UNIVERSITY FARM »<^ > ^B-f 1 ^ S^>.A.'ri DNIVERSITY OF CALIFORNIA LIBRARY THIS BOOK IS DITE ON THE LAST DATE STAMPED BELOW N&V 15 1934 HOV 301934 OCT «13 ^^*^ Rtli 5Tn-10,'22 Digitized by tine Internet Arciiive in 2007 witin funding from IVIicrosoft Corporation http://www.archive.org/details/essentibiolopreseOOhuntrich s > '^ So a> -4-> C3 cS e of use in forming food or new protoplasm for the plant. An animal absorbs into its body only food material that can be used, reject- ing material unfit for food. (4) Protoplasm grows, not as inorganic objects grow, from the outside , ' btU by a process of taking in food material and then changing it into living material. To do this it is evident that the same chem- * Home Experiment. — Make a strong solution of alum (two spoonfuls of pow- dered alum to half a glass of water). Suspend in the solution a thread with a pebble attached to the lower end. Notice where and how crystals of alum grow. COMPOSITION OF LIVING THINGS 33 loal elements must enter into the composition of the food sub- stances as are found in ii\'ing matter. The simplest plants and animals have tliis wonderful power as certainly developed as the most complex forms of life. (5) Protoplasm^ be iiin the body of a plant or of an animaly uses oxygen. It breathes. Thus substances taken into the body are oxidized, and release energ>' for movement and the other activi- ties of plants and animals. (6) Protoplasm has the power to rid itself of waste materials, especially those which might be hannful to it. A tree sheds its leaves, and as a result gets rid of the accumulation of mineral matter in the leaves. Plants and aninuAt alike pass off the carbon dioxide which results from the verj' prooeaBes of living, the oxidation of p>arts of their own bodies. Animals eliminate wastes containing nitrogen through the skin and the kidneys. (7) Protoplasm can reproduce^ that is, form other matter Hke iUdJ. New plants are constantly appearing to take the places of those tliat die. The supply of U\'ing thingiB upon the earth is not de- creasing; reproduction is constantly taking place. In a general way it is possible to say that plants and animals reproduce in a very similar manner. We shall study this more in detail later. To sum up, we find that living protoplasm has the properties of sensibility, motion, groii'th, and reproduction alike in its sim- plest state as a one-celled plant cr animal and as it enters into the composition of a hi^y complex organism such as a tree, a dog, or a man. Books pob RBFrnxmca Shaipe, A LabanUorii MamMoL American Book Company. Atkinson. Fint SUtdiet nf PlatU Life. Chap. XI. Ginn and Company. Snj-der. The Ckemutir^ ^ PImd ami Ammai Life. Tlie Macmillun Company. Coulter. Barnes, and Caf«leB.iirei««iftllinute Other Flower Visitors.' — Other insects besides the bee are pollen carriers for flowers. Among the most useful are moths and but- terflies. Both insects feed only on nectar, which they suck through a long tube- like proboscis. The heads and Ijodies of these insects are more or less thickly covered with hairs, and the wings are thatched with hairlike, tiny scales. All these structures are of use to the flower because they collect and carry pollen. Projecting from each side of the head of a butterfly is a fluff'y structure, the palp. This collects and carries a large amount of pollen, which is deposited upon the stig- mas of other flowers when the butterfly pushes its head down into the flower tube after nectar. Flies and some other insects are agents in cross-pollination. Humming birds are also active agents in some flowers. Snails are said in rare instances to carry pollen. Man and the domesti- cated animals undoubtedly frequently pollinate flowers by brush- ing past them through the fields. ' If the study of other insects is taken up in the fall in connection with the flower, the student sliould be referred to parts of Chapters XX and XXI and to the Lab- oratory Manual. The common swallow-tailed butterfly on clover. Bumblebees usually are the agents which cross-pollinate this flower. 44 FLOWERS AND THEIR WORK Cross-pollination of a Head (Clover). — In a flower cluster called a head, a closely massed cluster of little flowers as clover, cross-pollination is usually effected by bumblebees which rapidly work from one flower to another in the same cluster, inserting their tongues deep into the flower cup. The butterfly shown in the illustration inserts its proboscis (seen curled up like a watch spring on the under- side of the head) into the flower. Cross-pollination of a Composite Head. — This flower cluster, so often mistaken for a single flower, is found only in the great Composite family, to which so many of our commonest flowers and weeds belong. The daisy, aster, goldenrod, and sunflower are examples of the Compositse. The composite head is well seen in a daisy or the sunflower. This head has an outer circle of green parts. These parts look like sepals, but in reality are a whorl of leaflike parts. Taken together these form an involucre. Inside the involucre is a whorl of brightly colored, irregular flowers called the ray flowers. They appear to act, in some instances at least, as an attraction to in- sects by showing a definite color (see the common dogwood, Cornus florida). The flowers occupying the center of the cluster are the disk flowers. Such a flower examined under the hand lens is found to be perfect. A care- ful observer will find that the anthers are united in a ring around the pistil. This is a typical condition in the Com- positsB. The stamens ripen first and grow up around the stigma, which ripens later. The stigma splits (see a), and pollen from another flower brought to its surface will germinate there. A composite head. Section through composite head, showing a disk flower (a), a ray flower (c), and the involucre (d). Other examples. — Many other examples of adaptations to secm-e cross-poUination by means of the visits of insects might be given. The mountain laurel, which makes our hillsides so beauti- ful in late spring, shows a remarkable adaptation in having the stamens caught in little pockets of the corolla. The weight of the visiting insect on the corolla releases the anther of the stamen from the pocket in which it rests, and the body of the visitor is dusted with pollen. FLOWERS AND THEIR WORK 45 Milkweed, showing the flower cluster called an umbel. The milkweed or butterfly weed (Asdepias cornuti) is another example of a flower adapted to insect pollination.' Still another example of cross-pollination is found in the yucca, a desert-lov- ing semitropical lily (to be seen in most botanic gar- dens). In this flower the stigmatic surface is above the anther, and the pollen is sticky and could not be transferred except by in- sect aid. This is accom- plished in a remarkable manner. A little moth, called the pronuba, gathers pollen from an anther, flies away with this load to another flower, there deposits an egg in the ovary of the pistil, and then rubs its load of pollen over the stigma of the flower. The young hatch out and feed on the young seeds which have been fertilized by the pollen placed on the stigma by the mother. They eat some of the developing seeds and then bore out of the seed pod and escape to the ground, leaving the plant to develop the remaining seeds without further molestation. The fig insect {Blastophaga grossoriim) is another member of the insect tribe that is of considerable economic impor- Pod of yucca pierced by the pronuba. Pronuba polli- nating pistil of yucca. I For an excellent account of cross-pollination of this flower, the reader is re- ferred to W. C. Stevens, Introduction to Botany. Orchids are well known to botan- ists as showing some very wonderful adaptations. For simple reference reading, see Coultor, Plant Relations. A classic easily read Is Darwin, On the Fertilization of Orchids. 46 FLOWERS AND THEIR WORK tance. It is only in recent years that the fruit growers of Cali- fornia have discovered that the fertilization of the female flowers is brought about by a gallfly which bores into the young fruit.^ The last two cases are only some of the many examples of mutual help among plants and animals. Pollination by the Wind. — Not all flowers are dependent upon insects for cross-pollination. Many of the earliest of spring flowers appear almost before the insects do. These flowers, needing no conspicuous colors or showy corolla to attract insects, often lack this part altogether. In fact, we are apt en- tirely to overlook the flowers which appear in the spring upon our common forest and shade trees. In many trees the flowers appear before the leaves come out. Such flowers are dependent upon the wind to carry pollen from the stamens of one flower to the pistil of an- other. Most of our common trees, oak, poplar, maple, and others, are cross-pol- linated almost entirely by the wind. Among the adapta- tions that a wind-pollinated flower shows are : (1) The develop- ment of very many pollen grains to each ovule. In one of the insect-pollinated flowers, that of the night-blooming cereus, the ratio of pollen grains to ovules is about eight to one. In flowers which are to be pollinated by the wind, a large number 1 The teacher is referred to Yearbook of the Department of Agriculture for 1900 for data on the insect which pollinates the Smyrna fig. The staminate flower of the corn. Notice the hang- ing anthers full of pollen. FLOWERS AND THEIR WORK 47 of the pollen grains never reach their destination and are wasted. Therefore in such plants several thousands, perhaps hundreds of thousands, of pollen grains will be developed to every ovule produced. Such are the pines. In May and early June the ground under pine trees is often yellow with pollen, and the air may be filk^d with the dust for miles from the trees. Such, also, is the case with many of the grasses. (2) The anthers are usually exposed to the wind when ripe. The common plantain and timothy grass are excellent examples. (3) The pistil of the flower is peculiarly fitted to retain the pollen by having feathery projections along the sides which increase the stigmatic surface. This can be seen in the grass. In the Indian corn the stigmatic surface is the so-called silk which protrudes beyond the covering of modified leaves which form the husk of the ear of corn. All our grains, wheat, rye, oats, and others, have the typical feathery pistil of the wild grasses from which they descended. (4) The corolla is often entirely lacking. It would only be in the way in flowers that are dependent upon the wind to carry pollen. Imperfect Flowers. — Some flowers, the wind-pollinated ones in particular, are imperfect ; that is, they lack either stamens or pistils. In such flowers, cross-polli- nation must of necessity follow. If only the staminate flowers (those which contain only stamens) are developed on one plant, and only the pistillate (those which bear only pistils) on another, we call the plant dicecious. A common example is the willow. Other plants bear staminate and pistil- late flowers on the same plant. In this case they are said to be monoecious. The oak, hickory, beech, birch, walnut, and chestnut are familiar examples. The pine tree is another example of moncecious tree; the male or staminate flowers appear in tiny clusters called catkins, the female or pistillate flowers coming a little later as tiny cones, which in most species of pines take nearly two years to produce seeds. Water Pollination. — An unusual method of pollination is found in those plants which live almost entirely under the water. In eelgrass the pistillate flowers are attached to long, slender stalks and float on the Imperfect flowers of the squash, the corolla removed. Pistil- late flower at the left. 48 FLOWERS AND THEIR WORK surface of the water. The staminate flowers, when ripe, break away from their submerged stems and float to the surface. If these float under a pistillate flower, the protruding ends of the pistils catch and retain some of the pollen from the staminate flower. Thus fertilization follows. After pollination, the stalk of the pistillate flower coils up in a spiral and draws the flower under the surface of the water, so that the seeds may ripen in security. Summary. — If we now collect our observations upon flowers with a view to making a summary of the different devices flowers Flowers of the Lady Washington geranium showing the conditions of dichogamy ; A, flower with stamens ripe, but with the stigma not ready to receive pollen ; B, the same flower at a later stage ; the stamens have withered, but the stigma is now ready to receive pollen. have assumed to prevent self-pollination and to secure cross-pollina- tion, we find that they are as follows : — (1) The stamens and pistils may be found in separate flowers, either on the same or on different plants. (2) The stamens may produce pollen before the pistil is ready to receive it, or vice versa. This condition is called dichogamy. (3) The stamens and pistils may be so placed with reference to each other that pollination can be brought about only by outside assistance. In some flowers, as is shown by the primula of our hothouses, the stamens and pistils are each of two different lengths in different FLOWERS AND THEIR WORK 49 Condition of stamens and pistils in the spiked loose- strife {Lythrum aalicaria). flowers. Short styles and long or high-placed filaments are found in one flower, and long styles with short or low-placed filaments in the other. Pollination will be eff'ected only when some of the pollen from a low-placed anther reaches the stigma of a short- styled flower, or when the pollen from a high anther is placed upon a long-styled pistil. Flowers which have this peculiar condition are said to he dimorphic (Greek = of two forms). There are, as in the case of the loosestrife, trimorphic flowers having pistils and stamens of three lengths. Charles Darwin,who worked out the fertilization of this flower, describes it as follows : " When })ees suck the flowers, the anthers of the longest stamens . . . are rubbed against the abdomen and inner sides of the hind legs as is likewise the stigma of the long-styled form (see diagram). The anthers of the midlength stamens and the stigma of the midstyled form are rubbed against the upper side of the thorax and between the front pair of legs. And, lastly, the anther of the shortest stamens and the stigma of the short-styled form are rubbed against the proboscis and the chin; for the bees in suck- ing the flowers insert only the front part of the head into the flower. ... It follows that insects will generally carry the pollen of each form from the stamens to the pistil of corresponding length." 1 Protection of Pollen. — Pollen, in order to be carried effectively by the wind, insects, or other agencies, must be dry. In some flowers the irregular form of the corolla protects the pollen from dampness. Other flowers close up at night, as the morning-glory and four-o'clock. Still others, as the bellflower, droop during a shower or at night. Pollen is also protected from insect visitors which would carry » Forma of Flowers, page 169. HUNT. E8. BIO. 4 50 FLOWERS AND THEIR WORK off pollen but give the flower no return by cross-pollinating it. In some flowers access of ants, plant lice, or other small crawling insects to the stamens is rendered difficult by hairs which are developed upon the filaments or on the corolla. Sometimes a ring of sticky material is found making a barrier around the stalk underneath the flower. Many other adaptations of this sort might be mentioned. Artificial Cross-Pollination and its Practical Benefits to Man. — - Artificial cross-pollination is practiced by plant breeders and can easily be tried in the laboratory or at home. First the anthers must be carefully removed from the bud of the flower so as to elim- inate all possibility of self-pollination. The flower must then be covered so as to prevent access of pollen from without ; when the ovary is sufficiently developed, pollen from another flower, having the characters desired, is placed on the stigma and the flower again covered to prevent any other pollen reaching the flower. The seeds from this flower when planted may give rise to plants with some characters like each of the plants from which the pollen and egg cell came. Artificial fertilization has been made of great practical value to man. Rkference Books elementary Sharpe, A Laboratory Manual for the Solution of Problems in Biology. American Book Company. Andrews, Botany all the Year Round, pages 222-236. American Book Company. Atkinson, First Studies of Plant Life, Chaps. XXV-XXVI. Ginn and Company, Bailey, Lessons with Plants, Part III, pages 131-250. The Macmillan Company. Coulter, Plant Studies, Chap. VII. D. Appleton and Company. Dana, Plants and their Children, pages 187-255. American Book Company. Lubbock, Flowers, Fruits, and Leaves, Part I. The Macmillan Company. Newell, A Reader in Botany, Part II, pages 1-96. Ginn and Company. ADVANCED Bailey, Plant Breeding. The Macmillan Company. Campbell. Lectures on the Evolution of Plants. The Macmillan Company. Coulter, Barnes, and Cowles, A Textbook of Botany, Part II. American Book Com- pany. Darwin, Different Forms of Flowers on Plants of the Same Species. D. Appleton & Co. Darwin, Fertilization in the Vegetable Kingdom, Chaps. I and II. D. Appleton & Co. Darwin, Orchids Fertilized by Insects. D. Appleton and Company. Gray, Structural Botany. American Book Company. Lubbock, British Wild Flowers. The Macmillan Company. Miiller, The Fertilization of Flowers. The Macmillan Company. V. FRUITS AND THEIR USES Problem VTIT. A study of fruits to discover — {a) Tlielr uses to a plant. (J)) The means of scattering. (c) TJieir prote<^tion from animals and other enemies. {Laboratory Manual, Prob. VIII.) A Typical Fruit, — the Pea or Bean Pod. — If a withered flower of any one of the pea or bean family is examined carefully, it will be found that the pistil of the flower continues to grow after the rest of the flower withers. If we remove the pistil from such a flower and examine it carefully, we find that it is the ovary that has enlarged. The space within the ovary has become almost filled with a number of al- most ovoid bodies, at- tached along one edge of the inner wall. These we recognize as the young seeds. The Dod of a bean ^^^^ of the black locust; a legume, showing the ' attachment of the seeds. pea, or locust illustrates well the growth from the flower. The flower stalk, the ovary, and the remains of the style, the stigma, and the calyx, can be found on most unopened pods. If the pod is opened, the seeds will be found fastened to the ovary wall each by a little stalk. That part of the ovary wall which bears the seeds is the placenta. The walls of the pod are called valves. The pod, which is in reality a ripened ovary with other parts of the pistil attached to it, is considered as a fruit. By definition, a fruit is a ripened ovary together with any parts of the flower that may be attached to it. The chief use of the fruit to the flower is to hold and to protect the seeds ; it may ultimately distribute them where they can reproduce young plants. 51 52 FRUITS AND THEIR USES Formation of Seeds. — Each seed has been formed as a direct result of the fertilization of the egg cell {contained in the embryo sac of the ovule) by a sperm cell of the pollen tube. Seed Dispersal.^ — If you will go out any fall afternoon into the fields, a city park, or even a vacant lot, you can hardly es- cape seeing how seeds are scattered by the parent plants and trees. Several hundred little seedling trees may often be counted under the shade of a single maple or oak tree. But nearly all these young trees are doomed to die, because of the overshading and crowding. Plants, like animals, are dependent upon their Young cedars around parent tree. Photographed by Overton. surroundings for food and air. They need light even more than animals need it, because the soil directly under the shade of the old tree gives only raw food material to the plants, and they must have sunlight in order to make food. This overcrowding is seen in the garden where young beets or lettuce are growing. The gardener assists nature by thinning out the young plants so that they may not be handicapped in their battle for life in the garden by an insufficient supply of air, light, and food. 1 At this point a field trip may well be taken with a view to finding out how the common fall weeds scatter their seeds. Fruits and seeds obtained upon this trip will make a basis for laboratory work on the adaptations of seed and fruit for dispersal. FRUITS AND THEIR USES 53 The blackberry, a fruit having small seeds scattered by birds. It is evidently of considerable advantage to a plant to be able to place its progeny, which are to grow up from seeds, at a consider- able distance from itself, in order that the young plant may })e pro- vided with a sufficient space to get nourishment and foothold. This is the result which plants have to accom])lish. Some accom- plish the result more com- pletely than others, and thus are the more successful ones in the battle of life. Adaptations for Seed Disper- sal; Fleshy Fruits with Hard Seeds.- — Plants are fitted to scatter their seeds by having the special means either in the fruit or in the seed. Various agents, as the wind, water, or squirrels, birds, and other animals, make it possible for the seeds to be taken away from the plant. Fleshy fruits, that is, such fruits as contain considerable water when ripe, are eaten by animals and the seeds passed off undigested. Most wild fleshy fruits have small, hard, indigestible seeds. Birds are responsible for much seed planting of berries or other small fruit. Bears and other berry-feeding animals aid in this as well. Some seeds have especial adaptations in the way of spines or projections. Insects make use of these projections in order to carry them away. Ants plant seeds which they have carried to their nests for a food supply. Nuts are planted by squirrels and blue jays. Suggestions for Field Work. — Examine the fruit of huckleberry, black- berry, wild strawberry, wild cherry, black haw, wild grape, tomato, currant. Report how many of the above have seeds with hard coatings. Notice that in most, if not in all, edible fruits, the fruit remains green, sour, and inedible until the seeds are ripe. In the state of nature, how might this be of use to a plant ? Hooks and Spines. — Some fruits which are dry and have a hard external covering when ripe possess hooks or spines which enable the whole fruit to be carried away from the parent plant by animals or other moving objects. Cattle are responsible for the spread of 54 FRUITS AND THEIR USES The cocklebur. Note the curved hooks. some of our worst weeds in this way. The burdock and clotbur are famiHar examples. In both the mass of Uttle hooks is all that re- mains of an involucre. Thus the whole fruit cluster may be carried about and j^iiriife ^^Sl^ seeds scattered. In many of the Com- -^SHHRP' ^^S^ posites, as in the cockleburs and beg- ^T^TlffT^ ~^^^ gar's-ticks, the fruits are provided with strong curved projections which bear many smaller hooklike barbs. Pappus. — Probably the most im- portant adaptations for dispersal of seeds are those by which the fruit is fitted for dispersal by the wind. That much-loved and much-hated weed, the dandelion, gives us an example of a plant in which the whole fruit is carried by the wind. The parachute, or pappus, is an outgrowth of the ovary wall. Many other fruits, notably that of the Canada thistle, are provided with the pap- pus as a means of getting away. In the milkweed the seeds have developed a silky outgrowth which may carry them for miles. In New York city the air is sometimes full of the dowh from these seeds, which is brought from far over the meadows of New Jer- sey by the prevailing westerly wind. Dehiscent Fruits and how they Scatter Seeds. — One of the many meth- ods of getting rid of seeds is seen in dry fruits. These simply split to allow of the escape of the Examples of common fruits that split open (dehiscent) are seen Dandelion heads ; the middle one a mass of ripe fruits ready to be scattered by the wind. Photo- graphed by Overton. FRUITS AND THEIR USES 55 in the follicle of the milkweed, a fruit which splits along the edge of one valve, the pod or legume of a pea and the bean, and the capsule of Jimson weed and the evening primrose. In all of the above, the ovary wall does not split open until the seeds are fully ripe. This helps to insure the future growth of the seed. Some dehiscent fruits scatter their seeds through the explosion of the seed case. Such a fruit is the witch- hazel, which explodes with such force that the seeds are thrown several feet. The wild geranium, a five-loculed capsule, splits along the edge of each locule, snaps back, and throws the seed for some distance. Jewelweed fruits burst open in somewhat the same manner. Capsule of crane's- bill discharging its seed. Winged Seeds. — The seeds of the pine, held underneath the scales of the cone, are prolonged into wings, which aid in their dispersal. The seeds of many of our trees are thus scattered. Other Methods. — Sometimes whole plants are carried by the high winds of the fall. This is effected in the plants called tumble- weeds, in which the plant body, as it dries, assumes a somewhat spherical shape. The main stalk breaks off, and the plant may then be blown along the ground, scattering seeds as it goes, until it is ultimately stopped by a fence or bush. A single plant of Russian thistle may thus scatter over two hundred thou- sand seeds. Seeds or fruits (for example, the coconut) may fall into the water and be carried thousands of miles to their new resting place, the fibrous husk provid- ing a boat in which the seed is carried. Other seeds may collect in the mud along the banks of ponds or streams. Birds which come there to feed upon these and other material in the mud may carry many seeds in the mud attached to their feet. The great English naturalist, Charles Cross section of a coconut in its fibrous husk. 56 FRUITS AND THEIR USES Darwin, raised eighty-two plants from seeds thus carried by a bird. It is probable that by means of birds and water most of the vegetation has come into existence on the newly formed coral islands of the Pacific Ocean. Some Other Forms of Fruits and their Method of Dispersal. — Dry fruits which do not split open to allow of the escape of their seeds are known as indehiscent fruits. Some are known as grains. Such are corn, wheat, oats, etc. A grain is simply a one-seeded fruit in which the wall of the ovary has grown so closely to that of the seed that they cannot be separated. Such fruits are usually small and numerous, having a thin outer wall. The seed may easily germinate under favor- able conditions. Other indehiscent fruits are nuts, one-seeded fruits with usually hard outer covering, the so-called key fruits of the maples or ash, and many others. Some indehiscent fruits are light and carried by the wind ; others are extremely numerous and may be scattered by animals. The key fruits depend upon the wind, while nuts are often carried away, buried, and forgotten by blue jays and squirrels, and thus obtain a new foothold. Large Numbers of Seeds. — Plants which do not have especial means for scattering their seeds may make up for this by producing a large number of seeds and holding them in podlike fruits which are easily shaken by the wind. The Jimson weed is a familiar example of such a plant. Each capsule of Jimson weed contains from four hundred to six hundred seeds, depending upon its size. If all of these seeds develop, the whole earth would soon be covered with Jimson weed, to the exclusion of all other forms of plant life. That this is not the case is due to the fact that only those seeds which are advantageously placed can develop ; the others will, for various reasons (lack of moisture to start the young seed on its way, poor soil, lack of air or sunlight, overcrowding), fail to germi- uatQ. Grain; spikes of ened flowers. rip- Key fruit of maple. The acorn, a nut in which the involucre partly covers the fruit. FRUITS AND THEIR USES 67 The Struggle for Existence. — Those plants which provide best for their young are usually the most successful in life's race. Plants which combine with the ability to scatter many seeds over a wide territory the additional characteristics of rapid growth, resistance to dangers of extreme cold or heat, attacks of parasitic enemies, inedibility, and peculiar adaptations to cross-pollination or self- pollination, are usually spoken of as weeds. They flourish in the sterile soil of the roadside and in the fertile soil of the garden. By means of rapid growth they kill other plants of slower growth by usurping their territory. Slow-growing plants are thus actually exterminated. Many of our common weeds have been introduced from other countries and have, through their numerous adaptations, driven out other plants which stood in their way. Such is the Rus- sian thistle. P^irst introduced from Russia in 1873, it spread so rapidly that in twenty years it had appeared as a common weed over an area of some twenty-five thousand square miles. It is now one of the greatest pests in our Northwest. Problem IX. The economic value of some fruits, {Labor a- tory Manual, Prob. IX.) Economic Value of Fruits. — Our grains are the cultivated prog- eny of wild grasses. Domestication of plants and animals marks epochs in the advance of civihzation. The man of the stone age hunted wild beasts for food, and lived like one of them in a cave or wherever he happened to be; he was a nomad, a wanderer, with no fixed home. He may have discovered that wild roots or grains were good to eat ; perhaps he stored some away for future use. Then came the idea of growing things at home instead of digging or gathering the wild fruits from the forest and plain. The tribes which first cultivated the soil made a great step in advance, for they had as a result a fixed place for habitation. The cultivation of grains and cereals gave them a store of food which could be used at times when other food was scarce. The word "cereal" (derived from Ceres, the Roman Goddess of Agriculture) shows the impor- tance of this crop to Roman civilization. From earliest times the growing of grain and the progress of civilization have gone hand in hand. As nations have advanced in power, their dependence upon the cereal crops has been greater and greater. 58 FRUITS AND THEIR USES '* Indian corn," says John Fiske, in The Discovery of America, " has played a most important part in the discovery of the New World. It could be planted without clearing or plowing the soil. There was no need of threshing or winnowing. Sown in tilled land, it yields more than twice as much food per acre as any other kind of grain. This was of incalculable advantage to the English settlers in New England, who would have found it much harder to gain a secure foothold upon the soil if they had had to begin by preparing it for wheat or rye." i-,_U ^ CORN „^ ^ ^Stf^<7 to SZOO.bushels per scjuare mile " \ ^^ oyer 3200 ... -J Indian Corn Production— Percentage 30 40 50 60 70 m-- I I ^ — 'I II MP Jllincds Lowa Neb. Mo. Kan. Ohio Ind. Tex. Rest of United States To-day, in spite of the great wealth which comes from our mineral resources, live stock, and manufactured products, the surest index of our country's prosperity is the size of the wheat and corn crop. According to the last census, the amount of capital invested in agriculture was over $20,000,000,000, while that invested in man- ufacture was less than one half that amount. Corn. — About three billion bushels of corn were raised in the United States during the year 1910. This figure is so enormous that it has but little meaning to us. In the past half century FRUITS AND THEIR USES 59 our corn crop has increased over 350 per cent. Illinois and Iowa are the greatest corn-producing states, each having a yearly record of over four hundred million bushels. The Figure on page 58 shows the principal corn-producing areas in the United States. Indian corn is put to many uses. It is a valuable food. It con- tains a large proportion of starch, from which glucose and alcohol are made. Machine oil and soap are made from it. The leaves and stalk are an excellent fodder ; they can be made into paper and packing material. Mattresses can be stuffed with the husks. The pith is used as a protective belt placed below the water line of our huge battleships. Corn cobs are used for fuel, one hundred bushels having the fuel value of a ton of coal. Wheat. — Wheat is the cro]) of next greatest importance in size, and is of even greater money value to this country. Nearly seven Wheat Crop in United States— Percentage Source It TW^t I ' » t Minnesota Kansas N.Dak. S.Dak. Neb. O. Cal.Ind.Mo.Pa. Other Sutes hundred millions of bushels were raised in this country in 1910, representing a total money value of over $700,000,000. Seventy- two per cent of all the wheat raised comes from the North Central States and CaUfornia. About three fourths of the wheat crop is 60 FRUITS AND THEIR USES exported, nearly one half of it to Great Britain. Wheat has its chief use in its manufacture into flour. The germ, or young wheat plant, is sifted out during this process and made into breakfast foods. Flour-making forms the chief industry of Minneapolis, Minnesota, and of several other large and wealthy cities in this country. Other Grains. — Of the other grain and cereals raised in this country, oats are the most important crop, over one billion bushels having been produced in 1910. lUinois, Wisconsin, Minne- sota, and Iowa produce together over 50 per cent of the total yield. Oats are distinctly a Northern crop, over 95 per cent being grown north of the thirty-sixth parallel. Barley is another largely Northern crop; a staple of some of the northern countries of Europe and Asia, although such a hardy cereal. Almost three fourths of the total production in the United States comes from California, Minnesota, Wisconsin, Iowa; the production of these states may be roughly estimated as 86,000,000 bushels. In this country, it is largely used for making malt in the manufacture of beer. Rye is the most important cereal crop of northern Europe, Russia, Germany, and Austro-Hungary producing over 50 per cent of the world's supply. It makes the principal food for probably one third the people of Europe, being made into " black bread." It is of relatively less importance as a crop now in the United States than in former years. Perhaps one of the most important grain crops for the world (although relatively unimportant in the United States) is rice. A grassUke plant, its fruit, after thrashing, screening, and milling, forms the principal food of one third of the human race. More- over, its stems furnish straw, its husks make a bran used as food for cattle, and the grain, when distilled, is rich in alcohol. Nearly related to the grains are our grasses. There is a total forage crop (exclusive of corn stalks) of nearly 100,000,000 tons, valued at over $600,000,000. The best hay in the eastern part of the United States comes from dry timothy grass and clover, the stems and leaves as well as the fruits forming the so-called hay. In some parts of the West a kind of clover called alfalfa is much grown, it being adapted to the semiarid conditions of that part of the country. FRUITS AND THEIR USES 61 Cotton. — Among our fruits cotton is probably that of the most importance to the outside world. Over eleven million bales of five hundred pounds each are raised annually. Of this amount a large amount is exported, the United States producing over three fourths of the world's cotton supply. The relation of source and distribu- tion of the cotton crop can be seen by a glance at the accompany- ing diagram. COTTON ^ I to 20 bales ^era Food. External Factors which determine the Growth of Seeds.^ — We know that a dry seed, after lying dormant and apparently dead for months and sometimes for years, will, when the proper stimuli are appUed to it, start in its growth into a new plant. Something from outside the seed must evidently start the growth of the little embryo within the seed coats. There are several factors which 1 In making a series of experiments it is important to keep the conditions uni- fonn, varying only the one we are testing. SEEDS AND SEEDLINGS 75 are absolutely necessary for germination. One of these factors is the presence of a certain amount of moisture. Water a Factor. — We can prove that the bean seed will take up a considerable amount of water and that it swells during the process. Fill a flowerpot or a thin glass bottle almost to the top with dry beans, cover securely as shown in the illustration, and place in water overnight. The force exerted by the swelling seeds is sufficient to break the flowerpot or bottle. It is easy to prove that a dry seed wiU not germinate. The exact amount of water which is most favorable for the germination of a seed can bo clctorniinod only by careful experiment. In a very The expansive force of germinating seeds. The flowerpot to the left was filled with dry beans, a block of wood wired on, and the whole apparatus placed in a pail of water overnight. The result is shown at the right. Effect of water upon the growth of trees. The trees were all planted at the same time in soil that is sandy and uniform. They are irrigated by a small stream running from left to right. Most of the water soaks in before reaching the last trees. 76 SEEDS AND SEEDLINGS general way it may be said that an oversupply of water will pre- vent growth of seeds almost as effectually as no water at all. In gen- eral the amount most favorable for germination is a moderate supply. We shall find that although plants may live for a consider- able time in water or in sawdust or other materials well moistened in water, yet soil is an essential to the growth of most seed plants. Some plants, as some orchids and " Spanish moss " (a true seed plant), may exist without any connection with soil. Yet most plants need soil water and take from the soil materials needed to make up their living matter. Moderate Temperature Best. — Another factor influencing the germination of seeds is that of temperature. The temperature at which different seeds germinate varies greatly. Those of you who have a garden at home know that even some varieties of seeds germinate at lower temperatures than others of the same species ; for example, early peas, lettuce, or radish seed. As a general rule, increase in temperature is favorable up to a certain point, beyond which it is injurious to the young plant, and seeds exposed to a mod- erate temperature do better in the long run than those in the heat. Light has a certain marked effect on young seedlings, which will be considered when we take up the growth of the stem in more detail. Some Part of the Air a Factor. — We have already considered the chemical composition of the air in its place as part of the environment of plants and animals. But few of us reason out why air is a necessary factor in the growth of plants and animals. It is an easy matter to prove that peas or beans will not germinate without a supply of air. Equal numbers of soaked peas, placed in two bottles, one tightly stoppered, the other having no stopper, both bottles being exposed to identical conditions of light, tem- perature, and moisture, show that the seeds in both bottles start Experiment to show the effect of lack of air on germination. SEEDS AND SEEDLINGS 77 to germinate, but that those in the closed bottle soon stop while those in the open jar continue to grow almost as well as similar seeds placed in an open dish would do. Why did not the seeds in the covered jar germinate? We have seen that to release the energy contained in a piece of coal we must burn or oxidize it. To do this we must have a constant supply of fresh air containing oxygen. The seed, in order to re- lease the energy locked up in its food supply, must have oxygen, so that the oxidation of the food may take place. Hence a con- stant supply of fresh air is an important factor in gennination. It is important that air should penetrate between the grains of soil around a seed. The frequent stirring of the soil enables the air to reach the seed. Air helps break down (oxidizes) some materials in the soil and puts them in a form that the germinating seed can use. This necessity for oxygen shows us at least one reason why the farmer plows and harrows a field and one important use of the earthworm. Food oxidized in the Germinating Seed. — But can it be proved that food substances are burned up during the germination of the seeds ? To answer this question let us carefull}^ re- move the stopper from the stoppered jar and insert a Hghted candle. The candle goes out at once. The surer test of limewater shows the presence of carbon dioxide in the jar. The carbon of the foodstuffs of the pea united with the oxygen of the air, forming carbon dioxide. Growth stopped as soon as the oxygen was ex- hausted. The presence of carbon dioxide in the jar is an indication that a very important process which we associate with animals rather than plants, that of respiration, is taking place. I^roblem XTI. A study of yoitng plants until they are inde- pendent (^seedlings). {Laboratory Manual, Proh. XII,) Gennination. — If you plant a nimiber of soaked kidney beans in damp soil or sawdust and at the end of each day remove a single t The lim ewater test ; the tube at the right shows the effect of carbon dioxide. 78 SEEDS AND SEEDLINGS seedling, you will be able to obtain a complete record of the growth of the kidney bean. The first signs of germination are the break- A series of early stages in the germination of a kidney bean. ing of the testa and the pushing outward of the hypocotyl to form the first root. A little later the hypocotyl begins to curve down- ward. A later stage shows the hypocotyl lifting the cotyledon upward. In consequence the hypocotyl forms an arch, dragging after it the bulky cotyledons. The stem, as soon as it is released from the ground, straightens out. From be- tween the cotyledons the bud- like plumule or epicotyl grows upward, forming the first true leaves and all of the stem above the cotyledons. As growth continues, we notice that the cotyledons become smaller and smaller, until eventually their food contents having been absorbed into the young plant, they dry up and may fall off. The young plant is now able to care for Bean seedlings Note that in the older j^^^j^ ^^^ ^^ ^^-^ ^^ ^^^^ seedlings at the left the cotyledons have *^ been alnjost entirely used up. passed through the stages of SEEDS AND SEEDLINGS 79 germination. All the stages passed through by the young plant, from the time the seed be- gins to sprout until it cari take care of itself by means of its roots and leaves, are known as the stages of germination. In the pea, growth is like- wise at first made largely at the expense of the cotyledons, which never rise alxjve ground. Removal of the cotyledons from half the number of one lot of germinating peas, and exposure to the same conditions as the other half of the same lot, shows that the loss of the cotyledons retards growth and may result in the death of the seedlings.^ Experinu'nt to show the function of the cotyledons of the pea, photographed at the end of two weeks. Note the size of the plants at the left, without cotyle- dons. Cotyledons as Foliage Leaves. — In the young plants which we have just been studying, the cotyledons hold a reserve food supply, but do not serve at any time as true leaves for the plant. In many dicoty- ledons, however, the seed leaves do act as true leaves. This may well be seen in the squash seed- ling. Here the young plant has little or no Jood stored in the cotyledons; it must be prepared to take care of itself quickly. It does this by means of the rapidly growing coty- ledons, which soon unfold as true leaves to the sun. In the seeds of the pea and bean we have found that the embryo takes up all the space within the seed coats. There are some dicotyledonous plants that have food stored outside of the embryo. Such a plant is the castor bean. A section cut vertically through the castor bean discloses Arrangement of embryo in endosperm (Gray) : a, morning-glory ; 6, barberry ; c, potato ; d, four- o'clock. * It must be remembered that this is not quite a fair test to the pea, because we take away from the young plant part of its own body. 80 SEEDS AND SEEDLINGS a white oily mass directly under the seed coats. This mass is called the endosperm. If it is tested with iodine, it will be found to contain starch ; oil is also present in considerable quantity. Within the endosperm Ues the embryo, a thin, whitish structure. The Uses of Seeds. — Not only does a seed serve to continue a species of plant in a certain locality, but it serves to give the plant a foothold in new places. This can be done, as we shall see later, to a limited degree by cuttings, grafting, and in other ways, but the usual way is by the production and planting of seeds. Seeds may be blown by the wind or carried by animals, or by a hundred de- vices work their way to pastures new, there to establish outposts of their kind. Immense numbers of seeds may be produced by a single plant. This may be of great economic importance. A single pea plant may produce twenty pods, each containing from six to eight seeds. This would mean the possibility of nearly twenty-five thousand plants produced from the original parent by the end of the second season and the rapid production of a source of food for man- kind. A plant of Indian corn may produce over fifteen hundred grains of corn. On the other hand, many weeds produce seed in still greater numbers. A single capsule of Jimson weed has been found to hold over six hundred seeds. A single milkweed The thistle is even more Milkweed fruit, showing method of seed dispersal. may set free over two thousand seeds, prolific. Some seeds, especially those of weeds, are able to withstand great extremes of heat and cold and still to retain their ability to germinate. Some have been known to retain their vitality for over fifty years. In plants, the seeds of which show unusual hardiness, it is foimd that the food supply is often so placed as SEEDS AND SEEDLINGS 81 to protect the delicate parts of the embryo from injury. The food is in a form not easily dissolved by water or broken up by the action of frost, so that it is kept in a hard state until such a time as it can be softened by the process of digestion during the growth of the plant. It can be seen that plants bearing seeds having some of the above characters have a great advantage over plants bearing seeds that are poorly protected. Prohle^n XIII, A study of some methods of plant breeding. {.Laboratory Manual, Proh, XIII.) Plant Breeding : Variation of Plants. — Examination of a row of plants in a garden, of a hundred dandelion plants, or careful measurements made on the pupils in a classroom, would show us that no two plants and no two boys or girls have exactly the same measurements or characters. Each plant or animal in a state of nature tends to vary somewhat from its parent. This is a law among plants and animals. But a second law exists which we also know something about. A plant or animal hands down to its offspring some of the charac- teristics which it possesses. Each one of us in some way resembles our parents or, it may be, our grandparents. Each plant produced from seed will be in some respects like the plant which produced the seed. These two laws, of variation and of heredity, the bases on which Charles Darwin explained his theory of evolution, are made use of by plant and animal breeders. Since plants tend to vary and since such variations may be continued in their offspring, plant breeders have helped nature by artificially selecting and propa- gating the plants showing the characters wanted. Selective Planting. — By selective planting we mean choosing the best plants and planting the seed from these plants with a view of improving the yield. In doing this we must not necessarily select the most perfect fruits or grains, but must select seeds from the best plants. A wheat plant should be selected not from its yield alone, but from its ability to stand disease and unfavorable con- ditions. In 1862 a Mr. Fultz, of Pennsylvania, found three heads of beardless or bald wheat while passing through a large field of bearded wheat. He picked them out, sowed them by themselves, HUNT. ES. BIO. — 6 82 SEEDS AND SEEDLINGS Improvement of corn by selection : a, improved type ; b, original type from which it was developed. and produced a quantity of wheat now known favorably all over the world as the Fultz wheat. By careful seed selection, some Western farmers have increased their wheat production by 25 per cent. This, if kept up all over the United States, would mean over $100,000,000 a year in the pockets of the farmers. Boys and girls who have gardens of their own can easily try experiments in selec- tion with almost any garden vegetable. Corn is one of the best plants to experiment with. Gather for planting only the fullest ears and those with the largest kernels. You must also select from the plants those that produce the most ears. Plant such corn grains, carefully selected, in a plot by themselves in the garden, and compare their yield with that of the nonselected corn. The accompanying picture shows what can be done by selection. Plants thus produced may become in time varieties of the original species from which they came. Hybridizing. — We have already seen that pollen from one flower may be carried to another of the same species, thus producing seeds. If pollen from one plant be placed on the pistil of another of an allied species or variety, fertilization may take place and new plants be eventually produced from the seeds. Such plants are called hybrids. Hybrids are extremely variable and often are apparently quite unlike either parent plant. Such are some of the results of Luther Burbank's work with the hybrid plums, the Department of Agri- culture experiments in the crossing of oranges and lemons and the formation of thousands of new varieties of garden plants of various kinds — beans, peas, tomatoes, and the like. By far the greatest possibilities to the farmer or fruit grower SEEDS AND SEEDLINGS 83 seem to come from hybridizing. Of recent years new theories have been advanced accounting for the variation and heredity of plants and animals. One, by a Dutchman named Hugo de Vries, is that new species of plants and animals arise suddenly by " muta- tions " or steps. This means that new species instead of arising from very slight variations, continuing during long periods of years (as Darwin beheved), might arise very suddenly as a very great variation which would at once breed true. It is easily seen that such a condition would be of immense value to breeders, as new plants or animals quite unlike their parents might thus be formed and perpetuated. It will be the future problem of plant breeders to isolate and breed " mutants," as such plants are called.^ RSFEBENCB BoOKS ELEMENTARY Sharpe, A Laboratory Manual for the Solution of Problems in Biology. American Book Company. Andrews, Botany all the Year Round, pages 103-119. American Book Company. Atkinson, First Studies of Plant Life, Chaps. I, II, III, XXV. Ginn and Company. ComeU Nature Study Leaflets, XXVIII, XLII, XLIV. N.Y. Department of Agriculture. Dana, Plants and their Children, pages 50-98. American Book Company. Harwood, New Creations in Plant Life. The Macmillan Company. ADVANCED Coulter, Barnes, and Cowles, A Textbook of Botany, Part II. American Book Com- pany. De Candolle, Origin of Cultivated Plants. D. Appleton and Company. De Vries, Species and Varieties, edited by D. T. MacDougal. Open Court Pub- lishing Company. Farmers' Bulletin, 229. Goodale, Physiological Botany. American Book Company. MacDougal, Plant Physiology. Longmans, Green, and Company. Punnett, R. C, Mendelism. Cambridge, England. Thompson, Heredity. John Murray, London. University of Illinois Agricultural Station, Bulletin 87. University of Minnesota Agricultural Station, Bulletin 165. Wallace, Darwinism. The Macmillan Company. Yearbook, U.S. Department of Agriculture. ^ The part played by Mendel's law is too difficult to explain to high-school pupils. For a well-organized statement of recent work, see Bailey's P^nt Breeding or "The Relation of Certain Biological Principles to Plant Breeding " E. M. East, Bulletin 158, Conn. Agri. Exp. Station, New Haven, Conn. VII. ROOTS AND THEIR WORK JProhlem XIV. A study of roots. {Laboratory Manual, Prob. xir.) (a) Factors influencing direction of growth. (&) Structure. (c) How they absorb soil water. The development of a bean seedling has shown us that the root invariably grows first. One of the most important functions of the root to a young seed plant is that of a holdfast, an anchor to fasten it in the place where it is to develop. In this chapter we shall find many other uses of the root to the plant, the taking in of water and the mineral and organic matter dis- solved therein, the storage of food, chmbing, etc. All other functions than the first one stated arise after the young plant has begun to develop. Root System. — If you dig up a young bean seedling and carefully wash off the roots, you will see that a long root is developed as a con- tinuation of the hypocotyl. This root is called the primary root. Other smaller roots which grow from the primary root are called secondary, or tertiary, depending on their relation to the first root developed. Downward Growth of Root. Influence of Gravity. — Most of the roots examined take a more or less downward direction. We are all familiar with the fact that the force we call gravity influences life upon this earth to a great degree. Does gravity act on the grow- ing root ? This question may be answered by a simple experiment. 84 i' M ^ m ^. .-^ 1 y/ ; / i \ V A root system, showing primary and second roots. ROOTS AND THEIR WORK 85 Plant mustard or radish seeds in a pocket garden, place it on one edge and allow the seeds to germinate until the root has grown to a length of about half an inch. Then turn it at right angles to the first position and allow it to remain for one day undisturbed. The roots now will be found to have turned in response to the change in posi- tion, that part of the root near the growing point being the most sensitive to the change. This experiment seems to indicate that the roots are influenced to grow downward by the force we call gravity.^ The reaction of the plant {or any living thing) to this force is called geotropisni. Roots are stimulated by gravity to grow downward; hence they are said to he positively geotropic. Experiments to determine Influence of Moisture on a Growing Root. — The objection might well be interposed that possibly the roots in the pocket garden grew downward after water. That moisture has an influence on the growing root is easily proved. Plant bird seed and the seed of mustard or radish in the under- side of a sponge, which should be kept wet, and may be sus- pended by a string under a bell jar in the schoolroom window. Note whether the roots leave the sponge to grow downward, or if the moisture in the sponge is sufficient to counterbalance the force of gravity. Revolve this Figure in the direc- tion of the arrows to see if the roots of the radish respond to gravity. * The Pocket Garden. — A very convenient form of pocket germinator may be made in a few minutes in the following manner : Obtain two cleaned four by five negatives (window glass will do) ; place one flat on the table and place on the glass half a dozen pieces of colored blotting paper cut to a size a little less than the glass. Now cut four thin stiips of wood so as to fit on the glass just outside of the paper. Next moisten the blotter, place on it some well-soaked radish or mustard seeds or grains of barley, and cover it with the other glass. The whole box thus made should be bound together with bicycle tape. Seeds will germinate in this box, and with care may live for two weeks or more. 86 ROOTS AND THEIR WORK Another experiment is the following : Divide the interior of a shallow wooden box into two parts by an incomplete partition. Partly fill the box with sawdust and place the opening in the partition so that it is below the surface of the sawdust. Plant peas and beans in the sawdust on one side of the partition, water very slightly, but keep the other side of the box well soaked. After two weeks, take up some of the seedlings and note the effect on the roots. Water a Factor which determines the Course taken by Roots. — Water, as well as the force of gravity, has much to do with the direction taken by roots. Water is always found below the sur- face of the ground, but sometimes at a great depth. In order to obtain a supply of water, the roots of plants frequently spread out for very great distances. Most trees, and all grasses, have a greater area of surface exposed by the roots than by the branches. The mes- quite bush, a low-growing tree of the American and Mexican deserts, often sends roots downwards for a dis- tance of forty feet after water. The roots of alfalfa, a cloverlike plant used for hay in the Western states, often penetrate the soil after water for a distance of ten to twenty feet below the surface of the ground. Structure of a Taproot. — To understand fully the structure of the root, it will be necessary for us to examine some large, fleshy root (a taproot), so that we may get a little first-hand evidence as to its internal structure. If you cut open a parsnip or carrot so as to make a cross section of the root, you find two distinct areas — an outer portion, the cortex, and an inner part, the wood. If you cut another parsnip in lengthwise section, these structures show still Dandelion plant. Note the length of the root Photographed by Overton. ROOTS AND THEIR WORK 87 A cross section through a taproot (a parsnip) : C, cortex; W, wood. Notice in the right-hand specimen, which has been dipped in iodine, that the core of wood continues out into the rootlets which leave the main root. Where is most starchy food stored in a parsnip? more plainly. An additional fact is seen; namely, that all the smaller roots leaving the main or primary root have a core of wood which bores its way out through the cortex wherever the small rootlets are given off. Fine Structure of a Root. — If we could now examine a much smaller and more delicate root in thin longitudinal section under the compound microscope, we should find the entire root to be made up of cells, the walls of which are uniformly rather thin. (Cross sections and lon- gitudinal sections of tradescantia roots are excellent for demonstra- tion of these structures.) Over the lower end of the root is found a collection of cells, most of which are dead, loosely ar- ranged so as to form a cap over the growing tip. This is evidently an adaptation which protects the young and actively growing cells just under the root cap. In the body of the root the central cylinder can easily be distinguished from the surround- ing cortex. The cells of the former have somewhat thicker walls. In a longitudinal section a series of tubelike structures may be found within the central cylinder. These structures are cells which have grown together at the small end, the long axis of the cells running the length of the main root. In their develop- ment the cells mentioned have grown together in such a manner as to lose their small ends, and now form continuous hollow tubes with rather strong walls. Other cells have come to develop greatly thickened walls ; these cells give mechanical support to the tubelike cells. Collections of such tubes and supporting woody cells together make up what is known as fibrovascidar bundles. The end of a growing root, tipped and protected by the root cap ; g, the growing point. (Consider- ably magnified.) 88 ROOTS AND THEIR WORK Cross section of a young taproot : o, a, root hairs ; h, epidermis ; c, cortex ; d, fibrovascular cylinder or wood. Root Hairs. — Careful examination of the root of one of the seed- hngs of mustard, radish, or barley grown in the pocket germinator shows a covering of tiny fuzzy structures. These structures are very minute, at most 3 to 4 mm. in length. They vary in length according to their position on the root, the most and the longest root hairs being found near at the point marked R. H. in the Figure. These structures are outgrowths of the outer layer of the root (the epi- dermis), and are of very great im- portance to the living plant. Structure of a Root Hair. — A single root hair examined under a compound microscope will be found to be a long, round structure, almost colorless in appearance. The wall, which is very flexible and thin, is made up of cellulose, a substance somewhat Hke wood in chemical com- position, through which fluids may easily pass. If we had a very high power of the microscope focused upon this cellulose wall, we should be able to find under it another structure, far more delicate than the cell wall. This is called the cell membrane. Clinging close to the cell membrane is the protoplasm of the cell. The interior of the root hair is more or less filled with a fluid called cell sap. Forming a part of the living protoplasm of the root hair, sometimes in the hairlike prolongation and some- times in that part of the cell which forms the epidermis, is found a nucleus. The protoplasm, nucleus, and cell membrane are alive ; all the rest of the root hair is dead ^R.H. Young embryo of corn, show- ing root hairs (R. H), and growing stem (P.). ROOTS AND THEIR WORK 89 material, formed by the activity of the living substance of the cell. The root hair is a living plant cell with a wall so delicate that water and mineral sub- stances from the soil can pass through it into the interior of the root. How the Root absorbs Water. — The process by which the root hair takes up soil water can better be understood if we make an artificial root hair large enough to be easily seen. An egg with part of the outer shell removed so as neath is an example. Diagram of a CS, ceU sapi A'^, nucleus; root hair: CM, cell membrane; CW, cell wall ; P, protoplasm ; S, soil particles. to expose the soft membrane under- Better, a root hair may be made in the following way: Pour some soft celloidin into a tube vial; carefully revolve the vial so that an even film of celloidin dries on the inside of the vial. This is removed, filled with white of egg, and tied over the end of a rubber cork in which a glass tube has previously })een inserted. When placed in water, it gives a very accurate picture of the root hair at work. After a short time water begins to rise in the tube, having passed through the film of cel- loidin. If grape sugar, salt, or some other sub- stance which will dissolve in water were placed in the water outside the artificial root hair, it could soon be proved by test to pass through the wall and into the liquid inside. Osmosis. — To explain this process we must remember that gases and liquids of different densities, when separated by a membrane (a dehcate porous lining having no holes visible to the highest power microscope we possess), tend to flow toward each other and mingle, the greatest flow always being in the direction of the denser medium. The process by which two gases or fluidsj separated by a membrane j pass through the mem- An artificial root hair, showing os- mosis taking place. 90 ROOTS AND THEIR WORK brane and mingle with each other is called osmosis.^ The method by which the root hairs take up soil water is exactly the same pro- cess. It is by osmosis. The white of the egg is the best possible substitute for living matter; it has, indeed, almost the same chemical formula as protoplasm. The celloidin membrane sepa- rating the egg from the water is much like the dehcate membrane and wall which separates the protoplasm of the root hair from the water in the soil surrounding it. The fluid in the root hair is denser than the soil water ; hence the greater flow is toward the interior of the root hair. Passage of Soil Water within the Root. — We have already seen that in an exchange of fluids by osmosis the greater flow is always toward the denser fluid. Thus it is that the root hairs take in more fluid than they give up. The cell sap, which partly fills the interior of the root hair, is a fluid of greater density than the water outside in the soil. When the root hairs become filled with water, the density of the cell sap is less- ened, and the cells of the epidermis are thus in a position to pass along their supply of water to the cells next to them and nearer to the center of the root. These cells, in turn, becbme less dense than their inside neighbors, and so the transfer of water goes on until the water at last reaches the central cylinder. Here it is passed over to the tubes of the woody bundles and started ' For an excellent elementary discussion of osmosis see Moore, Physiology of Man and other Animals. Heniy Holt and Company. A potato osinuineter. The lower end of the potato was cut off and the remainder peeled for about one third of its length. A hole was bored to within three fourths of an inch of the cut end ; a small hole was bored at the side of the potato. In the latter was inserted a small L-shaped tube, the lower end being vaselined to make it air-tight. Sugar was then placed in the hole at the top and a cork inserted ; water was poured into the dish below. Within two hours the water had risen in the tube, as shown in the right-hand Figure. ROOTS AND THEIR WORK di up the stem. The pressure created by this process of osmosis is sufficient to send water up the stem to a distance, in some plants, of twenty-five to thirty feet. Cases are on record of water having been raised in the birch a distance of eighty-five feet. Physiological Importance of Osmosis, — It is not an exaggera- tion to say that osmosis is a process not only of great importance to a plant, but to an animal as well. Foods are digested in the food tube of an animal ; that is, they are changed into a soluble form so that they may pass through the walls of the food tube and become part of the blood. Without the process of osmosis we should be unable to use much of the food we eat. Problem XV. A study of some of the relations between roots and the soil. {Laboratory Manual, Prdb. XV,) (a) Origin of soil. {b) Kinds of soil. (c) Water-retaining ability, (d) Fertility of soils. (e) Hoot hmrs and soil, if) Boot tubercles and> crop rotation. Composition of Soil. — If we examine a mass of ordinary loam care- fully, we find that it is composed of numerous particles of varying size and weight. Between these particles, if the soil is not caked and hard packed, we can find tiny spaces. In well-tilled soil these spaces are constantly being formed and enlarged. They allow air and water to penetrate the soil. If we ex- amine soil under the micro- scope, we find considerable water clinging to the soil par- ticles and forming a delicate film around each particle. In this manner most of the water is held in the soil. How Water is held in Soil. — To understand what comes in with the soil water, it will be necessary to find out a little more about soil. Sci- entists who have made the subject of the composition of the earth a study, tell us that once upon a tune at least a part of the earth was molten. Inorganic soil is being formed by weathering. 92 ROOTS AND THETR WORK Later, it cooled into solid rock. Soil making began when the ice and frost, working with the heat, chipped off pieces of rock. These pieces in time became ground into fragments by action of ice, glaciers, running water, or the atmosphere. This process is called weather- ing. Weathering is largely a process of oxidation. A glance at almost any crumbling stones will con- vince you of this, because of the yeUow oxide of iron (rust) disclosed. So by slow degrees this earth became covered with a coating of what we call inorganic soil. Later, gen- eration after generation of tiny plants and animals which lived in the soil died, and their remains formed the first organic materials of the soil. You are all familiar with the difference be- tween the so-called rich soil and poor soil. The dark soil simply contains more dead plant and animal life, which forms the portion called humus. Humus contains Organic Matter. — It is an easy matter to prove that black soil contains organic matter, for if an equal weight of carefully dried humus and soil from a sandy road is heated red-hot for some time and then re weighed, the hu- mus will be found to have lost considerably in weight, and the sandy soil to have lost very little. The material left after heating is inorganic material, the organic matter having been burned out. Organic soil holds water much more readily than in- organic soil, as a glance at the accompanying Figure This picture shows how the forests help to cover the inorganic soil with an organic coating. :J tSH A B C D Experiment to illustrate the kind of soil which best retains water : A, gravel; 5,. sand; C, barren soil ; D, rich soil ; E, leaf mold ; F, dry leaves. ROOTS AND THEIR WORK 93 shows. If we fill each of the vessels with a given weight (say 100 grams each) of gravel, sand, barren soil, rich loam, leaf mold, and 25 grams of dry, pulverized leaves, then pour equal amounts of water (100 c.c.) on each and measure all that runs through, the water that has been retained will represent the water supply that plants could draw on from such soil. The Root Hairs take more than Water out of the Soil. — If a root containing a fringe of root hairs is washed off carefully, it will be found to have little particles of soil still clinging to it. Exam- ined under the microscope, these particles of soil seem to be ce- mented to the sticky surface of the root hair. The soil contains, besides a number of chemical compounds of various mineral sub- stances, — lime, potash, iron, silica, and many others, — a consider- able amount of organic material. Acids of various kinds are present in the soil — nitric acid, which comes from the dead bodies of plants and animals as they decay and oxidize ; carbonic acid, formed by the union of the carbon dioxide from the roots and the water in the soil, and other acids. These acids so act upon certain of the mineral substances that they become dissolved in the water which is absorbed by the root hairs. The proportion of each of these mineral materials is very small compared with the water in which they are found. A very great amount of water must be taken up by the roots in order that the plant may get the needed amount of mineral matter with which to build its protoplasm. Plants will not grow well without certain of these mineral sub- stances. This can be proved by the growth of seedlings in a so- called nutrient solution. Such a solution contains all the mineral matter that a plant uses for food.^ If certain ingredients of this solution are left out the plants placed in such a solution will not live. 1 A nutrient solution may be prepared as follows : — Distilled water (H2O) 1000.00 c.c. Potassium nitrate (KNOs) 1.00 tjx&ux Sodium chloride (NaCl) 0.50 gram Calcium sulphate (CaS04) 0.50 gram Magnesium sulphate (MgS04) 0.50 gram Calcium phosphate (Ca3[P04]2) 0.50 gram Ferric chloride (FeClg) 0.005 gram (Do not put the ferric chloride into the solution in the first place, but add a drop of it to each bottle when the seedlings are put in.) 94 ROOTS AND THEIR WORK Nitrogen in a Usable Form necessary for Growth of Plants. — • We learned that humus is made up of decayed plant and animal bodies. A chemical element needed by the plant to make proto- plasm is nitrogen. This element cannot be taken from either soil water or air in a pure state, but is usually obtained from the organic matter in the soil, where it exists with other substances in the form of nitrates. Ammonia and other organic compounds which contain nitrogen are changed by two groups of little plants called hac- teria which oxidize the compounds, first into nitrites and then nitrates,^ Relation of Bacteria to Free Nitrogen. — It has been known since the time of the Romans that the growth of clover, peas, beans, and other legumes in soil causes that ground to become more favor- able for growth of other plants. The reason for this has been dis- covered in late years. On the roots of the plants mentioned are found little swellings or nodules; in the nodules exist millions of bacteria, which take out nitrogen from the atmosphere and fix it so that it can be used by the plant ; that is, they form nitrates for the plants to use. Only these bac- teria, of all the living plants, have the power to take the free nitrogen from the air and make it over into a form that can be used by the roots. As all the compounds of nitrogen are used over and over again, first by plants, then as food for animals, eventually returning to the soil again, it is evident that any new supply of usable nitrogen must come by means of these nitrogen-fixing bacteria. 1 It has recently been discovered that under some conditions these bacteria are preyed upon by tiny one-celled animals living in the soil and are so reduced in num- Tubercles containing the nitrogen- fixing bacteria. ROOTS AND THEIR WORK 95 Rotation of Crops. — The facts mentioned above are made use of by careful farmers who wish to make as much as possible from a given area of ground in a given time. Such plants as are hosts for the nitrogen-fixing bacteria are planted early in the season. Later these plants are plowed in and a second crop is planted. The latter grows quickly and luxuriantly because of the nitrates left in the soil by the bacteria which lived with the first crop. For this reason, clover is often grown on land in which it is pro- posed to plant corn, the nitrogen left in the soil thus giving nourishment to the young corn plants. This is known as rotation of crops. The annual yield of the average farm may be greatly increased by this means. Soil Exhaustion may be Prevented. — Besides the rotation of crops, other methods are used by the farmer to prevent the exhaus- tion of raw food material from the soil. One method known as fallowing is to allow the soil to remain idle until bacteria and oxida- tion have renewed the chemical materials used by the plants. This is an expensive method, if land is dear. The most common method of enriching soil is by means of fertilizers, material rich in plant food. Manure is most frequently used, but many artificial fertilizers, most of which contain nitrogen, are used, because they can be more easily transported and sold. Such are ground bone, guano (bird manure), nitrate of potash, and many others. These contain as well other important raw food materials for plants, especially potash and phosphoric acid. Both of these substances are made soluble so as to be taken into the roots by the action of the carbon dioxide in the soil. Forms of Roots and their Relation to the Life of the Plant. — Roots assume various forms. The form or position of the root is usually de- pendent on the needs of the plant, the roots acting to help it succeed in certain localities. Food Storage in Roots and its Economic Importance. — The use to the plant of the food stored in the taproot may be understood if we take up the life history of the parsnip. Such a plant produces no seed until near the end of the second year of its existence, its growth the first summer forming the root we use as food. After forming seeds the plant dies. bers that they cannot do their work effectively. If then the soil is heated artificially or treated with antiseptics so as to kill the protozoa, the bacteria which escape multiply so rapidly as to make the land much richer than before. ROOTS AND THEIR WORK The food stored in its root enables it to get an early start in the spring, so as to be better able to produce seeds when the time comes. Such plants live only under rather cool climatic conditions. Examples of other roots which store food are carrot, radish, yam, sweet potato, etc. This food storage in roots is of much practical value to mankind. Many of our com- monest garden vegetables, as those mentioned above, and the beet, turnip, oyster plant, and many others are of value because of the food stored. The sugar beet has, in Europe especially, become the basis of a great industry. Water Roots. — In the duckweed, a plant living in water, the roots are short and contain few root hairs. The water supply is so great that few root hairs have been called forth. The water hyacinth is another example of slight development of roots. The plant is buoyed up by the water and does not need strong roots to hold it firm. Adventitious Roots. — Roots are often developed in unusual places. Roots coming out thus, as, for example, on the stem, are called adventitious. Such roots are developed along the stem of many climbing plants — for example, the roots of EngUsh ivy. Some plants, as strawberry, couch grass, and many others, develop new Couch grass, showing how the plant spreads by striking roots from a reclining stem. Corn roots, showing prop roots de- veloped at first node above ground. plants by striking root at any point on the reclining stem where it touches the ground. This fact is made use of by practical gardeners in the layering of plants. Examine the Indian corn for another kind of adventitious roots. Here they serve as props for the tall stem. In the young seedlings of corn, notice how early these roots develop. Also notice the manner in which they arise on the stem. ROOTS AND THEIR WORK 97 Air Roots. — In tropical forests, where the air is always warm and moist, some plants have come to live above the soil on the trunks of trees, or in other places where they can get a favorable foothold. Such plants are called epiphytes, or air plants. The tropical orchid seen in our green- houses is an example. Examine the roots of such a plant. Notice how thick they are. They are usually provided with a spongy tissue around the outside which has the function of absorbing water. Parasitic Roots. — A Jew plants live on other living plants, and develop by the aid of nourishment taken at their expense. Such a plant is called a parasite. The plant or animal on which the parasite lives is called the host. The mistletoe is an example of a parasitic plant. An examination of its roots shows that they have bored their way into the stem of the host. These roots not only penetrate the bark, but push toward the center of the tree, taking nourishment from the cells there. The dodder is another seed-bearing plant which has this habit. Dodder produces from seed, but is unable to live alone after it has passed the seedling stage, and will die if it cannot find a suitable host. It is found on many common weeds, as jewel weed and goldenrod. Many of the lower plants live as parasites, among them being mildew, rusts, and smuts found on roses, grain, and corn. Reference Books elementary Sharpe, A Laboratory Manual for the Solution of Problems in Biology. American Book Company. Andrews, Botany all the Year Round, Chap. II. American Book Company. Atkinson, First Studies of Plant Life, Chaps. IX, XI, XII. Ginn and Company. Coulter, Plant Studies, Chap. V. D. Appleton and Company. Goff and Mayne, First Principles of Agriculture. American Book Company. Moore, The Physiology of Man and Other Animals, Henry ITolt and Company. Stevens, Introduction to Botany, pages 31-44. D. C. Heath and Company. ADVANCED Coulter, Barnes, and Cowles, A Textbook of Botany, Part II. American Book Com^ pany. Detmer-Moor, Practical Plant Physiology. The Macmillan Company. Goodale, Physiological Botany. American Book Company. Gray, Structural Botany, pages 27-39, 56-64. American Book Company. Green, Vegetable Physiology, Chaps. V, VI. J. and A. Churchill. Farmers' Bulletin 86, U.S. Department of Agriculture. Kerner-Oliver, Natural History of Plants. Henry Holt and Company. MacDougal, Plant Physiology. Longmans, Green, and Company. Pfeffer, W., The Physiology of Plants. Clarendon Press. HUNT. ES. BIO. VIII. THE STRUCTURE AND WORK OF THE STEM Problem XVI. Relationship of buds to the growing plant (optional). (Laboratory Manual, Proh. XVI.) Structure of a Bud. — If we cut a head of cabbage through the long axis of its stem, we find that the stem is much shortened or dwarfed, and that the leaves are so placed as to cover it en- tirely. The cabbage is a big bud. If we carry out our definition of a bud, starting with what we have A. Cabbage head cut lengthwise to show that it is a big bud. B. The bud under favorable conditions has grown into an elongated stem. THE STRUCTURE AND WORK OF THE STEM 99 seen in the cabbage, we might say that a bud is a very much shortened branch, or, in reality, " the promise of a branch." Factors which influence the Opening of a Bud. — A bud responds to the same stimuli that we have seen call a young plant into active life from the seed. If a branch containing unopened buds (such as horse-chestnut or willow) is placed in water in a moderately warm room, it will respond to the factors without it and begin to open. The tips of branches, still attached to the tree outdoors, may be introduced into a warm room through a hole bored in the window sash. They will open to bear flowers and leaves during the coldest months of the year. The factors which influence the germination of seeds also act on the bud. Adaptations in the Bud of Horse-Chestnut. — If we now turn our at- tention to horse-chestnut buds which have been previously placed in water to open, we shall be able to get some notion of the wonderful adap- tations of the bud which fit it for its work. In the first place, a horse-chestnut bud is covered with a sticky ma- terial. Not only does this covering keep out unwelcome visitors which might bore into the bud and destroy the tender parts within, but it also serves as a waterproof cover- ing against the icy rains of the late fall and early spring, and against evaporation in dry weather. In the unopened buds the scales overlap like shingles on a roof. In buds which have begun to open, we find that not only have the tiny green leaves been pro- tected by the outer scales, but they have been additionally wrapped in soft, cottony sub- stance. The young leaves are always folded or rolled up in the bud. Two purposes are thus served — protection from the elements and from drying by little exposure of the deli- cate surface, and economy of space by means of the tight and compact stowing away of the parts thus folded. Why Buds are Covered. — When we consider that most of our earliest green leaves come from open- ing buds in the early spring, the importance of a protective covering is well seen. Nevertheless, buds are frozen time and again during the cold Opening bud of horse-chestnut : L., leaves ; L.S., leaf scar; S., scalelike leaves which cover bud. 100 THE STRUCTURE AND WORK OF THE STEM weather, only to thaw out again without injury to the plant. Sudden changes, however, do much harm, winter weather when temperature conditions are seemingly favorable ; a definite length of growth seems in that case to be necessary. Dur- ing warm weather plants give rise to buds which are devoid of pro- tective scale leaves. Such is also noticed in tropical forms, which are not called upon to meet rigorous climatic conditions. Position of the Bud on the Stem. — The growth of the stem from the bud can best be observed in a very young seedling. If, for example, we examine a pea seed- Ung, it will be seen that the plumule or epicotyl is the first bud of the plant. It produces the first stem Some buds do not open during mild and leaves. Buds come out at the ends of branches {terminal) and at the sides {lateral). Deliquescent Tree. — The position of the most active buds determines the form of the future tree. If you examine a A\dnter branch of the apple, elm, or oak tree, you will find that the lateral buds have developed more strongly and more rapidly than the terminal bud. Thus the tree has come to assume during its growth a rounded shape due to the rather more rapid development of the lateral buds. Such a tree, having a rather stout, short trunk, mth many low, spreading, lateral branches, is said to be deliquescent. A larch, an excurrent tree (at right) and an elm, a deliquescent tree (at left). Photographed by W. C. Barbour. THE STRUCTURE AND WORK OF THE STEM 101 Excurrent Tree. — If, on the other hand, the terminal buds of the tree get a better supply of light, food, or if other factors aid its growth, the tree will be tall and have but one main trunk, such as the Lombardy poplar, and pines and cedars. Such a tree is named excurrent. The picture shows trees of these two shapes. Problem XVTI. The structure ami work of stems. {Laboratory Manual, Prob. XVII.) (a) EMernal structure of a di- cotyledonous stem {optional). (b) Internal structure of a di- cotyledonous stem. (c) Circulation in stems, id) Condition of food parsing through the stem,. The External Structure of a Dicotyle- donous Stem. — A horse-chestnut twig in its winter condition shows the structure and position of the buds very plainly. As the twig grew last year the scales which covered the outside of the terminal bud dropped off, and the young shoot developed from the opened bud. The scales which dropped off left marks forming a little ring upon the surface of the twig. These rings, collectively named the hud scars, enable one to tell the age of the branch. Just above the lateral buds are marks, known as leaf traces, that show the points at which leaves were attached. A care- ful inspection of the leaf traces reveals certain tiny dotlike scars arranged more or less in the form of a horseshoe. These scars mark the former position of bundles of tubes which we have already studied in connection with roots. They are, in fact, continuations of the same fibrovascular l>undles which pass from the root up through the stem and out into the leaves, where we see them as the veins which act as the support of the soft green tissues of the leaf. The most important use to the plant of the fibrovascular bundles is the condvx^tion of fluids from the Throo-ycar-old apple branch, showing terminal and lateral buds and bud scars. 102 THE STRUCTURE AND WORK OF THE STEM roots to the leaves and jrotri the leaves to the stem and root. The position of the leaf traces on the branch give us a clew as to the appearance of the leafy tree. If the leaf traces are oppositely placed, then we know that the leaves and buds, which give rise to lateral branches, had a very definite arrangement in pairs. Such are the maple or horse-chestnut. If, on the other hand, the leaf traces are placed alternate to each other, we can picture a tree with much less regularity in the position of leaves and lateral branches, as in the apple, beech, and elm. Four years' growth in an ailanthus stem, showing the changes in the lenticels from round holes to elongated cracks in the bark. The lenticel in a young shoot is like the breathing hole of a leaf. Lenticels and their Uses. — The very tiny scars, which look like little cracks in the bark, are very important organs, especially during the winter season, for they are the breathing holes of the tree. A tree is alive in winter, although it is much more active in the warm weather. Oxidation takes place much more rapidly in the summer because the plant is grow- ing rapidly, and more fuel is consumed to release the energy needed for growth. We shall see later that the leaves are the chief breathing organs of the plant. But all the year round oxygen is taken in and carbon dioxide given off through the lenticels, as the breathing holes in the trunk and branches of a tree are called. The lenticels, which early in the Ufe of the stem are structures similar to the breathing holes in leaves (of which more later) , become quite changed in older stems, the tiny holes becoming cracklike scars. A Dicotyledonous Stem in Cross Section. — If we cut a cross sec- tion through a young horse-chestnut stem, we find it shows three THE STRUCTURE AND WORK OF TUE STEM 103 Section across a young twig of box elder, showing the four stem regions : e, epidermis, represented by the heavy bounding line ; c, cortex ; to, wood; p, pith. (From Coulter, Plant Relations.) distinct regions. The center is occupied by the spongy, soft pith; surrounding this is found the rather tough wood, while the outer- most area is called cortex or bark. More careful study of the bark reveals the presence of three layers — an outer layer, a middle green layer, and an inner fibrous layer, the latter usually brown in color. This layer is made up largely of tough fiberlike cells known as bast fibers. The most important parts of this inner bark, so far as the plant is con- cerned, are many tubelike struc- tures known as sieve tubes. These are long rows of living cells, having perforated sievelike ends. Through these cells food materials pass downward from the upper part of the plant, where they are manufactured. C In the wood will be noticed (see Figure) a number of lines radiating outward from the pith toward the cortex. These are the so-called medullary rays, thin plates of pith which separate the wood into a num- ber of wedge-shaped masses. These masses of wood are composed of many elongated cells, which, placed end to end, form thousands of little tubes connecting the leaves with the roots. In addition to these are many thick-walled cells, which give strength to the mass of wood. In sec- tions of wood which have Section across a twig of box elder three years old, showing three annual growth rings in the vascular cylinder. The ra- diating lines (m), which cross the wood (w), represent the pith rays, the prin- cipal ones extending from the pith to the cortex (c). (From Coulter, Plant Rela- tions.) 104 THE STRUCTURE AND WORK OF THE STEM taken several years to grow, we find so-called annual rings. The distance between one ring and the next (see Figure) usually rep- resents the amount of growth in one year. Growth takes place from an actively dividing layer of cells, known as the cambium layer. This layer forms wood cells from its inner surface and bark from its outer surface. Thus new wood is formed as a dis- tinct ring around the old wood. Use of the Outer Bark. — The outer bark of a tree is protective. The cells are dead, the heavy woody skeletons serving to keep out Experiment to show that the skin of the i)()tat() (:i .stem) retards evaporation. cold and dryness, as well as prevent the evaporation of fluids from within. Most trees are provided with a layer of corky cells. This layer in the cork oak is thick enough to be of commercial impor- tance. The function of the corky layer in preventing evaporation is well seen in the case of the potato, which is a true stem, though found underground. If two potatoes of equal weight are balanced on the scales, the skin having been peeled from one, the peeled po- tato will be found to lose weight rapidly. This is due to loss of water, which is held in by the skin of the unpeeled potato. Passage of Fluids up and down the Stem. — If any young grow- ing shoots (young seedlings of corn or pea, or the older stems of garden balsam, touch-me-not, or sunflower) are placed in red ink THE STRUCTURE AND WORK OF THE STEM 105 Apple twigs split to show the course of colored water up the stem. (eosin), left in the sun for a few hours, and then examined, the red ink will be found to have passed up the stem. If such stems were examined carefully, it would be seen that the colored fluid is confined to the collec- tions of woody tubes inamediately under the inner bark. Water evidently rises in that part of the stem we call the wood. But if willow twigs are placed in water roots soon begin to develop from that part of the stem which is under water. If now the stem is girdled by removing the bark in a ring just above where the roots are growing, the latter will even- tually die, and new roots will appear alx)ve the girdled area. The food ma- terial necessary for the outgrowth of roots evidently comes from above, and the passage of food materials takes place in a downward direction just outside the wood in the layer of bark which contains the bast fibers and sieve tubes. Food substances are also conducted to a much less extent in the wood itself, and food passes from the inner bark to the center of the tree by way of the pith plates or medullary rays. This can be proved by testing for starch in the medullary rays of young stems. It is found that much starch is stored in this part of the tree trunk. This experiment with the willow explains why it is that trees die when girdled so as to cut the sieve tubes of the inner bark. The food supply is cut off from the protoplasm of the cells in the part of the tree below the cut area. Many of the canoe birches of our Adirondack forest are thus killed, girdled by thoughtless visitors. In What Form does Food pass through the Stem? — We have already seen that materials in solution (those substances which will dissolve in the water) will pass from cell to cell by the process of osmosis. This is shown in the experiment illustrated on the iollowing page. Two thistle tubes were partly filled, one with starch and water, the other with sugar and water, and a piece of parchment paper was tied over the end of each. The lower 106 THE STRUCTURE AND WORK OF THE STEM Experiment showing the osmosis of sugar (right-hand tube) and non- osmosis of starch (left-hand tube). end of both tubes was placed in a glass dish under water. After twenty-four hours, the water in the dish was tested for starch, and then for sugar. We find that only the sugar, which has been dissolved by the water, can pass through the membrane. Digestion. — As we shall see later, the food for a plant is manu- factured in the leaves or in stems, etc., wherever green coloring mat- ter is found. Much of this food is in the form of starch. But starch, being insoluble, cannot be passed from cell to cell in a plant. It must be changed to a soluble form. This is accomplished by the process of digestion. We have already seen that starch was changed to grape sugar in the corn by the action of a substance (a digestive ferment) called diastase. This process of digestion seem- ingly may take place in all living parts of the plant, although most of it is done in the leaves. In the bodies of all animals, including man, starchy foods are changed in a similar manner, but by other digestive ferments, into soluble grape sugar. (See experiment, page 72.) The food material may be passed in a soluble form until it comes to a place where food storage is to take place, then it can be trans- formed to an insoluble form (starch, for example) ; later, when needed by the plant in growth, it may again be transformed and sent in a soluble form through the stem to the place where it will be used. Building of Proteids. — Another very important food substance stored in the stem is proteid. Of the building of proteid, little is known. We know it is an extremely complex chemical substance which is made in plants from compounds containing nitrogen, the nitrates and compounds of ammonia received through the roots from the organic matter contained in the soil, combined with sugar or starches in the body of the plant. Some forms of proteid substance are soluble and others insoluble THE STRUCTURE AND WORK OF THE STEM 107 in water. White of egg, for example, is very slightly soluble, but can be rendered insoluble by heating it so that it coagulates. Insoluble proteids are digested within the plant; how and where is but slightly understood. In a plant, soluble proteids pass down the sieve tubes in the bast and then may be stored in the bast or medullary rays of the wood in an insoluble form, or they may pass into the fruit or seeds of a plant, and be stored there. What forces Water up the Stem. — We have seen that the process of osmosis is responsible for taking in soil water, and that the enormous ab- sorbing surface exposed by the root hairs makes possible the absorption of a large amount of water. Frequently this is more than the weight of the plant in every twenty- four hours. Experiments have been made which show that at certain times in the year this water is in some way forced up the tiny tubes of the stem. During the spring season, in young and rapidly growing trees, water has been proved to rise to a height of nearly ninety feet. The force that causes this rise of water in stems is known as root pressure. But root pressure alone cannot account for the rise of sap (water containing materials taken out of the soil) to a height of several hundred feet, as in the stems of the California big trees. Other forces must play a part here. One way in which the rise of water can be partly accounted for is in the fact that capil- lary attraction may help in part. If you place in a glass containing red or other colored fluid three or four tubes of differ- ent inside diameter, the fluid will be found to rise very much higher in the tubes having a smaller diameter. This is caused by capillarity or capil- lary attraction. When we consider that the tubes in the stem are very much smaller than any we can make out of glass, it can be seen that water jnight rise in the stem to some height in tubes of microscopic diameter. The greatest factor, however, is one which will be more fully explained when we study the work of the leaf. Leaves pass off an immense quan- tity of water by evaporating it in the form of vapor. This evaporation seems to result in a kind of suction on the column of water in the stem. In the fall, after the leaves have gone, much less water is taken in by roots, showing that an intimate relation exists between the leaves and the root. Diagram to show the areas in a plant through which raw food materials pass up the stem and food materials pass down. (After Stevens.) 108 THE STRUCTURE AND WORK OF THE STEM Structure of a Monocotyledonous Stem. — A piece of cornstalk ex- amined carefully in cross and longitudinal section shows us that the main bulk of the stalk is made up of pith, while scat- tered through the pith are numerous stringy, tough structures. To these the name fibrovascular bundles has been given. The latter are the woody bundles of tubes which in this stem are scattered through the pith and run into the leaves at the nodes, where (in young specimens) they may be followed as veins. The outside of the corn stem is formed of large numbers of these bundles, which, closely packed together, form an outer rind. Thus the woody material gives mechanical support to an otherwise spongy stem. Structure of Fibrovascular Bundle in a Mono- cotyledonous Stem. — A fibrovascular bundle in a cross section under the microscope shows this arrangement: Around the outside of the bundle is a collection of thick-walled, woody cells. These cells serve to support the bundle. Inside of these cells are found a number of tubes of different diameters, some for conduction of water, others for air, and still others for liquid food material sent down from the leaves. These tubes were formed by the elongation of certain cells of the bundle which in their growth have divided so as to form a string of cells. The con- tents of some of these cells die: Longitudinal section of cornstalk, showing some of the fibrovas- cular bundles passing outward at the node just above the roots. a hollow tube' of cellulose remains, which admits the passage of material from one level of the stem to another through the open ends of the cells. The conducting tubes have various functions. Some carry soil water and air up the stem, while others take food material down toward the roots. The bundles elon- gate rapidly, but are limited in their growth outward by the hard-walled, woody cells. An old stem of a mono- cotyledon contains more bundles than does a young stem, the bundles growing out as veins into the leaves. Monocotyledonous fibrovascular bundle : ph, region in which food passes down ; d, woody portion or bundle ducts which carry air and water ; p, pith cell. THE STRUCTURE AND WORK OF THE STEM 109 Food Storage. — Many monocotyledonous trees which Uve for long periods of time store food in large quantities in the trunk. The sago palm is an example. The sugar cane is a mono- cotyledonous stem of great commercial value because of the sugar contained in its sap. Over 70 pounds of sugar on the average is used annually by each per- son in the United States. Most of the cane sugar grown in this country comes from Louisiana and Texas, although these states do not begin to supply the needs of this country. The diagram fol- lowing graphically shows the sources and kinds of sugars used in the United States. Roots and Stems as Food. — Underground stems and roots form some of the most important sources of man's food supply. Our commonest foods, as the potato, sweet potato, onion, carrot, parsnip, turnip, and beet, are well-known examples. The sago palm is the Kind and Sources Sugar Consumed in United States — Percentage 1,0 20 ^ 10 'p 7jD aO BO Palms and palmettos; typical monocotyledo- nous plants. Scene on Indian River, Florida. Beet East Indies United States Cuba Germany Rest World chief support of many of the natives of Africa. Each adult tree will furnish 700 pounds of sago meal, 2i pounds being enough to support a man one day. The cassava root, from which tapioca is made, is one of the main supports of African natives. Sugar, from the beet no THE STRUCTURE AND WORK OF THE STEM root, is a world-known commodity, beet-sugar production having greatly increased in recent years. Maple sugar is a well-known commodity which is obtained by boiling the sap of sugar maple until it crystallizes. Over 16,000 tons of maple sugar is obtained every spring, Vermont producing about 40 per cent of the total output. The following table shows the proportion of foods in some of the commoner roots and stems : — Water Proteids Carbohy- drates Fats Ash Potato . . . Carrot . . . Parsnip . . . Turnip . . . Onion . . . ^Sweet potato . Beet .... 75 89 81 92.8 91 74 82.2 1.2 .5 1.2 .5 1.5 1.5 .4 18 5 8.7 4.0 4.8 20.2 13.4 0.3 0.2 1.5 0.1 0.2 0.1 0.1 1.0 1.0 1.0 .8 .5 1.5 0.9 Budding. — We have said a bud is a promise of a branch ; it may be more, the promise of a new tree. If the owner of an apple or peach tree wishes to vary the quaUty of fruit borne by the tree, he may in the early fall cut a T-shaped incision in the bark and then insert a bud sur- rounded with a little bark from the tree bearing the desired fruit.^ The bud is bound in place and left over the winter. When a shoot from the embed- ded bud grows out the follow- I h Steps in Budding. 1 This bud should be taken from a tree of the same species. (a) twig having suitable buds to use ; (6) method of cutting out bud ; (c) how the bark is cut ; (d) how the bark is opened ; (e) inserting the bud ; (/) the bud in place ; (g) the bud properly bound in place. THE STRUCTURE AND WORK OF THE STExM 111 Steps in tongue grafting. ing spring, it is found to have all the characters of the tree from which it was taken. This process is known as budding. Grafting. — Of much the same nature is grafting. Here, however, a small portion of the stem of the closely allied tree is fastened into the trunk of the growing tree in such a manner that the two cut cambium layers will coincide. This will allow of the passage of food into the grafted part and insure the ultimate growth of the twig. Grafting and budding are of considerable eco- („) the two branches to be nomic value to the fruit grower, as it joined : (6) a tongue cut in enables him to produce at wiU trees ^^f^' (c) how fitted together ; , . , . . ^. /. r -x 1 (d) method of wrapping. bearmg choice varieties of frmt. In both of the above processes, the secret of successful growth lies in the fact that the cambium surface of the bud or the graft comes in contact with the cambium of the tree to which they are applied, thus putting them in direct communication with a supply of food from the already established tree. Modified Stems. — We have aeen in previous experiments, external forces may act on the organs of a plant so as to change its appearance and often its form and habit. A stem grown in complete darkness is white instead of green. The bleaching of the celery stems by covering them is a familiar example of this. Thus, in na- ture, forces which we know of as light, gravity, heat, moisture, wind, and per- haps other factors, influence the plant in its growth. Thus changes may take place which fit or adapt the parts of a plant better for life under certain con- ditions in which it must exist. Stems modified for Water or Food Storage. — Many stems store large quantities of food. The sago palm is an example of such a stem. In most woody stems food is stored during some parts of the year and is used as the plant comes to need it. In * For full directions for budding and grafting, see Goff and Mayne, First Princi- ples of Agriculture, Chap. XIX, or Hodge, Nature Study and Life, pages 16&-179. The ix)tat() tuber a stem ; note the branches growing from the "eyes" at one end. 112 THE STRUCTURE AND WORK OF THE STEM other stems the conditions of life are such that the plant has come to store water in the stem. The cactus, which we shall examine more in detail later, is a plant that has developed the stem for the storage of water, and is so adapted to desert conditions as to prevent the evapora- tion of water from the plant. The potato tuber is simply a much thickened storage stem, as one may easily prove by examination of the so-called "eyes" of a sprouting po- tato. The tiny projection growing within the eye is a bud, which may give rise to a branch later. Food and water are stored with the tuber. Underground Stems ; the Rootstock. — Other stems not only contain stored food, but run underground for the protection of the plant. Such a stem is the rootstock of the iris. Some underground stems do not store food, but grow with considerable rapidity, thus covering ground and starting new outposts of the plant at a distance from the original plants. The pest called quick grass or couch grass, found in almost every lawn, has such a stem. It may be cut in pieces, but each piece may strike root, thus multiplying the plant. Bulbs. — In the bulb of a lily or the onion the stem is covered with thickened leaves, the whole making a compact and reduced plant which, because of its storad food, enables the plant to make an early start in the spring. Reduced Stems. — In some plants the stem is so re- duced as to be almost lost. ' This may be of a distinct advantage to the plant in enabling it to escape destruc- tion from enemies. Such a plant is the common dan- delion, which, because of its short stem, escapes grazing animals and the knives of lawn mowers. Many other low-lying weeds are partly immune from dangers which beset taller plants. Climbing Stems. — Stems may twist around an object in order to climb. Such a plant is the morning-glory. Here the stimulus which draws tho Longitudinal section of a lily bulb. Note the much thick- ened leaves, and the flower cluster at the center. Pho- tographed by Overton. Catbrier ; the ten- drils {T) are modified sti- pules (parts of leaves) ; Th, thorn. THE STRUCTURE AND WORK OF THE STEM 113 plant upward is evidently the sun. In stems which make use of this method of climbing, it is noticed that each stem twines around the sui>- port in a given direction, some revolving with the course of the sun, others in the opposite direction. When such a stem touches an object during its first growth, it is im- mediately stimulated to turn toward the object and coil around it. Leaves and Stems modified as Holdfasts. — In the common nas- turtium (tropceolum) the leaves revolve in much the same man- ner as do the stems mentioned above. This movement results in some of the leafstalks fasten- ing around supports, thus draw- ing the stem up. Tendrils. — In some plants definite climbing organs, known as tendrils, are developed. A tendril, which has the appear- ance of a much twisted stem, may be modified from part of a leaf, as an entire leaf, or as part of a branch. Tendrils have the habit of at first stretching out as far from the main stem as pos- sible, then slowly revolving. After a support is touched they immediately coil around it and then begin to curl up somewhat after the manner of a watch spring. This draws up the stem of which they arc a part to the support. Stems modified as Thorns. — Leaves h.nd parts of leaves may be changed into thorns for the protection of the plant. In some instances the stem becomes a spine or thorn. Such is the case in the honey locust. In the case of the black locust, a part of the leaf, the stipule, becomes the thorn. All such modifications seem to result in the better protection of tender parts which might otherwise suffer from the attack of brows- ing animals. A honey locutit ; the thorns are branches. modified HUNT. 8. 114 THE STRUCTURE AND WORK OF THE STEM Reference Books elementary Sharpe, A Laboratory Marmal jor the Solution of Problems in Biology. American Book Company. Andrews, Botany All the Year Round, Chaps. VI, VII. American Book Company. Atkinson, First Studies of Plant Life, Chaps. IV, V, VI, VIII, XXI. Ginn and Company. Dana, Plants and their Children, pages 99-129. American Book Company. Goff and Mayne, First Principles of Agriculture. American Book Company. Hodge, Nature Study and Life, Chaps. IX, X, XI. Ginn and Company. Hunter and Valentine, Laboratory Manual of Biology. Henry Holt and Company. MacDougal, The Nature and Work of Plants. The Macmillan Company. ADVANCED Apgar, Trees of the United States, Chaps. II, V, VI. American Book Company. Coulter, Barnes, and Cowles, A Textbook of Botany, Vol. I. American Book Com- pany. Ganong, The Teaching Botanist. The Macmillan Company. Goebel, Organography of Plants, Part V. Clarendon Press. Goodale, Physiological Botany. American Book Company. Gray, Structural Botany, Chap. V. American Book Company. Kerner-Oliver, Natural History of Plants. Henry Holt and Company. Lubbock, Buds and Stipules. D. Appleton and Company. Strasburger, Noll, Schenck, and Schimper, A Textbook of Botany. The Macmillan Company. Ward, The Oak. D. Appleton and Company. Yearbook, U.S. Department of Agriculture, 1894, 1895, 1898-1910. IX. LEAVES AND THEIR WORK Problem XVIII. A study of leaves in relation to their enviromnent, {Ldboratory Manual, Prob. XVIII.) (a) Reactions of stems and leaves to light. (jb) Structure. (c) Important functions. {!) Absorption and respiration. (^) Food-making and its by-product. (5) Evaporation of excess waler. (4) TJie leaf as a mill {optional), (jd) Means of protection {optional). (e) Som£> leaf modifications {optional). (/) Importance to man. Differences between Roots and Stems. — A comparison of the young root and developing stem of a bean seedling show that sev- eral marked differences exist : (1) the color of the stem is greenish, while the roots are gray or whitish ; (2) the stem has leaves and branches leaving it in a more or less regular manner, while the smaller roots are extremely irregular in their method of growth ; (3) the stem grows up- ward, while the general direction taken by the roots is downward. Effect of Light on Plants. — In young plants which have been grown in total darkness, no green color is found in either stems or leaves, the latter often being reduced to mere scales. The stems are , J , A pocket garden which has been kept in com- long and more or less re- pj^^e darkness for several weeks. Notice the dining. We can explain bleached condition of stems and leaves. 115 1 ■ 1 116 LEAVES AND THEIR WORK the changed condition of the seedUng grown in the dark only by assuming that hght has some effect on the protoplasm of the seedling and induces the growth of the green part of the plant. Numerous instances could be given in which plants grown in sunlight are healthier and better developed as to their green parts than those in the shady parts of a garden or field. On the other hand, some plants thrive in the shade. Such plants are the mosses and ferns. Still other plants, minute organisms hardly visible to the eye, do not thrive in the Hght, and may be killed by its influence. Such are molds, mildews, and some bacteria. Such plants, however, are not green. As a The growth of young stems and leaves of oxalis toward the light. Two stages in an experiment to show that green plants grow toward the light. matter of fact, the stem of a green plant which has but little chlorophyll develops somewhat more rapidly under conditions where it receives no light. LEAVES AND THEIR WORK 117 Heliotropism. — We saw that the stems of the plants kept in the darkness did not always lift themselves erect, as in the case of stems in the light. If seedlings have been growing on a window sill, or where the light comes in from one side, you have doubtless noticed that the stem and leaves of the seedlings incline in the direction from which the hght comes. The tendency of young stems and leaves to grow toward sunlight is called positive heliotropism. The experiment pictured on the preceding page shows this effect of light very plainly. A hole was cut in one end of a cigar box and barriers were erected in the interior of the box so that the seeds planted in the sawdust received their light by an indirect course. The young seedling in this case responded to the influence of the stimulus of light so as to grow out finally through the hole in the box into the open air. This growth of the stem to the light is of very great importance to a growing plant, because, as we shall see later, food-making depends largely on the amount of sunlight the leaves receive. Effect of Light. — We have already found that seedlings grown in total darkness are almost yellow-white in color, that the leaves are but slightly de- veloped, and that the stem has developed far more than the leaves. We have also seen that a green plant will grow toward the source of light, even against great odds. It is a matter of common knowledge that green leaves turn toward the light. Place growing pea seedlings, oxalis, or any other plants of rapid growth near a window which receives - '■ i, -'^ I.*^' 'V ^ Tall straight stems of the hemlock ; the trees reach up toward the source of light. 118 LEAVES AND THEIR WORK full sunlight. Within a short time the leaves are found to be in positions to receive the most sunUght possible. Arrangement of Leaves. — A study of trees in any park, or in the woods, shows that the stems of trees in thick forests are usually tall and straight and that the leaves come out in clusters near the top of the tree. The leaves lower down are often smaller and less numerous than those near the top of the tree. Careful observa- tion of any plant growing outdoors shows us that in almost every case the leaves are so disposed as to get much sunlight. The ivy A lily, showing long, narrow leaves. The dandelion, showing a whorled arrange- ment of long, irregular leaves. climbing up the wall, the morning-glory, the dandelion, and the burdock all show different arrangements of leaves, each presenting a large surface to the light. Leaves are usually definitely arranged, fitting in between one another so as to present their upper surface to the sun. Such an arrangement is known as a leaf rnosaic. Good examples of such mosaics, or leaf patterns, are seen in trees having leaves which come up alternately, first on one side of a branch, then on the other. Here the leaves turn, by the twisting of their stalks, so that all the leaves present their upper surface to the sun. In the case of the dandelion, a rosette or whorled cluster of leaves is found. In the horse-chestnut, where the leaves come out oppo- site each other, the older leaves have longer petioles than the LEAVES AND THEIR WORK 119 young ones. In the mullein the entire plant forms a cone. The old leaves near the bottom have long stalks, and the little ones near the apex come out close to the main stalk. In every case each leaf receives a large amount of Ught. Other modifications of these forms may easily be found on any field trip. The Sun a Source of Energy. — We all know the sun is a source of most of the energy that is released on this earth in the form of heat or light. Solar engines have not come into any great use as yet, because fuel is cheaper. Actual experiments have shown that vast amounts of energy are given to the earth. When the sun is in the zenith, energy equivalent to one hundred horse power is received by a plot Of land twenty-five by one hundred feet, the size of a city lot. Plants receive and use much of this energy by means of their leaves. The Structure of a Leaf. — Let us now examine with some detail the structure of a simple leaf of a dico- tyledonous plant. A green loaf shows usually (1) a Palmately-veined leaf of the maple. Tho .skeleton of a notted- veined leaf : M.R., midrib ; P., the leafstalk or petiole ; v., the veins. flat, broad blade which may take almost any conceivable shape ; (2) a stem or petiole which (3) spreads out in the blade in a 120 LEAVES AND THEIR WORK number of veins. These veins usually present a netted appear- ance in the leaf of a dicotyledon, but run more or less parallel to one another in the blade of a monocotyledonous leaf. At the base of the leaf may be found a pair of outgrowths from the petiole called stipules. By means of these stipules in the rose leaf, for example, we are able to know that the leaf is compound, that is, each of the little leaflike parts is in reality part of a leaf blade Palmately-conipound leaf of rose, show ing stipules (st). that is so deeply indented that the blade is cut away to the midrib, or central vein, of the leaf — for a pair of stipules is found at the base of every complete leaf. These fall off early in many leaves. The Cell Structure of a Leaf. — The under surface of a leaf seen under the microscope Surface view of epidermis of lower sur- face of a leaf ; e, ordinary epidermal cell ; fir, guard cell. — Tschirch. Section of a leaf ; e, epidermis ; c, cells containing chlorophyll bodies ; p, in- tercellular passages ; g, g, guard cells of stoma. usually shows numbers of tiny oval openings. These are called stomata (singular stoma). Two cells, usually kidney-shaped, are found, one on each side of the stoma. These are the guard LEAVES AND THEIR WORK 121 cells. By change in shape of these cells the opening of the stoma is made larger or smaller. Larger irregular cells form the epidermis, or outer covering of the leaf. Study of the leaf in cross section shows that these stomata open directly into air chambers which penetrate between and around the loosely arranged cells composing the underpart of the leaf. The upper surface of leaves sometimes contains stomata, but more often they are lacking. The under surface of an oak leaf of ordinary size contains about 2,000,000. Under the upper epidermis is a layer of green cells closely packed together (called collectively the pali- sade layer). These cells are more or less columnar in shape. Under these are several rows of rather loosely placed cells just mentioned. These are called collectively the spongy parenchyma. If we hap- pen to have a section cut through a vein, we find this composed of a number of tubes made up of, and strengthened by, thick-walled cells. The veins are evidently a continuation of the tubes of the stem out into the blade or the leaf. Starch made by a Green Leaf. — If we examine the palisade layer of the leaf, we find cells which are almost cylindrical in form. In the protoplasm of such cells are found a number of little green colored bodies, which are known as chloroplasts or chlorophyll bodies. If we place the leaf in wood alcohol, wc find that the bodies still remain, but that the color is extracted, going into the alcohol and giving to it a beautiful green color. The chloroplasts are, indeed, simply part of the protoplasm of the cell colored green. If the plant is kept in the sun, the chloroplasts keep their green color, but in the dark this color is gradually lost. These bodies are of the greatest importance directly to plants and indirectly to animals. A h\(irangc;i plant, upf)!! tho k-aves of which disks of cork have been pinned in order to exclude sunlight from the leaf. 122 LEAVES AND THEIR WORK The chloroplasts, by means of the energy received from the sun, manu- facture starch out of certain raw materials. These raw materials are soil water, which is passed up through the bundles of tubes into the veins of the leaf from the roots, and carbon dioxide, which is taken in through the stomata or pores, which dot the under surface of the leaf. Light and Air necessary for Starch- Making. — If we pin strips of black cloth, such as alpaca, over some of the leaves of a growing geranium, place the plant in a sunny window for two or three days, and then remove some of the covered leaves after a day of bright sunlight, we find after ex- tracting the chlorophyll with wood alcohol (because the chlorophyll covers up the contents of the cells) that starch is present only in the portions of the leaves exposed to sunlight. From this experiment we infer that the sun has something to do with starch- making in a leaf. The ne- cessity of air for starch- making may also easily be proved, for the parts of leaves covered with vaseline will be found to contain no starch, while parts of the leaf unvaselined but exposed to the sun and air contain starch. Air is necessary for the process of starch-making in a leaf, not only because carbon dioxide gas is absorbed (there are from three to four parts in ten thousand present in the atmosphere), but also because the protoplasm of the leaf is alive and must have oxygen. This it takes from the air around it. Comparison of Starch-Making and Milling. — The manufacture of starch by the green leaf is not easily understood. The process has been compared to the milling of grain. In this case the mill is the green part of the leaf. The sun furnishes the motive power, the chloroplasts constitute the machinery, and soil water and carbon dioxide are the raw products taken into the mill. The manufactured Starchless areas in leaves caused by excluding sunlight by means of strips of black cloth. LEAVES AND THEIR WORK m product is starch, and a certain by-product (corresponding to the waste in a mill) is also given out. This by-product is oxygen. To understand the process fully, we must refer to a small portion of the leaf. Here we find that the cells of the green layer of the leaf, under the upper epi- dermis, perform most cf the work. The carbon dioxide is taken in through the stomata and reaches the green cells by way of the intercellular spaces and by diffusion from cell to cell. Water reaches the green cells through the tracheal tubes of the veins. It then passes into the cells ^^8™°» ^ ^"^^'^^^ *^« formation of starch. by osmosis, and there becomes part of the cell sap. The light of the sun easily penetrates to the cells of the palisade layer, Diagram (after Stevens) to illustrate the processes of breathing, food-maJcing, and transpiration which may take place in the cells of a green leaf in the sunlight. 124 LEAVES AND THEIR WORK giving the energy needed to make the food. This whole process is a very delicate one, and will take place only when external con- ditions are favorable. For example, too much heat or too little heat stops starch-making ; the presence of stored food in the leaf, or of too much carbon dioxide in the atmosphere, may stop its work. This building up of food and the release of oxygen by the plant in the presence of sunlight is called photosynthesis. Chemical Action in Starch-Making. — In the process of starch-making in a leaf, water (H2O) and carbon dioxide (CO2) are combined in such a way as to make starch, the molecule of which is expressed by the formula CeHioOs. This combination is expressed as follows : 5 H2O + 6 CO2 = CeHioOg + 12 O. The starch thus formed is either stored in the leaf or changed by digestion to some form which can pass by osmosis from cell to cell ; that is, a soluble material like grape sugar. The oxygen is passed off through the stomata of the leaf.i Proteid-Making and its Re- lation to the Making of Living Matter. — Proteid material is a food which is necessary to form protoplasm. Proteid food is present in the leaf, and is found in the stem or root as well. Proteids can apparently be manufactured in any plant cells, the presence of light not seeming to be a necessary factor. How it is manufac- tured is a matter of conjecture. The minerals brought up in the soil water form part of its composition, and starch or grape sugar give three elements. The element nitrogen is taken up by the roots as a nitrate (nitrogen in combination with lime or An oxaniple of how a tree may exert energy. This rock has been spHt by the growing tree. ^ It seems probable that food material is first made in the form of a sugar, then changed to starch ; when transported from one part of the plant to another, it is changed back to sugar. LEAVES AND THEIR WORK 125 potash). Proteids are probably not made directly into proto- plasm in the leaf, but are stored by the cells of the plant and used when needed, either to form new cells in growth or to repair waste. While plants and animals obtain their food in different waj^s, they probably make it into living substance (assimilate it) in exactly the same manner. Foods serve exactly the same purposes in plants and in animals ; they either build living matter or they are burned (oxidized) to furnish energy (work power). If you doubt that a plant exerts energy, note how the roots of a tree bore their way through the hard- est soil, and how stems or roots of trees often split open the hardest rocks, as illustrated on the opposite page. Rapidity of Starch- Making. — Leaves which have been in dark- ness soon show starch to be present when exposed to light. Squash leaves make three fourths of an ounce for each square yard of sur- face. A corn plant sends 10 to 15 grams of reserve material into the ears in a single day. The formation of fruit, and especially the growth of the grain fields, show the economic importance of this fact. Not only do plants make their own food and store it away, but they make food for animals as well. And the food is stored in such a stable form that it may be sent to all parts of the world in the form of grain or other fruits. Animals, herbivorous and flesh- eating, man himself, all are depend- ent upon the starch-making processes of the green plant for the ultimate source of their food. Oxygen given off by Green Plants. — It is possible to prove that oxygen is given off by green plants in sunlight. The common green frog scum seen in , ,, , . -, /• 11 /• 1 1 i_i Experiment to show that oxygen shallow ponds is often so full of bubbles -^ ^^^^ ^^ ^y green plants in that it is buoyed up by this means at the sunHght. o, oxygen. 126 LEAVES AND THEIR WORK the water's surface. If some of this plant or other green water weed is placed in a large battery jar or fruit jar in a sunny- window, bubbles of gas will be seen to arise from it, the amount increasing as the water is warmed by the sun's rays. If a glass funnel is placed upside down so as to cover the plants, and then a test tube full of water inverted over the mouth of the funnel, the gas may be collected by displacement. After two or three days of hot sun, enough of the gas can be obtained to make the oxygen test. That oxygen is given off as a by-product by green plants is a fact of far-reaching importance. Parks are in a city true " breathing spaces." The green covering of the earth is giving to animals an element that they must have, while the animals in their turn are supplying to the plants carbon dioxide, a compound used in food-making. Thus a relation of mutual helpfulness exists between plants and animals. Evaporation of ExcessWater. — In the manufacture of starch and proteid, an enormous amount of water is taken up by the roots and passed to the leaves to supply the needed amount of mineral matter. The excess of water is evaporated through the sto- mata. That water is passed through the blade of the leaf in the form of moisture is shown by the photograph above, drops of water having gathered on the inside of the bell jar. A small grass plant on a summer's day evaporates more than its own weight in water. This would make nearly half a ton of water Experiment to show transpiration. Notice that roots covered with root hairs have grown out of the main stem of the plant in response to the moist condition exist- ing outside of the rubber-covered flower- pot and within the bell jar. LEAVES AND THEIR WORK 127 distributed to the air during twenty-four hours by a grass plot twenty-five by one hundred feet, the size of the average city lot. According to Ward, an oak tree may pass off two hundred and twenty-six times its own weight in water during the season from June to October. From which Surface of the Leaf is Water Lost? — In order to find out whether water is passed out from any particular part of the leaf, we may re- move two leaves of the same size and weight from some large-leaved plant — a mullein was used for the illustrations given below — and cover the 1 xperiiiient to show through which surface of a leaf water passes off. • upper surface of one leaf and the lower surface of the other with vaseline. The petioles of each should be covered with wax or vaseline, and the two leaves exactly balanced on the pans of a balance which has previously been placed in a warm and sunny place. Within an hour the leaf which has the upper surface covered with vaseline will show a loss of weight. Examination of the surface of a mullein leaf shows us that the lower sur- face of the leaf is provided with stomata. It is through these organs, then, that water is passed out from the tissues of the leaf. Regulation of Transpiration. — The stomata of leaves close at night. On days when there is little humidity, they also tend to close, retarding transpiration, but when the water supply is abundant they open, increas- ing transpiration. This automatic action is of very great importance to the life of a plant, since evaporation of water is thus regulated. The Effect of Transpiration on Water within the Stem. — It has al- ready been noted that root pressure alone will not account for the rise 128 LEAVES AND THEIR WORK of water to the tops of very tall trees. Experiments show that evapora- tion of water through the stomata exerts a lifting power upon the fluids within the stem of the tree, thus aiding in the raising of water to the leaves in the upper branches. a b c Diagrams of a stoma : a, surface view of an opened stoma ; b, same stoma closed (after Hansen) ; c, diagram of a transverse section through a stoma — dotted lines indicate the closed position of the guard cells, the heavy lines the open condition. (After Schwendener.) Respiration by Leaves. — All li\ang things require oxygen. It is by means of the oxidation of food materials within the plant's body that the energy used in growth and movement is released. A plant takes in oxygen largely through the stomata of the leaves, to a less extent through the lenticels in the stem, and through the roots. Thus rapidly growing tissues receive the oxygen neces- sary for them to perform their work. The products of oxidation in the form of carbon dioxide are also passed off through these same organs. It can be shown by experiment that a plant uses up oxygen in the darkness ; in the light the amount of oxygen given off as a by-product in the process of starch-making is, of course, much greater than the amount used by the plant. Summary. — From the above paragraphs it is seen that a leaf performs the following functions : (1) breathing, or the taking in of oxygen and passing off of carbon dioxide; (2) starch-making, with the incidental passing out of oxygen ; (3) formation of proteids, with their digestion and assimilation to form new tissues; and (4) the transpiration of water. Economic Uses of Leaves. — The practical use of green plants to man is very great. Plants give off oxygen in the sunlight and use carbon dioxide, which is given off by animals in the breath. We should remember, as taxpayers, that money invested in public parks is money well invested, bringing as it does a source of oxygen supply where it is most needed, in the congested parts of our great cities. LEAVES AND THEIR WORK 129 Another very important use to man is seen in the fact that leaves, falhng to the ground, help to form a rich covering of humus, which acts as a coat to hold in moisture. The forests are our greatest source of water supply. The cutting away of the forest always means a depletion of the reserve water stored in soil, with conse- quent floods and droughts in alternation. Leaves are used directly by man for food. Examples are cab- bage, lettuce, kale, broccoli, and some others. These foods, properly admixed with certain fleshy foods, are of great importance in giving a balance to diet. In a wider sense, all animals depend upon leaves for their food supply either directly, — for herbivorous ani- mals feed upon the leaves of plants — or indirectly in foods obtained from roots, stems, seeds, and fruits. For in every case the stored food has been manufactured in the leafy part of the plant and transported within the plant to its place of storage. Even meat- eating animals are in the long run dependent upon plants, for they feed upon plant eaters. Modified Leaves. — In many plants the leaves are reduced to spines or have part of the leaf modified so as to form spines. In some leaves this appears to be for pro- tection against animals, but in some cases, as the cactus, it is a means of protecting the plant against loss of water through evaporation. If a cactus is cut open, it will be found to contain a very considerable amount of water. The Indians of the New Mexican desert region, when far from a source of water, sometimes cut oflf the top of a large cactus, mash up the soft interior of the thickened stem, squeeze out the pulp, and thus obtain several quarts of drinkable water. Protection by Hairs. — In the muUein, one of our hardiest weeds, the leaf is covered with a coating of finely branched hairs. Might such a covering be of use to the leaf? In what ways? HUNT. E8. BIO. 9 A cactus, showing the leaves modified into spines. 130 LEAVES AND THEIR WORK Storage of Food and Water in Leaves. — Leaves may be modified for the storage of food and water. Test an onion, which is a collection of thickened leaves closely wrapped to form what is called a bulb, for starch, sugar, and proteid. Squeeze any fleshy leaves and notice the water contained in them. The agave is a desert plant in which the leaves have become greatly thickened as a water and food storage. Leaves modified for Use in Climb- ing. — Sometimes, as in the leaf of the pea, a part of the leaf is modified for the purpose of climbing. In this case a part of the leaf, called the tendril, becomes especially sensitive to the stimulus of touch, and upon touching an object slowly coils around it. Almost any part of the leaf, or indeed the entire leaf, may be modi- fied to become a tendril. Reduced Leaves. — Leaves may be reduced to scales or lost al- together. In the asparagus, what seem to be tiny leaves are branches which spring from the axils of the true, very tiny, scalelike leaves. Leaves as Insect Traps. — Most curious of all are the modifications of the leaf into insect traps. It frequently happens that the habitat of a plant will not furnish the raw food materials ne- cessary to form proteid food and to build proto- plasm. Nitrogen is the lacking element. The plant has become adapted to these conditions and obtains nitrogenous food from the bodies of insects which it catches. Examples of insect traps are the common bladderwort (utricularia), the Venus's flytrap {Dioncea muscipula) , the sundew (Drosera rotundifolia) , and certain of the pitcher plants. Bladderwort. — The simplest contrivance for the ^^^^ captured insect. taking of animal food by the leaf is seen in the bladderwort. Here certain of the leaves are modified into little bladders provided with trapdoors which open inwards. Small water-swimming crustaceans (as water fleas, etc.) push their way into the trap and there Bladderwort, showing finely dissected submerged leaves bearing blades which capture little animals. Leaf of sundew closing LEAVES AND THEIR WORK lai die, perhaps of starvation. Bacteria, causing decay, soon break down their bodies into soluble substances, the nitrogenous portion of which is absorbed by the inner surface of the bladders and used by the plant as food. Venus's Flytrap. — In the Venus's flytrap, a curious plant found in our Southern states, the apex of the leaf is peculiarly modified to form an insect trap. Each margin of the leaf is provided with a row of hairs ; there are also three central hairs on each side of the midrib. The hairs are sensitive to a stimulus from without. The blade is so constructed that the slightest stimulus causes a closing of the leaf along the midrib. The surface of the leaf is provided with many tiny glands, which pour out a fluid capable of digest- ing proteid food. Thus an insect, caught between the halves of the leaf blade, is held there and slowly digested. Sundew. — In the sundew the leaves are covered with long glandular hairs, each of which is extremely sensitive to the stimulus of any nitrog- enous substance. These hairs exude a clear, sticky fluid which first renders more difficult the escape of the insect caught in the hairs, and then digests the nitrog- enous parts of the insect thus caught. Pitcher Plants. — The common pitcher plant has an urn-shaped leaf which is modified to hold water. Many small flies and other insects find their way into the pitcher and are eventually drowned in the cup. Whether the plant actually makes use of the food thus obtained is a matter unsettled, but some tropical forms undoubtedly do use the caught insects as food. Pitcher plant : a, leaf ; b, cross section ; c, longi- tudinal section. Note the insects at the bottom, and the inward-pointing hairs at the top. 132 LEAVES AND THEIR WORK Reference Books elementary Sharpe, A Laboratory Manual for the Solution of Problems in Biology, American Book Company. Andrews, Botany all the Year Round, pages 46-62. American Book Company. Coulter, A Textbook of Botany, pages 5-40. D. Appleton and Company. Dana, Plants and their Children, pages 135-185. American Book Company. Stevens, Introduction to Botany, pages 81-99. D. C. Heath and Company. ADVANCED Clement, Plant Physiology and Ecology. Henry Holt and Company. Coulter, Barnes, and Cowles, A Textbook of Botany, Part II, and Vol. II. American Book Company. Darwin, Insectivorous Plants. D. Appleton and Company. Goodale, Physiological Botany, pages 337—353 and 409—424. American Book Com- pany. Green, Vegetable Physiology. J. and A. Churchill. Lubbock, Flowers, Fruits, and Leaves, last part. The Macmillan Company. MacDougal, Practical Textbook of Plant Physiology. Longmans, Green, and Com- pany. Report of the Division of Forestry, U.S. Department of Agriculture, 1899. Strasburger, Noll, Schenck, and Schimper. A Textbook of Botany. The Mac- millan Company. Ward, The Oak. D. Appleton and Company. X. OUR FORESTS; THEIR USES AND THE NECESSITY FOR THEIR PROTECTION Problem XIX. Some uses of stems {optional). {Ldbordtory Manual, Prob. XIX.) {a) Special product from stems. (b) Some woods and their value. (c) Field work in forestry. The Economic Value of Trees. Protection and Regulation of Water Supply. — Trees form a protective covering for the earth's surface. They prevent soil from being washed away, and they hold moisture in the ground. Without trees many of our rivers might go dry in summer, while in the rainy season sudden floods would result. The devastation of immense areas in China and considerable damage by floods in parts of Switzer- land, France, and in Penn- sylvania has resulted where the forest covering has been removed. No one who has tramped through our Adi- rondack forest can escape noticing the differences in the condition of streams which flow through areas covered with forest and those from around which trees have been cut. The latter streams often dry up entirely in hot weather, while the forest-shaded stream has a never failing supply of crystal water. The city of New York owes much of its importance to its posi- tion at the mouth of a great river with a harbor large enough to float the navies of the world. This river is supplied with water 133 Working to prevent erosion after the removal of the forest in the French alps. 134 OUR FORESTS largely by the Adirondack and Catskill forests. Should these forests be destroyed, it is not impossible that the frequent freshets which would follow would so fill the Hudson River with silt and debris that the ship channels in the bay, already costing the government millions of dollars a year to keep dredged, would become too shallow for ships. If this should occur, the greatest city in this country would soon lose its place and become of second-rate importance. The story of how this very thing happened to the old Greek city of Poseidonia is graphically told in the following lines : — *' It was such a strange, tremendous story, that of the Greek Posei- donia, later the Roman Psestum. Long ago those adventuring mariners from Greece had seized the fertile plain which at that time was covefed with forests of great oak and watered by two clear and shining rivers. They drove the Italian natives back into the distant hills, for the white man's burden even then included the taking of all the desirable things that were being wasted by incompetent natives, and they brought over colonists — whom the philosophers and moralists at home maligned, no doubt, in the same pleasant fashion of our own day. And the colonists cut down the oaks, and plowed the land, and built cities, and made harbors, and finally dusted their busy hands and busy souls of the grime of labor and wrought splendid temples in honor of the benign gods who had given them the possessions of the Italians and filled them with power and fat- Eiosiou at Sayre, Penn., by the Chemung River. Photograph by W. C. Barbour. " Every once in so often the natives looked lustfully down from the hills upon this fatness, made an armed snatch at it, were driven back with bloody contumely, and the heaping of riches upon riches went on. And more and more the oaks were cut down — mark that ! for the stories of nations are so inextricably bound up with the stories of trees — until all the plain was cleared and tilled ; and then the foothills were denuded, and the wave of destruction crept up the mountain sides, and they, too, were left naked to the sun and the rains. OUR FORESTS 135 " At first these rains, sweeping down torrentially, unhindered by the lost forests, only enriched the plain with the long-hoarded sweetness of the trees ; but by and by the Uving rivers grew heavy and thick, vomiting mud into the ever shallowing harbors, and the land soured with the un- drained stagnant water. Commerce turned more and more to deeper ports, and mosquitoes began to breed in the brackish soil that was making fast between the city and the sea. " Who of all those powerful landowners and rich merchants could ever have dreamed that little buzzing insects could sting a great city to death ? But they did. Fevers grew more and more prevalent. The malaria- haunted population went more and more languidly about their business. The natives, hardy and vigorous in the hills, were but feebly repulsed. Carthage demanded tribute, and Rome took it, and changed the city's name from Poseidonia to Paestum. After Rome grew weak, Saracen corsairs came in by sea and grasped the slackly defended riches, and the little winged poisoners of the night struck again and again, until grass grew in the streets, and the wharves crumbled where they stood. Finally, the wretched remnant of a great people wandered away into the more wholesome hills, the marshes rotted in the heat and g^ew up in coarse reeds where corn and vine had flourished, and the city melted back into the wasted earth." Elizabeth Bisland and Anne Hoyt, Seekers in Sicily. John Lane Company. Prevention of Erosion by Covering of Organic Soil. — We have shown how ungovernecl streams might dig out soil and carry it far from its original source. Examples of what streams have done may be seen in the deltas formed at the mouths of great rivers. The forest prevents this by holding the water supply and letting it out gradually. This it does by covering the inorganic soil with humus or decayed organic material. In this way the forest floor becomes like a sponge, holding water through long periods of drought. The roots of the trees, too, help hold the soil in place. The gradual evaporation of water through the stomata of the leaves cools the atmosphere, and this tends to precipitate the moisture in the air. Eventually the dead bodies of the trees themselves are added to the organic covering, and new trees take their place. Other Uses of the Forest. — In some localities forests are used as A\indbreaks and to protect mountain towns against avalanches. In winter they moderate the cold, and in summer reduce the heat and lessen the danger from storms. The nesting of birds in woods protects many plants valuable to man which other^vise might be destroyed by insects. 136 OUR FORESTS Forests have great commercial importance as well. Even in this day of coal, wood is still by far the most-used fuel. It is useful in building. It outlasts iron under water, in addition to being durable and light. It is cheap and, with care of the forests, inexhaustible, while our mineral wealth will some day be used up. Hard woods are chiefly used in house building and furniture manufacture ; the soft woods, reduced to pulp, are made into paper. Distilled wood gives alcohol. Partially burned wood is charcoal. Vinegar and other acids are obtained from trees, as are tar, creosote, resin, turpentine, and other useful oils. The making of maple sirup and sugar forms a profitable industry in several states. FOREST REGIONS \ The forest regions of the United States. The Forest Regions of the United States. — The combined area of all the forests in the United States, exclusive of Alaska, is about 500,000,000 acres. This seemingly immense area is rapidly de- creasing in acreage and in quality, thanks to the demands of an increasing population, a woeful ignorance on the part of the owners of the land, and wastefulness on the part of cutters and users alike. A glance at the map shows the distribution of our principal forests. The following figures taken from the United States Census reports tell their own tale. In 1908, 31,231 sawmills cut OUR FORESTS 137 33,289,369,000 feet of lumber. They also cut over 12 billion shingles and nearly 30 billion laths. Nobody can tell how much lumber was wasted, either in the forest or at the mill. The census estimates, moreover, that owing to conditions caused by the panic, the amount cut was very considerably under that cut in 1907. Washington ranks first in the production of lumber. Here the great Douglas fir, one of the " evergreens," forms the chief source of supply. In the Southern states, especially Louisiana and Mississippi, yellow pine and cypress are the trees most lumbered. Uses of Wood. — In our forests much of the soft wood (the cone- bearing trees, spruce, balsam, hemlock, and pine), and poplars, aspens, basswood, with some other species, make paper pulp. The daily newspaper and cheap books are responsible for inroads on our forests which cannot well be repaired. It is not necessary to take the largest trees to make pulp wood. Hence many young trees of not more than six inches in diameter are sacrificed. Of the hundreds of species of trees in our forests, the conifers are probably most sought after for lumber. Pine, especially, is prob- ably used more extensively than any other wood. It is used in all heavy construction work, frames of houses, bridges, masts, spars and timber of ships, floors, railway ties, and many other purposes. Cedar is used for shingles, cabinetwork, lead pencils, etc. ; hemlock and spruce for heavy timbers and, as we have seen, for paper pulp. Another use for our lumber, especially odds and ends of all kinds, is in the packing-box industry. It is estimated that nearly 50 per cent of all lumber cut ultimately finds its way into the construction of boxes. Hemlock bark is used for tanning. The hard woods, ash, basswood, beech, birch, cherry, chestnut, elm, maple, oak, and walnut, are used largely for the " trim " of Transportation of lumber in the West. logging train. 138 OUR FORESTS Transportation of lumber in the East. Logs are mostly floated down rivers to the mills. our houses, for manufacture of furniture, wagon or car work, and endless other purposes. Structure of Wood. — Quite a difference in color and structure is often seen between the heartwood, composed of the dead walls of cells occupy- ing the central part of the tree trunk, and the sap wood, the living part of the stem. In trees which are cut down for use as lumber and in the manufacture of various furniture, the markings and differences in color are not always easy to understand. Methods of cutting Timber. — A glance at the diagram of the sections of timber show us that a tree may be cut radially through the middle of the trunk or tangentially to the „ 5 c middle portion. Most lumber is cut Diagrams of sections of timber : a, cross tangentially. Hence the yearly rings section; 6, radial; c, tangential, take a more or less irregular course. (From Pinchot, U.S. Dept. of Agr.) The grain of wood is caused by the OUR FORESTS 139 fibers not taking straight lines in their course in the tree trunk. In many- cases the fibers of the wood take a spiral course up the trunk, or they may wave outward to form little projections. Boards cut out of such a piece of wood will show the effect seen in many of the school desks, where the annual rings appear to form elUptical markings. Knots. — Knots, as can be seen from the diagram, are branches which at one time started in their outward growth and were for some reason killed. Later, the tree, continuing in its outward growth, surrounded them and covered them up. A dead limb should be pruned before such growth occurs. The markings in bird's-eye maple are caused by adventitious buds which have not developed, and have been overgrown with the wood of the tree. Section of tree trunk showing knot. Destruction of the Forest. By Waste in Cutting. — Man is responsible for the destruction of one of this nation's most valuable assets. This is primarily due to wrong and wasteful lumbering. A forest iu the far West totally destroyed by fire and wasteful lumberiug. Hundreds of thousands of dollars' worth of lumber is left to rot an- nually because the lumbermen do not cut the trees close enough to the ground, or because through careless felling of trees many other 140 OUR FORESTS smaller trees are injured. There is great waste in the mills. In fact, man wastes in every step from the forest to the finished product. By Fire. — Indirectly, man is responsible for fire, one of the great- est enemies of the forest. Most of the great forest fires of recent years, the losses from which total in the hundreds of millions, have been due either to railroads or to carelessness in setting fires in the woods. It is estimated that in forest lands traversed by railroads from 25 per cent to 90 per cent of the fires are caused by coal- burning locomotives. For this reason laws have been made in New York state requiring locomotives passing through the Adirondack forest preserve to burn oil instead of coal. This has resulted in a considerable reduction in the number of fires. In addition to the loss in timber, the fires often burn out the organic matter in the soil (the ''duff ") forming the forest floor, thus pre- venting the growth of forest there for many years to come. In New York and other states fires are fought by an organized corps of fire wardens, whose duty it is to watch the forest and to fight forest fires. Other Enemies. — Other enemies of the forest are numerous fungous plants of which we will learn more later, insect parasites. Our birds help protect our forests. This tree has been attacked by boring insects, but woodpeckers have dug them out and killed them. OUR FORESTS 141 which bore into the wood or destroy the leaves, and grazing animals, particularly sheep. Wind and snow also annually kill many trees. Forestry. — The American forests have long been our pride. In Germany, especially, the importance of the forest has long been recognized, and the German forester or caretaker of the forests is well known. In some parts of central Europe, the value of the forests was seen as early as the year 1300 a.d., and many towns consequently bought up the surrounding forests. The city of Zurich has owned forests in its vicinity for at least 600 years. In this country only recently has the importance of preserving and caring for our forests been noted by our government. Now, how- ever, we have a Division of Forestry of the Department of the Interior; and this and numerous state and university schools of forestry are rapidly teaching the people of this country the best methods for the preservation of our forests. The Federal Govern- ment has set aside a number of tracts of mountain forest in some of the Western states, some sixty reserves in all, making a total area of over 63,000,000 acres. New York has established for the same purpose the Adirondack Park, with nearly 1,500,000 acres of timber land. Pennsylvania has one of 700,000 acres, and many other states have followed their example. Methods for Keeping and Protecting the Forests. — Forests should be kept thinned. Too many trees are as bad as too few. They struggle with one another for foothold and light, which only a few can enjoy. In cutting the forest it should be considered as a harvest. The oldest trees are the '* ripe grain," the younger trees being left to grow to maturity. Several methods of renewing the forest are in use in this country. (1) Trees may be cut down and young ones allowed to sprout from cut stumps. This is called coppice growth. This growth is well seen in parts of New Jersey. (2) Areas or strips may be cut out so that seeds from neighboring trees are carried there to start new growth. (3) Forests may be artificially planted. Two seedlings planted for every tree cut is a rule followed in Europe. The greatest dangers are from fire and from careless cutting, and these dangers may be kept in check by the efficient work of our national and state foresters. A City's Need for Trees. — All over the United States the city governments are beginning to realize what European 142 OUR FORESTS cities have long known, that trees are of great value to a city. Many cities are spending money not only for trees, but for proper means of protection. Thousands of city trees are annually killed by horses, which " crib " upon them. This may be prevented by proper protection of the trunk. Washington spent more than $37,000 for shade trees last year; Newark, N.J., $27,000; Springfield, Mass., $21,500; and St. Louis, $14,000. Chicago has appointed a city forester, who has given the following excellent reasons why trees should be planted in the city : — WM (1) Trees are beautiful in form and color, ^K| inspiring a constant appreciation of nature. Hp[/ (2) Trees enhance the beauty of architecture. ™-^ (3) Trees create sentiment, love of country, state, city, and home. (4) Trees have an educational influence upon citizens of all ages, especially children. (5) Trees encourage outdoor life. (6) Trees purify the air. (7) Trees cool the air in summer and radiate warmth in winter. (8) Trees improve climate and conserve soil and moisture (9) Trees furnish resting places and shelter for birds. (10) Trees increase the value of real estate. (11) Trees protect the pavement from the heat of the sun. (12) Trees counteract adverse conditions of city life. Let us all try to make Arbor Day what it should be, a day for caring for and planting trees, for thus we may preserve this most important heritage of our nation. We must protect our city trees. A tree badly- wounded by " cribbing " of horses. Reference Books elementary Sharpe, A Laboratory Manual for the Solution of Problems in Biology, American Book Company. Gofif and Mayne, First Principles of Agriculture. American Book Company. Murrill, Shade Trees, Bui. 205, Cornell University Agricultural Experiment Station. Pinchot, A Primer of Forestry, Division of Forestry, U.S. Department of Agriculture. OUR FORESTS 143 ADVANCED Apgar, Trees of the United States, Chaps. II, V, VI. American Book Company. Coulter, Barnes, and Cowles, A Textbook of Botany, Part I and Vol. II. American Book Company. Goebel, Organography of Plants, Part V. Clarendon Press. Strasburger, Noll, Schenck, and Schimper, A Textbook of Botany. The Macmillan Company. Ward, Timber and Some of its Diseases. The Macmillan Company. Yearbook, U.S. Department of Agriculture, Division of Forestry, Buls. 7, 10, 13, 16, 17, 18, 20, 26, 27. XI. THE VARIOUS FORMS OF PLANTS AND HOW THEY REPRODUCE THEMSELVES Problem XX. Some forms of plant life. {Optional.) {Labo- ratory Manual, Proh. XX.) {a) An alga, (jb) A fungus. (c) A moss, id) A fern. Simplest Plant Body a Thallus. — It has been found by botanists that the plants which are the simplest in body structure are those which live in the water. Sometimes such simple plants are found upon rocks or on the bark of trees. In such plants we can distin- guish no root, stem, or leaf. The plant body may even be spherical in outline and con- sist of but a single cell. Such are the plants (pleurococcus) which give the green color to the bark of trees. Still other plants are threadlike in ap- pearance. Others, as sea- A red seaweed, an example of a thallus j t_ mi i j 1^^^ weeds, have a ribbon-shaped body. All these diverse shapes of plant body are grouped under the general name of thallus. The simplest forms of plants have a thalluslike body. Adaptation to Environment. — Plants, as well as animals, are greatly affected by what immediately surrounds them, their environ- ment. We have shown in our experiments that the environment (conditions of temperature, moisture, soil, etc.) is capable of chang- ing or modifying the structure of plants very greatly. The changes which a plant or animal has undergone, that jit it for conditions in which it lives, are called adaptations to environment, 144 THE VARIOUS FORMS OF PLANTS 145 The principal factors which act on plants and which make up their environment are soil, water, temperature, and light. The first plants • were prol^ably water-loving forms. It seems likely that, as more land appeared on the earth's surface, plants became adapted to changed conditions of life on dry land. With this change in habit came a need of taking in water, of storing it, of conducting it to various parts of the organism. So it does not seem unlikely that plants came to have roots, stems, and leaves, and thus became adapted to their environment on dry land. We find in nature that those plants or animals which are best adapted or fitted to live under certain conditions are the ones which survive or drive other competitors out from their immediate neighborhood. Nature selected those which were best fitted to live on dry land, and those plants eventually covered the earth with their progeny. Eventually, the forms of life grew more and more complex until at last very complicated organisms such as the flowering plants came to live upon the earth. Between the flowering plant and the simplest of all plants are several great plant groups which act as steps in complexity of structure between the most lowly and the most highly specialized plants. The simplest of all these forms are the alga?. Algae. — The algae are a diverse collection of plants, containing some of the smallest and simplest as well as some of the largest plants in the world. The tiny one-celled plant wliich lives on the bark of trees is an example of the former ; the giant kelp of the Pa- cific Ocean, which attains a length of over one thousand feet, of the latter. The body of the algas is a thallus, which may be platelike, circular, ribbon-formed, thread- like, or filamentous. It may even be composed of a single cell. A large number of the algae inhabit the water, fresh and salt. In color they vary from green through the shades of blue-green to yellow, brown, and red. The latter colors are best seen in the seaweeds, all of wliich, how- HUNT. ES. BIO. — • 10 A red seaweed, showing a finely divided thallus body. 146 THE VARIOUS FORMS OF PLANTS ever, contain chlorophyll. In the red and brown seaweeds the chloro- phyll is concealed by other coloring material in the plant body. In the olive-brown fucus (the common rockweed) it is easy to prove the presence of chlorophyll by cutting open the bladders which are found in the plant body. The red seaweeds are among the most beautiful and delicate of all plants. They may be mounted under water upon cardboard and then studied after drying. Rockweed, a brown alga, showing the distribution on rocks below high-water mark. Green Algae. — The plants known as the green algse are of more interest to us because of their distribution in fresh water, and also beqause of their economic importance as a supply of oxygen for fish and other animals in the waters of our inland lakes and rivers. Our attention is called to them in an unpleasant way at times, when, after multiplying very rapidly during the hot summer, they die rapidly in the early fall and leave their remains in our water supply. Much of the unpleasant taste and odor of drinking water comes from this cause. Pond Scum (Spirogyra). — This alga is well known to every boy or girl who has ever seen a small pond or sluggish stream. It grows as a slimy mass of green threads or filaments. Frequently it is so plentiful as almost to cover the surface of the water, buoyed THE VARIOUS FORMS OF PLANTS 147 up by little bubbles of a gas which seems to arise from the body of the plant. If we collect some of this gas, we can easily prove that it is oxygen. The person who sees a pond with a covering of slimy 1 1 ^ — > SI '«\ A, jar of water containing pond scum ; B, same jar after an hour in the sunlight ; the pond scum has risen to the top of the jar, buoyed up by the oxygen formed within it. pond scum, knowing this fact, should no longer feel that the pond is a menace to health, unless it is a place where mosquitoes live and breed. Under the low power of the microscope, the body of a pond scum Spirogyra : n, nucleus ; s, chlorophyll bands. is seen to be a thread made up of elongated cylindrical cells, each of which contains a spirally wound band of chlorophyll within it. 148 THE VARIOUS FORMS OF PLANTS Careful study shows the presence of strands held in the body of the cell by strands of protoplasm, the remainder of the space within the cell being occupied by the cell sap. Pond scum may grow by a simple division of the cells in a fila- ment. This method of asexual reproduction is the way growth takes place in the cells of the root, stem, or leaf of a flowering plant, but another method of reproduction is also seen in pond scum. The cells of two adjoining filaments may push out tubes which meet, thus connecting the cells with each other. Meantime the protoplasm of the cells thus joined condenses into two tiny spheres ; the bands of chlorophyll are broken down, and ulti- mately the contents of one of the cells passes over the tube and mingles with the cell of the neigh- boring filament, with which it was previously con- nected by the tube formed from the cell walls. The result of this process of fusion is a thick- walled resting cell which we call a zygospore. Conjugation. — The process in which two cells of equal size unite to form a single cell is called conjugation. It is believed to be a sexual process which corresponds in a way to the fertihzation in the higher plants.^ This cell thus formed can withstand considerable extremes of heat and cold, and may be dried to such an extent that it is found in dust or in the air. Under favorable conditions, this spore will germinate and produce a filament. Pleurococcus. — Many other forms of algse are well known to us. One of the simplest is ^^-^'--^ r pleurococcus. This httle plant consists of a pieurococcus. ^.single cell; smgle tmy cell, which by division may give b, colony of four cells rise to two, three, four, or even more cells formed from the original which cling together in a mass. The green cell A. ^ Material which shows conjugation is not always easy to obtain. Conjugation usually takes place most freely in the fall of the year. When material is obtained, it may be preserved in a 4 per cent solution of formol. Material killed in a 5 per cent solution of chromic acid and then preserved in 70 per cent alcohol or 4 per cent formol shows the details of cellular structure. Conjugation of Spirogyra; zs, zygospore; /, fusion in progress. THE VARIOUS FORMS OF PLANTS 149 color on tree trunks, stone houses, etc., is due to millions of these little plants. Diatoms. — These plants are found in vast numbers living on the mud or stones at the bottom of small streams. The plant body is inclosed in a cell wall composed largely of silica. Many of the diatoms are free-swimming. They compose a large percentage of the living organisms found near the ocean's surface. Diatoms are found as fossils, and make up a large proportion of many rocks. The siliceous skeletons in such rocks are of commercial importance, the rock forming a basis for polishing powders. Various forms of Di- atoms. Fungi, Parasites, and Saprophytes. — The thallus plants may be grouped in two great divisions: the Alg(£, water-loving ihallophytes containing chlorophyll, and the Fungi, thallus plants which do not contain chlorophyll. As a direct result of the lack of chlorophyll in the cells, the fungi are unable to make their own food. They must obtain food from other plants or animals. Some take up their abode upon living plants or ani- mals {in which case they are called parasites) ; others obtain their food from some dead organic matter. The latter are called saprophytes. The above facts make the group of the fungi of immense economic importance to man. Mold {Rhizopus nigricans). — One of the most common of all our fungi is the black mold which appears growing upon bread, cake, and other organic substances under certain con- ditions of temperature and moisture. The tangled mass of threads which cover the bread is called the mycelium, each thread being called a hypha. Many of the hyphse are prolonged into tiny upright threads, bearing at the top a httle ball. With the low power of the microscope each of these struc- tures is seen to contain many tmy bodies called spores. These Bread mold : r, rhizoids ; s, sporangium. 150 THE VARIOUS FORMS OF PLANTS spores have been formed by the division of the protoplasm mak- ing up the ball or sporangium into many separate bodies. This method of the production of spores is evidently asexual. These spores, if grown under favorable conditions, will produce more mycelia, which in turn bear sporangia. It has been found, however, that at some time during the life of the mold another method of reproduction is likely to occur. Formation of Zygospores. — Two hj^hse which are close-lying put out threads which communicate. The end of each of the threads cuts off a cell, and the two cells, each from a different hypha, flow together and mingle. In this condi- tion they remain as a single resting cell. This cell, which puts a heavy D wall around itself, is a zygospore. Here again we have a process of con- jugation similar to that we observed in the pond scum. The ultimate re- sult of the conjugation of the two cells is that a new plant grows from the zygospore after a period of rest. Dur- ing the resting stage the spore may undergo very unfavorable conditions, even to extreme dryness, heat, or cold. Conjugation of black mold : A, The use of the zygospore to the plant B, c, D, successive stages in jg evidently to Continue the species the formation of the zygospore, ^^^.j^^ ^^ unfavorable time in the Hfe history of the plant. The process of conjugation is probably a sexual process, as we have called it in pond scum. Physiology of the Growth of Mold. — Mold, in order to grow rapidly, evidently needs oxygen, moisture, and heat. It obtains its food from the material on which it lives. This it is able to do by means of digestive ferments which are given out by the rhizoids or rootlike parts of the hyphse, by means of which the mold clings to the bread. These ferments change the starch of 1 It seems to have been proved recently that zygospores are formed by the union of two cells, from different filaments, one of which has male, the other female, char- acters. THE VARIOUS FORMS OF PLANTS 151 the bread to sugar and the proteid to a soluble form which will pass by osmosis into the hypha?. Thus the plant is enabled to absorb the material. This food is then used to supply energy and make protoplasm. This seems to be the usual method by which saprophytes assimilate the materials on which they live. Other Saprophytic Fungi. — The mushroom resembles a tiny umbrella. The upper part is known to botanists as the cap ; the cap is held up by a stalk or stipe. The under surface of the cap discloses a number of struc- tures which radiate out from the central stipe to the edge of the cap. These are the gills. If you place the cap of a mush- room gills downward on the surface of a piece of white paper, being careful not to dis- turb for at least twelve hours, it will be found that when tho cap is removed a print of the shape and size of the gills re- mains on the paper. This is a spore print. It has been caused by the spores of the plant, which have fallen from the place where they were formed between the gills to the surface of the paper. Mycelium. — The mushroom is, then, the spore-bearing part of the plant. Where is the plant body? This question is an- swered if we dig up a little of the earth surrounding a mush- room. In the rich black soil is seen a mass of little whitish threads. These tlu-eads form the mycelium of the fungus. The hyphse of this part of the plant body take food from the organic matter in the soil and digest it in the same manner as did the hyphas of black mold. The mushroom is a saprophyte. No sexual stage has yet been discovered. Food Value of Mushrooms. — The food value of the edible mushroom has been much overestimated. Recent experiments seem to show that, although they have a sUght food value, they are far from taking the place of nitrogenous foods, as was formerly believed by scientists. Other Fungi. — Many other plants, both useful and harmful to man, belong in this group ; among them are the yeasts, the various parasitic Mushrooms ; the younger specimen, at the right, shows the mycehum. Photographed by Overton. 152 THE VARIOUS FORMS OF PLANTS rusts and smuts, causing plant diseases, and, most important of all, the bacteria. We shall consider several of these plants later in their direct relation to the human race. Mosses Mosses are mostly shade-loving and moisture-loving plants. They form velvety carpets in many of our forests, but they often show their preference for moist localities by covering the wooded shores of lakes and swamps. Pigeon-wheat Moss. — One of the mosses frequently seen and easily recognized i^ the so-called pigeon- wheat moss {Polytrichum commune). Unlike some mosses, it often inhabits dry localities. It may be found on some dry hillock close to the edge of the woods, where it forms a reddish brown carpet. This red color is due largely to the pres- ence of a great number of little upright stalks, bearing at the summit tiny cap- sules, which seem to grow up from the leafy moss plant. The resemblance of a large number of these stalks and capsules to a mimic field of grain has given the name pigeon- wheat moss to this form. Forms of Plants. — Three kinds of moss plants appear to be present : leafy plants, others bearing a stalk and cap- sule, and still others which terminate at the end in a little rosette of leaves, in- closing what appears to be a tiny flower. Leafy Moss Plant. — A leafy moss plant has rhizoids or hairlike roots, an upright stem, and green leaves. In the plants which have a stalk and capsule, the stalk grows directly from the end of the leafy plant. This capsule is provided with an outer cap which seems to have somewhat the structure of a thatched roof. Under the cap is found a lid, or cover, to the capsule. If this cover is removed and the capsule turned upside down, the dust that escapes will be found to be made up of a great number of spores. Sporophyte. — The capsule is the spore-producing part {sporangium) of the moss plant. The stalk and cap- sule together form the sporophyte or spore-producing generation of the moss. Two moss plants, showing the gametophyte (G) and the sporo- phyte iS). THE VARIOUS FORMS OF PLANTS 153 If we were to plant the spores of the moss in damp sand, taking care to keep the sand moist and warm, we might get them to grow. The spore germinates into a threadlike structure, very tiny, and not at all like the adult moss j)lant. This thread is called a prolonema. Adult Moss Plants. — The protonema soon develops rhizoids ; tiny buds appear which in time form the adult moss j)lant. These adult plants may grow only leaves, and become what are known as sterile plants; or they may develop into a plant that bears at the summit the little ro?ette of leaves previously referred to. Within the rosette lie a number of tiny organs which hold large numbers of sperm cells. Other moss plants not so tall as the sperm-producing plants bear at the summit of the stem a tuft of leaves which hide a number of small flask-shaped structures, each of which contains a single egg cell. These pUints form the sexual genera- tion of the moss. This stige of the -plant is called the gametophyte, because it produces the gametes or sexual cells, — eggs and sperms. After a sperm cell has been transferred (usually by means of a drop of dew) to the egg cell, a fusion of the two cells takes place. This, we remember, is the pro- cess of fertilization. In the mosses the fertilization of the egg cell results in the growth of that part of the plant which forms and bears the asexual spores. Alternation of Generations. — In the mosses we have what is known as an alternation of generations. The leafy moss, bearing among its leaves the organs producing sperms and eggs, antheridia and archegonia, gives place to a stalk and capsule bearing the asexual spores. This spore-bear- ing portion of the plant does not appear until after fertilization ; then it grows directly out of that part of the plant which produces the egg cell. In fact, if we make a microscopic examination of the egg-producing struc- ture (the archegonium) directly after fertilization, we find that the sporo- phyte is a direct outgrowth from the fertilized egg cell. Thus the sexual stage alternates with the asexual stage in the life of the plant. Sporophyte a Parasite. — One interesting fact comes out in connection with this growth of the sporophyte. It has no green leaves and must therefore obtain all its nourishment from the leafy moss plant, or game- tophyte. The spore-bearing part of the plant is thus actually a parasite upon the gametophyte. Ferns and their Allies The Ferns and their Allies. — The fern plants include the true ferns, the horsetails or scouring rushes, and the club mosses. The true ferns are moisture-loving and shade-loving plants ; they play an important part in the vegetation of the tropical forests. Many forms are found in the temperate regions ; we even have some common ferns that remain green all winter. Fossil ferns have been found in Greenland, thus showing that at one time the climate at the north was milder than it now is. 154 THE VARIOUS FORMS OF PLANTS A common fern is the polypody (Polypodium vulgare), the habitat of which is damp woods and rocky glens. These ferns are hard to pro- cure entire, as they have an underground stem, from which at intervals the leaves or fronds arise. The leaflets or pinnce at certain seasons show a series of little brown dots on the under surface. These structures, called col- lectively the sori (singular sorus), are made up of a number of tiny spore cases. These spore cases, or sporan- gia, hold the asexual spores. These spores under favorable conditions of heat and mois- ture may germinate to form a tiny thread of cells which soon develops into a flat, heart-shaped body not much bigger than a pinhead, called a prothallus. Prothallus. — The pro- thallus clings to the surface of the ground by means of its rhizoids. A careful examina- tion of the prothallus with a compound microscope reveals the fact that scattered among the rhizoids are some tiny rounded elevations ; immedi- ately above the rhizoids and between them and the little groove (see Fig- iu*e) in the prothallus are other structures ; both the above structures are too minute to find with the naked eye. Archegonia. — The last named are archegonia; they are found to be very tiny flask-shaped organs almost embedded in the surface of the prothallus. Each archegonium contains a single large egg cell. Antheridia. — The other structures found among the rhizoids are the antheridia. Each antheridium contains a large number of very minute objects which are able to move about in water by means of lashlike threads of pro- toplasm. Each of these motile cells is called an antherozoid ; they have, in fact, the 'same function as the sperm cells of the flowering plants. Because this part of the plant holds the egg cells and sperm cells, we recognize it as the sexual generation of the fern. Rock fern, polypody. Notice the underground stem giving off roots {R) from its under sur- face, and leaves (C) from the upper surface. The compound leaf or frond may bear sori (- in cc^utrcU \r\v York. of the ground is frozen, thus preventing w^ater from finding its way below the surface ; on the other hand, during excessive rains in the spring it might exist for a time under almost hydrophytic conditions. But many trees are annually killed in districts where lumbering is going on through the damming of streams and forma- tion of artificial ponds, which increase the water supply of the trees near by and soon kill them. Other Factors. — It is a matter of common knowledge that plants in different regions of the earth differ greatly from one another in shape, size, and general appearance. If we study the causes for PLANTS MODIFIED BY THEIR SURROUNDINGS 163 these changes, it becomes evident that the very same factor, water supply, which governs hydrophytic, xerophytic, and mesophytic conditions, determines, at least in part, the habits of the plants growing in a given region — be it in the tropics or arctic regions. But in addition to water supply, the factors of temperature, light, soil, wind, etc., all play important parts in determining the form and structure of a plant. The effect of wind upon txees in an exposed location. Photograph by W. C. Barbour. Cold Regions. — Here plants, which in lowland regions of greater warmth and moisture have a tall form and luxuriant foliage, are stunted and dwarfed ; the leaves are smaller and tend to gather in rosettes, or are otherwise closely placed for warmth and protection. As we climb a mountain we find that the average size of plants decreases as we approach the Une of perpetual snow. The largest trees occur at the base of the mountains ; the same species of trees near the summit appear as mere shrubs. Continued cold and high winds are evidently the factors which most influence the slow growth and the size and shape of plants near the mountain tops. Cold, 164 PLANTS MODIFIED BY THEIR SURROUNDINGS little light during the short days of the long winter, and a slight amount of moisture all act upon the vegetation of the arctic region, tending toward very slow growth and dwarfed and stunted form. Polar limit of trees, northern Russia. All these trees are full grown, and most of them are almost one hundred years old. Vegetation of the Tropics. — A rank and luxuriant growth is found in tropical countries with a uniformly high temperature and large rainfall. In general it may be estimated that the rainfall in such countries is at least twice as great as that of Region of Lichens. Region of Grasses. Shrubby Region. 5Z5y!MJl WV?SM\^^'"" °' cinchona t ^ /^^^^^^^%"^^^^i^UmltotOTdin&Ty\argetTeefi. NcW York StatC, y^r:^^.!^^^^ .^ ,., as great. -^ ■ ' <.*A>"^^^Jrv''trT^ Region of Palms. ***^ &ic«,u , T i:^:r>P^yikyj:. l^^^^ abundant Regions of the Vine. \ Region of Tree-ferns. and in many cases three to four times An water Plant regions in a tropical mountain. Explain the diagram. Supply, together PLANTS MODIFIED BY THEIR SURROUNDINGS 165 with an average temperature of over 80° Fahrenheit, causes ex- tremely rapid growth. One of the bamboo family, the growth of which was measured daily, was found to increase in length on the average nearly three inches in the daytime and over five inches during each night. The moisture present in the atmosphere allows the growth of many air plants (epiphytes), which take the moisture directly from the air Iw means of aerial roots. Conditions in a moist, s.-niitropical forest. The so-called "Plorida moss" is a flowering plant. Notice the resurrection ferns on the tree trunk. The absence of cold weather in tropical countries allows trees to mature without a thick coating of bark or corky material, plants all having a green and fresh appearance. Monocotyledo- nous plants prevail. Ferns of all varieties, especially the largest tree ferns, are abundant. Plant Life in the Temperate Zones. — In the state of New York, conditions are those of a typical temperate flora. Extremes of cold and heat are found, the temperature ranging from 30° Fahren- heit below zero in the winter to 100° or over in the summer. Condi- tions of moisture show an average rainfall of from 24 inches to 52 166 PLANTS MODIFIED BY THEIR SURROUNDINGS inches. Conditions of moisture in the country cause great differ- ences in the plant covering. In the eastern part of the United States the rainfall is sufficient to give foothold to great forests, which aid in keeping the water in the soil. In the Middle West the rainfall is less, the prairies are covered with grasses and other plants which have become adapted to withstand dryness. In the desert region of the Southwest we find true xerophytes, cacti, switch plants, yuccas, and others, all A rock society. Photograph by W. C. Barbour. plants which are adapted to withstand almost total absence of moisture for long periods. In the Temperate Zone the water supply is the primary factor which determines the form of plant growth. Plant Formations and Societies.^ — All of the factors alluded to act upon the plants we find living together in a forest, a sunny 1 Plant Societies. Field Work. — Any boy or girl who has access to a vacant lot or city park can easily see that plants group themselves into societies. Certain plants live together because they are adapted to meet certain conditions. Societies of plants exist along the dusty edge of the roadside, under the trees of the forest, along the edge of the brook, in a swamp or a pond. It should be the aim of the field trips to learn the names of plants which thus associate themselves and the condi- tions under which they live, and especially their adaptations to the given conditions. Suggestions for such excursions are found in Andrews, Botany All the Year Round; Lloyd and Bigelow, The Teaching of Biology ; and Ganong, The Teaching Botanist. A convenient form for an excursion is found in Hunter and Valentine, Manual, page 202. This trip may be taken in the early fall. PLANTS MODIFIED BY THEIR SURROUNDINGS 167 meadow, along a roadside, or at the edge of a pond. Any one familiar with the country knows instinctively that we find certain plants, and those plants only, living together under certain condi- tions. For example, the wild columbine, certain ferns, and mosses, and other shade, moisture, and rock-loving plants are found to- gether on rocky, shaded hillsides. We should not think of looking for daisies and buttercups there any more than we should look for v.^- # '3I^- Plant societies near a pond. Notice that the plant groups are arranged in zones with reference to the water supply, the true mesophytes being in the background. the marsh marigold (Caltha paliistris) or the pickerel weed {Ponte- deria cor data) in a dry and sunny field. Plants associated under similar conditions, as those of a forest, meadow, or swamp, are said to make up a formation, and a plant formation is brought about by the conditions of its immediate surroundings, the habitat of its members. If we investigate a plant formation, we find it to be made up of certain dominant species of plants ; that here and there definite communities exist, made up of groups of the same kind of plants. We can see that every one of these plant groups in the society evidently originally came from single individuals of species which thrive under the peculiar condi- tions of soil, water, light, etc., that we find in this spot. These 168 PLANTS MODIFIED BY THEIR SURROUNDINGS single plants have evidently given rise to the members of each Httle family group, and thus have populated the locality. So we find among plants communal conditions similar to those among some animals. The many individuals of the community live under similar conditions; they need the same substances from the air, the water, the soil. They all need the light; they use the same food. Therefore there must be competition among them, especially between those near to each other. The plants which are strongest and best fitted to get what they need from their surround- ings live; the weaker ones are crowded out and die. But their lives are not all competition. The dead plants and animals give nitrogenous material to the living ones, from which the latter make living matter ; some bacteria provide cer- tain of the green plants with nitrogen ; many of the green plants make food for other plants lacking chlorophyll, while some algse and fungi actually live together in such a way as to be of mutual benefit to each other. The larger plants may shelter the smaller ones, protect- ing them from wind and storm, while the trees hold the moisture in the ground, giving it off slowly to other plants. Animals scatter and plant the seeds far and wide, and man may even plant entire colonies in new localities. How Plants invade New Areas. — New areas are tenanted by plants in a similar manner. After the burning over of a forest, we find a new generation of plants springing up, often quite unlike the former occupants of the soil. First come the fireweed and other light-loving weeds, planted by means of their wind-blown seeds. With these are found patches of berries, the seeds of which were brought by birds or other animals. A little later, quick-growing trees having seeds easily carried for some distance by the Tvnnd, A community of trilliums. Photograph by W. C. Barbour. PLANTS MODIFIED BY THEIR SURROUNDINGS 169 like the aspen and wild cherry, which have the birds to help them out, invade the territory. Eventually we may have the area re- tenanted by its former inhabitants, especially if the destruction of the original forest was not complete. In like manner, on the upper mountain meadow or by the sand dunes of the seashore, wherever plants place their outposts, the A plant outpost. Tiu' struKult- li< n' is keen. Tlie advaiicing sand has killed the trees in the foreground. advance is made from some thickly inhabited area, and this advance is always aided or hindered by agencies outside of the plant — the wind, the soil, water, or by animals. Thus the seeds obtain a foot- hold in new territory, and thus new lands are captured, held, and lost again by the plant comnmnities. Reference Books elementary Sharpc, A Laboratory Manual for the Solution of Problems in Biology. Book Company. Andrews, Botany All the Year Round. American Book Company. Bergen and Davis, Principles of Botany. Ginn and Company. Coulter, Plant Relations. D. Appleton and Company. Leavitt, Outlines of Botany. American Book Company. Stevens, Introduction to Botany. D. C. Heath and Company. American ADVANCED Clements, Plant Physiology and Ecology. Henry Holt and Company. Coulter, Barnes, and Cowles, A Textbook of Botany, Vol. II. American Book Com- pany. Kerner, Natural History of Plants. 4 vols. Henry Holt and Company. Schimper, Plant Geography. Clarendon Press, XIII. HOW PLANTS BENEFIT AND HARM MANKIND Problem XXII, Tlie relations of fungi to man. {Laboratory Manual, Proh. XXIL) (a) Yeast, (h) Other fungi. The Economic Value of Plants. — Besides the other relations existing between plants and animals, there is a relation between man and plants measurable in dollars and cents. Plants are of direct value or harm to man. We call this an economic relation. We have seen how they supply him with his cereals and flour, his fruits and garden vegetables, his nuts and spices, his beverages and the sugar to sweeten them, his medicines and his dyestuffs. They supply the material out of which many of his clothes are made, the thread with which they are sewed together, the paper which covers the package in which they are delivered, and the string with which the package is tied. The various uses of the forest have been mentioned before; the need of trees to protect the earth, their usefulness in the holding of the water supply, their direct economic- importance for lumber and firewood. Many of us forget, too, that much of the energy released on this earth to man as heat, light, or motive power comes from the dead and compressed bodies of plants which thousands of years ago lived on the earth and now form coal. Plants are thus seen to be of immense direct economic importance to mankind. The Harm Plants Do. — Unfortunately, plants do not all benefit mankind. We have seen the harm done by weeds, which scatter their numerous seeds far and wide or by other devices gain a foot- hold and preempt the territory which useful plants might occupy were they able to cope with their better-equipped adversaries. Plants with poisonous seeds and fruits are undoubtedly responsi- ble for the death of many animals. But by far the most harmful plants to mankind are the fungi. 170 • HOW PLANTS BENEFIT AND HARM MANKIND 171 Hundreds of millions' yearly damage may l)o laid directly to them. More than that, they are doubtless responsible for one half of the total human deaths. This is because of their parasitic habits. Yeast. — Although as a group the fungi are harmful to man in the economic sense, nevertheless there are some fungi that stand in a decidedly helpful relationship to the human race. Chief of these are the yeast plants. Yeasts are found to exist in a wild state in very many parts of the world. They are found on the skins of fruits, in the soil of vineyards and orchards, in cider, beer, and other fluids, while they may exist in a dry state almost anywhere in the air around us. In a culti- vated state we find them doing oiu* work as A, yeast plant bud just form- the agents which cause the rising of bread, ing ; B, bud almost ready and the fermentation in beer and other alco- to l^^ve parent cell. Note holic fluids. **^^ ""^^^"« (^ dividing Size and Shape, Manner of Growth, etc.- ^"'^J^^J^'f' (^fterSedg- _- ^ 1 . 1 * • wick and Wilson.) The common compressed yeast cake contains millions of these tiny plants. In its simplest form a yeast plant is a single cell. If you shake up a bit of a compressed yeast cake in a mixture of sugar and water and then examine a drop of the milky fluid after it has stood overnight, it will be seen to contain vast numbers of yeast plants. The shape of such a plant is ovoid, each cell showing under the micro- scope the granular appearance of the protoplasm of which it is formed. Look for tiny clear areas in the cells ; these are vacuoles, or spaces filled with fluid. The nucleus is hard to find in an unstained yeast cell; it can, however, be found in specimens which liave been prepared by stain- ing the previously killed cells with iron-hsematoxylin.* Yeast cells repro- duce very rapidlj^ by a process of budding, a part o^ the parent cell forming one or more smaller daughter cells which eventually become free from the parent. Most yeast plants seem to produce spores at some time during their existence. The spores are formed within a yeast cell, as many as four being produced within a single cell. These spores, under proper condi- tions, will germinate and give rise to new plants. Conditions favorable to Growth of Yeast. — Under certain conditions yeast, when added to dough, will cause it to rise. We also know that yeast has something to do with the process we call fermentation. The following home experiment will throw some light on these points : — Label three pint fruit jars A, B, and C. Add one fourth of a com- pressed yeast cake to two cups of water containing two tablespoonfuls of molasses or sugar. Stir the mixture well and divide it into three equal > See Lee, Vade Mecum, or Sedgwick and Wilson, General Biology. 172 HOW PLANTS BENEFIT AND HARM MANKIND parts and pour them into the jars. Place covers on the jars. Put jar A in the ice box on the ice, and jar B over the kitchen stove or near a radiator ; boil the jar C by immersing it in a dish of boiling water, and place it next to B. After forty-eight hours, look to see if any bubbles have made their appearance in any of the jars. If the experiment has been successful only jar B will show bubbles. After bubbles have begun to appear at the surface, the fluid in jar B will be found to have a sour taste and will smell unpleasantly. The gas which rises to the surface, if collected and tested, will be found to be carbon dioxide. The contents of jar B are said to have fermented. Evidently, the growth of yeast will take place only under conditions of moderate warmth and moisture. Fermentation a Chemical Process. — In this process of growth the sugar of the solution in which they live is broken up by a digestive fer- ment or enzyme into carbon dioxide and alcohol. This may be expressed by the following chemical formula: CeHisOe = 2(C2H60) + 2(C02). This means that the sugar forms alcohol and carbon dioxide. This pro- cess, which we call fermentation, is of the greatest importance in the brewing industry. Beer-Making. — Brewers' yeasts are cultivated with the greatest care ; for the different flavors of beer seem to depend largely upon the condi- tion of the yeast plants. Beer is made in the following manner : Sprouted barley, called malt, in which the starch of the grain has been changed to grape sugar by digestion, is killed by drying in a hot kiln. The malt is dissolved in water, and hops are added to give the mixture a bitter taste. Now comes the addition of the yeast plants, which multiply rapidly under the favorable conditions of food and heat. Fermentation results on a large scale from the breaking down of the grape sugar, the alcohol re- maining in the fluid, and the carbon dioxide passing off into the air. The process is stopped at the right instant, and the beer is stored either in bottles or casks. Bread-Making. — In bread-making the rapid growth of the yeast plants is facilitated by placing the pan containing the mixture in a warm place overnight. Fermentation results from the digestion of grape sugar by the yeasts, this grape sugar being part of the starch in the flour which is changed by the diastase present in the grain of wheat. The carbon dioxide remains in the dough as the bubbles so familiar to the bread- maker, the alcohol produced being evaporated during the process of baking. Yeast Saprophytes. — The above paragraphs show yeast plants to be saprophytes. In order to grow, they must be supplied with food materials that will build up protoplasm as well as release energy. This food they obtain from the organic matter in the fluids in which they happen to be. The Shelf Fungus ; a Saprophyte. — A near relation to the mush- room is the bracket or shelf fungus. This fungus is familiar to any one who has been in a forest in this part of the country. HOW PLANTS BENEFIT AND HARM MANKIND 173 An examination of specimens shows that the shelf or bracket is in reaUty a spore case, which is usually provided with a very con- siderable number of holes, slits, or pores in which the spores are formed. The spores when ripe escape from the under surface of the spore-bearing body through the minute pores. The mycelium is within the tissue of the tree. Remove the bark from any tree infected with bracket fungus, and you will find the silvery threads of the myce- lium sending their greedy hyphue to all parts of the wood adjacent to the spot first attacked by the fungus. This fungus begins its life by the lodgment of a spore in some part of the tree which has become diseased or broken. Once established on its host, it spreads rapidly. There is no remedy except to kill the tree and burn it, so as to destroy the spores. Many fine trees, sound except for a slight bruise or other injury, are annually infected and eventually killed. In cities thousands of trees become infected through careless hitching of horses so that the horse may gnaw or crib on the tree, thus exposing a fresh surface on which spores may obtain lodg- ment and grow (see page 142). Shelf or bracket fungi on dead tree trunk. Suggestions for Field Work. — A field trip to a park or grove near home may show the great destruction of timber by this means. Count the number of perfect trees in a given area. Compare it with the number of trees attacked by the fungus. Does the fungus appear to be transmitted from one tree to another near at hand ? In how many instances can you discover the point where the fungus first attacked the tree? Parasitic Fungi. — Of even more importance are the fungi that attack a living host, true parasites. The most important of such 174 HOW PLANTS BENEFIT AND HARM MANKIND plants from an economic standpoint are the rusts, smuts, and mil- dews which prey upon grain, corn, and other cultivated plants. Some fungi are also parasitic upon fruit and shade trees. The chestnut canker, a fungus recently introduced on chestnuts planted near New York city, has within five years practically de- stroyed all the chestnut trees within a radius of twenty miles of the city, and is estimated to have done $10,000,000 damage already. Damage extending to hundreds of millions of dollars is annually done by the fungi. Corn smut, a fungus parasitic on corn ; the black mass consists almost entirely of ripe spores. Wheat Rust. — Wheat rust is probably the most destructive parasitic fungus. For hundreds of years wheat rust has been the most dreaded of plant diseases, because it destroys the one harvest upon which the civilized world is most dependent. For a long time past the appear- ance of rust has been associated with the presence of barberry bushes in the neighborhood of the wheat fields. Although laws were enacted nearly two hundred years ago in New England to provide for the destruction of barberry bushes near infected wheat fields, nothing was actually known of the relation existing between the rust and the barberry until recently. It has now been proved beyond doubt that the wheat rust passes part of its life as a parasite on the barberry and from it gets to the wheat plant, where it undergoes a complicated life history. The wheat leaf, its nour- ishment and living matter used as food by the parasite, soon dies, and no grain is produced. Some wheat rusts do not have two hosts, living only on the wheat and wintering over by means of thick-walled spores which remain in the stubble or in the ground until the young wheat plants appear the following year. Mildews. — Another group of fungi that are of considerable economic importance is made up of the sac fungi. Such fungi are commonly called mildews. Some of the most easily obtained specimens come from the Ulac, rose, or willow. These fungi do not penetrate the host plant to any depth, but cover the leaves of the host with the whitish threads of the mycelium. Hence they may be killed by means of applications of some fungus-kill- ing fluid, as Bordeaux mixture.^ They obtain their food from the outer 1 See Goff and Mayne, First Principles of Agriculture, page 59, for formula of Bordeaux mixture. HOW PLANTS BENEFIT AND HARM MANKIND 175 layer of cells in the leaf of the host. Among the useful plants preyed upon by this group of fungi are the plum, cherry, and peach trees. (The diseases known as ])lack knot and peach curl are thus caused.) Other sac fungi are the morels and truffles, the downy mildews, blue and green molds, and many other forms. One important member of this group is the tiny parasite found on rye and other grains, which gives us the drug ergot. Problem XXTII. A study of bacteria and of some of their relations to man. (Laboratory Manual, Frob. XXIIIJ (a) Conditions of gi'owth. (jb) Some relations to man. (c) Som,e methods of fighting Jiarmful bacterid. Bacteria, — The bacteria are found in the earth, the water, and the air. " Anywhere but not everywhere," as one writer has put it. They swarm in stale milk, in impure water, in the liv- ing bodies of plants and animals, and in any decaying material. These tiny plants, " man's invisible friends and foes," are of such importance to mankind that thou- sands of scientists devote their whole lives to their study, and a science called bac- teriology has been named after them. Size and Form. — In size, bacteria are the most minute plants known. A bac- terium of average size is about inrVg- of an inch in length, and perhaps 25000 of an inch in diameter. Some species are much larger, others smaller. A common spheri- cal form is 3~5 on of an inch in diameter. It will mean more to us, perhaps, if we re- member that several millions of bacteria of average size msLj be placed within the area formed in this letter 0. Three well-defined forms of bacteria are recognized : a spheri- cal form called a coccus, a rod-shaped bacterium, the bacillus, and a spiral form, the spirillum. Some bacteria are capable of movement when living in a fluid. Such Bacteria, highly magnified : a, the germ of typhoid fever, stained to show the cilia, little threads of liv- ing matter by means of which locomotion is ac- complished ; b, a spiral ciliated form ; c, a rod- shaped form, in chains ; d, a spherical form. — a, b, from Engler and Prantl. 176 HOW PLANTS BENEFIT AND HARM MANKIND movement seems to be caused by tiny lashlike threads of proto- plasm called cilia. The cilia project from the body, and by a rapid movement cause locomotion to take place. Bacteria reproduce with almost incredible rapidity. It is estimated that a single bacterium, by a process of division called fission, will give rise to over 16,700,000 others in twenty-four hours. Dr. Prudden has estimated that such a bacterium, if allowed to develop unchecked for five days, would fill all the oceans of this earth to a depth of one mile. Under unfavorable conditions they stop dividing and form spores, in which state they remain until conditions of temperature and moisture are such that growth may begin again. Method of Study. — In order to get a number of bacteria of a given kind to study, it becomes necessary to grow them in what is known as a pure culture. This is done by first growing the bacteria in some medium such as beef broth, gelatin, or on potato.^ The material used as a growth medium is at first sterilized by heating to such a temperature as to kill all life that might be there. If the material is exposed to the air of the schoolroom in a shallow dish (known as a Petri dish), or in a test tube in the case of beef broth, for say five minutes, and if then the dish or tube is covered and put away in a warm place for a day or two, little spots will appear on the surface of the gelatin or potato, or the beef broth will become cloudy. Pure Culture. — The spots are colonies composed of millions of bacteria. If now we wish to study one given form, it becomes nec- essary to isolate them from the others on the plate. This is done by the following process : A platinum needle is first passed through a flame to sterilize it; that is, to kill all living things that maybe on the 1 For directions for making a culture medium, see Peabody, Manual of Physiology. Culture tubes may be obtained, already prepared, from Parke, Davis, and Company. A Petri dish culture of bacteria ; the colo- . uies of bacteria are the little spots of various size and color. HOW PLANTS BENEFIT AND HARM MANKIND 177 needle point. Then the needle, which cools very quickly, is dipped in a colony containing the bacteria we wish to study. This mass of bacteria is quickly transferred to another sterilized plate, and this plate is immediately covered to prevent any other forms of bacteria from entering. When we have succeeded in isolating a certain kind of l)acteria in a given dish, we are said to have a pure culture. Bacteria cause Decay. * — Bacteria in several ways, either directly or indirectly, affect mankind. First of all, they cause decay. All organic matter, in whatever form, is sooner or later decomposed by the action of untold millions of bacteria which live in the air, water, and soil. To a considerable degree, then, these bacteria are useful in feeding upon the dead bodies of plants or animals, which other- wise would soon cover the surface of the earth to the exclusion of everything else. Bacteria may thus be scavengers. They oxidize organic materials, changing them to compounds of nitrogen that can be absorbed by plants and used in building protoplasm. Without bacteria and fungi it would be impossible for life to exist on the earth, for green plants would Ix? unaV)lc to get the raw food materials in forms that could l>e used in making food and living mat- ter. In this respect they are of the greatest service to mankind. When bacteria grow in sufficient numbers upon foods, meat, fish, or vegetables, they spoil them, and may form poisonous sub- stances called ptomaines. Such substances are formed as waste products by the bacteria, and are given off into the material in which the bacteria are living. Thus we, upon eating the food con- taining these poisons, may become violently ill as the result of ptomaine poisoning. Fish and meats that have been kept for some time in cold storage are very easily spoiled, and should be avoided. Jars of canned goods that have " worked," that is in which bacteria or yeasts have caused fermentation, are often unfit for food. Relation to Fermentation. — They may incidentally, as a result of this process of decay, aid in the process of fermentation. In making vinegar the yeasts first make alcohol (see p. 172), which the bacteria change to acetic acid. The lactic acid bacteria which sour milk, changing the milk sugar to an acid, grow very rapidly in a warm temperature; hence milk which is kept cool or which is pasteurized (that is, kept at a temperature of about 176° HUNT. ES. BIO. 12 178 HOW PLANTS BENEFIT AND HARM MANKIND Fahrenheit for five to twenty minutes for the purpose of killing the bacteria) will not sour readily, if kept in a cool place. Why ? These same lactic acid bac- teria may be useful when they sour the milk for the cheese-maker. Certain other bacteria give flavor to cheese and butter, while still others are used by the tanner. Nitrogen-fixing Bacteria. — Still other bacteria, as we have seen before, ' ' change over " nitrogen in organic A pasteurizing apparatus. material in the soil and even the free nitrogen of the air so that it can be used by plants in the form of a compound of nitrogen. The bacteria living in tubercles on the roots of clover, beans, peas, etc., have the power of thus " fixing " the free nitrogen in the air found between particles of soil. This fact is made use of by farmers who rotate their crops, growing first a crop of clover or alfalfa, which produce the bacteria, then plowing these up and plant- ing another crop, as wheat or corn, on the same area. The latter plants, making use of the nitrogen com- pounds there, produce a larger crop than when grown in ground containing less nitrogenous material. Bacteria cause Disease. Modules contain the nitrogen fixing bacteria on — The most harmful bac- the roots of clover. HOW PLANTS BENEFIT AND HARM MANKIND 179 teria are those which cause disease. This they do by becoming parasites in the human })ody. Millions upon millions of bacteria exist in the human body at all times — in the mouth, on the teeth, and especially in the lower part of the food tube. Some in the food tube are believed to be useful, others harmless; still others cause decay of the teeth, while a few kinds, if present there, may cause disease. It is known that bacteria, like any other living things, feed and give off organic waste. This waste, called a toxin, is poison to the hosts on which the bacteria live, and it is usually the production of this toxin that causes the symptoms of disease. Some forms, however, break down tissues and plug up the small blood vessels, thus causing disease. Diseases caused by Bacteria. — It is estimated that bacteria cause annually over 50 per cent of the deaths of the human race. As we will later see, a very large proportion of these diseases might be prevented if people were educated sufficiently to take the proper precau- tions to prevent their spread. These precau- tions might save the lives of some 3,000,000 of peo- ple yearly in Europe and America. Tuberculosis, typhoid fever, diphtheria, pneumonia, blood poison- ing, syphilis, and a score of other germ diseases ought not to exist. A good deal more than half of the present misery of this world might be prevented and this earth made cleaner and better by the cooperation of the young people now growing up to be our future home-makers. Germs or contagious diseases either enter the body by way A single cell scrap>ed from the roof of the mouth and highly magnified. The little dots are living bac- teria, most of them comparatively harmless. 180 HOW PLANTS BENEFIT AND HARM MANKIND of the mouth or nose, from air, food, or water, or may be trans- mitted from some person having disease to a well person by con- tact. Usually the germs enter the body through some opening, as the mouth, or through a cut or sore. With care by the civic authorities and by individuals a healthy person should easily keep from such diseases, if he takes proper precautions. Tuberculosis. — The one disease responsible for the greatest number of deaths — perhaps one seventh of the total on the globe — is tuberculosis. But this dis- ease is slowly but surely being overcome. It is believed that within perhaps fifty 3^ears, with the aid of good laws and sani- tary living, it will be almost extinct. Tuberculosis is caused by the growth of a bacterium, called the tubercle bacillus, within the lungs or other tis- sues of the human body. Here it forms little tul^ers full of germs, which close up the deh- cate air passages in the lungs, and in other tissues give rise to hip-joint disease, scrofula, lupus, and other diseases, depending on the part of the body they attack. Tuberculosis may be con- tracted by taking the bacteria into the throat or lungs by eating meat or drinking milk from tubercular cattle. Especially is it com- municated from a consumptive to a well person by kissing, drink- ing, or eating from the same cup or plate, using the same towels, or in any way coming in direct contact with the person having the germs in his body. Although there are always some of the germs in the air of an ordinary city street, and though we may take some of these germs into our bodies at anytime, yet the bacteria seem able to gain a foothold only under certain conditions. It is only when the tissues are in a worn-out condition, when we are " run down," as we say, that the parasite may obtain a foothold in the lungs. Microscopic appearance of ordinary milk showing fat globules and bacteria. The cluster of bacteria on left side are lactic- acid-forming germs. Tuberculosis germs are sometimes found in milk. HOW PLANTS BENEFIT AND HARM MANKIND 181 Even if the disease gets a foothold, it is quite jwssible to cure it if it is taken in time. The germ of tuberculosis is killed by exposure to bright sunlight and fresh air. Thus the course of the disease may be arrested, and a permanent cure Ijrought alx)ut, by a life in the open air, the patient sleeping out of doors, taking plenty of nourishing food and very little exercise. See also C'hapter XXIX. Typhoid Fever. — One of the most common germ diseases in this country and Europe is typhoid fever. This is a disease which is conveyed by means of water and food, especially milk, oysters, How sewage containing typhoid bacteria may get into drinking water : c, cesspool ; Im, layer of rock ; w, wash water. and uncooked vegetables. Typhoid fever germs live in the intes- tine and give off a toxin or poison which gets into the blood, thus causing the fever characteristic of the disease. The germs multi- ply very rapidly in the intestine and are passed off from the body with the excreta from the food tube. If these germs get into the water supply of a town, an epidemic of typhoid will result. Among the recent epidemics caused by the use of water containing typhoid germs have been those in Butler, Pa., where 1364 persons were made ill; Ithaca, N.Y., with 1350 cases; and Watertown, N.Y., where over 5000 cases occurred. Another source of infection is milk. Frequently epidemics have occurred which were confined to users of milk from a certain dairy. Upon investigation it was found that a case of typhoid had occurred on the farm where the milk came from, that the germs had washed into the well, and that this 182 HOW PLANTS BENEFIT AND HARM MANKIND water was used to wash the milk cans. Once in the milk, the bac- teria multiplied rapidly, so that the milkman gave out cultures of typhoid in his milk bottles. Proper safeguarding of our water and milk supply is necessary if we are to keep typhoid away. Tetanus, or Blood Poisoning. — The bacterium causing blood poisoning is another toxin-forming germ. It lives in the earth and enters the body through cuts or bruises. It seems to thrive best in less oxygen than is found in the air. It is therefore important not to close up with court-plaster wounds in which such germs may have found lodgment. It, with typhoid, is responsible for four times as many deaths as bullets and shells in time of battle. The wonderfully small death rate of the Japanese army in their war with Russia was due to the fact that the Japanese soldiers always boiled their drinking water before using it, and their surgeons always dressed all wounds on the battlefield, using powerful antiseptics in order to kill any bacteria that might find lodgment in the exposed wounds. Other Diseases. — Many other diseases have been traced to bacteria. Diphtheria is one of the best known. As it is a throat disease, it may easily be conveyed from one person to another by kissing, putting into the mouth objects which have come in con- tact with the mouth of the patient having diphtheria, or by food into which the germs have been carried. Another disease which probably causes more misery in the world than any other germ disease is syphilis. It is estimated that 80 per cent of blindness in newborn children is due to this cause. Grippe, pneumonia, whooping cough, and colds are believed to be caused by bacteria. Other diseases, as malaria, yellow fever, sleeping sickness, and probably smallpox, scarlet fever, and measles, are due to the attack of one-celled animal parasites. Of these we shall learn later in the chapter on Protozoa. Methods of fighting Germ Diseases. — As we have seen, dis- eases produced by bacteria may be caused by the bacteria being transferred from one person directly to another, or the disease may obtain a foothold in the body from food, water, by breathing in the germs in the air, or by taking them into the blood through a cut or a wound or a body opening. It is evident that as individuals we may each do something to HOW PLANTS BENEFIT AND HARM MANKIND 183 prevent the spread of germ diseases, especially in our homes. We may keep our bodies, especially our hands and faces, clean. Sweeping and dusting may be done with damp cloths so as not to raise a dust; our milk and water, when from a suspicious supply, should be sterilized, — that is, the germs contained killed by boiling or pasteur- izing for a few minutes. Wounds through which bacteria might obtain foothold in the body should be washed with some antiseptic, a substance like corrosive sublimate (1 part to 1000 water) or carbolic acid (1 part to 40 water), which kills the germs. In a later chapter we shall learn more of how we may cooperate with the authorities to combat disease and make our city or town a better place to live in.^ Reference Books elementary Sharpe, A Laboratory Manual for the Solution of Problems in Biology. American Book Company. Conn, Bacteria, Yeasts, and Molds in the Home. Ginn and Company. Conn, Story of Germ Life. D. Appleton and Company. Davison, The Human Body and Health. American Book Company. Frankland, Bacteria in Daily Life. Longmans, Green, and Company. Prudden, Dust and its Dangers. G. P. Putnam's Sons. Prudden, The Story of the Bacteria. G. P. Putnam's Sons. Ritchie, Primer of Sanitation. Worid Book Company. ADVANCED Conn, Agricultural Bacteriology. P. Blakiston's Sons and Company. Coulter, Barnes, and Cowles, A Textbook of Botany, Vol. I. American Book Com- pany. De Bary, Comparative Morphology and Biology of the Fungi, Mycetozoa, and Bacteria Clarendon Press. Duggar, Fringous Diseases of Plants. Ginn and Company. Hough and Sedgwick, The Human Mechanism. Ginn and Company. Muir and Ritchie, Maniud of Bacteriology. The Macmillan Company. Newman, The Bacteria. G. P. Putnam's Sons. Sedgwick, Principles of Sanitary Science and Public Health. The Macmillan Com pany. » Teachers may take up parts or all of Chapter XXIX at this point. I have found it advisable to repeat much of the work on bacteria after the students have taken up the study of the human organism. XIV. THE RELATIONS OF PLANTS TO ANIMALS Problem XXIV, TJie general hiological relations existing he- tiveen plant sand aniinals. {Labor abory Manual, Proh. XXIV.) (a) A balanced aquarUnn. (b) Relations between green filants and animals, (c) The nitrogen cycle, id) A hay infusion. Study of a Balanced Aquarium. — Perhaps the best way for us to understand the interrelation between plants and animals is to study an aquarium in which plants and animals live and in which a balance has been established between the plant life on one side and animal life on the other. Aquaria containing green pond weeds, either floating or rooted, a few snails, some tiny animals known as water fleas, and a fish or two will, if kept near a light window, show this relation. We have seen that green plants under favorable conditions of sunlight, heat, moisture, and with a supply of raw food materials, give off oxygen as a by-product while manufacturing food in the green cells. We know the necessary raw materials for starch manufacture are carbon dioxide and water, while nitrogenous material is necessary for the making of proteids within the plant. In previous experiments we have proved that carbon dioxide is given off by any living thing when oxidation occurs in the body. The crawling snails and the swimming fish give off carbon dioxide, which is dissolved in the water ; the plants themselves, night and day, oxidize food within their bodies, and so must pass off some carbon dioxide. The green plants in the daytime use up the carbon dioxide obtained from the various sources and, with the water taken in, manufacture starch. While this process is going on, oxygen is given off to the water of the aquarium, and this free oxygen is used by the animals. But the plants are continually growing larger. The snails and fish, too, eat parts of the plants. Thus the plant life gives food 184 THE RELATIONS OF PLANTS TO .VNIMALS 185 to at least part of the animal life within the aquarium. The ani- mals give off certain nitrogenous wastes of which we shall learn more later. These materials, with other nitrogenous matter from the dead parts of the plants or animals, form the part of the raw material of the proteid food manufactured within the plant. The animals eat the plants and give off organic waste, from which the A balanced aquarium. plants make their food and living matter. The plants give off oxygen to the animals, and the animals give carbon dioxide to the plants. Thus a balance exists between the plants and animals in the aquarium. Relations between Green Plants and Animals. — What goes on in the aquarium is an example of the relation existing between all green plants and all animals. Everywhere in the world green plants are making food which becomes, sooner or later, the food of 186 THE RELATIONS OF PLANTS TO ANIMALS animals. Man may not feed upon the leaves of plants, but he eats fruits and seeds in one form or another. Even if he does not feed directly upon plants, he eats the flesh of herbivorous animals, Carbon dioxide (CO2) Carbon dioxide >i (CO2) Simple Salts Plants with chlorophyll buildup complex organic substances They store up energy from the sun in the process and form lorganic food of Animals and plants without chlorophyll which tear down complex^ Ammonia organic substances I (NH3) and set free energy in the process in form of heat Energy from sub. Energy set free as heat. The relations between green plants and animals. which in turn feed directly upon plants. And so it is the world over; the plants are the food-makers and supply the animals. Green plants also give a very considerable amount of oxygen to the atmosphere every day, which the animals may make use of. The Nitrogen Cycle. — ^Animal Life )sing Bacteria The animals in their turn supply much of the carbon dioxide that the, plant uses in starch-making. They also supply most of the nitrogenous matter used by the plants, part being given the plants from the dead bodies of their own relatives and part being released through the agency of bacteria, which live upon the roots of certain plants. These bacteria are the only organisms that can take nitrogen from the air. Thus, in spite of all the nitrogen of the atmosphere, plants and animals are limited in the amount Nitrites ■■s Nitric Bacteria The nitrogen cycle. THE RELATIONS OF PLANTS TO ANIMALS 187 available. And the available supply is used over and over again, perhaps in nitrogenous food by an animal, then it may be given off as organic waste, get into the soil, and ])e taken up by a plant through the roots. Eventually the nitrogen forms part of the food supi)ly in the body of the plant, and then may become part of its living matter. When the plant dies, the nitrogen is returned to the soil. Thus the usable nitrogen is kept in cor- relation. Symbiosis. — Plants and animals are seen in a general way to be of mutual advantage to each other. Some plants, called lichens, show this mutual partnership in the fol- lowing interesting way. A lichen is composed of two kinds of plants, one at least of which may live alone, but which have formed a partnership for life, and have divided the duties of such life be- tween them. In most lichens the alga, a green plant, forms starch and nourishes the fungus. The fungus, in turn, produces spores, by means of which new lichen^ are started in life. The body of the lichen is usually protected by the fungus, which is stronger in structure than the green part of the combination. This process of living together for mutual advantage is called symbiosis. Some animals thus com- bine with plants; for example, the tiny animal known as the hydra with certain of the one-celled algse, and, if we accept the term in a wide sense, all green plants and animals live in this relation of mutual give and take. Animals also frequently live in this relation to each other, as the crab, which A lichen {Physcia slellaris). Photographed by W. C. Barbour. Stages in the formation of the lichen thallus, showing the re- lation of the threadlike fungus to the green cells of the alga. (After Bornet.) 188 THE RELATIONS OF PLANTS TO ANIMALS lives within the shell of the oyster ; the sea anemones, which are carried around on the backs of some hermit crabs, aiding the crab in protecting it from its enemies, and being carried about by the crab to places where food is plentiful. • A Hay Infusion. — Still another example of the close relation between plants and animals may be seen in the study of a hay Life in a late stage of a hay infusion. B, bacteria, swimming or forming masses of food upon which the one-celled animals, the paramoecia, are feeding ; G, gullet; F.V., food vacuole; C.V., contractile vacuole; P, pleuococcus ; P.D., pleurococcus dividing. infusion. If we place a wisp of hay or straw in a small glass jar nearly full of water, and leave it for a few days in a warm room, certain changes are seen to take place in the contents of the jar; the water after a little while gets cloudy and darker in color, and a scum appears on the surface. If some of this scum is examined under the compound microscope, it will be found to consist almost entirely of bacteria. These bacteria evidently aid in the decay which (as the unpleasant odor from the jar testifies) is taking place. As we have learned, bacteria flourish wherever the food supply is THE RELATIONS OF PLANTS TO ANIMALS 189 abundant. The water within the jar has come to contain much of the food material which was once within the leaves of the grass, — organic nutrients, starch, sugar, and proteids, formed in the leaf by the action of the sun on the chlorophyll of the leaf, and now released into the water by the breaking down of the walls of the cells of the leaves. The bacteria themselves release this food from the hay by causing it to decay. After a few days small one- celled animals appear; these multiply with wonderful rapidity, so that in some cases the surface of the water seems to be almost white with active one-celled forms of life. If we ask ourselves where these animals come from, we are forced to the conclusion that they must have been in the water, in the air, or on the hay. Hay is dried grass, which may have been cut in a field near a pool con- taining these creatures. When these pools dried up, the wind may have scattered some of these little organisms in the dried mud. or dust. Some may exist in a dormant state on the hay, the water serving to awaken them to active life. In the water, too, there may have been some living cells, plant and animal. At first the multipUcation of the tiny animals within the hay infusion is extremely rapid ; there is food in abundance and near at hand. After a few days more, however, several kinds of one- celled animals may appear, some of which prey upon others. Con- sequently a struggle for life begins, which becomes more and more intense as the food from the hay is used up. Eventually the end comes for all the animals unless some green plants obtain a foot- hold within the jar. If such a thing ha opens, food will be manu- factured witnin their bodies, a new food supply arises for the animals within the jar, and a balance of life results. Reference Books elementary Sharpe, A Laboratory Manual for the Solution of Problems in Biology. American Book Company. ADVANCED Eggerling and Ehrenberg, The Fresh Water Aquarium and its Inhabitants. Henry Holt and Company. Furneaux, Life in Ponds and Streams. Parker, Biology. The Macmillan Company. XV. THE PROTOZOA Problem XXV. The study of a one-celled animal. {Laboror tory Manual, Problem XXV.) (a) In Us relations to its surroundings. (Jb) As a cell. {Optional.) (c) In its relations to man. We have seen that perhaps the simplest plant would be exem- phfied by one of the tiny bacteria we have just read about. A typical one-celled plant, however, would contain green coloring matter or chlorophyll, and would have the power to manufacture its own food under conditions giving it a moderate temperature, a supply of water, oxygen, carbon dioxide, and sunlight. Such a simple plant is the pleurococcus, the *' green slime " seen on the shady sides of trees, stones, or city houses. This plant would meet one definition of a cell, as it is a minute mass of protoplasm contain- ing a nucleus. It is surrounded by a wall ^ of a woody material which covers a delicate membrane formed by the activity of the living matter within the cell. It also contains granules of protoplasm colored green, called chloroplasts. Of their part in the manufacture of organic food we have already learned. Such is a simple plant cell. Let us now examine a simple animal cell in order to compare it with that of a plant. The Paramoecium. — The one-celled animal most frequently found in hay infusions is the paramoecium, or slipper animalcule (so-called because of its shape). This cell is elongated, oval, or elliptical in outline, but somewhat flattened. Seen under the low power of the microscope, it appears to be extremely active, rushing about now rapidly, now more slowly, but seemingly always taking a definite course. The more pointed end of the body (the anterior) usually goes first. 1 This shows one practical reason why plant food often contains more indigestible matter than animal food of same bulk. 190 THE PROTOZOA 101 If it pushes its way past any dense substance in the water, the cell body is seen to change its shape as it squeezes through. The cell body is almost transparent, and consists of semifluid protoplasm which has a granular grayish appearance under the microscope. This protoplasm appears to be bounded by a very delicate membrane through which project numerous delicate threads of protoplasm called cilia. (These are usually invisible under the microscope.) The locomotion of the paramoecium is caused by the movement of these ciha which lash the water like a multitude of tiny oars. The cilia also send tiny particles of food into a funnel-like opening, the gullet on one side of the cell. Once within the cell body, the particles of food materials are gathered into little balls within the almost transparent protoplasm. These masses of food seem to be inclosed within a little area containing fluid, called a vacuole. Other vacuoles appear to be clear; these are spaces in which food has been digested. One or two larger vacuoles may be found; these are the contractile vacuoles; their purpose seems to be to pass off waste material from the cell body. This is done by pulsation of the vacuole, which ultimately bursts, pass- ing fluid waste to the outside. Solid wastes are passed out of the cell in somewhat the same manner. The nucleus of the cell is not easily visible in living specimens. In a cell that has been stained it has been found to be a double structure, consisting of one large and one small portion, called respectively the macro- nucleus and the micronu^leu^. Response to Stimuli. — In the paramoecium, as in the one-celled plants, the protoplasm composing the cell can do certain things. Protoplasm responds, in both plants and animals, to certain agen- cies acting upon it, coming from without; these agencies we call stimuli. Such stimuli may be light, differences of temperature, presence of food, electricity, or other factors of its surroundings. Paramoecium. Greatly maguified. From side. F.V., food vacuole ; C.F., contractile vacuole; M, mouth ; A^, nucleus ; W.V., water vacuole. (After Sedgwick and Wilson.) 192 THE PROTOZOA The original cell Plant and animal cells may react differently to the same stimuli. In general, however, we know that protoplasm is irritable to some of these factors. To severe stimuli, protoplasm usually responds by contracting, another power which it possesses. We know, too, that plant and animal cell^ take in food and change the food to protoplasm, that is, that they assimilate food; and that they may waste away and repair themselves. Finally, we know that new plant and animal cells are reproduced from the original bit of protoplasm, a single cell. Reproduction of Paramoecium. — Sometimes a paramoecium may be found in the act of dividing by the process known as fission, to form two new cells, each of which contains half of the original cell. This is a method of asexual reproduction. may thus form in succes- sion many hundreds of cells in every respect like the original parent cell. Frequently another method of reproduction may be observed. This is called conjugation, and somewhat resembles the same process in the simple plants. Two cells of equal size attach themselves together as shown in the Figure. Complicated changes take place in the nuclei of the two cells thus united, which results in an equal exchange of part of the material forming the nucleus. After a short period of rest the two cells separate. The stage of conjugation we believed in the plants to be a sexual stage. There seems every reason to believe that it is a Hke stage in the Hfe history of the paramoecium. Amceba. — In order to understand more fully the life of a simple bit of protoplasm, let us take up the study of the amoeba, a type 1 Amoebae may be obtained from the hay infusion, from the dead leaves in the bot- tom of small pools, from the same source in fresh-water aquaria, from the roots of MAC MIC Paramoecium divid- ing by fission. Greatly magnified. M, mouth; MAC, mac ronucleus ; Af 7C, micronucleus. (After Sedgwick and "Wilson.) Paramoecium. Greatly magnified. M, mouth ; MIC, micro- nucleus; MAC, ma- cronucleus ; C V, con- tractile vacuole. (After Sedgwick and Wilson.) THE PROTOZOA 193 of the simplest form of life known, either plant or animal. Unlike the plant and animal cells we have examined, the amoeba has no fixed form. Viewed under the compound microscope, it has the appearance of an irregular mass of granular protoplasm. Its form is constantly changing as it moves about. This is due to the push- ing out of tiny projections of the protoplasm of the cell, called pseiidopodia (false feet). The outer layer of protoplasm is not so granular as the inner part; this outer layer is called ectoplasm, the inside AnicL'ba, with pseudopodia (7^) ex- tended; EC, ectoplasm; END, endoplasm ; the dark area (A'^.) is the nucleus. From photo- graph loaned by Professor G. N. Calkins. Aniceba, showing the changes which take place during division. The dark body in each Figure is the nucleus ; the trans- parent drcle, the contractile vacuole ; the outer, clear portion of the body the ectoplasm ; the granular portion, the endoplasm ; the granular masses, food vacuoles. Much magnified. l)eing called endoplasm. In the central part of the cell is the nucleus. This important organ is difficult to see, except in cells that have been stained. The locomotion is accomplished, according to Professor Jennings of Johns Hopkins University, by a kind of roUing motion, " the upper and lower surfaces constantly interchanging positions.'* The pseudopodia are pushed forward in the direction which the animal is to go, the rest of the body following. duckweed or other small water plants, or from green al^ae growing in quiet localities. No awe method of obtaining them can be given. HUNT. ES. BIO. 13 194 THE PROTOZOA Although but a single cell, still the amoeba appears to be aware of the existence of food when food is near at hand. Food may be taken into the body at any point, the semifluid protoplasm simply rolling over and engulfing the food material. Within the body, as in the paramoecium, the food is inclosed within a fluid space or vacuole. The protoplasm has the power to take out such material as it can use to form new protoplasm or give energy. It will then rid itself of any material that it cannot use. Thus it has the power of selective absorption, a character found in the protoplasm of plants previously studied. Circulation of food material is accom- plished by the constant streaming of the protoplasm within the cell. The cell absorbs oxygen from the water by osmosis through its delicate membrane, giving up carbon dioxide in return. Thus the cell '' breathes " through any part of its body covering. Waste products formed from the oxidations which take place in the cell are passed out by means of the contractile vacuole. The amoeba, like other one-celled organisms, reproduces by the process of fission. A single cell divides by splitting into two others, each of which resembles the parent cell, except that they are of less bulk. When these become the size of the parent amoeba, they in turn each divide. This is a kind of asexual reproduction. When conditions unfavorable for life come, the amoeba, like some one-celled plants, encysts itself within a membranous wall. In this condition it may become dried and be blown through the air. Upon return to a favorable environment, it begins life again, as before. In this respect it resembles the spore of a plant. From the study of the amcebalike organisms which are known to cause malaria, and by comparison with the amoebae which live in our ponds and swamps, it seems likely that every amoeba has a complicated life history during which it passes through a sexual stage of existence. The Cell as a Unit. — In the daily life of a one-celled animal we find the single cell performing all the general activities which we shall later find the many-celled animal is able to perform. In the amoeba no definite parts of the cell appear to be set off to perform certain functions; but any part of the cell can take in food, can absorb oxygen, can change the food into protoplasm and excrete THE PROTOZOA 195 the waste material. The single cell is, in fact, an organism able to carry on the business of Hving as effectually as a very complex animal. Complex One-celled Animals. — In the paramoecium we find a single cell, but we find certain parts of the cell having certain definite functions : the cilia are used for locomotion ; a definite part of the cell takes in food, while the waste passes out at another definite spot. In another one-celled animal called vorticella, part of the cell has become elongated and is contractile. By this stalk the little animal is fastened to a water plant or other object. The stalk may be said to act like a muscle fiber, as its sole func- tion seems to be movement ; the cilia are located at one end of the cell and serve to create a current of water which will bring food par- ticles to the mouth. Here we have several parts of the cell each doing a different kind of work. This is known as physiological division of labor. Photograph of a living bell animalcule (vorti- cella) enlarged two hundred diameters. Notice the contractile stalk and the circle of cilia about the mouth. Habitat of Protozoa. — Protozoa are found almost everywhere in shallow water, seemingly never at any great depth. They ap- pear to be attracted near to the surface by light and the supply of oxygen. Every fresh-water lake swarms with them; the ocean con- tains countless myriads of many different forms. Use as Food. — They are so numerous in lakes, rivers, and the ocean as to form the food for many animals higher in the scale of life. Almost all fish that do not take the hook and that travel in schools, or companies, migrating from one place to another, live partly on such food. Many feed on slightly larger animals, which in turn eat the Protozoa. Such fish have on each side of the mouth attached to the gills a series of small structures looking like tiny rakes. These are called the gill rakers, and aid in collecting 196 THE PROTOZOA tiny organisms from the water as it passes over the gills. The whale, the largest of all mammals, strains protozoans and other small animals and plants out of the water by means of hanging plates of whalebone, the slender filaments of which form a sieve from the top to the bottom of the mouth. Relation of Protozoa to Disease. — The study of the hfe history and habits of the Protozoa has resulted in the finding of many parasitic forms, and the consequent explanation of some kinds of disease. One parasitic protozoan like an amoeba is called Plasmodium malarice. It causes the disease known as malaria. Part of its life is passed with- in the body of a mosquito (the anopheles), into the stomach of which it passes when the ^^l^'^K^^^B^^^^ mosquito sucks the blood from a ^^^^^»VP^^H^^ person having malaria. Within ^H^|E^^^ ^I^^^B the body of the mosquito a com- ^S^j^^^w^^^ ^^^^ plicated part of the life history ^^^^^^^^1 ^^^H takes place, which results in a stage of the parasite establish- ing itself within the glands which secrete the saliva of the mos- quito. When the mosquito pierces its human prey a second time, some of the parasites are introduced into the blood along with the saliva. These para- sites enter the corpuscles of the blood, increase in size, and then form spores. The rapid process of spore formation results in the chill of malaria. Later, when the spores almost fill the blood corpuscle, it bursts, and the parasites enter the fluid portion of the blood. There they release a poison which causes the fever. The spores may again enter the blood corpuscles and in forty-eight or seventy-two hours repeat the process thus described. Yellow fever is undoubtedly conveyed by another species of mosquito, and is probably due to the presence of a protozoan similar to that of malaria in the blood. That these diseases may be stamped out by the destruction of the mosquitoes, by preventing their breed- Blood corpuscles of a patient with malarial fever. Two corpuscles con- tain the parasites. Photograph, greatly enlarged, by Davison. THE PROTOZOA 197 ing in swamps with the use of oil, by draining the swamps, or by the introduction of fish which eat the mosquito larva? has been proved from our experiences along the Panama Canal, in the Philippines, in Cuba, and in New Orleans. Many other diseases of man are probably caused by parasitic protozoans. Dysentery of one kind appears to be caused by the presence of an amcebalike animal in the digestive tract. Small- pox, rabies, and possibly other diseases may be caused by the action of these little animals. Another group of protozoan parasites are called trypanosomes. One of this family lives in the blood of native African zebras and antelopes; seem- ingly it does them no harm. But if one of these parasites is transferred by the dreaded tsetse fiy to one of the domesticated horses or cattle of the colonist of that region, death of the animal results. Another fly carries a specimen of trypanosome to the natives of Central Africa, which causes "the dreaded and incurable sleeping sickness." This disease carries off more than fifty thousand natives yearly, and many Europeans have succumbed to it. Its ravages are now largely confined to an area near the large Central African lakes and the Upper Nile, for the fly which carries the disease flies near water, seldom going more than 150 feet from the banks of streams or lakes. The British government is now trying to control the disease in Uganda by moving all the villages at least two miles from the lakes and rivers. Why? In this country many fatal diseases of cattle, as "tick," or Texas fever, among cattle are probably caused by protozoans. Skeleton Building. — Some of the Protozoa build elaborate skeletons. These may be formed outside of the body, being composed of tiny micro- How to tell the common mos- quito iculex), a, from the malarial mosquito (anopheles), b, when at rest. Note the position of body and legs. 198 THE PROTOZOA scopic grains of sand, or other ma- terials. In some forms the skeleton is internal, and may be made of lime which the animals take out of the water. Still other Protozoa construct shells which house them for a time ; then, growing larger, they add more chambers to their shell, forming ul- timately a covering of great beauty. These shells or skeletons of Protozoa, falling to the sea bottom, cover the ocean floor to a depth of several feet in places. The Protozoa have also played an important part in rock building. The chalk beds of Kansas and other chalk formations are made up to a large ex- tent of the tiny skeletons of Protozoa, called Foraminifera. Some lime- stone rocks are also composed in large part of such skeletons. Skeleton of a radiolarian. Highly magnified. From model at Amer- ican Museum of Natural History. Classification op Protozoa The following are the principal classes of Protozoa, examples of which we have seen or read about : — Class I. Rhizopoda {Gk.= root-footed). Having no fixed form, with pseudopodia. Either naked as Amoeba or building limy (Foraminifera) or glasslike skeletons (Radiolaria) . Class II. Infusoria (in infusions). Usually active ciliated Protozoa. Examples, Paramcecium, Vorticella. Class III. Sporozoa (spore animals). Usually parasitic and nonactive. Exam- ple, Plasmodium malaricB. Reference Books elementary Sharpe, A Laboratory ManuM for the Solution of Problems in Biology. American Book Company. Davison, The Human Body and Health, Chap. XXIV. American Book Company. Davison, Practical Zoology, pages 178-184. American Book Company. Jordan, Kellogg, and Heath, Animal Studies. D. Appleton and Company- Ritchie, Human Physiology, Chap. XXVI. World Book Company. ADVANCED Calkins, G. N., The Protozoa. The MacmUlan Company. Linville and Kelly, General Zoology, Chap. XXI. Ginn and Company. Parker, T. J., Lessons in Elementary Biology. The Macmillan Company. Seaman, L. S., "The Sleeping Sickness," Outlook, Jan. 15, 1910. Wilson, E. B., The Cell in Development and Inheritance. The Macmillan Company. XVI. THE METAZOA — DIVISION OF LABOR I^ohletn XXVI, An introductory study of many-celled an- imals. {Laboratory Manual, Proh. XXVI.) (a) Devetopm^ent. (.b) Sponges. (c) TJie hydra. id) Development of tissues and organs. (e) Common functions. Reproduction in Simple Plants. — Although there are very many plants and animals so small and so simple as to be com- posed of but a single cell, by far the greater part of the animal and plant world is made up of individuals which are collections of cells living together. In a simple plant like the pond scum, a string or filament of cells is formed by a single cell dividing crosswise, the two cells formed give rise each to two more, and eventually a long thread of cells results. Such growth of cells is asexual. In some instances, however, a single cell was formed by the union of two cells, one from each of the adjoining filaments of the plant. Around this cell eventually a hard coat was formed, and the spore^ as it was called, was thus protected from unfavorable changes in the surroundings. Later, when conditions became favorable for its germination, the spore might form a new filament of pond scum. In the seed plants, too, we found a little plant within the seed which, under favorable conditions, might give rise, through the rapid multiplication of the cells forming it, to a new plant. But the plant within the seed first arose from two cells, one of which, called a sperm, came from a pollen grain, the other of which, the egg, was found within the embryo sac of the ovary. Reproduction in Simple Animals. — In many-celled animals, as well as many-celled plants, the new animal is formed by the 199 200 THE METAZO A — DIVISION OF LABOR union of a sperm and an egg cell. A common bath sponge, an earthworm, a fish, or a dog, — each and all of them begin life in precisely the same way. Animals which are thus composed of many cells are known as the Metazoa, as distinguished from the Protozoa, which are made of but a single cell. Sexual Development of a Simple Animal. — In a many-celled animal the life history begins with a single cell, the fertilized egg. This cell, as we remember, has been formed by the union of two other cells, a tiny (usually motile) cell, the sperm, and a large cell, the egg. After the egg is fertilized by a sperm cell, it splits into two, four, eight, and sixteen cells ; as the number of cells increases, a hollow ball of cells called thehlastulais formed; later this ball sinks • mm mm0k 9 Stages in the segmentation of an egg, showing the formation of the gastrula. in on one side, and a double-walled cup of cells, now called a gas- trula, results. Practically all animals pass through the above stages in their development from the egg, although these stages are often not plain to see because of the presence of food ma- terial (yplk) in the egg. In the sponge the gastrula, which swims by means of cilia, soon settles down, a skeleton is formed, other changes take place, and the sponge begins life as an animal attached to some support on the water. The early stages of life, when an animal is unUke the adult, are known as larval stages ; the animal at this time being called a larva. The young sponge consists of three layers of cells : those of the outside, developed from the outer layer of the gastrula, are called ectoderm; the inner layer, developed from the inner layer of the gastrula, the endoderm. A middle almost structureless layer, called the mesoderm, is also found. In higher animals this layer gives rise to muscles and parts of other internal structures. THE METAZOA — DIVISION OF LABOR 201 A horny fiber sponge : IP, the incurrent pores ; O, osculum. Notice that this sponge is made up of apparently several individuals. One fourth natural size. The Structure of a Sponge. — The simplest kind of a sponge has the form of an urn, attached at the lower end. A common sponge living in Long Island Sound is a tiny urn-shaped animal less than an inch in length. It has a skeleton made up of very tiny spicules of lime, of different shapes. Cut lengthwise, such an animal is seen to be hollow, its body wall being pierced with many tiny pores or holes. The bath sponge, the skeleton of which is made up of fibers of horn, or a variety known as the finger sponge, shows the pores even better than the smaller limy sponge. In a bath sponge, however, we probably have a colony of sponges living together. Each sponge has a large number of pores opening into a central cavity, which in turn opens by a larger hole, called the osculum, to the surrounding water. A microscopic examination shows the pores of the sponge to be lined on the inside with cells having a collar of living matter surrounding a single long cilium or flagellum. The flagella, lashing in one direction, set up a current of water toward the large inner cavity. This current bears food particles, tiny plants and animals, which are seized and digested by the collared cells, these cells probably passing on the food to the other cells of the body. The jellylike middle layer of the body is composed of cells which secrete lime to form the spicules and the reproductive cells, eggs, and sperms. Diagram of a simple sponge : /, inhalant openings ; 0, exhalant opening or osculum. 202 THE METAZOA — DIVISION OF LABOR The Hydra. — Another very simple animal, which unlike the sponge lives in fresh water/ is called the hydra. This little crea- ture is shaped like a hollow cylinder with a circle of arms or ten- tacles at the free end. It is found attached to dead leaves, sticks, stones, or water weed in most fresh-water ponds. When disturbed they contract it into a tiny whitish ball little larger than the head of a pin. Expanded, it may stretch its tentacles in search of food almost an inch from their point of attachment. The tentacles are provided with batteries of minute darts or stinging cells, by means of which prey is caught and killed. The outer layer of the animal serves for protection as well as movement and sensation, certain cells being fitted for each of those different purposes. Food Taking. — The tentacles then reach out like arms, grasp the food, and bend over with it to- ward the mouth. Certain cells lining the hollow body cavity pour out a fluid which aids in digest- ing the food. Other cells with long cilia circulate the food, while still other cells lining the cavity put out pseudopodia, which grasp and ingest the food particles. The tentacles are hollow, and the body cavity extends into them. The outer layer of the animal does not digest the food, but receives some of it already' digested from the inner layer. This food passes from cell to cell, as in plants, by osmosis. The oxygen necessary to oxidize the food is passed through the body wall, seemingly at any point, for there are no organs for respiration (breathing). 1 A few sponges, for example, spongilla, live in fresh water. Longitudinal section of a hydra : 6, bud ; ha, attached end ; m, mouth ; ov, ovary ; sp, sper- mary holding sperm cells. THE METAZOA — DIVISION OF LABOR 203 Reproduction. — The hydra reproduces itself either by budding or by the production of new animals by means of eggs and sperms, sexually. The bud appears on the body as a little knob, sometimes more than one coming out on the same hydra. At first the bud is part of the parent animal, the body cavity extending into it. After a short time (usually a few days) the young hydra separates from the old one and begins life anew. This is asexual reproduction. The hydra also reproduces by eggs and sperms. These sperms are collected in little groups which usually appear near the free end of the animal, the egg cells developing near the base of the same hydra. Both eggs and sperms grow from the middle layer of the animal. The sperms, when ripe, are set free in the water; one of them unites with an egg, which is usually still attached to the body of the hydra, and development begins which results in the growth of a new hydra in a new locality. The stages passed through in development resemble closely those already described on page 200, and it would not be hard to imagine the gastrula stage, turned upside down with a circle of tentacles at the open end. Our gastrula would then be a hydra. Division of Labor. — If we compare the amoeba and the para- moecium, we find the latter a more complex organism than the former. An amoeba may take in food through any part of the body ; the paramoecium has a definite gullet ; the amoeba may use any part of the body for locomotion ; the paramoecium has definite parts of the cell, the cilia, fitted for this work. Since the structure of the paramoecium is more complex, we say that it is a ** higher " animal. In the vorticella, a still more complex cell, part of the cell has grown out like a stalk, has become contractile, and acts and looks like muscle. As we look higher in the scale of life, we invariably find that certain parts of a plant or animal are set apart to do certain work, and only that work. Just as in a community of people, there are some men who do rough manual work, others who are skilled work- men, some who are shopkeepers, and still others who are profes- sional men, so among plants and animals, wherever collections of cells live together to form an organism, there is division of labor, some cells being £tted to do one kind of work, while others are fitted to do work of another sort. 204 THE METAZOA — DIVISION OF LABOR As we have seen in plants, this results in a large number of collections of cells in the body, each collection alike in structure and performing the same function. Such a collection of cells we call a tissue. (See Chapter III.) Frequently several tissues have certain functions to perform in conjunction with one another. The arm of the human body performs movement. To do this, several tissues, as muscles, nerves, and bones, must act together. A collection of tissues per- forming certain work is called an organ. In the sponge, division of labor occurs between the cells of the simple animal, some cells lining the incurrent pores creating a current of water, and feeding upon the minute organisms which come within reach, other cells building the skeleton of the sponge, still others becoming eggs or sperms. Division of labor of a more complicated sort is seen in the hydra. Here the cells which do the same kind of work are collected into tissues, each tissue being a collection of cells, all of which are more or less alike and do the same kind of work. But in higher animals which are more complicated in structure and in which the tissues are found work- ing together to form organs, division of labor is still more devel- oped. In the human arm, an organ fitted for certain movements, think of the number of tissues and the complicated actions which are possible. The most extreme division of labor is seen in the organism which has the most complex actions to perform and whose organs are fitted for such work. In our daily life in a town or city we see division of labor between individuals. Such division of labor may occur among other ani- mals, as, for example, bees or ants. But it is seen at its highest in a great city or in a large business or industry. In the stockyards of Chicago, division of labor has resulted in certain men performing but a single movement during their entire day's work, but this movement repeated so many times in a day has resulted in wonder- ful accuracy and increased speed. Thus division of labor obtains its end. Tissues in the Human Body. — Every animal body above the protozoan is composed of a certain number of tissues. The cells making up these tissues have certain well-defined characteristics. In very simple animals the cells are all very much alike, but in more THE METAZOA — DIVISION OF LABOR 205 complex animals the cells are more and more unlike as their work becomes more and more differenc. Let us see what these cells may be, what their structure is, and, in a general way, what func- tion each has in the human body. Muscle Cells: — A large part of our body is made up of muscle. Muscle cells are elongated in shape, and have great con- tractile power. Their work is that of causing movement, and this is usually done by means of attachment to a skeleton inside the body. In man they may be of two kinds, voluntary (under con- trol of the will) and involuntary. Diagrams of sections of cells, greatly magnified, e, flat cell (epithelium) from mouth ; c, columnar epithelium from food tube ; 6, bone-forming cell ; I, liver cell ; m, muscle cell ; /, fat cell ; n, nerve cell. Epithelial Cells. — Such cells cover the outside of a body or line the inside of the cavities in the body. The shape of such cells varies from flat plates to little cubes or columns depending upon their position inside or outside the body. Some bear ciha, an adaptation. Can you think of their purpose ? Connective Tissue Cells. — Such cells form the connection between tissues in the body. They are characterized by possess- ing numerous long processes. They also secrete, as do many other cells, a substance like jelly, called intercellular substance. This stands in the same relation to the cells as does mortar to the bricks in a wall. Several other types of cells might be mentioned, as blood cells, cartilage cells, bone cells, and nerve cells. A glance at the Figure shows their great variety of shapes and sizes. 206 THE MET AZOA— DIVISION OF LABOR Functions Common to All Animals. — The same general functions performed by a single cell are performed by a many-celled animal. But in the Metazoa the various functions of the single cell are taken up by the organs. In a complex organism, like man, the organs and the functions they perform may be briefly given as follows : — (1) The organs of food taking: food may be taken in by indi- vidual cells, as those lining the pores of the sponge, or definite parts of a food tube may be set apart for this purpose, as the mouth and parts which place food in the mouth. (2) The organs of digestion: the food tube and collections of cells which form the glands connected with it. The enzymes in the fluids secreted by the latter change the foods from a solid form (usually insoluble) to that of a fluid. Such fluid may then pass by osmosis through the walls of the food tube into the blood. (3) The organs of circulation : the tubes through which the blood, bearing its organic foods and oxygen, reaches the tissues of the body. In simple forms of Metazoa, as the sponge and hydra, no such organs are needed, the fluid food passing from cell to cell by osmosis. (4) The organs of respiration: the organs in which the blood receives oxygen and gives up carbon dioxide. The outer layer of the body serves this purpose in very simple animals ; gills or lungs are developed in more complex animals. (5) The organs of excretion : such as the kidneys and skin, which pass off nitrogenous and other waste matters from the body. (6) The organs of locomotion: muscles and their attachments and connectives; namely, tendons, ligaments, and bones. f (7) The organs of nervous control: the central nervous system, which has control of coordinated movement. This consists of scattered cells in low forms of life; such cells are collected into groups and connected with each other in higher animals. (8) The sense organs : collections of cells having to do with the reception of sight, hearing, smell, taste, and touch. (9) The organs of reproduction: the sperm and egg-forming glands. Almost all animals have the functions mentioned above. In most, the various organs mentioned are more or less developed, although in the simpler forms of animal life some of the organs mentioned above are either very poorly developed or entirely lacking. THE METAZOA — DIVISION OF LABOR 207 FORMS OF SIMPLE METAZOANS. SPONGES Sponges may be placed, according to the kind of skeleton they possess, in the following groups : — (1) The limy sponges, in which the skeleton is composed of spicules of carbonate of lime. Grantia is an example. (2) The glassy sponges. Here the skeleton is made of silica or glass. Some of the rarest and most beautiful of all sponges belong in this class. The Venus's flower basket is an example. (3) The horny fiber sponges. These, the sponges of commerce, have the skeleton com- posed of tough fibers of material somewhat like that of cow's horn. This fiber is elastic and has the power to absorb water. In a living state, the horny fiber sponge is a dark- colored fleshy mass, usually found attached to rocks. The warm waters of the Mediter- ranean Sea and the West Indies furnish most of our sponges. The sponges are pulled up from their resting place on the bottom, either by means of long-handled rakes operated by men in boats, or are secured by divers. They are then spread out on the shore in the sun, and the living tissues allowed to decay ; then after treatment consisting of beating, bleaching, and trimming, the bath sponge is ready for the mar- ket. CCELENTERATES The hydra and its salt- water allies, the jellyfish, hydroids, and corals, belong to a group of animals known as the Ccelenterata. The word " coelenterate " (cadom =hody cavity, en/eron= food tube) explains the structure of the group. They are animals which have a common body cavity and food tube, the animal in its simplest form being little more than a bag. Venus's flower basket; a Bponge with a glassy skele- ton. Medusa {Gonionemus murhachii), showing ten- tacles, mouth, digestive canals, and reproduc- tive bodies. Photographed from the model at the American Museum of Natural History. 208 THE MET AZOA— DIVISION OF LABOR Medusa. — Among the most interesting of all the coelenterates inhabit- ing the salt water are the jellyfishes or medusae. These animals vary greatly in size from a tiny umbrella-shaped animal little larger than the head of a pin to huge jellyfish several feet in diameter. Development. — Many species of medusae pass through another stage of life. As medusae they reproduce by eggs and sperms, that is, sexually. The egg of the medusa segments, forming ultimately a ball of cells (the blastrula) which swims around by means of cilia. Ulti- mately the little animal settles down on one end and becomes fixed to a rock, seaweed, or pile. The free end becomes indented in the same manner as a hollow rubber ball may be pushed in on one side. This indented side becomes a mouth, tentacles develop around the orifice, and we have an animal that looks very much like the hydra. This animal, now known as a hy- droid polyp, buds rapidly and soon forms a colony of little polyps, each of which is con- nected with its neighbor by a hollow food tube. The hydroid polyp differs from its fresh-water cousin, the hydra, by usually possessing a tough covering which is not alive. Alternation of Generations in Coelenterates. — The lives of a hydroid and a medusa are seen thus to be intimately connected with each other. A hydroid colony produces new polyps by budding. This we know is an asexual method of reproduction. There come from this hydroid colony, however, little buds which give rise to medusae. These me- dusae produce eggs and sperms. Their reproduction is sexual, as was the reproduction by means of eggs and sperms from the prothal- lus of the fern. So we have in animals, as well as in plants, an alternation of generations. Sea Anemone. — Those who have visited our New England coast are familiar with another coelenterate called the sea anem- one. This animal gets its name A hydroid colony of six polyps : /, feeding polyp ; r, reproductive polyp ; m, a medusa ; y, young polyp. Sea anemone. About one half natural size. The right-hand specimen is expanded. Note the mouth surrounded by the ten- tacles. The left-hand specimen is con- tracted. From model at the American Museum of Natural History. THE MET AZOA — DIVISION OF LABOR 209 A branching nmdreporic coral. because, when expanded, it looks like a beautiful flower of a golden yellow or red color. The body of the sea anemone is like the hydra, a column attached at one end. The free end is provided with a mouth surrounded with a great number of tentacles. These, when expanded, look like the petals of a flower. The sea anemone is a very voracious flower, for by means of the bat- teries of stinging cells in its ten- tacles it is able to catch and devour fishes and other animals almost as large as itself. When disturbed or irritated, the ani- mal contracts into a slimy ball, making it difficult to dislodge from its attachment. Although the sea anemone is like a large hydra in appearance, its interior is different. Th(> hollow digestive cavity contains a number of partitions more or less complete, which run from the outer wall toward the middle of the cavity. These partitions, known as mesenteries, are found in pairs. Part of the cavity, as in the hydra, is g^iven up to digesting the food. Food is killed by means of stinging cells found in the long threadlike tentacles. Coral. — If a i^ioce of madreporic coral is examined with a hand lens, a number of little depressions will be seen in the limy surface, each of which has tiny partitions within it. These cuplike depressions were once occu- pied by the coral animals or polyps, each in its own cup. The mesenteries of the coral polyp are paired and hollow on the under surface. The partitions seen in the coral cups lie be- tween the pairs of mesenteries, and are formed by them when the animal is alive. Sea water has a considerable amount of lime in its composition. This lime (calcium carbonate) is taken from the water by certain of the cells of the coral polyp and deposited around the base of the animal and between the mesenteries, thus giving the appearance just seen in the cups of the coral branch. Asexual Reproduction. — These polyps reproduce by budding, and when alive cover the whole coral branch with a continuous living mass of A single coral cup, showing the walls of lime built by the mesenteries. From a photograph loaned by the American Museum of Natural History. HUNT. ES. BIO. 14 210 THE METAZOA — DIVISION OF LABOR polyps, each connected with its neighbor. In this way great masses of coral are formed. Coral, in a living state, is alive only on the surface, the polyps building outward on the skeleton formed by their predecessors. Economic Importance of Corals. — Only one (astrangia) of a great many different species of coral lives as far north as New York. In tropical waters they are very abundant. Coral building has had and still has an immense influence on the formation of islands, and even parts of conti- nents in tropical seas. Not only are many of the West Indian islands composed largely of coral, but also Florida, Australia, and the islands of the southern Pacific are almost entirely of coral formation. Coral Reefs. — The coral polyp can live only in clear sea water of moderate depth. Fresh water, bearing mud or other impurities, kills them immediately. Hence coral reefs are never found near the mouths of large fresh-water rivers. They are frequently found building reefs close to the shore. In such cases these reefs are called fringing reefs. The so-called barrier reefs are found at greater distance (sometimes forty tb fifty miles) from the shore. An example is the Great Barrier Reef of Australia. The typical coral island is called an atoll. It has a circular form inclosing a part of the sea which may or may not be in communica- tion with the ocean outside the atoll. The atoll was perhaps at one time a reef outside a small island. This island disappeared, probably by the sinking of the land. The polyps, which could live in water up to about one hundred and fifty feet, continued to build the reef until it arose to the surface of the ocean. As the polyps could not exist for long above low- water line, the animals died and their skeletons became disintegrated by the action of waves and air. Later birds brought a few seeds there, perhaps a coconut was washed ashore; thus plant life became estab- lished in the atoll, and a new outpost to support human life was estab- lished. Classification of Ccelentbrates Class I. Hydrozoa. Body cavity containing no mesenteries, usually alternation of generation. Examples : Hydra, hydroids. Class II. Scyphozoa. Examples : large jellyfishes. Class III. Actinozoa. Mesenteries present in body cavity. Examples : sea anem- ones and corals. Class IV. Ctenophora. Reference Books elementakt Sharpe, A Laboratory Manual for the Solution of Problems in Biology. American Book Company. Agassiz, A First Lesson in Natural History. D. C. Heath and Company. Holder, Half Hours with the I^ower Animals. American Book Company. Jordan, Kellogg, and Heath, Animal Studies. D. Appleton and Company. THE METAZOA— DIVISION OF LABOR 211 ADVANCED Hertwig, R., General Principles of Zoology. Henry Holt and Company. Miner, A Guide to the Sponge Alcove. Guide Leaflet, No. 23, American Museum of Natural History, New York. Parker, Elementary Biology. The Macmillan Company. Parker and Haswell, Textbook of Zoology. The Macmillan Company. Sedgwick and Wilson, General Biology. Henry Holt and Company. Verworn, General Physiology. The Macmillan Company. XVII. THE WORMS, A STUDY OF RELATIONS TO EN- VIRONMENT Trohlem XXVII, The relation of the earthworrvh to its sur- roundings {optional). {Laboratory Manual, Prob. XXYII.) Effect of Surroundings on Plants. — Animals as well as plants are influenced very greatly by their surroundings or environment. We have seen how green plants behave toward the various factors of their environment ; how heat and moisture start germination in a seed; how the roots grow toward water; how gravity influences the root and the stem, pulling the root downward and stimulating the stem to grow upward ; how the stem grows toward the source of light ; and how the leaves put their flat surfaces so as to get as much light as possible; and how oxygen is necessary for life to go on. It is quite possible to show that the factors of environment act upon animals as well as plants, although it is much harder to ex- plain why an animal does a certain thing at a certain time. How One-celled Animals respond to Stimuli. — We have seen that the single-celled animals respond to certain stimuli in their surroundings. The presence of food attracts them; when they run into an object, they respond immediately by backing away, thus showing that they have a sense of touch. If part of a glass slide containing paramoecia is heated slightly, the animals will respond to the increase in heat by moving toward the cooler end. Many other experiments might be quoted to show that the living matter of a simple animal is sensitive to its surroundings. The Earthworm in its Relation to its Surroundings. — The earthworm, familiar to most boys as bait, shows us in many ways how a many-celled animal responds to stimuli. Careful observation of the body of a living earthworm shows us that its long tapering body is made up of a large number of rings or segments. The num- ber of these segments will be found to vary in worms of different size, the larger worms having more segments. If the two ends of the worm be touched Ughtly with a small stick 212 THE WORMS 213 or straw, one end will be found to respond much more readily to touch than the other end. The more sensitive end is the front or anterior end, the other end being the posterior end. Jar the dish in which the worm is crawling; it will immediately respond by contracting its body. Living earthworms tend to collect along the sides of a dish or in the corners. This seems to be due to an instinct which leads them to inhabit holes in the ground. An earthworm placed half in and half out of a darkened box soon "X/ Au earthworm crawling over a smooth surface. responds by crawling into the darkened part and remaining there. There are no eyes visible. A careful study of the worm with the microscope, however, has revealed the fact that scattered through the skin, particularly of the anterior segments, are many little struc- tures which not only enable the animal to distinguish between light and darkness, but also light of low and high intensity, as well as the direction from which it comes. A worm has no ears or special organs of feeling. We know, however, that although a worm responds to vibrations of low intensity, the sense of touch is well developed in all parts of the body. It also responds to the presence of food, as can be proved if bits of lettuce or cabbage leaf are left overnight in a dish of earth where worms are kept. Locomotion of an Earthworm. — If we measure an earthworm when it is extended and compare with the same worm contracted, we note a difference in length. This is accounted for when we understand the method of locomotion. Under the skin are two sets of muscles, an outer set which passes in a circular direction 214 THE WORMS around the body, and an inner set which runs the length of the body. The body is lengthened by the contraction of the cir- cular muscles. How might the body be shortened ? The under surface of the worm is provided with four double rows of tiny bristles called setae, every segment except the first three and the last being provided with setae. Each seta has attached to it small muscles, which turn the seta so it may point in the opposite direc- tion from which the worm is moving. If you watch a specimen carefully, you will see that locomotion is accomplished by the thrusting forward of the anterior end; then a wave of muscular contraction passes down the body, thus shortening the body by drawing up the posterior end. The setae at the anterior end serve as anchors which prevent the body from slipping back- ward as the posterior end is drawn up. How the Worm digs Holes. — A feeding worm will show the proboscis, an extension of the upper lip which is used to push food into the mouth. Diagram to show how movement of a seta is accomplished; M, muscles; S, seta ; W, body wall. (After Sedgwick and Wilson.) Forepart of an earthworm with the left body wall removed to show the body cavity and food tube within it: m, mouth ; p, pharynx, c, g, i, food tube. The earthworm is not provided with hard jaws or teeth. Yet it literally eats its way through the hardest soil. Inside the mouth opening is a part of the food tube called the pharynx. This is very muscular so that it can be extended and withdrawn by the worm. When applied to the surface of the soil, which is first moistened by the worm, it acts as a suction pump and draws it into the food tube. As the worms take organic matter out of the ground as food, they pass the earth through the body in order to THE WORMS 215 Diagrammatic cross section of the body of a coe- lenterate, and that of a worm. get this food. The earth is mixed with fluids poured out from glands in the food tube, and is passed out of the body and deposited on the surface of the ground, in the form of little piles of moist earth. These are familiar sights on all lawns ; they are called worm casts. Charles Darwin cal- culated that fifty-three thousand worms may be found in an acre of ground, that ten tons of soil might pass through their bodies in a single year and thus be brought to the surface, and that they plow more soil than all the farmers put together. Earthworms, in spite of their fondness for some garden vegetables and young roots, do much good by breaking up the soil, thus allowing water and oxygen to penetrate to the roots of plants. Comparison between Hydra and Worm. — The digestive tract of the worm is an almost straight tube inside of another tube. The latter is divided by partitions which mark the boundary of each segment. The outer cavity is known as the body cavity. In the hydra no distinction existed between the body cavity and digestive tract. In the animals higher than the coelenterates the digestive tract and body cavity are distinct. Food is digested within the food tube, is passed through the walls of this tube into the body cavity, and is in part carried by the blood to various parts of the body. No gills or lungs are present, the thin skin acting as an organ of respiration. But the worm is unable to take in oxygen unless the membranelike skin is kept moist. Development. — Notice in some worms the swollen area called the girdle (about one third the distance from the anterior end). This area periodically forms a little sac in which the eggs of the worm are laid. As it passes toward the anterior end of the worm, it receives from the body openings the sperms and a nutritive fluid in which the eggs live. The fertilized eggs are then left to hatch. The capsules may be found in manure heaps, or under stones, in May or June ; they are small yellow- ish or brown bags about the diameter of a worm. Regeneration. — If a one-celled animal be cut into two pieces, each piece, if it contains part of the nucleus, will grow into a whole cell. The hydra, some hydroids, jellyfish, and flatworms, if injured, may grow again parts that are lost. This power is known as regeneration. Earth- worms possess to a large degree the power of replacing parts lost through accident or other means. The anterior end may form a new posterior end, while the posterior end must be cut anterior to the girdle to form a new anterior end. This seems to be in part due to the greater com- plexity of the organs in the anterior end. 216 THE WORMS The Sandworm. — Other segmented worms are familiar to some of us. The sandworm, used for bait along our eastern coast, is a segmented worm which lives between tide marks in sandy locahties. It is plainly segmented, each segment bearing a pair of loco- motor organs called parapodia (meaning side feet). A part of each parapodium is prolonged into a triangular gill. The animal has a distinct head, which is provided with tentacles, palps, and eye spots. The mouth has a pair of hard jaws which may be protruded. In this way the animal seizes and draws prey into its mouth. The sandworm swims near the surface of the water, the body bending in graceful undulations as the parapodia, like little oars, force the worm forward. They spend much of the time in tubes in the sand, which are constructed in part of slime excreted from the body of the worm. The Leech. — The common leech or bloodsucker is a flattened segmented worm, inhabiting fresh-water ponds and rivers. The adult is provided with two sucking disks, by means of which it fastens itself to objects. The mouth is on the lower surface close to the anterior disk. Loco- motion is accomplished by swimming or by means of the suckers, somewhat after the manner of a measuring worm. They feed greedily and are often found gorged with blood, which they suck from the body of the victim. The sandworm Discomfort, but no danger, attends the bite of the blood- (nereis). sucker, so dreaded by the small boy. Problem XXVIII, A study of some animal associations, {Laboratory Manual, Proh. XXVIII.) worms are unseg- Some Worms which harm Man. — Some mented ; such are the flatworms and roundworms. A common leaflike form of flatworm may be found cling- ing to stones in our fresh-water ponds or brooks. Most flatworms are, how- ever, parasites on other animals; that is, they obtain food and shelter from some other living creature, but give them no benefits in return. Parasit- ism is one-sided, the host giving everything, the parasite receiving everything. Consequently, the parasite frequently becomes fastened to its host during adult life A flatworm ( Yungia Aurantiaca), much magnified. From model in the American Museum of Natural History. THE WORMS 217 and often is reduced to a mere bag through which the fluid food prepared by its host is absorbed. Such animals as have lost power to move about freely, or are otherwise changed by their surroundings, are said to have degenerated. Sometimes a complicated life history has arisen from their para- sitic habits. Such is seen in the life history of the liver fluke, a flatworm which kills sheep, and in the tapeworm. Cestodes or Tapeworms. — These parasites infest man and many other vertebrate animals. The tapeworm {Tcenia solium) passes through two stages in its hfe history, the first within a pig, the second within the intestine of man. The eggs of the worm are taken in with the pig's food. The worm develops within the intestine of the pig, but soon makes its way into the muscles. If man eats pork containing these worms, he may become a host for the tapeworm. Another common tapeworm parasitic on man lives part of its life as an embryo within the muscles of cattle. The adult worm consists of a round headlike part provided with hooks, by means of which it fastens itself to the wall of the intestine. This head now buds off a series of segmentlike struc- tures, which are practically bags full of eggs. These structures, called proglottids, break off from time to time, thus allowing the eggs to escape. The proglottids have no separate digestive systems, but the whole body surface, bathed in digested food, absorbs it and is thus enabled to grow rapidly. Roundworms. — Still other wormhke creatures called round- worms are of importance to man. Some, as the vinegar eel found in vinegar, or the pinworms parasitic in the lower intestine, par- ticularly of children, do little or no harm. The pork worm or trichina, however, is a parasite which may cause serious injury. It passes through the first part of its existence as a parasite in a pig or other vertebrate (dog, cat, ox, or horse), where it encysts itself in the muscles of its hosts. In the case of pork, if the meat is eaten in an uncooked condition, the cyst is dissolved off by the action of the digestive fluids, and the living trichina becomes free in the intestine of man. Here it bores its way through the intestine walls and enters the muscles, causing inflammation there. This causes a painful and often fatal disease known as trichinosis. The Hookworm. — The discovery by Dr. C. W. Stiles of the 218 THE WORMS Bureau of Animal Industry, that the laziness and shiftlessness of the '' poor whites " of the South is partly due to a parasite called the hookworm, reads like a fairy tale. The people, largely farmers, become infected with a larval stage of the hookworm, which develops in moist earth. It enters the body usually through the skin of the feet, for children and adults alike, in certain localities where the disease is common, go barefoot to a considerable extent. A complicated journey from the skin to the intestine now fol- A family of poor whites in North Carolina. All infected with hookworm lows, the larvae passing through the veins to the heart, from there to the lungs ; here they bore into the air passages and eventually reach the intestine by way of the windpipe. One result of the injury of the lungs is that many thus infected are subject to tuber- culosis. The adult worms, once in the food tube, fasten themselves and feed upon the blood of their host by puncturing the intestine wall. The loss of blood from this cause is not sufficient to account for the bloodlessness of the person infected, but it has been discovered that the hookworm pours out a poison into the wound which pre- THE WORMS 219 vents the blood from coagulating (see page 367) rapidly; hence a considerable loss of blood occurs from the wound after the worm has finished its meal and gone to another part of the intestine. The cure of the disease is very easy; thymol, which weakens the hold of the worm, being followed by Epsom salts. For years the entire South undoubtedly has been retarded in its development by this parasite, and hundreds of millions of dollars and, what is more vital, thousands of lives, have been needlessly sacrificed. " The hookworm is not a bit spectacular : it doesn't get itself dis- cussed in legislative halls or furiously debated in political campaigns. Modest and unassuming, it does not aspire to such dignity. It is satis- fied simply with (1) lowering the working efficiency and the pleasure of living in something like two hundred thousand persons in Georgia and all other Southern states in proportion ; with (2) amassing a death rate higher than tuberculosis, pneumonia, or typhoid fever; with (3) stub- bornly and quite effectually retarding the agricultural and industrial de- velopment of the section ; with (4) nullifying the benefit of thousands of dollars spent upon education; with (5) costing the South, in the course of a few decades, several hundred millions of dollars. More serious and closer at hand than the tariff; more costly, threatening, and tangible than the Negro problem ; making the menace of the boll weevil laughable in comparison — it is preeminently the problem of the South." — Atlanta Constitution. Parasitic worms are of vital importance to mankind. Not only do they levy a tax of death and illness on man himself, but they destroy as well unestimated millions of dollars' worth of ani- mals. Of the 2,000,000 persons infected with hookworm, 500,000 are wage earners (and this is a small estimate) ; their earnings at $1.50 a day would amount to about $225,000,000 a year. If their wage-earning capacity were decreased only 10 per cent, it is seen that a loss of over $20,000,000 a year could be directly attributed to this pest. Other Parasitic Worms. — Some roundworm parasites live in the skin, and others live in the intestines of the horse. Still others are parasitic in fish and in insects, one of the commonest being the hair snake, often seen in country brooks. 220 THE WORMS Classification of Segmented Worms (Annulata) Class I. Choetopoda (bristle-footed). Segmented worms having setae. Subclass I. Polychoeta (many bristles). Having parapodia and usually head and gills. Example : sandworm. Subclass II. Oligochceta (few bristles). No parapodia, head, or gills. Ex- ample : earthworm. Class II. Discophora (bearing suckers). No bristles, two sucking disks present. Example : leech. Platyhblminthes (Flat worms) Body flattened in dorso-ventral direction. Class I. Turbellaria. Small, aquatic, mostly not parasitic. Example : planarian worm. Class II. Trematoda. Usually parasitic worms which have complicated life history. Example : liver fluke of sheep. Class III. Cestoda. Internal parasites having two hosts. Example : tape- worm. Nemathelminthes (Roundworms) Threadlike worms, mostly parasitic. Examples: vinegar eel. Trichina, and hook- worm. Reference Books elementary Sharpe, A Laboratory Manual for the Solution of Problems in Biology. American Book Company. Davison, Practical Zoology, pages 150-161. American Book Company. Herrick, Textbook in General Zoology, Chap. IX. American Book Company. Jordan, Kellogg, and Heath, Animal Studies, VI. D. Appleton and Company. Ritchie, Primer of Sanitation. World Book Company. ADVANCED Darwin, Earthworms and Vegetable Mold. D. Appleton and Company. Sedgwick and Wilson, General Biology. Henry Holt and Company. XVIII. THE CRAYFISH. A STUDY OF ADAPTATIONS Problem, XXIX. A study of the idea of adaptations as shou/n in the crayfish {optional). (Laborai^ory Manual, Prob. XXIX.) (a) Protection. (b) Locomotion. (c) Surroundings. (d) Feeding. (e) Breathing. Adaptations. — Plants and animals are in a continual struggle to hold the places they have obtained upon the earth. Continually we see garden plants driven out or killed by the competing weeds, simply because the weeds are better fitted or adapted to live under the conditions which exist in the garden, especially if it is unculti- vated. An adaptation in a plant or animal is some structure, habit, or abihty which is of advantage to the organism in its battle for life. We have seen many examples of adaptations in plants, — adaptations in flowers for securing cross-pollination, in fruits for seed-scattering, in young plants for protection, in roots for water- securing ; the Hst is endless. In animals, likewise, the successful competitors are the ones with adaptations to fit them for living in the particular environment or surroundings in which nature has put them. Examples are often seen where animals, hke sheep or goats, which have a woolly cover- ing, when introduced by man into a warmer country, die because the outer coat is too warm. An adaptation for withstanding cold becomes harmful to the animal under conditions of greater heat. One adaptation which we have already noticed in animals is always protective. This is resemblance of the animal to the sur- roundings in which it fives. Other adaptations aid the animal in obtaining and digesting food, in protecting itself or its young from attack by enemies, and in many other ways aiding the animal to battle successfully with the dangers around it. 221 222 THE CRAYFISH The Crayfish. Adaptations for Protection. — An animal which well illustrates adaptation for life in the water is the fresh-water crayfish or the salt-water lobster, both members of a large group of animals known as crustaceans. The body of such an animal is seen to be covered more or less completely with a hard covering, which is jointed in the posterior region. This exoskeleton (outside skeleton) is composed largely of lime, as may be proved by testing with acid. The exoskeleton fits over the anterior part of the animal, forming an unjointed carapace, or armor. This armor is clearly protective and is thus an adaptation. If the crayfish is watched in a balanced aquarium, the colors, too, are seen to blend remarkably with the stones and water weeds of the bottom. The animal is protec- tively colored. The under s'de of the animal is seen to be less well pro- m Ch. C.P ---^^^^b. 1 4, i Crayfish: A., antennae; E., stalked eye; C.P., cephalothorax ; Ab., abdomen; C.F., caudal fin; M., mouth; Ch., chehpeds. From photograph. tected than the upper, and the joints of the abdomen, or posterior region, are seen to extend completely around the body. The animal is thus seen to be segmented, the abdomen showing this plainly. The seven segments in the abdomen are constant for every crayfish. Locomotion. — Those of us who have caught crayfish in fresh-water streams or lakes know that it takes skill and quickness. They dart backwards through the water with great rapidity, or they may move forward by crawling on the bottom. Examination of a crayfish shows us five pairs of walking legs attached to the under side of the cephalothorax (head + thorax), the anterior part of the body. These legs are jointed, the first three bearing pinchers. The large pincher claw is used partly for food-catching, and for locomotion as well. Try to find out, in a hving specimen, exactly what part it plays. Under the abdomen, one to each segment except the last, are found jointed appendages, made up of three parts, a base and two branches. These are called smmmerets, though they are not used for swimming. Now look at the broad pair of appendages that, together with the last THE CRAYFISH 223 segment of the abdomen, form a finlike apparatus, the caudal fin. The caudal fin is composed of two large swimmerets and the last body segment. Crayfish normally swim very rapidly by means of a sudden jerking in a backward direc- tion of the caudal fin. The abdomen is provided with powerful muscles which are attached to the exoskeleton. It is by these muscles that the rapid swimming is ac- complished. How the Crayfish gets in Touch with its Surroundings. — Several other appendages besides those used for loco- motion are found. Two pairs of *' feelers," the longer pair called the antenncB, the shorter the antennules (little anten- nse), protrude from the front of the body. The longer feelers appear to be used as organs of touch. Certain hairlike structures projecting from the antennae have to do with the sense of smell. The smaller antennules hold at their bases little sacs called "ears." These "ears" have largely to do with the function of balancing rather than hearing. Just above the antennules, projecting on stalks, are the eyes. These eyes are made up of many small structures called ommatidia, each of which is a very simple eye. A collection of ommatidia is known as a compound eye. A little bit of the outer covering of the eye, mounted under a compound microscope, shows these eye units to be shaped like tiny rectangles in cross section. Such an eye probably does not have very distinct vision at a distance. A cray^fish, however, easily distinguishes moving objects and prefers darkness to light, as may be proved by experi- ment. Feeding. — If it is possible to have the aquarium holding the crayfish in the schoolroom, the method of feeding may be watched. The pincher claws (chelipeds) are used to hold and tear food, as well as for defense and offense. Living food is obtained with the aid of the chelipeds. P^ood is shoved by the chelipeds toward the mouth; it is assisted there by three pairs of small appendages called foot jaws (maxillipeds), and to a Female lobster, showing eggs attached to the swimmerets. From photograph loaned by the American Museum of Natural History. 224 THE CRAYFISH slight degree by two still smaller paired maxillce just under the maxil- lipeds. Ultimately the food reaches the hard jaws and, after being ground between them, is passed down to the stomach. Breathing. — The mouth parts of a crayfish resting in the aquarium are observed to be constantly in motion, despite the fact that no food is present. If a crayfish is taken out of the water and held with the ventral surface upmost, a little carmine (dissolved in water) may be dropped on the lower surface and allowed to run down under the cara- pace. If now the animal is held in water in the same position, the carmine will reappear just beyond from both sides of the mouth, seemingly pro- pelled by something which causes it to emerge in little puffs. If we Some appendages of the crayfish: 1, the jaw, with palp; 2, first maxilla (second maxilla not shown) ; 3, third maxilliped ; 4. second maxilliped, showing baler ; J, first maxilliped, showing gill attached ; 6, walking appendage, showing attach- ment of gill ; 7, swimmeret ; 8, uropod. remove the maxillipeds and maxillae from a dead specimen, we find a groove leading back from each side of the mouth to a cavity of con- siderable size on each side of the body under the carapace. This is the gill chamber. It contains the gills, the organs which take oxygen out of the water. The second maxillae are prolonged down into the groove to serve as bailers or scoops. By rapid action of this organ a current of water is maintained which passes over the gills. The gills are outside of the body, although protected by the carapace. If the carapace is partly removed on one side, they will be found looking somewhat like white feathers. The blood of the crayfish passes by a series of vessels into the long axis of the gill ; in this organ the blood tubes divide into very minute tubes, the walls of which are extremely THE CRAYFISH 226 delicate. Oxygen, dissolved in the water, passes into the blood by os- mosis, during which process the blood loses some carbon dioxide. The gills are kept from drying by being placed in a nearly closed chamber, which is further adapted to its function by means of the row of tiny hairs which border the lower edge of the carapace. Thus crayfish may live for long periods away from water. Circulation. — The circulation of blood in the crayfish takes place in a system of thin-walled, flabby vessels which are open in places, allowing the blood to come in direct contact with the tissues to which it flows. The heart lies on the dorsal side of the body, inclosed in a delicate bag, into which all the blood in the body eventually finds its way during its circulation. Crayfish with the left half of the body structures removed : a, intestines ; 6, ventral artery ; c, brain ; e, heart ; et, gastric teeth ; i, oviduct ; /, digestive gland : m, muscles ; n, green gland (kidney) ; o, ovary ; p, pyloric stomach ; r, nerve cords : 8, cardiac stomach ; st, mouth ; u, telson ; w, openings of veins into the peri- cardial sinus. Natural size. (Davison, ZoQlogy.) Digestion. — Food which is not ground up into pieces small enough for the purpose of digestion is still further masticated by means of three teeth, strong projections, one placed on the mid-line and two on the side walls of the stomach. The exoskeleton of the crayfish extends down into the stomach, thus forming the gastric mill just described. The stomach is divided into anterior and posterior parts separated from each other by a constriction. The posterior part is lined with tiny projections from the wall which make it act as a strainer for the food passing through. Thus the larger particles of food are kept in the anterior end of the stomach. Opening into the posterior end of the stomach are two large digestive glands which further prepare the food for absorption through the walls of the intestine. Once in the blood, the fluid food is circulated through the body to the tissues which need it. Nervous System. — The internal nervous system of a crayfish con- sists of a series of collections of nerve cells {ganglia) connected by means of a double line of nerves. Posterior to the gullet, this chain of ganglia is found on the ventral side of the body, near the body wall. It then en- HUNT. ES. BIO. — 15 226 THE CRAYFISH circles the gullet and forms a brain in the head region, the latter formed from several ganglia which have grown together. From each of the ganglia, nerves pass off to the sense organs and into the muscles of the body. These nerve fibers are of two sorts, those bearing messages from the outside of the body to the central nervous system (these messages result in sensations), and those which take outgoing messages from the central nervous system (motor impulses), which result in muscular move- ments. Development. — The sexes in the crayfish are distinct. The eggs are fertihzed by the sperm cells as they pass to the outside of the body of the female. The developing eggs, which are provided with a considerable supply of food material called yolk, are glued fast to the swimmerets of the mother, and there develop in safety. The young, when they first hatch, remain clinging to the swimmerets for several weeks. Excretion of Wastes. — On the basal joint of the antennae are found two projections, in the center of which are found tiny holes. These are the open- ings of the green glands, organs which have the function of the elimination of nitrogenous waste from the blood, the function of the human kidneys. North American lobster. This specimen, preserved at the U.S. Fish Commission at Woods Hole, was of unusual size and weighed over twenty pounds. Notice the chelipeds. The North American Lobster. — In structure it is almost the counterpart of its smaller cousin, the crayfish. Its geographical range is a strip of ocean bottom along our coast, estimated to vary from thirty to fifty miles in width. This strip extends from Labrador on the north to Delaware on the south. The lobster is highly sensitive to changes in temperature. It migrates from deep to shallow water, or vice versa, according to the temperature of the water, which in winter is relatively warmer in deep water and cooler in shallows. Sudden changes in the water of a given locality may cause them to disappear from that place. The more abundant food supply near the shore also aids in determining the habitat of the lobster. Lobsters do not appear to migrate north and south along the coast. While little is known about THE CRAYFISH 227 their habits on the ocean bottom, it is thought that they construct burrows somewhat Hke the crayfish, in which they pass part of the time. As they have the color of the bottom and as they pass much of their time among the weed-covered rocks, they are able to catch much living food, even active fishes falling prey to their formidable pinchers. They move around freely at night, usually remaining quiet during the day, especially when in shallow water. They eat some dead food ; and thus, like the crayfish, they are scavengers. Development. — The female lobsters begin to lay eggs when about seven inches in length. Lobsters of this size lay in the neighborhood of five thousand eggs; this number is increased to about ten thousand in lobsters of moderate size (ten inches in length) ; in exceptionally large speci- mens as many as one hundred thou- sand eggs are sometimes laid. The eggs are laid every alternate year, usually during the months of July and August. Eggs laid in July or August, as shown by observations made along the coast of Massa- chusetts, hatch the following May or June. The eggs are provided with a large supply of yolk (food), the development of the young ani- mal taking place at the expense of this food material. After the young escape from the egg, they are almost transparent and little like the adult in form. During this period of their lives the mortality is very great, as they are the prey of many fish and other free-swimming animals. It is estimated that barely one in five thousand survives this period of peril. At this time they grow rapidly, and in conse- quence are obliged to shed their exoskeleton (molt) frequently. During the first six weeks of life, when they swim freely at the surface of the water, they molt from five to six times. ^ ^ Recent economic investigations upon the care of the young developing lobster show that animals protected during the first few months of free existence have Metamorphosis of a shrimp : a, nau- plius or earliest stage ; b, c, d, later larval stages ; e, adult. Note that as the animal grows more append- ages appear, and that these develop backward from the anterior end. 228 THE CRAYFISH Molting. — During the first year of its life the lobster molts from fourteen to seventeen times. During this period it attains a length of from two to three inches. Molting is accomphshed in the follow- ing manner : The carapace is raised up from the posterior end and the body then withdrawn through the opening between it and the abdomen. The most wonderful part of the process is the with- drawal of the flesh of the large claws through the very small openings which connect the Hmbs with the body. The blood is first with- drawn from the appendage ; this leaves the flesh in a flabby con- dition (a state similar to the taproot which has lost water by osmosis) so that the muscles can be drawn through without injury. The lobster also molts a part of the lining of the digestive tract as far as the posterior portion of the stomach. Immediately after molt- ing the lobster is in a helpless condition, and is more or less at the mercy of its enemies until the new shell, which is secreted by the skin, has grown. Economic Importance. — The lobster is highly esteemed as food, and is rapidly disappearing from our coasts as the result of overfishing. Between twenty million and thirty million are yearly taken on the North Atlantic coast. This means a value at present prices of about $15,000,000. Laws have been enacted in New York and other states against overfishing. Egg-carrying lobsters must be returned to the water ; all smaller than six to ten and one half inches in length (the law varies in different states) must be put back; other restrictions are placed upon the taking of the animals, in hope of saving the race from extinction. Some states now hatch and care for the young for a period of time; the United States Bureau of Fisheries is also doing much good work, in hope of restocking to some extent the now almost depleted waters. Shrimps. — Several other common crustaceans are near relatives of the crayfish. Among them are the shrimps and prawns, thin-shelled, active crustaceans common along our eastern coast. In spite of the fact that they form a large part of the food supply of many marine animals, especially fishes, they do not appear to be decreasing in numbers. Be- a far better chance of becoming adults than those left to grow up without protec- tion. Later in life they sink to the bottom, and because of their protectively colored shell and the habit of hiding under rocks and in burrows, they are comparatively safe from the attack of enemies. THE CRAYFISH 229 sides this value as a food, they are also used by man, the shrimp fisheries in tliis country aggregating over $1,000,000 yearly. The Blue Crab. — Another edible crustacean of considerable economic importance is the blue crab. Crabs are found inhabiting muddy bot- toms ; in such localities they are caught in great numbers in nets or traps baited with decaying meat. They are, indeed, among our most valu- able sea scavengers, although they are carnivorous hunters as well. The body of the crab is short and broad, be- ing flattened dorso-ventrally. The abdomen is much re- duced in size. Usually it is carried close to the under surface of the cephalothorax ; in the female the eggs are carried under its ventral surface, fastened to the rudimentary swimmerets in the position which is usual for other crustaceans. The young crabs differ considerably in form from the adult. They undergo a complete metamorphosis (change of form), and their method of life differs from the adult. Immediately after molting, crabs are greatly desired by man as an article of food. They are then known as " shedders," or soft-shelled crabs. Other Crabs. — Other crabs seen along the New York coast are the prettily colored lady crabs, often seen running along our sandy beaches at low tide ; the fiddler crabs, interesting because of their burrows and gre- garious habits; and perhaps most interesting of all, the hermit crabs. The edible blue oral). From photograph loaned by the American Museum of Natural History. The fiddler crab. From photograph loaned by the American Museum of Natural History. Hermit crab, about twice natural size. From photograph loaned by the Amer- ican Museum of Natural History. The hermit crabs use the shells of snails as homes. The abdomen is soft, and unprotected by a limy exoskeleton, and has adapted itself to its con- 230 THE CRAYFISH ditions by curling around in the spiral snail shell, so that it has become asymmetrical. These tiny crabs are great fighters and wage frequent duels with each other for possession of the more desirable shells. They exchange their borrowed shells for l^irger ones as growth forces them from their first homes. The habits of these animals, and those of the fiddler crabs, might be studied with profit by some careful boy or girl who spends a summer at the seashore and has the time and inclination to devote to the work. Of especial interest would be a study of the food and feeding habits of the fiddler crabs. A deep-water crab often seen along Long Island Sound is the spider crab, or " sea spider," as it is incorrectly called by fishermen. This animal, with its long spider- like legs, is neither an active runner nor swimmer; it is, however, colored like the dark mud and stones over which it crawls ; thus it is enabled to approach its prey without be- ing noticed. The resemblance to the bottom is further heightened by the rough body covering, which gives a hold for seaweeds and sometimes sessile animals, as barnacles, hydroids, or sea anemones, to fasten themselves. A spider crab from the Sea of Japan is said to be the largest crustacean in the world, specimens measuring eighteen feet from tip to tip of the first pair of legs having been found. Giant spider crab from Japan. From photograph loaned by the American Museum of Natural History. Symbiosis. — Certain of the spider crabs, as well as some of the larger deep-water hermit crabs, have come to live in a relation of mutual helpfulness with hydroids, sponges, and sea anemones. These animals attach themselves to the shell of the crab and are carried around by it, thus receiving a constant change of position and a supply of food. What they do for the crab in return is not so evident, although one large Chinese hermit regularly plants a sea anemone on its big claw ; when forced to retreat into its shell, the entrance is thus effectually blocked by the anemone. The THE CRAYFISH 231 living of animals in a mutually helpful relation has been referred to as symbiosis. Of this we have already had some examples in plants as well as among animals. (See page 187.) Habitat. — Most crustaceans Site adapted to live in the water ; a few forms, however, are found hving on land. Such are the wood lice, the pill bugs, which have the habit of rolling up into a ball to escape attack of enemies, the beach fleas, and others. The coconut crab of the tropics climbs trees in search of food, return- ing to the water at intervals to moisten the gills. Characters of Cra3rfish and its Allies. — Our study of cray^sh shows us that animals belonging to the same group as itself have several well-marked characteristics. The most important are the presence of a segmented Umy exoskeleton, gills, jointed appendages, usually a pair to each segment of the body (except the last), stalked compound eyes, and the fact that they pass through a metamor' phosis or change of form before they reach the adult state. We find that the Crustacea fall naturally into two classes, those in which the number of pairs of appendages varies, and those in which the number is fixed at nineteen. In this latter class are placed the crayfish, lobster, blue crab, shrimp, and most of our common crustaceans. Entomostraca. — Another sub- class of crustaceans, in which the number of appendages varies, is the group Entomostraca. They are mostly small animals, some species existing in countless numbers. One of the largest Entomostracans in- habiting fresh water is the fairy shrimp (branchippus) found ap- pearing in early spring in fresh- water ponds, a little translucent swimming animal from one half to three fourths of an inch in length. Another fresh-water form often seen in aquaria is the water flea (daphnia). From the economic standpoint, probably the most un- Cyclops (note the single eye-spot). This portant crustaceans that we shall is a very common copepod and is mag- study are the copepods. These tiny nified about forty times, e, egg masses. 232 THE CRAYFISH animals are barely visible to the naked eye. They are found in almost every part of the world, from the arctic seas to those of the tropics, and in fresh as well as salt water. They are so numerous that the sea in places is colored by their bodies. So prolific are they that it is estimated that one copepod may produce in a single year four billion five hundred million offspring. These animals form a large part of the food supply of many of our most important food fishes as well as the food of many other aquatic animals. The whale, for example, subsists largely on this kind of food. They are, then, in an indirect way, of immense economic value. Degenerate Crustaceans. — One of the most interesting forms to a zoologist is the goose barnacle. This crustacean, like all others of the group, is free-swimming during its early life. Later, however, after passing through several changes in form during its development, the barnacle settles down on a rock or some floating object, fastens itself along the dorsal surface, and remains fastened during the rest of its life. Food comes to it in a current of water, which is set in motion by the rhyth- mical beating of the appendages. Thus food particles are carried along the ventral side of the body to the mouth. Such animals, having lost the power of locomotion, are said to be degenerate. Parasitic Crustaceans. — Other crustaceans have become even more helpless and have come to take their living from other animals. In some cases they become simply a bag for absorbing nourishment from the host on which they are fastened. Such is the sacculina, a degenerate crusta- cean that lives attached to the body of the crab. Others attach them- selves to fishes and are known to fishermen as fish lice. Reference Books elementary Sharpe, A Laboratory Manual for the Solution of Problems in Biology. American Book Company. Burnet, School Zoology, pages 67-73. American Book Company. Davison, Practical Zoology, pages 133-141. American Book Company. Herrick, Textbook in General Zoology, Chap. XIII. American Book Company. Jordan and Kellogg, Animal Life, Chap. VIII. D. Appleton and Company. Jordan, Kellogg, and Heath, Animal Studies, Chap. IX. D. Appleton and Com- pany. ADVANCED Herrick, The American Lobster, Report of U.S. Fish Commission, 1895. Huxley, The Crayfish. D. Appleton and Company. Mead, Reports of the R.I. Inland Fisheries Commission. Parker, Elementary Biology. The Macmillan Company. Parker and Haswell, Textbook of Zoology. The Macmillan Company. XIX. THE INSECTS Problem XXX, A study of some anirndl likenesses and dif- ferences, and the classification of insects {optional). {Laboratory Manual, Prob. XXX.) {a) Grasshopper— a straight-winged insect. (b) Butterfly or moth— a scale-winged insect, (c) Tlie typlwid fly — a two-winged insect, (d) A beetle— a sheath-winged insect, ie) A bug — a ha2f -winged insect. (/) The dragon fly — a nerve-winged insect, ig) The bee — a membrane-winged insect. (Jv) Summ^ary of differences between orders, (i) Making a logical definition. Insects the Winners in Life's Race. — We are all familiar with common examples of insect life. Bees and butterflies we have already studied in connection with their work in the cross-pollina- tion of flowers. Mosquitoes and flies all too often come to our notice as pests ; the common household insects sometimes annoy us, while we often hear and see in a small way the harm done by insects in the field and garden. Insects are a successful group. They outnumber all the other species of animals on the face of the earth. They hold their own in the air, in the water, and on land. Fitted in many ways to lead the successful life, they have become winners in life's race. We have already, from our study of a bee, formed some idea of what an insect is. But it would be unfair to expect to know all insects from our slight knowledge of one form. Our object in the study of this chapter will be to get some first-hand knowledge of some common insects so that we may classify them and distinguish one from another. This great group, containing more than half of the known representatives of animal life on the earth, is made up of a number of groups called orders. The insects contained in these orders have certain characters of structure and 23a 234 THE INSECTS life history in common, yet each differs somewhat from the other orders. The characters which all the groups contain in common give us a working definition of an insect. One of the most common insects in the United States is the locust or grasshopper, as it is commonly called. The study of a living specimen (or if it cannot be obtained, a dead locust) will, better than any other insect, give us insight into the structure and life processes of this great group. The Locust (Red-legged Grasshopper). — The segmented body is divided into a head, sl middle portion (the thorax), and a pos- terior part, the abdomen. The legs, six in number, and two pairs of wings are attached to the thorax. The animal lives a rather active life in the fields, the hind pair of legs be- ing adapted by shape, position, and in structure for leaping. Careful ex- amination of the foot of the animal shows a num- ber of tiny hooks and pads, by means of which the foot is fitted for chnging to the swaying grass stalks. Wings. — The membranelike wings, when spread out, show differences in structure. Notice the many veins. The outer pair, strong and narrower than the inner pair, serve to protect the inner wings, used for flying, which when at rest fold up like a fan. The animal, when in its natural habitat, is nearly the color of the grass on which it lives. The tough exoskeleton covering the body is formed largely of chitin, a substance somewhat Hke that which forms the horns of a cow. Thorax. — Three segments form the thorax, each bearing a pair of jointed legs, the two posterior segments bearing wings also. The Abdomen. — The segmented abdomen does not bear ap- pendages, but at the posterior end of the abdomen of the female are found paired movable pieces which together form the egg layer or ovipositor. The male grasshopper has a rounded abdomen. Locust (lubber grasshopper) : AB, abdomen; ANT, antennae; E, eye; M, mouth; P, pads on feet; T, thorax; OV, ovipositor. THE INSECTS 235 Breathing Organs. — Observation of the abdomen of a Hving grasshopper shows a frequent movement of the abdomen. Along the side of the abdomen in eight of the segments (in the red-legged grasshopper) are found tiny openings called spiracles. A large spiracle may easily be found in the middle segment of the thorax. These spiracles open into little tubes called trachece. The tracheae carry air to all parts of the body. By the movements of the abdo- men just noted, air is drawn into and forced out of the tracheae. The tracheae divide and subdivide like branches of a tree, so that all the body cavity is reached by their fine endings. Some even pass outward into the veins of the wings. Each of these tubes contains air. The blood of an insect does not circulate through a system of closed blood tubes as in man, but instead it more or less completely fills that part of the body cavity which is not filled with other organs. Oxygen is thus brought in contact with the blood by means of the tracheae. Muscular Activity. — Insects have the most powerful muscles of any animals of their size. Relatively, an enormous amount of energy is released during the jumping or flying of a grasshopper. The tracheae pass directly into the muscles and other tissues. Here oxygen is passed into the tissues, and oxidation takes place when work is done. Food-Taking and Blood-Making. — The grasshopper is provided with two pairs of jaws, a forklike ventral-lying pair, the maxillce, and a pair of hard cutting jaws, the mandibles. These parts are covered when not in use by two flaps, the upper and lower hps. The plant food taken by the grasshopper is held in place in the mouth by means of the little jaws, or the maxillae, while it is cut into small pieces by the mandibles. Just behind the mouth is a large crop into which empty the contents of the salivary glands. It is this fluid mixed with digested food that we call the " grass- hopper's molasses." After the food is digested by the action of the Cross section through the body of an insect: a, food tube; h, heart; n, nerve cord; t, tracheae opening at t by spiracle. 236 THE INSECTS saliva and other juices, it passes in a fluid state through the walls of the intestine, where it becomes part of the blood. As blood it is passed on to tissues, such as muscle, to make new material to be used in repairing that which is used up during the flight of the insect or to be oxidized to release energy for the active insect. Eyes. — A considerable part of the surface of the head of the grass- hopper is taken up by the compound eyes. Examination with a lens shows the whole surface to be composed of tiny hexagonal spaces called facets. Each facet is believed to be a single eye, with perhaps distinct vision from its neighbor. The grasshopper also has three simple eyes on the front of the head. The simple eyes probably are only able to perceive light and darkness. The sepa- rate units of the compound eye probably each give a separate impression of light and color. Thus a com- pound eye is most favorable for perceiving the move- ment of objects. Other Sense Organs. — The segmented feelers, or antennce, have to do with the sense of touch and smell. The eardrum, or tympanum, of the grasshopper is found under the wing on the first segment of the ab- domen. Covering the body and on the appendages, are found hairs (sensory hairs) which appear to make the insect sensitive to touch. Thus the armor-covered animal is put in touch with its surroundings. Nervous System. — The nerve chain, as in the cray- fish, is on the ventral side of the body. As in the crayfish, it passes around the gullet near the head to the dorsal side, where a collection of ganglia forms the brain. Nerves leave the central system as outgoing fibers which bear motor impulses. Other nerve fibers pass inward, and produce sensations. These are called sensory fibers. Longitudinal section of part of the com- pound eye of an insect : a, facets ; c, nerves. Life History. — The female red-legged locust lays its eggs by- digging a hole in the ground with her ovipositor, or egg-layer, the modified end of the abdomen. From twenty to thirty eggs are laid in the fall; these hatch out in the spring as tiny wingless grasshoppers, otherwise like the adult. As in the crayfish, the young molt in order to grow larger, each grasshopper undergoing several molts before reaching the adult state. No great change in form occurs, the metamorphosis being said to be incomplete. In the fall most of the adults die, only a few surviving the winter. Relatives of the Locust. — Among the near relatives are the brown or black crickets, cockroaches and " waterbugs," the katydid, THE INSECTS 237 Part of the ving of a moth (aamia), magnified to show the arrangement of scales partly nibbed oflf. praying mantis, and many others. All of the above insects have the hind wings, when present, folded up lengthwise against the body when at rest, mouth parts fitted for biting, and an incomplete metamorpho- sis. They are thus placed in an order called Orthoptera because the posterior wings are folded straight against the body when at rest {orthos, straight, pteron, wing). The Butterfly. — The body of the butterfly, as that of the grasshopper, is composed of three regions. Compared with the grasshopper, the wings and legs show the greatest differences in structure. The legs of the butterfly are relatively smaller and weaker than those of the grasshopper, while the wings are rela- tively larger in the first-named insect. Evidently the butter- fly spends much of its time in the air. If the wing is rubbed with the finger, dust comes off it, leaving the wing transparent or membrane-like. Under the microscope the wing is seen to be covered with thou- sands of little colored scales, each of which fits into a socket in the wing. These scales cause the name Monarch butterfly : adults, larva, and pupa on milk- T '^ f (1 ' weed. From photograph loaned by the American ^^P^^aoptera {lepiS, Museum of Natural History. SCale, pteron, wing) to 238 THE INSECTS be given to this order of insects. The long proboscis, a sucking tube through which the insect sucks nectar from flowers, is an- other character by which the Lepidoptera may be known. Life History. — The monarch or milkweed butterfly (Anosia plexippus) is one of our commonest insects. Its orange-brown, black-veined wings are famihar to every boy or girl who has been outdoors in the country during the fall months. The adult female lays her eggs in the late spring on the milkweed. The eggs, tiny sugar-loaf-shaped dots a twentieth of an inch in length, are fas- tened singly to the underside of milkweed leaves. Some won- derful instinct leads the animal to deposit the eggs on the milkweed, for the young feed upon no other plant. Eggs laid in May hatch out in four or five days into rapid-growing caterpillars, each of which will molt several times before it becomes full size. These caterpillars possess in addition to the three pairs of true legs, additional pairs of prolegs or caterpillar legs. The animal at this stage is known as a larva. Formation of Pupa. — After a life of a few weeks a.t most, the caterpillar stops eating and begins to spin a tiny mat of silk upon a leaf or stem. It attaches itself to this web by the posterior pair of prolegs, and there hangs until a last molt (which occurs within twenty-four hours after attachment) gives the animal the form it assumes in the stage known as the chrysalis or pupa. The Adult. — After a week or more of inactivity, the exoskeleton is split along the dorsal side, and the adult butterfly emerges. At first the wings are soft and much smaller than in the adult. Within fifteen minutes to half an hour after the butterfly emerges, however, the wings are full-sized, having been pumped full of blood. In the adult form the animal may survive the winter. The milkweed butterfly is a strong flyer, and has been found over five hundred miles at sea. They may migrate southward upon the approach of the cold weather. Some common forms, as the mourning cloak (Vanessa antiopa), hibernate in the North, passing the cold weather under stones or overhanging clods of earth. Comparison between a Moth and a Butterfly. — The big electric light moth cecropia (Samia cecropia) is an insect familiar to most of us. In general it resembles a butterfly in structure. Several differences, however, occur. The body is much stouter than that of the butterfly. The wings THE INSECTS 239 and body appear to have a thicker coating of hairs and scales, and the antennas are feathery. The position of the wings when at rest forms another easy way of dis- tinguishing the one in- sect from the other. (See Figures, page 237.) Development. The Egg. — The eggs, cream- colored and as large as a pinhead, are deposited in small clusters on the underside of leaves of the food plant. The young are at first tiny black caterpillars, which later change color to a bluish green, with projec- tions of blue, yellow, and red along the dorsal side. The Pupal Stage. — Unlike the butterfly, the moth passes the quies- cent stage in a case of silk or other material called a cocoon. The co- coons of cecropia may be found in the fall on willows or alders. Such cocoons found in mead- ows or fields are usually larger than those found on the hillsides, probably because of a difference in the food supply of the larva which spun the cocoon. If the cocoon is cut open lengthwise (see Figure), the dormant insect or chrysalis will be found to- gether with the cast-oflF skin of the caterpillar which spun the case. Silkworms. — The Ameri- can silkworm (Telea polyphe- mus) is another well-known mbth. The cocoons, made in part out of the leaves of the elm, oak, or maple, fall to the ground when the leaves drop, and hence are Life history of the cecropia moth. Above, the adult ; the larva (caterpillar) in center ; the pupal case to right, below ; the same cut open at left, below. From photograph loaned by the American Mu- seimi of Natural History. Polyphemus, one half natural size, graphed by Davison. Photo- 240 THE INSECTS not so easily found as those of the cecropia. This moth is a near relative of the Chinese silkworm, and its silk might be used with success were it not for the high rate of labor in this country. The Chinese silkworm is now raised with ease in southern California. China, Japan, Italy, and France, because of cheap labor, are still the most successful silk-raising countries. Differences Between Moths and Butterflies Butterfly Moth Antennae threadlike, usually Antennae feathery or threadlike, knobbed at tip. never knobbed. Fly in daytime. Usually fly at night. Wings held vertically when at Wings held horizontally or folded rest. over the body when at rest. Pupa naked. Pupa usually covered by a cocoon. Moths and butterflies are both characterized by having a sucking proboscis, membranous wings covered with scales, and both undergo a complicated metamorphosis or change of form. By these characters we know them to be members of the order Lepidoptera. Diptera. The Typhoid Fly. — This name has been recently given to the common house fly by L. O. Howard, the Chief of the Bu- reau of Entomology, United States Department of Agriculture. Life history of house flies, showing from left to right the eggs, larvaj, pupae, and adult flies. Photograph, about natural size, by Overton. We shall later see with what reason this name is given. The body of the fly, as in other insects, has three divisions. The membran- ous wings appear to be two in number, a second pair being reduced THE INSECTS 241 to tiny knobbed hairs called balancers. Their function is seemingly that of equilibrium. The head is freely movable, the compound eyes being extremely large. Seemingly the fly has fairly acute vision. Home experi- ments can be easily made which prove its keenness of scent and caste. It is well equipped to care for itself in its artificial environ- ment in the house. The mouth parts of the fly are prolonged to form a proboscis, which is tonguelike, the animal obtaining its food by lapping and sucking. It is the rubbing of this file- like organ over the surface of the skin that causes the painful bite of the horsefly. If possible, we should examine the foot of a fly under the compound mi- croscope. The foot shows a wonderful adaptation for clinging to smooth sur- faces. Two or three pads, each of which bears tubelike hairs that secrete a sticky fluid, are found on its under surface. It is by this means that the fly is able to walk upside down. Hooks are also pres- ent which doubtless aid in locomotion in this position. Development. — The development of the typhoid fly is extremely rapid. A female may lay from one hundred to two hundred eggs. These are usually deposited in filth or manure. Dung heaps about stables, ash heaps, garbage cans, and fermenting vegetable refuse form the best breeding places for flies. In warm weather, within a day after the eggs are laid, the young maggots, as the larvae are called, hatch. After about one week of active feeding, these wormlike maggots become quiet and go into the pupal stage, whence under favorable conditions they emerge within less than another week as adult flies. The adults breed at once, and in a short summer there may be over ten generations of flies. This accounts for the great number. Fortunately few flies survive the winter. Other Diptera. — Other examples of this group are the mos- quitoes, of which more will be said hereafter; the Hessian fly, the HUNT. ES. BIO. — IG Foot of a fly, showing the hooks, hairs, and pads. 242 THE INSECTS larvae of which feeds on young wheat; the botfly, which in a larval state is a parasite on horses ; the dreaded tsetse fly of South Africa, which causes disease in horses and cattle by means of the transference of a parasitic protozoan, much like that which causes malaria in man ; and many others. Among the few flies useful to man may be mentioned the tachina flies, the larvae of which feed on the cutworm, the army worm, and various other kinds of injurious caterpillars. Characters of the Diptera. — Members of this group have only one pair of wings; the mouth parts are fitted for sucking, rasping, or piercing, and they pass through a com- plete metamorphosis. Coleoptera. Beetles. — Beetles are the most widely distributed and among the most nu- merous of all insects. There are over one hundred thousand living species. Any beetle will show the following charac- teristics: (1) The body is usually heavy and broad. Its exoskeleton is hard and tough, the chitinous body covering being better developed in the beetles than in any other of the insects. (2) The three pairs of legs are stout and rather short. (3) The outer wings are hard and fit over the under wings like a shield. These sheathlike wings are called elytra. (4) The mouth parts, provided with an upper and lower lip, are fitted for biting. They consist of very heavy curved pincher-shaped mandibles, which are provided with palps. The Life History of a Beetle. — The June beetle (May beetle) and potato beetle are excellent examples. May beetles lay their eggs in the ground, where they hatch into cream-colored grubs. A grub differs from the larva fly or maggot in possessing three pairs of legs. These grubs Hve in bur- rows in the ground. Here they feed on the roots of grass and garden plants. The larval form remains underground for from two to three years, the latter part of this time as an inactive pupa. During the latter stage it lies dormant in an ovoid area excavated by it. Eventually the wings (which are budlike in the pupa) grow larger, and the adult beetle emerges fitted for its life in the open air. Order Hemiptera. Bugs. Characteristics. — The cicada, or, as it is incorrectly called, the locust, is a familiar insect to all. Its droning song is one of the accompaniments of a hot day. The song of the cicada is Stag beetle : a, antenna; e. eye ; m, mandible ; p, pal- pus. Photograph one half natural size. THE INSECTS 243 Cicada: /, adult with wings spread, showing abdomen (-46.), head (H.), ihor&x iTh.) ; 2, pupal case, showing the split down the back ; 3, ventral view, showing beak (B.), eye (E.). produced by a drumlike organ which can be found just behind the last pair of legs. The sound is caused by a rapid vibration of the tightly stretched drumhead. The body is heavy and bulky. The wings, four in number, are relatively small, but the powerful muscles give them very rapid movement. The anterior wings are larger than the posterior. The legs are not large nor strong, the movement when crawling being slug- gish. One of the characteristics of the cicada, and of all other bugs, is that the mouth parts are prolonged into a beak with which the animal first makes a hole and then sucks up the juices of the plants on which it lives. Life History. — The seventeen-year cicada lays her eggs in twigs of trees, and in doing this causes the death of the twig. The young leave the tree immediately after hatching, burrow under- ground, and pass from thirteen to seventeen years there, depending upon the species of cicada. In the South this period is shortened. They live by sucking the juices from roots. During this stage they somewhat resemble the grub of the beetle (June bug) in habits and appearance. When they are about to molt into an adult, they climb aboveground, cling to the bark of trees, and then crawl out of the skin as adults. Aphids. — The aphids are among the most in- teresting of the bugs. They are familiar to all Maple scale, five adults and many young. From pho- tograph, enlarged twice, by Davison. 244 THE INSECTS as the tiny green lice seen swarming on the stems and leaves of the rose and other cultivated plants. They suck the juices from stem and leaf. Plant lice have a remarkable life history. Early in the year eggs develop into wingless females, which produce living young, all females. These in turn reproduce in a similar manner, until the plant on which they live becomes overcrowded and the food supply runs short. Then a genera- tion of winged aphids is produced. These fly away to other plants, and reproduction goes on as before until the approach of cold weather, when males and females appear. Fertilized eggs are then produced which give rise to young the following season. The aphids exude from the surface of the body a sweet fluid called honeydew. This is given off in such abundance that it is estimated if an aphid were the size of a cow, it would give two thousand quarts a day. This honeydew is greatly esteemed by other insects, especially the ants. For the purpose of obtaining it, some ants care for the aphids, even pro- viding food and shelter for them. In return the aphid, stimulated by a stroking movement of the antenna of the ant, gives up the honeydew to its protector. The Order Neuroptera The Dragon Fly. — The dragon fly receives its name because it preys on insects. It eats, when an adult, mosquitoes and other insects which it captures while on the wing. Its four large lacelike wings give it power of very rapid flight, while its long narrow body is admirably adapted for the same purpose. The large compound eyes placed at the sides of the head give keen sight. It possesses powerful jaws (almost covered by the upper and lower lips). The long, thin abdomen does not contain a sting, contrary to the belief of most children. These insects deposit their eggs in the water, and the fact that they may be often seen with the end of the abdomen curved down under the surface of the water in the act of depositing the eggs has given rise to the belief that they were then engaged in stinging something. The egg hatches into a form of larva called a nymph, which in the dragon fly is characterized by a greatly developed lower lip. When the animal is at rest, the lower lip covers the large biting jaws, which can be extended so as to grasp and hold its prey. The nymphs of the dragon fly take oxygen out of the water by means of gill-like structures placed in the posterior Dragon fly. Notice the long abdomen and large compound eyes. THE INSECTS 245 part of the food tube. They may live as larvae from one summer to as long as two years in the water. They then crawl out on a stick, molt by sphtting the skin down the back, and come out as adults. A nearly related form is the damsel fly. This may be distinguished from the dragon fly by the fact that when at rest the wings are carried close to the abdomen, while in the dragon fly they are held in a horizontal position. May Flies. — Another near relative of the dragon fly is the May fly. These insects in the adult stage have lost the power to take food. Most of their life is passed in the larval stage in the water. The adults some- times live only a few hours, just long enough to mate and deposit their The Order Hymenoptera We have already learned something of the structure of the bee, an example of this order. Other relatives are the wasps, ichneumons (wasp- like insects with long ovipositors), and the ants. The structural characters of this group are the presence of two pairs of membranous wings, the mouth parte being fitted for biting and lapping. All undei^o a complete meta- morphosis, the young being helpless wingless creatures somewhat like the maggots of the fly. Of this group we shall learn more later. The orders of insects mentioned above are only some examples of this very large group. In all of the above forms we have seen certain like- nesses and certain differences in structure, but all of the above have had three body divisions, three pairs of legs, and have possessed in the adult state air tubes called tracheae. These are the principal characters by which we may identify the insects. Spiders and Myriapods. — Spiders are not true insects, although they are nearly allied to them. The body shows the same division as do the higher crustaceans, cephalothorax and abdomen ; four pairs of walking legs mark another difference. These animals usually have four pairs of simple eyes and breathe by means of lunglike sacs in the abdomen, the openings of which can sometimes be seen just behind the most pos- terior pair of legs. Another organ possessed by the spider, which insects do not have (except in a larval Tarantula on its back : p, poison fang ; s, spin- neret. Reduced from photograph by Davi- 246 THE INSECTS form), is known as the spinneret. This is a set of glands which secrete in a liquid state the silk which the spider spins. On exposure to air, this fluid hardens and forms a very tough building material which com- bines lightness with strength. Uses and Form of the Web. — The web-making instinct of spiders forms an interesting study. Our common spiders may be grouped ac- cording to the kind of web they spin. The web in some cases is used as a home ; in others it forms a snare or trap. In some cases the web is used for ballooning, spiders having been noticed clinging to their webs miles out at sea. The webs seen most frequently are the so-called cobwebs. These usually serve as a snare rather than a home, some species remain- ing away from the web. Other webs are funnel-shaped, still others are of geometrical exactness, while one form of spider makes its home under- ground, lines the hole with silk, and makes a trapdoor which can be closed after the spider has retreated to its lair. A poisonous centipede from Texas. Half natural size. From photograph by Davison. Myriapods. — We are all familiar with the harmless and common thousand legs found under stones and logs. It is a representative of the group of animals known as the millepedes. These animals have the body divided into two regions, head and trunk, and have two pairs of legs for each body segment. The centipedes, on the other hand, have only one pair of legs to each segment. Both are representatives of the class Myriapoda. None of the forms in the eastern part of the United States are poisonous. Insects and Crustaceans Compared. — Both crustaceans and insects belong to a great group of animals which agree in that they have jointed appendages and bodies, and that they possess an exoskeleton. This group or phylum is known as the Arthropoda. Spiders and myriapods are also included in this group. Insects differ structurally from crustaceans in having three regions in the body instead of two. The number of legs (three THE INSECTS 247 pairs) is definite in the insects ; in the crustaceans the number sometimes varies (as in the Entomostraca), but is always more than three pairs. The exoskeleton, composed wholly of chitin in the insects, is usually strengthened with lime in the crustaceans. Both groups have compound eyes, but those of the Crustacea are staked and movable. The other sense organs do not differ greatly. The most marked differences are physiological. The crustaceans take in oxygen from the water by means of gills, while the insects are air breathers, using for this purpose air tubes called trachece. The young of both insects and crustaceans usually undergo several changes in form before the adult stage is reached. They are thus said to pass through a metamorphosis. Both insects and crustaceans, because of their exoskeleton, must molt in order to increase in bulk. Classification of Arthropoda Phylum Arthropoda Class, Crustacea. Arthropods with limy and chitinous exoskeleton, rarely more than 20 body segments, usually breathing by gills, and having two pairs of antennse. Subclass I. Entomostraca., Crustacea with a variable number of segments, chiefly small forms with simple appendages. Some degenerate or parasitic. Examples: barnacles, water flea (Daphnia), and copepod (Cyclops). Subclass II. Malacostraca. Usually large Crustacea having nineteen pairs of appendages. Examples: American lobster (Homarus Americanns), crab (Cancer), and shrimp (Paloemonetes) . Class, Hexapoda (insects). Arthropoda having chitinous exoskeleton, breathing by air tubes (trachea), and having three distinct body regions. Order, ^por of cases of illness among babies. Economic Loss from Insects. — The money value of crops, forest trees, stored foods, and other material destroyed annually by insects is beyond belief. It is estimated that they get one tenth of the country's crops, at the lowest estimate a matter of some $300,000,000 yearly. '* A recent estimate by experts put the yearly loss from forest insect depredations at not less than $100,000,000. The common schools of the country cost in 1902 the sum of $235,000,000, and all higher institu- tions of learning cost less than $o0,000,000, making the total cost of edu- cation in the United States considerably less than the farmers lost from insect ravages. " Furthermore, the yearly losses from insect ravages ag^egate nearly twice as much as it costs to maintain our army and navy; more than twice the loss by fire ; twice the capital invested in manufacturing agri- cultural implements; and nearly three times the estimated value of the products of all the fruit orchards, vineyards, and small fruit farms in the country." — Slingerland. In 1874-1876 the damage to crops by the Rocky Mountain locust has been estimated at $200,000,000. At certain times, these locusts migrate from Colorado, Wyoming, and Dakota, where they seem always to be found, and descend in countless millions upon the grain fields to the eastward. Fortunately, these invasions have been rare in recent years. The total value of all farm and forest 262 CONSIDERATIONS FROM STUDY OF INSECTS crops, excluding animal products, in New York, is perhaps $150,000,000, and the one tenth that the insects get is worth $15,000,000. It may seem incredible that it costs such a sum to feed New York's injurious insects every year, but it is an average of $66 for each of the 227,000 farms in the state ; and there are few farms where the crops are not lessened more than this amount by insects. Insects which damage Garden and other Crops. — The grass- hoppers have been mentioned as among the most destructive of these. The larvae of various moths do considerable harm here, especially the " cabbage worm," the various caterpillars of the hawk moths which feed on grape and tomato vines, the cutworm, a feeder on all kinds of garden truck, the corn worm, a pest on corn, cotton, tomatoes, peas, and beans. The last annually damages the cotton crop to the amount of several millions of dollars. Among the beetles which are found in gardens is the potato beetle, which destroys the potato plant. This beetle formerly lived in Colorado upon a wild plant of the same family as the potato, and came east upon the introduction of the potato into Colorado, evi- dently preferring culti- vated forms to wild forms of this family. The asparagus and cucumber beetles are also often in evidence. The one beetle doing by far the greatest harm in this country is the cotton-boll weevil. Im- ported from Mexico, since 1892 it has spread over eastern Texas and into Louisiana. The beetle lays its eggs in the young cotton fruit or boll, the larvai feeding upon the substance within the boll. It is estimated that if unchecked this j^est would destroy yearly one half of the cotton crop, a matter Cotton-boll weevil : a, larva ; b, pupa ; c, adult. Photograph, enlarged four times, by Davison. CONSIDERATIONS FROM STUDY OF INSECTS 263 of $250,000,000. Fortunately, the United States Department of Agriculture are at work on the problem, and, while they have not found any way of exterminating the beetle as yet, it has been found that, by planting more hardy varieties of cotton, the crop matures earlier and ripens before the weevils have increased in sufficient numbers to destroy the crop (see page 62). The bugs are among our most destructive insects. The most familiar examples of our garden pests are the squash bug ; the chinch bug, which yearly does damage estimated at $20,000,000, by sucking the juice from the leaves of grain; and the plant lice, or aphids. Some aphids are extremely destructive to vegetation. One, the grape Phylloxera, yearly destroys immense numbers of vines in the vineyards of France, Germany, and California. The Hessian fly, the larvae of which live on the wheat plant, was introduced accidentally by the Hessians in their straw bedding during the Revolution, and has become one of our most serious insect pests. Insects which harm Fruit and Forest Trees. — Great damage is done annually by the larvie of moths. Massachusetts has already spent over $3,000,000 in trying to ex- terminate the imported gypsy moth. The codling moth, which bores into apples and pears, is estimated to ruin yearly $3,000,000 worth of fruit in New York alone, which is by no means the most important apple region of the United States. Among these pests, the most important to the dweller in a large city is the tussock moth, which destroys our shade trees. The cater- pillar may easily be recognized by its hairy, tufted red head. The eggs are laid on the bark of shade trees in what look like masses of foam. (See Figure.) By collecting and burning the egg masses in the fall, we may save many shade trees the following year. Other enemies of the shade trees are the fall webworm, the forest Female tussock moth which has just emerged from the cocoon at the left, upon which it has deposited over two hundred eggs. Photograph, slightly- enlarged, by Davison. 264 CONSIDERATIONS FROM STUDY OF INSECTS caterpillar, and the tent caterpillar; the last spins a tent which serves as a "shelter in wet weather. The larvae of some moths damage the trees by boring into the wood of the tree on which they live. Such are the peach, apple, and other fruit-tree borers com- mon in our orchards. Some species of beetles produce bor- ing larvse which eat their way into trees and then feed upon the sap of the tree. Many trees in our Adirondack Forest Reserve annually succumb to these pests. Many trees are killed because the beetle girdles the tree, cutting through the tubes in the cambium region. Most fallen logs will repay bore between the bark and Larva of tussock moth. Photograph, natural size, by Davison. a search for the larvse which wood. i Among the bugs most destructive to trees are the scale insect and the plant lice, or aphids. The San Jos6 scale, a native of China, was introduced into the fruit groves of California about 1870 and has spread all over the country. It lives upon numerous plants, and is one of the worst pests this country has seen. It is interest- ing to know that a ladybird beetle, which has also been imported, is the most effective agent in keeping this pest in check. Insects of the House or Storehouse. — The weevils are the greatest pests, frequently ruining tons of stored corn, wheat, and other cereals. Roaches feed on almost any kind of breadstuffs as well as on clothing. The carpet beetle is a recognized foe of the housekeeper, the larvse feeding upon all sorts of woolen material. The larvse of the clothes moth do an immense amount of damage to stored clothing especially. Fleas, lice, and especially bedbugs are among man's personal foes.^ Beneficial Insects. — Fortunately for mankind, many insects are found which are of use because they either prey upon injurious 1 Directions for the treatment of these' pests may be found in pamphlets issued by the U.S. Department of Agriculture. CONSIDERATIONS FROM STUDY OF INSECTS 265 insects or become parasites upon them, eventually destroying them. The ichneumon flies are examples already mentioned. They undoubtedly do much in keeping down the nimiber of de- structive caterpillars. Several beetles are of value to man. Most important of these is the natural enemy of the orange-tree scale, the lady bug, or lady- bird beetle. In New York state it may often be found feeding upon the plant hce, or aphids, which hve on rosebushes. The carrion beetles and many water beetles act as scavengers. The sexton beetles bury dead carcasses of animals. Ants in tropical countries are particularly useful as scavengers. Insects, besides pollinating flowers, often do a service by eating harmful weeds. Thus many harmful plants are kept in check. We have noted that they spin silk, thus forming clothing, that in some cases they are preyed upon, and support an enormous multitude of birds, fishes, and other animals with food. Make a balance sheet showing the benefits and harm done man by insects. How the Damage done by Insects is Controlled. — The com- bating of insects by the farmer is controlled and directed by two bodies of men, both of which have the same end in view. These are the Bureau of Entomology of the United States Department of Agriculture and the various state experiment stations. The Bureau of Entomology works in harmony with the other divisions of the Department of Agriculture, giving the time of its experts to the problems of controlling insects which, for good or ill, influence man's welfare in this country. Such problems as the destruction of the malarial mosquito and control of the typhoid fly ; the destruction of harmful insects by the introduction of their natural enemies, plant or animal ; the perfecting of the honeybee (see Hodge, Nature Study and Life, page 240), and the introduction of new species of insects to pollinate flowers not native to this coun- try (see Blastophaga, page 45), are some to which these men are now devoting their time. All the states and territories (except Indian Territory) have, since 1888, established state experiment stations, which work in cooperation with the government in the war upon injurious insects. These stations are often connected with colleges, so that young 266 CONSIDERATIONS FROM STUDY OF INSECTS men who are interested in this kind of natural science may have opportunity to learn and to help. The good done by these means directly and indirectly is very great. Bulletins are published by the various state stations and by the Department of Agriculture, most of which may be obtained free. The most interesting of these from the high school standpoint are the Farmers' Bulletins, issued by the De- partment of Agriculture, and the Nature Study pamphlets issued by the Cornell University in New York state. Reference Books elementary Sharpe, A Laboratory Manual for the Solution of Problems in Biology. American Book Company. Craigin, Our Insect Friends and Foes. G. P. Putnam's Sons. C^a^3^ Insects and their Near Relatives and Birds. J. Blakiston's Son and Com- pany. Dahlgren, The Malarial Mosquito. Guide Leaflet 27, American Museum of Natural History. Davison, Practical Zoology. American Book Company. Dickinson, Moths and Butterflies. Henry Holt and Company. Doane, Insects and Disease. Henry Holt and Company. Farmers' Bulletins, 45, 59, 70, 78, 99, 155. Howard, L. O., Insects as Carriers of Disease. Year Book, U.S. Department of Agriculture, 1902. Howard, L. O., Mosquitoes. McClure, Phillips, and Company. Lubbock, Bees, Ants, and Wasps. D. Appleton and Company. ADVANCED Bulletins of Division of Entomology, 1, 4, 5, 12, 16, 19, 23, 33, 34, 35, 36, 47, 48, 51. Folsom, Entomology with Reference to its Biological and Economic Aspects. P. Blaki- ston's Son and Company. Sanderson, E. D., Insects injurious to Staple Crops. John Wiley and Sons. Wheeler, Ants. The MacmUlan Company. XXI. THE MOLLUSKS rroblem XXXIII {OptlotMil) . A study ofmollushs and their eneinies tcith reference to tJielr economic importance. {.LaJboro/- tory Manual, Prdb. XXXIII.) To the average high school pupil a clam or oyster on the ** half shell " is a familiar object. The soft " body " of the animal lying between the two protecting" valves " of the shell gives the name to this group (Latin mol- lis— soft). Mostmollusks have a limy shell, either bivalve (two-valved), as the oyster, clam, mussel, and scallop, or univalve, as in the snail. Usually the univalve shell is spiral in form, some of nature's most beautiful objects being the spiral shells of some marine forms. Still other moUusks, for example, the garden slug, have no external shell whatever. This limy shell envelope when present, is formed from the outer edge and surface of a deUcate body covering called the mantle. The mantle may be found in the opened oyster or clam sticking close to the inside of the valve of the shell in which the body rests. Between the mantle and the body of the clam or oyster is a space, the mantle cavity. In the space hang the gills, plateUke striated structures. By means of cilia on the inner surface^ of the mantle and on the gills a con- stant cmrent of water is maintained through the mantle cavity bearing oxygen to the gills and carbon dioxide away. This current of water passes, in most mollusks, into and out from the mantle cavity through the siphons, the muscular tubes forming the *' neck " of the ** soft clam " being an example of such an organ. The food of clams or oysters consists of tiny organisms, plant and animal, which are carried in the current of water to the mouth of the animal, this water current being maintained in part by the action of ciha on the palps or Uplike flaps (p. 269) surrounding the mouth. A single muscular foot aids in locomotion when the animal moves about. Many mollusks, as the oyster, are fixed when adult. The shallow water of bays and other quiet bodies of salt water where clams and oysters live, Uterally swarm with tiny plants. The conditions for the growth of such plants is ideal. Water from the rivers contain- ing organic waste and depositing daily its load of mud on the bottom 267 Fulgar, a univalve mollusk common in Long Island Sound, which does much harm by boring into the shells of edible mollusks. 268 THE MOLLUSKS gives one basis for the support of these plants. The carbon dioxide from the thousands of species of fish, mollusks, crustaceans, worms, and other forms of animal life gives another source of raw food material for the plant. The sunlight penetrating through the shallow waters supplies the energy for making the food. Thus conditions are ideal for rapid multi- plication ; hence the water becomes alive with all kinds of plant life, especially the lower forms. Among these plants are always found bac- teria, both harmless and harmful. Mollusks feed upon these plants, in- cluding the bacteria ; man feeds on the mollusks, and, if he eats them raw, may eat living bacteria as well. Thus disease might result, and, as a mat- ter of fact, epidemics of typhoid fever have been traced to such a source. Some Common Mollusks. — The fresh-water clam, a common resi- dent in shallow water in inland ponds and rivers, although not useful for food to man, has become the source of a very impor- tant industry. The making of pearl buttons has so de- pleted the number of adult clams in our Middle West that the state and United States governments have un- dertaken the study of the life habits of these animals with a view to restocking the rivers. The development of the fresh-water clam or mussel is complicated. The egg develops into a free-swimming larval form which fastens to the gills of a fish and there lives as a parasite until almost mature. Then it drops off and begins life in the sand of the river or lake where it lives. The Oyster. — The chief difference between the oyster and the clam lies in the fact that the oyster is fastened by one valve to some solid ob- ject, while the clam or fresh-water mussel moves about. This results in an asymmetry in the shell of the oyster. Oysters are never found in muddy localities, for in such places they would be quickly smothered by the sediment in the water. They are found in nature cUnging to stones or on shells or other objects which project a little above the bottom. Here food is abundant and oxygen is obtained from the water surrounding them. Hence oyster raisers throw oyster shells into the water and the young oysters attach themselves. In some parts of Europe and this country where oysters are raised ar- Shell of fresh-water clam, the left half polished to show the prismatic layer from which buttons are made. Shell of oyster, showing asym- metry. THE MOLLUSKS 269 tificially, stakes or brush are sunk in shallow water so that the young oyster, which is at first free-swimming, may escape the danger of smoth- ering on the bottom. After the oysters are a year or two old, they are taken up and put down in deeper water as seed oysters. At the age of three and four years they are ready for the market. The oyster industry is one of the most profitable of our fisheries. Nearly $65,000,000 a year has been derived during the last decade from such sources. Hundreds of boats and thousands of men are engaged in dredging for oysters. Three of the most important of our oyster grounds are Long Island Sound, Narragansett Bay, and Chesapeake Bay. Sometimes oysters are artificially " fattened " by placing them on beds near the mouths of fresh-water streams. Too often these streams are the bearers of much sewage, and the oyster, which lives on microscopic organ- isms, takes in a number of bacteria with other food. Thus a person might become infected with the typhoid bacillus by eating raw oysters. It is evident that state and city supervision ought to be exercised with refer- ence not only to the sale of shellfish which comes from contaminated localities, but also to prevent the growth of oysters or other mollusks in the neighborhood of the openings of sewers or sewage-bearing rivers. Clams. — Other bi- valve mollusks used for food are clams and scal- lops. Two species of the former are known to New Yorkers, one as the "round," another as the "long" or "soft- shelled " clams. The former ( Venus merce- neria) was called by the Indians " quahog," and is still so called in th(^ Eastern states. The blue area of its shell was used by the Indians as wampum, or money. The quahog is now ex- tensively used as food. The "long" clam {Mya arenaria) is considered better eating by the inhabitants of Massa- chusetts and Rhode Island. This clam was highly prized as food by the Indians. The clam industries of the eastern coast aggregate nearly SI, 000,000 a year. Round clam {Venus merceneria) : A AM, anterior ad- ductor muscle ; ARM, anterior retractor muscle ; PAM, posterior adductor muscle; PRM, posterior retractor muscle; F, foot; C, cloacal chamber; IS, incurrent siphon; FS., excurrent siphon; EO, heart; G, gills; M, mantle; DGL, digestive glands ; *S, stomach ; /, intestine ; P, palp ; R, pos- terior end of digestive tract. 270 THE MOLLUSKS Scallop. — The scallop, another moUuscan delicacy, forms an impor- tant fishery. Only the single adductor muscle is eaten, whereas in the clam the soft parts of the body are used as food. Pearls and Pearl Formation. — Pearls are prized the world over. It is a well-known fact that even in this country pearls of some value are sometimes found within the shells of such common bivalves as the fresh- water mussel and the oyster. Most of the finest, however, come from the waters around Ceylon. If a pearl is cut open and examined carefully, it is found to be a deposit of the mother-of-pearl layer of the shell around some central structure. It has been believed that any foreign substance, as a grain of sand, might irritate the mantle at a given point, thus stimu- lating it to secrete around the substance. It now seems likely that most perfect pearls are due to the growth within the mantle of the clam or oyster of certain parasites, stages in the development of a flukeworm. The irritation thus set up in the tissue causes mother-of-pearl to be deposited around the source of irritation, with the subsequent formation of a pearl. I Gastropods. — Snails, whelks, slugs, and the ^^^ ^ like are called gastropods, because the foot ^■Hfcjjk^^^ occupies so much space that most of the organs ^^^^^^Bt"^^ of the body, including the ^^^Bjjjj^^^ stomach, are covered by ^^^Hf it. Such animals are par- ■j^P tially covered by a more or less spirally formed Forest snail, showing the two tentacles with an eye on the end of each. From photograph by Davison. shell which has but one valve. In most gastro- pods the body is spirally twisted in the shell. In the garden slug, the man- tle does not secrete an external shell, and the naked body is symmetrical. Gastropods of various species do considerable damage, some in the garden, where they feed upon young plants, others in the sea, where they bore into the shells of other living moUusks in order to get out the soft part of the body which they use as food. Cephalopods. — Another class of mollusks are those known as cephalopods. The name "ceph- alopod" means head-footed. As the Figure shows, the mouth is surrounded with a circle of tentacles. The shell is internal or lacking, the so-called pen of the cuttlefish being all that remains of the shell in that form. A cuttlefish is strangely modified for the life it leads. It moves rapidly through the water by squirting water from the siphon. It can seize its prey with the suckers on the long tentacles The squid. One fourth natural size. THE MOLLUSKS 271 and tear it in pieces by means of its homy, parrotlike beak. It is pro- tected from its enemies and is enabled to catch its prey because of its ability to change color quickly. In this way the animal simulates its surroundings. The cuttlefish has an ink bag near the siphon which contains the black sepia. A few drops of this ink squirted into the water may efifectually hide the animal from its enemy. To this group of animals belongs also the octopus, or devilfish, a ceph- alopod known to have tentacles over thirty feet in length, the paper nautilus and the pearly nautilus, the latter made famous by our poet Holmes. Habitat of the Mollusks. — Mollusks are found in almost all parts of the earth and sea. They are more abundant in temperate localities than elsewhere, but are found in tropical and arctic countries. They are found in all depths of water, but by far the greatest number of species live in shallow water near the shore. The cephalopods live near the surface of the ocean, where they prey upon small fish. The food supply evidently determines to a large extent where the animal shall live. Some mollusks are scavengers ; others feed on living plants. We have found in the forms of mollusks studied that almost all mol- lusks live in the water. There is one great group which forms a general exception to this, certain of the snails and plugs called pulmonates. But even these animals are found in damp locahties, and at the approach of drought they become inactive, remaining within the shell. The Euro- pean snail ( Helix -pomatia) imported to this country as a table delicacy exists for months by plugging up the aperture to the shell with a mass of slimy material which later hardens, thus protecting the soft body within. Economic Importance. — In general the mollusks are of much economic importance. The bivalves especially form an important source of our food supply. Many of the mollusks also make up an important part of the food supplj^ of bottom- feeding fishes. On the other hand, some mol- lusks, as natica, bore into other moUusk shells and eat the animal thus at- tached. Some boring mollusks, for example the shipworm ( Teredo navalis), do much dam- age, especially to wharves, as they make their home in piles. Still others bore holes in soft rock and live there. The shells of mollusks are used to a large extent in manufactures and Piece of timber, showing holes bored by the shipworm. 272 THE MOLLUSKS in the arts, while they form a money basis still in parts of the world. Sepia comes from the cuttlefish. The Starfish. — By all means the most important enemy of the oyster and other salt-water mollusks is the starfish. The common starfish, as the name indicates, is shaped like a five-pointed star. A limy skeleton which is made up of thousands of tiny plates gives shape to the body and arms. Slow movement is effected by means of tiny suckers, called tube feet. Breathing takes place through the skin. The mouth is on the under surface of the animal, and, when feeding, the stomach is protruded and wrapped around its prey. The body of the starfish, as well as that of the sea urchin and others of this group, is spiny; hence the name Echinoderm (spiny- skinned) is given to the group. Food of the Starfish.— Starfish are enormously de- structive of young clams and oysters, as the following evi- dence, collected by Professor A. D. Mead of Brown Uni- versity, shows. A single star- fish was confined in an aqua- rium with fifty-six young clams. The largest clam was about the length of one arm of the starfish, the smallest about ten millimeters in length. In six days every clam in the aquarium was devoured. The method of capturing and killing their prey shows that they wrap themselves around the valves of the mollusk and actually puU apart the valves by means of their tube feet, some of which are attached to one valve and some to the other of their victim. Once the soft part of the mollusk is exposed, the stomach envelops it, and it is rapidly digested and changed to a fluid. This it can do because of the five large digestive glands which occupy a large part of each ray, and which pour their digestive fluids into five pouchlike extensions of the stomach extending into each ray. Hundreds of thousands of dollars' damage is done annually to the oysters in Connecticut alone by the ravages of starfish. During the Ventral or under surface of the starfish. The dark circle in the middle is the mouth, from which radiate the five ambulacral grooves, each filled with four rows of tube feet. Photo- graph half natural size, by Davison. THE MOLLUSKS 273 summer months the oyster boats are to be found at work raking the beds for starfish, which are collected and thrown ashore by the thousands. Classification of Mollusks Class I. Pelecypoda (Lamellibranchiata). Soft-bodied unsegmented animals show- ing bilateral symmetry. Bivalve shell, platelike gills. Examples : clam (Mya arenaria), scallop (pecten), oyster (Ostrea), and fresh-water mussel (Unto). Class II. Gastropoda. Soft bodies asymmetrical ; univalve shell or shell absent. Some forms breathe by gills, others by lunglike sacs. Examples * pond snail, land snail (Helix), and slug. Class III. Cephalopoda. Bilaterally symmetrical mollusks with mouth sur- rounded by tentacles. Shell may be external (nautilus), internal (squid), or altogether lacking (octopus). Examples: squid, octopus. Reference Books elementary Sharpe, A Laboratory Manual for the Solution of Problems in Biology. American Book Company. Davison, Practical ZoOlogy, pages 142-150. American Book Company. HeUprin, The Animal Life of our Seashore. J. B. Lippincott Company. Jordan, Kellogg, and Heath, Animal Studies. D. Appleton and Company. Morgan, Animal Sketches, Chap. XXI. Longmans, Green, and Company. ADVANCED Bulletin, U.S. Fish Commission, 1889. Brooks, The Oyster. Johns Hopkins Press. Cooke, "The Mollusca," Cambridge Natural History. The Macmillan Company. Kellogg, The Life History of the Common Clam. Bulletin, U.S. Fish Commission, Vol. XIX, page 193. Kellogg, The Shellfish Industries. Henry Holt and Company. Parker, Elementary Biology. The Macmillan Company. Parker and Haswell, Textbook of Zoology. The Macmillan Company. HUNT. ES. BIO. 18 XXII. THE VERTEBRATE ANIMALS Increasing Complexity of Structure and of Habits in Plants and Animals. — In our study of biology so far we have attempted to get some notion of the various factors which act upon and interact with living things. We have learned something about the various physiological processes of plants and animals, and have found them to be in many respects identical. We have examined a number of forms of plants and have found all grades of complexity, from the one-celled plant, bacterium or pleurococcus, to the complicated flowering plants of considerable size and with many organs. So in animal life the forms we may have studied, from the Protozoa upward, there is constant change, and the change is toward greater complexity of structure and functions. A worm is simpler in structure than an insect, and in many ways, especially by its actions, shows that it is not so high in the scale of life as its more lively neighbor. We are already awake to the fact that we, as living creatures, are better equipped in the battle for life than our more lowly neigh- bors, for we are thinking creatures, and can change our surroundings at will, while the lower forms of animals are largely con- trolled by stimuli which come from without; tem- perature, moisture, light, the presence or absence of food, — all these result in movement and other re- actions. In structure we also differ. Particularly is this difference seen in the skeleton. We call ourselves vertebrates, because we have a 274 Cross section through (/) an invertebrate ani- mal and (F) a vertebrate animal: a, food tube; 6, heart; c, vertebrate column; n, central nerv- ous system. THE VERTEBRATE ANIMALS 275 bony vertebral column, made up of pieces of bone joined one to another, forming a flexible yet strong support for the muscles and protecting the delicate central nervous system. This kind of an endoskeleton, or inside skeleton, is possessed by fishes, frogs, turtles or snakes, and birds, and by mammals, such as the dog, cat, and man. All such animals are called vertebrates. We are now to take up the study of some types of various kinds of vertebrates, with the view to a better understanding of man. Fishes Problem XXXIV, A study of how a fish is fitted for tlie life it leads. (^Laboratory Manual, Prob, XXXIV.) The Body. — One of our common fresh-water fish is the bream, or golden shiner. The body of the bream runs insensibly into the head, the neck being absent. The long, narrow body with its smooth surface fits the fish admirably for its life in the water. Certain cells in the skin secrete mucus or slime, another adapta- tion. The position of the scales, overlapping in a backward direction, is yet another adaptation which aids in passing through The fins of a fish : A, dorsal ; B, caudal ; C, anal ; Z>, pelvic ; E, pectoral. the water. Its color, olive above and bright silver and gold below, is also protective. Can you see how? The Appendages and their Uses. — The appendages of the fish consist of paired and unpaired fins. The paired fins are four in number, and are believed to correspond in position and structure 276 THE VERTEBRATE ANIMALS with the paired limbs of a man. Note the Figure on page 326 and locate the paired pectoral and pelvic fins. (These are so called because they are attached to the bones forming the pectoral and pelvic girdles. See page 426.) Find, by comparison with the Figure, the dorsal, anal, and caudal fins. How many unpaired fins are there? The flattened, muscular body of the fish, tapering toward the caudal fin, is moved from side to side with an xmdulating motion which results in the movement forward of the fish. This movement is almost identical with that of an oar in sculling a boat. Turning movements are brought about by use of the lateral fins in much the same way as a boat is turned. We notice the dorsal and other single fins are evidently useful as balancing and steering organs. The Senses. — The position of the eyes at the side of the head is an evident advantage to the fish. Why? The eye is globular in shape. Such an eye has been found to be very nearsighted. Thus it is unlikely that a fish is able to perceive objects at any great distance from it. The eyes are unprotected by eyelids, but the tough outer covering and their position afford some protection. Feeding experiments with fishes show that a fish becomes aware of the presence of food by smelling it as well as by seeing it. The nostrils of a fish can be proved to end in little pits, one under each nostril hole. Thus they differ from our own, which are connected with the mouth cavity. In the catfish, for example, the barbels, or horns, receive sensations of smell and taste. The sense of per- ceiving odor is not as we understand the sense of smell, for a fish perceives only substances that are dissolved in the water in which it lives. The senses of taste and touch appear to be less developed than the other senses. Along each side of most fishes is a line of tiny pits, provided with sense organs and connected with the central nervous system of the fish. This area, called the lateral line, is believed to be sensitive to mechanical stimuli of certain sorts. The " ear " of the fish is under the skin and serves partly as a balancing organ. A fish must go after its food and seize it, but has no structures for grasping except the teeth. Consequently we find the teeth small, sharp, and numerous, well adapted for holding hving prey. The tongue in most fishes is wanting or very slightly developed. THE VERTEBRATE ANIMALS 277 Breathing. — A fish, when swimming quietly or when at rest, seems to be biting when no food is present. A reason for this act is to ))e seen when we introduce a Httle finely powdered carmine into the water near the head of the fish. It will be found that a current of water enters the mouth at each of these biting move- ments and passes out through two slits found on each side of the head of the fish. Investigation shows us that under the broad, flat plate, or operculum, forming each side of the head, lie several long, feathery, red structures, the gills. Gills. — If we examine the gills of any large fish, we find that a single gill is held in place by a bony arch, made of several pieces of bone which are hinged in such a way as to give great flexibility to the gill arch, as the support is called. Covering the bony framework, and extending from it, are numerous delicate fila- ments of flesh, covered with The head of a fish, with the operculum j r x u cut away to show the gUIs. ^ ^^^y delicate membrane or skin. Into each of these fila- ments pass two blood vessels; in one blood flows downward and in the other upward. Blood reaches the gills and is carried away from these organs l)y means of two large vessels which pass along the bony arch previously mentioned. In the gill filament the blood comes into contact with the free oxygen of the water bathing the gills. An exchange of gases through the walls of the gill filaments re- sults in the loss of carbon dioxide and a gain of oxygen by the blood. Gill Rakers. — If we open wide the mouth of any large fish and look inward, we find that the mouth cavity leads to a funnel-like opening, the gullet. On each side of the gullet we can see the gill arches, guarded on the inner side by a series of sharp-pointed struc- tures, the gill rakers. In some fishes in which the teeth are not well developed, there seems to be a greater development of the gill rakers, which in this case are used to strain out small organisms from the water which passes over the gills. Many fishes make such use of the gill rakers. Such are the shad and menhaden, which feed almost entirely on plankton, a name given to the small plants and animals found by millions in the water. 278 THE VERTEBRATE ANIMALS Digestive System. — The gullet leads directly into a baglike stomach. There are no sahvary glands in the fishes. There is, however, a large liver, which appears to be used as a digestive gland. This organ, because of the oil it contains, is in some fishes, as the cod, of considerable economic importance. Many fishes have outgrowths like a series of pockets from the intestine. These structures, called the pyloric cosca, are believed to secrete a digestive fluid. The intestine ends at the vent, which is usually located on the ventral side of the fish, immediately in front of the anal fin. Anatomy of the carp : br, branehi:Te, or gills ; c, heart bladder; d, intestine. /, liver ; vn, swimming Swim Bladder. — An organ of unusual significance, called the swim bladder, occupies the region just dorsal to the food tube. In young fishes of many species this is connected by a tube with the anterior end of the digestive tract. In some forms this tube persists throughout life, but in other fish it becomes closed, a thin, fibrous cord taking its place. The swim bladder aids in giving the fish nearly the same weight as the water it displaces, thus buoying it up. The walls of the organ are richly supplied with blood vessels, and it thus undoubtedly serves as an organ for supplying oxygen to the blood when all other sources fail. In some fish (the dipnoi, p. 284) it has come to be used as a lung. Circulation of the Blood. — In the vertebrate animals the blood is said to circulate in the body, because it passes through a more or less closed system of tubes in its course around the body. In the fishes the heart is a two-chambered muscular organ, a thin-walled auricle, the receiving chamber, leading into a thick-walled muscular ventricle from which the blood is forced out. The blood is pumped from the heart to the gills ; there it loses some of its carbon dioxide ; it then passes on to other parts THE VERTEBRATE ANIMALS 279 of the body, eventually breaking up into very tiny tubes called capillaries. From the capillaries the blood returns, in tubes of gradually increasing diameter, toward the heart again. During its course some of the blood passes through the kidnej's and is there relieved of part of its nitroge- nous waste. (See Chapter XXVII.) Circulation of blood in the body of the fish *'-. is rather slow. The temperature of the blood being nearly that of the surrounding media in which the fish hves, the animal has incorrectly been given the terra "cold-blooded." Nervous System. — As in all other vertebrate animals, the l)rain and spinal cord of the fish are partially inclosed in a series of bony structures called vertebra;. The central nervous system con- sists of a brain, with nerves leading to the oi^ans of sight, taste, smell, the ear, and to such parts of the body as possess the sense of touch ; a spinal cord; and spinal nerves. Nerve cells located near the outside of the body send in messages to the central system, which are there received as sensations. Cells of the central nervous sys- tem, in turn, send out messages which result in the movement of muscles. Skeleton. — In the vertebrates, of which the bony fish is an example, the skeleton is under the skin, and is hence called an endoskeleton. It consists of a bony framework, the vertebral column, and certain attached bones, the ribs, with other spiny bones to which the unpaired fins are attached. The paired fins are attached to the spinal column by two collections of bones, known respectively as the pectoral and pelvic girdles. The bones serve in the fish for the attachment of powerful muscles, by means of which locomotion is accomplished. In most fishes, the exo- skeleton, too, is well develoi)ed, modifications appearing from scales to complete armor. Plan of circulation in fishes : a, auricle ; b, ventricle ; c, branchial artery ; e, bran- chial veins, bringing blood from the gills, d, and unit- ing in the aorta, /; g, vena cava, returning blood to heart. Prohlem XXXV (Ojttional). A study of sortie of the relations of fislies to tJieir food supply. (^Laboratory Manual, Prob. XXXV.) Food of Fishes. — We have already seen that in a balanced aquarium tlie l)alance of food was preserved by the plants, which furnished food for the tiny animals or were eaten by larger ones, — for example, snails or fish. The smaller animals in turn became 280 THE VERTEBRATE ANIMALS food of larger ones. The nitrogen balance was maintained through the excretions of the animals and their death and decay. The marine world is a great balanced aquarium. The upper layer of water is crowded with all kinds of little organisms, both plant and animal. Some of these are microscopic in size; others, as the tiny crustaceans, are visible to the eye. On these little organisms some fish feed entirely, others in part. Such are the menhaden ^ (bony, bunker, mossbunker of our coast), the shad, and others. Other fishes are bottom feeders, as the blackfish and the sea bass, living almost entirely upon mollusks and crusta- ceans. Still others are hunters, feeding upon smaller species of fish or even upon their weaker brothers. Such are the bluefish, squeteague or weakfish, and others. What is true of salt-water fish is equally true of those inhabiting our fresh-water streams and lakes. It is one of the greatest prob- lems of our Bureau of Fisheries to discover this relation of various fishes to their food supplies so as to aid in the conservation and balance of life in our lakes, rivers, and seas. The Egg-laying Habits of the Bony Fishes. — The eggs of most bony fishes are laid in great numbers at the time of spawning. This number varies from a few thousand in the trout to many hundreds of thousands in the shad and several millions in the cod. The time of egg-laying is usually spring or early summer. At the time of spawning the male usually deposits milt, consisting of mil- lions of sperm cells, in the water just over the eggs, thus accomplish- ing fertihzation. Some fishes, as sticklebacks, sunfish, toadfish, etc., make nests, but usually the eggs are left to develop by themselves, sometimes attached to some submerged object, but more frequently free in the water. In some eggs a tiny oil drop buoys up the egg to the surface, where the heat of the sun aids development. They are exposed to many dangers, and both eggs and developing fish are eaten, not only by birds, fish of other species, and other water inhabitants, but also by their own relatives and even parents. Consequently a very small percentage of eggs ever reach maturity. * It has been discovered by Professor Mead of Brown University that the in- crease in starfish along certain parts of the New England coast was in part due to overfishing of menhaden, which at certain times in the year feed ahnost entirely on the young starfish. THE VERTEBRATE ANIMALS 281 The Relation of the Spawning Habits to Economic Importance of Fish. — The spawning habits of fish are of great importance to us because of the economic value of fish to mankind, not only directly as a food, but indirectly as food for other animals in turn valuable to man. Many of our most desirable food fishes, notably the salmon, shad, sturgeon, and smelt, pass up rivers from the ocean to deposit their eggs, swimming against strong currents much of the way, some spe- cies leaping rapids and falls, in order to de- l)osit their eggs in Salmon leaping a fall on their way to their spawning beds. Photographed by Dr. John A. Sampson. suitable localities, where the conditions of water and food are requisite, and the water shallow enough to allow the sun's rays to warm the water sufficiently to cause the eggs to develop. The Chinook salmon of the Pacific coast, the salmon used in the Western canning industry, travels over a thousand miles up the Columbia and other rivers, where it spawns. The salmon begin to pass up the rivers in early spring, and reach the spawning beds, shallow de- posits of gravel in cool mountain streams, before late summer. Here the fish, both males and females, remain until the temperature of the water falls to about 54° Fahrenheit. The eggs and milt are then deposited, and the old fish die, leaving the eggs to be hatched out later by the heat of the sun's rays. 282 THE VERTEBRATE ANIMALS This instinct of this fish and other species to go into shallow rivers to deposit their eggs has been made use of by man. At the time of the spawning migration the salmon are taken in vast numbers. The salmon fisheries net over $16,000,000 annually, the shad at least $1,500,000, the smelt fishery nearly $150,000 more. The total annual value of the fisheries of the United States is over $50,000,000. Migration of Fishes. — Some fishes change their habitat at dif- ferent times during the year, moving in vast schools northward in summer and southward in the winter. In a general way such migrations follow the coast lines. Examples of such migratory fish are the cod, menhaden, herring, and bluefish. The migra- tions are due to temperature changes, to the seeking after food, Fisheries— Percentage Product ifi 40 5^ 6,0 TO ME _e£_ United States Gt.Brit. & Ir. Can. & Newf. Japan Russia France ^'^ , Rest of World and to the spawning instinct. Some fish migrate to shallower water in the summer and to deeper water in the winter ; here the reason for the migration is doubtless the change in temperature. The herring fisheries have always been a source of wealth to the inhabitants of northern Europe. The banks and shallows of the coast of Newfoundland were undoubtedly known to the Norse-, men long before the discovery of this country by Columbus. THE VERTEBRATE ANIMALS 283 rrobleni XXXVl (Oj}tional). The artificial propagation of fislies. {Laboratory ManicaJ, Froh. XX'X'VI.) The Work of National and State Governments in protecting and propagating Food Fishes. — But the profits from the fisheries are steadily decreasing because of the yearly destruction of untold millions of eggs which might develop into adult fish. Fortunately, the government through the Bureau of Fisheries, and various states by wise protective laws and by artificial prop- agation of fishes, are beginning to turn the tide. Certain days of the week the salmon are allowed to pass up the Columbia unmo- lested. Closed breeding seasons protect our trout, bass, and other game fish, and also prohibit the catching of fish under a certain size. Many fish hatcheries, both government and state, are en- gaged in artificially fertilizing millions of fish eggs of various species and protecting the young fry until they can be placed in ponds or streams at a size when they can take care of themselves. This artificial fertiUzation is usually accomplished by first squeezing out the ripe eggs from a female into a pan of water; in a similar manner the milt or sperm cells are obtained, and poured over the eggs. The fertilized eggs are carefully protected, and, after hatching, the young fry are kept in ideal conditions until later they are shipped, sometimes thousands of miles, to their new home. State and government interposition, however, is in many cases coming too late, for at the present rate of destruction many of our most desirable food fishes will soon be extinct. The sturgeon, the eggs of which are used in the manufacture of the delicacy known as caviare, is an example of a fish that is almost extinct in this part of the world. The shad is found in fewer numbers each year, and in fewer rivers as well. The salmon will undoubtedly soon meet the fate of other fishes which are taken at the spawning season, unless conservation of a radical sort takes place. Classification of Fishes. — The animals we recognize as fishes are grouped by naturalists into four groups : — 1. The Elasmobranchs. — These fishes have a skeleton formed of cartilage which has not become hardened with lime. The gills com- municate with the surface of the body by separate openings instead of having an operculum. The skin is rough and the eggs few in number. 284 THE VERTEBRATE ANIMALS Sand shark, an elasmobranch. Note the sUts leading from the gills. From photo- graph loaned by the American Museum of Natural History. Sturgeon {Acipenser sturio), a ganoid fish. 'M: In some members of this group the young are born alive. Sharks, rays, and skates are elasmobranchs. 2. Ganoids. — The bodies of these are ganoids protected by a series of platelike scales of considerable strength. These fishes are the only rem- nant of what once was the most powerful group of animals on the earth, the great armored fishes of the Devonian age. The gar pike is an example. 3. The Teleosts, or Bony Fishes. — They compose 95 per cent of all living fishes. In this group the skeleton is bony, the gills are protected by an operculum, and the eggs are numerous. Most of our common food fishes belong to this class. 4. The Dipnoi, or Lung Fishes. — This is a very small group, in many respects more Uke amphibians than fishes, the swim bladder being used as a lung. They live in tropical Africa, South America, and Australia, inhabiting the rivers and lakes there. They withstand drying up in the mud during the dry season, lying dormant for long periods of time in a ball of mud and waking to active life again when the mud coat is removed by immersion in water. A bony fish. THE VERTEBRATE ANIMALS 285 Reference Books elementary Sharpe, A Laboratory Manual. American Book Company. Davison, Practical Zoology, pages 185-199. American Book Company. Herrick, Textbook in General Zoology, Chap. XIX. American Book Company. Jordan, Kellogg, and Heath, Animal Studies, XIV. D. Appleton and Company. ADVANCED Jordan and Evermann, American Food and Gam^ Fishes. Doubleday, Page, and Company. Jordan, Fishes. Henry Holt and Company. Kingsley, Textbook of Vertebrate Zoology. Henry Holt and Company. Riverside Natural History. Houghton, Mifflin, and Company. Amphibia. The Frog Problem XXXVII. Some adaptations in a living frog. {Laboratory Manual, Prob. XXX VII.) Adaptations for Life. — The most common frog in the eastern part of the United States is the leopard frog. It is recognized by its greenish brown body with dark spots, each spot being outlined in a Hghter colored background. In spite of the apparent lack of harmony with their sur- roundings, their color, on the contrary, appears to give almost perfect protection. In some species of frogs the color of the skin changes with the surroundings of the frog, another means of pro- tection. Adaptations for life in the water are numerous. The ovoid body, the head merg- ing into the trunk, the slimy ^^^^ l^^ . ^^^^ ^ covering (for the frog is pro- vided, like the fish, with mucus cells in the skin), and the power- ful legs with webbed feet, are all evidences of the Ufe which the frog leads. 286 THE VERTEBRATE ANIMALS Locomotion. — You will notice that the appendages have the same general position on the body and same number of parts as do your own (upper arm, forearm, and hand ; thigh, shank, and foot, the latter much longer relatively than your own). Note that while the hand has four fingers, the foot has five toes, the latter connected by a web. In swimming the frog uses the stroke we all aim to make when we are learning to swim. Most of the energy is liber- ated from the powerful backward push of the hind legs, which in a resting position are held doubled up close to the body. On land, locomotion may be by hopping or crawling. Sense Organs. — The frog is well provided with sense organs. The eyes are large, globular, and placed at the side of the head. When they are closed, a delicate fold, called the nictitating mem" hrane (or third eyelid), is drawn over each eye. Frogs probably see best moving objects at a few feet from them. Their vision is much keener than that of the fish. The external ear (tympanum) is located just behind the eye on the side of the body. Frogs hear sounds and distinguish various calls of their own kind, as is proved by the fact that frogs recognize the warning notes of their mates when any one is approaching. The inner ear also has to do with balancing the body as it has in fishes and other vertebrates. Taste and smell are probably .not strong sensations in a frog or toad. They bite at moving objects of almost any kind when hungry. Experience has taught these animals that moving things, insects, worms, and the like, make good food. These they swallow whole, the tiny teeth being used to hold the food. Touch is a well- developed sense. They also respond to changes in temperature under water, remaining there in a dormant state for the winter when the temperature of the air becomes colder than that of the water. Breathing. — The frog breathes by raising and lowering the floor of the mouth, pulling in air through the two nostril holes. Then the little flaps over the holes are closed, and the frog swallows this air, thus forcing it down into the baglike lungs. The skin is provided with many tiny blood vessels, and in winter, while the frogs are dormant at the bottom of the ponds, it serves as the only organ of respiration. Although we shall take up the study of the internal structure of THE VERTEBRATE ANIMALS 287 the frog more in detail when we discuss the structure and uses of the parts of the bociy in man, we may now learn something of the position and use of some of the structures found within the body cavity. The Food Tube and its Glands. — The mouth leads like a funnel into a short tube, the gullet. On the lower floor of the mouth can be seen the slitlike glottis leading to the lungs. The gullet widens almost at once into a long stomach, which in turn leads into a much- BaMone_Omiuct Spinal cord_^^^g^^^ Tongue Glottis Liver Pancreas Diagram of the internal anatomy of a frog. coiled intestine. This widens abruptly at the lower end to form the large intestine. This in turn leads into the cloaca (Latin, sewer) into which open the kidneys, urinary bladder, and repro- ductive organs {ovaries or spermaries). Several glands, the function of which is to produce digestive fluids, open into the food tube. These digestive fluids, by means of the ferments or enzymes contained in them, change insoluble food materials into a soluble form. This allows of the absorption of food material through the walls of the food tube into the blood. The glands (having the same names and uses as those in man) are the salivary glands, which pour their juices into the mouth, the gastric glands in the walls of the stomach, and the liver and pancreas, which open into the intestine. (See Digestion, pages 352-365.) Circulation. — The frog has a well-developed heart, composed of a thick-walled muscular ventricle and two thin-walled auricles. The heart pumps the blood through a system of closed tubes to all parts of the body. Blood enters the right auricle from all parts of the body ; it then con- 288 THE VERTEBRATE ANIMALS tains considerable carbon dioxide ; the blood entering the left auricle comes from the lungs, hence it contains a considerable amount of oxygen. Blood leaves the heart through the ventricle, which thus pumps blood contain- ing much and little oxygen. Before the blood from the tissues and lungs has time to mix, however, it leaves the ventricle and by a delicate adjust- ment in the vessels leaving the heart most of the blood containing much oxygen is passed to all the various organs of the body, while the blood deficient in oxygen, but containing a large amount of carbon dioxide, is pumped to the lungs, where an exchange of oxygen and carbon dioxide takes place by osmosis. In the tissues of the body wherever work is done the process of burning or oxidation must take place, for by such means only is the energy necessary to do the work released. Food in the blood is taken to the muscle cells or other cells of the body and there oxidized. The prod- ucts of the burning — carbon dioxide — and any other organic wastes given off from the tissues must be eliminated from the body. As we know, the carbon dioxide passes off through the lungs and to some extent through the skin of the frog, while the nitrogenous wastes, poisons which must be taken from the blood, are eliminated from it in the kidneys. Thus wastes are passed off from the body. Problem XXXVIII. The development of a frog. {Laboratory Manual, Proh. XXXVI.) {a) Conditions favorable. (b) Metamorphosis. (c) Development of a toad {optional). Field and Home Work. — During the first warm days in March or April, look for gelatinous masses of frogs' eggs attached to sticks or water weed in shallow ponds. Collect some and try to hatch them out in a shallow dish in the window at home. Make experiments to learn whether temperature affects the development of the egg in any way. Place eggs in dishes of water in a warm room and in a cold room, also some in the ice box. Make observations for several weeks as to rate of development of each lot of eggs. Also try placing a large number of eggs in one dish, thus cutting down the supply of available oxygen, and in another dish near by, under the same conditions of light and heat, place a few eggs. Do both batches of eggs develop with the same rapidity? In all these experiments be sure to use eggs from the same egg mass, so as to make sure that all are of the same age. Development. — The eggs of the leopard frog are laid in shallow water in the early spring. Masses of several hundred, which may- be found attached to twigs or other supports under water, are de- THE VERTEBRATE ANIMALS 289 posited at a single laying. Immediately before leaving the body of the female they receive a coating of jellylike material, which swells up after the eggs are laid. Thus they are protected from the attack of fish or other animals which might use them as food. The upper side of the egg is dark, the light-colored side being weighted down with a supply of yolk (food). The fertilized egg soon segments (divides into many cells), and in a few days, if the weather is warm, these cells have each grown into an oblong body which shows the form of a tadpole. Shortly after the tadpole wriggles out of the jelly hke case and begins life outside the egg. At first it remains attached to some water weed by means of a pair of suckerlike projec- tions; later a mouth is formed at this point, and the tadpole begins to feed upon alga? or other tiny water plants. At this time, about two weeks after the eggs were laid, gills are pres- ent on the outside of the body. Soon after, the ex- ternal gills are replaced by gills which grow out under a fold of the skin which forms an operculum somewhat as in the fish. Water reaches the gills through the mouth and passes out through a hole on the left side of the body. As the tadpole grows larger, legs appear, the hind legs first, although for a time locomotion is performed by means of the tail. In the leopard frog the change from the egg to adult is com- pleted in one summer. In late July or early August, the tadpole begins to eat less, the tail becomes smaller (being absorbed into other parts of the body), and before long the transformation from the tadpole to the young frog is complete. In the green frog and bullfrog the metamorphosis is not completed until the begin- ning of the second siunmer. The large tadpoles of such forms HUNT. ES. BIO. — 19 rogs' eggs from three to ten hours old. All stages from four cells to thirty-two cells may- be noted. Photograph, enlarged four times, by Davison. 290 THE VERTEBRATE ANIMALS l:)ury themselves in the soft mud of the pond bottom during the winter. Shortly after the legs appear, the gills begin to be absorbed, and lungs take their place. At this time the young animal may be seen coming to the surface of the water for air. Changes in the diet of the animal also occur; the long, coiled intestine is trans- formed into a much shorter one. The animal, now insectivorous in its diet, becomes provided with tiny teeth and a mobile tongue, instead of keeping the horny jaws used in scraping off algae. After the tail has been completely absorbed and the legs have become full grown, there is no further structural change, and the metamorphosis is complete. The Common Toad. — One of the nearest of the allies of the frog is the common toad. The eggs, like those of the frog, are deposited in fresh-water ponds, especially small pools. The egg-laying season is later than that of the frog. The eggs are laid in strings, as many as eleven thousand eggs having been laid by a single toad. Suggestions for Field Work. — The egg-laying season in New York state is early May. At this time procure a female that has not laid her eggs and place her in an aqua- rium. If undisturbed, she may lay her eggs in cap- tivity. Compare the bulk of the eggs after they are laid with the size of the in tliL- lifi' ol tadpulfsof the greeu frog. The two large tadpoles are in their second summer. Photographed by Overton. The comnion toad. THE VERTEBRATE ANIMALS 291 toad that laid them. This apparent discrepancy is caused by the swelling of the gelatinous substance around them. If possible, count the number of eggs laid by one female.^ Toad tadpoles may be distinguished from those of the frog, as they are darker in color, and have a more slender tail and a rela- tively larger body than those of the frog. The metamorphosis occupies only about two months in the vicinity of New York, but varies greatly with the temperature. During the warm weather the tail is absorbed with wonderful rapidity, and the change from a tadpole with no legs to that of the small toad living on land is often accomplished in a few hours. This has given rise to the story that it has rained toads, because during the night thousands of young toads have changed their habitat from the water to the land. The toad is of great economic importance to man because of its diet. No less than eighty-three species of insects, mostly injurious, have been proved to enter into the dietary.^ A toad has been ob- served to snap up one hundred and twenty-eight flies in half an hour. Thus at a low estimate it could easily destroy one hundred insects during a day and do an immense service to the garden during the summer. It has been estimated by Kirkland that a single toad may, on account of the cutworms which it kills, be worth $19.88 each season it lives if the damage done by each cut- worm be estimated at only one cent. Toads also feed upon slugs and other garden pests. Other Amphibians. — The tree frogs (called tree toads) are familiar Spotted salamander. From photograph loaned by the American Museum of Natural History. to us in the early spring as the ** peepers " of the swamps. They are among the earliest of the frogs to lay their eggs. During adult life they spend most of their time on the trunks of trees, where they receive im- ^ See Hodge, Nature Study and Life. 2 See Kirkland, Habits, Food, and Economic Importance of the American Toad. Bui. 46, Hatch Experiment Station, Amherst, Mass. 292 THE VERTEBRATE ANIMALS munity from attack because of their color markings. The feet of the tree toad are modified for climbing by having little disks on the ends of the toes, by means of which it is able to cling to vertical surfaces. Another common amphibian is the newt, a salamander. This smooth- skinned, four-limbed animal, often incorrectly called a lizard, passes its larval life in the water, where it breathes by means of external gills. Later it loses its gills, becomes provided with lungs, and comes out on land. Its coat, which was greenish in the water, now becomes bright orange in color. In this condition we sometimes find them crawling on wood roads after a rain. After over two years' life on land, it again returns to the water, becomes green with red spots (as seen in the Figure), and now is able to reproduce its kind. Some salamanders never have lungs, but breathe through the moist skin. Newt. From photograph loaned by the American Museum of Natural History, Still other amphibians are the mud puppies, sirens or mud eels, and the axolotl. All of the above animals differ from the reptiles in having a smooth skin with no scales, and in passing the early stage of their existence in the water. Characteristics of Amphibia. — The frog belongs to the class of vertebrates known as Amphibia. As the name indicates (amphi, both, and hia, life), members of this group pass more or less of their life in the water, although in the adult state they are provided with lungs. In the earlier stages of their development they take oxygen into the blood by means of gills. At all times, but especially during the winter, the skin serves as a breathing organ. The skin is soft and unprotected by bony plates or scales. The heart has three chambers, two auricles and one ventricle. Most amphibians undergo a complete metamorphosis. Classification op Amphibia Mentioned Order I. Urodela. Amphibia having usually poorly developed appendages. Tail persistent through life. Examples : mud puppy, newt, salamander. Order II. Anura. Tailless Amphibia, which undergo a metamorphosis, breathing by gills in larval state, by lungs in adult state. Examples : toad and frog. THE VERTEBRATE ANIMALS 293 Reference Books elementary Davison, Practical Zoology, pages 199-211. American Book Company. Herrick, Textbook in General Zoology, Chap, XX. American Book Company. Hodge, Nature Study and Life, Chaps. XVI, XVII. Ginn and Company. Jordan, Kellogg, and Heath, Animal Studies. D. Appleton and Company. Nature Study Leaflets, Cornell Nature Study, BuQetins XVI, XVII. ADVANCED Ditmars, The Batrachians of New York. Guide Leaflet 19, American Museum of National Historj-. Dickinson, The Frog Book. Doubleday, Page, and Company. Dickinson, Salamanders. Doubleday, Page, and Company. Holmes, The Biology of the Frog. The Macmillan Company. Morgan, The Development of the Frog's Egg. The Macmillan Company. Parker and Haswell, Textbook of Zoology. The Macmillan Company. Reptiles Turtles and Tortoises, Adaptations for Life. — The turtles and tortoises, the latter land animals, form a large and interesting group. The body is flattened, and is covered on the dorsal and ventral sides by a bony framework. This covering is composed of plates cemented to the true bone underneath, the whole form- ing one horny cover. This covering, an adaptation for protection, is more perfect in the box tortoise, where a hinge on the ventral side allows the animal to retreat within the shell, the head and legs being completely covered. Western painted turtle. Adaptations for Food Getting. — The long neck and powerful horny jaws are factors in the food procuring. Turtles have no teeth. Prey is seized and held by the jaws, the claws of the front legs being used to tear the food. Turtles are very strong for their size. The stout legs carry the animal slowly on land, and in the water, being slightly webbed, they are of service in swimming. In some water turtles the front limbs are modified into flippers for swimming. The strong claws are used for digging, especially at egg-laying season, for some turtles dig holes in sandy beaches in which the eggs are deposited. 294 THE VERTEBRATE ANIMALS Box tortoise {Cistudo Carolina). From photo- graph loaned by the American Museum of Natural History. Some Different Turtles. — Turtles are mostly aquatic in habit. Some exceptions are the box tortoise {Cistudo Caro- lina) and the giant tortoise of the Galapagos Islands. Many of the sea-water turtles are of large size, the leatherback and the green turtle often weighing six hundred to seven hundred pounds each. The flesh of the green turtle and especially the diamond-back terrapin, an animal found in the salt marshes along our southeastern coast, are highly esteemed as food. Unfortunately for the preservation of the species, these animals are usually taken during the breeding sea- son when they go to sandy beaches to lay their eggs. Lizards. — Lizards may be recognized by the long body with four legs of nearly equal size. The body is covered with scales. The animal never lives in water, it is active in habit, and it does not undergo a metamorphosis. Lizards are generally harmless creatures, the Gila monster of New Mexico and Arizona, a poisonous variety, being one exception. Lizards are of economic importance to man, because they eat insects and include the injurious ones in their dietary. The iguana of Central America and South America, growing to a length of three feet or more, has the distinc- tion of being one of the few edible lizards. The Gila monster. Photograph one tenth nat- ural size, by Davison. ^mjm i3» A garter 8nake,one of our commonest harmless reptiles. THE VERTEBRATE ANIMALS 295 Snakes. — Probably the most disliked and feared of all animals are the snakes. This feeling, however, is rarely deserved, for, on the whole, our common snakes are beneficial to man. The black snake and the milk snake feed largely on injurious rodents (rats, mice, etc.), the pretty green snake eats injurious insects, and the little DeKays snake feeds partially on slugs. If it were not that the rattlesnake and the copi erhead are venomous, they also could be said to be useful, for they live on English sparrows, rats, mice, moles, and rabbits. Snakes are almost the only legless vertebrates. Although the limbs are absent, still the pelvic and pectoral girdles are developed. The very long backbone is made up of a large number of vertebrae, as many as four hundred being found in the boa con- strictor. Ribs are attached to all vertebriB in the region of the body cavity. Locomotion. — Locomotion is performed by pulling and pushing the body along the ground, a leverage being ob- tained by means of the broad, flat scales, or scutes, with which the ventral side of the body is covered. Snakes may move without twisting the body. This is accomplished by a regular drawing forward of the scutes and then pushing them backward rather violently. Feeding Habits. — The bones of the jaw are very loosely joined to- gether. Thus the mouth of the snake is capable of wide distention. It holds its prey by means of incurved teeth, two of which (in the poisonous snakes) are hoUow or grooved, and serve as a duct for the passage of poison. The poison glands are at the base of the curved fangs in the upper jaw. The tongue is very long and cleft at the end. It is an organ of touch and taste, and is not, as many people believe, used as a sting. The food is swallowed whole, and pushed down by ryhthmic contractions of the muscles surrounding the gullet. They usually refuse other than living prey. Adaptations. — Snakes are usually protectively colored. They are not extremely prolific animals, but hold their own with other forms of life, because of their numerous adaptations for protection, their noiseless movement, protective color, and, in some cases, by their odor and poison. Skull of boa constrictor, two thirds natural size. Note the inpointing teeth. Photograph by Davison. 296 THE VERTEBRATE ANIMALS Poisonous Snakes. — Not all snakes can be said to be harmless. The bite of the rattlesnake of our own country, although dangerous, seldom kills. The dreaded cobra of India has a record of over two hundred and fifty thousand persons killed in the last thirty-five years. The Indian government yearly pays out large sums for the extermination of venomous snakes, over two hundred thousand of which have been killed during a single year. Alligators and Crocodiles. — The latter are mostly confined to Asia and Africa, while the former are natives of North and South America. The chief structural difference between them is that the teeth in alligators Young alligator. One fourth natural size. are set in long sockets, while those of the crocodile are not. Both of these great Uzardlike animals have broad, vertically flattened tails adapted to swimming. The eyes and tip of the snout, the latter holding the nos- tril holes, protrude from the head, so that the animal may float motion- less near the surface of the water with only eyes and nostrils visible. The nostrils are closed by a valve when the animal is under water. These rep- tiles feed on fishes, but often attack large animals, as horses, cows, and even man. They seek their prey chiefly at night, and spend the day bask- ing in the sun. The crocodiles of the Ganges River in India levy a yearly tribute of many hundred lives from the natives. Characteristics of Reptilia. — The animals described belong to the class of vertebrates known as Reptilia. Such animals are characterized by having scales developed from the skin. These in the turtle have become bony and are connected with the internal skeleton. Reptiles always breathe by means of lungs, differing in this respect from the amphibians. They show their distant THE VERTEBRATE ANIMALS 297 relationship to birds in that their large eggs are incased in a leath- ery, limy shell. Classification of Reptilss Order I. Chelonia (turtles and tortoises). Flattened reptiles with body inclosed in bony case. No teeth or sternum (breastbone). Examples: snapping turtle, box tortoise. Order II. Lacertilia (lizards). Body covered with scales, usually having two- paired appendages. Breathe by lungs. Examples : fence lizard, horned toad. Order III. Ophidia (snakes). Body elongated, covered with scales. No limbs present. Examples : garter snake, rattlesnake. Order IV. Crocodilia. Fresh-water reptiles with elongated lx)dy and bony scales on skin. Two paired limbs. Examples : alligator, crocodile. Reference Books elementary Davison, Practical Zoology, pages 211-226. American Book Company. Ditmars, The Reptiles of New York. Guide Leaflet 20, American Museum of Natural History. Herrick, Textbook in General Zodlogy, Chap. XXI. American Book Company. Jordan, Kellogg, and Heath, Animal Studies, Chap. XVI. D. Appleton and Company. advanced Ditmars, The Reptile Book. Doubleday, Page, and Company. Parker and Haswell, Textbook of Zodlogy. The Macmillan Company. Riverside Natural History. Houghton, MifSin, and Company. Birds Problem XXXIX, Study of some adaptations in and re- actions of birds. {Laboratory Manual, Prob. XXXIX.) Adaptations. — Birds among all other animals are known by their covering of feathers and the peculiar modification of the fore limbs for flight. In no other group of animals may we study adaptations so well as here. Field Work. — Bird activities may best be studied out of doors. Any city park offers more or less opportunity for such study, for several of our native birds make the parks their home. If not these, then the Eng- Ush sparrow can be found anywhere in the East. The best time for making observations is early in the morning, especially in the spring season. Body. — The body of a bird, under its covering of feathers, is rounded and more or less pointed at each end. Powerful muscles, 298 THE VERTEBRATE ANIMALS attached to the wings, aid in locomotion, while the wing itself, a modified arm, is one of the most evident adaptations to life in the air. Flight. — Watch a bird in flight. The tip of the wing usually describes a curve which results in the forming of the figure 8. The rate of movement of the wing differs greatly in different birds. The wing of a bird is slightly concave on the lower surface when outstretched. Thus on the downward stroke of the wing more resistance is offered to the air. Birds with long, thin wings, as the hawks and gulls, move the wing in flight with much less rapidity than those with short, wide wings, as the grouse or quail. The latter birds start with much less apparent effort than the birds with longer wings ; they are, however, less capable of sustained flight. Feathers. ^- Few people realize that the body of a bird is not completely covered with feathers. Featherless areas can be found on the body of any common bird, although tiny " pin feathers " are found on such areas as well as on other parts of the body. Soft down feathers cover the body, serving for bodily warmth. Larger feathers give the rounded contour to the body. In the wings we find quill feathers ; these are adapted for service in flight by having a long hollow shaft, from which lateral interlocking branches are given off, the whole making a light structure offering considerable resistance to the air. Feathers are developed from the outer layer of the skin, and are formed in almost exactly the same manner as are the scales of a fish or a lizard. The first feathers developed on the body 1 ^^HpT^H ^^■^1 1 ^^^^K^ wb^^^I ^^^H&N P'VjflB^B I^H -^umi t!^ ■^m^BHH K' 1 ^ ^Bkl mB^M Feathers of a meadow lark. Which of the above are used for flight ? How do you know ? From photograph loaned by the American Museum of Nat- ural History. THE VERTEBRATE ANIMALS 299 are evidently for protection against cold and wet, but later in life they serve other uses. The feathers of most male birds are brightly colored. This seems to make them attractive to the females of the species ; thus the male may win its mate. Adaptations in the Lower Limbs. — The ankle of a bird is extremely long and reptile-like. Scales are found on the ankle and foot. The most extraordinary adaptations are found in the feet of various birds. Some have the foot adapted to perching, others for swim- Adaptations in the feot of birds. Explain, after reading the paragraph on adapta- tion in the lower limbs, how each of the above feet is fitted to do its work. From photograph loaned by the American Museum of Natural History. ming, others wading, etc. We are able, by looking at the feet of a bird, to decide almost certainly its habitat, method of hfe, and per- haps its food. In the perching birds we find three toes in front and one behind, the hind toe playing an important part in holding the foot in place. In swallows, rapid and untiring flyers, the feet are small. In the case of the parrots, where the foot is used for holding food, climbing, and clinging, we find the four-clawed toes arranged two in front and 300 THE VERTEBRATE ANIMALS two behind. Hawks and eagles are provided with strong talons with which the prey is seized and killed. Adaptation for semiaquatic life is seen in plovers, herons, or storks, where long legs and long toes enable the birds to seek their food in soft mud among reeds or lily pads, or along sand fiats. True aquatic birds, on the other hand, are provided with webbed toes. The foot of the common barnyard duck, for example, is much like that of the alligator. In the ostrich and cassowary the wings are not used for flight ; here the lower limbs have taken up the function of rapid motion. Perching. — The habit of perching is an interesting one. In many perching birds the tendons of the leg and foot, which regulate the toes, are self -locking ; while asleep such birds hold themselves perfectly. A certain part of the ear, known as the semicircular ca- nals, has to do with the function of balancing. In the flamingoes and other birds, which do not perch, balancing appears to be automatic ; thus the bird is able to sleep when in an upright position. Tail. — The tail is sometimes used in balancing; its chief func- tion, however, appears to be that of a rudder during flight. Most birds have under the skin of the tail a large oil gland, whence comes the supply of oil that is used in waterproofing the feathers in preen- ing. The Skeleton. — The skeleton combines lightness, flexibility, and strength. Many bones are hollow or have large spongy cavities. The bones of the head and neck show many and varied adaptations to the life that the bird leads. The vertebrae which form the frame- work of the neck are strong and flexible. They vary in shape and Skeleton of a fowl : C, clavicle ; CV, cervical vertebrae ; K, keeled ster- num ; PG, pelvic girdle ; PcG, bones of pectoral girdle (except clavicle). THE VERTEBRATE ANIMALS 301 in number. The swan, seeking its food under water, has a neck containing twenty-three long vertebrae ; the EngHsh sparrow, in a different environment, has only fourteen short ones. Some bones, notably the breastbone, are greatly developed in flying birds for the attachment of the muscles used in flight. Bill. — The form of the bill shows adaptation to a wonderful degree, the bills varying greatly according to the habits of the birds. Adaptations in the bills of birds. Could we tell anything about the food of a bird from its bill? Do these birds all get their food in the same manner? Do they all eat the same kind of food ? A duck l.«as a flat bill for pushing through the mud and straining out the food ; a bird of prey has a curved or hooked beak for tearing; the woodpecker has a sharp, straight bill for piercing the bark of trees in search of the insect larvae which are hidden underneath. Birds do not have teeth. The edge of the bill may be toothlike, as in some fish-eating ducks; these, however, are not true teeth. Frequently the tongue has sharp toothUke edges which serve the same purpose as the recurved teeth of the frog or snake. Adaptations for Active Life. — The rate of respiration, of heart- beat, and the body temperature are all higher in the bird than in man. ^ 302 THE VERTEBRATE ANIMALS This is one of the greatest adaptations to the active life led by a bird. Man breathes from twelve to fourteen times per minute. Birds breathe from twenty to sixty times a minute. The lungs are not large, the bronchial tubes being continued through the lungs into hollow spaces filled with air, which are found between the organs of the body. Only the lungs, however, are used for breath- ing. Because of the increased activity of a bird, there comes a necessity for a greater and more rapid supply of oxygen, an increased blood supply to carry the material to be used up in the release of energy, and a means of rapid excretion of the wastes resulting from the process of oxidation. A bird may be compared to a high-pres- sure steam engine ; in order to release the energy which it uses in flight, a large quantity of fuel which will oxidize quickly must be used. Birds are large eaters, and the digestive tract is fitted to digest the food quickly and to release the energy when needed, by having a large crop in which food may be stored in a much softened condition. As soon as the food is part of the blood, it may be sent rapidly to the places where it is needed, by means of the large four- chambered heart and large blood vessels. The high temperature of the bird is a direct result of this rapid oxidation; furthermore, the feathers and the oily skin form an insulation which does not readily permit of the escape of heat. This insulating cover is of much use to the bird in its flights at high altitudes, where the temperature is often very low. The Nervous System and the Senses. — The central nervous system is well developed. A large forebrain is found, which, according to a series of elaborate experiments with pigeons, is found to have to do with the conscious life of the bird. The cerebellum takes care of the acts which are purely mechanical. Sight is probably the best developed of the senses of a bird. The keen- ness of vision of a hawk is proverbial. It has been noticed that in a bird which hunts its prey at night, the eyes look toward the front of the face. In a bird which is hunted, as in the dove, the eyes are placed at the side of the head. In the case of the woodcock, which feeds at night in the marshes, and which is in constant danger from attack by owls, the eyes have come to lie far back on the top of the head. Hearing is also well developed in most birds; this fact may be demonstrated with any canary. The sense of smell does not appear to be well developed in any bird, and is especially deficient in seed-eating birds. THE VERTEBRATE ANIMALS 303 Nesting Habits. — Among the most interesting of all instincts shown by birds are the liabits of nest building. We have found that some invertebrates, as spiders and ants, protect the eggs when laid. In the vertebrate group some fishes (as the sunfish and stickleback) make nests for the depo- sition of the eggs. But most fishes, and indeed other vertebrates lower than the birds, leave the eggs to be hatched by the heat of the sun. Birds in- cubate their eggs, that is, hatch them, by the heat of . , , « , , . IT TT Nest of a phcebe under the barn floor. thei^: own bodies, llence a nest, in which to rest, is needed. The ostrich is an exception; it makes no nest, but the male and the female take turns in sitting on the eggs. Such birds as are immune from the attack of enemies because of their isolation or their protective coloration (as the puffins, gulls, and terns), build a rough nest among the rocks or on the beach. The eggs, especially those of the tern, are marked and colored so as to be almost indistin- guishable from the rocks or sand on which they rest. Other birds have made the nest a home and a place of refuge as well as a place to hatch the eggs. Such is the nest of the woodpecker in the hollow tree and the hang- ing nest of the oriole. Some nests which might be easily seen be- cause of their location are often rendered inconspicuous by the builders ; for example, the lichen-covered nest of the humming birds. Nest of the chimney swift. 304 THE VERTEBRATE ANIMALS Care of the Young. — After the eggs have been hatched, the young in most cases are quite dependent upon the parents for food. Most young birds are prodigious eaters; as a result they grow very rapidly. It has been estimated that a young robin eats two or Common tern {Sterna hirundo) and young, showing nesting and feeding habits. From group at American Museum of Natural History. three times its own weight in worms every day. Many other young birds, especially kingbirds, are rapacious insect eaters. In the case of the pigeons and some other birds, food is swallowed by the mother, partially digested in the crop, and then regurgitated into the mouths of the young nestlings. Problem XL, How birds are of economic importance. (Lab- or atorj/ Manual, Prob. XL.) Food of Birds. — The food of birds makes them of the greatest economic importance to our country. This is because of the rela- tion of insects to agriculture. A large part of the diet of most of our native birds includes insects harmful to vegetation. Investi- THE VERTEBRATE ANIMALS 305 gallons undertaken by the United States Department of Agricul- ture (Division of Biological Survey) show that a surprisingly large number of birds once believed to harm crops really perform a serv- ice by killing injurious insects. Even the nmch maligned crow lives to some extent upon insects. During the entire year, the crow has been shown to eat about 25 per cent insect food and 29 per cent grain. In May, when the grain is sprouting, the crow is a pest, but he makes up for it dur- ing the remainder of the summer by eating harmful insects. The robin, whose presence in the cherry tree we resent, during the rest of the summer does untold good by feeding upon noxious in- sects. Birds use the food sub- stances which are most abundant around them at the time.^ Not only do birds aid man in his battles with destructive insects, but seed-eating birds eat the seeds of weeds. Our native sparrows (not the English sparrow), the doves, partridges, and other forms feed largely upon the seeds of many of our common weeds. This fact alone is sufficient to make birds of vast economic importance. * The following quotation from I. P. Trimble, A Treatise on the Insect Enemies of Fruit and Shade Trees, bears out this statement : " On the fifth of May, 1864, . . . seven different birds . . . had been feeding freely upon small beetles. . . . There was a great flight of beetles that day ; the atmosphere was teeming with them. A few days after, the air was filled with Ephemera flies, and the same species of birda were then feeding upon them." During the outbreak of Rocky Mountain locusts in Nebraska in 1874-1877, Professor Samuel Aughey saw a long-billed marsh wren carry thirty locusts to her young in an hour. At this rate, for seven hours a day, a brood would consume 210 locusts per day, and the passerine birds of the eastern half of Nebraska, allowing only twenty broods to the square mile, would destroy daily 162,771,000 of the pests. The average locust weighs about fifteen grains, and is capable each day of con.suming its own weight of standing forage crops, which at $10 per ton would be worth S1743.26. This case may serve as an illustration of the vast good that is HUNT. ES. BIO. 20 Food of some common birds. 306 THE VERTEBRATE ANIMALS Not all birds are seed or insect feeders. Some, as the cormorants, ospreys, gulls, and terns, are active fishers. Near large cities gulls especially act as scavengers, destroying much floating gar- bage that otherwise might be washed ashore to become a menace to health. Sea birds also live upon shellfish and crustaceans (as small crabs, shrimps, etc.) ; some even eat lower organisms. The kea parrot, once a fruit eater, now takes its meal from the muscles forming the backs of living sheep. Birds of prey (owls) eat living mammals, including many rodents, for example, field mice, rats, and other pests. Extermination of our Native Birds. — Within our own times we have witnessed the almost total extermination of some species of our native birds. The American passenger pigeon, once very abundant in the Middle West, is now practically extinct. Audu- bon, the greatest of all American bird lovers, gives a graphic account of the migration of a flock of these birds. So numerous were they that when the flock rose in the air the sun was dark- ened, and at night the weight of the roosting birds broke down large branches of the trees in which they rested. To-day hardly a single specimen of this pigeon can be found, because they were slaughtered by the hundreds of thousands during the breeding season. At the present time nearly $3000 is offered to the person finding a pair of nesting passenger pigeons. The wholesale killing of the snowy egret to furnish ornaments for ladies' headwear is another example of the improvidence of our fellow-countrymen. Charles Dudley Warner said, '' Feathers do not improve the ap- pearance of an ugly woman, and a pretty woman needs no such aid." Wholesale kiUing for plumage, eggs, and food, and, alas, often for mere sport, has caused the decrease of our birds to 46 per cent in thirty states and territories within the past fifteen years. Every crusade against indiscriminate killing of our native birds done every year by the destruction of insect pests fed to nestling birds. And it should be remembered that the nesting season is also that when the destruction of injurious insects is most needed ; that is, at the period of greatest agriciJtural activity and before the parasitic insects can be depended on to reduce the pests. The encouragement of birds to nest on the farm and the discouragement of nest robbing are therefore more than mere matters of sentiment ; they return an actual cash equivalent, and have a definite bearing on the success or failure of the crops. — • Year Book of the Department of Agriculture. THE VERTEBRATE ANIMALS 307 should be welcomed by all thinking Americans. Without the birds the farmer would have a hopeless fight against insect pests. The effect of killing native birds is now well seen in Italy and Japan, where insects are increasing and do greater damage each year to crops and trees. Of the eight hundred or more species of birds in the United States, only two species of hawks (Cooper's and the sharp-shinned hawk), the great horned owl, the cowbird, and the EngHsh spar- row may be considered as enemies of man. The English Sparrow. — The English sparrow is an example of a bird introduced for the purpose of insect destruction, that has done great harm because of its relation to our native birds. Introduced at Brooklyn in 1850 for the purpose of ex- terminating the cankerworm, it soon abandoned an insect diet and has driven out most of our native insect feeders. Investigations by the United States Department of Agriculture have shown that in the country these birds and their young feed to a large extent upon grain, thus showing them to be injurious The proportions of food of the to agriculture. Dirty and very prolific, ^^ la sp r it already has worked its way from the East as far as the Pacific coast. In this area the bluebird, song sparrow, and yellowbird have all been forced to give way, as well as many larger birds of great economic value and beauty. The English sparrow has be- come a national pest, and should be exterminated in order to save our native birds. It is feared in some quarters that the English starling which has recently been introduced into this country may in time prove a pest as formidable as the English sparrow. Geographical Distribution and Migrations. — Most of us are aware that some birds remain with us in a given region during the whole year, while other birds appear with the approach of spring, departing southwards with the warm weather in the fall of the year. Such birds we call migrants, while those that remain the year round are called residents. In Europe, where the problem of bird migration has been 308 THE VERTEBRATE ANIMALS studied carefully, migrations appear to take place along well- defined paths. These paths usually follow the coast very exactly, although in places they may take the line of coast that existed in former geological times. In this country the Mississippi valley, a former arm of the sea, forms one line of migration, while the north Atlantic seacoast forms another route/ It has been shown that the southern movement of migratory birds in the fall of the year is not due entirely to the advent of cold weather, but is largely a matter of adjustment to food supply. A migrant almost always depends upon fruits, seeds, and grains as part of its food. Most win- ter residents, as the crow, are omnivorous in diet. Others, as the sparrows, may be seed eaters, but under stress may change their diet to almost anything in the line of food ; still others, as the wood- peckers, although insect-eat- ing birds, manage to find the desired food tucked away under the bark of trees. Many insect-eating birds, however, because their food is found on green plants, appear to be forced south- ward by the cold weather. Classification of Birds. — ■ African ostrich {Struthio camelus). ^^^^' are divided into two great groups, depending on the de- velopment of the keel; that is, the part of the breastbone to which the muscles used in flight are attached. Hence all flying birds are placed in a group called the Carinatoe. Birds in which the keel of the breastbone is not well developed, such 1 There is opportunity for a careful observer to learn much of the spring or fall migrations in the particular part of the country in which he resides. All informa- tion thus obtained should be sent to the secretary of the American Ornithologists' Union or to W. W. Cooke of the Biological Survey, who has done much to estab- lish what we already know about bird migration in this country. THE VERTEBRATE ANIMALS 309 White-throated spairow {Zonotrichia albicoUia). as the ostrich and cassowary, are said to belong to the liatilw. These birds make up for their lack of wing de- velopment by having the legs strong and long. The flying birds are further subdivided into a number of orders, the clas- sification based upon the adaptations of dififerent parts of the bird, especially the legs and feet, the wings and the bill, to different functions. We shall not trouble ourselves to learn all the different groups, but shall content ourselves with picking out some of the more evident and important ones, especially those which we might meet in field trips. I. Perching Birds. — To this order belong most of our common birds, — sparrows, swallows, larks, blackbirds, orioles, kingbirds, and many others well known to every bird lover. In this group the toes are so placed, three toes being turned forward and one backward, as to be perfectly adapted to perching. A large number of our sweetest song- sters belong among the perch- ers, the warblers, wrens, thrushes, bluebirds, and, last but not least, our robin. II. The Fowls or Gallina- ceous Birds. — This order is of great economic impor- tance. From the jungle fowl, found wild in the jungles of India, most of our domesti- cated fowls have descended. A, ptarmigan in winter; B, ptarmigan in summer. How do you account for the change in plumage ? May this change be of use to the bird ? 310 THE VERTEBRATE ANIMATE Other familiar examples are the turkeys, quails, partridge or ruffed grouse, and the pheasants and prairie chickens. In this group the legs are strong and stout, the body thickset, the bill and claws rather blunt. Birds of this order do not fly far in a state of nature, preferring to live on or near the ground. Such birds as the ruffed grouse, which nest on the ground, are almost invariably protectively colored. Another interesting example of protective resemblance in this group is seen in the ptarmigan. This bird in the winter is white as the snow which surrounds it ; in the spring it molts, turning to a gray and white, thus resembling the lichens among which it feeds. III. Birds of Prey. — These birds are characterized by the strong hooked beak, adapted to tearing, and by the sharp claws, which are curved and strong. Members of this group that are best known to us are the hawks, the condor, with its great sweep of ten feet from wing to wing, and the eagle. IV. Waders. — These are birds with unusually long legs and long necks, the latter character being a natural correlation of greatest service in food getting. Examples are the mud hen or coot, the snipe, crane, heron, and stork. The last two are the giants of the group. The Swimmers and Divers. — Birds placed in these orders have the feet webbed ; the wings are often adapted for long and swift flight. In this division are placed the gulls, terns, ducks, geese, loons, auks, and puffins. Other Orders. — Other orders of birds include the doves, the only remaining native representative being the mourning dove; the wood- peckers, strong and long of bill, the friend of the lumberman as a savior of the trees from boring pests which live under the bark ; the swifts and humming birds, the latter among the tiniest of all vertebrate animals ; and the parrots, of which we have only one native form, the Carolina paroquet (Conurus carolinensis) . This bird once had a range north as far as the Great Lakes ; now it is found only in South America. Relationship of Birds and Reptiles. — The birds afford an interesting example of how the history of past ages of the earth has given a clew to the structural relation which birds bear to other animals. Several years ago, two fossil skeletons were found in Europe of a birdlike creature which Golden eagle (Aquila chrysaUos). North America and Europe. Copyright, 1901, by N.Y. Zoological Society. THE VERTEBRATE ANIMALS 311 had not only wings and feathers, but also teeth and a lizardlike tail. From these fossil remains and certain structures (as scales) and habits (as the egg-laying habits), naturalists have concluded that birds and rep- tiles in distant times were nearly related and that our existing birds probably developed from a reptile-like ancestor millions of years ago. Classification of Birds Division I. Ratitoe. Running birds with no keeled breastbone. Examples* ostrich, cassowary. . Division II. Carinatce. Birds with keeled breastbone. Order i. Passeres. Perching birds ; three toes in front, one Ijehind. One half of all species of birds are included in this order. Examples : sparrow, thrush, swallow. Order ii. Gallince. Strong legs; feet adapted to perching. Beak stout. Ex- amples : jungle fowl, grouse, quail, domestic fowl. Order III. Raptores. Birds of prey. Hooked beak. Strong claws. Examples: eagle, hawk, owl. Order iv. Grallatores. Waders. Long neck, beak, and legs. Examples : snipe, crane, heron. Order v. Natatores. Divers and swimmers. Legs short, toes webbed. Ex- amples : gull, duck, albatross. Order vi. Columhce. Like Gallinae, but with weaker legs. Examples ; dove, pigeon. Order vii. PicaruB. Woodpeckers. Two toes point forward, two backward, and adaptation for climbing. Long, strong bill. Reference Books elementary Walker, Our Birds and their Nestlings, American Book Company. Beebe, The Bird. Henry Holt and Company. Nature Study Leaflets, XXII, XXIII, XXIV, XXV, Cornell Nature Study Bulle- tins. Walter, H. E. and H. A., Wild Birds in City Parks. advanced Apgar, Birds of the United States. American Book Company. Bulletins of U.S. Department of Agriculture, Division of Biological Survey, Nos. 1, 6, 15, 17. See also Yearbook, 1899, etc. Chapman, Bird Life. D. Appleton and Company. Riverside Natural History, Vol. IV. Houghton, Mifflin, and Company. Mammals Mammals. — Dogs and cats, sheep and pigs, horses and cows, all of our domestic animals (and man himself), have characters of structure which cause them to be classed as the type of vertebrate 312 THE VERTEBRATE ANIMALS animal known as mammals. These characters are the possessions of a hairy covering, of lungs, and warm blood. They bear young developed to a form similar to their own,^ and nurse them with milk secreted by glands known as the mammary glands; hence the term '' mammal." Instincts. — Mammals are considered the highest of vertebrate animals, not only because of their compUcated structure, but be- cause their instincts are so well developed. Monkeys certainly seem to have many of the mental attributes of man. Professor Thorndike of Columbia University sums up their habits of learning as follows : — " In their method of learning, although monkeys do not reach the human stage of a rich life of ideas, yet they carry the animal method of learning, by the selection of impulses and association of them with differ- ent sense-impressions, to a point beyond that reached by any other of the lower animals. In this, too, they resemble man ; for he differs from the lower animals not only in the possession of a new sort of intelligence, but also in the tremendous extension of that sort which he has in common with them. A fish learns slowly a few simple habits. Man learns quickly an infinitude of habits that may be highly complex. Dogs and cats learn more than the fish, while monkeys learn more than they. In the number of things he learns, the complex habits he can form, the variety of lines along which he can learn them, and in their permanence when once formed, the monkey justifies his inclusion with man in a separate mental genus." Adaptations in Mammalia. — Of the thirty-five hundred species, most inhabit continents ; few species are found on different islands, and some, as the whale, inhabit the ocean. They vary in size from the whale and the elephant to tiny shrew mice and moles. Adapta- tions to different habitat and methods of life abound ; the seal and whale have the limbs modified into flippers, the sloth and squirrel have limbs peculiarly adapted to climbing, while the bats- have the fore limbs modeled for flight. Carnivorous Mammals. — As the word '' carnivorous " denotes, these animals are to a large extent flesh eaters. In a wild state they hunt their prey, which is caught and torn with the aid of well-developed claws and long, sharp teeth. These teeth, so well developed in the dog, are known as canine teeth or dog teeth. All flesh-eating mammals are wandering hunters in a state of nature ; 1 With the exception of the monotremes. THE VERTEBRATE ANIMALS 313 Skull of a dog. Notice the size and shape of the canine teeth. many, as the bear and lion, have homes or dens to which they retreat. Some (for example, bears and raccoons) live at least part of the time upon berries and fruit. Seals, sea lions, and walruses are adapted to a life in the water. Especially in the seals, the hind limbs are almost use- less on land. Some of the fur bearers, as the otter and mink, lead a partially aquatic life. Others in this great group prefer regions of comparative dryness, as the inhabitants of the South African belt. A few have come to live most of their time in the trees, the raccoon being an example. Many have adaptations for food getting and escape from enemies; the seasonal change in color of the weasel is an example of an adapta- tion which serves both of the above purposes. This is only one of hundreds of others that might be mentioned. Economic Importance. — The Carnivora as a group are of much economic importance as the source of most of our fur. The fur seal fisheries alone amount to many millions of dollars annually. Otters, skunks, sables, weasels, iind minks are of considerable importance as fur producers. Our domestic cats (particularly deserted cats) are such factors in the extermination of our native birds that their place as house pets is seriously questioned by some people. In India tigers, and in Africa lions, are man- eating in certain localities, and in our own country wolves, pumas, and wild cats do some damage. Rodents. — Mammals known as rodents have the teeth so modified that on the upper and lower jaw two prominent incisor teeth can be used for gnawing. These teeth keep their chisel-like The Calilorma soa iion [Zniophu.s califor- nianus). Photographed in the Philadel- phia Zoological Gardens by Davison. 314 THE VERTEBRATE ANIMALS Skull of a porcupine, a rodent. Notice the large overlapping incisor teeth. Compare them with the teeth of a dog (see page 313). edge because the back part of the teeth is softer and wears away- more rapidly. The canine or dog teeth are lacking. We are all familiar with the destructive gnawing qualities of one of the commonest of all ro- dents, the rat. The common brown rat is an example of a mammal, harmful to civilized man, which has fol- m,'^^ ^ ^HVS^^^I^HHHi lowed in his footsteps Ik ^HBh^HHBO^I ^^^ over the world. HL ^^^^^B^^J^^H Starting from China, it am ^^JBHH spread to eastern Europe, thence to west- ern Europe, and in 1775 it had obtained a lodg- ment in this country. In seventy-five years it reached the Pacific coast, and is now fairly common all over the United States, being one of the most prolific of all mammals. A determined effort is now being made to exterminate this pest be- cause of its connection with bubonic plague. Although most rodents may be considered as pests (as the rat and mouse), others are of use to man. Some of this order furnish food to man, as the rabbit, hares, and squir- rels. Rabbits, although rapid breeders, are kept in check in most parts of this country by their nat- ural enemies, birds of prey, and flesh-eating mammals. But in Australia, where they were intro- duced by man, they have become so numerous as to require govern- ment action in the form of a bounty for their destruction. Thou- sands of sheep are starved to death each year because rabbits eat up their pasturage. The fur of the beaver, one of the largest of Beaver (Castor canadensis). North America. Copyright, 1900, by A. Rad cliff e Dugmore. THE VERTEBRATE ANIMALS 315 this order, is of considerable value, as are the coats of several other rodents. The fur of the rabbit is used in the manufacture of felt hats. The quills of the porcupines (greatly developed and stiffened hairs) have a slight commercial value. Ungulates: Hoofed Mammals. — This group includes the domesticated animals, as the horse, cow, sheep, and pig. A group of animals which originally roamed wild, many species eventually came under the subjugating influence of man. Now they form a source of the world's wealth, and are an impor- tant part of the wealth of the United States. The order of ungulates is a very large one. It is characterized by the fact that the nails have grown down to become thickened as hoofs. In some cases only two (the third and fourth) toes are largely developed. Such animals have a cleft hoof, as in the ox, deer, sheep, and pigs. These form the even-toed ungulates. The deer fam- ily are the largest in number of species and individuals among our native forms, and in fact the world over. Among them are the common Virginia deer of the Eastern states, the white-tailed deer of our Adirondack forests. The bison, or buffalo, is nearly related to the deer and wild cattle. Formerly bisons existed in enormous Virginia door. From photograph loaned by the American Museum of Natural History. 1 h(' bisou. 316 THE VERTEBRATE ANIMALS numbers on our Western plains. They were hunted by whites and Indians for the hides and tongues only, and thousands of carcasses were left to rot after a hunt. They are now almost extinct. Geologic History of the Horse. — In some ungulates the middle toe of the foot has become largely developed, ^vith the result that the animal stands on it. Such are the zebra and the horse. We have, from time to time, made reference to the fact that certain forms of life, now almost extinct, flourished on the earth in former geologic periods. It is interesting to note that America was the original home of the horse, although at the time of the earliest explorers the horse was unknown here, the wild horse of the Western plains having arisen from horses introduced by the Spaniards. Long ages ago, the first ances- tors of the horse were probably little animals about the size of a fox. The earliest horse we have knowledge of had four toes on the fore and three toes on the hind feet. Thousands of years later we find a larger horse, the size of a sheep, with a three-toed foot. By gradual changes, caused by the tendency of the animals to vary and by the action of the surroundings upon the animal in preserving these variations, there was eventually produced our present horse, an animal with legs adapted for rapid locomotion, with feet particularly fitted for the life in open fields, and with teeth which serve well to seize and grind herbage. Domestication of Animals; Breeding by Selection. — The horse, which for some reason disappeared in this country, con- tinued to exist in Europe, and man, emerging from his early savage condition, began to make use of the animal. We know the horse was domesticated in early Biblical times, and that he soon became one of man's most valued servants. In more recent times, man has begun to artificially change the horse by breeding for certain desired characteristics. To do this, the horses which have varied so as to show the char- acters desired by the breeder are selected and bred together. The young from these animals are likely to be like the parents and, be- cause of the tendency of animals to vary, will be even more likely to show the characters the breeder desires than their parents. If this process is repeated for several generations, it will be seen that THE VERTEBRATE ANIMALS 317 man, by artificial selection, might have considerably modified the type of horse with which he started. In this mamier have been estabhshed and improved the various types of horses famihar to us as draft horses, coaches and hackneys, and the trotters. In a similar manner have been obtained the various breeds of cattle, sheep, swine, etc. It is needless to say that all the various domesticated animals have been tremendously changed in a similar manner since civilized man has come to live on the earth. When we realize the very great amount of money invested in domesticated animals; that there are over 60,000,000 each of sheep, cattle, and swine and over 20,000,000 horses owned in this country, then we may see how very important a part the domestic animals play in our lives. Other Orders of Mammals. — The lowest are the monotremes, animals which lay eggs like the ])irds, although they are provided with hairy covering like other mammals. Such are the Australian spiny anteater and the duck mole. All other mammals bring forth their young developed to a form similar to their own. The kan- garoos and opossum, however, are provided with a pouch on the ventral side of the body in which the very immature, bhnd, and helpless young are nour- ished until they are able to care for themselves. These pouched animals are called marsupials. The other mammals, in which the young are born able to care for themselves, and have the form of the adult, may be briefly classified as follows : — Virginia opossum. Photograph, one eighth natural size, by N. F. Davis. Character Edentates Toothless or with very simple teeth Rodents Incisor teeth, chisel-shaped, usu- ally two above and two below Cetaceans Adapted to marine life, teeth of whales sometimes platelike Examples Anteater Sloth Armadillo Beaver, rat Porcupine, rabbit Squirrels Whales Porpoise 318 TPIE VERTEBRATE ANIMALS Ungulates Hoofs, teeth, adapted for grinding (a) (b) Carnivora Long canine teeth, sharp and long claws, usually aggressively colored Chiroptera Fore limbs adapted to flight, teeth pointed Primates Erect or nearly so, fore appendage provided with hand Reference Books elementary Odd-toed Horse Rhinoceros Tapir Even-toed Ox Pig Sheep Deer Dogs Cats Lions Bears, etc. Seals and sea Bat Monkeys Apes Man lions Sharpe, A Laboratory Manual for the Solution of Problems in Biology. American Book Company. Hodge, Nature Study and Life. Chap. III. Ginn and Company. Ingersoll, Wild Neighbors. The Macmillan Company. Lucas, Animals of the Past. McClure, Phillips, and Company. Matthew, The Evolution of the Horse, Guide Leaflet No. 9, American Museum of Natural History. Stone and Cram, American Animals. Doubleday, Page, and Company. Wright, Four-footed Americans. The Macmillan Company. ADVANCED Flower, The Horse. D. Appleton and Company. Kingsley, Riverside Natural History. Houghton, Mifflin, and Company. Schaler, Domesticated Animals, their Relation to Man and to His Advancement in Civilization. Charles Scribner's Sons. XXIII. MAN, A MAMMAL jproblein XLI. A study of man as a vertebrate compared with tJiefrog' {Laboratory Manual, Prob. XLI.) (a) Comparison of body covering, (,b) TJw study of muscles. (c) Adaptations in the skeleton, id) Jfervous system. Man's Place in Nature. — Although we know that man is sepa- rated mentally by a wide gap from all other animals, in our study of physiology we must ask where we are to place man. If we attempt to classify man, we see at once he must be placed with the vertebrate animals because of his possession of a vertebral column. Evidently, too, he is a manamal, because the young are nourished by milk secreted by the mother and because his body has at least a partial covering of hair. Anatomically we find that we must place man with the apelike mammals, because of thdse numerous points of structural likeness. The group of mammals which includes the monkeys, apes, and man we call the primates. Although anatomically there is a greater difference between' the lowest type of monkey and Lhe highest type of ape than there is between the highest type of ape and the lowest savage, yet there is an immense mental gap. Undoubtedly there once lived upon the earth races of men who were much lower in their mental organization than the present inhabitants. Evolution of Man. — If we follow the early history of man upon the earth, we find that at first he must have been Uttle better than one of the lower animals. He was a nomad, wandering from place to place, living upon whatever living things he could kill with his hands. Gradually he must have learned to use weapons, and thus kill his prey, first using rough stone implements for this purpose. As man became more civihzed, implements of bronze and of iron 319 320 MAN, A MAMMAL were used. About this time the subjugation and domestication of animals began to take place. Man then began to cultivate the fields, and to have a fixed place of abode other than a cave. The beginnings of civilization were long ago, but even to-day the earth is not entirely civilized. The Races of Man. — At the present time there exist upon the earth five races or varieties of man, each very different from the other in instincts, social customs, and, to an extent, in structure. These are the Ethiopian or negro type, originating in Africa; the Malay or brown race, from the islands of the Pacific; the Amer- ican Indian; the Mongolian or yellow race, including the natives of China, Japan, and the Eskimos; and, finally, the highest type of all, the Caucasians, represented by the civilized white in- habitants of Europe and America. The Human Body a Machine. — In all animals, and the human animal is no exception, the body has been likened to a ma- chine in that it turns over the latent or potential energy stored up in food into kinetic energy (mechanical work and heat), which is manifested when we perform work. One great difference exists between an engine and the human body. The engine uses fuel unlike the substance out of which it is made. The human body, on the other hand, uses for fuel the same substances out of which it is formed ; it may, indeed, use part of its own substance for food. It must as well do more than purely mechanical work. The human organism must be so delicately adjusted to its surroundings that it will react in a ready manner to stimuli from without ; it must be able to utilize its fuel (food) in the most economical manner; it must be fitted with machinery for transforming the energy re- ceived from food into various kinds of work; it must properly provide the machine with oxygen so that the fuel will be oxidized, and the products of oxidation must be carried away, as well as other waste materials which might harm the effectiveness of the machine. Most important of all, the human machine must be able to repair itself. In order to understand better this complicated machine, the human body, let us examine the structure of its parts and thus get a better idea of the interrelation of these parts and of their functions. MAN, A MAMMAL 321 Structure of the Skin. — In man, the outer covering of the skin is composed of two layers. The outer part (called the epidermis) is composed largely of flattened dead cells. It is part of this layer that peels off after sunburn, or that separates from the inner part of the epidermis when a water blister is formed. The inner cells of the epidermis are provided with more or less pigment or coloring matter. It is to the varying quantity of this pigment that the light or dark complexion is due. The inmost layer of the epidermis is made up of small cells which are constantly dividing to form new cells to take the place of those in the outer layer which are lost. Suheutaneo»» Infer of connective tUtue and /at Diagram of a section of the skin. (Highly magnified.) The dermis, or inner layer, is largely composed of connective tissue filled with a network of blood vessels and nerves. This layer con- tains the sweat glands, some of the most important glands in the body. Other organs connected with the nervous system, and called the tactile corpuscles, cause this part of the skin to be sensitive to touch. Nails and Hairs. — Nails are a development from the horny layer of the epidermis. A hair is also an outgrowth of the horny layer, although it is formed in a deep pit or depression in the dermis ; this pit is called the hair follicle. HUNT. ES. BIO. — 21 322 MAN, A MAMMAL The Glands of the Skin. — Scattered through the dermis, and usually connected with the hair follicles, are tiny oil-secreting glands, the sebaceous glands. The function of the sebaceous gland is to keep the hair and surface of the skin soft. The other glands, known as sweat glands, are to be found in profusion, over 2,500,000 being present in the skin of a normal man. These glands carry off certain wastes from the blood in the water they pass off. Thus the skin not only protects the body, but also serves as an excretory organ. Its most important function, however, is the regulation of the h^t of the body. How it does this, we shall learn later. (See (phapter XXVII.) Connective Tissue. — The layer immediately beneath the der- mis is known as the subcutaneous layer. It is an important storage place for fat. Underneath this layer we find a mass of flesh or muscle. Intermixed with this is a considerable amount of fat. The fat, muscle, — in fact, all the tissues in the body, — are held together by fibrous threads called connective tissue. Muscles and Movement. — We are all aware that motion in any of the higher animals is caused by the action of the muscles. These contract to cause move- ment. In man and the other vertebrate ani- mals, the muscles are almost always fastened to bones, which, acting as levers, give wide range of motion. Arrangement of Voluntary Muscles in the Human Body. — Muscles are usually placed in pairs; one, called the extensor, serves to straighten the joint; the other, the flexor, bends the joint. Locate, by means of feeling the muscles when expanded and when con- tracted, the extensors and flexors in your own arm. Use the leg of a frog to deter- mine which muscles are extensors and which flexors (see the Figure). This paired arrange- Muscles of the left leg of ment of muscles is of obvious importance, a the frog ; h, M. biceps ; flexor muscle balancing the action of an ex- L.^M.temImembmn- ^^usor ou the other side of the joint. The osus ; tr, M. triceps. end of the muscle that has the wider move- MAN, A MAMMAL 323 ment in a contraction is called the insertion; the part that moves least is the origin. Microscopic Structure of Volun- tary Muscle, — With a sharp pair of scissors cut through a muscle at right angles to the long axis ; examina- tion will show that it is composed of a number of bundles of fibers. These fibers are held together by a sheath of connective tissue. Each of these bundles may be separated into smaller ones. If we continue this so as to separate into the smallest possible bits that can be seen with the naked eye, and then examine such a tiny portion under the compound microscope, it will present somewhat the appearance shown in the Figure. The muscle is seen to be made up of a number of tiny threads which lie side by side, held together by the sheath. Muscles, then, are bundles of long fibers. In man, muscles which are under the control of the will have a striated appearance, while those which are involuntary are unstriated. Both kinds are supplied with nerves, which control them (see Figures). A bit of voluntary muscle fiber, showing the cross striations as seen under the microscope. (Highly magnified.) The delicate endings of nerves in vol- untaiy muscle. (Highly magnified.) Muscle Tissue and its Uses. — Muscles evidently form a large part of the body, in man, nearly half the body weight being muscle. Nearly every muscle in the human body is attached to a bone either at one or at both ends. Move- ment is performed by means of the muscles, leverage being obtained by means of their attachment to the bones. Movement is, indeed, the chief function of muscles. In the human body there are over 324 MAN, A MAMMAL five hundred muscles, varying from one smaller than a pinhead to a band almost two feet in length. Every movement of the body, be it merely a change of expression or change in the pitch of the voice, directly results from contraction of a muscle. Muscles also give form to the body, and are useful in protecting the delicate organs and large blood vessels within them. Muscles and the Skeleton. — Muscles would be of httle use to animals if they were not attached to hard parts of the body which serve as levers. In many invertebrate animals (for example, crustaceans, insects, and mollusks), the muscles are attached to the exoskeleton. In man they are attached to the endoskeleton. In the hind leg of the frog, if we cut through the muscles of the thigh to the bone, we may make out exactly how and where the muscles of the thigh are attached to the bone. Moving the leg in as many different directions as possible, we notice that it may be flexed or bent ; that it may be ex- tended to its original position ; that it may be moved to and from the midline of the body ; that, with the knee held stiff, the whole limb may be made to de- scribe the arc of a circle.^ These same movements are possible in the leg of a man. This movement between bones is obtained by means of joints. If, in the frog, we carefully separate the muscles of the thigh to the bone, we find that they are attached to the bone by white, glistening tendons. Careful examination shows that the bones themselves are held together by very tough Hinge joint, showing ^j^j^^ ^^^^^ ^^ ^^^^^ . ^^^^^ ^^^ ^^^ ligaments. We Sndon (6) ^""^ '*^ ^^^' ^^^' ^^^* ^^® ®^^ ^^ ^^® ^^^^® *^^^ ^^^® ^*^ into a socket in the hip bone or pelvic arch. It is thus easy to see how such free movement is obtained in the leg. Levers in the Body. — It is evident that movement of a joint is caused by muscles which act in cooperation with the bones to which they are at- tached ; the latter thus form true levers. A lever is a structure by which either greater work power or greater range of motion is obtained. In this apparatus, the lever works against a fixed point, the fulcrum, in order to raise a certain weight. A seesaw is a lever ; here the fulcrum is in the middle, the weight is at one end, and the power to lift the weight is ap- plied at the other end. There are three classes of levers, named accord- ing to the position of the fulcrum. In the first class, the fulcrum lies between the weight and the power ; 1 At this point demonstration with a human skeleton should be made. MAN, A MAMMAL 326 the seesaw is an example of this. The l)est example in the human body of a lever of the first class is seen when the head nods. Here the fulcrum is the vertebra known as the atlas; the power is the muscles of the neck attached to the back of the skull and to the spine ; the weight is the front part of the head. When one keeps the head erect, this lever is used; the nodding head when one is napping shows this plainly. \ ^ .^ B C Three classes of levers. A, a lever of the first class; B, a lever of the second class; C, a lever of the third class. (See text.) A lever of the second class has the fulcrum at one end, and the weight between it and the power ; when we rise on our toes, we use this kind of lever. In a lever of the third class, the fulcrum is at one end, with the power between it and the weight. This is the kind of lever seen most frequently in the human body. The flexing (drawing up) of the lower leg or the fore- arm is an example of the use of this kind of lever. In such a lever, a wide range of movement is obtained. General Structure and Uses of the Skeleton. — Evidently bones form a framework to which muscles are attached; thus they are used as levers for pur- poses of movement. Second, they give pro- tection to delicate or- gans ; they form a case around the brain and spinal cord ; as ribs they protect the or- gans in the body cavity. Third, they give rigidity and form to the body. The skeleton of a dog; a typical mammal. 326 MAN, A MAMMAL The skeleton of vertebrate animals consists of two distinct regions : a vertebral column of backbone which, with the skull, forms the dxial skeleton; and the parts attached to this main axis, the ap- pendicular skeleton (the append- ages). All skeletons of vertebrates have the same general regions, the size and shape of the bones in these regions differing somewhat in each kind of animal. In the axial skeleton of the frog, as well as in man, the vertebral column is made up of a number of bones of irregular shape, which fit more or less closely into each other. These bones are called vertehroe. Notice that the vertebrae possess long processes to which muscles of the back are attached. Certain of the vertebrae bear ribs (arched, flat bones) , the special function of which is to protect the organs of the upper body cavity. Adaptations in the Vertebral Col- umn. — The vertebral column in man is made up of many separate pieces of bone : thirty-three in a child; twenty-six in the adult, several bones in the region of the pelvis later growing together. Each vertebra presents the general form of a body or centrum of bone and a bony arch with seven projections ; in this arch runs the spinal cord. The surface of the centrum and those parts of the vertebrae, each of which fits into its next neighbor, are covered with pads of cartilage. Two of the processes in each vertebra project forward and two back- Skeleton of man : CR, cranium ; CL, clavicle; ST, sternum; SC, scapula; H, humerus; VC, ver- tebral column ; R, radius ; U, ulna ; P, pelvic girdle ; C, carpals ; MC, metacarpals; Ph, phalanges; F, femur ; Fi, fibula ; T, tibia ; Tar, tarsals; MT, metatarsals. MAN, A MAMMAL 327 ward ; these form articulations or joints with the neighboring verte- brae. Of the other processes, one projects dorsally and two project laterally ; these give attachment to the muscles of the back. The two vertebrae directly beneath the head are modified so as to permit the skull to rest in the upper one ; this articulates freely with the second vertebra, thus permitting of the nodding and turning move- ments of the head. Besides these individual adaptations, the vertebral column, as a whole, is peculiarly adapted to protect the brain from jar; this is seen in the double bend of the vertebral column and the pads of cartilage between the individual vertebrae. The whole column of vertebrae joined each to the other supports the weight of the body. The largest vertebrie at the base are joined to the huge pelvic bones for the better support of the body above. That part of the vertebral column of man which bears the ribs is known as the thoracic re- gion. The ribs, twelve in number, are long, curved bones which combine lightness with strength; joined by elastic cartilage to the sternum in front and to the vertebrae behind, they form a wonderful pro- tection to the organs in the thoracic cavity, and yet allow free movement in breathing. The Appendages. — The parts of the skeleton to which the bones of the anterior and posterior appendages are attached are respectively known as the pectoral girdle (from which hangs the arm) and the pelvic girdle (which joins the leg bones to the axial skeleton). The bones of the appendages attached to the pectoral and pelvic girdles are adapted peculiarly to locomotion and sup- port ; for this purpose the bones are long and strong, hinged by very flexible joints. The latter are especially free in the hand to allow for grasping. In the leg, where weight must be supported as well as carried, the bones are bound more firmly to the axial skeleton. The bones of the foot are so arranged that a springy arch is formed which aids greatly in locomotion. Vertebra, showing attachment of ribs ; C, centrum ; R, riba ; SP, spinous process. 328 MAN, A MAMMAL The skull: F., frontal bone; P., parietal bone; T., temporal bone ; SP., sphenoid bone; O., occi- pital bone; U.J., superior maxillary (upper jaw) bone ; L.J., inferior maxillary (lower jaw) bone. The Human Skull. — The skull shows wonderful adaptations for its varied functions. The brain case is compactly built, its arched roof giving strength. The eye and inner ear are protected in sockets of bone. The lower jaw works upon a hinge, and furnishes attach- ment for strong muscles which move the jaw. The skeleton, besides the purposes already described, protects certain organs in the body cavity of man. Other Organs. ^ — ^ We have seen that a body cavity has developed in all animals which are more complex than the baglike hydra, and that a food tube has come to lie within this space. In all such animals the structures which have to do with digestion and absorption of food, most of the structures which have to do with the circulation of this food and of the blood, and organs which give oxygen to the blood, as well as the organs of excretion and of reproduction, lie within the body cavity. These organs we shall discuss in detail later. Nerves. — Other structures, known as nerves, are found in prac- tically all parts of the body. We find that nerves have their end- ings in the skin, in muscle, and in the cells of glands in various parts of the body; we find a nerve supply to the heart, lungs, and other structures within the body cavity. The most important part of the nervous system in vertebrate animals lies within the cavity formed by bones making up the skull and the vertebral column. This central nervous system, the spinal column and the hrain, is a characteristic of the vertebrate animals. General Functions of the Nervous System. — We have seen that, in the simplest of animals, one cell performs the functions neces- sary to its existence. In the more complex animals, where groups of cells form tissues, each having a different function, a nervous system is developed. Thefundions of the human nervous system are : MAN, A MAMMAL 329 (1) the providing of man with sensation, by means of which he gets in touch with the world about him; (2) the connection of organs in dif- ferent parts of the body so that they act as a united and harmonious whole; (3) the giving to the human being a will, a provision for thought. Cooperation in word and deed is the end attained. We are all familiar with examples of the cooperation of organs. You see food ; the thought comes that it is good to eat ; you reach out, take it, raise it to the mouth ; the jaws move in response to your will ; the food is chewed and swallowed ; while digestion and absorption of the food are taking place, the nervous s^'stem is still in control. The nervous system also regulates pumping of blood over the body, respiration, secretion of glands, and, indeed, every bodily function. Man is the highest of all animals because of the extreme develop- ment of the nervous system. Man is the thinking animal, and as such is master of the earth. Reference Reading for This and Succeeding Chapters on Hitman Biology elementary Sharpe, A Laboratory Manual Jor the Solution of Problems in Biology. American Book Company. Davison, The Human Body and Health. American Book Company. Eddy, General Physiology. American Book Company. Hall, Elementary Physiology. American Book Company. Clodd, Primer of Evolution. Longmans, Green, and Company. Clodd, The Story of Primitive Man. Longmans, Green, and Company. Ritchie, Human Physiology. Worid Book Company. advanced Halliburton, Kirk^s Handbook of Physiology. P. Blakiston's Son and Company. Hough and Sedgwick, The Human Mechanism. Ginn and Company. Howell, Physiology, 3d edition. W. B. Saunders Company. Schafer, Textbook of Physiology. The Macmillan Company. Stewart, Manuxil of Physiology. W. B. Saunders Company. Verworn, General Physiology. The Macmillan Company. XXIV. FOODS AND DIETARIES Problem XLII. A study of food values and diets. (^Laboror- tory Manual, Proho XLII.) {a) Food values and cost. (Jb) JVutritive values as compared with cost. (c) The family dietary. (d) Food values. Why we need Food. — We have already defined food as anything that forms material for the growth or repair of the body of a plant or animal, or that furnishes energy for it. The millions of cells of which the body is composed must be given material which will form more living matter or material which can be oxidized to release energy when muscle cells move, or gland cells secrete, or brain cells think. Food, then, not only furnishes our body with material to grow, but also gives us the energy we expend in the acts of walking, running, breathing, and even in thinking. Nutrients. — Certain nutrient materials form the basis of food of both plants and animals. These have been stated to be proteids (such as lean meat, eggs, the gluten of bread), carbohydrates (starches, sugars, gums, etc.), fats and oils (both animal and vege- table), and mineral matter and water. The parts of the human body, be they muscle, blood, nerve, bone, or gristle, are built up from the nutrients in our food. Proteids. — Proteids, in some manner unknown to us, are manu- factured in the bodies of green plants. Proteid substances contain the element nitrogen. Hence such foods are called nitrogenous foods. Man must form the protoplasm of his body (that is, the muscles, tendons, nervous system, blood corpuscles, the living parts of the bone and the skin, etc.) from nitrogenous food. Some of this he obtains by eating the flesh of animals, and some he obtains directly from plants (for example, peas and beans). Because of their chemical composition, proteids are considered to 330 FOODS AND DIETARIES 331 be flesh-forming foods. They are, however, oxidized to release energy if occasion requires it. Fats and Oils. — Fats and oils, both animal and vegetable, are the materials from which the body derives part of its energy. The chemical formula of a fat shows that, compared with other food substances, there is very little oxygen present; hence the greater capacity of this substance for uniting with oxygen. The rapid burning ol fat compared with the slower combustion of a piece of meat or a piece of bread illustrates this. A pound of butter releases over twice as much energy to the body as does a pound of sugar or a pound of steak. Human fatty tissue is formed in part from fat eaten, but carbohydrate or even proteid food may be changed and stored in the body as fat. Carbohydrates. — We see that the carbohydrates, like the fats, contain carbon, hydrogen, and oxygen. Here, however, the oxygen and hydrogen are united in the molecule in the same proportion as are hydrogen and oxygen in water. Carbohydrates are essentially energy-producing foods. They are, however, of use in building up or repairing tissue. It is certainly true that in both plants and animals, such foods pass directly, together with foods containing nitrogen, to repair waste in tissues, thus giving the needed proportion of carbon, oxygen, and hydrogen to unite with the nitrogen in forming the protoplasm of the body. Inorganic Foods. — Water forms a large part of almost every food substance. The human body, by weight, is composed of about 60 |)er cent water. It is used to make the blood, and a sufficient quantity is most essential to health. When we drink water, we take with it some of the inorganic salts used by the body in the making of bone and in the formation of protoplasm. Sodiiim chloride (table salt), an important part of the blood, is taken in as a flavoring upon our meats and vegetables. Phosphate of lime and potash are important factors in the formation of bone. Phosphorus is a necessary substance for the making of living matter, milk, eggs, meat, whole wheat, and dried peas and beans containing small amounts of it. Iron also is an extremely important mineral, for it is used in the building of red blood cells. Meats, eggs, peas and beans, spinach and prunes, are foods containing some iron. Some other salts, compounds of calcium, magnesium, potassium, and 332 FOODS AND DIETARIES phosphorus, have been recently found to aid the body in many of its most important functions. The beating of the heart, the contraction of muscles, and the ability of the nerves to do their work appear to be due to the pres- ence of minute quantities of these salts in the body. Uses of Nutrients. — The following table sums up the uses of nutrients to man : ^ — Proteid Forms tissue (mus- White (albumen) of eggs, curd cles, tendon, and (casein) of milk, lean meat, probably fat). All serve as gluten of wheat, etc. fuel and yield Fats Form fatty tissue. energy in form Fat of meat, butter, olive oil, of heat and mus- oils of corn and wheat, etc. cular strength. Carbohydrates Transformed into fat. Sugar, starch, etc. Mineral matters (ash) .... Aid in forming bone, Phosphates of lime, potash, assist in digestion, etc. soda, etc. How the Exact Nutritive Value of Food has been Discovered. — For a number of years, experiments have been in progress in different parts of the civilized world which have led to the beliefs regarding food just quoted. One of the most accurate and important series of experiments was made a few years ago by the late Professor W. O. Atwater of Wes- leyan University, in cooperation with the United States Department of Agriculture. By means of a machine called the respiration calorimeter (Latin, color = heat + metrum = measure), which measures both the products of respiration and the heat given off by the body, it has been possible to determine accurately the value of different kinds 6f food, both as fuel and as tissue builders. This respiration calorimeter is described by Professor Atwater as follows : — " Its main feature is a copper- walled chamber 7 feet long, 4 feet wide, and 6 feet 4 inches high. This is fitted with devices for maintaining and measuring a ventilating current of air, for sampling and analyzing this air, for removing and measuring the heat given off within the chamber, and for passing food and other articles in and out. It is furnished with a fold- ing bed, chair, and table, with scales and appliances for muscular work, and has telephone connection with the outside. Here the subject stays for a period of from three to twelve days, during which time, careful analyses and measurements are made of all material which enters the body in the food, and of that which leaves it in the breath and excreta. * W. O. Atwater, Principles of NiUrition and Nutritive Value of Food, U.S. De- partment of Agriculture, 1902. FOODS AND DIETARIES 333 Record is also kept of the energy given oflf from the body as heat and muscular work. The difference between the material taken into and that given off from the body is called the balance of matter, and shows whether the body is gaining or losing material. The difference between the energy of the food taken and that of the excreta and the energy given off by the body as heat and muscular work, is the balance of energj% and, if cor- rectly measured, should equal the energy of the body material gained or lost. With such apparatus it is possible to learn what effect different con- ditions of nourishment will have on the human body. In one experiment, for instance, the subject might be kept quite at rest, and in the next do a certain amount of muscular or mental work with the same diet as before, then by comparing the results of the two, the use which the body makes of its food under the different conditions could be determined ; or the diet may be sUghtly changed in the one experiment, and the effect of this on the balance of matter or energy, observed. Such methods and appa- ratus are very costly in time and money, but the results are proportionately more valuable than those from simpler experiments." Fuel Values of Nutrients. — In experiments performed by Professor Atwater and others, and in the appended tables, the value of food as a source of energy is stated in heat units called calories. A calorie is the amount of heat required to raise the tem- perature of one kilogram of water from zero to one degree Centi- grade. This is about equivalent to raising one pound four degrees Fahrenheit. The fuel value of different foods may be computed in a definite manner. This is done by burning a given portion of a food (say one pound) in the apparatus known as a calori- meter. By this means may be determined the number of degrees the temperature of a given amount of water is raised during the process of burning. The Best Dietary. — Inasmuch as all living substance contains nitrogen, it is evident that proteid food must form a part of the dietary ; but proteid alone is not usable. If more proteid is eaten than the body requires, then immediately the liver and kidneys have to work overtime to get rid of the excess of proteid which forms a poisonous waste harmful to the body. We must take foods that will give us, as nearly as possible, the proportion of the dif- ferent chemical elements as they are contained in protoplasm. It has been found, as a result of studies of Atwater and others, that a man who does muscular work requires a little less than one quarter of a pound of proteid, the same amount of fat, and about one pound 334 FOODS AND DIETARIES of carbohydrate to provide for the growth, waste, and repair of the body and the energy used up in one day. Put in another way, At- water's standard for a man at light exercise is food enough to yield 2816 calories; of these, 410 calories are from proteid, 930 calories from fat, and 1476 calories from carbohydrate. That is, for every 100 calories furnished by the food, 14 are from proteid, 32 from fat, and 54 from carbohydrate. In exact numbers, the day's ration as advocated by Atwater would contain about 100 grams or 3.7 ounces proteid, 100 grams or 3.7 ounces fat, and 360 grams or 13 ounces carbohydrate. Professor Chittenden of Yale University, another food expert, thinks we need proteids, fats, and carbohydrates in about the proportion of 1 to 3 to 6, thus differing from Atwater in giving less proteid in proportion. Chittenden's standard for the same man is food to yield a total of 2360 calories, of which proteid furnishes 236 calories, fat 708 calories, and car- bohydrates 1416 calories. For every 100 calories furnished by the food, 10 are from proteid, 30 from fat, 60 from carbohydrate. In actual amount the Chittenden diet would contain 2.16 ounces proteid, 2.83 ounces fat, and 13 ounces carbohydrate.^ A German named Voit gives as ideal 25 proteids, 20 fat, 55 carbohydrate, out of every 100 calories ; this is nearer our actual daily ration. In addition, an ounce of salt and nearly one hundred ounces of water are used in a day. By means of the table on the following page (from Atwater ^), which shows the composition of some food materials, the nutritive and fuel value of the foods may be seen at a glance. The amount of refuse contained in foods (such as the bones of meat or fish, the exoskeleton of crustaceans and mol- lusks, the woody coverings of plant cells) is also shown in this table. A Mixed Diet Best. — Knowing the proportion of the different food substances required by man, it will be an easy matter to determine from this table the best foods for use in a mixed diet. Meats contain too much nitrogen in proportion to the other sub- stances. In milk, the proportion of proteids, carbohydrates, and fats is nearly right to make protoplasm ; a considerable amount of * Page 18, Bill. 6, Cornell Reading Course. 2 W. O. Atwater, Principles of NiUrition and Nviritive Value of Food, U.S. De- partment of Agriculture, 1902. FOODS AND DIETARIES 335 5~l,Codfl«h, dres^f J >s f Beef, loin m% Matton, leg Cam, Bmoked , Codfish, dreiutcd Oysters Egg« Milk, tuv^inuned Bntter Sngar m ^m^ ^^^^^-^M LLJ nz mm ]^a w^m Table of food values. Determine the percentage of water in codfish, loin of beef, milk, potatoes. Percentage of refuse in leg of mutton, codfish, eggs, and potatoes. What is the refuse in each case? Find three foods containing a high percentage of proteid ; of fat ; of carbohydrate. Find some food in which the proportions of proteid, fat, and carbohydrate are combined in the right proportions. 336 FOODS AND DIETARIES The composition of a bottle of milk. Why is it con- sidered a good food? mineral matter being also present. For these reasons, milk is exten- sively used as a food for children, as it combines food material for the forming of protoplasm with mineral matter for the building of bone. Some vegetables (for example, peas and beans) contain the nitrogenous material needed for protoplasm formation in consider- able proportions, but in a less digestible form than is found in some other foods. Vege- tarians, then, are correct in theory when they state that a diet of vegetables may contain every- thing neces- sary to sustain life. But a mixed diet is healthier. A purely vege- table diet contains much waste material, such as the cellulose forming the walls of the plant cells, which is indigestible. The Japanese army ration consists almost entirely of rice. A recent report by their surgeon-general intimates that the diminutive stature of the Japanese may, in some part at least, be due to this diet. The Relation of Work to Diet. — It has been shown experimentally that a man doing hard, muscular work needs more food than a person doing light work. The mere exercise gives the individual a hearty ap- petite ; he eats more and needs more of all kinds of food than a man or boy doing light work. Especially is it true that the person of sedentary habits, who does brain work, should be careful to eat less food and food that will digest easily. His proteid food should also be reduced. Rich .or hearty foods may be left for the man who is doing hard manual labor out of doors, for any extra work put on the digestive organs takes away just so much the ability of the brain to do its work. The Relation of Environment to Diet. — We are all aware of the fact that the body seems to crave heartier food in winter than in summer. The temperature of the body is maintained at 98^° in winter as in sum- mer, but much more heat is lost from the body in the cold weather. Hence feeding in winter should be for the purpose of maintaining our fuel sup- Three portions of foods, each of which furnishes about the same amount of nourishment. FOODS AND DIETARIES 337 ply. We need heat-producing food, and we need more food in winter than in summer, the latter partly because we exercise more in winter. We may use carbohydrates for this purpose, as they are economical and digestible. The inhabitants of cold countries get their heat-releasing foods largely from fats, because no plants are produced there. In tropical countries and in hot weather little proteid should be eaten and a considerable amount of fresh fruit used. Food Economy. — The American people are far less economical in their purcliase of food than most other nations. Nearly one half of the total income of the average workingman is spent on food. Not only does he spend a large amount on food, but he wastes money in purchasing the wrong kinds of food. A comparison of the daily diets of persons in various occupations in this and other countries show that as a rule we eat more than is necessary to supply the necessary fuel and repair, and that our workingmen eat more than those of other countries. Another waste of money by the American is in the false notion that a large proportion of the daily dietary should be meat. Many people think that the most expensive cuts of meat are the most nutritious. The falsity of this idea may be seen by a careful study of the table on page 338, compiled by Atwater, which shows the relative amount of various foods purchasable for 10 cents (present-day prices are from 20 per cent to 50 per cent higher than here quoted). Daily Fuel Needs of the Body. — It has been pointed out that the daily diet should differ widely according to age, occupation, time of year, etc. The following table shows the daily fuel needs for several ages and occupations: — Daily Calorie Needs (Approximately) Obs. 1. For child under 2 years 900 calories 2. For child from 2-5 years 1200 calories 3. For child from 6-9 years 1500 calories 4. For child from 10-12 years 1800 calories 5. For child from 12-14 (woman, light work also) . . . 2100 calories 6. For boy (12-14), giri (1.5-16), man sedentary .... 2400 calories 7. For boy (15-16) (man, light muscular work) .... 2700 calories 8. For man, moderately active muscular work .... 3000 calories 9. For farmer (busy season) 3200 to 4000 calories 10. For ditchers, excavators, eto 4000 to 5000 calories 11. For lumbermen, etc 5000 and more calories HUNT. ES. BIO. — 22 338 FOODS AND DIETARIES CARBOHYDRATES FUEL VALUE FOOD MATERIALS Beef, round Beef, shonlder Hntton, leg Pork, loin Pork, salt, fat Codfish, fresh, dressed Oysters 35 cents per qnart Milk, 6 cents per qnart Eggs, 24 cents per dozen Wheat bread Oat meal Beans, white, dried PoUtoes, 60 cents per bushel Sugar 2>i .83 ■ .56 POUNDS OF NUTRIENTS AND CALORIES OF FUEL VALUE IN 10 CENTS WORTH 2. 000 OAL. 4.000 CAL. EL HZ a Table showing the cost of various foods. Using this table, make up an enonomical dietary for one day, three meals, for a man doing moderate work. Give reasons for the amount of food used and for your choice of foods. Make up another dietary in the same manner, using expensive foods. What is the difference in your bill for the day ? FOODS AND DIETARIES 339 This table was worked out from a knowledge that different amounts of energy are released by the body at different times and under differing conditions. Normal Heat Output. — The following table gives the result of some experiments made to determine the hourly and daily expendi- ture of energy of the average normal grown person when asleep and awake, at work or at rest. Average Normal Output op Heat from the Body ) Conditions of Musculab Activitt Man at rest, sleeping Man at rest, awake, sitting up Man at light muscular exercise .... Man at moderately active muscular exercise Alan at severe muscular exercise .... Man at very severe muscular exercise . . AVERAQB Caloriks PEB HotJB 65 calories 100 calories 170 calories 290 calories 450 calories 600 calories It is very simple to use such a table in calculating the number of calories which are spent in twenty-four hours under different bodily conditions. For example, suppose the case of a clerk or school- teacher leading a relatively inactive Ufe, who sleeps for 9 hours X 65 calories = 585 works at desk 9 hours X 100 calories = 900 reads, writes, or studies 4 hours .... X 100 calories = 400 walks or does light exercise 2 hours . . X 170 calories = 340 2225 This comes out, as we see, very close to example 6 of the table ^ on page 337. How we may find whether we are eating a Properly Balanced Diet. — We already know approximately our daily calorie needs and about the proportion of proteid, fat, and carbohydrate needed. Dr. Irving Fisher of Yale University has worked out a very easy method of determining whether one is living on a proper diet. He 1 The above tables and those which foUow have been taken from the excellent pamphlet of the Cornell Readmg Course, No. 6, Human Nutrition, 340 FOODS AND DIETARIES has made up a number of tables, a portion of which follow/ in which he has designated portions of food, each of which furnishes 100 calories of energy. The tables show the proportion of proteid, fat, and carbohydrate in each food, so that it is a simple matter by using such a table to estimate the proportions of the various nutrients in our dietary. We may depend upon taking somewhere near the proper amount of food if we take a diet based upon either Atwater's, Chittenden's, or Voit's standard. One of the most interesting and useful pieces of home work that you can do is to estimate your own personal dietary, using the tables giving the 100 calorie portion to see if you have a properly balanced diet. From the table on page 342 make out a simple dietary for your- self, estimating your own needs in calories and then picking out 100 calorie portions of food which will give you the proper pro- portions of proteid, fat, and carbohydrate. A Graphic Method of Determining Food Values.^ — Another method to be used in the laboratory or at home is shown below. Suppose we take any food from our table, — for example, milk. In the triangle at the left, the line PC represents the proteid value of a given food, the line CF repre- = = = f 10 ea 90^ io jo 60 70 80 90 100 A food map, the composition of milk being represented by the point O. 80 N \ K T» \ \ \ \ \ w X \ .^• X 1 0 X « a 0 4 0 j « e Y 0 1 0 fl Kr 0 90 100 Food map showing the normal rec- tangle. * For more complete tables see Laboratory Marvual, Proh. XLII. They were com* piled by Dr. Irving Fisher of Yale University, and are reproduced from the Journal of the American Medical Association, Vol. XLVIII, page 16. * See Irving Fisher, " New Methods for indicating Food Values," American Jour- nal of Physiology, Vol, XL, No. 1, and " A Graphical Method in Practical Dietetics," Journal of the American Medical Association, Vol. XLIII, pages 1316-1324. FOODS AND DIETARIES 341 senting its fat value ; F and P represent 100 per cent fat and proteid respectively. The threefold constitution of any particular food may be represented graphically by the position of a point 0 in this triangle. Thus the point 0 representing milk is located at a height above C/^ 19 per cent of the total height of PC, which shows that 19 per cent of the food value of milk is proteid; and at a distance to the right of CP towards F, 52 per cent of the distance, signifying that 52 per cent of the food value of milk is fat. In the triangle at the right, the rectangle wxyz is known as the normal rectangle, and shows where a well-balanced food or combination of foods would be approximately located. Two or more foods may be plotted as follows: The combination of portions equal in calorie value is represented by a point midway between them. If the portions are unequal, the point 0 will, of course, be pro- portionally nearer the point locating the larger portion. Likewise, when three foods are combined, the point is first located for two, then this with the third, the resulting combination with the fourth, etc. Thus we can demonstrate to the eye the value of various foods or combinations of food in a dietary. (For laboratory directions, see Lahora^ tory Manual, Proh. XLII.) Food Waste in the Kitchen. — Much loss occurs in the improper cooking of foods. Meats especially, when overdone, lose much of their flavor and are far less easily digested than when they are cooked rare. The chief reasons for cooking meats are that the muscle fibers may be loosened and softened, and that the bacteria or other parasites in the meat may be killed by the heat. The common method of frying makes foods less digestible. Stewing is an economical as well as healthful method. A good way to pre- pare meat, either for stew or soup, is to place the meat, cut in small pieces, in cold water, and allow it to simmer for several hours. Rapid boiling toughens the muscle fibers by the too rapid coagula- tion of the albuminous matter in them, just as the white of egg becomes solid when heated. Boiling and roasting are excellent methods of cooking meat. In order to prevent the loss of the nutri- ents in roasting, it is well to baste the meat frequently; thus a crust is formed on the outer surface of the meat, which prevents the escape of the juices from the inside. Vegetables are cooked in order that the cells containing starch grains may be burst open, thus allowing the starch to be more easily attacked by the digestive fluids. Inasmuch as water may dissolve 342 FOODS AND DIETARIES Tables op Food Values, Units \ AND ] Prices Calories furnished ^AMrm nv Vr\r\n Portion containing 100 Food Units Weight OF 100 Calories BY Price PER X^AJttXU yjl A:\J\JU Prot. Fat Carbo. Pound 1. Vegetable Ounces Cents Crackers 2 crackers .9 10 20 70 12 Wheat bread Thick slice 1.3 9 7 84 5 Corn meal Cereal dish .96 10 5 85 4 Oatmeal 1^ servings 5.6 18 7 75 7.5 Beans (baked) Side dish 2.66 21 18 61 6 Rice Cereal dish 3.1 10 1 89 10 Sugar 3 teaspoons .86 — — 100 6 Potatoes (boiled) 1 large size 33.62 11 1 88 1.5 Cabbage 4 servings 11 20 8 72 2.5 Tomatoes 4 average servings 15.2 21 7 72 6 Lettuce 5 average servings 18 25 14 61 10 2. Animal Beef (sirloin) Small steak 1.4 31 69 — 30 Brisket Ordinary serving 1.80 42 58 — 8 Mutton (leg) Large serving 1.2 35 65 — 16 Pork (loin) Small serving .97 18 82 — 15 Ham Ordinary serving 1.1 28 72 — -2 Veal (leg) Large serving 2.4 73 27 — 18 Chicken Large serving 3.2 79 21 — 24 Codfish 2 servings 4.9 95 5 — 15 Oysters 1 dozen 6.8 49 22 29 25 Lobster 2 servings 4.1 78 20 2 35 Eggs 1 large egg 2.1 32 68 — 25 3. Dairy Products Whole milk Small glass 4.9 19 52 29 4 Buttermilk U glass 9.7 34 12 54 2 Butter Small pat 0.44 0.5 99.5 — 30 Cheese (Amer.) li cubic inch .77 25 73 2 18 4. Fruits, nuts. etc. Bananas 1 large 3.5 5 5 90 7 Oranges 1 large 9.4 6 3 91 7 Watermelon 1 whole 27.0 6 6 88 3 Apples 2 7.3 3 7 90 1.5 Peanuts 13 .62 20 63 17 5 Chocolate i square .56 8 72 20 40 FOODS AND DIETARIES 343 out nutrients from vegetable tissues, it is best to boil them rapidly in a small amount of water. This gives less time for the solvent action to take place. Vegetables should be cooked with the outer skin left on when it is possible. Problem XLIII. A study of some farms of food ajdulterou- tions, {Laboratory ManioaZ, Prob. XLIII.) Adulterations in Foods. — The addition of some cheaper sub- stance to a food, with the view to cheating the purchaser, is known as adulteration. Many foods which are artificially manufactured have been adulterated to such an extent as to be almost unfit for food or even harmful. One of the commonest adulterations is the substitution of grape sugar (glucose) for cane sugar. Most cheap candy is so made. Flour and other cereal foods are sometimes adulterated with some cheap substitutes, as bran or sawdust. Prob- ably the food which suffers most from adulteration is milk, as water can be added without the average person being the wiser. By means of an inexpensive instrument known as a lactometeTf this cheat may easily be detected. In most cities, the milk supply is carefully safeguarded, because of the danger of spreading typhoid fever (see Chapter XXIX) from impure milk. Milk is often treated with preservatives which kill the bacteria in it and pre- vent the milk from souring rapidly. Such preservatives are often harmful to health. Coffee, cocoa, and spices are subject to great adulteration; cottonseed oil is often substituted for olive oil; butter is too frequently artificial; while honey, sirups of various kinds, cider and vinegar, have all been found to be either artificially made from cheaper substitutes or to contain such substitutes. Pure Food Laws. — Thanks to the National Pure Food Law passed by Congress in 1907, and to the activity of various city and state boards of health, the opportunity to pass adulterated foods on the pubhc is greatly lessened. Impure Water. — Great danger comes from drinking impure water. This subject has already been discussed under Bacteria, where it was seen that the spread of typhoid fever in particular is due to a contaminated water supply. As citizens we must aid all 344 FOODS AND DIETARIES legislation that will safeguard the water used by our towns and cities. Boiling water for ten minutes or longer will render it safe from all organic impurities. Stimulants. — We have learned that food is anything that sup- pHes building material or releases energy in the body; but some materials used by man, presumably as food, do not come under this head. Such are tea and coffee. When taken in moderate quantities, they produce a temporary increase in the vital activities of the person taking them. This is said to be a stimulation; and material taken into the digestive tract, producing this, is called a stimulant. In moderation, tea and coffee appear to be harmless. Some people, however, cannot use either without ill effects, even in small quantity. It is the habit formed of relying upon the stimulus given by tea or coffee that makes them a danger to man. In large amounts, they are undoubtedly injurious because of a stimulant called caffeine contained in them. Cocoa and chocolate, although both contain a stimulant like caffeine, are in addition good foods, having from 12 per cent to 21 per cent of proteid, from 29 per cent to 48 per cent fat, and over 30 per cent carbohydrate in their compo- sition. Is Alcohol a Food? — The question of the use of alcohol has been of late years a matter of absorbing interest and importance among physiologists. A few years ago Dr. Atwater performed a series of very careful experiments by means of the respiration calorimeter, to ascertain whether alcohol is of use to the body as food.i In these experiments the subjects were given, instead of their daily allotment of carbohydrates and fats, enough alcohol to supply the same amount of energy that these foods would have given. The amount was calculated to be about two and one half ounces per day, about as much as would be contained in a bottle of light wine.^ This alcohol was administered in small doses six times during the day. Professor Atwater's results may be summed up briefly as follows : — 1 Alcohol is made up of carbon, oxygen, and hydrogen. It is very easily oxidized, but it cannot, as is shown by the chemical formula, be of use to the body in tissue building, because of its lack of nitrogen. 2 Alcoholic beverages contain the follomng proportions of alcohol : beer, from 2 to 5 per cent ; wine, from 10 to 20 per cent ; liquors, from 30 to 70 per cent. Pat- ent medicines frequently contain as high as 60 per cent alcohol. (See page 350.) FOODS AND DIETARIES 345 1. The alcohol administered was almost all oxidized in the body. 2. The potential energy in the alcohol was transformed into heat or muscular work. 3. The body did about as well with the rations including alcohol as it did without it. The committee of fifty eminent men appointed to report on the physiological aspects of the drink problem reported that a large number of scientific men state that they are in the habit of taking alcoholic liquor in small quantities, and many report that they do not feel harm thereby. A number of scientists seem to agree that within limits alcohol may l>e a kind of food, although a very poor food. On the other hand, we know that although alcohol may techni- cally be considered as a food, it is a very unsatisfactory food and, as the following statements show, it has an effect on the nervous system which foods do not have. Alcohol a Poison. — A commonly accepted definition of a poison is that it is any substance which ^ when taken into the body, tends to cause serious detriment to health or the death of the organism. That alcohol may do this is well known by scientists. The follow- ing quotations show that a large number of very eminent pro- fessors and physicians have this belief. ** The rather recent experiments of At water, which were made under special conditions to exclude everything but the one question of the heat and energj'-producing action of alcohol in the human body, have been published and quoted over and over again as showing that it is in all respects a valuable food and not in any way deleterious to the system. The fact that these experiments had no reference to the action of the agent on the circulatory or nervous systems, which are by far its most important effects, is never mentioned. The single truth that alcohol is consumed in the body, producing heat and energy, proves no more that it is a useful food, as one of Professor Atwater's colleagues says, than would the fact that gunpowder burns up, producing heat and energy, prove it a profitable fuel for the stove." — Journal of the American Medical Association, Editorial, Nov. 25, 1899, page 1365. *' Life is not to be accounted for upon the theory of oxidation pro- cesses, but rather to be viewed under the aspect that with the vital processes is associated a constant consumption of energy and transfor- mation of the same into other forms, — work and heat. This puts a new aspect upon the theory that alcohol is a fuel food. Only substance? 346 FOODS AND DIETARIES which can enter the cell and become living matter can be food and have an animating effect. This alcohol cannot do. " Hence the idea that alcohol economizes heat by its abundant heat production is a fallacy." — Dr. A. Holitscher, Pirkenhammer, Interna- tional Monatsschrift, April, 1907. " Obviously only such substances can be called food material, or be employed for food, as, like albumen, fat, and sugar, exert non-poisonous influence in the amounts in which they reach the blood and must circu- late in it in order to nourish. . . . Although alcohol contributes energy, it diminishes working ability. We are not able to find that its energy is turned to account for nerve and muscle work. Very small amounts, vvhose food value is insignificant, show an injurious effect upon the nervous system." — Professor Grube, President of the Royal Institute of Hygiene, Munich, in the Miinchener Neuesten Nachrichteny May 19, 1903. *• In view of the current tendency to regard alcohol as a food, it seemed desirable to make a study of its effects on hepatic glycogenesis, for if alcohol can replace the carbohydrates in food, it ought to spare the car- bohydrate radical of the tissue proteids. An accumulation of glycogen in the liver after exclusive feeding with alcohol might therefore be ex- pected. . . . ** This suggestion was put to an experimental test. The investigation was carried out entirely on rabbits which were fed exclusively on alcohol for periods of 4 to 6 days. Alcohol was given by mouth by means of a stomach tube in amounts varying between 3 to 9 cc. per kilo per rabbit, diluted to 30 and 60 per cent. As controls, rabbits were used that had been starved for the same number of days as the alcohol rabbits. Instead of alcohol, water was given by mouth with a stomach tube. At the expiration of the periods named, the rabbits were killed under ether anesthesia and the liver examined for glycogen according to Pfliiger's shorter method. . . . The results at this stage of the investigation showed that in rabbits fed exclusively on alcohol (10 cc. 30% per kilo, or 12 cc. 60 % per kilo) daily for four or five days, there is no accumulation of glycogen in the liver, which shows that glycogen is not formed in the liver of rabbits when fed on alcohol alone." — William Salant, American Medicine, April, 1906, page 41. "Alcohol is not a Food. — It is said to be a food because eminent chemists tell us it can be oxidized, but it has been pointed out that some of the substances that are most readily oxidized are the most virulent poisons. Alcohol is a poison; it acts as a poison; it is oxidized as a poison. It contains certain elements of food necessary for the production of heat, but they are arranged in such a form that they cannot be prop- erly utilized by our bodies as at present constituted. It is not a food because it contains certain elements that are necessary for the building up of our bodies. It is only when these are in proper form that they do FOODS AND DIETARIES U7 not in any way act as poisonous susbstances." — Professor G. Sims Wood- head, M.A., M.D., F.R.S.E., Professor of Pathology, Cambridge Univer- sity, England. " From an exhaustive definition we shall have to class every substance as a poison which, on becoming mixed with the blood, causes a disturb- ance in the function of any organ. That alcohol is such a poison cannot be doubted Very appropriately has the English language named the distiu-bance caused by alcoholic beverages intoxication, which, by der- ivation, means poisoning." — Dr. Adolph Fick, Professor of Physiology, Wiirzburg, Germany. " We know that alcohol is mostly oxidized in our body. . . . Aloohol is, therefore, without doubt, a source of living energy in our body, but it does not follow from this that it is also a nutriment. To justify this assumption, proof must be furnished that the living energy set free by its oxidation is utilized for the purpose of a normal function. It is not enough that potential energy is transformed into living energy; the transformation must take place at the right time and place, and at defi- nite points in definite elements of the tissues. These elements are not adapted to be fed with every sort of oxidizable material. We do not know whether alcohol can furnish to the muscles and nerves a source of energy for the performance of their functions. ... In general, alcohol has only paralyzing properties, etc." — G. Bunge, Lehrhuch der Physi- ologischen und Pathologischen Chemie. *' Alcohol, also, when not taken in too large quantities, may be oxidized in the body, and furnish a not inconsiderable amount of energy. It is, however, a matter of controversy at present, whether alcohol in small doses can be considered a true foodstuff capable of serWng as a direct source of energy, and of replacing a corresponding amount of fats and carbohydrates in the daily diet." — William H. Howell, American Text- book of Physiology. " The nutritive value of alcohol has been the subject of considerable discussion and not a few experiments. Some of these tend to show that in moderate non-poisonous doses it acts as a non-proteid food in dimin- ishing the oxidation of proteid, doubtless by becoming itself oxidized. Its action, however, in this respect, is relatively small, and, indeed, a certain proportion of the alcohol ingested is exhaled with the air of respiration. " Moreover, in large doses it (alcohol) may act in a contrary manner, increasing the waste of tissue proteid. It cannot, in fact, be doubted that any small production of energy resulting from its oxidation is more than counterbalanced by its deleterious influence as a drug upon the tissue ele- ments, and especially upon those of the nervous system." — E. A. Schaefer, A Textbook of Physiology. Dr. Kellogg points out that strychnine, quinine, and many other drugs are oxidized in the body, but surely cannot be called foods. 348 FOODS AND DIETARIES The following reasons for not considering alcohol a food are taken from his writings : — "1. A habitual user of alcohol has an intense craving for his accus- tomed dram. Without it he is entirely unfitted for business. One never experiences such an insane craving for bread, potatoes, or any other particular article of food. " 2. By continuous use the body acquires a tolerance for alcohol. That is, the amount which may be imbibed and the amount required to produce the characteristic effects first experienced gradually increase until very great quantities are sometimes required to satisfy the craving which its habitual use often produces. This is never the case with true foods. . . . Alcohol behaves in this regard just as does opium or any other drug. It has no resemblance to a food. " 3. When alcohol is withdrawn from a person who has been accus- tomed to its daily use, most distressing effects are experienced. . . . Who ever saw a man's hand trembling or his nervous system unstrung because he could not get a potato or a piece of cornbread for breakfast? In this respect, also, alcohol behaves like opium, cocaine, or any other enslaving drug. " 4. Alcohol lessens the appreciation and the value of brain and nerve activity, while food reenforces nervous and mental energy. " 5. Alcohol as a protoplasmic poison lessens muscular power, whereas food increases energy and endurance. " 6. Alcohol lessens the power to endure cold. This is true to such a marked degree that its use by persons accompanying Arctic expeditions is absolutely prohibited. Food, on the other hand, increases ability to endure cold. The temperature after taking food is raised. After taking alcohol, the temperature, as shown by the thermometer, is lowered. " 7. Alcohol cannot be stored in the body for future use, whereas all food substances can be so stored. " 8. Food burns slowly in the body, as it is required to satisfy the body's needs. Alcohol is readily oxidized and eliminated, the same as any other oxidizable drug." The Use of Tobacco. — A well-known authority defines a nar- cotic as a substance " which directly induces sleep, blunts the senses and, in large amounts, produces complete insensibility." Tobacco, opium, chloral, and cocaine are examples of narcotics. Tobacco owes its narcotic influence to a strong poison known as nicotine. Its use in killing insect parasites on plants is well known. In ex- periments with jellyfish and other lowly organized animals, the author has found as small a per cent as one part of nicotine to one hundred thousand parts of sea water to be sufficient to profoundly FOODS AND DIETARIES 349 affect an animal placed within it. The illustration here given shows its effect upon a fish, one of the vertebrate animals. Nico- tine in a pure form is so powerful a poison that two or three drops would be suf- ficient to cause the death of a man by its action upon the nerv- ous system, especially the nerves controlling; the beating of the heart. This action is well known among boys training for athletic contest. The heart is affected; boys become "short-winded'' as a result of the action on the heart. It has been demonstrated that tobacco has, too, an important effect on muscular development. The stunted appearance of the young smoker is well known. Experiment (by Davison) to show how tobacco afTects the nervous system. The nicotine, caught in the water by passing through it the smoke from six cigarettes, was sufficient to kill the fish in the jar. Brohlem XL IV. A study of some medical frauds. iLabo" ratory Manual, Prob. XLIV.) Use and Abuse of Drugs. — The American people are addicted to the use of drugs and, especially, patent medicines. A glance at the street car advertisements shows this. Most of the medicines advertised contain alcohol in greater quantity than beer or wine, and nearly all of them have opium, morphine, or cocaine in their composition. Dr. George D. Haggard of Minneapolis has shown by many analyses that a large number of the so-called '' malts," " malt extracts," and '' tonics," including several of the best known and most advertised on the market, are simply disguised beers and, frequently, very poor beers at that. These drugs, in addition to being harmful, affect the person using them in such a manner 350 FOODS AND DIETARIES that he soon feels the need for the drug. Thus the drug habit is formed, — a condition which has wrecked thousands of Uves. A number of articles on patent medicines recently appeared in a ff^MflU mri ml si t^ ti)l tel KEJ The amounts of alcohol in some liquors and in some patent medicines. a, beer, 5 % ; 6, claret, 8 % ; c, champagne, 9 % ; d, whisky, 50 % ; e, well-known saraaparilla, 18 % ; /, g, h, much-advertised nerve tonics, 20 %, 21 %, 25 % ; t, another much-advertised sarsaparilla ; j, a well-known tonic, 28 % ; A;, I, bitters, 37 %, 44 % alcohol. leading magazine and have been collected and published under the title of " The Great American Fraud." Every boy and girl should read these so as to be forearmed against such evils. Reference Reading on Foods Sharpe, A Laboratory Manual for the Solution of Problems in Biology. American Book Company. Davison, The Human Body and Health. American Book Company. Bulletin 13, American School of Home Economics, Chicago. The Great American Fraud. American Medical Association, Chicago. Allen, Civics and Health. Ginn and Company. Cornell University Reading Course, Buls. 6 and 7, Human Nutrition. Lusk, Science and Nutrition. W. B. Saunders Company. The Propaganda for Reform in l^roprietary Medicines. American Medical Associa- tion. Some Government Publications on Nutrition and Foods (To be obtained from the Secretary of Agriculture, Washington.) No. Farmers' Bulletin : 23 Foods : Nutritive Value and Cost. FOODS AND DIETARIES 351 142 Principles of Nutrition and Nutritive Value of Food. 34 Meats : Composition and Cooking. 128 Eggs : Their Use as Food. 85 Fish as Food. 121 Legumes as Food. 132 Nuts and their Use as Food. 298 Corn and Corn Products. 42 Facts about Milk. 249 Cereal Breakfast Foods. 93 Sugar as Food. 182 Poultry as Food. 295 Potatoes and other Root Crops as Food. Reprint from Yearbook, 1901, Atwater, Dietaries in Public InstittUiona. Reprint from Yearbook, 1902, Milner, Coat of Food related to its Nutritive Value. Experiment Station, Circular 46, Langworthy, Functions and Uses of Food. XXV. DIGESTION AND ABSORPTION Purpose of Digestion. — We have learned that starch and proteid food of plants are formed in the leaves. A plant, however, is unable to make use of the food in this condition. Before it can be transported from one part of the plant body to another, it is changed into a soluble form. In this state it can be passed from cell to cell by the process of osmosis. Much the same condition exists in animals. In order that food may be of use to man, it must be changed into a state that will allow of its passage in a soluble form through the walls of the alimentary canal, or food tube. Digestion consists in the changing of foods from an insoluble to a soluble form, so that they may pass through the walls of the alimentary canal and become part of the blood. Problem XLV, Study of the digestive system of a frog in order better to understand that of man. {Laboratory Manual, Prob. XLV.) Alimentary Canal. — In all vertebrate animals, including man, food is normally taken in the mouth and passed through a food tube during the process of digestion. This tube is composed of different portions, named, respectively, as we the gullet, stomach, small and I J Picture of the organs of digestion : a, in- testine, leading out of the pylorus ; 6, liver ; c, esophagus ; d, pancreas ; e, stomach ; /, spleen ; g, i, j, k, m, n, parts of large intestine ; h, I, small intestine. (From Johonnot and Bouton.) pass from the mouth, posteriorly, large intestine, and rectum. 352 DIGESTION AND ABSORPTION 353 Glands. — In addition to the alimentary canal proper, we find a number of digestive glands, varying in size and position, connected with the canal. As we have already learned, a gland is a col- lection of cells which takes up materials from within the body and pours out this material as a secretion. An example of glands in plants is found in the nectar glands of a flower. Certain substances called enzymes formed by glands cause the digestion of food. The enzymes secreted by the cells of the glands and poured out into the food tube act upon insoluble foods so as to change them to a soluble form. Structure. — The entire inner surface of the food tube is covered with a soft lining of mucous membrane. This is always moist be- cause certain cells, called mucus cells, empty out their contents into the food tube, thus lubricating its inner surface. When a large number of cells which have the power to secrete fluids are collected together, the surface of the food tube may become indented at this point to form a pitlike gland. Often such depres- sions are branched, thus giving a greater secreting surface, as is seen in the Figure. The cells of the gland are always supplied with blood vessels and nerves, for the secretions of the glands are under the control of the nervous system. Think of a sour pickle and note what happens. Attached to the digestive tract of man are found, besides the salivary glands in the mouth, gastric glands in the walls of the stomach, the liver and the pancreas, two large glands which empty HUNT. E8. BIO. 23 Diagram of a gland : i, the common tube which carries off the secretions formed in the cells lining the cavity c: a, arteries carrying blood to the glands; v, veins taking blood away from the gland. 354 DIGESTION AND ABSORPTION into the small intestine just below the stomach, and certain glands {intestinal glands) in the wall of the intestine. It will be the purpose of this chapter to follow the various food substances in the passage through the food tube in order to find how and where the changes take place in the various nutrients which prepare them to become part of the blood. Mouth Cavity in Man. — In our study of a frog we found that the mouth cavity had two unpaired and four paired tubes leading from it. These are (a) the gullet or food tube, (b) the windpipe (in the frog opening through the glottis), (c) the paired nostril holes (posterior nares), (d) the paired Eustachian tubes, leading to the ear. All of these openings are found in man. ^ Opening of Eusta- chian tube Soft palate — Pharynx Epiglottis Glottis Esophagus Laryno) Hard palate Tongue The mouth cavity of man. In man the mouth cavity, and all internal surfaces of the food tube, are lined with a mucous membrane. The mucus secreted from gland cells in this lining makes a slippery surface so that the food may slip down easily. The roof of the mouth is formed in front by a plate of bone called the hard palate, and a softer continuation to the back of the mouth, the soft palate. These separate the nose cavity from that of the mouth proper. The part DIGESTION AND ABSORPTION 355 of the space back of the soft palate is called the pharynx, or throat cavity. From the pharynx lead off the gullet and windpipe, the latter placed ventral to the former. The lower part of the buccal cavity is occupied by a muscular tongue. Examination of its surface with a looking-glass shows it to be almost covered in places by tiny projections called papilke. These papillae contain organs known as taste buds, the sen- sory endings of which deter- mine the taste of substances. The tongue is also used in moving food about in the mouth, and in starting it on its way to the gullet, while it plays an important part, as we know, in speaking. The Teeth. — In man the teeth, unlike those of the frog, are used for the mechanical preparation of the food for di- gestion. Instead of holding prey, they crush, grind, or tear food so that more surface may Teeth i, iucisors; c, cauine; p, premolars ; m, molars. be given for the action of the digestive fluids. The teeth of man are divided, according to their functions, into four groups. In the center of both the upper and lower jaw in front are found eight teeth with chisel-like edges, four in each jaw ; these are the incisors, or cutting teeth. Next is found a single tooth on each side (four in all) ; these have rather sharp points; they are the canines; look for them in a cat or dog. Then come two teeth on each side, eight in all, called premolars. Lastly, the flat-top molars, or grinding teeth, of which there are six in each jaw. Food is caught between irregular Section of a tooth : a, projections on the surface of the molars and enamel; b, dentine; crushed tO a pulpy maSS. c, pulp cavity contain- ing blood vessels and Internal Structure of a Tooth. — If a tooth is nerves; d, cement. cut lengthwise, it is found to be hollow; this 356 DIGESTION AND ABSORPTION cavity, called the pnlp cavity, corresponds to the cavity containing marrow in bones. In life it contains living material — the blood vessels, nerves, and cells which build up the bony part of the tooth. The bulk of the hard part of the tooth consists of a limy material called dentine. Outside of this is a very hard substance called enamel; this substance, the hardest in all the body, is thickest on the exposed surface or crown of the tooth. Each tooth is held in its place in the jawbone by a thin layer of bony substance called cement. Problem XL VI. How foods are chemically prepared for ah- sorption into the hlood. {Laboratory Manual, Frob. XL VI.) id) In the mouth. (h) In the stomach. (c) In the small intestine. Salivary Glands. — We are all familiar with the substance called saliva which acts as a lubricant in the mouth. SaUva is manufactured in the cells of three pairs of glands which empty into the mouth, and which are called, according to their position, the parotid (under the ear), the suh~ maxillary (under the jawbone), and the sublingual (under the tongue). Digestion of Starch. — If we col- lect some saliva in a test tube, add to it a httle starch paste, place the tube containing the mixture for a few minutes in tepid water, and then test with Fehling's solution, we shall find grape sugar present. Careful tests of the starch paste and of the saliva made separately will usually show no grape sugar in either. If another test be made for grape sugar, in a test tube containing starch paste, saliva, and a few drops of any weak acid, the starch will be found not to have changed. The digestion of starch to grape sugar is caused by the presence in the saliva of an enzyme, or digestive ferment. You will remember that starch in the growing corn grain was changed to grape sugar A B Experiment showing non-osmosis of starch in tube A, and osmosis of sugar in tube B. DIGESTION AND ABSORPTION 357 by an enzyme called diastase. Here the same action is caused by an enzyme called ptyalin. This ferment, as we can prove, acts only in an alkaline medium at about the temperature of the lx)dy. How Food is Swallowed. — After food has been chewed and mixed with saliva, it is rolled into little balls and pushed by the tongue into such position that the muscles of the throat cavity may seize it and force it downward. Food, in order to reach the gullet from the mouth cavity, must pass over the glottis, the open- ing into the windpipe, or trachea. When food is in the course of being swallowed, the upper part of this tube forms a trapdoor over the opening. When this trapdoor is not closed, and food " goes down the wrong way," we choke, and the food is expelled by coughing. The Gullet, or Esophagus. — In man this part of the food tube is much longer proportionately than in the frog. Like the rest of the food tube it is Hned by soft and moist mucous membrane. The wall is made up of two sets of muscles, — the inside ones running around the tube ; the outer band of muscle taking a longitudinal course. After food leaves the mouth cavity, it gets beyond our direct control, and the muscles of the gullet, stimulated to activity by the presence of food in the tube, push the food down to the stomach by a series of contractions until it reaches the stomach. The gullet passes directly through a muscular partition, the dia- phragm, which is lacking in the frog. The diaphragm separates the heart and lungs from the other organs of the body cavity. Stomach of Man. — The stomach is a pear-shaped organ capable of holding about three pints. The end opposite to the gullet, which empties into the small intestine, is provided with a ring of muscle forming a valve called the pylorus. Gastric Glands. — If we open the stomach of the frog, and remove its contents by carefully washing, its wall is seen to be thrown into folds internally. Between the folds Inside of the stomach and intestine, showing the folds of the mucous membrane. 358 DIGESTION AND ABSORPTION in the stomach of man, as well as in the frog, are located a number of tiny pits. These form the mouths of the gastric glands, which pour into the stomach a secretion known as the gastric juice. The gastric glands are little tubes, the lining of which secretes the fluid. This fluid is largely water. It is slightly acid in its chemical reaction, containing about .2 per cent free hydrochloric acid. It also contains a very important enzyme called pepsin, and another less important one called rennin. Action of Gastric Juice. — If proteid is treated with artificial gastric juice at the temperature of the body, it will be found to become swollen and then gradually to change to a substance which is soluble in water. Most proteid substances are insoluble. They belong to the class of substances known as colloids — substances that do not easily pass through a membrane by osmosis. After proteid is digested in the stomach, it is known as a peptone. Digestion of proteid results in a change of a colloid substance to one which will diffuse readily through a membrane, or a crystalloid. Peptones are crystalloid substances. A peptic gland, from the stomach, very much magnified. A, central or chief cell, which make pepsin ; B, bor- der cells, which make acid. (From Miller's Histology.) The other enzyme of gastric juice, called rennin, curdles or coagulates a proteid found in milk ; after the milk is curdled, the pepsin is able to act upon it. "Junket" tablets, which contain rennin, are used in the kitchen to cause this change. The hydrochloric acid found in the gastric juice acts upon lime and some other salts taken into the stomach with food, changing them so that they may pass into the blood and eventually form the mineral part of bone or other tissue. Movement of Walls of Stomach. — The stomach walls, provided with three layers of muscle which run in an oblique, circular, and longitudinal direction (taken from the inside outward), are well fitted for the constant churning of the food in that organ. Here, as elsewhere in the digestive tract, the muscles are involuntary, muscular action being under the con- trol of the so-called sympathetic nervous system. Food material in the stomach makes several complete circuits during the process of digestion DIGESTION AND ABSORPTION 359 in that organ. Contrary to common belief, the greatest amount of food is digested after it leaves the stomach. But this organ keeps the food in it in almost constant motion for a considerable time, a meal of meat and vegetables remaining in the stomach for three or four hours. While movement is taking place, the gastric juice acts upon proteids, softening them, while the constant churning movement tends to separate the bits of food into finer particles. Ultimately the semifluid food, most of it still undigested, is allowed to pass in small amounts through the pyloric valve, into the small intestines. This is done by the expansion of the ringlike muscles of the pylorus. The partly digested food in the small intestine almost immediately comes in contact with fluids from two glands, the liver and pancreas. We shall first consider the function of the pancreas. Position and Structure of the Pancreas. — The most imp>or- tant digestive gland in the human body is the pancreas. The gland is a rather diffuse structure ; its duct empties in a common opening with the bile duct, a short distance below the pylorus. In internal structure, the pancreas resembles the salivary glands. Appearance of milk under the nucroscope, showing the natural grouping of the fat globules. In the circle a single group is highly magnified. Milk is one fonn of an emulsion. (S. M. Babcock, Wis. Bui. No. 61.) Starch added to artificial pancreatic fluid and kept at blood heat is soon changed to sugar. Proteid, under the same conditions, is changed to peptone. Fats, which so far have been unchanged except to be melted by the heat of the body, are changed by the action of the pancreas into a form which can pass through the walls of the food tube. If we test pancreatic fluid, we find it strongly 360 DIGESTION AND ABSORPTION alkaline in its reaction. If two test tubes, one containing olive oil and water, the other oHve oil and a weak solution of caustic soda, an alkali, be shaken violently and then allowed to stand, the oil and water will quickly separate, while the oil, caustic soda, and water will remain for some time in a milky emulsion. If this emulsion be examined under the microscope, it will be found to be made of millions of little droplets of fat, floating in the liquid. The presence of the caustic soda helped the forming of the emul- sion. Fat in this form may be. absorbed. Pancreatic fluid simi- larly emulsifies fats and changes them into soft soaps and fatty acids. The process of this transformation is not well understood. Liver. — The liver is the largest gland in the body. In man, it hangs just below the diaphragm, a Httle to the right side of the body. During Hfe, its color is deep red. It is divided into three lobes, between two of which is found the gall bladder, a thin-walled sac which holds the bile, a secretion of the liver. Bile is a strongly alkaline fluid of greenish color. It reaches the intestine through a common opening with the pancreatic fluid. Al- most one quart of bile is passed daily into the digestive canal. Functions of Bile. — The action of bile on foods is not very well known. It is slightly antiseptic, and thus may prevent fermenta- tion within the intestine by destroying bacteria. It also has the very important faculty of aiding the passage of fats through the walls of the intestine. If two funnels, each containing filter paper, one moistened with bile, the other dry, be filled with oil, the oil will be found to pass through the moistened funnel with much greater ease. Formation of Glycogen. — Perhaps the most important func- tion of the liver is the formation within it of a material called glyco- gen, or animal sugar. The liver is supplied by blood from two sources. The greater amount of blood received by the liver comes directly from the walls of the stomach and intestine to this organ. It normally contains about one fifth of all the blood in the body. This blood is very rich in food materials, and from it the cells of the liver take out sugars to form glycogen.^ Glycogen is stored in the liver until such a time as a food is needed that can be quickly oxidized ; then the glycogen is carried off by the blood to the tissue 1 It is known that glycogen maybe formed in the body from proteid, and possibly from fatty foods. DIGESTION AND ABSORPTION 361 which requires it, and there used for this purpose. Glycogen is also stored in the muscles, where it is oxidized to release energy when the muscles are exercised. Brohleni XL VII, A study of where and how digested foods pass into tJie hlood. {Laboratory Manual, Proh. XL VII.) The Absorption of Digested Food into the Blood. — The object of digestion is to change foods from an insoluble to a soluble form. This has been seen in the study of the action of the various diges- tive fluids in the body, each of which is seen to aid in dissolving soHd foods, changing them to a fluid, and, in case of the bile, ac- tually assisting them to pass through the wall of the intestine. A small amount of digested food may be absorbed by the blood in the blood vessels of the walls of the stomach. Most of the absorption, however, takes place through the walls of the small intestine. Structure of the Small Intestine. — The small intes- tine in man is a slender tube nearly twenty feet in length and about one inch in di- ameter. Its walls contain muscles which, by a series of slow waves of contraction, force the fluid food gradually toward the posterior end of the tube. The movements of the muscles of the coat are of very great importance in the process of absorption, and these movements are caused to a great extent (as is the secretion of the various glands of the food tube) by the me- chanical stimulus of the food within the food tube. If the chief function of the small intestine is that of absorp- tion, we must look for adap- tations which increase the absorbing surface of the tube. This is gained in part by the Diagram of a bit of the wall of the small intestine, greatly magnified, a, mouths of intestinal glands; 6, villus cut lengthwise to show blood vessels and lacteal (in center) ; e, lacteal sending branches to other villi; i, intestinal glands; m, artery ; v, vein; I, t, muscular coats of intestine wall. 362 DIGESTION AND ABSORPTION inner surface of the tube being thrown into transverse folds which not only retard the rapidity with which food passes down the intestine, but also give more absorbing surface. But far more important for absorp- tion are millions of little projections which cover the inner surface of the small intestine. The Villi. — So numerous are these projections that the whole surface presents a velvety appearance. Collectively, these struc- tures are called the villi (singular villus). They form the chief organs of absorption in the intestine, several thousand being distributed over every square inch of surface. By means of the folds and villi the small intestine is estimated to have an absorb- ing surface equal to twice that of the surface of the body. Between the vilU are found the openings of many small tubeUke glands, the intestinal glands. These glands manufacture a digestive fluid, strongly alkaline, which aids in diges ing fats, and acts some- what like the pancreatic fluid. Internal Structure of a Villus. — The internal structure of a villus is best seen in a longitudinal section. We find the outer wall made up of a thin layer of cells, the epithelial layer. It is the duty of these jugular vein ^ells to absorb the semifluid food from within the intestine. Underneath these cells lies a network of very tiny blood vessels, while inside of these, occupying the core of the villus, are found spaces which, because of their white appearance after absorption of fats, have been called lacteals. Absorption of Foods. — Let us now attempt to find out exactly how foods are passed from the intestines into the blood. Food substances in solution may be soaked up as a sponge would take up water, or they may pass by osmosis into the cells lining the villus. These cells are alive, and therefore have the power of select- ing certain substances and rejecting others. Once within the villus, the sugars and digested proteids pass through tiny blood vessels into lagmm s o'^i^K <^w ^^^q larger vessels comprising the portal circu- cuiation. lation. These pass through the liver, where, DIGESTION AND ABSORPTION 363 as we have seen, sugar is taken from the blood and stored as glycogen. From the liver, the food within the blood is sent to the heart, from there is pmnped to the lungs, from there returns to the heart, and is pumped to the tissues of the body. A large amount of water and some salts are also absorbed through the walls of the stomach and intestine as the food passes on its course. The fats in the form of soaps and fatty acids pass into the space in the center of the villus. Later they are changed into fats again, probably in certain groups of gland cells known as mesenteric glands, and eventually reach the blood by way of the thoracic duct without passing through the liver. Large Intestine. — The large intestine has somewhat the same struc- ture as the small intestine, except that the diameter is much greater. It also contains no villi. Considerable absorption, however, takes place through its walls as the mass of food and refuse material is slowly pushed along by the muscles within, its walls. In this portion of the intestine live millions of bacteria, some of which manufacture poisonous substances from the foods on which they Uve. These substances are easily absorbed through the walls of the large in- testine, and passing into the blood, cause headaches or sometimes serious trouble. Hence it follows that the lower bowel should be emptied of this matter as frequently as possible, at least once a day. Constipation is one of the most serious evils the American people have to deal with, and it is largely brought about by the artificial life which we lead, with its lack of exercise, fresh air, and sleep. Vermiform Appendix. — At the point where the small intestine widens to form the large intestine, a baglike pouch is formed. From one side of this pouch is given off a small tube about four inches long, closed at the lower end. This tube, the function of which in man is unknown, is called the vermiform appendix. It has come to have unpleasant noto- riety in late years, as the site of serious inflammation. It often becomes necessary to remove the appendix in order to prevent this inflammation from spreading to the surrounding tissues. Hygienic Habits of Eating ; the Causes and Prevention of Dys- pepsia. — From the contents of the foregoing chapter it is evident that the object of the process of digestion is to break up solid food so that it may be absorbed to form part of the blood. Any habits we may form of thoroughly chewing our food will evidently aid in this process. Undoubtedly much of the distress known as dyspepsia is due to too hasty meals with consequent lack of proper 364 DIGESTION AND ABSORPTION mastication of food. The message of Mr. Fletcher in bringing before us the need of proper mastication of food and the attendant evils of overeating is one which we cannot afford to ignore. It is a good rule to go away from the table feeling hungry. Eating too much overtaxes the digestive organs and prevents their working to the best advantage. Still another cause of dyspepsia is eating when in a fatigued condition. It is always a good plan to rest a short time before eating, especially after any hard manual work. Eating between meals is also condemned by physicians because it calls the blood to the digestive organs at a time when it should be in other parts of the body. Effect of Alcohol on Digestion. — It is a well-known fact that alcohol extracts water from tissues with which it is in contact. This fact works much harm to the interior surface of the food tube, especially the walls of the stomach, which in the case of a hard drinker are likely to become irritated and much toughened. In small amounts alcohol stimulates the secretion of the salivary and gastric glands, and thus seems to aid in digestion. It is doubtful, however, whether this aid is real. The following results of experiments on dogs, published in the American Journal of Physiology, Vol. I, Professor Chittenden of Yale University gives as " strictly comparable," because " they were carried out in succession on the same day." They show that alcohol retards rather than aids in digestion : — Number of Experiment ^a Lb. Meat with Water 1*0 Lb. Meat with Dilute Alcohol XVII a 9 : XVII $S: XVIII a 8: XVIII i8 2: XIX «9: XIX XX XX VI VI &2: a 9: j82: a 9: )3l: 15 A.M. 00 P.M. 30 A.M. 10 P.M. 00 A.M. 30 P.M. 15 A.M. 30 P.M. 15 A.M. 00 P.M. Digested in 3 hours Digested in 2 : 30 hours Digested in 2 : 30 hours Digested in 2 : 15 hours Digested in 3 : 15 hours Digested in 3 : 15 hours Digested in 3 : 00 hours Digested in 3 : 00 hours Digested in 2 : 45 hours Digested in 3 : 45 hours Average 2 : 42 hours 3 : 09 hours DIGESTION AND ABSORPTION 365 As a result of his experiments, Professor Chittenden remarks: " We believe that the results obtained justify the conclusion that gastric digestion as a whole is not materially modified by the introduction of alcoholic fluids with the food. In other words, the unquestionable acceleration of gastric secretion which follows the ingestion of alcoholic beverages is, as a rule, counterbalanced by the inhibitory effect of the alcohohc fluids upon the chemical process of gastric digestion, with perhaps at times a tendency towards preponderance of inhibitory action." Dr. Kellogg, Sir WilUam Roberts, and others have come to the same or stronger conclusions as to the undesirable action of alcohol on digestion, as a result of their own experiments. Horsley and Sturge say: " Hundreds of men and women who haunt the out-patient departments of hospitals suffer from chronic atony and slight dilatation of the stomach, which arise in part from the badly cooked food they eat, but chiefly owe their origin to the debilitating effect of alcohol upon the muscular walls of this organ and the fermentation of its retained contents." XXVI. THE BLOOD AND ITS CIRCULATION Problem XL VIII, To study the composition of the blood. {Laboratory Manual, Prob. XL VI 1 1.) Function of the Blood. — The chief function of the digestive tract is to change foods to such form that they can be absorbed through the walls of the food tube and become part of the blood. ^ By means of a system of closed tubes, this fluid tissue circulates to all parts of the body, equalizing the body temperature by de- positing its burden of food in places where it is most needed and where it will be used, either in the repair and building of tissues or for oxidation within the cells of the body to release energy. If we examine under the microscope a drop of blood taken from the frog or man, we find it made up of a fluid called plasma and two kinds of bodies, the so-called red corpuscles and colorless corpiiscles, floating in this plasma. Composition of Plasma. — The plasma of blood (when chemically examined in man) is found, to be largely (about 90 per cent) water. It also contains a considerable amount of proteid, some sugar, fat, and mineral material. It is, then, the medium which holds the fluid food (or at least part of it) that has been absorbed from within the intestine. The almost constant temperature of the body is also due, as we shall see, to the blood which brings to the surface of the body much of the heat given off by oxidation of food in the muscles and glands within. When the blood returns from the tissues where the food is oxidized, the plasma brings back with it to the lungs the carbon dioxide Uberated from the tissues of the body where oxidation has taken place. Blood returning from the tissues of the body has from 45 to 50 c.c. of carbon dioxide * This change is due to the action of certain enzymes upon the nutrients in various foods. But we also find that peptones are changed back again to proteids when once in the blood. This appears to be due to the reversible action of the enzymes acting upon them. (See page 72.) 366 THE BLOOD AND ITS CIRCULATION 367 to every 100 c.c. (See Chapter XXVII.) Some waste products, to be spoken of later, are also found in the plasma. Clotting of Blood. — If fresh beef blood is allowed to stand overnight, it will be found to have separated into two parts, a dark red, almost solid clot and a thin, straw-colored liquid called serum. Serum is found to be made up of about 90 per cent water, 8 to 9 per cent proteid, and from 1 to 2 per cent sugars, fats, and mineral matter. In these respects it very closely resembles the fluid food that is absorbed from the intestines. If another jar of fresh beef blood is poured into a pan and briskly whipped with a bundle of little rods (or with an egg beater), a stringy sub- stance will be found to stick to the rods. This, if washed carefully, is seen to be almost colorless. Tested with nitric acid and ammonia, it is found to contain a proteid substance called fibrin. Blood plasma, then, is made up of serum, a fluid portion, and fibrin, which, although in a fluid state in the blood vessels within the body, coagulates when blood is removed from the blood vessels. It is this coagulation which aids in the formation of a blood clot. A clot is simply a mass of fibrin threads with a large number of corpuscles tangled within. The clotting of blood is of great physi- ological importance, for otherwise we might bleed to death from the smallest wound. In blood within the circulatory system of the body, the fibrin is held in a fluid state called fibrinogen. An enzyme, acting upon this fibrinogen, the soluble proteid in the blood, causes it to change to an insoluble form, the fibrin of the clot. The Red Blood Corpuscle; its Structure and Functions. — The red corpuscle in the blood of the frog is a true cell of disklike form. The red corpuscle of man, however, lacks a nucleus. Its form is that of a biconcave disk. So small and so numerous are these corpuscles that over five million are found in a drop of normal blood. The color, which is found to be a dirty yellow when separate corpuscles are viewed under the microscope, is due to a proteid Human blood as seen under the high power of the compound microscope ; at the extreme light is a colorless corpuscle. 368 THE BLOOD AND ITS CIRCULATION material called hcemoglohin. Haemoglobin contains a large amount of iron. It has the power of uniting very readily with oxygen whenever that gas is abundant, and, after having absorbed it, of giving it up to the surrounding media, when oxygen is there present in smaller amounts than in the corpuscle. This function of carrying oxygen is the one most important function of the red corpuscle, although the red corpuscle also removes part of the carbon dioxide from the tissues on their return to the lungs. The taking up of oxygen is accompanied by a change in color of the mass of corpuscles from a dull red to a bright scarlet. The Colorless Corpuscle ; Structure and Functions. — A colorless corpuscle is a cell irregular in outline, the shape of which is con- stantly changing. These corpuscles are somewhat larger than the red corpuscles, but less numerous, there being about one colorless corpuscle to every three hundred red ones. They have the power of movement, mn ^^re, Diagram showing how the colorless corpuscles pass through the walls of the capillaries (smallest blood tubes) and ingulf the bacteria at m. A colorless corpuscle catching and eating a germ. for they are found not only inside blood vessels, but outside the blood tubes, showing that they have worked their way between the cells that form the walls of the blood vessels. A Russian zoologist, Metschnikoff, after studying a number of simple animals, such as medusae and sponges, found that in such animals some of the cells lining the inside of the food cavity take up or ingulf minute bits of food. Later, this food is changed into the protoplasm of the cell. Metschnikoff beheved that the colorless THE BLOOD AND ITS CIRCULATION 369 corpuscles of the blood have somewhat the same function. This he later proved to be true. Like the amoeba, they feed by ingulfing their prey. This fact has a very important bearing on the relation of colorless corpuscles to certain diseases caused by bacteria within the body. If, for example, a cut becomes infected by bacteria, inflammation may set in. Colorless corpuscles at once surround the spot and attack the bacteria. If the bacteria are few in number, they are quickly eaten by certain of the colorless cor- puscles, which are known as phagocytes. If bacteria are present in great quantities, they may prevail and kill the phagocytes by poisoning them. The dead bodies of the phagocytes thus killed are found in the pus, or matter, which accumulates in infected wounds. In such an event, we must come to the aid of nature by washing the wound with some antiseptic, as weak carbolic acid or hydrogen peroxide. The Amount of Blood and its Distribution. — The protoplasm of the body, as we know, is composed largely of water. Blood forms, by weight, about one thirteenth of the body. Its distribution varies somewhat ac- cording to the position assumed by the body, and the amount of undigested food in the stomach and intestines. Normally, about one half of the blood of the body is found in or near the organs lying in the body cavity, about one fourth in the muscles, and the rest in the heart, lungs, large arteries, and veins. Blood Temperature. — The temperature of blood in the human body is normally about 98.5° Fahrenheit, although the temperature drops almost two degrees after we have gone to sleep at night. It is highest about 5 P.M. and lowest about 4 a.m. In fevers, the temperature of the body sometimes rises to 107° or higher ; but unless this temperature is soon reduced, death follows. Any considerable drop in temperature be- low the normal also would mean death. Body heat, as we know, results from the oxidation of food ; the constant circulation of blood keeping the temperature nearly uniform in all parts of the body. The body tempera- ture may be from two to three degrees higher immediately after violent exercise. Why ? Cold-blooded Animals. — In animals which are called cold-blooded, the blood has no fixed temperature, but varies with the temperature of the medium in which the animal lives. Frogs, in the summer, may sit for hours in water with a temperature of almost 100°. In winter, they often endure freezing so that the blood and lymph within the spaces under the loose skin are frozen into ice crystals. Such frogs, if thawed out carefully, will live. This change in body temperature is evidently an adaptation to the mode of life. HUNT. ES. BIO. — 24 370 THE BLOOD AND ITS CIRCULATION Circulation of the Blood in Man. — The blood is the carrying agent of the body. Like a railroad or express company, it takes materials from one part of the hmnan organism to another. This it does by means of the organs of circulation — the heart and blood vessels. These blood vessels are called arteries where they carry blood away from the heart, veins where they bring blood back to the heart, and capillaries where they connect the arteries with the veins. The organs of circulation thus form a system of connected tubes through which the blood flows in a continuous stream. The Heart; Position, Size, Pro- tection.— The heart is a cone-shaped muscular organ about the size of a man's fist. It is located immediately above the diaphragm, and lies so that the muscular apex, which points down- ward, moves while beating against the fifth and sixth ribs, just a little to the left of the midline of the body. This fact gives rise to the notion that the heart is on the left side of the body. The heart is surrounded by a loose membranous bag called the pericardium, the inner lining of which secretes a fluid in which the heart lies. When, for any reason, the pericardial fluid is not secreted, inflammation arises in that region. Do you know why? Internal Structure of Heart. — If we should cut open the heart of a mammal down the midline, we could divide it into a right and a left side, each of which would have no internal connection with the other. Each side is made up of a thin-walled portion with a rather large internal cavity, the auricle, which opens into a smaller portion with heavy muscular walls, the ventricle. The auricles occupy the base of the cone-shaped heart ; the ventricles, the apex. Commu- nication between auricles and ventricles is guarded by little flaps Diagram showing the front half of the heart cut away : a, aorta ; I, arteries to the lungs ; la, left auricle ; Iv, left ventricle ; m, tricuspid valve open ; n, bi- cuspid or mitral valve closed; p and r, veins from the lungs; ra, right auricle ; rv, right ven- tricle ; V, vena cava. Arrows show direction of circulation. THE BLOOD AND ITS CIRCULATION 371 of muscle called valves. The auricles receive blood from the veins. The ventricles pump the blood into the arteries. From each ven- tricle, large arteries leave the heart ; that of the left side is called the aorta. Through the aorta, blood passes to all parts of the body. From the right ventricle the pulmonary artery carries blood to the lungs. The openings to these arteries are guarded by three half- nioon-shaped flaps, which open so as to allow blood to pass away from the ventricle, but not to go back into it when the muscles relax. The Heart in Action. — The heart is con- structed on the same plan as a force pump, the .valves preventing the reflux of blood into the auricle after it is forced out of the ven- tricle. Blood enters the auricles from the veins because the mus- cles of that part of the heart relax; this allows the space within the auricles to fill. Al- most immediately the muscles of the ventricles relax, thus allowing blood to pass into the chambers within the ventricles. Then, after a short pause, during which time the muscles of the heart are resting, a wave of muscular contraction begins in the auricles and ends in the ventricles, with a sudden strong contraction which forces the blood out into the arteries. Blood is kept on its course by the valves, which act in the same manner as do the valves in a pump, thus forcing the blood to pass into the arteries upon the con- traction of ventricle walls. The Course of the Blood in the Body. — Although the two sides of the heart are separate and distinct from each other, yet every drop of blood that passes through the left heart likewise passes through the right heart. There are two distinct systems of cir- The heart is a force pump ; prove it from these diagrams. 372 THE BLOOD AND ITS CIRCULATION culation in the body. The pulmonary circulation takes the blood through the right auricle and ventricle, to the lungs, and passes it back to the left auricle. This is a relatively short circulation, the blood receiving in the lungs its supply of oxygen, and there giving up some of its carbon dioxide. The greater circulation is known as the systemic circulation; in this system, the blood leaves the left ventricle through the great dorsal aorta. A large part of the blood passes directly to the muscles ; some of it goes to the nervous system, kidneys, skin, and other organs of the body. It gives up its supply of food and oxygen in these tissues, receives the waste Capillaries Diagram of the circulation of blood in mammal. 1 See Hough and Sedgwick, products of oxidation while passing through the capillaries, and returns to the right auricle through two large vessels known as the ven(B cavce. It requires from twenty to thirty seconds only for the blood to make the complete circulation from the ventricle back again to the starting point. This means that the entire volume of blood in the human body passes three or four thousand times a day through the various organs of the body.^ Portal Circulation. — Some of the blood, on its return to the heart, passes by an indirect path to the walls of the food tube and to its glands. From there it passes with its load of absorbed food to the liver. Here the vein which carries the blood (called the portal vein) breaks up into capillaries around the cells of the liver. We have already learned that the liver is a great storehouse of animal sugar called glycogen. This glyco- gen is a food that may be easily The Human Mechanism, page 136. THE BLOOD AND ITS CIRCULATION 373 oxidized to release energy, and is stored for that purpose. The sugar that becomes glycogen is carried to the liver directly from the walls of the stomach and intestine, where it has been absorbed from the food there contained. From the liver, blood passes directly to the right auricle. The portal circulation, as it is called, is the only part of the circulation where the blood passes through two sets of capillaries. Problem XLIX. A study of the circulation of the blood, { Laboratory Manual, Prob. XLIX,) Circulation in the Web of a Frog's Foot. — If the web of the foot of a live frog or the tail of a tadpole is examined under the com- pound microscope, a network of blood vessels will be seen. In some of these the corpuscles are moving rapidly and in spurts; these are arteries. The arteries lead into smaller vessels hardly greater in diameter than the width of a single corpuscle. This network of capillaries may be followed into larger veins in which the blood moves regularly. This illustrates the condition in any tissue of Capillary circulation in the web of a frog's foot, as seen under the compound microscope, a, b, small veins ; c, pigment cells in the skin ; d, capillaries in which the oval corpuscles are seen to follow one another in single series. 374 THE BLOOD AND ITS CIRCULATION man where the arteries" break up into capillaries, and these in turn form veins. Structure of the Arteries. — A distinct difference in structure exists between the arteries and the veins in the human body. The arteries, because of the greater strain received from the blood which is pumped from the heart, have thicker muscular walls, and in addition are very elastic. Cause of the Pulse. — The pulse, which can easily be detected by press- ing the large artery in the wrist or the small one in front of and above the external ear, is caused by the gushing of blood through the arteries after each pulsation of the heart. As the large arteries pass away from the heart, the diameter of each individual artery becomes smaller. At the very end of their course, these arteries are so small as to be almost microscopic in size and are very numerous. There are so many that if they were placed together, side by side, their united diameter would be much greater than the diameter of the large artery (aorta) which passes blood from the left side of the heart. This fact is of very great impor- tance, for the force of the blood as it gushes through the arteries becomes very much less when it reaches the smaller vessels. This gushing move- ment is quite lost when the capillaries are reached, first, because there is so much more space for the blood to fill, and secondly, because there is considerable friction caused by the very tiny diameter of the capil- laries. Capillaries. — The cap- illaries form a network of minute tubes everywhere in the body, but especially near the surface and in the lungs. It is through their walls that the food and oxygen pass to the tissues, and carbon dioxide is given up to the plasma. They form the connection that completes the system of circulation of blood in the body. Diagram of capillary circulation. Note that the artery breaks up into smaller vessels, which unite again to form a vein. The plasma passes through the walls of the capillaries to nourish the body cells ; some of the lymph then enters the lymph vessels and the rest returns to the capillaries. THE BLOOD AND ITS CIRCULATION 375 Function and Structure of the Veins. — If the arteries are supply- pipes which convey fluid food to the tissues, then the veins may be hkened to drain pipes which carry away waste material from the tissues. Extremely numerous in the extremities and in the muscles and among other tissues of the body, they, Uke the branches of a tree, become larger and unite with each other as they approach the heart. If the wall of a vein is carefully examined, it will be found to be neither so thick nor so tough as an artery wall. When empty, a vein collapses; the wall of an artery holds its shape. If you hold your hand downward for a little time and then examine it, you will find that the veins, which are relatively much nearer the surface than are the arteries, appear to be very much knotted. This appearance is due to the presence of tiny valves within. These valves open in the direction of the blood current, but would close if the direction of the blood flow should be re- versed (as in case a deep cut severed a vein). As the pressure of blood in the veins is much less than in the arteries, the valves thus aid in keeping the flow of blood in the veins toward the heart. The higher pressure in arteries and the suction in the veins (caused by the enlargement of the chest cavity in breathing) are the chief factors which cause a steady flow of blood through the veins in the body. Trohlem L. Some changes in the composition of the blood* {Laboratory Manual, Prdb. L.) Function of Lymph. — Different tissues and organs of the body are traversed by a network of tubes which carry the blood. Inside these tubes is the blood proper, consisting of a fluid plasma, the colorless corpuscles, and the red corpuscles. Outside the blood tubes, in spaces between the cells which form tissues, is found another fluid, which is in chemical composition very much Uke plasma of the blood. This is the lymph. It is, in fact, fluid food in which some colorless amoeboid corpuscles are found. Blood gives Valves in a vein. No- tice the thin walls of the vein. 376 THE BLOOD AND ITS CIRCULATION REOy CORPUSCLES „ WHITE CORPUSCLES LEUCOCYTE Diagram showing the exchange between blood and the cells of the body. up its food material to the lymph. This it does by passing it through the walls of the capillaries. The food is in turn given up to the tissue cells which are bathed by the lymph. Some of the amoeboid corpuscles from the blood make their way between the cells forming the walls of the capillaries. Lymph, then, is practically blood- plasma plus some colorless corpuscles. It acts as the medium of exchange between the blood proper and the cells in the tissues of the body. By means of the food supply thus brought, the cells of the body are able to grow, the fluid food being changed to the proto- plasm of the cells. By means of the oxygen passed over by the lymph, oxidation may take place within the cells. Lymph not only gives food to the cells of the body, but also takes away carbon dioxide and other waste materials, which are ultimately passed out of the body by means of the lungs, skin, and kidneys. Lymph Vessels. — The lymph is collected from the various tissues of the body by means of a number of very thin-walled tubes, which are at first very tiny, but after repeated connection with other tubes ultimately unite to form large ducts. These lymph ducts are provided, like the veins, with valves. The pressure of the blood within the blood vessels forces continually more plasma into the lymph; thus a slow current is The lymph vessels ; the dark spots are lymph glands: Zoc, lacteals; re, thoracic duct. THE BLOOD AND ITS CIRCULATION 377 maintained from the lymph spaces toward the veins. On its course the lymph passes through many collections of gland cells, the lymph glands. In these glands some impurities appear to be removed and colorless corpuscles made. The lymph ultimately passes into a large tube, the tnoracic ductj which flows upward near the ventral side of the spinal column, and empties into the large subclavian vein in the left side of the neck. Another smaller lymph duct enters the right subclavian irein. The Lacteals. — We have already found that part of the digested food (chiefly carbohydrates, peptones, salts, and water) is absorbed directly into the blood through the walls of the villi and carried to the liver. Fat, however, is passed into the spaces in the central part of the villi, and from there into other spaces between the tissues, known as the lacteals. The lacteals form the most direct course for the fats to reach the blood. The lacteals and lymph vessels have in part the same course. It will be thus seen that lymph at different parts of its course would have a very differ- ent composition. The Nervous Control of the Heart and Blood Vessels. — Although the muscles of the heart contract and relax without our being able to stop them or force them to go faster, yet in cases of sudden fright, or after a sudden blow, the heart may stop beating for a short interval. This shows that the heart is under the control of the nervous system. Two sets of nerve fibers, both of which are connected with the central nervous system, pass to the heart. One set of fibers accelerates, the other slows or inhibits, the heartbeat. The arteries and veins are also under the control of the sympathetic nervous system. This allows of a change in the diameter of the blood vessels. Thus, blushing is due to a sudden rush of blood to the surface of the body, caused by an expansion of the blood vessels at the surface. The blood vessels of the body are always full of blood. This results from an automatic regulation of the diameter of the blood tubes by a part of the nervous system called the vasomotor nerves. These nerves act upon the muscles in the walls of the blood vessels. In this way, each vessel adapts itself to the amount of blood in it at a given time. After a hearty meal, a large supply of blood is needed in the walls of the stomach and intestines. At this time, the arteries going to this region are dilated so as to receive an extra supply. "When the brain performs hard work, blood is supplied in the same manner to that region. Hence, one should not study or do mental work immediately after a hearty meal, for blood will be drawn away to the brain, leaving the digestive tract with an in- sufficient supply. Indigestion may follow as a result. The Effect of Exercise on the Circulation. — It is a fact familiar to all that the heart beats more violently and quickly when we are doing hard work than when we are resting. Count your own pulse when sitting quietly, and then again after some brisk exercise in the 378 THE BLOOD AND ITS CIRCULATION gymnasium. Exercise in moderation is of undoubted value, be- cause it sends the increased amount of blood to such parts of the body where increased oxidation has been taking place as the result of the exercise. The best forms of exercise are those which give as many muscles as possible work — walking, out-of-door sports, any exercise that is not violent. Exercise should not be attempted im- mediately after eating, as this causes a withdrawal of blood from the walls of glands of the digestive tract to the muscles of the body. Neither should exercise be continued after becoming tired, as poisons are then formed in the muscles, which cause the feeling we call fatigue. Remember that extra work given to the heart by extreme exercise may injure it, causing possible trouble with the valves. Treatment of Cuts and Bruises. — Blood which oozes slowly from a cut will usually stop flowing by the natural means of the formation of a clot. A cut or bruise should, however, be washed in a weak solution of carbolic acid or some other antiseptic in order to prevent bacteria from obtaining a foot- hold on the exposed flesh. If blood, issuing from a wound, is bright red in color and gushes in distinct pulsations, then we know that an artery has been severed. To prevent the flow of blood, a tight band- age must be tied between the cut and the heart. A hand- kerchief with a knot placed over the artery may stop bleed- ing if the cut is on one of the limbs. If this does not serve, then insert a stick in the handkerchief and twist it so as to make the pressure around the limb still greater. Thus we may close the artery until the doctor is called, who may sew up the injured blood vessel. Stopping flow of blood from an artery by- applying a tight bandage (ligature) be- tween the cut and the heart. THE BLOOD AND ITS CIRCULATION 379 The Effect of Alcohol upon the Blood. — It has recently been discovered that alcohol has an extremely injurious effect upon the colorless corpuscles of the blood, lowering their ability to fight disease germs to a marked degree. This is well seen in a comparison of deaths from certain infectious diseases in drinkers and abstainers, the percentage of mortality being much greater in the former. Dr. T. Alexander MacNichol, in a recent address, said : — '* Massart and Bordet, Metchnikoff and Sims Woodhead, have proved that alcohol, even in every dilute solution, prevents the white blood cor- puscles from attacking invading germs, thus depriving the system of the cooperation of these important defenders, and reducing the powers of resisting disease. The experiments of Richardson, Harley, Kales, and others have demonstrated the fact that one to five per cent of alcohol in the blood of the living human body in a notable degree alters the appear- ance of the corpuscular elements, reduces the oxygen bearing elements, and prevents their reoxygenation." Emphasis is frequently placed on the destruction and deterioration of the leucocytes or white blood corpuscles by writers on the subject. Dr. Grosvener declares : — *' The poisoning and paralyzing influences of alcohol lead to the con- clusion that the alcoholized organism presents a lessened resistance to the attacks of microorganisms. The detailed experiments of Abbot upon lower animals lean strongly toward the same conclusion. His experiments upon rabbits showed that the normal vital resistance to some organisms was markedly diminished. . . . " Rubin as reported in Journal oj Infectious Diseases, May 30, 1904, studied the effect of alcohol upon infectious disease as shown in rabbits. He found that the number of leucocytes was much less in alcohohzed than in the control rabbits, that as soon as the leucocytes began to decrease the bacteria increased, that there existed a negative chemotoxis." Alcohol in the stomach is rapidly absorbed and passes into the blood stream. There the strong affinity of alcohol for oxygen, which leads them to enter very rapidly into chemical combination, causes the alcohol to appropriate the oxygen of the red corpuscles of the blood, which, as we have seen, are the great oxygen carriers in the body. This tends to impoverish the blood and render it less valuable to the tissues. — Macy, Physiology. The Effect of Alcohol on the Circulation. — Alcoholic drinks affect the very delicate adjustment of the nervous centers control- ling the blood vessels and heart. Even very dilute alcohol acts upon the muscles of the tiny blood vessels, consequently, more 380 THE BLOOD AND ITS CIRCULATION blood is allowed to enter them, and, as the small vessels are usually near the surface of the body, the habitual redness seen in the face of hard drinkers is the ultimate result. As a result of experiments performed in 1869, Zimmerberg declares : " In the light of these experiments one is not only justified in denying to alcohol any stimulating power whatever for the heart, but, on the con- trary, in declaring that it lowers the working capacity of that organ." Dr. J. H. Kellogg, head of the Battle Creek Sanitarium, says : " The full bounding pulse usually produced by the administration of an ounce or two of brandy properly diluted, gives the impression of an increased vigor of heart action; but it is only necessary to determine the blood pressure by means of a Riva-Rocci instrument, or Gaertner's tonometer, to discover that the blood pressure is lowered instead of raised. This lowering may amount to twenty or thirty millimeters, or even more. . . . It can readily be seen, then, that the bounding pulse is not the result of increased heart vigor, but indicates rather a weakened state of the heart, combined with a dilated condition of the small vessels." In an address before the Liverpool Medical Association, Dr. James Barr, president of the association, discussing the effects of medicinal doses of alcohol upon the circulation, remarked : "It causes dilatation of the arterioles and of all arteries well supplied with muscular fibers, owing to its paretic effect upon the vasomotor nervous system, and its direct action as a protoplasmic poison on the muscular fiber. It has a similar, though less marked, action on the cardiac muscle. From these causes the systolic blood pressure is lowered, the systolic output from the heart is diminished, and the cardiac energy is wasted in pumping blood into relaxed vessels ; the large bounding pulse with comparatively short systolic period, which gives a deceptive appearance of vigor and force in the circulation, is due to the large wave in the dilated vessels." " The first effect of diluted alcohol is to make the heart beat faster. This fiUs the smaU vessels near the surface. A feeling of warmth is pro- duced which causes the drinker to feel that he was warmed by the drink. This feeling, however, soon passes away, and is succeeded by one of chilli- ness. The body temperature, at fiirst raised by the rather rapid oxida- tion of the alcohol, is soon lowered by the increased radiation from the surface. " The immediate stimulation to the heart's action soon passes away and, like other muscles, the muscles of the heart lose power and contract with less force after having been excited by alcohol." — Macy, Physiology. Alcohol, when brought to act directly on heart muscle, lessens the force of the beat. It may even cause changes in the tissues, which eventually result in the breaking of the walls of a blood vessel or the plugging of a vessel with a blood clot. This condition may cause the disease known as apoplexy. THE BLOOD AND ITS CIRCULATION 381 Effects of Tobacco upon the Circulation. — " The frequent use of cigars or cigarettes by the young seriously afifects the quality of the blood. The red blood corpuscles are not fully developed and charged with their normal supply of life-giving oxygen. This causes paleness of the skin, often noticed in the face of the young smoker. Palpitation of the heart is also a common result, followed by permanent weakness, so that the whole system is enfeebled, and mental vigor is impaired as well as phys- ical strength." — Macy, Physiology. XXVII. RESPIRATION AND EXCRETION Trohlem LI, A study of the organs and process of respiror tion. {Laboratory Manual, Proh. LI.) ia) Organs of respiration in frog, (b) Mechanics of respiration, (o) Process of respiration in the lungs. Necessity for Respiration. — We have seen that plants and ani- mals need oxygen in order that the life processes may go on. Food is oxidized to release energy, just as coal is burned to give heat to run an engine. As a draft of air is required to make fire under the boiler, so, in the human body, oxygen must be given so that foods or tissues may be oxidized to release energy used in growth. This oxidation takes place in the cells of the body, be they part of a muscle, a gland, or the brain. Blood, in its circulation to all parts of the body, is the medium which conveys the oxygen to that place in the body where it will be used. The Organs of Respira- tion in Man. — We have alluded to the fact that the lungs are the organs which give oxygen to the blood and take from it carbon dioxide. The course of air passing from the outside of the lungs in man is much the same as the frog. Air f—l in Air passages in the human lungs: a, larynx ; 6, trachea (or windpipe) ; c, d, bronchi ; e, bron- chial tubes ; /, cluster of air cells. , . , , , , i through the nares, the glottis, and into the windpipe. This cartilaginous tube, the top of which may easily be felt as the Adam's apple of the throat, 382 RESPIRATION AND EXCRETION 383 divides into two bronchi. The bronchi within the lungs break up into a great number of smaller tubes, the bronchial tubes, which divide somewhat like the small branches of a tree. This branch- ing increases the surface of the air tubes within the lungs. The bronchial tubes, indeed all the JBroncKial passages, are lined with TijlDe I Ftowv ■pulmoriaTy artery •pvcL-monarv uevn Diagram to show what the blood loses and gains in one of the air sacs of the lungs. air ciUated cells. The ciha of these cells are constantly in motion, beating with a quick stroke toward the outer end of the tube, that is, toward the mouth. Hence, if any- foreign material should get into the windpipe or bronchial tubes, it will be expelled by the action of the cilia. It is by means of cilia that phlegm is raised from the throat. Such action is of great im- portance, as it prevents the filling of the air passages with foreign matter. The bronchi end in very minute air sacs called alveoli, — little pouches having elastic walls, — into which air is taken when we inspire or take a deep breath. In the walls of the alveoli are numerous capil- laries, the ends of arteries which pass from the heart into the lung. It is through the very thin walls of the alveoli that an inter- change of gases takes place which results in the blood giving up part of its load of carbon dioxide^ and taking up oxygen in its place. The Pleura. — The lungs are covered with a thin elastic membrane, the pleura. This forms a bag in which the lungs are hung. Between the walls of the bag and the lungs is a space filled with lymph. By this means the lungs are prevented from rubbing against the walls of the chest. Breathing. — In every full breath there are two distinct movements, inspiration (taking air in) and expiration (forcing air out). In man an inspiration is produced by the contraction of the muscles between the ribs together with the contraction of the diaphragm, the muscular wall just below the heart and lungs ; this results in pulUng down the diaphragm and pulling upward and outward of the ribs, thus making the space within 384 RESPIRATION AND EXCRETION diaphragm^ Diagram showing portion of diaphragm and ribs in (a) inspiration ; (6) expiration. the chest cavity larger. The lungs, which lie within this cavity, are filled by the air rushing into the larger space thus made. An expiration is simpler than an inspiration, for it requires no muscular effort ; the muscles relax, the breastbone and ribs sink into place, while the dia- phragm returns to its orig- inal position. A piece of apparatus which illustrates to a de- gree the mechanics of breathing may be made as follows : Attach a string to the middle of a piece of sheet rubber. Tie the rub- ber over the large end of a bell jar. Pass a glass Y tube through a rubber stop- per. Fasten two small toy balloons to the branches of the tube. Close the small end of the jar with the stopper. Adjust the tube so that the balloons shall hang free in the jar. If now the rubber sheet is pulled down by means of the string, the air pressure in the jar is reduced and the toy balloons within expand, owing to the air pressure down the tube. When the rubber is allowed to go back to its former position, the balloons collapse. Rate of Breathing and Amount of Air Breathed. — During quiet breathing, the rate of inspiration is from fifteen to eighteen times per minute ; this rate largely depends on the amount of physical work per- formed. About 30 cubic inches of air are taken in and expelled during the ordinary quiet respiration. The air so breathed is called tidal air. In a " long breath," we take in about 100 cubic inches in ad- dition to the tidal air. This is called complemental air. By means of a forced expiration, it is possible to expel from 75 to 100 cubic inches more than tidal air ; this air is called reserve air. What remains in the lungs, amounting to about 100 cubic inches, is called the residual air. The value of deep breathing is seen by a glance at the diagram. It is only by this means that we clear the lungs of the reserve air with its accompanying load of carbon dioxide. Respiration under Nervous Control. — The muscular movements which cause an inspiration are partly under the control of the wiU, but in Apparatus showing mechanics of breath- ing. RESPIRATION AND EXCRETION 385 230 cu. in. part the movement is beyond our control. The nerve centers which govern inspiration are part of the sympathetic nervous system. Anything of an irritating nature in the trachea or larynx will cause a sudden expiration or cough. When a boy runs, the quickened res- piration is due to the fact that oxygen is used up rapidly and a larger quantity of carbon di- oxide is formed. Thus the nervous center which has control of respiration is stimulated to greater activity, and quickened inspiration follows. I*roblein LIT. A study of the prod- ucts of respiration. {Laboratory Man- ual, Prob. LI I.) Changes in Air in the Lungs. — Air is much wanner after leaving the lungs than before it enters them. Breathe on the bulb of a thermometer to prove this. Expired air contains a considerable amount of moisture, as may be proved by breathing on a cold polished surface. This it has taken up in the air sacs of the lungs. The presence of carbon di- oxide in expired air may easily be de- tected by the limewater test. Air such as we breathe out of doors contains, by volume : — Nitrogen 79 Oxygen 20.96 Carbon dioxide .04 ' Ciilii ph II \ i 1 ,r„t al I'KI tv/. in. Tidal Ail- .:n ci(. in. Ju SI ll\ ^;M /on ril ni . i:.sni ml Ail loo cn 1)1. ^ Diagram showing the relative amounts of tidal, comple- mental, reserve, and resid- ual air. The brace shows the average lung capacity for the adult man. Air expired from the lungs contains : — Nitrogen 70 Oxygen 16.02 Carbon dioxide 4.38 Water 60 In other words, there is a loss of between four and five per cent oxygen, and nearly a corresponding gain in carbon dioxide, in expired air. There are also some other organic substances present. HUNT. ES. BIO. — 25 386 RESPIRATION AND EXCRETION The volume of carbon dioxide given off is always a little less than the volume of oxygen taken in. This seems to show that some oxy- gen unites with some of the chemical elements in the body. Changes in the Blood within the Lungs. — Blood, after leaving the lungs, is much brighter red than just before entering them. The change in color is due to a taking up of oxygen by the hcemo- glohin of the red corpuscle. Changes taking place in blood are obviously the reverse of those which take place in air in the lungs. Blood in the capillaries within the lungs gains from four to five per I ^,.;:i^-_-_v-:rr-— . 1/ ^^^^ ^f oxygen, which the air loses. ~ '^:^}l^5?}^^~-';-^/:<'^'^ At the same time hlood loses the four per cent of carbon dioxide, which the air gains. The water, of which about half a pint is given off daily, is mostly lost from the blood. a Problem LIU. J_ study of ven- tilation. {Laboratory Manual, Froh. LIII.) Need of Ventilation. ■ — During the course of a day the lungs have lost to the surrounding air nearly two pounds of carbon dioxide. This means that about three fifths of a cubic foot is given off from each person during an hour. When we are confined for some time in a room, it becomes necessary to get rid of this carbon dioxide. This can be done only by means of proper ven- tilation. Other materials are passed off from the lungs with carbon di- oxide. It is the presence of these wastes in combination with carbon dioxide that makes breathed air particularly unwholesome. The presence of impurities in the air of a room may easily be determined by its odor. The close smell of a poorly ventilated room is due to organic impurities given off with the carbon dioxide. This, fortunately, gives us an Three ways of ventilating a room: i, inlet for air ; o, outlet for air. Which is the best method of ven- tilation ? Explain. RESPIRATION AND EXCRETION 387 index by which we may prevent poisoning. Air containing from 6 to 8 parts of carbon dioxide to 10,000 parts of air is bad ; while from 12 to 14 parts in 10,000 makes a very dangerous amount. Among the factors which take oxygen from the air in a closed room and produce carbon dioxide are burning gas or oil lamps, stoves, the presence of a number of people, etc. Proper Ventilation. — Ventilation consists in the removal of air that has been used, and the introduction of a fresh supply to take its place. If we remember that warm air is lighter than cold air, and carbon dioxide is heavier than air, we can see that ventila- tion outlets should be on the level of the floor. The inlets should be near the top of the room, especially in houses heated by any method of direct radiation, such as steam or hot water. A good method of ventilation for the home is to place a board two or three inches high between the lower sash and the frame of a window. An open fireplace in a room aids in ventilation because of the constant draft up the fluo. Sweeping and Dusting. — It is very easy to dem- onstrate the amount of dust in the air by follow- ing the course of a beam of light in a darkened room. We have already proved that spores of mold and yeast exist in Plate culture exposed for five minutes in a school the air. That bacteria ^^^^ ^^^'^^ p"p^^^ ^^'"^ passing to recitations. , . , Each spot is a colony of bacteria or mold. are also present can be proved by exposing a sterilized gelatin plate to the air in a schoolroom for a few moments.^ ^ Expose two sterilized dishes containing culture media ; one in a room being swept with a damp broom, and the other in a room which is being swept in the usual manner. Note the formation of colonies of bacteria in each dish. does the most growth take place? In which dish 388 RESPIRATION AND EXCRETION Many of the bacteria present in the air are active in causing viiseases of the respiratory tract, such as diphtheria, membranous croup, and tuberculosis. Other diseases, as colds, bronchitis (inflammation of the bronchial tubes), and pneumonia (inflam- mation of the tiny air sacs of the lungs), are probably caused by bacteria. Dust, with its load of bacteria, will settle on any horizontal sur- face in a room not used for three or four hours. Dusting and sweeping should always be done with a damp cloth or broom, otherwise the bacteria are simply stirred up and sent into the air again. The proper watering of streets before they are swept is also an important factor in health. Ventilation of Sleeping Rooms. — Sleeping in close rooms is the cause of much illness. Beds ought to be placed so that a constant supply of fresh air is given without a direct draft. This may often be managed with the use of screens. Bedroom windows should be thrown open in the morning to allow free entrance of the sun and air, bedclothes should be washed frequently, and sheets and pillow covers often changed. Bedroom furniture should be simple, and but little drapery allowed in the room. Hygienic Habits of Breathing. — Every one ought to accustom himself upon going into the open air to inspire slowly and deeply to the full capacity of the lungs. A slow expiration should follow. Take care to force the air out. Breathe through the nose, thus warming the air you inspire before it enters the lungs and chills the blood. Repeat this exercise several times every day. You will thus prevent certain of the air sacs which are not often used from becoming hardened and permanently closed. The Relation of Tight Clothing to Correct Breathing. — It is im- possible to breathe correctly unless the clothing is worn loosely over the chest and abdomen. Tight corsets and tight belts prevent the walls of the chest and the abdomen from pushing outward and interfere with the drawing of air into the lungs. They may also result in permanent distortion of parts of the skeleton directly under the pressure. Other organs of the body cavity, as the stomach and intestines, may be forced downward, out of place, and in conse- quence do not perform their work properly. Relation of Exercise. — We have already seen that exercise re- RESPIRATION AND EXCRETION 389 suits in the need of greater food supply, and hence a more rapid pumping of blood from the heart. With this comes need of more oxygen to allow the oxidations whit^h supply the greater energy used. Hence deeper breathing during time of exercise is a prime necessity in order to increase the absorbing surface of the lungs. Suffocation and Artificial Respiration. — Suffocation results from the shutting off of the supply of oxygen from the lungs. It may be brought about by an obstruction in the windpipe, by a lack of oxygen in the air, by inhaling some other gas in quantity, or by drowning. A severe electric shock may paralyze the nervous centers which control respiration, thus causing a kind of suffocation. In the above cases, death often may be pre- vented by prompt recourse to artificial respiration. To accomplish this, place the patient on his back with the head lower than the body ; grasp the arms near the elbows and draw them upward and outward until they are stretched above the head, on a line with the body. By this means the chest cavity is enlarged and an inspiration produced. To produce an ex- piration, carry the arms downward, and press them against the chest, thus forcing the air out of the lungs. This exercise, regularly repeated every few seconds, if necessary for hours, has been the souj-ce of saving many lives. Common Diseases of the Nose and Throat. — Catarrh is a disease which people with sensitive mucous membrane of the nose and throat are sub- ject to. It is indicated by the constant secretion of mucus from these membranes. Frequent spraying of the nose and throat with some mild antiseptic solutions is found useful. Chronic catarrh should be at- tended to by a physician. Often we find children breathing entirely through the mouth, the nose being seemingly stopped up. When this goes on for some time the nose and throat should be examined by a physician for adenoids, or growths of soft masses of tissue which fill up the nose cavity, thus causing a shortage of the air supply for the body. Many a child, backward at school, thin and irritable, has been changed to a healthy, normal, bright scholar by the removal of adenoids. Sometimes the tonsils at the back of the mouth cavity may become enlarged, thus shut- ting off the air supply and causing the same trouble as we see in a case of adenoids. The simple removal of the obstacle by a doctor soon cures this condition. Cell Respiration. — It has been found, in the case of very simple animals, such as the arnceba, that when oxidation takes place in a cell, work results from this oxidation. The oxygen taken into the lungs is not used there, but is carried by the blood to such parts of the body as need oxygen to oxidize food mate- rials in the cells. The quantity of oxygen used by the body is 390 RESPIRATION AND EXCRETION The respiration of cells. nearly dependent on the amount of work performed. From twenty to twenty-five ounces is taken in and used by the body every day. Oxygen is constantly taken from the blood by tis- sues in a state of rest and is used up when the body is at work. This is proved by the fact that in a given time a man, when working, gives off more oxygen (in carbon di- oxide) than he takes in during that time. While work is being done certain wastes are formed in the cell. Carbon dioxide is released when carbon is burned. But when proteids are burned, another waste product containing nitrogen is formed. This must be passed off from the cells, as it is a poison. Here again the blood and l^nnph, common carriers, take the waste material to points where it may be excreted or passed out of the body. Organs of Excretion. — All the life processes which take place in a living thing result ultimately, in addition to giving off of carbon di- oxide, in the formation of organic wastes within the body. Such or- ganic waste contains nitrogen, and in animals is usually called urea. In man, the skin and kidneys per- form this function, hence they are called the organs of excretion. The Human Kidney. — The hu- man kidney is about four inches long, two and one half inches wide, and one inch in thickness. Its color is dark red. If the structure of the medulla and cortex (see Fig- ure above) is examined under the compound microscope, you will find these regions to be composed of a vast number of tiny branched and twisted tubules. The outer end of each of these Suprarenal body Ureter Longitudinal section of kidney. RESPIRATION AND EXCRETION 391 tubules opens into the pelvis, the space within the kidney; the inner end, in the cortex, forms a tiny closed sac. In each sac, the outer wall of the tube has grown inward and carried with it a very tiny artery. This artery breaks up into a mass of capillaries. These capillaries, in turn, unite to form a small vein as they leave the little sac. Each of these sacs with its contained blood vessels is called a glomendus. Wastes given off by the Blood in the Kidney. — In the glomerulus the blood loses by osmosis, through the very thin walls of the capillaries, first, a consider- able amount of water (amounting to nearly three pints daily) ; second, a ni- trogenous waste material known as urea ; third, salts and other waste organic sub- stances, uric acid among them. Diagram of kidney circula- tion, showing a glomerulus and tubule : a, artery bring- ing blood to part ; 6, capil- lary bringing blood to glomerulus ; 6', vessel con- tinuing with blood to tu- bule ; c, vein ; t, tubule ; (?, glomerulus. These waste products, together with the water eontaiiiing them, are known as urine. The total amount of nitrogenous waste leav- ing the body each day is about twenty grams ; this is nearly all accounted for in the urea passed off by the kidney, as urine is secreted in the kidney. It is passed through the ureter to the urinary bladder; from this reservoir it is passed out of the body, through a tube called the urethra. After the blood has passed through the glomeruli of the kidneys it is purer than in any other place in the body, because, before coming there, it lost a large part of its burden of carbon dioxide in the lungs. After leaving the kid- ney it has lost much of its nitrogenous waste. So dependent is the body upon the excretion of its poisonous material that, in cases where the kid- neys do not do their work properly, death may ensue within a few hours. Structure and Use of Sweat Glands. — If you examine the sur- face of your skin with a lens, you will notice the surface is thrown into Httle ridges. In these ridges may be found a large number of very tiny pits; these are the pores or openings of the sweat- secreting glands. From each opening a little tube penetrates deep within the epidermis; there, coiling around upon itself several times, it forms the sweat gland. Close around this coiled tube are 392 RESPIRATION AND EXCRETION found many capillaries. From the blood in these capillaries, cells lining the wall of the gland take water, and with it a little carbon dioxide, urea, and some salts (common salt among others). This forms the excretion known as sweat. The combined secretions from these glands amount normally to a little over a pint during twenty-four hours. At all times, a small amount of sweat is given off, but this is evaporated or is absorbed by the underwear; as this passes off unnoticed it is called insensible perspiration. In hot weather or after hard manual labor the amount of perspiration is greatly increased. Relation of Bodily Heat to Work Performed. — The bodily tem- perature of a person engaged in manual labor will be found to be but httle higher than the temperature of the same person at rest. When a man works, he releases energy by oxidizing food material or tissue in the body. Thus we know from our previous experi- ments that heat is released. Muscles, nearly one half the weight of the body, release about five sixths of their energy as heat. At all times they are giving up some heat. How is it that the bodily temperature does not differ greatly at such times? Regulation of Heat of the Body. — The temperature of the body is largely regulated by means of the activity of the sweat glands. The blood carries much of the heat, liberated in the various parts of the body by the oxidation of food, to the surface of the body, where it is lost in the evaporation of sweat. In hot weather the blood vessels of the skin are dilated ; in cold weather they are made smaller by the action of the nervous system. The blood thus loses water in the skin, the water evaporates, and we are cooled off. The object of increased perspiration, then, is to re- move heat from the body. With a large amount of blood present in the skin, perspiration is increased ; with a small amount, it is diminished. Hence, we have in the skin an automatic regulator of bodily temperature. Sweat Glands under Nervous Control. — The sweat glands, like the other glands in the body, are under the control of the sympathetic nervous system. Frequently the nerves dilate the blood vessels of the skin, thus helping the sweat glands to secrete, by giving them more blood. *' Thus regulation is carried out by the nervous system determining, on the one hand, the loss by governing the supply of blood to the skin and the RESPIRATION AND EXCRETION 393 action of the sweat glands ; and on the other, the production by diminish- ing or increasing the oxidation of the tissues." — Foster and Shore, Physi- ology. Comparison with Cold-blooded Animals. — We have seen the bodUy temperature of a frog remain nearly that of the surrounding medium. Fishes, all amphibious animals, and reptiles are alike in this respect. This change in the bodily temperature is due to the absence of regulation by the nervous system. A sort of regulation is exerted, however, by outside forces, for the cold in winter causes the cold-blooded animals to become inactive. Warm weather, on the other hand, stimulates them to greater activity and to increased oxidation. This is naturally followed by a rise in bodily tem- perature. Brohlem LTV, J. final study of changes in the composition of Wood in various parts of the body, {Laboratory Manual, Prob. LIV,) Summary of Changes in Blood within the Body. — We have already seen that red corpuscles in the lungs lose part of their load of carbon dioxide that they have taken from the tissues, replacing it with oxygen. This is accompanied by a change of color from purple (in blood which is poor in oxygen) to that of bright red (in richly oxygenated blood). Other changes take place in other parts of the body. In the walls of the food tube, especially in the small intestine, the blood receives its load of fluid food. In the muscles and other working tissues the blood gives up food and oxygen, receiving carbon dioxide and organic waste in return. In the liver, the blood gives up its sugar, and the worn-out red corpuscles which break down are removed (as they are in the spleen) from the circulation. In glands, it gives up materials used by the gland cells in their manufacture of secretions. In the kidneys, it loses water and nitrogenous wastes {urea). In the skin, it also loses some waste materials, salts, and water. Hygiene of the Skin. — The skin as an organ of excretion is of importance. It is of even greater importance as a regulator of bodily temperature. The mouths of the sweat glands must not be allowed to become clogged with dirt. The skin of the entire body should, if possible, be bathed daily. For those who can stand it, a cold sponge bath is best. Soap should be used daily on parts exposed to dirt. Exercise in the open air is important to all who -1907: — Air Keep outdoors as much as possible. Breathe through the nose, not through the mouth. When indoors, have the air as fresh as possible — (a) By having aired the room before occupancy. (6) By having it continuously ventilated while occupied. Not only purity, but coolness, dryness, and motion of the air, if not very extreme, are advantageous. Air in heated houses in winter is usually too dry, and may be humidified with advantage. Clothing should be sufficient to keep one warm. The minimum that will secure this result is the best. The more porous your clothes, the more the skin is educated to perform its functions with increasingly less need for protection. Take an air bath as often and as long as possible. Water Take a daily water bath, not only for cleanhness, but for skin gym- nastics. A cold bath is better for this purpose than a hot bath. A short hot followed by a short cold bath is still better. In fatigue, a very hot bath lasting only half a minute is good. A neutral bath, beginning at 97"* or 98", dropping not more than 5**, and continued 15 minutes or more is an excellent means of resting the nerves. Be sure that the water you drink is free from dangerous germs and impurities. " Soft " water is better than " hard " water. Ice water should be avoided unless sipped and warmed in the mouth. Ice may contain spores of germs even when germs themselves are killed by cold. Cool water drinking, including especially a glass half an hour before breakfast and on retiring, is a remedy for constipation. Food Teeth should be brushed thoroughly several times a day, and floss silk used between the teeth. Persistence in keeping the mouth clean is not only good for the teeth, but for the stomach. Masticate all food up to the point of involuntary swallowing, with the attention on the taste, not on the mastication. Food should simply be 426 HEALTH AND DISEASE chewed and relished, with no thought of swallowing. There should be no more effort to prevent than to force swallowing. It will be found that if you attend only to the agreeable task of extracting the flavors of your food, Nature will take care of the swallowing, and this will become, like breathing, involuntary. The more you rely on instinct, the more normal, stronger, and surer the instinct becomes. The instinct by which most people eat is perverted through the " hurry habit " and the use of abnor- mal foods. Thorough mastication takes time, and therefore one must not feel hurried at meals if the best results are to be secured. Sip liquids, except water, and mix with saliva as though they were solids. The stopping point for eating should be at the earliest moment when one is really satisfied. The frequency of meals and time to take them should be so adjusted that no meal is taken before a previous meal is well out of the way, in order that the stomach may have had time to rest and prepare new juices. Nor- mal appetite is a good guide in this respect. One's best sleep is on an empty stomach. Food puts one to sleep by diverting blood from the head, but disturbs sleep later. Water, however, or even fruit may be taken before retiring without injury. An exclusive diet is usually unsafe. Even foods which are not ideally the best are probably needed when no better are available, or when the appetite especially calls for them. The following is a very tentative list of foods in the order of excellence for general purposes, subject, of course, to their palatability at the time eaten: fruits, nuts, grains (including bread), butter, buttermilk, salt in small quantities, cream, milk, potatoes, and other vegetables (if fiber is rejected), eggs, custards, digested cheeses (such as cottage cheese, cream cheeses pineapple cheese, Swiss cheese, Cheddar cheese, etc.), curds, whey, vegetables, if fiber is swallowed, sugar, chocolate, and cocoa, putrefactive cheeses (such as Limburger, Rochefort, etc.), fish, shellfish, game, poultry, meats, liver, sweetbreads, meat soups, beef tea, bouillon, meat extracts, tea and coffee, condiments (other than salt), and alcohol. None of these should be absolutely excluded, unless it be the last half dozen, which, with tobacco, are best dispensed with for reasons of health. Instead of exclud- ing specific food, it is safer to follow appetite, merely giving the benefit of the doubt between two foods, equally palatable, to the one higher in the list. In general, hard and dry foods are preferable to soft and wet foods. Use some raw foods — nuts, fruits, salads, milk, or other — daily. The amount of proteid required is much less than ordinarily consumed. Through thorough mastication the amount of proteid is automatically reduced to its proper level. The sudden or artificial reduction in proteid to the ideal standard is apt to produce temporarily a ** sour stomach," unless fats be used abun- dantly. HEALTH AND DISEASE 427 To balance each meal is of the utmost importance. When one can trust the appetite, it is an almost infallible method of balancing, but some knowledge of foods will help. The aim, however, should always be — and this cannot be too often repeated — to educate the appetite to the point of deciding all these questions automatically. Exercise and Rest The hygienic life should have a proper balance between rest and exer- cise of various kinds, physical and mental. Generally every muscle in the body should be exercised daily. Muscular exercise should hold the attention, and call into play will power. Exercise should be enjoyed as play, not endured as work. The most beneficial exercises are those which stimulate the action of the heart and lungs, such as rapid walking, running, hill climbing, and swimming. The exercise of the abdominal muscles is the most important in order to give tone to those muscles and thus aid the portal circulation. For the same reason erect posture, not only in standing, but in sitting, is important. Support the hollow of the back by a cushion or otherwise. Exercise should always be limited by fatigue, which brings with it fatigue poisons. This is nature's signal when to rest. If one's use of diet and air is proper, the fatigue point will be much further off than other- wise. One should learn to relax when not in activity. The habit produces rest, even between exertions very close together, and enables one to con- tinue to repeat those exertions for a much longer time than otherwise. The habit of lying down when tired is a good one. The same principles apply to mental rest. Avoid worry, anger, fear, excitement, hate, jealousy, grief, and all depressing or abnormal mental states. This is to be done not so much by repressing these feelings as by dropping or ignoring them — that is, by diverting and controlling the atten- tion. The secret of mental hygiene lies in the direction of attention. One's mental attitude, from a hygienic standpoint, ought to be optimistic and serene, and this attitude should be striven for not only in order to pro- duce health, but as an end in itself, for which, in fact, even health is properly sought. In addition, the individual should, of course, avoid infection, poisons, and other dangers. Occasional physical examination by a competent medical examiner is ad- visable. In case of illness, competent medical treatment should be sought. Finally, the duty of the individual does not end with personal hygiene. He should take part in the movements to secm-e better public hygiene in city, state, and nation. He has a selfish as well as an altruistic motive to do this. His air, water, and food depend on health legislation and ad- ministration. 428 HEALTH AND DISEASE All the foregoing rules are important. The results which may- be obtained by following them depend largely on the thorough- ness with which they are followed. This is true especially of fresh air and mastication. If all the rules are followed and followed thoroughly, including the one most commonly neglected, — namely, keeping within the fatigue limit, — the average man may reasonably expect to double his length of life, his activity per day, his satisfactions and his usefulness. The laws of " humaniculture " can be depended upon as much as those of agriculture, horticulture, or §tock raising. Public Hygiene. — Although it is absolutely necessary for each individual to obey the laws of health if he or she wishes to keep from disease, it has also become necessary, es- pecially in large cities, to have general super- vision over the health of people living in a community. This is done by means of a department or board of health. It is the function of this de- partment to care for public health. A list of regulations and laws known as the Sanitary Code is given out to the citizens. These regulations concern the care of buildings and plumbing, of the clean- liness of street cars and other public vehi- cles, the protection and supervision of foods sold, the inspection of our supplies of milk and water, and particularly, the control of disease. Examples of what public control of disease will do is seen when -400 -300 -400 \ ■^ \ s \ ^ .100 18 50 ISfeO, 18T0 1880 la'go 190019061 The curve showing a decreasing death rate from tu- berculosis. Why do fewer people die from the disease than formerly ? HEALTH AND DISEASE 429 we consider the specific case of the disease known as smallpox. In the eighteenth century 5,000,000 people are said to have died from it; one hundred years ago it was exceedingly common in all large cities in this country. To-day an epidemic of smallpox is impos- sible, thanks to the discovery of vaccination and prompt action by the health department. Tuberculosis at the present time kills more people annually than any other disease, and yet it is believed by sanitary living we will stamp out the disease within fifty years if Deaths from tuberculosis contrasted with the other contagious diseases in the center of New York in 1908. we go on at the present rate. Public hygiene is largely responsible for the lessening of deaths from typhoid fever and other diseases which are transmitted through the milk or water supply. It is estimated that pure milk, pure water, and pure air supplied to all would lengthen the average human life in the United States eight years. At the present rate human life is being lengthened about 14 years every century in Massachusetts, 17 in Europe, and 27 per century in Prussia.^ In India, on the other hand, where little hygiene is known or practiced among the masses of people, the length of life is stationary. 1 This result is obtained by the saving of the lives of thousands of young children, who now grow to become adults. 430 HEALTH AND DISEASE Ex-President Roosevelt said in one of his latest messages to Congress : — '* There are about 3,000,000 people seriously ill in the United States, of whom 500,000 are consumptives. More than half of this illness is prevent- able. If we count the value of each life lost at only $1700 and reckon the average earning lost by illness at $700 a year for grown men, we find that the economic gain from mitigation of preventable disease in the United States would exceed $1,500,000,000 a year. This gain can be had through medical investigation and practice, school and factory hygiene, restriction of labor by women and children, the education of the people in both pub- lic and private hygiene, and through improving the efficiency of our health service, municipal, state, and national." Infectious Diseases and Quarantine. — One of the important means for prevention of the spread of diseases caused by bacteria or Protozoa is by quarantine. The board of health at once isolates any case of disease which may be communicated from one person to another. This is called quarantine. No one save the doctor or nurse should enter the room of the person quarantined. After the disease has run its course, the clothing, bedding, etc., in the sick room is fumigated. This is usually done by the board of health. Formaldehyde in the form of candles for burning or in a liquid form is a good disinfectant. The room should be tightly closed to prevent the escape of the gas used, as the object of the disin- fection is to kill all the disease germs left in the room. Immunity. — In the prevention of germ diseases we must fight the germ by attacking the parasites directly with poisons that will kill them (such poisons are called germicides or disinfectants), and we must strive to make the persons coming in contact with the disease unlikely to take it. This insusceptibility or immunity may be either natural or acquired. Natural immunity seems to be in the constitution of a person, and may be inherited. Immunity may be acquired by means of such treatment as the antitoxin treatment for diphtheria. This treatment, as the name denotes, is a method of neutralizing the poison (toxin) caused by the bacteria in the system. It was discovered a few years ago by a German, Von Behring, that the serum of the blood of an animal immune to diphtheria is capable of neutralizing the poison produced by the diphtheria-causing bacteria. Horses are rendered immune HEALTH AND DISEASE 431 by giving them gradually larger doses of the diphtheria toxin or poison. The serum (or liquid part) of the blood of these horses is then used to inoculate the patient suffering from or exposed to diphtheria, and thus the disease is checked or prevented altogether by the antitoxin injected into the blood. Vaccination. — Smallpox was once the most feared disease in this country; 95 per cent of all people suffered from it. As late as 1898, over 50,000 persons lost their lives annually in Russia from this disease. It is probably not caused by bacteria, but by a tiny animal para- site. Smallpox has been brought under absolute control by vaccina- tion, — the inoculation of man with the substance (called virus) which causes cowpox in a cow. Cowpox is like a mild form of smallpox, and the introduction of this virus gives complete immunity to smallpox for several years after vaccination. This immunity is caused by the formation of a germicidal substance in the blood, due to the in- troduction of the virus. The Work of the Department of Street Cleaning. — In any city one menace to the health of its citizens exists in the refuse and garbage. The city streets, when dirty, contain countless millions of germs which have come from decaying material, or from people ill with disease. In most large cities a department of street cleaning not only cares for the removal of dust from the streets, but also has the removal of garbage, ashes, and other waste as a part of its work. The practice of putting open cans contain- ing ashes and garbage into the street for disposal is an indirect means of spreading disease, for flies breed and germs may thrive there. The street-cleaning department should be aided by every citizen; rules for the separation of garbage, papers, and ashes should be kept. Garbage and ash cans should be covered. The practice of upsetting ash or garbage cans is one which no young citizen should A bad condition of the streets, lower East Side, New York. 432 HEALTH AND DISEASE allow in his neighborhood, for sanitary reasons. The best results in summer street-cleaning are obtained by washing or flushing the Removal of ashes by department of street great tanks ; from this cleaning. New York. material the fats are ex- tracted, and the soHd matter is sold for fertilizer. Ashes are used for filling marsh land. Thus the removal of waste matter may p&y for itself in a large city. The Necessity of a Pure Milk and Water Supply. — The city of New York is spending hundreds of millions of dollars to bring a supply of pure water to her citizens. Other cities are doing the same. The world has awakened to the necessity of a pure water supply, largely because of the number of epidemics of typhoid which have been caused by contaminated water. Typhoid fever germs live in the food tube, hence the excreta of a typhoid patient will contain large numbers of germs. In a city with a system of sewage such germs might eventually pass from the sewers into a river. Many cities take their water supply directly from rivers, sometimes not far below another large town. Such cities must take many germs into their water supply. Many cities, as Cleve- land and Buffalo, take their water from lakes into which their sewage flows. In cities which drain their sewage into rivers and lakes, the question of sewage disposal is a large one, and many cities now have means of disposing of their sewage in some manner as to render it harmless to their neighbors. Filtering such water by means of passing the water through settling basins and sand filters removes about 98 per cent of the germs. The result of drinking unfiltered and filtered water in certain large cities is shown graphi- cally on the following page. In the country typhoid may be spread by the germs getting into a well or spring from whence the supply of water comes. This HEALTH AND DISEASE 433 may be avoided by having priv- ies and cesspools some distance from the well and so placed that they will drain away from it. Wells should have a ce- mented cap around the top so as to keep out surface water, as germs rarely live long more than five feet below ground. Serious outbreaks of typhoid have been traced to contami- nated milk supplies. A case of typhoid exists on a farm; the sewage gets into the well from which water is used for the washing of milk cans. Typhoid germs thrive in milk. Thus the milkman spreads disease. The diagram following illustrates a recent epidemic in Stamford, Conn., which was traced to a farm on which was a person having typhoid. Growth of bacteria in a drop of impure water allowed to run down a sterilized culture in a dish. 20 40 (BO ao 100 120 140 160 laO 200 220 A 1906 1 . 7M/Jf/A 1696 |H^H ^ 1 1901 W/M 1692 ^H^l ■ 1 C I 1696 WM I9O6 m^ ■ l> I9O6 IT w/m Cases of typhoid per 100,000 inhabitants before filtering water supply (solid) and after (shaded) in A, Watertown, N.Y.; B, Albany, N.Y.; C, Lawrence, Mass.; D, Cincinnati, Ohio. What is the effect of filtering the water supply ? HUNT. ES. BIO. — 28 434 HEALTH AND DISEASE Railroads are often responsible for carrying typhoid and spread- ing it. It is said that a recent outbreak of typhoid in Scranton, Pa., was due to the fact that the excreta from a typhoid patient traveling in a sleeping car was washed by rain into a reservoir near which the train was passing. Railroads are thus seen to be great open sewers. Some more sanitary kind of toilet should be used so that filth and disease will not be scattered over the country. 1 M II 1 1 1 L 1 I 1 L f 1 n M^BnsiBAEU L««»«»«i 1 1 ■ _ ™^^ j ; ^ ^ 1 1 D — l:::^^ 1 ] J|L 1 11 i 1 II 1 • • 1 • ,.L • -1 r A diagram to show how typhoid may be spread in a city through an infected milk supply. The black spots in the blocks mean cases of typhoid. A, a farm where typhoid exists ; the dashes in the streets represent the milk route. B is a, second farm which sends part of its milk to A ; the milk cans from B are washed at farm A and sent back to B. A few cases of typhoid appear along B's milk route. How do you account for that ? How the Board of Health fights Typhoid. — Pure water is the first essential in preventing epidemics of typhoid. Health board officials are constantly testing the supply, and, if any harmful bacteria are found, a warning is sent out to boil the water. Boil- ing water at least 10 minutes kills most harmful germs. HEALTH AND DISEASE 435 The milk supply is also subject to rigid inspection. Milk brought into a city is tested, not only for the amount of cream present to prevent dilution with water, but also for the presence of germs. Thecleanliuess of the cans, wapjons, etc., is also subject to inspection. *' The patients live out of doors." The cows are also inspected to see if they have tuberculosis, for such cows might spread the dis- ease to human beings. During the summer months many babies die from cholera infantum. This disease is al- most entirely spread through impure milk. Flies are largely responsible for the spread of the disease by carrying the germs to milk. Spread of such diseases through milk can only be prevented by careful pasteurization (heating to 170 for a few minutes). In many large cities pasteurized milk is sold at a reasonable price to poor people, and thus much disease is pre- vented. Disease germs of various sorts, typhoid, tuberculosis, pneumonia, 436 HEALTH AND DISEASE diphtheria, and many others may be transferred through the agency of food. Fruits and vegetables may be carriers of disease, especially if they are sold from exposed stalls or cars and handled by the passers-by. All vegetables, fruits, or raw foods should be care- fully washed before using. Spoiled or overripe fruit, as well as meat which is decayed, is swarming with bacteria and should not be used. The board of health has supervision over the sale of fruit, meats, fish, etc., and frequently in large cities food unfit for sale is condemned and destroyed. How the Board of Health fights Tuberculosis. — Tuberculosis, which a few years ago killed fully one seventh of the people who died from disease in this country, now kills less than one tenth. This decrease has been largely brought about because of the treatment of the disease. Since it has been proved that tuberculosis if taken early enough is curable, by quiet living, good food, and 'plenty of fresh air and light, we find that numerous sanatoria have come into existence which are supported by private or public means. At these sanatoria the patients live out of doors, especially sleep in the air, while they have plenty of nourishing food and little exercise. In this way and by tenement-house laws which require proper air shafts and window ventilation in dwellings, by laws against spitting in public places, and in other ways the boards of health in our towns and cities are waging war on tuberculosis. Reference Books Sharpe, A Laboratory Manual for the Solution of Problems in Biology. American Book Company. Allen, Civics and Health. Ginn and Company. Davison, The Human Body and Health. American Book Company. Gulick Hygiene Series, Town and City. Ginn and Company. Hough and Sedgwick, The Human Mechanism. Ginn and Company. Richman and Wallach, Good Citizenship. American Book Company. Ritchie, Primer of Sanitation. World Book Company, Reports, etc. American Health Magazine. Annual Report of Department of Health, City of New York (and other cities). Bulletins and Publications of Committee of One Hundred on National Health. School Hygiene, American School Hygiene Association. INDEX (Illustrations are indicated by page numerals in bold-faced type.) Accommodation of eye, 410. Acts, automatic, 404. Adaptation, 28, 41, 221. Adaptations, for pollination, 44, 46 ; for seed dispersal, 53, 54, 56, 66, 80; in birds, 297, 299, 301 ; in frogs, 285 ; in mammalia, 312 ; in snakes, 295 ; in turtles, 293 ; in vertebral column, 326 ; to environment, 144, 249. Adenoids, eflfects of, 389. Aggressive resemblance, 250, 261. Air, amount of, in breathing, 384, 386; changed in lungs, 385 ; composition of, 17 ; factor in germination, 76 ; fresh, how to get, 419 ; necessity of, 405. Alcohol, and abihty to do work, 413 ; and disease, 412, 422 ; and longevity, 424 ; a poison, 345 ; as a food, 344, 346 ; effect on blood, 379 ; effect on bodily heat, 395 ; effect on circulation, 379 ; effect on digestion, 364 ; effect on excretion, 397 ; effect on intellectual ability, 413 ; effect on leucocytes, 423 ; effect on respiration, 395 ; in patent medicines, 350 ; in treatment of disease, 422 ; paralyzes nervous system, 411. Alcoholic poisoning, economic, moral, and social effects of, 416 : AlgaB, 145. Alimentary canal, 362. Alligator, 296. Alternation of generations, in coelen- terates, 208 ; in fern, 155 ; in mosses, 153 ; in spermatophytes, 156. Alveoli, 383. Amoeba, parts of, 193 ; reproduction of, 193. Amphibia, 285 ; characteristics of, 292 ; classification of, 292. Angiosperms, 157. Animals, cold-blooded, 369 ; domestication, 316 ; relation of, to man, 14. Annulata, classification of, 220. Antennae, 223, 244. Antennules, 223. Antheridia, 153, 166. Antherozoid, defined, 154, 166. Ants, 255 ; and their "cows," 266; artificial nest for, 256. Aphids and ants, 256. Appendages of skeleton, 327. Arachnida, 245, 247. Archegonium, 153, 166. Arteries, structure of, 374. Arthropoda, classified, 247. Asexual reproduction, amoeba, 193 in coelenterates, 208, 209 ; in fern, 155 ; in hydra, 203 ; in mold, 150 ; in moss, 152 ; in paramoecium, 192 ; in Spirogyra, 148. 437 438 INDEX Asymmetry in oyster, 268. Atwater's experiments, 332. Auricle, 370. Bacillus, 175. Bacteria, and fermentation, 177 ; carried by fly, 260, 261, 420 ; cause decay, 177 ; cause disease, 178 ; from human mouth, 179 ; in impure water, 433 ; in milk, 180 ; in schoolroom, 387 ; in streets, 419 ; nitrogen-fixing, 178; size and form, 175 ; their relation to man, 14. Bacteriology, defined, 14. Bark, use of, 104. Balanced aquarium, 185. Balancing in birds, 300. Bean, 65. Bean seedlings, 78. Beans, as food, 68. Beaver, 314. Bees, 40, 43, 253, 254. Beer making, 172. Beetle, characters of, 242. Benedict's test, 71. Berry, 53, 63. Bile, functions of, 360. Biology, civic, 418 ; reasons for study of, 13. Bird, body of, 297. Birds, care of young, 304 ; classification of, 308, 311 ; distribution of, 307 ; economic importance of, 304 ; extermination of, 306 ; feathers of, 298 ; feet of, 299 ; flight of, 298 ; migrations of, 307 ; nesting habits of, 303, 304 ; perching, 309 ; perching in, 300. Bison, 315. Bladder, urinary, 391. Bladderwort, 130. Blastula, 200. Blood, amount of, 369 ; and its circulation, 366 ; changes in, in body, 393 ; changes in, in lungs, 383, 386 ; clotting of, 367 ; course of, 372 ; distribution of, 369 ; exchange in, 376 ; function of, 366 ; temperature of, 369 ; vessels, congestion in, 394 ; wastes of, to kidney, 391. Bodily heat, affected by alcohol, 395 ; in cold-blooded animals, 393 ; regulation of, 392. Body, daily fuel needs of, 337 ; normal heat output of, 339. Box elder twigs, sections of, 103. Brain, functions of parts, 403 ; of man, 401. Bread mold, 149 ; growth of, 150. Breathing, and lacing, 388 ; hygienic habits of, 388 ; mechanics of, 384 ; movements in, 383, 384 ; rate of, 384. Bronchi, 382. Bruises, treatment of, 378, 394. Bryophytes, 157. Bud, structure of, 98, 99. Budding, 110. Buds, factors in opening of, 99; position of, 100. Bugs, 242, 243. Bumblebee, 40, 41, 42, 253. Burns, treatment of, 394. Butterfly, 237 ; compared with moth, 238. Calorie, defined, 333. Calorimeter, respiration, 332. Calyx, 34. Cambium layer, use of, 104, 111. Canal, semicircular, 408. Capillary circulation in frog's foot, 373. Carapace, 222. Carbohydrates, 24, 331. Carbon, properties of, 21. INDEX 439 Carbon dioxide, test for, 22. Carnivorous, defined, 312. Catarrh, 389. Catkin, 47. Cell, 29 ; as a unit, 194. Cell membrane, 8&. Cell sap, 89. CeU tissue, 205. Cells, 206 ; sizes and shapes of, 30. Centipede, poisonous, 246. Centrum, 327. Cephalopods, 270, 273. Cephalothorax, 222. Cerebellum, 401. Cerebrum, 401 ; functions of, 403. Cestodes, 217. Chelipeds, 222. Chemical element and compound, 18. Chlorophyll bands, 147. Chlorophyll bodies in leaf, 120. Chromosomes, 29. Chrysalis, 237, 238. Cicada, 242, 243. Cilia, 191. Circulation, effects of alcohol on, 379 ; effect of exercise on, 377 ; effect of tobacco on, 381 ; in a mammal, 372 ; in capillaries, 373, 374 ; in crayfish, 225 ; in fishes, 279 ; in frog, 287, 373 ; in kidney, 391 ; in man, 370 ; organs of, 206 ; portal, 362, 372 ; pulmonary, 372 ; systemic, 372. Clam, fresh-water, shell of, 268 ; round, parts of, 269. Class, defined, 157. Club mosses, 156. Coelenterates, 207, 208, 209 ; compared with worms, 215. Colds, cause of, 394. Coleoptera, 242, 247. Colloid, defined, 358. Combustion, 22. Composite head, parts of, 44, Conjugation, 148, 160; in black mold, 160 ; in paramcecium, 192. Contagious diseases, death rafte from, 429. Copepod, 231. Coral, madreporic, 209. Coral reefs, 210. Corn, grain of, 69 ; production of, 68. Corn grain, foods in, 70, 73. Corn smut, 174. Corolla, 34. Corpuscle, red, function of, 367; structure of, 367. Corpuscle, colorless, functions of, 388 ; structure of, 367, 368. Corpuscles, tactile, 321, 406. Cortex, 87 ; in stem, 103. Cotton, 61. Cotton boll weevil, 62, 262. Cotyledons, as foliage leaves, 79 ; food in, 66 ; functions of, 79 ; in bean, 66 ; of corn, 69. Crab, blue, 229 ; fiddler, 229 ; giant spider, 230 ; hermit, 229. Crayfish, adaptation for protection, 222; and allies, characters of, 231 ; appendages, 224; external structure, 222 ; internal structure, 226 ; senses of, 223. Crops, rotation of, 95. Cross-pollination, defined, 38. Crustacea, degenerate, 232. Crustaceans, 222 ; habitat of, 231 ; parasitic, 232. Crystalloid, defined, 358. Culture, pure, 176. Cuts, treatment of, 378, 394. Cytoplasm, 30, 440 INDEX Dandelion, 86; leaves of, 118. Decay by bacteria, 177. Deliquescent tree, 100. Dermis, 321. Development, of bee, 254 ; of crayfish, 226 ; of fly, 241 ; of frog, 288, 289, 290; of lobster, 227 ; of moth, 239. Diaphragm, 357 ; in respiration, 384. Diastase, action of, 72. Diatoms, 149. Dichogamy, 48. Dicotyledons, 73. Dietary, best, 333. Digestion, 352 ; and absorption, 352 ; effect of alcohol on, 364 ; in corn grain, 71 ; in crayfish, 225 ; in fishes, 278 ; in plants, 106 ; of starch, 356 ; organs of, 206, 352 ; purpose of, 352. Digestive tract in frog, 287. Dipnoi, 284. Diptera, 240, 241, 242, 247 ; prevention of, 418. Disease of nose and throat, 389. Diseases, due to insects, 258, 259, 260; infectious, 430. Division of labor, 199 ; in hydra, 203 ; in vorticella, 195. Dragon fly, 244. Drone, 254. Drugs, use and abuse of, 349. Dusting, 387. Dyspepsia, causes and prevention of, 363. Ear, human, 408. Earthworm, development of, 215 ; locomotion in, 214 ; relation to surroundings, 212. Eating, hygienic habits of, 363. Economic importance, of alcoholic poisoning, 416 ; of birds, 304 ; of carnivora, 313 ; of corals, 210 ; of earthworms, 215 ; of ferns, 156 ; of food in roots, 95 ; of insects, 261, 262, 263, 264, 265; of leaves, 128 ; of lobster, 228 ; of moUusks, 269, 271 ; of parasitic worms, 219 ; of plants, 170 ; of roots and stems, 109 ; of snakes, 295 ; of starfish, 272 ; of trees, 133, 135. Ectoderm, defined, 200. Egg, development of, 200. Egg cell, 37, 153, 155, 227, 280, 288. Egg-laying habits of fishes, 280. Elasmobranch, 283, 284. Embryo sac, 36, 156. Endoderm, defined, 200. Endoskeleton, 275, 279. Endosperm, use of, 69, 72. Energy, defined, 20. Entomostraea, 231. Environment, 17. Enzyme, action upon fibrinogen, 367; in saliva, 357. Enzymes, 72, 353 ; in blood, 366, 367 ; in gastric juice, 358 ; reversible action of, 366. Epicotyl, 65. Epidermis, 321. Epiglottis, 354. Erosion, by streams, 133, 134 ; prevented by organic covering, 135. Esophagus, 352, 354, 357. Eustachian tube, 354, 408. Excretion, effect of alcohol upon, 397; in crayfish, 226 ; organs of, in man, 390. INDEX 441 Excurrent tree, 100. Exercise, and health, 421 ; in hygiene, 427. Exoskeleton, 222. Expiration, 384. Eye, coats of, 409 ; defects in, 410; human, 409 ; image formed in, 410 ; of crayfish, 223 ; of insect, 236. Facets, 236. Family, defined, 157. Fatigue, defined, 378. Fats, 24, 331. Fermentation, chemistry of, 172. Ferns, characteristics of, 155. Fertilization, 37, 155, 153. Fevers, 394. Fibrin, 367. Fibrinogen, 367. Fibrovascular bundles, 88 ; of a monocotyledon, 108; use of, 101. Filament, 34. Fisheries of world, 282. Fishes, appendages of, 276 ; body of, 275 ; classification of, 283 ; migration of, 282 ; protection of, 283. Fission, 30, 192. Flatworms, 216. Flower, color and odor of, 41 ; dimorphic, 49 ; fertilization of, 36 ; pistillate, 47, 68 ; relation to fruit, 65 ; staminate, 46, 47, 68 ; structure of, 34 ; trimorphic, 49. Prowers, work of, 34. Fly, foot of, 241 ; typhoid, 240, 260. Food, 24 ; and dietaries, 330 ; and health, 420 ; discovery of value of, 332 ; economy, 337 ; Food, in hygiene, 425 ; laws, 343 ; necessity of, 405 ; storage in stem, 109 ; swallowing of, 357 ; vacuoles, 191, 193 ; values, 340, 341 ; waste in kitchen, 342 ; why we need, 330. Food taking, in clams, 267 ; in crajiish, 223 ; in earthworm, 214 ; in fishes, 279 ; in hydra, 202 ; in insects, 235 ; in snakes, 295 ; in the starfish, 272 ; in turtles, 293 ; organs of, 206. Foods, absorbed into blood, 361, 362; adulterations in, 343 ; costs of various, 338 ; inorganic, 24, 331 ; in roots and stem, 110 ; organic, 23 ; values of, 336. Foraminifera, 198. Forest destruction, 139, 140. Forest regions in United States, 136. Forestry, 141. Forests, protection of, 141 ; their uses and protection, 133. Fowls, 309. Frog, leopard, 286 ; study of, 285 ; tree, 291. Frond, 164. Fruit, 51. Fruits, and their uses, 51 ; economic value of, 57 ; garden, 63 ; orchard, 63. Function, defined, 27. Functions, of an animal, 27, 206; of parts of a plant, 26. Fungi, 149; parasitic, 173, 174; saprophytic, 171, 172. 442 INDEX GaU-bladder, 352, 360. Gametophyte, 152, 153, 155. in fern, 155 ; in moss, 152. Ganglia, 399. Ganoid, 283, 284. Gastric juice, 358. Gastric mill, 225. Gastropods, 270, 273. Gastrula, 200. Genus, defined, 157. Geotropism, 85. Germination, defined, 74 ; factors in, 74 ; of bean, 78. Gila monster, 294. Gill rakers, 277. Gills, fish's, structure of, 277. Girdle, pectoral, in man, 327 ; pelvic, in man, 327. Glands, gastric, 358; intestinal, 360 ; lymph, 377 ; mesenteric, 363 ; salivary, 356 ; structure of, 353 ; sweat, 391. Glomerulus, 391. Glottis of man, 354. Glycogen, formation of, 360. Grafting, 111. Grain, 56. Grape sugar, tests for, 70, 71. Guard cells, 120. Gullet, 352, 354. Gymnosperms, 157. Habits, formation of, 404 ; importance of right, 404. Hasmoglobin, 368. Hair protection, in leaves, 129. Hairs, development of, 321. Halophytes, 161. Hay infusion, life in, 188. Health, and disease, 418 ; department of, 434, 436. Hearing, organ of, 407, 408. Heart, a force pump, 371. Heart, in action, 371 ; nervous control of, 377 ; Heart, position of, 370 ; protection of, 370 ; structure of, 370 ; valves in, 370, 371. Heliotropism, 116, 117. Hemiptera, 242, 247. Honeybee, 253. Hookworm, 217, 218. Hornets' nest, 254. Horny fiber sponge, 201. Horse, geologic history, 316. Human blood, 367. Human body a machine, 320. Humus, 21, 92. Hybridizing, 82. Hydra, 202. Hydrogen, 21. Hydroid colony, 208. Hydrophytes, 160. Hygiene, personal, 418; public, 428. Hymenoptera, 245, 247. Hypha, 149. Hypocotyl, 65. Ichneumon fly, 257. Immunity, 430. Inorganic soil, relation to organic, 92. Insects, 233 ; and crustaceans compared, 246 ; beneficial, 264 ; communal life, 252 ; control of damage by, 265 ; disease-carrying, 258, 259, 260, 261; divisions of, 247 ; noxious, 262, 263, 264 ; relation to mankind, 258 ; winners in life's race, 233. Inspiration, 384. Instincts, 312. Intestine, large, 363 ; small, structure of, 361. Irritability, defined, 32. Invertebrate, cross section of, 274. Joint, hinge, 324. Key fruit, 56. INDEX 443 Kidney, human, 390. Knots, cause of, 139. Lacteals, 361, 362, 377. Larval stages, defined, 200, Larynx, 364. Lateral line, function of, 276. Leaf, cell structure of, 120 ; functions of, 128 ; respiration in, 128 ; structure of, 119. Leaves, as holdfasts, 113; arrangement of, 118 ; as insect traps, 130, 131 ; climbing, 130; modified, 129, 130, 131 ; reduced, 130. Lens of eye, 410. Lenticels, use of, 102. Lepidoptera, 247. Leucocytes, alcohol upon, 423. Levers, classes of, 326 ; in body, 324. Lichens, 187. Life history, of beetle, 242 ; of butterfly, 237 ; of Cecropia, 239 ; of cicada, 243 ; of fly, 240, 241 ; of frog, 288, 289. 290 ; of honeybee, 254 ; of locust, 236 ; of shrimp, 227. Light, effect of, upon plants, 116, 116, 117. Lily, leaves of, 118. Liver, 362, 360. Living matter, composition of, 23. Living things, environment of, 17 ; functions and composition of, 26. Lizards, 294. Lobster, North American, 226. Locomotion, in crayfish, 222 ; in frogs, 286 ; in snakes, 295 ; of earthworm, 214. Locust, 234 ; relatives of, 236. Locule, 37. Lumber, transportation of, 137, 138. Lymph, function of, 375. Lymph vessels, 376. Macronucleus, 192. Malacostraca, 247. Malaria and the mosquito, 197, 258. Mammal, circulation in, 372 ; man a, 319. Mammals, 311 ; classification of, 317 ; hoofed, 316. Man, brain of, 401 ; circulation in, 370 ; evolution of, 319; place of, in nature, 319; races of, 320 ; stomach of, 363, 367. Mantis, 261. Mantle cavity, 267. Maxillipeds, 224. May flies, 245. MeduUa, 401. Medusa, 207, 208. Membrane, tympanic, 407. Mesoderm, 200. Mesophytes, 162. Metamorphosis, defined, 247. Metazoa, 199. Micronucleus, 192. Micropyle, of bean, 65 ; of ovule, 36. Mildews, 174. Milk, an emulsion, 369 ; and typhoid, 434 ; bacteria in, 180 ; necessity of pure, 432, 434. Milkweed, dispersal in, 80. Mimicry in insects, 261, 262. Mineral matter, in Uving things, 22. Molars, 366. MoUusks, classification of, 273 ; habitat of, 271 ; some common, 268, 269, 270. Molting, 228. Monarch butterfly, 237, 261. Monocotyledons 73. Mosquito and malaria, 196 ; and yellow fever, 259 ; kinds of, 197, 258; malarial, 197, 259, 269. AAA INDEX Mosses, 162. Mucus, 353. Muscle tissue, use of, 323. Muscles, and skeleton, 324 ; arrangement of voluntary, 322 ; extensor, 322 ; flexor, 322 ; nerve endings in, 323 ; structure of voluntary, 323. Mushrooms, 151. Mycelium, 149, 151. Myriapods, 246, 247. Nails, development of, 321, Narcotics, in common use, 417. Natural resources, conservation of, 15. Nectar glands, 38, 42. Nectar guides, 42. Nerve, optic, 409 ; parts of, 401. Nerve fibers, 399. Nerves, motor, 401, 402 ; sensory, 401, 402 ; vasomotor, 377. Nervous control, of blood vessels, 377; of heart, 377 ; of respiration, 384 ; of stomach, 358 ; of sweat glands, 392 ; organs of, 206. Nervous system, and sense organs, 399; cerebro-spinal, 400 ; divisions of, 399 ; function of, 328 ; governing stomach, 358 ; in birds, 302 ; in fishes, 279 ; in man, 328 ; of crayfish, 225 ; of frog, 402 ; of insects, 236 ; sympathetic, 402, 403. Neuroptera, 244, 247. Newt, 292. Nicotine, 349, 417. Nictitating membrane, 286. Nitrogen, in air, 17 ; Nitrogen, in plant growth, 94 ; properties of, 18. Nitrogen cycle, 186. Nitrogen-fixing bacteria, 94. Nucleolus, 29. Nucleus, 29 ; in amoeba, 193 ; in paramcecium, 191. Nutrients, 24, 330 ; fuel values of, 333 ; in beans, 67 ; uses of, 332. Nymph, 244. Oils, 24, 331. Ommatidia, 223. One-celled animals, 195. Operculum in fishes, 277. Opium, 417. Orchid, wild, 38. Order, defined, 157. Organ, defined, 26, 204. Organic and inorganic matter, 31. Organism, defined, 26. Organs of a plant, 27. Orthoptera, 247. Osculum, 201. Osmometer, potato, 90. Osmosis, 90 ; importance of, 91 ; of sugar, 106. Ostrich, African, 308. Ovipositor, 234. Ovule, development of, into seed, 37 ; fertilization of, 37. Oxidation, 19; heat the result of, 20 ; in germination, 77 ; in human body, 22 ; of carbon, 21 ; rapid, 22 ; slow, 20. Oxygen, evolved in starch making, 126, 147 ; preparation of, 18, 19 ; properties of, 19. Oyster, shell of, 268 ; and typhoid, 269. Palate, hard, 364. INDEX 445 Palate, soft, 364. Pancreas, position of, 362, 359; structure of, 359. Pancreatic juice, function of, 360. PapillaB, 355. Pappus, 64. Paramoecium, 191, 192; response to stimuli in, 191. Parapodia, 216. Parasites, 149. Parasitism in insects, 267. Pasteurizing, 178. Patent medicines, alcohol in, 360. Pearl formation, 270. ''Peepers," 291. Pepo, 63. Pepsin, 358. Peptone, 358 ; changed to proteid, 366. Pericardium, 370. Perspiration, insensible, 392. Petal, 34. Phagocytes, 369. Pharynx, 364. Phosphorus, in living matter, 331. Photosynthesis, 124. Physiology, human, defined, 13. Pigeon-wheat moss, 162. Pistil, 34, 36. Pitcher plants, 131. Plant, and animal compared, 26. Plant body, simplest, 144. Plant breeding, 81. Plant invasions, 168. Plant life, in temperate zones, 165; forms of, 144 ; in tropics, 164 ; upon mountains, 164. Plant modification, cold a factor in, 164; water a factor in, 160, 161, 162 ; wind a factor in, 163. Plant outpost, a, 169. Plant societies, 166, 167. Plants, beneficial and harmful, 171 ; classification of, 157 ; harm done by, 170 ; modified by surroundings, 159, 160 ; relations to animals, 13, 15, 184, 185, 186. Plasma of blood, 366. Plasmodium malaria;, 196. Pleura, 383. Pleurococcus, 148. Plumule, 66. Pocket garden, 85. Pollen, growth of, 35, 36. Pollen, protection of, 49. Pollination, 38 ; artificial, 50 ; by hunmiing bird, 43 ; by insects, 40 ; by water, 47 ; by wind, 46 ; history of, 37. Polycotyledon, 73. Polyphemus moth, 239. Polypody, 164. Polyps, coral, 209 ; hydroid, 208. Pond lihes, 169. Pond scum, 147. Potato tuber. 111. Premolars, 366. Proboscis, 43. Proglottids of tapeworm, 217. Prolegs, 238. Pronuba, 46. Protective resemblance, 249, 260 seasonal, 309. Proteid making in plant, 124. Proteids, 24, 67, 330 ; building of, 106. Prothallus, 154, 166. Protonema, 153. Protoplasm, composition of, 31 ; properties of, 32. Protozoa, 190; classification of, 198 ; habitat of, 195 ; relation to disease, 196 ; use as food, 195. Pseudopodia, 193. Pteridophytes, 157. Ptomaines, 177. Ptyalin, 357. Pulmonates, 271. Pulse, cause of, 374. Pupa, 238, 239. Pylorus, 367. 446 INDEX Radiolarian, 198. Ray flower, 44. Reflex action, nervous, 403. Regeneration, defined, 215. Relation, of alcohol to disease, 412 ; of bacteria to fermentation, 177 ; of birds and reptiles, 310 ; of bodily heat to work, 392 ; of breathing to exercise, 388 ; of environment to diet, 336 ; of flies to disease, 260, 261 ; of Protozoa to disease, 196 ; of spawning to economic value, 281; of work to diet, 336. Rennin, 358. Reptiles, study of, 293. Reptilia, characteristics of, 296 ; classification of, 297. Reproduction, in simple plants, 199 ; in simple animals, 199 ; Respiration, artificial, 389 ; effect of alcohol on, 395 ; effect of tobacco on, 396 ; excretion, 382 ; in a cell, 389, 390 ; in birds, 301 ; in crayfish, 224 ; in fishes, 277 ; in frog, 286 ; in insects, 236 ; necessity for, 382 ; nervous control of, 384 ; organs of, in man, 382. Rest, necessity of, 405, 427. Rhizoids, 149, 153, 155. Ribs, attachment of, 327 ; in respiration, 384. Rock fern, 154. Rodents, 313. Root, absorption in, 89 ; effect of moisture on, 85, 86 ; food storage in, 95 ; influence of gravity upon, 84 ; passage of soil water in, 90 ; tip of, 87. Root form, relation of, to plant, 95. Root hair, 88, 89. Root pressure, 107. Root system, 84. Roots, adventitious, 96 ; air, 97 ; and their work, 84 ; different from stems, 115; parasitic, 97 ; prop, of corn, 96 ; water, 96. Roundworms, 217. Salamander, spotted, 291. Saliva, function of, 356. Salmon leaping a fall, 281. Sand shark, 284. Sandworm, 216. Saprophytes, 149, 151. Sea anemone, 208. Sea lion, 313. Seasonal variation of plumage, 309. Seaweeds, 144, 145. Seed dispersal, 52, 53, 80. Seedling, defined, 79. Seeds, and seedlings, 65 ; formation of, 52 ; uses of, 80 ; winged, 55, 56. Selective absorption, 194. Selective breeding, 316. Selective planting, 81, 82. Self-control vs. appetite, 416. Self-pollination, 38. Sense organs, 206, 286, 236. Senses, in birds, 302 ; in fishes, 276 ; in man, 406. Serum of blood, 367. Sexual development of simple ani- mal, 200. Sexual reproduction, in animals, 192, 194, 203, 208, 209, 215, 280, 288; in plants, 148, 150, 153, 154, 156. Shelf fungus, a saprophyte, 173. Shipworm, damage by, 271. Shrimps, 227, 228. Skeleton, and muscles, 324 ; appendicular, 326, 327; axial, 326 ; of birds, 300 ; of dog, 325 ; of fishes, 279 ; INDEX 447 Skeleton, of man, 326 ; structure of, ii25 ; uses of, 325. Skeleton building in Protozoa, 198. Skin, hygiene of, 393 ; structure of, 321. Skull, of dog. 313 ; of man, 328; of porcupine, 314. Sleep, and health, 421 ; necessity of, 405. Smell, organs of, 407. Snail, forest, 270. Snake, garter, 294. Snakes, value of, 295 ; poisonous, 296. Soil, composition of, 21, 91 ; organic matter in, 92 ; water in, 91, 92; weathering of, 91. Soil exhaustion, prevention of, 95. Solution, Fehling's, 70 ; iodine, 66 ; nutrient, 93. Sound, character of, 409. Sparrow, P]nglish, 307 ; white-throated, 309. Species, defined, 157. Spermatophytes, defined, 156, 157. Sperm cell, 36, 199, 200, 208. Spiders, 245. Spinnerets of spiders, 245. Spiracles, 236. Spirogyra, 147. Sponge, structure of, 201. Sponges, 207. Sporangium, 149, 154. Spores, 149. Sporophyte, a parasite, 153 ; in fern, 155 ; in moss, 152. Squid, 270. Stamens, 34, 35. Starch, in bean, 66 ; non-osmosis of, 106 ; to grape sugar, 71 ; test for, 66. Starch grains, 66. Starch making, and milling, 123 ; Starch making, by green plants, 121 ; chemistry of, 124 ; light and air in, 122 ; rapidity of, 125. Starfish, 272. Stem, dicotyledonous, 101, 103 ; modified. 111; movement of fluid in, 106, 107 ; monocotyledonous, 108; structure and work of, 98. Stems, 112, 113. Stigma, 35, 69. Stimulants, 344. Stimuli, response to, in paramoecium, 191. Stomach, movement of walls of, 358 ; nervous control of, 358 ; of man, 363, 357. Stomata, 120, 128. Street cleaning, 432. Streets, condition of, 431. Struggle for existence, 57. Sturgeon, 284. Style, 35. Suffocation, 389. Sugar, consumption of, 109; osmosis of, 106. Sun, a source of energy, 119. Sundew, 130. Sunlight, in starch making, 122. Sweat, 392. Sweat glands, 321. Sweeping, 387. Swim bladder, 278. Swimmerets, 222. Symbiosis, 187; between plants and insects, 40, 257; in crabs, 230 ; in lichens, 187 ; in nitrogen-fixing bacteria, 94. Systematic botany, 157. Tadpoles, of frog, 290. Tail of birds, function of, 300. Tapeworms, 217. Taproot, structure, 87. Tarantula, 245. Taste, organs of, 406. Taste buds, 355, 406. 448 INDEX Teeth, canine, 313 ; incisor, 314 ; kinds of, in man, 355. Teleosts, 284. Temperature, feeling of, 406 ; in germination, 76. Tentacles, 202. Thallophytes, 157. Thallus, 144. Thallus plants, divisions of, 149. Thoracic duct, 377. Thorax, 234 ; in man, 327. Timber, cutting of, 138. Tissue, 28, 204, 322, 323. Tissues of human body, 204. Toad, common, 290. Tobacco, effect on circulation, 381 ; effect on nervous system, 349 ; effect on respiration, 396 ; use of, 348. Tongue, 354. Tooth, section of, 355. Tortoise, box, 294. Touch, organs of, 406. Tracheae, 235. Transpiration, in plants, 126, 127. Tree, wounded by "cribbing," 142. Trees, city's need for, 141. Trilliums, 168. Trypanosomes, 197. Tuberculosis, 180; death rate from, 428, 429 ; fighting, 436. Turtles, 293. Tussock moth, 263, 264. Typhoid fever, 181 ; due to milk supply, 434 ; due to water supply, 433 ; fighting, 434. Underwing moth, 250. Ungulates, 315. Urea, 393. Ureter, 390, 391. Urethra, 391. Uropod, 224. Vaccination, 431. Vacuole, contractile, 191, 192, 193. Vacuole, food, 191, 193. Veins, 370, 375. Ventilation, need of, 386 ; of sleeping rooms, 388 ; proper, 386, 387. Ventricle, 370. Venus's flower basket, 207. Venus's flytrap, 131. Vermiform appendix, 363. Vertebra, 326, 327. Vertebral column, 326. Vertebrates, compared with inver- tebrates, 274. Viceroy butterfly, 251. Villus, structure of, 362. Virginia deer, 315. Vorticella, 195. Walking stick, 249. Warning coloration, 251. Wasp, solitary, 253. Water, and health, 420 ; and typhoid, 433 ; composition of, 20 ; factor in germination, 76 ; in hygiene, 425 ; in living things, 23 ; necessity of pure, 432, 433. Water storage, in leaves, 130 ; in roots and stems. 111. Water supply, factor in modifica- tion, 160; regulated by forests, 133. Web, spiders', uses and forms, 246, Weed, 26. Wheat, production of, 59. Wheat rust, 174. Wing, of moth, 237. Wings, of grasshopper, 234. Wood, structure of, 138 ; uses of, 137. Worms, harmful, 216 ; study of adaptations, 212. Xerophytes, 160, 161. Yeast, 171, 172. Yellow fever, caused by mosquito, 259. Zygospore, formation of, 150. ( THIS BOOK IS DUE ON THE LAST DATE STAMPED BELOW RENEWED BOOKS ARE SUBJECT TO IMMEDIATE RECALL JUW2 13^^ WE MWu8?f^;ApY 3UE JUL JUL 6 REC'll 1970 LIBRARY, UNIVERSITY OF CALIFORNIA, DAVIS Book Slip-14,800-8,'66(G5531s4)458 1946 0H315 Hunter H8 Essentials of bloloar HUV 151934 NOV 3 019:)4. oc^>3 ni, ^^u.^i HZ \^^(c UNIVERSITY OF CAUFORNIA LIBRARY