. Nearly 150 years later, in 1922, Dr. Herbert Evans of the University of Cali¬ fornia proved that an organic com¬ pound from the pituitary glands of cat¬ tle, when injected into rats, caused the rats to grow into giants. Today we know that the pituitary gland secretes several organic compounds and puts them “aboard” the blood stream. One of these compounds helps to determine how tall a person is. The storv of Charles O Brien calls J attention to the fact that the human body makes organic compounds that help to regulate the body in one way or another. The nervous system and several other internal mechanisms all help to regulate the body. This chapter is about these internal regulating de¬ vices and how they work. INTERNAL REGULATION AND CO-ORDINATION 373 a THE DUCTLESS GLANDS The pituitary gland in the head is a ductless gland. It is called a gland be¬ cause it secretes organic compounds. It is ductless because it has no duct. Instead of delivering; its secretions through a duct the way the liver de¬ livers bile and the salivary glands de¬ liver saliva, the pituitary gland delivers its secretions directly into the blood, which then carries the secretions to other parts of the body. You have a number of ductless glands, all of which secrete organic compounds and pass them on directly to the blood stream. The more techni¬ cal name of the ductless glands is the endocrine ( en doh kryne ) glands, of¬ ten called the endocrines , for short (Figures 14-1 and 14-2). Each endocrine gland secretes at least one organic compound into the blood stream. In one or more of the body’s organs or tissues, this organic compound “excites” one response or an¬ other. For example, one organic com¬ pound from the pituitary “excites growth response in the long bones of the body. Secretions of the endocrine glands of animals are called hormones. Hormones: chemical messengers In a sense, hormones are chemical messengers, in that they “travel” over the body and bring to different organs or tissues “messages” that cause them to respond in one way or another. Spec- tor’s Handbook of Biological Data (al¬ ready cited on page 57) lists 41 verte¬ brate hormones known to biochemists. Of these, we shall discuss only a few of the better-known ones. But first we shall locate the glands that secrete these hormones. LEARNING WHERE SOME ENDOCRINE GLANDS ARE LOCATED. Use Human Body Chart 8, following page 336. In that chart, the following endocrine glands are shown and labeled: Pituitary body, also correctly called pituitary gland 14-1 DUAL NATURE OF THE PANCREAS Not only does the pancreas deliver pancreatic juice through a duct into the duodenum, but certain cell islets secrete insulin that dif¬ fuses directly into blood capillaries. The pancreas is both endocrine and digestive gland. (The common duct shown opening into the duodenum is in most people two separate ducts opening at a common point and sometimes hound together by a sphincter muscle.) Capillaries (into which Opening of common duct (through which bile and pancreatic juice reach the duodenum) Pineal (PIN ee M) body Parathyroid (pair uh thy royd) glands Thyroid gland Thymus gland Adrenal (ad ree n'l) glands Pancreas, certain portions of which se¬ crete a hormone Find the location of each of the above glands in the human body by studying Human Body Chart 8. (Don't worry about memorizing the names of the glands right now. You will do that easily and naturally as you proceed with this chapter.) Title a fresh page in your record book Endocrine Glands. On that page, record these items: 1. Draw a simple outline "map" of the human head and trunk, with an X to mark the approximate spot where each of the above glands is located and a label for each. 2. In complete sentences, write the an¬ swer to each of these questions: a. Which human endocrines are single glands? b. Of which do you have two or more? c. Of which have you heard or read something before now? The pituitary or "master gland" You already know that the pituitary gland produces one hormone that stim¬ ulates the growth of long bones, thus helping to control your height. It also produces a number of other hormones. The pituitary gland secretes one hor¬ mone that stimulates the thyroid gland to secrete its hormone, another that stimulates the parathyroids to produce their hormone, at least one and prob¬ ably more that stimulate the adrenal glands to secrete their hormones, and so on. By way of these and other endo¬ crine-stimulating hormones, the pitui¬ tary gland “directs” the other glands. For this reason, it is often called the “master gland.” As one author put it, “the pituitary gland runs the whole hor¬ mone show.” But this isn’t the complete picture. The hormones from other en¬ docrine glands also affect the function¬ ing of the pituitary gland. So perhaps we should say that all the endocrines work together “as a team,” with the pi¬ tuitary as “the acting captain.” In any case, the pituitary gland secretes a number of hormones that stimulate other endocrines. The pituitary hor¬ mone that stimulates the thyroid gland is called the thyrotropic ( thy roh TROPik) hormone. The ones that stim¬ ulate the adrenal glands are called ad- renotropic ( ad ree noh trop ik ) hor¬ mones. What glands would the para- thyrotropic hormone stimulate ( Fig¬ ure 14-2)? One more pituitary hormone must be mentioned. It is the one that stimu¬ lates the mammary glands of female J O mammals to secrete milk after the young are born. The name of this hor¬ mone is prolactin ( proh lak tin ) . The injection of prolactin into a male cat has actually enabled that cat to nurse kittens. Injected into a rooster, this hor¬ mone makes him act like a mothering hen toward baby chicks. The pancreas and its hormone You may know someone who has dia¬ betes ( dy uh ree teez ) , a condition which people often call “sugar dia¬ betes.” If you do know such a person, you probably also know that he takes insulin ( in suh lin ) by hypodermic nee¬ dle, probably once a day. Insulin is a hormone. It is secreted by certain close-knit groups of cells scattered through the pancreas but not connected with the ducts from the pan¬ creas. These groups of cells in the pan¬ creas are commonly called islet cells INTERNAL REGULATION AND CO-ORDINATION 375 THE PITUITARY AS “MASTER” GLAND Parathyroid glands Pancreas Reproductive glands, mammary glands, etc. Bone Pituitary gland 1 4-2 The pituitary gland consists of three main parts— an anterior lobe, a posterior lobe, and an intermediate part which connects the two lobes. All the pituitary hormones in¬ dicated here are produced by the anterior lobe. Most of these hormones stimulate other endocrine glands to secrete their hormones. (eye let ) because they are little islands of cells. These islet cells in the pancreas (Figure 14-1) secrete insulin and de¬ liver it to the blood stream directly. J You must have insulin in your blood stream if your cells are to absorb and use glucose correctly. The exact role of insulin in the use of glucose still isn’t known with certainty, however. Re- searches with insulin that had been tagged with a radioisotope were report¬ ed late in 1957. They seem to indicate that insulin molecules cling to the out¬ side of the cell membranes of all your cells and in so doing make those cell membranes highly permeable to glu¬ cose molecules. It is too soon to be sure this is correct. In any case, you must have insulin in your blood to use glu¬ cose correctly. J For some still unknown reason, in some people the islet cells in the pan¬ creas lose their ability to secrete an adequate amount of insulin. The re¬ sult is a case of diabetes. In untreated diabetes, the amount of glucose in the blood rises. It may go up to two, three, or even five times the amount in the 376 THE HUMAN BODY blood of a healthy person. In a healthy person the amount of glucose in the blood, usually called the blood-sugar level, is about 90 to 130 milligrams to each 100 cubic centimeters of blood. When the blood-sugar level reaches 180 milligrams or so, the kidneys begin to excrete sugar. Then sugar shows up in the urine. All urine specimens sent to a doctor’s office or to a hospital laboratory are tested for sugar. Finding sugar in the urine does not prove you have diabetes. Sugar often shows up in the urine when you are badly frightened or become very angry. But finding sugar in the urine does call for further tests, as your doctor will tell you. A diabetic who follows strictly his doctor’s orders gets along fairly com¬ fortably. Usually he can live much as usual. Before insulin was discovered in 1922, a diabetic was doomed to a slow, prolonged illness, and in the end, to certain death. Since 1922, insulin has been used to help control diabetes. Usually, it must be continued as long as the patient lives. To this day, no cure for diabetes is known. There is one bit of good news for dia¬ betics, especially for those who dread the daily needle. Researchers are on the track of an insulin substitute that can be taken by mouth. Insulin taken by mouth is not effective because it never reaches the blood stream. Insulin is a protein. The pepsin and trypsin in the food tube digest it. A substitute for insulin that can be taken by mouth, at least in mild cases of diabetes, seems to be in the making. The thyroid gland The thyroid gland is a two-lobed gland in your neck ( Human Body Chart 8). This gland must have iodine to make its hormone (Figure 14-3). There are four atoms of iodine in each molecule of its hormone, as well as atoms of carbon, hydrogen, oxygen, and nitrogen. This hormone is called thyroxin (thy roks in). You will be sur¬ prised to learn that the average per¬ son’s thyroid gland secretes somewhat less than 250 milligrams (about 1/2,000 of a pound) of thyroxin in a whole year. But that bit of thyroxin makes a great difference. Thyroxin regulates the rate of oxida¬ tion of food molecules in your living 14-3 DIAGNOSIS OF THYROID FUNCTION Because the thyroid gland must have iodine to make its hormone, physicians are able to diagnose thyroid function by substituting radioactive iodine, which can be “traced by instruments such as the one shown here. Nuclear-Chicago Corp. Massachusetts General Hospital 14-4 BASAL METABOLISM TEST This test determines how rapidly the resting body uses oxygen. It aids the diagnosis of thy¬ roid disorders. cells. Too much thyroxin speeds up oxi¬ dation; too little slows it down. Doctors often use what they call a basal metab¬ olism test (Figure 14-4) to measure the rate at which the body uses oxygen. This test thus measures, indirectly, the function of the thyroid gland. (You will remember from Chapter 2 that metabo¬ lism is the sum total of all the chemical changes that take place in a cell or or¬ ganism. ) The thyroid gland may produce too little or too much thyroxin because of some abnormality in the gland itself — or because of some abnormality in the pituitary gland that causes it to pro¬ duce too little or too much of its thvro- J tropic hormone. Too little thyroxin Too little thyroxin may result in a condition called myxedema ( mik suh dee muh), a disease in which the pa¬ tient develops a kind of puffy fatness, dryness and swelling of the skin, and other marked changes. Doctors give such patients thyroxin with excellent results. But as with insulin, the patient must continue to take thyroxin. Too little thyroxin in childhood causes a type of human imbecile known as a cretin ( kree tin ) . An occasional child is born with a small thyroid gland O or even with almost none at all. Such children, if not treated, are dull men¬ tally and may never exceed the intelli¬ gence of a five-year-old, even though they live many years. They grow only slowly and are dwarfed for life. If the cretin is given thyroxin alone (or some¬ times thyroxin plus the thyrotropic pituitary hormone) regularly through¬ out childhood, then instead of becom¬ ing an imbecile he develops a normal intelligence, and his growth is not stunted. In other words, giving thy¬ roxin to a cretin in childhood makes the difference between a dwarfed imbecile and a normal person. Unfortunately, a cretin who remains untreated to the age of twenty or twenty-one cannot be restored to normal. As you probably know, an enlarged thyroid gland is called a goiter. Simple goiter is due, indirectly, to too little thyroxin, which is due, in turn, to too little iodine, especially in childhood. Soils far away from the oceans are like¬ ly to be low in iodine. Hence foods raised in those soils lack this element. Not too long ago, simple goiter was common among inland peoples, but it is much less common today, since most people use iodized salt and eat sea foods (rich in iodine) now and then. Simple goiter can be prevented by mak¬ ing sure that children and adults, too, get enough iodine in their food. O O Too much thyroxin Too much thyroxin causes the cells to J oxidize foods more rapidly than is nor- 378 THE HUMAN RODY mal. Increased oxidation simply “burns up” the food. A person whose thyroid gland secretes too much thyroxin usu- ally has a high energy drive, a quick¬ ened heartbeat, and a tendency to show a tremor of the hands. He is likely to be restless and exceedingly active— to feel that he must be doing something every minute of his waking hours. In many cases, the eyes bulge out more and more until they seem to be about to pop out of the person’s head. Extreme cases of this kind are called toxic goiter. Real toxic goiter is a serious condi- tion. It is sometimes possible to bring it under control by medical treatment. In other cases, it is necessary to remove part of the gland. You can see that thyroxin plays an important part in your life. The parathyroid glands The parathyroid glands are usually located on the back of the thyroid gland (Human Body Chart 8), but sometimes they are buried inside the thyroid gland. Parathyroid means “near the thyroid.” The number of parathy¬ roid glands is as low as two in some people, as high as twelve in others. The parathyroid hormone is neces¬ sary for the proper utilization of cal¬ cium and phosphorus. If there is a shortage of this hormone, the calcium content of the blood and lymph falls below normal, while the phosphorus content rises above normal. Soon the muscles begin to twitch. These twitch- ings become more and more severe un¬ til violent muscular contractions, com¬ monly called convulsions, occur. When these conditions are due to lack of para¬ thyroid hormone, the person is said to be suffering from a disease called tet¬ any (TETuhnee). (Tetany is not to be confused with tetanus, which is the doctor’s name for lockjaw. ) Persons suffering from tetany must take para¬ thyroid hormone regularly, as long as they live. In rare cases, parathyroid tissue has been successfully trans¬ planted into persons with tetany. The transplanted tissue may produce enough hormone to cure the condition. The adrenal glands Lying atop each kidney is a cap¬ shaped ductless gland, the adrenal gland (Human Body Chart 8). The in¬ ner core, or medulla, of this gland (Fig- 14-5 ADRENAL GLAND AND ITS BLOOD SUPPLY This diagram shows the left adrenal gland, cut in half to show the two main parts of the gland, the medulla and cortex. In a healthy adult, this gland measures approximately two inches by one and one half inches by less than half an inch thick. bmall arreries Cortex Medulla Vei kidney Adrenal gland Capillary network mmama amammemamm ure 14-5) secretes the hormone adren¬ alin ( ad ren uh lin ) . The outer part, or cortex, of the adrenal gland secretes cortisone * ( kor tih sohn ) . Cortisone has made the headlines more than once. It was hailed as a “wonder drug.” Bedridden patients were walking again, the newspapers and magazines said. And it was true. The “bedridden patients” were badly crippled by rheumatoid arthritis (roo muh toyd ar thry tis ) , a kind of rheu¬ matism involving painful and swollen joints. After a few days of cortisone injections, many patients could “walk again.” Today, cortisone or a similar sub¬ stance ( 28 substances of much the same chemical nature have already been ex¬ tracted from the adrenal cortex of ani¬ mals ) is used in treating a number of chronic diseases. But, like insulin, corti¬ sone is a treatment, not a cure. Corti¬ sone treatment may have harmful side effects. Physicians check patients regu¬ larly while under cortisone treatment. When signs of harmful side effects show up, they stop the cortisone treat¬ ment for a while. Then the harmful side effects disappear. You may have heard or read about the pituitary hormone that stimulates the adrenal cortex to secrete cortisone. It is commonly called ACTH 00 and is often used, either alone or along with some cortisone, in rheumatoid arthritis and other conditions known to improve under cortisone treatment. Remarkable results with ACTPI have made the headlines many times in the past decade or so. * The cortisone that doctors give patients was once extracted from the adrenal cortex of beef cattle, but is now being produced on a large scale bv partial synthesis. 00 ACTH stands for adrenocorticotropic hormone. Selye's theory of stress reactions Dr. Hans Selye (sELLyay) of the University of Montreal has advanced a theory about ACTH and cortisone. This theory is being widely discussed and tested but still is not considered fully established. It may take many years to prove or disprove Dr. Selye’s theory. So remember as you read the next paragraphs that they refer to a theory not yet fully proved. Dr. Selye calls his theory the alarm reaction. According to this theory, an attack by germs, or a severe burn, or exposure to great heat or cold, or other stress, starts a chain of events in the body. Let’s take a severe burn as our example. The burn causes some still unknown chemical messenger to be sent to the patient’s pituitary gland. That gland at once delivers ACTH to the blood. As soon as ACTH, by way of the blood stream, reaches the adrenal cortex, it releases cortisone and prob¬ ably other hormones into the blood. These adrenal cortex hormones then start the body’s “fight” against the effects of the injury. For one thing, they cause white blood cells to move into the burned area, where they destroy germs and the tissue cells that were killed by the burn. Cortisone or some other hormone also causes the blood vessels around the burn to enlarge. The increased blood supply makes the area around the burn red— inflamed, we sav. These and other reactions help the body to meet the emergency. That is the theory known today as the alarm reaction. Dr. Selye goes on to explain that long-continued stress, such as prolonged illness, keeps the alarm reaction going until the cells of the adrenal cortex are exhausted. They can no longer do their work efficiently. Then the tissues ( espe- 380 THE HUMAN BODY dally the connective tissues) that are starved for cortisone and probably other cortical hormones, undergo changes. In some cases, one kind of arthritis devel¬ ops; in others a severe and usually fatal skin disease is the result; in still other cases different kinds of disturbances follow. So Dr. Selye’s theory, in full, is sometimes spoken of as the alarm- reaction-and-cortical-exhaustion theory. Only future research will tell if it is cor¬ rect. Effects of adrenalin The effects of adrenalin on the body are quite well known. When injected into the blood stream, adrenalin causes a rapid rise in blood pressure, a faster pulse rate and breathing rate, a quick change of glycogen to glucose in the liver, and a consequent increase in the glucose content of the blood. It even reduces the time it takes your blood to clot. These are facts estab¬ lished by extensive and careful experi¬ ments. These facts have led to a widely accepted theory that adrenalin helps a person to meet an emergency. Accord¬ ing to this theory, adrenalin, released during fear or anger, prepares the body to meet danger. For instance, if some¬ one assumes a threatening attitude to¬ ward you, the theory is that adrenalin brings about quick changes that actu¬ ally enable you to hit harder or run faster, whichever you may decide to do. And the bleeding from any wounds you may receive will stop more quickly than usual because of the decrease in the time it takes your blood to clot. It is a beautiful theory, but it has not yet been proved conclusively. It is pos¬ sible to remove the medulla (core) of both adrenals from an animal (under an anesthetic, of course) without no¬ ticeably disturbing any of these known responses to adrenalin. In fact, such an animal goes on living in apparently nor¬ mal fashion. If the adrenals do play the role assigned them in this theory, then there must be something else that can take over the role after the medulla of the adrenals has been removed. The reproductive glands As you already know, in higher ani¬ mals the ovaries produce eggs and the testes produce sperms. The sperms fer¬ tilize the eggs, which then grow into embryos and finally into young and then adult animals. This type of repro¬ duction is sexual. ( Two sexes, male and female, are involved). The glands that produce the eggs and sperms are often called the reproductive glands. Biolo¬ gists call them gonads ( gon adz ) . The gonads of higher animals, includ¬ ing man, secrete hormones, often called sex hormones. One hormone from the male gonads ( testes ) is testosterone (tess toss ter ohn ) . One group of hor¬ mones from the female gonads (ova¬ ries ) goes by the group name estrogens (ess truh jens ). But both males and fe¬ males have both testosterone and estro¬ gens, males having much more testos¬ terone and much less of the estrogens than females, and vice versa. The sex hormones play a part, but not the only part, in the changes that take place in the body during the teens. (The gonads usually do not mature un¬ til a boy or girl reaches the early teens, hence do not produce sex hormones to any extent until then.) For example, testosterone helps to make boys’ voices change and their beards grow. Other endocrine glands There are two other glands that are usually listed among the ductless INTERNAL REGULATION AND CO-ORDINATION 381 glands— the pineal body in the head and the thymus gland in the chest (Human Body Chart 8). The function of neither gland is well understood. There are also other hormones. You will remember that the pancreatic juice and bile are delivered into the duo¬ denum almost as soon as food arrives there. How do the gall bladder and pancreas “know” when food arrives in the duodenum? They do not “know,” of course. The presence of food in the duodenum causes glands in its walls to secrete two hormones. One speeds to the gall bladder and causes it to send bile through a duct into the duodenum. The other hormone, called secretin ( see KREEtin), travels through the blood to the liver and pancreas. It causes the liver to speed up its secretion of bile. It causes the pancreas to send pancreatic juice through a duct into the duodenum. Summing up: hormones in human life Today we know that hormones play many important parts in the life of a human being. They are chemical mes¬ sengers and they exert what you might call a “fine and measured control over many and probably all life processes. Along with the nervous system, they co-ordinate the reactions and processes in healthy people all the time. Table 14- A summarizes briefly some of our knowledge of the hormones. Use it as your summary of this section J J on hormones. THE STABILITY OF THE BLOOD Your blood stream is the shipping system of your body. It is always pick¬ ing up materials at one place and de¬ livering them to another. And yet the total make-up of the blood stays pretty TABLE 14- A SOME HORMONES IN THE HUMAN BODY Name of hormone(s) Where it comes from What it does Growth hormone Pituitary gland Stimulates growth of long bones ACTH Pituitary gland Stimulates adrenal cortex Prolactin Pituitary gland Stimulates mammary glands and mothering behavior Thyrotropic hormone Pituitary gland Stimulates thyroid gland Parathyrotropic hormone Pituitary gland Stimulates parathyroid glands Insulin Islet cells of pancreas Necessary in carbohydrate metabolism Thyroxin Thyroid gland Regulates the rate of oxidations in cells Adrenalin Adrenal medulla Believed to stimulate many changes that prepare the body to meet an emergency Cortisone Adrenal cortex Probably plays many roles in stress and strain situations Parathyroid hormone Parathyroid glands Necessary for the proper utilization of calcium and phosphorus Secretin Mucous lining of duodenum Stimulates pancreas and liver Testosterone Testes Stimulates voice change and beard growth, etc., in boys Estrogens Ovaries Stimulate body changes connected with grow¬ ing up in girls 382 THE HUMAN BODY Red blood cell ■$ - Blood platelets Plasma (55 per cent) Formed ^elements (45 per cent) 14-6 MAKE-UP OF HUMAN BLOOD Left. The formed elements of the blood are shown here ( 1,800 X ). Red blood cells average some 8/25,000 of an inch in diameter and less than 2/25,000 of an inch in thickness. The smallest of the several kinds of white cells are about the size of red cells. Right. The formed elements in this blood have settled to the bottom of the test tube. much the same all the time. It is as if the freight trains of the nation always carried about the same loads of much the same materials in about the same number of cars, not for a week or a month but for years. J Composition of the blood You already know that your blood is plasma with red and white cells in it. Besides the red and white cells, the blood also contains blood platelets (Figure 14-6). The cells and platelets together make up the formed elements of your blood. The formed elements make up about 45 per cent of the total blood of a healthy person. The other 55 per cent of human blood is made up of blood plasma. Some 90 per cent of the plasma is water. The rest of it consists of various salts, plus amino acids, digested fats, glucose, vitamins, hormones, enzymes, and urea, carbon dioxide, and other cell wastes. Dissolved in the plasma, there are also certain plasma proteins. You already know about prothrombin, one of the plasma proteins. Another one is fibrin¬ ogen (fy brin uh jen). Fibrinogen plays a part in the clotting of the blood. Take the fibrinogen and formed elements out of the blood and the almost clear liquid left is blood serum.* Perhaps the most amazing thing about blood plasma is its stability in the presence of constant change. For in¬ stance, the inorganic salts in blood plasma remain at about 0.9 per cent bv weight, no matter how much salt vou may take by mouth. The blood sugar (glucose) stays close within a given amount, about 90 to 130 milligrams per 100 cubic centimeters, varying normal¬ ly only within these limits. All other substances in the plasma also stay at even levels, under normal conditions. * The lymph that bathes all cells is blood plasma minus certain of its blood proteins, but with fibrinogen still in it. INTERNAL REGULATION AND CO-ORDINATION 383 The formed elements The numbers of each of the formed elements of the blood likewise remain approximately the same in a normal, healthy person. The red-cell count is about 5,000,000 per cubic millimeter ( a cubic millimeter is about one small drop ) in a healthy man, and about 4,500,000 in a healthy woman. The white-cell count is usually about 5,000 to 7,000 per cubic millimeter in an adult, although apparently healthy in¬ dividuals may have counts of 9,000 or sometimes more. Blood-platelet num¬ bers vary more widely. STUDY OF FORMED ELEMENTS. Use a slide of stained Human blood. (If you want to make your own slides, turn back to page 47 for directions.) Examine the slide under the high power objective of your microscope. Look care¬ fully for stained platelets as well as red and white cells. With colored pencils, sketch all three of these formed elements as they look when stained. Name each type. Be¬ neath your sketches, list the normal cell counts in an adult, per cubic centimeter. Hemoglobin The red blood cells contain hemo¬ globin. Hemoglobin has a remarkable ability to combine loosely with oxygen where oxygen is plentiful, as in your lungs, and to set that oxygen free where oxygen is less plentiful, as in your tis¬ sues. Unfortunately, hemoglobin com- bines even more rapidly with carbon monoxide than with oxygen, when ex¬ posed to both gases in the air you breathe. Once it has combined with carbon monoxide, hemoglobin cannot combine with oxygen. Hence, in carbon monoxide poisoning, the hemoglobin cannot carry enough oxygen to the cells, and as a result the cells die of suffoca¬ tion. The amount of hemoglobin stays about the same all the time in a healthy person. Normally there are about 14 to 17 grams of hemoglobin in each 100 cubic centimeters of a man’s blood, and a little less in a woman’s blood. What keeps cell counts constant? New red blood cells are being made all the time in the red marrow of cer¬ tain bones (Figure 14-7). Recent re¬ search with radioisotopes seems to show that red cells live some 100 to 120 days. Then they are destroyed. This destruction goes on all the time. But as fast as red cells are destroyed, new ones take their place. So the cell count stays about the same in a healthy person. What becomes of the worn-out red cells? They are destroyed in the spleen and liver. In the capillaries of these two organs, certain cells are arrayed along the inside walls. These special cells en¬ gulf their food the way an ameba or a white blood cell does. As the red cells pass through the liver or spleen capil¬ laries, some of them are engulfed and digested by the specialized cells. The spleen and liver are the junk yards, so to speak, of worn-out red cells. Some of the products of this breaking down of red cells are used by the liver in the making of bile. The red-cell-making mechanism can be speeded up. The red-cell count rises gradually to 6-7,000,000 in persons who stay some time at 14,000 feet above sea level. There is evidence, too, that the red-cell count may rise rapidly during violent exercise; at least, increases have been demonstrated in horses at work. The red-cell count may also fall, owing to various causes, such as hemor- 384 THE HUMAN BODY Mature red blood cell and cast-off nucleus 14-7 FORMATION OF RED BLOOD CELLS The red marrow inside some of your bones makes millions of new red cells every minute. Usually only mature red cells enter the blood stream, but after severe bleeding, some nucleated cells may enter it. (675x and 2,800 X) rhage, some diseases, food deficiencies, and sometimes for unknown reasons. When a person’s red-cell count falls, he is said to have anemia. Each case of anemia must be studied to determine its type, and then treated accordingly. White blood cells are also dying and being removed from the blood stream all the time. They are replaced by an equal number of new white cells. This keeps the white-cell count about the same from day to day in a healthy per¬ son. What makes the blood clot? The clotting of blood is one of the many life-saving devices of the body. If your blood did not clot, you might bleed to death from the smallest cut. Do you have any idea what makes your blood clot? People used to think that air was the “starter” that made the blood from a small cut or scratch in the skin clot. Today we know better. A whole array of devices comes into play in the clotting process. The “clot starter” is an enzyme, or perhaps several enzymes. These en¬ zymes come from broken-down blood platelets and from the injured cells. The enzymes initiate a chain of reactions that lead to the formation of the clot that plugs the wound. Calcium ions (particles of calcium carrying an electrical charge) are nor¬ mally present in the blood, as you al¬ ready know. Without sufficient calcium ions, the blood will not clot, but in their INTERNAL REGULATION AND CO-ORDINATION 385 presence, the enzymes from the plate¬ lets and injured cells change prothrom¬ bin into thrombin. Then the thrombin changes the plasma protein, fibrinogen, into the fibrous protein called fibrin (fy brin). Tbe threads of fibrin enmesh the formed elements of the blood, and thus the clot is formed. Usually the whole process takes from two to sev¬ en minutes; this is called the clotting time. Table 14-B summarizes the whole process. Within the blood vessels, blood does not ordinarily clot; but an injury to the wall of a blood vessel releases the clot¬ starting enzymes, and a clot forms, thereby plugging the wound. Normally this is a useful device because it pre¬ vents internal bleeding, but sometimes the clot blocks the blood vessel. If it is an artery that supplies a vital organ, the results may be serious. We have shown only a few of the highlights in the clotting process, but even this brief account may convince you that clotting is indeed a complex as well as a life-saving process. Blood types One feature of your blood stays the same all your life. That is your blood type. Do you know your blood type? If not, you can easily find out what it is. Any hospital laboratory will deter¬ mine your blood type for a small fee. You can easily determine it yourself, in biology class, if you have the mate¬ rials. Your teacher will decide whether to include blood-typing in your activ¬ ities and will direct the proceedings if you do the typing. (Full directions are on page 399; see also Figure 14-8.) Four blood types are recognized. The most widely used symbols for them today are O, A, B, and AB. All living persons today have one or another of these blood types. In blood transfusions, it is important to give only the correct type of blood. The donor and the patient should be¬ long to the same blood group. For ex¬ ample, if group A blood is given a patient with group B blood the results may be serious. The reason is this. If group A blood serum is mixed (it can be done experimentally on a microscope slide ) with red cells from group B blood, in a little while the cells will clump together (Figure 14-8). On the other hand, if group B cells are mixed with group B serum, no clumping oc¬ curs. If clumping were to occur in a person’s body, the clumps might block some of the capillaries in his heart or brain or in some other vital organ, with serious results. That is why it is impor¬ tant to give only the correct type of blood in a transfusion. Why does group A serum make group B cells clump together? Simplv because group A serum contains a sub¬ stance that has this effect on cells from group B blood. This substance is an agglutinin ( uh gloo tih nin ) and the clumping is called an agglutination (uh gloo tih nay shun). TABLE 14-B STEPS IN THE BLOOD-CLOTTING PROCESS 1. Blood platelets and injured cells release enzymes. 2. enzymes, in the presence of calcium ions, change prothrombin to thrombin. 3. thrombin changes fibrinogen to fibrin. 4. fibrin forms the network that enmeshes the formed elements of the blood. 386 THE HUMAN BODY DETERMINING BLOOD TYPE ACCORDING TO CLUMPING CHARACTERISTICS Anti-A Anti-B Clumping No clumping Anti-A serum Anti-B serum plus unknown cells plus unknown cells Unknown has type A blood, since anti-A clumps the cells. Anti-A Anti-B Clumping Clumping Anti-A serum Anti-B serum plus unknown cells plus unknown cells Unknown has type AB blood, since both serums clump the cells. Anti-A Anti-B No clumping Clumping Anti-A serum Anti-B serum plus unknown cells plus unknown cells Unknown has type B blood, since anti-B clumps the cells. d _ Anti-A Anti-B No clumping No clumping Anti-A serum Anti-B serum plus unknown cells plus unknown cells Unknown has type O blood, since neither serum clumps the cells. Drawing by Marion Cox, from Experiences in Biology, by Morliolt and Smith, Harcourt, Brace and Company, 1954 14-8 Use these diagrams as a guide if you determine your blood type as part of a class activity. Slide a indicates tvpe A blood; slide b, type B; slide c, type AB; slide d, type O. Group A agglutinin also clumps AB cells, but it does not make O cells ag¬ glutinate. In B serum there is a different agglutinin that makes A and AB cells agglutinate, but it does not agglutinate O cells. That’s why, in an emergency, doctors sometimes give treated O blood to patients with blood of another group. This used to be done frequently, but is generally avoided today, except in a serious emergency when blood of the necessary type is not quickly available. There is another factor that must be considered in relation to blood transfu¬ sions. It is called the Rh factor. The Rh factor is a substance in the red blood cells of persons who are Rh-positive. Most people (some 85 per cent) in this country are Rh-positive, the rest are Rh-negative. Persons in any of the four main blood groups may be either Rh- positive or Rh-negative. As you will learn in a later chapter, Rh-positive blood should never be given to an Rh- negative person. Before a blood transfusion (Figure 14-9), technicians mix donor’s cells with patient’s serum and vice versa. If no agglutination occurs, the transfu¬ sion is doubly safe. The percentage of each blood type occurring in one group of people may INTERNAL REGULATION AND CO-ORDINATION 387 differ markedly from that of another J (Table 14-C). Nearly all American In¬ dians have type O blood. Among Amer¬ icans of European descent, between 80 and 90 per cent have either type O or type A blood; type AB is rare. Usually less than three per cent of these Ameri¬ cans have type AB blood. In one high school in Ohio, 175 bi- ology students determined their blood types with these results: Type No. of students Per cent o 80 45.7 A 74 42.3 B 17 9.7 AB 4 2.3 175 100.0 Summing up: the stability of the blood The composition of the human blood stays amazingly constant in people who are in good health. The formed ele- ments make up about 45 per cent and the plasma about 55 per cent of the blood volume. The blood platelets and at least two blood proteins (prothrombin and fibrin¬ ogen) play essential roles in the com¬ plex and life-saving process of clotting. The red-cell and white-cell counts stay about the same when you are in good health, the red-cell count being close to 5,000,000 per cubic millimeter in men and 4,500,000 in women. White¬ cell counts usually run from about 5,000 to about 7,000 in healthy adults. All living people have blood that be¬ longs to one of four groups: O, A, B, or AB. In transfusions, it is important to give only blood of the same type as that of the patient, or, in rare emergencies, to give treated O blood. O THE NERVOUS SYSTEM More than forty years ago, a boy of four fell and broke his collarbone. The bone soon “knit, but even then this boy could not use his arm. He could feel touch and pain in the arm and hand, but he couldn’t move his fingers, 14-9 GIVING BLOOD The man on the hospital table is giving a pint of blood which will be stored and later given as a blood transfusion to a patient who needs it. Acme TABLE 14-C PERCENTAGES OF SEV¬ ERAL GROUPS OF PEOPLE HAVING EACH OF THE FOUR BLOOD TYPES * Human groups 0 A B AB American Indians 98.5 1.5 0 0 (Argentina) American Indians 91.0 7.0 2.0 0 (South Dakota) Eskimos 41.1 53.8 3.7 1.4 Japanese 30.1 38.4 21.9 9.6 Chinese 34.2 30.8 27.7 7.3 Biology students 45.7 42.3 9.7 2.3 (an Ohio high school) * All except the last item from Genetics and the Races of Man by William Boyd, Little, Brown, 1950 bend his elbow, or use his wrist. His arm remained sensitive but was com¬ pletely paralyzed. What had happened? How is it pos¬ sible to be unable to move a hand and arm and yet be able to feel with them? As you know, nerves connect each arm with the spinal cord. Impulses from the hand and arm travel along sensory nerve fibers into the cord and thence to the brain, and “feeling” (pain or heat, etc. ) results. Impulses also travel out from the cord along motor nerve fibers to the muscles of the arm, and movements result. Without these motor nerve impulses, muscles cannot con¬ tract. They become paralyzed. Obvi¬ ously, the boy’s fall had broken the motor nerve connections— but not the sensory ones— between his spinal cord and arm muscles. This accident occurred more than 40 years ago. Then, no one on earth could have repaired the nerve injury. Today the ends of a severed nerve can some¬ times be successfully joined together and the nerve connections thus re¬ stored. But any severed nerve means a broken line of communication in the human body, unless the cut nerve ends can be reunited. The boy with the paralyzed arm learned to get along very well with only one active arm. In high school, he even made the basketball team. Later he took up an active occupation and was successful in it. But he did all this with only one active arm. Co-ordination of the human body All the parts of the human body work together well. You already know that the hormones, in their role of chemical messengers, play some part in the over-all co-ordination of the body. The nervous system plays an even larger role. Of course no higher animal’s body could exist without its nervous system, but if it could, such a body would be a mere collection of loosely related cells, tissues, and organs. Parts of the nervous system Refer often to Human Body Chart 4 following page 336, as you read on. The central nervous system consists of the brain and the spinal cord. The “lines of communication” are the nerves —12 pairs of cranial nerves and 31 pairs of spinal nerves. As you learned while studying the frog, the cranial nerves join the brain, and the spinal nerves join the spinal cord. You also have a series of semi-inde¬ pendent nerve centers consisting largely of two chains of ganglia (nerve-cell clusters ) that lie along— but outside of— the backbone. These two chains of ganglia plus a few other ganglia are called the autonomic ( aw toll nom ik) ganglia. They are centers of communi¬ cation in the autonomic nervous sys¬ tem, about which you will learn later. INTERNAL REGULATION AND CO-ORDINATION 389 LEARNING THE PARTS OF THE NERVOUS SYSTEM. Turn to Human Body Chart 4. On the left-hand chart, look for these parts of the brain: cerebrum, cerebellum, and medulla. Next look for the spinal cord and the spinal nerves shown. "Nerves to arms" and "nerves to legs" are spinal nerves, as well as those labeled "spinal nerves." Next look for the "chains of autonomic ganglia." Lastly look for the vagus (vay gus) nerve. It is the only cranial nerve shown in the chart. Title a fresh page in your record book Ports of the Nervous System. Divide the page into three columns. Head one column Central Nervous System , a second Nerves , and a third Ganglia. Under the correct heading, copy each label from Human Body Chart 4, left-hand page. There is one more essential feature of the nervous system; namely, the sense organs— eyes, ears, nostrils, taste buds on the tongue, and nerve endings in the skin, muscles, and internal or¬ gans. The sense organs “put you in touch with the outside world.” In the next chapter, you will study the sense organs in connection with your reac- tions to external stimuli. Here we are concerned primarily with internal con¬ trol. For a summary of the parts of the nervous system, see Table 14-D. The forty-three pairs of nerves Your 12 pairs of cranial nerves and 31 pairs of spinal nerves make 43 pairs of nerves in all. Through these nerves, nerve impulses travel into and out of the central nervous system. Of the 12 pairs of cranial nerves, one pair (the optic nerves) connects the eyes with the brain. Another pair (the olfactory nerves) connects the nostrils with the brain. Still another pair (the auditory nerves) connects the inner ears with the brain. Other pairs of cranial nerves connect various other parts of the head with the brain. Only two pairs of cranial nerves extend to parts of the body below the neck. One of these two pairs extends to the shoulder muscles. The other pair connects the medulla of the brain with the heart, stomach, intestine, adrenal glands, and other internal organs. The two nerves of this pair are called the vagus nerves. Vagus means “wander¬ ing,” so these are the “wandering” nerves; they “wander” down into the thorax and abdomen, in contrast with other cranial nerves which do not “wander” away from the head. The 31 pairs of spinal nerves connect the spinal cord with the arms and legs and other parts of the body below the neck. Each spinal nerve is connected to the spinal cord by two roots, as Fig¬ ure 14-10 shows. The dorsal root of a spinal nerve has a ganglion on it, the ventral does not. The dorsal root car- TABLE 14-D PARTS OF THE NERVOUS SYSTEM Name of parts Component parts Central nervous Cerebrum system Cerebellum Medulla Spinal cord Nerves Cranial nerves (12 pairs) Spinal nerves (31 pairs) Sense organs Eyes Ears Nostrils Taste buds Nerve endings in the skin Nerve endings in muscles and in many internal tissues and organs Autonomic nervous Two chains of autonomic system ganglia plus some other parts 390 THE HUMAN BODY White matter Spinal nerve Ventral root (motor) Dorsal root (sensory) Ganglion Photo by Eastman Kodak Co. 14-10 X-RAY PHOTOGRAPH AND DIAGRAM OF PART OF THE SPINAL CORD The gray mat¬ ter is made up largely of cell bodies of neurons, the white matter largely of axons and dendrites of neurons. Note that a spinal nerve has two roots, one sensory, one motor. lies nerve impulses into the cord, so it is the sensory root. The ventral root is the motor root of a spinal nerve. Which root of a spinal nerve was affected in the boy’s accident that re¬ sulted in paralysis of his arm? The central nervous system You already know the parts of the central nervous system of other verte¬ brates. Your central nervous system has the same parts, as you also know, and each part controls about the same re¬ sponses as in other vertebrates, but with great and important “improvements.” In general, the cerebrum “controls’ what we call conscious behavior. The cerebellum controls the behavior in¬ volved in keeping your balance and co-ordinating the movements of your skeletal muscles. The medulla helps to control such involuntary responses as peristalsis, heartbeat, the flow of diges¬ tive juices, and breathing movements. The spinal cord is the center of reflexes below the neck, such as those that jerk your hand away from a hot baking dish. When biologists say that the medulla controls the flow of saliva, they do not mean that the medulla “bosses” the flow of saliva, the way a contractor bosses (controls) the men who work for him. They do mean that all impulses must pass through the medulla to reach the salivary glands and make the saliva flow. The picture of a roast beef starts impulses inward along pathways in the optic nerve. These impulses must reach and pass through pathways in the me¬ dulla before they go on to the salivary glands. Then your mouth waters. It would be more accurate to say that the saliva-flow response is centered in the medulla than controlled by it. The same thing is true of any other response controlled by the medulla or by any other part of the central nervous system. When biologists say that a par¬ ticular part of the brain controls a par¬ ticular part of the animal’s behavior, they usually mean that all impulses must pass through this part of the brain to reach the muscles (or other struc¬ tures ) used in that behavior. The human cerebrum Your cerebrum (Figure 14-11) is per¬ haps the most complex and least under- INTERXAL REGULATION' AND CO-ORDINATION 391 stood organ in your body. It seems to be the most complex mass of organized protoplasm in existence. Someone has estimated that it contains some twelve billion neurons. The cell bodies of the neurons in the cerebrum lie close to the surface, in a layer of gray matter called the cerebral (ser uh brul ) cortex. The inner or white matter is largely nerve fibers— axons and dendrites. All of the muscles over which a human being has conscious or volun¬ tary control receive impulses from areas in the cerebral cortex. The muscles on the right side of the body receive im¬ pulses from areas in the cortex on the left side of the brain, and vice versa. Thus the fingers of your right hand re¬ ceive impulses from the left side of your cerebrum. Sensory areas are numerous in the cortex. Impulses from the eyes reach the sight centers. Those from the ears reach the auditory centers. There are centers of smell, centers of taste, cen¬ ters of skin sensations, etc., in different parts of the cortex (Figure 14-12). Fur¬ thermore, injury to one specific part of the cortex results in the loss of the abil¬ ity to understand or use numbers. In¬ jury to another part of the cerebrum results in the loss of the ability to speak. These facts suggest that various capacities, such as the ability to speak 14-11 PHOTOGRAPH OF A HUMAN BRAIN The volume of the brain of a man is about 1,500 cubic centimeters, which is about 55 times the volume of the spinal cord. Folds or convolutions increase the surface area many times over what it would otherwise be. A. F. Jacques, Photographic Department, Rhode Island Hospital Spinai cord 14-12 DIAGRAM OF SENSORY AND MOTOR CENTERS IN THE CEREBRUM When brain tis¬ sue is destroyed, other areas in the brain may in some cases take over the functions of the destroyed tissue. In other cases, abilities are permanently lost. or to do arithmetic, are centered in specific, specialized areas in the cortex, even as sight, smell, and other sensory reactions are. You will be interested in studies of memory when patients had to undergo brain surgery. Often brain surgery is done under local anesthesia, because it is important that the patient be able to talk to the surgeon during the opera¬ tion. Even so, the surgery is virtually painless. During one such operation, an electrical stimulus was applied to spe¬ cific, exposed points in the cortex, to find out whether these points had suf¬ fered injury and should be removed. Every time the electrical stimulus was applied to one specific point in the cortex, the patient said she heard a specific song. Her memory of that song seemed to be centered in that specific point in her cortex. This and many simi¬ lar discoveries at least suggest that our memory of specific past experiences is centered in specific parts of the cortex, but only future studies will prove whether this is or is not correct. You can begin to see that the cere¬ brum, to the best of our present knowl¬ edge, plays a central role in what we usually call “conscious, intelligent be¬ havior,” such as speaking, using num¬ bers, and remembering specific past ex¬ periences. Certainly persons with badly damaged cerebrums, resulting from ac¬ cidents, cerebral hemorrhage, or infec¬ tion by certain germs, no longer show this behavior. Often they cannot speak or otherwise communicate with us. Then we say they are “unconscious.” The lack of conscious, intelligent be¬ havior in cases of serious and exten¬ sive injury to the cerebrum seems to indicate clearly that the cerebrum is essential to such behavior. The autonomic nervous system Every time you blush, your auto¬ nomic nervous system plays its part in bringing the flush to your cheeks. Goose pimples on the body, usually formed when the air is cool, are the result of the functioning of the auto¬ nomic nervous system. INTERNAL REGULATION AND CO-ORDINATION 393 The autonomic system controls inter¬ nal organs— the beating of the heart, breathing movements, peristalsis, se¬ cretion of digestive juices, and similar internal adjustments. CAN YOU "CONTROL" AUTONOMIC RE¬ ACTIONS? Test yourself in the following ways. Record what you find out in your record book. 1. Try to make yourself blush, simply by "telling" yourself to blush. Can you do it? 2. Tell yourself to "break out in a sweat." Do you start sweating? 3. Time yourself while you hold your breath. How long can you hold it? 4. Try to make tears flow and run out of your eyes. Can you do it? 5. Count your pulse. Then try to make your heart beat faster simply by "telling" it to beat faster. Count your pulse again. Did it beat faster? All of the above reactions are centered in your autonomic system. Do you conclude that you can change those reactions, to any extent, simply by willing a change? In other words, does your cerebrum (nerve center of what we call thinking ) seem to be involved to any great extent in the func¬ tioning of your autonomic system? There are two parts of the autonomic nervous system : ( 1 ) the sympathetic system and ( 2 ) the parasympathetic (pair uh sim puh thet ik) system. The nerve centers (ganglia) of the sympa¬ thetic nervous system are located out¬ side of the central nervous system, but the parasympathetic system includes centers in the medulla, the midbrain (at the floor of the cerebrum), and the lower part of the spinal cord. Nerve impulses from the sympathetic system have an effect on an organ op¬ posite to the effect of nerve impulses from the parasympathetic system. For example, nerve fibers from the sympa¬ thetic ganglia to the heart carry im¬ pulses that speed up its beat. The para¬ sympathetic vagus nerves carry im¬ pulses to the heart that slow down its beat. A nice balance between “speed¬ up” and “slow-down” impulses keeps the heart beating smoothly at a normal rate. So you might say that the sympa¬ thetic and parasympathetic systems are “checks and balances” in the regulation of such vital processes as heartbeat and breathing. Autonomic ganglia and nerves The two chains of ganglia that lie along the ventral side of the backbone contain the cell bodies of many of the neurons in the autonomic system. Re- fer again to Human Body Chart 4 fol¬ lowing page 336 and to Frog Chart 3 following page 304 and look at the parts labeled “chains of autonomic gan¬ glia.” You also have some autonomic ganglia that are not in the chains. One cluster of these ganglia, often called the solar plexus, lies just back of the stomach; another lies buried in the heart (see cardiac plexus in the heart shown in Human Body Chart 4, right- hand page); a third lies high in the neck; and still another, low in the abdo¬ men. Nerve fibers connect these autonomic ganglia with one another and with each of several internal organs. Nerve fibers also connect some of these ganglia with the spinal cord. All these ganglia and their nerve fibers constitute the sym¬ pathetic system (Figure 14-13). The vagus nerves (one pair of the cranial nerves), certain nerve fibers emerging from the midbrain (at the floor of the cerebrum), and certain 394 THE HUMAN BODY erebru Contracts pupil Dilates pupil Midbra in Stimulates flow of saliva Cerebell Relaxes salivary glands / Speeds heartbeat^^ S Slows heartbeat Medulla Salivary gland Heart Promotes muscle^N tone and digestion Inhibits digestion Stomach Small intestine f Stimulates adrenal glands Adrenal gland/ Inhibits elimi¬ nation of wastes intestine Rectum To blood vessels, sweat glands, etc., of lower limbs Promotes elimination of wastes THE AUTONOMIC NERVOUS SYSTEM 14-13 In this diagram, dotted lines indicate nerves of the sympathetic system; solid lines, nerves of the parasympathetic system. Black circles indicate autonomic ganglia (of the sympathetic system). Each body organ illustrated here has a double nerve sup¬ ply, one sympathetic and the other parasympathetic. The whole automonic system plays a large role in keeping your body functioning smoothly. INTERNAL REGULATION AND CO-ORDINATION 395 fibers emerging from the medulla and from three (usually) pairs of spinal nerves in the lower part of the spinal cord constitute the nerves of the para¬ sympathetic system (Figure 14-13). Your autonomic system plays a vital role in your life— almost entirely with¬ out your ever thinking of what it does —in regulating such vital processes as heartbeat, breathing, peristalsis, and so on. How do nerve impulses speed up and slow down the heartbeat? You have just learned that sympa¬ thetic nerve impulses are constantly speeding up the heartbeat while para¬ sympathetic nerve impulses constantly slow it down. How do the nerve im¬ pulses produce these effects on the heartbeat? Take the “slow-down” impulses first. Just as an impulse reaches the end of a vagus nerve fiber, that ending dis¬ charges an organic compound into the heart muscle cell. This compound is acetylcholine ( as uh til koh leen ) . The nerve is believed to secrete acetylcho¬ line somewhat as the thyroid secretes thyroxin, and the nerve impulses cause the acetylcholine to be discharged into the heart muscle cells, which then relax. On the other hand, impulses coming from the sympathetic autonomic gan¬ glia to the heart cause these nerve end¬ ings to discharge another substance in¬ to the heart muscle cells. This sub¬ stance causes the muscle cells to con¬ tract. It used to be called sympathin (sim puh thin ) , but is so much like ad¬ renalin that many biochemists now call it noradrenalin. Sympathin (noradren- alin) causes the heart muscle to con¬ tract, whereas acetylcholine causes it to relax. The discharge of these two substances into the heart muscle deter¬ mines the rate of the heartbeat. Of course, other factors affect the rate of the heartbeat; for example, a rapid pulse is associated with too much thy¬ roxin, and a slow one with too little. However, the rate of the heartbeat is regulated largely through its double nerve supply. Other functions of the autonomic system The numerous other functions of the autonomic system are similarly main¬ tained through a double nerve supply to each organ and gland and blood ves¬ sel. One set stimulates each structure concerned; the other set relaxes it. The size of the small blood ves¬ sels, for example, is regulated largely through the autonomic nervous system. One nerve ( or several ) relaxes the mus¬ cular walls, making the blood vessel larger; the other contracts the muscu¬ lar walls, making the vessel smaller. When you blush, the relaxing impulses have the upper hand for the moment. The blood vessels in your face relax and enlarge; then someone says, “You’re blushing!” Most of the time, the relaxing im¬ pulses to the salivary glands predomi¬ nate. But food in the mouth, or the sight or smell of food, intensifies the stimulating impulses, and the saliva flow increases. The nerve impulses that stimulate the flow of saliva come from parasympathetic nerves originating in the medulla (Figure 14-13). Similarly, stimulating and relaxing impulses, usually kept in perfect bal¬ ance, control the functioning of the stomach and intestine, the bladder and the rectum, the gastric glands and other digestive glands, the sweat glands— in short, all the so-called “involuntary” 396 THE HUMAN BODY structures of the body. It may be that the relaxing impulses produce their re¬ sponses by means of acetylcholine, and the stimulating impulses by means of noradrenalin in all the structures they control. Autonomic system and body stability Many nicely exact adjustments which help to keep our internal environment constant are achieved partly through the autonomic nervous system. This system plays a part in the change of glycogen to glucose in the liver and the consequent release of additional glu¬ cose into the blood stream during an emergency. It also plays a part (dur¬ ing the same emergency) in the in¬ crease of pulse and breathing rates and of blood pressure. In other words, the autonomic nervous system seems to do all that the adrenals are given credit for doing in preparing the body “to fight harder or run faster” when dan¬ ger threatens. You will recall that the cores of the adrenal glands can be re¬ moved without radically changing an animal’s behavior in times of stress. It may be that the adrenalin-secreting portions of the autonomic system sub¬ stitute for the missing adrenal core. The autonomic system also helps the body to get rid of heat rapidly during violent muscular activity. Through the action of this system the surface blood vessels enlarge, thus letting more blood come to the body’s surface, where it loses heat rapidly. Through this system, too, the sweat glands are stimulated to pour out sweat rapidly. The evapora¬ tion of the sweat uses up heat. In cold weather, in turn, the surface blood ves¬ sels are contracted and sweating is re¬ duced to a minimum, again through the action of the autonomic nervous sys¬ tem. CHAPTER FOURTEEN: SUMMING UP In this chapter, we have discussed three important factors in body regu¬ lation and control: (1) the endocrine glands and their hormones, (2) the composition of blood and its relative stability, and (3) the nervous system. The endocrine glands secrete hor¬ mones which serve as chemical mes¬ sengers and regulators. The pituitary gland secretes many hormones. Among them is one that stimulates the growth of the long bones, and another (pro¬ lactin ) that stimulates the mammary glands. Still other pituitary hormones are “directive,” in that each one stimu¬ lates a particular endocrine gland to secrete its hormone: the thyrotropic hormone stimulates the thyroid to se¬ crete thyroxin; ACTH, the adrenal cor¬ tex to secrete cortisone; and so on. Thy¬ roxin regulates the rate of oxidation; insulin from the pancreas regulates the use of glucose in cells. Adrenalin and cortisone seem to help the body to meet emergencies. The parathyroid hormone enables the blood to absorb calcium compounds from the food tube. Other hormones are known and prob¬ ably many remain to be discovered. The blood plays a big part in the over-all stability of the body and in its adjustments to emergencies. Its ability to clot keeps a person from losing much blood from small wounds. The chemical make-up of the blood plasma stays about the same in a healthy per¬ son. The blood of all people is much alike, but certain agglutinins in the blood plasma and factors in the red cells vary. On the basis of these varia¬ tions, people can be sorted into four main blood groups: those with ( 1 ) type O blood, (2) type A blood, (3) type B blood, and (4) type AB blood. INTERNAL REGULATION AND CO-ORDINATION 397 The nervous system consists of (1) the central nervous system (brain and spinal cord ) , ( 2 ) 43 pairs of nerves branching off the brain and cord, (3) autonomic ganglia and nerve fibers, and (4) the sense organs. What we usually call “conscious” or voluntary behavior in man seems to depend upon the functioning of the cerebral cortex and will be discussed in more detail in the next chapter. Involuntary reactions like breathing and heartbeat are regu¬ lated largely through the autonomic system. Your Biology Vocabulary Make sure that you understand and can use these terms correctly. pituitary gland testosterone blood platelets ductless or endocrine "lands O prolactin blood serum insulin central nervous system fibrinogen adrenalin autonomic nervous system: fibrin thyroxin sympathetic thrombin thyrotropic hormone parasympathetic agglutinin adrenal "lands O autonomic ganglia agglutination cortisone Selye’s alarm-reaction theory acetylcholine ACTH gonads cerebral cortex secretin Rh factor thyroid estrogens basal metabolism test parathyroid Testing Your Conclusions Here is a list of some of the structures and substances which contribute to the self¬ regulation and self-adjustment of the human body. Copy the list, and beside the name of each structure or substance state briefly something it does which helps body regula¬ tion or adjustment. Example: enzyme from blood platelets: It initiates clot formation. 1. insulin 2. thyroxin 3. adrenalin 4. acetylcholine 5. sensory nerve fibers 6. motor nerve fibers 7. bone marrow 8. hemoglobin 9. thrombin 10. fibrin 11. agglutinins 12. spleen 13. liver 14. sweat glands 15. ACTH 16. prolactin 17. cranial nerves 18. spinal nerves 19. sympathin 20. vagus nerve impulses to heart More Explorations 1. Clotting time. (Optional.) You can easily determine your own clotting time, hut first get your parents’ and teacher’s permission, and remember to follow directions care¬ fully, to make sure no infection results when you prick a finger (see page 34). Scrub your finger thoroughly with ethyl alcohol, then prick it with a needle that has been 398 THE HUMAN BODY thoroughly cleaned with sterile gauze soaked with alcohol. Place a drop of blood on a clean microscope slide and note the time to the second, using a watch with a second hand. After a minute or two, try to pick up the blood with a needle. Repeat until the needle picks up a visible thread of fibrin, and once more note the time. How long did it take your blood to clot? That is your clotting time. 2. Blood typing. (To be done only under careful supervision.) It is easy to determine your own blood type, if your parents and teacher are willing. You will need clean toothpicks, sterile gauze or cotton, a clean microscope slide, a clean needle, and some 70-per-cent ethyl alcohol. Your teacher will need two bottles of human blood serum, one from a person with type A blood and the other from a person with type B blood. Blood typing serums are available at some biolog¬ ical supply houses and from American Hospital Supply Corporation, 40-05 128th Street, Flushing, N.Y., or 2020 Ridge Avenue, Evanston, Ill. a. With a wax pencil, draw a line across the middle of a clean microscope slide. Lay the slide on a sheet of paper. Write anti-A below one half of the slide and anti-B below the other half. b. Put a drop of B serum which contains the anti-A factor in the space above anti-A on your slide. In the space above anti-B, put a drop of A serum which contains the anti-B factor. c. With sterile cotton or gauze pad soaked with ethyl alcohol, scrub the end of the third finger on your left hand and wipe the needle thoroughly. Puncture the end of your finger and squeeze out a drop of blood (see cautions on page 34). d. With one end of a clean toothpick, pick up a bit of blood and stir it into the anti-A serum. With the other end of the toothpick, add a little blood to the anti-B serum and stir it in. e. Watch the slide for a little while— perhaps two minutes. You may or may not see agglutination (clumping) of red cells in either or both drops of blood serum. f. Compare your slide with Figure 14-8 to discover what your blood type is. Thought Problems 1. The insulin used by diabetics is manufactured from the pancreases of animals killed in slaughterhouses. These pancreases must be treated at once to inactivate the pan¬ creatic juice. Why is this necessary? Hint: Pancreatic juice contains trypsin. 2. The breathing center is located in the medulla. Carbon dioxide in the blood stimu¬ lates the breathing center. Can you use this fact to help explain why a basketball player breathes rapidly during a game? Further Reading Prepare a report on one of these noted scientists: Frederick Banting (insulin); Walter B. Cannon (adrenalin and emergencies). Here are some references: 1. The Wisdom of the Body by Walter B. Cannon, Norton, 1932, and Cannon’s auto¬ biography, The Way of an Investigator , Norton, 1945, include discussions of adrena¬ lin, as well as many other topics discussed in this chapter. 2. Living Biographies of Great Scientists by Henry Thomas and Dana Lee Thomas, Garden Citv Publishing Co., 1941, contains a chapter on Dr. Frederick Banting. Banting’s Miracle by Seale Harris, Lippincott, 1946, is a biography ol Dr. Banting. INTERNAL REGULATION AND CO-ORDINATION 399 CHAPTER Human Behavior and the Nervous System Standing on a slack rope , Mr. Dieter Tasso , star of ti Hi ogling Brothers - Barnu m and Bailey Circus , has already tossed and caught on his head eight saucers and seven cups. The eighth cup is on its way up. What makes such complex skills possible? European Skill on the slack rope The skill of a Dieter Tasso calls for well-nigh perfect co-ordination of the body to external stimuli. Such co-ordi¬ nation and control come only with long and grueling practice, years and years of it. There is a constant play of external stimuli upon the sense organs of the body. These stimuli initiate nerve im¬ pulses which in turn initiate and co¬ ordinate responses of the body. Look again at the picture of Dieter Tasso. How many external stimuli can you mention that are “playing upon his nervous system”? What are some of his responses to those stimuli? Obviously, light reflected from the eighth cup is stimulating Mr. Tasso’s eyes and he is responding in ways that will let that eighth cup arrive on top of the pile on his head. As you already know, this re¬ markable example of human behavior is centered in Mr. Tasso’s nervous svs- J tern, just as more common aspects of his behavior are. In this chapter, you will explore the role of the nervous system in some of the phases of human behavior relating to the constant reactions and adjust¬ ments of the body to external condi¬ tions— that is, to the environment. THE SENSE ORGANS Your sense organs put you in touch with the outside world. If you could not see or hear or smell or taste or feel or in any way sense anything, you would know nothing at all about the world around you. But you do have sense organs, and they do put you in touch with your environment. 400 THE HUMAN BODY Your sense organs contain nerve tis¬ sues that are sensitive to external stim¬ uli. These sensitive nerve tissues in your sense organs receive stimulation from outside your body; hence they are often called the receptors of the nerv¬ ous system. You have receptors that are sensitive to light waves and sound waves, odors and flavors (chemical stimuli), temperature, pressure or touch, and other stimuli. The receptors that are sensitive to light waves are in the eye, the sense organ we shall con¬ sider first. The human eye The light-sensitive receptors in the eye are specialized neurons located in the retina ( ret ih nuh ) that lines all but the front part of the eyeball (Fig¬ ure 15-1). There are two kinds of light- sensitive neurons in the retina, the rods and the cones. The cones are sensitive to colors (cones and colors start with c), the rods only to white light. The rods do not function well unless plenty of vitamin A is present in the retina. The rods and cones are the real light receptors. The other parts of the eye play a secondary role. Impulses resulting from the stimula¬ tion of the rods and cones by light travel into dendrites in the optic nerve and then to “seeing centers” in the cerebrum. The lens of the eye (Figure 15-1), aided by its ring of muscle, serves the same purpose as the lens of a camera —it is the focusing apparatus. You know that the lens of a movie projector fo¬ cuses the picture on the screen. The distance of the lens from the screen determines whether the image is clear or not. In a normal eye, the lens fo¬ cuses an image directly upon the retina. In farsighted persons the lens focuses the image back of the retina, and in nearsighted persons the lens focuses the image in front of the retina. Both defects can be corrected with artificial lenses of glass. The iris ( eye riss ) , shown cut across in Figure 15-1, is a circular dia¬ phragm, open in the center, which en¬ larges or contracts in response to the varying brightness of the light, thus regulating the amount of light that strikes the retina. The pupil is the open¬ ing which admits the light. The humors are very clear liquids which keep the eyeball distended. The choroid (koh royd) coat, like the black lining of a camera, keeps out all light except that coming through the pupil. The sclerotic 15-1 DIAGRAM OF THE HUMAN EYE Note that the image of the pencil (not drawn to scale) is upside down on the retina. This is normal. Eyeglasses have been made that put images right side up on the retina. To an adult who first wears these glasses, every¬ thing looks upside down, but in due time will seem once more to be right side up. Retina Vitreous humor Bone of skull Semicircular canals Cochlea Auditory nerve 15-2 DIAGRAM OF THE HUMAN EAR The true sense organs of the ear are the cochlea (hearing) and the semicircular canals (sense of balance). All other ear parts play a sup¬ porting role to hearing. These other parts transmit sound waves to the cochlea or, in the case of the Eustachian tubes, equalize air pressure on both sides of the ear drum. Often you can feel a change in your ears when ascending or descending in an elevator. (skier ox ik ) coat is the tough white outer covering of the eyeball. It helps to protect the eye. The “bulge” on the front of the eye is covered by the clear cornea (KORneeuh). When you read or hear about “eye transplants,” remem¬ ber it is the cornea that is removed from an eye and transplanted to the eye of another person. Right now, light reflected from this page is stimulating the retinas in your eyes. Impulses are traveling from your retinas to the sight centers in your cere¬ bral cortex. If you are reading aloud, nerve impulses are also moving through your cortex to speech centers and on to your lips, tongue, and vocal cords. These are some of the almost innumer¬ able responses you may make to light stimuli. How many others can you name? (Hint: Name things you could not do, or know, if you were blind. ) The human ear The human ear is a complex struc¬ ture with many parts. Study Figure 15-2 as you read on. The outer ear is familiar to vou. The eardrum is a mem¬ brane stretched across the ear canal. In the middle ear there are three small bones, often called the hammer, the anvil, and the stirrup, because of their shapes. (See Figure 15-2.) The hammer is in contact with the eardrum, and the stirrup touches a membrane stretched across the opening into one part of the inner ear. A hollow Eustachian tube connects the middle ear with the 402 THE HUMAN BODY throat, thus allowing air to enter and to keep the air pressure about equal on either side of the eardrum. When a per¬ son has a cold, the Eustachian tubes are likely to swell, and thus to be par¬ tially closed. The inner ear consists of two parts: the cochlea ( kok lee uh ) and the semi¬ circular canals (Figure 15-2). The cochlea is a hollow bony canal, so coiled that it resembles a snail shell. It is filled with a liquid. The receptors that are sensitive to sound vibrations are lo¬ cated in the cochlea. These receptors are the outer endings of one branch of the auditory nerve, which connects the inner ear with the brain. Sound waves in the air are “caught” O by the outer ear and pass in through the ear canal to the eardrum. The vi¬ brations of the eardrum pass through the hammer, anvil, and stirrup to the membrane at the opening into the coch¬ lea, and thence into the liquid within the cochlea. In the cochlea, the audi¬ tory nerve endings are stimulated, thus starting the impulse along the auditory nerve to the hearing center in the brain. The impulses that reach the cerebrum by way of the auditory nerves enable people to hear. And hearing plays a major role in human behavior. The balance organs The sense organs of balance are lo¬ cated in the semicircular canals of the inner ear (Figure 15-2). Here there are three canals ( in each inner ear) which are sensitive to changes in the position of the head. Each canal is filled with liquid. When a person is dizzv or seasick, the sensation is caused by a disturbance in the liquid in these semicircular canals. Nerve endings in your muscles also serve as receptors to stimuli, which set up nerve impulses that travel to the cerebellum. These impulses from mus¬ cles, along with those from the semi¬ circular canals, are co-ordinated in the cerebellum, with the result that we are able to keep our balance. Dieter Tasso’s skill on the slack rope is dependent to a large extent upon his sense organs of balance and the co-ordination in his cerebellum (and cerebrum) of nerve impulses from these sense organs. The chemical senses Taste and smell are spoken of as the chemical senses. On your tongue there are four kinds of sensory nerve endings, called taste buds (Figure 15-3), which are the receptors of flavors. Certain of these nerve endings are sensitive to salt, others to sweet, others to sour, and still others to bitter stimuli. Strangely enough, it is not the taste of the onions, but their smell, that gives you the greater part of your particular reac¬ tions to them. 15-3 DIAGRAM OF A TASTE BUD The darkened cells in the taste hud are sensi¬ tive to one or another of the four taste stimuli: salty, sweet, sour, or hitter sub¬ stances. Such substances must he in solu¬ tion to enter the taste pore of the hud. Taste pore with hairlets Supporting Sensory Nl_ Nerve cell cell Fibers \ > Epidermis ✓ Dermis Nerve 15-4 DIAGRAM OF SENSE ORGANS IN THE SKIN What people usually call the sense of feeling is actually not a single sense. Some end organs in the skin are sensitive to pain¬ ful stimuli, others to hot or cold stimuli, and still others to pressure or touch. TESTING YOUR TASTE BUDS. You will need bits of raw onion and apple, tooth¬ picks, and a blindfold. Work with a partner. While one of you is blindfolded and holds his nose, the other will use toothpicks to place, one after an¬ other, bits of onion and apple on your tongue. Tell him which bit each one seems to you to be, onion or apple. He will "keep score" on your answers. Reverse the situation and keep score on the other partner. Finally, without being blindfolded or holding your nose, put a bit of onion, then one of apple in your mouth. In your record book, tell what you learned from these tests. You have no receptors in your tongue sensitive to the peculiar onion stimulus. Onions do give off a gas which stimu¬ lates receptors in the lining of the nos¬ trils. Many other substances also stimu- late these receptors, but to do so they must be in a form that can be inhaled with the air. The end organs both in the tongue and in the nostrils are con- nected with the brain by nerve fibers. Receptors in the skin What you have learned to call the sense of feeling (touch) is due to the combined action of several receptors. In the skin all over the body are various kinds of nerve end organs (Figure 15- 4). Some are sensitive only to pressure, others to pain, and others to tempera¬ ture (heat and cold). These receptors connect with the central nervous sys¬ tem through sensory nerve fibers, over which impulses travel. Bv means of the stimulation of these receptors, we are able to “feel,” as we say. Summing up: the sense organs Your sense organs put you in touch with your surroundings. The eye is so built that it exposes the rods and cones of the retina to light stimuli. Taste buds are so built that thev ex- pose taste receptors to chemical stim¬ uli, to four of which thev are sensitive: sour, sweet, saltv, and bitter substances. Nerve end organs in the nostrils are sensitive to manv chemical stimuli J which reach them in the air you inhale. 404 THE HUMAN BODY The nerve end organs that enable you to hear sounds are located in the cochlea of the inner ear. The end or¬ gans having to do with keeping your balance are located in the semicircular canals and in your muscles. In the skin all over the body are re¬ ceptors, some sensitive to pressure, oth¬ ers to pain, still others to temperature. The sense organs play an important part in human behavior, in that they make it possible for external stimuli to act upon the nervous system. INBORN AND CONDITIONED RESPONSES The play of external stimuli on the receptors in our sense organs is only the first step toward responses that enable us to react to things around us. Inborn and conditioned responses also play a part in human behavior, even as they do in the behavior of other vertebrates. External stimuli start nerve impulses along nerve pathways. The nerve im¬ pulses may travel over inborn reflex arcs (Figure 11-14, page 322) and re¬ sult in inborn responses. Or the nerve impulses may travel over nerve path¬ ways formed after birth and result in co n cl ition eel responses. This is not to say that all nerve im¬ pulses coming in from the receptors travel over simple, direct nerve path¬ ways and result in specific responses, either inborn or conditioned. As you will soon learn, nerve impulses may fol¬ low complex and generalized nerve pathways, too. But for now we are con¬ sidering inborn and conditioned re¬ sponses (reflexes) only. Inborn responses Usually with its first breath, a new¬ born baby cries. This first cry is an in¬ born response. The nerve pathways in¬ volved are already “hooked up" and ready to function at birth (Figure 15-5). The same is true of the nerve pathways involved in sucking and swal¬ lowing, sneezing and yawning, blink¬ ing, salivating, coughing, stretching, and breathing. One student of the be¬ havior of young infants has listed a to¬ tal of 66 responses that are inborn in human beings. Can you name several that have not already been used as ex¬ amples? Inborn responses constitute a goodly share of the reactions of a young infant to his environment. And they function in your behavior and in that of all hu¬ man beings of all ages. Pepper in your nose makes you sneeze. Bright light makes the pupils of your eyes con¬ tract. These are inborn responses. 15-5 INBORN BEHAVIOR This infant did not have to learn to cry. She probably cried after drawing her first breath. Black Star HUMAN BEHAVIOR AND THE NERVOUS SYSTEM 405 TESTING AN INBORN RESPONSE. Work with a partner. You will need a flashlight. Find an area (away from a window) where illumination is poor. Note the size of the pupils in your partner's eyes. Now shine the flashlight in his eyes for about 30 seconds, and again note the size of his pupils. Turn off the flashlight, wait two minutes, and once again note the size of his pupils. Reverse positions while your partner tests your responses to bright light. In your record book, tell what you did and what responses took place. Conditioned responses Almost as soon as they are born, hu¬ man infants start building conditioned responses into their behavior. Take the responses of a bottle-fed baby to the feeding bottle, for example. The first time the bottle is given to the baby, he shows only inborn responses to the nip¬ ple in his mouth— he sucks and swal¬ lows. Gradually the baby’s behavior to¬ ward the bottle changes. Before long, the mere sight of the bottle makes him respond in new ways. He may throw his arms about, kick, and even smile or laugh. We say he has learned that the “bottle” means “food.” In time, he “learns” to reach up, take the bottle in his hands, and hold it to his mouth. Then the inborn responses— sucking and swallowing— occur. Obviously the external stimulus, the bottle, now calls forth new responses. He has developed conditioned responses toward a bottle. All biologists agree today that ac¬ quiring conditioned responses plays a part in human learning. So you will be interested in the researches that first led to an understanding of how condi- tioned responses may develop. These researches were carried out by a Rus- sian physiologist, Ivan Pavlov ( pah vluf), who lived from 1849 to 1936. Pavlov's experiments on dogs Pavlov (Figure 15-6) had been ex¬ perimenting on digestion in dogs. In the course of his investigations he had become interested in the way the sight of food could make a dog s mouth wa¬ ter. In fact, he had become so inter¬ ested that in 1900 he turned away from the study of digestion in dogs, and be¬ gan a series of experiments on their behavior. Pavlov knew that dogs, like many other animals, have an inborn response in which food is the stimulus and sa¬ liva flow is the response. He wanted to find out whether this response could be modified, and if so, how. Pavlov set up experiments to collect his facts. For instance, he placed a dog in a small bare room with nothing in it to distract its attention. When the dog be¬ came quiet, a circular patch of bright light appeared before its eyes, and after a few seconds a plate of food was lowered on a string from a concealed 15-6 IVAN PAVLOV Pavlov conducted and directed researches on dog behavior from 1900 until his death in 1936. He demonstrated how dogs develop condi¬ tioned reflexes, or conditioned responses as we now call them. Science Service 406 THE HUMAN BODY position. The dog sniffed and ate, and when it had finished, the plate was re¬ moved by the string. After a suitable time had elapsed for the dog to be¬ come hungry again, the circular spot of bright light was again flashed and the plate of food lowered. The response was the same as before. This procedure was repeated several times, and as Pavlov watched his dog through a peephole, he saw that its behavior began to O change after a number of repetitions of the procedure. At first the dog made no response at all to the light, but did show the inborn responses to the food. After a few experiences of having the light followed by food, the dog’s saliva began to flow as soon as the light ap¬ peared! Then Pavlov again made the light appear before the dog, but did not lower any food. The dog salivated as much as if food were present. Pavlov and his assistants repeated similar experiments hundreds of times, using many kinds of stimuli, such as the ringing of a bell, the ticking of a met¬ ronome, or the lowering of a white square. They used innumerable dogs, and always, in each dog, there came a time when the bell, or the ticking, or the white square made the dog’s saliva flow (and produced the typical food- expectation behavior), even when no food was there. Pavlov's conclusions When Pavlov had gathered his facts, he was in a position to draw conclu¬ sions from them. The facts explain how a dog’s inborn behavior can be changed by experience. A new stimu¬ lus, such as a circle of light, if presented often enough along with food, causes all the responses originally caused only by the food itself. The logical conclu¬ sion was that a new stimulus will, in Science Service 15-7 CONDITIONED CHANGES IN BEHAV¬ IOR A white rat, a kitten, and a dog have learned to share food. Is this natural to animals that have not been conditioned? time, induce a conditioned response, if the new stimulus is presented repeat¬ edly along with the original stimulus. Animals vary a great deal in their capacity to develop conditioned re¬ sponses. Pavlov’s dogs varied individu¬ ally in this capacity. Some dogs were conditioned after a few trials; others required many repetitions. Some dogs were also easily deconditioned by be¬ ing presented repeatedly with the new stimulus but no food; others were not. Each animal’s individual make-up plays an important part in determining how much its behavior can be changed by conditioning (Figure 15-7). Among all the animal phyla, only the vertebrates show much capacity for de¬ veloping conditioned responses ( al¬ though certain lower animals can be conditioned in some ways ) . Of the ver¬ tebrates, fish show the least of this ca¬ pacity and mammals the most. Man far surpasses all other vertebrates in this respect. Conditioned responses in human beings You can probably think of dozens of conditioned responses you have ac¬ quired since you were born. How do HUMAN BEHAVIOR AND THE NERVOUS SYSTEM 407 you acquire conditioned responses? Two types of experimental studies will help to answer that question. One has to do with the feeding reflexes, the other with reflexes that cause the pupils of the eyes to change size. One researcher used chocolate in the mouth of a child as the original stimu¬ lus, and the rate of swallowing as the measure of the flow of saliva in re¬ sponse to the chocolate. Just as the chocolate was placed in the child’s mouth, the investigator put a bandage over the eyes of the child. After eight or nine repetitions with normal chil¬ dren, the saliva flowed in response to the eye bandage, without the presence of any chocolate. The same procedure with several feeble-minded children proved that with them many more repe¬ titions were necessary than with normal children to develop the conditioned re¬ sponse to the bandage over the eyes. Several experimental studies of the reactions of the pupil of the eye to light have been made. The pupil of the eye contracts in bright light, and enlarges in dim light. This is an inborn response. The ringing of a bell normally does not produce any change in the size of the pupil. One investigator rang a bell and at the same time reduced the light in a room where the subject of the experi¬ ment was sitting. The pupil of the eye enlarged but the individual was un¬ aware of the fact. This procedure was repeated until presently the ringing of the bell caused the pupil to enlarge, even though the light was not dimmed. The subject of the experiment did not know that his eye responses had oc¬ curred at all. Apparently you can de¬ velop conditioned responses without even knowing it. These and many more experimental studies show that human beings build many conditioned responses into their behavior in much the same way that Pavlov’s dogs did; that is, by associat¬ ing a new stimulus over and over again with an old one. LISTING CONDITIONED RESPONSES. Conditioned responses play a part in your behavior every day. Can you recognize some of your own conditioned responses? For example, how many stimuli besides food in your mouth make you salivate? Does the word "lemon" make your saliva flow? If so, start your list of some of your own conditioned responses with: "The word lemon makes me salivate." List as many more of your own conditioned re¬ sponses as you can. Use a fresh page in your record book and title it Some of My Conditioned Responses. Generalized responses The behavior of young infants is not limited strictly to inborn and newly developed conditioned responses. Ba¬ bies (and everyone else) continue to meet new situations, to which they are not yet conditioned or accustomed. To some new stimuli, a baby makes gen¬ eralized responses involving most of his body. Have you ever watched a baby re¬ spond to a brightly colored rattle the first time he sees it? If he is a few weeks old, he may squeal, kick and squirm, throw his arms about, wrinkle his face, and even laugh aloud. The new stimu¬ lus, a rattle, induces generalized re¬ sponses, not one or more specific re¬ sponses the way food in the mouth does. Light and perhaps sound waves from the rattle stimulate eye and ear recep¬ tors, starting impulses inward along sen¬ sory nerve pathways. When these im¬ pulses reach sensory centers in the 408 THE HUMAN BODY cerebrum, they pass on into many motor pathways— to the arms and legs and face and voice box— and induce responses all over the body. The baby has no inborn nerve pathways already “hooked up” and ready to function at the sight of the rattle. So the nerve impulses travel on through many motor pathways. In time, the baby learns to reach out and take the rattle in his hand. His generalized responses have now changed to a particular, specific re¬ sponse. Sensory pathways from the eyes have been “hooked up” with motor pathways to the arm and hand. A child continues to make general¬ ized responses to new stimuli as he grows older. Out of his generalized responses, specific responses gradually develop (Figure 15-8). When he learns to walk, he “gets into everything.” He walks or runs everywhere, climbs up 15-8 LEARNING TO WALK Gradually the waste motions of generalized responses are being eliminated; specific responses are emerging. Tana Hoban, from Rapho-Guillumette on anything he can, opens drawers and pulls everything out of them. He tends to reach for and take hold of anything he can find, such as knives, pans, spools of thread, blocks, candy, cats, dogs, grasshoppers, worms, matches— every¬ thing, even fire. This way of responding to anything and everything in the en¬ vironment involves such specialized ac¬ tivities as grasping and walking. And yet it seems to grow out of the inborn capacity for generalized reactions. Emotional behavior Still one more type of infant behavior must be mentioned. This is emotional behavior. When we observe emotional behavior in an infant, we say that he is angry or frightened or excited or happy. People usually call anger, fear, excite¬ ment, and joy emotions, as though they were specific entities, separate and apart from a person in which they are observed. To a biologist, emotional be¬ havior is a more meaningful term, since we can observe it in, and as a part of, another human being ( while we cannot observe an emotion as a separate en¬ tity). Babies are born with a capacity for emotional behavior. A sudden loud noise stimulates generalized emotional responses in most babies. They may scream and turn red in the face and breathe faster, or even “hold the breath until blue in the face.” A sudden fall or a complete restraint of movement in¬ duces similar emotional responses in many infants. Patting, cuddling, or rock¬ ing a baby often induces what we usu¬ ally call pleasure reactions. Emotional behavior involves general¬ ized muscular responses. It also in¬ volves disturbances in the functioning of such vital processes as heartbeat, breathing, and peristalsis. Hormones, 409 such as adrenalin, play a part in fear and anger responses, and the autonomic nervous system plays a part in changes in breathing, heartbeat, and peristalsis. In other words, the emotional be¬ havior we can observe directly is re¬ lated to the functioning of internal regu- lating systems, as well as to the whole nervous system. Our emotional behavior, like all phases of human behavior, changes in many ways as we grow up. An infant shows no fear of, say, a rattlesnake, but he can “learn to fear” it and many other things. An infant shows no pleasure at the sight of a colorful sunset. But peo¬ ple “learn to enjoy” sunsets and many, many more things. J O You may or may not want to call the J J changing of generalized responses to specific ones, or the “learning” of emo¬ tional responses to new stimuli, exam¬ ples of conditioned responses. Some biologists do. Others do not. The latter restrict the use of the term “condi¬ tioned response” to such specific acts as salivating in response to a bandage over the eyes or contracting the pupils of the eyes at the sound of a bell. It doesn’t much matter to vou which J way different biologists use the term “conditioned responses.” What is im¬ portant is that human beings do learn to make new types of responses all through childhood and early adult life and, to some extent, as long as thev live. A STUDY OF EMOTIONAL RESPONSES. Title a page in your record book Stimuli That Induce Emotional Responses. On this page, list stimuli that you know induce emo¬ tional behavior, in yourself or in other people you know. Include stimuli that in¬ duce pleasure responses as well as stimuli that induce fear, anger, worry, or excited responses. You might begin with this example: "A well-prepared and well-served meal in¬ duces pleasure responses/' Nerve pathways and conditioned responses An inborn response, such as salivat¬ ing when food is in the mouth, is pos¬ sible because some nerve pathways are already “hooked up” and ready to func¬ tion at birth. A conditioned response, such as salivating at the sight of the feeding bottle, is possible because some new neurons have been “hooked up with some of those in the inborn path¬ way. How does a “new line” of sensory neurons get “hooked up” with the “old line” to the salivary glands? Research¬ ers have found what mav be at least a J partial answer to that question. You may remember that the axon of one neuron is not continuous with the dendrite of the next neuron in a nerve pathway. The point at which the end of an axon is in contact or near-contact with the end of a dendrite is a synapse, as you know (page 321). Researchers have learned that an impulse is accom¬ panied by, and partly consists of, an electrical charge, and that chemical O 7 changes take place in a synapse when an impulse crosses it. It has been defi¬ nitely established that molecules of either acetylcholine or of an adrenalin¬ like substance appear at the synapses in the autonomic system, when impulses cross those synapses. There is evidence that the same or similar chemical changes occur when nerve impulses cross any synapses anywhere in the nervous system. Inborn nerve pathways probably function partly because the necessary chemical changes in their synapses oc¬ cur readily from birth onward. If this is true, then new nerve pathways are 410 THE HUMAN BODY set up when the necessary chemical changes in their synapses gradually come to occur readily when nerve im¬ pulses reach them. How do synapses reach the stage at which the necessary chemical changes occur readily? It would seem that the repeated passage of nerve impulses across new synapses gradually brings about this change. The more often nerve impulses cross new synapses, the more readily will they cross these new synapses again. In time, the new syn¬ apses transmit impulses as readily as synapses in inborn pathways do. It seems reasonable to believe that an impulse, partly electrical in nature, would have trouble crossing a synapse unless some chemical connection could be made at that point, between two neurons. So in the evidence of the chemical changes that take place at synapses we may have a partial expla¬ nation of how we form new nerve pathways, including those that func¬ tion in conditioned responses. Reaction time You have probably heard people speak of reaction time. Do you know what this term means? Suppose you prick your finger. An impulse is started along the sensory neuron. It travels along this “one-way street’' until it reaches the cell body in the ganglion on the sensory root of the spinal nerve. Next it passes along the axon away from the cell body and across a synapse into associative neurons in the spinal cord, and then onward across other synapses, one of which leads into a motor neuron which transmits the im¬ pulse to the muscles that jerk your hand back (Figure 15-9). It actually takes some time for the impulse to travel over this reflex arc, but the time required is only a fraction of a second. Notice in Figure 15-9 that the stimulus of a pain¬ ful finger prick has induced nerve im¬ pulses which have traveled over nerve pathways and in turn induced several responses. What are the responses? Our fastest nerve impulses travel at 15-9 RESPONSES TO A PAINFUL STIMULUS When you prick your finger, you jerk away before you make other responses. The reflex pathway from finger to spinal cord and back to arm muscle is shorter than reflex pathways from the finger to the cerebrum to other muscles. (The question mark placed in the association area of the brain denotes lack of exact knowledge as to the complexity of reflex pathways in the brain. ) Muscles Face muscles Association area of brain Sensory receiving terminals Lip muscles Associative neurons Spinai cord Sensory root of spina nerve Motor root of spinal nerve an average speed of some 225 miles an hour, our slowest at an average of only about Mo of a mile per hour. Even so, it does require a little time for you to re¬ act to any stimulus. The time required is spoken of as your reaction time. Machines have been devised that en¬ able an experimenter to measure accu¬ rately a person’s reaction time to many different kinds of stimuli. Several in¬ vestigators have made innumerable tests. These show that reaction times of different persons differ considerably; indeed, an individual’s reaction time will vary from one time to another. Tests show, too, that it takes longer to react to heat and pain stimuli and to tastes and odors, than it does to stimuli of sounds, light, and touch. Reaction times are measured in thousandths of a second, as Table 15-A shows. Habits and skills Habits and skills resemble condi¬ tioned responses in that they are not inborn. They also result from the build¬ ing of new pathways through the nerv¬ ous system. Most biologists seem to agree that habits and skills are usually complex behavior patterns (skills always are complex), while conditioned responses are simpler, specific responses. For ex¬ ample, salivating when you see a pic¬ ture of a roast beef is a simple, condi¬ tioned response. On the other hand, writing (a skill) is a complex behavior pattern of responses to paper and pencil and other stimuli. Undoubtedly, condi¬ tioned responses enter into the forma¬ tion of habits and skills. Probably there is no hard-and-fast dividing line be¬ tween conditioned responses and habits or skills. No one knows just which parts of our learned behavior are simple, conditioned responses, and which are TABLE 15-A AVERAGE REACTION TIMES FOR ADULT HUMANS Type of stimulus Reaction time (in thousandths of a second) Sound 120 to 180 Light 150 to 225 Touch 130 to 185 not. But any complex behavior pattern that had to be learned by repeated practice is a habit or skill. A TEST OF WRITING SKILLS. Work with a partner to make this test. Let him time you while you write your name ten times. Then let him time you while you again write your name ten times, but with the other hand. Reverse your roles and time your partner while he does the same two things. In your record book, record the time it took you to write your name ten times with the hand you usually use and then with the other hand. Then answer these questions. 1. Why does it take so much longer to write your name ten times with one hand than with the other? 2. How would you go about developing equal speed with the other hand? 3. How much time did you save with the "trained hand" as compared with the "un¬ trained hand"? 4. What other skills or habits do you have that save much time every day? One example might be the habit of "tying a shoe lace." (Watch a child trying to form this habit to get some idea of the time saved.) List at least ten more examples. Habits are to a large extent auto¬ matic and somewhat fixed behavior patterns, but they can be changed. They can even be eliminated. Skills are usually defined as more complex and less fixed than habits. Writing and 412 THE HUMAN BODY playing the piano may be called skills; tying your shoe laces may be called a habit. But there is no hard-and-fast distinction between habits and skills. Repetition is a major factor in the formation of both habits and skills. “Practice makes perfect” is an old, old saying that still applies. Can you ex¬ plain why? Realization of the need, or having the desire, to form a particular habit or skill is said to facilitate its formation. Most of you can probably form good driving habits more quickly and easily than you can learn to read Latin well, because you feel the need to learn to drive well but may not feel a need to learn to read Latin readily. This brings us directly to the role of motivation in human behavior, and especially in learning. So we shall next explore some biological aspects of motivation. Summing up: inborn and conditioned responses Both inborn and conditioned re¬ sponses play a part in human behavior. Human beings, like other vertebrates, develop conditioned responses when a new stimulus, such as the sight of a feeding bottle, is associated over and over again with another stimulus, such as food in the mouth, which is already effective in producing an inborn re¬ sponse. Generalized responses to new stimuli and emotional responses to a few stim¬ uli are observable in infants. We gradu- allv develop specific responses to stim¬ uli that originally induced generalized ones. And new stimuli can induce emo¬ tional behavior as we grow up. At synapses in nerve pathways, the secretion of acetylcholine or adrenalin molecules probably enables nerve im¬ pulses to cross the synapses, at least in the autonomic system, and perhaps in the whole nervous system. Reaction time is the time required for nerve impulses to travel from re¬ ceptors over nerve pathways and pro¬ duce responses. Reaction times are measured in thousandths of a second. Habits and skills may include condi¬ tioned responses, but are complex be¬ havior patterns rather than simple re¬ sponses. Repetition and motivation (which we shall study next) facilitate the formation of habits and skills. Many habits are time-savers. Habits can be built into behavior, and a specific habit can be “broken” or changed. MOTIVATION IN HUMAN BEHAVIOR You are now ready to consider an¬ other phase of human behavior, a phase that has to do with motivation. Here we shall consider motivation mainly in a biological sense, rather than in a psy¬ chological sense as well. We have a surer footing of research into motives that amount (or almost so) to biologi¬ cal needs that are expressed rather uniformly in all people. Let s start with an example that has to do with hunger as a motive to behavior. An empty stomach and behavior It is almost lunch time. Your stomach is empty. Wave after wave of peristalsis passes over your stomach. These con¬ tractions of your stomach start nerve impulses along nerve pathways to your cerebrum. Soon you may think or say, “I am hungry.” Then you do something about it. You eat your lunch. The con¬ tractions of an empty stomach tend to induce behavior that leads to taking food. HUMAN BEHAVIOH AND THE NERVOUS SYSTEM 413 You might put it this way. Feeling hunger is equivalent to feeling a need for food. The need induces behavior that tends to “satisfy” the need. Even in a newborn baby, an empty stomach induces behavior that tends to lead to feeding. Blood-sugar levels and behavior You may remember that a healthv J j person’s blood-sugar level ranges from about 90 milligrams to about 130 milli¬ grams per 100 cubic centimeters. It is highest shortly after a meal, when it reaches 120 to 130 milligrams. Some two hours later, in most people, the blood-sugar level starts to fall. You can see why. Sugar molecules diffuse out of the blood stream into liver and muscle cells and into all living cells. Some four or five hours after a meal (if you eat nothing in the meantime), your blood- sugar level may fall to 90 milligrams or sometimes less. When the blood-sugar level falls close to 90 milligrams, you “feel hungry.” You eat another meal. More sugar en¬ ters your blood stream. This again raises the blood-sugar level, thus main¬ taining the normal level or the stability of the sugar level in the blood. Then your need for food disappears. Hunger, then, is a felt need for food; it induces behavior that helps to main¬ tain the stability of the body. You have already learned that hormones and the autonomic system play important parts in “keeping your body about the same in the face of constant change.” Hunger and other stimuli also help to maintain the body’s stabilitv in the face of con- stant change. Needs and motivation Our language is full of expressions that refer to what we call human mo¬ tives. We say, “People listen to music because they like it” or “He became a doctor because he wanted to” or "1 can't eat liver because I dont like it. In other words, we use expressions such as “like or “want” or “don’t like” to de¬ scribe people’s motives for what they do. Our language shows that we think motives induce behavior. Undoubtedly they do. But the biologist asks, “What induces motives?” and “What is the na¬ ture of motives?” Biologists can answer these questions in part, but not fully. Biologists agree that behavior is motivated. They agree that biological needs, such as those ex¬ pressed as hunger and thirst, motivate behavior that tends to satisfy the needs. Hunger and thirst motivate behavior that helps to maintain the stability of the bodv. J According to Life, by George Gay¬ lord Simpson et ah, “The most wide¬ spread motivation for behavior is the maintenance of the stability of the body” and, speaking of animal behavior in general, “. . . as a rule, or on an average, it [an animal’s behavior] tends to satisfy an organic need.” * Motivation that stems from a need to maintain the body’s stability is often called a biological drive. Seeking relief from hunger and thirst are familiar ex¬ amples of biological drives. And you do not have to be aware of a “need to maintain the stability of the body” to have certain needs motivate some of your behavior. On the other hand, you are often aware of your motives. You feel hun¬ gry. If you think about it, you know that hunger motivates eating. Feeling sleepy motivates sleeping. Feeling a toothache motivates going to your den- ° See page 247 in Life, already cited on page 49. 414 THE HUMAN BODY tist. In other words, you consciously do things that help to maintain the sta¬ bility of your body. And you also un¬ consciously do many things that serve the same purpose. In your sleep, you shift your position to relieve cramped circulation or difficult breathing. Or, when awake, you may feel restless and uneasy. Perhaps you eat something, and you notice that you are no longer rest¬ less. Possibly you were hungry without realizing it. Biological drives, both con¬ scious and unconscious, lead to behavior that helps to maintain the stability of your body. You are studying biology. Right now you are reading this page. Have you any idea what motivates the reading you are doing right now? Are you read¬ ing because you are conscious of a need to maintain your body’s stability? Of course not. Could such a need make you want to read this page, without your knowing it? It seems most un¬ likely, doesn’t it? And yet, in some way, part of your motivation may be tied up in some indirect way with some of your needs. Are you asking whether all motiva¬ tion is tied to biological needs? Our language is full of expressions that im¬ ply otherwise. “You can do anything you want to, if you want to badly enough” is one example. Expressions like this one imply that “making up your mind” or “wanting badly to do something” will supply the motivation necessary to carry it out. Certainly this conception of motivation would appear to explain, at least partly, why we go to the trouble of acquiring skills other than those necessary to earning a living. According to the dictionary, the study of the mind and its role in behavior is psychology (sy kol uh jee). Many psy¬ chologists, probably most of them, teach 15-10 A CONDITIONED REACTION Spot had been conditioned to assume this posi¬ tion when he heard the sounds, “Sit up.” Does this mean that Spot understands the words “sit up” in the way you do? What could the motivation have been? that some of your motives are psycho¬ logical (derived from the mind), while others are biological ( derived from bio¬ logical needs). For a discussion of cur¬ rent theories about psychological mo¬ tives (Figures 15-10 and 15-11), we can only refer you to psychology itself. We cannot treat psychological motivation, necessarily an individual matter to a large extent, with the same certainty with which we can treat motivation stemming from biological drives. In any case, motivation— psychologi¬ cal or biological or both— plays a basic part in learning processes. Some biolo¬ gists go so far as to say that there is no learning without motivation. We shall explore learning processes in the next section. HUMAN BEHAVIOR AND THE NERVOUS SYSTEM 415 Shoop Photo 15-11 BUILDING SKILLS Linda is gradual¬ ly building skills into her nervous and muscular systems. At age two years, she is a bit awkward with the pencil and ham¬ mer, but practice will eliminate the awk¬ wardness. What do you think motivates her behavior? Summing up: motivation in human behavior Biologists agree that human behavior is motivated, at least in part, by organic needs. You may or may not be aware of the organic needs that motivate some of your behavior. Motivation of some kind— biological or psychological or both— plays a basic part in learning processes. LEARNING PROCESSES AND PROBLEM-SOLVING Human beings begin to learn soon after birth, and they go on learning, at least to some extent, as Ions as they live. Human beings also solve prob¬ lems, many kinds of problems. Solving certain kinds of problems leads to more and more control over the environment. Biologists and everyone else agree that human beings learn many things and solve many problems. But when it comes to questions of how we learn or how we solve problems, we run at once into conflicting theories— disagreements even among specialists in the study of behavior. A lack of agreement even among specialists usually means that no one yet knows exact, scientific an¬ swers to the questions involved. Dis¬ agreement as to how we learn and how we solve problems is no exception. Ex¬ perimental studies of learning and prob¬ lem-solving have been going on for years. Beliable evidence is accumulat¬ ing. But remember, as you read on, that the evidence is interpreted differently by different people, and that the study of human behavior is still young. Animal experiments Experimental studies of learning processes in animals usually involve some system of rewards and punish- 416 THE HUMAN BODY ments. When an animal makes one re¬ sponse, he is rewarded, usually with food. When he makes another response, he is subjected to some punishment, often a mild electric shock. White rats have been widely used in learning experiments, not so much because the investigator is primarily concerned with how rats learn, but because white rats are convenient for use as experimental animals and may provide at least some hints as to how human beings learn. In one such experi¬ ment, a hungry white rat is placed in a cage. If he pushes open one “door,” he finds food— a reward. If he pushes open the other door, he receives a mild elec¬ tric shock— a punishment. The observer keeps an accurate record of how many repetitions are necessary before the hungry rat always pushes open the “door to food,” never the “door to elec¬ tric shock.” Or a hungry rat may be placed in a maze. By following a specific course through the passageways, he comes to a compartment with food in it. The observer keeps a record of each “trial run” and the number of failures until finally one trial leads to the food. Next day, the experiment is repeated. Gradu¬ ally, the “trial runs” decrease in num¬ ber each day. Eventually the hungry rat immediately follows the one and only path to the food, every time. We say he has “learned” how to go straight to the food. (For a more difficult ex¬ periment, see Figure 15-12.) Similar experiments with rats that have just been fed give different re¬ sults. A recently fed rat usually ignores the maze of passageways. He has no motive to find his way to the food. These and hundreds upon hundreds of similar experiments have led to one theory of learning, a theory that goes by the name of trial-and-error. The hungry animal tries one pathway after another. He errs (makes a wrong turn¬ ing) often. But eventually he hits upon the pathway to the food. Next day he hits upon it a little more easily. Even¬ tually he learns the pathway to the food. The trial-and-error theory explains this type of learning as due to trying one thing after another until the ani¬ mal happens to make the responses that lead him to the food or to some other “satisfying” reward. The biological drive we call hunger motivates the rat’s responses. Without motivation (in this case, hunger), the rat usually learns nothing about the way to the food. From these and similar experiments, some general conclusions seem to emerge. Learning, in rats, seems to be motivated. And learning may come about after numerous incorrect trials with an occasional “accidental” correct trial. Rewards (in this case, food) and punishments ( in this case, failure to find food) play a part in learning. Re¬ wards, in these experiments, satisfy a biological need to maintain the stabil¬ ity of the body. Punishments do not, but they do seem to reinforce the bio¬ logical drive toward food-finding and thus to facilitate learning. Do these generalizations also apply to human behavior? Do you learn by trial-and-error? Do rewards and pun¬ ishments affect your learning rate? Do biological drives motivate your learn¬ ing, or at least some of it? Most stu¬ dents of human behavior would answer all these questions in the affirmative, but would go on to say that, of course, there is more than that involved in human learning. An experiment with chimpanzees may help you to under¬ stand a little more about human learn¬ ing. HUMAN BEHAVIOR AND THE NERVOUS SYSTEM 417 15-12 BARNABUS THE RAT In a most difficult maze of four floors (left), Barnabus was trained to: (1) enter at the ground floor, depress a food bar to get a single pellet of food, and climb the circular stairway (top left ) to the second floor; (2) cross a drawbridge and climb a ladder (top right ) to the third floor; (3) pull a “railroad” car to him, pedal it to the end of the line (bottom left), and climb a stairway to the fourth floor; (4) pass through a tunnel, enter the elevator (bottom right), and descend to the first floor again for his reward— a full meal. Barnabus was taught last step first, then next-to-the-last step, and so on. Thus each step learned was followed by a double reward— something he already knew, and a meal. Experiments with chimpanzees Dr. Herbert G. Birch, at the Yerkes Laboratories of Primate Biology at Orange Park, Florida, completed in 1944 an especially interesting series of researches on learning in chimpanzees. In his laboratories, Dr. Birch raised six chimpanzees from the time they were two weeks old. All of them had been born in captivity. He called them Alf, Bard, Ken, Art, Jenny, and Jojo. He let them play every day in a large, fenced yard, containing a tree, sticks, a slide, and other objects. He watched them for hours each day and kept a detailed diary on each chimp. When the chimps were between four and five years old, Dr. Birch set up a problem for them. One at a time, each animal was put in a cage for a half- hour. Outside the cage, beyond its reach, was a banana. Lying not far from the banana but within reach of the animal was a stick, long enough to use in pulling in the banana. Would the chimps look the situation over, as you would, then pick up the stick and pull the banana within reach? That’s what Dr. Birch kept wondering, as he watched one after another animal take its half-hour “test.” Alf, Jenny, Art, and Ken failed the test completely. Then came Jojo’s turn. She stood a second looking at the banana. Then she glanced at the stick. At once she picked up the stick, pulled the banana within reach, and picked it up and ate it. It took just 12 seconds of her half-hour. She passed her test with flying colors. But why? Did she “get the idea”? Had she what people often call insight? Dr. Birch leafed excitedlv through Jojo’s diary. Notations in the diary showed that Jojo had often used a stick in one way or another. On occasions she had reached through her indoor cage with a stick and flicked an electric light switch on and oft. Not another chimp had been seen even to play with a stick. So that was it. What looked like insight in Jojo’s behavior turned out to be memory of past experiences. Would you say she had developed conditioned responses during those past experi¬ ences? Bard was last to take the test. And his test proved most interesting of all. His actions were something like this. He reached for the banana. He “begged Dr. Birch for it. He wandered around the cage. He “begged” some more. Then he tried once more to reach the banana. In doing so, his arm hap¬ pened to hit the nearby stick and move it a few inches. The other end of the stick hit the banana. Bard stared hard for a minute. Then he pushed the stick deliberately and moved the banana. After that he quickly used the stick to pull the banana within reach, picked it up, and ate it. From that day on, Bard was quick to use the stick to get the banana. Would you say that he had gained insight? Many psychologists do say that, and explain this type of learn¬ ing by what they call the goal-insight theory. For further discussion of this 15-13 INTELLIGENCE TEST The chimpan¬ zee is fitting pegs into their correct places. ])(ige 419 theory, we refer you to reference books dealing with psychology itself. Figure 15-13 shows a chimpanzee in another learning situation. In what way do you suppose this chimp arrived at the correct solutions? Human learning How much of what we have learned about learning in other animals applies to human learning? No one yet knows, for sure. Let’s consider one example of human behavior that illustrates one of the big differences between learning in human beings and in other animals. Linda was two and a half years old. She talked unusually well for her age. J O For some months she had used plurals correctly: dogs, books, blocks, and oranges. Then one day she came out of her mother’s room with one stocking. Showing it to her mother, she said “Linda has mummy’s hoe." Puzzled at J first, her mother soon saw what had happened. The child naturally thought that if two stockings are hose, one stocking must be a lioe. Linda’s misuse of the word hoe shows that even a small child can dis¬ cover and use a generalized rule. The rule she had used was “Add the s sound to a word and it means two or more. Take the s sound away and it means just one.” Linda made a generalization and used it. Just what making a generalization and acting upon it involves, as far as the nervous system is concerned, no one knows. But it seems obvious to everv- J one that people do have a far greater ability to make and use generalizations than any other animals have. Another thing seems obvious. Human beings solve problems more quickly when they “get an idea” as to a possible generaliza¬ tion or solution. THE HUMAN BODY Problem-solving Perhaps the ability of a human being to solve problems is his most unique feature and the hardest one to explain. Here “ideas" play a major role. Auto¬ biographies of noted scientists who have spent years in research often give examples of the role of “bright ideas” or “hunches" or “flashes of insight" in problem-solving. In typical cases, these ideas have come to an investigator sud- denlv, but only after months or years of intensive investigation of a problem. Here is one example. Walter B. Cannon, who worked out the emergency theory of adrenalin ( see page 381), says in his autobiography, “Then, one wakeful night, after a con¬ siderable collection of these [bodily] changes had been brought to light, the idea flashed through my mind. . . .” What is a “flash of insight”? How does one occur? No one knows, for sure. One theory is that it comes when a number of “memories,” stored some¬ how in the brain, suddenly connect and fall into a pattern. But exactly how memories are “stored in the brain” or “connected into a pattern” no one knows. People do have “sudden 15-14 TRIAL-AND-ERROR PROBLEM SOLV¬ ING Which key will fit the lock? Will she try them one by one, or will she studv them and eliminate those that are obvious¬ ly not even the right size? Hays, from Monkmeyer 420 Science Service 15-15 A COMPLEX PROBLEM SOLVED The problem: how to replace damaged parts of an artery in the human body. The answer: a nylon Y graft. Solutions to problems such as this one give man increased control over his world— and his life. flashes,” “bright ideas,” or “hunches,” and these do sometimes— but far from always— play a part in problem-solving. Many “hunches” turn out to lead no¬ where, as you know. You should not conclude that scien¬ tists solve problems by “hunches” or "flashes of insight” alone. They often O J follow a step-by-step procedure that g;oes something; like this: 1. They become interested in some problem they have heard or read about or thought up, and from this they “get an idea.” (“Hunches” often help here.) 2. They ask a clear, meaningful ques¬ tion. 3. They read up on what, if anything, has been done in the past to answer the question. 4. They collect all possible facts by observation or experiment, or both. 5. They scan all the assembled facts to see what possible generalizations (answers to the question ) the facts sug¬ gest. They list possible generalizations. (“Hunches” often help here. ) 6. They test what seems like the likeliest generalization first, with more experiments or observations or both. 7. They keep on testing possible gen¬ eralizations until one stands up to all the known facts. 8. They publish the results so others can check and recheck. 9. They revise or discard any gen¬ eralization if new facts require it. As you can see, much of the work of a scientist has to do with testing; an idea, or, better, a generalization. Man surpasses all other animals in many ways. His ability to solve prob¬ lems is one of those ways (Figures 15- human BEHAVIOR AND THE NERVOUS SYSTEM 421 Stanley Rice 15-16 LANGUAGE— THE CHIEF TOOL OF PROGRESS Three students and their biology in- structor are discussing a prominent insect, the grasshopper. How could they possibly share their thoughts and experiences without language? 14 and 15-15). One day he will prob¬ ably solve more fully the problems of his own behavior. Control over the environment Among certain insects, life in the hive or nest is possible because the work of the community is divided among the individuals. The individuals are born with special organs that enable them to do their particular work. Termite sol¬ diers are born with huge jaws. Bee queens are born with well-developed egg-producing organs. Each type of in¬ dividual insect takes its place in the community more or less automatically, because of its inborn make-up. These inborn traits of some insects give them a limited measure of control over the environment. With man it is different. Carpenters aren’t born with saws or hammers as parts of their bodies. And certain lv airplane pilots aren’t born equipped with wings. Babies are not born al¬ ready equipped to do one line of work in human society. They may be born with certain abilities that enable them to learn to do some kinds of work bet¬ ter than others. Physically, man is in many ways in¬ ferior to other animals. He cannot run as fast as a deer. His senses of hearing and smell are inferior to those of the dog, and his eye is far less keen than the eagle's. He is no match for a lion or a tiger in hand-to-claw combat. He can neither fly like a bird nor swim like a fish. He is neither physically adapted to the desert as the camel is, nor to the sea as the whale is, nor to the jungle as tigers are, nor to Arctic regions as rein¬ deer are. He is neither as sure-footed as the Rocky Mountain goat, nor as 422 TIIE HUMAN BODY good a climber as the squirrel. And yet man has a far greater degree of control over his environment than any other organism has. Instead of developing wings, man in¬ vented an airplane. Instead of increas¬ ing his hairy covering in cold climates, he invented all kinds of tools to build warm homes and to make warm cloth¬ ing. In other words, the complex hu¬ man life of today is possible partly be¬ cause of the invention and improvement of tools, not because of inborn special¬ ized body parts. Man invents tools and uses them. With the tool we call a gun, man is the superior of any lion or tiger. With boats man can move about on water, per¬ haps not as well as a fish swims, but very well. With the plow man can dig better than the mole. With climbing spurs the telephone lineman can climb almost as well as a squirrel. With tele¬ scopes and microscopes man can see far better than the eagle. With trains and automobiles and airplanes he can travel much faster than the deer. Tools give man physical superiority over animals to which he is physically inferior. Even so, tools in the hands of one human being would not have placed the species in the position of dominance it now holds. Suppose one man had in¬ vented a bow and arrow, but had found no way to teach other men or his own children to use it. The bow and arrow would have helped that one man, but not his descendants. As soon as that one man died, the bow and arrow would have been lost. The same thing would have happened to any other tool in¬ vented. Human society as we know it could never have developed if an in¬ ventor of a new tool had not been able to teach others, particularly his chil¬ dren, how to make and use that tool. Man developed language, which is an¬ other tool, a special tool used in ex¬ changing ideas. Because of language, a bow and arrow once invented became a part of the social equipment of all those men who learned about it, and of their children and their children’s chil¬ dren (Figure 15-16). Man is indeed the dominant living organism. With each year that passes, he learns more and more about what makes his dominance possible. Yet he has not learned enough to be able to say, “Here is the full, scientific explana¬ tion of human intelligence and human learning.” CHAPTER FIFTEEN: SUMMING UP Your behavior has changed in many ways since you were born. You have acquired many conditioned responses, many habits, and certain skills. You talk and read and write and under¬ stand ideas. You have learned and will go on learning many things. Psychologists do not agree as to the exact nature of the learning process. Many psychologists, but not all, agree that trial-and-error and getting the idea play a part in human learning, with getting the idea, or insight, playing the major role, especially in solving prob¬ lems. Scientific methods get at correct an¬ swers to questions with more certainty than other methods. “Hunches” and “flashes of insight” often seem to plav a role in scientific research, but only after the investigator has accumulated and thought a great deal about many rele¬ vant facts. Even then, a “hunch” is checked and rechecked, with new ex¬ periments and observations, and it is discarded if it doesn’t square with all the facts. HUMAN BEHAVIOR AND THE NERVOUS SYSTEM 423 Your Biology Vocabulary Here are the new terms yon have met in this chapter, plus one or two that you have encountered before. You will surely want to be able to use each one correctly. inborn responses conditioned responses generalized responses emotional behavior motivation biological drive reaction time habits psychology trial-and-error theory of learning J O goal-insight theory of learning Eye Parts retina lens pupil iris cornea sclerotic coat choroid coat optic nerve Ear Parts ear canal eardrum middle ear semicircular canals cochlea hammer, anvil, stirrup Eustachian tube auditory nerve Testing Your Conclusions 1. Using thirst as an example, explain in your own words its motivation of human be¬ havior, in terms of a need to maintain the body’s stability. 2. List at least ten things you have learned through the use of language. 3. 1 ry to think of some experience of your own in which getting an idea affected your behavior. Describe this experience in writing. More Explorations 1. Repetition and learning. Test the value of repetition in this way. Below is a list of terms you met earlier in this course. Which ones do you now use easily? Which ones have you forgotten? Explain the results. Leeuwenhoek pteridophytes neuron tissues chordates cvtoplasm cell respiration ptyalin 2. Advertising and human behavior. Not many years ago, a company that produces table salt used a huge billboard showing a person putting salt on half a grapefruit. The sign read, “It’s better with salt.” Undoubtedly many people put salt on their grapefruit as a result of reading this advertisement. Advertising often affects human behavior. Look for other examples of the way advertisers attempt to influence human be¬ havior. Keep a record of examples and discuss them in class. 424 TIIE HUMAN BODY 3. Solving a puzzle. Use a mechanical puzzle you have, or one you can borrow— a puzzle with blocks and a certain arrangement to be made, or a similar puzzle. Time your¬ self while you solve the puzzle. Did you solve it by trying one thing after another until you had the solution? Or did you solve it by getting an idea and applying it? Let someone else solve the puzzle and compare results. Thought Problems 1 . Less than fifty years ago, physicists considered it proved that, because of the nature of light, no microscope could ever be built that would magnify more than the best lenses on our compound microscopes. Then came the electron microscope with its magnification of 50,000 times and more. The electron microscope uses, not light, but electrons. Physicists at once accepted the new facts and changed their previous ideas to conform with them. If all scientists had stuck to the old idea about micro¬ scopes, would the electron microscope have been discovered? Can you think of any current example in which sticking to an old belief may be blocking a search for new discoveries? 2. A recent investigation shows that people are more prone to ‘‘blow their tops’’ during the hour before mealtime than at any other time of day. Can you fit this fact into the theory that biological needs help motivate at least some human behavior other than that directed toward “satisfaction’’ of these needs? Further Reading L Animal IQ, The Human Side of Animals by Vance Packard, Dial Press, 1950, reports on many experiments on animal learning. This is a fascinating book. 2. Animal Behavior, a new book by John Paul Scott, Univ. of Chicago Press, 1958, is a rewarding adventure into the lives of many animals. 3. The Way of an Investigator, A Scientist’s Experiences in Medical Research by Walter B. Cannon, W. W. Norton, 1945, contains a chapter called “The Role of Hunches.’’ This chapter contains many interesting examples of “hunches” among scientists. See page 62, in particular. 4. The Art of Clear Thinking by Rudolf Fleseh, Harper & Bros., 1951, is almost sure to interest you, particularly Chapters 1, 12, 14, 15, and 17. On pages 126-127, you will find more examples of “hunches,” and on pages 138-148, you may learn “How Not to Rack Your Brain.” 5. The Process of Persuasion by Clyde R. Miller, Crown, 1946, pages 37-60, discusses “Persuasion by Conditioned Reflex.” 6. Educational Psychology by Lee J. Cronbach, Harcourt, Brace, 1954, pages 44-66, discusses several fascinating topics, including oversimplified learning theories (a very good section on the dangers of assuming that learning can be understood too readily), and principles of learning as observed in a typing class. 7. Introduction to Psychology, Second Edition, by Ernest R. Hilgard, Harcourt, Brace, 1957, discusses psychological motivation on pages 127-149, emotions and learning on pages 150-175, and the nature of learning on pages 232-259. HUMAN BEHAVIOR AND THE NERVOUS SYSTEM 425 Dr. Oliver Wendell Holmes was a great physician as well as a noted American poet and humorist. In 1843, before the Boston Society for Medical Improvement, he read a paper on childbed fever, a disease which in those days killed many new mothers within a few days after a child was born. Dr. Holmes cited evidence to show that doctors or midwives carried some invisible "something” on their hands from a childbed fever patient to other new mothers. This was more than forty years before it was proved that germs cause many diseases. Naturally, other doctors did not like to think that they might transmit a deadly disease from one patient to another. Dr. Charles Meigs of Philadelphia led the opposition to Holmes’ suggestion. Meigs cited the noted Dr. Simpson of Edinburgh, Scotland, who was known to be "an eminent gentleman,” but who him¬ self had had cases of childbed fever. Dr. Holmes replied by citing these facts. Dr. Simpson, at one time, helped to do a post-mortem on a woman who had died of childbed fever. His next four childbed patients contracted and died of childbed fever. Dr. Holmes concluded with these words, "As Dr. Simpson is a gentleman, and as a gentleman’s hands are clean, it follows that a gentleman with clean hands may carry the disease.” J / THE FIGHT FOR HEALTH Dr. Holmes was right. It has taken improved microscopic techniques and, in many cases, use of a modem electron microscope to isolate and identify some of the many kinds of microorganisms that cause disease, and that “a gentleman with clean hands” may carry. The photographs on the opposite page and at the top of this page are of disease-producing microorganisms that are invisible unless highly magnified with the aid of a compound or electron microscope ( the microscope being used by the scientist in the photograph at the top of this page is an electron microscope ) . Today, before delivering a baby or starting an operation, doctors scrub their hands thoroughly and put on sterilized surgical gloves, gown, cap, and mask, as you see in the illustration at the bottom of this page. In this unit, you will learn about man’s fight for health and the ways in which he has gained a measure of control over many diseases.. Chapters 16. Diseases and Their Causes 17. Improved Controls over Diseases 18. Health Problems Yet to Be Solved CHAPTER Diseases and Their Causes Louis Pasteur lived in the ‘good old days. He played a leading role in researches that staiied us on our way to the days of better health in which we now live. Pasteur is best known for helping to prove the germ theory of disease , and especially for his treatment to prevent . - ■ V v rabies. "The good old days" You have probably heard some older person speak of the days of his youth as “the good old days.” “The good old days” of a hundred years ago would hardly seem good to anyone, if he had to return to them. Diphtheria and small¬ pox and bowel infections killed little children so fast that hardly a family raised all its children. Many families lost all their children before they were five years old. If diseases of childhood didn’t carry people off as babies, ty¬ phoid fever, yellow fever, tuberculosis, or some other disease was likely to kill them before they were 25 or 30 years old. Today, the average length of life in our country is about 70 years. In 1850, it was less than 40 years. And no wonder. A hundred years Culver Service ago, garbage and sewage were often dumped in the streets. Pigs and chick¬ ens and cows might be kept in pens close to a family’s living quarters. Milk wasn’t pasteurized. Foods were hung; in the sun to dry, where flies O J 7 swarmed over them. No wonder germ diseases were common. With the discovers of germs as agents of disease, a new day dawned. O 7 J Today we have achieved controls over many diseases— controls our ancestors never even dreamed would be possible. MICROORGANISMS AND DISEASE As early as the sixteenth century, an Italian advanced the idea that diseases which are contagious (catching) might 428 THE FIGHT FOR HEALTH t be caused by tiny living particles that spread from the sick to the well. Oliver Wendell Holmes was the first American doctor to advance a somewhat similar theory, at least as regards childbed fever. That was in 1843. In the vears J 1847-1849, Semmelweiss (zEM’lvys) proved in a Vienna hospital that child¬ bed fever could be reduced almost to zero, if doctors scrubbed their hands thoroughly in chlorinated limewater before examining their patients during childbirth. By 1867 an English surgeon, Lord Lister, had proved that infection of surgical incisions could be prevented if the operating room, the surgical instru¬ ments, the surgeon’s hands, the surgi¬ cal linens, and everything else that might come in contact with the inci¬ sion were treated with dilute carbolic acid. We know today that Lister’s pro¬ cedure was effective because the car¬ bolic acid killed the germs that might otherwise have infected the incision. But at that time, most other doctors still opposed the idea that invisible living particles cause infections or diseases. In the meantime, in France, Louis Pasteur ( pahs ter ) had been doing many brilliant investigations that sup¬ ported the theory that germs cause contagious diseases. By 1882, a German, Robert Koch (kok), had proved be¬ yond doubt that a specific germ does indeed cause the disease we now call tuberculosis. Today we know that microorganisms of several kinds are agents of disease. Many of these microorganisms are bac¬ teria. The special field of biological science that treats of bacteria is called bacteriology. Leeuwenhoek had actu¬ ally discovered bacteria by 1675, but the science of bacteriology began to take form only in the latter half of the last century. Where are bacteria found? It is almost literally true that bacteria are found everywhere— in the lower levels of the sky, in the air about us, on the land, in the soil, in the water, on and in almost every living thing, and in dead bodies. Their spores have been found frozen in icebergs, and yet alive. The air in almost any public place con¬ tains thousands of them per cubic yard; they float about on bits of dust. You may ask how we know these J things if bacteria are invisible. Bac¬ teriologists have learned how to plant and grow bacteria cultures. In Figure 16-1 (right) is an agar culture slant with colonies of bacteria in it. Bacte¬ riologists culture bacteria (and molds) 16-1 AGAR CULTURES Left. This agar culture plate (in a Petri dish) has a growth of mold on it. Right. This tvpe of culture is called an agar culture slant. It contains bacteria. Bacteriologists also use several other kinds of culture media besides agar. Left: E. R. Squibb & Sons; right: General Biological Supply House, Inc., Chicago in several ways, but the agar culture plate (Figure 16-1, left) and agar slant are the most widely used. You can easily culture bacteria on agar, but first you will want to examine O 7 J some bacteria. EXAMINING LIVING BACTERIA. Mount and examine a drop of sauerkraut juice under high power of your microscope. You will have to focus sharply and look closely to see the bacteria, because they are mere specks, even under high power. Sketch any bacteria you see. Repeat, using a bit of sour milk mounted in a drop of water. Figure 16-2 is a photo¬ micrograph (photograph taken through a microscope) of bacteria in sour milk. CULTURING BACTERIA. You can buy cul¬ ture plates and culture slants, all ready to use, from biological supply houses. Or you may prefer to make your own. To prepare culture plates, boil together: 500 cubic centimeters water 5 grams beef bouillon cubes 14 teaspoon soda 14 teaspoon salt 714 grams agar Filter this preparation into small Petri dishes. Cover the dishes. Place them in the top of a double boiler and boil for an hour. Let stand overnight and repeat the boiling, to make sure that all mold and bacteria spores are killed— that is, that the plates have been sterilized. If you prefer, slices of raw potato may be used as a medium instead of the agar. Place a slice of raw potato in each of sev¬ eral Petri dishes, add a little water, cover, and sterilize, as above. Keep one dish permanently covered. It will serve as a control to see whether all organisms were killed during sterilization. Expose the other dishes as directed below, then keep them in a warm, dark place. U.S.D.A., Bureau of Dairy Industry 16-2 BACILLI IN SOUR MILK These are the bacteria that cause milk to sour. ( 1,000 x) If you have an oven, keep the dishes at a temperature of about 98 F., or 37°C. Expose one plate to each of the follow¬ ing: 1. drop of raw (unpasteurized) milk 2. drop of pasteurized milk 3. air in the room 4. tip of finger 5. swab from mouth 6. coin 7. soil particles 8. water from aquarium 9. drop of drinking water Watch for colonies to appear. At the end of three or four days, try to count the colonies on each exposed plate. Did colo¬ nies show up on the dish that wasn't ex¬ posed? If so, what does that prove? V/hat should you do then? Record your results on a fresh page in your record book. Before you wash your culture plates, be sure to soak them overnight in Lysol or some other strong germ killer. How are colonies of bacteria produced? At each point on a culture plate where a bacterium alights (or is plant¬ ed), that bacterium starts reproducing by dividing. It divides into two, the 430 THE FIGHT FOR HEALTH two into four, the four into eight bac¬ teria, and so on. At room temperature, divisions may occur about once an hour. If so, one original bacterium could pro¬ duce over 16 million bacteria in 24 hours! That many bacteria make a visi¬ ble “spot” on the culture plate. Such a “spot” is called a colony. By this amaz¬ ing rate of reproduction, colonies of bacteria are produced on culture plates —or in your throat, when you have a sore throat. The rate at which bacteria divide varies with the temperature. For ex¬ ample, the ones that cause milk to sour divide every hour at 70° F., but only every two hours at 60° F., and only ev¬ ery 30 hours at 40° F. You can see why keeping milk cold in a refrigerator de¬ lays its souring. Types of bacteria There are a great many species of bacteria, but only three common shapes among them. Some are shaped like short sticks or rods. All species of bac¬ teria that are rod-shaped (Figure 16- 3a ) are called bacilli ( buh sil eye— sin¬ gular, bacillus). Other bacteria are round in shape like the period at the end of this sentence ( Figure 16-3b ). All bacteria of this shape are called cocci (kok sy— singular, coccus , kokus). Still other bacteria are curved or spiral (Figure 16-3c) and are called spirilla (spy bil uh— singular, spirillum ) . How big are bacteria? Bacteria differ in size considerably more than people do, for some bacteria are five and even ten times as big as others. Nevertheless, it is possible to talk of their size in terms of averages, much as we talk of the average height and weight of human beings. The average coccus is about four mi¬ crons ( my kronz ) in diameter. The word micron is probably new to you. It is a unit used in measuring micro¬ scopic objects. You might as well try to measure your fingernail in miles or fractions thereof as to try to measure bacteria in inches. A micron is 1/25,000 of an inch. An average-sized coccus is four microns in diameter. In other words, it would take 6,250 of them to reach one inch. There is room for over 200 billion of them in one cubic inch. Many bacteria are even smaller. With this background, you are ready to study the relation of some specific bacteria to specific diseases. Discovery of specific germs Bv 1882, Robert Koch had established beyond reasonable doubt that one spe¬ cific kind of germ (a bacillus) causes anthrax, a disease then common among cattle and sheep and occurring some¬ times in human beings. He had also established that another specific kind of germ (Figure 16-3a) causes tuberculo¬ sis. Koch’s researches, like those of Louis Pasteur, were historical events of major importance. You can read about them in some of the references cited at the end of this chapter; only space limi¬ tations prevent their inclusion here. You will find excitement and drama in the accounts of the lives and work of these two investigators. From 1882 on, many men did many investigations that led to the discovery of specific germs of many diseases. Diphtheria was soon proved to be caused by a bacillus and Asiatic chol¬ era ( kol uh ruh ) by a spirillum. By 1900, thirty different diseases had been proved to be caused by specific micro¬ organisms, all of which had been iden¬ tified. Since 1900, many more diseases have been added to the list. DISEASES AND THEIR CAUSES 431 Photos, top: New York Scientific Supply Co.; R. C. A. Photo; center: Chas. Pfizer & Co., Inc.; Society of American Bacteriologists; bottom ; New York Scientific Supply Co.; Society of American Bacteriologists 16-3 DISEASE-CAUSING BACTERIA Three shapes of bacteria are represented here by: A. bacilli of tuberculosis ( 1,280 X on the left and 18,300 X on the right); B. diplococci (double cocci) that cause a common kind of pneumonia ( 1,000 X and ll,800x); C. syphilis-causing spirilla, called spirochetes (spy roh keetz) to distinguish them and other corkcrew-shaped spirilla from curved spirilla ( 1,000 X and 7,600x). 432 II IE FIGHT FOR HEALTH Many of the germs so far discovered are bacteria; some disease-producing bacteria are bacilli, others are cocci, and still others are spirilla. A spirillum causes the disease syphilis ( sif uh lus ) . In Figure 16-3c, you see a greatly en¬ larged photograph of the syphilis germ. This germ lives and reproduces in the human blood stream. As vou undoubtedly know, most J J states require a blood test before issu¬ ing a marriage license. The required blood test is for syphilis. If a person has syphilis in a contagious stage, medi¬ cal treatment is necessary before it is safe to marry. Fortunately, modern drugs usually cure syphilis, if it is dis¬ covered in an early stage. So the blood tests required before marriage are one of the effective ways of preventing the spread of the syphilis germ— to wife or husband or children. Not all germs are bacteria. Some are protozoa and others are moldlike fungi. Viruses and rickettsias ( rik et see uhz) also cause disease, but calling them “germs” is questionable. You will recall that a virus can re¬ produce only when it is inside a living cell. The same thing is true of rickett¬ sias. Are viruses and rickettsias true microorganisms? Probably not. If not, they are not true germs. But they do cause several contagious diseases. Hence, we are including them among the germs. So here the germs include: (1) bacteria, (2) protozoa, (3) mold¬ like fungi, (4) viruses, and (5) rickett¬ sias. Protozoa that cause disease It was in 1894 that a British army doctor proved that African sleeping sickness is caused by a protozoon car¬ ried from the sick to the well by the tsetse ( tset seh ) fly. Since that time several other diseases have been proved to be caused by protozoa. The most widespread are malaria and amebic dysentery, but there are others. Moldlike fungi Have you ever had athlete’s toot or ringworm? If so, you had a moldlike fungus growing on the skin somewhere on the body. Both athlete’s foot and ringworm may recur often, once a per¬ son has had either one. One reason is that the spores of these fungi are hard to kill. Ordinary washing, say, of socks, does not kill the spores of athlete’s foot. Valley fever is another fungus dis¬ ease. It is rather common in our South¬ west. The spores are spread in the dust that often blows about in small or large dust storms. These spores may be in¬ haled and may lodsfe in a bronchial tube and start to grow, causing a case of valley fever. Usually, rest in bed cures valley fever. J Virus diseases Louis Pasteur did one of his most famous investigations on rabies (ray beez), the disease that makes dogs go “mad.” Other animals also get rabies, as do human beings. Pasteur soon found that the saliva of a rabid (mad) dog contains the “germ” of the disease. But try as he would, he could never find that “germ” under his best microscope. Today we know why. Rabies is caused by a virus. And a virus is too small to be seen under a compound microscope. It takes an elec¬ tron microscope to get pictures like those in Figure 16-4. Viruses are now known to cause a number of diseases besides rabies. Among them are chicken pox, small¬ pox, measles, influenza, one type of DISEASES AND THEIR CAUSES 433 Top: E. R. Squibb & Sons; bottom: Virus Laboratory, University of California, Berkeley, California 16-4 TWO KINDS OF VIRUSES The influ¬ enza virus (above) and the tobacco mosaic virus (below) are shown under the electron microscope (25,000 X and 31,000 x, re¬ spectively). pneumonia, yellow fever, and poliomy¬ elitis (often called polio for short, and commonly known as infantile paraly¬ sis). The common cold may be due to a virus, too, but usually bacteria also play a part in this infection. Newer ideas of viruses You have alreadv read about Stan- J ley’s researches on viruses. Turn back to page 94 and read about these re¬ searches again. In 1956, Stanley published a num¬ ber of new conclusions about viruses, based on the researches he and his fel¬ low workers have done. For one thing, Stanley says they have good evidence that all of us are born with viruses in some of our cells, and that we acquire new ones during our lives. In many people, the viruses in their cells just stay there and do no harm, perhaps for a whole lifetime. But in some people, conditions favorable to virus reproduc¬ tion arise in some of their cells. Then the viruses go on a rampage and a virus disease is the result. Cold sores are an example. The virus that causes cold sores lies dormant (inactive) most of the time, but in times of stress, as when you have a cold or get overtired, the cold-sore viruses may start reproducing. Then vou 2!et a cold sore. j O Rickettsial diseases The cause of typhus has been proved to be certain tiny granular bodies that grow within the cells of the patient. These granular bodies are rickettsias (Figure 16-5). Their exact nature is not yet known, but they do cause typhus. 16-5 TYPHUS FEVER RICKETTSIAS Like vi¬ ruses, rickettsias reproduce only inside liv¬ ing cells. ( 21,000 X ) From The Electron Microscope by E. F. Burton and W. H. Kohl, Reinhold Publishing Corp. 434 THE FIGHT FOR HEALTH Left: photo by Dr. Stuart Mudd, University of Pennsylvania, School of Medicine; right: Chas. Pfizer & Co., Inc. 16-6 TWO COMMON COCCI Left. Staphylococci or “staph” are usually seen in clumps. Right. Streptococci or “strep” often are seen in chains. “Staph” and “strep” infections still occur frequently, but are usually controlled quickly with antibiotics. They resemble the viruses in that they can grow only within living cells. They differ from viruses in that they are large enough to be seen under the com¬ pound microscope. Several human dis¬ eases are caused bv rickettsias. J Germs and their toxins Sometimes germs find “food and lodging” in some part of your body. Then they grow and multiply. Like all other organisms, germs excrete wastes, and the wastes of some germs are poi¬ sonous to man. Such wastes are called toxins. Take diphtheria and scarlet fever as examples. In both diseases, the germs grow in the throat and excrete toxins. The toxins diffuse into the patient’s blood stream and are carried all over the body. Scarlet fever toxin causes a skin rash. Both diphtheria and scarlet fever toxins cause fever and aching and other effects that involve the whole body, not just the throat where the germs are growing. So the toxins of these germs cause most of the bodily reactions which go with a case of diph¬ theria or scarlet fever. The germs of a number of other dis¬ eases produce illness by means of their toxins. Examples are lockjaw, whoop¬ ing cough, measles, and epidemic men¬ ingitis ( men in jy tiss— an infection of the membranes that cover the brain and spinal cord ) . Germs and tissue damage Many kinds of germs do their chief damage by injuring one or another tissue in the body. Polio virus injures nerve tissue, sometimes severely. Ty¬ phoid germs damage the lining of the intestine. Tuberculosis and valley fever germs injure lung tissue. Tuberculosis germs may also attack and damage any tissue in the body. Many kinds of germs may injure the heart— especially its valves— if carried to the heart in the blood. Streptococci ( strep toll kok sy ) may infect a cut or burn, or a kidney, or a sinus, or the throat, or even the blood stream, and injure the tissue they in¬ fect. What is more, streptococci have recently been proved to release a sub¬ stance that causes heart damage of the type that sometimes follows rheumatic fever or scarlet fever. Certain strains of streptococci and of staphylococci ( staf ih loh kok sy— the germs most common in boils and pim¬ ples) release into the blood substances that cause the red blood cells to lose their hemoglobin. As you probably know, doctors call these germs (Figure 16-6) strep and staph, for short. You have heard of or perhaps even had strep throat. Doctors call the strains that injure the red blood cells hemo¬ lytic ( hee moh lit ik ) strep or hemo¬ lytic staph. You are almost sure to hear these terms sooner or later. DISEASES AND THEIR CAUSES 435 In untreated syphilis, the germs spread through the whole body. In time, sometimes only after some years, the syphilis germs attack and damage almost any tissue, but especially the brain. The germs of amebic dysentery “eat’ bits of the lining of the intestine, so that it bleeds. These germs often in¬ vade the liver and damage it. Some¬ times they invade the appendix where they may cause one type of appen¬ dicitis. Virtually all germs damage some tis¬ sue. Often the tissue heals completely once the disease is over. In some dis¬ eases, the tissue damage is permanent. Are germ diseases inherited? The available evidence indicates that the only way you can get a germ dis¬ ease from your parents is to get the germ of that disease from them— you cannot inherit the disease from them as you inherit such traits as eye color and curly or straight hair. For example, the only way a child can get tuberculosis from a parent is to get tuberculosis germs from an infected parent. There is evidence that children may inherit either susceptibility or resistance to specific germ diseases, but not the diseases themselves. Children who in¬ herit a high degree of susceptibility must still pick up the germ to get the disease. Those who inherit an ability to resist a specific type of germ infection may not contract the disease even when exposed to the germ. Only in these ways can heredity affect the individual s in¬ fection by germs, to the best of our present knowledge. Infection and contagion Germ diseases may be due to bac- teria, protozoa, moldlike fungi, viruses, or to riekettsias. (Viruses and rickettsias are called “germs” only for conven¬ ience.) Doctors call such diseases in¬ fectious, because infection with some germ ( or with a parasitic worm ) causes them. All germ diseases are infectious, but not all are contagious. For example, ap¬ pendicitis is caused by an infection of the appendix, so it is an infectious dis¬ ease. But you can’t “catch” appendicitis from someone who has it. So it is not contagious. Can you think of other ex¬ amples? TABLE J 6- A AGENTS OF INFECTIOUS DISEASES Disease agent Examples of diseases caused Parasitic worms Tapeworm, hookworm, trichinosis, and several others Molds or other fungi Athlete’s foot, ringworm, valley fever, and certain other diseases Protozoa Amebic dysentery, African sleeping sickness, malaria Bacteria Pneumonia, tuberculosis, typhoid fever, streptococcus diseases of many kinds (such as scarlet fever, childbed fever, and erysipelas), plague, cholera, diphtheria, bacillary dysentery, gonorrhea, impetigo, meningitis, lockjaw, rabbit fever, undulant fever, whooping cough, and many more Rickettsias (can grow only in¬ side of living cells) Typhus, Rocky Mountain spotted fever, trench fever, and at least two others Viruses (can grow only in¬ side of living cells) Smallpox, chicken pox, rabies, poliomyelitis (often called infantile paralysis), yellow fever, probably mumps, the common cold, and influenza 436 THE FIGHT FOR HEALTH Summing up: microorganisms and disease Germs are microorganisms that cause disease. They include bacteria, proto¬ zoa, moldlike fungi, and for the pur¬ poses of our discussion, viruses and rick- ettsias. Usually one kind of germ causes only one disease, but there are many excep¬ tions, like the streptococci and staphy¬ lococci that may cause a number of dif¬ ferent diseases and infections. All germ diseases are infectious, and many are also contagious. Table 16- A lists the agents of infectious diseases. HOW GERMS ARE SPREAD How does a healthy person pick up germs from a person who has a germ disease? In other words, how do germs spread from the sick to the well? There are several different means by which such transfers occur. Air-borne germs With every breath, you inhale some dust particles. There is good evidence that several kinds of germs may be car¬ ried on dust particles in the air. Cold germs are air-borne. It has been shown that a cough or sneeze may throw germs as far as 25 feet, unless the person covers his nose and mouth. Other air-borne germs include those of tuberculosis, pneumonia, influenza, and other infections of the nose, throat, and chest. The spores of valley fever are said to be inhaled with the dust in the air. The germs of such childhood diseases as mumps, measles, and chick¬ en pox may be air-borne. Germs carried in water and food A number of kinds of germs can be transmitted in water and food. The germs of typhoid fever used to spread widely through many communities in contaminated city water, or in milk or other foods. This made typhoid fever epidemics common. Today we almost never hear of a typhoid fever epidemic. Chlorination of water and pasteuriza¬ tion of milk, as well as other measures, have almost eliminated this disease from our country. Raw unpasteurized milk transmits some disease germs, even today. The most common one so transmitted is the germ of undulant fever, found in milk from cows that have Bang’s disease. Unpasteurized milk may also transmit germs that cause what a doctor calls gastro-intestinal upsets, with vomiting and diarrhea. Raw vegetables sometimes carry the germs that cause amebic dysentery. Hence it is important to wash all such vegetables thoroughly before serving. Ptomaine poison is a bacterial toxin that may occur in food. The bacteria that give oft this toxin are anaerobic (an ay er oh bik ) bacteria. This means that they live and thrive where there J is no air— say, in a can of food which wasn’t heated enough during canning to kill all the spores of the anaerobic bacteria in the food. Inside the can (or in certain foods that aren’t thoroughlv cooked and are then kept covered), the bacteria grow and give off their toxin. This toxin is highly poisonous to human beings. When vou read about cases of ptomaine poisoning in the paper, you will know that a food-borne bacterial toxin caused the poisoning. Insect-borne germs Houseflies and several other kinds of insects may carry germs. Rat lice are known to carry germs of bubonic plague— once called the Black DISEASES AND THEIR CAUSES 437 Death— from infected rats to people. Sometimes lice of other kinds also carry certain germs from infected animal hosts to man. The tsetse flv carries the germ of African sleeping sickness. Certain mosquitoes (Figure 16-7) may carry germs from sick people to healthy ones. One mosquito, technically known as the Anopheles (uliNOFeh leez), transmits the protozoon that causes malaria. Another, the Aedes ( ay EEdeez), transmits the virus of yellow fever. Malaria and yellow fever are not very common in most parts of our na¬ tion, but they are still widespread in tropical areas of the world. In fact, over the world as a whole, malaria kills more people than any other disease, to say nothing of the millions of people it dis¬ ables for long periods. Germs spread by direct contact A healthy person can get germs of certain diseases only (or usually only) 16-7 ANOPHELES MOSQUITO The Anoph¬ eles transmits malaria germs. It is shown here piercing human skin (above) and sucking blood (below). Note how the mos¬ quito’s abdomen swells with blood. Department of Health, Education, and Welfare by direct contact with an infected per¬ son. Syphilis and gonorrhea ( gon er ee uh) are examples. As you may know, these germs are usually spread by sex¬ ual contact, or from an infected mother to an unborn child. Soil-borne germs At least two kinds of germs are usu¬ ally picked up from the soil, and sev¬ eral more may be. The germs that cause lockjaw and those that cause gas gan¬ grene may get into dirty wounds along with soil, or on a rusty nail that has lain in the soil. When a person steps on a rusty nail, it isn’t the nail or the rust but the germs that lead to infection. Germs spread by human "carriers" Almost everyone has heard of Tv- phoid Mary. She carried and transmit¬ ted typhoid germs, although she her¬ self was not ill. A number of seemingly healthy persons have now been proved to be carriers of disease germs of one kind or another. An outbreak of amebic dvsenterv J J during the Chicago World’s Fair of 1933 was traced to carriers among the kitchen help of a hotel. Summing up: the spread of germs Germs may be transmitted from the sick to the well in a number of ways: through the air, in water and food, by direct contact, by soil, bv human car¬ riers, and by a number of insects, in¬ cluding houseflies, lice, and some mos¬ quitoes. OTHER CAUSES OF DISEASE Many diseases are not infectious be- cause they are not caused by germs. For example, germs do not cause goiter or hav fever or rickets. These and all other noninfectious diseases that we know do have natural causes, however. Causes of noninfectious diseases You already know the causes of some noninfectious diseases; others may be new to you. These causes include: (1) nonliving foreign substances, which may cause allergy; (2) food deficien¬ cies, which cause such diseases as scurvy, rickets, and simple goiter; (3) disturbed functions of the endo¬ crine glands, which cause such diseases as diabetes and toxic goiter; (4) dis¬ turbed functions of other organs or tis¬ sues; and (5) harmful habits, such as overindulgence in alcoholic drinks or the unlawful use of certain drugs. Allergies There are many persons who cannot eat eggs or foods containing even small amounts of egg. One such person col¬ lapsed and remained unconscious for hours after eating mashed potatoes to which a little beaten egg white had been added. To this person, eggs were poison. There are many other substances which seem to be poison to a few peo¬ ple, even though these substances are perfectly harmless or even beneficial to most of us. One person’s skin blisters if he comes in contact with turpentine. Another is poisoned by the chemicals on adhesive tape. Some become ill if they eat sea food; others, if they eat watermelon; still others, if they eat strawberries. Sometimes the illness takes the form of violent vomiting and diarrhea. In many cases, the skin breaks out in a rash, or hives suddenly appear all over the body. Sometimes the reac- tion is a fit of violent and prolonged sneezing. Apparently these persons are sensitive to a particular foreign sub- U.S.D.A., Bureau of Plant Industry 16-8 TWO RAGWEEDS Left. Giant rag¬ weed. Right. Common ragweed. Many per¬ sons are allergic to ragweed pollen and develop hay fever when they inhale it. stance, such as eggs or turpentine or strawberries. This condition of being sensitive to a particular foreign substance is called allergy (al er jee). The person affected is said to be allergic (uliLERjik), and the foreign substance which causes the reaction is called the allergen ( al er jen). Today doctors know that almost any¬ thing, from a piece of ice to scalp dan¬ druff, may serve as an allergen for some human being. Hives, asthma, diarrhea, indigestion, eczema (ek suhmuh), “se¬ rum sickness,” hay fever, and even ivy poisoning are some of the illnesses that may be caused by allergens. The most common allergen of hay fever is the pollen of ragweed (Figure 16-8) or roses or other flowers. It has been esti¬ mated that about 10 per cent of the population has a marked allergy of some kind. It seems probable that near¬ ly half of us suffer from some less vio¬ lent form of allergy, and probably all of us are capable of becoming allergic to some foreign substance. DISEASES AND THEIR CAUSES 439 LISTING ALLERGENS. Various members of your class probably know of persons who are allergic to some substances. What substances are the allergens in cases of allergy known to any of your classmates? (Of course, you will not name persons in your discussion, just as doctors and nurses never discuss any patient's case under the patient's name.) List in your record book all the allergens discussed in class. Deficiency diseases Diseases which are caused by the lack of necessary food elements are called deficiency diseases. Table 16-B will help you recall some of the more common deficiency diseases you have already studied in Chapter 13. Gland disturbances You have already studied some of the diseases that are caused by disturb¬ ances of one kind or another in the functioning of the endocrine glands. Table 16-C will help you review these diseases. If you wish to review more extensively, see Chapter 14. TABLE 16-B DEFICIENCY DISEASES Disease or condition Substance lacking Beriberi Thiamin Certain eye and skin conditions Riboflavin Certain nervous condi- tions Riboflavin Pellagra Niacin Night blindness (some eases) Vitamin A Scurvy Vitamin C Pickets Vitamin D Failure of blood to clot (most but not all Vitamin K, calcium cases) in blood Anemia (some cases onlv) Iron Simple goiter Iodine Heat exhaustion (some cases only) Table salt TABLE 16-C DISEASES CAUSED BY DISTURBED GLAND FUNCTIONS Disease Cause Simple goiter Lack of iodine for use by thyroid Toxic goiter Too much thyroxin from thy¬ roid Cretinism Abnormal inborn condition of the thyroid gland Myxedema Too little thyroxin from thy¬ roid Diabetes Lack of (or too little) insulin from pancreas Tetany and Lack of parathyroid hormone convulsions or calcium salts or both Pernicious anemia One form of anemia is now thought to be caused partly by a disturbed gland function and partly by a food de¬ ficiency. This is pernicious anemia (Fig¬ ure 16-9), a primary disease, not sec¬ ondary to some other chronic illness, as many anemias are. Before 1928, per¬ nicious anemia eventually killed the pa¬ tient. Since then, liver extract and, more recently, folic acid and vitamin Bl2 have brought the disease under control, but they do not cure it. So it seems that this disease may be caused by a lack of something from the liver (perhaps a hormone?) and also by a lack of certain vitamins (folic acid and vitamin BL2). Alcohol and disease People who habitually use alcoholic beverages to excess are called alco¬ holics and are said to suffer from the disease called alcoholism. Not many years ago, most people thought alcoholics were simply people with “lack of will power ’—people who were undeserving of help. Today the picture is changing. First a group of alcoholics or former alcoholics banded together to help each 440 THE FIGHT FOR HEALTH other. And they proved they could help many but not all alcoholics. That group of people, called Alcoholics Anony¬ mous, did more than anyone else to call attention to the problem and to show that something can be done about it. For some years now, a number of science research teams have been study¬ ing the effects of alcoholic beverages on the human body. Here are some of the things scientists have now discovered: 1. Alcohol passes rapidly into the blood stream and thence into every tis¬ sue in the body. 2. Body cells oxidize alcohol and get energy out of it. 3. Alcohol is called a depressant be¬ cause it depresses (slows down) vital processes. It is not a stimulant (a sub¬ stance that speeds up life processes), as so many people think. 4. Alcohol enters the brain more rap¬ idly and in greater quantity than it en¬ ters other tissues, because of the greater circulation in the brain. It acts as a tox¬ in to the central nervous system. 5. Alcohol is a moderately effective painkiller. 6. Even small amounts of alcohol slow down the drinker’s reaction time, reduce his accuracy of vision, and af¬ fect his judgment. This fact probably accounts for the high number of auto¬ mobile accidents among persons who are under the influence of alcohol. 7. In larger quantities, alcohol radi¬ cally changes the drinker’s behavior. He staggers, stumbles, mumbles, sees “double,” and becomes nauseated. 8. Still greater amounts of alcohol (only three to six drops in each 1,000 drops of blood) cause the drinker to pass into an unconscious condition. His temperature falls, his skin may turn bluish, his breathing is slow and diffi¬ cult, and his pulse can barely be felt. Just a little more alcohol (six drops in each 1,000 drops of blood) may cause death, although in most persons a con¬ centration higher than this is necessary to cause death. 9. The long-continued use of exces¬ sive amounts of alcohol will usually re¬ sult in chronic alcoholism. 10. Some persons are allergic to al¬ cohol and cannot take any at all with¬ out serious reactions. 11. Heavy drinkers show a higher death rate at every age than nondrink- 16-9 STAINED BLOOD SMEARS (HUMAN) Compare the appearance of normal blood (left) and blood from a person who has pernicious anemia (right). In the diseased blood, note the scarcity of red cells, their distorted shapes, and the cell with a nucleus. (600 x) General Biological Supply House, Inc., Chicago ers and moderate drinkers. Heart at¬ tacks, “strokes,” and what is usually called “hardening of the liver” * are much more common among alcoholics than among other people. Alcoholics do not live as long, on the average, as other people do. 12. The body chemistry of alcoholics shows significant differences from nor¬ mal in several ways: deficiency of vita¬ mins, especially the B complex vita¬ mins; marked variations from normal in white-cell counts, in the amounts of sodium, potassium, and calcium in the blood, and in blood-sugar levels; and variations in the composition of the urine. ## All the scientific evidence to date in¬ dicates that the habitual use of exces¬ sive amounts of alcohol must be in¬ cluded among the causes of disease. Does smoking cause disease? In July, 1957, Surgeon General Le¬ roy E. Burney of the United States Public Health Service reported on the results of 18 independent studies of smoking in relation to death rate and cancer. He said that these studies “have confirmed beyond reasonable doubt that there is a high degree of statistical association between lung cancer and heavy and prolonged cigarette smok- • » mg. All studies of death rates show: 1. A higher death rate among smok¬ ers than nonsmokers. 2. A higher death rate among heavy smokers than among light smokers. 3. A higher death rate among ciga¬ rette smokers than among pipe smokers. ° The medical name for this liver condi¬ tion is cirrhosis ( sih roh sis ) of the liver. 00 For a report on recent researches in this field, see Science News Letter, December 7, 1957, page 363. 4. That about one out of every ten heavy smokers may be expected to de¬ velop lung cancer, but only about one in every 270 nonsmokers may be ex- expected to develop it. 5. That heart attacks and “strokes” are much more common among heavy smokers than among nonsmokers. No one has yet proved that smoking is the cause of lung cancer. N onsmokers do get it. Other factors that seem to play a part are smog, automobile ex¬ haust fumes, and coal smoke, especially in big cities. All the available evidence seems to indicate that smoking, or at least heavy cigarette smoking, must be included among the probable causes of disease. t Drugs and disease Some people misuse drugs and de¬ velop the drug habit. Doctors call such people drug addicts. Drug addiction may cause serious illness and must be listed among the causes of disease. You will learn more about controlling the use of drugs in a later chapter. Summing up: noninfectious diseases Causes of noninfectious diseases in¬ clude: allergens, food deficiencies, gland disturbances, disturbances in other features of body chemistry, ex¬ cessive use of alcohol (and probably tobacco), and the misuse of drugs. BODY STABILITY AND DISEASE A new point of view is gradually de¬ veloping in the outlook upon disease. This modern outlook involves the con¬ cept that all diseases mankind is heir to affect the natural stability of the whole body. Let’s try to trace the growth of the modern viewpoint out of older concepts of disease. 442 THE FIGHT FOR HEALTH Older theories of disease Through the years, people have looked upon illnesses in various ways. Not too long ago, nearly everybody thought that evil spirits or witches or bad night air made people sicken and die. Then came the germ theory. The germ theory led scientists to look for specific natural causes of every dis¬ ease known. And they have already found many specific causes, as you have just learned. Most scientists today ac¬ cept the idea that every disease is due to natural causes. Specific causes Pasteur’s and Koch’s researches cli¬ maxed the investigations that finally proved beyond all doubt that one spe¬ cific kind of germ is the direct cause of one specific disease. Tuberculosis germs cause tuberculosis. Anthrax germs cause anthrax. This was a new and productive point of view in 1882. As you also know, a number of dis¬ eases have now been traced to deficien¬ cies in specific vitamins or minerals. A number of other diseases have been traced to deficiencies or excesses of spe¬ cific hormones. You might say that the first half of this century was the period of the “spe- cific-causes-of-diseases” point of view. This point of view also involves “spe¬ cific medicines” and “specific treat¬ ments,” and it has resulted in the fast¬ est advance in the control of disease in human history. There is, however, a growing tend¬ ency today among doctors to get away from the idea that any disease has just one specific cause or one specific treat¬ ment. Perhaps an example or two will help you to see the reason. Take tuberculosis as the first exam¬ ple. Without a doubt, the tuberculosis germ has to get into the lungs before anybody can get tuberculosis of the lungs. But millions of people, especiallv those who live in cities, get tuberculo¬ sis germs into their lungs and never come clown with the disease. All the evidence to date indicates that a per¬ son’s inherited susceptibility or resist¬ ance and his living conditions and his diet— these and other factors— help to determine whether he gets tuberculosis. Here is a second example. In an auto¬ mobile accident, a man had the flesh torn off the whole inside of his hand. He was in the hospital for weeks while the wound healed. That man developed all the symptoms of diabetes, but as soon as his hand healed, the diabetes symptoms disappeared. Twenty years later, he had had no recurrence of the symptoms. Did his injured hand cause diabetes? Or did the injury simply so disturb his body chemistry, that his blood-sugar level went up? The newer point of view The newer point of view among doc¬ tors and other biologists is that every injury, every germ infection, every food deficiency, and everything else that causes illness disturbs the patient’s body chemistry. An unknown number of factors— diet, heredity, living condi¬ tions, the nervous system, and the duct¬ less glands, to mention a few— deter¬ mine how serious the effects will be. In a previous chapter, you learned a little about the body’s amazing ability to stay much the same in the face of constant change. Walter B. Cannon, noted for his researches into this abil¬ ity of the human body, invented a word for it. He called the ability of the body to stay about the same in the face of constant change homeostasis (hohmee oh STAY sis ) . DISEASES AND THEIR CAUSES 443 TABLE 16-D A NEWER OUTLOOK UPON DISEASES AND THEIR CAUSES 444 THE FIGHT FOR HEALTH We can state the newer point of view of diseases in terms of homeostasis in this way. Every disease disturbs the body’s homeostasis to a greater or lesser degree. Alcohol certainly disturbs the body’s homeostasis. So does tobacco. So do certain drugs. So does a broken bone, or an invasion of germs, or even a small cut or burn. So do food deficiencies and hormone deficiencies and excesses. So perhaps biologists will eventually use the term specific cause to apply only to the immediate factor that disturbs homeostasis and will recognize and try to deal with other contributing causes, in treating anything from paralysis to boils. One thing is sure. The modern, up-to-date doctors are practicing scien¬ tists, at work on the whole, complex hu¬ man being. Table 16-D presents a sum¬ mary of some of the newer points of view in medical diagnosis. CHAPTER SIXTEEN: SUMMING UP We now know the specific agents of about two thirds of all known diseases. The known specific agents of disease in¬ clude: (1) parasitic worms, (2) molds or other fungi, (3) protozoa, (4) bac¬ teria, (5) rickettsias, (6) viruses, (7) foreign substances ( allergens ) , (8) vitamin and mineral deficiencies, (9) disturbed gland functions, and (10) a few others that are hard to clas¬ sify, such as those that result in alco¬ holism, drug addiction, or high death rates among heavy smokers. It seems likely that all diseases may be due to natural causes, but probably no disease is due to any single cause. Doctors are gradually coming to look upon illnesses as involving a disturbed homeostasis, and upon the body’s responses during disease as its attempts to restore the delicate balances in its body chemistry. Your Biology Vocabulary Here are the important new terms you have met in this chapter. You will want to understand them and be able to use them. microorganisms bacteriology culture plates bacilli cocci spirilla rickettsias syphilis anthrax toxins hemolytic streptococci hemolytic staphylococci infectious diseases contagious diseases anaerobic bacteria ptomaine poisoning pernicious anemia Anopheles mosquito Aedes mosquito deficiency diseases allergy allergens alcoholism depressant stimulant drug addiction homeostasis DISEASES AND THEIR CAUSES 445 Testing Your Conclusions 1 . On a fresh page in your record book, copy the list of diseases in Column A below. Beside each disease write the letter of the item in Column B that indicates the im¬ mediate cause (but probably not the only cause) of that disease. Column A 1. goiter 2. typhus 3. typhoid fever 4. hay fever 5. athlete s foot 6. rickets 7. influenza 8. scarlet fever 9. malaria 1 0. ringworm Column B a. bacteria b. viruses c. rickettsias d. protozoa e. moldlike fungi f. allergens g. food deficiencies h. gland disturbances 2. List four ways in which germs may spread from the sick to the well, and give ex¬ amples. 3. In your own words, explain two or three reasons why biologists are convinced that there is some connection between cigarette-smoking and lung cancer. 4. Write a short report on some illness you have had, such as the common cold. Explain what factors other than germs may have helped to cause the illness. Had you lost sleep? Were you overtired? Were you eating a balanced diet? Does your example seem to illustrate the newer point of view that many factors besides specific ones help to cause disease? More Explorations 1. Testing clean hands. You will need three sterile culture plates. Label them 1, 2, and 3. Remove the lid of No. 1 and rub the end of your finger over the surface of the agar. Replace the lid. Next wash your hands thoroughly with soap under running water and dry them on a paper towel. Remove the lid of No. 2 and rub your finger over the agar. Use No. 3 as a control. Keep all three culture plates in a warm, dark place or in an oven at 98° F. or 37° C. for a week or ten days. Then count the colonies on each plate. In your record book, tell what you did and what happened. What conclusions do you draw about clean hands? Are they totally germ free? Are they more nearly germ free than unwashed hands? 2. Life history of a malaria germ. Look up the life history of the protozoon that causes the most common kind of malaria. You will find it in almost any college zoology text. Report in class. Use drawings or diagrams on the chalkboard to make your report meaningful. 3. An examination of stained bacteria. Swab your teeth with a bit of cotton and smear the material on a clean slide. Pass the slide through the flame of a Bunsen burner four or five times to fix (fasten) the bacteria on it. Then stain by pouring a few drops of Loeffler’s methvlene blue stain (or ordinary blue ink) over it. Let it stand 446 THE FIGHT FOR HEALTH two minutes. Wash with water and dry. Examine under the high power objective of your microscope. What different shapes of bacteria do you find? Record in sketches. What were these bacteria using for food in your mouth? Why are you not ill, if there are bacteria in your mouth? Thought Problems 1 . Why did it take mankind so long to find out what causes germ diseases? Give at least two reasons. 2. There was a “grain of truth” in the old belief that night air caused malaria. Can you explain just what the “grain of truth” was? Further Reading 1. Paul de Kruif’s Microbe Hunters, Harcourt, Brace, 1932 (also available in Pocket Books), has been for nearly thirty years a popular book on the history of the germ theory of diseases. It contains some exciting chapters on Semmelweis, Pasteur, Koch, and several other microbe (microorganism) hunters. 2. The Metropolitan Life Insurance Company, New York and San Francisco, publishes a number of highly readable pamphlets. One called Health Through the Ages in¬ cludes interesting histories of diseases (Black Death, for instance) and of researches into their causes. Metropolitan will send your teacher this and other pamphlets upon request. 3. Read the Science News Letter and any other science news magazines that are avail¬ able regularly. Most newspapers today also carry science news regularly. This is the only way (short of reading professional journals) you can keep up with new dis¬ coveries and new points of view in the field of health. DISEASES AND THEIR CAUSES 447 9 CHAPTER Improved Controls over Diseases Why aren't you sick all the time? You have just finished a chapter on the causes of disease. Has the number of germs and other agents of disease that are all around you left you won¬ dering why you aren’t sick all the time, or even much of the time? There are a number of reasons. For one thing, the human body has several built-in defenses against germ invasion. It was largely these built-in defenses that made it possible for many people to survive the epidemics so com¬ mon a hundred years and more ago. For another thing, the great medical discoveries of the past 75 years are be- ing applied on a wide scale to protect your health and well-being. These dis- Frederic Lewis coveries include ways to take advantage of some of the body’s natural defenses against germs, better methods of diag¬ nosis, many new medicines, modern surgery, methods of preventing the spread of germs, and ways to prevent serious results from injuries. All these and many more discoveries are helping to give the people of today better health and longer lives. DEFENSES AGAINST GERMS Your body has a number of built-in defenses against germs. If some germs get past the first line of defense, any or all of several secondary lines of de¬ fense come into play. 448 THE FIGHT FOR HEALTH Your first line of defense Your first line of defense against in¬ fections and germ diseases is the out¬ side layer of your skin. Only a few germs, such as those of athlete’s foot and ringworm, can establish themselves and grow upon the outer layer of the human skin, and even these can do so only under favorable conditions. Most kinds of germs must get past the outer layer of the skin and into the interior body tissues to cause infections or germ diseases. Germs may get inside the body through breaks in the skin ( Figure 17-1) or through the nose or mouth or other openings. In the case of pimples and boils, they probably get into inner lay¬ ers of the skin through the ducts of the sweat glands. Most of the time, your skin is an effective protection against germs. A secondary line of defense One of your secondary lines of de¬ fense against germs is your lymph sys¬ tem and especially the lymph nodes strung along your lymph vessels. As you have already learned, the lymph nodes strain germs and other harmful materials out of the lymph, on its way back to the heart. For example, when a person has an infected tooth, the lymph nodes under the jaw become swollen and sore because of the collec¬ tion of strained-out germs and other harmful materials in those nodes. Your lymph nodes hold back an infection, at least for a while, and keep the germs from entering the general circulation. Sore, swollen lymph nodes usually mean that germs have entered the body at some point and have caused an infec¬ tion (Figure 17-1). They also usually mean that the time has come for you to see your doctor. 17-1 THREE LINES OF DEFENSE AGAINST GERMS Your skin is your first defense against germs. When the skin is cut or broken, other defenses take over against germs that enter the wound. White blood cells move out of the capillaries and ingest many germs. Most of the germs that get past the white blood cells enter lymph ves¬ sels and are strained out of the lymph by lymph nodes. Skin break IMPROVED CONTROLS OVER DISEASES 449 Another secondary line of defense Another and very important second¬ ary line of defense is often called the body’s “standing army.” It consists of certain of your white blood cells— those that ingest germs (Figures 17-1 and 17-2) in much the way that amehas in- gest food. These white blood cells that “eat germs are called phagocytes (fag oh sytes). Your phagocytes help to defend the body against germ invasion. For exam¬ ple, germs ( perhaps staphylococci ) may gain entrance through a broken blister from a burn on your hand. Phagocytes quickly move out of your blood capil¬ laries, ameboid fashion, and into the in¬ jured tissues. There, the phagocytes be¬ gin at once to ingest the staphylococci and then to digest them. If the phago¬ cytes can thus destroy the germs rapidly enough, no visible infection develops. If not, more and more phagocytes are produced in the body and move to the point of germ invasion. Then pus, con¬ sisting largely of phagocytes, dead tis¬ sue cells, and germs, forms. In time, a new growth of connective tissue may “wall off” the infected spot, which may then “come to a head,” as people say. Once this happens, the spot may drain to the outside and finally heal. If this fails, the lymph nodes come into play, and then it is time to see your doctor. Your phagocytes also produce a sub¬ stance called phagocytin ( fag oh sy tin) which is known to kill certain bacteria that invade the body. In these and other ways, your phagocytes are an im¬ portant line of defense against germ invasion. Chemical defenses: what are they? In times of germ invasion, your body also has the ability to produce specific protective chemicals. The story of the conquest of smallpox will help you to understand this type of defense against germs. An example: the conquest of smallpox Sam Lee had smallpox when the pic¬ ture reproduced in Figure 17-3 was taken. His face was scarred for life. You will probably never see anybody with a face scarred by smallpox, but 300 years ago, “pock-marked” people were common everywhere. For example, in Gloucestershire, England, by 1750, the people of the countryside often said that their milkmaids were almost their only beautiful women. Milkmaids got cowpox from milking infected cows, but they almost never got smallpox, so their faces were not scarred. Edward Jenner was born and grew up in Gloucestershire. A milkmaid told jenner that the country people in that region thought that getting cowpox from the cows they milked kept milk¬ maids from getting smallpox. At the time, Jenner was studying medicine with John Hunter, a great surgeon, teacher, and scientist in London. Jen¬ ner told Hunter that he thought he could somehow use cowpox, on a large scale, to protect children from small¬ pox. Hunter replied, “Don't think, try; be patient, be accurate.” Jenner followed Hunter's advice when he went home to Gloucestershire to practice medicine among the country people. In 1778, Jenner began to record his observations regarding cowpox as a preventive of smallpox. By 1796, he was ready to “try his idea. On May 14, 1796, Jenner took an eight-year-old boy, James Phipps, to a farm, where a milkmaid, Sarah Nelmes, had cowpox sores on her arm. Jenner scratched the bov’s skin. Then he took some matter J from one of Sarah’s cowpox sores and 450 THE FIGHT FOR HEALTH Clms. Pfizer & Co., Inc. 17-2 BACTERIA IN THE BLOOD STREAM This is a stained smear of blood from a person who had a “strep’ blood stream infection. One white blood cell (center) has ingested and partially destroyed many of the germs. ( 3,300 X ) rubbed it into the scratch. James Phipps soon had a typical cowpox sore at the site of the scratch. Soon the sore healed. After that, Jenner took James with him to call on smallpox patients, but James did not get smallpox. Finally, on July 1, 1796, Jenner once more scratched the boy’s skin and de- liberately rubbed matter from a small¬ pox sore into the scratch. James did not come down with smallpox. Jenner had put his idea to the test and it had been successful. As you know, we call this process vaccination. Next, Jenner vac¬ cinated his own children and many others. Each of them developed a cow- pox sore but none of them came down with smallpox, even when exposed to it. In 1798, Jenner published his results. Vaccination with cowpox spread quick¬ ly throughout Europe and America. And the death rate from this former killer began to fall. O Todav, doctors often vaccinate ba- bies against smallpox, and most states require this vaccination before children start school. As a result, smallpox is almost, but not quite, nonexistent in the United States. Occasionally a person from some part of the world where vac¬ cination still isn’t widely practiced brings the disease into this country. Then a small epidemic may break out among those who have never been vac¬ cinated or those who have been vacci¬ nated years ago but never revaccinated (vaccinated a second time). For this and other reasons it is still important for all children to be vaccinated before starting school, and for older persons IMPROVED CONTROLS ON ER DISEASES 451 to be revaccinated if they plan to go abroad, or if a case of smallpox appears in the community in which they live. Vaccination has been a great boon to mankind. Jenner was not the first to use vaccination, but he was the first to put the practice on a scientific basis. For that, he deserves great credit. Today we know that cowpox and smallpox are caused by viruses and that the two viruses are much alike. When a doctor injects cowpox virus into the skin, that virus induces the body to produce a protective chemical that keeps the person from contracting either cowpox or smallpox, even when exposed to them. A person who is thus protected from cowpox and smallpox is said to be immune to these diseases. Vaccination, then, is one example of the body’s ability to produce specific protective chemicals that make a per¬ son immune to specific germs or toxins or other poisons. Today we call all such protective chemicals produced by the body antibodies. The cowpox anti- 17-3 SMALLPOX SORES Sam Lee’s whole hody was scarred by smallpox. Vaccination would have prevented it. Acme bodies in James Phipps’s body made him immune to both cowpox and smallpox. Doctors today immunize children, and adults, too, against many diseases, either by injecting weakened or dead germs or their toxins into or under the skin. Doctors call these injections inocu¬ lations ( in ok yoo lay shuns ) . Each in¬ oculation induces the body to produce antibodies. When a toxin is injected, the antibodies produced are antitoxins, meaning “against toxins.” Another example: treating diphtheria with immune serum Working in Koch’s laboratory in Germany at the end of the last century, Emil von Behring (bay ring) weakened diphtheria germs and injected them into guinea pigs. The animals contracted mild cases of diphtheria. When they recovered, Von Behring withdrew some of their blood and treated it to remove the formed elements and the fibrinogen. What he had left, as you already know, was blood serum, but with diptheria antitoxin in it. Such serum is called immune serum. In 1893, Von Behring treated human beings, ill with diphtheria, with im¬ mune serum containing diphtheria anti¬ toxin. These patients usually recovered quickly, especially when the immune serum was given soon after the onset of diphtheria. In 1901, Von Behring was awarded the first Nobel Prize in medicine for this research. To this day, doctors treat diphtheria with antitoxin in immune serum ( obtained from horses ) . A third example: the conquest of rabies It was Louis Pasteur who discovered a way to prevent rabies. The Pasteur page 452 treatment consists of daily injections of progressively stronger rabies virus. The first day a very weak solution of the virus is injected, too weak to cause ill¬ ness but strong enough to start the production of rabies antibodies in the body. The second day a stronger dose of virus is injected, which stimulates the production of more rabies anti¬ bodies. After 14 days of progressively stronger virus injections, the body has produced enough antibodies to be im¬ mune to the disease. Rabies is a particularly horrible dis¬ ease. It cannot be cured, but it can be prevented by Pasteur treatment, if given in time. For this reason, it is urgent that anyone who has been ex¬ posed to rabies see his doctor imme¬ diately so that the treatment can be started promptly. Dogs most often contract and spread rabies, but cows, sheep, and other ani¬ mals, such as squirrels, bats, and foxes, also do so. Any suspected animal, in¬ cluding any dog that bites a person, should be reported at once to the local board of health. The exposed person should consult a physician immediately. We still have an occasional death from rabies in this country. Such deaths are due to carelessness or to ignorance of the necessary precautions. A fourth example: control of polio You have undoubtedly heard about the Salk vaccine for polio (Figure 17-4). You may have been inoculated 17-4 DR. JONAS SALK Dr. Salk is injecting Salk vaccine to protect the child from polio. The work of many biologists laid the foundations upon which Dr. Salk and his team of co-workers based the research that finally led to the discovery of Salk vaccine. Testing the vaccine took years, but by 1958, the evidence was conclusive that this vaccine does protect most persons from paralytic poliomyelitis. The National Foundation for Infantile Paralysis with it. In 1954 and 1955, the vaccine was tried out on a wide scale, with re¬ sults so promising that it came into gen¬ eral use. Bv the end of 1957, the United States Public Health Service reported that cases of paralytic polio (polio re¬ sulting in paralysis of some part of the body) had decreased SO per cent in two years. To make the Salk vaccine, polio virus is first grown in test-tube cultures of living tissue from the kidneys of mon¬ keys. Then the virus is extracted, killed, and used in inoculation (Fig¬ ure 17-4). The nature of your chemical defenses You probably see now what we mean by your body’s chemical defenses against germ diseases. If certain germs O O O get by the skin, the lymph glands, and the white blood cells and start a dis¬ ease— say, diphtheria— your chemical de¬ fenses take up the battle against them. In cases of diphtheria, whooping cough, and lockjaw, the germs release a toxin in the patient’s body. This toxin stimulates the body to produce an anti¬ toxin that neutralizes the toxin. If a whooping cough patient in the “good old days” could produce the antitoxin fast enough, he got well. All too often, he couldn’t. Then he died. But if he got well, the antitoxin stayed in his body for vears or even for the rest of his life. j That is why a person who has had whooping cough once is unlikely ever to get it again. The antitoxin in his body is a chemical defense against it. You probably know, too, that persons can gradually become immune to some deadly poisons, even snake poisons. This happens when small amounts of the poison enter the body at first, and then larger amounts over a period of time. Gradually the body produces some kind of protective antibody that neutralizes the poison. All the substances which can induce the human body to produce antibodies are called, collectively, antigens (an tihjenz). Diphtheria toxin is one anti¬ gen. Typhoid germs are another. Snake poison is still another. And there are many more. Your ability to produce antibodies when antigens get into your body is one of your best protections against many diseases. Immunizing infants and children Today doctors usually give babies a series of three “shots” before they are many weeks old. These “shots” immu- nize the infants to diphtheria, lockjaw, and whooping cough. Each “shot” is a mixture of normal saline with the toxins of diphtheria, lockjaw, and whooping cough germs. These toxins induce each baby’s body to produce the antitoxins that make him immune to the three dis¬ eases. The immunity thus induced may last a year or more. Then the doctor usually recommends a second series of “shots,” usually called “booster shots,” since they boost the falling immunity. Doctors often vaccinate babies against smallpox, too, but usually wait until the child is approaching school age. Salk vaccine to prevent polio is given to many children of varying ages. Types of immunity We are born immune to many bac¬ teria and other agents of disease. Hu¬ man beings do not contract distemper from dogs, or virus disease from tobacco plants infected with tobacco mosaic. Like other animal species, we are natu¬ rally immune to some germs and sus¬ ceptible to others. Furthermore, the different tissues in the human bodv J vary in their susceptibility to specific 454 THE FIGHT FOR HEALTH agents of disease. For example, most of our tissues are relatively immune to the polio virus and to the tetanus bacillus or the meningitis coccus, but unfortu¬ nately our nerve tissue is highly suscep¬ tible to all three. We have certain inborn immunities of the whole body; we also have inborn tissue immunities. These are spoken of as inborn immunities, in contrast to acquired immunities, which we acquire during our lifetime, either by having the disease or by being immunized against it. Table 17- A summarizes the methods now in use in inducing immunity to a number of germ diseases. STARTING AN IMMUNITY RECORD. Title a page in your record book My Immunity Record. Find out from your parents what germ diseases you have had. List them. Beside each one, tell whether you are likely to get it again. Example: "Whooping cough— I am probably immune to it." Also list the diseases to which you have been immunized. Your parents will know what shots you had when an infant. Use Table 17-A to help you make this list. TABLE 17-A METHODS OF INDUCING IMMUNITY TO GERM DISEASES Type of injection used Some diseases prevented bp these injections Weakened viruses Smallpox, rabies, polio, yellow fever Dead Typhoid fever, whooping microorganisms cough, some pneumo¬ nias, epidemic meningitis Toxins Diphtheria, lockjaw, scar¬ let fever, whooping cough Antitoxins Lockjaw, measles, epi¬ demic meningitis Immunization is widely used to pre¬ vent disease. It has helped to reduce death rates from diphtheria, smallpox, typhoid fever, and several other dis¬ eases to new lows with each passing year. Summing up: defenses against germs Your own body is your best defense against germ diseases. Built into your body are a number of defensive mech¬ anisms. They include: (1) your skin, (2) your lymph nodes, (3) your “stand¬ ing army,” the white blood cells called phagocytes, and (4) your antibodies (plus your ability to make new kinds when needed). Today, doctors immunize young in¬ fants against diphtheria, whooping cough, lockjaw, and smallpox. They immunize children against polio. They may immunize people against several other germ diseases, including typhoid fever, influenza, rabies, scarlet fever, and yellow fever. Booster shots may be necessary to keep up the level of the antibodies that protect you from diphtheria, lockjaw, and a number of other diseases. NEW MEDICINES The last 40 years have brought a number of new medicines into the news. Before 1920, there were only a few specific drugs for specific diseases. Two of them were quinine for malaria and arsenic compounds for syphilis. Then in 1922 came insulin for diabetes. The year 1928 brought liver extract for pernicious anemia. Since then, one specific drug after another has been produced, until today some medical men look hopefully to a time when there will be a “drug for everv human ill.” IMPROVED CONTROLS OVER DISEASES 455 Sulfa drugs In 1935 the sulfa drugs were news. Newspapers carried headlines like these: “New Miracle Drug Cures Blood Poisoning” or “New Drug Stops Pneu¬ monia in 24 Hours.” Today such sulfa drugs as sulfanilamide ( sul fuh nil uh myde), sulfadiazine (sulfuhDYuh zeen ) , and sulfathiazole ( sul fuh thy uh zohl ) have become commonplace, or nearly so. Since their discovery, the sulfa drugs have restored to health many thousands of people— people who would have died, only a few years earlier, of such diseases as strep throat, strep pneu¬ monia, strep blood stream infection (“blood poisoning’), childbed fever, certain types of meningitis, and many more. Sulfa drugs are to be used only under the direction of a physician, since they sometimes produce harmful side effects. Penicillin By 1929, Dr. Alexander Fleming had proved that “something” made by the mold Penicillium would stop the growth of staphylococci. He named this “something penicillin. But it took a team of scientists to learn how to ex¬ tract penicillin from the mold. This team of scientists was successful dur¬ ing the early part of World War II. Toward the end of the war, penicillin was widely used in treating wounded men in the Armed Services. By 1946, biochemists had learned how to syn- thesize penicillin and to produce suffi¬ cient quantities of it to treat all pa¬ tients who need it. Since 1946, penicillin has been widely used, along with a sulfa drug, to treat bacterial pneumonia. The death rate from pneumonia has been falling steadily ever since 1937, when the first sulfa drug began to be used in treating it, and it has fallen rapidly since penicillin became avail¬ able (Figure 17-5). Today the pneu¬ monia death rate is only a fraction of what it was before 1937. Penicillin has also been widelv used J in treating nearly everything from the common cold ( in which it is of little di¬ rect benefit), boils, carbuncles, and in¬ fected wounds to syphilis, gas gangrene, bladder infections, mastoid infections, and many more. Like the sulfa drugs, penicillin sometimes produces harmful side effects and should be used only un¬ der a doctor’s direction. You undoubtedly know that penicil¬ lin is an antibiotic ( an tih by ot ik ) . An antibiotic is any antibacterial or anti¬ germ substance produced by a living organism, especially by a bacterium or by a mold or some other fungus. Many antibiotics are in use today. LISTING ANTIBIOTICS. You have un¬ doubtedly known of the use of antibiotics. You may have been given one or another for some illness or infection. Let each member of the class name any antibiotics he has heard of and the disease or condition it was used to treat. On the chalkboard, list each item named. Title a fresh page in your record book Antibiotics and Their Uses. On this page, copy the completed list from the chalk¬ board. More and more antibiotics New antibiotics are being discovered all the time. Several hundred are now known, but most of these cannot be used in treating diseases of human be¬ ings, because they have toxic (poison¬ ous ) effects on man. In 1956 some 46 antibiotics were available for treating human diseases, 456 THE FIGHT FOR HEALTH 17-5 The first sulfa drug effective against pneumonia came into use in 1937. Penicillin became available to the general public in the United States in 1945-46. The value of these two drugs shows up in falling death rates. according to William S. Spector’s Handbook of Biological Data (W. B. Saunders Company, Philadelphia, 1956, pages 404-06). Of these, only a few are widely used. Here, we need men¬ tion only five. Antibiotics now widely used include: Penicillin Streptomycin ( strep toh my sin ) Achromycin ( ak roll my sin ) Chloromycetin ( klor oh my see tin ) Erythromycin ( ee rith roll my sin ) Table 17-B summaries the uses of these antibiotics. Better control over tuberculosis Streptomycin, along with certain other new drugs, the isoniazids (eye soli ny uh zidz ) , which are not anti¬ biotics, is helping to bring tuberculosis under increasingly better control. Tu¬ berculosis death rates have been falling ever since the turn of the century and they have fallen even more rapidly since the discovery of streptomycin and the isoniazids. Decrease in effectiveness of new medicines Unfortunately, both the sulfa drugs and some of the antibiotics prove less and less effective, the more widely they are used. In any given case of infectious disease, there are usually a few germs that are resistant to sulfa drugs or to an antibiotic. These few survive the treatment. Gradually the more resistant germs increase in number as the less resistant ones perish. After sulfa drugs and antibiotics have been used for a few years, more and more strains of highly resistant germs appear. Then the drugs are less effective. Even so, the sulfas and the antibiotics will con- IMPROVED CONTROLS OVER DISEASES 457 tinue to be among our most useful means of controlling germ diseases. Better antimalarial drugs World War II resulted in the expo¬ sure of millions of young Americans to malaria, particularly in the Southwest Pacific and in Africa. Quinine, the spe¬ cific for malaria, was available only in small quantities, since the Japanese had control of the great quinine-producing area in the Dutch East Indies. Fortu¬ nately, another fairly effective preven¬ tive drug was available. This was Ata- brine (ATuhbrin). Yellow Atabrine tablets were given regularly to all per¬ sons in war areas where malaria was known to be present. Research during recent years has added several antimalarial drugs to the list. Two quite effective ones are Amo* diaquin ( am oh dy uh kin ) and Aralen (AiRuhlen). Nevertheless, over the world as a whole, malaria is still man’s number-one enemy among germ dis¬ eases. Late in 1957, a world movement to try to control and eventually eradi¬ cate malaria was being planned. Other new drugs: tranquilizers Many other new and effective chem¬ ical treatments are now available for a wide range of illnesses. You already know about a number of them: vita¬ mins, minerals, and hormones. You have probably heard or read of the new drugs that we call tranquilizers (tran kwih lyz erz ) . Many doctors hail the tranquilizers as the greatest forward step yet toward the control of what they call mental illnesses. All doctors agree that it will take a long time to find out how safe and how widely effective the several tranquilizers are. But already, these drugs— used under a doctor’s careful direction— have proved useful in help¬ ing to control such conditions as alco¬ holism, drug addiction, and high blood pressure. You often hear people call someone a neurotic ( noo rot ik ) . Doctors call the less severe cases of nervous disor¬ ders neuroses ( noo roh seez ) and the more severe cases, “mental illnesses’’ or psychoses ( sy koh seez ) . The tranqui¬ lizers, used under a doctor’s direction, certainly do help in many neuroses and certain types of psychoses. Treatment with these drugs has calmed manv dis- turbed or violent patients, so that they can rationally discuss their problems with a psychiatrist. Hundreds and hun¬ dreds of mental-hospital patients are now back at home, and many are back at work, thanks to the doctor’s careful use of tranquilizers, along with other procedures, in treating them. As with all other new drugs that hit the headlines, tranquilizers may arouse false hopes of permanent cures or lead people to other incorrect conclusions. Already, there is some experimental evidence that tranquilizers may pro¬ duce some harmful side effects in lab- oratorv animals, when huge doses are given. Only future tests and experience will tell how useful the tranquilizers are. Summing up: new medicines Drugs and other new chemical treat¬ ments that have been developed in the last 40 years, but mostly in the last 20 years, have played a major role in bringing most germ diseases and sev¬ eral noninfectious diseases and condi¬ tions under control. Table 17-B summarizes a few of the most widely used drugs and other chemicals used in the treatment of hu¬ man disease. 458 THE FIGHT FOR HEALTH TABLE 17-B DRUGS AND OTHER CHEMICALS USED IN TREATING HUMAN DISEASES Name Conditions or diseases treated Achromycin Ear, sinus, and throat infections, bone in¬ fections, pneumonia, scarlet fever, menin¬ gitis, gonorrhea, un- dulant fever, and many more diseases Amodiaquin, Aralen, Atabrine Malaria Chloromycetin Parrot fever, rabbit fe¬ ver, typhus fever, one kind of pneumonia, smallpox, and many more bacterial, rick¬ ettsial, and virus dis¬ eases Erythromycin Certain rickettsial and virus diseases, second¬ ary syphilis, and oth¬ ers Hormones Diabetes, cretinism, tet¬ any, and degenerative diseases of the aging Isoniazids Tuberculosis and certain others Penicillin Pneumonia, colds, boils, syphilis, gas gangrene, epidemic meningitis, kidney and bladder infections, and many more bacterial dis¬ eases Quinine Malaria Streptomycin Tuberculosis, rabbit fe¬ ver, ulcers of the cor¬ nea of the eye, and several more Sulfa drugs Many bacterial diseases Tranquilizers High blood pressure, al¬ coholism, drug addic¬ tion, neuroses, psy¬ choses Vitamins and Deficiency diseases such minerals as rickets, scurvy, pel¬ lagra, beriberi, and others IMPROVED METHODS OF DIAGNOSIS The modem doctor has at his com¬ mand not only greatly improved meth¬ ods of fighting diseases, but also far better ways of finding out what is wrong with a person who is ill. The word for finding out what is wrong with one who is ill is diagnosis ( dy ug noh sis ) . When a doctor sees a sick person, his first task is diagnosis. Tools and laboratory tests The doctor has many tools to help him. He has a clinical thermometer with which he can discover the patient’s temperature. He has a stethoscope (steth oh skohp ), with which to listen to heart sounds and sounds in the lungs or in the abdomen. He has a device with which to take the patient’s blood pressure. He has instruments with which he can look into ears, eves, nos- trils, and throat. He has other tools, too. He also has at his disposal a modern hospital laboratory where he can have many tests made when they are indi¬ cated. In the laboratory, urine is tested for sugar, for albumin, and for pus and blood. Counts of both red and white blood cells are made, when necessary. The amount of hemoglobin in the blood can be measured and compared with a known norm. The amount of sugar and other substances in the blood can be determined. The basal metabolism test (see page 378) may be made. The doc¬ tor can have any of these and other lab¬ oratory tests made to help him arrive at a correct diagnosis. A white-blood-cell count is especially helpful in the diagnosis of certain infec¬ tious diseases. When certain kinds of germs invade the body, the white- IMPROVED CONTROLS OVER DISEASES 459 blood-cell count goes up (see Table 17-C). Indeed, the increase in the num¬ ber of white blood cells during an acute infection is so common that doctors usu¬ ally use the white-blood-cell count, along with what they call a differential white-blood-cell count (a count of the different types of white blood cells, made to discover which types, if any, are on the increase), to determine whether there is an infection and to judge its acuteness. It is a very useful aid to diagnosis. X-ray examination is still another valuable means for helping discover certain types of disease. A doctor may refer a patient to an X-ray specialist for examination of almost any part of the body. It takes long years of training and experience to enable a doctor to become a specialist in the use of X rays in diagnosis and treatment. Only spe¬ cialists are competent to render this service. Doctors who are X-ray special¬ ists are called roentgenologists (rent g’n ol oh jists), from Roentgen, the dis¬ coverer of X rays. TABLE 17 -C WHITE-BLOOD-CELL COUNTS Condition White-cell counts commonly found Good health 5,000 to 7,000 * Acute appendicitis 12,000 to 15,000 or more Ruptured appendix 18,000 to 25,000 or more Pneumonia (bacterial) May be 20,000 or more Whooping cough 20,000 to 30,000 or more Scarlet fever 20,000 to 30,000 or more Leukemia Usually very high, 50,000 to 100,000, or even 200,000 or more * These numbers and all of those that follow indicate the number of white blood cells per cubic millimeter of blood. Knee Broken ends of leg bones Bone chip Ankle 17-6 X-RAY PHOTOGRAPH OF A BROKEN LEG After the bones have been “set,” an¬ other X-ray photograph is made to make sure that the broken ends meet properly. ! X rays in diagnosis You probably know of several per¬ sons who have had X-ray pictures taken of broken bones (Figure 17-6), so that the bones could be “set’’ correctly, but there are many other uses of X rays in diagnosing and treating the sick. X rays are used in diagnosing tuberculosis (Figure 17-7), gallstones, kidney dis¬ ease, bone tumors, bone infections, gas¬ tric ulcers, rickets, scurvy, cancer of the stomach and of other parts of the ali¬ mentary canal, brain tumors, and other conditions. X-ray pictures of organs made up of soft tissues, such as the stomach, gall bladder, or kidney, cannot be taken successfully unless some foreign sub¬ stance which is opaque ( oh payk ) to X rays has first been put into that soft tissue. (An opaque substance is one 460 THE FIGHT FOR HEALTH through which light rays or X rays will not readily pass.) For instance, a pa¬ tient must drink about a pint of liquid that contains barium sulfate before the roentgenologist can make an X-ray ex¬ amination of the stomach and intestine. Barium sulfate stops X rays, much as bones do; therefore, a stomach contain¬ ing barium sulfate can be photographed by X rays (see Figure 12-4, page 333). An ulcer, if present, will then show up in the X-ray photograph. Similarly, some substance that stops X rays must be in the gall bladder or the kidneys before good pictures of these organs can be taken. The need for moderation in use of X rays It has taken studies of dangers from the fall-out of atomic weapons to call our attention fully to possible dangers in using X rays too freely. The radio¬ active effect of X rays is cumulative; that is, each X ray an individual takes adds a certain amount of radioactivity that stays with him throughout his life. There is no need for alarm, since it would take far more X rays than the average person ever gets to cause defi¬ nite physical harm. And yet there are many people who get so many X rays during their life that harmful effects must be considered more than a remote possibility. In consideration of possible cumula¬ tive effects of X rays, the National Tu¬ berculosis Association now recommends that periodic X rays not be used on school children for the detection of early stages of tuberculosis unless a skin test has first been given, with positive results. In other words, only those chil¬ dren who react positively to a skin test will be given a chest X ray to determine definitely whether or not they have the 17-7 X-RAY PHOTOGRAPH OF THE LUNGS The dark areas indicate the lungs; the light area between them, the heart. These lungs are normal; they are without the spots characteristic of tuberculosis. disease. As for other uses of X rays, you should not fear them, but generally you should submit to them only if they are administered by a roentgenologist. Early diagnosis of tuberculosis is important Tuberculosis can be arrested or cured in its early stages (Figure 17-8). The more advanced it is, the less curable it becomes. This does not mean that more advanced cases are hopeless. With streptomycin and the isoniazids, ad¬ vanced cases may respond. But early treatment is much better. There are certain tuberculosis “dan¬ ger signals” which should send anyone to his physician at once. Among these danger signals, the following are com¬ mon: 1. A persistent, hacking cough. 2. A slight rise in temperature each afternoon, perhaps to 100° F. IMPROVED CONTROLS OVER DISEASES 461 Wide World Photo 17-8 ISONIAZIDS AND TUBERCULOSIS Both white mice were infected with tuber¬ culosis. The one on the right was given an isoniazid and remained healthy. The other died. 3. A rapid loss of weight. These “danger signals” do not neces¬ sarily mean that a person has tubercu¬ losis. They do mean that he should see his physician at once. The tuberculosis death rate has been falling rather rapidly for years. In 1900, it was 254 per 100,000 people in this country. Today it is considerably less than 10 per 100,000 people, and is fall¬ ing more every year. Early diagnosis and correct modern treatment may J wipe this former killer “off the slate” in the not-too-distant future. Radioactive tracers In Chapter 14 you read about the endocrine glands and their work. Cer¬ tain endocrine disorders can be diag¬ nosed by the use of radioactive tracers, or radioactive isotopes of common ele¬ ments. For example, radioactive iodine may be administered to a patient with a suspected thyroid disorder. Instru¬ ments that can trace the path of the io¬ dine through the body then help check on how well the thyroid gland utilizes J O the iodine. Summing up: improved methods of diagnosis Improved methods of diagnosis are playing their part in the control of many diseases. The modern doctor brings a whole battery of tools and tests into play when a person falls ill. He makes a personal examination, checking heartbeat, breathing sounds, blood pressure, and many other matters. He calls on roentgenologists for needed X rays, and on laboratory technicians for blood-cell counts and urine tests. When he suspects disease, he may call on specialists in the study of diseased tissues. Many people and their services are needed for modern diagnosis. MODERN SURGERY There are some diseases in which a surgical operation is necessary. Acute appendicitis and gallstones are exam¬ ples. Other conditions that are treated successfully by operation are: infected tonsils, stomach ulcers, cancer in early stages, toxic goiter, crooked bones, and many more. Several discoveries have made modern surgery possible. Partial conquest of pain The modern surgeon could hardly play his part in the fight against disease without some means of preventing and relieving pain. On March 30, 1842, Dr. Crawford W. Long of Jefferson, Geor¬ gia, performed the first known opera¬ tion using ether. On October 16, 1846, at the Massachusetts General Hospital in Boston, Dr. William Morton admin¬ istered ether while Dr. J. C. Warren re¬ moved a tumor. The operation was per¬ formed before an audience and was entirely painless. This public demon¬ stration that a way had been found to make surgical operations painless led to its general use. It was Dr. Oliver Wen- 462 THE FIGHT FOR HEALTH dell Holmes who suggested the name anesthetic ( an us thet ik ) , from a Greek word meaning “not feeling.” The painless condition of “not feeling” produced by anesthetics is called anes¬ thesia ( an es thee zhuh ) . Those who are specialists in administering anes¬ thetics are anesthesiologists ( an es thee zhee ol oh jists ). “Laughing gas” (ni¬ trous oxide) and chloroform, as well as ether, have been used as anesthetics for years. In recent years several new anes¬ thetics have been put into use. Sodium pentathol ( pen tuh thol ) is widely used for operations that do not take too long. There are also ways to relieve the pain when the patient recovers con¬ sciousness following an operation. Mor¬ phine is one of the most effective pain¬ killing drugs, but many others are also in use. It was a great day for mankind when a way was found to get morphine out of opium and to control the size of the dose so that it could be used safely to relieve pain. Even with ether and other anesthetics, it is hardly likely that modern surgery could be used as widely and successfully as it is without morphine and other pain-relieving drugs. In recent years, the treatment of pa¬ tients who have just undergone surgery has changed. Most postoperative pa¬ tients are now allowed to eat on the same day after surgery and are up and about in a day or two; though, of course, there are many exceptions. Many patients leave the hospital in two or three days or, at least, in less than a week. These practices make operations today much less painful and serious events than they used to be. Prevention of infection A hundred years ago, it was not un¬ usual for 95 out of 100 patients who underwent surgery to die— not from the operation, but from infection of the incision. In those days, able-bodied men assisted the surgeons bv holding down the writhing, screaming patients. Instruments were not sterilized, and the linens used about the patients were often not even clean. Surgeons wore street clothes while operating. Natu¬ rally, many infections occurred. Today, infections following opera¬ tions are exceedingly rare. Surgeons and their assistants scrub their hands and arms with liquid soap and with antiseptics, such as bichloride of mer¬ cury. They wear sterile gowns, caps, masks, and gloves during the operation (Figure 17-9). Instruments are ster¬ ilized by being placed in boiling water for 20 minutes or more. Linens used about the patient, as well as dressings, are sterilized by being placed under high steam pressure for at least 30 min¬ utes. Operating rooms are kept as near¬ ly free from germs as it is possible to keep them. In these ways, the death rate from infection following operations has been reduced almost to the vanish¬ ing point. Partial conquest of appendicitis In the earlv days of our nation there was a common and highly fatal disease known then as “acute inflammation of the stomach and the bowels.” This con¬ dition usually originated in the appen¬ dix (Figure 17-10), which you remem¬ ber is a hollow tube, smaller in diam¬ eter than a pencil and some two or three inches long, projecting from that portion of the large intestine which is located on the lower right side of the abdomen. In appendicitis, bacteria (or some¬ times amebas ) attack the tissues of the wall of the appendix. White blood cells IMPROVED CONTROLS OVER DISEASES 463 Conrad Eiger 17-9 MODERN OPERATING ROOM The surgeon, two assistant surgeons, the surgical nurse, and the anesthesiologist (right), all in sterile caps and gowns, are experts in practices which prevent infections of incisions. (phagocytes) rush to the scene of the attack. If they cannot destroy all of the germs, the appendix swells and its walls 17-10 NORMAL AND INFLAMED APPENDIX The appendix is attached to the caecum, the “blind” end of the large intestine. The inset shows a badly infected appendix. weaken. If this continues without medi¬ cal treatment, the appendix may rup¬ ture (burst open). This releases germs into the abdomen, where they infect the lining of the abdomen, causing peritonitis ( pehr ih toh ny tiss ) . Peritonitis used to kill a high percent¬ age of those who had it. Today, it is usually treated successfully, but it is still a serious disease. So it is important to know what to do and what not to do when you get a severe “stomach ache” that doesn’t go away. Any pain in the abdomen, any “stomach ache,” may be due to appendicitis, if you still have your appendix. Here’s what to do when abdominal pain strikes, pain that may come from an infected appendix: 1. Don’t take anything by mouth ex¬ cept water. 2. Keep quiet and apply an ice pack, but not a hot-water bottle. 3. Above all, dont take a laxative, like Epsom salts or castor oil. A laxa¬ tive may make an infected appendix rupture. 4. If the pain persists for three or four hours, call your doctor and do as he says. Today, doctors can often bring ap¬ pendicitis under control without opera¬ tion. But only your doctor can find out whether or not you have acute appen¬ dicitis and, if so, whether operation is necessary. Summing up: modern surgery Surgery is one of the effective ways of controlling some diseases, such as appendicitis, and the only way yet known to get rid of gallstones and some other conditions. Anesthetics, pain-relieving drugs, sterile instruments and linens, and im¬ proved postoperative care are among the things that make surgery so success¬ ful today. PREVENTION OF INFECTIONS AND OTHER SERIOUS RESULTS OF INJURIES Perhaps you do not ordinarily think of the results of injuries as diseased conditions, but we shall nevertheless include here discussions of some of the things you can do to help prevent in¬ fections and other serious results of in¬ juries, since this knowledge plays a part in the maintenance of health and of life itself. Treatment of minor wounds You can usually prevent infection in small wounds or burns you may re¬ ceive. As you know, any break in the skin means a possible entrance for germs. The important thing is to wash away any germs that enter and to pre¬ vent the entrance of other germs. To treat a small wound, you need some sterile ( germ-free ) gauze, a fresh cake of soap or a bottle of liquid soap such as doctors use, and running tap water. With soap on the sterile gauze, scrub the wound thoroughly under run¬ ning tap water to clean out every bit of dirt. This will wash out most of the germs. Rinse the wound with clean wa¬ ter, dry it with sterile gauze, and cover it with a sterile but not airtight dress¬ ing. Keep the dressing dry and clean until the wound heals. Sometimes it is not possible to wash out small cuts, as when you are on a field trip. Then it may be advisable to apply iodine to a small cut. Be sure to use a 2-per-cent ( never more) tincture of iodine. Never apply iodine to deep open wounds, as it may burn the ex¬ posed tissues. Usually it is better not to apply a dressing to a wound treated with iodine. Major wounds should not be washed. A doctor should take care of major wounds as soon as possible. Small burns should be cleaned care¬ fully. One of the special ointments sold for burns may be applied, and a sterile dressing used to cover it. An extensive burn should not be treated at all with home remedies, but the patient should be taken at once to a physician or to a hospital. Bone fractures A broken bone always needs the at¬ tention of a physician. In many cases, especially when the extent of the in¬ jury is unknown, the best thing you can do is to keep the patient quiet and warm and call an ambulance. If you IMPROVED CONTROLS OVER DISEASES 465 American Red Cross Photo 17-11 EMERGENCY FIRST AID Splints have been applied to the patient’s broken leg. cannot reach an ambulance and must move the patient, you will need to be careful not to cause further injury to the soft tissues near the break. For ex¬ ample, you may bind a broken leg to a board or some similar object by placing bindings (not tight bindings) above and below the knee and above and below the injury, but not right over the injury (Figure 17-11). Moving the patient after that is not likely to cause the broken bone to do further damage to nearby tissues, and you can get him safely to a hospital or doctor. Compound fractures are those in which the broken bone punctures the skin. In these cases, you should try to keep dirt and germs out of the wound by covering it with sterile gauze or any “clean cloth at hand. Then keep the patient quiet and warm until he is un¬ der medical care. Control of bleeding Most common wounds stop bleeding naturally as soon as the blood has time to clot (normally in from two to seven minutes). Sometimes, however, a large vein or an artery may be cut. In such cases, the bleeding must be brought under control bv artificial means. In J nearly all cases of severe bleeding, the very best thing an onlooker can do is to apply pressure to the bleeding wound. If you have sterile gauze, use it to cover the wound, then apply pressure with your hand. If you have no sterile gauze, press the bare palm of your hand over the bleeding wound. Get someone to cover the patient with something to keep him warm and call an ambulance or a doctor, while you keep on apply¬ ing pressure. Or get someone to drive the patient and you to a hospital while you continue to apply pressure. Many a life has been lost unnecessarily from severe bleeding because no onlooker knew how to control the bleeding bv applying pressure. Severe blows on the head A severe blow on the head may re- suit in unconsciousness. When this hap¬ pens, lay the patient flat on his back and keep him warm while someone calls a doctor or an ambulance. In the meantime, don’t let anyone raise the patient’s head or move him at all. Do¬ ing so may increase the internal in¬ juries in the head and do serious harm. Summing up: care of injuries You can take care of minor wounds and burns yourself. Clean them thor¬ oughly and apply a sterile dressing. In any serious injury, keep the pa¬ tient quiet and warm, apply pressure to a seriously bleeding wound, and get medical help. PREVENTION BETTER THAN CURE Today the main emphasis in health is on prevention. “An ounce of prevention is worth a pound of cure” is a major 466 THE FIGHT FOR HEALTH theme in modern life. Yon and your family do many things every day that help to keep you well. So do thousands and thousands of other people. But still, you and everybody else could do even more. Your daily habits and health You may and probably already do have important health habits, such as cleanliness, regular eating and sleeping habits, and a balanced diet. All of these things help to keep you in good health, and good health is your best protection against many diseases. Cheerfulness and good health According to Selye’s theory (page 380), prolonged stress and strain in time exhaust the body’s ability to ad¬ just to stress and strain. Then a person may develop a neurosis or even a psy¬ chosis. It pays to cultivate cheerfulness. If you worry a lot, especially over small things, talk over your problems at home or with a friend. Better yet, if you can’t change the worry habit, if it is a habit, see your doctor. He is better able to help you today than ever before. Public health agencies The United States Public Health Service and state, countv, and citv de- J 7 J partments of health are busv the year round. Their main work is to guard the public health; that is, to prevent rather than cure. However, public health serv¬ ices do maintain hospitals, both state and federal, where certain types of ill¬ nesses are treated. And these services, especially the federal health service, do important and extensive researches on diseases. But most of their work is pre¬ ventive. Here is a list of some of the things federal, state, or local health agencies do, probably in your own community and certainly in your state. 1. They supervise the treatment of city water supplies (filtration, chlorina¬ tion) to make sure that the water is germ-free. Bacterial counts of city wa¬ ter are made often, usually every day or two. 2. They inspect cattle barns and dairies and make sure these meet re¬ quired standards. This includes inspect¬ ing the pasteurization of milk, now re¬ quired in most states, to see that it is done correctly (Figure 17-12). 3. They inspect meats and other foods. When you see “U. S. INSP’D & PSD" (inspected and passed) on a beef roast, you know a federal inspector put it there (Figure 17-13). 4. They test meat animals, especially beef cattle, for tuberculosis and Bang’s disease (called undulant fever in hu¬ man beings). 5. They keep vital statistics, such as birth and death records, and records of contagious diseases, such as measles, 17-12 PASTEURIZATION INSPECTION Most health departments require that the tem¬ perature of milk undergoing pasteurization he checked. Why? City of New York. Department of Health mumps, whooping cough, scarlet fever, typhoid fever, and tuberculosis. 6. They direct and record premari¬ tal, prenatal (before birth), and occu¬ pational blood tests. In many states, a blood test and other health examina¬ tions are now required of all people who handle food for sale in markets and public eating places and of all bar¬ bers and other persons in occupations that are of critical importance in the campaign against diseases. 7. They make sure that sewage and garbage are so disposed of that they do not transmit diseases. 8. When necessary, they see that vaccinations are given to prevent ra¬ bies, polio, smallpox, and other dis¬ eases. 9. They help to enforce all state and federal laws that help guard the public health (Figure 17-13). 10. State governments set up and have charge of industrial insurance to cover workers who are injured on the job. School nurses and doctors and public health nurses and doctors spend part of their working day, or often all of it, 17-13 MEAT INSPECTION Inspected meat carries a stamp which shows that the meat has been inspected. Why is this important? U.S.D.A. protecting the health of school children and the general public. Without these and dozens of other government health services, life as we know it today could not go on. Federal and state control of narcotics You read and hear about "dope” in newspapers and magazines rather often these days. It is true that some teen¬ agers have become drug addicts. Na¬ tional, state, and city governments have become concerned about the problem, so much so that many states have passed laws requiring that the dangers of drug addiction be taught in the public schools. Drug addiction, as you already know, is one cause of illnesses that are sometimes fatal. So what are the facts? Narcotic drugs Narcotic drugs are those which, in moderate doses, allay sensations, re¬ lieve pain, and induce in some people profound sleep, but in large doses pro¬ duce unconsciousness, stupor, or even convulsions or death. Narcotic drugs include morphine, heroin (hehr oh in), opium, codeine ( koh dee in ) , marijua¬ na ( mair uh wah nuh ), and others. All of those named except marijuana are derived from the opium poppy. All of these narcotics, with the pos¬ sible exception of marijuana, are not merely habit-forming, but addicting. Doctors call a user of narcotic drugs an addict when the habit is so firmly es¬ tablished that he cannot stop using the drug without suffering withdrawal sick¬ ness, a mentally and physically painful and serious condition. Extent of drug addiction We probably have about 60,000 drug addicts in the nation. Of these, some 13 per cent are under 21 years of age. Some are under 15. These figures come from a report which appeared in three articles in the Journal of the American Medical Association, beginning with the issue of November 30, 1957. The same report goes on to say that there was an increase in the number of teen-age drug addicts following World War II, even as there was following World War I. It also says that the stud¬ ies of a council on mental health ap¬ pointed by the American Medical As¬ sociation show that drug addiction usually spreads from person to person, with an addict giving drugs to a “friend” who is not an addict. Some¬ times, but not often, according to the report, “drug peddlers” who work for a “dope ring” start a person on the way to addiction. Federal control The sale and use of drugs that may lead to addiction are rigidly controlled by federal laws. For one thing, it is against the law for anyone to possess marijuana or heroin. For another, a doctor’s prescription is necessary to get any of the other narcotic drugs. For still another, doctors, hospitals, phar¬ macists, and all others who may legiti¬ mately dispense narcotics for useful purposes must keep accurate records of all narcotics purchased and dispensed. If our current laws were fully obeyed, we should have virtually no drug ad¬ diction at all. But unfortunately there are criminals who make big money out of peddling illegal drugs. Law enforce¬ ment officers are busy all the time trying to prevent this traffic in illegal drugs, but it takes the co-operation of an in¬ formed public as well as law enforce¬ ment officers to stamp out this crime. The United States Public Health De¬ partment maintains two hospitals where drug addicts are treated and many are cured. Doctors who have treated teen¬ age addicts report that these addicts usually complain that no one had ever told them of the dangers they faced in using “dope.” Certain narcotics, used under a doc¬ tor’s careful supervision, have been and will continue to be a great blessing to those who suffer severe pain, postoper- atively or in serious accidents or ill¬ nesses. But the use of narcotics “just for a thrill” or for any other reason ex¬ cept the medical ones mentioned is in¬ jurious to health and may cause death. Mental health and narcotics Many doctors are convinced that drug addiction is due, partly, to some form of mental illness, even as alcoholism may be at least partly of psychological origin. So one phase of the addiction problem has to do with finding better ways to prevent and to cure mental ill¬ nesses. Besearches in this field are go¬ ing on all the time. Already the tran¬ quilizers are helping, in that they re¬ lieve many of the discomforts that usu¬ ally accompany withdrawal sickness. Other treatments are also helpful. One thing is sure. A person stands little chance of becoming a drug addict if he never uses narcotics unless pre¬ scribed by his physician. Most people in our nation never use narcotics il¬ legally. The comparatively few who do may be treated, and often cured. Pre¬ vention is certainly far easier than cure. CHAPTER SEVENTEEN: SUMMING UP Epidemics never did kill off all the people, or we wouldn’t be here today. In spite of diseases, Homo sapiens has survived through the ages, largely be¬ cause the human body has its own IMPROVED CONTROLS OVER DISEASES 469 built-in defenses against many diseases. The body’s defenses include: (1) the skin, ( 2 ) the lymph nodes, ( 3 ) the phagocytes, and (4) the body’s ability to produce antibodies. Some 300 years ago, people began to discover artificial ways to prevent or control one disease after another— small¬ pox by vaccination with cowpox, and malaria with quinine. These led to our use of inoculation to prevent a whole host of germ diseases, and to the use of specific drugs to prevent or to cure a whole host more. Now comes the dawn of still another new day, with a still wider point of view upon health and disease. This growing point of view is that every in¬ jury and every disease disturbs the body’s homeostasis. This means that the up-to-date doctor looks at each pa¬ tient as a whole individual, one whose heredity and past life must be consid¬ ered, both in health and disease. Your Biology Vocabulary Below is a list of the important new terms in this chapter. All of you will hear, read, and use most of them all your life. Those of you who plan to become nurses, doctors, dentists, hospital laboratory technicians, or pharmacists will need to know all of these terms. Pha gocytes phagocytin vaccination inoculation antitoxin antibodies Salk vaccine booster shots inborn immunity acquired immunity Testing Your Conclusions immune serum antigens sulfa drugs antibiotics stethoscope roentgenologist anesthetics anesthesiologist penicillin peritonitis tranquilizers isoniazids quinine Atabrine mental illness neurosis psychosis diagnosis drug addiction narcotic drug To summarize the main ideas in this chapter, answer the following questions. 1. What is meant bv immunization? J 2. Against what diseases should children be immunized before they are a year old? before going to school? 3. What diseases may be treated with antitoxin? 4. Against what diseases are toxins commonly used to inoculate infants? 5. When should persons be given Pasteur treatment? 6. What is the chief difference between such chemicals as sulfa drugs or isoniazids and antibiotics? (Remember the sources of each.) 470 THE FIGHT FOR HEALTH 7. Name several improved methods of diagnosis. 8. Why must a person drink a solution of barium sulfate before having his stomach X-rayed? 9. How may you avoid serious results from appendicitis? 10. Why is modern surgery usually successful and comparatively comfortable? List at least four reasons. 11. What are some of the methods used to kill germs outside the body, or to prevent their spread? 12. What are three danger signals of tuberculosis? 13. Why is it advisable to use only pasteurized milk? 14. What is the most successful way for a bystander at the scene of an accident to treat a cut artery? 15. How many antigens can you name that are known to cause the human bodv to produce antibodies? 16. List at least five laboratory tests that may help a doctor diagnose an illness. More Explorations 1. Question box. Prepare a question box that can be set up in the classroom. Make a list of questions you would like to have answered on any phase of disease control. You need not sign your name. Drop your list in the box. These questions may then be discussed in class. The school nurse or physician may be able to help. 2. A personal record. At the top of a fresh page in your record book, place the title A Record of My Own Illnesses. Under this title, record the following items: a. All of the diseases that you have ever had b. Which of these diseases you are unlikely ever to have again, and why c. Diseases against which you have been immunized d. Diseases against which booster shots may be needed Thought Problems What would you do in each of the following situations? 1. A fellow student offers you a bite of his candy bar. 2. A child falls from a tree and bumps his head hard on a rock. He loses consciousness. 3. A friend develops a dry, hacking cough and loses weight for no apparent reason. 4. A neighbor’s dog bites your little brother. 5. Your best friend develops a pain in the abdomen. 6. It is ten years since you were vaccinated, and a case of smallpox develops in your neighborhood. 7. You cut your finger with a paring knife. 8. You are always quite tired by four o’clock. Further Reading Antibiotics by Robertson Pratt and Jean Dufrenoy, Lippincott, 1949. Yellow Magic, the Story of Penicillin by J. D. Ratcliff, Random House, 1945. Miracles from Microbes, the Road to Streptomycin by Samuel Epstein and Beryl Wil¬ liams, Rutgers University Press, 1946. Natural History of Infectious Disease by Sir Frank M. Burnet, Cambridge Universitv Press, 1953. American Red Cross First Aid Textbook, Revised Fourth Edition, Blakiston Division. McGraw-Hill, 1957. IMPROVED CONTROLS OVER DISEASES 471 CHAPTER Health Problems Yet to Be Solved "Just one wish" What would you wish, if you were sure that you could make just one wish and have it come true? One noted doc¬ tor said that his “one wish” would be that cancer start with severe pain. He knew that severe pain at the onset of cancer would send a patient to a physi¬ cian in time to be cured— for most can¬ cers can be cured if diagnosed in time. Dr. Chester M. Southam and his co¬ workers at the Sloan-Kettering Institute began a whole series of tests on prison volunteers in 1956, to find out whether injecting cancer cells would induce im¬ munity to cancer. Bv 1957, this team of investigators had shown that volun- teers previously injected with certain types of cancer cells had developed what looked like an immunity to a sec¬ ond implant of the same types of cancer cells. Of course, this research is not con- Brookhaven National Laboratory elusive in its findings, but it does offer another lead for further research. Cancer is one of the two main health problems still unsolved. Heart and cir¬ culatory diseases are the other (Figure 18-1). In this chapter, you will learn some of the hopeful aspects in our fight to control these diseases. CANCER AND ITS CONTROL The word cancer is often used to mean a “growth.” In this sense, a plant gall (Figure 18-2) may be called a plant cancer. So may any “growth” on any animal. When the word is so used, it may be said that cancer is common to all living things, both plant and ani¬ mal. It occurs in many animals— Hies as well as fish, frogs, birds, and mammals. 472 THE FIGHT FOR HEALTH Cancer in human beings Cancer occurs in all living peoples. Not only that; prehistoric man also had cancers. The first fossil thighbone ever found of the prehistoric Java Man con¬ tained a fossilized bone cancer. Can¬ cer may be as old as life itself, and cer¬ tainly it is widespread today. People past 40 years of age are more likely to develop cancer than younger people, but it may occur at any age. It has even been found in the newborn. It kills more persons under 20 years of age than any three infectious diseases ex¬ cept tuberculosis. On the average, it eventually enters one of every two homes in our country. Also on the aver¬ age, about one of every eight adults now living in the United States may be ex¬ pected to die of cancer. Cancer ranks in second place among the causes of death in this nation. This is a most disturbing picture. It is especially disturbing when you con¬ sider the fact that general use of knowl¬ edge already available could change the picture. If only everyone knew enough about cancer and its early symptoms to see a competent physician “in time,” many cancer deaths could be prevent¬ ed. Actually, of all the highly fatal dis¬ eases in this nation, cancer is the one most often curable. What is cancer? Cancer is a growth. Like any other growth it is produced by cell division. Cell divisions that result in growth usu¬ ally involve mitosis (chromosome du- plication), during which chromosomes become visible under the microscope. This is true of normal cells. It is also true of cancer cells. But cancer cells are not normal cells. Normal growth goes on all through childhood. Even in the adult, there is IMPORTANT TRENDS IN DEATH RATES Each symbol represents one death per 1000 of population TOTAL DEATH RATE HEART AND CIRCULATORY DISEASES CANCER TUBERCULOSIS PICTOGRAPH CORPORATION 18-1 How do death rates in your city or county compare with the national death rates shown here? Consult your local board of health to find out. normal growth of new cells. New skin cells grow beneath the outer layer and replace those dead skin cells at the sur¬ face that are rubbed and washed off. New blood cells are continually being added to the blood. When you cut your¬ self, new cells grow from old cells; these new cells crow until the wound is O HEALTH PROBLEMS YET TO BE SOLVED 473 healed. When a bone is broken, new cells grow and heal the break. Then growth stops. In normal growth, the new cells change quickly to a useful form. In the healing wound, for instance, some new cells change into epithelial cells, others into connective tissue cells, and so on. Normal growth produces new useful cells. Normal growth also stops in due time, as when a wound has healed. Cancer is not a normal growth. Its cells do not change into useful cells. And its cells do not stop dividing. At times, in some individuals, cells that have always behaved normally in the past suddenly turn unruly. They divide repeatedly, but not in normal fashion. Often a single cell divides into three instead of two cells. Cancer cells, to the best of our knowledge, never return to normal, but go on and on dividing into larger and larger numbers of useless cells (Figure 18-3). 18-2 TWO OAK GALLS Plant galls are sometimes called plant tumors or cancers because they are abnormal growths. Most of them are growth responses to “stings’ and egg deposits by gall wasps. Tumors Cancer is an abnormal growth. Any abnormal growth is called a tumor, but not all tumors are cancers, as doctors use the word. In the language of the doctor, tumors are of two types: be¬ nign (or harmless) tumors; and malig¬ nant tumors (or cancer). A benign tumor is an abnormal growth of useless cells in a mass or lump— a growth walled off by a cover¬ ing or capsule which keeps its cells lo¬ calized in one place. Examples of be¬ nign tumors are warts, wens, corns, cysts, fibroid and fatty tumors, and moles. Usually tumors of this type are harmless, but they may sometimes change to a malignant form when sub¬ jected to continued irritation or certain other harmful conditions. Hence physi¬ cians often recommend their removal. There are several types of malignant tumors, or cancers. All of them are ab¬ normal growths of useless cells which are not enclosed in capsules; hence, cancer cells may spread from the origi¬ nal site to other areas in the body. How cancer spreads A cancer mav start at any point in the body. As the cells multiply, they soon form a lump or mass. In the be¬ ginning these cancerous cells are lo¬ cated all together in one mass. But as the cells continue to multiply, they spread out into nearby tissues. At first they spread between the normal cells, and later they shut off the food and oxygen supply of those normal cells. Multiplication of the cancer cells goes on and on. After a time some of the cancer cells enter a lymph vessel and are carried away in the lymph. Or thev may enter a blood vessel. Cancer cells carried away in the lymph may be caught in a lymph node. 474 THE FIGHT FOR HEALTH GROWTH- NORMAL AND CANCEROUS 18-3 Normal growth results in differen¬ tiated tissues, reaches its limit, and stops. Cancerous growth results in larger and larger masses of undifferentiated cells. Cancers do not usually stop growing un¬ less removed before they spread to new sites. Thousands and thousands of cancer patients have been cured by the discovery and early removal of cancerous growths. Those carried away in the blood may be caught in a capillary in any nearby or even a distant part of the body. Wherever these traveling cancer cells lodge, they go right on multiplying, thus starting new cancers at one or more points in the body. The original or primary cancerous growth may crowd surrounding healthy tissues; then by invading these tissues, it may injure and even kill healthy cells. The new or secondary cancers in new locations crowd and injure tissues in that area. Eventually, except in very rare cases, untreated cancer so injures a vital organ or a major artery or some other part of the body as to cause the death of the patient.* Importance of early diagnosis You can see now why early diagnosis of cancer is important. If the original lump or mass is removed before any of its cells have invaded surrounding tis¬ sues or have been carried away by lymph or blood, that case of cancer is cured. If, however, treatment is de¬ layed, as it so often is, until cancerous cells have spread to new locations, cure is very much more difficult and often impossible. Early diagnosis of cancer is nearly always a life-and-death matter. And early diagnosis requires a knowl¬ edge of early symptoms of cancer. Danger signals Every adult should know the early symptoms of cancer. If early cancer is present, he should look upon the symp¬ toms as friendly guideposts pointing the way to a competent physician and the probability of cure. If cancer is not present, the sure knowledge that it is not is worth a great deal. The danger signals listed in Table 18-A may or may not indicate an early stage of cancer. Any one of these sig¬ nals may be due to other causes, but the only way to find out is to see your doctor. Remember, if certain forms of cancer are treated early, 75 to 95 per cent of them are curable. Even in mod¬ erated advanced cases, 15 to 40 per cent may be curable. Delay is the thing to be feared when any of the danger signals appears. Memorize these signals, and tell your parents about them. Tell them, too, that cancer is more often curable than any 0 A very few cases are known in which a cancerous growth has receded spontaneously and finally disappeared. HEALTH PROBLEMS YET TO BE SOLVED 475 TABLE 1 8-A WARNING SIGNALS OF CANCER 1. A crack or sore that does not heal in ten days or so, particularly one about the tongue, mouth, or lips 2. Any lump or thickening, especially one in the breast, lip, or tongue 3. Any irregular bleeding from any of the natu¬ ral body openings 4. Any sudden and progressive change in the size or color of a wart, mole, or birthmark 5. Persistent indigestion, especially in persons past 35 years of age 6. Persistent hoarseness, unexplained cough¬ ing, or difficulty in swallowing 7. Any marked change in normal bowel habits other highly fatal disease, but usually only if it is diagnosed early. Diagnosis X-ray photographs are useful in di¬ agnosing such internal cancers as lung or liver cancer or cancer of the food tube. But the only sure way to find out whether a tumor is malignant or benign is to remove it, section and stain a bit of it, and examine it under the micro¬ scope. The surgical removal and mi¬ croscopic examination of a bit of tissue from a tumor is called a biopsy ( by op see). A surgeon may remove the tissue. A pathologist ( puh thol oh jist ) exam¬ ines it microscopically. A pathologist is a doctor who has specialized in the study of diseased tissues. He knows how to tell cancer cells from noncan- cerous ones, under the microscope. As you must know, many women still die of cancer of the breast. Biopsy of any lump that appears in the breast, as soon as that lump is discovered, may and often does prove it to be nonmalig- nant. Even if the pathologist finds ma¬ lignant cells, early diagnosis often makes a complete cure possible. Biopsy is an important tool in the control of cancer of the breast, as well as other types of the disease. Biopsies of tissue cells from the mouth of the uterus ( yoo ter us ) are now being done routinely every six months on many women past 35 years of age. The uterus is the organ in which the embryo develops before birth. It is the most common site of cancer in women past 35 years of age. For some years now, doctors have known how to remove, without operation, a few loose cells from the mouth of the uterus, so that a pathologist can examine them for cancer cells. Often, cancer of the uterus is detected, treated, and cured before there are any noticeable symp¬ toms at all of cancer. Death rates from cancer of the uterus are now lower than they were a few years ago, and they continue to fall, as more and more wom¬ en see their doctors regularly for this easy examination. Precancerous conditions No one knows exactly what causes cancer. But a good deal is known about precancerous conditions and agents that may produce them. You have already read about the sta¬ tistics that show there must be some tie-up between heavy cigarette smok¬ ing and lung cancer. In a 44-month study of 188,000 men between the ages of 50 and 70 years, it was found that heavy cigarette smokers may be ex¬ pected to die, on the average, seven to eight years before the age at which, on the average, nonsmokers die. Many chemicals are known to induce cancerous growths when applied again and again to the skin of some labora¬ tory animals. Among these are coal tars, paraffin, aniline dyes, lubricating oils, and arsenic compounds. 476 THE FIGHT FOR HEALTH Long-continued irritation or repeated injury may bring about changes in a tissue that predispose it to cancerous growth. A pipe stem or cigar on the lip, a sharp jagged corner on a tooth, or a pressure from poorly fitted dental plates, over a prolonged period, may set up a precancerous condition. Other precancerous conditions include warts and dark moles (especially if they are undergoing a noticeable change), dry scaly patches on the skin, persistent sores or ulcers, and unrepaired injuries due to childbirth. This is not to say that every one who develops a precancerous condition will sometime have cancer. Far from it. Mil¬ lions of precancerous conditions never lead to cancer. But it is important for people to be alert to such conditions, so that they will consult a physician if one of the conditions arises. In many and probably in most cases, the physi¬ cian will find no danger of cancer pres¬ ent, but when he does find such dan¬ ger, he can treat the condition in time to prevent cancer. Radiations and cancer Prolonged and often-repeated expo¬ sure to radiations (from X rays, radium, or other radioactive substances) may be followed by cancer. For example, repeated exposure of the same skin area to radiation may result in cancer of the skin at that point. Just how much the fall-out from atom and hydrogen bomb tests will affect the occurrence of cancer in human beings, no one yet knows. Heredity and cancer Fleredity is another factor that seems to play a part in making people re¬ sistant or susceptible to cancer. This is not to say that people actually inherit cancer. But some people do seem to in¬ herit “something" that makes them more likely to develop cancer— if sub¬ jected to cancer-inducing agents— than other people are. That doesn’t mean that a person whose grandfather had cancer is sure to get cancer. A person whose grand¬ father had black hair isn’t sure to have black hair. And yet heredity helps to determine hair color. It seems also to help to determine how susceptible a person may be to cancer-inducing agents. Leukemia and Hodgkin's disease Leukemia and Hodgkin’s disease are usually included among the types of cancer. Both are more common among young than among older people. Leu¬ kemia is on the increase in the United States, particularly in five western states, according to United States Pub¬ lic Health reports in 1957. You hear and read a good deal about leukemia today. It is often called “can¬ cer of the blood,’’ but that isn’t an ac¬ curate name. Leukemia may be any one of several diseases, all of which are thought to be cancerous conditions in bone marrow, the spleen, and the lymph system, and several of which cause abnormally high white-blood-cell counts (Figure 18-4). Do diseased bone tissues produce new white cells much faster than usual? Or do the white cells live abnormally long, as recent research with “tagged" white cells seems to in¬ dicate? We must all wait for new evi¬ dence. See Table 17-C on page 460 for the high white-blood-cell counts usu¬ ally (but not always) found in leu¬ kemia. Hodgkin’s disease is sometimes called cancer of the lymph nodes. It is not very common at any age but does oc- HEALTH PROBLEMS YET TO BE SOLVED 477 Bausch & Lonib Optical Co. 18-4 LEUKEMIA BLOOD SMEAR Compare this blood smear with that of normal blood (Figure 16-9, left). In that smear only three white blood cells are visible. How many white blood cells do yon count in this smear from a case of leukemia? cur most often in boys in their late teens. Actually it is a disease that affects the spleen, and often the liver and kid¬ neys, as well as the lymph nodes. Treatments To date, the most widely used treat- ments for cancer are surgical removal and X rays ( radium has also been used). In the early stages, before can¬ cer cells have moved into new tissues, these treatments are most often suc¬ cessful. Thousands of people are alive and well who have been “cured” of cancer. Skin cancers are cured most often— some 95 per cent are curable when the doctor sees them. Why? Because it is easy to see a mole enlarging, or a sore that doesn’t heal, or a patch of dark, scaly skin. Many people today are alert to these precancerous or even cancer¬ ous skin conditions. Other newer treatments are being tried out all the time. Besides X rays, nitrogen mustard and a similar drug are used in treating both leukemia and Hodgkin’s disease. They do not cure, but they do benefit these patients. Several substances have been found which arrest the cell multiplications in cancerous tissues in animals or in test- tube cultures. Some of these are: syn- thetic vitamin K, sodium fluoride, and an extract from the root of the May ap¬ ple. Unfortunatelv, some of these can¬ cer-arresting chemicals are poisonous to man, and only future research will tell whether or not they may be useful in treating human cancer. Summing up: cancer and its control We have made progress toward the control of cancer, but its full control must come in the future. At present, the most important factor is early diag¬ nosis. The more people who know and heed the danger signals for cancer, the better will our present means of con¬ trol be applied. Surgery and X rays are the most widely used and effective cancer treat¬ ments now available. HEART AND CIRCULATORY DISEASES AND THEIR CONTROL President Eisenhower’s heart attack in 1955 put the term coronary throm¬ bosis into nearlv evervbodv’s vocabu- ✓ J J larv. A coronarv thrombosis is onlv one J J J of several kinds of heart diseases. Heart and circulatory diseases cause more than a third of all deaths in the United States. Major killers Diseases of the coronary arteries (ar¬ teries leading to heart muscle), includ¬ ing coronary thrombosis, rank high, but not first, among the fatal heart and eir- 478 THE FIGHT FOR HEALTH dilatory conditions. Degenerative dis¬ eases associated with ‘‘hardening of the arteries’ rank first, coronary diseases second, conditions associated with high blood pressure third, and chronic rheu¬ matic-fever heart disease fourth, as causes of death. There are still other types of heart and circulatory diseases, all of which are usually much less serious than those mentioned above. Occasionally some¬ one develops an infection and inflam¬ mation of the covering of the heart or of its lining. Or germs may lodge and grow on one or more heart valves and so injure a valve that it does not close completely. This condition, commonly called “leakage of the heart,” is called a heart murmur by doctors, because a leaking valve causes a “murmur” sound that can be detected with a stetho¬ scope. Some heart murmurs are serious, but many people have mild heart mur¬ murs that never cause serious trouble. Heart injuries due to infections may follow pneumonia, scarlet fever, strep throat, or some other germ disease. To¬ day, these diseases usually respond well to treatment, thus preventing heart in¬ juries. All of the diseases so far mentioned involve some type of injury to the heart itself (or to arteries leading to heart muscle or away from the heart). Doc¬ tors call all such diseases organic heart diseases, because an injury or organic condition is involved. Many people have heart murmurs not caused by dis¬ eased or injured heart valves, or they may have what may be called “nervous hearts,” with no organic heart disease at all. People with “nervous hearts” may have palpitations, heart skips, or other disturbances in the heart function. Such disturbances are functional heart dis¬ eases, in which no organic injury exists. Functional heart diseases usually are not serious, but only a doctor can make sure whether a disturbed function, like palpitation, is strictly functional or not. Hence anyone who is aware of some change in heart function should see his doctor for a check-up. Doctors say that people who “think there is something wrong” with their hearts quite often have no organic heart disease at all. Since the more serious types of or¬ ganic heart disease are often associated with high blood pressure, you will want to know something about blood pres¬ sure. What is blood pressure? Blood pressure is simply the pressure of the blood against the walls of the arteries. Just as the water in the pipes of a house exerts a pressure against those pipes, so does the blood exert a pressure against the walls of the ar¬ teries. Everyone has blood pressure. Everyone’s blood pressure goes up and down with each heartbeat. It is highest at the instant when the heart pumps a new load of blood into the arteries; it is lowest at the instant when the heart pauses between beats and the auricles are filling with blood. When a physi¬ cian takes your blood pressure, he re¬ cords two pressures; for example, 120 over 80. This means 120 and 80 milli¬ meters of mercury. A blood pressure of 120 will lift a mercury column 120 mil¬ limeters (Figure 18-5). The 120 is the pressure at the instant of the beat; the 80 is the pressure at the instant of rest. The size of the very smallest branches of the arteries affects blood pressure. These tiny arterial branches, which pass the blood along to the capillaries, are the arterioles. The arterioles have mus¬ cular walls, and the muscles are con- HEALTH PROBLEMS YET TO BE SOLVED 479 William C. Stoddard 18-5 APPARATUS FOR TAKING BLOOD PRES¬ SURE Physicians check blood pressure as part of all routine examinations. trolled by nerves. During emotional disturbances (anger, fear, worry, joy) and prolonged nervous tension, the muscular walls of the arterioles con¬ tract, thus decreasing their size. Then blood pressure goes up. The smaller the arterioles are, the higher the blood pressure is, and the harder the heart muscle must work to push the blood along. Still other factors besides the size of the arterioles affect blood pressure. If the amount of blood is reduced by hemorrhage, blood pressure goes down. It may be raised quickly by a blood transfusion or merely by injecting ster¬ ile salt water (normal saline) into a vein. If the blood is thicker or thinner than normal, there is a corresponding change in blood pressure. A change in the normal elasticity of the walls of the arteries also affects blood pressure. Probably you have alreadv realized J J J that your body’s ability to change your blood pressure in response to stresses and strains is part of the built-in mech¬ anisms that help your body to main¬ tain its homeostasis. In most people under 40, changes in blood pressure are part of the useful devices of the body that help it meet emergencies. In many people as they grow older, and in some young people, there is per¬ sistent high blood pressure. Doctors call this condition hypertension ( hy per ten shun ) . One theory is that prolonged stress and strain tend to bring on hyperten¬ sion. According to Selye’s alarm-reac¬ tion and exhaustion theory, hyperten¬ sion may be one of the results when prolonged stress has exhausted the cells of the pituitary that produce ACTH, those of the adrenal cortex that produce cortisone, and those of other tissues involved in the alarm-reaction system. This theory may or may not stand the test of further investigations. No one can tell you exactly what your blood pressure should be. It is lower in children than in adults, and it normally is lower in young than in older adults. In a child of twelve, doc¬ tors expect the top pressure ( at the instant the heart beats ) to be about 105, whereas at sixty it is expected to be about 135. Only a physician can give you advice about your blood pressure. Blood pressure and the heart When blood pressure goes up, the heart has to work harder to pump the blood. When blood pressure stays up only a short time, the heart readily ad¬ justs itself to the change and is not harmed. For example, your blood pres¬ sure goes up when you exercise strenu¬ ously, as in a basketball game. But there is no reliable evidence that stren¬ uous exercise in reasonable amounts 480 THE FIGHT FOR HEALTH among young people damages the heart. Doctors say there is no such thing as athletes’ heart. Temporary in¬ creases in blood pressure due to normal causes do not injure the heart, to the best of our knowledge. Hypertension can and does harm the heart. It forces the heart to work harder all the time. Gradually this prolonged overwork may damage the heart, which then begins to enlarge. The added strain year after year causes more and more fatigue in the heart muscle, and finally it is worn out and “fails” alto¬ gether. Not all persons with hyperten¬ sion have damaged hearts, even after many years, but heart damage, called degenerative heart disease, and hyper¬ tension do go hand in hand often enough to justify regular medical atten¬ tion in all cases. "Hardening of the arteries" The walls of the arteries and arteri¬ oles change gradually as we grow old¬ er. In normal young people the walls of these vessels are elastic. They ex¬ pand when the heart pumps blood into them. Then they contract, thus helping to push the blood onward. The arteries and arterioles gradually lose some of their elasticity when fibrous tissue thickens them, when calcium deposits “harden” them, and when a certain fatty substance which is often in the news today, cholesterol ( koh less ter ohl), is deposited in them. In some in¬ dividuals this thickening and hardening of the vessel walls is more rapid than in others. As the walls thicken, the inside diameter of the arteries and arterioles decreases. Doctors call this hardening of artery and arteriole walls arteriosclerosis (ahr teer ee oh skier oh sis). Hypertension is usually but not always associated with arteriosclerosis. Can you explain why the thickening of artery walls may cause increased blood pressure or hy¬ pertension? Arteriosclerosis in an advanced form is serious, because a hardened artery, say, in the head, may break under pres¬ sure and let out blood. Then a blood clot forms in the brain. This usually causes paralysis of some part of the body. People usually say the person has had a stroke. Doctors say he has had a cerebral hemorrhage. Coronary heart disease Arteriosclerosis in coronary arteries results in coronary heart disease. The internal diameter of the coronary ar¬ teries grows smaller, so that less and less blood reaches the heart muscle. As the condition progresses, severe at¬ tacks of pain under the breastbone, of¬ ten radiating down the arms, are likely to occur. Doctors call this pain angina pectoris ( an jy nuh pek toll ris ) . People who suffer from angina pectoris carry nitroglycerine tablets all the time. As soon as an attack starts, they put a tablet under the tongue. The nitro¬ glycerine diffuses quickly out of the mouth into the blood, relaxes the coro¬ nary arteries, and relieves the pain. In coronary thrombosis, a blood clot in a coronary artery closes or partially closes that artery (Figure 12-11, page 341). This is a really serious “accident.” It shuts off most of the blood supply to part of the heart. Severe pain, weak¬ ness, paleness, and sweating accom¬ pany the attack. These attacks were once commonly called “acute indiges¬ tion” because the pain may seem to be in the upper abdomen. Not many years ago, close to half of the people who had a coronary throm¬ bosis died during the first attack. To- HEALTH PROBLEMS YET TO BE SOLVED 481 clay most patients who follow their doc¬ tor’s orders not only survive the first at¬ tack of coronary thrombosis but recover and are able to go back to work, just as President Eisenhower did. And these people may live out an average life span, if they follow the doctor’s advice and learn to live in a way that keeps them fairly free of stress and strain. Symptoms of heart and circulatory diseases There is no single symptom or set of symptoms that point to positive diag¬ nosis of a heart or circulatory disease. But there are a number of symptoms that should send anyone to his physi¬ cian at once to check up, especially if the person is past forty. These signals may or may not mean a heart or circu¬ latory disease. The thing to do is to find out. Table 18-B lists symptoms which mean “See your doctor.” Certain heart conditions result from injuries caused by streptococcus infec¬ tions or rheumatic fever, or from ab¬ normalities present since birth. When these conditions involve the heart valves or openings in the heart walls, they can often be corrected by surgery. TABLE 18-B WARNING SIGNALS OF HEART AND CIRCULATORY DISEASES 1. Shortness of breath, when at rest or after mild exertion 2. Rapid pulse 3. Palpitation, skipped beats 4. Indigestion 5. Unexplained cough 6. Chest pain or discomfort, especially if it follows exertion or excitement 7. Swelling of the feet and ankles 8. Dizzy spells or fainting spells 9. Asthmatic attacks in older persons who have not had asthma previously CHAPTER EIGHTEEN: SUMMING UP Heart and circulatory diseases and cancer rank at the top of the list of un¬ solved health problems. There are sev¬ eral types of each of these diseases. We still do not know exactly what causes most heart and circulatory con¬ ditions or cancer. But we already have enough knowledge to help control them, if patients get to a competent physician “in time.” For you, the important thing is to know the danger signals and heed them. Your Biology Vocabulary You will want to understand and be able to use the following new terms from this chapter. benign tumor precancerous conditions leukemia malignant tumor cerebral hemorrhage Hodgkin’s disease biopsy cancer blood pressure 482 THE FIGHT FOR HEALTH hypertension angina pectoris functional heart diseases arteriosclerosis organic heart diseases coronary thrombosis Testing Your Conclusions On a clean sheet in your record book make a list of the danger signals for cancer and a list of the danger signals for heart and circulatory diseases. Then write out a list of “Don’ts” and “Do’s” which you think the citizens of your community should practice in order to help reduce the ravages of these diseases. Compare your lists in class. More Explorations Reporting on local death rates. From your local public health office, find out what the death rates were in your community for heart and circulatory diseases and cancer last year. If you wish, get death rates for the ten leading causes of death in your community. Ask for national death rates, too, and compare the two. Report in class. Thought Problems 1. In the light of what you have now read about cancer and heart and circulatory dis¬ eases, do you think it is likely that any single scientist or any single team of scientists will come up with the solution to these problems? Why? 2. Cancer of the skin is highly curable. Some 95 per cent of all skin cancers are said to be cured today, while a much smaller percentage of lung or stomach cancers are cured. What is probably the main reason for the difference? Further Reading 1. Your class can get a number of pamphlets on cancer from the American Cancer Soci¬ ety, 521 W. 57th St., New York City. The American Heart Association, 44 E. 23rd St., New York City, also publishes educational pamphlets on heart diseases. 2. Man Against Cancer by I. Berenblum, Johns Hopkins Univ. Press, 1952, presents the problem in a hopeful light. This book is factually reliable, as well as interesting. 3. Living with All Your Heart: In Health and Disease, by Henry C. Crossfield, Twayne, 1957, is a book written by a heart specialist for the use of everyone who would like to know more about his heart and how to live wisely. Looking Ahead In the next chapter, you will need several flowers to examine; apple, peach, pear, orange, or forsythia blossoms may be forced by collecting twigs and keeping them in jars of water in a warm place for several days. Daffodils, sweet peas, spring beauties, violets, lilacs, and almost any other colorful flowers may also be collected (or purchased) and kept fresh for study in the next chapter. HEALTH PROBLEMS YET TO BE SOLVED 483 You would not have to see the parents of the small, furry creature pictured at the top of this page to know that you were looking at a young opossum. And while the penguin chick in the photograph at the bottom of the facing page is by no means an exact duplicate of the parent on whose feet it is huddled for warmth, it will gradually grow to resemble the parent. Each plant and animal species produces offspring of its own kind. And yet there are differences between the offspring and their parents, and differences among adult plants or animals of a species. Take the ears of hybrid corn shown in the photograph at the top of the facing page. Each grain, if planted under suitable conditions, woidd grow into a corn plant. But all the corn plants would not be the same size, nor would they produce ears of corn all of the same size. Furthermore, the grains of corn on the ears on different plants would not have exactly the same color, shape, size, or taste. Plant and animal breeders are well aware of differences in traits within a species, and they cultivate plants and breed animals that have traits most desirable to man. Why do corn grains produce corn plants and not other kinds of plants? You could ask the same question about other plants and their seeds, or about animals and their eggs. Each plant and animal species produces offspring of its own kind, yet different in ways. What is taking place in the photograph at the bottom of the facing page? You are right if you guess that a cell is dividing and that the dark, stringlike bodies clustered at opposite ends of the dividing cell are chromosomes. You first read about chromosomes in Chapter 1. What have they to do with the inheritance of traits? In this unit you will learn how living things produce offspring that are like their parents and yet different in some ways. You will learn how traits are inherited and how new traits arise— how, given a long enough period of time, enough differences in traits arise to result in new kinds of plants and animals. And you will learn how man is putting his knowledge of plant and animal reproduction and the inheritance of traits to use for his own benefit. Chapters 19. Reproduction in Higher Organisms 20. How Traits Are inherited 21. How New Varieties May Arise 22. Inheritance Through the Ages 23. Inheritance in Plant and Animal Breeding CHAPTER f&r* Reproduction in Higher Organisms The turkey chick p\ here serves its a gr~‘ biological reminder that 47? .-'UK' ■ rVi • *"f \ the normal life function organism are subject to The mother of this I j [{Pj, fj • $V •• ,> v Vj* &${■' {C’f'r turkey chick produced her single offspring without mating. There teas no m • "jt « ’ .Wttfjl ‘ -a- WlmM HHBEH Science Service, Inc. y,A chip off the old block/# You often hear people say of a boy who resembles his father strongly, “He certainly is a chip off the old block.” Actually this common expression does not apply to human children, since they have two parents and resemble both in some ways. But the turkey chick pic¬ tured above is literally a “chip off the old block,” in the sense that this chick had a mother but no father. It came from an egg laid by a turkey hen that had been kept locked in a pen where there were no male turkeys. To the best of our knowledge, a fatherless verte¬ brate like this turkey chick is a rare ex- ception. Most vertebrates have two parents. Many organisms, however, have only one parent. Examples are African vio¬ lets started from a leaf of a parent plant, potatoes raised from potato tu¬ bers, and microorganisms that result from the cell division of a single-celled parent. How many more examples can you think of? In general, organisms reproduce in one of two ways, or in both of these ways. Either reproduction starts with the uniting of two cells, an egg and a sperm, or it doesn’t. Reproduction that begins with the uniting of two cells is sexual reproduction. Reproduction that begins without the uniting of two cells is asexual ( ay sek shoo ul ) reproduc¬ tion. REPRODUCTION IN FLOWERING PLANTS Anyone who has a vegetable or a flower garden knows that we raise many plants from seeds and many others from 486 THE CONTINUITY OF LIFE bulbs, cuttings, or similar “chips” off a single parent plant. Plants raised from seeds are reproduced sexually. Those raised from some part of a single parent are reproduced asexually. Asexual reproduction In many ways, people take advantage of the ability of flowering plants to re¬ produce asexually. Many of you are un¬ doubtedly familiar with several ex¬ amples. SETTING UP A PROJECT. Below is a list of several plants and one method of asex¬ ual reproduction for each. Select one plant on the list and grow it by the type of asex¬ ual reproduction listed beside it. Keep a record of what results you get and report in class. White potato— Plant a piece of a tuber with two or three "eyes" (buds). Sweet potato— Set one end of a sweet po¬ tato in a jar of water. Onion— Plant some onion "sets" (small bulbs). Rose— Place twig cuttings in water. African violet— Remove one leaf, lay it on water until roots form, then plant. Easter lily— Plant one or more bulbs. Those of you who have planted pota¬ toes or picked strawberries know that most of the potatoes you eat come from plants produced asexually, and that strawberry vines grow runners that start new vines (Figure 19-1). Many of you know that gardeners plant bulbs or tu¬ bers to raise such flowers as dahlias, gladioluses, daffodils, narcissuses, and many more. Some trees like poplars and hazelnuts produce “suckers' around their bases. All of these and many more examples illustrate the ability of flow¬ ering plants to reproduce asexually. Man has invented several artificial ways to use asexual reproduction to get young plants of a desired kind. A com¬ mon method is to take slips or cuttings or even single leaves from one plant and start new plants from these “chips off the old block.” Roses, geraniums, begonias, and African violets are easily reproduced asexually by these proce¬ dures. Of course, each new plant start- 19-1 ASEXUAL REPRODUCTION IN STRAWBERRY PLANTS Two of these three strawberrv plants were produced asexually by means of runners from the third plant. The runners started new vines. Other examples of asexual reproduction are the growing of new plants from tubers (potato plants, for example), bulbs (lilies, etc.), or twig cuttings (forsythia and roses, among others). Brooklyn Botanic Garden ed asexually is like its single parent, because its cells contain the same kinds of chromosomes as those of the parent plant. Plants grown from seeds are not en- O tirely like either parent; their seeds do not “come true,” as nurserymen say. Therefore, some method of asexual re¬ production is necessary to get offspring with all the traits of a single parent. In the case of our fruit trees, budding or grafting is used to get young trees that will come true. Budding and grafting Usually in budding or grafting, a nurseryman attaches a bud or a twig from a desired tree to the top of a young tree of a closely related variety. The bud or twig used is called the scion (svun), and the seedling stump to which it is attached is called the stock. (See Figure 19-2.) When the scion has grown into a good-sized twig, the nurs¬ eryman cuts off all the original twigs of the stock, leaving only the scion to grow into the top of the young tree. When you buy, for example, a young Delicious apple tree to plant in your yard, only the trunk, branches, and leaves of the young tree have Delicious apple chromosomes in their cells. The root system of your young tree may have come from a seed of a wild crab apple tree. But since a scion bears fruit like that of the tree from which it came, not like that of the tree from which the stock came, your tree will bear only Delicious apples. The root system has little effect on the upper parts of the tree, because the upper parts of the tree are controlled by their own chromo¬ somes. Most of the fruits you eat come from budded or grafted trees. Can you ex¬ plain how young trees that will bear seedless oranges and grapefruit can be produced? Sometimes you see an orange tree with one branch bearing lemons, or an 19-2 BUDDING AND GRAFTING A. A section of bark with a live bud is cut from a tree that is to be reproduced and inserted into a T-shaped cut made through the bark of the stock. The bark around the cut is raised to accommodate the bud. When the bud is in place, the stock is wrapped and waxed. B. A graft is made in this manner when the scion and stock are about the same size. Again wrapping and waxing are the last steps. C. When the scion is small and the stock large, a cleft graft is made, as shown here. The scions are set in clefts in the stock and are waxed in place. After Farmer’s Bulletin, No. 1567, U.S.D.A. A B C Carolina Biological Supply Co., Elon College, N.C. 19-3 CHROMOSOMES IN AN ANIMAL EGG The black, ribbonlike structures in this egg of Ascaris are chromosomes. Fertilization has already taken place, and the egg is about to undergo its first division. Two of the four chromosomes are from the father; the other two from the unfertilized egg. apple tree with some branches bearing Baldwin, others Delicious, and still oth¬ ers Rome Beauty apples. Can you ex¬ plain how budding or grafting was used to produce such fruit trees? Sexual reproduction Before we study sexual reproduction in flowering plants, let’s review some of the ideas and terms used previously. 1. Sexual reproduction starts with the uniting of the nuclei of two cells, called gametes. 2. The male gamete is usually a sperm and the female gamete, an egg. So sexual reproduction starts with the uniting of the sperm nucleus with the egg nucleus. 3. The uniting of sperm and egg nu¬ clei is called fertilization. After that, the egg is called the fertilized egg. 4. In animals, an egg-making organ is an ovary and a sperm-making organ is a testis. 5. The female parent (or mother) is the one that produces female gametes or eggs, while the male parent (or fa¬ ther) is the one that produces male gametes or sperms. 6. A fertilized egg grows by cell divi¬ sion into an embryo. Remember the bean embryo you examined previously? (See page 142.) That bean embryo came from a fertilized egg. In higher animals, the embryo usually develops inside the egg, or inside the uterus in the mother’s body. After a seed sprouts or an egg hatches or a mammal is born, the young is no longer an embryo. 7. Chromosomes, as you learned in Unit One, transmit hereditary traits from parents to offspring. A sperm car¬ ries chromosomes from the male par¬ ent; an egg carries chromosomes from the female parent. So a fertilized egg carries chromosomes from both par¬ ents (Figure 19-3). That means that young organisms produced sexually resemble both parents in some ways. Sex in flowering plants You already know the main parts of a flower: sepals, petals, stamens, and pistils (Figure 19-4). Of these, the sta¬ mens are the source of sperms and the pistils produce the eggs. Obviously, it is necessary for sperms from the sta¬ mens to reach the eggs in the pistils. To understand how they do that, you first need to examine some flowers and “sprout” some pollen grains. (If you can’t do all the following investiga¬ tions for lack of materials, refer often to Plant Chart 3, following page 288, as you read on. ) EXAMINING AN APPLE BLOSSOM. Ex¬ amine an apple blossom or another blos¬ som or flower that you have collected (as REPRODUCTION IN HIGHER ORGANISMS 489 Stigma Stamen Pistil Styles Ovule Ovary Petal Anther Filament Sepal 19-4 DIAGRAM OF AN APPLE BLOSSOM Two styles, several stamens, some sepals and petals, and part of the ovary were cut away to get this lengthwise section. directed on page 483) * and locate the four main parts: sepals, petals, stamens, and pistil (Figure 19-4). Remove the petals. Then carefully re¬ move all the stamens and save them. With scissors remove the five sepals. What you have left is the pistil of the apple blossom. The little green structure at the base of the pistil is, as you already know, the ovary, in which the ovules are found. The five little "branches'7 arising from the ovary (you see three of these in Figure 19-4) are the styles. The top of each style is a stigma. Now examine one stamen. Its "stem" is the filament and its top is the anther. The anther produces the pollen. Title a fresh page in your record book Flowers and Their Parts. On it sketch and label all three parts of the pistil and two parts of the stamen. EXAMINING OTHER FLOWERS. Exam¬ ine several different flowers, such as sweet peas, buttercups, daffodils, forsythias, ° Orange, peach, pear, or cherry blossoms, daffodils, or other available flowers will do. The same parts are found in all these and in many other flowers, but the numbers and ar¬ rangement of the parts differ from flower to flower. spring beauties, violets, or almost any others available. Try to include at least one monocot flower, such as a daffodil, narcis¬ sus, dogtooth violet (not a violet, but a member of the lily family), or any lily. In your record book, sketch each flower and label: sepals, petals, stamens, pistil (or pistils). Remove, sketch, and label a stamen and a pistil of each flower examined. Choose one of the flowers which has a rather large ovary, cut the ovary in half lengthwise, and look for the little green ovules inside it (Figure 19-4). After pollina¬ tion and fertilization, the ovules grow into seeds. Make a slide of pollen from an anther. Examine it under low and high power. Sketch a few pollen grains. Repeat, using pollen from different flowers. (At first, a pollen grain is a single cell with a single nucleus— it is actually a spore.) SPROUTING POLLEN. Pollen grains will sprout in sugar water. To watch this hap¬ pen, you will need the items printed in italics below. 1. In a bottle , put 18 tablespoons of water. Add Vi teaspoon of sugar, prefer¬ ably dextrose. Mix well. 2. Near the middle of a microscope slide , put a ring of Vaseline about the size of a cover slip. 3. With a medicine dropper , put a drop of the sugar water inside the ring of Vaseline. 4. With a toothpick (or a dissecting needle), take some pollen off the anther of a stamen and put it in the drop of sugar water. Add a cover slip. 5. Examine under low power after half an hour and again after 24 hours. 6. In your record book, sketch any pollen grains that have "sprouted"; that is, any that have grown pollen tubes (Fig¬ ure 19-5). 490 THE CONTINUITY OF LIFE New York Scientific Supply Co. 19-5 SPROUTING POLLEN GRAINS Each of the three highly magnified pollen grains shown here is growing a pollen tube, much as it would if it were on the stigma of a flower pistil (Figure 19-6). Pollination and fertilization Pollen grains are made in the an¬ thers of stamens. At first, each pollen grain is a single, thick-walled cell, a spore. To “sprout” in its usual way, a pollen grain has to get to the stigma of a flower pistil. Insects or wind may carry or blow a pollen grain from one flower onto the stigma of another flow¬ er. Or it may simply fall on the stigma of the same flower. Once on the stigma, a pollen grain starts to grow. Even before it left the anther that produced it, its nucleus had already divided into two nuclei, the tube nucleus and another nucleus, the latter of which divided again to become two sperm nuclei. (The sperm nuclei become the male gametes, or sperms.) Now, on the stigma, the pollen grain “sprouts” a pollen tube. The pollen tube grows out of the pollen grain and down through the style into the ovary, where it enters an ovule, as in Figure 19-6. At the same time, the nucleus of the original cell (also a spore) inside the ovule has divided into two nuclei, the two into four, and in most flowers * the four into eight nuclei. One of the eight is the egg nucleus and becomes the fe¬ male gamete, or the egg (Figure 19-6). Inside the ovule, one sperm fertilizes the egg. Then the fertilized egg di¬ vides again and again and becomes the embryo. The ovule and ovary also grow. The ovule ( together with the embryo it contains) becomes a seed and the ovary a fruit. The growing embryo seems to produce a growth hormone that diffuses into nearbv tissues and J makes them grow also. ( Many plants produce more than one seed per fruit, as you know. Could this happen to the plant in Figure 19-6?) In most flowers, as in Figures 19-6 and 19-7, it takes pol¬ lination and fertilization to make ovules and ovaries grow into seeds and fruits. In case you want to know, a pollen tube with its three nuclei is the male gametophvte. It produces male gametes (sperms). And the contents of the ovule with its eight nuclei (or four, in lilies) is the female gametophvte. It produces a female gamete, the egg. Remember the gametophytes of the fern, the prothallia? And those of the moss, the leafy moss plants? (See pages 124 and 136. ) Seed plants have a game- tophyte generation, too, but what peo¬ ple see is the sporophyte, the plant with its flowers. The whole apple tree is a sporophyte, since its flower anthers produce male spores (pollen grains) and its flower ovules produce female spores ( the original cells inside the ovules, before nuclear divisions occur). So there is an alternation of genera¬ tions in seed plants, but this isn’t very important to most people. To a biol- ° In lilies and some other flowers, only four nuclei are produced and one of these becomes the egg. REPRODUCTION IN HIGHER ORGANISMS 491 POLLINATION 19-6 The function of the pollen tubes in Figure 19-5 is made clear by this diagram showing pollen tubes penetrating the length of a pistil. The tubes serve as pas¬ sageways through which sperm nuclei reach egg nuclei. ogist, it is interesting, because it sug¬ gests that seed plants may have come from plants with an obvious alternation of generations. Fruits and seeds In biology, string beans are fruits. So are milkweed pods and corn kernels. All of them come from flower ovaries, and they contain one or more seeds. The beans inside the pod are the seeds. They come from ovules. A seed is any matured ovule, and consists of an em¬ bryo plant, often within a seed coat. To the flowering plant, fruits and seeds are a means of reproduction, sex¬ ual reproduction. They are an efficient means of reproduction, too, for several reasons. For one thing, fruits and seeds are large enough to store large amounts of food. When the seed sprouts, the growing plant uses the stored food un¬ til it has grown its own roots and green leaves and can make its own food. For another thing, fruits and seeds protect the embryo plants inside the seeds. They keep the embryos from dying by drying out. They protect them during cold winters, or dry seasons in desert areas. In annual plants, like garden peas and beans, the seeds alone maintain the continuity of the species year after year, because the plants die every fall. Fruits and seeds are useful to the species in still another way. They are easily scattered to new locations. The scattering of seeds is usually called seed dispersal. Nearly all fruits and seeds are especially suited to some kind of dispersal, by wind or by ani¬ mals or by water. Look back now at a drawing you have seen before, Figure 5-14 on page 143. It shows two pine seeds and their “wings.” The wings aid dispersal of the seeds by the wind. Hickory nuts and pecans are seeds; in this case, animals, especially squirrels, aid the dispersal of the seeds. Fruits and seeds are important to the plant species that produces them, in that they help to perpetuate the species. Complete and incomplete flowers An apple blossom has four main parts: sepals, petals, stamens, and pis- 492 THE CONTINUITY OF LIFE tils. So do many other flowers. Flowers with sepals, petals, stamens, and pistils are said to be complete flowers. Many flowers are incomplete flowers, in that they have no sepals or petals. Pussy willows, the flowers of grasses, corn, poplar trees, skunk cabbage, jack-in- the-pulpit— all these and many more have no sepals or petals, and are there¬ fore incomplete flowers. Since incom¬ plete flowers produce fruits and seeds, it is obvious that sepals and petals are not essential parts of a flower. The es¬ sential parts are the stamens and pistils. Perfect and imperfect flowers Apple blossoms have both stamens and pistils in the same flower. So do many other blossoms. Flowers of this type are said to be perfect flowers, be¬ cause they have both essential flower parts— stamens and pistils. Apple blos¬ soms are both complete and perfect. The flowers of jack-in-the-pulpit are perfect but incomplete, since they have both stamens and pistils but no sepals or petals. Flowers of corn are incomplete, and they are also imperfect flowers. A sin¬ gle flower has either stamens or pistils but not both, and no sepals or petals. In corn, the tassels are clusters of flow¬ ers bearing only stamens, and the young ears are clusters of flowers bearing only pistils. Each little “grain” on a young ear is an ovary, and the corn silk is the style with a stigmatic surface (Figure 19-8). Yes, the pollen tube of corn must grow all the way down through the silk (style) and into the ovary to reach the ovule, where fertilization takes place. Can you guess why a “ripe” ear of corn often has several little un¬ developed “grains” at one end? Many other flowers are both incom¬ plete and imperfect, among them pussy 19-7 FLOWERS, FRUIT, AND SEEDS IN A GIANT SAGUARO From the buds on this cactus flop) come mature flowers (center), and later, fruit and seeds (bottom). A. W. Schoof 493 19-8 STAMINATE AND PISTILLATE FLOWERS IN CORN The corn tassel (left) is a cluster of staminate flowers, bearing only stamens. The ear of corn is a cluster of pistillate flowers, on which each kernel with its silk (right) is a pistil. willows and the flowers of many nut trees. Imperfect flowers that bear only stamens are called staminate flowers, those that bear only pistils, pistillate flowers. Types of pollination In imperfect flowers, it is obvious that the pollen must be transferred from one flower (the staminate) to another flower (the pistillate). The transfer of pollen from one flower to another is commonly known as cross-pollination. Many complete flowers are cross-pol¬ linated by insects. In some perfect flow¬ ers, the pollen is transferred from the stamens to the pistil of the same flower. This type of pollination is commonly known as self-pollination, or selfing. The two common types of pollination are cross-pollination and selfing. As you examine flowers during the coming months, try to discover whether a given flower is complete or incomplete, per¬ fect or imperfect, and whether it is probably cross-pollinated or selfed un¬ der usual conditions. The growth of seeds EXAMINING SEEDS. You have already sprouted both beans and corn (pages 204 and 267-268), but you will want to know more about their parts and how they grow. 494 TIIE CONTINUITY OF LIFE Once more soak some corn kernels and dry beans overnight. Then do these things. 1. Examine the whole bean. Look for the scar, or hilum (hy lum), where it was attached to the pod. Near the end of the hilum, look for a little hole, the micropyle (MY kroh pyle). That is the place where the pollen tube entered (Figure 19-9). Remove the seed coat and compare the embryo with Figure 19-9. The two seed leaves are the cotyledons (kot ih lee d'ns); the little shoot, made up primarily of the first true leaves, is the plumule (PLOO myool); and the little root is the hypocotyl (hy poh KOT 'I). Now lay a soaked corn kernel down and cut it in two lengthwise. Apply dilute io¬ dine to the cut surface. The food in a corn kernel is stored in the endosperm (EN doh sperm). Much of the stored food is starch. So the iodine should make it easy to find the endosperm (Figure 19-9). Make sketches (with labels) both of the bean and the corn. When seeds germinate (sprout), the hypocotyl (little root) usually appears first. Then the plumule (little shoot) pushes upward. In most dicots, the two cotyledons come up above ground and turn green (refer back to Figure 10-1, page 267 ) . In monocots, the one cotyle¬ don stays underground. So it is usually easy to tell monocot and dicot seedlings apart as soon as they come up. In most dicot seeds, the stored food is in the cotyledons. As the plant grows, it uses food from the cotyledons, which shrivel up and finally drop off. In the corn kernel and in most other monocot seeds, the one cotyledon acts as a digestive organ. It secretes an en¬ zyme (diastase, in corn) into the endo¬ sperm. The enzyme speeds up the diges¬ tion of the stored starch— that is, its change into sugar. Sugar in solution circulates through phloem into the growing root and shoot. The chromosomes in the cells of the embryo plant play a big part in deter¬ mining how each seedling grows. The chromosomes make corn kernels grow into corn plants and beans into bean Summing up: reproduction in flowering plants Most flowering plants can reproduce both asexually and sexually. Asexual methods include tubers, bulbs, cuttings, runners, shoots, and budding and graft¬ ing. The flower is the organ of sexual re¬ production. The stamens and pistils are the essential parts of the flower, be¬ cause the stamens produce pollen and the ovules of the pistil produce eggs. Pollination puts pollen on the stigma of a pistil. Then pollen tubes grow down through the style into the ovary, carrying the sperms into the ovules, where fertilization takes place. Then the fertilized egg grows into an em¬ bryo, the ovule (including the embryo) into a seed, and the ovarv into a fruit. 19-9 BEAN SEED AND CORN KERNEL Each contains an embryo plant and a supply of stored food. REPRODUCTION IN EARTHWORMS Every earthworm is both male and female. It has both ovaries and testes. Any animal that has both ovaries and testes is a hermaphrodite ( her maf roh dyte), after Hermaphroditus, supposed in Greek mythology to have been both man and woman in one body. So an earthworm is a hermaphrodite. ( In some books on flower classification, per¬ fect flowers are described as being her¬ maphroditic. Can you explain why?) Earthworms have two parents In theory, any earthworm could be both mother and father of its offspring, but it never is, because there is no way for the sperms of a worm to get to its own eggs. Before earthworms can re¬ produce, two worms must mate. Dur¬ ing mating, each worm fills the sperm pockets (Figure 19-10) of the other worm with sperms. After that, each earthworm lays its own eggs and ferti¬ lizes them with the sperms received from the other worm during mating. So each worm is both mother and father, but not to the same offspring. How the young are produced After two worms have mated, the girdle or, more properly, the clitellum (kliliTELum) (Figure 19-10) of each worm enlarges and secretes a cocoonlike sac. The cocoon then loosens and slips forward over the body toward the head. When the cocoon is about half way be¬ tween the girdle and the head, eggs are deposited in the cocoon through a pair of openings connected to the ovaries by hollow tubes called the oviducts ( egg tubes ) . At the same time, sperms are discharged from the sperm pockets into the cocoon. (Of course, these sperms came from another worm.) Then the cocoon slips off over the worm’s head. Inside the cocoon, sperms fertilize the eggs, and the fertilized eggs grow into embryos. Soon young 19-10 An earthworm’s reproductive system includes both ovaries and testes, but the worm is not both the father and the mother of its own offspring (see text). There are two ovaries, four testes, six sperm sacs, four sperm pockets, and so on. In this drawing, half of these structures (those on the near side of the body) have been cut away. REPRODUCTIVE ORGANS OF EARTHWORM Sperm sacs of male (cut open below, to show testes) Sperm pockets Testes Sperm duct Oviduct Ovary worms hatch from the eggs, still inside the cocoon. In due time, the cocoon breaks open and releases young worms into the soil. Try to find some earthworm cocoons in your garden and bring them to class. Summing up: reproduction in earthworms Earthworms are hermaphrodites, but the exchange of sperms during mating precedes reproduction and results in young worms with two different par¬ ents. Inside the cocoon, the eggs of the cocoon-making worm are fertilized by sperms from another worm. The ferti¬ lized eggs grow into embryos inside the eggs. In due time, the eggs hatch, also inside the cocoon. A little later, young worms emerge from the cocoon. REPRODUCTION IN FROGS Frogs, like other vertebrates, have two parents— a male parent and a fe¬ male parent. Production of eggs and sperms A female frog has two ovaries and two long, much-coiled oviducts (see Frog Chart 7, following page 304). The ovaries produce two large masses of black-and-white eggs. The eggs move through the two long oviducts, where each egg is covered with a jellylike sub¬ stance, and finally leave the body through the cloaca. The male frog has two testes, lying just ventral to the anterior ends of the kidneys (Frog Chart 7). The testes produce sperms which move out through the hollow tubes called sperm ducts and finally leave the body through the cloaca. Frogs mate just at egg-laying time. As the female lays the eggs, the male deposits sperms over them, just as they leave her body. Then sperms fertilize the eggs. Usually most but not all of the eggs in the mass are fertilized. Growth of frog eggs The fertilized egg of the common leopard frog ( Rana pipiens— ray nuh pip ee enz ) has 13 pairs of chromosomes in it. One of each pair came from the sperm, the other from the egg. In other words, a sperm has 13 chromosomes in its nucleus and an egg has 13 chromo¬ somes in its nucleus. When the two nuclei unite at fertilization, this puts 13 pairs or 26 chromosomes in the fer¬ tilized egg. The fertilized egg undergoes mitotic cell division. It will pay you to turn back now to page 38 and Figure 1-13 and reread the discussion of mitotic cell division. As you know, during mitosis each chromosome builds another one exactly like itself. So in the frog’s fer¬ tilized egg, each of the 26 chromosomes duplicates itself, making 52 in all. Actu¬ ally this makes two identical sets of the 13 pairs of chromosomes. The rest of the steps in mitotic cell division have to do with getting one of the two iden¬ tical sets of 13 pairs into each daughter cell. When the frog’s fertilized egg fi¬ nally divides into two daughter cells, each cell has 26 chromosomes (or 13 pairs) in its nucleus. And the 13 pairs in one cell are exactly like those in the other, unless an accident happens to a chromosome. You will learn later about certain accidents that may happen to chromosomes. Right now, the important thing is to understand that mitotic cell division results in two daughter cells with identical sets of chromosomes. By mitotic cell division, the frog’s egg becomes a two-celled embryo. Then these two cells undergo mitotic cell di- REPRODUCTION IN HIGHER ORGANISMS 497 vision, making a four-celled embryo. Mitotic cell divisions continue, making 8 cells, then 16, 32, and so on. At first, all the cells in the embryo look alike (Figure 19-11). But soon certain layers of cells appear, first two layers, then three. These three layers (Figure 19-11) correspond roughly to the . ectoderm, endoderm, and meso¬ derm layers of planarians. At this stage, the cells in one layer are no longer exactly like those in another. As the embryo grows, some ectoderm cells change into epithelial cells and others into nerve cells, while endoderm cells change into food tube cells, and meso¬ derm cells change into muscle cells and other specialized tissues. This is cell differentiation. The frog’s egg grows into an embryo by mitotic cell divisions and cell differ¬ entiation. So do the fertilized eggs of most animals and plants. You, yourself, came from a fertilized egg. In a few days, the frog embryos have completed their development. Then the tadpoles wriggle out of the eggs and the surrounding jellylike mass and swim around on their own. At this stage they breathe by external gills. They eat algae. Soon the external gills are gone and the tadpole breathes like a fish, with internal gills. In due time, in some species a year or more, the tadpole turns into a frog . — . — — 19-11 DEVELOPMENT OF A FROG FROM A FERTILIZED EGG Eight stages in the de¬ velopment of a frog are shown (read down on the left, then down on the right). The first three stages show early cell divisions and are highly magnified, the fourth and fifth stages are not so highly magnified; the many-celled embryo is beginning to take shape. The last three stages show tad¬ poles and immature frogs; the frog in the last stage has lost most of its tail and is nearing maturity. 498 THE CONTINUITY OF LIFE (Figure 19-11 and the cover of the Frog Charts ) . It loses its tail and gills, devel¬ ops legs and bones and lungs, and fi¬ nally hops out on shore. A frogs fertilized egg grows into a tadpole, and a tadpole into a frog, by repeated cell divisions and by cell dif¬ ferentiation. What is more, if no acci¬ dents have happened along the way, each cell in the frog’s body has 13 pairs of chromosomes in its nucleus. And the 13 pairs in one cell are exact duplicates of the 13 pairs in every other cell. What's in a chromosome? You already know that chromosomes transmit such hereditary traits as eye color. But you still do not know what is in the chromosomes. Inside of every chromosome in any plant or animal are two long coiled threads. Located along those threads in a definite order are hundreds of ultrami- croscopic particles called genes ( jeenz). Actually it is the genes, not the whole chromosomes, which transmit particu¬ lar traits like eye color, webbed feet, or “leopard” skin markings in the leopard frog. (Inside of the 23 or 24 pairs of chromosomes in each cell in your own body are some 20,000 genes. These genes transmitted to you the traits you inherited from your ancestors. ) In Unit One, you learned that each chromosome duplicates itself before a cell divides. Actually it is more correct to say that each gene duplicates itself * * There is evidence that duplication takes place on even a lower level than the gene— that each of two parts of a gene duplicates itself, and that one old part and one new part goes into the make-up of each of the two genes that result. Thus, a gene would not “duplicate” itself, but instead contribute part of its make-up to each of two new genes. Photos left and top right : Carolina Biological Supply House ; others : The American Museum of Natural History REPRODUCTION IN HIGHER ORGANISMS 499 and each of the two threads in a chro¬ mosome duplicates itself. At this early stage in mitosis, each chromosome con¬ tains four coiled threads with identical genes in identical order located along their whole length. Later, each chro¬ mosome divides, making two chromo¬ somes, each with two coiled threads bearing all its genes. So the end result of mitotic cell division is two new cells with identical sets of chromosomes and genes. One more structure in a chromosome is important. This is a specialized “beadlike” body called the centromere (sen troh meer), which may be located at any point along a chromosome but always at the same point in the same chromosome and in the other chromo¬ some of a given pair. During mitotic cell division, the centromere divides when the chromosome divides. It is by its centromere that each of two dupli¬ cate chromosomes seems to be maneu¬ vered first toward the center of the di¬ viding cell and then toward one end or side of the cell. With this picture of what’s in a chro¬ mosome, you are ready to study the process by which sperms and eggs “ripen” or mature. Maturation of sperms and eggs Certain cells in the frog’s testes pro¬ duce sperms by two successive cell di¬ visions, but not mitotic cell divisions. These cells that produce sperms are often called sperm mother cells. Egg mother cells in the ovaries produce eggs by two successive cell divisions, but not mitotic cell divisions. Of course, each of the frog’s sperm mother cells contains 13 pairs of chro¬ mosomes, just as the other body cells do. So does the egg mother cell. If these mother cells were to undergo mitotic cell division, each sperm and egg would get 13 pairs of chromosomes. But each sperm gets just 13 chromosomes, not 13 pairs of them. So does each egg. In other words, during the two cell divi¬ sions that result in sperms and eggs, the chromosome number is reduced to half the number in a body cell. That is why these two cell divisions are often called reduction division. The technical name for what takes place in the cell nuclei during reduction division is mei- osis ( my oh sis ) , so that reduction di¬ vision may also be termed meiotic cell division (or divisions). During the first of the two meiotic cell divisions, the genes in each chro¬ mosome duplicate themselves, just as they do in mitotic cell division. But the centromere in each chromosome neither duplicates itself nor divides. So the resulting “double” chromosome (re¬ placing each of the 13 chromosomes making up one of each original pair ) is held together by its centromere, and passes on into one of the two daughter cells. This results in two daughter cells, each with 13 “double” chromo¬ somes, and with each “double” chromo¬ some held together by its centromere. 19-12 The differences between mitotic and meiotic cell division can be seen by com¬ paring this drawing with the drawing in Figure 1-13, page 38. Essentially, in mitotic cell division, chromosomes are duplicated once and the mother cell divides once; thus each new cell has the same number of chromosomes (and the same type) as the mother cell had. But in meiotic cell division the mother cell divides twice while the chromo¬ somes are being duplicated only once; thus, each new cell gets only half as many chromo¬ somes as the original mother cell had. The cell shown dividing here is a sperm mother cell; the four new cells (C) gradually mature as sperms (those shown are not yet mature). 500 THE CONTINUITY OF LIFE MEIOTIC CELL DIVISION In the second cell division, genes do not duplicate themselves and chromosomes do not divide. But this time the centro¬ meres do divide, causing each “double” chromosome to become an identical pair of chromosomes. Then one of each pair of duplicate chromosomes goes into one daughter cell and the other of the pair into the other daughter cell. This results in four daughter cells, each having exactly 13 chromosomes, or one duplicate of only one of each of the 13 pairs in the original mother cell. These four daughter cells become the sperms. Eggs with 13 chromosomes are also pro¬ duced by meiotic cell divisions, but three of the possible four daughter cells perish, so that only one egg comes from one mother cell. This is true of the mat¬ uration of the eggs of many higher or¬ ganisms. You can see that meiotic cell divisions produce sperms and eggs with only half the original number of chromosomes. Study Figure 19-12 to get a better un¬ derstanding of this important point. (For simplicity, the sperm mother cell in Figure 19-12 has only 2 pairs of chromosomes, rather than 13 pairs, as in the frog.) What would happen if there were no reduction division? At each generation, the chromosome number would double. In frogs, starting with 26 chromosomes, the next generation would get 52, the next 104, the next 208, and so on, until no single cell could hold so many chro¬ mosomes. This problem doesn’t arise because of reduction division. Important ideas and terms If this discussion of chromosomes and reduction division applied only to frogs, it would not be very important to you. But it applies to virtually all organisms that reproduce sexually. The only way you can understand how people inherit blue or brown eyes, red or blond or brown hair, and other traits is to understand mitosis, meiosis, and the nature of the cell divisions that follow each of these processes. Why? Because the genes in the chromosomes are the carriers of heredity. It is important that you understand the ideas and terms listed here. 1. Mitotic cell division results in two daughter cells with the same number and kinds of chromosomes and genes as the mother cell had. 2. Meiotic cell division, or reduction division, results in daughter cells (usu¬ ally sperms or eggs) with only half as many chromosomes as the mother cell had. 3. A sperm or an egg gets a duplicate of only one of each pair of chromosomes in the original mother cell. 4. The normal number of chromo¬ somes for most body cells is often called the double number, or, more techni¬ cally, the diploid ( dip loyd ) number. In the leopard frog, this number is 26. 5. The half number of chromosomes in an egg or sperm is called the haploid (hap loyd ) number. The haploid num¬ ber in the leopard frog is 13. 6. The symbol 2n is used for the dip¬ loid number of chromosomes, n for the haploid number. Haploid and diploid numbers Your own diploid number is either 46 or 48. Until recently, 48 was accepted as correct, but improved methods for separating and counting chromosomes have led to some counts of 46 (oddlv enough, Figure 19-13 shows 47). Ac¬ cording to Doctors J. H. Tjio and T. T. Puck of the Colorado Medical Center, Denver, Colorado, the normal chromo¬ some number in human males is 46. 502 THE CONTINUITY OK LIFE J. H. Tjio and T. T. Puck, “The Somatic Chromo¬ somes of Man,” 1958, proceedings of the National Academy of Sciences (in the press) 19-13 HOW MANY CHROMOSOMES? Ac¬ cording to this photograph (greatly en¬ larged), there were 47 chromosomes in the human cell from which the chromo¬ somes were taken. The normal count is probably one more— or one less— than this number. Table 19-A lists several organisms with their diploid and haploid num¬ bers. In some organisms, each body cell contains the haploid number, not the diploid. In mosses and ferns, the game- tophyte generation ( the leafy moss plant and the fern prothallium) is an example. In mosses, each cell in the bristle ( the sporophyte generation) contains the diploid number, and reduc¬ tion division occurs when spores are produced. Also, in ferns, the familiar fern plant (the sporophyte generation) has the diploid number in each cell, and reduction division occurs when spores are produced. So in ferns and mosses, gametophytes are haploid, sporophytes diploid. In flowering plants, reduction divi¬ sion occurs when a pollen mother cell in the anther produces four haploid pol¬ len grains, or when an ovule produces four large haploid spores ( three of which perish while the other one pro¬ duces the four or eight nuclei of which one becomes the haploid egg). Summing up: reproduction in frogs Frogs reproduce sexually. By meiotic cell divisions, the testes of the male produce sperms and the ovaries of the female produce eggs. Each sperm and egg has 13 chromosomes. One sperm fertilizes one egg, so the fertilized egg has 13 pairs or 26 chromosomes in its nucleus. By mitotic cell divisions and subse¬ quent cell differentiation, the fertilized egg grows into an embryo, then the em¬ bryo hatches and becomes a tadpole. In due time, the tadpole changes into a frog. In each body cell of a frog, there are identical sets of chromosomes and genes. The genes transmit traits to the offspring. TABLE J9-A CHROMOSOME NUMBERS OF SEVERAL ANIMALS AND PLANTS* Organism Diploid no. 2n Haploid no n Homo sapiens 46 or 48 ** 23 or 24 Rana pipiens 26 13 Canis familiar is 78 39 (dog) Earthworm 32 16 Garden pea 14 7 Fruit fly (common 8 4 species) Oak 24 12 Elm 28 14 A scar is (one species) 2 1 (another species) 4 2 * The counts given here are based on two books, Chromosome Atlas of Cultivated Plants by C. D. Darlington and Janaki Ammal, Allen & Unwin, London, 1945, and Chromo¬ some Numbers in Animals by Sajiro Makino, Iowa State College Press, 1951. ** Improved methods of counting chromo¬ somes seem to indicate that the diploid number in man may be 46 rather than 48. REPRODUCTION IN HIGHER ORGANISMS 503 REPRODUCTION IN MAMMALS Mammals come from fertilized eggs, but the eggs are fertilized internally and the embryos develop inside the uterus of the mother’s body (except in the platypus and spiny anteater, which lay eggs with shells). Rabbits, white rats, and hamsters make excellent laboratory animals for the study of mammalian reproduction. Here we shall discuss rabbit reproduc¬ tion. This discussion fits almost any mammal that has several young in a lit¬ ter. Rabbit reproduction Any female mammal that is “carry¬ ing unborn young is said to be preg¬ nant ( preg n’nt ) , as you probably know. In Figure 19-14, you see the re¬ productive organs of a pregnant rabbit, with an enlarged drawing of one em¬ bryo at the left. Note the two ovaries, the two short oviducts, and the com¬ pound uterus with five enlargements. Inside each enlargement is an embryo. The ovaries produce eggs with the haploid chromosome number. The eggs move down the oviducts. The male’s testes produce sperms, also with the haploid chromosome number. During mating, sperms are deposited in the birth canal. The sperms swim up the oviducts. When the sperms reach the eggs, fertilization occurs. In mammals generally, fertilization takes place in the oviducts. (This is also true of birds and reptiles. Internal fertilization must precede the forma¬ tion of the shells of their eggs. ) In rabbits, as many as ten or twelve eggs may be fertilized at about the same time. Each fertilized egg has the diploid number of chromosomes, whose genes, as you know, will “control” the growth of the embryo and transmit hereditary traits. Each fertilized egg moves out of the 19-14 The rabbit uterus shown here has five embryos in it, one of which is shown enlarged at the left. Many mammals bear numerous young at one time, but in man this is rarely the case. Ovaries, oviducts, a uterus, and a birth canal are typical of mammals. The eggs are produced in the ovaries and are usually fertilized in the oviducts by sperms that gained entrance through the birth canal. The fertilized eggs develop into offspring in the uterus and are born through the birth canal. REPRODUCTIVE ORGANS OF FEMALE RABBIT Ovary Oviduct Placenta Uterus Umbilical Cord Birth canal oviduct into the compound uterus. Soon it attaches itself to the wall of the uterus by a structure that is called the placenta ( pluh sen tuh ) . (See Figure 19-14, left.) The embryo is joined to the placenta by the umbilical ( um bil ih k’l ) cord, commonly called simply the cord. Most of the cells in the placenta and all of those in the cord come from the embryo. So you might say that the rabbit embryo grows a cord and pla¬ centa by means of which it fastens itself to the lining of the uterus. In the cord there are three blood ves¬ sels— two arteries and a vein. The ar¬ teries carry the blood of the embryo to the placenta. The vein carries the blood back to the embryo. In the placenta, the arteries branch into many capil¬ laries, which are surrounded by moth¬ er’s blood. However, the walls of the capillaries keep the blood of the embryo separate from that of the mother. Mother’s blood does not flow through the embryo. The blood in the rabbit embryo (and in that of other mam¬ mals ) is its own blood, made in its own body. You might compare the rabbit em¬ bryo’s capillaries in the placenta to those in the lungs, the food tube walls, and the kidneys of the animal after it is born. Why? Because oxygen and di¬ gested food molecules diffuse out of the mother’s blood through the capil¬ lary walls into the embryo’s blood. And carbon dioxide and other wastes diffuse out of the embryo’s blood capillaries into the mother’s blood. Before birth, the mammal’s placenta does the work later done by its lungs, kidneys, and the villi in its intestines. As the rabbit embryo grows bigger, the uterus enlarges around it. In some 30 days, the rabbits are born. After a rabbit is born, its placenta (afterbirth) is also discharged from the mother’s body, and the uterus begins to contract. Fertilization effects Fertilization somehow stimulates the growth of the fertilized egg into an embryo. Many experiments have been done to try to find out just how fertiliza¬ tion stimulates growth. To date, the re¬ sults of these experiments seem to indi¬ cate that fertilization stimulates rapid chemical changes in the egg. Usually it takes fertilization to make an egg grow, but there are exceptions. The fatherless turkey chick on page 486 seems to be one example. Today biolo¬ gists know of several more. Drones (male bees ) come from unfertilized eggs. Dandelions and several other flow¬ ers may produce fruits and seeds with¬ out pollination and fertilization. Of course there is a word for it. Biologists use the word parthenogenesis (pahr thuh noh jen uh sis ) to signify the growth of an unfertilized egg (plant or animal) into an embryo. Partheno¬ genesis is fairly common among insects, crustaceans, and worms, but is rare among frogs, mammals, and other ver¬ tebrates. It is also rare among flowering plants. In higher organisms, it usually takes fertilization to make eggs grow. Mammal embryos A mammal embryo, be it rabbit or man, is an individual organism from the time the fertilized egg starts to grow. The embryo lives as a parasite within its mother’s body until it is born; the embryo grows by mitotic cell divisions and cell differentiation, and develops its own tissues and organs, even its own blood tissue. Unless acci¬ dents occur to chromosomes, every cell in a mammal embryo or an adult mam¬ mal contains identical sets of chromo- REPRODUCTION IN HIGHER ORGANISMS 505 somes and genes, half of which came from the father through the sperm and the other half from the mother through file egg. The time from fertilization to birth varies from mammal to mammal. In rabbits, it is about 30 days; in man, about nine months. This time is the period of gestation ( jes tay shun ) . Table 19-B lists periods of gestation of a number of mammals. Development of mammal embryos Like the embryos of frogs and other vertebrates, mammal embryos at one stage develop three layers of cells: ecto¬ derm, mesoderm, and endoderm. Each tissue in a mammal’s body comes from one or another of these three layers. Hair or fur, skin, nails, and the whole central nervous system are developed by cell divisions and cell differentiation from the ectoderm, as are the neurons in the nervous system. From the endo¬ derm come the windpipe, liver, pan¬ creas, lining of the food tube, and some of the endocrine glands. The mesoderm helps to produce the heart muscle and the voluntary or skeletal muscles, the lining of the two body cavities (thorax and abdomen), the bones, the blood and the linings of the blood vessels, the ovaries and testes, and the connective tissue. TABLE 19-B PERIODS OF GESTATION OF SOME COMMON MAMMALS Opossum Less than two weeks (13 days) Rat Three weeks (21 days) Rabbit More than four weeks (30 days) Cat 8 to 9 weeks Dog and guinea pig 9 weeks Man 9 months Cow 9fo months (41 weeks) Elephant 20 to 22 months The complex processes in the growth of the mammal embryo, like that of the frog embryo pictured in Figure 19-11, involve a whole series of changes from the one-celled level of organization to the tissue, organ, and organ-system level of the animal at birth. Advantages of mammalian reproduction over other kinds Mammals nurse their young. The mother and often both parents care for the young in many ways: they protect them against enemies, keep them clean and warm, and look after them gen¬ erally until they are old enough to look after themselves, in some cases for years. This parental care greatly re¬ duces death rates among young mam¬ mals. Embryos that grow inside the moth¬ er’s body have a much better chance to survive than those that develop in a pond, like fish and frog embryos, or on the ground, like snake and turtle eggs, or even in a nest, like bird’s eggs. In these and other ways, mammalian reproduction has advantages over other kinds. Human reproduction Is there anything on earth more amazing, more unbelievable, or more helpless than a newborn baby? The hu¬ man infant is more helpless at birth and needs care for a longer time than al¬ most any other animal. In a way, the long period of childhood and youth are an advantage to human beings. It gives you time to acquire knowledge. Human ovaries produce eggs (Fig¬ ure 19-15), usually only one at a time. A better name for the true female gam¬ ete is ovum (plural— ova ), since the word egg is also used for a whole bird's egg, of which onlv the yolk is the ovum. 506 THE CONTINUITY OF LIKE From You and Heredity by Amram Scheinfeld, permission of the author and publisher, J. B. Lippincott Co. Left: Dr. Gregory G. Pincus, of Harvard University; right: Dr. Seymour F. Wilhelm, New York 19-15 HUMAN OVUM AND SPERMS Most of the size of the ovum (left) consists of its large nucleus. Both the ovum and the sperms (right) are magnified the same amount, showing the ovum to be many times larger than a single sperm. The testes produce sperms (Figure 19-15), often called spermatozoa (sperm uhtohzoHuh), meaning swim¬ ming sperms. An ovum, with its 23 or 24 chromo¬ somes, moves into the oviduct. There, if sperms are present, one sperm with its 23 or 24 chromosomes fertilizes the ovum, so the fertilized ovum has 23 or 24 pairs (46 or 48) chromosomes. The fertilized ovum divides several times (Figure 19-16) as it moves down the oviduct into the single uterus. There the embryo grows a placenta and cord. Through the placenta, the growing em¬ bryo gets its food and oxygen and gets rid of wastes. The embryo continues to grow. It passes through about the same stages that other mammal embryos do. Then it begins to develop features of a human being. After about nine months, the baby is born, a miniature but usually “perfect” little Homo sapiens. What about twins, you ask? Or trip¬ lets? Twins often come from two fer¬ tilized ova. In this case, the ovaries produced two ova, not just the usual one ovum, at a time. Two-egg twins, or fraternal twins, are not any more 19-16 SIXTY-HOUR HUMAN EMBRYO This embryo (greatly enlarged) consists of only a small cluster of cells, two of which are visible. Carnegie Institution of Washington through Science Service alike than any other brothers and sis¬ ters. But human beings also produce one-egg twins. One-egg twins come from a single fertilized egg that divides once or a few times, after which the embryo then separates into two em¬ bryos. These one-egg twins have iden¬ tical chromosome sets, of course. They look so much alike that we call them identical twins. HOW OFTEN DO PEOPLE HAVE TWINS? If you are interested, ask your librarian to help you find out about how often people have twins, triplets, quadruplets, and quin¬ tuplets. In your record book, record your findings. Then report in class. Also try to find out whether "having twins" runs in families, and report. Care of mother and baby A woman who is pregnant should be under a doctor’s care. For one thing, pregnancy puts an extra load on the kidneys. Most doctors want to see a woman at least once a month, at first; later, every two weeks; and near the end of her pregnancy, every week. At each visit to her physician, a woman who is expecting a baby will be care¬ fully checked. The testing of a urine specimen each time is especially im¬ portant. For another thing, a woman’s diet must supply all her needs and those of the growing child. So she needs a phy¬ sician’s advice as to the best diet to follow. For still another thing, most states now require a blood test during pregnancy, just as they do before mar¬ riage. For these and other reasons, medical care during pregnancy is of vital importance. When the child is born, it is quite helpless. During the first few months, the baby may be breast-fed. Many doc¬ tors feel that babies usually get along best if they are breast-fed for at least six months, but many other doctors think otherwise. In any case, cod-liver oil and orange juice are usually added to the baby’s diet quite early. When the baby is about two months old, most doctors recommend that he be immunized to diphtheria, lockjaw, and whooping cough, and perhaps to polio. Improved care of babies has re¬ duced their death rate tremendously in the past 50 years. Nevertheless, the first year is still one of the most dangerous periods of life. More human beings die during the first year of life than in any other year except those of advanced old age. The fight is still on to reduce the death rate among infants to lower and lower figures. The Rh factor and pregnancy On page 387 you learned a little about Rh-positive and Rh-negative blood. A woman who is Rh-negative runs some risk of losing her baby dur¬ ing pregnancy if her husband is Rh-pos¬ itive. It works this way. You will remember that the Rh fac¬ tor is located in the red blood cells of persons who are Rh-positive. You will remember also that some 85 per cent of us are Rh-positive. If an Rh-negative woman marries an Rh-positive man, the children are likely but not sure to be Rh-positive. Sometimes a small break in the placenta allows some of the em¬ bryo’s blood to leak through into the mother’s blood. If the embryo is Rh- positive, the Rh factor in its red blood cells acts as an antigen to an Rh-nega¬ tive mother. An antigen, as you know, causes the body to produce antibodies, and these antibodies are likely to re- J main in the mother’s blood all her life. 508 THE CONTINUITY OF LIFE Such a woman s first pregnancy is likely to go well, but a second preg¬ nancy may not. If the second baby is also Rh-positive, it is likely to be seri¬ ously injured by the antibodies from the mother’s blood. These antibodies dif¬ fuse into the placenta and thence into the embryo, where they cause a clump¬ ing of its red blood cells. Sometimes the antibodies injure the embryo so badly that it dies, during about the seventh month. However, the baby is usually born alive but needs immediate treatment. Most doctors today run a blood test to see if a pregnant woman is Rh-nega- tive. If she is, the husband’s blood may then be tested. If he is Rh-positive, the doctor watches for any unfavorable symptoms and prepares to meet them. Under this kind of care, the babies are often saved. Boy or girl? Man has probably always wondered why one baby is born a boy and an¬ other a girl, or why one egg hatches into a hen and another a rooster. Many fan¬ tastic notions have been entertained at various times about what determines the sex of offspring. Just what does determine whether a given fertilized egg will grow into a male or a female of the species? Sixty years ago no one could have answered that question scientifically, for it is only since 1900 that the facts have been slowly worked out. Today the answer is certain. It is the chromosomes that de¬ termine whether a baby will be a boy or a girl, just as they determine whether a bee will be a drone or a female, or a chicken will be a hen or a rooster. The sex of a baby is determined in the same way that the sex of a fruit fly is. Since fruit flies have only four pairs of chromosomes in each body cell and man has 23 or 24 pairs, it is much sim¬ pler to study the way fruit-fly chromo¬ somes determine the sex of the offspring. Figure 19-17 is a diagram of the fruit fly’s four pairs of chromosomes and what happens to them during reduc¬ tion division and fertilization. Refer of¬ ten to this diagram as you read on. In the female fruit fly the two chro¬ mosomes in each pair look alike, but in the male fruit fly the two chromosomes in one of the four pairs do not look like each other. One of the pair is a straight rod; the other is bent at one end. The straight chromosome of this pair is called the X chromosome; the bent one is called the Y chromosome. Each male has one X and one Y chro¬ mosome in this pair of chromosomes, but each female has two similar X chro¬ mosomes in the corresponding pair. During reduction division, the two chromosomes of any given pair are separated. One chromosome of a pair goes to one sperm, the other of the pair goes to a second sperm. Naturally, half of the sperms get one X chromosome, and half get one Y chromosome. Each egg gets one X chromosome. If a sperm containing an X chromosome fertilizes the egg with its X chromosome, the fer¬ tilized egg will contain two X chromo¬ somes and will develop into a female with a pair of X’s in each cell. On the other hand, if a sperm with a Y chro¬ mosome fertilizes an egg with its X chromosome, the fertilized egg will have one X and one Y chromosome and will develop into a male with the XY pair in each cell. In man and many other animals, as well as in the fruit fly, the sex of the offspring is determined by the sex chro¬ mosome ( X or Y ) of the sperm that fer¬ tilizes the egg. How unscientific it was REPRODUCTION IN HIGHER ORGANISMS 509 19-17 DIAGRAM OF SEX DETERMINATION IN FRUIT FLIES Because fruit flies have only four pairs of chromosomes, it is easy to follow what happens as eggs and sperms are produced and as eggs are fertilized. Note the sex chromosomes (shown in green). How is the sex of an offspring determined— by the sperm or the egg? for men of early times to blame their wives if only daughters were born! It is the father whose X or Y chromosome determines whether the child will be a girl or a boy. O J As you know, biologists have had new and far more powerful microscopes to use in recent years. With these micro- scopes, they are finding out that “acci¬ dents” may happen to the sex chromo¬ somes. Sometimes an ovum gets XX rather than X. Then the fertilized ovum may be XXY or XXX. Still other things happen, with surprising combinations, such as XX YY or even XYY. Watch for further news on the human sex chro¬ mosomes. In the meantime, the important point is that the sex chromosomes determine whether a child will be a boy or a girl. 510 THE CONTINUITY OF LIFE CHAPTER NINETEEN: SUMMING UP Higher organisms reproduce in sev¬ eral ways, all of which can be classified as sexual or asexual reproduction. Most flowering plants can reproduce both ways, sexually following pollination, or asexually by means of tubers, bulbs, runners, shoots, or budding and graft¬ ing. Earthworms reproduce sexually, but an earthworm is both mother and father, although not to the same off¬ spring. When two of these worms mate, each deposits sperms in the other’s sperm pockets. Then the worms sep¬ arate, and into the cocoon of each go its own eggs and the sperms it received from the other worm. Fertilization and embryo development take place in the cocoon. Frogs reproduce sexually. The male frog deposits sperms on the female’s eggs immediately after the eggs leave the female’s body. Other vertebrates also reproduce sexually; only rarely do thev reproduce asexually. Mammals reproduce sexually. A sperm fertilizes an ovum, or several sperms fertilize several ova, in the fe¬ male’s oviducts. The embryos develop inside the uterus— a compound uterus in rabbits and many other mammals, a single uterus in human beings and sev¬ eral other mammals. The embryo grows by mitotic cell di¬ visions. It is attached to the lining of the uterus by the placenta, to which it is joined by the umbilical cord. The mammal embryo is an individual, from the first. It lives as a parasite with¬ in the mother’s body until it is born, but it builds its own tissues and organs and organ systems, including its own blood. Human reproduction is sexual. Usu¬ ally the period of gestation is nine months. The human child requires care for years, but the comparatively long childhood of a human being is an ad¬ vantage in that it allows a long period of training and education. That train¬ ing and education give each new gen¬ eration the advantage of the knowledge gained bv previous generations. Your Biology Vocabulary Of the new terms introduced in this chapter, many will be useful to all of you all your lives. Make sure that you understand and can use correctly each of the following terms. sexual reproduction asexual reproduction parthenogenesis budding grafting anther filament (of anther) stigma ovary ovule style pollen tube fruit seed staminate flowers pistillate flowers seed dispersal cross-pollination REPRODUCTION IN HIGHER ORGANISMS 511 self-pollination or selfing cotyledon hypocotyl plumule endosperm hermaphrodite oviduct sperm duct clitellum cell differentiation meiosis reduction division genes sperm mother cell egg mother cell haploid number diploid number ovum embryo pregnant mammal uterus umbilical cord placenta spermatozoa sex chromosomes: X chromosome Y chromosome Testing Your Conclusions 1. Some of the following statements are false. Pick out the true statements and copy them. Then correct the false statements by changing the italicized words. Add the corrected statements to your list. a. The essential parts of a flower are the stamens and the pollen. b. The pollen tube grows down through the style and carries sperms from the pollen grain to the ovule in the ovary. c. The primary function of the flower is reproduction. d. The parts of the pistil are the ovary, the style, and the stigma. e. A seed is a ripened ovule. f. Fruits never ripen unless fertilization occurs. g. The parts of the stamen are the filament and the anther. h. Fertilization of the egg takes place within the ovule of the flower. i. Flowering plants that have seeds with “wings” are probably dispersed mainly by animals. j. The fertilized egg is the first cell of a new plant that will be more or less like the parent plants’ cells. 2. In your record book, answer the following questions. Use complete sentences. a. What mammal has the longest gestation period? How long is the human gestation period? b. What do biologists call the “afterbirth”? How is this structure useful to the mam¬ mal embryo? c. A human ovary usually produces only one ovum at a time. Then some 28 days later, the other ovary produces an ovum. The two ovaries alternate, producing alto¬ gether some 13 ova a year. How often, then, does each ovary produce an ovum? d. If the diploid number of chromosomes were as indicated below, what would the haploid number be? Why are diploid numbers even and not odd? Diploid 4 12 28 300 More Explorations Haploid ? ? • ? ? 1. An examination of ovules after fertilization. Select an old flower, preferably a lily or daffodil, and look at the ovary. Has the ovary enlarged? If so, fertilization has prob¬ ably been accomplished. Open the ovary. Have the ovules changed in any way? If so, how? Make sketches. After this, how will you be able to tell whether fertilization has. occurred in a withered flower? 512 THE CONTINUITY OF LIFE 2. A record of how seeds travel. Examine 12 or 15 different kinds of fruits or seeds collected last fall. Write their names in a list in your book. After each kind tell how it may be carried to new locations, or use sketches to show the adaptations. 3. Observing laboratory animals. It is both easy and interesting to study the reproduc¬ tion of one or more animals in the laboratory. Hamsters, frogs, and tropical fish are excellent. You will find full directions for breeding them and several other vertebrates in Home-Made Zoo by Sylvia S. Greenberg and Edith L. Raskin, David McKay, 1952. 4. Dissections. Do the following dissections. One or two students may perform each dissection before the class. a. The frog. Open the bodies of two preserved frogs, a male and a female. Point out the masses of eggs and the oviducts of the female, and the testes of the male ( see Frog Chart 7, following page 304). Or kill a male frog, remove a testis, crush it, then mount and view a bit of the tissue under high power. You may find living sperms. b. A mammal. You can get a uterus of a pig from many biological supply houses. Or you may want to anesthetize a pregnant rabbit, open its body, and remove the oviducts and uterus. Open one of the swollen places in the uterus. Locate the embryo, the umbilical cord, and the placenta. Gently loosen the placenta from the wall of the uterus, then remove it along with the embryo. In your record book, sketch what you find. Thought Problems 1. There is usually more difference between offspring produced sexually than asexually. Have you any idea why? 2. A female moth came out of its cocoon in the laboratory. Within a day or two the moth laid 75 eggs. Not a single egg hatched. Why? 3. In the light of the fact that Baldwin apple trees are reproduced by grafting, can you explain why it is very likely that all Baldwin apple trees now living are directly related? Further Reading 1. Scientific American, May, 1952, pages 49-56, “The Control of Flowering” by Aubrey N. Naylor, discusses what makes plants start to produce flowers at given times but not at other times. 2. The following references will give you more knowledge of human reproduction. Fundamentals of Human Reproduction by Edith L. Potter, McGraw-Hill, 1948. Men and Women by Amram Scheinfeld, Harcourt, Brace, 1944, discusses such topics as “The Weaker Sex: Males” and “Marriage of Tomorrow.” Elements of Healthful Living, Third Edition, by Harold Sheely Diehl, McGraw-Hill, 1955, contains a chapter on parenthood. Birth Atlas, Maternity Center Association, 654 Madison Avenue, New York 21, N.Y., contains a series of pictures showing stages in the development of a human embryo. Human Growth by Lester Beck, Harcourt, Brace, 1949, will help you understand human growth and development. REPRODUCTION IN HIGHER ORGANISMS 513 CHAPTER 20 How Traits Are Inherited Shown here are a mother and her two daughters. All three have a streak of white hair, hi ceiiain other features they are also alike , but in still others different . Why do some traits seem to he passed along so unmistakably to offspring , while other traits appear not to have been passed along at all P From a Life Photo © Time, Inc., 1947 The inheritance of blaze hair Some few people have a streak of white hair running back from the mid¬ dle of the forehead. This is a hereditary trait called blaze hair, or just blaze. Above, you see members of two gener¬ ations of a family in which blaze hair is found: a mother and her two young daughters. Interested biologists have studied several such families and found that every person with blaze hair has at least one parent with this trait. Ap¬ parently you can’t inherit blaze hair unless one of your parents has the trait. But you can inherit red or blond hair or blue eyes even if both of your par¬ ents have brown hair and brown eyes. Red or blond hair and blue eyes may “skip a generation’’ or even several gen¬ erations and still show up again, but blaze cannot. Would you like to know why? Would you like to know how peo¬ ple inherit traits? To understand how people inherit traits like hair color and eye color, you need first to understand some of the basic principles of genetics ( juh net iks), the science of heredity. That calls for a review of the researches of Gregor Mendel (1822-1884), who was a monk in a monastery in Briinn, Austria— now Brno ( ber noh ) , Czechoslovakia. Greg¬ or Mendel is often called “the father of genetics ’ because he was the first to discover some basic principles of this science and record his discoveries for others to know. 514 THE CONTINUITY OF LIFE DISCOVERY OF THE PRINCIPLES OF GENETICS What is a trait? We have been using this common word fairly often, but in order to study genetics, we need to specify exactly what we mean when we say “trait.” A trait is defined as “a dis¬ tinguishing quality; characteristic; pe¬ culiarity;' and dictionaries do not spec¬ ify whether it is an inherited or an ac¬ quired characteristic, or perhaps an outgrowth of both heredity and envi¬ ronment. However, when we use the word trait in the study of genetics, we usually mean hereditary characteristics —genetic traits, such as eye color in ani¬ mals or flower color in angiosperms. Genetic traits are invariably acted upon by environmental factors, to be sure, but these traits at least have their basis in heredity. The genetic traits you are most likely to notice are traits in which individuals differ. This is only natural, but you should remember that distinguishing traits of individuals are relatively few as compared with the huge numbers of genetic traits that are common to a whole species, or to several species as opposed to all other organisms. With these observations in mind, let us con¬ sider the nature of genetic traits. No one knows what human being first noticed that some “traits run in fam¬ ilies,” nor who first tried to explain how traits can be inherited. But we do know that people have held many false beliefs about heredity, just as they have about the causes of disease. Here is a list of some things that are not true of heredity. Things not true of heredity 1. It is not true that the members of a family are “blood relatives” (in that they all have the same type of blood) any more than that they are “muscle relatives” or “bone relatives.” 2. It is not true that a blood transfu¬ sion can transmit traits from the per¬ son who gives the blood to the patient who receives it. 3. It is not true that a baby receives hereditary traits by way of the blood. 4. It is not true that a pregnant woman can “mark her baby” during the late months of pregnancy. 5. It is not true that either heredity or environment must determine everv J given trait, as, for example, greenness in grass. It takes both heredity (inherit¬ ed genes) and environment (light) to determine greenness in plants. Both heredity and environment help to deter¬ mine all the traits of an organism. En¬ vironment may not seem to play much of a part in a trait such as eye color, but it does play its part. And in a trait such as height, environmental factors (food, maintenance of health, etc.) play an unmistakable part in support of hered¬ itary factors. The evidence that proves some of the common misconceptions about heredity false will unfold, as you learn how cer¬ tain traits are inherited. Right now, the important thing to remember is that he¬ reditary traits are transmitted through (or in a manner having relation to ) the genes in the chromosomes that go into the offspring. Inheritance of single traits You inherited all of your genetic traits together, not one at a time. This is true of all organisms. But to get at the basic principles of genetics, it is necessary first to study the inheritance of a single trait and ignore the rest. That is the way Mendel made his dis- HOW TRAITS ARE INHERITED 515 coveries. It is also necessary, at first, to ignore the role of the environment in helping to determine the traits of an organism. But as you read on, try to remember that tracing single traits and ignoring environmental effects does not give you the whole picture. What you already know about genetics You already know more about how traits are inherited than anyone on earth knew a hundred years ago. You even know some things Mendel did not know, even when he published his now- famous article, Experiments in Plant Hybridization (hy brid ih zay shun), in 1866. For example, you know that the genes in the chromosomes (Figure 20-1) transmit traits from one genera¬ tion to the next. Chromosomes weren’t even named until 1887, three years after Mendel died. You also know that all the genes in one chromosome are thought to be “linked” together in a definite way. We refer to this condition as linkage. And linkage wasn’t named until 1917. Let’s review the things you have al¬ ready learned about chromosomes and genes, things that are basic to genetics. 1. Chromosomes occur in pairs in each cell of the body of an adult organ¬ ism. Your cells contain 23 or 24 pairs of chromosomes. One of each pair came from your father, the other from your mother. 2. Chromosomes normally do not oc¬ cur in pairs in the gametes (eggs and sperms) of higher organisms. On the contrary, each gamete contains just one of each pair of chromosomes, unless a rare genetic “accident” has occurred. 3. Genes normally occur in pairs in each cell of the body of an adult organ¬ ism. One gene of a pair lies in one chro¬ mosome and the other gene of the pair lies at the same point in the other chro¬ mosome of that chromosome pair. 4. Genes normally do not occur in pairs in a gamete. On the contrary, each gamete contains just one of each pair of genes, unless, again, a rare genetic “accident” has occurred. 5. Meiotic cell division (reduction division) distributes just one of each pair of chromosomes and , with it, one of each pair of genes to each gamete. Now you are ready to study some of Mendel’s experiments and the facts he discovered. Mendel's experiments with tall and dwarf garden peas Mendel cross-pollinated tall and dwarf garden peas. He transferred pol¬ len from a flower on a tall vine to the stigma of a flower on a dwarf vine and labeled the flower. Then he transferred pollen from a flower on a dwarf vine to the stigma of a flower on a tall vine and labeled the flower. He made several such crosses and saved the seeds that were produced. This was in 1858. The next year Mendel planted all the seeds from the cross-pollinated flowers. Every seed that grew produced a tall vine , in spite of the fact that one parent had been a dwarf. This time (the year 1859) Mendel let all the flowers pol¬ linate themselves, and again he saved the seeds. (Peas are normally self-pol¬ linating. See Figure 20-2.) The next year (1860) Mendel plant¬ ed the seeds he saved in 1859. Most of them produced tall vines, but some pro¬ duced dwarfs. Apparently, garden peas can inherit dwarfness, even when the parents (in this case, one parent) are tall, much as people can inherit red hair even when both parents have brown hair. 516 THE CONTINUITY OF LIFE Top: Dr. Berwind P. Kaufman, Carnegie Institution of Washington, Department of Genetics, Cold Spring Harbor, L.I. ; bottom: Pease and Baker, University of Southern California, from Genetics, A. M. Winchester, 1951, Houghton Mifflm Co. 20-1 PHOTOGRAPH OF A GENE? Above. Several giant chromosomes from the salivary glands of a fruit fly are shown as they appear under the compound microscope. Note their beadlike structure. Below. A small portion of one such chromosome is shown as it appears, much more highly magnified, under the electron microscope. Circled in white is a definite body, protein in nature, which may be a gene. If so, then this is the first known photograph of a gene. Note that the beadlike structures are not considered to be the genes; however, the genes are thought to be located near these structures. HOW TRAITS ARE INHERITED 517 Photo by Hugh Spencer 20-2 FLOWER OF A GARDEN PEA Two of the five petals of this flower are united and folded in such a way that they form a “cup” in which the stamens and pistil are en¬ closed. Self-pollination is the natural result. Mendel continued growing the seeds from selfed peas for several years. He found that selfed dwarfs always pro¬ duce dwarf offspring, but that some selfed tails produced part tall and part dwarf offspring, while other selfed tails produced all tall offspring. Studies of other traits Also starting in 1858, Mendel crossed pea vines having red ( actually red- violet) flowers with vines having white flowers. In 1859, all the seeds from these crosses grew into vines with red flow¬ ers. But in 1860, some of the seeds from the selfed red-flowered plants of the year before grew into plants with white flowers, the rest into plants with red flowers. Mendel followed this trait through several more generations. He found that red flowers are inherited like tallness, white flowers like dwarf ness. In 1858, Mendel also made other crosses (Figure 20-3). Altogether, he made crosses involving these seven traits of garden peas: Stem length: tall X dwarf Flower color: red X white Seed color: yellow X green Seed form: smooth X wrinkled Flower position (on stem): axial X ter¬ minal Pod form: inflated X constricted Pod color: yellow X green In each case, the pea vines of the first generation, produced by the cross of parents with contrasting traits, were all alike in the trait being studied. As you know, in the first cross listed above, the peas were all tall, and in the sec¬ ond cross, they were all red-flowered. In the third cross, they were all yellow- seeded; in the fourth, all smooth-seed- 518 THE CONTINUITY OF LIFE ed; in the fifth, all flowers were axial (strung along the steins); in the sixth cross, all plants bore inflated pods; and in the seventh, all pods were yellow. The plants of the next or second gen¬ eration proved that green seeds, wrin¬ kled seeds, terminal flowers, constricted pods, and green pods were all inherited like dwarf ness and white flowers. Table 20- A summarizes Mendel’s re¬ sults, but to understand this table, you need first to learn some common ge¬ netic terms and symbols. Tallness, red flowers, and other traits inherited in the way they are have been named dominant traits. Dwarfness, white flowers, and other traits inherited in the way they are have been named recessive traits. Blaze hair in human beings is in¬ herited like tallness and red flowers in garden peas. These are dominant traits. Red and blond hair and blue eyes are inherited like dwarfness and white flowers in garden peas. They are reces¬ sive traits. The plants ( or animals ) originally crossed are called the parental genera¬ tion, designed in tables and charts as The offspring from the first cross (Mendel’s 1859 garden peas) are called the first filial ( fil ee ul ) generation, or the F1 generation. The next generation (Mendel’s 1860 garden peas) is called the Fo generation, the next the F3 gen¬ eration, and so on. How would you des¬ ignate Mendel’s 1862 garden peas? Now examine Table 20-A carefullv- From it you can learn something else that is important. Look at the percent¬ ages listed at the right side of the table. As you can see, about 75 per cent (%) of the Fo plants from each cross showed the dominant trait, and about 25 per cent (fi) showed the recessive trait. So the ratio of plants with the dominant 20-3 COMMON TRAITS IN GARDEN PEAS Three of the seven traits Mendel studied in garden peas are shown in this diagram— tallness vs. dwarfness, yellow vs. green coty¬ ledons, and smooth vs. wrinkled seeds. TABLE 2 0-A MENDEL'S RESULTS IN CROSSING GARDEN PEAS Traits of Pi generation Visible traits of F i genera¬ tion F2 generation: no. of plants F 2 generation: per¬ centage Dominant * Recessive Total Dominant Recessive Stem length: tall X dwarf All tall 787 277 1,064 73.96 26.04 Flower color: red X white All red 705 224 929 75.90 24.10 Seed color: yellow X green All yellow 6,022 2,001 8,023 75.06 24.94 Seed form: smooth X wrinkled All smooth 5,474 1,850 7,324 74.74 25.26 Flower position: axial X terminal All axial 651 207 858 75.87 24.13 Pod form: inflated X constricted All inflated 882 299 1,181 74.68 25.32 Pod color: yellow X green All yellow 428 152 580 73.79 26.21 * The dominant trait is the one that is visible in the Fi generation. trait to those with the recessive trait is about 3 to 1, often written 3:1. You will learn later why this ratio is com¬ mon in the F2 generation of many or¬ ganisms. Useful new ideas and terms You can better understand Mendel’s work and his results if you will become familiar with a few ideas and terms in common use among geneticists today. 1. We now know that one pair of genes on a pair of chromosomes in a garden pea vine controls the height of the plant. The two genes of this pair may be both for tall or both for dwarf or one for tall and one for dwarf. It is customary to use symbols to designate genes. Here we will designate the gene for a dominant trait with a capital let¬ ter and that for a recessive trait with the same letter, but in lower case. For example, the gene for tallness in gar¬ den peas may be designated as T and that for dwarfness as t; while that for red flowers may be called R, and that for white flowers, r. We call the two genes of a pair al¬ leles ( uh leelz ) . The two alleles for height in a given pea vine may be TT, Tt, or tt; while the two for flower color may be RR, Rr, or rr. Obviously, a white-flowered plant must carry the al¬ leles rr and a dwarf must carry the alleles tt. But a tall vine may carry either TT or Tt and a red-flowered vine either RR or Rr. Can you guess which of the selfed tall vines, TT or Tt, may produce some dwarf offspring? Which can produce only tall offspring? 2. If both alleles of a pair of genes are alike (TT or tt), we say that the organism is pure, or homozygous (hoh mohzygus), for that trait. Mendel’s parental generation pea vines were all homozygous either for tallness or for dwarfness (or for red or white flowers, and so on). He carefully spent two years breeding plants that were pure in these traits, before starting his fam¬ ous experiments. 3. If the two alleles of a pair of genes are not alike (Tt or Rr, for example), we say that the organism is hybrid, or 520 THE CONTINUITY OF LIFE heterozygous ( het er oh zy gus ) , for that trait. All of the Fx generation plants in Mendel s experiments were hybrid, or heterozygous, for height (or flower color, or cotyledon color, and so on). 4. All of the hybrid pea vines of the Fx generation from a tall-dwarf cross are tall and can’t be told from the tall parent (Figure 20-4). But the genes for height in a hybrid tall vine are Tt while those for height in the tall par¬ ent are TT. Obviously the genetic make-up of tall vines may differ. This is true of nearly all organisms showing a dominant trait. For this reason, it is useful to have a term that refers to the genetic make-up of any organism and a different term that refers to the actual appearance of the organism. Geneti¬ cists use the term phenotype ( fee noh type), meaning “visible type,” to refer to the appearance of the organism and genotype ( jen oh type ) to refer to its genetic make-up. The phenotype of all tall garden peas is tallness, but the genotype may be either Tt or TT. The phenotype of all dwarf garden peas is dwarfness and the genotype is tt. What is the genotype of a white-flowered gar¬ den pea? Of a red-flowered one? Turn back to Table 20- A and give the geno¬ type of each kind of pea vine listed there under the F1 generation. The principles of genetics As you know, Mendel was the first to discover some of the basic principles of genetics. His discoveries failed to at¬ tract much attention until the year 1900, when three men in three different nations came across his 1866 article and brought it to the attention of interested biologists. Since 1900, there have been hundreds and hundreds of experiments and hundreds of observational studies, many similar to those Mendel carried out, and others of a different nature. Modern researchers have added much evidence that supports Mendel’s con¬ clusions and other evidence that has led to some modifications and exten¬ sions of them. The amazing thing is that Mendel’s conclusions, arrived at with no knowledge of chromosomes and genes, have stood up so well to the tests of modern research. The basic principles of genetics may be summarized briefly as follows: 1. With a few exceptions, a sexually produced organism inherits at least one pair of genes for each trait. If the two alleles of such a pair of genes are un¬ like, one usually dominates the other. This is commonly spoken of as the principle of dominance. (There are many exceptions to this principle, as you will learn later.) 2. Several pairs of genes may affect the same trait or one pair of genes may affect several traits. Probably all of the genes in a fertilized egg interact in con¬ trolling the development of that egg. This is known as the principle of gene interaction. 3. During meiotic cell divisions, the two alleles of a pair of genes separate {segregate) , one going into one gamete and the other into another gamete. This is usually spoken of as the principle of segregation. 4. Because of linkage, all the genes in one chromosome are usually trans¬ mitted together. (Chromosomes do sometimes break, as you will learn, but we are ignoring this fact for the pres¬ ent. ) This may be referred to as the principle of linkage. 5. During meiotic cell division, the two chromosomes of each pair sepa¬ rate, one going into one gamete and the other into another gamete. In this way, the chromosomes are sorted inde- HOW TRAITS ARE INHERITED 521 © Parents F2 generation • . . ' 522 THE CONTINUITY OF LIFE pendently of each other into the gam¬ etes. Naturally all the genes in one chromosome are also sorted independ¬ ently of those in other chromosomes. This is referred to as the principle of independent assortment. To sum up briefly, the basic princi¬ ples of genetics are: dominance, gene interaction, segregation of genes, link¬ age, and independent assortment (of chromosomes). Common ratios in the F2 generation From his results with garden peas, Mendel drew the conclusion that the plants in the F2 generation usually show about three plants with the dominant trait to one with the corresponding re¬ cessive trait. This conclusion may be referred to as the 3 : 1 ratio. This is the phenotype (visible traits) ratio. In Fig¬ ure 20-4, the four pea vines illustrated at the bottom of the page (the F2 gen¬ eration ) clearly show the phenotype ratio. As you know, the genotype of the tails (dominants) in the F2 generation may be either TT or Tt, while that of all the dwarfs is tt. The genotype ra¬ tios of tails and dwarfs in the F2 gen¬ eration may be written thus: 1 TT to 2 Tt to 1 tt or 1 TT : 2 Tt: 1 tt To make the genotype ratio general, it is written: 1 dominant to 2 hybrids to 1 recessive This genotype ratio (Figure 20-4) is commonly referred to as the 1:2:1 ra¬ tio. For example, among 1,000 F„ hy¬ brid tails, you may expect about 250 pure (homozygous) tails, 500 hybrid (heterozygous) tails, and 250 dwarfs. The phenotype ratio of 3 : 1 and the genotype ratio of 1:2:1 occur quite commonly among F2 generations of or¬ ganisms, both plants and animals. They are due to the operation of what peo¬ ple usually call the laws of chance. You can investigate the laws of chance ap¬ plying here by drawing beads from a box. DEMONSTRATION OF LAWS OF CHANCE. You will need 100 beads of one color and 100 beads of another color, but all 200 of the same size. Let's say you have 100 red beads and 100 white ones. Count out 50 red beads and 50 white beads and put them all together in a box. Put another 50 red beads and 50 white beads into another box. Without looking, pick one bead out of each box. You may get two red beads or two white beads or one red and one white bead. Work with a partner. Let one partner draw beads and the other record the re¬ sults like this: two reds or RR : J-HT 1 one red and one white or Rr : J4TT44TT two whites or rr : 111 Keep on until you have drawn all the beads in pairs, one of each pair from each box. How many RR (two red) combinations did you get? According to the laws of 20-4 PHENOTYPE AND GENOTYPE FOR TALLNESS OR DWARFNESS IN GARDEN PEAS When a tall and a dwarf garden pea are crossed, and their offspring crossed, the tall plants of the Fj and F2 generations all look alike— that is, they have the same phenotype. Yet some are pure for tallness and others hybrid. A good way to distinguish between their geno¬ types is to let them pollinate themselves, then plant in separate places the seeds pro¬ duced by each of them. If all the offspring of a tall plant are also tall, the parent was pure for tallness. If some of the offspring are dwarf, the parent was hybrid for tallness. HOW TRAITS ARE INHERITED 523 chance, you could expect to get two red beads about 50 times. How many Rr (one red and one white) combinations did you get? About 100? How many rr (two white) combinations did you get? About 50? Did your ratio come out about 1 : 2 : 1? According to the laws of chance, it should. As you may have guessed, the red beads might symbolize genes for red flowers; the white beads, genes for white flowers. These genes, during re¬ duction division in selfed F, generation red-flowered peas, sort into sperms in such a way that half the sperms carry the gene for red flowers (R) and the other half carry the gene for white flowers (r). These genes also sort into eggs in the same way. So the chances of getting fertilized eggs RR, Rr, and rr are the same as they are in drawing beads from the two boxes. That is the explanation of the 1:2:1 genotype ratio. Incomplete dominance Mendel never ran across an example of incomplete dominance, but many modern geneticists have done so. A classical example has to do with red- flowered and white-flowered four- o’clocks. If you cross a red with a white four- o’clock, the flowers of the F, generation are not red but pink (Figure 20-5). But if you cross the pink ones, about If of the F2 generation plants have red flowers, /2 have pink flowers, and have white flowers. Here, the princi¬ ple of gene segregation applies, but the principle of dominance does not. We conclude that neither gene ( R or W ) is completely dominant or completely re¬ cessive. So we call this incomplete dom¬ inance. Another example has to do with “blue” Andalusian fowl. If a black rooster is kept with a flock of white hens, the eggs from these hens produce “blue” fowl, known as the Andalusian breed. Here again, neither the gene for black nor for white is completely dominant or completely recessive. Geneticists today have evidence that some degree of incomplete dominance is widespread, even though the results are not always as obvious as in pink four-o’clocks and “blue” Andalusian fowl. Here is one example in human be¬ ings. An occasional man is a bleeder. His blood will not clot in two to seven minutes, as yours will, but may only clot slightly in 30 to 40 minutes. The re¬ cessive gene for the condition of being a bleeder is in the X chromosome but not in the Y chromosome. As you know, a daughter always gets an X chromo¬ some but never a Y chromosome from her father. So all daughters of a bleeder carry the recessive gene for this condi¬ tion. The daughters are not bleeders be¬ cause the dominant gene on the X chro¬ mosome from the mother prevents the condition. However, it has now been found that the daughters of bleeders often have longer than normal clotting times, say 10 to 12 minutes or even more. So apparently the gene for normal clotting is not completely dominant over that for being a bleeder, but instead both genes help to affect the clotting time. Summing up: discovery of the principles of genetics The important principles and ideas discussed may be summed up briefly thus: 1. The principle of dominance. Of the two alleles of a gene pair in a hy¬ brid (Fj) organism, one is usually dom- 524 TIIE CONTINUITY OF LIFE inant and the other recessive, but many examples of incomplete dominance are known. 2. The principle of gene segregation. The two alleles of a gene pair separate during reduction division, one going to one gamete and the other to another. 3. The principles of linkage and in¬ dependent assortment of chromosomes. All of the genes in one chromosome are usually transmitted together, one chro¬ mosome of each pair going to one gam¬ ete and the other to another. 4. The phenotype and genotype ra¬ tios. In the F2 generation the pheno¬ type ratio tends to be three organisms showing the dominant trait to one show¬ ing the recessive trait, or 3:1, while the genotype ratio tends to be one ho¬ mozygous dominant to two hybrid dom¬ inants to one recessive, or 1:2:1. 5. The principle of gene interaction. All the pairs of genes in a fertilized egg help to determine all of the genetic traits of the organism. And several gene pairs may affect one trait, or one gene pair may affect several traits. (The en¬ vironment also affects all of the traits.) EXPLANATIONS AND APPLICATIONS OF GENETIC PRINCIPLES Now that you understand some of the principles of genetics, you are prob¬ ably wondering about many things. Why are most color-blind people men? Why do some twins look so much alike that their own mother finds it difficult to tell them apart? Are there only two alleles of the gene pair having to do with eye color, and if so, why don’t all people have either brown or blue eyes instead of so many shades ( green, hazel, or gray)? How can one tell whether a particular individual with a dominant trait like blaze hair is pure (homozy- 20-5 INCOMPLETE DOMINANCE IN FOUR- O'CLOCKS When a red four-o’clock is crossed with a white one, the offspring are neither red nor white, but pink. Appar¬ ently neither gene is dominant or recessive to the other. gous ) or hybrid ( heterozygous ) for that trait? Let’s take first the last question- how to identify a hybrid. How to tell a heterozygous from a homozygous individual How can you tell whether an F2 tall garden pea is hybrid ( Tt) or pure ( TT) for height? Let it be selfed and save the seeds. If any of the seeds grow into dwarf vines ( F3 generation ) , you know the F2 tall was hybrid, but if all the seeds grow into tall vines, the F2 tall was homozygous or pure for height. But higher animals can’t fertilize their own eggs. Take domestic chick¬ ens, for example. In them, rose comb is dominant to single comb (see Figure 20-6). Suppose you wanted to find out whether a rose-combed rooster is ho- HOW TRAITS ARE INHERITED 525 mozygous ( RR ) or hybrid (Rr) for comb form. Put the rose-combed roost¬ er with a flock of single-combed hens. Incubate the eggs. If you get 90 chicks and all of them are rose-combed, you know the rooster is homozygous for rose comb (RR). But if some of the chicks show single comb, you know the rooster is hybrid for rose comb (Rr). This is called a test cross. You can use what we will call a “checkerboard” to find out about what percentages of the chicks from a hy¬ brid rose-combed (Rr) parent and a single-combed (rr) parent may be ex¬ pected to have each type of comb. USING THE CHECKERBOARD. Study the checkerboard in Figure 20-7 carefully. Each square in the checkerboard shows the genes for comb in the fertilized egg produced by the union of the sperm with the gene for comb shown at the left and the egg with the gene for comb shown above the checkerboard. As you can see, about 50 per cent of the offspring have rose combs; 50 per cent, single combs. Now close your book and make a check¬ erboard of four squares and use it to de¬ termine what types of comb you may ex¬ pect chicks to have if a rooster, homozy¬ gous for rose comb (RR), is bred to hens that are homozygous for single comb (rr). Wyandotte chickens are expected to have only rose combs. If some single- combed chicks turn up among their off¬ spring, the breeder knows that some of his hens and roosters are heterozygous (hybrid— Rr) for rose comb. Most breeders simply destroy all single- combed chicks, but instead they could do test crosses on all birds in the flock and then destroy all birds proved to be hybrid for rose comb. J USING THE CHECKERBOARD FURTHER. Use the checkerboard to discover what kinds and ratios of offspring may be ex¬ pected in the following cases. 1. A snapdragon, pure for red, is crossed with one that is hybrid for red. SYMBOLS FOR GENES SYMBOLS IN SPERMS RR and Rr R and R SYMBOLS FOR GENES IN EGGS R and r 2. A snapdragon, hybrid for red, is crossed with a white one. SYMBOLS FOR GENES SYMBOLS IN SPERMS Rr and rr R and r SYMBOLS FOR GENES IN EGGS r and r 3. In guinea pigs, black coats are domi¬ nant, white are recessive. A pure or homo¬ zygous black is BB, a hybrid black Bb, and a white bb. Use a checkerboard for this mating: Bb and Bb. What are the results? Inheritance of two traits at once So far, we have ignored all but one trait and its two alleles. But as you know, an organism does not inherit its genetic traits one at a time. Let’s see now how we may use the checkerboard to trace two traits at once. In guinea pigs, both black hair and short hair are dominant, while white hair and long hair are recessive. If a black short-haired male, homozygous for both traits, is bred to a white long¬ haired female, all of the offspring, the F, generation, will be black and short- haired. If these offspring are bred, the F2 generation animals will be of four types: black short-haired, black long¬ haired, white short-haired, and white long-haired. Figure 20-8 shows you how a 16-square checkerboard is used to find out what ratio may be expected among the four phenotypes of F2 animals. This 526 THE CONTINUITY OF LIFE U.S.D.A. 20-6 ROSE COMB AND SINGLE COMB These two chickens look much alike except for their combs. Rose comb (left) is dominant to single comb (right). type of cross is called a dihybrid cross, in contrast to a monohybrid cross in¬ volving only the two expressions of a single trait, such as tallness and dwarf¬ ness. In a dihybrid cross, the expected phenotype ratio is 9:3:3: 1. You could use a 64-square checker¬ board to see what results to expect in the Fo generation from a trihybrid cross, such as TTRRSS crossed with ttrrss, but doing so wouldn’t be very useful to you. To use the method to find what results to expect from a seven- hybrid cross would require a checker¬ board with 128 squares on each side or 128 X 128 squares in all. It would be a waste of time to try to use a checker¬ board on a seven-hybrid cross. Geneti¬ cists have worked out mathematical formulas to enable them to predict the results of such complicated crosses. But the point is that in garden peas, the F2 generation plants of a seven-hybrid cross produce 128 different kinds of gametes and that these gametes may be recombined in fertilized eggs in 128 X 128 or 16,384 ways. One of the advantages of sexual reproduction is that genes segregate and then may en¬ ter into many new combinations, mak¬ ing for variety among the offspring. No such thing is possible in asexual repro¬ duction, because the offspring have the same set of genes and chromosomes the parent has, unless an accident happens to a gene or chromosome. 20-7 PLOTTING INHERITANCE OF A SINGLE TRAIT Checkerboard calculations of this type enable you to predict what percent¬ age of offspring will have the dominant or recessive trait being studied. HEN: pure for single comb ( rr segregation into eggs) 70 _Q X O' LU I— to O O oc E 0 CL _o CO E O 0 c u c 0 CO 0 0 •*— k. 0 1_ CD 0 O i— CD <1) CO r r Rr Rr (rose - combed) (rose - combed) ■ rr rr (single - (single- combed) combed) HOW TRAITS ARE INHERITED 527 FEMALE: BbSs (segregation into eggs) BS Bs bS bs i/> £ Q) a) to RESULTS: black with short hair BBSS = 1 BBSs = 2 BbSS = 2 BbSs = 4 BBss = 1 Bbss = 2 bbSS = 1 bbSs = 2 bbss = 1 } white with long hair black with long hair white with short hair 20-8 PLOTTING INHERITANCE OF TWO TRAITS AT ONCE Compare these calcula¬ tions for a cross of two guinea pigs with the calculations shown in Figure 20-7. How large a checkerboard would be re¬ quired to plot the inheritance of three traits? of four? USING A 16-SQUARE CHECKERBOARD. Use a 16-square checkerboard to find out what types and phenotype ratio of plants may be expected in the F2 generation of a dihybrid cross of tall garden peas with red flowers and dwarf vines with white flowers. The genotype of all F, plants (the par¬ ents in this problem) is TtRr. At segregation, the gametes may be any of four types: TR, Tr, tR, or tr, as indicated in the checker¬ board at the top of the next column. Copy the checkerboard and fill in all the squares. These plants will be of four phenotypes, as listed below the checkerboard. How many of each phenotype are indicated by your checkerboard calculations? TtRr segregation into eggs TR Tr tR tr «/» E a> o_ V) O C c o o O) a) U) O' £ Tall, red-flowered (TTRr, TtRR , or TtRr) Tall, white-flowered ( TTrr or Ttrr) Dwarf, red-flowered (ttRR or ttRr ) Dwarf, white-flowered (ttrr). Is the phenotype ratio here 9:3:3: 1 , as it is in the dihybrid guinea pig cross shown in Figure 20-8? As you know, a human being has 23 or 24 pairs of chromosomes in each cell. There are 8,388,608 different ways in which 23 pairs (or 16,777,216 different ways in which 24 pairs ) could be sorted into the gametes during reduction divi¬ sion. The chances that any two gametes would get identical sets of chromosomes are very small. You may have noticed that no two human beings are exactly alike. How could they be? The chances of getting exactly the same set of genes and chromosomes into two fertilized eggs are almost zero. Even with iden¬ tical twins, developed from the same fertilized egg, environmental factors bring about degrees of difference in these offspring. Inheritance of human blood groups Your blood group was determined when the ovum was fertilized nine months before you were born. A single pair of genes determines a person’s 528 THE CONTINUITY OF LIFE blood group. But there are three (not just two) alleles of the gene for blood group. The three alleles may be desig¬ nated A, B, and O. Any fertilized ovum gets two of these three alleles. Both of the alleles A and B are dominant to O, but neither A nor B is dominant over the other. The genotype of a person may be OO, OA, OB, AA, BB, or AB. Table 20-B shows the possible geno¬ types of persons in each of the main blood groups. TABLE 20-B GENES AND HUMAN BLOOD GROUPS * Blood group Possible genotypes 0 OO A AA or OA B BB or OB AB AB * Many subgroups within human blood groups are now known, but we are ignoring them here because they complicate the picture unnecessarily. Years ago, one sometimes read of a supposed mix-up of babies in a hospi¬ tal. Today this is virtually impossible, because of the fingerprints and foot¬ prints that are taken. But in former years, typing the blood of all four par¬ ents and of both babies could help prove which baby belonged to which pair of parents. Table 20-C shows the blood types possible among the chil¬ dren of parents of various blood groups. TABLE 20-C POSSIBLE BLOOD GROUPS OF CHILDREN FROM PARENTS OF SEVERAL BLOOD GROUPS Blood, group Possible blood groups of parents of children 1. 0 and 0 0 2. 0 and A o, A 3. 0 and B 0, B 4. A and A 0, A 5. B and B 0, B 6. A and B 0, A, B, AB 7. 0 and AB A, B, AB 8. A and AB A, B, AB 9. B and AB A, B, AB 10. AB and AB A, B, AB possible, carry the investigation as far back as your great-grandparents. There are many traits which might be selected for your investigation. The follow¬ ing list may contain one which you wish to choose, but do not hesitate to investigate the inheritance of any other family trait that may interest you. color of eyes color of hair curly hair straight hair birthmarks tallness or shortness length of fingers tendency to freckles complexion premature gray hair diabetes musical ability tendency to stoutness length of arms asthma hay fever webbed toes quality of teeth shape of head eye defects (such as nearsightedness and farsighted¬ ness) blood pressure A STUDY OF ONE OF YOUR OWN TRAITS. Blood type is only one of many of your own traits that you can study. Pick out some other trait, such as hair color, in which you resemble either your mother or your father, but not both. Then try to find out what relatives on your mother's or father's side, if any, possessed the same trait. If Prepare a diagram on a blank page of your notebook to record the facts you dis¬ cover. Does the trait seem to be dominant, recessive, or incompletely dominant? In¬ vent a symbol to signify the occurrence of the trait and place it in the proper places in your diagram. Explain your symbol in the space below your diagram. Model your HOW TRAITS ARE INHERITED 529 diagram after the one which follows, in which circles represent women and squares represent men. Multiple alleles The three alleles of the gene for blood group are called multiple alleles. Many other examples of multiple al¬ leles are known. The first ones discov¬ ered were those of the gene for eye color in fruit flies ( Drosophila melano- gaster— druh sof uh luh mel uh noh gas ter). Fruit flies have been widely used in genetic experiments for over 50 years, so that geneticists probably know more about the genetics of fruit flies than they do about that of any other organ¬ ism. Fruit flies may produce a new gen¬ eration every ten days or two weeks, not once a year as garden peas do. They are also small and easy to raise and cross-breed in small bottles. They are convenient animals for genetic investi¬ gations. Most wild fruit flies have red eyes (dominant), but some have white eyes (recessive). This was first discovered by T. H. Morgan in 1910. Since that date, a total of 14 alleles of the gene for eye color have been found in Dro¬ sophila. A few examples are alleles for red, eosin (reddish), apricot, buff, or white eyes. Many examples of multiple alleles are now known in many organisms, but the variations in eye color in man seem to be due to the interaction of several pairs of genes, rather than to multiple alleles of the same gene. Like eye color, hair color in human beings is affected by several pairs of genes. So are many other hereditary traits in man. Such traits are referred to as multiple-gene effects and are due to gene interaction. There are excep¬ tions, however, in which a single gene pair (along with, of course, the over¬ all interaction of all gene pairs and the environment) seems to control a trait. Such traits are often referred to as single-gene effects. (All of the traits Mendel studied in garden peas seem to be single-gene effects.) Single-gene effects in man Your blood group is a single-gene effect, because only one pair of genes acted in producing it. The ability to taste PTC * is another example. Some people can taste PTC. Others cannot. The ability to taste PTC seems to be due to a dominant gene T; the in¬ ability to taste it, to two recessive genes tt. Use a checkerboard to find out what types of children may result from each of these marriages: Tt and Tt; Tt and tt; Tt and TT; TT and tt. EXPERIMENT WITH PTC. You can get PTC test papers from the American Genet¬ ics Association, Washington 5, D.C. Chew a piece of PTC test paper. Car you taste it? If so, you are a taster, and your genotype may be TT, but is much ° PTC stands for phenylthiocarbamide. 530 THE CONTINUITY OF LIFE more likely to be Tf. If you can't taste the PTC, you are a nontaster, and your geno¬ type is ft . Take test papers home and ask each member of your family if he can taste PTC. Keep a record of the results. On the blackboard, summarize all the results of a class taste test. Include the re¬ sults from testing members of your families. Copy the results into your record book. Another example of a single-gene effect is the so-called “black urine” of some human beings. Most of us have an enzyme that makes it possible to oxidize the substance causing “black urine.” Thus, most of us do not show this condition. The gene that enables us to make the necessary enzyme is dominant. Call it A. Most of us are AA or Aa. A few persons are aa. They can¬ not oxidize the substance causing “black urine,” so it is excreted in the urine. If allowed to stand, such urine turns black. Geneticists have found some hun¬ dreds of human traits that are due to the effects of single genes or gene pairs. Most of these are abnormal traits, like bleeder’s disease, color blindness, “black urine,” eye abnormalities, and others. Except for the blood groups, the ability or inability to taste PTC, the direction of the fine hair on the forehead, and perhaps red hair and a few other traits, all so-called normal human traits seem to be affected by more than one pair of genes. Human twins Sometimes two babies are born to the same mother at the same time. Such babies are twins. Some twins are no more alike than any other brothers and sisters. Such twins come from two dif¬ ferent fertilized eggs and are called two-egg or fraternal twins (Figure 20-9). Other twins look almost exactly alike and are both girls or both boys. 20-9 FRATERNAL TWINS This brother and sister look much alike, hut in sex and in other ways they are different. They are twins, hut not identical twins. I. L. Firshein HOW TRAITS ARE INHERITED 531 Lew Merrim, from Monkmeyer 20-10 IDENTICAL TWINS These two brothers look almost exactly alike. Unlike the fra¬ ternal twins shown in Figure 20-9, these twins were produced from a single fertilized egg and have identical sets of chromosomes and genes. Such identical twins come from a single fertilized egg. When that egg divides, the two daughter cells separate and each one develops into a baby. Identi¬ cal twins are one-egg twins (Figure 20-10). One-egg twins have identical sets of chromosomes and genes, since both came from the same fertilized egg. Hence, they have identical genetic traits —at least they usually do. There are ex¬ ceptions about which you will learn a little later. And yet identical twins are never exactly alike. Often one is larger than the other at birth, because it crowded the smaller one in the uterus. This is an environmental, not genetic, effect. Most of the differences between identical twins are due to environmental effects, not genetic effects. Many thorough studies of identical twins have been made. The results in¬ dicate clearly that twins with identical sets of genes are strikingly alike in most traits. If one twin has curly hair, so has the other. If one twin has light hair, so has the other. Even the shade of light¬ ness is practically identical. Eye color is the same. The shape of the nose and of other facial features is the same. Height and weight, form and figure, and even health are certainly affected by genes, since identical twins resemble each other closely in these traits. Even the fingerprints of one twin are much like those of the other. Sometimes, how¬ ever, they are reversed; that is, one twin’s fingerprints must be held up to a mirror in order to match those of the other twin. One twin is often but not always the mirror image of the other. But identical twins are not exactly J alike. For example, 63 individuals with diabetes were found to have identical twins (Table 20-D). Investigation showed that in 53 of the 63 pairs of 532 THE CONTINUITY OF LIFE identical twins, both twins had diabetes. In the other ten pairs, only one twin had it. Geneticists do not know why. An even more startling example is a pair of identical twins, one of whom is an albino ( al by noh ) with no color at all, while the other is normal in coloring. These and many more examples show that even identical twins are not ex¬ actly alike. Studies of identical twins certainly show that their identical sets of chro¬ mosomes and genes make their visible features almost identical. But what about disposition and intelligence? How do they compare? Perhaps you know some identical twins and can answer for them. But of course identical twins usually grow up together. So even if their dispositions are much alike, per¬ haps the common training ( environ¬ ment) made them that way. Several investigators have located a considerable number of identical twins who were separated at birth or soon afterward, perhaps because of the death of the mother. One pair of iden¬ tical twin girls had been adopted into different families at the age of two weeks. The girls never saw each other again until they were 18 years old. One girl went to school for only four years. The other finished high school and had TABLE 20-D TWINS AND DISEASES * Identical twins Fraternal twins No. of No. of Total pairs Total pairs no. of sharing no. of sharing Disease pairs trait pairs trait Diabetes 63 53 70 26 Tuberculosis 80 52 125 31 Rickets 60 53 74 61 * From studies made by a German investi¬ gator and reported in German scientific journals in 1932 and 1941. some university training. Nevertheless, when they were brought together and compared, the two girls not only looked alike, but they also liked the same foods and similar kinds of clothes. And their intelligence quotients (I.Q.’s) were within two or three points of each other. In a similar case, the twin with more education had an I.Q. twelve points above that of her twin. And sev¬ eral times, the twin raised in a more favorable environment had a somewhat better disposition. You can see that we cannot really draw any valid conclusions about dif¬ ferences in disposition and intelligence in identical twins, although there is some indication that these differences, where they exist, are likely to be the re¬ sult of environmental differences rather than genetic ones. Sex-linked traits Bleeder s disease, or hemophilia ( hee mohFiLeeuh), is a sex-linked trait. It occurs in men but almost never in wom¬ en. A sex-linked trait is due to a gene (or perhaps two or three genes) in the X chromosome. A male carries only one X chromo¬ some in each cell (his other sex-deter¬ mining chromosome being a Y chromo¬ some), and therefore he has only one each of the genes that lie in X chromo¬ somes. So even a recessive gene like that for hemophilia can produce the condition in a man, since this gene would be his only gene having to do with blood-clotting. A woman, on the other hand, carries two X chromosomes in each cell. The gene or allele for nor¬ mal clotting is dominant (showing in¬ complete dominance, apparently, as you read on page 524), that for hemophilia is recessive. In a woman, the dominant gene may be paired with the recessive, HOW TRAITS ARE INHERITED 533 but such a woman is not a true hemo¬ philiac. That’s why virtually all bleed¬ ers are men. Can you explain the ex¬ tremely rare case in which a woman might be a bleeder, even though this condition seems for the most part to occur only in men? Another example of a trait that is sex- linked in man is one in which the skin is exceedingly sensitive to light, as shown by increased freckling and red¬ dening of the skin. One rare form of night blindness is also sex-linked. Other sex-linked traits in man include a pecu¬ liar scaly thickening of the skin, webbed toes, dense growths of long hair on the ears, and red-green color blindness. Summing up: applications of genetic principles A hybrid, or heterozygous, plant or animal can be told from a homozygous one by crossing it with others showing the recessive trait. If any of the off¬ spring show the recessive trait, you know that the parent showing the domi¬ nant trait is hybrid for that trait. One advantage of sexual reproduction is that the offspring show new combi¬ nations of chromosomes and the genes in them. This results in variety in the offspring. The study of dihybrid, trihy¬ brid, and other crosses reveals the wide variation in combinations that is pos¬ sible. Many genes occur in only two forms, two alleles, but there are multiple alleles of many genes, such as those for blood group in people and those for eye color in fruit flies. Many traits seem to be single-gene effects, but most traits of human beings are multiple-gene effects. One-egg twins nearly always have identical sets of chromosomes and genes. That’s why they have almost identical genetic traits. Differences in identical twins are usually due * to en¬ vironment, not heredity. Sex-linked traits are inherited by both men and women but usually express themselves only in men (or only in women, in a few cases), because the genes for these traits lie in the X chro¬ mosome. Examples of sex-linked traits are eye color in fruit flies and hemo¬ philia and color blindness in men. NATURE OF CHROMOSOMES AND GENES Most and perhaps all of your chromo¬ somes and genes are probably exact duplicates of some of those that were present in each cell in the bodies of your parents, grandparents, and other, earlier ancestors. This is true of the chromosomes and genes of all organ¬ isms. But once in a while “accidents” do happen to chromosomes or to genes within a chromosome. Next we shall discuss such “accidents” and their re¬ sults. But first let’s look into the nature of genes. The nature of genes Under the microscope, each chromo¬ some in a cell that is dividing usually looks solid; most of them look some¬ thing like short, solid rods, bent at the middle (Figure 20-11), but they aren’t. As you know, each chromosome has two long coiled threads within it. By special techniques of staining, it is pos¬ sible to make the coils in a chromosome visible under the highest power of a compound microscope (Figure 20-12). Strung along the coiled threads in a chromosome are ultra-small particles, each of which is thought to be a loca¬ tion of one or more genes— a gene locus. Each gene has its own place with re- 534 THE CONTINUITY OF LIFE A. M. Winchester of Stetson University, Deland, Florida 20-11 CHROMOSOMES IN A LIVING CELL The cell is a greatly enlarged pollen grain of a spiderwort, a flowering plant that produces distinctive blue or violet flowers. Within the pollen grain, which was photographed while undergoing cell division, the chromo¬ somes can be seen. Each chromosome looks like a short, bent rod. spect to each particle in line on each coiled thread. For example, in garden peas the gene for tall or dwarf plants is at the same point, or gene locus, on both chromosomes of the pair that carry this gene. Today geneticists have good evidence that each gene may be a molecule of a nucleic acid (called DNA,* for short) coated with a protein. (You may re¬ member that at least some viruses are believed to consist of single molecules of nucleic acids, coated with a protein.) The DNA molecules alone seem to transmit hereditary traits; the protein coating seems to have nothing to do with heredity. DNA molecules are re¬ markably stable; that is, they do not readily undergo chemical changes. * DNA stands for c/eoxyribose nucleic ncid. 20-12 TWO STAINED CHROMOSOMES Special techniques of staining make the long coiled threads within chromosomes visible under high magnification. Note the difference between what is seen of the chromosomes here and in a living cell (Figure 20-11). Professor J. Herbert Taylor, Department of Botany, Columbia University Hundreds of the genes in your cells are probably exact duplicates of genes that occurred in the cells of your grand¬ parents and more distant ancestors. DNA molecules are individually stable, but at the same time, one DNA molecule may differ from another in any of thousands of minor details of chemical make-up. If these DNA mole¬ cules, known to be present in chromo¬ somes, are in reality the genes, then each gene in its locus on each coiled thread in a chromosome differs slightly from the next gene. In a chromosome, the entire coiled threads, each particle on which is thought to be a gene locus (see Figure 20-1), are surrounded by a substance enclosed by a surface membrane, but these latter parts of a chromosome seem only to be the carriers of the genes, not to be genetic material themselves. One geneticist several years ago esti¬ mated how much space would be occu¬ pied by all the human genes that would go into the fertilized eggs that would produce the next generation of people all over the earth. He estimated that all of those genes would occupy a space about the size of an aspirin tablet. You may think of chromosomes as “tape recordings of directions for the building of the offspring.” But these “tape recordings” are alive and they are unimaginably small. Just how an ultra¬ small gene transmits its “directions,” say, for blaze hair, no one knows for sure. But in a few cases (brown hair in man, for example), there is reason to believe that a gene produces an enzyme useful in the chemical changes involved in producing a trait. In man, one or probably several (multiple) genes seem to produce an enzyme useful in making the brown pigment (coloring matter ) in brown hair. One thing is certain. A gene is not a trait, in extreme miniature. Your curly hair was not present in miniature in the genes in the fertilized ovum that be¬ came you. Genes are not ultramicro- scopic patterns of traits. All the evidence indicates that genes bring about their effects by way of chemistry, but the exact chemistry is still almost unknown. We say almost , because it is known that some genes in some organisms cause the formation of certain enzymes that help to produce certain traits in the organism. Do all genes produce their effects through enzymes? Geneticists simply do not know. As you can see, geneticists know a great deal more about gene effects than they do about the chemical nature of genes and how they transmit traits. The few clues already at hand make us hope that we may understand the nature and work of genes more fully in the not-too- distant future. In the meantime, it is well to remember that any gene (or gene pair) may affect more than one trait, that multiple genes ( or gene pairs) may affect the same trait, and that it takes a suitable environment as well as genes to produce any trait. And it is especially important to remember that the whole gene system is involved in the transmission of traits to offspring. Accidents may happen to genes Accidents may happen, even to genes. When they do, changes may show up in the offspring. For example, a sweet potato plant with some red sweet po¬ tatoes showed up in a field of normal- colored sweet potatoes. The color change was due to a changed gene. A biology student once reported in class that a dahlia plant in his flower garden was showing one white flower 536 THE CONTINUITY OF LIFE Wide World Photo Marion A. Cox 20-13 TWO MUTANTS An albino koala and an albino branch on a geranium are both mutants. In the case of the geranium, only the one small branch is a mutant; the muta¬ tion occurred in the bud that produced this branch. Can you explain why the geranium would die if the entire plant was albino— if there were no normal branches? and several pink ones. Being urged to prove his statement, the student potted the dahlia plant and brought it to class. Sure enough, he was right. Geneticists explain the situation in this way: In the cell that started the bud that grew into the branch with the white dahlia, a change occurred in a gene that controls the color. Geneti¬ cists have reason to believe that a small chemical change occurred in the gene.* All the cells in the dahlia branch that * In February, 1959, a report of work performed by Professor R. Alexander Brink at the University of Wisconsin included the fol¬ lowing information: that a gene responsible for color in corn underwent a change ap¬ parently as a result of being paired with a particular one of its alleles. The gene no longer produced color in corn, even after it had been removed from the influence of the suspected allele. Is the pairing of a gene ivith a particular one of its alleles one way of pro¬ ducing a mutation? Or is the theory of the individuality of genes in need of revision? Only further research can provide an answer. grew from that one cell carried the changed gene. When a flower opened on that branch, the blossom was white, not pink. Biologists call such a change in any organism a mutation, from the the Latin mutare, “to change.” Many mutations have been observed. In a nest of young robins, sometimes there is one white robin, or albino. There are also albino rabbits and frogs and snakes and human beings. The eyes of albinos are usually pink. In albinos, the genes for color have been changed in some way. Any albino occurring through mutation has a new heritable trait, different from that trait in its ancestors; thus, it is called a mu¬ tant (Figure 20-13). Mutations were known among domestic plants and ani¬ mals long before their cause was un¬ derstood. Breeders called such changed offspring as a hornless calf or a tailless pup “sports.” Today we know that “sports” are simply striking mutants. HOW TRAITS ARE INHERITED 537 What makes genes mutate? Dr. Herman J. Muller ( Figure 20-14), now of the University of Indiana, dis¬ covered more than 30 years ago ( 1927) that the genes in the reproductive cells of a fruit flv could be changed by bom¬ barding the fly with X rays. Flies known to carry only genes for red eyes pro¬ duced white-eyed offspring after being subjected to X rays. What is more, the white-eyed offspring produced only white-eyed descendants, thus showing that the gene for red eyes had been changed. Many similar heritable changes were induced in the same way. Fruit-fly descendants were actually 20-14 INDUCING MUTATIONS IN FRUIT FLIES Dr. Herman J. Muller, Nobel prize-win¬ ning geneticist, is shown in his laboratory as he prepares to induce mutations in fruit flies by bombarding them with X rays. The flies are in capsules too small to be visible. Life Photo © Time, Inc. produced that no one could recognize as fruit flies at all. Here is Muller’s own description of his results: “All types of mutations large and small, ugly and beautiful, burst upon the gaze. Flies with bulging eyes or with flat or dented eyes; flies with white, purple, yel¬ low, or brown eyes; flies with curly hair, with ruffled hair, with parted hair, with fine and with coarse hair, and bald flies; flies with swollen antennae, or extra an¬ tennae, or legs in place of antennae; flies with broad wings, with narrow wings, with upturned wings, with downturned wings, with outstretched wings, with truncated wings, with split wings, with spotted wings, with bloated wings, and with virtually no wings at all. Big flies and little ones, dark ones and light ones, active and sluggish ones, fertile and sterile ones, long-lived and short-lived ones. Flies that preferred to stay on the ground, flies that did not care about the light, flies with a mixture of sex characters, flies that were especially sensitive to warm weather. They were a motley throng. What had been done? The roots of life— the genes— had indeed been struck, and had yielded.” * Dr. Muller was awarded the 1946 Nobel prize in medicine for this impor¬ tant piece of research. Since his first experiments, many other investigators have used X rays to induce mutations in many organisms. This is conclusive evidence that at least one environ¬ mental factor— namely, X rays— can and does change the genes and thus pro¬ duces mutations. Other causes of mutations X rays are not the only known cause of mutations. Radiations of many other kinds may cause them. There is also evidence that higher temperatures 0 From the Scientific Monthly, December, 1929. Quoted with permission. 538 THE CONTINUITY OF LIFE sometimes increase the mutation rate, and some chemicals may cause muta¬ tions, at least in some organisms. The best evidence that at least one chemical can induce mutations comes from research with mustard gas. It has been proved that mustard gas, a poison gas used during World War I, can cause mutations in a certain fungus (Neurospora) . More than 20 mutants were found among the offspring of this fungus after its exposure to mustard gas. It may be that mustard gas brings about a chemical change in some of the genes of this fungus, thus producing mutations. There is also evidence that this gas may induce mutations in fruit flies, viruses, and in some molds and bacteria. Gene transduction New knowledge is constantly being added to what we already know of genes. One of the newest discoveries is that genes may be transferred from some individuals to others by viruses— at least in bacteria. When such a trans¬ fer has been effected, the bacterium that receives the new gene (or genes) passes it along to the next generation as a part of their hereditary make-up. The discovery of gene transduction, as it is now called, won a Nobel prize in 1958 for Dr. Joshua Lederberg of the University of Wisconsin. We cannot call gene transductions mutations, be¬ cause the chemical make-up of the genes is not changed. Rather, a virus that infects one bacterium takes from it one or more genes, and later gives these genes up to another bacterium which it infects. The transfer alone is note¬ worthy, but that the bacterium receiv¬ ing the genes should incorporate them completely into its genetic make-up is truly remarkable. "Doubling" chromosome numbers As long ago as 1937 the first reports on the use of the poison colchicine ( kol chih seen) in treating seeds of the Jim- son weed were published. Drs. Albert F. Blakeslee and Amos G. Avery of the Carnegie Institution of Washington, D.C., did the early research. They soaked seeds of the Jimson weed in so¬ lutions of colchicine and then germi¬ nated them. The plants that grew from these seeds were much larger than usual. Their leaves were rough and coarse, and their pollen grains were very large. The new plants were dif¬ ferent in many ways from the parents. These plants were self-pollinated and their seeds were grown. Cells of plants in this second generation were exam¬ ined under the microscope and were found to have twice the normal diploid number or four times the normal hap¬ loid number of chromosomes. Thus it was discovered that colchicine may cause the doubling of the chromosome number in the Jimson weed. Doubling the chromosome number was shown to be a cause of changes in the offspring.* Since 1937 many more experiments have been carried out with colchicine (Figure 20-15). We now know that col¬ chicine stops cell division in the sec¬ ond stage. So it prevents the formation of two nuclei and two cells. Instead, the double number of chromosomes be¬ comes incorporated in a single nucleus, and the normal chromosome number is thus doubled. Plants with doubled chromosome numbers are frequently larger and more vigorous. Already new types of cotton, tobacco, and several fruits have been produced in this way. * Most geneticists reserve the word “muta¬ tion” for changes in genes and do not consider changes due to doubled chromosome numbers to be mutations. HOW TRAITS ARE INHERITED 539 J. G. O’Mara, in the Journal of Heredity, from Genet¬ ics, A. M. Winchester, 1951, Houghton Mifflin Co. 20-15 EFFECT OF COLCHICINE ON AN ONION CELL Note the double chromo¬ somes. Colchicine has stopped the process of cell division that was taking place in this onion cell. Thus, the cell now has twice its normal number of chromosomes. Many of our apples of today come from trees with doubled or tripled or even quadrupled chromosome numbers (Figure 20-16). So do many other fruits and vegetables. In most of these cases, the doubled (or tripled) chromosome number arose “spontaneously,” not arti¬ ficially, as with those induced by man’s use of colchicine. You already know that n is often used as the symbol for the haploid number and 2n for the diploid number of chro¬ mosomes. Then 4n is the doubled dip¬ loid and 6n the tripled diploid num¬ ber. In some cases, the diploid number is not doubled, but is increased by mul¬ tiples of the haploid (n) number; thus, offspring may be 3n, 5n, and so on. Any condition of chromosome num¬ bers of 3n or more is referred to as polyploidy ( pol ee ploy dee ) . Poly¬ ploidy is fairly widespread, occurring even in some cells of some people. Crossing over Changes in heredity are sometimes induced in another way. Sometimes during meiotic cell division (reduction division ) , parts of two chromosomes exchange places, as is shown in Figure 20-17. Thus different genes, once in sep¬ arate chromosomes, come to be linked together in the same chromosome. This is called crossing over of genes. Cross- 20-16 NORMAL AND POLYPLOID APPLES Left. A normal McIntosh apple has 34 chromo¬ somes (2 n) in each cell. Right. This polyploid McIntosh apple has 68 chromosomes (4n) in each cell. It is much larger than the normal fruit. U.S.D.A. ing over may change slightly the pat¬ tern of inheritance, and this results in one or more new combinations of spe¬ cific traits in the offspring. In fruit flies, the genes for black body color, stubby wings, and purple eyes are located in the same chromosome. If the chromosome bearing these three genes were to break, for instance, at a point between the gene for black body and the other two, then it would be pos¬ sible for a fertilized egg to receive the gene for black body without receiving the other two. This would result in new combinations of traits in the offspring. To summarize, hereditary changes in the offspring may come about (1) by changed genes, called mutations (see footnote, page 537 ) , ( 2 ) by polyploidy, (3) by crossing over, and— at least in bacteria— (4) by gene transduction. Cytoplasm and heredity This chapter, up to this point, might lead you to think that the genes in the chromosomes are the only things that can transmit traits to offspring. Geneti¬ cists have also found that some particles in the cytoplasm of the cells of some organisms may also act like genes. In 1909, two geneticists proved that the chloroplasts and other colored bodies in the cytoplasm of plant cells act like chromosomal genes in three ways: (1) they duplicate themselves, just as chromosomal genes do, (2) they trans¬ mit the color trait ( green in the case of chloroplasts), and (3) they sometimes undergo mutation. Certain other par¬ ticles in cytoplasm are also known to duplicate themselves, to transmit traits, and to undergo mutation occasionally. All particles of this type in cytoplasm are sometimes called plasma genes, in contrast to the chromosomal genes in the nucleus. CROSSING OVER OF GENES Locus gene C A* Locus gene c A Locus gene S Before meiofic Locus gene s \ During meiofic cell k division, crossing over may occur After . ► meiofic cell division 20-17 The genes C, c, S, and s here refer to traits in two types of corn. One type has colored grains (C) that are also smooth (S). The other type has white grains (c) that are shrunken (s) . Normally the two types remain distinct because genes for both traits are carried by the same chromo¬ some. If crossing over occurs, however, new combinations of traits result. The evidence today leads geneticists to think that, in some organisms at least, both plasma genes and chromo¬ somal genes transmit traits, but chro¬ mosomal genes play the major role. The consensus now seems to be that cytoplasmic inheritance, where it oc¬ curs, is the result of an interaction of plasma and chromosomal genes, with the latter playing a major role even here. HOW TRAITS ARE INHERITED 541 General applications of genetics You have now studied some of the basic ideas that underlie genetics. You might think that this young science deals primarily with garden peas, fruit flies, four-o’clocks, and guinea pigs. This is not the case. Genetics includes the study of he¬ redity in all plants and animals, in¬ cluding ourselves. The great basic dis¬ covery is that human beings, amebas, garden peas, and apparently all other organisms inherit traits from their an¬ cestors in about the same way. Take two examples, one having to do with bacteria, the other with people. You will remember that the sulfa drugs or the antibiotics do increasingly less good, the longer they are used in a com¬ munity. To start with, a few germs of those responsible for a disease are re¬ sistant to the drug. They survive and reproduce. After a time, only the drug- resistant germs survive. Then the drug does little good. Such results are caused by genes in the original bacteria. A few of these bacteria had genes for resist¬ ance to penicillin, perhaps. The rest had genes for susceptibility to the drug. The susceptible bacteria died off. The resistant ones reproduced. The off¬ spring of the resistant bacteria got genes for resistance from their parents and transmitted them to their offspring. Soon virtually all the surviving bacteria had the genes for resistance. A similar event has occurred among human beings several times. A good example is what happened to the In¬ dians when the Europeans brought measles to America. Before then, this disease was unknown among the In¬ dians. When a tribe was exposed to measles for the first time, many mem¬ bers of the tribe sickened and died, but some had only mild cases, and a few didn’t even get the disease. After a few generations, measles killed fewer and fewer Indians. Can you explain why? The point is that the things you have been learning in this chapter have general application among plants and animals. Today, geneticists have con¬ vincing evidence that every trait of every plant and animal is affected by its genes. They have equally convincing evidence that every trait is also affected by the environment, both internal and external. In some traits, such as the color of human hair or eyes, the genes seem to be of greater importance. In other traits, such as Yehudi Menuhin's great skill as a violinist, the environ¬ ment ( training and practice, in this case ) may seem to play the major role. But in any case, it takes genes to give the organism its capacity to develop certain features. And it takes the cor¬ rect environment to let the features de¬ velop. CHAPTER TWENTY: SUMMING UP The basic principles and ideas of genetics may be summarized briefly. 1. Principle of dominance. Of the two or more alleles of a gene at a given gene locus in a chromosome, one is usually dominant, but many examples of incomplete dominance are also known. 2. Principle of gene interaction. Sev¬ eral pairs of genes may interact, affect¬ ing the same trait, and one pair of genes may affect several traits. This phase of gene interaction is often referred to as multiple-gene effects. Overall, all of the genes in a fertilized egg interact in con¬ trolling the growth of the organism. 3. Principle of segregation. During meiotic cell division, the two chromo¬ somes of a pair separate, thus separat- 542 THE CONTINUITY OF LIFE ing the two genes of each gene pair. One chromosome of each pair goes into each of the two gametes. 4. Principle of linkage. All of the genes in one chromosome are linked together and, unless crossing over oc¬ curs, are transmitted together. Sex- linked traits are due to genes carried by the X chromosome that have no alleles on the Y chromosome. 5. Principle of independent assort¬ ment. The two chromosomes of each pair, along with their respective sets of genes, are sorted into gametes inde¬ pendently of each other. 6. Mutations. X rays and other radia¬ tions, mustard gas, and probably other environmental factors may cause genes to change or mutate. 7. Polyploidy. In a number of plants and in some animals, chromosome num¬ bers of 3n, 4n, 5n, 6n , and so on, are found. This condition, called poly¬ ploidy, may result in changes in the traits of an organism. 8. Ratios in F., generations. Individ¬ uals in the F2 generation of a mono¬ hybrid cross are likely to show a pheno¬ type (visible) 3 : 1 ratio; in a dihybrid cross, a 9 : 3 : 3 : 1 ratio. The genotype ratio, distinguishing homozygous (pure) from heterozygous ( hybrid ) individ¬ uals for any given trait, is, of course, different from the phenotype ratio. 9. Multiple alleles. Two or more al¬ leles of a gene at a given locus in a chromosome may exist, but one individ¬ ual gets only one pair of these alleles or even just one of them, if it lies in the X chromosome. 10. Heredity and environment. The interaction of heredity and environ¬ ment makes an individual organism what it is. On the whole, neither is more important than the other, and neither can function without the other. 11. Nature of genes. No one yet knows for sure the exact chemical make-up of a gene, but there is evi¬ dence that a gene may be a molecule of DNA. In a few cases, genes seem to produce their effects by way of en¬ zymes, but the exact chemistry of gene effects is not yet known. Your Biology Vocabulary Make sure that you understand and can use correctly the following genetic terms. genetics dominant traits recessive traits parental generation generation F., generation homozygous heterozygous (or hybrid) alleles genotype phenotype mutation mutant gene transduction segregation of chromosomes and genes independent assortment of chromosomes linkage 1:2:1 ratio HOW TRAITS ARE INHERITED 543 3 : 1 ratio incomplete dominance test cross monohybrid and dihybrid crosses single-gene effects multiple-gene effects sex-linked traits gene interaction hemophilia (or bleeder’s disease) polyploidy DNA plasma genes Testing Your Conclusions 1. Using a checkerboard of four squares, work out what types of offspring are possible in each of the following cases, and the ratio that might be expected if a large enough number of offspring were produced by parents of the types indicated. a. Parents: hen, hybrid for white (dominant) and red (recessive); rooster, homo¬ zygous for white. Symbols: W and w b. Parents: pink four-o’clock and white four-o’clock. Symbols: R and W c. Parents: clover, hybrid for resistance to wilt disease. Resistance is dominant. Symbols: R and r. Two hybrids are crossed. d. Parents: red-eyed male fruit fly, hybrid for eye color, and a white-eyed female. Symbols: R and r. 2. Answer these questions. a. Who is ranked as “the father of genetics”? b. Who proved first that X rays cause mutations? 3. In what three ways do chloroplasts act like chromosomal genes? 4. In terms of genes, explain the difference between those organisms that are homozy¬ gous for a given trait and those that are heterozygous or hybrid for the same trait. 5. Can organisms that are homozygous for a given dominant trait usually be told from those that are heterozygous for the same trait, simply by looking at them? Cite one case where the hybrid is easily recognized. 6. Does a selfed plant with a visible recessive trait produce offspring showing the domi¬ nant trait? In other words, do selfed white snapdragons produce offspring with red flowers? Why? More Explorations 1. Breeding fruit flies. You can easily raise fruit flies in the classroom, cross them, and follow one trait, such as eye color, through two or more generations. You may collect wild fruit flies or buy them from the genetics department of some of the large uni¬ versities or from some biological supply houses. Full directions are included in the workbook that accompanies this text, and in Methods and Materials for Teaching Biological Sciences, by David F. Miller and Glenn W. Blaydes, McGraw-Hill, 1938, pages 410-12. However, a much more thorough treatment of fruit flies and their heredity, including excellent illustrations, appears in Teaching High School Science: A Sourcebook for the Biological Sciences, by Evelyn Morholt, Paul F. Brandwein, and Alexander Joseph, Harcourt, Brace, 1958, pages 196-205. 2. A long-term investigation. If you have a flower garden, you may want to try crossing two plants that show a pair of contrasting traits, perhaps a white gladiolus with a red one, or a double daffodil with a single one. In most cases, you will need to cover 544 THE CONTINUITY OF LIFE a flower with cellophane after transferring pollen to its stigma, for most of our garden flowers are naturally cross-pollinated. Thought Problems 1 . Holstein cattle may be either a solid color or spotted. Solid color is dominant, spotted is recessive. If a spotted cow is bred to a spotted bull, would you expect the calf to be spotted or of a solid color? Why? 2. Would it be possible to produce a pure line of red cattle from a roan bull (Rr) and a herd of white cows (rr)? Explain. 3. If Mendel had started his experiments with cattle in place of garden peas, it isn't likely that he would have been able to collect enough facts to draw his conclusions. Why? Give as many reasons as you can think of. 4. Some human beings have what geneticists call spidery fingers. The finger bones are unusually long. Nearly all persons with spidery fingers also have misplaced eye lenses and heart defects. This fact may be explained in either of two ways. What are they? Further Reading 1. New You and Heredity by Amram Scheinfeld, Frederick A. Stokes Company, N.Y., 1951, is a very popular book on human heredity. If you merely leaf through it and look at the color plates, you are almost sure to want to read it, or parts of it. 2. Our literature contains a number of stories of identical twins. Two of the most amusing of these stories are A Comedy of Errors by William Shakespeare, and “An Encounter with an Interviewer” by Mark Twain. You may enjoy reading one or both of them. 3. Science News Letter reports new discoveries in genetics frequently. So does Scientific American. Watch for such articles. 4. Genetics by A. M. Winchester, Houghton Mifflin, 1951, is a college text, but a highly readable one that has excellent illustrations. 5. Genetics Is Easy by Philip Goldstein, Garlan Publications, 77-79 River Street, Hoboken, N.J., 1947, contains many diagrams, which may be useful to you. 6. Mendel’s original paper, Experiments in Plant Hybridization, has been reprinted by Harvard Univ. Press, Cambridge, Mass. 7. Pedigrees and Checkerboards by E. F. Barrows, Edwards Brothers, 300 John Street, Ann Arbor, Mich., is just what you want if you enjoy checkerboard problems. 8. “ ‘Transduction’ in Bacteria,” by Norton D. Zinder, Scientific American, Nov. 1958, pp. 38—43, is an account of the recent discovery of gene transduction, written by one of the scientists who helped make the discovery. Be sure to read this article; what it reports may open a new frontier in our understanding of heredity. HOW TRAITS ARE INHERITED 545 CHAPTER How New Varieties May Arise A new variety of sheep In the early days in New England, farmers built rather low stone fences around their fields. Sheep often jumped these fences and destroyed crops grow¬ ing in nearby fields. Seth Wright had a flock of sheep consisting of 15 ewes and one ram. Among the lambs born in 1791, he noticed a male with oddly short and crooked legs. He thought how helpful it would be to have a whole flock of sheep with legs like that. Then the animals couldn’t jump the fences. Wright decided to get rid of his adult ram and let the crooked-legged lamb grow up to father the next genera¬ tion. In 1792, 15 lambs were born. Of these, two had crooked legs like their father’s. By interbreeding the crooked¬ legged sheep for generation after gen¬ eration, Wright produced a new variety or breed of sheep within the species. These sheep are now called ancon ( ang kon) sheep, from a Greek word mean¬ ing “bent arm” or “elbow,” a term de¬ scriptive of the short crooked legs of 546 THE CONTINUITY OF LIFE these sheep. Ancon sheep are rare to¬ day, for the variety has not been so maintained that it has spread widely. You have probably guessed that the first ancon ram resulted from a gene mutation. If so, you are right. Mutations and several other factors * enter into the rise of new varieties of organisms. MUTATIONS AND NEW VARIETIES The genetic systems of particular populations of organisms, such as gar¬ den peas or fruit flies, tend to stay much the same for generation after generation, sometimes for long periods of time. And yet the genetic systems of all organisms so far studied by geneti¬ cists carry within themselves the capac¬ ity to change. Gene mutations and selection Ancon sheep came from a gene mu¬ tation, one that probably occurred two * See footnote, page 537. Life Photo © Time, Inc., 1947 or more generations before the first ancon lamb was born. The ancon-type legs are due to a recessive gene. So we know that both the mother and the father of the first ancon sheep must have carried that same recessive gene, even though neither parent had crooked legs. Furthermore, the fact that two ancon sheep were born to Wright’s flock in 1792 proves that some of his 15 ewes carried the recessive gene. In the wild, a lamb with short crooked legs would probably perish long before it was old enough to breed, but under domestication, the owner selected crooked-legged animals as the parents of the next generation. In the wild, sheep with strong jumping legs have a much better chance to get food and survive than do ancon sheep. You might say that, in the wild, strong¬ legged sheep have survival value that the ancon sheep lack. The strong¬ legged sheep are selected by natural factors as the surviving animals and the parents of each new generation, while under domestication ancon sheep may be selected. In either case, the selection of the parents of the next generation is important in determining whether a particular mutant trait will spread through future generations of a popula¬ tion or will tend to disappear. Take the Washington navel orange as another example. Sometime before 1820, a bud mutation on an orange tree near Bahia ( bah ee ah ) , Brazil, had re¬ sulted in one branch that bore a su¬ perior type of navel oranges. From this branch, by budding and grafting, a number of trees were produced that bore the superior type of navel oranges (Figure 21-1). They came to be known as the Bahia navel orange variety. In 1870, a missionary stationed at Bahia, Brazil, sent twelve potted Bahia navel orange trees to William Saunders, then superintendent of gardens and grounds of the United States Department of Agriculture in Washington, D.C. Saunders propagated these trees and in 1873 gave three of them, now known as the Washington navel orange, to Mrs. Luther C. Tibbets. Mrs. Tibbets took the three trees to Riverside, Cali¬ fornia, and planted them. One of them was still growing and bearing fruit in 1937. In the navel orange, you have another example of a new variety, produced first as a mutation, and then selected and propagated by man. Since navel orange trees bear seedless fruit, they cannot reproduce in the wild. Hence, in the wild, they have no survival value at all and could not be selected as par¬ ents of the next generation. Let’s turn now to an example of a gene mutation in fruit flies. Geneticists know from experimental studies that every known gene (and several hun¬ dred are known) in fruit-fly chromo¬ somes has mutated in the past. As a re¬ sult, at every gene locus in each of a pair of chromosomes in the fruit fly, usually two or more alleles for a trait may occur. In other words, these are not mere gene pairs, of which one gene oc¬ curs in each of a pair of chromosomes, but multiple genes, or alleles. For the sake of simplicity, however, we shall ignore all but two alleles (one gene pair) in considering the determination of the length of the wings of the fly. Most wild fruit flies have long wings, but a few are born with mere stubs of wings, commonly called vestigial wings (Figure 21-2). The gene for long wings, a dominant trait, may be indicated by L and that for vestigial wings by /. The genotype of a long-winged fruit fly may be LL or Ll, but that of a fly with ves- HOW NEW VARIETIES MAY ARISE 547 21-1 WASHINGTON NAVEL ORANGE TREE The tree within the enclosure is a living monument in honor of the woman who first introduced this variety of navel orange in California. Since the fruit is seedless, the original mutant tree would not have repro¬ duced if it had not been found and propagated by man through budding and grafting. Artificial selection, not natural selection, was responsible for the survival of this type of orange tree. .-.rs L_av - uzn \\\ A?~ « ..rr zpm a W ,'Vr.l T >fvST ..vw : 5 teyZL oka^E, V I* ZAUfO i *&. 6V, s 1 -fii -M' -f-fe..; | r*urt ttt tigial wings is always //. As you know, in the cross Ll X LI, the genotypes of the offspring may be of three types, LL, Ll, or //, probably in the 1:2:1 ratio. Only those flies of genotype 11 develop vestigial wings. In the wild, flies with vestigial wings are severely handicapped because they can’t fly about in search of food. Hence they are likely to die before they mate. As you can see, in the wild, long- wan ged flies are selected as the parents of the next generation, not by man, but by natural processes. Biologists call this type of selection of parents natural se¬ lection, in contrast with the artificial se¬ lection man uses in propagating desir¬ able crop plants and domestic animals. Natural selection makes for the sur¬ vival of long-winged fruit flies and for the elimination of those with vestigial wings. And yet some flies with vestigial wings keep on appearing, generation after generation, for two reasons: (1) many long-winged flies carry and transmit the recessive gene, and (2) the gene for long wings, L, can at any time mutate again into the reces¬ sive gene, 1. In these two ways, a trait lacking survival value may show up in a few offspring, generation after genera¬ tion, even though individuals showing the trait rarely live long enough to mate. You can see that gene mutations of this tvpe do not result in new varie¬ ties or breeds of plants or animals in 548 THE CONTINUITY OF LIFE the wild, merely because these muta¬ tions lack survival value, and thus work against the natural selection of plants and animals in which they occur. But other gene mutations do result in new varieties of plants, new breeds of ani¬ mals, and new species of both wild plants and animals. Naturally, these mutations are the ones which do have survival value. Both gene mutations and natural selection help to make new varieties and new species possible, as you will see. Let’s consider an exam- pie. Can you guess what might eventu¬ ally happen if mutations, say, in rab¬ bits, were to produce a new kind of rabbit that could not only easily out¬ distance dogs and sense impending at¬ tacks by birds of prey and other rabbit foes, but also run greater distances be¬ fore becoming exhausted? Explain your answer in terms of survival value and natural selection. Mutations and mutation rates in fruit flies For 50 years, geneticists have been studying the genetics of fruit flies. With a new generation about every two weeks, or 26 generations a year, you 21-2 TWO TYPES OF WINGS IN FRUIT FLIES Long wings (left) are a dominant trait, vestigial wings (right) recessive. There are also many other types of wings in fruit flies. Of the two varieties of flies shown here, which has the better chance for survival in the wild? Reprinted with permission from P. D. Strausbaugh and B. R. Weimer, General Biology (Third Edition) (Plate 20) John Wiley & Sons, Inc., © 1938, '47, '52 can see that a single geneticist could follow inherited traits through more than a thousand generations in 50 years. To follow hereditary traits in people through a thousand generations would take at least 20,000 years and probably more like 30,000 vears. That’s one rea- 7 J son why geneticists now know so much more about fruit-fly genetics than about human genetics. Among the many things now known about fruit-flv frenetics, their mutations are of special interest at this point. Over 500 gene loci ( loh sy— plural of locus ) , or points at which one or more genes are located, are now known in the four chromosomes in a fruit-fly gamete. Ge¬ neticists have discovered at least one and often several gene mutations at every one of these gene loci. The gene for vestigial wings is one example of a gene mutation at the locus of the gene that controls wing length. Another gene mutation at this locus may result in the recessive trait of curved wings, another in bent wings, and still another in no wings at all. That makes five known al¬ leles at this one gene locus, and others are also known. How can we tell which of several re¬ lated traits in fruit flies is (or are) dom¬ inant? We usually find that the trait (or traits ) most common in the wild mem¬ bers of a species is the dominant trait (in fruit flies, long wings). However, there are exceptions, mainly because it is possible that some recessive traits have much more survival value than the related dominant traits. (Can vou explain how even recessive traits of this tvpe have a good chance of eventuallv becoming dominant traits?) In anv case, we distinguish between dominant normal traits and all related traits, which usually are the results of s;ene mutations and are called recessive ab- HOW NEW VARIETIES MAY ARISE 549 normal traits (in fruit flies, vestigial or bent wings, no wings, etc. ) . Literally thousands of gene muta¬ tions are known to occur in fruit flies. These are not necessarily one-way mu¬ tations, from normal to abnormal. A mutant gene, such as the one for curved wings, sometimes mutates back into a gene for the normal trait, long wings in this case. These are known as re¬ verse mutations, in contrast to direct mutations from normal to abnormal. Geneticists have proved that both di¬ rect and reverse mutations may occur again and again at the same gene locus. And geneticists know the rate at which mutations are likelv to occur at each J gene locus in fruit-fly chromosomes, O J even though mutation rates vary at dif¬ ferent gene loci. In general, some sort of gene mutation is likely to occur in about one out of every 20 gametes of fruit flies, according to estimates made by Dr. H. J. Muller of Indiana Univer¬ sity, who, as you know, first proved that X rays can be one cause of gene mutations in fruit flies. Mutation rates in man The available evidence indicates that mutation rates in fruit flies are, on the average, some ten times higher than they are in human beings. But the mu¬ tation rates at some gene loci in human chromosomes are rather high. For ex¬ ample, the gene for normal clotting of the blood mutates into that for hemo¬ philia (bleeder’s disease) at an esti¬ mated rate of one per 50,000 gametes produced. Mutation in reverse is less frequent and its rate has not yet been estimated, but it is known to occur. In any case, gene mutations, both direct and reverse, do occur at some¬ what regular rates in people, as they do in fruit flies and in other organisms. Gene pools of populations Ancon sheep did not come from a single sheep but from a flock of sheep. Wright’s flock of 15 ewes and a ram made up a population of sheep. A pop¬ ulation, in this sense, is a group of plants or animals in which reproduc¬ tive functions are limited to members of the group and do not occur between a group member and an individual out¬ side the group. In some of Wright’s ewes, the recessive allele for ancon- type legs occurred, along with the gene for normal legs. This gene pair was one of hundreds or perhaps thousands of gene pairs (many made up of some two of a larger number of multiple alleles ) in each animal, making many thousands of pairs in the whole flock of sheep. Geneticists sometimes refer to all of the pairs or groups of alleles pres¬ ent in a specific population as the gene pool of that population. If the members of the population interbreed, all of the members of the next generation will have genes that have come out of the gene pool, except for an occasional mutant gene that may arise. Gene mutation is the onlv known J way for a new trait to be added to the J gene pool of a population that breeds onlv within itself.* And natural selec- J tion (or sometimes artificial selection) will usually determine whether indi¬ viduals with the new trait survive and reproduce or not. Most gene mutations today result in some trait that is a disadvantage, as vestigial wings are in fruit flies. But oc- casionally a mutant gene determines a new trait that gives its possessors added survival value; that is, a good chance of being selected as parents of the next generation. With each generation, the * See footnote, page 537. 550 THE CONTINUITY OF LIFE mutant gene may be present in more and more of the individuals in the pop¬ ulation. In the course of several genera¬ tions, the new gene may became so widespread that most of the population shows the new advantageous trait. Sooner or later the mutant gene comes to make up a somewhat fixed percent¬ age of all the allelic genes at the same gene locus of all of certain chromo¬ somes in the population. In subsequent generations from that population, about the same percentage of the individuals will show the mutant trait. Traits that apparently have no effect upon survival value may also become widespread in a population. For exam¬ ple, about 70 per cent of Americans of European descent are PTC tasters, gen¬ eration after generation, while about 85 per cent of them are Rh-positive. Among certain populations of Ameri¬ can Indians, as many as 98 per cent have group O blood. Any population with a common ancestry is likely to have about the same percentage of each generation showing each hereditary trait. Geneticists then speak of a popu¬ lation equilibrium. New varieties You have already learned that gene mutations may result in new hereditary 21-3 TWO TYPES OF EAR LOBES IN MAN Not all traits have or lack survival value. Many bear no relation at all to survival value, as in the case of free (/eft) and attached (right) ear lobes. Journal of Heredity traits either having or lacking survival value; or, they may result in traits of neither more nor less survival value than existing traits (Figure 21-3). Over a long enough period of time, mutations and natural selection may gradually result in a new variety or even in a new species, derived from a former variety or species ( Figure 21-4). But other factors, particularly new com¬ binations of genes (crossing over) and of chromosomes (at each fertilization) also play a part, as you will see. Summing up: mutations and new varieties Gene mutations may result in new traits in one or more individuals in a population. Natural selection usually determines whether such individuals reproduce and pass on the mutant genes, but in today’s world, artificial selection (by man) may instead be the determining factor. In time, in a popu¬ lation that interbreeds, mutations and natural or artificial selection may result in a new variety or a new species, with a population equilibrium. NEW COMBINATIONS AND VARIETY AMONG THE OFFSPRING Only changes in genes are known to add new hereditary traits to succeed¬ ing generations. But polyploidy can “ex¬ aggerate” existing traits, and new com¬ binations of genes and chromosomes at fertilization can add to the variety among the offspring. Every fertilization a new deal As vou already know, every time a sperm fertilizes an egg, a new combina¬ tion of chromosomes and their crenes O occurs. Even in the seven pairs of ge¬ netic traits Mendel studied in garden HOW NEW VARIETIES MAY ARISE 551 peas, there are over 16,000 combina¬ tions possible in the fertilized eggs of the F2 generation. In sexual reproduc¬ tion, especially among higher organ¬ isms, the chances that two fertilized eggs might receive identical sets of chromosomes and genes are so small as to be virtually nonexistent. That is one reason why no two individuals other than identical twins ever have identical hereditary traits. Of course, in asexual reproduction the offspring do receive identical sets of genes and chromosomes, except after a mutation occurs in one but not in an¬ other individual. Offspring produced asexually show little variety. But off¬ spring produced sexually show a wide range of variety, largely because every fertilization “deals” out new combina¬ tions of chromosomes and genes in the gene pool of a population. VARIETY IN FRUIT FLIES. Ask your teach¬ er for directions as to how to set up cul¬ tures and study the genetic traits of fruit flies. Or locate these directions for yourself. You will find them in two books cited at the end of Chapter 20 for their excellent presentations of genetics in fruit flies. Carry out the directions. In each generation of fruit flies, look for variations in eye color, eye form, body color, body form, wing form, wing position, and other visible traits. Keep a record of the number of flies in each generation and each variation of the following traits: eye color— red, pink, purple, white; wing form —long, curved, bent, vestigial; body color —gray, black. New combinations from crossing over Figure 20-17 on page 541 illustrates one example of how crossing over of parts of the two chromosomes of a pair may result in the linkage of genes not previously linked in the same chromo¬ some. As you know, before crossing over occurs, any corn plant with colored grains must also have smooth grains, O O 7 since both genes are dominant and linked together and hence must be transmitted together. After crossing over, new corn plants could have colored, shrunken grains or white, smooth ones, new combinations of traits. Crossing over occurs fairlv often dur- O J ing reduction division. Hence it con- tributes quite often to an increase in variety among sexually produced off¬ spring. Gene transduction and new varieties In bacteria, new variety among the offspring follows gene transduction. When a virus infects two bacteria one after the other, it may take one or more genes from the first bacterium and give them up to the second bacterium (which incorporates the new genes as part of its genetic make-up). Natu¬ rally, when either of the two bacteria —the donor or the recipient— repro¬ duces, the offspring will adhere to the new genetic pattern established by the gene transduction. To date, no one knows whether gene transduction occurs in organisms other than bacteria. Polyploidy and new varieties As you know, one varietv of McIn¬ tosh apples is a polyploid with double the diploid (or four times the haploid) number of chromosomes (Figure 20-16, page 540). In this case, polyploidy re¬ sults in a new variety which man propa¬ gates by grafting. Many and perhaps most of the varie¬ ties of fruits we raise are polyploids, 552 THE CONTINUITY OF LIFE Left: National Park Service, Grand Canyon National Park; right: Dale L. Slocum, Arizona Development Board 21-4 SQUIRRELS ON E|HER SIDE OF THE GRAND CANYON Originally these two closely related varieties of squirrels must have come from the same parentage; but because they could not interbreed freely across the Grand Canyon, they have developed sepa¬ rately. The Kaibab (KYbob) squirrel (/eh) has a whiter tail and darker undersides than the Abert (AYbert) squirrel (right). Otherwise the two varieties are almost iden¬ tical in size, shape, color, and other features. but often artificial selection is neces¬ sary to preserve the new variety. Natural selection and variety Some new combinations of genes are more useful to the individuals having them than others are. In these cases, the individuals with more useful com¬ binations tend to be selected as par¬ ents, generation after generation. In this way, new combinations enter into the gradual changes in generation after generation until new varieties or breeds may arise, but in conjunction with the transmission of gene mutations. Summing up: new combinations and variety among the offspring Sexual reproduction makes for wide variety among each generation of off¬ spring of a population. New combina¬ tions of genes may result from crossing over. Every fertilization results in new combinations of chromosomes. These new combinations of hereditary mate¬ rials in sexual reproduction account for much of the variety among offspring. Natural selection, acting upon that variety and upon gene mutations, gen¬ eration after generation, may result in new varieties or species of organisms. VARIETY AMONG LIVING PEOPLES So far we have been considering ge¬ netic principles and variety among off¬ spring in terms of any or all plants and animals. Now let’s see how these prin¬ ciples help to explain a variety— the American Indians— of a species we are all familiar with, Homo sapiens. Columbus found people on the is¬ land in the Bahamas where he landed on October 12, 1492. He thought he had sailed around the world to the East Indies. So did the people in Spain when he returned. “They saw certain Indians gathering shel fyshes by the sea banks.” So says the first book on the subject in English, published in 1553. The first Americans were called Indi- HOW NEW VARIETIES MAY ARISE 553 Smithsonian Institution 21-5 NATIVE AMERICANS Upper left. Ten to fifteen thousand years ago, this man, today called Tepexan man, lived in what is now Mexico. The head is a model based on skull bones that have been found. Note the Mongoloid features. Lower left. This modern Apache Indian from Arizona resembles Tepexan man in many ways. Upper right. In some ways, this Pawnee Indian also resembles Tepexan man. Studies of Pawnee culture sug¬ gest a relationship to ancient Mongoloid peoples of Asia. Lower right. A Cheyenne Indian reflects obvious differences in appearance between American Indians and their ancestors. ans, by mistake. But the name stuck. It is better, however, to call them Ameri¬ can Indians in order to distinguish them from the peoples of India and the East Indies. American Indians We know that people have lived in the Americas for at least 10,000 years and probably much longer (Figure 21-5). Bones and other remains of some 554 THE CONTINUITY OF LIFE of these people have been dated by radiocarbon dating. * Until comparatively recently, the American Indians were isolated from the other peoples on earth. During their long period of isolation, these early Americans gradually developed certain traits that made them look different from all other peoples on earth (Figure 21-5). The study of mankind is called an¬ thropology ( an throh pol oh jee ) and those who specialize in this science are anthropologists. Most anthropologists today agree that the American Indians belong to the same species, Homo sa¬ piens, that Europeans and all other liv¬ ing peoples belong to. Most anthropolo¬ gists also agree that the American In¬ dians belong to the same racial stock that most Asiatic peoples belong to. They call this racial stock the Mon¬ goloid (MONGg’loyd) stock. Finally, most anthropologists agree that the American Indians constitute one of several varieties of the Mongoloid stock of Homo sapiens. It is the custom among anthropolo¬ gists to call a variety of a racial stock a “race.” Using the word race in this sense, they say that the American In¬ dians constitute a race of the Mongol¬ oid stock of the species Homo sapiens. You must already have realized that an isolation of 10,000 years and prob¬ ably more gave plenty of time for a new variety of people, the American Indians, to develop on this continent. You probably are also thinking of the roles of gene mutations, new combina- * Radiocarbon dating is a comparatively new method of determining the approximate age of a piece of charcoal (or any other re¬ mains of what was once an organic material with carbon in it). The method is explained in Radiocarbon Dating by Willard F. Libby, University of Chicago Press, 1952. tions of genetic materials, and natural selection in the development of this variety or “race” of people. Three racial stocks Most anthropologists today recognize three racial stocks of living peoples. They are: (1) the Mongoloid stock, which you already know, (2) the Ne¬ groid ( nee groyd ) stock, and ( 3 ) the Caucasoid ( kaw kuh soyd ) stock. An¬ thropologists recognize several varieties or “races” of each main stock, but they do not agree as to just how many va¬ rieties or “races” of each there are. Hence we shall not attempt to list them here. Blood groups and racial stocks As you undoubtedly know, many per¬ sons have formed the habit of classify¬ ing peoples according to such superfi¬ cial traits as skin color, head shape, type of hair, and so on. This method of classification is biologically confusing, because these traits are not uniform among the peoples of any of the three racial stocks. For example, the Mon¬ goloid stock is not “composed of peo¬ ple with yellow skin”; think of the American Indians. Also, Hindus are Caucasoids but are not white-skinned. And finally, the Negroid stock includes peoples of several skin colors, although neither the Negroid nor Mongoloid stock includes peoples with white skins. There is a growing tendency among biologists all over the world to look for a system of classification re- fleeting more fundamental traits of given peoples— traits that tend to ex¬ press themselves in terms of a popula¬ tion equilibrium. One such trait now being widely studied is the frequency of the occur¬ rence of the main blood groups (A, B, HOW NEW VARIETIES MAY ARISE 555 AB, and O) in various peoples. Cer¬ tainly Group O blood is much more common among American Indians and certain other Mongoloid peoples than among Caucasoid peoples. Many subgroups of the main blood groups have already been discovered. The Rh factor is one, as you know. The M and N factors are others. (These two factors, somewhat like the Rh factor, serve as antigens when given in a blood transfusion to a person whose blood does not contain them. The patient’s blood produces antibodies of the ag¬ glutinin type, but only in rare cases do these antibodies cause clumping, or ag¬ glutination, of red blood cells. ) A new blood factor, the E factor, has just re¬ cently come to light. The frequency of occurrence of each blood factor in given peoples in many parts of the world is being studied. For example, the popu¬ lation equilibrium of the E factor is fairly high among some Mongoloid peoples, while that of another factor (or gene allele) that affects red blood cells is highest among some Negroid peoples; neither factor is common among Caucasoid peoples. Geneticists and other biologists now look upon the levels of population equi¬ librium for certain blood groups and subgroups as being more indicative of a given variety of people than the more unevenly scattered traits that have been in use in the past. Living peoples today The three main racial stocks of living peoples commonly recognized by an¬ thropologists, and the varieties within each one, developed in much the same way that new varieties of other sexually reproducing organisms do. Gene mutations and new combina¬ tions of genetic materials occur within an isolated group of people. Natural selection helps to determine which mu¬ tant genes and which individual varia¬ tions are transmitted to succeeding gen¬ erations. Given a long enough time, a new variety may arise out of an iso¬ lated group of people, as the American Indians seem to have developed from the earliest peoples in America. CHAPTER TWENTY-ONE: SUMMING UP A new variety may arise from a pre¬ viously existing population or from a group of populations living near each other, if reproduction is sexual, and if all parents of each generation come from that group and none or almost none from any outside group. Gene mutations, new gene combina¬ tions resulting from crossing over, new chromosome combinations in every fer¬ tilized egg, and sometimes polyploidy (and— in bacteria at least— gene trans¬ duction)— all acted upon by natural selection (or by artificial selection in crop plants and domestic animals) — may gradually result in a new variety, usually after many generations. The survival value of the trait resulting from each gene mutation, as related to natural or artificial selection, largely determines whether any given gene mu¬ tation will contribute to the rise of a new variety or species. Naturally, a mu¬ tant with less survival value than the previously existing members of its spe¬ cies has little chance to be the forerun¬ ner of a new variety or species. An¬ other possibility is that a new variety could arise as a result of gene muta¬ tions that produce traits having no ef¬ fect at all on survival value. In any case, new traits that result in new vari¬ eties are not biologically harmful traits. 556 THE CONTINUITY OF LIFE Your Biology Vocabulary Make the following terms a part of your permanent vocabulary. ancon sheep direct mutation natural selection reverse mutation artificial selection population survival value gene pool of a population Mongoloid racial stock Negroid racial stock Caucasoid racial stock anthropology Testing Your Conclusions In your record book, answer these questions. 1. Why must we assume that the gene mutation that resulted in one male ancon lamb in 1791 must have occurred in a previous generation, not in the one that produced the first recorded ancon sheep? Hint: Like most mutant genes, this one is recessive. 2. Why is it impossible for a single gene mutation in one gamete to result in a new breed or variety in the next generation? Hint: It takes many individuals to constitute a new variety. 3. What three racial stocks of living peoples are commonly recognized today? 4. You are probably familiar with the Golden Bantam variety of sweet corn. If so, vou know that the grains are yellow and smooth. If you found, in a patch of Golden Bantam corn, an ear of corn with smooth white grains, would you guess that a gene mutation, a doubled chromosome number, or a new combination of genes in a chromosome was the cause? Why? 5. Most but not quite all anthropologists today believe that the American Indians are descended from Mongoloid peoples who came from Asia into North America across a land belt where the Bering Strait now is. What facts about the recently discovered blood factor E support this belief? More Explorations 1. Clippings for a scrapbook. Your biology class may want to start a scrapbook to con¬ tain current news items that have to do with anthropology. First discuss in class the kinds of items to look for. Then choose a committee to take charge of the clippings and to mount them in the scrapbook. For the rest of this year, watch for items on anthropology in newspapers and magazines. Clip them and turn them over to the committee. A period of class discussion on these news items toward the end of the school year should prove interesting. HOW NEW VARIETIES MAY ARISE 557 2. A study of variations. The individuals in any group vary in nearly every trait. It is easy to demonstrate variations in height among the students in your biology class. Line up according to height, with the tallest person at one end and the shortest at the other end of the line. Are most of you quite tall, quite short, or are most of you about as tall as the middle person in the line? Or measure the height of each individual in the class and summarize the heights on the blackboard, somewhat like this: 72 inches 1 69 inches 1 1 68 inches Wi TLLL 67 inches TTTT 11 Etc. Copy your results in your record book. Thought Problems L One species of smartweed often grows partially under water and partially above wa¬ ter. The underwater leaves of this smartweed are finely subdivided, but the leaves that grow above water are not. No botanist would try to breed this smartweed to pro¬ duce a new variety with only leaves that are not subdivided. Why not? Hint: En¬ vironment acts upon hereditary traits. All the leaves of a given plant contain identical sets of genes, unless a part of that plant has undergone a mutation or had parts of other plants attached to it by budding or grafting. 2. One successful cross of the cabbage and the radish has been made. Each plant’s diploid number of chromosomes is 18, but radish chromosomes differ in so many ways from those of cabbage that any seedling hybrids produced are usually sterile (un¬ able to produce seeds). But one such hybrid did produce seeds. The plants that grew from those seeds had 36 chromosomes in each cell. These hybrids were highly fertile. From them breeders produced what some botanists call a new plant species. Did gene mutations play a part in the rise of this new type of plant? Did crossing over or poly¬ ploidy enter into the situation? (Of course, you can't be sure of vour answers, because you do not have detailed information. But what do vou think about each question?) Further Reading 1. The chapter “Gene Mutations," pages 223-237, in Genetics bv A. M. Winchester, Houghton Mifflin, 1951, describes many examples of mutations. The pictures alone will tell you much about mutations. 2. Study the tables on pages 79—96 in Radiocarbon Dating by Willard F. Libby, Univer¬ sity of Chicago Press, 1952. Pick out the dates that refer to early man or his products in America. Or refer to current issues of Scientific American , Science, or Science News Letter for articles on radiocarbon dating of man in America. Take notes on all such datings you find and report in class. 3. Some of you may enjoy reading H. J. Muller's article “Genetic Principles in Human Populations” on pages 277—286 in the Scientific Monthly for December. 1956, prob¬ ably available in your public library. 558 THE CONTINUITY OF LIFE CHAPTER Inheritance Through the Ages Sixty million years ago the I ancestors of modern horses stood only a foot or so high, If there were no men on earth at that time , how has this and other knowledge of I inheritance th rough the ages been revealed? Horses and their ancestors Palomino ( pal oh mee noh ) horses, like the one pictured in Figure 22-1, represent a variety or line that arose from ancestors of Arabian stock. The phenotype (visible traits) of the palo¬ mino includes a golden brown body color, while that of the Arabian in Fig¬ ure 22-1 does not. And yet, of course, palominos carry many genes which are undoubtedly exact duplicates of genes occurring in Arabians. For example, like all modern horses, palominos and Ara¬ bians carry genes that result in many common traits: (1) a single hoof on each foot, (2) teeth with hard ridges on top, (3) long legs, (4) mane and tail, and many more. Sixty million years ago, the genes of modern horses had not yet developed. There weren’t any horses anywhere on earth, but their ancestors were here. Those ancestors were little three-toed and four-toed mammals about the size of our fox terrier dogs. Biologists have The American Museum of Natural History named these remote ancestors of the horse Eohippus ( ee oh hip us ) , which means “the dawn horse.” You see a photograph of a model of Eohippus on this page. You must be wanting to know how biologists found out that Eohippus gave rise to other species which in turn gave rise to our modern horses. In this chap¬ ter, the story of horses and their ances¬ tors will unfold, along with that of many other organisms. MODERN HORSES AND THEIR ANCESTORS The plants and animals of today have parents who had parents who had par¬ ents— generation upon generation of an¬ cestors takes us far back into the past. Scientists have traced the ancestral line of modern horses back about 60 million years to Eohippus populations, then alive. INHERITANCE THROUGH THE AGES 559 There were no people on earth 60 million years ago to write the history of Eohippus. Written history goes back only some seven thousand years and j J even prehistoric human history only perhaps a million years. Hence, all that we know about Eohippus, scientists have learned from “remains” of these animals that they have found in the earth’s crust. You undoubtedly know that the remains of ancient plants and animals are called fossils. Scientists who specialize in the study of fossils are paleontologists ( pay lee on tol uh jists ) and the study of fossils is paleontology. A word about fossils You have probably seen specimens of petrified wood; you may even have visited the Petrified Forest of Arizona. These remains of ancient trees are fos¬ sils. So are the imprints of leaves in coal, the insects preserved in amber, the so-called saber-toothed tigers pre¬ served in tar pits, and the hairy ele¬ phants preserved in the frozen earth of northern Siberia. Any remnant or trace of a living thing of past ages— even the footprint of some prehistoric animal— is a fossil. Known fossils of ancestors of the horse Paleontologists have found Eohip¬ pus fossils in North America and in many other parts of the world. From these fossils, we know that Eohippus stood about a foot high and had four toes on each front foot and three on each hind foot. In the lower leg, Eohip¬ pus had two bones, in contrast to the one bone in the lower leg of our mod¬ ern horses. Judging by its fossil teeth, paleontologists conclude that Eohippus was a browser; that is, it ate soft leaves of plants, perhaps of shrubs and trees. Its teeth were small and showed on top only the beginnings of the ridges that are prominent on the tops of the teeth of today’s horses, ridges that are espe¬ cially useful in grazing and in chewing tough vegetation such as grass and hay. Paleontologists have learned from the fossil record that Eohippus gave rise to at least four different lines of descend¬ ants, not all at once in a single genera¬ tion, but gradually over a period of some 10 to 20 million years. Just as new varieties of plants and animals arise today bv the action of natural selection upon the possible survival value of (1) gene mutations and (2) new com¬ binations of genetic materials at each 22-1 PALOMINO AND ARABIAN HORSES A palomino ( /eff ) and an Arabian (right) are quite similar in most ways, yet in body color, length of head and neck, and other ways they differ. Compare both with the model of Eohippus on the preceding page. Left: Palomino Horse Breeders Association; right: Freudy Photos Mi: ■ mmmmi , ; Wmmm . . . . . . .>m"»' mmmmmmm mmmmrnmmmmm Mesohippus fMMM mwmiiiiunimiiinw Eohippus ■ A Tlie American Museum of Natural History 22-2 "TIME-LAPSE" PHOTOGRAPHS OF SIXTY MILLION YEARS OF HORSE HISTORY Ar¬ ranged in order from the bottom to the top are four stages in horse development. The skulls and legs are shown by relative size. Note the two-, three-, and four-toed legs of the ancestors of Equus. For the age of each specimen, see Figure 22-3. fertilization, even so did new lines arise from Eohippus populations of long ago. Only one of the four lines of descend¬ ants from Eohippus was ancestral to the modern horse. An example of this line is known by its fossils and is called J Mesohippus ( mess oh hip us ) . Refer frequently to Figure 22-2 as you read on. Mesohippus was a three-toed browser— or so paleontologists conclude from a careful study of fossils of its legs and teeth. INHERITANCE THROUGH THE AGES 561 During many millions of years, Meso- hippus populations gave rise to two main lines: (1) three-toed browsers, and (2) three-toed grazers. Merychip- pus (merihKiPus) fossils, known to be some 30 million years old, may J 7 J typify the first three-toed grazers. Merv- chippus had a foot that looked much like that of a modern horse, although there were still two very small side toes J that did not touch the ground. The small bone in the lower leg was fused with the larger bone, thus making only one bone in the lower leg. The teeth were real horse’s teeth, well suited to grazing. Merychippus had the general appearance of the modern horse, but was much smaller than our horses are. Merychippus gave rise to two main lines: (1) the three-toed grazers, and (2) the one-toed grazers. Our modern horses, genus Equus (ee kwus), are de¬ scended from the line of one-toed graz¬ ers * (Figure 22-3). The horses of today are different in many ways from their distant ancestors: Eohippus, Mesohippus, Merychippus, and others, ft took some 60 million years of gene mutations, new combina¬ tions of genetic materials at each fer¬ tilization, and the natural selection of parents with more favorable traits in * The only line from Eohippus that has survived until our time is the line of one-toed grazers, of which zebras and horses are exam- pies. All the other lines died out completely in prehistoric times. If you are interested, look into George Gaylord Simpson’s book, Horses, The Story of the Horse Family in the Modern World and Through Sixty Million Years, Ox¬ ford University Press, New York, 1951. Your public library probably has a copy. each generation to give rise to modern horses. During this long period of time, many other new lines arose and flour¬ ished for perhaps a few million years, only to die out completely (Figure 22-3). But one line, the one-toed graz¬ ers, has survived and become our mod¬ ern genus Equus , horses and zebras. Horses in America Fossils of Eohippus, Merychippus, and some other ancestral lines have been found in North America, but all of them died out completely in prehis¬ toric times. All the horses in America today are descended from horses im¬ ported by man from Europe and Asia. Nevertheless, we now have several American breeds of horses, among them the American Trotter, the Kentucky Saddle Horse, and the Morgan Horse. The “Quarter horse” was developed as a “cow pony” in our West but has never had its pedigree recorded. So it is not a registered breed. A purebred Kentucky Saddle Horse differs in sev¬ eral traits from a Morgan Horse, al¬ though both breeds were developed by artificial selection from imported horses of the Thoroughbred breed, a breed developed in England. The point is that new lines of horses are still arising today. By artificial se¬ lection, man may speed up the proc¬ esses involved in the rise of new lines or varieties or breeds. But it takes a long time for a distinctly different new line, like Equus, to develop from an an¬ cestral line like Merychippus, because natural selection is a slow process as 22-3 The oldest known ancestor of modern horses is Eohippus, beginning with which the development of horses is shown in this diagram. Each red line ending in a circled letter “X” represents a line of descendants that developed hut became extinct— some after thriving for millions of years. Note that most of the development took place in North America hut that North American horses became extinct. Where have today’s North American horses come from? 562 THE CONTINUITY OF LIFE HISTORY OF THE HORSE FAMILY INHERITANCE THROUGH THE AGES 563 compared with artificial selection. Even so, the results of natural selection among modern horses can still be ob¬ served in the wild horses in some parts of our West. The wild horses are de¬ scendants of imported horses which es¬ caped. And these wild horses, after just a few generations in the wild, are al- ready different in several ways from their domesticated ancestors. Other ancestral lines In the storv of ancestral lines of the J modern horse, you have an example of what paleontologists have been able to do in tracing ancestral lines back for many millions of years. Other lines that have also been traced back through the fossil records include those of the cam¬ els and elephants. In a more general way, the history of living things has been traced back some 500 million years. To understand the general out¬ line of that history, you need first to learn a little about the history of the earth itself, as you will do in the next ' J section. Summing up: modern horses and their ancestors Modem horses are one -toed grazers with Ion" neck and legs, one bone in the lower leg, and teeth with hard ridges on top. Merychippus, Mesohippus, and Eohippus typify some of the horse’s known ancestors of Ion" ago. Figures 22-2 and 22-3 summarize the main out¬ lines of the history of horses. The development of the horse over a period of 60 million years gives us a good view of how gene mutations, new combinations of genes at fertilization, and natural selection can produce new varieties, species, and families of organ¬ isms. This kind of development is going on today, in some species accelerated by artificial selection, but even so, our lives are not long enough to enable us to see many of the changes that take place. THE EARTH AND ITS HISTORY You must be wondering how paleon¬ tologists know that Eohippus lived some 60 million years ago and that Merychippus didn’t arise until perhaps 30 million years ago. A hundred years ago, no one could have told you. Then, few people even knew that fossils are the remains of ancient living things, as the story of the Haddonfield giant will show. The Haddonfield giant A hundred years ago a real giant was discovered in Haddonfield, New Jer¬ sey, now a suburb of Philadelphia. The giant wasn’t alive, and hadn’t been for perhaps 140 million years. But its bones were there, buried in the softish, rock¬ like marl in Haddonfield. Excavators kept uncovering one strange bone after another, huge bones that had been “turned to stone. ’ What were they? Where had thev come from? And how had they ever got into that softish, rocklike marl bed? No one in Haddon- field could even guess the answers. The bones of the Haddonfield giant were presented to the Philadelphia Academy of Natural Sciences in 1858. J There Dr. Joseph Leidy pieced the bones together into the skeleton shown in Figure 22-4. A few vertebrae and other parts were missing but there was enough of the assembled skeleton to show that the animal had been some 28 feet long, as long as an average dwelling house. This was one of the first giants to be found in the rocks of North America. It is, of course, one of 564 TIIE C ONTINUITY OF LTFE the dinosaurs (dy noh sawrs ), the one known today as Hadrosaurus ( had roll sawrus), or the Haddonfield giant. Its fossilized bones are still preserved in the Philadelphia Academy of Natural Sciences. The changing earth You would not recognize your native land if you could go back to the time of the prehistoric dinosaur, Hadrosau¬ rus. For one thing, there were no Rocky Mountains, and the Appalachians were much higher and more rugged than they are today. For another, the shore lines were not the same as they are now. The earth has always been chang¬ ing, and it still is. Changes today are so gradual that you may not notice them, but they are still going on. If you find it hard to imagine that any real changes are taking place all over the earth at the present time, con¬ sider these facts. According to Farmers of Forty Centuries by F. PI. King (Har- court, Brace, 1927), the city of Shang¬ hai, China, was built on the seacoast. Today it lies 20 miles from the shore. In 220 b.c., the town of Putai, China, was only one third of a mile from the sea. By 1900, it was 48 miles inland. In both cases, rivers have emptied so much sediment into the sea that the shore line has literally moved out into the ocean. To understand somethin £ of the way O J in which rivers affect the ever-changing earth, read the following quotation from Samuel Clemens’ ( Mark Twain’s) Life on the Mississippi. ‘‘An article in the New Orleans Times- Democrat, based upon reports of able engi- 22-4 FOSSIL SKELETON OF HADROSAURUS This ancient dinosaur died and was par¬ tially preserved near what is now a suburb of Philadelphia. Hadrosaurus was some twenty-eight feet long and stood taller than a modern one-story house. Philadelphia Academy of Natural Sciences neers, states that the river annually empties four hundred and six million tons of mud into the Gulf of Mexico— which brings to mind Captain Marry at’s rude name for the Mississippi— the Great Sewer. This mud, solidified, would make a mass a mile square and two hundred and forty-one feet high. “The mud deposit gradually extends the land— but only gradually; it has extended it not quite a third of a mile in the two hundred years which have elapsed since the river took its place in [written] history. The belief of the scientific people is, that the mouth used to be at Baton Rouge, where the hills cease, and that the two hundred miles of land between there and the Gulf was built by the river. This gives us the age of that piece of country, with¬ out any trouble at all— one hundred and twenty thousand years. Yet it is much the youthfulest batch of country that lies around there anywhere. “The Mississippi is remarkable in still another way— its disposition to make pro¬ digious jumps by cutting through narrow necks of land, and thus straightening and shortening itself. More than once it has shortened itself thirty miles at a single jump! These cutoffs have had curious ef¬ fects: they have thrown several river towns out into the rural districts, and built up sand bars and forests in front of them. The town of Delta used to be three miles below Vicksburg: a recent cut-off has radi¬ cally changed the position, and Delta is now two miles above Vicksburg.” * The earth has changed in the past and is changing now. The plants and animals that lived on this earth a half¬ billion years ago were not the same as the ones that live here now. Let’s look at life more than 100 million years ago. Life in the time of Hadrosaurus In the time when Hadrosaurus lived, there were no horses, elephants, bears, * Quoted from pages 23-24 of Life on the Mississippi by Samuel Clemens, 1883. men, or other modern mammals. Had¬ rosaurus may have seen some birds, but the birds of that time looked more like lizards with feathers than like our birds. Hadrosaurus probably lived in the water along the shores of lakes and streams. The features of his head and teeth seem to indicate that he ate wa¬ ter plants. (He had some two thousand teeth arranged in rows. ) There were plenty of algae at that time. On land, there were mosses, ferns, seed ferns, gymnosperms, and some primitive flow¬ ering plants, or angiosperms. But the land animals of that time never saw a lily or an orchid. And of course they never saw an orchard of apples or or¬ anges, a field of potatoes, or a field of grain. The face of the earth and the living things on it were quite different from what you see today. And yet all the main phyla of both plants and ani¬ mals were there. How do we know all these things? Geologists (specialists in geology, the study of the earth’s crust) have now learned a good deal about the earth’s crust, how it was formed, how it changes, and how old it is. How old is the earth? Evidence has been accumulating for a hundred years that the earth is very old. Unfortunatelv, there is as yet no J 7 J sure and accurate way of finding out exactly how old it is, but there is abun¬ dant evidence that it is some billions of years old. We know that the earth is more than three billion years old because there are rocks exposed in its crust that are that old and older. Many of these rocks have been “dated” (that is, their age has been determined) by examining crystals of certain radioactive minerals 566 THE CONTINUITY OF LIFE embedded in the rocks. Embedded crystals that contain the radioactive element uranium are useful in deter¬ mining how old a rock is. As you know, uranium constantly dis¬ integrates, just as all radioactive ele¬ ments do. A stable end product of the disintegration of uranium is one of the isotopes of lead. When a mineral con¬ taining uranium first crystallized long ag°> it contained none of this lead iso¬ tope. But as soon as the mineral crys¬ tallized, the uranium began to disinte¬ grate into the lead isotope. And ura¬ nium is known to disintegrate at a con¬ stant rate. By comparing the amount of the lead isotope with the amount of uranium remaining in a cluster of min¬ eral crystals, scientists are able to esti¬ mate the age of the crystals and hence the age of the rock in which the crystals are embedded. By this method, some rock formations in the Black Hills of South Dakota have been estimated to be about 1/2 billion years old and others in Canada close to 2 billion years old or even older. By 1952, scientists at the Carnegie Institution of Washington, D.C., had dated certain mineral crystals from a rock formation in Manitoba, Canada, at 3 billion years, not by the uranium-lead method, but by a similar one, using less rare radioactive minerals and their sta¬ ble end products. Scientists know that there are rock formations older than the one dated at 3 billion years, but they still haven’t been able to date the older ones. In any case, the earth is very old, at least more than 3 billion years old. During its long history, the earth’s crust has undergone many changes and it still is changing. One change that is always going on is the formation of new rock layers. How are the rock layers formed? There are many kinds of rocks, as you probably know. The kind that in¬ terests us here is laid down in layers. Somewhere you must have seen layers of solid rock that were exposed in a railroad cut or a stone quarry, on the sides of a ravine or a steep mountain cliff (Figure 22-5). The rock layers were formed from the layers of sedi¬ ment deposited by the seas and rivers of long ago. Streams and rivers and lakes and seas drop some of their sedi¬ ment wherever water currents are slowed down by obstacles, or where they reach level stretches. The Missis¬ sippi is depositing millions of tons of sediment in its delta every year. As time goes on, more and more sedi¬ ment is dropped on top of the oldest deposits. The weight of the constantly increasing layers of sediment presses down harder and harder on the bottom 22-5 SEDIMENTARY ROCK Layer upon layer of sedimentary rock has been ex¬ posed as this stream has cut its channel. Ewing Galloway layers. Finally the pressure changes the compressed sediment into rock. Rock produced in this way is called sedi¬ mentary rock (Figure 22-5). How do fossils get into rocks? It is obvious that leaves, twigs, shells, and many other parts of organisms, as well as the dead bodies of whole or¬ ganisms, will be mixed with the sedi- ment that is dropped wherever moving water is slowed down. In most cases these organic remains decay quickly, but sometimes they do not. When, for any reason, decay fails to occur quick¬ ly, the specimens are likely to become fossils. IIow are fossils made? Thev are made J very slowly. Bit by bit, minerals in the water filter into and replace some of the organic matter in parts of these un¬ decayed dead organisms. In most cases only the hard parts of an organism are preserved. The bones of vertebrates, the shells of diatoms and of mollusks, the exoskeletons of arthropods, the woody tissues of plants persist, but the soft tissues slowly disintegrate. As time goes by, mineral matter continues to filter into bone or shell or wood until the bone or shell or wood is mineral¬ ized. The materials in plant cell walls, particularly those of the woody tissue, are replaced bit by bit by mineral mat¬ ter. After a long enough time, mineral matter infiltrates all the heavy cell walls. So perfectly does the mineral matter infiltrate the wood that the cell structure is beautifully preserved (see photograph, page 132). Thin slices of such fossils under the microscope give proof that they are indeed the remains of past organisms, for only organisms have cells. In other cases, a print of a leaf (Fig¬ ure 22-6) may be left in the rock while Marion A. Cox 22-6 FOSSIL SEED FERN LEAF None of the leaf tissues have survived, but the leaf print was preserved in rock. all the leaf tissues slowly disintegrate. A foot track in mud may be preserved until the mud has become stone (Fig¬ ure 22-7). In these and other ways, fos¬ sils are made. By the time layers of sediment have become sedimentary rock, the plant and animal remains that were original¬ ly in that sediment have become fossils (if thev did not decay quickly). Natu¬ rally, those fossils will be embedded in the rock. This is the way fossils get in¬ to rock. Naturally, too, the fossils in any par¬ ticular sedimentary rock are the re¬ mains of plants and animals that were living at the time the original sediment was being washed away and deposited. If the rock in which a fossil is found is shown to be 500 million years old, we conclude that the fossil is the remains of an organism that lived 500 million years ago. 568 THE CONTINUITY OF LIFE How do undersea fossils get exposed? You must be wondering; how geolo- O O gists ever find fossils in rock layers laid down beneath the sea. Figure 22-8 shows seashell fossils found in sedi¬ mentary rock in Ohio. The point is that what is now Ohio was once under the sea. So were most of the other parts of the country, not all at the same time, but at one time or another in the past. At various times during the history of the earth, vast and violent changes took place comparatively suddenly. During these times of violent change, mountain ranges were upheaved. New land masses appeared and old ones sank beneath the sea. When things quieted down again, old rock layers that had been beneath the sea had be¬ come part of a continent, even part of a high mountain range. There they are today, with their various fossils ready 22-7 FOSSIL DINOSAUR TRACKS The dino¬ saur is gone, but the tracks he made near what is now a Texas stream have been preserved for 150 million years or more. The American Museum of Natural History to be exposed by erosion, river action, railroad cuts, or the geologist’s pick. The record in the rocks shows that violent changes have occurred many times in the past. Each period of vio¬ lent upheaval lasted quite a while, per¬ haps 10 million years. But the quieter, calmer times between upheavals lasted longer, sometimes even 100 million years. That’s why the words “compara¬ tively suddenly,” were used above. Any¬ thing that takes less than 10 million years is “comparatively sudden,” in geologic time. Earth history History is a record of things that have happened in the past. The geo¬ logical history of the earth is a record of things that have happened to the earth and the living things on it, in the past. As you already know, no one can set an exact date for the beginning of earth history. And no one can set an exact date for the beginning of life on earth. And no one can say exactly how long ago Hadrosaurus lived. But geologists have learned in about what order the big events in earth history took place and in what order the main groups of chordates appeared on earth. They have learned these things from a study of the earth’s crust, more or less all over the world, and the fossils preserved in it. You could follow the history of the United States without exact dates if vou knew the order of the main events, and you could divide that history into periods and give each period a name. That is a useful way to look at earth history. Geologists divide the history of the earth into five main parts and call these parts eras. A period of violent change marks the end of one era and the begin- 569 i ! « ning of the next. Eras are subdivided into periods and periods into epochs. These eras, periods, and epochs are not based on guesswork. They are based on evidence in the rock record, and geologists generally agree that they did occur and that they occurred in the or- der given in Table 22-A (which in¬ cludes the eras and periods, but not the epochs). Start at the bottom of the table and read upward. Table 22-A is a geological timetable, but the dates given are merely the best estimates, not in any sense exact. Actually the exact dating of geological history isn't very O O O J J important. It is the order of events that is important. Look at Table 22-A now. Do not try to memorize it. Just make yourself fa¬ miliar with it. For instance, look for the period that is subtitled Coal Measures. The great coal forests grew in the fifth period of the the third era. This period is commonly called the Carboniferous (kar bun if er us ) , but in the United States, geologists usually consider the Carboniferous as two periods— the Mis- sissippian and the Pennsylvanian. Refer often to Table 22-A as you read about past life on earth in the follow¬ ing section. TWENTY-FOUR HOUR TIME SCALE. You could think of the history of life on earth in terms of a 24-hour period, supposing that the first life appeared at 12:00 noon and that the present moment is 12:00 noon the next day. From 12:00 noon until 6:00 A.M. the next morning, living things were on the increase, but their fossil record is scanty. A few fossils of lowly organisms are known. So start with 6:00 A.M., the last six hours of your 24-hour day, and list 6:30, then 7:00, and so on, until 12:00 noon. Then list the items at the bottom of page 571 at the correct place on your time scale. 22-8 FOSSIL SEA SHELLS These fossils were found in Ohio. Similar fossils found all across the United States indicate that, at one time or another, all parts of the country were covered with water. Marion A. Cox TABLE 22 -A TIMETABLE OF GEOLOGY Eras Periods Years since beginning of period Plants Animals Cenozoic; Age of Mammals and Angio- sperms Two periods with 7 epochs 1 million Man appears 75 million Angiosperms be¬ come abundant Mammals become abundant Eohippus appears Cretaceous 135 million First angiosperms Last dinosaurs Mesozoic: Age of Reptiles Jurassic 165 million First birds Giant dinosaurs abundant First true mammals Triassic 200 million First dinosaurs Permian 225 million Reptiles increase Carboniferous (Coal Measures) 280 million Coal forests of ferns, seed ferns, and gymnosperms All plant groups ex¬ cept angiosperms First reptiles Amphibians increase Paleozoic : Age of Ancient Life Devonian 325 million Land plants become widespread First amphibians First insects Silurian 360 million First known land plants First air-breathing animal — a scorpion Fishes increase Ordovician 425 million Algae abundant in the seas First primitive fishes, the first vertebrates Cambrian 500 million Algae, bacteria All animal phyla ex¬ cept chordates Trilobites abundant Precambrian Time: two long eras Periods un¬ certain At least 3,000 million Fossils of both plants and animals scarce; all known are of lowly organisms, algae, pro¬ tozoa, “worms” 6:00 A.M. Fossils show that life had be¬ come abundant. All animal phyla present except chor- dates, but all organisms lived in the water. 8:00 a.M. Fossils show that plants had moved out of the water onto the land. 8:30 a.M. Insects and amphibians on the land 9:30 a.M. Beginning of the Age of Rep¬ tiles 11:00 a.M. End of Age of Reptiles and beginning of Age of Mam¬ mals 1 1 :5 9 a.M. First people i,4 second before 12:00 noon. Recorded hu¬ man history began.* # Adapted with permission from Life by George Gaylord Simpson et al, Harcourt, Brace and Company, 1957, page 735. INHERITANCE THROUGH THE AGES 571 Summing up: the earth and its history All the known facts derived from sci¬ entific studies of the earth’s crust show that the earth is very old, more than 3 billion years at the least. Rock formations show that the earth’s history divides naturally into five great eras. Each era ended in a period of vio¬ lent change. Life on earth had become abundant, as the fossil record shows, about 500 million years ago. The order of events in the history of life since then is pretty well known and is summarized in Table 22- A. AN OUTLINE OF THE HISTORY OF LIVING THINGS Living things existed during the time before the beginning of the third era of earth history. We know that because a few fossils have been found in rocks more than 500 million years old. These fossils include some lime-secreting algae, bacteria, protozoa, and some “worm-tracks”— all fossils of organisms that lived in the water. No fossils of land-living organisms have been found in rock formations known to be more than 400 million years old. This leads paleontologists to the conclusion that the first living things were water-living forms. Living things did exist in the seas be¬ fore the third era began. They may have been abundant. But volcanic activ¬ ity and other natural forces have so changed the rock formations of the first two eras of earth history that little can be learned from them. But by the be¬ ginning of the third era, living things had become abundant. Hence our main outline of the history of living things on earth begins with the first period of the third era. The third era is called the Paleozoic ( pay lee oh zoh ik ) Era, as Table 22-A tells you. Its six periods are also named in Table 22-A, but we shall list them here with their pronunciations, and the dates of their oldest known rock formations.* 1. Cambrian (kam breeun), 500,000.- 000 years 2. Ordovician ( or doh vish un ) , 425,- 000,000 years 3. Silurian ( sy loo rih un ) , 360,000,000 years 4. Devonian (dee voh nee un), 325,- 000,000 years 5. Carboniferous (kar bun if er us ), 280,000,000 years 6. Permian ( per mee un ) , 225,000,000 years J Living things in the Cambrian Period In Cambrian rock formations, paleon¬ tologists have found fossils of animals of every invertebrate phylum of the animal kingdom, but none of verte¬ brates. They have found fossils of pro¬ tozoa, sponges, coelenterates, mollusks, arthropods, and other invertebrates. MAKING A TIMETABLE. Divide two fac¬ ing pages in your record book into six col¬ umns. Title the first column Cambrian, the next, Ordovician, and so on, with the names of the six Paleozoic periods. Under column one, list every type of organism mentioned here as being known to have lived in the Cambrian. As you read on, follow the same procedure for each Paleozoic period. The dominant (most abundant) ani¬ mals of the Cambrian were arthropods of the type now called trilobites (try n All these are approximate. Radioisotope dating involves technical difficulties that make it necessary to allow for certain margins of error. 572 THE CONTINUITY OF LIFE 22-9 FOSSIL TRILOBITES These ancient arthropods were abundant in Cambrian seas, but have long been extinct. Note the many-segmented bodies. loll bytes). (See Figure 22-9. ) Like all other known Cambrian organisms, tri- lobites lived in the water. They were J abundant and of many varieties. Of the plants, algae were abundant and highly diversified in the seas. Bac¬ teria existed, too. No fossils of land plants have yet been found in Cam¬ brian rock formations. The Ordovician Period By the latter part of the Ordovician, all the major animal phyla and 33 ani¬ mal classes are known by their fossils. Some fossils show that lime-secreting algae and the flagellates were present, but not any diatoms. Sponges, corals, and clamlike mollusks were abundant, as were sea snails. Of the arthropod phylum, trilobites were abundant and a few fossil eurypterids (yoo rip ter ids) occur. (See Figure 22-10.) Eurypterids somewhat resemble crustaceans but seem rather to have been ancestral to spiders and scorpions. A few crusta¬ ceans existed, but none at all like our lobsters and shrimps. No fossils of in¬ sects have been found in Ordovician rock formations. Echinoderms were abundant and varied by the end of the Ordovician. J Also by late Ordovician time the first vertebrates (jawless fishes) had ap¬ peared, but their fossils show that they were primitive and not numerous. List all Ordovician animals and plants mentioned above in the second column previously prepared in your record book. The Silurian Period The Silurian Period is noteworthy for two firsts : ( 1 ) the first definitely recognizable land-plant fossils, and (2) the first fossils of air-breathing ani¬ mals. Most of the land-plant fossils found in rock formations of the middle Silu¬ rian are small psilopsids. (If you have forgotten what a psilopsid is, refer back to Figure 5-9, page 140.) They were extremely simple vascular plants— prim¬ itive forerunners of later pteridophytes like the ferns and their relatives. It seems likelv that moisture-loving non- vascular land plants with some traits of bryophytes (mosses and liverworts) must have preceded the psilopsids, but no identifiable fossils of such plants have yet been found in earlier rock formations. ( Bryophytes have no true wood; their soft tissues would not be INHERITANCE THROUGH THE ACES 573 likely to last long enough, after the plants died, to become fossilized. ) In the late Silurian rock formations, the first fossils of animals that were probably air-breathers are found. They were scorpions so much like the air- breathing scorpions of today that pale¬ ontologists agree they were probably air-breathers. If so, they were probably the first. This line of scorpions arose from some of the populations of sea scorpions, already plentiful. As in previous periods of the Pale¬ ozoic Era, in the Silurian new species and genera of animals arose and former ones died out. Gene mutations and new combinations of genetic materials oc¬ curred in each generation, and natural selection helped to determine which organisms survived and eventually de¬ veloped into new lines, and which de¬ clined and disappeared. The Devonian Period This period is sometimes called the “Age of Fishes,” because fishes became abundant and varied at this time. Some new lines arose only to die out later. Other new lines became even more diversified. The primitive fishes of the Silurian were jawless, but during the Devonian a line of fishes with jaws arose. The first known fossils of primitive amphibians are found in Devonian rock formations and represent the begin¬ nings of air-breathing vertebrates. Some land-inhabiting invertebrate animals certainly lived in Devonian times. All of these seem to have been arthropods: a mite, a primitive spider¬ like animal, and a primitive insectlike animal. During the Devonian, land plants of the pteridophyte phylum (ferns and 22-10 MODEL OF LIFE IN AN ORDOVICIAN SEA The large arthropod at the left is a variety of eurypterid, as are the two smaller organisms to its right, among the plants. Note the snails on the sea floor. Chicago Natural History Museum Chicago Natural History Museum 22-11 CARBONIFEROUS FOREST The leafy plant at the lower left, in the foreground, is a seed fern. Above it are the leaves of a taller seed fern. The fallen “trunks” in the fore¬ ground are those of large lyeopods. Above them is a primitive dragonfly. The dark, slender “trunk” rising up at the left is that of a tree fern. their relatives ) became plentiful. Some of these primitive plants reached tree size and constituted the first known forests on earth. Fossils of a few primi¬ tive gymnosperms of a type long since extinct have also been found in late Devonian rock formations. Remember to list the plants and ani¬ mals of the Silurian and Devonian in your record book. The Carboniferous Period The name Carboniferous, meaning carbon-bearing, refers to the great de¬ posits of coal (including those of the Pennsylvania coal fields ) in the rock formations of this period. ( Other much younger deposits of coal also occur in the United States and in other parts of the world.) This coal, rich in carbon, consists of the compressed remains of the extensive coal forests that grew in swampy regions in the Carboniferous Period (Figure 22-11). The trees of the coal forests included several species of tree ferns, seed ferns, lyeopods, and several more that have long since died out. Late in this period, a distinct line of cone-bearing gvmno- sperms had appeared. In the coal forests, land animals were common and of many kinds. For the first time, fossils of land snails occur. Many kinds of insects also left fossils in the Carboniferous rock formations, but only two kinds (a cockroach and a primitive dragonflv) belonged to insect orders still in existence today. Many new lines of amphibians arose during the Carboniferous and continued into the next (Permian) period. One genus, called Eryops (Ameeops), INHERITANCE THROUGH THE AGES 575 found in the early Permian, reached a yard and a half in length (Figure 22-12). In the late Carboniferous rock forma¬ tions, the first fossils of primitive reptile¬ like animals have been found. The Permian Period Fossils known to represent true rep¬ tiles of two main types have been found in rock formations of the sixth and last period of the Paleozoic Era. None of the Permian reptiles looked anything like any of our modern reptiles. The two main types of Permian reptiles were: (1) the “root reptiles,” so called because they were the stock from which most of the later lines were derived, and (2) the mammal-like reptiles, so called because certain features of the skull resembled features of mammal skulls rather than other reptilian skulls. At the close of the Paleozoic Era, fossils of all of the main plant groups except angiosperms (flowering plants) and of all the main animal phyla were present. All of the vertebrate classes except birds and mammals were repre¬ sented. In your record book, complete your lists of life in the Permian Period. End of the Paleozoic Era The world must have looked like a very different place at the end of this era than at the beginning, for life had become abundant on the land. The era was brought to a close by tremendous changes. Lands were elevated. Moun¬ tains, among them our Appalachians, were upheaved. Climates changed. The eastern and much of the central por¬ tion of our continent has been dry land ever since. During these changes, the trilobites disappeared entirely; they became extinct. History of the vertebrates in the Paleozoic Era In Cambrian times there were no fishes in the sea, no vertebrates of any kind, not even primitive ones. Toward the end of the Ordovician, the first primitive fishes (jawless fishes) ap¬ peared. Fishes became abundant and varied during the next (third) period. In the fourth period, amphibians ap¬ peared and were the first vertebrates to move out upon the land. It seems probable that certain primitive fish gave rise to the first amphibians. The rocks of the Carboniferous Pe¬ riod contain the fossils of the first primi¬ tive reptiles, which appear to have de¬ scended from the amphibians. At the close of the Paleozoic Era, then, three of the five common classes of verte¬ brates had appeared— fishes, amphib¬ ians, and reptiles. Still there were no birds or mammals. The Age of Reptiles The fourth era is the Mesozoic ( mess ohzoHik), usually called the “Age of Reptiles.” This era began some 200 mil¬ lion years ago and ended some 70 to 60 million years ago. CONTINUING YOUR TIMETABLE. Divide a new page in your record book into three columns. As you read on, list at the top of each column the name of the appropriate period of the Mesozoic Era, and under each heading the organisms that lived in that period. The three periods of the Mesozoic Era, along with the approximate ages of their oldest known rock formations, are: 1. Triassic (tryAsik), 200,000,000 years 576 THE CONTINUITY OF LIFE 2. Jurassic ( joo ras ik ) , 165,000,000 years 3. Cretaceous ( kree tay shus ) , 135,- 000,000 years At the end of the Paleozoic and the beginning of the Mesozoic, there were ‘hoot reptiles” and mammal-like rep¬ tiles, but no dinosaurs. From the “root reptiles” came a line of descendants in the Triassic from which all the dino¬ saurs as well as all modern reptiles except turtles and all our modern birds later descended. During the Jurassic and Cretaceous Periods, six main lines of dinosaurs arose. There were other dinosaurs, too, and not all of them were giants. Some were only about a foot long. The six main types of dinosaurs known are these: 1. Flesh-eating dinosaurs. These were among the biggest and the fiercest of the dinosaurs. One species, called Ty¬ rannosaurus ( tih ran uh sawr us ) rex (Figure 22-13), the king of the dino¬ saurs, had a most formidable set of jaws and teeth. The ‘ king” measured 50 feet in length, stood 18 to 20 feet tall, and lived during the Cretaceous Period of the Mesozoic. 2. Giant dinosaurs. These were the biggest dinosaurs, but they had small teeth and were vegetarians. One of them, Diplodocus ( dih plod oh kus ) , reached a length of 90 feet or more and weighed as much as 40 tons (Figure 22-13). These dinosaurs lived mostly during the Jurassic Period, but some survived into the Cretaceous. 3. Plated dinosaurs. These had two rows of triangular-shaped plates on their backs and were vegetarians. Steg¬ osaurus ( stej oh sawr us ) , of the late Jurassic Period, was one of them (Fig¬ ure 22-13). These dinosaurs were big¬ ger than an elephant, but the fossil skulls show that the brain was no big¬ ger than a walnut. 4. Armored dinosaurs. These reptiles of the Cretaceous Period were covered with armor plate like a modern battle tank. The bony plates overlapped each other. 5. Duck-billed dinosaurs. These lived during the Jurassic and Cretacous Pe¬ riods and get their name from the shape of the head. Hadrosaurus (Figure 22-4) was a duck-billed dinosaur. 6. Horned dinosaurs. These were the last comers, occurring during the late Cretaceous Period. They were about as big as elephants and got their name from their horns. The dinosaurs appeared, spread out, gave rise to new types, and “reigned supreme” during the Mesozoic. Then they died out completely during the 10 to 15 million years that brought this fourth era to a close, some 60 million years ago. No wonder this is called the “Age of Reptiles.” But other important events in the history of life also took place in the Mesozoic. 22-12 FOSSIL SKELETON OF ERYOPS This early Permian amphibian reached a length of 1/2 yards. It had short, sprawling legs and a large, flattened head. The American Museum of Natural History The American Museum of Natural History 22-13 THREE ONCE-ABUNDANT DINOSAURS Top. Although not the largest of dinosaurs, Tyrannosaurus was the most formidable of the flesh-eating reptiles. Middle. The largest of all dinosaurs was Diplodocus, which reached a length of as much as 90 feet. It was a vegetarian. Below. Stegosaurus was a vegetarian with its own “armor-plating.” 578 l'HE CONTINUITY OF LIFE Carnegie Museum. Pittsburgh 22-14 FOSSIL OF ARCHEOPTERYX This oldest known bird is shown reconstructed in Figure 22-15. Rise of birds, mammals, and flowering plants Early in the Triassic Period of the Mesozoic, fossils of the first primitive mammals are found. Earlier, we men¬ tioned mammal-like reptiles; probably these reptiles gave rise, over a long period of time, to the first mammals. Near the end of the Triassic, fossils of the first flying reptiles are found. Some¬ what later, in the Jurassic Period, the fossil of the oldest known bird occurs. It is called Archeopteryx ( ar kee op ter iks). (See Figures 22-14 and 22-15.) It was about the size of a crow. Its fossils prove that it possessed a strange com¬ bination of bird and reptile features. It had a long reptile-like tail, reptilian claws, and a full set of reptilian teeth. On the other hand, its jaws were shaped like a bird’s, and it had feath¬ ered wings and body, with the feathers extending in two rows down the full length of the tail. This and other fossils seem to indicate that birds are de¬ scended from reptiles of long ago. Angiosperms (flowering plants) ap¬ peared upon the earth and spread wide¬ ly near the end of the Cretaceous Pe¬ riod, probably about 130 million years ago. By the end of the Mesozoic Era, all plant phyla and all animal phyla had appeared. All five classes of verte¬ brates were here, too, but the mammals were still only small, primitive forms. This era was brought to a close by great upheavals, some of which produced our Rocky Mountains. The dinosaurs be¬ came extinct during the changes which brought this era to a close. In your record book, complete your listing of organisms for the Mesozoic Era. The Cenozoic Era We are living today in the fifth era, called the Cenozoic ( see noh zoh ik) Era. Geologists recognize two periods in this era and divide them into epochs. The names of the seven commonly recognized epochs, and the approxi- 22-15 MODEL OF ARCHEOPTERYX Its wings and feathers identify it as a bird, but its claws and teeth, as well as the length of its tail, seem to relate it to the ancient reptiles. Probably birds were de¬ scended from reptiles. The British Museum of Natural History The American Museum of Natural History 22-16 MASTODON This ancestor of modern elephants lived millions of years ago. Its head was low and flattened on top, unlike that of the mammoth in Figure 22-17 and the African elephant of today (but somewhat like that of the Asian elephant of today). mate ages at which they began, are O J O 7 listed here: 1. Paleocene ( pay lee oh seen ), 75,000.- 000 years 2. Eocene (ee oh seen), 60,000,000 years 3. Oligocene ( ol ih gob seen ), 40,000.- 000 years 4. Miocene ( my oh seen ) , 30,000,000 years 5. Pliocene (ply oh seen), 10,000.000 years 6. Pleistocene ( plyse toh seen ), 1.000,- 000 years 7. Recent, 10,000 years COMPLETING YOUR TIMETABLE. In your biology record book, divide a page into two columns headed First Period of the Cenozoic Era and Second Period of the Cenozoic Era. Under the first period, list the first five epochs, and under the second period, the last two epochs. Read on, then turn back to the beginning of the chapter and review the story of the horse and its development. In the correct column, list the ancestors of the horse. Also list other mam¬ mals and modern angiosperms in the cor¬ rect columns. Eohippus (“dawn horse”) fossils are first found in the Eocene Epoch. In the Oligocene Epoch, Mesohippus ap¬ peared, and in the Miocene Epoch came Merychippus. To the best of our present knowledge, man did not appear until the Pleistocene Epoch, perhaps a million years ago. The Paleocene, Eocene, and Oligo¬ cene were clearly epochs marking the 580 THE CONTINUITY OF LIFE rise of mammals. Until the dinosaurs had disappeared at the end of the Mesozoic Era, the only known mammals were few in type and small in size— all smaller than most dogs of today. But in the first three epochs of the Cenozoic Era, every order and most families of mammals had come into existence. Of course, you might not have recognized many of the ancestors of our modern mammals, but they were there. Exam¬ ples are Eohippus, which you already know; a small, primitive camel without a hump on its back; the sabertooths (sometimes called “saber-toothed ti¬ gers,” although they were not really tigers); the first mastodons (Figure 22-16); and the first lemurs, monkeys, and other early primates. Later, in the Miocene and more re¬ cent epochs, more mammals appeared, and some of these have since become extinct. Mammoths (Figure 22-17) ap¬ peared in the Pleistocene, but are a now-extinct species of elephant. The sabertooths and many other species be¬ came extinct, and modern mammals took their places. In the plant kingdom, angiosperms (flowering plants ) were already the most widely spread plants by the end of the Mesozoic Era, and during all epochs of the Cenozoic Era continued to spread, replacing the stately tree ferns, seed ferns, and other ferns and mosses that had dominated the Carbon¬ iferous forests. Today, known species of mosses, club mosses, and tree ferns are but remnants of a bygone age. You might call the Cenozoic Era the Age of Mammals or of Angiosperms. Changes in living things: the genetic record You have now reviewed briefly part of the fossil record of the long, long his- 22-17 MAMMOTH This fur-covered animal is so modern in form that it can only be called a species of elephant; nonetheless, it is a now-extinct species. The American Museum of Natural History tory of living things from Cambrian times to modern times. All through these 500 million years, changes have been going on. Species, genera, families, and orders have arisen, many only to die out (become extinct), to give rise to new lines of descendants. Table 22-A on page 571 summarizes briefly the history of living things on earth. Only a few species of today look much like their ancestral species of the Paleozoic, Mesozoic, and early Ceno- zoic Eras. And yet the ancestry of plants and animals now living can be traced back through the ages. The plants and animals of today are the changed descendants of the plants and animals of long ago. Gene mutations and new combinations of genetic mate¬ rials at each fertilization furnish the “changes that are possible." The proc¬ ess of natural selection determines in a general way which individuals with 22-18 CHARLES DARWIN The first edition of his Origin of Species, published in 1859, sold out on the day of publication— an amazing record for a scholarly publication. Culver Service changed hereditary traits in each gen¬ eration survive and reproduce, thus transmitting changed hereditary traits to the next generation. Change is the rule in the history of living things, even as it is in the history of an individual organism. Inheritance through the ages has involved many, many genetic changes. Evolution The history of life on earth— the gradual changes in organisms through¬ out the ages— is known as evolution. One of the first generally satisfactory theories of evolution was published 100 years ago by Charles Darwin (Figure 22-18) in his Origin of Species. Dar¬ win’s theory of natural selection (see pp. 547-48) was briefly that: 1. Organisms of a given species tend to reproduce more of their kind than can be supported by the environment. 2. Survival is threatened both by natural enemies of a given species (for example, tigers feeding on horses or ze¬ bras ) and by possible shortages of food (for example, plants used as food by horses or zebras ) . As a result, there is a struggle for existence, or survival, among members of a species. 3. Within any species there is variety in many traits. Certain traits adapt the individuals that possess them to their environment more successfully than other traits do. As a result, individuals that are adapted successfully tend to survive and become parents of the next generation; other individuals tend to die out. Darwin called it “survival of the fittest.” It is true that Darwin's theory left certain questions unanswered, but it provided a foundation on which evi¬ dence later provided by genetics could build. Brussels sprouts Kohlrabi Wild ancestor of mustard family 22-19 SIX GARDEN VEGETABLES AND THEIR COMMON ANCESTOR The thousands upon thousands of kinds of plants today are in many cases closely related in ancestry. The history of living things is a long one. Much of it is still unknown. What is known about that history has already enabled us to understand better how to breed more and more new varieties of more useful crop plants and domestic animals, as you will learn in the next chapter. CHAPTER TWENTY-TWO: SUMMING UP The earth is at least more than 3 bil¬ lion years old. Living things have been abundant in the seas for half a billion years and probably more. Land plants and animals have been abundant and varied since Devonian times. From generation to generation, the genetic make-up of any line of organ¬ isms does change. Given time enough, the changes become extensive (Figure 22-19). And there has been time enough, in half a billion years, for all of our modern lines of plants and ani¬ mals to have been derived from lines present in the Cambrian. It is only when we “telescope" 500 million years or more of history into a few pages, as we have in this chapter, that changes in living things seem remarkable. And perhaps they are. Yet even today, from generation to generation, the changes go on. INHERITANCE THROUGH THE AGES 583 Your Biology Vocabulary Here are the terms you should make a point of remembering after reading this chapter. Eohippus Mesohippus Merychippus Equus paleontology paleontologists geology geologists fossils dinosaurs uranium-lead isotope method of dating rocks sedimentary rock Archeopteryx eras periods epochs “root reptiles” mastodon mammoth extinct Testing Your Conclusions Rearrange each of the following lists of organisms so that they are named in the order of their appearance on earth. For instance, look at the first list. Which plants on the list appeared first? Which appeared next? Continue thus to the end. It will be an advantage if you remember that the simplest forms usually appeared first and the most complex forms last. When you are satisfied that you have arranged the list in the right order, write it in your record book. When you have finished all three lists, check with your classmates. List 1: Plants pteridophytes seed ferns algae angiosperms gymnosperms List 2: Horses Equus Mesohippus Eohippus Merychippus List 3: Animals amphibians dinosaurs protozoa trilobites true fishes primitive birds and mammals primitive fishes primitive reptiles More Explorations 1. A fossil collection. Make a collection of fossils, if any are to be found in your region. Keep a record of the place where each fossil was found, and the conditions surround¬ ing it; that is, whether it was embedded in limestone, shale, coal, or other matter, or was lying loose on the surface. Compare these fossils with pictures in a college geology book or in a paleontology textbook (see Further Reading). If you can identify your fossils, print their names on cards and display your collection in the classroom. 2. Early theories of evolution provide interesting topics for classroom reports. (One of these theories, known popularly as the “use and disuse” theory, held that offspring tended over long periods of time to be born with organs that their recent ancestors used, and without organs that the ancestors did not seem to use.) Ask your teacher to help you decide on a report on one of the following: Charles Darwin Jean Baptiste Lamarck ( lah mark) Alfred Russel Wallace Hugo De Vries (dehvREEs) 584 THE CONTINUITY OF LIFE 3. A museum visit. If you live in or near a city that has a natural history museum, visit it and look at the fossil collections. Look for displays from the Cambrian, the Car¬ boniferous, and the Age of Reptiles. Report in class. 4. Germination of dicots. Plant several kinds of dicot seeds in a large flat box of earth. Mark the kind of seed planted in each area. Water them every day. When they come up, compare their first leaves. What do you discover? What does this fact suggest about their ancestry? Seeds that may be planted are: pansy, sweet pea, zinnia, tomato, pepper, radish, lettuce, pumpkin, endive, mustard, marigold, melon, cucumber, bean, buckeye. Thought Problems 1 . If a person were to find a fossil pine cone among fossils from Cambrian rock, paleon¬ tologists would suspect that someone was trying to play a practical joke. Why? 2. Students often ask such questions as, “What is the Japanese beetle good for?” The question implies that it must be “good for something” or it would not be here. It implies, also, that every living thing must be useful to man. What facts from paleon¬ tology disprove this opinion? 3. The White Cliffs of Dover consist chiefly of the minute white shells of protozoa that lived in the seas of long ago. How did these shells get into the White Cliffs? Further Reading 1. The Dinosaur Book by Edwin H. Colbert, American Museum of Natural History. New York, 1945. This is a fascinating book with fine illustrations. 2. The Book of Prehistoric Animals by Raymond L. Ditmars, Lippincott, 1935. 3. In the Morning of Time by Charles G. D. Roberts, Stokes, 1919. Riology students of past years recommend this book highly to you. Your public library may have a copy. 4. Under a Lucky Star by Roy Chapman Andrews, Viking, 1943. See Chapter 21, “Where the Dinosaur Laid Her Eggs.” 5. Probably the best over-all textbook treatment of living things on earth is Life by George Gaylord Simpson et al., Harcourt, Brace, 1957, already cited many times. See pages 733—799, especially. Some of the text may be too advanced for you to read easily. But don’t miss a look at the illustrations in Life, anyway. 6. Principles of Invertebrate Paleontology, Second Edition, by W. PI. Twenhofel and R. R. Shrock, McGraw-Hill, 1953. The text in this book is very difficult, but you can use the excellent illustrations to help you identify fossils you may find. 7. Vertebrate Paleontology, Second Edition, by Alfred S. Romer, Univ. of Chicago Press, 1945. In this book, too, the text is very difficult, but you can use the illustrations to help you identify fossils. INHERITANCE THROUGH THE AGES 585 CHAPTER Inheritance in Plant and Animal Breeding Corn— then and now M ore than a hundred years before Columbus discovered America, Tonto Indians were busy building cliff dwell¬ ings near where Roosevelt Lake is now located in Arizona. In 1907, the federal government set aside the Tonto Nation¬ al Monument to preserve what is left of those cliff dwellings. In excavating the ruins, people found some ears of corn, presumably the kinds raised by the Tonto Indians of 600 years ago. Above you see one tiny ear of corn, only two inches or so long, found in these excavations; other ears found at the same time were larger, but still quite small compared to the normal ear of hybrid corn we raise today. It must be obvious to you that the corn raised bv these Indians was quite inferior to the corn with which you are famil- iar. Even so, we now know that the American Indians did develop im¬ Marion A. Cox proved varieties, almost certainly by means of artificial selection. By the time our American Revolution was over, the Iroquois Indians had two varieties of sweet corn, and other In¬ dians of the upper Mississippi had four kinds of sweet corn among the 104 corn varieties they were cultivating. The use of artificial selection to im¬ prove crop plants and domestic ani¬ mals was fairly common long before the principles of genetics were dis¬ covered. But applying a knowledge of genetics makes artificial selection much more effective, as you will see in this chapter. Our need for better domestic plants and animals is obvious when you con¬ sider that the population of the earth may double during vour lifetime. One J J of the main reasons why our earth can now support larger populations of peo- 586 THE CONTINUITY OF LIFE pie than ever before is that the applica¬ tion of genetics to plant and animal breeding is increasing our food supply many times. ARTIFICIAL SELECTION FOR A SINGLE TRAIT People have long selected the domes¬ ticated plants or animals with traits most desired by man to be the parents of the next generation. Generally, early examples of artificial selection were on a trial-and-error basis. Sometimes they produced better plants and animals, but sometimes they failed. By 1900, cattle were much improved over the wild park cattle from which they are believed to have been developed. Chickens and other poultry, cotton, po¬ tatoes, beets, corn, and many other plants and animals had also been im¬ proved. Some examples of traits that are gen¬ erally considered improvements are: re¬ sistance to disease; larger fruits (in plants) or larger percentages of meat (in animals ) ; fruits or meats with a bet¬ ter taste or texture; plants and animals suited to specific climatic and geo¬ graphic conditions; and many more. Let’s consider some individual cases of artificial selection for one or another of these traits. One of the first attempts, perhaps the very first, to produce a disease-resistant strain of organisms had to do with red clover in Tennessee. Disease-resistant red clover In the early 1900’s, the farmers of Tennessee were having serious trouble with one of their important crops. Each year, late in June, more and more of the fields of red clover blackened and died (Figure 23-1). By 1904, the clover crops in many parts of the state were total failures. Samuel M. Bain, a botanist,* tackled the red-clover problem early in 1905, with S. H. Essary as his assistant. The first job was to find out what was kill¬ ing the clover. Early in the summer of 1905, Bain discovered a new species of fungus and proved that it was the cause of the disease that made whole fields of red clover blacken and die. Bain and Essary tramped through field after field of dead red clover dur¬ ing August and September, 1905. Here and there they found two or three clover plants still alive and healthy, in the midst of the dead plants. In all, they located over 200 healthy plants in the many ravaged fields they examined, and they collected and labeled the seeds of each of these healthy plants. In 1906, Bain took the seeds he had saved and laid his plans carefully. First, he chose a field at the Tennessee Ex¬ periment Station where red clover had been killed off by the fungus the year before. He had the ground disked rather than plowed, so that the fungus spores would not be buried. Here Bain planted all the seeds from the 200 healthy clover plants, in labeled rows, alternating with rows planted with ordi¬ nary clover seed. When all the plants were well up, dead clover plants from the year before were scattered all over the field to make sure that the new crop would be exposed to the fungus. What happened? By June 20, the rows of clover from ordinary seeds were blackening and dying. The rows from selected seed were virtually all healthy * He was at the time Professor of Botany at the University of Tennessee, Botanist at the Tennessee Agricultural Experiment Station, and Special Agent of the Bureau of Plant In¬ dustry of the U.S. Dept, of Agriculture. INHERITANCE IN PLANT AND ANIMAL BREEDING 587 and normal. During July, the whole field was mowed, as clover fields usu¬ ally are. By September, less than five per cent of the nonselected clover plants were still alive, while more than 95 per cent of the selected ones were alive and, for the most part, healthy. Bain reported that some of the plants from his selected seeds developed spots of fungus infection and that some died during the late fall and early winter.* But he estimated that at least 50 se¬ lected plants to each nonselected one had survived in good health. Bain had good evidence that resistance to the fungus disease was hereditary in the red-clover plants that survived the fun¬ gus disease. In 1906, genetics was still a young science. There was growing evidence that genes affect both resistance and * S. M. Bain and S. H. Essary, Selection for Disease-Resistant Clover, A Preliminary Report, Bulletin of the Agricultural Experi¬ ment Station of the University of Tennessee, Vol. XIX, No. 1, December, 1906. susceptibility to disease. But many peo¬ ple, including some geneticists, still doubted. Bain’s carefully controlled ex¬ periments with red clover furnished evidence which no one who knew the facts could doubt. The research went on. Bv 1909, the Experiment Station had enough seed from the fungus-resistant red clover to start supplying it to Tennessee farmers. That strain of clover, known technically today as Tennessee anthracnose-re- sistant red clover, is still an important crop in the South (Figure 23-1). Bain’s research saved this crop. What is even more important, it added to the grow¬ ing science of genetics as applied to plant breeding and stimulated similar searches for resistant strains of many other crop plants. Selection for larger eggs At the Mt. Hope Experimental Farm in Williamstown, Massachusetts, dur¬ ing the 1920’s, chicken breeders began 23-1 RED CLOVER IN TENNESSEE Left. This disease-resistant red clover was developed by selecting plants that survived a widespread fungus disease and cultivating them, generation after generation, until susceptibility to the disease had been eliminated through survival tests. Right. A dead plant that failed the test— it succumbed to the fungus disease. Tennessee Agricultural Experiment Station TT.S.D. A. 23-2 SELECTION OF POULTRY FOR LARGER EGGS Here, as with red clover, selection for a single trait worked. Often, however, undesirable traits of other kinds may appear during the process of breeding for the single trait desired. trying to breed a strain in which the hens laid larger eggs (Figure 23-2). For mothers, they selected hens that laid the largest eggs. After several genera¬ tions of such selection, they had a flock of hens that laid large eggs. Selection for increased milk production Long ago, dairymen learned to select cows that gave the most milk as the mothers of the next generation. Over the years, they succeeded in building up herds with an increased milk yield. But it took a long time for dairymen to find out that the bulls needed to be se¬ lected, too. For example, the owners of one large dairy farm bought a prize¬ winning bull to use as a breeder. They paid a huge price for the bull. So you can imagine their dismay when the fe¬ male offspring of this bull always gave less milk than their mothers. The bull was a prize winner in cattle shows, but he simply didn’t carry the genes for high milk production. So his daughters couldn’t inherit genes he didn’t have. Today dairymen select both parents carefully if they want high milk yield; bulls as well as cows are chosen from a line of cattle with a high rate of milk production. Selection for one trait is not enough Plant and animal breeders have learned that selecting for one trait only often fails to produce good results. By selecting for one trait, Bain was able to produce a strain of red clover resistant to fungus disease and yet with most of the other desirable features of red clover. But an attempt to produce a strain of cotton resistant to cotton wilt did not turn out that way, as you will see in the next section. Summing up: artificial selection for a single trait Breeders use selection to improve crop plants and food animals. They se¬ lect as parents of succeeding genera¬ tions those plants and animals that are most outstanding in traits useful to man. But selecting for a single trait isn’t enough. Methods of breeding that combine selection for several traits must be used. INHERITANCE IN PLANT AND ANIMAL BREEDING 589 HYBRIDIZATION AND SELECTION FOR SEVERAL TRAITS In 1900, W. A. Orton of the Bureau of Plant Industry of the U.S. Depart¬ ment of Agriculture began to investi¬ gate a disease of cotton called cotton wilt. Orton often found a healthy plant or two in an otherwise dead field. Breeding from these resistant plants, Orton and several other men were able to produce resistant strains, but the strains often lacked other desirable fea¬ tures, such as large bolls, long lint, and early fruiting. (At that time, early fruiting seemed to be the best defense against the inroads of the boll weevil.) Something else was necessary. The solution to a cotton problem Orton crossed his wilt-resistant strains with nonresistant ones that had large bolls, long lint, and early fruiting. Many crosses were made during 1908, 1909, 1910, and 1911. By then, geneti¬ cists knew that thev must look to the J F2 generation for one or more plants with the combinations of traits thev J wanted. In this case, they produced at least eight strains of cotton that com¬ bined wilt-resistance with other desir¬ able features. Of these, the strain called Dixie-Triumph proved best. It is still in production in parts of the South. Other examples of improved plants Research like that on wilt-resistance in cotton showed the value of cross¬ breeding or hybridization, in success¬ fully applying artificial selection to the improvement of crop plants. The list of disease-resistant crop plants now on the market proves that these early in¬ vestigators, like Bain and Orton, were on the right track. Virtually every crop plant or garden flower we raise has been improved in this way. A few ex¬ amples of disease-resistant strains are wilt-resistant tomatoes, watermelons, cowpeas, and flax; rust-resistant and yellow-streak-resistant wheats (Figure 23-3); mosaic-resistant sugar cane and celery; curly-top-resistant sugar beets; mildew-and-blight-resistant lettuce; and yellows-resistant cabbage. There are hundreds of other strains resistant to various diseases. Selective cross-breeding has given us disease-resistant strains of many crop plants. Unfortunately, resistant strains aren’t always permanent. Wheat rust flared up in the West in 1951, in spite of the resistant strains used. Rusts may mutate, and a wheat strain that is re¬ sistant to a former rust may not be re¬ sistant to the mutant rusts. Or the genes for resistance in the wheat may mutate, with the same result. So the work must go on and on. Plant breeders are busy all the time trying to develop more dis¬ ease-resistant crop plants and to main¬ tain those already developed. You have undoubtedly seen fields of hybrid corn. You may even have helped to plant hybrid corn. If so, you know that the farmer buys the seed for hy¬ brid corn each year. He doesn’t try to save his own seed. If he did, the next year’s crop would represent the F2 gen¬ eration, and some undesirable recessive traits would be bound to show up in some plants in the field, just as dwarf¬ ness shows up in the offspring of hybrid tall garden peas. Hybrid vigor Many hybrids from a cross of two J J purebred lines (Figure 23-4) are larger, stronger, and more vigorous than either parent. Hybrid corn is taller than ordinary corn, produces more and larger ears, and is more sturdy in the face of drought, wind, or heavy rainstorms. 590 THE CONTINUITY OF LIFE The yield from hybrid corn may be as much as 250 per cent of the yield from ordinary corn. That is an example of hybrid vigor. A hybrid sorghum, from a cross of two particular purebred lines of sor¬ ghum, yields much larger heads— show¬ ing hybrid vigor. The cattalo ( kat uh loll ) is a hybrid that is produced by breeding cows to male buffaloes. Male cattaloes are not fertile, but the females are. They may be bred to bulls of either cattle or buf¬ falo. By this type of breeding, buffalo genes and their resulting traits have been widely scattered among cattle all over the nation. The cattalo is a larger and sturdier animal than either of its parents. It has hybrid vigor. Many but not all hybrids show hy¬ brid vigor. Mendel’s tall hybrid peas were usually a little taller than the tall parent plant. Breeders often speak of the value of “new blood” in building up greater vigor in an animal breed. Of course, it isn’t new blood but new com¬ binations of genes that produce hybrid vigor, when it occurs. Geneticists do not know the precise explanation of hybrid vigor. They tell us that it may be due to the fact that most traits undesirable to man are due to recessive genes. When animals are inbred and plants are selfed for several generations, more and more recessive (and often undesirable) traits show up. Can you explain why, in terms of Mendel’s discoveries? PREPARING A CLASS REPORT. In the Yearbooks of Agriculture of the U.S. De¬ partment of Agriculture for 1936 and 1937, you will find accounts of breeding methods used to improve almost all of our crop plants and domestic animals. On the next page is a list of suggested topics for re¬ ports, but choose others if you wish. Prepare a report on methods used to improve any of the plants or animals listed at the top of the next page. 23-3 THE FIGHT AGAINST WHEAT RUST Left. Here is a close-up view of wheat infected with wheat rust. Right. By hybridization techniques, rust-resistant wheat that also has other desirable traits can be developed. But the fight is never finished; wheat rusts may mutate and attack wheat that was resistant to earlier rusts. Development of new rust-resistant strains goes on constantly. U.S.D.A. sheep pigs cattle poultry cotton wheat sugar beets corn draft horses oranges rice potatoes In the light of the reports given in class, answer as many of the following questions as you can. 1. How are plant and animal breeders taking advantage of our modern knowl¬ edge of genetic principles? 2. Is polyploidy included in improvement of food crops other than fruits? 3. Is it your impression that selecting parents on the basis of a single desired trait (such as egg size) is enough, or that breeders must select parents on the basis of a number of desired traits? 4. Mention one illustration of the fact that environment (soil conditions, living space, etc.) as well as heredity affects our crop plants. pure lines. A pure line is one in which the genes in all the gene pairs that con¬ trol a given trait or several traits are alike. A pure-line tall pea is one that carries only genes for tallness and none for dwarf ness. You already know that pure-line breeding has one definite disadvantage. When plants or animals are inbred to produce a pure line, the resulting pure line mav have a pair of recessive genes giving all its members some undesirable trait. When this happens, the pure line must be cross-bred with another line which does not have the undesirable trait, and the offspring selected and in- bred in such a way that another pure line, related to the first but without the undesirable trait, is produced. This pro¬ cedure is expensive, but in some cases it is still worthwhile. Summing up: hybridization and artificial selection Crossing two strains is not a new method of breeding. Hundreds of years ago, American Indians had learned that it paid to mix corn kernels of dif¬ ferent colors, perhaps blue, yellow, and white, before planting. They had dis¬ covered by trial-and-error that they got a better yield in that way. Genetics has put selective hybridiza¬ tion on a more scientific basis. Breeders can and do produce almost any type of crop plant or food animal they wish by applying genetic principles. LIMITATIONS AND VALUES OF PURE-LINE BREEDING Mendel started his experiments on peas by pure-line breeding before he did any crossing. You will recall that he spent two years trying to establish Pure-line breeding in corn Not only is pure-line breeding some¬ times worthwhile for its own sake, but it is also necessarv to hybridization. Hybrid corn is the result of crossing pure lines. So pure-line breeding must precede hybridization in producing hy¬ brid corn. Several people have developed pure lines of corn, now crossed each year to produce hybrid corn seed. This is the seed which farmers buy each year to raise hybrid corn. Pure-line breeding in corn is started by planting all the grains from a single ear of corn. Then the silk on a young ear is pollinated by hand with pollen from the same plant; that is, each plant is selfed. This is done year after year. Gradually, any ordinary corn sorts out into several pure lines. If two desirable pure lines are obtained, these lines are crossed. The seeds from the cross grow into hybrid corn. Often two pure lines 592 THE CONTINUITY OF LIFE Life photographer George Strock, © Time. Inc. 23-4 STEPS IN CROSSING WINTER SQUASH WITH SUMMER SQUASH Left. A male flower of winter squash is trimmed to expose the stamens. The pollen is collected for transfer to a female flower of summer squash. Right. After being pollinated, the female flower of summer squash is tied shut to prevent the entry of pollen from male flowers of sum¬ mer squash. The seeds produced by this cross will grow into hybrid plants that bear firmer fruit than either parent produced. are crossed, and two other pure lines are crossed. Then the two F-, hybrids are crossed, to produce hybrid corn seed for sale. This kind of hybrid corn is called double-cross hybrid corn. Pure-line breeding combined with hy¬ bridization has produced corn far bet¬ ter in many ways than any we have ever had before. Pure-line breeding in animals Pure-line breeding in animals is more difficult, because self-fertilization is im¬ possible. The nearest approach to it is obtained by breeding within a family. For example, in cattle there are father- daughter, mother-son, and brother- sister matings. In this way an approach is made to pure lines. So-called pure- INHERITANCE IN PLANT AND ANIMAL BREEDING 593 U.S.D.A. 23-5 POLLED HEREFORD BULL This breed of Hereford cattle is popular not only because it is hornless but because it is a sturdy breed with a high ratio of meat yield per total body weight. bred animals are highly inbred. If the pure line produced seems to have no major genetic weaknesses, it often is maintained and spread widely, until it represents a significant portion of the living members of its animal genus or species. Registered animals are pure-line ani¬ mals that have their ancestry recorded in registries, often for many genera¬ tions. Polled Herefords (Figure 23-5) are a good example of registered ani¬ mals. Polled cattle are hornless. The first hornless Herefords came from mating purebred Hereford cows to a mutant hornless bull with a white face and red coat. Later, a cattle raiser in Iowa set out to produce a hornless strain of Herefords. He sent out circulars to the 25,000 members of the American Hereford Cattle Breeders’ Association and thus located four hornless bulls and ten hornless cows. Apparently they were mutants. This breeder bought O seven of these polled cows and all four bulls and began breeding them. In due course, seven registered horned Here¬ ford cows also were bred to hornless bulls. These matings proved that nearly all progeny of polled bulls and horned cows are hornless. From these beginnings, the polled Hereford strain of cattle was developed. They are today one of the important breeds, as is proved by the fact that over 50,000 polled Herefords are reg¬ istered in the American Polled Here¬ ford Record. They are raised in all parts of this country, and in Canada, South America, Australia, and several other countries. Another interesting example of the wav registered animals are sometimes J O produced is the Santa Gertrudis ( ger troo diss ) Breed, developed on the King Ranch, Kingsville, Texas. Back in 1910, the ranchers began to cross American Brahmans with Shorthorns. They were J 594 THE CONTINUITY OF LIFE trying to produce beef cattle better suited to conditions in their area. In 1920, a bull named Monkey was born. Continued breeding, done in the light of genetics, resulted by 1940 in a new line of purebred beef cattle, the Santa Gertrudis Breed, said to be the first dis¬ tinctively North American breed of cat¬ tle (Figure 23-6). Santa Gertrudis cattle are superior in some ways to both their Shorthorn and their Brahman ancestors in the region where they are raised. For one thing, they stand the heat and the dry climate better. For another, they are better grazers. In 1948, there were some 7,000 purebred Santa Gertrudis cattle on the King Ranch. All 7,000 can be traced back to Monkey. J Summing up: limitations and values of pure-line breeding Purebred or registered animals are produced by pure-line breeding. In plants, pure lines may be developed by selfing. Often, other breeding methods are combined with pure-line breeding to get desired results, especially if first at¬ tempts have resulted in a pure line with one or more definitely undesirable traits. OTHER FACTORS IN PLANT AND ANIMAL BREEDING Several other factors enter into the methods used by the modern plant and animal breeders. For one thing, they take advantage of desirable mutations. For another, they know how to produce plants with doubled or tripled chromo¬ some numbers. Mutations and breeding Mutations turn up fairly often among crop plants and domestic animals. Many of these are undesirable. For example, there is a marked tendency among some strains of cultivated strawberries to mutate to a yellow-leafed form, which 23-6 SANTA GERTRUDIS BULL This American breed of cattle is better suited to dry, hot climates than most other breeds. It resulted from cross-breeding experiments with Brahman and Shorthorn cattle. U. A. Dodd, from Santa Gertrudis Breeders International is undesirable. Breeders must either abandon such strains or try to breed out the undesirable trait. Many mutations prove useful. The now-famous Washington navel orange is one example, as you know. Mammoth tobacco is a giant strain that originated as a mutation. It will flower only when days are short. So it is called a short-clay plant. As long as the days are long, as they are in the South during the growing season, Mam¬ moth tobacco keeps on growing till it becomes a giant. It may reach a height of ten feet or more. Ever since H. J. Muller proved in 1927 that X rays induce mutations, breeders have been trying to induce useful mutations in crop plants. For the most part, the results are harmful rather than desirable. However, a few successful mutations have been achieved. In 1947 and 1948, as many as 13 mutations of varying value were in¬ duced in barley. Some in wheat and oats have also been reported, enough to make further efforts worthwhile. Radiation genetics With the advent of controlled atomic radiation has come a long series of ex¬ periments in plant genetics (Figures 23-7 and 23-8). At the Brookhaven Na¬ tional Laboratories on Long Island (not far from New York City), scien¬ tists have been experimenting since 1950 with the effects of atomic radia¬ tion on plants. On a ten acre plot of land, a wheel-shaped garden has been laid out, with a controlled source of 23-7 BROOKHAVEN "HOTHOUSE" Here is a greenhouse or “hothouse” that is “hot’’ in a special sense. Located on Long Island, near New York City, it is part of a center for experiments in radiation genetics. The two scientists seen here are cheeking plants for effects of gamma-ray radiation given off by radioactive cobalt. The source of the radia¬ tion is the metal stand between the scientists. At the time the photograph was taken, the radioactive cobalt had been lowered fifteen feet underground to protect personnel from harmful effects of radiation. Brookhaven National Laboratory radiation at the center, or “hub.” Rows of crops are planted as if they were “spokes” in this huge “wheel.” Thus, the effects of radiation on a single type of plant can be roughly determined with respect to the distance of each plant of that type from the source of radiation. More than seventy crops have been tested at the gamma garden, as it has been named (gamma rays are the tvpe of radiation given off by the source in use). The strength of the radiations is enough to prove fatal to a man stand¬ ing for an hour within four or five feet of the source (Figure 23-8). Many plant mutations have resulted, among them a variety of peach whose fruits ripen two weeks earlier than usual, a rust-resistant strain of oats, a disease- resistant type of navv bean, and a hardy, short-stemmed rice plant. Other experiments are being con¬ ducted with small laboratory animals. What the results of these and future experiments will be, no one knows. We do know that we have an effective means for studying genetic patterns in manv living things. Selection for polyploidy Many strains of our food plants to- dav have a double number of chromo¬ somes in each cell. Some even have a triple number. This is particularly true of our fruits. The McIntosh apples you read about in Chapter 20 (see Figure 20-16, page 540) are a good example. The apple at the left in Figure 20-16 contains the ordinary diploid number of chromosomes (2 n or 34) in its cells. The one at the right has 4 n or 68 chro¬ mosomes in each cell. You can see how much larger the 4 n apple is. Most of our apples today contain the diploid number of chromosomes (34). Brookhaven National Laboratory 23-8 BROOKHAVEN GAMMA GARDEN The “hub” of this wheel-shaped experimental garden is seen here, with the source of the gamma rays in the pole at the right. Twice each dav the radioactive cobalt within the pole is lowered into the ground so that scientists can safely cultivate and examine the crops. Many mutations have been produced by the radiation. The haploid number ( n ) is, of course, 17. Some 3n strains of Baldwin apples have been developed from chance seed¬ lings. These apples have very few seeds. The 3n trees are large, fine trees, propa¬ gated by grafting. As you know, plants with more than the 2 n number of chromosomes are called polyploids. You can see why breeders are always on the lookout for polyploids. A few common polyploids today are: Sn strawberries; 4 n grapes, cherries, cranberries, and blueberries; 4 n and 6n plums; and up to 12n blackberries. Nor INHERITANCE IN PLANT AND ANIMAL BREEDING 597 are polyploids limited to fruits. Exam¬ ples of artificially induced polyploids include: 4/i red clovers, ryes, and tur¬ nips; and both 3n and 4n sugar beets. In each case, the polyploids are con¬ sidered superior to their diploid rela¬ tives. The possibilities for bigger and better crop plants through polyploids seem enormous. As one speaker, in talking about polyploids, told the American Societv for Horticultural Sciences at their Milwaukee meeting in October, 1949, “The materials are now available . . . so that the builder [breeder] can create . . . what he wishes”— within limits, of course. You might add that the principles of genetics, in general, are making it more and more possible to produce bigger and better plants. The application of genetics to animal breed¬ ing is equally valuable. CHAPTER TWENTY-THREE: SUMMING UP Since the early 1900’s, the principles of genetics have been applied more and more to the improvement of our crop plants and domesticated animals. Bv 1936 and 1937, so much had already been accomplished that it took two large volumes to report, often briefly, on the achievements. For two years, the Yearbook of Agriculture, published by the U.S. Department of Agriculture, was devoted to reports of their Com¬ mittee on Genetics. These Yearbooks are subtitled Better Plants and Animals 1 (1936) and II (1937). In these books you can read about the breeding of virtually any crop plant or domestic animal, from “Popcorn Breeding” and “Heredity in the Dog” to “Improving Horses and Mules’ and “The Origin of Hybrid Corn. A few of the achieve¬ ments have been discussed in this chap¬ ter. For example, you have seen how pure-line breeding, hybridization, poly¬ ploidy, and mutation are of value in artificial selection for securing more useful domestic plants and animals. You will probably live to see the day when twice as many people will be living on this earth as are now living here. That means that we must learn how to produce twice as much food, clothing, shelter, and other essentials as we do now. within the next 50 years. . ci Your Biology Vocabulary You have met only a few new terms in this chapter. It will be easy for you to make sure you understand and can use each of the following ones correctly. breeding methods: selection for one trait hybridization pure-line breeding breeding of desirable mutants radiation genetics hybrid vigor registered purebred animals cattalo short-da v plants 598 THE CONTINUITY OF LIFE Testing Your Conclusions In your own words, write the story of one of the researches listed below. wilt-resistant cotton Santa Gertrudis cattle fungus-resistant red clover hybrid corn polled Hereford cattle McIntosh apples More Explorations 1. Reports. Select some crop plant, garden flower, or domestic animal that interests you, such as dogs, horses, roses, oranges, or dahlias. Use the U.S. Department of Agricul¬ ture Yearbooks for 1936 and 1937. Find out all you can about the breeding of your chosen plant or animal, and report in class. If your library does not have these Year¬ books, use government reports, encyclopedias, or any other reference material at hand. You will find a good article, “Hybrid Corn,” in Scientific American, August. 1951, pages 39-47. 2. A long-term project. If you have a flower garden, you may want to try to improve one kind of flower that you usually raise every year. You might try selecting for larger flowers or hybridizing flowers of different colors (say, white and red sweet peas), or any similar project. Of course, it will take you at least several years and perhaps more to complete such a project, but it is an interesting hobby and can pay off. Thought Problems 1. Many years ago Luther Burbank crossed a small wild white blackberry with a large domestic berry. He got 65,000 F„ plants. He said to the men who were planting them, “If I only knew which one of these plants I wanted, you could plant it and throw the rest away.” He wanted a plant with large, white blackberries. Why was it neces¬ sary for the men to plant all the F„ plants so that Burbank could find the one he wanted? 2. Breeders have crossed a large, yellow-flowered African marigold with a dwarf, red- flowered French marigold and produced a hybrid with large red-and-gold flowers. This hybrid almost never produces seeds. How can breeders keep on producing the beautiful hybrid marigold year after year? Further Reading 1. Two Blades of Grass by T. Swann Harding, Univ. of Oklahoma Press, Norman, Okla¬ homa, 1947. You will find many interesting breeding experiments in this book. 2. Almost any college text on genetics discusses plant and animal breeding. One with unusually interesting photographs and discussion is Winchester’s Genetics, already cited several times. 3. The Genetics of Garden Plants, Fourth Edition, by Morley B. Crane and Wil¬ liam J. C. Lawrence, Macmillan (St. Martin’s Press), 1952. Here is the book for the amateur gardener who wishes to know more about the plants he grows. 4. Inheritance in Dogs, by Ojvind Winge, Comstock, Ithaca, N.Y., 1950. If you are a dog lover, you will enjoy this book. Its section on breeding hunting dogs is especially good. INHERITANCE IN PLANT AND ANIMAL BREEDING 599 iNo plant or animal lives alone on this earth. Wherever one animal or plant lives, there are others of its species. And wherever there are animals, there are also plants. We know this to be true, because living things are interdependent. The photograph at the right shows part of a typical desert scene in Arizona Would you guess that only a small number of living things would be found here? If so, you are wrong. Desert life is abundant in Arizona. There are stately saguaros, such as those on the left in the photograph, and several other species of cactus. There are mesquite (mesKEET) and paloverde (pah loh ver day) trees, devil’s claw vines, creosote bushes, fairy dusters, manv-fruited spurges, yucca plants, and many other types of plant life. Among the animals you would expect to find in this desert, if vou were familiar with animal life in this setting, would be Western diamondback rattlesnakes, sidewinders (also rattlesnakes ) , Gila monsters and other species of lizards, rabbits, ground squirrels, mice, desert foxes, an occasional wildcat, birds ranging in size from cactus wrens to hawks and owls, and many other soecies of animal life. In a desert or forest or swamp, or on a prairie or mountain, you will find populations of many living things. All LIVING POPULATIONS AND THEIR INTERDEPENDENCE the plant and animal populations in one particular area affect each other in many ways. Each one depends on the others in certain ways, for better or for worse. All of the plant and animal populations in any one area make up a community of living things. What have plant and animal populations and communities to do with you? More than you can even guess. You are one member of a population of people in your locality. You affect them and they affect you, every day of your life. Your population of people is only one of several populations in your community. Even in a city, there are several populations in every neighborhood— one of houseflies, one of mice, one of lawn grass, and so on. Can you name more? You do not and cannot live alone. 4 Your welfare is tied up with that of other people and other organisms. This unit is about the biology of populations, rather than that of individuals. In it you will studv some of the biological principles that apply to populations, and some of the problems we must face in using these principles to our advantage, today and tomorrow. Chapters 24. The Biology of Group Interactions 25. Man and Conservation CHAPTER MThe Biology of Group Interactions Living things depend upon each other . Take deer , for example . They depend upon certain plants for food and upon coyotes and mountain lions for protection against overpopulation . In turn . the plants , mountain lions , and coyotes depend upon still other living things , Too many or not enough? In 1924, the whole country in the Grand Canyon National Game Pre- J serve “looked as though a swarm of locusts had swept through it,” as one observer wrote. But it wasn’t locusts. It was deer, such as the one pictured on this page, that had done the damage. It sounds unbelievable, doesn’t it? But it is true. Here is how it happened. In 1906, our government prohibited the hunting of deer in the Grand Can¬ yon National Monument. At the same time it offered to pay bounties ( so much money per head) for killing animals that usually prey upon deer. Between 1906 and 1924, the records show that people killed at least 781 mountain lions, 30 wolves, 4,889 coyotes (Fig¬ ure 24-1), and 544 wildcats there. Any biologist trained today in the field of the mutual interdependence of Dale L. Slocum, from Arizona Development Board plants and animals and their environ¬ ment could predict what would— and did— happen. In 1906, there was an estimated deer population of 4,000 in that game preserve. By 1924, it had increased to about 100,000. Without natural enemies to keep down the deer population, the number of deer had grown far beyond what the area could support, especially in the winter months. Thousands and thousands of deer starved to death during the win¬ ter of 1924. Thev had literallv “eaten J J themselves out of food.’ Why? Be¬ cause there were too many deer and too few natural enemies of deer. It took years to restore the Grand Canvon National Game Preserve, but it has been restored— by taking the bounties off the predators ( pred uh ters —animals that prey on others ) and bv 602 LIVING POPULATIONS AND THEIR INTERDEPENDENCE allowing controlled deer hunting in the game preserve. A new word for a particular popula¬ tion in a particular area is gradually coming into use. That word is deme (deem). The deer in the Grand Canyon National Game Preserve are one deme, the coyotes another, the mountain lions another, and each species of plant found there still another of the many demes in that particular area. All the plant and animal demes found in the Grand Canyon National Game Preserve form a community, or biome ( by ohm ) . All the demes in any biome are dependent upon each other, for better or worse. For example, the very welfare of the deer deme, and of all the plant demes threatened by too large a deer deme, is tied up with that of the coyotes and other predators. WILDLIFE POPULATIONS AND THEIR HISTORY Before people interfered in 1906, the various plant and animal demes in what became the Grand Canyon National Game Preserve were pretty well bal¬ anced. The area could support a deme of some 4,000 deer, year after year after year. There was a natural balance be¬ tween predators, prey, and vegetation that made for a more or less permanent community. Communities or biomes Nearly all plants and animals live in some kind of community. Look at your school lawn. You probably see more grass plants than other kinds of organ¬ isms. But other organisms are there;’ probably a few dandelions or a few plantains, perhaps a few mushrooms, and some clover. In the soil beneath the lawn there are several demes— bacteria, soil fungi, earthworms, threadworms, and perhaps some ground moles. Yes, even your school lawn is a community of demes. It is a biome. There are many kinds of biomes. There are prairies and forests and deserts and swamps and bogs and many more. At any particular spot, a particu¬ lar kind of biome exists. A beech-maple woods is a common type of biome in northeastern parts of the United States. Biomes of ponderosa ( pon der oh suh) pine are common in northern New Mex¬ ico and Arizona, and biomes of Douglas fir occur in our great Northwest. Oak- hickory woods, tail-grass prairies, bogs, swamps, ponds, lake shores, and several other types of biomes occur within a small radius of Chicago. In each biome, specific kinds of plants and animals live together in relations of mutual in¬ terdependence. Such plant-animal bi¬ omes are made up of many demes, or populations of different kinds of or¬ ganisms. Some biologists specialize in the study of the complex interdependence between plants and animals and their environment in any biome, and between biomes existing near each other. Such biologists are ecologists ( ee kol oh jists) and this special field of biology is ecology ( ee kol oh jee ) . A MINIATURE BIOME. You can easily set up a miniature biome in the classroom. Fill a three-gallon bottle (Figure 24-2) about one half full of pond water. Add eight or ten ounces of soil and a small amount of algae from any pond. When the materials have settled and the water is clear, add four or five sprigs of elodea. Then introduce a guppy, a snail or two, and a piece of clam shell (to neutralize acid wastes). Cork the bottle so that it is THE BIOLOGY OF GROUP INTERACTIONS 603 H. Armstrong Roberts 24-1 COYOTE This flesh-eating predator is not very popular with man. Yet his pred¬ atory habits help to control population numbers of the animals he preys upon. airtight. Set the corked bottle in a well- lighted part of the classroom, but not in direct sunshine. Its temperature should not rise much above 70° F. The iiving things in this sealed bottle may live and grow for months, because there is a natural balance between the plants, animals, soil, and water. The nature of the interdependence of the organisms in this biome is brought out by the following questions. From what you have already learned, you can probably answer these questions. Write your answers on a fresh page of your record book. 1. Where does the oxygen used by the animals and plants come from? 2. How do the plants get their food? 3. What does the guppy eat? 4. Where do the plants get the carbon dioxide used in photosynthesis? 5. Where do the plants get the energy used in photosynthesis? 6. How do the animals get their energy? 7. How do the plants get the energy for all of their life processes, other than photo¬ synthesis? 8. Why would the plants and animals soon die if the sealed bottle were placed in a dark cupboard? 9. How do the plants get their neces¬ sary nitrates? Biomes are somewhat like organisms Ecologists agree that any particular community of living things is compa¬ rable in many ways to the human body or to the body of any other complex, many-celled organism. You know that the human bodv is a communitv of J j many billions of cells living together in close interdependence. Similarly, a beech-maple woods is a complex of many kinds of organisms living together in intimate relations of mutual benefit (Figure 24-3). You will recall the amazing ability of the human body to maintain its stabil¬ ity in the face of constant change. A biome under natural conditions tends to maintain a balance or equilibrium, just as the human body does. Just as the welfare of the body depends upon in¬ ternal equilibrium, so does the welfare of each biome of plants and animals depend upon the natural equilibrium among its demes. Anything that disturbs the natural equilibrium disturbs all the demes of the biome, some more than others. If you set your sealed-jar biome of ani¬ mals and plants in the dark for a few days, photosynthesis will cease. The guppy will die for lack of oxygen, even before it can starve for lack of food. Or add two or three more guppies. This is equally fatal, for the oxygen and food supplies are insufficient for three guppies. Death soon overtakes the members of the biome. Under natural conditions the equilib¬ rium between the members of a biome and their nonliving environment is 604 LIVING POPULATIONS AND THEIR INTERDEPENDENCE maintained almost as automatically as it is in the human body. When some natural disturbance, such as an earth¬ quake or a flood, does destroy the bal¬ ance, the particular biome may perish. As soon as the flood subsides or the earthquake ends, natural mechanisms begin once more to re-establish a bal¬ ance between whatever denies of plants and animals survive in, or invade, the area. Man-made disturbances People disturbed the balance in the biomes of the Grand Canyon National Game Preserve by killing off predators and prohibiting the hunting of deer. Wherever man goes, he changes the face of nature. He plows the fields to raise crops. He pastures his herds in the grasslands. He dams rivers, builds 24-2 BIOME IN A BOTTLE The guppy, snails, and water plants in this sealed bottle may exist together indefinitely. There is a natural balance between the plants, animals, air, soil, and water. roads, factories, and cities. In these and other ways, he sets up his own biomes in ways that serve his interests. But all too often, in doing so he creates dis¬ turbances in the natural equilibrium that injure his own welfare, instead of advancing it. The dust storms of the early 1930’s startled the nation, but did not surprise trained ecologists. During and follow¬ ing World War I, men plowed up mil¬ lions of acres of the natural grasslands in the Southwest in order to plant wheat. The grasses were the natural binders of the soil. Their removal ex¬ posed the soil to wind and water ero¬ sion. The first prolonged drought was bound to mean huge and destructive dust storms. Toward the end of the 1930’s, measures of artificial control, combined with a natural swum to heav- O ier rainfall, restored much of the so- called Dust Bowl to normal. During World War II, much of this area was highly productive, but once more, much of the renewed grass cover was plowed up. By the summer of 1947, ecologists were warning the nation that the next prolonged drought would prob¬ ably bring dust storms once again. They were right (Figure 24-4). By 1957, the great Dust Bowl was pretty well under control again, but dust storms are and probably will continue to be common in the arid desert areas of Arizona and California. Here again, man is partly but not entirelv to blame for the dust J storms. We have disturbed the natural bi¬ omes of our country in many other ways. We have cut down and virtually destroyed the forests on many of our watersheds. (A watershed is all the high, ridged land or mountains divid¬ ing two different drainage areas, such as those of the Mississippi and the THE BIOLOGY OF GROUP INTERACTIONS 605 Colorado Rivers.) We have overgrazed tlie natural plant cover on other water¬ sheds. Ecologists now know that re¬ moving the natural plant cover on any watershed increases the water runoff during rains, with several results harm¬ ful to the human population of the nation. You have probably read about the millions of buffaloes and passenger pi¬ geons that made up a part of our wild¬ life 150 years ago. Today the passenger pigeons are extinct, and only a few herds of buffaloes survive— and these only under man’s care. Antelope, wolf, bear, moose, and caribou are rare today in comparison with the numbers here in pioneer days. The heath hen and the great auk, as well as the passenger pi¬ geon, are gone forever. However, we seem to get along quite well without millions of buffaloes or vast darkening clouds of passenger pigeons. It is not that we meant to wipe out portions of the wildlife of our nation. It is just that we either couldn’t help it, if we were to evolve a modern civilization on this continent, or that, in some cases, we simply didn’t know enough about the need for conservation. The idea that all wildlife decreases as civilization spreads is entirely false. Many animals have been eminently successful in learning to live in the changed conditions brought about by man, and in some cases man helps to ensure this result. For example, the bob- white quail thrives best where there is woodland, brushland, and grassland, plus cultivated fields. Wildlife man¬ agers try to arrange a suitable distribu¬ tion of all four types of habitat to sup¬ port a maximum quail population. The bobwhite quail has increased in num¬ bers in our eastern states with the spread of agriculture. The opossum, the coyote, and the Colorado potato beetle have also increased in numbers and spread to new areas. Such animals as house mice, some rats, starlings, Eng¬ lish sparrows, ring-necked pheasants, houseflies, bedbugs, and a host of other insects seem to live and thrive better in man-made conditions than they do in the wild. Man does disturb biomes of wildlife and set up his own biomes in their place. This is inevitable. The important thing is for man to recognize the point at which his activities throw his own and other biomes out of balance so much that his well-being is threatened. Then he must set up and carry out plans to restore and maintain the bal¬ ance necessary for human welfare. This planning can be guided only by ecolog¬ ical principles. Natural successions Every biome, like every human be¬ ing, has a history. You realize full well that a man 90 years of age was not al¬ ways as he is now. Not so long ago he was middle-aged. Before that he was a young man, a youth, a boy, an infant. These natural stages in the growth of an individual are familiar to you, but did you ever realize that a forest or an expanse of prairie or a bog or a desert also has a past history? The vegetation that the first Europeans found in Flor¬ ida had not always been there. It had passed through many previous stages. Any particular biome has a biographi¬ cal history, just as any particular plant or animal has. Biography of a biome A beech-maple forest, for example, was not the first plant community to occupy the spot where it now grows. Before this forest could grow in its 606 LIVING POPULATIONS AND THKIR INTERDEPENDENCE American Forest Products Industries, Inc.; inset: National Audubon Society C. Huber Watson, from National Audubon Society 24-3 BEECH-MAPLE BIOME In addition to beeches and maples, hemlocks and a few other trees are found in beech-maple forests. Other forest plants include Indian pipe (above), mosses, mushrooms, algae, and ivy. Some of the animals found in beech-maple forests are flickers (inset, top of page), deer (right), foxes (below right), snails (below left), wood frogs, and squirrels. Allan 1). Cruickshank, from National Audubon Society Hugh Spencer, from National Audubon Society Hal H. Harrison, from National Audubon Society * Soil Conservation Service 24-4 DUST STORM In many parts of the Southwest, man’s farming and cattle-raising activities have denuded the land of natural plant cover. The results are not serious until a period of drought sets in. Then wind erosion reaches disastrous proportions. This photograph was taken in Dallam County in the Texas panhandle. present location, a whole series of pre¬ vious communities of different types had to succeed one another. Without the preceding communities, the soil conditions and other factors essential for a beech-maple forest would not have developed. The spot may once have been a barren rocky upland. The first and only plants to grow on bare rock surfaces are lichens (Figure 24-5a). The lichens slowly dissolve a little of the surface of the rock until they form a thin layer of soil. Then mosses and, in moist places, liverworts spring up and in time replace the li¬ chens ( Figure 24-5b ). The decay of the dead lichens and of some of the mosses adds organic matter to the ever-thick¬ ening soil layer. In time, ferns invade the location, starting the third biome in the series (Figure 24-5c). Still more changes follow. The fern stage eventually gives way to such herbs as grasses, alum root, dandelions, mulleins, and goldenrods (Figure 24-5d). These herbs and their associ¬ ated soil bacteria and animal demes change the conditions still more. Next comes a shrub stage (Figure 24-5e), with such plants as blackberries, lo¬ custs, sumacs, and wild crabs. The shrubs have their day, only to be suc¬ ceeded by light-tolerant trees such as some of the poplars and pines (Figure 24-5f). Each succeeding stage adds to the thickness and richness of the soil, and at the same time makes it possible for the soil to hold more moisture. 608 LIVING POPULATIONS AND THEIR INTERDEPENDENCE The light-tolerant trees prepare the way for their own downfall. They are replaced in due time by trees whose seeds are able to sprout and whose seedlings are able to grow in the ever- changing soil and light conditions. An oak woods or an oak-hickory woods (Figure 24-5g) may replace the poplars or pines. Even the oak woods is not permanent, for the acorns are not able to sprout and grow in the damp, dark conditions of the forest floor that de¬ velop as the oaks grow to old age. Then at long last, young beech and maple trees appear in the undergrowth of the aging oak woods. As the oaks die out, they are gradually replaced by beeches and maples (Figure 24-5h). A beech-maple forest does not con¬ sist of a pure stand of the two trees; it merely contains more beeches and ma¬ ples than any other kind of tree, hence the name. Associated with them are other trees, often including hemlocks, and a considerable undergrowth of young saplings of the same species as the mature trees, for now the seeds of the older trees are able to sprout and grow beneath the parent trees. Largely for this reason this forest is called the climax biome, since it is more or less permanent once it is established. The floor of the climax forest is richly car¬ peted with herbs in the spring, before the leaves come out on the trees and keep the sunlight from reaching the floor. After that, most herbs give way to mushrooms, mosses, Indian pipes, and other plants requiring little light. So far we have discussed only some of the plant denies in a beech-maple biome. How many animal denies of that biome can you think of? There are many— rabbits, several kinds of squir¬ rels, many kinds of birds, no one knows how many kinds of insects, and several kinds of burrowing animals. There may be deer and fox demes and several more. The beech-maple forest is indeed a complex, close-knit community with a past history of several stages. The stages may not always be the same as those just outlined, but several stages of some type have preceded the climax forest. Such a series of stages in the history of any plant community is called a natural plant succession. The stages in the natural succession leading to a beech-maple climax for¬ est are listed below. But remember, there is no hard and fast dividing line between one stage and the next. Each stage overlaps into the next, in any plant succession. Common Stages in a Plant Succession (Figure 24-5) 1. Barren rock surfaces with lichens 2. Mosses and/or liverworts 3. Ferns (brake fern and others) 4. Annual seed plants (grasses, alum root, etc.) 5. Shrubs (blackberries, sumacs, lo¬ custs, etc.) 6. Light-tolerant trees (poplars and pines) 7. Oaks 8. Beech-maple forest White pines in New England The forests that clothed the New England hills in 1620 were mixed for¬ ests; that is, thev were a mixture of some conifers ( cone-bearing ever¬ greens ) and many deciduous ( deh sij oo us) trees. (Deciduous trees are those that shed their leaves in the fall. ) To the north were mixed stands of hard maple, beech, yellow birch, and bass¬ wood, along with such conifers as red spruce, balsam fir, hemlock, and white THE BIOLOGY OF GROUP INTERACTIONS 609 PLANT SUCCESSIONS LEADING The story of a climax forest of beeches and maples covers hundreds of years. It often begins with rock surfaces that are invaded by lichens ( 24-5a ). These hardy little alga- fungus communities begin to break down the rock and form a thin layer of soil. Mosses and liverworts ( 24-5b ) get their start in the bits of soil and organic matter left by the lichens, and gradually enough soil is built up to support ferns ( 24-5c ). The breaking down of rock and the addition of organic matter from plants goes on more rapidly once 24-5a: John H. Gerard, from National Audubon Society; 24-5h: Marion A. Cox; 24-5e and f: U.S. Forest Service 24-5a 24-5 b 24-5e 24-5f 610 LIVING POPULATIONS AND THEIR INTERDEPENDENCE TO A BEECH -MAPLE BIOME ferns are growing. Next, annual seed plants appear (24-56), and they in turn are re¬ placed by shrubs (24-5e, background) . Shrubs are replaced by light-tolerant poplars and pines ( 24-5f ), and the poplars and pines give way to hickory and oak trees ( 24-5g ). The last step takes place most slowly of all; the hickory and oak trees crowd each other until their seedlings cannot get enough light, and beeches and maples, trees that do not require so much light, gradually take over (24-5U) . 24-5c: Hugh Spencer; 24-5d: H. E. Stork, from National Audubon Society; 24-5g: John H. Gerard from National Audubon Society; 24-5h: American Forest Products Industries, Inc. 24-5c BBSS 24-5g 24-5h THE BIOLOGY OF GROUP INTERACTIONS 611 pine. To the south (but still in New- England) the native forests consisted of several species of oak mixed with hickory, chestnut, black birch, and pitch pine. These native forests were largely de¬ stroyed by the settlers. By 1830 nearly 80 per cent of the forested regions had long since been replaced by cultivated fields, pastures, and orchards. Unfor¬ tunately, no one then realized that poor farming practices “wear out” the soil. By 1830 the soils of many New England farms were wearing out so badly that men began to abandon their farms and go west. No sooner was a farm aban- doned than wild plants began to invade its acres. Weeds first took over. White pines and a few hardwoods soon sprang up among the weeds. The white pines soon overshadowed all other trees. In a few years pure stands of white pines “marked the spots” where crops had been grown not many years before. By 1900 the white pines had reached marketable size. Lumbering began on a large scale. But the lumbering was done after the fashion usual in those days. The trees were so cut that the whole stand was destroyed. Then the “trash” was burned and the place aban¬ doned. The cut-over areas did not grow up again in pines. Naturally not, the ecologist says. Pine seedlings do not O J O grow in such places. Such tree seedlings as red and white oak, red and hard ma¬ ple, white ash, birch, cherry, and pop¬ lar did grow there. Let alone, they grew into a very inferior wooded area O J in about 20 years. J Today foresters have learned that a little wise management changes these results. First, the white pines are felled in a wav that saves the undergrowth of young trees. Then natural succession is allowed to take its course for six or seven years. After that, trained men go through the stand and cut out old stump sprouts and the weed trees (birch, cherry, poplar), and they thin out some of the other trees. The re¬ maining trees mature into a stand of fine timber. Summing up: wildlife populations and their history On a fresh page of your record book, answer these questions. 1. Would you expect all the organ¬ isms of a cleme to have similar genetic systems? Explain why you answered as you did. 2. Would you expect all the organ¬ isms of a biome to have similar genetic systems? Explain why you answered as you did. 3. How do predators help to main¬ tain the stability of a biome? J 4. In Cook’s National Forest in Penn¬ sylvania, there is an almost pure stand of aged white pines. Here and there, an old pine tree dies. At these places, seedling trees come up. Remembering the natural succession in most of the northeastern United States, would you expect these seedlings to be pines or deciduous trees? 5. Outline the main stages in a natu¬ ral succession from lichen on a bare rocky upland to a climax beech-maple woods. EXCHANGES OF MATERIALS You are not exactly the same today as you were yesterday. You are even less like what you were a year ago. Bi- ologv students used to ask often, “Is it o; true that your w hole body changes ev¬ ery seven years?” People used to say that it did. Research with radioactive atoms that 612 LIVING POPULATIONS AND THEIR INTERDEPENDENCE can be traced into and out of the hu¬ man body has changed the idea of “a complete change” every seven years. However, even in the light of present knowledge, it seems likely that only two per cent of the atoms in your body were there a year ago. The other 98 per cent have left your body in your breath, sweat, urine, and other excreted materials, or in the cells rubbing off your skin, the hair and nails that have been cut, and in other ways. About 98 per cent of the atoms that were in your body a year ago are gone and have been replaced by new ones, taken in by mouth and in the air you breathe, and in some people, by hypodermic injec¬ tions, as in intravenous feeding. Materials are constantly flowing into and out of your body. These materials are exchanges you make with air, wa¬ ter, and especially with other kinds of organisms. Eskimos and material exchanges The Eskimos illustrate well the proc¬ esses of exchange of materials among living things. Let’s look at their food intake. The food of the Eskimo is largely of animal origin. They prize salmon, trout, whitefish, and herring. They eat cari¬ bou, walrus, and seal meat, too. When really hungry, they eat polar bear. Eskimos get most of their food from animals. The animals have to eat, too. Take the polar bear, for example. Its favorite food seems to be seal. Seals eat herring and other fish. These fish eat smaller fish and crustaceans. The small¬ est fish and crustaceans eat diatoms. The diatoms, as you know, do not eat anything. They make their own food out of carbon dioxide, water, and min¬ erals which diffuse into these one-celled plants. Diatoms in the Arctic Sea are the food-makers. You might call them the producers. All the animals that live in the sea are consumers. So are the land animals that eat sea food. The Eskimos eat the bear that eats the seal that eats the herring that eats smaller fish and crustaceans that eat the diatoms. Here we have a food chain, going in order from consumer to producer (Figure 24-6 ) . From producer to consumer, one food chain of the Eskimo goes like this: dia¬ toms, crustaceans and small fish, large fish, seals, polar bear, Eskimo. Food chains All food chains, going from producer to consumer, start with a producer and pass on from one consumer to another. The one just cited has six links in it. Go back and count them. Here is another food chain. Eskimos eat caribou meat. Caribou eat red top grass. This food chain has only three links in it. Can you give one with only two links? Food chains are universal among ani¬ mals and nongreen plants. Hawks eat field mice. Field mice eat grain. Here the grain plants are the producers. Tick- birds eat the ticks on a rhinoceros’ back, the ticks suck the rhino’s blood, and the rhino eats grass. A mountain lion eats a sheep that grazed on filaree ( fil er ee ) , a desert plant. A dragonfly eats mos¬ quitoes that sucked blood from a per¬ son who had eaten venison from a deer that had eaten grass. And so it goes. All animals are consumers in food chains, while green plants are the pro¬ ducers. You can undoubtedly think of any number of food chains with yourself as consumer. You eat an egg from a hen. A hen eats grain. Or you eat oysters that had eaten diatoms. Every human THE BIOLOGY OF GROUP INTERACTIONS 613 food can be traced back to green plants. Knowing the food chains of the ani¬ mals in any biome helps the conserva¬ tionist to set up the best conditions to achieve the ends in view. This phase of ecology is especially useful in wildlife conservation. Complexity of food chains You can probably trace out dozens of food chains ending with a human be¬ ing. Most other animals eat a variety of foods. Only very few animal species, if any, are limited to a single link in a food chain. The food chain of Eskimos, discussed previously, is only one of many, as you see in Figure 24-6. This is also true of the food chains of the other animals in that example of a food chain. Try to think of all the demes in a beech-maple forest and the food chains involved. A snake may eat any of sev¬ eral different rodents. Each rodent, in turn, may have eaten nuts or seeds or roots of any of several different plants. In any biome, food chains overlap. The exchange of food materials rarely, if ever, follows a single direct line. That is one reason why the welfare of each deme is tied up with that of all other demes. In a general way, food chains can be summarized thus: green plants, animals that eat plants, flesh-eating animals. That is an oversimplification, but the general idea is useful. Ten to one? Ecologists used to think in terms of about ten to one, when thinking of the number of individuals in one link as compared to the number in the next link of a food chain. In other words, since it seemed to take about 10 deer a year to keep one mountain lion alive and active, it was supposed that about ten times as many deer as mountain lions could live in a given biome. This ten-to-one figure was never an accurate one. But the ideas back of it are important. For one thing, the pro¬ ducers ( green plants ) in a given biome must outnumber by many times the herbivores (plant-eaters). And they also outweigh the herbivores by many times. Not only that. The producers, or green plants, produce many times as much food as the herbivores get from them. The plants also have available to them many times as much energy as the herbivores have. A similar situation holds when the herbivores and carnivores (flesh-eaters) in a biome are compared. The herbi¬ vores outnumber and outweigh the car¬ nivores many times over. Here is another interesting idea. The smaller an organism is, the more of them there are likely to be in any bi¬ ome. You can get the picture better if you think of insects, squirrels, and deer. Insects outnumber and outweigh all the rest of the animals put together. Squir¬ rels outnumber the deer in a biome sev¬ eral times over. In general, the larger an organism is, the fewer of them there are. One reason is that there isn’t any¬ where near enough food available to support a squirrel deme of numbers even approaching the number of mos¬ quitoes in that deme. It takes only a little food for a mosquito each day, but more for a squirrel, and several pounds for a deer. Exchange of materials with the nonliving environment Organisms exchange other materials besides foods, as you know. They also exchange materials with their nonliving environment. 614 LIVING POPULATIONS AND THEIR INTERDEPENDENCE 24-6 More than a dozen different food chains are shown here, all of which start with diatoms in the sea. How many of these food chains can you trace? By no means all of the food chains in the Arctic start with diatoms. Another group starts on land with so- called reindeer moss (not a moss at all). Can you trace three of these chains involving reindeer, wolves, and people? Are there any food chains that start with animals, rather than plants? How can you be sure of your answer? THE BIOLOGY OF GROUP INTERACTIONS 615 THE OXYGEN-CARBON DIOXIDE CYCLE 24-7 Both plants and animals take in oxygen and give off carbon dioxide during respira¬ tion. But plants, in making their own food, take in even larger amounts of carbon dioxide than they give off in respiration. And they give off, as a by-product of food-making, much more oxygen than they take in during respiration. Thus a good balance between oxygen and carbon dioxide in the air is maintained. For you and other animal organisms, oxygen is the most immediately neces¬ sary material you get from your non¬ living environment. You get it from the air, and so do many other organisms. Still others get it from the air dissolved in water. In the oxvgen-carbon dioxide J O cycle (Figure 24-7), green plants play a vital part, adding oxygen to the air during daylight hours. Salt (sodium chloride) is another material you get directly from the non- living environment. Often you get wa¬ ter directly, too, but you also get it in¬ directly in milk and all foods. You get nitrogen from the air, too, but only indirectly, by way of nitrogen¬ fixing bacteria, plants, and animals. The exchanges of materials between you and your environment are often illustrated as cycles. Figure 24-7 is an example. Interdependence of living things Green plants are the primary food- producers. Herbivores depend upon green plants for food. Carnivores de¬ pend upon herbivores. So a general food chain is: green plants, herbivores, carnivores. ( Of course, you are both a herbivore and a carnivore, since you eat both vegetable and animal foods. ) Understanding food chains helps man to manage his deme and those about him more wisely, so that people every¬ where may have enough food of the 616 LIVING POPULATIONS AND THEIR INTERDEPENDENCE required kinds. You and all other peo¬ ple depend upon the natural resources of the world— for your very life. Using those resources as wisely as possible is often called conservation. Conservation is important to you and to everyone else. Some of the methods of wise conservation will be discussed in the next chapter. CHAPTER TWENTY-FOUR: SUMMING UP A local group or population of one kind of organisms, such as pine trees or mice, is a deme. In any given area, a whole community of plant and animal demes makes up a biome. All of the individuals and all the demes in a biome are interdependent in many ways, and neighboring biomes also affect each other. Food chains il¬ lustrate one tvpe of interdependence. Under natural conditions, biomes tend to maintain an equilibrium, with the result that a given biome may per¬ sist in much the same condition for a long time. Over much longer periods, even a seemingly durable biome may be grad¬ ually displaced by another, in a natural succession, until a climax biome is reached. A beech-maple woods, a Douglas fir forest, and a saguaro for¬ est are examples of climax biomes in various parts of our country. Can you think of more? Man tends to displace natural bi¬ omes and to set up his own. In doing so, he sometimes causes changes that are not to his own interest, at least not in the long run. On the other hand, any¬ thing that contributes to maintaining old biomes and to setting up new ones that are beneficial to man is wise con¬ servation. Your Biology Vocabulary Knowing how to use the following words correctly will help you to understand better the practice of conservation, today and tomorrow. deme predator biome ecology natural succession climax biome natural equilibrium watershed light-tolerant trees deciduous trees food chains herbivores and carnivores Testing Your Conclusions On a fresh page in your record book, make each list called for below and title each list. Use your book, if necessary. 1. List five possible food chains with the final consumer being a mosquito that takes human blood as food. THE BIOLOGY OF GROUP INTERACTIONS 617 2. List ten kinds of atoms that your body is constantly losing to your environment and replacing with others from your environment. 3. List several probable stages in the past history of a spot now occupied by a beech- maple woods. 4. List three examples of man’s unwise interference in natural biomes. More Explorations 1. Observing a succession. A natural succession of species of protozoa in a laboratory culture is easy to observe. Set up several cultures as directed on page 49. After five days, examine drops of water from the cultures under the microscope. Repeat once a day until the cultures are two to three weeks old. Keep records of the dates when one species is most abundant, and the date when each abundant species begins to give way to another. If you can t find the names of the protozoa, use sketches to indicate each one that becomes abundant. 2. Study of your own area. Whether you live in a city or town or in a rural area, you are a member of a plant-animal community. You may find it interesting to collect some specific information about some of the nonliving factors that affect living things in your region. Try to find answers to the following questions and enter them in your record book. a. What is the usual date of your last killing frost each spring? b. How high, on the average, does the temperature go in summer, and how low in winter? c. How long is your longest day? your shortest day? d. What is your annual rainfall? e. How far underground, on the average, is the water table in your area? f. Is the rock underlying your area sandstone, limestone, or some other type? The underlying rock helps to determine the nature of the soil in most regions. g. What is the highest elevation above sea level in your region? the lowest? Thought Problems 1. In Utah, for years cattle have grazed the grasslands which were originally dominated by wheat grass. After several years of heavy grazing, the wheat grass began to dis¬ appear and a mixture of other grasses began to spread and take over. As heavy grazing continued, these grasses gave way to perennial weeds, and these finally to annual weeds, which provide very poor pasturage in contrast to the original wheat grass. If cattle are now taken off the range or reduced radically in numbers, the annual weeds will gradually give way to perennials, these to mixed grasses, and these to wheat grass once more. What ecological principle is exemplified in this story? 2. Many foreign species of plants and animals have been introduced into this country, intentionally or otherwise. Among them are witchweed, English sparrows, Scotch thistles, chestnut blight, Dutch elm disease, Hessian flies, Japanese beetles, and many more. Frequently these introduced species increase rapidly until they are far more abundant than they were in their original habitats. What ecological principles may help to explain such results? 618 LIVING POPULATIONS AND THEIR INTERDEPENDENCE 3. In 1886, Pennsylvania offered a bounty (a sum of money) for the head or carcass of any hawk or owl, because these birds were taking chickens from the farms. In time, people found out that farmers were out some millions of dollars in lost grain, and the bounties were removed. How do you suppose these bounties became so expensive? Hint: Hawks and owls eat field mice. Further Reading 1. This Green World by Rutherford Platt, Dodd, Mead, 1944. The theme of this book seems to be that the plants around us “are not fixtures of the landscape, but active units in a great moving drama.” “The Day-length Timetable of Flowers,” pages 97-104, and “How Flowers and Insects Fit Each Other,” pages 126-142, are espe¬ cially interesting. 2. Basic Ecology by Ralph and Mildred Buchsbaum, Boxwood Press, Pittsburgh, 1957. This small paper-bound book of fewer than 200 pages is an excellent guide to the understanding of natural succession of biomes in different parts of the world. Learn to “tell the fortune” of the biomes in your community. 3. Natural Communities by L. R. Dice, Univ. of Michigan Press, Ann Arbor, 1952, is another excellent book for gaining a basic understanding of biomes. Here the em¬ phasis is on a survey of plant-animal biomes today. 4. Fading Trails, The Story of Endangered American Wildlife, prepared by a Committee of the U.S. Dept, of the Interior, National Park Service, and Fish and Wildlife Service, edited by Charles Elliott, Macmillan, 1942. Pages 1-39 discuss “Primitive Days,” “Civilization’s Heavy Heel,” “American Tragedies,” and “Plans and Progress.” 5. Cooperation Among Animals bv W. C. Alice, Henry Schuman, N.Y., 1951, relates the stories of many animal denies and how thev live in association with other denies. 6. Natural Principles of Land Use by Edward H. Graham, Oxford Univ. Press, N.Y., 1944. The excellent pictures alone tell an important and interesting story. 7. The Sea Around Us bv Rachel Carson, Oxford Univ. Press, N.Y., 1951 (also available in paper-bound edition. Mentor Books). The author, a staff member of the U.S. Fish and Wildlife Service, tells a fascinating storv of life in the sea. THE BIOLOGY OF GROUP INTERACTIONS 619 CHAPTER Man and Conservation Over 200 forest fires occur each day in the United States. Millions of dollars of damage can he done in a matter of hours. And with each forest lost , a new area of soil— the former forest floor— is exposed to erosion by wind and water. A famous forest fire A raging forest fire is one of the most awesome sights in the world. The now- famous Tillamook fire in Oregon in 1933 was one of the worst in onr history. It all started on a hot, dry August day, with atmospheric humidity at a low point of 20. Under these conditions most logging operations were stopped, but one crew continued work in Gales Creek Canyon. Douglas firs, three to four centuries old, were being cut. A loop of steel wire was fastened around the butt of one huge log and the engine began to apply the power. The log was dragged through the underbrush toward the landing. On its way, it passed over a dry, dead cedar. The friction set sparks flying. In an instant, the fire was on its way. This was on August 14. In spite of all the efforts of hundreds U.S. Forest Service of fire fighters, the fire continued dav after day, sometimes almost checked, then bursting forth again with renewed fury. On the morning of August 24, a hot, dry east wind began whipping the fire forward. By noon, it was raging along a 15-mile front. Smoke rolled in O billows to heights of many thousands O J of feet. The roar was deafening. On and on across Oregon the wall of fire ad- vanced until smoke and burning em- bers rolled out over 40 miles of shore line into the Pacific Ocean. The fire-fighting efforts of some three thousand men had been in vain. Ap¬ proximated 12/2 billion board feet of fine timber had been killed. (A board foot is a board one foot square and about an inch thick. ) The entire tim¬ ber cut in the whole United States was only some 12/2 billion board feet in 620 LIVING POPULATIONS AND THKIR INTERDEPENDENCE 1932. So trees enough for a year's sup¬ ply for the whole nation at that time were killed in eleven days in the Tilla¬ mook fire. Reclaiming the Burn The Tillamook Burn is now being reclaimed. Its third of a million acres are being brought back into produc¬ tion. For years, the salvage of lumber from the burned trees has been going on. Extensive studies have been made, especially since 1945, to discover the best ways to reforest the area. This re¬ search is under the direction of the Ore¬ gon State Board of Forestry. After re¬ search had shown what trees were best suited to each area and the best method of planting them, reforestation was be¬ gun on a large scale. In some areas seeds are scattered by planes during the fall. In other areas trees are planted by hand during the late fall, winter, and early spring. Bv 1952, some 40,000 acres had been reforested.* Many agencies in Oregon co-operate with the State Board of Forestry. For example, all the schools in Portland take an active, year-round part in the work ( Figure 25-1 ) . What can you do in your state to help solve conservation problems? This chapter may help you find the answer. Conservation today We have gone a long way forward since the days when bounty laws, closed seasons on certain animals, set¬ ting out trees, and fighting forest fires were the chief conservation methods in use. No less than all the people can carry out our conservation program to- * See the artiele “Tillamook Burn: The Regeneration of a Forest,” pages 139-148, Scientific Monthly, September, 1952. day, and this they can do well only under the direction of trained men and women in many governmental and pri¬ vate organizations. The agencies in the federal govern¬ ment most directly concerned with conservation of our biological resources are these: Soil Conservation Service and Forest Service, both under the De¬ partment of Agriculture; Fish and Wild¬ life Service, National Park Service, and Bureau of Land Management, all under the Department of the Interior. These agencies carry out extensive research as well as educational programs. The individual states also have their own agencies, and many communities are active through both public and pri¬ vate organizations. They, too, maintain educational services. The big, over-all problems in the con¬ servation of our biological resources are: soil and water conservation, forest conservation, and wildlife conservation. SOIL AND WATER CONSERVATION You get your living from the soil, di¬ rectly or indirectly. So does everyone else. Anything that reduces the soil’s fitness for growing crops, or anything that makes ground water more scarce, is a threat to all people, city dwellers as well as farmers. If you want to go on eating well and living well, you will need to understand and take your part in our conservation program. Anything that helps to keep soil pro¬ ductive or increase its productivity is soil conservation. In general, soil is in- jured in two ways: by erosion (Figure 25-2), and by loss of organic matter and minerals, called soil depletion. So whatever helps to control erosion (Fig¬ ure 25-2) or keep the organic and MAN AND CONSERVATION 621 mineral content of the soil up to stand¬ ard is soil conservation. Anything that helps to maintain our water supplies, already dangerously low in many areas at certain times of J the year, is water conservation. Soil and water conservation are closely related. What is soil made of? All soil comes in one way or another from rocks. Many agents help to break rocks into the particles (clay, fine silt, and sand) that make up soil. Freezing and thawing may split rocks. Moving water (rain, streams, rivers, lakes, oceans) is a powerful eroding agent. Glaciers scour large and small pieces loose from the underlying rock. Lichens attack bare rock surfaces. Tree roots sometimes grow into rock crevices and split off pieces of the rock. In these and other ways, the lifeless particles of soil are formed. Soils are of many kinds, but in gen¬ eral they fall into two groups: topsoil and subsoil. As you know, it is largely the topsoil that supports both the crops that feed and help clothe a nation and the forests that supply lumber, paper, and a hundred more items. Topsoil is not mere lifeless particles of rock. Topsoil teems with life. A sin¬ gle soil particle of surface loam may house 60 million bacteria. Molds and other fungi and the roots of plants mingle intimately with soil particles. Counts of earthworms in some soils show a population as high as million per acre, with 50,000 per acre quite common. Ninety-five per cent of all in¬ sects invade the soil at some point in their life cycles. One report on a 25-1 RECLAIMING THE TILLAMOOK BURN Today, more than twenty-five years after the Tillamook fire of 1933 in Oregon, the vast burned-out area is still in the process of being reclaimed. These high school students from Portland, Oregon, are planting young Douglas firs, a project they take part in each year. Portland Public Schools meadow in Maryland states that more than 13 million invertebrates may live in a single acre "at a depth no greater than a bird can scratch.” Add to these the burrowing animals, such as moles, gophers, and muskrats, and you have a picture of life in the soil. Soil, then, is made of rock particles, and topsoil also contains surprisingly large numbers of living things. Even that isn’t all. Some water is present in all soils, at least part of the time, and topsoil also contains nonliving organic matter— excreted animal wastes and dead and decaying organisms, or parts of them. The organic matter in soil is called humus. All topsoils are made of much the same things. And yet topsoils differ widely, largely because the proportions of the various materials they are made of differ. Some soils are rich in organic matter, others are not. Some soils are dry, others are moist. Some are acid, others are alkaline. Clay particles pre¬ dominate in clay soils, sand particles in sandy soils. Some soils are rich in minerals need¬ ed by crop plants; others are not. Worn- out soils lack both the organic matter and some of the minerals needed to support crop plants. All these and more soil features are taken into consideration by those who are concerned with soil conservation. Soil conservation districts In 1937, W. J. Waits raised only 80 bales of cotton on 250 acres of his farm in Holmes County, Mississippi. Then he and other farmers signed up with the Holmes County Soil Conservation Dis¬ trict. They agreed to practice conserva¬ tion farming on all their land. By 1944, Mr. Waits was raising 125 bales of cot¬ ton on 175 acres. His annual cash in¬ Soil Conservation Service 25-2 EROSION CONTROL These two photographs show the same terrain five years apart in time. Above. Rapid soil ero¬ sion created this gulley. Black locust trees were planted in an effort to control the erosion. Below. Five years later, the black locust trees averaged 15 feet in height and the rapid erosion had been controlled. come from cotton had increased by more than $17,000. With the help of trained experts in the Orchard Mesa Soil Conservation District in Colorado, Donald Rook raised the yield of sugar beets from MAN AND CONSERVATION 623 eight to sixteen tons per acre. No won¬ der farmers all over the nation are set¬ ting up soil conservation districts and agreeing to do conservation farming. It pays off. Soil conservation districts are local government units, set up and run by farmers on a voluntary basis under state laws. Experts from the Soil Conserva¬ tion Service and state conservation de¬ partments co-operate with the farmers. The first district was set up in North Carolina in 1937. Bv July 1, 1952, there were soil conservation districts in ev- erv state and some of the territories. Today over a million farmers do eon- servation farming on all their 162,726,- 125 acres. That is nearly one third of all the good cropland in the country. How is soil conserved? The methods of soil conservation now in use are so numerous and varied that a whole book could not do them justice. Here only a few of the most useful practices can be described. The illustrations will help you to see how some of these practical measures are carried out. Soil is conserved in many ways, among which are crop rotation, contour cultivation and strip cropping, terrac¬ ing, planting cover crops and other soil¬ binding plants, restoring organic matter and minerals depleted by crops or ero¬ sion, and wise planning of land use. Crop rotation At one time the same crop was raised in the same field year after year until the soil was worn out (depleted). Now we know better. Conservation farming calls for a rotation of crops; perhaps, corn one year, wheat or oats the next, and clover the third year. Then the se¬ ries is repeated. The wheat and clover Soil Conservation Service 25-3 RESULTS OF CROP ROTATION The corn on each side of the farmer was planted from the same bag of seed. The yield of the tall corn on the left averaged 28 bushels per acre, that of the corn on the right, 7 bushels per acre. The reason for the difference?— the corn on the left followed four years of planting with a leg¬ ume crop, that on the right, four years of planting with cotton and more corn. are close-growing crops. They hold back the runoff of water and reduce erosion to a minimum. The corn is an open-tilled crop that exposes soil to ero¬ sion and permits large runoffs of rain water. Alternating open-tilled and close¬ growing crops reduces erosion and wa¬ ter losses tremendously. For example, a field planted in corn for several years in a row lost some 25 tons of topsoil a year, while a nearby field planted in corn one year and in oats and wheat the next two years lost an average of six tons of topsoil a year. Crop rotation has many other advan¬ tages. Usually at least one legume crop 624 LIVING POPULATIONS AND THEIR INTERDEPENDENCE is included in the rotation. That crop adds nitrates to the soil. Figure 25-3 shows the results in one case. In this and other ways, crop rotation helps to reduce soil depletion. On the other hand, grassland farming is now being done on an extensive basis. This involves no crop rotation, because all the productive land is turned into grassland for meadow or for harvesting as feed to be placed in storage. Usually a legume like clover is planted along with grasses. Cattle are pastured in summer on the tallest meadows and fed in winter largely or entirely on products harvested from the grasslands. Under this system, the pasturing is rotated rather than the crops; that is, the ani¬ mals are pastured perhaps ten days in one meadow, then ten days in another, and so on. Animal manure is returned to the fields in winter. Lime and fer¬ tilizer may also be applied each spring. In these ways, the need for crop rota¬ tion is avoided. Contour cultivation and strip cropping Contour cultivation is used on hill¬ sides and sloping fields. Plowing and planting are done around the hill in¬ stead of up and down it. Why? Terrac¬ ing is a special form of contour culti¬ vation. Terraces are built on hillsides, and crops are raised on the terraces. Strip cropping (Figure 25-4) is used on hillsides and, recently, on level fields, too. Broad strips of an open-tilled crop like corn or potatoes alternate with strips of a close-growing crop, like clover or wheat or grass for meadow or hay. The close-growing crop slows down the runoff of rain water and re¬ tards erosion from the whole area. When it is a legume crop, it also re¬ duces soil depletion and makes possible crop rotation within the strips. Soil Conservation Service 25-4 STRIP CROPPING Not only is strip cropping used on this Iowa farm to reduce erosion, but crops are rotated from strip to strip to reduce soil depletion. Soil-binding plants A plant cover is perhaps the best natural protection against erosion. When the natural plant cover has been removed, erosion increases rapidly (Figure 25-2). The best way to control erosion is to establish a new plant cover as quickly as possible. Workers in the Forest Service helped to solve a pressing problem of this type in Southern California not many years ago. The chaparral (shap uh ral) thick¬ ets (dense growth of thorny shrubs or dwarf evergreen oaks ) that spread over the steep mountains there are among the most highly inflammable forests in MAN AND CONSERVATION 625 the country. Once a fire starts, it burns fast and furiously until everything is burned to the ground. After one such fire, rainstorms were washing away ter¬ rifying quantities of soil. Forest Serv¬ ice workers were looking for a way to establish a new plant cover quickly in these burned-over areas. They tried out more than a hundred species of plants before they found the answer. And what do you think it was? Common black mustard. Airplanes can sow mustard seeds over 10,000 acres in a week. Within a few weeks, the plants are two feet high and serve as excellent plant cover in preventing severe erosion. Grasses are excellent soil-binding plants and are widely used. Several legumes are useful, and even the weeds that invade any exposed land soon re¬ duce the erosion. Trees of almost all kinds may serve as soil-binding plant cover. In the con¬ trol of gullies, for example, black lo¬ custs, hazelnuts, and some fruit trees are useful. Forests naturally keep the runoff of water at a minimum, partly because the trees break the force of the fall of the raindrops and partly because a forest floor, with its litter of leaves and undergrowth of small plants, serves as a huge natural filter that holds the rain water and allows it to penetrate the soil rather than to run off. Restoring organic matter Organic matter may be returned to the soil in several forms: (1) crop residues, ( 2 ) animal manure, and (3) green-manure crops. Crop residues include such materials as stubble and straw from wheat and rye; stalks of corn, cotton and sorghum; parings of apples and potatoes; pods of peas and beans; and any other of the crop materials we do not use. Until comparatively recently most of these crop residues went to waste. For years now, gardeners have been saving all crop residues and building 25-5 DEEP PLOWING In many parts of the United States, plowing to a depth of eight inches or more has been given up as wasteful (especially if the topsoil layer is thin). But in the dry Southwestern grasslands, deep plowing results in less wind erosion than would be caused by scratching the surface with a rotary tiller (Figure 25-6). The scene of this photograph is a farm in Dallam County in the Texas panhandle. U.S.D.A. U.S.D.A. 25-6 SURFACE TILLING In contrast to the turning of earth with a plow, tilling soil with a rotary tiller merely stirs the surface of the earth, while at the same time it works into the ground the residue or stubble of the previous crop. a compost ( kom pohst ) heap of them each year. Cuttings from the lawn, corn husks, all fruit and vegetable parings, all organic “garbage” from the kitchen are placed in the compost heap, where bacteria of decay attack them. Each spring, decayed compost is added to the garden plot. Those who are using this means of restoring organic matter to the soil write glowingly of the im¬ proved yields of their gardens. Even in large-scale cultivation, many grain fields are disked rather than plowed; this works some of the crop residues into the topsoil and leaves some of the litter on top of it. The litter helps pre¬ vent runoff and erosion. In one test plot this procedure increased grain yields by as much as seven bushels to the acre in five years’ time. The use of animal manure on culti¬ vated fields is an old practice. The com¬ bining of dairy and grain farming is a wise practice, because the grain helps to feed the animals and the animal manure helps to restore organic matter to the soil. A green-manure crop, as the name implies, is a crop that is grown only to be plowed under or disked into the top¬ soil. For years, many gardeners have been sowing their gardens in rye, or rye and a legume, in the fall and plow¬ ing it under in the spring. Legumes such as clovers, vetches, and soybeans are being used more and more as green- manure crops. Organic matter and the plow We have witnessed a change in plow¬ ing methods during the past ten or fif¬ teen years. More and more gardeners have given up plowing with a plow¬ share that turns the topsoil under eight inches or more (Figure 25-5). Instead they use a rotary tiller (Figure 25-6) that stirs the surface, perhaps about six inches deep, and at the same time works a green-manure crop, animal manure, crop residues, compost, or MAN AND CONSERVATION 627 some other organic matter into the top layer of soil, leaving part of the residue on top. Lon mm ' - j|^B: rj Ok R»| i '\F\M «, ' 8rav&2K*3BB pKp^Si jv-> dft{ face water shortages? Why is the water table falling, in some areas as much as 10 to 15 feet a year? You know the answer. We are using more water than we used to. For one thing there are more of us, some 170 million people in the United States in 1957. Each of us needs to take in, each year, some 200 gallons of water (in the form of water or milk or other foods with water in them). For another thing, as one writer put it, we have become a nation of “water gluttons.” In how many ways do you use more water than your grandparents used? Stop and list all you can think of. Don’t forget water¬ cooling systems, swimming pools, and sewage systems, among many more. The people of the United States today use about 170 billion gallons of fresh water a day, and the amount may double by 1975. We face water shortages in some places because people in those places use water faster than rain, snow, and sleet replace it. Water conservation Water conservation is tied closely to soil conservation. Anything that con¬ serves one may help to conserve the other. Much of what you have just read applies to water conservation. One phase of the problem that deserves spe¬ cial mention is flood control. Floods are little more than headlines in a paper to many people, but a real tragedy to those in affected areas, as a May, 1952, bulletin of the Soil Conser¬ vation Service puts it. This bulletin, Where Floods Begin, discusses the com¬ plete treatment of the Sandstone Creek Watershed, one of many small water¬ sheds in the Washita River valley in Oklahoma and Texas. The bulletin points out that creeks flood more land than rivers do. In the Washita valley, 72 per cent of all flood damage occurs along small streams before they flow into the river. The bulletin shows, too, what a better approach to flood control can do. What has been done? A land-treat¬ ment program and a water-control pro¬ gram were drawn up and applied. The use of cover crops and strip cropping, the seeding of grasslands, the use of terracing, wiser use of each parcel of land, and some other procedures made up the land-treatment program. As part of the water-control program, small retarding dams with grass-lined spill¬ ways were built far up the tributary streams. These dams retard the rush of water downstream. As a result, it is esti¬ mated that annual flood damage will be reduced some 98 per cent in the Sand¬ stone Creek Watershed. There are many phases to the water conservation problem (Figure 25-8). The falling water table in many parts of the nation is causing serious water shortages in many cities and on many farms. The problem is to stop the rapid runoff of water after a rain, so that the water goes into the soil instead of “run- ning off to sea.” The best method of slowing down the runoff in many places is to restore the natural plant cover to watersheds. 25-8 WATER CONSERVATION IN ARIZONA Canyon Lake, near Phoenix, Arizona, is the third in a series of four man-made lakes that supply water and electric power to that city, and also supply water needed for irrigation of croplands. Projects such as this one have made it possible to store runoff water following rains and turn former desert land to the cultivation of some of the best crops produced in the United States. MAN AND CONSERVATION 631 Irrigation is a method of supplying water to yards, gardens, and farmland, where rainfall is insufficient to support crops. Much of our Southwest could raise no crops at all without irrigation. With irrigation, even the desert bears abundantly (Figure 25-9). Several methods now in use are making irriga¬ tion more effective in the Southwest. 1. Farmers have learned that many crops can be grown with much less wa¬ ter than was formerly used. So every effort is made to use no more water from the irrigation ditches than is neces¬ sary. 2. Experts have proved that the cot¬ tonwood trees that spring up along irrigation ditches use up huge amounts of the water. So the cottonwoods are now being; removed. 3. Irrigation canals and ditches are being lined with concrete in many places in the Southwest. This saves wa¬ ter by preventing seepage into the 25-9 IRRIGATED COTTON FIELD IN ARIZONA Water from a man-made lake such as the one in Figure 25-8 has helped to turn this former desert land into choice cropland. Marion A. Cox ground beneath the canals and ditches. Another big possibility for increasing our water supply is to learn to convert sea water into fresh water cheaply enough to do so on a large scale. In¬ cidentally, the sea could become a new source of many materials we need, if we could learn how to extract them at a reasonable cost. For example, in each cubic mile of sea water, besides hydro¬ gen and oxygen atoms in the water it¬ self, there are 166 million tons of useful atoms, of which some 143 million tons are table salt (a compound of sodium and chlorine atoms). To date, we have not solved the problems involved in tapping the material resources of the sea on a huge scale on a paying basis. We may yet do so. If we do, it will help solve our water problems. Summing up: soil and water conservation The water conservation problem is far from solved, as repeated water shortages in many places prove. Wider application of what we already know is helping, but the work must go on and on. As you well know, people today have become soil-conservation conscious. The soil conservation districts have played a major role in making them so. The countv extension services and 4-H J clubs, the former CCC camps, and other federal agencies have also contributed. So have state departments of soil con¬ servation and many private groups and organizations. Conservation education in both public and private schools has been another factor. We have made great gains in recent years, hut the work must go on. It will take the co¬ operation of all the people to keep our soil productive and our water supplies adequate. FOREST CONSERVATION Today we cut and use more wood than any other nation in the world. Some six times as much wood per per¬ son is used in the United States as in any European country. It takes about 100 acres of spruce trees to make enough paper for a single Sunday edi¬ tion of a large New York newspaper. We cut or lose to fire, insects, and dis¬ ease considerably more sawtimber each year than is replaced by new growth although we are steadily cutting down this margin of loss. Forest insects, such as gypsy moths, and diseases of forest trees cause a greater yearly loss of commercial tim¬ ber in the United States than does fire, but fire also does great damage. Most forest fires are started by human be¬ ings. Twenty per cent of them are blamed on careless smokers; most of the other eighty per cent are due to poorly extinguished campfires, unat¬ tended trash fires, fires that have been deliberately set, lumbering, sparks from railroad engines, and aspects of other human activities. Almost every forested area in the nation has had one or more serious fires. The need for forest conservation is obvious. Forests as continuing crops Today, wise lumbermen look upon a forest as a continuing crop, from which only certain well-chosen trees are to be cut. The trees are so felled that they do as little damage as possible to other trees and to the undergrowth of young trees (Figure 25-10). This allows the young trees to grow up and replace those cut. A forest managed in this way gives a continual yield of lumber. Trained foresters apply this policy in our national forests, where more than U.S. Forest Service 25-10 FORESTS AS A CONTINUING CROP The mature trees of this forest have been cut in such a way as to leave the younger trees undamaged. In this way a continuing crop is made possible. 7 billion board feet of timber are har¬ vested each year. Many privately owned forests are also being handled as con¬ tinuing crops, especially in large hold¬ ings. But only a small fraction of the smaller holdings are so handled. The more widely this policy is applied to all forest lands, the better are our chances of having a continuing supply of lum¬ ber and wood products. Forests and animals Forest managers also consider the re¬ lations of forests to their animal inhab¬ itants. Grazing animals, whether wild (such as deer) or domesticated (such as cows and sheep) have a marked ef¬ fect upon many forests. Where grazing is heavy in hardwood ( deciduous ) for¬ ests of the East and South, the under- MAN AND CONSERVATION 633 growth of tree seedlings, shrubs, and herbs may be partially or almost com¬ pletely destroyed and the soil seriously compacted (hardened or compressed). If this heavy grazing is allowed to con¬ tinue, there will be no young trees to replace the old ones, and eventually the forest may die out. Damage from grazing animals in evergreen or conif¬ erous forests is less serious. However, forest rangers in our great national for¬ ests control the numbers of deer, elk, and livestock to prevent damage both to young trees and to forage plants. The rangers try to keep the number of grazing animals in balance with the available forage on the land. Small mammals also play an impor¬ tant part in the life of the forest. Porcu¬ pines, squirrels, mice, and other small mammals, particularly other rodents, may eat tree bark, young seedlings, and tree seeds, but under natural condi¬ tions the harm they may do is out¬ weighed by the good. For one thing, rodents carry and plant many tree seeds, such as acorns and other nuts. The planting of forest-grown black wal¬ nuts has been done largely by squirrels. They carry the nuts from beneath the trees and bury them at a distance. Not only do rodents carry seeds, but some of them burrow into the soil and bring about changes in it that make it suit¬ able for certain tree seedlings. On some of the rocky plateaus of the Northwest, pocket gophers help to bring about soil conditions that are suitable first for grass and then for yellow pines. The value of birds as destroyers of in¬ sects has been quite generally recog¬ nized, but few persons realize that toads and snakes and many small mammals J play a large part in holding insect enemies in check. Shrews, moles, mice, chipmunks, some squirrels, and other small mammals were once looked upon as more harmful than useful in any for¬ est or wood lot. However, studies in northeastern forests, reported in 1940, show that the diets of these animals range from 20 to 75 per cent insects. Ecologists are beginning to think our forests would be very poor without the small mammals that inhabit them. One of the conclusions drawn from extensive studies of forest animals is that it is well to try to fight any par¬ ticular enemy animal species (insect pests, for example) by encouraging its natural enemies, as well as by fighting it directly. Insect sprays and dusts are necessary when insect populations erupt, but biological control is of far greater over-all value when it can be accomplished. Forest conservation today Many public and private agencies are busy all the time with the conservation of our forests. They are doing a better and better job. And yet we still have an average of over 200 forest fires a day. Why? Mostly because so many people deliberately set fires or are careless with matches, cigarette butts, trash fires, and campfires. We still are using the continuing crop method of lumbering on far too little of our privately owned timberland. Government agencies and just some of the people can t carry out a wholesale plan of forest conservation. All the peo¬ ple need to help. Forest owners and farmers can apply wise methods to their use of wood lots and stands of timber. All people can support intelligent legis¬ lation for better and better conserva¬ tion. Nearly everybody can help to plant trees where they are needed, even as high school students from Portland, Oregon, are doing on the Tillamook 634 LIVING POPULATIONS AND THEIR INTERDEPENDENCE Burn. Everybody everywhere can help to stop the carelessness that causes some 90 per cent of our forest fires. Conservation of forests is everybody’s job. WILDLIFE CONSERVATION You may have heard of the extinct heath hen and passenger pigeon, ani¬ mals that vanished in the face of ad¬ vancing civilization. Saving other spe¬ cies of wildlife from total destruction is part of the wildlife conservation pro¬ gram, but there is far more to it than that. Wildlife conservation today means nothing less than the application of ecological principles on a nation-wide scale. Intelligent wildlife conservation means first of all that a balance must be maintained in any biome where wildlife is to flourish. This calls for a wide knowledge of natural foods, cover needs, and other factors in the natural homes ( habitats ) of the wildlife we wish to conserve (Figure 25-11). It also calls for knowledge of the ecolog¬ ical relations among all the organisms in each habitat. Today those most con¬ cerned with wildlife conservation try first of all to supply and maintain the best possible habitats. After that they try to apply whatever measures work best for the protection and best use of the wildlife resources in each habitat. Wildlife conservation agencies The Fish and Wildlife Service takes the lead among federal agencies in the wildlife conservation movement, but many other agencies play important parts. The Forest Service and the Soil Conservation Service are examples. Conservation farming and reforesta¬ tion also contribute. To a great extent, however, it is the state wildlife departments that carry the chief responsibility in this field. With the exception of conservation measures for migratory birds and na¬ tional forests, the states themselves di¬ rect the wildlife conservation programs. Many groups and organizations of private individuals co-operate exten¬ sively. For example, the local sports¬ men’s clubs often make wildlife con¬ servation a chief aim. The National Wildlife Federation, the Isaac Walton League, the American Forestry Associa¬ tion, and the American Nature Associa¬ tion are other examples. We shall explore a few modern phases of wildlife conservation. Refer to the list of references at the end of this chapter for more information. 25-11 BANDING THE LEG OF A WILD DUCK Game management and wildlife conserva¬ tion agents learn much about the migra¬ tory habits of ducks by catching banded ducks and keeping records of where they were found. Rex Gary Smith, from U.S. Fish and Wildlife Service MAN AND CONSERVATION 635 Wildlife refuges The first tract of land set aside as a wildlife refuge was in California. This was in 1870. Around the turn of the century, other states began to do like¬ wise— Indiana in 1903 and others soon after. Bv 1942 we had some 17/2 million J acres of wildlife refuges. In the beginning, the idea was to set aside an area for a particular kind of wildlife and to prohibit hunting or fish¬ ing or any other interference in that area. No attempts were made to tend the refuges or to control conditions within them. During the 1920 s it be¬ came obvious that this “set-aside and let-alone" policy wasn't enough. All too often the “protection" of big game in such conditions resulted in its too-rapid increase until the food supply was in¬ adequate and the species began to starve. Or sometimes large numbers of animals were released in a refuge in which the living conditions had not been studied. During the past 25 years or so, a new phase of wildlife management has been developing. The keynote of this phase is that all measures adopted to protect wildlife shall establish and maintain as nearly suitable conditions as possible for each species we wish to protect. Wildlife refuges are no longer “set aside and let alone." Trained ecologists study each refuge to discover all the interrelated factors and their effects upon a particular species. Refuge man¬ agers are appointed to direct the use of each area. Censuses of the population of various species are made frequently to see if they are increasing or decreas¬ ing, and measures are adopted to offset any marked shift in either direction. Modern wildlife managers, thorough- O 7 o lv trained in ecology, look upon all bounties as mistakes. The wholesale killing of any common species of animal is likely to have serious consequences in the biome. The control of so-called enemy species is usually more wisely done by working hand in hand with natural processes, instead of by using artificial methods of control. In rare cases, natural and artificial control are purposely blended. For ex¬ ample, plans for wildlife management today sometimes include a new aim: the conscious production of a surplus population of a given species in an area, to be followed by licensed hunting or fishing of that species. Just as wise lum¬ bering is now done in our national for¬ ests, so is wise hunting and fishing per¬ mitted in many of our wildlife refuges when surpluses have been produced. In 1940 in the Chautauqua Refuge in Illinois, some 9,000 anglers caught more than 125,000 fish during the four and a half months when fishing was per¬ mitted. Similar takes of game animals and birds, fur bearers, and other wild¬ life under wise supervision in our ref¬ uges are not only a source of pleasure to sportsmen, but also a measure of con¬ trol in keeping populations in balance. Ecologists explain that wildlife, like timber or wheat or beef or mutton, is a product of the land. They recommend that the management of areas set aside for wildlife be tied in with the general plans for wise land management in the area. Artificial breeding and restocking You have probably seen or read about fish hatcheries and their work (Figure 25-12). They are one example of the practice of artificial breeding to restock wildlife habitats. Game birds, such as pheasants, are also bred and released. Most checks made after birds are re¬ leased show that this is often a waste- 636 LIVING POPULATIONS AND THEIR INTERDEPENDENCE ful procedure. Sometimes many of the animals die after release into a wild habitat. Very few ever turn up in the sportsman’s bag. Breeding and releas¬ ing game birds is one of the most expen¬ sive and least successful measures in use. Fish hatcheries supply billions of eggs and fishes to restock rivers and lakes and ponds. In Michigan, for ex¬ ample, trout are cultivated in the state hatcheries and supplied to many coun¬ ties to release in the lakes. In New York State, hatcheries cultivate as many as 2 million young shad each year to be re¬ leased in the Hudson River. Many states also have laws that regulate the pollu¬ tion of streams, since pollution often renders the water unfit for fish. Control of enemies You have already read of several at- tempts to protect wildlife or chickens or some crop plant by killing off the natural enemies, such as hawks in the case of chickens, or covotes and moun- tain lions in the case of deer, or crows in the case of corn. In some carefully controlled situations, this is necessary and beneficial, but all too often it dis¬ turbs the natural balance so much as to be positively harmful. It certainly is more harmful than helpful to kill off the hawks and crows. Harvesting One of the phases of wildlife conser¬ vation most in need of improvement has to do with “harvesting the crop.” Intel¬ ligent harvesting is one of the most im¬ portant measures of control. But all too often no one in a given state has the proper knowledge or authority to direct it. Often, too, sportsmen themselves fail to understand the need for it. For ex¬ ample, sportsmen may be unwilling to E. P. Haddon, from U.S. Fish and Wildlife Service 25-12 TROUT SPAWN IN A HATCHERY The spawn being poured into the barrel will soon be on their way to the culture station of the U. S. Fish and Wildlife Service in Yellowstone National Park. From there the young trout, when old enough, will be released into lake waters. kill does (female deer), even when the total situation makes it desirable. This very fact has spelled catastrophe for more than one deer herd. Too much game can be as disastrous as too little. Wise harvesting can prevent disaster. The protection of birds About 750 different species of birds breed in the United States and Canada. More than half of them are land birds of the type usually referred to as song¬ birds. Most states prohibit the killing of songbirds, but unfortunately many boys break the law. Cats are destroyers of birds, too, especially homeless cats. Such cats should be turned over to the proper authorities. MAN AND CONSERVATION 637 Hugh Spencer 25-13 LADY'S SLIPPER This lovely flower is growing more and more scarce, mainly because its natural habitat has been de¬ stroyed in many places. Migratory game birds, like wild ducks and geese, come under the pro¬ tection of the federal government. Un¬ der treaties with Canada and Mexico, and under a number of laws passed by Congress, birds that migrate between Canada, the United States, and Mexico are protected. Federal laws prohibit the hunting, killing, capture, sale, or transportation of protected migratory birds, except as authorized under federal regulations. The sale of wild birds is prohibited ex¬ cept for waterfowl raised on farms for propagation or food purposes. Still oth¬ er federal laws make federal aid avail¬ able to state wildlife conservation de¬ partments. Every state in the Union has a professional conservation staff. One federal statute requires that all persons over 16 years of age must at the time of hunting game birds (wild ducks and wild geese, including the small dark geese called brant) have on their person a current Migratory Bird Hunt¬ ing Stamp. These stamps are issued an¬ nually and sold by post offices for $2.00 each. The money that is collected from the sale of duck stamps is used to in¬ crease the protection over our water- fowl. Most of it is used by the Fish and J Wildlife Service to help establish and maintain waterfowl refuges throughout the nation. Part of this money is being used to help restore certain large marshes in the Northwest, so that they may once more become the waterfowl havens they were before mistaken drainage projects ruined them. Most states also have laws that regu¬ late the hunting of game birds; they limit the number of birds a hunter mav J kill and prohibit their sale entirely. What can you do? You can do many things to help pro¬ tect the birds, no matter where you live. Here are some suggestions. 1. You can help to eliminate the esti¬ mated 2 million stray cats by turning any you find over to the proper au¬ thorities in your community. 2. You can keep sunflower seeds, grains, suet, and water on a board, especially during the winter months. 3. You can join or help to organize a local group to establish local bird sanctuaries. 4. You can supply birdhouses if you want to attract birds to your yard. Specifications are available from the Fish and Wildlife Service in Washing¬ ton, D.C., or from your state depart¬ ment of conservation, or from the Na¬ tional Association of Audubon So¬ cieties. 5. You can help to build up a senti¬ ment against the shooting of songbirds by careless or ignorant boys. 638 LIVING POPULATIONS AND THEIR INTERDEPENDENCE 6. You can plant shrubs and other plants that offer shelter and nesting places, or food in the form of berries and other fruits. Lists of desirable plants are available from the sources named in item 4. 7. You can help prevent the shooting of crows, hawks, and owls, even though some varieties are not protected by law. Wild-flower conservation Many of our wild flowers must be listed among the vanishing Americans. Those plants which require the cool, shady, moist conditions of the virgin forest have naturally grown more and more scarce with the continued cutting of these forests. On the other hand, plants that thrive in fields, fence rows, open woods, and meadows have in¬ creased in numbers and range. Among these latter flowers are goldenrod, as¬ ters, violets, spring beauties, and blu¬ ets. All of these and many other wild flowers that live in similar conditions may be picked freely without danger of eliminating them. This is not true of such flowers as the delicately scented trailing arbutus or the lovely pink or yellow lady’s slipper (Figure 25-13) or the exquisite gentian about which Bryant wrote the poem, “To a Fringed Gentian.” These flowers grow more and more rare, in some places because their natural homes have been destroyed, in others because of ruthless picking for commercial sale. Such flowers as tril- lium, flowering dogwood, azalea, moun¬ tain laurel, rhododendron, Dutchman’s breeches, and squirrel corn are also listed among those needing protection. Many states have passed laws that prohibit the picking of particular kinds of wild flowers. The Wild Flower Pres¬ ervation Society is carrying on a gen¬ eral program for the conservation of wild flowers. The establishment of a National Wild Flower Day was recom¬ mended in 1919, and many states and communities now recognize such a day at whatever time is most appropriate in each area. Wild flower sanctuaries, both public and private, have been es¬ tablished in many parts of the country. Many state and national parks help to preserve the wild flowers for all of us to enjoy. But some of the people can’t save the vanishing wild flowers. It calls for the co-operation of all of the people. CHAPTER TWENTY-FIVE: SUMMING UP Conservation problems are mostly man-made; they can also be solved by man. We already have made great gains in ecological knowledge which can guide an over-all conservation program. To a considerable extent ecological principles are guiding conservation ac¬ tivities today, but many obstacles still block their full application, just as many factors block the full application of health knowledge among all the peo¬ ples of our nation and of the world. Co-operation is the keynote of conser¬ vation— co-operation of all persons in restoring and maintaining natural equilibria that serve human interests. U.S. Forest Service MAN AND CONSERVATION 639 Your Biology Vocabulary Make sure you understand and can use the following terms correctly. humus soil depletion crop residues compost heap contour cultivation topsoil subsoil trace elements crop rotation green-manure crops forests as continuing crops strip cropping cover crops erosion Testing Your Conclusions Leaf through this chapter again. As you do so, make a list of things you can do to help conserve our biological resources. Then pick out one item on your list and explain in more detail just how you can carry it out. More Explorations 1. Studi / of soil composition. You can easilv examine the make-up of a soil sample. Do these two things. a. Put about % cup of topsoil in a tall glass jar. Add enough water to cover the soil bv about an inch. Cover the jar and shake well. Let the mixture stand until the soil particles have settled. Look for layers in the settled soil. What do you discover? b. Place two small glass jars in water, bring the water to a boil, and let it boil for at least 20 minutes. When the jars are cool, add a half-pint of fresh pasteurized milk to each jar. To one jar add also a teaspoon of topsoil. Cover both jars and keep them in a warm dark place for from ten days to two weeks. How do you explain the differ¬ ences in the appearance and odor of the milk in each container? 2. A national wildlife organization. The National Wildlife Federation publishes wildlife conservation stamps each year to help raise money to use in their conservation pro¬ gram. You can get the stamps from the National Wildlife Federation, 3308 Fourteenth Street, N.W., Washington 10, D.C. 3. A field trip. Virtually every community contains one or more places that illustrate either the need for conservation or methods used in conservation. Even in a city, a park or a lawn or a garden may show either or both situations. Plan a field trip to such a place. Here are some suggestions. a fish hatchery a fur farm an eroding hillside a highway with new roadside shoulders a reforested area a wood lot a state or national park or forest a fire lookout in a forest a wildlife refuge a large dam 640 LIVING POPULATIONS AND TIIE1R INTERDEPENDENCE Thought Problems 1. Years ago at the University of Missouri the runoff of water from grasslands was com¬ pared with that from corn fields. The researchers discovered, among other things, that it would take 56 years to erode seven inches of soil in one place and 3,500 years to erode the same amount of soil in the other. Which would take the shorter time for erosion, the grasslands or the corn fields? Why? 2. In 1708 New Hampshire passed a law forbidding anyone to cut a tree more than two feet in diameter without permission from the government. At the time, huge logs from the largest trees were each bringing as much as one hundred English pounds (between $400 and $500) in the English market. Would you say the law just men¬ tioned was aimed at conservation? Why? Further Reading 1. Breaking New Ground by Gifford Pinchot, Harcourt, Brace, New York, 1947. This is the lively autobiography of a famous conservationist. It traces the growth of the modern forest conservation movement. 2. Water: 1955 Yearbook of Agriculture, U.S.D.A., discusses present and future uses of our water supplies, their availability and scarcity in various parts of the country, and many aspects of water conservation. 3. Conservation Education in American Schools, Yearbook of the American Association of School Administrators, National Educational Association, Washington, D.C., 1951. This is a valuable guide to the teaching of conservation in the public schools. 4. Burning an Empire by Stewart H. Holbrook, Macmillan, 1943, tells the story of many destructive forest fires, including the Tillamook fire. 5. Many excellent government publications are available. The following are especially recommended. They are available from the Superintendent of Documents, Govern¬ ment Printing Office, Washington 25, D.C. Know Your Watersheds, U.S. Forest Service, 1948. A Summanj of the Timber Resource Review (reprinted from Timber Resources for Americas Future, Forest Resource Report No. 14), Forest Service, U.S.D.A., Janu¬ ary 1958. (For more detailed information, the complete Timber Resources for America’s Future is available from the same source.) Trees: 1949 Yearbook of Agriculture, U.S.D.A., 1949. Making Land Produce Useful Wildlife, U.S.D.A. Farmers’ Bulletin 2035, 1951. Youth Can Help Conserve These Resources— Soil, Water, W oodland, Wildlife, Grass, Soil Conservation Service, U.S.D.A. Information Bulletin 52, 1951. What Is a Conservation Farm Plan ? Soil Conservation Service, U.S.D.A. Leaflet 249, 1948. 6. Soil Conservation Service Films (Soil Conservation Service, U.S.D.A.) and Forest Service Films (U.S. Forest Service). A single copy of each list may be obtained free. 7. What Man May Be, The Human Side of Science by George R. Harrison, Morrow, 1956, is a very readable book containing much human ecology. Chapter Five, “The Human Body,” pages 88-113, is especially interesting. MAN AND CONSERVATION 641 BIOLOGY AND SPACE TRAVEL Earth: The Great Launching Pad In May, 1952, two monkeys and two mice were passengers in a United States Air Force rocket which was hurled in¬ to the stratosphere from Holloman Air Force Base in New Mexico. This rocket reached a velocity of 1,909 miles per hour and a peak elevation of 36 miles (about 190,000 feet). Both monkeys were recovered alive and apparently unharmed. The one pictured on the next page, a Philippine macaque (mah kahk), was photographed late in 1958 in a Washington zoo, where he has lived since his historic flight. To all ap¬ pearances he is and has been in good health. By 1957, a number of other experi¬ ments had helped to prove that ani¬ mals can travel at high velocities to great heights without being seriously harmed. Biological problems of space flight For years, doctors and other biol¬ ogists have been investigating the bio- 642 BIOLOGY AND SPACE TRAVEL House of Photography logical problems involved in space flight. Some of these problems are: 1. How will the necessary high veloc¬ ities affect the human body? A rocket, in order to overcome the earth’s grav¬ ity and escape into space, must reach a velocity of up to 25,000 miles per hour. Experiments have now shown that a high velocity, in itself, is no problem to men adequately protected in a sealed space vehicle, as long as the velocity is fairly constant. Within a space ship, men can travel about as comfortably at 25,000 miles per hour as they now trav¬ el at 300-400 miles per hour in a com¬ mercial airliner. 2. How will the necessary accelera¬ tion at blast-off affect man? A space ship that accelerates to 25,000 miles per hour within a few minutes after blasting off subjects its passengers to tremendous pressures of up to ten times the normal force of gravity. Many experiments are being directed toward finding exactly what stresses the human body can take. 3. Hoiv will conditions of zero grav¬ ity, in which men and objects have no weight, affect man? The sensation of weightlessness has many implications, both physical and psychological, for space travelers. Unless an artificial “gravity” were to be supplied, there would be no right side up in a space ship, no walking by pushing off from the floor, no taking of a shower in the usual manner. Anyone who stood with his feet against one side of the space ship and pushed off in the normal man¬ ner for walking would hit the opposite side of the space ship. And water be¬ ing forced under artificially applied pressure from a showerhead would pin a man taking a shower against the op¬ posite side of the shower stall. (Unless some means of creating water pressure artificially were devised, water would not run out of a showerhead at all.) 4. How will man supply the neces¬ sary food and oxygen for his body in a space ship? In space there is no air to breathe, no food to eat. Man must take with him plant life that will help sup¬ ply both requirements. In other words, his space ship must be a balanced biome, much as the sealed bottle in Figure 24-2 (page 605) is a balanced biome for a guppy, two snails, and several water plants. 5. Will the cosmic rays at high al¬ titudes and the known bands of heavy SPACE PIONEER This Philippine macaque of the United States Air Force (Retired) is a veteran rocket flier, having survived a flight that took him 190,000 feet above the earth in May, 1952. Because of his unusual accomplishment, he still must “report” for his annual physical examination. To date he has suffered no harmful physical effects from his flight. Wide World Photos EARTH: THE GREAT LAUNCHING PAD 643 radiation that begin at about 250 miles above the earth hinder further space travel ? Much research is yet to be done on this point; at present, opinion is that while cosmic rays and radiation zones represent dangers, they should not dis¬ courage us from attempting space flights, or at least from planning flights while awaiting further research. The story of the flight of a little squirrel monkey in a mighty Jupiter missile on December 13, 1958, may well introduce a few of the many excit¬ ing, recent space-travel experiments. Recent experiments in space travel A little squirrel monkey, much like the one pictured on the next page, was trained for weeks until he was used to being “dressed” for space travel and usually fell asleep soon after being placed in a well-padded, sealed cap¬ sule. All these preparations took place under the general direction of Captain Norman Lee Barr, M.D., Director of the U.S. Navy’s Bureau of Medicine at the Navy’s School of Aviation Medi- cine and Research at Pensacola, Flor¬ ida. After careful preparations, it was de¬ cided to make the great experiment on December 13, 1958. The dav before, doctors once again “dressed” the 13- inch monkey, nicknamed “Old Relia¬ ble,” for space travel. They attached various small instruments to various parts of the monkey’s body, then placed him in the padded capsule. The instru¬ ments were to record such body proc¬ esses as pulse and breathing rates, blood pressure, body temperature, and voice, breathing, and heart sounds. The instruments were connected with a “broadcasting system” that would re¬ lay information back to the doctors on earth. On December 13, one half hour be¬ fore launching time, the capsule and its passenger were placed in the nose cone of a Jupiter missile on the launch¬ ing pad at Cape Canaveral, Florida. The monkey soon fell asleep, as was his custom. He was still asleep when the rocket left the pad. The take-off caused Old Reliable to wake up, but the instruments showed that he was not much disturbed. His pulse rate, on awakening, rose from 230 to 250, an increase of about the same proportion as that of a human being just awakening. For 20 to 30 seconds, the breathing rate was regular, but after that the monkey began holding his breath and exhaling in big sighs. His pulse rate rose again from 250 to 280. For 2/2 minutes, the rocket and its passenger hurtled outward to a distance of 290 miles, subjecting the monkey to a force or “pull” of some 10 times the force of gravity. Then the nose cone separated from the rocket and went into temp¬ orary free flight under conditions of neutral gravity that made the object and the monkey weightless. The listening doctors admit that they were excited. This was the moment they had been waiting for. They were about to “watch” a primate’s reactions while traveling close to 70,000 miles per hour in zero-gravity conditions. What happened? At once, the mon¬ key’s breathing returned to normal. In less than a minute, his pulse rate stead¬ ied down to normal. For the rest of the eight minutes and 20 seconds of free flight, all of Old Reliable’s responses were normal. He chattered away hap¬ pily as was his habit during waking hours on earth. As far as observers could tell, the weightless condition pro¬ duced no ill effects. 644 BIOLOGY ANTD SPACE TRAVEL On the return trip to earth, with a pull of some 40 times that of gravity acting upon his body for a little while, the monkey reacted with a consider¬ ably increased pulse rate and breath¬ ing rate, but he never lost conscious¬ ness. As soon as the parachutes on the nose cone opened at 8,000 feet, Old Reliable calmed down and remained so. Unfortunately, the nose cone was lost in the Atlantic Ocean, despite all efforts to recover it. The failure to re¬ cover Old Reliable was a keen disap¬ pointment, but the data derived from this 13-minute flight of a 13-inch mon¬ key seem to have blazed a highly hope¬ ful trail for human space flight. By the time you are reading these words, it is possible that one or more manned satellites will have been put in orbit, left there a week or so, and then returned to earth. To bring into focus the evidence that man really is entering the age of space flight, we shall list here a few of the many events of recent years. 1. In August, 1953, Lt. Colonel Mar¬ ion E. Earl flew a Douglas D-558-2 Skyrocket to an altitude of 83,325 feet (almost 16 miles) where 97 per cent of the earth’s atmosphere was below him. Of course, he rode in a sealed, pressur¬ ized cabin. He was unharmed. 2. On October 4, 1957, Sputnik I went into an orbit with a minimum al¬ titude of 160 miles and a maximum al¬ titude of 560 miles, traveling at about 18,000 miles an hour. Weight: 184 pounds. 3. On November 3, 1957, Sputnik II went into orbit with a minimum alti¬ tude of 140 miles and a maximum alti¬ tude of 1,017 miles, traveling about 18,- 000 miles per hour. Weight: 1,120.3 pounds. Sputnik II carried a dog, Laika (ly kuh ) , shown in the photograph on Official U.S. Navy Photo SQUIRREL MONKEY IN FLIGHT CAPSULE This space trainee is shown in a capsule like that in which Old Reliable, another squirrel monkey, was fastened during a rocket flight that took him 290 miles above the earth into space. The capsule is cushioned with foam rubber, and the monkey’s head and body are protected by a helmet and body sheath of rubber padding. Underneath the padding are tiny instruments that record pulse and breathing rates, blood pressure, voice, and other body processes. Old Re¬ liable’s space flight demonstrated beyond reasonable doubt that man can withstand without physical harm the acceleration necessary to reach escape velocity. page 646. Laika lived in a sealed cabin in the satellite for a week. 4. On January 31, 1958, Explorer I went into orbit with a minimum alti¬ tude of 220 miles and a maximum of 1,590 miles, traveling at about 18,000 miles per hour. Weight: 30.8 pounds. 5. On March 26, 1958, Explorer III went into orbit with a minimum alti- earth: the great launching pad 645 Sovfoto PASSENGER IN SPUTNIK II The dog Laika is shown in her cabin shortly before it was sealed and placed in the nose cone of a Russian rocket. The rocket was fired in No¬ vember, 1957, and the nose cone went into orbit as Sputnik II. Laika lived for a week on food and oxygen supplies stored in the satellite. During this time, Russian scien¬ tists were evaluating a steady stream of in¬ formation (radio signals from the satel¬ lite) on the dog’s physical condition. tude of 125 miles and a maximum of 1,735 miles. Weight: 30.8 pounds. 6. On May 25, 1958, Sputnik III went into orbit. This satellite weighed over a ton. 7. On December 18, 1958, Atlas went into orbit with a minimum altitude of 114 miles and a maximum altitude of 928 miles. Weight: several tons. Atlas carried a communications svstem de- J signed to record messages from the earth and play them back on cue. From Atlas, people heard the first human voice ever to come in from outer space, the voice of the President of the United States, Dwight D. Eisenhower. 8. On October 11, 1958, Pioneer was fired at the moon and reached an alti¬ tude of 71,350 miles above the earth. From there it fell back again, short of its goal, but holding the temporary record for highest altitude reached. 9. By the end of 1958, several pilots had flown Navy Douglas rockets and Air Force Bell rockets at altitudes of up to 25 miles. Balloon flights had car¬ ried men up to the 19-mile level. A North American X-15 rocket was al- readv scheduled for a 1959 manned J flight to an altitude of 100 miles above the earth. 10. On January 2, 1959, the first Cosmic rocket, nicknamed Lunik, but later named Mechta ( myetch tah ) , meaning “dream,” zoomed away from its pad somewhere in the Soviet Union, aimed toward the moon. On earth this multi-staged missile weighed some 250 tons. The last-stage rocket weighed about 3,245 pounds. The payload (in¬ struments to record conditions and send signals to earth) weighed about 794 pounds. On the evening of January 3, 1959, Mechta passed within 5,000 miles of the moon but did not go into orbit. In¬ stead, it sped on toward an orbit around the sun and was reported to have gone into orbit as a new “planet” between the orbits of the earth and Mars on January 6, 1959. Mechta had traveled close to 3,000,- 000 miles away from the earth when radio contact was lost. It had attained a velocity of 25,000 miles per hour to escape the earth’s gravity. In other words, its escape velocity was 25,000 mph. 11. On March 3, 1959, Pioneer IV, a 60 ton Army rocket, blasted off at Cape Canaveral, Florida, bearing a 13 pound pay load of instruments. The next day, it passed within 37,000 miles of the moon and later proceeded into an orbit around the sun. 646 BIOLOGY AND SPACE TRAVEL Official U.S. Air Force Photo EXPERIMENT ON ACCELERATION EFFECTS Lt. Col. John P. Stapp of the United States Air Force is shown strapped in a sitting position on a rocket sled that in five seconds time accelerated from 0 to 421 miles per hour. From left to right. Col. Stapp is being sub¬ jected to an acceleration force that reached 12 g’s. These are merely the high lights marking the first years of the space- flight age. But to some extent, they do indicate that man has at least partially solved some of the biological problems of space flight. Let’s look once more at each of those problems: 1. It has now been established that velocity, of itself, seems to have no ef¬ fect upon the human organism. But sudden acceleration or deceleration (loss of speed) does affect the human body and affect it seriously if main¬ tained for any great length of time. So EXPERIMENT ON DECELERATION EFFECTS Aboard the same rocket sled on which he was photographed during acceleration (see photographs at top of page), Col. Stapp is shown here as the sled decelerated, after the rockets burned out and the sled hit a zone of water (serving as a brake). From left to right, Col. Stapp is being subjected to a deceleration force that reached 22 g’s. Official U.S. Air Force Photo to conserve both fuel and health, es¬ cape velocity must be reached rapidly. 2. Rapid acceleration is a necessity if a space ship is to attain a velocity generation following a cross of an organism that is a homozygous dominant for a trait with another organism that is recessive for the same trait; usually the ratio is 3 to 1 in monohybrid crosses phloem (floh ’m) : the hollow tissue through which dissolved foods flow from one part of a vascular plant to another Pholcus (fol kus) : a genus of spiders with long, slender legs phosphates: compounds of phosphorus, needed in some quantity by plants, and ob¬ tained from the soil; also, organic phos¬ phates are compounds that play a part in releasing energy in muscle cells of many animals photosynthesis (foh toh sin thuh siss) : the process by means of which green plants (and certain algae of other colors) manu¬ facture glucose, using water and carbon dioxide in the presence of sunlight Phycomycetes (fy koh my see teez) : the class of fungi to which bread molds, potato blight, and certain other fungi belong phylum (fy lum — plural, phyla): a main divi¬ sion of the plant or animal kingdom Physalia (fy say lih uh) : a genus of coelen- terates that include the Portuguese man-of- war physical change: any change in matter that does not involve a change in the kinds or number of atoms in the molecules physics: the science of matter and its motions (energy) pineal (pin ee ’1) body: a structure present in the head of higher vertebrates and usually listed among the endocrine glands; its func¬ tion is not understood Pinus (py nus): the genus of pine trees pistil : the organ of a flower in which the ovary is located pistillate flowers: flowers containing pistils but no stamens pith : soft tissue in the center of dicot stems and filling most of the interior of monocot stems pituitary (pill tyoo ih ter ee) gland or body: an endocrine gland in the head of higher vertebrates; often called the “master gland” GLOSSARY 673 because it helps co-ordinate the work of other endocrine glands pit viper: a rattlesnake, copperhead, or cotton- mouth water moccasin, so called because of a “pit” on each side of the head between the nostril and the eye placenta (pluh sen tuh) : a vascular tissue formed early in pregnancy and through which a mammalian embryo gets food and oxygen and excretes wastes placental mammals: all mammals except egg-layers and marsupials; or, all mammals nourished before birth through a placenta planarian (pluh nair ee un) : any of certain common fresh-water flatworms plant hormones: chemicals that affect plant growth and behavior, as the auxins, which affect growth; produced in certain parts of most plants plasma (plaz muh) : the liquid part of the blood in animals that have formed elements (blood cells, etc.) in the blood plasma genes: structures present in the cytoplasm of cells and showing character¬ istics similar to those of chromosomal genes plasma proteins. See blood proteins Plasmodium (plaz moh dee um) : a genus of protozoa that cause malaria Platycerium (plat ih see rih um): a genus of tropical ferns including the staghorn fern Platyhelminthes (plat ee hel min theez): phylum of the flatworms, such as tapeworms and planarians; first phylum whose members have true organs platypus (plat ih pus): an egg-laying mammal of New Zealand; it lives along the banks of streams and pools and is a powerful swim¬ mer; also called duckbilled platypus Pleistocene (plyse toh seen) Epoch: the sixth epoch of the Cenozoic Era; it began roughly a million years ago and ended 10,000 years ago pleura (floor uh): the lining of the chest cavity of a mammal pleurococcus (ploor uh kok us) : any of cer¬ tain single-celled green plants commonly found in green smears on the shady side of tree trunks; also known as protococcus (proh tuh kok us); also, Pleurococcus or Protococcus , the genus of these plants Pliocene (ply oh seen) Epoch: the fifth epoch of the Cenozoic Era; it began roughly 10 million years ago and ended a million years ago plumule (pLOomyool): the part of a seed- plant embryo which produces the shoot polled cattle: hornless cattle pollen: grains that are produced by the anther of a flower or by the male cone of a conifer, and that in turn produce the male sex cells (sperm nuclei) pollen tube: the tube produced by a pollen grain, usually on a stigma of a flower or on parts of a female cone (in conifers); the tube grows toward an ovule, or the comparable structure in conifers, and serves as a passage¬ way through which sperm nuclei reach and fertilize egg nuclei Polychaeta (pol ih kee tuh) : the class of annelids to which Nereis and certain other segmented worms with prominent bristlelike structures belong Polygordius (pol ih gor dih us) : a genus of annelids with little or no external evidence of the segmentation of their bodies Polyorchis (pol ih or kiss): a genus of certain common jellyfish polyploidy (pol ee ploy dee) : a condition in which chromosome numbers are increased by multiples of the haploid number, pro¬ ducing organisms with chromosome counts of 3 n, 4 n, 5 n, and so on Polystichum (poh liss tih kum) : a genus of ferns including the Christmas fern pond scums: a common name for filamentous algae, such as spirogyras, which “float” like green scum on ponds and pools ponderosa (pon der oh suh) pine: a species of pines common in the western and south¬ western United States population: a particular group of closely re¬ lated individual organisms living in a parti¬ cular area; also called a deme population equilibrium: balance among the several populations in a biome pore : a minute opening, such as those in human skin, or those in sponges, or the lenticels and stomates in plants Porifera (poh rif er uh) : the phylum of the sponges posterior (poss teer ee er) end: the rear end or tail end of an animal potash: a compound of potassium, needed in some quantity by plants and obtained by them from the soil potassium nitrate: an organic compound of phosphorus, nitrogen, and oxygen precancerous condition: a condition that may, in time, lead to cancer; examples are prolonged irritation (as in poorly fitted dental plates) and moles predators (pred uh ters) : animals that prey on other animals pregnant (preg n’nt): being with young, as a female rabbit or other mammal primary root: the first root to sprout from a seed primate (pry mayt): any mammal that walks more or less upright; also, Primates (pry may teez), the order that includes these mammals principles of genetics. See dominance, in¬ complete dominance, gene interaction, segregation of genes, independent as¬ sortment, and linkage 674 GLOSSARY Proboscidea (proh bah sid ee uh) : the order of mammals that includes elephants prolactin (proh lak tin) : a pituitary hormone that stimulates the mammary glands of a mammal to secrete milk protective-muscular tissue: the outer layer of tissue in hydra and other coelenterates proteins (proh tee ins) : giant molecules of many kinds, but all composed of carbon, oxygen, hydrogen, nitrogen, and sometimes other elements (sulfur occurs in most pro¬ teins); one of the essential nutrients in both plants and animals; protein foods are lean meat, eggs, milk, cheese, nuts, beans, fish, and so on proteose: any of a certain class of compounds that are produced by the partial digestion of proteins; further digestion converts proteoses (and peptones) into amino acids prothallium (proh thal ee um — plural, pro- thallia): a type of plant produced by a fern spore and which, in turn, produces gametes; the sexual generation in a fern’s life cycle prothrombin (proh throm bin) : a blood or plasma protein, made in the liver, and of im¬ portance in the clotting of blood protists (proh fists): a name sometimes used for microorganisms that are not clearly differentiated as either plants or animals protococcus (proh toh kok us). See pleuro- coccus proton (proh ton): one of the constituents of the nucleus of all atoms protoplasm (proh toh plazm) : any living substance Protozoa (proh toh zoh uh) : the phylum of one-celled animals and a few microorganisms that live as colonies of cells pseudopod (soo doh pod): a projected lobe of cytoplasm by means of which an ameba or any of certain other protozoa moves psilopsid (sy lop sid) : a primitive vascular plant, known from fossils dating back to 300 million years ago ; two genera survive today psychology (sy kol uh jee) : the study of animal behavior and learning psychosis (sy koh sis) : a severe mental illness requiring extended psychiatric treatment; often the patient has withdrawn from the world of reality PTC : phenylthiocarbamide (fen il thy oh car buh myde), a substance which is tasteless to some persons but bitter to others; used as an indicator in testing inheritance of a single taste trait Pteridophyta (tehr ih doff ih tuh): the phylum of the ferns, club mosses, and horse¬ tails; members of the phylum are called pteridophytes (tehr ih doh fytes) Pteridospermae (tehr ih doh sper mee) : a group of extinct fernlike plants that bore seeds; the seed ferns ptomaine poison: a toxin produced by certain anaerobic bacteria that may be present in canned foods that were not thoroughly processed; more correctly called bacterial food poison ptyalin (TYuhlin): an enzyme in saliva; ii activates the change of starch to maltose pulse: the beat felt in an artery, as in the wrist of man pupa (pyoo puh — plural, pupae, pyoo pee) : the resting stage in the life history of moths and many other insects; it follows the larva stage, and is followed by the adult stage pupil: the opening in or near the center of the iris of the eye in vertebrates; light enters the eye through the pupil pure (for a trait). See homozygous purebred animals: animals that are homo¬ zygous for a large number of particular traits, as a result of generations of inbreeding pure-line breeding: in plants, breeding by self-pollination, or in animals, inbreeding, to produce or maintain purebred lines pyloric caeca (py lor ik see kuh) : the blind pouches of a fish’s intestine, located near the opening from the stomach; also, the blind pouches opening into the stomach of a grass¬ hopper or any of certain other insects; also, the digestive glands of a starfish pylorus (py loh rus) : the opening from an animal’s stomach into the intestine pyrenoids (py ruh noyds) : centers of starch manufacture in the chloroplasts of spirogyras and certain other algae quaking hog: a bog with a floating mat of plants, largely peat moss rabies (ray beez) : a virus disease of dogs and other mammals; fatal in man radial symmetry: symmetrical around a central point, as a wheel or a starfish radiation genetics: the study of plant and animal mutations induced by exposure to radioactive elements; many new varieties of plants and animals have been produced by this means radioactive elements: elements which grad¬ ually decay, giving off particles and rays (such as gamma rays) radioisotope. See isotope liana pipiens (ray nuh PiPeeenz): the spe¬ cies of frog commonly called the leopard frog reaction: a response of an organism to a stimulus reaction time: the time required for a nerve impulse to travel over a nerve pathway, as a result of a stimulus, and induce a response reagent (ree ay j’nt): any substance that, be¬ cause of its known properties while taking part in certain chemical reactions, is used as GLOSSARY 675 an indicator or as a means of measuring concentrations, and so on Recent Epoch: the seventh and current epoch of the Cenozoic Era; it began roughly 10,000 years ago receptor: a sense organ or sensitive nerve end organ recessive trail: the trait of a contrasting pair that does not appear in organisms that are hybrid with respect to that trait red marrow: the part of the bone marrow, in vertebrates, in which red blood cells and some white blood cells are made reduction division. See meiotic cell division reflex or reflex act: an almost automatic response or reaction to a stimulus; a response that requires no conscious thought reflex arc: a pathway through an animal’s nervous system, involving three or more neurons along which an impulse travels from the point of stimulus to the organ that makes the response reproduction: the process of producing off¬ spring reproductiv e glands : gamete-producing glands in animals Kept ilia (rep til ee uh) : the class of verte¬ brates to which lizards, snakes, alligators, and turtles belong; members of the class are called reptiles respiration: the oxidation of food within a living cell, including the taking in of the oxygen by the cell or organism and the giving off of the carbon dioxide produced; sometimes used to denote breathing only in higher animals respiratory enzymes. See enzyme respiratory system or breathing system: the system of organs in higher animals by means of which oxygen from the air or from air dissolved in water is brought into close contact with blood capillaries, as in gills or lungs; also, in many insects, a similar process that brings oxygen into contact with many parts of the body directly, as well as into contact with blood response: the reaction of an)^ organism to a stimulus retina (RKTihnuh): the light-sensitive mem¬ brane that lines most of the eyeball in vertebrates reverse mutation: a mutation from a new genetic trait back to the previous trait rheumatoid arthritis (roo mull toyd ar THRYtis): a distressing condition in man (and probably some other vertebrates), in¬ volving painful and swollen joints Kh f actor: a blood factor present in many people and in certain other vertebrates (in¬ cluding the Rhesus monkey, after which it was named) rhizoids (RYZoyds): rootlike structures of mosses and liverworts; composed of cells end to end in mosses, but single elongated cells in liverworts; not true roots Rhodophyceae (roh doh fy seh ee) : a class of red algae riboflavin (rv boh flay vin) : vitamin B2, which helps to keep the eyes, skin, and nervous system healthy in man Riccia (rik sih uh) : a genus of liverworts rickets: a disease of man and certain other vertebrates caused by the lack of vitamin D rickettsia (rik et see uh): an agent of disease, intermediate in size between viruses and bacteria; Rocky Mountain spotted fever, typhus fever, and a few other diseases are caused by rickettsias rind: the epidermis of a corn stalk; also, the outer covering of some parts of certain other plants rockweed: any of certain brown algae (salt¬ water-inhabiting) with leathery, ribbonlike branches, at the ends of which are air bladders that help to keep the plant afloat (except for its point of attachment to rocks underwater) Rodentia (roh den shee uh) : an order of gnaw¬ ing mammals, commonly called rodents (rats, beavers, etc.) rods: certain light-sensitive neurons in the retina of the eye in vertebrates; they are sensitive only to degrees of light from white to black, not to color roe: fish eggs, especially before they are laid roentgenologist (rent g’n ol oh jist): a doctor who has specialized in the use of X rays root: in higher plants, an organ useful in anchoring the plant, storing food, and ab¬ sorbing water and minerals (and passing these along to the stem) root cap: a tissue which caps the ends of rootlets of higher plants that grow in soil root cortex. See cortex root hair: an elongation of an epidermal cell of a root, useful in absorbing soil water and minerals root reptiles: primitive reptiles that were ancestors to the dinosaurs and to most rep¬ tiles of today rotary tiller: a tiller that, unlike a plow, stirs the topsoil rather than turning it under Rotifera (roh tif er uh) : a phjdum of micro¬ scopic but many-celled and specialized ani¬ mals, in the adults of which cell boundaries usually disappear; named after the rhythmic motion of the cilia on their heads; commonly called rotifers (roh tih ferz) roundworms: a phylum of round, unseg¬ mented worms, including trichina and hook¬ worm; Phylum Nemathelminthes rusts: certain fungi that usually form reddish spores and that often attack and infect grain plants 676 GLOSSARY sabertooths: a type of mammal known only from fossils; sometimes incorrectly called “sabertoothed tigers” sacrum (say krum) : that part of the back¬ bone which forms part of the pelvis in verte¬ brates; in man, it consists usually of five fused vertebrae saguaro: any of certain giant cactus plants ( Cereus giganteus ) of the southwestern United States salamander (sal uh man der) : an amphibian with a long tail and four legs saliva (sul ly vuh) : digestive juice secreted by salivary glands near the mouth in most vertebrates sand dollar: any of certain flat, circular sea urchins that live on sandy bottoms in shallow water near seashores Santa Gertrudis (ger troo diss) : a breed of cattle developed on the King Ranch in Texas saprophyte (sap roh fyte): any organism that lives upon dead, decaying organic matter Sarcodina (sahr koh dy nuh) : the class of protozoa to which amebas and foraminifera belong scalpel (skal p’l) : a dissecting knife Scapliopoda (ska fop oh duh) : a class of mollusks with tusk-shaped or tube-shaped shells scapula (skap yoo luh) : the shoulder blade in vertebrates Schistosoma (skiss toh zoh muh) : a genus of blood flukes (Phylum Platyhelminthes) Schizomycetes (skiz oh my see teez) : the class of thallophytes to which bacteria belong scintillator (sin tuh lay ter) : a sensitive de¬ tector of radiation scion (sy un) : a bud or twig cut from one tree and attached to the trunk or a branch of another tree in budding or grafting, as in fruit trees sclerotic (skier ot ik) coat: the outer, pro¬ tective coat of the eyeball in vertebrates scouring rushes: one species of horsetails (Equisetum hiemale), so called because pio¬ neers used them to scour pots and pans scurvy (sker vee) : a disease of man and cer¬ tain other vertebrates caused by lack of ascorbic acid (vitamin C) Scypha (sy fuh) : a genus of small sponges of the Atlantic Coast Scyphozoa (sy foh zoh uh) : the class of coelen- terates to which most of the common jelly¬ fish belong sea anemone: any of certain salt-water-in- habiting coelenterates with a flowerlike appearance sea cucumber: a salt-water-inhabiting echino- derm shaped like an ordinary cucumber sea horse: any of certain small, bony fish whose heads and upright position in the water are suggestive of a horse sea lily: any of certain stalked echinoderms with a crown of much-branched arms that give it a plantlike appearance sea squirt: a saclike chordate with a U-shaped food tube and no evidence of the notochord it had as an embryo and larva sea urchin: an echinoderm that has a flat¬ tened, globular shape and that is covered with movable spines seaweed: a mass or growth of sea plants, espe¬ cially red and brown algae secondary roots: roots that branch out from the primary root of a plant second filial generation: the F2 generation; the second generation following a cross of two organisms for genetic study secretin (see kree tin) : a hormone secreted by the lining of the duodenum in man and cer¬ tain other vertebrates; it stimulates the liver to secrete bile, and the pancreas to deliver pancreatic juice, through a duct into the duodenum sedimentary rock: rock formed in layers from sediments dropped by water in lakes and oceans seed : a matured ovule following fertilization seed dispersal: the scattering of seeds (and fruits), as by wind and animals seed ferns. See Pteridospermae seed leaf: a leaf present in an embryo plant within a seed seed plant: any plant that produces seeds segment: a ringlike section of the body of certain animals; annelids and arthropods are especially noted for segmented bodies segmented worm: an annelid segregation of genes: the separation of all gene pairs during meiotic cell division; one gene of each pair goes into one gamete, the other into a different gamete Selaginella (sel uh jih nel uh) : a genus of club mosses selection: the determination of which or¬ ganisms and traits, among all similar organ¬ isms with different traits, will survive; natural selection is the tendency under natural conditions for those organisms with traits that especially suit them to survive in their environment to become the parents of the next generation; artificial selection is man’s selection of plants and animals with traits desirable to him to produce the next generation of plants and animals of that species self-duplication: in chromosomes, the dupli¬ cation of the genes and of the chromosomes themselves early in mitosis, or during the two stages of cell division associated with meiosis self-pollination: the transfer of pollen from a stamen to a pistil of the same flower or plant; often called “selfing” GLOSSARY 677 semicircular canals: sense organs of balance in the inner ear of man and certain other vertebrates semipermeable (sem ill per mee uh b’l) membrane. See membrane sense organ: an ear, eye, taste bud, etc., in higher animals; also, certain structures in other animals, as sensory lobes and eyes in planarians sensitivity: the ability to be stimulated by certain external agents such as light, heat, chemicals, gravity, or touch sensory cells: cells of certain lower animals, as in hydras, that are sensitive to touch, food materials, etc., much as higher animals’ sense organs are sensitive to the same stimuli (as well as others) sensory lobes: sense organs of planarians sensory neuron. See neuron sensory root: in vertebrates, the dorsal root of a spinal nerve, through which nerve impulses from sensory nerves enter the spinal cord sepal (see p’l): the outermost leaflike flower organ, usually green; sepals enclose the bud; not present in all flowers sequoia (sill kwoy uh): either of two species of giant, coniferous California trees seta (see tuh — plural, setae, see tee): a bristle such as those of earthworms sex chromosomes: the chromosomes (X and Y) which determine the sex of the offspring of most higher animals sex-linked trait : a trait which usually appears only in males or only in females; most often due to a gene present in the X but lacking in the Y chromosome sexual reproduction: reproduction which begins with the union of the nuclei of two gametes, usually the nuclei of an egg and a sperm sheath: the tissue surrounding a vein in a leaf; or, the tissue surrounding a neuron or a nerve in animals Shorthorns: a breed of cattle sieve (siv) plate: the opening through which a starfish (or a similar echinoderm) takes in the water that fills its tube feet silica: silicon dioxide, present in stems of horsetails and in skeletons of some sponges Silurian (sy loo rill un) Period: the third period of the Paleozoic Era; it began roughly 360 million years ago and ended 325 million years ago single-gene effects: traits due primarily to a single pair of genes skeletal muscles: the voluntary muscles in vertebrates (and in arthropods and mollusks) ; nearly all of them are attached to the skeleton skin gills: breathing organs of the starfish and other echinoderms slipper animal. See paramecium smooth muscles: the involuntary muscles in vertebrates and certain other higher animals; generally, they are concentrated in the walls of the food tube smuts: fungi that live as parasites on corn and other grains; their spores are usually black sodium fluoride: a compound of fluorine used to help prevent tooth decay sodium nitrate: an organic compound of sodium, nitrogen, and oxygen, much used as a soil fertilizer sodium pentathol (pen tuh thol): one of the newer anesthetics soft-bodied animals. See Mollusca soil-binding plants: plants useful in holding and protecting the soil, such as grasses soil depletion: loss of organic and essential mineral matter from soil, usually as a result of raising crop plants year after year on the same soil sol: the semifluid state of a colloid; colloids may exist either as semifluids or semisolids solar plexus: a cluster of autonomic ganglia lying just back of the stomach in most vertebrates solpugids (sol pyoo jids): an order of hairy, spiderlike arachnids solution: a liquid containing a dissolved substance (a solid or another liquid or a gas); usually it is a solid that dissolves in a liquid, as the molecules of the solid diffuse evenly throughout the liquid species (spee sheez) : in taxonomy, a sub¬ division of a genus; the genus and species names, together, make up the scientific name of any organism specific germ: a germ that causes a specific disease, as the diphtheria bacillus sperm: a male sex cell or gamete Spermatopliyta (sper muh toff ih tuh) : the phylum of the seed plants; members of the phylum are called spermatophytes (sper muh toh fytes) spermatozoa (sperm uh toh zoh uh) : swim¬ ming sperms sperm duct: a duct or tube through which sperms leave a testis in an animal sperm mother cell: a male germ cell that produces sperms by meiotic cell division sperm nuclei: the two male gametes produced by a pollen grain in a seed plant; also, the nuclei of sperms of animals sperm pocket: any of the sperm receptacles of an earthworm, into which another worm deposits sperms during mating or conjuga¬ tion Sphagnum (sfag num) : a genus of peat mosses sphincter (sfink ter) muscle: any of several ringlike muscles between the organs of the food tube in higher animals; there is a sphincter between the gullet and stomach, 678 GLOSSARY the stomach and small intestine, and so on Sphyrna (sfur nuh) : a genus of sharks spinal cord: the main nerve cord of verte¬ brates; it is always dorsal in the body spinal frog: a live frog that has had its brain destroyed spinal nerves : nerves that- branch off from the spinal cord of vertebrates spindle: the threadlike network along which chromosomes in a cell are arranged during mitosis and meiosis spiny-skinned animals: the echinoderms spiracle (spy ruh k’l) : any of the breathing pores of insects spirillum (spy RiL um — plural, spirilla): a spiral-shaped bacterium spirochete (spy roh keet): a corkscrew-shaped spirillum spirogyra (spy ruh jy ruh) : a filamentous alga common in pond scums; also, Spirogyra , the genus of these algae, of which Spi rogyra protecta (proh tek tuh) is one species and Spirogyra punctata (punk tay tuh) another sponges: animals of Phylum Porifera spongy layer: a layer of loosely fitting cells in a green leaf sporangium (spoh ran jee um — plural, spo¬ rangia) : a spore-making organ of many molds, mildews, ferns, and certain other plants spore: a single-celled (occasionally two-celled) reproductive body, formed sexually or asexually, and produced by many plants and some protozoa spore case: a plant structure in which spores are formed, as in mosses sporophyte (spoh roh fyte) : a plant that produces spores, as the moss bristle or the leafy fern plant Sporozoa (spoh roh zoh uh) : a class of pro¬ tozoa that includes the malarial germ ( Plasmodium ); at some time in their life history, they reproduce by forming spores stable suspension. See suspension stage: the part of a compound microscope on which the slide is placed stamen (stay men) : a pollen-producing organ in a flower; it consists of a filament and an anther staminate flower: a flower that has stamens but no pistils staphylococcus (staf ih loh kok us — plural, staphylococci, staf ih loh kok sy) : a bac¬ terium of the coccus type, usually found in a cluster with others of its kind; common as a cause of boils, pimples, and many other infections; often called “staph,” for short Stegosaurus (stej uh sawr us) : a genus of vegetarian, plated dinosaurs stem : an organ of higher plants (and of mosses and liverworts) useful in furnishing support to the leaves, in transporting dissolved foods and water (bearing minerals), and in storing food sterilize: to treat something, usually with heat, until all microorganisms on or in it are destroyed stethoscope (steth oh scohp) : an instrument used by doctors to listen to internal sounds, especially in the chest stigma : the part of a pistil of a flower on which pollen grains germinate stigmasterol (stig mass ter ohl) : a vitamin, present in such foods as kale, alfalfa, fresh cream, and soybeans; it corrects a condition in which calcium deposits have been built up in soft body tissues (as in muscle tissue) stimulant: any agent that produces a tempo¬ rary increase in such vital processes as rate of breathing and heartbeat stimulus (stim yoo lus) : anything that induces a response in a plant or an animal stinging cell : a glandular cell bearing a stinging fluid and equipped with a hair which penetrates the prey and delivers the fluid; commonly found in hydra, jellyfish, and other coelenterates stirrup: one of three bones of the human ear stock: the part of a plant to which a scion is budded or grafted, as in fruit trees stomate (stoh mayt) : one of many openings in the epidermis of a plant leaf, through which there takes place an exchange of oxygen and carbon dioxide between air¬ spaces inside the leaf and air outside the leaf; during transpiration, water is given off through the stomates streptococcus (strep toh kok us) : a bacterium of the coccus type, usually found with others of its kind, clinging together in short or long chains; often called “strep,” for short streptomycin (strep toh my sin). See anti¬ biotics strip cropping: the planting of crops in strips in such a way that several rows of an open- tilled crop (corn, for example) are bordered by several rows of a close-growing crop that retards soil erosion striped muscle: the kind of muscle of which skeletal muscles in vertebrates are com¬ posed style: a part of a pistil of a flower, connecting the stigma and the ovary subphylum: a subdivision of a phylum subsoil: the layer of soil beneath the topsoil; it differs most from topsoil in lacking organic matter suckerlike roots: roots, as of dodder, by means of which certain parasitic plants obtain sap from other plants; the roots grow into the phloem tissues of the host plant sucrose (soo krohs): cane or beet sugar sulfa drugs: synthetic organic compounds used extensively in treating many germ GLOSSARY 679 diseases; some of the well-known ones are sulfadiazine (sul full dy uh zeen), sulfanil¬ amide (sul fuh nil uh myde), and sulfa- thiazole (sul fuh thy uh zohl) sunshine vitamin: vitamin D, so called be¬ cause sunlight causes a substance in the skin of man (and in tissues of many other animals and certain plants) to be converted into vita¬ min D Surinam (soor ih nahm) toad: a large toad found in South America; its offspring develop in holes in the skin of the mother’s back survival value: the usefulness of a specific trait or of many traits of an organism in enabling it to survive and become a parent of the next generation suspension: a mixture of two substances in which finely divided particles of one, a solid, are dispersed throughout the other, usually a liquid (but possibly another solid or a gas); a stable suspension remains as it is, but in an unstable suspension, the suspended particles settle to the bottom after a time swim bladder. See air bladder sw im mere t: any of several relatively un¬ specialized, jointed appendages of a lobster or similar crustacean symbionts (sim bee onts) : two unlike organ¬ isms that live intimately together in a mutually helpful way, as man and the bacteria that live in the human colon and produce vitamin K; the relationship is called symbiosis (sim bee oh sis) sympathetic nervous system: one of two divisions of the autonomic nervous system of vertebrates; its action speeds heartbeat and breathing rate and inhibits digestion, among other things sympathin (sim puh thin) : another name for noradrenalin, secreted by nerve fibers of the autonomic nervous system in vertebrates synapse (sill naps): the point at which, in animals with highly specialized nerve tissue, an impulse passes from an axon of one neuron into a dendrite of another neuron synthetics: man-made drugs and other man¬ made substances, such as plastics syphilis (siFuhlus): a contagious disease of man, caused by a spirochete, and running a course that begins with sores on the reproductive organs and ends, if untreated, with insanity and death; transmitted by sexual contact system of organs: a group of organs that function together in a particular type of work, as the digestive system in taking in and digesting food and eliminating food wastes tadpole: an early stage in life cycle of frogs, toads, and other amphibians; characterized by gills (that later are replaced by lungs) and a long tail used in swimming (the tail is later absorbed and is replaced by four legs) Taenia (tee nih uh) : a genus of tapeworms, including those that commonly infest man talons: enlarged toenails of predatory birds taproot: a primary root which grows straight downward and is often a storage organ, as in dandelions tarantula (tuh ran tyoo luh) : a large, black, hairy spider of the group sometimes called “banana spiders” taste bud: any of many receptors imbedded in the tongues of vertebrates; in man, they are sensitive to sweet, sour, salty, and bitter substances taxonomy (taks on uh mee): the science of the classification of organisms; a taxonomist is one who specializes in taxonomy tendon: a tough cord of dense, white, fibrous connective tissue uniting a muscle to another structure, usually to a bone Tennessee anthracnose-resistant red clover: a variety of red clover developed by a combination of natural and artificial selec¬ tion for its resistance to a certain fungus disease tentacles (ten tuh k’ls): arms of the jellyfish and its relatives, or similar structures of other animals terminal flower: a flower that buds from the end of a plant stem terracing: a method of planting crops on a steep hillside; they are planted on flat ter¬ races supported by walls, banks, or turf, terrarium (teh rair ee um) : a tank or other structure in which land plants and animals are planted or raised, especially in classrooms, greenhouses, and similar locations test cross: a cross of two organisms made experimentally, often to determine whether or not one of the parent organisms is pure or hybrid for a given trait, or traits testes (tess teez — singular, testis): sperm¬ making organs of animals testosterone (tess toss ter ohn) : a hormone secreted by the testes of higher animals tetanus (tet uh nus) : lockjaw, a disease of many vertebrates; it is caused by certain anaerobic bacteria tetany (tet uh nee): a disease of many verte¬ brates, caused by too little parathyroid hormone; characterized by convulsions Thallophyta (thuh lof ih tuh) : the phylum of the lowliest plants, the algae and the fungi; members of the phylum are called thallophytes (thal oh fytes) thiamin (thy uh min): a B complex vitamin; it prevents and cures beriberi thoracic vertebrae: vertebrae dorsal to the chest area 680 GLOSSARY thorax (thoh raks): the middle portion of the body of a higher animal; it lies between the head and the abdomen thrombin (THROMbin): a blood protein derived from prothrombin; it activates the change of fibrinogen to fibrin in the blood¬ clotting process in man and certain other vertebrates thymus (thy mus) gland: an endocrine gland of man and many other vertebrates; its hormone seems to bear some relation to growth thyroid (thy royd) gland: an endocrine gland in the neck of man and many other vertebrates; its hormone, thyroxin (thy roks in), regulates the rate of oxidation of food molecules in the body thyrotropic (thy roh trop ik) hormone: a pituitary hormone that stimulates the thyroid gland to secrete thyroxin tissue: a group of similar cells specialized in a certain type of work, as muscle tissue is specialized in movement, or fat tissue in the storage of fats and oils tobacco mosaic disease: a virus disease of tobacco plants topsoil: the top layer of soil, containing organic and mineral matter toxic goiter. See goiter toxin: a specific poison produced by the metabolism of one organism, and poisonous to the host of that organism (as the toxins of certain bacteria are poisonous to man) trace elements: elements needed in only minute quantities by plants and animals; boron and zinc are trace elements of tomatoes and beets trachea, or tracheal (tray kee ul) tubes: air tubes of insects; air enters through spiracles and is “piped” throughout the body in these tubes trait: a distinguishing quality or character¬ istic; a peculiarity; a genetic trait is one that is hereditary, such as eye color in many higher animals or flower color in angio- sperms tranquilizer (tran kwih lyze er) : any of certain comparatively new drugs used (under doctor’s prescription) to restore calmness, especially to neurotics or psychotics transpiration: the loss of water by evapora¬ tion from leaves Trematoda (tree muh toh duh) : the class of parasitic flatworms known as flukes trial-and-error theory: the theory that higher animals often learn by trying one thing after another until they hit upon a satisfying response Triassic (try as ik) Period: the first geological period of the Mesozoic Era; it began roughly 200 million years ago and ended 165 million years ago triceps (try seps) : the muscle on the back side of the upper arm of many vertebrates; it is used in straightening the arm trichina (trih ky null) : a certain parasitic roundworm, commonly infecting hogs; human beings may become infected by eat¬ ing undercooked pork trichinosis (trik uh noh sis) : a disease of human beings, caused by infection with trichinas trilobite (try loh byte) : a primitive arthro¬ pod, known from fossils that occur in Paleozoic rocks Triton (try tun): a genus of salt-water- inhabiting, snail-like mollusks trochophore (trok oh fohr) : a free-swimming, ciliated larva of any of certain salt-water- inhabiting worms, or of any of several other invertebrates, such as starfish tropism (troh pizm) : the turning of an organism away from or toward a stimulus; a positive tropism is toward; a negative tropism is away from; examples include hydrotropism (hy drot roh pizm), geot- ropism (jee ot roh pizm), chemotropism (kem ot roh pizm), photo tropism (foh tot roh pizm), thermotropism (ther mot roh pizm), and others trypanosome (trip uh noh sohm) : a type of flagellated protozoon trypsin: an enzyme which activates the changing of proteins and proteoses to amino acids tsetse (tset seh) fly: the fly that carries the trypanosome causing African sleeping sick¬ ness tube feet : the muscular tubes used as feet by the starfish and some of its relatives tube nucleus: one of the nuclei produced within a pollen grain; the nucleus that affects the growth of the pollen tube tubule (too byool) : a little tube, as the collecting tubules in the kidney of a verte¬ brate tumor: any abnormal growth of useless cells, usually walled off in a lump; a benign tumor is a harmless one, such as a wart, corn, or cyst; a malignant tumor is a cancer Turbellaria (ter beh lay ree uh) : the class of flatworms to which planarians and certain other free-living flatworms belong turgid (TEitjid): distended by some internal substance, as by water in plant cells; not wilted turgor (ter ger) : the state of being turgid two-egg twins: fraternal twins, not produced by the same fertilized egg Tyrannosaurus (tih ran uh sawr us) rex: a species of flesh-eating dinosaurs, often called the king of the dinosaurs because of its size and formidable teeth GLOSSARY 681 umbilical (um bil ih k’l) cord: the cord or stalk connecting a mammalian embryo to the placenta, with the uterus Ungulata (ung gvoo lay tuh) : the order of mammals that includes the herbivorous, hoofed mammals such as cows, pigs, sheep, deer, and horses; members of the order are called ungulates (ung gyoo layts) unstable suspension. See suspension urea: a waste product produced in the bodies of many higher animals by deaminization of amino acids followed by a chemical combi¬ nation of amino groups with carbon dioxide ureter (yoo ree ter): a tube leading from the kidney to the bladder in vertebrates urethra (yoo ree thruh) : a tube through which urine is expelled from the bladder of a vertebrate urinary bladder: the bladder in vertebrates in which urine is stored urine (yoorin): the liquid excreted by the kidneys of vertebrates; it contains most of the waste products produced by the body cells (except for carbon dioxide, most of which is excreted by the respiratory organs) l rochorda (yoo roh kor duh): the subphylum of chordates to which sea squirts belong uterus (yoo ter us): an organ in many verte¬ brates in which eggs are stored until laid; or, in most mammals, the organ in which the embryo develops vaccination: strictly, the application of cow- pox virus to a scratch in the skin in order to induce immunity to smallpox; more broadly, inoculation to produce immunity to any disease vacuole (vak yoo ohl) : a small cavity in the cytoplasm of a cell, containing air or fluid or food particles; a food vacuole is a cavity in which food is digested in amebas and other protozoa, and in internal cells of sponges and coelenterates; a contracting vacuole is a cavity which functions to eliminate excessive water and some wastes from amebas or other protozoa; vacuoles in plant cells contain cell sap vagus (vay gus) nerve: one of a pair of cranial nerves which in vertebrates lead to organs in the chest and abdomen; a nerve of the parasympathetic system valves: structures in the heart and in veins which keep the blood from flowing back¬ ward in vertebrates variety: a subdivision within a species vascular (vass kyoo ler) plants: plants that have vascular tissue; pteridophytes and spermatophytes (and a few bryophytes, al¬ though their vascular tissue is very primitive and not commonly called xylem and phloem) vascular tissue: xylem and phloem; water- and food-conducting tissues in higher plants vein: a fibro vascular bundle in a leaf; also, in animals, a blood vessel carrying blood toward the heart venom: a poison, such as snake venom ventral (ven tr’l) nerve cord: the nerve cord running along the ventral side of earthworms, arthropods, and many other invertebrates ventral side: the lower side of an animal; the front of the human body ventricle: a chamber of the vertebrate heart; when a ventricle contracts, blood is pumped out of the heart and into an artery V en us’s-flo wer-basket : one kind of sponge, so called because of its shape and the appear¬ ance of its skeleton vertebra (ver tuh bruh — plural, vertebrae, ver tuh bree) : a bone of the backbone or spinal column in those chordates with true bony skeletons Vertebrata (ver tuh bray tuh) : the sub¬ phylum of those chordates which have back¬ bones made up of true bony vertebrae (or, in a few cases, cartilaginous tissue); mem¬ bers of the subphylum are called verte¬ brates (ver tuh brayts) vestigial wings: mere stubs of wings, a trait found in some fruit flies Victoria cruziana (vik toh rih uh kroo zy ah nuh) the species of the largest water lily, which grows in the Amazon River villus (vil us — plural, villi, viLeye): one of the small, hairlike projections on the lining of the small intestine of vertebrates; through the villi, digested food is absorbed into the blood stream virus (vYrus): a submicroscopic causative agent of certain diseases, visible only under an electron microscope; outside of living cells, viruses are inert, but inside living cells, they can reproduce vital processes: all processes necessary to the life of an organism vitamin: an organic compound necessary in small amounts to maintain an organism in health; fat-soluble vitamins include vita¬ mins A, D, and K; water-soluble vitamins include the B complex, and vitamins C and E vocal sacs: in male frogs, the sacs used to receive and discharge air during “singing” voice box. See larynx voluntary muscles: those muscles that are under the control of the central nervous system of a vertebrate; the skeletal muscles Volvox: a genus of flagellated, colonial pro¬ tozoa; in the manv-celled colony, some of the life processes are carried out by specialized cells, others by each cell individually Vorticella (vor tih sel uh) : a genus of ciliated protozoa that have contractile stalks by which they attach themselves to water plants or other underwater objects 682 GLOSSARY warm-blooded : a term applied to animals (birds and mammals) that maintain a con¬ stant body temperature watershed: high, ridged land that separates two drainage areas water-vessel system : a system of xylem cells through which water is transported in vascular plants wet mount: a temporary microscope slide, made by mounting objects in water whelk: a large, flatfooted mollusk with a coiled shell that is more or less pointed on both ends (on one end of the shell, the point is an opening through which water and food reach the animal inside the shell) withdrawal sickness: a sickness, at times serious, that develops when a drug addict stops using the drug X chromosome: one of the sex chromosomes in animals; there are two in each cell of a female, one in each cell of a male xylem (zYl’m): woody tissue in vascular plants; water vessels Y chromosome: one of the pair of sex chromo¬ somes in animals, found only in males Zea (zee uh) mays: the scientific name of American corn Zygote (zy goht). See fertilized egg GLOSSARY 683 INDEX A page reference in bold type indicates a drawing or photograph. abalone, 188 abdomen: of arthropods, 207, 209; of grass¬ hopper and other insects, 207, 218, 219, 220; of lobster, 214, 215; of mammals, 249-50 abdominal cavity, of man, 184, 337 abdominal organs: a lobster, 215; of grass¬ hopper, 219; of lancelet, 233; of yellow perch, 301; of frog, Frog Chart 6 follow¬ ing 304; of man, Human Body Chart 7 fol¬ lowing 336 absorption: by roots, 284, 287; of water through animal membrane, 286, 286; of digested foods, 302, 334 “acellular organisms,” 80, 99 acetylcholine, 396, 397; in synapses, 410 achromycin, 457; table, 459 acorn worms, 232, 233, 234, 238, 257 acreage: in farms, ranches, hatcheries, green¬ houses, forests, and roads, 628-29; in wild¬ life refuges, 636 ACTH: secretion and medical uses of, 380; in stress, 380-81, 382; and blood pressure, 480 “acute indigestion,” 481 adaptations: of fish to water, 236-37; of birds to flight, 246, 248; of frogs, 306. See also specialization addiction: to alcohol, 440-42; to drugs, 442, 468-69 adrenal glands, 375, 376, 382, 395; Human Body Chart 8 following 366; parts of, 379, 380; and reactions to stress, 380-81; re¬ moval of core of, 381, 397 adrenalin, 379-80; effects on body, 381, 382; and noradrenalin, 396, 397; in fear and anger, 410; Cannon’s theory, 420 adrenotropic hormone, 375, 382 Aedes, 438 African sleeping sickness, 226; trypanosomes as germs of, 163, 433, 436; and tsetse fly, 438 african violets, 486, 487 afterbirth: defined, 252; of rabbit, 505. See also placenta agar-agar: source of, 113; use in bacterial cul¬ tures and slants, 429, 430 Age of Ancient Life, 571 Age of Angiosperms, 581 Age of Fishes, 574 Age of Mammals, 571, 581 Age of Reptiles, 571, 576-79, 578 agglutination, of red blood cells, 386, 387 agglutinins, in human blood groups, 386, 387 air: motion of molecules of, 61; per cent of oxygen in, 62; dissolved, in water, 75; and protozoa, 75-76; nitrogen in, 274; changes in, in human lungs, 338 air bladders: of rockweeds, 113; of fish, 237, 238, 301; as lungs, 238. See also swim bladder air-breathers, first, 571, 573 air-borne germs, 437 air pressure, on ear drum, 403 air roots, of vines, 283 air sacs: of grasshopper, 219; of human lungs, 337, Human Body Chart 6 following 336 alarm reaction, Selye’s theory of, 380-81 albinos, 537, 537; identical twins, 533 albumin, 94; formula of, in egg, 59; in urine, 459 alcohol: from yeasts, 62; and disease, 439, 440-42; effects of, on body, 441-42; oxida¬ tion in body cells, 441; a depressant, 441; fatal amounts of, in blood, 441; and death rates, 441-42; and homeostasis, 445 alcoholics. See alcoholism Alcoholics Anonymous, 441 alcoholism, 440, 441, 469; and tranquilizers, 458, 459 alder, 149 alfalfa, 150; weevils, 223; and potash, 628 algae, 89, 93, 95, 123, 152, 185, 566, 607; described, 86; classification of, 103, 107-13; habitats, 108; grass-green, 109-10; red and brown, 112, 113; importance to man, 113; raising, for food of cattle, 113; in lichens, 117, 118; classes of, and classification sum¬ mary, 120; culturing, 129; reference books on, 131; in sponges, 162; percentage of total photosynthesis by, 294; as food of tadpoles, 498; ancient, 571, 572, 573; in miniature biome, 603, 605; in future biomes in space, 649-50 684 INDEX alleles: defined, 520; and human eye color, 525; in dihybrid crosses, 526; and human blood groups, 529; multiple, 530, 550; in fruit flies, 547, 549. See also multiple genes allergens, 439, 440 allergies, 439-40 alligators, 241, 242, 245; heart of, 314 alternation of generations: defined, 126; in mosses, 123, 125, 126; in ferns, 135-36; in club mosses, 139; in seed plants, 147, 491- 92; in jellyfish, 168; in coelenterates, 174; and reduction division, 503 altitude, and red-blood-cell counts, 384 alum root, 608, 609 Amanita, 115, 116 Amaryllis family, classification summary, 148 ameba, 52, 92, 124, 158, 160, 163, 167, 179, 192; as an organism, 44; detailed study of, 76—79, 77; dividing, 78; life functions, 78-79 Ameba proteus, 158 amebic dysentery, 158-59; germs of, 433, 436; transmission by raw vegetables, 437; human carriers of, 438 American Forestry Association, 635 American Indian, 188; example of classifica¬ tion of, 105. See also Indian American Nature Association, 635 Americans, blood groups in: of European de¬ scent, 388; table, 389 amino acids: number known, chemical nature, and making of, 276, 359; in protein foods of man, 334; made by colon bacteria, 334; in human cells, 343; absorption into human blood, 343; deaminization of, 346; essential in man, 358-60; synthesis in human body, 359; in human blood, 383 amino group, formula of, 346 ammonia, excretion of, in man, 346 Amodiaquin, 458, 459 Amphibia: defined, 235; classification sum¬ mary, 258. See also amphibians amphibians, 235, 236, 246, 248, 250, 296, 297; as a class, 238-41, 258; how to tell from lizards, 239; cloaca of, 308; first known, 571, 574, 577; in Carboniferous, 575, 576; in Paleozoic, 576 Amphineura, 189 Amphioxus, 257 amylase, 334 anaerobic bacteria, 437 anal pore, of paramecium, 80 anchorage, by roots, 284 ancon sheep. See sheep Andalusian fowls, genetics of color of, 524 Andrews, Roy Chapman, 585 anemia, 440; defined, 385; pernicious and treatment, 440; blood picture in pernicious, 441; discovery of treatment for pernicious, 455 anesthesia, 463 anesthesiologists, 463 anesthetics: discovery and use of, 462-63; origin of name, 463; kinds of, 463 anger: and adrenalin, 381; and behavior, 409 angina pectoris, 481 Angiospermae: defined, 145; classification summary, 148-50. See also angiosperms angiosperms, 107, 476, 566; defined, 145; classes of, 143, 145; families, 148, 149, 150; organs and organ systems, 269-92; parasitic, 283; tissues and organs of typi¬ cal, Plant Charts 2 and 3 following 288; first known, 571, 579; spread of, in Ceno- zoic, 581 animal breeding, 484; genetics and, 588-89, 591, 593, 594, 595, 597, 598; pure-line, 592, 593, 594, 595; mutations and, 595—97 “animalcules,” 74, 75, 159 animal kingdom, 103; classification of animals in, 158—263. See also animals animals: defined, 158; sizes of, 24, 25, 158, 249; one-celled, 40, 44, 52, 75-82; life processes of lower, 75-82; life processes of higher, 90-93; classification, 158-263; clas¬ sification summaries, 163-64, 174-75, 180, 189, 201, 227, 228, 257-60; with jointed legs, 205-31; poisonous, 206, 211, 212, 230- 31, 239, 241, 243; with backbones, 232-63; warm- and cold-blooded, 246, 248, 251; variations in learning ability, 407; learning and problem-solving, 416-19; rabid, 453; history of on earth, 564—85; timetable of history of, 571; first known air-breathing, 574; radiation experiments, 597; in beech- maple biome, 607. See also interdepend¬ ence, food chains, and names of individual kinds of animals Annelida: defined, 190; classification sum¬ mary, 197. See also annelids and segmented worms annelids, 190, 196, 197, 216, 217. See also segmented worms annual rings, 89, 280, 281; defined, 282; ex¬ amining, 293-94 annuals, 492; defined, 142; in plant succes¬ sion, 608, 609, 611 Anopheles, 438 ant “cows,” 225 anteaters, giant, 259. See also spiny anteaters antelopes, as ungulates, 254 antennae: of arthropods, 207; of praying man¬ tis, 207; of shrimp, 210; of centipede, 211; of lobster and other crustaceans, 213, 214, 215, 217; of grasshopper and other insects, 218, 219, 220 anterior end, defined for animals, 170, 171 anther, of flower, 489, 490, 492; source of pollen, 491. See also flowers Anthozoa, classification summary, 174 anthrax, 443; discovery of germ of, 431 INDEX 685 anthropology, 555 antibiotics, 53, 119, 470; defined, 456; in tu¬ berculosis, 444, 461: discovery of, 456; use in human diseases, 456; five most widely used, 457; decrease in effectiveness of, 457— 58; table, 459 antibodies: defined, 452; and immunity to diseases, 454-55; to Rh factor, 508-09 antigens; defined, 454; Rh factor as example of, 508-09 antiseptics, use to prevent infections during surgery, 463 antitoxins: defined, 452; inoculation as means of inducing production of, 454. See also immunization antivenin, for snake bite, 245 ants, 218, 251; classification of, 223-24, 228 anus, 91, 92, 172, 179, 180, 202, 331; first animals with, 176; of roundworms, 176; of Ascaris, 176, 177; of mollusks, 184, 185; of earthworm, 193; of starfish, 199; of lob¬ ster, 214, 215; of lancelet, 233, 234; of fish, 300, 301 anvil, of ear, 402, 403 aorta: of fish, 301; of man, Human Body Chart 5 following 336, 339, 340 aortic arches, 298; of earthworm, 191, 194 apes, as primates, 255 Appalachian Mountains, 565, 576 appendages. See antennae, arms, cilia, fins, flagella, legs, pincers, swimmerets, and ten¬ tacles appendicitis: and amebic infection, 436; in¬ fectious but not contagious, 436; specific cause and treatment of, 444; white-blood cell counts in acute, 460; surgery and, 462; symptoms and what to do for, 463-64 appendix, 463; human, 335, Human Body Chart 7 following 336; amebic infection, 436; normal and infected, 464; ruptured, 464; effect of laxatives on infected, 465 appetite: vitamins and, 364; as motivation for specific behavior, 413-14 apple blossom, 490; examining, 489, 490; as example of perfect flower, 493 apples, 145, 150, 566; as fruits with seeds, 144; and insect pollination, 223; polyploidy in, 540, 597 apple tree: amount of sugar made bv, 274; water losses from, 278; grafting and, 488 apple “worms,” 207, 222 Arabellidae, 197 Arachnida, 211; classification summary, 227. See also arachnids arachnids, 211, 212, 213, 227. See also spiders Aralen, 458, 459 Archeopteryx, 579 Archiannelida, classification summary, 197 Arizona: cactus plants of, 106, 600-01; scor¬ pions of, 212; desert biome of, 600-01; deer in, 602; irrigation in, 630, 631, 632 arm, of microscope, 22 arms: of starfish, 199, 201; of mammals, 250; of hydra, 265 army “worms,” 222 arterial bulb, of fish, 301, 303 arteries: defined, 91, 296, 297; of clam, 187, 188; of lobster, 215; of grasshopper, 219; of lancelet, 233; of vertebrates, 236; “pulse” of, 298; of fish, 301; of man. Human Body Chart 5 following 336, 339, 340, 341; in circulatory and heart diseases, 479, 480, 481; and blood pressure, 481; of umbilical cord, 505 arterioles, 340-41; and blood pressure, 479- 80; and arteriosclerosis, 481 arteriosclerosis, 481; in cerebral hemorrhage, 481; in coronary heart disease, 481-82 arthritis, and stress, 381 Arthropoda: defined, 206; classification sum¬ mary, 227-29. See also arthropods arthropods, 205-31, 227-28, 235, 297, 300, 572; defined, 206; number of species of, 184, 206, 227; success of, 206; similarities among, 206-09; body parts of, 207; repro¬ duction in, 207-08; exoskeletons of, 208-09; main classes of, 209; compound eye of, 216; neurons of, 324; ancient, 573, 574. See also crustaceans, insects, etc. artificial selection for survival, 547-48, 587- 98 asbestos gauze, 19, 20 Ascaris, 179, 180, 188, 202; body plan and life processes, 176, 177; chromosomes of, 489, 503 Ascomvcetes, classification summary, 121 ascorbic acid, 366; daily requirements, table, 355; in common foods, table, 356—57; test¬ ing foods for, 366; effects of cooking on, 368. See also vitamin C asexual reproduction: defined, 486; in flower¬ ing plants, 487-89; lack of variations in off¬ spring, 527. See also names of individual plants and animals ash, 280 Asiatic cholera, 431, 436 asparagus, 133; leafless, 269 assimilation: defined, 78; in spirogyra, 84 association areas in brain, 411 associative neurons. See neurons Asteroidea, classification summary, 201 asters, 639 asthma, 439 Atabrine, 458, 459 athlete’s foot, 119, 449; germs and spores of, 433, 436 athlete’s heart, 480-81 atom bombs, 53, 54; isotopes as by-products of the making of, 57 atomic energy, 54 atomic numbers, 55 atoms, 53—58, 54, 63, 93; sizes, 53; weights 686 INDEX of, 54; hydrogen, 55; disintegration of, 56; nucleus of, 57, 58; gains and losses of, in human body each year, 57, 351, 612-13; in stick models of molecules, 60; in food¬ making in seed plants, 271, 272, 273, 274 auditory nerve, 402, 403; in man, 390. See also ear auricles: of fish’s heart, 301, 303; of three- chambered heart (frog), Frog Chart 4 following 304, 309, 310; of four-chambered heart (man), 313, 339, 341, Human Body Chart 5 following 336 automobile accidents, and drinking, 441 autonomic ganglia: in frog, Frog Chart 3 fol¬ lowing 304; in man, Human Body Chart 4 following 336, 389, 390. See also autonomic nervous system autonomic nervous system: of frog, Frog Chart 3 following 304; of man, Human Body Chart 4 following 336, 389, 390, 395; structure and functions of human, 393-98, 395; sympathetic and parasympa¬ thetic, 394, 395; and control of heartbeat, 396; and body stability, 397; changes in synapses of, 410 auxins, 291, 293, 294 average length of life, 428; effects of smoking on, 442, 476 Avery, Dr. Amos G., 539 Aves, 235, 245, 248, 250; classification sum¬ mary, 258. See also birds axial flowers, 518, 519 axons, 320, 321, 392, 410. See also neuron azalea, 639 B12, and pernicious anemia, 440 babies, human. See infants baboons, 254 bacillus, 121; of tuberculosis, 426, 432; in sour milk, 430; described, 431. See also bacteria backbone, 158, 236; of snake, 232: and rela¬ tion to position of spinal cord, 249; human, 255, 256, Human Body Chart 2 following 336; examination of, 262; of yellow perch, 301; of frog, Frog Chart 2 following 304 bacteria, 95, 113; as food of paramecia, 79; classification of, 114; in sour milk, 117; useful, 119; and diseases, 119, 429-33, 437, table, 436; as food-makers, 272; nitrogen¬ fixing, 274-77, 275, 277; of decay, 276, 277; in human colon, 334, 359, 367; filtered out of lymph, 342-43; discovery of, 429; where found, 429—30; how to culture, 429— 30; reproduction in, 430-31; how to ex¬ amine, 430, 446-47; sizes of, 431—32; three main types of, 431, 432; anaerobic, 437; spread of disease-causing, 437-38; in hu¬ man blood stream, 451; mutations in, 539; gene transduction in, 552; ancient, 572-73; in soil, 603, 622 bacterial counts, of city water, 467 bacteriology, defined, 429 badlands, 629 Bain, Samuel M., 587-88, 589 balance: fish’s sense of, 303; frog’s sense organ of, 312; human organs of, 402, 403 balance of nature. See natural equilibrium Ball, Dr. Eric G., 354 ballooning, of spiderlings, 205-06 bamboo, 148 banana spiders. See tarantulas Bang’s disease, of cattle, 437; and cattle in¬ spection, 467 Banting, Dr. Frederick, and insulin, 399 banyan tree, 283 barberry, spines of, 269 barium sulfate: in X ray of stomach, 333; use of, preceding X rays, 460-61 bark, 89, 281; cells of, 40; of cherry twig, 281; of pine stem, Plant Chart 1 following 288 barley, 148, 596 barnacles, 213, 227 Barr, Captain Norman Lee, 644 Bartram, John, 105 basal metabolism test, 378, 459 Basidiomycetes, classification summary, 121 bass, 258 basswood, 609 bath sponge, 162 bats, 246, 249, 259; and rabies, 453 B complex vitamins, 364—65; and respiratory enzymes, 365; and alcoholism, 442. See also vitamins beaker, 19, 19 beaks, of birds, 246, 247 bean, 133, 150, 280; as a dicot, 142, 143, 145; seed and embryo of, 142, 495; growing seedlings of, 204, 290; parts of, 267; navy, 597 bean weevils, 223 beards, and male hormones, 381, 382 bears, 260, 313, 566; polar, 613, 615 beaver, 253 bedbugs, 606 Beebe, William, quotation, 262-63 beech, 149, 609 beech-maple woods, 603, 606, 607; as climax biome, 607-09, 611; food chains in, 614 beef cattle, improved, 594-95 bees, 218, 422; and pollination, 223; classifica¬ tion of, 223-24, 228, 228 beetles, 218, 222-23; diving, 154; lady and ground, 222; number of known species, 222; wings of, 222; classification of, 222-23. 228^ 228; harmful, 223 beets, 268, 282, 587, 628 begonia, 44, 487 behavior: defined, 289, 318; of microscopic INDEX 687 behavior ( continued ) plants and animals, 75-86; of earthworms, 195-96; of seed plants, 289-92; experiment on plant, 290; of vertebrates, 318-24; cen¬ ters of control for human, 391—93, 394—97; motivation of, 414-16. See also human be¬ havior and names of individual plants and animals behavior patterns, habits and skills as, 413 Benedict’s solution, 332 benign tumors. See tumors beriberi, 363, 440, 459; in rats, 363; early re¬ search on, 363 biceps: defined, 345; in man, Human Body Chart 3 following 336 bicuspids, 333 biennials, defined, 142 bilateral symmetry. See symmetry bile: in fish, 302; in frog, 308; in man, 332; action on fats, 333, 334; and use of products of breakdown of red blood cells, 384 bile duct: common, 301, 302, 308-09, Frog Chart 6 following 304, Human Body Chart 7 following 336 bills: of birds, 246, 247; of duckbilled platy¬ pus, 250; of spiny anteater, 251 binomial system, of nomenclature, 104-07 biochemistry, 50-73; defined, 53; and plant behavior, 291 biological control: of insect pests, 223; birds and, 248; and forest conservation, 634 biological drives, defined, 414-15 biological needs: and habit formation, 413; and motivation, 413, 416; hunger and thirst as, 413-14; and body stability, 414 biological success: defined, 209; of arthropods, 206, 209; of fish, 237, 299 biology: defined, 15-18, 16-17; a unified sci¬ ence, 93 biomes: defined, 603; interdependence of, 603-12; types of in U.S., 603; how to make a miniature, 603-04, 605; man-made, 605; history of successions of, in plants, 606-12; food chains in, 614; and wildlife conserva¬ tion, 635; and necessity of in space flights, 643, 649-50 biophysics, defined, 53 biopsy, defined, and use in cancer diagnosis, 476 Birch, Dr. Herbert G., 419 birch family, classification summary, 149 birch trees, 149, 609, 612 birds, 232, 238, 296, 297, 566, 576, 609; as a class of vertebrates, 236, 245-48, 258; common names of, 245; chief features of, 245-46; running, 246; body temperature of, 246; feet and beaks of, 246, 247; water, 246, 247; perching, 246, 247; and bird guides, 246—47, 263; specialization of body of, 248; cloaca of, 308; and warm-blooded¬ ness, 312—18, 316; brains of, 319; ancestry of, 571, 577, 579; value of, in forest con¬ servation, 634; number of nesting species in U.S., 637; feeding, “housing,” and shelter¬ ing, 637-39 bird study, as a hobby, 247 birth: of young rattlers, 245; of mammals, 250; of pouched mammals, 251, 252; of placental mammals, 251—52 birth canal, of rabbit, 504 birthmarks, and cancer, 476 bison, 254 bivalves, 184, 186, 189; defined, 186, 187 blackberries, 44; polyploidy in, 597; white, 599; in a plant succession, 608, 609 blackbirds, 245 Black Death, 437-38 black urine, in man, 531 black widow spider, 206, 211-12, 227 bladder, urinary, 310; of man, 346, 395, 396 blade, of leaves, 267. See also leaves Blakeslee, Dr. Albert F., 539 blaze hair, 514, 519, 525, 536 bleeder's disease, 524, 531, 533-34; rate of mutation producing, 550 bleeding, control of, 466 blister beetles, 223 blood: as a tissue, 30, 35, 43, Human Body Chart 5 following 336; of frog, 30, 308, 309, 310; taking from finger, 34; how to prepare a smear of, 47, 48, 49; of horse, in diphtheria, 50, 452; water in, 51; of fish, 91, 92; and malaria, 159; germs in human, 163, 451; loss, in hookworm infection, 178; of clams, 186, 188; of earthworm, 193, 194; of starfish, 200; of grasshopper, 219; glucose in human, 273; Harvey’s research into circulation of, 295-96; amounts in man, 296, 342; circulation of in fish, 300; “pure” and “impure,” 309, 310; circulation of in men, Human Body Chart 5 following 336, 339-43, 340, 341; color changes in hu¬ man, 339; and stability of human body, 347, 383-84, 397-98; and human excretion, 345, 346, 347; calcium ions in, 360; clot¬ ting of human, 360, 367, 383, 385-86; hormones in human, 373, 374, 376; com¬ position of human, 383-84; in pernicious anemia, 440, 441; radiations and human, 472; and spread of cancer cells, 474; mother’s and embryo’s, 505; typing and Rh factor, see blood groups blood cells: of frog, 30; of man, 34, 35, 37, 38, 193, 342, 383; origin of new red, in man, 34, 384, 385; counts of red and white, in man, 34, 384, 385, 388, 459, 460; of fish, 326; iron in red, 360-61; agglutination of human red, 386, 387, 388; and blood stream infection, 435; nucleated red, in pernicious anemia, 441; germs destroyed by white, 449, 450, 451; locomotion of white, 450; 688 INDEX counts of red and white, in leukemia, 478; and Rh factor, 509 / blood counts. See blood cells ' blood groups, human, 386, 387, 388; per¬ centages of in various peoples in each of four basic, 387, 388; Rh factor and, 387, 508-09, 551, 556; how to determine, 399; inheritance of, 528—29, 530; subgroups, 529; and racial stocks, 555-56; M, N, and E factors, 556 blood platelets, 383, 384; in clotting of blood, 385-86 blood pressure, 459; defined, 479-80; adrena¬ lin and, 381; nerve control over, 397; high, 444, 458, 459; measuring, 480; factors that affect, 480, 481; in arteriosclerosis, 481 blood proteins, 342, 367 “blood relatives,” 515 bloodroot, 150 blood serum, 383; used to determine blood types, 386, 387. See also serum blood sinuses. See sinuses blood smear, how to make, 47, 48, 49 blood stream, of man, 382; germs in, 433, 450, 451; germ toxins in, 435; infections of, and heart damage, 435. See also blood, blood cells, blood serum, and circulation blood sugar, in man, 273; in diabetes, 377; and adrenalin, 381; normal levels of, 383; and hunger, 414 blood tests: premarital, 433; premarital and prenatal, 468 blood transfusions, 50, 388; and blood groups, 386, 387; Rh factor in, 387; and nontrans¬ fer of genetic traits, 515 — ^ blood types, 386-88; how to determine, 387, 399; use of, to help determine parentage, 529. See also blood groups blood vessels, 102, 132, 178; smooth muscle in walls of, 40, 41, 43; of clam, 186, 187, 188; of earthworm, 190, 191, 193, 194; of lobster, 215, 216; total length in man, 236; in food tube, 331; nerve control over, 396; of umbilical cord, 505. See also circulatory system blueberries, polyploidy in, 597 bluebirds, 245, 258 bluegills, class of, 236 bluegrass, 148 blue-green algae, 109, 117 bluets, 639 blushing, 393, 394, 396 board feet: defined, 620; of lumber harvested each year, 633 body cavity: primitive, in roundworms, 176, 177; true, in Bryozoa, 178, 180; of starfish, 198; of mammals, 249-50; of fish, 302; di¬ vided by diaphragm in man, 337. See also coelom body plan: of ameba, 77; of paramecium, 80; of spirogyra, 83; of pleurococcus, 85; of Volvox, 111; of bread mold, 114; of mushroom, 116; of lichen, 118; of moss, 123; of fern, 134; of corn and bean, 143; of Vorticella, 159; of sponge, 161; of hydra, 166; of planarian, 171; of Ascaris, 176; of chiton, 185; of fresh-water clam, 187; of earthworm, 191; of starfish, 199; of lobster, 215; of grasshopper, 219; of lancelet, 233; of mammals, 249-50; of pine, corn, and buttercup, Plant Charts following 288; of frog. Frog Charts following 304; of man, Human Body Charts following 336 body regions: of arthropods, 207, 209; of grasshopper and all insects, 217-18, 220 body temperature: of birds, 246, 313; of cold- and warm-blooded vertebrates, 312; of man, 313; oxidations and, 314-15; nerve control over human, 397 bog, quaking, 122, 603 boils, 435, 449; penicillin and, 456 boll weevil, cotton, 590 bomb tests, radiations from, 477 bone cells, 40 bone marrow, and leukemia, 477 bones: calcium in, 68, 235; of chordates, 232; highly specialized in birds, 248; examining, in frog’s leg, Frog Chart 1 following 304, 306, 307; and vertebrate behavior, 318; of human body, 344-45, Human Body Chart 1 following 336mihinerals needed in, 360; vitamin D and/B67; growth of long, 375, 382; of human ear, 402; fractured, 460, 465, 466; fossils, 568. See also skele¬ tons bone tissue, 42, 43 bony fish: class of vertebrates, 235, 236, 237, 238; number of known species, 236 “book lungs,” 227 booster shots, 454 borderline: between living; and nonliving; things, 95; between lowly plants and ani¬ mals, 110 boron, 55, 284; needed by crop plants, 628 botanist, first great American, 105 botany: college texts, 130 bounties, 619, 621; on birds, 248; dangers of, 602 bowel infections, 428 brace roots, of corn, 283, Plant Chart 2 fol¬ lowing 288 Brahmans, 594, 595 brain, 43, 44, 51; nerve cells in, 42; of fish, 93, 301, 303, 319; of earthworm, 195; of lobster, 214; of vertebrates, 236, 298-99, 300, 301, 319; of amphibians, 241, 319; of mammals, 249; of primates, 254; of man, 256, 389, 390, 392, 393, Body Charts 4 and 8 following 336; how to remove fish’s, 304; of frog, Frog Chart 3 following 304, 319; of pigeon, 319; of horse, 319; number of neurons in human, 320; nerve pathways in, INDEX 689 brain ( continued ) 321-22; volume of man’s, 392; surgery on man’s, 393; in meningitis, 435; syphilis damage, 436; absorption of alcohol by hu¬ man, 441; tumors of human, 460 bn ike fern, 133 bread, and milk, as source of amino acids, 359 bread mold, 121. See also molds breast cancer, 476 breath, moisture in, 62 breathing: in protozoa, 75-76; in fish, 91, 92, 236, 300; in planarians, 172; in arthropods, 209; in scorpions, 212; in insects, 218; in grasshoppers, 218, 219; in tadpoles, 238; in frogs, 240; in birds, 246; in mammals, 250; mechanics of, in frog, 307-08; mechanics of, in man, 337-38; rate and adrenalin, 381; nerve control of human, 391, 394, 395, 396, 397; as inborn response, 405; in emotional behavior, 409, 410. See also respiration breathing system. See respiratory system breeds, rise of new, 547—58; of sheep, 546; navel orange, 547, 548; of modern horses, 562. See also varieties, races, etc. brine shrimp, 208 Brink, Prof. R. Alexander, footnote, 537 bristle, of moss, 123, 123, 124 brittle stars, 200, 201 bronchi, of man, Human Body Chart 6 fol¬ lowing 336, 337 bronchial tubes, Human Body Chart 6 fol¬ lowing 336, 337 Brookhaven experimental garden, 596, 597 brown hair, genes and enzymes of, 536 browsers, 560, 561, 562 - Brussels sprouts, and ancestor, 583 Bryophyta, 122-26; classification summary, 127. See also bryophytes bryophvtes, 132; defined, 122-27; identify¬ ing, 122, 123, 130; classification summary of, 126, 127; rhizoids, 267; lacking in early fossil record, 573, 574. See also alternation of generations Bryozoa, 178-79; classification summary, 180, 202 bryozoans, 183. See also Bryozoa bubonic plague, 436; and rat lice, 437 Buchsbaum, Dr. Ralph, 179, 619 budding: in yeasts, 117; in sponges, 162; in hydra, 167, 168; in Bryozoa, i80; of fruit trees, 488, 489, 547 bud mutation, 537 buffalo, 254, 606; crossed with cattle, 591 bugs, true, 217; classification of, 226, 228 building foods. See foods bulbs, of plants, 487, 488 bullfrog, 239—40 Bunsen burner, 19, 20 Burbank, Luther, 599 Bureau of Land Management, 621 Bureau of Plant Industry, 587, 590 Burney, Surgeon General Leroy E., 442 burning. See oxidation burns: enzymes and healing of, in human skin, 316; treatment of, 465 burrow, of earthworm, 192 buttercup, 149, 490; leaves, 269; Plant Chart 3 following 288 butterflies, 206, 207, 218; larva of black swal¬ lowtail, 208; classification of, 220-22; met¬ amorphosis of monarch, 221 cabbage, 150, 192; crossed with radish, 558; ancestry of, 583; disease-resistant, 590 Cactaceae, 107. See also cactus family cactus family, classification summary, 150 cactuses, leafless, 269. See also cactus family and saguaro caecum: defined, 302; and pyloric caeca of fish, 301; of human colon, 335, 464; Human Body Chart 7 following 336 Calcispongiae, classification summary, 164 calcium, 440; as a nutrient, 68; in plants, 284; amount in human body, 352; daily needs, table, 355; in common foods, table, 356-57; ions in human body, 360; salts and bone¬ building, 360; foods rich in, table, 361; and vitamin D, 367; and blood clotting, 385, 386 calcium carbonate, in limy skeleton of coral, 169 calcium deposits, in artery walls, 481 California, 205, 223; first navel oranges in, 547, 548; replanting after forest fires in, 625-26; first wildlife refuge in, 636 calorie, great: defined, 353; measures, in foods, 353, 354; estimating daily intake, 354; human daily needs, 354, 355, table, 355; in common food portions, table, 356- 57 ' Calvin, Dr. Melvin, 650 cambium, 280, 281, 282; and growth of new phloem and xylem, 281; in roots, 283; Plant Charts following 288 Cambrian Period, 571, 572; living things in, 571, 572-73 camels, 260, 422; classification of, 254, 260; ancestry of, 564; first, 581 Canadian thistle, 279 canals, of sponges, 161, 162; excretory, of planarian, 171; ring, of starfish, 199 cancer, 56; defined, 472, 474-75; and viruses, 95, 472-78; tobacco and lung, 442; X rays in diagnosing, 460; surgery for, 462; ex¬ periments on immunization against, 472; cell divisions in cells of, 473; death rates from, 473; rank as cause of death, 473; age and occurrence in man, 473, 476, 477; as abnormal growth, 474; spread of through 690 INDEX human body, 474-75; primary and second¬ ary, 475; danger signals and early diagnosis, 475-76; curability, 475-76, 478; possible causes, 476-77; hereditary and, 477; treat¬ ments, 478 cane sugar, 59; making of, in green plants, 273. See also sucrose canines, 333; as fangs, 254 Canis fa miliar is, 503 Cannon, Walter B., 420, 443 capillaries, 92; in earthworm’s skin, 194; of vertebrates, 236; discovery of, 297; of human villi, 335; in human lungs, 337, Human Body Chart 6 following 336; in human circulation, 339, 342; of human kid¬ neys, 346, 347; of human skin, 347; growth of new, with gains in weight, 355; of pan¬ creas, 374; of adrenal glands, 379; of mam¬ malian placenta, 505 capsules, of tubules of kidneys, 346, 347 capvbara, 253 carapace, of lobster, 214, 215 carbohydrates: defined, 68; digestion of, in man, 334; in foods, 352; as energy foods, 352-53; daily needs, table, 355; in common food portions, table, 356-57. See also di¬ gestion carbolic acid, as a germicide, 429 carbon, 55; diagram of atom and isotopes of, 56, 57; symbol of, 59; in nutrients, 68; ex¬ amining, from organic matter, 72; amount in human bodv, 352 carbon compounds, and organisms, 60 carbon dioxide, 59, 60, 84, 128; stick model of molecule of, 60; from yeast action and burning, 62; from oxidation, 69; in sugar making, 82, 88, 271-72; radioactive, 272; in frog’s blood, 308, 309; excretion of, by man, 337; in human blood, 383 Carboniferous Period, 570, 571, 572; life in, 575, 576, 581 carbon monoxide, and hemoglobin, 384 carbuncles, 456 cardiac plexus, 394; Human Body Chart 4 following 336 cardinals, 245 caribou, 613 carmine powder, 97-98 Carnivora, 260 carnivores, 254; in food chains, 614 carotene, 365 carpet beetles, 223 carrion beetles, 223 carrots, 282, 283; food storage in, 269 cartilage, 42, 43; in certain fish skeletons, 234-35; in frog’s larynx, 307 cassava, 268 castings, of earthworms, 192 castor oil, 274 caterpillars, 207 catfish, 236 Catharinea, 127 cats, 250, 254, 260; gestation period in, 506; and destruction of birds, 637; number of stray, in U.S., 638 cattalo, 591 cattails, 142 cattle, 109; anthrax in, 431; inspection of, 467; improved by breeding, 589, 593, 594, 595 Caucasoids, 555 cauliflower, and ancestor, 583 celery: fibro vascular bundles of, 135; part eaten, 268; stems of, 278 cell body, of neurons, 320 cell differentiation: in normal growth, 474; in frog embryo, 498, 499; in mammal em¬ bryo, 506 cell division, 36, 38, 39, 484; defined, 39; mi¬ totic, 35-40, 36, 38; main steps in, 38—39; average duration of, 39; of ameba, 78; of paramecia, 81; and growth of spirogyra, 84; of V orticella, 159; of protozoa, 163; and growth of seed plants, 268; rates of, in bacteria, 431; abnormal, in cancer tissue, 473; and growth of embryos, 498, 499, 506; mitotic and meiotic, 502; meiotic, in mosses, ferns, and flowering plants, 503; effects of colchicine on mitotic, 539, 540 cell layers: animals with two and three, de¬ fined, 165; of jellyfish, 168; of vertebrate embryos, 498, 499, 506 cell membrane, 31, 33, 85, 110; as a gel, 66; and flow of materials, 84, 102, 285, 287, 288; insulin and, of human cells, 376 cell respiration. See respiration cell sap, 33, 83, 84 cell theory, origin of, 27. See also cells cell walls, 29, 31’, 33, 85. See also cells and cellulose cell wastes, 195, 309, 310 cells, 26-49; living, 26; history of knowledge of, 26-27; naming, 27; onionskin, 29; cheek lining, 30; comparing, 30-31, 31, 33, 35; typical animal and plant, 31; living and nonliving parts of, 31, 33; of green leaf, 33, 270, 271, Plant Charts following 288; in tissues, 40-43; of human body, 41, 42, Human Body Charts following 336; examin¬ ing several kinds, 47; number of molecules in liver, of man, 66; plant, 88, 89, Plant Charts following 288; in organs and sys¬ tems, 95; and flow of materials, 102; in fos¬ sils, 132, 568; specialized in, hydra, 166, 167; auxins and, 291; viruses and rickettsias in, 433, 434, 435. See also blood cells, nerve cells, muscle cells, cancer, etc. cellulose, in plant cell walls, 32, 33, 158; and ameba, 78; in termite digestion, 225 Cenozoic Era, table, 571, 579-81, 582 centipedes, 206, 207, 208, 209, 210, 211, 227; giant desert, 211 INDEX 691 central cylinder, of roots, 283, Plant Charts following 288 central nervous system, defined, 298; of grass¬ hopper, 218; of vertebrates, 235-36; of fish, 303-04; of frog, Frog Chart 3 follow¬ ing 304, 311; neuron cell bodies in, 320; of man, Human Body Chart 4 following 336, 389, 390, 391 centromere, 500, 501, 502 centrosome, 37, 38, 501 century plant, 264, 264 Cephaloehorda, classification summary, 257 Cephalopoda, classification summary, 189 cephalothorax: defined, 213; of arachnids, 211; of crustaceans, 213, 214, 215 cerebellum, 298, 319, 395; of fish, 300, 301, 319; of frog, Frog Chart 3 following 304, 311, 319; of pigeon, 319; of horse, 319; human, 390, 392; functions of human, 391; and sense of balance, 403; and muscle co¬ ordination, 403 cerebral cortex, of human brain, 392; sen¬ sory and motor centers in, 393; sight and speech centers of, 393, 402 cerebral hemorrhage, 481. See also strokes cerebrum, 298, 303, 304, 319, 392, 395; of fish, 300, 301, 319; of frog, Frog Chart 3 fol¬ lowing 304, 311, 319; of pigeon, 319; of horse, 319; number of neurons in human, 320, 391—92; and learning ability, 324; human, 390, 391, 392, 393, Body Chart 4 following 336; motor and sensory areas, 392, 393; centers of sight, 401; and sense of balance, 403 Cereas giganteus, 106, 107. See also saguaro Cestoda, classification summary, 175 Cetaceae, classification summary, 260 changes in living things through geologic ages, 559-83 chaparral, 625 Chautauqua Wildlife Refuge, 636 checkerboard: and monohybrid crosses, 526- 27, 527; and dihybrid crosses, 526-29, 528 cheek lining cells, 29, 30, 40 cheese, blue, 119 chemical bonds, 59 chemical changes: defined, 62; in protoplasm, 69-70; during cell respiration, 69, 276; during photosynthesis, 271-73; during food¬ making, 271-76; in proteins in human body, 358; and nerve impulse transmission across synapses, 410-11 chemical defenses, against germ diseases, 450-55 chemicals: as building materials of living things, 50-73; as stimuli to man, 403. See also names of individual chemicals chemical senses, 403, 404 chemical stimuli, 401, 403, 404 chemistry, 52; defined, 53; organic, defined, 60; and plant behavior, 290-91 chemotropisms, 290 cherry trees, 150, 612; twig, 281; polyploidy in, 597 chest, lining, 184; of mammals, 249, 250; hu¬ man, 337-38; X ray of human, 461 chestnut, 149, 612 chestnut blight, 618 chicken pox, 94, 95; cause of, 433, 436; spread of, 437 chickens, 246, 248; and beriberi, 363, 364; test crosses for rose and single comb, 525- 26, 527; improved, for egg size, 588, 589 childbed fever, 429, 436; sulfa drugs and, 456 childbirth, unrepaired injuries of, and cancer, 477 children, diseases of: 100 years ago, 428; im¬ munization of, 454. See also infants chimpanzees, 255, 260; experiments on learn¬ ing ability of, 419, 420 chinchilla, order and fur, 253 Chinese, blood groups of, 389 chipmunks, 634; teeth of, 253 Chiroptera, classification summary, 259 chitin, in arthropod exoskeletons, 208 chiton, 184, 185, 186, 189, 202 chlorination, of water, 437, 467 chlorine, symbol, 59; amount in human bodv, 352 chloroform, 463 chloromvcetin, 457; table, 459 Chlorophvceae, classification summary, 120, 130 chlorophyll, 33, 34; magnesium in, 68; in algae, 85, 86, 113; lowly plants with, 106- 13; lacking in fungi, 114; and photosynthe¬ sis, 272. See also photosynthesis Chlorophyta, 121, 130 chloroplasts, 33, 44, 83, 108, 110, 111, 270, 271; resemblance to genes, 541. See also photosynthesis and chlorophyll cholesterol, and arteriosclerosis, 481 Chondrus, 120 Chordata, defined, 234; classification sum¬ mary, 257-60. See also chordates chordates: defined, 234; blueprint of primi¬ tive, 233; number of species, 234, 257; classification of, 236, 257-260; ancient, 571 choroid coat, of eye, 401 Christmas fern, 135, 141 chromosome numbers, in crop plants, 597-98 chromosomes, 36, 37, 535; in mitosis, 38, 39, 40, 497, 499, 500, 501, 502; self-duplication of, 38-40, 499, 500, 502, 504; of ameba, 79; of paramecium, 81; in cancer cells, 473; of Ascaris, 489, 503; and growth of seeds, 495; number in human cells, 499, 503; nature and make-up of, 499, 534-42; hap¬ loid and diploid numbers, 502, 503; of rab¬ bit, 504; in human fertilized ovum, 507; and sex determination, 509, 510; of fruit flies, 509, 510, 517, 547; when named, 516; re- 692 TXDEX view of nature of, 516; and principles of genetics, 521; coiled threads of, 534, 535; multiple numbers of, 539, 540, 551, 552, 598; and crossing over, 540, 541; in radish- cabbage hybrid, 558 chrysanthemums, delayed blooming of, 292 Chrysaora, 174 Chrysophyceae, classification summary, 120 cicadas, 218, 226 cilia: defined, 81; of paramecia, 80; of plant sperms, 124, 139; of Vorticella, 159, 160; of planarian, 172; of cells of human wind¬ pipe, 178, 338; of rotifers and Bryozoa, 180; of clams, 186; of starfish, 199, 200 Ciliata, defined, 160; classification summary, 163 ciliates, defined, 160, 163 cinnamon fern, 133, 137, 141 Ciona, 257 circulation of blood: observing in goldfish, 91, 92; and trichinosis, 178; Harvey’s discovery of, 295, 296. See also circulatory system circulatory diseases, 478-82 circulatory system, 44, 158, 177; of planarians, 172; first specialized, 183; of mollusks, 184, 189; of chiton, 185; of clam, 186, 187, 188; open and closed, 188, 193, 198, 202; of earthworm, 190, 193, 194, 195; of starfish, 198, 199, 201; of lobster, 215, 216, 217; of grasshopper, 219; of vertebrates, 235, 236, 297-98; of fish, 300, 301, 302-03; of frog, Frog Chart 4 following 304, 309, 310; double, in birds and mammals, 313; of warm-blooded animals, 313, 314; of man, Human Body Chart 5 following 336, 339- 42, 340; summary of human, 343-44 cirrhosis, of liver, 442 citrus fruit, and adequate diet, 366, 369, 370 clams, 183, 184, 186, 188, 190, 194, 198, 202, 216; blueprint of, 187; how to dissect, 203; in food chains, 615 classes, of organisms: defined, 104, 105; of thallophytes, 120-21; algae, 120; of fungi, 121; of bryophytes, 127; of pteridophytes, 141; of spermatophytes, 147-50; of gvrnno- sperms, 147; of angiosperms, 148-50; of protozoa, 163; of sponges, 164; of coelen- terates, 174; of flatworms, 175; of round- worms, 180; of rotifers, 180; of bryozoans, 180; of mollusks, 189; of annelids, 197; of echinoderms, 201; of arthropods, 227- 28; of chordates, 257-60; of vertebrates, 258-60. See also names of classes ( arach¬ nids, crustaceans, insects, blue-green algae, ungulates, etc. ) classification, 103-07; examples of, 105; plant, 100-55; of thallophytes, 120-21; of bryo¬ phytes, 127; of pteridophytes, 141; of spermatophytes, 147-50; animal, 156—263; of protozoa, 163; of sponges, 164; of coe- lenterates, 174; of flatworms, 175; of roundworms, rotifers, and Bryozoa, 180; of mollusks, 189; of echinoderms, 201; of arthropods, 227-28; of man, 255; of chor¬ dates, 257—60 clavicle, Frog Chart 1 following 304, Human Body Chart 1 following 336, 344 claws, bird, 248 climax biomes, 607, 609, 611 clips, of compound microscope, 22 clitellum, of earthworm, 496 cloaca: defined, 308; functions, in frog. Frog Charts 6 and 7 following 304, 308, 310, 311, 497 Clonorchis, 175 closed circulatory system, defined, 188 closed seasons, in hunting, 621 clothes moth, 222 clotting of blood, 383, 385—86; vitamin K and, 440 clotting time: reduced by adrenalin, 381; how to determine, 398—99; in bleeders and in hybrid normals, 524 “cloud effect” in atom, 58 clover, 150, 603; insect pollination of, 223, Plant Chart 4 following 288; rust-resistant, 587, .588, 589; polyploidy in, 598; in crop rotation, 624; in strip cropping, 625; as green-manure crop, 627; and potash, 628 club fungi, 121 club mosses, 133, 138, 139, 140, 141, 581 clumping, of red cells, 386, 387, 509. See also agglutination coal, 140 coal forests, 137, 138, 139, 152, 575 Coal Measures, 570, 571, 575 coarse adjustment, of microsope, 21, 22 cobalt, in human body, 352, 361; radioactive, in plant breeding, 596, 597 cobra, 244 cocci, 121, 427, 431; of pneumonia, 432. See also bacteria coccyx, of man, 255 cochlea, 402, 403 cockroaches, 220, 227 coconuts, 146 cocoon: of insects, 221, 231; of lungfish, 238; of earthworm, 496 codeine, 468 codfish, 113, 235, 236; brain of, 319 codling moth, 222 coelacanth, 258 Coelenterata, 165—69, 172, 173; classification summary, 174. See also coelenterates coelenterates, 165—76, 174, 202, 572; fresh¬ water, 165; tissues of, 167 coelom, 179, 180, 189, 197, 201, 202; defined, 177; first true, 183; of mollusk, 184; of chiton, 185; of clam, 187, 188; of earth¬ worm, 190; of starfish, 198, 199, 200; of lob¬ ster, 215, 217; of lancelet, 233, 234; divided, in mammals, 249 INDEX 693 Colaptes auratus, 106 Colbert, Edwin H., 585 colchicine, 539; effects on mitosis, 539, 540 cold-blooded animals, 246, 257, 310 cold sores, 94, 95, 434 Coleoptera: defined, 222; classification sum¬ mary, 228 collarbone, Frog Chart 1 following 304, Hu¬ man Body Chart 1 following 336, 344 collards, and ancestor, 583 collecting: algae, fungi, mosses, 108-09; wild flowers, 152; water animals, 154; insects, 204 colloid: defined, 65; examples, 65; gel and sol states, 66, 67; and foods in human proto¬ plasm, 353 colloidal system, protoplasm as a, 65 colon, 334, Human Body Chart 7 following 336, 345; bacteria in, 359. See also food tube of man colonies: Volvox, 111; protozoan, 163; coelen- terate, 174; bryozoan, 180; insect, 223; bee, 223, 224; termite, 224, 225; bacterial, 430- 31 Colorado River toad, poisonous to dogs, 239 color blindness, 525, 531 colors, as stimuli of cones in retina, 401 columbine, 149 Columbus, 26, 74, 553; scurvy on voyage of, 362 comb, of bees, 224 common cold: causes of, 434, 436; spread of, in air, 437; penicillin and, 456 common duct. See bile duct complete flowers. See flowers complete metamorphosis, 221, 222; of moths and butterflies, 222; of bees, ants, and wasps, 223; of other insects, 228 composite family, classification summary, 150 compost heaps, 626, 627 compound eyes, 211; of lobster, 214, 216 compound leaf. See leaves compound microscope, 20-23; use of, 20-22; focusing of, 21-22; parts of, 22 compounds: defined, 59; nature of, 58-63; familiar, table, 59; organic, 59, 60; nitro¬ gen, and protein-making, 274-76 conchology, 188 conditioned responses: defined, 323, 324; in man, 405, 406, 407-08; experiments with, in man, 408; derived from generalized re¬ sponses, 409; and emotional behavior, 410, nerve pathways and, 410-11; and learning, 419. See also reflexes cones: male and female pine, 144, 144, Plant Chart 1 following page 288; of gymno- sperms, 144, 147; of retina of human eye, 401 Congo eels, 239 conifers, 146, 147, 634; learning to know, 151; in plant succession, 609, 610, 612. See also pines, firs, etc. conjugation: in paramecia, 81; in spirogyra, 84, 85; in V orticella, 159; in protozoa, 163 connective tissue, 42, 43, 197, 331; and pro¬ longed stress, 381 consciousness, and motivation, 415. See also behavior and human behavior conservation, 617, 620-41; defined, 617; of wildlife, 606, 614, 635-39; of forests, 633— 35; of soil and water, 621-32; improved, in recent years, 621; food chains and, 614; summarized, 639; field trips to ob¬ serve, 640 conservation farming: extent of, 624; and wise land use, 629 contagious diseases, 428, 429, 433, 436, 437; vital statistics, recorded, 467-68. See also diseases continuity of life, 484-85. See also reproduc¬ tion in seed plants, in higher animals, and plants and animals, history of contour cultivation, 624, 625 contractile fibers, of hydra, 166, 167 contractile stalk of V orticella, 159, 160 contractile vacuoles: of ameba, 77; of para- mecium, 80; of Euglena, 110; of Volvox , 111; of V orticella, 159; and water-logging, 237 controls, in culturing bacteria, 430 convolutions, of brain, 392 convulsions, 379, 440, 468 Cook’s National Forest, 612 Cooper’s hawk, 247 copper, in human body, 352, 360-61; foods that contain, table, 361 copperhead, 243, 244 coral reefs, 168, 169 corals, 165, 168-69, 173, 202; beads from skeletons of, 168, 169; living, 174; ancient, 573 coral snake, 243, 244 cork cells, 27, 33, 40, 280. See also seed plants corn, 100, 101, 148, 277; as a monocot, 143, 145; seedlings, 204, 268, Plant Chart 2 fol¬ lowing 288; amount of sugar made by, 273; flowers of. Plant Chart 1 following 288, 485, 493, 494; parts of, grain, 495; crossing over in, 552; Golden Bantam, 557; number of varieties cultivated by In¬ dians, 586; sweet, 586; ear from Indians of 600 years ago, 586; breeding by selection, 586-87; in crop rotation, 624, 625; and potash, 628. See also hybrid corn corn borers, 222 cornea, of eye, 401, 402; transplanting, 402; ulcers of, 459 corn grain, digestion and diffusion in sprout¬ ing, 287-88 corns, 474 corn smut, 115 694 INDEX cornstalk: tissues in, 279, 280, Plant Chart 2 following 288 coronary arteries, 339, 341, Human Body Chart 5 following 336; defined, 339; in heart “attacks” and strokes, 339-40, 341 coronary heart disease, symptoms of, 481 coronary thrombosis, 478-79, 481-82 cortex: of root, 88, 89, 283, 287, Plant Charts following 288; of fern stem, 134; of dicot stems, 280, 281, Plant Chart 3 following 288; of adrenal glands, 379, 380, 382; of cerebrum, see cerebral cortex cortisone: secretion and medical uses of, 380, 382; and stress, 380-81; and blood pres¬ sure, 480 cortisonelike substances from adrenal cortex, number known, 380 cotton, 146; insect pollination of, 224; poly¬ ploidy in, 539-40; improved, 587; hybridi¬ zation and wilt-resistant, 589, 590; desir¬ able traits of, 590; Dixie Triumph, 590; yields per acre, 623; irrigation of, 632 cotton boll weevils, 223 cottonmouth. See water moccasin cottonwood, veins in leaf of, 271; and water loss from irrigation ditches, 632 cotyledons, 495. See also dicots and monocots coughing, 405 cover crops, 624, 631 covering tissue, 40, 41, 43; of sponges, 167; of leaves, 270 cover slip, 20, 28 cowpeas, wilt-resistant, 590 cow pony, 562 cowpox, and control of smallpox, 450—52 cows, 173, 217, 260; and tapeworms of man, 173; stomach of, 253; as ungulates, 254; and rabies, 453; gestation period in, 506; crossed with buffalo, 591 coyotes, 254, 604, 606, 637; in balance of na¬ ture, 602, 603 crabs, 208, 213, 227; molting of, 208; spider, 227 cranberries, 142 cranial nerves: of fish, 301, 303; of frog, 311, Frog Chart 3 following 304; of man, Hu¬ man Body Chart 4 following 336, 389, 390. See also nervous system cranium: of lamprey, 234; of frog. Frog Chart 1 following 304; of man, Human Body Chart 1 following 336, 349 crayfish, 154, 206, 208, 209, 213, 214, 227 Cretaceous Period, 571, 577, 579 cretin, 378 cretinism, 440, 459 crickets, 218, 226, 227 Crinoidea, classification summary, 201 crocodiles, 241, 242, 245, 258, 314, 316 crop: of earthworm, 191, 193, 194; of grass¬ hopper, 219 crop residues, 626, 627 crop rotation, 624-25; example of, 624 crops: disease-resistant, 590; close-growing and open-tilled, 624, 625; green-manure, 627. See also names of particular crops, such as corn cross-breeding. See hybridization crossing over: during meiosis, 540, 541; and new varieties, 552 cross-pollination: of clover, Plant Chart 4 fol¬ lowing 288; opposed to other methods of pollination, 494; Mendel’s use of, 516; and experiments on genetics of garden flowers, 544—45. See also hybridization crowfoot family, 149 crows, value of, 248, 637 Crustacea, 213, 217; classification summary, 227. See also crustaceans Crustaceans, 213-17, 227, 573; as food of fish, 299; parthenogenesis in, 505; in food chains, 613, 615 crying, of infant, 405 cud chewing, 253, 254 cultures: defined, 49; of protozoa, 49; of bac¬ teria, 113, 429-430; of hydra, 169; of polio virus, 448 cup fungi, 121 cuspids, 333 cuticle, of annelids and arthropods, 208-09, 213 cuttings, plant, 487 cuttlefish, 189 Cyanophyceae, classification summary, 120 Cyanophyta, 121 cycads, 144, 145 Cycas revoluta, 145 Cyclostomata: defined, 234; classification summary, 258 cypress, 142 cysts: of parasitic worms, 173, 177, 178; as abnormal growths, in man, 474 cytoplasm, 29, 31, 33; of red blood cells, 34; visible particles in, 52; molecular motion in, 61; of pleurococcus, 85; of neurons, 320; and heredity, 541. See also cells daddy longlegs, 211 daffodil, 148, 487, 490 dahlia, 150, 487; pink and white flowers on same plant, 536-37 daily habits, and health, 467 dairy foods, 369, 370 daisy, 150, 280 daisy family. See composite family dams, and flood control, 631 damsel Hies, 154, 226 dandelion, 150, 603, 608; examining leaves of, 269; stems of, 278; roots of, 282; par¬ thenogenesis in, 505 danger signals: of tuberculosis, 461-62; of cancer, 475-76; of heart diseases, 482 INDEX 695 Darwin, Charles, 192, 206, 582, 582, 584 dates, 146 deaminization, 346 death rates: among drinkers and nondrinkers, 441—42; among smokers and nonsmokers, 442; from pneumonia, 456, 457; from tuber¬ culosis, 457, 462, 473; total, 473; from cancer and heart diseases, 473; and cancer of uterus, 476 decay, bacteria and, 119 deciduous forests, 633—34 deciduous trees, defined, 609 deer, 18, 109, 250, 260, 422, 607, 609; as ungulates, 254; in Grand Canyon National Game Preserve, 602, 603, 605; in food chains, 613, 614; and forest, 633; controlled hunting of, 637 deficiency diseases: and lack of minerals, table, 361, table, 440; and lack of vitamins, 362-65, table, 440. See also diseases, non- infectious degenerative diseases of aging, 459, 479 deme, defined, 603. See also biomes Demospongiae, classification summary, 164 dendrites, 320, 321, 410; in brain, 392 Dentalium, 189 depletion: of soil, 625-26; reduced by crop rotation, 624-25 depressants, defined, 441. See also drugs deserts: lichens on, 118; mosses on, 122; toads and frogs on, 240; as biomes, 600-01, 600-01, 603; dust storms on, 605; irriga¬ tion of, 629, 630, 632 devil’s apron, 113 Devonian Period, 571, 572; life during, 574- 75 DeVries, Hugo, 152, 584 dew sores, 178 diabetes, 347, 439, 440; and sugar in urine, 347; and insulin, 375, 376, 377, 455, 459; in identical twins, 532-33 diagnosis: modern point of view toward, 444- 45; modern methods of, 459-62; tools used in, 459; laboratory tests as part of, 459-60; use of X rays in, 460, 461; of cancer, 475, 476 diamond, 38-39 diamondback rattlers. See rattlesnakes diaphragm, 249, 307; defined, 249; use in breathing, Human Body Chart 6 following 336, 337, 338 diarrhea: and raw milk, 437; as an allergy, 439 diastase, 495 diatomaceous earth, 86, 113 diatoms, 85, 86, 107, 120; examining, 85—86; in seas, 113; and food chains in Arctic, 299-300, 613, 615 dicots: defined, 145; compared with mono¬ cots, 143, 145—46, 268, Plant Charts follow¬ ing 288; examining leaves of, 146; stems of, 280, 281; germination of seeds of, 495, 585. See also Dicotyledonae Dicotyledonae, 107, 143, 145, 146; classifica¬ tion summary, 149-50; Plant Chart 3 fol¬ lowing 288. See also dicots diet: how to record daily, 350; indispensable foods in daily, 352; adequate daily, 369, 370; faulty, and diseases, 440. See also foods diffusion, 270, 284-86, 288; in guard cells, 270; of plant hormones, 290; in gills of fish, 300; in frog’s lungs and skin, 308—09; in in¬ testines, 334, 335; in mammalian placenta, 505. See also osmosis digestion: as metabolism, 70; in protozoa, 76; in ameba and paramecium, 79; in spirogyra, 84; in hydra, 165-67; in planarians, 172; in earthworm, 192-93; in starfish, 198-99; in termites, 225; diffusion and, 287-88; in fish, 302; enzymes and, 315; protein, 330; in man, table, 334; and vitamins, 364; nerve control of, 395; in dogs, 406; in sprouting corn, 495 digestive enzymes. See enzymes digestive food vacuoles: of ameba, 77, 78; of paramecium, 80, 80; of V orticella, 159; of hydra, 166; of planarians, 172 digestive glands: of chiton, 185; of clam, 187; of lobster, 214, 215; of grasshopper, 219; of lancelet, 233; of frog, Frog Chart 6 following 288; of man, 330, 331-32, table, 334, Human Body Chart 7 following 336 digestive juices: nerve control of flow, 319, 391, 394, 395; human, 331-32, table, 334. See also saliva, gastric juice, etc. digestive-muscular tissue, in hydra, 167, 169 digestive system, 44; of planarians, 170, 171; of Ascaris, 176; of mollusks, 184; of chiton, 185; of fresh-water clam, 186, 187; of earth¬ worm, 191, 192-93; of starfish, 199; of lob¬ ster, 215; of grasshopper, 219; of lancelet, 233; of yellow perch, 301; of frog. Frog Chart 6 following 304; of man, 330—36, Human Bodv Chart 7 following 336. See also food tube, digestive glands, etc., and names of particular animals dihybrid crosses, 526-28. See also hvbridi- zation dinosaurs, 158, 241, 565, 571, 577, 578; six main types of, 577; extinction of, 577 dinosaur tracks, 569 diphtheria, 50, 428, 436; germ of, 431; toxin, 435; treatment with antitoxin, 452; pre¬ vention with toxin inoculation, 454, table, 455 Diplodocus, 577, 578 diploid number, 502, 503, 504, 540; in man, 502-03, 503; in various plants and animals, table, 503; in apples, 597 Diptera, 226; classification summary, 228 diseases of man, 426-83; protozoa and, 158— 696 INDEX 59; and worm parasites, 173, 175, 177-78; causes of, 428-45, table, 436, table, 440, table, 444; contagious, 428, 429, 433; in¬ fectious, 436, 437, 444; noninfectious, 439- 42; and body stability, 442-45; newer out¬ look upon, 444; control of, 448—71; mental, 458-59; unsolved problems of, 472-83; heart, cancer, and degenerative, 472-83. See also names of specific diseases dispositions, of identical twins, 533 dissecting tools, 19, 20, 21 dissection. See earthworm, fish, frog, etc. distemper, 454 Ditmars, Raymond L., 585 DNA, and genes, 535, 536 dobson flies, 218 doctors: scrubbing hands and arms before surgery, 427; in surgery, 463, 464; when to call, in case of accidents, 465, 466; impor¬ tance of regular visits to, 475, 479, 482; visits to, during pregnancy, 508 dodder, 152, 283 dog, 44, 160, 260, 407; and tapeworms, 175; as carnivores, 254; poisoned by some toads, 239; temperature regulation of, 317; and behavior with an opossum, 318, 322; black tongue of, 365; inborn and conditioned responses of, 406-07, 415; rabies and, 448, 453; chromosome numbers in, 503; gesta¬ tion period of, 506 dogfish, 234, 235, 258 dogtooth violet, 490 dogwood, 639 dolphins, 260 domesticated plants and animals, mutations and selection among, 547 dominance, principle of, in genetics, 521, 524, 525, 542; incomplete, 524-25, 525 dominant traits. See traits dope, and dope rings, 469 dorsal blood vessel, of earthworm. See blood vessels dorsal ganglia. See ganglia dorsal nerve cords. See nerve cords dorsal side, defined, 170, 171 dragonflies, 154, 205, 226, 613; ancient, 575 drones, in bee colony, 224, 505 Drosophilia melanogaster, 530. See also fruit flies drought, and dust storms, 605, 608 drug addiction: and tranquilizers, 458, 459; extent of, in U.S., 468-69; dangers in, 468- 69; how spread, 469 drug addicts, 442, 468-69; government hos¬ pitals for, 469 drugs: unlawful use of, and disease, 439, 442; specific, 455-58; and use in surgery, 463. See also names of drugs (penicillin, isonia- zids, etc. ) duck banding, 635 duckbilled platypus, 250, 251 duck-foot tiller, 628 ducks, 246, 247, 258; wild, 638 duckweed, 142, 269 ductless glands, of man: Human Body Chart 8 following 336, 374-82. See also endo¬ crine glands ducts: of digestive glands, 331; lymph, 336, 343; of sweat glands, 347, 449; of liver and pancreas, 374, Frog Chart 6 following 304, Human Body Chart 7 following 336. See also common duct and bile duct Dugesia, 175 duodenum, 333, 374; defined, 333; hormones secreted by, 382. See also food tube, of man dust storms, 605, 608 Dutchman’s breeches, 639 Dutroehet, 27 dysentery, bacillary, 436. See also amebic dysentery eagle, 422, 423 ear canal, lining of, 40 eardrum: of grasshopper, 218; of frog, 305, 311-12; of man, 402, 403 Earl, Lt. Col. Marion E., 645 ear lobes, of man, 551 ears, 43, 44; of fish, 304; of frog, 311; of man, 390, 402, 403 earth: changing features of, 565-66; changing shorelines in China, 565; age of, 566-67 earth history, 564-72; violent changes in past, 569; subdivisions of, 569, 570; order of events in, 569, 570, 571; plotting on 24- hour time scale, 570, 571; timetable of, 571. See also life, history of, on earth earthworm, 24, 25, 44, 157, 183, 190-97, 191, T9iri977 262, 207, 211, 214, 298, 305, 306, 603; how to collect and preserve, 155; muscle layers of, 191; how to dissect, 192- 93; locomotion and castings of, 192; diges¬ tion in, 192-93; breathing of, 194-95; ex¬ cretion, 195; nervous system and reactions of, 195; scientific name, 197; reproduction in, 196, 496-97, 496; neurons of, 324; chro¬ mosome numbers in, table, 503; counts per acre, 622 Echinodermata, 198; classification summary, 201. See also echinoderms echinoderms, 198—200, 201, 202; blueprint of typical, 199; in Ordovician Period, 573 Echinoidea, classification summary, 201 ecology, 602-19; defined, 603 economic importance: of pteridophytes, 140; of seed plants, 146; of mollusks, 188; of spiders, 212; of beetles, 222, 223; of bees, 223; of vertebrates, 234; of birds, 248. See also names of other organisms ectoderm, 166, 167, 168, 174, 498; of hydra, 166, 167; of jellyfish, 168; tissues from em- INDEX 697 ectoderm ( continued ) bryonic, 169, 506; of planarian, 170, 171, 172; of starfish, 199 Edentata, classification summary, 259 egg-laying mammals, 250, 251, 259 egg mother cell, 500, 501 egg nucleus, in ovule, 491, 492 eggs: as single cells, 35; divisions in, 37; of flowers, 89, 90, 491, 492; of mosses, 124, 125, 125; of sponges, 162; of hydra, 167; of planarian, 172; of grasshoppers, 218, 219; of monarch butterfly, 221, 222; of ter¬ mites, 225; in insects, 226; of toads, 239; with shells, 245, 247, 251; of birds, 247; in osmosis experiment, 285-86; of frog, Frog Chart 7 following 304, 308, 310, 311, 497, 498; of penguin, 316; growth of un¬ fertilized, 486; chromosomes in, 489, 500, 501; of earthworm, 496; maturation of, in higher animals, 500, 502; of mammals, 504; human, 506, 507 ( see also ovum ) ; sex chromosomes in, 509, 510; of fruit fly, 510 egg white, 52; as a colloid, 65, 66; experiment with, 332—33 Eijkman, Dr. Christiaan, 363 Elasmobranchii: defined, 234; classification summary, 258 elbow, bending and straightening of, Frog Chart 1 following 304, 307, Human Body Chart 3 following 336 elderberry, twigs of, 280 electrical impulses, of nerve pathways, 410, 411 electron microscope, 32, 427 electrons, 54, 55, 56, 93, 95; speed of, 55; in orbit, 58 elements, 55—56, 95; defined, 55; table of first ten, 55; number known, 55-56; in common compounds, 59; in nutrients, 68; in all liv¬ ing things, 68-69; in human body, 351, 352, table, 352; needed by crop plants, 628 elephant, 35, 40, 44, 260, 566; gestation pe¬ riod of, 506; ancestors of, 564, 580, 581; extinct, 581 elk, 254, 634 elk kelps, 113 elm, 149, 280; examining leaves of, 269; ehromosome numbers in, table, 503; and Dutch elm disease, 618 elm family, classification summary, 149 clodea, 33, 165, 603; examining leaf of, 72 embryos, 143, 172, 489; of bean, 142, 267, 495; of seed plant, defined, 143; of sponge, 162; of planarian, 170; animals with 3- layered, 172, 179, 498; of mollusks, 186; of starfish, 198, 200; of vertebrates, 200, 236, 498; notochords in chordate, 233, 257; of mammals, 250, 504, 505, 506; of corn, Plant Chart 2 following 288, 495; rabies vaccine from chick, 448; of seeds, 491; of earth¬ worm, 496; of frog, 497, 498, 499; of rabbit. 504; 60-hour human, 507, 508; Rh factor and human, 508-09. See also frogs and mammals emotional behavior, in man, 409-10; inborn and acquired, 409-10; and blood pressure, 480 emotions, 409 emulsification, of fats, in digestion, 333 emulsion, defined, 65 Endameba, 158 endocrine glands; Human Body Chart 8 fol¬ lowing 336, 373—82; defined, 374; summar¬ ized, 397, table, 382; and diseases, 440, 444 endoderm, 172, 174, 498; of hydra, 166, 167; of jellyfish, 168; tissues derived from em¬ bryonic, 169, 506; of planarian, 170, 171 endodermis, of fern stem, 134 end organs: of taste and smell in man, 404; in skin of man, 404 endoskeleton, 213, 215; lime salts in, 213; chordate, 232, 257; of frog, Frog Chart 1 following 304; of man. Human Body Chart 1 following 336 endosperm, of corn, 495 enemies, value of natural, 223 energy; from food, 69, 195; from oxidation, 69; used and stored in photosynthesis, 272; from cell respiration, 276, 278; from human metabolism, 343; used in muscles, 345; measuring, stored in foods, 353, 354 energy foods. See foods energy needs, of human body, 353-55, table, 355; summarized, 358 environment: man’s control over, 256, 423; man’s reactions to, 400-25; exchanges of materials with, by organisms, 614, 616. See also heredity and environment enzymes, 314-16; defined, 315; respiratory, 314-15; digestive, 315; speed of reactions due to, 315; in photosynthesis, 316; from fig tree, 316; in blood, 316, 383, 385, 386; and vitamins, 352; and heredity, 531, 536 Eocene Period, 563, 580, 581 Eohippus, 559, 560, 561, 562, 563, 564, 580, 581 epidermis: of green leaves, 43, 89, 270-71, Plant Charts following 288; of roots, 89, 283, Plant Charts following 288; of fern stem, 134; of worms and arthropods, 208; examining leaf, 269; of stems, 280, 281, Plant Charts following 288. See also skin, human epiglottis, defined, 338 epithelial tissue: of man, 40, 41; of hydra, 167; of planarian, 170; of mammalian body cavity, 250. See also tissues epithelium: defined, 40, 41; of respiratory system of man, 338 epochs, geologic, 570, 571 equation, of photosynthesis, 272 698 INDEX equator, of the spindle during cell division, 39 equipment, for biology experiments, 19-21, 19. 20, 21 Equisetineae, 139, classification summary, 141 Equisetum, 139 Equisetum arvense, 141 Equisetum heimale, 139, 141 Equus, 561, 562, 563 eras, geologic, 569, 570; in timetable, 571 erepsin, 334 erosion, 605, 621; by wind, 605, 608; after forest fires, 620; due to water, 623. See also soil conservation Eryops, 575, 576, 577 erysipelas, 436 erythromycin, 457, table, 459 escape velocity, and space travel, 643, 646, 648 Eskimos: blood groups of, 389; food chains of, 613, 614, 615 esophagus, of earthworm, 191, 193, 194; of frog. Frog Chart 6 following 304; Human Body Chart 7 following 336. See also gul¬ let Essary, S. H., 587, 588 essential amino acids. See amino acids estrogens, 381, 382 ether, 463; first uses in surgery, 462 ethvl alcohol, 34 Euglena, 110, 120, 160, 163 eurypterids, 573, 574 Eustachian tubes: of frog, 305, 306, 311; of man, 402, 403 Evans, Dr. Herbert, and research on pituitary, 373 evaporation: and molecular motion, 62; and cooling of leaves, 278; as diffusion, 285; and cooling of birds and mammals, 317 evening primrose, 152 evergreen trees, 144. See also conifers and specific names (fir, pine, spruce, etc.) evolution, defined, 582 ewe, 546 excitement, as behavior, 409 excretion: defined, 76, 345; in protozoa, 79, 160; in pleurococcus, 85; by gills, 91, 92; in fish, 91, 303; in sponges, 161; in earth¬ worm, 195; in frog, Frog Chart 5 following 304, 310; in man. Human Body Chart 8 following 336. See also excretory system, kidneys, etc. excretory pore, of clam, 187 excretory system: of planarian, 170, 171, 172; of roundworms, 176; of chiton, 185; of clam, 186, 187; of lobster, 215, 217; of man, Human Body Chart 8 following 336, 345, 346, 347, 348. See also kidneys excretory tubules, 194; defined, 195; of earth¬ worm, 191; of grasshopper, 219. See also kidney exercise: and production of carbon dioxide, 338; and red blood cell counts, 384; and blood pressure, 480 exoskeleton: of chiton, 185; of fresh-water clam, 186, 187; of starfish, 199; of arthro¬ pods, 207, 213, 215, 216, 217, 218, 219; and molting, 208; secretion of arthropod, 208—09; fossilized, 568 experience, and learning, 407 Explorer satellites, 645-46 extinct, defined, 576 eye color, and heredity, 499, 502, 515, 525, 538 eyelids, of frog, 311 eye muscles, of lobster, 216 eyepiece, of microscope, 20, 22 eyes, 43, 44, 69, 195, 395; transplanting cornea of, 50, 402; of planarians, 171, 172; of mantis, 207; compound, 209, 215, 216, 217, 218, 219; of centipede, 211; detailed structure of compound, in lobster, 216; of grasshopper, 219; insect, 220; of primates, 254; of fish, 304; of frog, 311; and vitamin needs for functioning of, 365, 366; of man, 390, 401, 401, 402 eye spot, 110, 111, 234 Fx and F2 . See generations fall-out, radioactive, and cancer, 477 families, of organisms: defined, 104; table, 105; of flowering plants, 148, 149, 150: origin of new, 582 family, genetic chart of a human, 530 fan worms, 196, 197 farsightedness, 401 fat, in burning candle, 62 fat bodies, of frogs, 311; Frog Chart 7 fol¬ lowing 304 fat cells, in human skin, 347 fats, 66, 68, 69; as source of energy, 69, 352- 53; made by plants, 274; digestion and ab¬ sorption of, in man, 334; daily required amounts of, in man, table, 355; amounts of, in common food portions, table, 356-57; in human blood, 334; in human foods, 552 fat-soluble vitamins, 362, 365, 367-68 fat tissue, 42, 43, 343 fatty tumors, 474 fear: adrenalin and reactions to, 381; as be¬ havior, 409 feathers, 245; advantages of, to birds, 245; and warm-bloodedness, 317 feeding experiments, 363, 364, 372 feeling. See sensitivity feet: sweating of, 62; webbed, 246, 247; of birds, 247; of man, Human Body Chart 3 following 336; of horse ancestors, 560, 561, 562 femur: Frog Chart 1 following 304; Human Body Chart 1 following 336; broken, 344 fermentation, 118 INDEX 699 ferns. 44, 95, 102, 103, 108, 118, 123, 132- 41, 566, 571, 581; sporangia of, 115, 135; cells of fossil stem of, 132; stems of, 132, 133, 134, 135; how to identify, 133; charac¬ teristics of, 133, 134, 135, 136, 137; sword, 134; how to examine, 134; Christmas, 135; life cycle of (reproduction), 135-36; alter¬ nation of generations in, 135—36; prothallia of, 136; class of, 136, 137; staghorn, 136, 137; of coal forests, 136-37; cinnamon, 137; origin, age, and ancestry of, 139-40, 573; classification summary of, 141; how to examine prothallia of, 152; reduction divi¬ sion in, 503; in plant succession, 608, 609, 611 fertilization: of lobster eggs, 216; internal, in birds, reptiles, and mammals, 247, 250, 504; of eggs, 489; in flowering plants, 491, 492; of frog’s eggs, 497; effects of, 505; and sex chromosomes, 509, 510; and new gene combinations, 551-52 fertilized eggs: of fish, 93; of mosses, 124, 125, 125; of seed plants, 143; mitotic cell division of, 497; of mammals, 504. See also eggs and ovum fertilizers, for crop lands, 625, 628 fever, in germ diseases, 435 fibers: nerve, 43 (see also nerves); from plants, 146; muscle, of planarian, 171 fibrillar network, in cell, 67 fibrin, 386 fibrinogen, 383, 386 fibroid tumors, 474 fibrous roots, 282 fibrovascular bundles: in fern stem, 134; tis¬ sues in, 134-35; arrangement of, in mono¬ cots and dicots, 268; in seed plant stems, 279, 280, 281; Seed Plant Charts following 288 fibrovascular system, radioisotopes in, of leaf, 273 field mice, 330; as prey of birds, 246; as de¬ stroyers of grain, 248; in food chains, 613' figs, 283 figwort family, 150 filaments: of pond scum, 82; of spirogyra, 84; of algae, 102, 107, 109; of molds, 114, 115; of orchid seed embryos, 143; of flowers, 490, 490, 492 filaree, 613 Filicineae, classification summary, 141 fine adjustment, of compound microscope, 22, 22 finger, safety in pricking, to get a drop of blood, 34, 48 fingerprints, of identical twins, 532 fin rays, of lancelet, 233 fins, 92, 303; of lancelet, 233; of fish, 92, 236, 237, 301; of lungfish, 238; of yellow perch, 300, 301 firefly, 168, 223 firs, 147, 205; Douglas, 603; balsam, 609 fish, 92, 154, 160, 198, 232, 246, 248, 251; life processes of, 89-93, table, 91; breath¬ ing, 90; reproduction in, 93, jawless, 234, 258; cartilaginous, 235, 235, 258; bony, 333, 258; deep ^0^2.37) age of, from scale*, 262; habitats, 299; study of yellow perch, 299-304 ;_ organ, _ systems of. 300^04,. 3017— blueprint of, 301; how to-removc brain of, 304; brain of, 319; first, and history of early, 571, 573, 574, 576; in food chains, 613, 615 Fish and Wildlife Service, 621, 635, 638 fish hatcheries, 636-37 fishing worms, 190. See also earthworms fish roe. See roe flagella: of Euglena, 110; of Volvox, 111; of cells in sponges, 161, 164; of protozoa, 163; of cells in hydra, 166, 167, 169; of cells in coelenterates, 169 flagellates: defined, 110; examination of, 110- 12, 110, 111 ; as borderline organisms ( al¬ gae and protozoa), 110-12; classification summary, 120, 163; in food tube of ter¬ mites, 225 flagellum, defined, 110. See also flagella flamingo, 246 flasks, 19, 19 flatworms, 95, 169-73, 171, 176; classification summary, 175 flavors, as stimuli, 401, 403, 404 flax, 146, 590 Fleming, Sir Alexander, 456 flesh-eating animals. See carnivores flesh-eating mammals, 260. See also Carnivora flicker, 106, 607 flies, 218; classification of, 226. See also houseflies flight: adaptations of birds for, 246, 248; man and space, 642-44, 647-52 floods, 605, 631 Florida, 162 flower color, 515, 518; genotype and pheno¬ type ratios in F2 generation of garden peas, 524 flowering plants, 88; defined, 145; organs of, 43, 44, 87—90, 90; life processes of, 87—90; classes and families of, 143, 145, 146, 148, 149, 150, 151; asexual reproduction in, 486-89; sexual reproduction in, 489-95; alternation of generations in, 491-92; re¬ duction division in, 503; parthenogenesis in, 505. See also angiosperms flowers, 43, 44, 144, 266, 276, 490-94; parts of typical, 87, 88, 490, 491; apple, 490; complete and incomplete, perfect and im¬ perfect, 492-94; saguaro, 493; essential parts of, 493; color in, 515, 518; garden pea, 518; genotype and phenotype ratios in Fj and F2, generations of, 525, 525 700 INDEX flukes, 173, 175, 202; classification summary, 175 fluorine, 55, in human body, 352; in drinking water, 361 fly: mounting wing of, 20—21; classification of, 228; damsel, see damsel fly flycatchers, vermilion, 245 flying fish, 246 flying saucers, 205-06 flying squirrels, 246, 252 focusing: of microscope, 21, 22; of human eye, 401 folic acid, 365, 440 food: ingestion of, defined, 77; making of, in plants, 82, 113, 271-76, 278; percentage of human, obtained from grains, 146; of earthworm, 192, 195; of centipede, 211; of millipede, 211; of crayfish, 214; of termite, 225; of frog, 240; of copperhead snake, 244; of birds, 246, 247; of platypus, 251; storage of, in plants, 267, 268-69, 282, 284, 492, 495; transport of, in plants, 280; of fish, 299; and animal learning, 417, 418, 419; germs spread in, 437. See also foods of man food and drug laws, 370 food cavity, in coelenterates, 166, 169 food chains, 613, 614, 615, 616 food deficiencies, and disease, 440 food-getting: in ameba and paramecium, table, 79; in fish, 90, 299-300; in vorticella, 160; in sponges, 161; in hydra, 165; in planarian, 172; in chiton, 185; in clam, 186; in starfish, 198—99; in frog, 305 food labels, 370, 372 food-making, defined, 82; in algae, 82, 113; steps in, for all green plants, 271—76, 278 food tests, for sugar, 332; for ascorbic acid, 366 food-transport tissue, 43, 108, 113. See also phloem food tube, 158, 165, 166, 179; muscles of, 40, 41, 43; of planarian, 172; of Ascaris, 176, 177; of Bryozoa, 180; of mollusks, 184; of clams, 186, 187; of earthworm, 191, 192, 193; of lobster, 215, 217; of grasshopper, 218, 219; of fish, 300, 301, 302; of frog, 308—09, 311, Frog Chart 6 following 304; of man, 330-31, Human Body Chart 7 fol¬ lowing 336 food vacuoles. See vacuoles food vessels, in roots and steins, 88, 89. See also phloem foods of man, 188, 268, 328, 351-71; from mollusks, 188; from plant organs, 268; in human cells, 343; indispensable, 352-53; energy, 353—54; calories in, 353—54; tables of common portions, 355, 356-57, 361; rich in proteins, 359, 360; rich in minerals, 361; essential, in adequate diet, 369, 370. See also food “fool’s gold,” 54 foot, muscular: of chiton, 185, 186; of snail, 186; of clam, 187 forage crops, water and land, 109 foraminifera, 163 forest fires, 620; number of, each day, 620, 634; reclaiming of burned-out areas of, 621, 622; in California, 625—26; causes of, 633; prevention, 639 forest management, in New England, 612 Forest Service, 621, 626, 635 forests: first known, 575; as biomes, 603; and water run-off, 626; acreage in U.S., 629; enemies of, 633; new annual growth of, 633; injuries to, caused by disease, 633; and animals, 633-34; conservation of, 633- 35; as continuing crops, 633, 634 formaldehyde, and preserving earthworms, 155 formed elements, of blood, 384; how to ex¬ amine, 383 forsythia, 487, 490 fossils: of fern stem, 132; cell structure pre¬ served in, 132, 568; of horse ancestors, 560, 561, 562; and how they get into rocks, 568; of seed fern, 568; and how they are made, 568; of dinosaur tracks, 569; ex¬ posure of, 569; of sea shells, 569, 570; of first land plants, 573; of first land animals, 573, 574. See also earth history and living things, history of four o’clocks, color inheritance in, 524, 525 foxes, 254, 607, 609; and rabies, 453 foxglove, 150 fractures, bone, simple and compound, 465-66 fraternal twins. See twins free-living, defined, 173 frog legs, as food, 240 frogs, 24, 25, 108, 154, 232, 235, 236, 239, 240, 258, 295, 297; characteristics of, 238, 240; metamorphosis in, 238, Frog Chart Cover following 304; wood, 239, 607; bark¬ ing of desert, 240; leopard, 304-12, Frog Charts following 304; anatomy and physiol¬ ogy of, 304-12, Frog Charts following 304; bones of, Frog Chart 1 following 304; skeletal muscles of, Frog Chart 2 following 304; nervous system of, Frog Chart 3 following 304, 311-12; circu¬ latory system of, Frog Chart 4 following 304, 309-10; breathing of, Frog Chart 5 following 304, 307-08; digestive system of, Frog Chart 6 following 304, 308-09; re¬ production in, Frog Chart 7 following 304, 497-503, 513; heart of, Frog Chart 4 fol¬ lowing 304, 310; mouth of, 305; removing skin from legs of, 306; locomotion and length of jump of, 306; tree and singing, 308, 309; excretion in, 310; how to dissect, 310-11 fronds, of ferns, 133, 134, 135; of seed fern, 138 INDEX 701 fructose, 273 fruit Hies: chromosome numbers of, 503, 509; sex determination in, 509, 510; giant chro¬ mosomes of, 517; alleles for eye color in, 530; mutant, from X rays, 538; mutations in, 539, 547-50, 549; crossing over of genes in, 541; how to breed, 544, 552; alleles for wing length in, 547, 548; dominant and recessive traits of, 549-50; length of time from one generation to next in, 549 fruits, 89, 90; compared with cones, 144; as seed containers, 145; and insect pollination, 224; in adequate human diet, 363, 369, 370; as matured flower ovaries, 491, 492; of saguaro, 493; polyploidy in, 552. See also apples, etc. fruit trees, budding and grafting of, 488 Fucus, 120 Fuglio, 121 fungi: defined, 117, 121; as a class, 114, 115, 116, 117; in lichens, 117, 118; importance of, to man, 118-19; classification summary, 121; and club moss gametophytes, 139; as termite crops, 225; as germs, 433, 436, 437; and rust of clover, 587 Funk, Casimir, 364 funnel, 19, 19 fur: of rodents, 253; and warm-bloodedness, 317 g See gravity, and space travel gall bladder: of fish, 301, 302, 308; of frog, Frog Chart 6 following 304; of man, 332, Human Body Chart 7 following 336 galls: plant, 472; oak, 474 gallstones: X rays in diagnosing, 460, 461; surgery for, 462 game birds, 248; breeding and releasing of, 636-37; controlled hunting of, 638 game preserve, 602; Grand Canyon National, 602-03, 605 gametes, 124, 147, 489; defined, 124; of mosses, 126; of flowers, 491; chromosomes and genes in, 516, 521, 528. See also sperms, eggs, and ovum gametophytes, 503; of mosses, 125, 126; of ferns, 136, 141; of club mosses, 139; of psilopsids, 140; of flowering plants, 147, 491. See also alternation of generations gamma garden, 596, 597 ganglia, 236, 298; of clam, 186, 187; of earth¬ worm, 190, 191, 194, 195-96; of lobster, 214, 215, 217; of grasshopper, 219; of frog, Frog Chart 3 following 304; autonomic, of man, Human Body Chart 4 following 336, 389, 390, 391, 394, 395 garbage disposal, 468 garden pea: self-pollination in, 494, 518; chromosome numbers in, 503; Mendel’s ex¬ periments with, 516-20; flower of, 518; heredity of height, 523; dihybrid cross, 528; possible gene combinations in fertilized egg, 552; hybrid vigor in, 591 garden toad, 240 gas gangrene: germs in soil, 438; treatment, 459 gases, 64 gastric glands, of man, 331, 332, 396 gastric juice, 330, 331; action of, 332-33 Gastropoda, classification summary, 189 gazelles, 254 geese, 246, 638 Geiger counter, 56 gel state, of colloid, 66 gene, possible photograph of, 517. See also genes gene interaction, principle of, 521, 525 gene locus, 534-35, 536, 547; defined, 534; number known in fruit flies, 549 gene pools, 550 genera: defined, 104; table, 105; origin of new, 574, 582. For names of individual genera, see italicized entries generalization: cell theory as example of, 35; ability to make, 420 generations: alternation of, 123, 125, 126, 135-36, 491-92; Fx and F2 defined, 519; length of time from one to another in fruit fly and man, 549 genes: and bleeder’s disease, 524; number in human cells, 499; self-duplication of, 499- 500; arrangement in chromosomes, 500, 534-35; linkage of, 516; in mitotic and meiotic cell divisions, 516; in paired chro¬ mosomes, 520-21; and principles of ge¬ netics, 521; and human blood groups, 529; nature and chemical make-up of, 534-42; space occupied by all, of next human gen¬ eration, 536; mutations of, 536, 537, 538, 539, 547, 549, 550; transduction of, 539, 552; translocation in crossing over, 540, 541; plasma, 541; of ancon sheep, 546, 547; and rise of new varieties, 551, 552, 553, 591; of horses, 559; and cow’s milk produc¬ tion, 589; and disease resistance, 590; of buffalo, in cattle lines, 591. See also gene, gene locus, and gene pool genetic systems, stability and mutability of, 546 genetics, 514—45; defined, 514; false beliefs about, 515; principles of, 515-34; useful terms of, reviewed, 520-21; summarized, 521-22, 524, 525, 534; of identical twins, 532-33; applications of, 542; and evolution, 581-83; and plant and animal breeding, 586-99 genotype, 521, 522, 547, 548; defined, 521; ratios in F2 generation, 522, 523; of hu¬ man blood groups, 529 gentians, 639 genus, defined, 104. See also genera 702 INDEX geology, 152; defined, 566; timetable of, 571. See also fossils, earth history, and living things, history of geotropisms, 290, 291 geranium, 87, 280, 487; albino branch of, 537 Gerard, Ralph W., 99, 315 germ diseases, heredity and, 436. See also diseases germ theory of disease, 428, 443; early history " of, 429-31 germination, directions for, of peas, beans, and corn, 204; explanation of, 495 germs, 44; of diphtheria, 50; protozoa as, 158-59, 163, 433, 436; and how spread, 226, 437-38; bacteria as, 431-33, 436, 437; fungi as, 433, 436; viruses as, 433—34, 436; rickettsias as, 434; toxins of, 435, 436; and tissue damage, 435-36; man’s natural de¬ fenses against, 448—50; in wounds, 449, 465, 466; immunization against, 450-55. See also diseases Gertsch, Dr. Willis J., 205, 206, 208 gestation period, 506 giant, 373 gibbons, 260 Gila monster, 241 gill arch, 300 gill chamber, 91, 300 gill filaments, 92, 300, 303 gill rakers, 90, 92, 299, 300 gills, 91, 92, 194; of mushroom, 116; of chiton, 185; of clam, 186, 187; of fan worms, 196; of starfish, 199, 200; of lob¬ ster, 214, 215, 216, 217; of lancelets, 234; of fish, 237, 301, 307; of lungfish, 238; examining, 300; of tadpoles, 498 gill slits, 90, 233, 299 Ginkgo, 144, 147 giraffes, 254 girdle, of earthworm, 191, 496; of chiton, 185 girdling a tree, 282 gizzard, of earthworm, 191, 193, 194 gladiolus, 487 glands, digestive. See digestive glands glands, ductless, 374-82; of toad skin, 239—40 glassware, useful in biology, 19-20, 19, 20 glottis, of frog, Frog Charts 5 and 6 follow¬ ing 304, 305, 306, 308 glow worms, 223 glucose, manufacture of, in green leaves, 271- 73; in human blood, 273, 383; temperature necessary for oxidation of, 314-15; absorp¬ tion of, into human blood, 335; from carbo¬ hydrate digestion, 334; stored in human liver, 339; in human cells, 343; from deami¬ nization, 346; made from glycogen in liver, 397. For formula and stick model of mole¬ cule, see grape sugar glycerol, 274; from fat digestion, 334; in hu¬ man cells, 343 glycogen, 339, 397 gnats, 226 gnawing mammals. See rodents goal-insight theory, 419-20 goats, 254, 260 goiter: simple and toxic, 378, 379, 438, 439, 440; surgery in toxic, 462 golden plover, flight of, 246 goldenrod, 150, 608, 639 golden-winged woodpecker, 106 goldfish, 90, 92, 165; classification of, 236; locomotion of, 237; behavior in, 304 gonads, defined, 381 gonorrhea, 436; spread of germs of, 438; treatment for, 459 goose pimples, 393, 394 gophers, 623 gorillas, 255, 260 government agencies, active in conservation, 621 grafting, 488, 489; of navel orange, 547 grain fields, 566 grains, 143, 145-46; as fruits, 145; as human food, 146. See also corn, wheat, rye, rice, etc. Grantia, 161, 164 granular particles, in cell, 67 grapefruit, seedless, 488 grape sugar, 93; formula and stick model of molecule, 59, 60. See also glucose grapes: sugar from, 50; polyploidy in, 597 grass, 192; red top, 613; in food chains, 613. See also grasses grasses: underground stems of, 279; roots of, 282; flowers of, 493; as soil binders, 626 grass family, classification summary, 148 grasshopper, 44, 156, 156, 207, 227; jointed exoskeleton and legs of, 209; dissection and study of, 217, 218, 219; classification of, 226, 227; how to keep living, in class¬ room, 230 grassland f arming, w 625 grasslands: plant o^er of, 605; of southwest¬ ern U.S., 625 gravity: effects on solutions and suspensions, 64-65; plant responses to, 289, 290; and space travel, 643, 644, 645, 647, 648, table, 648 gray matter: of spinal cord, 391; of brain, 392 grazers: in horse ancestry, 562; cattle as, 595 grazing, and forests, 633, 634 great auk, 606 Greek names, 105, 106 green glands, of lobster, 215, 216, 217 green-manure crops, 626-27 green plants. See plants, seed plants, flower¬ ing plants Grew, Nehemiah, 27 gristle, 43. See also cartilage ground itch, 178 ground pine, 138, 139 INDEX 703 growth: cell division during, 40; of protozoa, 75; at root and stem tips, 89, 268; of fern fronds, 133; and vitamins, 364, 365; normal and abnormal, 473-74, 475. See also repro¬ duction, embryos, etc. growth hormones, in plants, 291—93. See also auxins growth responses, to auxins, 292, 293 growth rings: of clam shell, 187; of scales of fish, 262; of trees, see annual rings growths. See tumors guard cells, 270-71, 270, Plant Charts fol¬ lowing 288 guinea pig: gestation period of, 506; genetics of color, 526; dihybrid cross of, 526, 527, 528 gullet: of paramecium, 80; of fish, 91, 301, 302; of Vorticella, 159; of earthworm, 191, 193, 194; of grasshopper, 219; of frog, Frog Chart 6 following 304, 305, 306; of man, 331, 332, Human Body Chart 7 following 336. See also esophagus gulley, before and after planting black locust trees, 623 guppies, 603, 604, 605 Gymnospermae, 145; classification summary, 147. See also gymnosperms gymnosperms, 145, 147, 566, 575; first known, 1 ' 575 habitats: of algae, 49, 108, 109, 112, 113; of protozoa, 49, 158—59; of fungi, 114, 116; of lichens, 118; of mosses, 122, 124; of liverworts, 126; of ferns, 135; of horse¬ tails, 139; of seed plants, 142, 147; of sponges, 162, 164; of planarians and other flatworms, 169, 175; of coelenterates, 174; of roundworms, 176, 178; of Bryozoa, 178; of rotifers, 178; of chitons and other mol- lusks, 185, 189; of earthworms and other annelids, 190, 197; of echinoderms, 201; of centipedes and millipedes, 211; of crusta¬ ceans, 213; of insects, 217, 226; of lancelets, 234; of fish, 236-37, 299; of newts and sala¬ manders, 239; of poisonous snakes, 242-45; and warm-bloodedness, 248; of mammals, 250; of bacteria, 429; of wildlife, 635 habits, 412-13; compared with simple reflex acts, 412; and health, 439; drug, 468-69 Haddonfield giant, 564. See also Hadrosaurus Hadrosaurus, 565, 569, 577, life in time of, 566; number of teeth of, 566 hagfish, 258 hair: root of, in human skin, 347; color of, hereditary, 514, 516, 527; white streak in human, 514 half life, of radioisotopes, 57 hammer, of ear, 402, 403 hamsters, 504 hand lens, 20 haploid number of chromosomes, 502, 503, 504, 540; in polyploid fruits, 597-98 “hardening of the arteries,” 479, 480; possible causes of, 481. See also hypertension and arteriosclerosis hard woods, 146, 612 harvestmen, 211, 212 Harvey, William, 295, 296, 297, 326 hawks, 248, 258, 330, 637; value of, 248; bounties on, 248, 619; in food chains, 613 hay fever, 438, 439 hazelnuts, asexual reproduction in, 487; as soil binders, 626 head: of flatworms, 175; of chiton, 185; of arthropods, 207, 209; of mantis, 207; of centipede, 211; of grasshopper, 217, 218, 219; of snakes, 244; of birds, 247; of fish, 301; of frog, Frog Charts following 304, 305, 309; of man, Human Body Charts fol¬ lowing 336; severe blows on human, 466 health: foods and, 351-72; weight and, 355; man’s fight for, 426-83; daily habits and, 439, 467; public, agencies and what they do, 467-68; unsolved, problems, 472-83. See also diseases hearing centers, 393 heart, 40, 41, 43; of fish, 91, 300, 301, 302-03, 314; of mo Husks, 184; of chiton, 185; of clam, 186, 187, 188; of lobster, 214, 215, 216; of grasshopper, 219; of vertebrates, 236, 258, 259, 297, 298, 300, 310, 313; of amphibians, 241, 310; of birds, 248, 314; of mammals, 250, 314; of frog, Frog Chart 4 following 304, 309, 310, 314; of man, see heart, human heart, human: inside of, 17; amount of blood leaving, per hour, 296; functioning of, 313, Human Body Chart 5 following 336, 339; photographs of, 340; and body weight, 355; nerve control of, 395; valve injuries and murmur, 435, 479; in rheumatic fever, 435; X ray showing, 461. See also heart attacks and heart diseases heart attacks: coronary, 339-40; and blocked coronary artery, 341; in heavy drinkers and smokers, 442 heartbeat: nerve control of, 303, 391, 394, 395; in emotional behavior, 409, 410 heart diseases, 478-82; death rates, 473; types of, 478-79; germs and, 479; organic and functional, 479; and ages when they may occur, 479; blood pressure and, 480-81; hypertension and, 480-81; degenerative, 481; coronary, 481-82; danger signals, 482 “hearts,” of earthworm, 193. See also aortic arches heat: as energy of molecular motion, 61; from oxidation, 62, 314; from cell respiration, 276, 278; as a stimulus, 290, 291, 292; measured in calories, 353, 354 704 INDEX heat exhaustion, 361, 440 heath hen, 606, 635 height: of man, and functioning of endo- crines, 373, 375, 382; of garden peas, 519 helium, 55 hellbenders, 239 Hemichorda, classification summary, 257 Hemiptera, classification summary, 228 hemlocks, in beech-maple climax, 606, 607, 609 hemoglobin, 34, 94; formula of human, 59; iron and copper and, 68, 352, 360-61; of earthworm’s blood, 193, 194; of frog’s blood, 309; amount and function in man, 384; and hemolytic infections, 435 hemolytic “strep” and “staph” infections of blood stream, 435 hemophilia, 533, 550. See also bleeder’s dis¬ ease hemorrhage: of newborn infants, 367; and red-blood-cell counts, 384-85; and blood pressure, 480 Hepaticae, 126; classification summary, 127 herbivores, defined, 614 herbs, stems of dicot, 280 hereditary traits. See traits heredity, and disease, 436, table, 444, 477. See also genetics heredity: and environment, 515, 516, 536, 542; and identical twins, 532-33. See also ge¬ netics Herefords, polled, 594 hermaphrodite, defined, 496 heroin, 468, 469 herons, 154 Hessian flies, 618 heterozygous, 520-21, 525. 526, 527. See also genetics and hybrid hibernation: and body temperature, 313; study of frog, 326 hickory, 149, 612 hickory nuts, dispersal of, 492 highholder, 106 high power objective, of microscope, 22, 23, 23 hilum, 495 Hindus, 555 hippopotamus, 254 Hirudinea, classification summary, 197 Hirudo, 197 histology, defined, 297 hives, 439 hobbies, biological, 18 Hodgkin’s disease, 477-78 Hoffman, Joseph A., 350 Hoffmeister, Prof. D. F., 66 Holmes, Dr. Oliver Wendell, 426-27, 429, 462-63 Holothuroidea, classification summary, 201 Holstein cattle, 545 homeostasis, 443, 445; defined, 443; and dis¬ ease, 445; and blood pressure, 480. See also stability of the body Hominidae, table, 105, 255 homogenized milk, as stable suspension, 64-65 Homoptera, 226; classification summary, 228 Homo sapiens, 105; classified, table, 105; as a mammal, 249; chief traits of, 255-56; chromosome numbers in, 502, 503, table, 503; reproduction in, 506-10; racial stocks of, 553-56. See also man homozygous: defined, 520; for blaze hair, 525; for rose comb in chickens, 525-26, 527. See also genetics honey, from bees, 224 hoof: of various ungulates, 253-54; of ancient and modern horses, 559, 560, 561, 562 hoofed mammals, 260. See also ungulates Hooke, Robert, 26-27, 28 hookworms, 178, 180, 202 hormone-like secretions of nerves, 396-97 hormones: and plant reactions, 290-91; ani¬ mal, 291; auxins as, in plants, 291, 292, 293; number of known, in vertebrates, 374; human, 374-82, table, 382; and emotional behavior, 409-10; human, and diseases, 440, 443, 445, 458, 459, table, 459; and growth of fruits, 491. See also insulin, thy¬ roxin, etc. horned lizard, 241 horned “toad.” See horned lizard horse family, history of, 563 horsehair worms, 154 horses, 18, 217, 250, 566; classification of, 254; brain of, 319; ancestry of, and modern breeds, 559, 560, 561, 562, 563, 564; Ara¬ bian, 559, 560; palomino, 559, 560; wild, of western U.S., 564. See also diphtheria anti¬ toxin horsetails, 133, 138, 139, 141; ancestry of, 140. See also Equisetum hosts: of tapeworms, 175; of trichina, 177 houseflies, 212, 226, 228, 606; as food of spiders, 212; classification of, 228; rate of reproduction of, 230; as germ carriers, 437 howling monkeys. See monkeys human behavior, 400-25; sense organs and, 400-05; inborn and conditioned responses in, 405, 406, 407-08; generalized responses in, 408—09; emotional, 409—10; motivation of, 413-16; and problem solving, 416-23; summarized, 423; alcohol and, 441 human beings. See man and human body and Homo sapiens human body, 95, 305, 328-50, 328, 329; di¬ gestive system of, 331-35, Human Body Chart 7 following 336; anatomy and physi¬ ology of. Human Body Charts following 336; breathing in, Human Body Chart 6 following 336, 337-38, 337; circulatory system of, Human Body Chart 5 following 336, 339—44, 340; bones and muscles in, INDEX 705 human body ( continued ) Human Body Charts 1-3 following 336, 344—45; excretory system of, Human Body Chart 8 following 336, 345-48, 346; ner¬ vous system of, Human Body Chart 4 fol¬ lowing 336, 400-25; internal regulation and control of. Human Bodv Charts 4 and 8 fol- lowing 336, 373-99; foods and nutrition in, 351-72; changing make-up of, 351, 612-13; diseases of, 428-45; natural defenses of, against germs, 448-50; reproduction in, 506-10 human carriers of germs, 438 hummingbirds, 16, 246, 247 humors, of eye, 401 humus, defined, 623 hunches, in scientific research, 420, 421 hunger: empty stomach and, 413; low blood sugar and, 414; as motivation of behavior, 417, 418, 419 Hunter, Dr. John, 373, 450 hunting, controlled, in game preserves, 602- 03, 636 hyacinth, 148 Hyalospongiae, classification summary, 164 hybrid: defined, 520-21; in Fj generation, 521; in F2 generation, 523. See also hybrids and heterozygous hybrid corn, 101, 485; “seed" of, 590; hybrid vigor in, 590-91; how bred, 592—93 hybridization: defined, 590; in plant and ani¬ mal breeding, 590-93 hybrids: identifying by test crosses, 525; fer¬ tility of, 558 hybrid vigor, 590-91 hydras, 95, 165-67, 166, 169, 170, 171, 173, 174, 179; collecting, 154; examining, 165; blueprint of, 166; nerves and reactions of, 167; reproduction in, 168 hydrocarbons, 352, 353. See also fats and oils hydrochloric acid, in stomach, 331, 332, 333 hydrogen: atoms of, 53, 55, 62; half life of, 57; symbol of, 59; in nutrients, 68; in oxi¬ dation of sugar, 69; amount of, in human body, 352. See also water molecule, photo¬ synthesis, respiration hydrogen peroxide, 315-16 hydrotropisms, 290 Hydrozoa, 167; classification summary, 174 hyenas, 254 Hymenoptera, 223; classification summary, '227 hvpertension: defined, 480; and heart disease, '481 hypocotyl, 495 ichneumon wasps, 224 ideas, and problem-solving, 420 identical twins. See twins Illinois, wildlife refuge in, 636 image, focusing of, on retina, 401 imbecile, of cretin type, 378 immune, to a disease, defined, 452 immune, serum. See serum immunity, inborn and acquired, 454, 455 immunization, 453-55; methods of, 444, table, 455; of children today, 452; of infants, 454, 508; experiments on cancer, 472 imperfect flowers. See flowers impetigo, 436 inborn responses: defined, 323; in man, 405, 406. See also behavior, responses, and re¬ flexes inbreeding, 591, 592, 593, 594 inch, number of millimeters in, 271 incisors: of rodents, 259; of man, 333 incomplete flowers. See flowers incomplete metamorphosis, defined, 222. See also metamorphosis independent assortment, of genes and chro¬ mosomes into gametes, 521-22, 525 Indian pipe, 152, 268, 607, 609 Indians, American: table, 105, 551, 557; blood groups of, 388, table, 389; and mea¬ sles, 542; origins and types of, 553, 554, 555; corn raised by early, 586 indigestion, 439 indophenol, 366 infants: crying of, as an inborn response, 405; stimuli and behavior of, 406, 408, 409; and learning to walk, 409; hunger and behavior of, 414; immunization of, against diseases, 454, 508; care of, 508; blood typing of, 529; possible phenotypes of blood groups of, from given parents, 529 infected tooth, 449 infections: and swollen lymph nodes, 449; walling off of, 450; of various organs, 459; white-blood-cell counts in acute, 460; X rays in diagnosing bone, 461. See also dis¬ eases and diseases, infectious infectious diseases, defined, 436, 437. See also diseases inflammation, in trichinosis, 178 influenza: causes of, 433, 434; air-borne germs of, 437 ingestion of food, defined, 77-78. See also food, food-getting, and foods of man inheritance, of traits from one generation to the next, 485, 515-34, 536-43, 551-53; and mutations, 536—39, 546—51; through the ages, 559—85. See also genetics, traits, and living things, history of injuries, first aid and care of, 465-66 inner ear, 403 inoculation: defined, 452; against polio, 453, 454; with toxins, 454; table of methods, 455. See also immunization inorganic compounds, 60 Insecta, 217; classification summary, 227, 228. See also insects insect-borne germs, 437-38 706 INDEX Insectivora, classification summary, 259 insect pests, 230; biological control, 223, 224, 634 insects, 154, 156-57, 184, 236, 300, 308, 609; collecting, 154, 156-57, 204; as arthropods, 205—06; number of known species of, 205, 206, 227; body parts of, 207; class and orders of, 209, 217-26, 227, 228; habitats and main characteristics of, 217, 218, 220; reproduction in, 218, 220; blueprint of grasshopper as typical, 219; orders, 220-26, 227, 228; useful, 223; as man’s chief com¬ petitors, 226; and pollination of flowers, 233, 494; as food of frogs, 240; social, 422; as germ carriers, 437, 438; parthenogenesis in, 505; preserved in amber, 560; first known, 571, 574; of Carboniferous, 575; in food chains, 614; soil and, 622; and forest damage, 633 insight, 419, 420 insulation: fur and feathers as, 317; skin as, 317 insulin, 375, 382; and diabetes, 375-77; and use of glucose in living cells, 376; date of first use of, in diabetes, 455. See also dis¬ eases, noninfectious intelligence, centers of, 304. See also cere¬ brum and human behavior intelligence quotients, of identical twins, 533 interchangeable substances in living things, 50 interdependence: of animals and green plants, 273; among all living things, 600-01, 602- 19; summarized, 616—17 internal environment, stability of, of human body, 397 intestinal juice, in man, 332, 333. See also di¬ gestive juices intestine: lining of human, 40; of fish, 91, 301, 302; of planarian, 171; of roundworm, 176, 177; trichinas in human, 178; of chiton, 185; of clam, 187; of earthworm, 191, 193, 194; of lobster, 214, 215; of grasshopper, 219; of lancelet, 233; large and small, of frog, Frog Chart 6 following 304, 308, 309, 310; large and small, of man, 331, 334, Human Body Chart 7 following 336; circu¬ lation in human, 340; nerve control of hu¬ man, 395, 396; X rays of, 461. See also food tube intravenous feeding, 613 invertase, 334 invertebrates, 158-231, 232, 233, 235, 247; in Cambrian, 572; in topsoil, 623 involuntary behavior, 396-97 involuntary muscles. See muscles involuntary responses, in man, 391, 393-97. See also autonomic nervous system iodine: how to make dilute, for staining cells, 28; as test for starch, 62; as a nutrient, 68; foods that contain, 361; in thyroxin, 377; and thyroid disorders, 378—79, table, 440; in human body, 352; use of, on small wounds, 465 ions: calcium, in human body, 360; and blood clotting, 385, 386 iris, 145; leaves of, 269; of eye, 401. See also eyes, human iron: isotopes, 57; symbol, 59; in seed plants, 284; amounts' in human body, 352; human daily needs of, table, 355; in common foods, tables, 356-57, 361; in hemoglobin, 360; and deficiency diseases, table, 440 irrigation, 630, 631, 632 islet cells, of pancreas, 374, 375, 376, 382 isolation: and rise of races, 555; and rise of racial stocks, 556 isoniazids, 444, 457, 459, 461; and tubercu¬ losis in rats, 462 Isoptera: defined, 224; classification summary, 227 isotopes, 55, 56, 63; defined, 56 ivy vine, 279, 283, 607 jack-in-the-pulpit, 493 jaguars, 254 Janssen brothers, 26 Japanese, blood groups of, 389 Japanese beetle, 585, 618 jawless fish, 234, 234, 258 jaws, of arthropods, 209 jellyfish, 24, 51, 51, 165, 167, 168, 169, 170, 171, 173, 174, 202; sizes of, 51, 168; water in, 51; poison of, 167 Jenner, Edward, 450-51 Jimson weed, 539 jointed legs, animals with, 205-31. See also arthropods joints: and arthropod exoskeletons, 209, 215, 218, 219; and endoskeletons of vertebrates, 215, 255, 301, Frog Chart 1 following 304, Human Body Charts 1 and 3 following 336; ball and socket, 307 jonquil, 148 joy, as behavior, 409, 410 juniper, 147 Jurassic Period, 571, 577, 579 kale, and ancestor, 583 Kalmia latifolia, 105, 106 kangaroo, 252, 259. See also pouched mam¬ mals katydids, 226 kelps, 112, 120; defined, 113 kidneys, 44, 92; human, transplanted, 50; of clam, 186, 187; human, 195, 340, 345, 346, 347, Human Body Chart 8 following 336; of fish, 301, 303; of frog, Frog Chart 7 following 304, 310, 497; diseases of human, and X rays for diagnosis, 460, 461; of lob¬ ster, see green glands; of earthworm, see nephridia; of chiton, see kidney tubules INDEX 707 kidney stones, 368 kidney tubules, of chiton, 185 king crab, 227 kingdom: plant, 102-55; animal, 103, 130, 158-263; borderline between plant and ani¬ mal not sharply defined, 105, 110; protist, 111, 130 kingfisher, 154, 245 kite, and study of gastric juice, 330 kitten, 407 kiwis, 246 koala, 252; albino, 537 Koch, Robert, 429, 431, 443, 447 kohlrabi, and ancestor, 583 lactase, 334 lacteal: of villus, 335; and lymph circulation, 343 ladybird beetles, 222, 223 lady’s slipper, 148, 638, 639 Lagomorpha, classification summary, 260 Laika, Russian dog in satellite, 645, 650 lakes, man-made, 630 Lamarck, Jean Baptiste, 27, 584 lamb, 546' lamprey, 234, 258 lancelet, 232, 233, 257; blueprint of, 233; described, 234 land: wise use of, 628—29, 629; acres devoted to various uses, 628-29 land-dwellers, features enabling reptiles to be, 245 land plants, first, 571 language, advantages of, 256, 422, 423 larkspur, 149 larva: of monarch butterfly, 221, 222,; of sphinx moth, with wasp pupa cases, 224 larvae: of arthropods, 207, 208; of barnacles, 213; of lobster, 216; injurious insect, 222; of beetles, 223; of flies, 226; of insects, 226; as food of woodpeckers, 246, 247 larynx: of frog, Frog Chart 5 following 304, 307, 308; of man, Human Body Chart 6 following 336, 338 lateral line, of fish, 301, 304 Latin names, 105, 106 laughing gas, 463 laws of chance: demonstrating, with beads, 523, 524; and genetic ratios, 522, 524, 527- 28; and number of possible new combina¬ tions of human chromosomes in fertilized ovum, 528 laxatives, to be avoided, in appendicitis, 465 leaf, 33, 50; cells of green, 33; how to ex¬ amine with microscope, 33; as an organ with tissues, 43-44; of elodea, 72; com¬ pound, of rose, 87, 88; how to examine structure of, 269. See also leaves leaf beetles, 223 leaflets, of bean leaf, 267 leakage of the heart. See heart murmur learning: centers of, 304; in fish, 304; in frog, 311; in vertebrates, 324; and size of cere¬ brum, 319; conditioned responses in human, 406; in human infants, 406; and drives, 415; and problem solving, 416-23; by trial- and-error or by insight, 417, 419 learning processes: experiments on, in ani¬ mals, 416, 417, 418, 419; rewards and punishments and, 417; in man, 420 leaves, 43, 44; moss, 123, 123; fern, 133; of psilopsids, 140; of corn and bean, 143, 268, Plant Chart 2 following 288; parallel- and netted-veined, 143, 146; compound, 267; compound and simple, 268; large, of water lily, 269; of seed plants, 269-79, Plant Charts following 288; functions of, in seed plant, 271, 278, 279; and food-making, 271-78; cooled by evaporation of water, 278; onion, 279; oxygen from dead, 294; reproduction by, 487 Lederberg, Dr. Joshua, 539 leeches, 154, 196, 202; on turtles, 154; medici¬ nal, 197; pond, 197 Leeuwenhoek, 74-75, 82, 99, 110, 160; dis¬ covery of Vorticella by, 159; discovery of bacteria by, 429 legs: of arthropods, 206, 209; jointed, of mantis, 207; of shrimp, 210; of arachnids, 211; of centipedes and millipedes, 211; of lobster, 214, 215, 217; of insects, 218, 220; of grasshopper, 219; of mammals, 250; how to remove skin of frog’s, 306 legumes, 277; nodules on roots of, 274, 275; and soil enrichment, 275; in crop rotation, 624-25; as soil binders, 626; as green- manure crops, 627; need of, for alkaline soils, 628 Leidy, Dr. Joseph, 564 lemons, 488 lemurs, 254, 260; first, 581 length of life, average, in 1850 and today, 428 lens: corneal, of lobster eyes, 216; of human eye, 401 lenticles, 280, 281 leopard frog, 239; anatomy and physiology, 304-12, Frog Charts following 304; repro¬ duction of, 497 leopards, 254 Lepidoptera: defined, 221; classification sum¬ mary, 228. See also moths and butterflies lettuce, 192, 590. See also foods, of man leukemia: white-blood-cell counts in, 460; as “cancer of the blood,” 477; blood smear, 478; treatment of, 478 levels of organization, in mammalian embryos, 506 lice, rat, and bubonic plague, 437 lichens, 118, 119, 121, 126; as double plants, 117, 118; defined, 118; three types of. 708 INDEX 118; in plant succession, 608, 609, 610; and soil formation, 622 life: indefinable, 44, 74; and protoplasm, 65, 70, 74-95; in a drop of water, 74, 75; history of, on earth, 559-85; summarized history of, 581-83; possibility of, else¬ where in universe, 650, 652. See also living things life cycle: of mosses, 125; of ferns, 135-36; of club mosses, 139; of trichinas, 177-78; of arthropods, 208. See also metamorphosis, alternation of generations, and reproduc¬ tion life functions. See life processes life processes, 74-95; listed, 76; of ameba, 76-79; of paramecium, 79-81; tables of, 79, 86, 91; of algae, 82-86; spirogyra, 82-84; of pleurococcus, 85; of flagellates, 110-11; of mosses, 123-26; of ferns, 135-36; of Vorticella, 160; of sponges, 161-62; of hy¬ dras, 165-67; of planarians, 172-73; of chiton, 185; of earthworm, 190-93, 195; of starfish, 198; of grasshopper, 219; and structures of seed plants, 266-94; of verte¬ brates, 295-327 light: from rapid oxidation, 63; animals that give off, 168, 237; as stimulus to earth¬ worm, 195; and guard cells, 270; and pho¬ tosynthesis, 271, 272, 278; as stimulus to plants, 289, 290; and eyes, 400, 401, 402, 405 light-sensitive cells, of earthworms, 195 lilies, 145, 491, 566; leaves of, 269; from bulbs, 487; flowers of, 490 lily family, classification summary, 148 limbs, of mammals, 250 lime, on crop lands, 625, 628. See also skele¬ tons lime juice, for scurvy, 363 “limeys,” 363 Lind, Dr., 363 linen, 146 lining: of coelom, 177; of chest and abdomen, 250; of stomach, 331; of intestine, 335. See also covering tissue, endoderm, and epi¬ thelial tissue linkage: defined, 516; principle of, 521, 525; changed, by crossing over, 540, 541 Linnaeus, 104, 105 lions, 254, 260, 422, 423 lipase, 333, 334 Lister, Lord, 429 lithium, 55 litmus paper, 19 liver, 395; number of molecules in one cell of, 66; eaten by planarians, 169; of fish, 301; of frog, Frog Chart 6 following 304, 308; of man, 332, Human Body Chart 7 following 336; circulation in human, 339, 340; glucogen in, 339; and breakdown of amino acids from protein foods, 346; vita¬ min A in, 365-66; and vitamin K, 367; secretion of, 382; and removal of red blood cells in man, 384; amebic infection of, 436; “hardening” of, or cirrhosis, 442; cancer of, 476 liver extract, for pernicious anemia, 440 liver flukes. See flukes liverworts, 108, 122, 126, 128; described and classified, 126, 127; in plant succession, 608, 609, 610 living conditions, and disease incidence, 443, 444 living things: similarities in, 24-99; history of, 559-85; timetable of history of, 571. See also animals, plants, and names of specific organisms lizards, 232, 235, 241, 242, 245, 258; how to tell, from amphibians, 239; Gila mon¬ ster, 241. See also reptiles loam, 622 lobster, 113, 206, 207, 214, 227, 298, 299; molting of, 208; detailed study and blue¬ print of, 214, 215, 216; how to dissect, 214; edible parts of, 215; reproduction of, 216; level of organization of body of, 216, 217 lockjaw, 379, 436; toxin of germs of, 435; germs in soil, 438; inoculation against, 454, table, 455 locomotion: in protozoa, 75; in ameba, 77; in paramecia, 79; in diatoms, 86; in Vorti¬ cella, 159; in hydras, 166, 167; in jellyfish, 168; in planarians, 172; in earthworms, 190, 192; in Nereis, 196; in starfish, 199-200; in arthropods, 206, 209; in centipedes and millipedes, 211; in crayfish, 214; in fish, 236-37; in frogs, 240, 306; in vertebrates, 297 locust, black: spines of, tree, 269; in plant succession, 608, 609; and gulley control, 623; as soil binder, 625, 626 locusts, 226. See also grasshoppers Long, Dr. Crawford W., 462 lotus, 149 low power objective of compound microscope, 21, 22, 23 lumbar vertebrae, 255 lumber, 146, 621 lumbering: destructive, 612; for continuing crop, 633 Lumbricus, 197 lung cancer, and smoking, 476. See also can¬ cer lungfish, 237, 238, 258, 300 lungs, 44, 50, 178, 194, 236; of lungfish, 238; of frog, 240, Frog Chart 5 following 304, 308, 309, 310, 499; of reptiles, 241, 245; discovery of capillaries in, 297; of warm¬ blooded animals, 314; of man, Human Body Chart 6 following 336, 337, 338, 340, 345; change of blood color in human, 339; INDEX 709 lungs ( continued ) surgical collapse of human, 444; X ray of human, 461 Lutz, Dr. Frank, 223 Lycopodineae, 138; classification summary, 141 Lycopodium, 139, 141 Lycopodium clavatum, 138 Lycopodium powder, 140 lycopods, ancient, 575; of coal forests, 138— 39 lymph: defined, 342, 383; circulation of, in human body, 336, 339, 342—43; in tissues, 342; and spread of cancer cells, 474 lymph ducts. See ducts lymph glands. See lymph nodes lymph nodes, of man, 336, 342-43; as filters, 449 lymph system: as defense against germs, 449; in leukemia and Hodgkin’s disease, 477-78 lymph vessels, germs in, 449 lysine, in milk, 359 mackerel, 236 magnesium, in chlorophyll, 68; burning, rib¬ bon, 72; absorbed in soil water by roots, 284; amount in human body, 352, 361 magnification, of compound microscope, 23, 23, 74 maidenhair fern, 133 maidenhair tree, 144, 147 malaria, 159, 206, 226; germs of, 159, 433, 436; and mosquitoes, 438; as a killer, 438; life history of germs of, 446; specific drugs for, 455; new drugs for, 458, table, 459 male parent, 489. See also sexual reproduction malignant tumors. See tumors Malpighi, Marcello, 297 maltase, 334 maltose, 332, 334 Mammalia: defined, 235; classification sum¬ mary, 259, 260. See also mammals mammals, 238, 296, 297, 298, 566, 576; as a class of vertebrates, 235, 236, 245, 248- 56; number of known species of, 248; main traits of, 248-49; body plan of, 249-50; sizes of, 249; subclasses of, 250; number of orders of, 250; reproduction in, 250, 252-53, 504-10; common orders of, 251- 56, 259, 260; cerebrum of, 304; warm¬ bloodedness of, 312-18; brain of (horse), 319; first known, 571, 579; rise and spread of, 580-81; extinct, 581; and forest con¬ servation, 634 mammary glands, 250; of marsupials, 252; of primates, 254 mammoths, 581 man, 35, 40, 102; weight of adult and egg of, 37; algae and, 113; classification of, 105, 232, 255, 260; and spermatophytes, 146; basic needs of, 146; and tapeworms, 175; and insect competitors, 206; and birds, 248, 638-39; as a primate, 254, 255, 256, 260; distinguishing traits of species of, 256; and photosynthesis, 273; and nitrogen-fix¬ ing bacteria, 276, 277; amount of blood in body of, 296; as a vertebrate, 296, 324; warm-bloodedness of, 313, 317; num¬ ber of neurons in brain of, 320; calorie requirements of, 354; conditioned re¬ sponses of, 407-08; learning processes of, 416—20; gestation period of, 506, 507; reproduction in, 506-10; genetic traits of, 514, 525, 529, 530, 531, 545, 551; genetics of blood groups in, 529; sex-linked traits of, 533-34; mutations in, 537; length of one generation of, 549; mutation rates in, 550; racial stocks of modern, 553-56; first known, in America, 554, 560, 580; in ge¬ ologic time, 571; and balance of nature, 605, 606; and food chains, 613, 614; and forest fires, 633; and space travel, 642-44, 647-52. See also human body, diseases, foods of man, and behavior mandibles, of lobster, 214, 215 mandrills, 254 manganese, 284, 352 mangrove, 283 mantis, 207, 226, 227 mantle, 185, 186, 189; defined, 185; of chiton, 185; of clam, 187 mantle chamber, of bivalves, 186 manures, green and animal, 626, 627, 628 maple, 146, 280, 609, 612. See also beech- maple woods Marchantia, 127 marigolds, breeding experiments with, 599 marijuana, 468, 469 marrow, red, and new blood cells, 34, 385 marshes, 629 Marsupialia, classification summary, 259 marsupials, 251, 252, 259 Mastigophora, classification summary, 163 mastodon, 580, 581 mastoid infection, 456 mating: in earthworms, 496; in frogs, 497; in rabbits, 504 matter: composition of, 53-58; defined, 53; three states of, 64 maturation, of eggs and sperms of higher ani¬ mals, 500, 501, 502 May apple, 478 mazes, and animal learning, 417, 418 mealy “bugs,” 223, 226 measles, 433, 467; cause of, 433; toxin of germs of, 435; air-borne germs of, 437; immunization against, 455; among Ameri¬ can Indians, 542 measly pork. See pork meat, 369, 370; inspection of, 467, 468. See also proteins and foods 710 INDEX Mechta, Russian moon rocket, 646 medicines: new, 53; specific, 443, 455-59, table, 459; and control of diseases, 455- 59; decreasingly effective, 457-58 medulla, 299, 319; of fish, 300, 301, 303, 319; of frog, Frog Chart 3 following 304, 311, 319; and body temperature regulation, 317; of bird, 319; of horse, 319; of adrenal glands, 379, 380, 381, 382; of man, Human Body Chart 4 following 336, 390, 391, 392; and parasympathetic system of man, 394, 395 Meigs, Dr. Charles, 426 meiosis, 500, 501, 502; and segregation of chromosomes and genes, 516, 521; and crossing over, 540, 541. See also cell divi¬ sion membranes: demonstrating diffusion through, 285, 286; permeable and semipermeable, 285, 286, 287; cell, and diffusion, 287 memory: centers of, 304; study of centers of, during brain operations, 393; and learning centers, 392—93 Mendel, Gregor, 514, 515, 545, 551, 591; and publication of his researches, 516; and his experiments with garden peas, 516-21; and rediscovery of his researches, 521-25 meningitis: epidemic, 435, 436; and nerve tis¬ sues, 455; immunization against, 455; sulfa drugs and, 456; treatment, 459 mental health: council on, 469; and drug ad¬ diction, 469 mental illnesses, 458, 459 Menuhin, Yehudi, 542 Merychippus, 561, 562, 563, 564, 580 mesoderm, 170, 183, 498; defined, 170; of planarian, 171; and coelom, 183; of verte¬ brate embryos, 498; tissues and organs de¬ rived from, in mammal embryos, 506 Mesohippus, 561, 562, 563, 580 Mesozoic Era, 571, 576-79, 582 “messages,” carried by nerves, 43, 167, 195, 196. See also nerve impulses metabolism: defined, 70; basal, test, 70; in seed plants, 276, 278; two phases of human, 343; thyroxin and basal, 378; faulty, in high blood pressure, 444 metamorphosis: defined, 208; complete and incomplete, defined, 222; in arthropods, 209; in lobster, 216; in grasshopper and other insects, 218, 220, 221, 222, 223, 226; in frogs, 238; in amphibians, 258 metazoa, 99 methods, scientific, of problem solving, 421 mice, 253, 259, 606, 634; in rocket flights, 642. See also field mice Michigan, trout hatcheries, 637 micron, defined, 431 microorganisms, and disease, 428-37. See also bacteria, protozoa, etc. micropyle, 495 microscope: learning to use compound, 20- 23, 22, 23; invention of compound, 26; Leewenhoek’s, 74; electron, 32, 427 microscope lamp, 21 microscope slide, 20-21, 28; wet mount and permanent, 29 midbrain: center of temperature regulation, 317; and parasympathetic nervous system, 394, 395 migrations, distances of bird, 246 Migratory Bird Hunting Stamp, 638 mildews, 116, 119 milk: formula of, casein, 59; as a suspension, 64-65; of mammals, 232, 235; of platypus, 251; as source of amino acids, 359; in ex¬ periment with white rats, 364; homogen¬ ized, 367; testing whether a complete food, 372; prolactin and secretion of, 375; germs in unpasteurized, 437 milkmaids, and cowpox, 450 milkweed pods, as fruits, 144, 492 Millikan, Dr. Robert A., 54 millimeters, and inches, 271 millipedes, 206, 207, 208, 209, 210-11, 227 milt, 93, 302 Mimosa Pudica. See sensitive plant minerals: as nutrients, 66, 68, 352, 353; need¬ ed by plants, 84, 284; needed by man, 352-53; table, 355, table, 356-57, 360-61, table, 361; in treatment of diseases, table, 459; in soil, 621-22, 623; restoring, to soil, 626, 628 minks, 254 Miocene Epoch, 563, 580, 581 mirror, of compound microscope, 20 Mississippian Period, 570 mistletoe, 283 mites, 206, 211, 212, 227; red spider, 158; ancient, 574 mitosis: defined, 39, 40; in cancer cells, 473; chromosomes and genes during, 500. See also mitotic cell division mitotic cell division, 38, 39; in ameba, 78; in growth of frog’s eggs, 497, 498, 499. See also embryos Mtiium, 123, 124, 127 molars, 333 molds, 114, 115; how to grow bread, 114; mutations in, 539. See also penicillin, dis¬ eases, fungi, etc. mole, 249, 423 molecules: of iron pyrite, 54; of water, 58; how to model, with beads, 58-59; symbols for common, 59; stick models of, 60; giant, of proteins, 61, 276; sizes of, 60-61; mo¬ tion of, 61, 62; and chemical changes, 62, 70; and diffusion, 92, 284, 285, 288; and levels of organization, 93-94, 95; virus, 94; in photosynthesis and other food-mak¬ ing in green plants, 272, 273, 274, 275, 276; direction of greatest flow, in diffusion, INDEX 711 molecules ( continued ) 286—87; number of, activated per second by respiratory enzymes, 315; changes in water, in human body each week, 351; number of known kinds of protein, 358; genes and DNA, 535, 536 moles, 259, 603, 634; as benign tumors, 476, 477 Mollusca, 184, 202; classification summary, 189. See also mollusks mollusks, 213, 297, 572; classification and descriptions of, 183—88; classes of, 184; blueprints of, 185, 187; nonshelled, 186; classification summary, 189; of Ordovician, 573 molting, in arthropods, 208; in grasshoppers, 218, 220 monarch butterfly, metamorphosis of, 221 Mongoloids, 554, 555 monkeys, 17, 249, 260; “mother machines” for, 17; classification of, 254; tissues of, used in making Salk vaccine, 454; first known, 581; macaque and squirrel, in rock¬ et flights, 642, 644-45 monocots: defined, 145-46; compared with dicots, 143, 145-46, 268; classification of, 148; flowers of, 148, 490; structure and functions of corn, as typical of, 280, Plant Chart 2 following 288; germinated seeds of, 495 Monocotyledonae: defined, 143, 145; classifi¬ cation summary, 148 monohybrid cross: defined, 527; checker¬ board of, 527 Monotremata, classification summary, 259 moose, 254 morphine, 463 Morton, Dr. William, 462 mosquitoes, 159, 613; as germ carriers, 159, 206, 226, 438; wrigglers, 207; classification of, 226, 228 moss animals. See Bryozoa mosses, 44, 95, 103, 118, 122-26, 566, 573, 581, 607; food and water vessels in, 102; leaves of, 122; underwater, 122; reproduc¬ tion in, 123-26; blueprint of typical, 123; classification of, 126, 127; importance of, to man, 126; reduction division in, 503; in plant succession, 608, 609 mother-of-pearl, 185, 188 moths, 218; classification of, 220-22, 228 motivation, in human behavior, 413-16 motor areas, in cerebrum, 392, 393 motor end plates, in muscle, 411 motor nerve fibers, 389 motor neurons. See neurons motor root, of spinal nerve, 391, 411 mountain laurel, 105, 639 mountain lions, 18, 603, 606, 613, 614. See also puma Mt. Hope Experimental Farm, 588 mounting a specimen for microscopic exami¬ nation, 20-21, 28, 29 mouse: in research with toxin from radiation, 472; cancer in, 475 mouth, 92, 110, 158, 202; of fish, 92, 299; of Euglena, 110; of Vorticella, 159; of hy¬ dra, 165, 166; of planarian, 171, 172; of roundworm, 176, 177; of mollusks, 184; of clam, 187; of earthworm, 191, 193; of star¬ fish, 198, 199; of lancelets, 233, 234; of frog, 305, 306, 307-08; of man, 331, 332 mouth parts: of grasshopper, 219; of com¬ mon insect orders, 220-24; of moths and butterflies, 221; of bugs, 226 movement, in plants, 89 movies, of cell division, 36-37 mucous membrane: of food tube, 331; of stomach, 331 mucus: defined, 331; from cells lining human windpipe, 338 mud puppy? 239 mulleins, 608 Muller, Dr. H. J., 538, 550, 558, 596 multiple alleles. See alleles multiple gene effects, 530; in man, 530, 536 multiple genes. See alleles mumps, 94, 95, 436, 468; air-borne germs of, 437 Musci, 126; classification summary, 127. See also mosses muscles, 167; from mesoderm, 170; of planar¬ ian, 170, 171, 172; of Ascaris, 176; trichina cysts in, 177, 178; of oysters and clams, 186, 187, 187; of earthworm, 191, 192, 193; of arthropods, 209; of lobster, 215; of lan- celet, 233; system of, in vertebrates, 236, 297; of artery walls, 298; of fish, 301, 303; of frog, Frog Chart 2 following 304, 306, 307; and vertebrate behavior, 318; sphinc¬ ter, defined, 331; of man, Human Body Charts 2 and 3 following 336, 337—38, 344— 45; of human eye, 401; nerve endings in human, 403, 411 muscle tissue, kinds of, in man, 40, 41, 43; experiment using living, 330 mushrooms, 102, 114, 115, 116, 603, 609; edible, 119; classification of, 121; culture of, 129 muskrats, 249, 623 mussels, 154, 186, 189; blueprint of (as fresh-water clam), 187 mustards: family of, 150; vegetables from family, 583; used to reseed forest burns, 626 mutants, 537. See also mutations mutation rates: in fruit flies, 549-50; in man, 550 mutations, 536-39, 537; definition of, 537, footnote, 539; mustard gas and X-ray in¬ duction of, 538, 539; in sheep, 546; and rise of new breeds, 546-51; of a bud, 547; 712 INDEX in fruit flies, 547-50, 549; direct and re¬ verse, 550; and origin of new species and genera, 550, 574, 582; and disease resist¬ ance, 590; in plant and animal breeding, 595-97 mycelium, 114, 115, 116 Myriapoda, classification summary, 227 myriapods, defined, 211 myxedema, 378, 440 Myxomycetes, classification summary, 121 naked seeds: of pines and other gymnosperms, 144, 144, 145, Plant Chart 1 following 288. See also gymnosperms names, scientific, 100-01, 104-07, 159; given new species, 105—06 narcissus, 148, 487, 490 narcotics: federal and state control of, 469; several kinds of, 468. See also drugs and drug addiction national forests, controlled lumbering in, 633 National Park Service, 621 National Wildflower Day, 639 National Wildlife Federation, 635, 640 natural enemies, in balance of nature, 602- OS, 637 natural equilibrium, of denies in a biome, 603; defined, 604; man-made disturbances of, 605-06 natural selection, 547; defined, 548; and new varieties, 553; and rise of racial stocks, 556; and origin of horses, 562; slowness of, 562, 564; and origin of new species and genera, 574; role of, in history of living things, 582 “nature’s plow,” 192 nautilus, 189 nearsightedness, 401 nectar, in flowers, 221, 222, 224 Negroids, 555 Neiss, Oliver K., Air Force Surgeon General, 649 Nemathelminthes, 176, 177, 178, 202; clas¬ sification summary, 180 Nematoda, classification summary, 180 neon, 55 nephridia, of earthworms, defined, 195 Nereis, 196, 197 nerve cells, 40, 42, 43; oxidation in, 69; of hydra, 166, 167. See also neurons nerve centers. See centers nerve collar (or ring): of chiton, 185; of earthworm, 191; of lobster, 215; of grass¬ hopper, 219 nerve cord, 298; of planarian, 171; of Ascaris, 176, 177; of chiton, 185; of earthworm, 191, 195-96; dorsal, of chordates, 233, 234, 236. See also spinal cord nerve endings, as sense organs, 347, 390 nerve fibers: length of, 42; of lobster’s eye, 216; in human skin, 347; in human auto¬ nomic system, 394; in human taste buds, 403 nerve impulses: in fish, 303; and regulation of body temperature, 317; and nerve path¬ ways, 320, 321, 322, 323; opposite effects of, in autonomic system, 394, 395; and heartbeat, 396; speed of transmission, 411, 412 nerve injury, and paralysis of arm, 388—89, 391 nerve pathways: and learning in vertebrates, 321, 322, 323, 324; human, 405, 409, 410- 11, 411. See also reflex arcs nerve ring: of Ascaris, 176, 177; of chiton, 185 nerves, 43; of fish, 93; of roundworm, 176; of earthworm, 196; of frogs, Frog Chart 3 following 304; as bundles of fibers of neu¬ rons, 320, 321; of food tube, 331; of man, Human Body Chart 4 following 336; and vitamins, 364; number of pairs of, branch¬ ing from brain and spinal cord in human body, 389; to right and left sides of human body, 392. See also nervous system nerve tissue, 43; of hydra, 169; damaged by polio, 435; susceptibility of, to polio, tet¬ anus, and meningitis, 455 nervous system, 44, 158; of fish, 92-93, 300, 301, 303-04; of hydra, 166; of planarian, 170, 171, 172; of roundworms, 176, 177; of mollusks, 184-85; of clam, 186, 187; of earthworm, 190, 191, 194-95; of starfish, 199; of lobster, 214, 215; of vertebrates, 235, 236, 297, 298-99; central, defined, 298; of frog, 311-12, Frog Charts follow¬ ing 304; of man, Human Body Chart 4 following 336, 373, 388-98, table, 390, 391, 400-05 nest: of termites, 224; number of bird species known to, in U.S., 246; of platypus, 251 neurons: defined, 319; sensory and motor, 320, 321, 322; associative, 321, 322; and learning ability, 324; number in human cerebrum, 392; in sense organs, 401; in nerve pathway, 410, 411. See also nerve cells neuroses: defined, 458; and tranquilizers, 458, 459 Neurospora, 539 neutrons, 54, 55, 56, 93, 95 newborn, hemorrhage of, 367 newts, 154, 239, 240 New York State, shad hatcheries, 637 niacin, 364, 440; daily requirements of, table, 355; in common foods, table, 356-57; de¬ ficiency in dogs, 365; and pellagra, 365 night air, and malaria, 447 night blindness, table, 440 night crawlers, 190. See earthworms nitrates: in soil, 275-76; used in protein-mak¬ ing, 276; diffusion into roots, 284; as soil INDEX 713 nitrates ( continued ) fertilizers, 628. See also nitrogen-fixing bac¬ teria nitrogen, 55, 284; symbol, 59; in nutrients, 68; in cell wastes from proteins, 346; amount in human body, 352. See also nitro¬ gen-fixing bacteria and deaminization nitrogen cycle, 277 nitrogen-fixing bacteria, 119, 274, 275, 276, 277, 616 nitrogen mustard, in treatment of leukemia and Hodgkin’s disease, 478 nitrogenous wastes. See urea nitrous oxide, 463 Nobel Prize winners: W. M. Stanley, 94; E. von Behring, 452; H. J. Muller, 538; Joshua Lederberg, 539 nodules, of legumes, 274, 275 noradrenalin, 396-97 normal saline. See saline nose, 158; lining of, 40, 41 nosepiece, of compound microscope, 21, 22 nostrils, 44, 337; of fish, 303, 304; of frog, 305, 306, 307, 308, 311; of man, 390 notochord, 233, 233, 236, 257; defined, 233; of mammal embryos, 249. See also chor- dates nuclear membrane, 37, 38; function of, 37, 39; as a gel, 66 nucleic acids: and viruses, 94, 95; and genes, 535. See also DNA nucleolus, 37, 38, 63 nucleus, 29, 31, 32; lacking in red blood cells of man, 34, 35; in mitotic cell division, 36, 37, 38; of tissue cells, 41, 42; of atom, 57, 58; of ameba, 77; of paramecium, 80; of spirogyra, 83; of pleurococcus, 85; of Eu- glena, 110; of Vorticella, 159; ejected from red blood cell of man, 385; in meiotic cell division, 501 numbers, man’s ability to use, 392, 393 nutrients: classes and chemical make-up of, 66, table, 68; used by man, 352, 353, tables, 356-57. See also foods of man nutrition, human, 351-71 nuts, as fruits, 145 nymphs: of grasshopper, 218, 220; of ter¬ mite, 225 oak family, classification summary, 149 oak-hickory woods, 603 oaks, 102, 146, 280, 612; galls of, 474; chro¬ mosome numbers in, 503; in plant succes¬ sion, 609, 611; evergreen, 625 oats: useful mutations in, 596, 597; in crop rotations, 624 Obelia, 174 occupations, biological, 18 oceans, diatoms in, 86. See also seas octopus, 184, 186, 188, 202 Odonata, 226; classification summary, 228 odors: diffusion of, 284; as stimuli, 401, 404 Oenothera, 152-53 Ohio, fossils from, 138, 572 oil, mixing with water, 64 oil glands, in human skin, 347 oils: molecules of, in liver cell, 66; made by plants, 271, 274; absorption into blood, 334; in human foods, 352-53. See also nu¬ trients olfactory lobes, 298, 319; of fish’s brain, 301, 303, 319; of frog’s brain, 311, 319; of pigeon’s brain, 319; of horse’s brain, 319 olfactory nerves, of fish, 301 Oligocene Period, 563, 580, 581 Oligochaeta, classification summary, 197 one-celled animals, 75-82, 76, 77, 78, table, 79, 80, 81, 15&-60, 159; classes of, 163. See also protozoa and animals one-egg twins. See twins, identical onion, 148, 276, 279; taste of, 403-04; plant¬ ing, sets, 487 onionskin cells, 28-29; how to make a wet mount of, 28; structure of, 29, 31; examin¬ ing under microscope, 29; comparing with blood cells, 30; water in, 51 opaque substances, used in X-raying stomach, etc., 460—61 open circulatory system, defined, 188. See also circulatory systems operating room, 463, 464 Ophiuroidea, classification summary, 201 opium, 463 opossum, 251, 259, 484, 606; with young, 251; and dog, 318, 322; gestation period of, 506 optic lobes: of fish, 301, 303, 319; of frog, 311, 319; of pigeon, 319 optic nerves: of lobster, 216; of fish, 301, 303, 319; of frog, 311, 319; of pigeon, 319; of horse, 319; of man, 390, 401 Opuntiales, 107 oral groove, of paramecium, 79, 80, 81 orange, 50; seedless, 488; Washington navel, 547, 548, 596 orange trees: and ladybird beetles, 223; bud¬ ding, 488-89 orangutans, 255 orchid family, classification summary, 148 orchids: embryos in seeds of, 143; as mono¬ cots, 145 orders: of organisms, defined, 104, table, 105; of insects, 220-26, 227, 228; of mam¬ mals, 259, 260; of mammals present in Oligocene, 581; origin of new, 582 Ordovician Period, 571, 572, 573, 574 Oregon State Board of Forestry, 621 organelles, 80, 163, 170, 179, 202; defined, 80; of paramecium, 80; of Euglena, 110; of Vorticella, 159, 160 organic chemistry, defined, 60 7 1 4 INDEX organic compounds, 59, 60; number known, 60; made in test tubes, 60; made by seed plants, 271-76; enzymes as, 314—15 organic gardening, 628-29 organic matter: in soil, 119, 621; as humus, 623; restoring, to soil, 626, 627; plowing under, 627—28 organic phosphates, 345 organisms, 44-45; defined, 44; simple and complex, 95; acellular, 99. See also animals and plants organization: keynote of life, 44-45, 93-95; levels of, table, 95, 170, 183; in bryophytes, 122; in all plant phyla, 146; in Vorticella, 160; in sponges, 160, 162; iri ' hydra, 167; in coelenterates, 169; in Jk st four animal phyla, table, 172; in nfanarians, 172; in roundworms, 179; in ten animal phyla, 200, table, 202; in arthropods, 208-09; in lob¬ ster, 216-17; in vertebrates, 235-36, 299; in fish, 238; in amphibians, 240-41; in rep¬ tiles, 245; in birds, 248; in placental mam¬ mals, 252 organs, 40, 43, 44, 45, 50, 89, 95, 179; of flowering plant, 43, 87, 88, 266; first true, 165, 169; of planarians, 170-73, 171; of roundworms, 176, 177; of chiton, 185; of fresh -water clam, 187; of earthworm, 191, 194; of starfish, 199; of lobster, 215; of grasshopper, 219; of lancelet, 233; of fish, 301; of frog. Frog Charts following 304; of man, Human Body Charts following 336; reproductive, of higher organisms, 487, 489, 492, 493, 494, 496, 504; embryonic origin of mammalian, 506 organ systems, 44, 165, 172, 179; of ani¬ mals, 158, 202; of planarians, 170, 171; of flatworms, 175; of roundworms, 176, 177; of clams, 186, 187, 188; of starfish, 198, 199; of echinoderms, 201; of lobster, 215, 216; of grasshopper, 219; of vertebrates, 235-36, 297; of fish, 301; of frog, 304-12, Frog Charts following 304; of human body, 330-49, Human Body Charts following 336 Orthoptera, 226; classification summary, 227 Orton, W. A., 590 Oscillatoria, 109, 120 osmosis: defined, 285; demonstrated, 285, 286; irr transpiration, 288; in spirogyra, 294 Osmunda cinnamomea, 141 Osteichthyes : defined, 235; classification sum¬ mary, 258. See also bony fish otters, 254 ovaries: of flowers, 87, 88, 90, 490, 491, 492; of hydra, 168; of clam, 186; of starfish, 200; of lobster, 215, 216, 217; of frog, Frog Chart 7 following 304, 311; hormones from vertebrate, 381, 382; of corn, 493, 494; of earthworm, 496; of mammal, 504; human, 506, 507; cell from, of fruit fly, 510 oviduct: of eartnworms, 496; of mammals, 504, 505; human, 507 ovule, 87, 88, 90, 490, 490, 491, 492; matura¬ tion of egg nucleus in, 491 ovum, human, 507; fertilization and growth of, 507, 508 oxidation: defined and related to living things, 69; in living cells, 69, 276, 278; in protozoa, 76; in warm-blooded animals, 314; in human cells, 343; rates of, and thyroxin, 377, 379, 382; of alcohol in human cells, 441 oxygen, 52, 55; in protoplasm, 52; and burn¬ ing, 62; in nutrients, 68; released by photo¬ synthesis, 128, 272, 273, 276; isotopes of, in photosynthesis studies, 273; in roots and leaves, 288; in fish’s blood, 300; in frog’s blood, 308, 309; diffusion into human blood, 337; in human cells, 343; amount of, in hu¬ man body, 352; in hemoglobin, 384. See also elements oxygen-carbon dioxide cycle, 616 oxygen mask, 16 oyster, 44, 189, 202; opening an, 186; and starfish, 198, 200; in food chains, 613 pain: nerve and organs sensitive to, 404; and pathways of nerve impulses, 411, 411; and anesthetics, in surgery, 462-63; relief of, by drugs, 463 Paleocene Period, 580, 581 paleontology, defined, 560. See also fossils Paleozoic Era, 571, 582; periods in, 572; end of, 576 palisade layer, in green leaves, 271, Plant Charts following 288 palm, “sago,” 145 palm family, classification summary, 148 palm tree leaves, size, 269 palomino horses. See horses palpitation, of the heart, 479 pancreas: of frog, Frog Chart 6 following 304, 308, 309; of man, 332, Human Body Charts 7 and 8 following 336, 374, 375, 376; cell islets of, 375-76, 382; and secretin, 382 pancreatic juice: of frog, 309; of human being, 332, 333. See also digestive juices paralysis, 388-89, 481 paramecium, 79, 80, 160; life processes of, table, 79; classification of, 163 parasites: defined, 173; flatworms as, 173, 175; roundworms as, 177, 178; segmented worms as, 197; mites and ticks as, 212; wasp, on moth larva, 224; lampreys as, 234; among angiosperms, 283; as micro¬ organisms of disease, 428-36; mammal em¬ bryos as, 505 parasympathetic nervous system. See auto¬ nomic nervous system parathyroid glands, Human Body Chart 8 INDEX 715 parathyroid glands ( continued ) following 336, 375, 376, 382; and ability to use calcium and phosphorus, 379 parathyroid hormone, 440 parathyro tropic hormone, 375, 382 parentage, and blood typing, 529 parental care, in birds, 247; in mammals, 250, 252. See also infants parental generation, of hybrid offspring, 519 parents: one and two, 486; earthworm, 496; selection of both, in plant and animal breeding, 587, 589. See aho reproduction and natural selection parrot fever, 459 parthenogenesis, 505 partridge berry, 108 passenger pigeons, 606, 635 Pasteur, Louis, 428, 429, 431, 433, 443, 447, 452-53 pasteurization of milk: and typhoid fever germs, 437; inspection of, 467 pasture rotation, 625 pathologists: defined, 476; role of, in cancer diagnosis, 476 patterns, in brain, 420 Pavlov, Ivan, 406; researches of, on condi¬ tioned reflexes of dogs, 406-07 peach, 145, 597 peanut, 142, 150; seed leaves of, 145; oil in, 274 pear, 150 peas, 150; sprouting of, 204. See also garden peas peat, 122 peat moss, 122, 126 pecan, 149, 492 Pelecypoda, classification summary, 189 pelicans, 264, 265 pellagra, 365, 440, 459 penguins, 316, 485 penicillin, 53, 119, 458, table, 459; discovery and use of, 456; synthesis of, 456; and re¬ sistant germs, 457-58, 542 Penicillium, 121, 456 Pennsylvanian Period, 570 pentathol. See sodium pentathol peppermint oil, and diffusion, 284-85 peppers, 133 pepsin, 315, 334; in man, 331; testing action of, 332 peptide chains, 276 peptones, 333, 334 perch, 258; blueprint of, 301 perennials, defined, 142 perfect flowers. See flowers pericardial cavity: of chiton, 185; of clam, 187, 188; of lobster, 215, 216; of grass¬ hopper, 219; of fish, 301 periods, geologic, 570, 571 peristalsis: defined, 334; nerve control of, 391, 394, 395, 396; in emotional behavior, 409, 410; and hunger, 413 peritoneum: defined, 184; of mollusks, 184; of starfish, 200; of mammals, 250 peritonitis, 464 Permian Period, 571, 572, 576; fossil from, 577 pernicious anemia, 440. See also anemia perspiration, and salt loss, 360, 361 petals, 87, 88, Plant Charts following 288, 489, 490, 492, 493 petiole: defined, 267; of bean leaves, 267; of celery, table, 268; and seed plant leaves in general, 269; of sensitive plant, 291, 292 Petri dish, 19, 20, 429 Petrified Forest, 560 petrified wood, 560 Phaeophyceae, classification summary, 120 phagocytes, 450, 451; in appendicitis, 464 phagocytin, 450 phalangers, 252 pharynx: of planarian, 171, 172; of Ascaris, 176; of chiton, 185; of earthworm, 191, 193, 194; of lancelet, 233 pheasants, 606 phenolphthalein, as color test for carbonic acid, 338 phenotype, 521, 522; defined, 521; of garden pea, for height, 523; ratio in F2 generation, 523; in dihybrid crosses, 526, 527, 528; of human blood groups, 529; of various horses, 559 phloem, 134, 135; defined, 135; in fern stem, 134; in leaf veins, 271, Plant Charts follow¬ ing 288; in stems, 280, 281, Plant Charts following 288; from cambium, 281; in roots, 283, Plant Charts following 288 Pholcus, 227 phosphates: as fertilizers, 628; mining rocks bearing, 628 phosphorus, table, 59, 66, 68, 72, 284; symbol of, table, 59; radioactive, in plants, 272, 273; in proteins, 274; amount of, in human body, 352; daily human needs of, table, 355; in common foods, table, 356—57; salts, in bone-building, 360; foods rich in, table, 361; vitamin D and use of salts of, 367 photosynthesis, 271-73; defined, 272; phases of and number of steps in, 271; formula for, 271-72; recent research on speed of, 272-73; importance of, to man and animals, 273; compared with respiration, 276, 278; percentage of total, accomplished by algae, 294; and enzymes, 316; in balance of na¬ ture, 604 phototropism, 290, 291 Phycomycetes, classification summary, 121 phylum, defined, 103—04 Physalia, 174 physical change, 63 Physical Growth Records, 355 716 INDEX physics, 52; defined, 53 pigeon-wheat moss, 122, 123 pigments, and food-making, 113 pigs: and tapeworms, 175; and trichinas, 177; classification of, 254, 260 pimples, 435, 449 pincers, of lobster, 214, 215, 217 pine, 144, 144, 146, 147; cone and seeds of, 144, Plant Chart 1 following 288; leaves of, 269, Plant Chart 1 following 288; twigs or stems of, 282, Plant Chart 1 following 288; roots of, Plant Chart 1 following 288; dispersal of seeds of, 492; ponderosa, 603; in plant succession, 608, 609, 610; white, in New England, 609, 612 pineal body, 375, 382 pineal gland. See pineal body Pinus, 147, Plant Chart 1 following 288 pistil, 87, 88, 90, 489, 490, 492, 493; of corn, 493, 494; of garden pea, 518 pistillate flowers, defined, 494 pitchblende, 57 pith: of cornstalk, 230, 279, Plant Chart 2 following 288; of dicot stems, 280, 281, Plant Chart 3 following 288 pituitary body. See pituitary gland pituitary gland, Human Body Chart 8 follow¬ ing 336, 374, 375; of giant, 373; average size of, in human adult, 373; as master gland, 375, 376; and reactions to stress, 380-81, table, 382 pit vipers, 244 placenta: defined, 253; of rabbit, 504, 505; human, 507, 508; diffusion of Rh factor antibodies through human, 509 placental mammals, defined, 253. See also mammals plague. See bubonic plague planarians, 169, 171, 175, 202; how to collect, 154, 169-70; blueprint of, 171; regenera¬ tion of parts, 181 plantains, roots of, 282, 603 plant behavior, 265, 289-92 plant breeding, 484; genetics and, 586-88, 590, 591, 592, 593, 596, 597, 598; muta¬ tions and, 595—97; polyploidy in, 597-98 plant cover, and floods, 631 plant hormones. See hormones plant kingdom, 103 plant lice, 218, 223, 225, 226 plants: microscopic, 40, 75, 85; life processes of, 82-90; classification of, 100-55; border¬ line, and animals, 110; oldest living, 142; economic importance of seed, 146; struc¬ ture and functions of seed, 266-94, Plant Charts following 288; reproduction in seed, Plant Charts following 288, 486-95; hor¬ mones and behavior of, 289-92; history of, on earth, 566; timetable, 571, 581-83; first known land, 573; improved crop, 590; in balance of nature, 602-05; in food chains, 613, 614, 615, 616; soil-binding, 624, 625. See also genetics, plant breeding, conser¬ vation, and names of plant phyla , classes, genera, and individual plants plant successions, 606-12, 610, 611; defined, 609; of Utah grasslands, 618 plasma: defined, 342; in kidney excretion, 347; of human blood, 383 plasma proteins, 383; and clotting of blood, 386. See also blood proteins Plasmodium, 159 Platycerium, 141 Platyhelminthes, 165, 169-73, 202; blueprint of typical example of, 171; classification summary, 175 platypus, 250, 251, 259, 504 “playing possum,” 318, 322 Pleistocene Epoch, 563, 580, 581 pleura, 250 pleurococcus, 85, 92, 102, 107, 120; classifi¬ cation of, 109 Pliocene Epoch, 563, 580 plowing, deep, 626; shallow, 627 plums, 150; polyploidy in, 597 plumule, 495 pneumonia: bacterial germs of, 432, 436; viruses of, 433-34; germs of, air-borne, 437; immunization against, 455; treatment of, 456, 459; death rates from, 457; white- blood cell counts in bacterial, 460; and heart injuries, 479 pock marks, from smallpox, 450, 452 poisons: of hydra and jellyfish, 167; of black widow spiders, 206, 211-12; of centipedes, 210-11; of scorpions, 212. 213; of Gila monster, 241; snake, as antigens, 454; ini' munity to, 454. For poisons of microorgan¬ isms, see toxins polio, 94; cause of, 434, 436; nerve damage in, 435; and Salk vaccine, 453-54, 455, 468; and nerve tissue, 455 poliomyelitis, 94. See polio polled cattle, defined, 594 pollen, 89, 90, Plant Charts following 288; how to germinate, 490; with tube, 491; in pollination and fertilization, 491. See also pollination pollen tube, 90, Plant Charts following 288, 491, 492, 493 pollination: by moths and butterflies, 222; by bees, 223-24, Plant Chart 4 following 288; in flowering plants, Plant Charts 2 and 3 following 288, 491, 492; wind, in corn, Plant Chart 4 following 288, 493; self- and cross-, Plant Chart 4 following 288, 494 Polvchaeta, classification summary, 197 Polygordius, 197 Poly orchis, 174 polyploidy, 539-40; in apples, 540; and new varieties, 551, 552; in plant breeding, 597- 98 INDEX 717 polypody fern, 135 Polystichum, 141 pond scums, 44, 107, 115, 160; discovery of, 75; how to examine, 82; and diatoms, 85; classification of, 109. See also spirogyra and Oscillatoria pondweeds, 112, 142; collecting hydras from, 165 poplar trees, 149, 612; leaf of cottonwood, 271; from suckers, 487; flowers of, 493; in plant succession, 608, 609, 610 poppy family, 150 population: defined, 550; increases in human, 586 population equilibrium: defined, 551; blood groups in, of man, 556 populations: genetics of, 550-51; interdepend¬ ence among plant and animal, 600-01, 603- 06, 609, 612-14, 615, 616-17; demes as particular, 603; wildlife, and their history, 603; censuses of wildlife, 636 porcupines, 253 pores: anal, of paramecia, 80; of sponges, 160, 161, 164; excretory, of planarians, 171; of human taste bud, 403. See also human skin Porifera, 160, 170, 172, 202; defined, 160; classification summary, 164 pork: worm parasites in, 173, 177-78; “measly,” 177 porpoises, 260 portal vein: of fish, 301; of man, 340 Portuguese man-of-war, 169, 174 posterior end, defined, 170, 171 posture, erect, in man, 255, 256 potash, as soil fertilizer, 628 potassium, 284; amount of, in human body, 352, 361 potato beetles, 223, 606 potato blight, 121 potatoes, 150, 566; underground stems of, 268; improved, 587; in strip cropping, 625; and potash, 628 potato family, classification summary, 150 pouched mammals, 251, 252, 259. See also opossum and Marsupialia poultry, improved, 587 prairie dogs, 252, 259; classification of, 253 prairies, as biomes, 603 praying mantis, 207 precambrian times, 571 precancerous conditions, 476-77; chemicals that induce, 476 predators: defined, 602; in balance of nature, 602-03, 605. See also natural enemies pregnancy, human, 508; Rh factor and human, 508—09; and birth marks, 515 pregnant, 504; reproductive organs of, rabbit, 504 pressure, end organs of, in skin, 404 Primates, table, 105; classification summary, 260. See also primates primates, 254-56; chief features of, 254; early, 581 problem-solving, 416-23; in man, 420-22; in scientific research, 421 Proboscidea, classification summary, 260 professions, biological, 18 prolactin, and milk secretion, 375, 382 protective-muscular tissues, in hydra, 167, 169 proteins: size of molecules of, 61; in human liver cell, 66; as nutrients, 66, 68, 352; nitrogen in molecules of, 68; as energy source, 69, 353; and covering of a virus, 94-95; made by seed plants, 264-65, 271, 274, 276; digestion of, in man, 330, 333, 334; changing of, in human body, 343, 358; urea from breakdown of, 345, 346; as in¬ dispensable human nutrients, 352; human daily needs of, table, 355; in common food portions, table, 356-57; plant and animal, as sources of essential amino acids, 359. See also amino acids and nitrogen-fixing bacteria proteoses, 333, 334 prothallia, fern, 135, 136; how to examine, 152 prothrombin, 367, 383, 386; vitamin K and, 367 Protista, 130 protists, 111, 130 protococcus. See pleurococcus protons, 54, 55, 56, 93, 95 protoplasm, 32; as a convenient term, 32; dif¬ ferences in, in different organs and organ¬ isms, 45; nature and make-up of, 51-53, 55, 63-70; living, of ameba, 52; consist¬ ency of, 52-53; tracing radioisotopes in, 57; chemical make-up summarized, 70; human, 343, 352. See also colloids, cells, etc. Protozoa, 158-60; classification summary, 163. See also protozoa protozoa, 76, 89, 93, 95, 170, 171, 172, 173, 175, 176, 202, 237, 275; defined, 76; life processes of, 74-82; how to observe, 75; number of species known, 76, 163; as germs, 433, 436, 437; ancient, 572. See also names of specific kinds, such as ameba and paramecium pseudopod, 77, 158, 163; of hydra cells, 166 psilopids, ancient and living genera, 140; of Silurian, 573 psychology, defined, 415 psychoses: defined, 458; and tranquilizers, 458, 459 PTC tests, 530-31 Pteridophyta: defined, 132; classes of, 133; classification summary, 141. See also pteri- dophytes pteridophytes, 132-42; defined, 132; classes of, 133, 141; origin of, and ancient, 139-40, 573; number of known species of, 140; of 718 INDEX Devonian, 574-75; of Carboniferous, 575. See also coal forests ptomaine poison, 437 ptyalin, 332, 334 public health agencies, 467—68 puffballs, 114, 115, 119, 121 pulmonary arteries, Frog Chart 4 following 304, Human Body Chart 5 following 336 pulmonary veins, Frog Chart 4 following 304, Human Body Chart 5 following 336 . cause of human, 298, 342; and adren^P Jin. 381; nerve control ok-397 - puma, 260 pupa, 221, 222, 226 pupil, of eye, 395, 401, 408; responses of, to light, 305, 306 pure, for a trait, 520. See also homozygous purebred animals, 594, 595 pureline, 590; defined, 592. See also plant breeding and animal breeding pus: defined, 450; in urine, 459; in appendix, 464 pussy willows, flowers of, 493, 494 pyloric caeca, of fish, 301, 302 pylorus, defined, 302 pyrenoids, of spirogyra, 83 quail, bobwhite, 247, 606 quaking bog, 122 queen, in bee hive, 224 queen palm, 148 quinine and malaria, 455, table, 459 rabbit fever, 436, 459 rabbits, 250, 260, 549, 609; reproduction in, 504, 505; gestation period in, 506; albino, 537 rabies: cause of, 433, 436; making vaccine of, 448; Pasteur treatment to prevent, 452-53; animals subject to, 453; immunization against, 455, 468 races, defined, 555; of men, 555 racial stocks, of man, 555; blood groups and, 555-56 radial symmetry. See symmetry radiation: from medical use of X rays, 461; toxic effects of, on blood, 472; from fall out, X rays, radium, and cancer, 477; and muta¬ tions, 538, 538; in plant breeding, 536-97, 596, 597 radiation genetics, in plant breeding, 596-97, 596, 597 radioactive carbon, and research on photo¬ synthesis, 272 radioactive elements, defined. 56-57 radioactive “fall out,” from atom and hydro¬ gen bombs, dangers of, 461 radioactive tracers, in diagnosis, 462; iodine as example of, 462 radioautograph, of leaf, 273 radiocarbon dating, 555 radioisotopes, 57, 63; defined, 57; half life of, 57; used as tracers in research, 57; in photo¬ synthesis, 272-73; in research on exchange of atoms of human body, 351, 612-13; in research on insulin, 376; iodine, and thyroid function tests, 377; in research on red-blood cells, 384; dating rocks with, 567. See also radioactive tracers radishes, 268, 282, 290; crossed with cabbage, 558 radium, 478; half life of, 57. See also cancer, treatment of ragweeds, and hay fever, 439 rainfall, and dust storms, 605, 606, 608 Ralph, Dr. P. H., 37 ram, 546 Rana, 258 Rana pipiens, 304, Frog Charts following 304, 305; chromosomes in, 497. See also frogs ratios: in monohybrid cross, 519, 520, 522, 525; determining with checkerboard, 526- 28, 527, 528; in dihybrid cross, 527, 528 rats, 259, 606; order of, 253; white, and vita¬ min deficiencies, 363, 364, 366; and pitui¬ tary hormone, 373; white, and learning processes, 417, 418; and spread of bubonic plague, 437; white, and use of isoniazids, 462 rattlesnakes, 242, 243, 244; diamondback, and scales on skin, 241; treatment of bites of, 244-45; born alive, 245; acquired fear of, 410 raw materials, of photosynthesis and respira¬ tion, 278 rays, 235, 258 reacting. See reactions reactions: of one-celled animals, 75-76; of plants to stimuli, 84, 289; of fish, 92-93, 303; of earthworm to stimuli, 195; of dog and opossum, 318. See also sensitivity, be¬ havior, etc. reaction time, 411-12, table, 412; and alcohol, 441 reagents, 19 Reamur, 330 Recent Epoch, 563, 580 receptors, in sense organs, 401-04; defined, 401; light-sensitive, 401; to sound waves, 403; to flavors, 403, 404; in skin, 404; and responses in man, 405. See also eyes, ears, etc. recessive traits. See traits rectum, 331, 395 red blood cells. See blood cells redbud, 150 red corpuscles, of frog, 309. See also red blood cells red marrow, of bones, and new red blood cells, 384, 385 INDEX 719 reduction division, 39, 500, 501, 502; and sex determination, 509, 510; crossing over dur¬ ing, 552. See also meiosis and meiotic cell division redwood, 24, 25, 35, 40, 44, 51 reflex acts. See reflexes reflex arcs, 322; defined, 322; in vertebrates, 322, 323; and learning ability, 324; inborn, in man, 405 reflexes, 322; in man, 323; in young squirrels, 323; inborn and conditioned, defined, 323. See also inborn responses and conditioned responses reforestation, 621, 622 registered animals, defined, 594 reindeer, 422 reindeer moss, 117, 118 repetition, and habits and skills, 413 reproduction, 75; in ameba, 79; in paramecia, 81; in spirogyra, 84, 85, 110; in flowering plants, 87, 88, 486-95; in fish, 93, 301; in viruses, 94; in Volvox, 111; in fungi, 114— 16; in yeasts, 117; in mosses, 123, 124-26, 125; in ferns, 135-36; in V orticella, 159; in sponges, 162; in hydra, 166, 167, 168; in planarians and other flatworms, 172, 175; in coelenterates, 174; in trichinas and other roundworms, 176, 177-78; in clams, 186, 187; in earthworms, 191, 193, 194, 196, 496—97; in starfish, 199, 200; similarities in, among all arthropods, 207, 208; in lobsters, 216; in grasshoppers and other insects, 218, 219, 220; in moths and butterflies, 221, 222; in bees, 224; in termites, 225; rate in houseflies, 230; in lancelets, 233; in rep¬ tiles, 245; in birds, 247; in mammals, 250, 252-53, 504-10; in platypus, 251; in opossum, 251, 252; in frogs. Frog Chart 7 following 304, 497-503; sexual and asexual, defined, 486; in man, 506—10; sexual and asexual, and variations in offspring, 552 reptiles, 246, 248, 250, 296, 297; classification of, 235, 236, 241-45, 258; chief traits of, 241—42, 245; cloaca of, 308; first primitive and first true, timetable, 571, 576; “root” and mammal-like, 576, 577; dinosaurs as, 577, 578 Reptilia: defined, 235; classification summary, 258. See also reptiles resistance: genetics and, to diseases, 436, 587- 88, 590; and tuberculosis, 443, 444; of germs to antibiotics, 457-58, 542; of man to measles, 542 respiration: as oxidation, defined, 69; as me¬ tabolism, 70; in protozoa, 76, 79; in spiro¬ gyra, 84; in rosebush, 88; compared with photosynthesis, 276, 278, table, 278; chemi¬ cal changes during, 278, 315; in living cells, 314; and enzymes, 314-15. See also re¬ spiratory system respiratory enzymes, 314-15; and B complex vitamins, 365 respiratory system, 44, 177; of mollusks, 184; of chiton, 185; of clam, 186, 187; of Nereis, 196; of starfish, 198, 199, 200; of grasshop¬ per, 218, 219; of vertebrates, 236, 297; of fish, 300, 301; of frog, Frog Chart 5 follow¬ ing 304; of man, Human Body Chart 6 fol¬ lowing 336, 337-40 responses: defined, 289; of seed plants to light and gravity, 289; of man, summarized, 413. See also behavior, reflexes, etc. retina, 401; rods and cones, 401 rheumatic fever, and heart damage, 435, 482 rheumatoid arthritis, 379 Rh factor, in blood, 387, 551, 556; and preg¬ nancy, 508-09 rhinoceros, 254, 260, 613 rhizoids: of mosses, 123, 124, 127; of psilop- sids, 140; similarity of root hairs, 267 rhododendron, 639 Rhodophyceae, classification summary, 120 riboflavin, table, 355, table, 356-57, 364, 440; man’s daily needs of, table, 355; in common food portions, table, 356-57; deficiency of, 364; rich sources of, 365; cooking and, 368 ribs: of snake, 232; of man, 255, Human Body Chart 1 following 336; of fish, 301 Riccia, 127 rice, 148, 597; polishings, and beriberi, 363, 364 rickets, 367, 438, 439, 440, 459; X rays in diagnosis of, 460 rickettsias: 433, 434, 436, 437; treatment of diseases caused by, 459 rind, of cornstalk, 279, Plant Chart 2 follow¬ ing 288 ring stand, 20 ringworm, 433, 436, 449 roan cattle, 545 robin, 44, 157; albino, 537 rockets, and space travel, 256, 642-44, 647-52 rocks: action of lichens on, 118, 610, 622; dating, with radioisotopes, 567; as source of soil, 622 rockweed, 112, 113, 120 Rocky Mountain goat, 422 Rocky Mountains, 565; origin of, 579 Rocky Mountain spotted fever, 436 Rodentia, classification summary, 259. See also rodents rodents, 252, 253, 259; in food chains, 614; and their value to forests, 614 rods, of retina, 401 roe, of fish, 93, 302 roentgenologists, defined, 460 Romer, Alfred S., 585 rooster, effects of prolactin, 375 root cap, 268 root hairs, 88, 89, 267, 287 roots, 40, 43, 44, 87, 89, 267, 278, Plant 720 INDEX Charts following 288; of fern, 134; of bean embryo, 142; of bean and corn compared, 268; as human food, 268; study of elonga¬ tion of, 268; of legume, 275; of onion, 279; structure and functions of, in monocots, dicots, and gymnosperms, 282-84, 283, Plant Charts following 288; types of seed plant, 282-83 root tip, how to stain and examine cells of, 47 rose beetles, 223 rose “bugs.” See rose beetles rosebush, 44, 87, 88, 93, 102; life processes of, table, 91; X ray of, 265; in bucket, 266; grown from cuttings, 487 rose comb, test cross for, in chickens, 525-26, 527 rose family, classification summary, 150 rotary tiller, 626, 627 Rotifera, 178-79, 180, 202; classification sum¬ mary, 180. See also rotifers rotifers, 75, 178-79, 180, 183, 188, 202 roundworms, 176—78; blueprint of Ascaris as typical of, 176; sizes of, 176 rubber, 276 runners, of strawberries, 487 rusts, 114, 116, 119, 121; mutations in wheat, 590 rye, 276; polyploidy in, 598; as green manure, 627 sabertooths, 560, 581 sacrum, 255 sago palm, 144 saguaro, 106, 150, 600; flowers of, 493. See also giant cactus sailors, and scurvy, 363 salamanders, 154, 239, 240, 258; number of species known, 239 saline, how to make, 30; normal, 34, 52; use in immunization, 454 saliva: flow of, 318, 406, 407, 408; action of, 332; control of flow of, centered in medulla, 391, 395 salivary glands: of chiton, 185; of grasshopper, 219; of man, 331, 332; nerve control of, in man, 391, 394, 395, 396 Salk, Dr. Jonas, 453 Salk vaccine, 94, 453, 454 salmon, 113, 232, 258; classification of, 235, 236 salt: in living things, 50; in solution, 51, 61; in protoplasm, 52; formula of, 59; in sweat, 347; table, 440, 616 salts: as nutrients, 66, 68; needed by human body, 360; per cent in human blood, 383. See also calcium salts, phosphorus salts, and minerals salt water, and plasmolysis of cells, 84. See also saline sand: in suspension, 64; in soils, 622, 623 sand dollars, 200, 201, 202 sand lily, 148 sandpipers, 246 sandworms, 196, 202 Santa Gertrudis cattle, 594-95 Sarcodina, 163 sauerkraut juice, bacteria of, 430 Saunders, William, 547 scale insects, 218, 226; and California citrus orchards, 223 scales: of pine cone, 144; of fish, 237; of lizards, 239; of snake skin, 241; of reptiles, 241-42; of bird’s feet, 246, 247 scalpel, 20, 21 Scaphopoda, 189 scapula, Frog Chart 1 following 304, Human Body Chart 1 following 336, 344 scarlet fever, 436, 468; germs and toxin of, 435; and heart damage, 435; immunization against, 455; treatment of, 459; white-blood¬ cell counts in, 460; and heart injuries, 479 scavenger beetles, 223 Schizomycetes, classification summary, 121 Schleiden, 27 Schwann, 27 Science News Letter, address, 129 scientific methods, 421 scientific names, value of, 106. See binomial system and names, scientific scintillator, 57 scion, in budding and grafting, 488 sclerotic coat, of eye, 401, 402 scorpions, 211, 212, 213, 227; ancestors of, 573; of Silurian, 574 Scotch thistles, 618 Scott, Gordon H., 331 scouring rushes, 139, 141 scurvy, 362-63, 369, 439, 440, 459; early his¬ tory of, 362-63; X rays in diagnosis of, 460 Scypha, 161, 164, 202 Scyphozoa, 168; classification summary, 174 sea anemone, 158, 169, 174, 202 sea cucumbers, 200, 201, 202 sea fans, 169 sea foods, 113; iodine in, 378 sea horses, 237, 258 seal, 615 sea lettuce, 102, 112 sea lilies, 200, 201, 202 sea mosses, 112 sea oranges, 113 sea pens, 169, 174 seas, over North America, 569 sea scorpions, ancient, 212, 574 sea shells: sorting, 183, 184, 189; fossil, 569, 570 seasickness, 403 sea snails, of Ordovician, 573 sea squirts, 232, 233, 234, 238, 257 sea urchins, 200, 201, 202 INDEX 721 sea water, similarity to that in organisms, 52; getting fresh water from, 632; contents per cubic mile of, 632 seaweed, 102, 108, 112, 113, 178 secretin, 382 secretion: of shells by mantles of mollusks, 185; in arthropods, 208-09. See also glands, digestive juices, etc. sediment, deposited by Mississippi, 555—56 sedimentary rocks, 567; formation of, 567—68; fossils in, 568 seed coat, 142, 267 seed dispersal, 492, 634 seed ferns, 137, 138, 145, 566, 568, 571, 581; of Carboniferous, 575 seeding, by airplane, 621, 626 seed leaves, 142, 143, 143, 145, 267; food storage in bean, 269. See also cotyledons seedlings: bean and corn, 267, 268; diffusion in corn, 287-88; use of, to demonstrate plant reactions, 290 seed plants, 87, 88-89, 88, 95, 103, 123, 132; sizes of, 142; classification of, 142-46, 147, 148, 149, 150; importance of, to man, 146, 613, 614; life processes of, 266-94, Plant Charts following 288; leaves, stems, and roots of, 269-84, Plant Charts following 288; elements required by, 284; diffusion in, 288; reproduction in, Plant Charts follow¬ ing 288, 486-95, 487, 488, 490, 492, 493; behavior in, 289-92, ancestry of, 492, 583; genetics of, 516, 518-21, 519, table, 521, 522, 523, 523-25, 525, 537, 540, 547, 579, 583, 586-88, 590, 591, 592-93, 593, 596- 97, 596, 597; as crop plants, 586-89, 590, 591, 592-93, 596-98, 624-26, 633-35; in biomes, 602, 603, 604, 605, 605, 606-12, 607, 610, 611; in food chains, 613, 614 seeds, 89, 90, 132; and seed-making, 90, Plant Charts following 288; of angiosperms, 142, 143, 143-45, 267, Plant Charts 2 and 3 fol¬ lowing 288, 494-95, 495; of gymnosperms, 143, 144, Plant Chart 1 following 288; pro¬ duced sexually, 488; as matured ovules, 490, 491, 492; of garden pea, and genetic traits, 519 segmented worms, 190-97, 202, 208, 210; blueprint of earthworm as typical of, 191; classification summary, 197. See also an¬ nelids segments, body, 175, 192; defined, 190; in arthropods, 207, 208; in centipede, 211; in lobster, 214; in grasshopper, 218, 219 segregation, principle of, in genetics, 521, 525; and new combinations of genes and chromosomes, 527. See also meiosis Selaginella, 141 selection: in plant and animal breeding, 546- 51; natural and artificial, defined, 548, 562, 564, 586, 587-88; artificial, for single traits, 587-89; and hybridization, 590-92 selection of parents, natural and artificial, 547, 548, 550 self-duplication: of chromosomes, 38, 39, 40; of viruses, 94; of chromosomes and genes, 499-500, 501-02, 504 self-pollination, in flowers, Plant Chart 4 fol¬ lowing 288, 494; in garden peas, Plant Chart 4 following 288, 516—20; and appear¬ ance of recessive traits, 592, 593. See also pure-line breeding Selye’s theory of stress, 380-81 semicircular canals, 402, 403 Semmelweis, 429, 447 sense organs, 43; of fish, 93, 304; and eyes and sensory lobes of planarians, 171, 172; of earthworm, 195; of arthropods, 209; of lob¬ ster, 214, 215, 216; of vertebrates, 236, 299; of frog, 311; of man, 400-05, 401, 402. See also eyes, ears, skin, lateral line, etc. sensitive fern, 133 sensitive plant, responses of, 291, 292 sensitivity, 75, 79; of one-celled animals, 75- 76; of spirogyra, 84; of fish, 92-93; of seed plants, 289-92, 289; of sensitive plant, 291, 292. See also reactions, responses, sense organs, and behavior sensory areas (centers), in human cerebrum, 392, 393; and generalized responses, 408-09 sensory cells, 169; in hydra, 166, 167; in eye of planarian, 172; in earthworm, 195; in human taste bud, 403. See also sense or¬ gans sensory lobes, of planarians, 172 sensory nerve fibers, 389 sensory neurons. See neurons sensory root, of spinal nerve, 391, 411 sepals, 87, 88, Plant Charts following 288, 489, 490, 492, 493 sepia paper, 188 sequoias, 147; age, 142 serum, immune, defined, 452. See also blood serum serum treatment, for scorpion bites, 212 setae, 191, 196; of earthworm, 191, 192, 194 sewage disposal, 468 sex chromosomes, 509, 510; in fertilized hu¬ man ova, 510; and bleeder’s disease, 524; and sex-linked traits, 533—34 sex determination, 509, 510 sex hormones, 381, 382 sex-linked traits, in man, 533-34 sexual reproduction, 81, 84, 486; in paramecia, 81; in spirogyra, 84; in flowering plants, 90, Plant Charts 2 and 3 following 288, 489-95; in fish, 93; in gametophytes of mosses and ferns, 124—25, 125, 135-36; in hydras, 168; in planarians, 173; in lob¬ sters, 216; in grasshoppers, 218; in frogs, Frog Chart 7 following 304, 497-99; in earthworms, 496-97; in mammals, 504-06; 722 INDEX in humans, 506-10; and variety in offspring, 527, 552. See also flowers and gameto- phytes sexual spore. See spore shad, hatcheries, in New York, 637 Shapley, Dr. Harlow, 650 sharks, 234, 235, 258 sheath: of leaf vein, 271; of nerve, Frog Chart 3 following 304; of neuron branches, 320 sheep, 254, 260; classification of, 254; anthrax in, 431; rabies in, 453; ancon, 546, 547; a population of, defined, 550; in food chains, 613 sheep ticks, 212 shells: of diatoms, 86; of protozoa, 163; of mollusks, 183, 184, 185, 186, 189; of crus¬ taceans, 207, 213, 215; of turtles, 241; fos¬ sil sea, 568, 569, 570. See also eggs, with shells shepherd’s purse, 150 Shorthorns, 594, 595 shrews, 249, 259, 634; as smallest mammals, 249 shrimp, 113, 210, 213, 227 shrub stage, in plant succession, 608, 609, 610 “side effects,” harmful, of new medicines, 380, 456, 458 sieve plate, of starfish, 199 sight centers, 401 silica, in horsetails, 139 silt, 622 Silurian Period, 571, 572; living things in, 573 Simpson, George Gaylord, quotation from, on motivation, 414 single comb, of chickens, 525-26, 527 single-gene effects, 530; in man, 530-31 sinuses, blood, 186, 187, 188, 215, 216, 298 sisal, 148 skates, 235, 258 skeletal muscles, defined, 345. See also mus¬ cles skeletal muscle tissue, 40, 41, 43, Human Body Chart 3 following 336 skeletal system. See skeletons skeletons, 158; of sponges, 160, 162; of corals, 169; of chitons, 185; of clams, 186, 187; of starfish, 199; of cartilaginous fish, 234, 235; of frog, Frog Chart 1 following 304; of man, Human Body Chart 1 following 336, 344—45. See also exoskeleton and en- doskeleton skills, 412-13; testing writing, with both hands, 412; child learning, 416 skin: of earthworms, in breathing and excre¬ tion, 190, 194, 195; of amphibians, 239; of frogs, in breathing and excretion, 308, 310; as sense organ in frogs, 312; human, 347; vitamins and human, 365; as defense against germs, 449; new growth of, 473; light-sensitive human, 534 skin cancers, curability of, 478 skin disease, and stress, 381 skin divers, 237 skin gills. See gills skin grafting, 316 skin rash, in scarlet fever, 435 skull, 232, 236, 254, Frog Chart 1 following 304, Human Body Chart 1 following 336. See also cranium skunk cabbage, 493 skunks, 254 slime mold, 121 slipper animal, life processes of, 79-82. See also paramecium slugs, land, 186 smallpox, 94, 95, 428, 436; cause of, 433; vaccination and conquest of, 450-52; a case of, 452; vaccination of, 454, 455, 468; treatment of, 459 smartweed, 558 smell, and “tastes” of foods, 403 smell centers, 393 smokers, and forest fires, 633 smoking, and death rates, 442; and lung can¬ cer, 442, 476 smooth muscle, 41, 43; in food tube walls of man, 331 smuts, 114, 119, 121; corn, 115, 116 snails, 154, 183, 184, 186, 189, 202, 603, 604, 605, 607; as human food, 188; ancient sea, 574; first land, 575 snake, X ray of, 232 snake bite, treatment of poisonous, 244-45 snakes, 154, 235, 241, 242, 258, 537; water, 236; poisonous, of U.S., 241, 242, 243, 244, 245; certain poisonous, known as pit vi¬ pers, 244; red rat, 244; food of, 614 snapdragon, 150; genetics of color of flower of, 526 sneezing, 405 soap, liquid, as a germicide, 463, 465 social insects, 223, 224, 225 sodium, amount of, in human body, 352, 361 sodium fluoride, 361 sodium pentathol, 463 soft-bodied animals, 183-84. See also mol¬ lusks soft woods, 146 soil: and lichens, 118; composition of, 118, 622-23; and bacteria, 119; formation of, 126, 608; roundworms in, 176; earthworms and enrichment of, 192; and growth of wil¬ low tree, 266; nitrogen-fixing bacteria in, 275; iodine in, 378; disease germs in, 438; number of organisms in, 603, 622-23; de¬ pletion of minerals in, 621, 623, 624; acid and alkaline, 623. See also soil conserva¬ tion soil acidity, 628 INDEX 723 soil conservation, 621-32 soil conservation districts, 623, 624 Soil Conservation Service, 621, 631, 635; and Holmes County, Mississippi, 623; and Or¬ chard Mesa, of Colorado, 623 sol, as state of colloids, 66 solar plexus, 394 solids, 64 Solomon’s seal, 279 solpugids, 230 solutions, 51, 63; defined, 51; and molecular motion, 61-62; and diffusion, 285, 286 sorghum, hybrid vigor in, 591 sounds, as stimuli, 401, 403 sour milk, bacteria in, 430, 431 Southam, Dr. Chester M., 472 sow bugs, 154, 213 space travel, biological problems of, 642-44, 647-52 sparrows, 246, 247, 258, 606, 618 specialization: lack of, in algae, 108; relative lack of, in stem tissues of mosses, 123; in tissues of higher plants, 132; of animal tissues, 169; in arthropods, 208-09; in lobster, 217; in vertebrates, 235-36, 296- 99, 324, 330; in chordates, 256. See also organization, levels of species: defined, 104; table, 105; naming new, 105-06; origin of new, 549, 551, 553, 574, 582; of horse, 559-64; natural selec¬ tion and origin of new, 560-61. See also species, number of known species, number of known: of Oscillatoria and spirogyra, 109; of fungi, 114; of thal- lophytes, 120; of mosses, 122; of horsetails, 139; of pteridophytes, 140, 141; of seed plants, 142, 147; of flowering plants, 145; of gymnosperms, 145; of sponges, 162, 164; of protozoa, 163; of coelenterates, 174; of flatworms, 175; of roundworms, rotifers, and Bryozoa, 180; of mollusks, 184, 189; of arthropods, 184, 206, 227; of chordates, 184, 257; of annelids, 197; of echinoderms, 200, 201; of insects, 205, 206; of crusta¬ ceans, 213; of beetles, 222; of termites, 224; of bony fish, 236; of lungfish, 238; of amphibians, 239; of salamanders, 239; of rattlesnakes, 242; of nesting birds in U.S., 246; of mammals, 248 specific causes of disease, 443. See also dis¬ eases, causes of specific medicines. See medicines speech centers, 392, 393, 401 Spermatophyta, 107; defined, 132; classifica¬ tion summary, 147, 148, 149, 150. See also spermatophytes spermatophytes: defined, 132; subphyla and classes, 142-46, 147, 148, 149, 150. For structures and functions of, see seed plants and flowering plants spermatozoa, 507 sperm ducts, in earthworms, 496 sperm mother cell, 500, 501 sperm nuclei, in pollen tube, 491, 492 sperm pockets, of earthworms, 496 sperms: of flowers, 89, 90, 489, 491, 492; of mosses, 124, 125; of club mosses, 139; of hydra, 167, 168; of planarian, 173; of lob¬ ster, 216; of frog, Frog Chart 7 (text) fol¬ lowing 304, 308, 497; of earthworm, 496; number of chromosomes in, 500, 501, 502; of mammals, 504; human, 507; sex chro¬ mosomes in, 509, 510; of fruit fly, 510 Sphagnum, 122 sphincter muscles, of human food tube, 331, 333 sphinx moth larva, parasites on, 224 Sphyrna, 258 spiderlings, ballooning, 205-06 spider mite, 158 spiders, 206, 207, 217; collecting, 154; “larvae” of, 208; black widow, 206; clas¬ sification of, 211-12; ancestors of, and first primitive, 573, 574 spiderweb, 205-06 spiderwort, chromosomes in pollen grain of, 535 spinal cord, 43, 233, 236, 320, 321; nerve cells in, 42; of fish, 93, 301, 303; of mam¬ mals, 249; of frog, 298, Frog Chart 3 fol¬ lowing 304, 311; nerve pathways in, 321, 322, 411; of man, Human Body Chart 4 following 336, 389, 390, 391, 392; volume of human, compared to brain, 392; role of, in human autonomic system, 394, 395; in meningitis, 435 spinal frog, defined, 326 spinal nerves: of fish, 301, 303; of frog, Frog Chart 3 following 304, 311; roots of, in man, 321, 322, 391, 411; of man, Hu¬ man Body Chart 4 following 336, 389, 390; functions of human, 390-91 spindle, in mitosis, 38, 39 spines, of starfish, 199; as modified leaves, 269 spiny ant eaters, 251, 259, 504 spiny-skinned animals, 198. See also echino¬ derms spiracles, of grasshopper, 218, 219 spirilla: defined, 431; of syphilis, 432, 433 spirochetes, of syphilis, 432 spirogyra, 95, 102, 120; life processes and structure of, 82, 83, 84, 85; how to stain pyrenoids of, 82—83; conjugation in, 84, 85; classification of, 104, table, 105, 109-10; observing osmosis in, 294 Spirogyra, classification summary, 120; pro¬ tecta and punctata, 104, 105 spleen: of fish, 301; of frog, 311; human, 384; human, and leukemia, 477 splints, for bone fractures, 466 sponges, 95, 154, 158, 166, 167, 171, 172, 173, 175, 176, 202; collecting, 154; classification 724 INDEX of, 160-62; blueprint of Scypha as typical of, 161; kinds of, 162, 164; ancient, 572, 573 spongy tissue, of leaf, 43-44, 271, Plant Charts following 288 sporangia, 114; defined, 115; of molds, 115; of fern, 135; of psilopsids, 140 spore case, of mosses, 123, 123, 124 spores: of spirogyra, 84, 85, 110; of mold, 114; of corn smut, 115; of mosses, 123, 124, 125; of ferns, 133, 135; of club mosses, 139; of Lycopodium, 140; of bacteria, 429; of germs, 433, 437 ; of flowering plants, 490, 491 sporophytes: of mosses, 124, 125, 126, 503; of ferns, 135, 503; of club mosses, 139; of psilopsids, 140; seed plants as, 147, 491 Sporozoa, classification summary, 163 “sports,” as mutations, 537 spring beauties, 490, 639 spruce, 146, 147, 609, 633 Sputnik satellites, 645-46 squash, cross-breeding of, 593 squid, 186, 188, 189, 202; “ink” from, 188 squirrel corn, 639 squirrels, 156, 259, 423, 607, 609, 634; clas¬ sification of, 253; teeth of, 253; baby, climbing, 323; and rabies, 453; and seed dispersal, 492; Kaibab and Abert, 553; in food chains, 614 stability: defined, 383; of blood stream, 382- 88; of human body, 397, 443, 445, 480; and felt needs, 414; and disease, 442-45 stage, of compound microscope, 22 staghorn fern, 136, 137, 141 Stahnke, Dr. Herbert L., 212 stain: iodine as a, 28; Wright’s, 47; Loeffler’s methylene blue, 446 stamens, 87, 88, 90, Plant Charts 2, 3, and 4 following 288, 490, 490, 491, 492, 493; of corn, 494; of garden pea, 518 staminate flowers, of corn, 494; defined, 494 Stanley, Wendell M., 94 staphylococci, 435, 437; hemolytic, 435; de¬ stroyed by white blood cells, 450 Stapp, Lt. Col. John P., 647, 649 starch: action of yeast upon, 62; as nutrient, 66, 68; in yeast cake, 117; made in green leaves, 271, 274; in sprouting corn, 287- 88; digestion of, in man, 332. See also foods and nutrients starfish, 44, 183, 202; eating a fish, 198; struc¬ ture and life functions of, 198—200; blue¬ print of, 199; classification of, 201; how to dissect, 203 starlings, 606 Stegosaurus, 577, 578 stems, 43, 44, 87, 132; of mosses, 122; of ferns, 133, 134; of psilopsid, 140; of bean and corn, compared, 268; of onion, 279; structure and functions of seed plant, 279- 82, Plant Charts following 288; of mono¬ cots, 280, Plant Chart 2 following 288; of dicots, 280, 281, Plant Chart 3 following 288; of gymnosperm, Plant Chart 1 follow¬ ing 288 sterilization: of culture plates, 430; of linens, surgical instruments, caps, gowns, gloves, before surgery, 463 stethoscope, 459, 479 stickleback fish, 247 stick models of molecules, 60 stigma: of pistil of flower, 90, Plant Charts 2 and 3 following 288, 490, 490, 491, 492; of corn silk, 493, 494 stigmasterole, 368 stimulants, defined, 441 stimuli: and plant behavior, 289, 291, 292; and animal behavior, 400; and sense or¬ gans, 400-05; and emotional reactions, 410 stimulus, defined, 289. See also stimuli sting, of scorpions, 213 stinging cells: of coral, 169; of hydra, 165, 166, 167, 169 stirrup, of ear, 402, 403 stock, in budding and grafting, 488 stomach: lining of, 40; of fish, 90, 301; of chiton, 185; of clam, 187; of starfish, 198, 199; of lobster, 215, 216, 217; of grass¬ hopper, 219; of cow, 253; of frog, Frog Chart 6 following 304, 306; of man, 331, 332, Human Body Chart 7 following 336; lining of human, 331, Human Body Chart 7 following 336; X ray of human, 333, 461; circulation in, 340; nerve control of human, 395, 396; ulcers, 460, 461, 462 “stomach ache,” 464 stomach worms. See Ascaris stomates, 270—71, 270; regulation of size of, 270, 291 strawberries, 150; asexual reproduction in, 487; mutant, 595-96; polyploidy in, 597 strep throat, 435; sulfa drugs and, 456; and heart injuries, 479 streptococci, 435, 437; and tissue damage, 435; hemolytic, 435; and heart injuries, 435, 482; in blood stream, 451, 456 Streptococcus, 121. See also streptococci streptomycin, 444, 457, table, 459, 461 stress, 380-81, 397; body’s reactions to, 380- 81, 382; and blood pressure, 444, 480. See also Selye’s theory string beans, as fruits, 492 strip cropping, 624, 625, 631 striped muscle, of heart, and of skeletal mus¬ cles, 41, 43 “strokes”: and blood clots, 340; in heavy drinkers and smokers, 442. See also ar¬ teriosclerosis study, suggestions on how to, 23 INDEX 725 style, of flower, 90, Plant Charts 2 and 3 fol¬ lowing 288, 490, 490, 491, 492 subatomic particles, 95 subphyla, 104, 105; of thallophytes, 107, 117, 120, 121; of chordates, 234, 236, 257, 257- 58 subsoil, 622 success, biological. See biological success “suckers,” and asexual reproduction, 487 sucrose, defined, 273. See also cane sugar suffocation, carbon monoxide, 384 sugar: in protoplasm, 52; formulae of grape and cane, 59, 66; stick model of molecule of grape, 60; as nutrient, 66, 68; oxidation of grape, 69; making of, in photosynthesis, 271-73; tagged with radioisotope, 272- 73; amounts made by various plants and by all green plants per year, 273-74; in protein-making, 276; from digested starch, 287, 332; testing for, 332; in daily human diet, 358; urine tested for, 459 sugar beets, 268; percentage of, made up by sucrose, 273; disease-resistant, 590; poly¬ ploidy in, 598; yield per acre, 623-24; and potash, 628 sugar cane, 148, 268; research on, with radio¬ isotopes, 272; percentage of, made up by sucrose, 273; disease-resistant, 590 sugar water, and attracting of moss sperms, 124 sulfadiazine, 456 sulfa drugs, 53; discovery and use of, 456, table, 459; decrease in effectiveness of, 457— 58 sulfanilamide, 456 sulfathiazole, 456 sulfur: table, 59, 72, 284; symbol of, 59; in proteins, 274; amount of, in human body, 352, 361 sumachs, in plant succession, 608, 609 sunflower, 150 sunshine vitamin, 367 superstitions: about amphibians, 239; about genetics, 515 surgery: prevention of infection during, 429, 463; in tuberculosis and appendicitis, 444; control of pain during and after, 462-63; and control of diseases, 462-64; in cancer, 478 Surinam toad, 240 survival value, 547, 560; of mutant traits, 547, 548, 549, 550 susceptibility: heredity and, to disease, 436, 542, 588; and tuberculosis, 443, 444; of bacteria to antibiotics, 542 suspensions, stable and unstable, 64-65 swamps, as biomes, 603 sweat, 347, 358; and regulation of body tem¬ perature, 317, 397; and salt loss, 360 sweat glands, 317, 347, 348; nerve control of, 394, 396, 397; and pimples, 449 sweet flag, leaves of, 269 sweet peas, 490 sweet potato, red, 536 swimmerets, 214, 217; of lobster, 214, 215 sword fern, 134, 141 symbionts, 275-76; defined, 225; bacterial, of man, 334 symbiosis: defined, 225; of legumes and bac¬ teria, 277 symbols: chemical, 59; for genes of garden peas, 520 symmetry: bilateral, defined, 170; radial, de¬ fined, 198 sympathetic nervous system. See autonomic nervous system sympathin, 396 symptoms, of diseases. See danger signals synapses, 321; defined, 321; in reflex arcs of vertebrates, 322, 323; chemical changes in, 410 synthesis: of proteins, 264-65, 276; of cane sugar, 265; of vitamins, 362 synthetic rubber, 53 synthesis, 53 syphilis: germ of, 432, 433; blood tests for, 433; tissue damage in untreated, 436; spread of germs of, 438; specific drugs for treatment of, 455, 459 systems of organs, 44, 45, 89. See also organ¬ ization, level of tadpoles: of frogs, 235, 238, Frog Chart Cover following 304, 307, 498, 499; of toads, 239, 240 Taenia, 175 talons, of hawks and owls, 246, 247 tapeworms, 169, 173, 175, 190, 202, 436 tapioca, 268 tapirs, 254 taproots, 282 tap water, how to dechlorinate, 49 tarantula, 212, 227 tar pits, fossils from, 560 tassels, corn, 493, 494 Tasso, Dieter, 400 taste buds, of man, 390, 403, 404; how to test, 404 taste centers, in human cerebrum, 393 tasters, PTC, 530-31, 551 tastes, four, in man, 403, 404 taxonomy, defined, 103 tea, 268 teal, green-winged, 247 teen-agers, hormones and, 381, 382 teeth, 43; calcium and, 68; of lobster’s stom¬ ach, 214; of rodents, 253; of carnivores, 254; of frog, 305; human, 332, 333; vita¬ min D and, 367; of horses, 559, 560, 561, 562 temperature, and mutations, 538—39 726 INDEX temperature, of body. See body temperature temperature, receptors to, in human skin, 401, 404 tendons, of frogs, 307; of man, Human Body Charts 1 and 3 following 336 tendrils, of pea vines, 269 Tennessee Agricultural Experiment Station, 587 tentacles: of hydra, 165, 166, 167; of jellyfish, 168, 174; of corals, 169, 174; of Portuguese man-of-war, 174; of bryozoans, 180; of octopus, 186; of echinoderms, 201 tent caterpillar, 222 Tepexan man, 554 terminal flowers, of garden peas, 518, 519 termites, 224-25, 227, 275, 422; king, queen, and soldier, 225 terracing, 624, 625; and flood control, 631 terrarium, 108, 240 test cross: defined, 525; in genetics, 525-26 testes: of hydras, 168; of jellyfish, 168; of clam, 186; of starfish, 200; of lobster, 215, 216, 217; of frog. Frog Chart 7 following 304, 311, 497; hormones of vertebrate, 381, 382; of earthworm, 496; maturation of sperms in, 500, 501; of rabbit, 504; hu¬ man, 507 testosterone, 381, 382 tests: for acidity, with phenolphthalein, 338; for ascorbic acid, 366 test tube rack, 19, 20 test tubes, 19, 20 tetanus, 379, 455 tetany, 379, 440, 459 Thallophyta: table, 105; defined, 107; clas¬ sification summary, 120, 121. See also thallophytes thallophytes, 107-21, 122, 132; defined, 107; how to identify, 120, 121, 130 thermometer, clinical, 459 thermostat, 317 thermotropisms, 290 thiamin, 364, 440; human daily needs of, table, 355; in common food portions, table, 356-57; and cooking, 368; rich sources of, 368 thirst, a felt need, 414 thistle tube, in osmosis demonstration, 286 thoracic duct, 336 thoracic vertebrae, 255 thorax: of mantis, 207; of arthropods, 207, 209; of lobster, 215; of grasshopper, 219; of man, Human Body Charts 6 and 7 fol¬ lowing 336, 337, 506 thousand-legged worms. See centipedes and millipedes threadworms, 603. See Nemathelminthes thrombin, 386 thumbs: of primates, 254; of man, 256 thymus gland, Human Body Chart 8 follow¬ ing 336, 375, 382 thyroid gland, Human Body Chart 8 follow¬ ing 336, 375, 376, 377-79, 382, 440; test¬ ing for disorders of, 377, 378 thyrotropic hormone, 375, 382 thyroxin, 377-79, 382, 440; defined, 377; amount secreted per year in man, 377; too little, 378; in treating cretins and myxe¬ dema, 378; too much, 378-79 Tibbets, Mrs. Luther C., 547 tick birds, 613 ticks, 206, 211, 212, 227 tigers, 254, 422, 423 Tillamook Burn, 620-21, 622, 634-35 tissue: defined, 40; damage to, by germs, 435- 36. See also tissues tissues, 40-43, 45, 47, 50, 89, 95, 107, 179, 202; number of, in human body, 40; of man, 41, 42, 43, 44; of seed plants, 43, 89, 147, 279, 280, 281, Plant Charts following 288; of mosses, 123; in fern stem, 134, 135, 136; primitive, in sponges, 162, 164; ani¬ mals with first true, 165, 169, 172; of hydra, 166, 167, table, 169; derived from 3 layers of planarian, 170; of green leaf, 270-71; immunity and susceptibility of various human, 455; pathologists and dis¬ eased, 476; derived from 3 layers of embryo of vertebrates, 498; of mammal embryo, 506 toads, 156, 232, 235, 258; metamorphosis in, 239; superstitions about, 239; varieties of, 240 tobacco, 150; and death rates, 442; and homeostasis, 445; polyploidy in, 539-40; mammoth, 596 tobacco mosaic disease, 94, 434, 454 toenails: of lizards, 239; of reptiles, 241 tomatoes, 68, 133, 150, 366, 590, 628; zinc in seeds of, 68; as fruits, 144; water losses in, 278; water used by, 284 tongue, 44; of frog, 305. See also taste buds tonsils, removal of infected, 462 Tonto National Monument, 586 tools: used in biology, 19-23, 19, 20, 21, 22; and man’s hands, 256; and human progress, 422-23 toothless mammals. See Edentata tooth shells, 184, 189 topsoil, 622; living tilings in, 622-23; losses of, with and without crop rotation, 624-25 touch: and lateral line in fish, 304; and sense organs in frog, 312; centers of, in human cerebrum, 393; human sense of, 401, 404 toxins: of germs, 435; in ptomaine poison, 437; used in immunization, 452; radiation, and blood, 472 trace elements, and crop plants, 628 tracheal tubes, 218, 227; of grasshopper, 218, 219 trailing arbutus, 639 traits: defined, 515; inheritance of single, 515-16; genetic, of garden peas, 516-20; INDEX 727 traits ( continued ) dominant and recessive, defined, 518; Men¬ del’s studies of, in garden peas, 518, 519, 521; dominant and recessive, of garden peas, 519-20; followed, in dihybrid crosses, 526-28; genetic, of man, 529, 530; abnor¬ mal, of man, 531; sex-linked, of man, 533- 34; how genes may produce, 536; summary of how, are transmitted, 542-43; survival value of genetic, 547, 548, 549; tracing, through several generations, 549; dominant normal and recessive abnormal, 549-50; harmless but useless, 551; desirable, in crop plants, 587; undesirable recessive, in corn, 590. See also genetics tranquilizers, 458, table, 459 transpiration, 278, 288, 291 tree ferns, 133, 575, 581 tree frog, 238; singing, 308, 309 tree green. See pleurococcus trees, 142; food storage in, 269; light-tolerant, 608, 609, 610; as soil binders, 626. See also seed plants, plant successions, annual rings, etc. Trematoda, classification summary, 175 trench fever, 436 trial-and-error, in learning, 417, 418, 420 Triassic Period, 571, 576, 579 trichina, 177, 178, 202 trichinosis, 177-78, 436 trihybrid crosses, 527 trillium, 639 trilobites, 571, 572, 573 tripod, 19 Triton, 189 trochophore, 200 tropisms, 290-91; defined, 290; positive and negative, 290 trout, 232; classification of, 235, 236; state, hatcheries, 235, 236 truffles, 115 trypanosomes, 163 trypsin, 334 tsetse fly, 433, 438 tube, of compound microscope, 20, 22 tube feet, of starfish, 198, 199, 200 tube nucleus, of pollen, 491, 492 tuberculosis, 428, 436, 443, 468; germ of, 429, 431, 432; tissues damaged by, 435; and heredity, 436; germs of, air-borne, 437; contributing factors to, other than germs, 443; specific and underlying causes and treatment of, table, 444; new drugs for, 457, 459; X rays in diagnosing, 460, 461; early symptoms and early diagnosis of, 461-62; isoniazids and, in rats, 462; death rates from, 462, 473; testing cattle for, 467 tubers, 487 tube worms, 196 tubules, excretory; of earthworm, 191, 195; of human kidneys, 346, 347 tulip, 148 tumors: as abnormal growths, 473-74, 475; benign and malignant, 474, 476; types of, 474; surgical removal of, 462. See also cancer tungsten, atoms in crystal of, 54 Turbellaria, classification summary, 175 turgid, defined, 291 turgor, defined, 291 turkey chick, fatherless, 486 turkeys, 246 turnip, 150; polyploidy in, 598 turpentine, 276 turtles, 154, 232, 235, 241, 242, 245, 258, 577; leeches on, 154; water, 236 tusks, of elephants, 260 twigs, examining, 280; cross sections of, 281, Plant Chart 1 following 288 twins: kidney transplants in, 50; fraternal and identical, 508, 525, 528, 531, 531-33, 532; diseases of identical, table, 533 two-egg twins. See twins, fraternal typhoid fever, 428, 436, 468; and damage to intestines, 435; germs of, spread in food and water, 437; human carriers of, 438; immunization against, 455 typhoid Mary, 438 typhus fever, germ of, 434, 436; treatment of, 459 Tyrannosaurus rex, 577, 578 ulcers: of cornea, 459; gastric, X rays in diag¬ nosis of, 460, 461; surgery for, 462; per¬ sistent, and cancer, 477 umbilical cord, 504, 505, 507 unconsciousness: defined, 393; after a severe blow to head, 466 underground stems, 268, 279 undulant fever, 436, 467; germs of, spread in raw milk, 437; treatment for, 459 Ungulata, classification summary, 260 ungulates, 253, 254 uranium atoms, 54, 55; isotopes of, 56 uranium-lead dating of rocks, 567 urea: of frog, 310; formation and excretion of, 345-48; formula of, 346; in blood, 383 ureters, human, 346, 347 urethra, 347 uric acid, excretion of, 346 urinary bladder, of human, 346, 347 urine, 310, 347, 358; of frog, 310; amount and composition of, in man, 347; sugar in human, 347, 377 urine tests, 459; in pregnancy, 508 Urochorda, classification summary, 257 U.S. Atomic Energy Commission, 57 uterus: defined, 476; biopsies in diagnosis of cancer of, 476; of rabbit, 504, 505; human, 507; examining, of a mammal, 511; crowd¬ ing of twins in, 532 728 INDEX vaccination, 343, 468; and swollen lymph nodes, 343; early history of smallpox, 450- 51; smallpox, and need for revaccination, 451-52. See also inoculation and immuniza¬ tion vaccine: rabies, 452; Salk, for polio, 453, 454 vacuoles, 81; in plant cells, 33, 84, 85; food, 77, 78; contracting, 77, 79; in paramecium, 80; in spirogyra cell, 83; in V orticella, 159; in hydra cells, 166, 167; in planarian cells, 172 vagus nerves, 390, 394 valley fever, 119; germs and spores of, 433, 436; germs of, air-borne, 437 valves: heart, 298, 303, Frog Chart 4 follow¬ ing 304, 309, Human Body Chart 5 follow¬ ing 336, 341-42; of veins, 298 van Helmont, 295; and willow tree experi¬ ment, 266 varieties, rise of new, 547-58. See also breeds, rise of new variety, in living things, 100-263 vascular plants, 132, 141, 147; defined, 132; classification of, 132-53; first-known fossils of, 140, 573 vascular tissue, in ferns, 132, 133, 134; in psilopsids, 140; in seed plants, 147, 271, 279, 280-82, 281, 283, 283, 287, Plant Charts following 288. See also seed plants vegetables, and adequate diet, 369, 370 vegetarians, millipedes as, 211 veins, blood: defined, 92; of clam, 187, 188; of lancelet, 233; of vertebrates, 236; of man, 296, 297, Human Body Chart 5 following 336, 339, 340, 341; valves of, 298; of fish, 301; of frog, Frog Chart 4 following 304; of umbilical cord, 505. See also circulatory systems veins, of leaves, 134, 146, 267, 271, 271, Plant Charts following 288 venom, of snakes, 245 ventral blood vessel, of earthworm. See blood vessels ventral nerve cords. See nerve cords ventral side, defined, 170 ventricles: of fish heart, 301, 303; of frog’s heart, Frog Chart 4 following 304, 309, 310; of human heart, 313, Human Body Chart 5 following 336, 339, 341. See also circulation of blood Venus’s-flower-basket, 164, 202 vertebrae, 233, 234, 236, 564; true body, 235; of mammals, 249; of man, 255, Human Body Chart 1 following 336; of fish, 301, 303; of frog, Frog Chart 1 following 304 Vertebrata, table, 105; defined, 234; classifica¬ tion summary, 258, 259, 260. See also ver¬ tebrates vertebrates: classification of, 232-63; noto¬ chord in embryo, 233; classes of, 234, 235, 236, 296; body organization of, 235, 236, 295-99; nervous systems of, 235-36; cir¬ culatory systems of, 235, 236, 313, 314; water-living, 236; comparing, 262; brains of, 298-99, 318; air-breathing, 308; be¬ havior, 318-24, 407; first-known, 571, 573; first air-breathing, 574; history of, in Pa¬ leozoic, 576 Victoria cruziana, 269 villi, 335, 339 vinegar eels, 176, 202 vines, 142 violets, 490, 639 Virginia creeper, 283 viruses: 24, 24; defined, and diseases caused by, 94-95; Stanley’s research on, 94, 434; as protists. 111; as agents of diseases, 433, 434, 436, 437; and rabies, 448; of smallpox and cowpox, 452; antibiotics for use against, 459; and genes, 535; mutations of, 539; and gene transduction, 552 vision centers, in human cerebrum, 393 vital statistics, keeping, 467-68 vitamins, 50, 53, 66, 68, 352, 362-69, 383, 440, 478; synthesis and composition of, 68, 362; made by colon bacteria, 334; as indis¬ pensable nutrients, 352—53; daily human requirements of, table, 355; contained in common portions of foods, table, 356-57; fat- and water-soluble, 362; history and naming of, 362—64; deficiency, and diseases, 366, 458, table, 459; cooking and, 368 vocal cords, of frog, 308 vocal sacs, of frog: openings into, 305, 306; and singing, 308 voice box. See larynx voices: of amphibians, 241; of frogs, 308; changing of boys’, 381, 382 voluntary muscles. See muscles Volvox, 111, 120; classification of, 163 von Behring, 452 Vorticella, 159, 202; classification of, 163 walking fern, 133 walking legs: of arachnids, 211; of lobster, 214, 215 walking sticks, 218, 226 wallabies, 252 walnut family, classification summary, 149 walnuts, planted by squirrels, 634 walrus, 615 wampum, 188 warbles, 226 warm-bloodedness, 246; in birds and mam¬ mals, 250, 258, 312-18; factors in, 316-18 Warren, Dr. J. C., 462 warts, 239, 474, 476, 477 Washita River Valley, controlling floods in, 631 wasps, 218; classification of, 223-24 water: in living things, 50, 51; amount in INDEX 729 water ( continued ) human body, 51; formula and stick model of molecule, 59, 60; number of molecules in glass of, 60-61; mixing oil and, 64; num¬ ber of molecules of, in human liver cell, 66; in foods, 66, 68, 352-53; life in drop of, 74, 75; getting rid of excess, from ani¬ mals, 78-79, 80, 172; and sugar-making in plants, 82, 88, 128, 271, 273; flow, in sponges, 161; earthworms and, 194, 195; fish adaptations to, 236-37; lost by tran¬ spiration, 278; xylem and transport of, 280; and osmosis, 286, 287; as a stimulus to plants, 290; and human kidneys, 347; per cent of, in blood plasma, 383; germs spread in, 437; conservation of, 621, 629—32, 641; and soil, 622, 624, 625, 626; amount used in U.S., 631 water boatmen, 154 water-conducting tissue, in plants, 43, 102. See also xylem water dog, 239 water fleas, 75, 213, 227; and hydras, 165, 167 water lily, 165; largest, 269; stomates of leaf of, 270 water lily family, classification summary, 149 watermelons, wilt-resistant, 590 water moccasins, 242, 243 watersheds: defined, 605-06; need to restore and maintain plant cover on, 606; plant cover on, 631 water-soluble vitamins, 362, 365 water supplies, purification of, 467 water table, 631; falling, 631 water-vascular system, of echinoderms, 202 water-vessel system: in rosebush, 88; of star¬ fish, 199, 200; of bean and corn seedlings, 267. See also xylem weasels, 254 weeds: birds in biological control of, 248; in plant succession, 612; as soil binders, 626 weevils, 223 weight: “normal,” 355; rapid loss of, and tuberculosis, 462 wens, 474 wet mount, 29 whales, 25, 236, 422; protoplasm of, 51; blue, and sizes of, 249; classification of, 260; in food chain, 615 wheat, 101, 148; rust resistant, 590, 591; use¬ ful mutations in, 596; in strip cropping, 625 wheat germ, 365 wheat rust, 116, 590 wheel animals. See rotifers whelk, 189 whip scorpion, 213 white-blood-cell counts: in diagnosis, 459-60; table, 460; differential, 460. See also blood cells, counts of white blood cells. See blood cells White Cliffs of Dover, 585 white matter: of spinal cord, 391; of brain, 392 white rat, 407, 504. See also rats whiting fish, 258 whooping cough, 435, 436; inoculation with toxin of, 454, table, 455; white-blood-cell counts in, 460 wildcats, in balance of nature, 602 wild crab, 488, 608 wild ducks, 246. See also game birds wild-flower conservation, 639 wild flowers. See flowers Wild Flower Preservation Society, 639 wildlife: history of populations of, 603-12; conservation of, 635-39; harvesting of, 637. See also wildlife refuges wildlife refuges, improved control of, 636 willow family, classification summary, 149 willow tree, van Helmont and, 266 wilting, of plants, 291 windpipe: ciliated cells in lining of human, 40, 178, 338; of frog, 306; of man, Human Body Chart 6 following 336, 337-38 wings: of grasshopper, 218, 219; of butterfly, 220; of beetle, 222; of bees, wasps, and ants, 223; of termite, 224, 225; of flies and mosquitoes, 226; of true bugs, 226; of cicadas and plant lice, 226; rudimentary, of some birds, 246; of mammals, 250; fruit fly, and heredity of various types of, 547, 548, 549 wintergreen, 108 witchweed, 618 wolves, 254, 260, 602 wombats, 252 wood: primitive, in some mosses, 122, 123; fossil of fern, 132; soft and hard, 146; and termites, 225. See also xylem wood cells, 33, 40, 88, 89, 102. See also xylem woodchuck, 259 wood frog, 239, 240 woodland mosses, 108 woodpeckers, 245, 258; bills of, 246, 247; pileated, 247 “woolly bear,” 50 workers, in bee and termite colonies, 224, 225 worms, 207; parasitic, 173, 175, 177, 178; soft-water-inhabiting, 196; parthenogene¬ sis in, 505. See also earthworms, sand worms, etc. “worm tracks,” fossil, 572 worrv, as emotional behavior, 410 wounds, care of minor, 465; healing of, 473-74 Wright, Seth, 546 Wright’s stain, how to use, 47, 49 X chromosome, 509, 510; and bleeder’s dis¬ ease, 533-34 X rays: in diagnosis, 460, 461; need for mod- 730 INDEX eration in use of, 460, 461; and cancer diag¬ nosis, 476; and cancer treatment, 477, 478; and mutations, 538, 596 xylem: defined, 135; in ferns, 132, 134, 135; in seed plant leaves, 271, Plant Charts fol¬ lowing 288; in seed plant stems, 280, 281, Plant Charts following 288; from cambium, 281-82; in seed plant roots, 283, 287, Plant Charts following 288 Y chromosome, 509, 510 yarrow, 133 yawning, 405 yeasts, 44, 95, 114, 121; testing action of, on starch, 62; how to grow, 116; budding, 117 yellow fever, 226, 428; cause of, 434, 436; and mosquitoes, 438; immunization against, 455 yellowhammer, 106 yellow perch: how to examine mouth of, 299; anatomy and physiology of, 299-304; how to dissect, 300, 302; blueprint of, 301 yellow-shafted flicker, 106 yucca, 148 Tea mays, 101, 101. See also corn zebras, 260, 562; classification of, 254, 260 zinc: in tomato seeds, 68; in human body, 352; needed by crop plants, 628 zinnia, 150 Zygnemataceae, table, 105 Zygnematales, table, 105 INDEX 731 „ J . ** ~*71L MEfl . * ■ ■»» Dr,15 V * = «r v S A1 I TH> fz ft I ' CURRICULUM 216480 ' '* *?•% > r*4 / COMPACT STORAGE EDUCAi'^w uaa*^x QH 308.5 S64 1959 c.l Smith, Ella Thea. Exploring biology, the science EDUC 0 0004 8739 643 ' •/•/V • 1 • : ♦ -i • «'• t > : ::Xi jfrv cn >gjw»o#Cf . *. jWWjJ; i£& WflHi th §ij| v.;. 4$ ■A* In* vWl'l'j Ir * •:r> . . 1 .