Marine Biological Laboratory ReceivecL 16 7Tav '41 Accession No._ Given By_ Dr. B. lanson Rockefeller Foundation Place,_ "*-•-• 6 0 EXPERIMENTAL MORPHOLOGY THE MACMILLAN COMPANY NEW YORK • BOSTON • CHICAGO ATLANTA • SAN FRANCISCO MACMILLAN & CO., LIMITED LONDON • BOMBAY • CALCUTTA MELBOURNE THE MACMILLAN CO. OF CANADA, LTD. TORONTO 6 • *? • EXPERIMENTAL MORPHOLOGY BT CHARLES BENEDICT DAVENPORT, PH.D. INSTRUCTOR IN ZOOLOGY IN HARVARD UNIVERSITY Nefo gorfe THE MACMILLAN COMPANY LONDON: MACMILLAN & CO., LTD. 1908 All right* reserved COPYRIGHT, 1896, 1899, BY THE MACMILLAN COMPANY. Nsw edition, two parts in one volume, April, 1908. NortoooD J. 8. Gushing Co. — Berwick & Smith Co. Norwood, Mass., U.S.A. DeDtcateti TO THE MEMORY OF THE FIRST AND MOST IMPORTANT OF MY TEACHERS IN NATURAL HISTORY MY MOTHER Die morphologische Betrachtung setzt also eine genaue chemisch physikalische Kenntniss, 1. des betreffenden Kbrpers selbst, und 2. aller der bei seiner Entstehung auf ihn einwirkenden Stoffe und Kbrper voraus. — JAEGER, Zoologische Briefs, p. 9. La vie ne se con9oit que par le conflit des proprie"tes physico-chimiques du milieu exterieur et des proprietes vitales de 1'organisme reagissant les unes sur les autres. — BERNARD, Rapport sur les progres de la physiologic generate en France, 1867, p. 5. There can be little doubt, indeed, that every science as it progresses will become gradually more and more quan- titative. Numerical precision is doubtless the very soul of science, as Herschel says. — JEVONS, Principles of Science, chap. xiii. PREFACE THE problem which, since the time of Aristotle, has stood first in interest and importance among the great questions of Biology is that of the causes which direct the development of the individual — that marvellous process by which the germ is built up into the complex organism, by which the embryo clothes itself with the characters peculiar to its species, by which even minute individual traits of form and action are exactly reproduced in the offspring from its parents. The burden of clearing up this problem has fallen, naturally enough, upon the shoulders of students of morphology. For since morphologists deal with form, they are properly especially concerned with the interpretation of form — they may well be asked to account for it. Thus the problem of development is an acknowledged morphological problem. Several distinct steps can be recognized in the progress which has been made in the interpretation of form. The earlier studies were concerned chiefly with answering the ques- tion, What are the differences between the various adult forms ? The results of observations and reflections relating to this question constitute the sciences of descriptive and comparative anatomy. Next, a more fundamental inquiry was entered upon : How are these forms produced or developed ? The results of observations and reflections upon this subject con- stitute the science of comparative embryology. Finally, in these later days a still more fundamental question has come to the front : Why does an organism develop as it does ? What is that which directs the path of its differentiation ? This is the problem which the new school of " Entwicklungsmecha- nik " has set for itself — it is likewise the problem with which this book is concerned. Vll viii PREFACE The causes which determine the course of an organism's development are numerous, but fall into two general categories ; namely, internal causes, which include the qualities of the devel- oping protoplasm ; and external causes, which include the chemical and physical properties of the environment in which the protoplasm is developing. The internal and external causes may be studied separately, and in order to disentangle their effects they must needs be studied separately. It is the pur- pose of the present work to consider the effects resulting from external causes. When we wish to isolate the separate effects in any complex of causes, we must resort to the well-known procedure of experimentation, — and we find, indeed, that these external causes lend themselves readily to this method of treatment. Accordingly we call in experiment to get an insight into the causes of organic form, and thus justify the name which we have applied to our study, — Experimental Morphology. The primary subdivision of the subject is based upon the morphogenic processes to be treated of ; and of these, four principal classes may be recognized. The first includes those processes which are characteristic of all living protoplasm; the second, those connected with growth ; the third, those involved in cell-division ; and the fourth, those producing differentiation. It is proposed to devote one part of the work to each of these four classes of processes. The secondary subdivision may be based upon the chemical and physical agents whose effects we wish to isolate. These may be grouped into eight categories, determined largely by convenience ; namely, 1, chemical substances ; 2, water ; 3, den- sity of the medium ; 4, molar agents ; 5, gravity ; 6, electri- city ; 7, light ; and 8, heat. It is proposed to devote one chapter to a consideration of the effects of each of these agents upon protoplasm, upon growth, upon cell-division, and upon differentiation. Two words should be said about the point of view from Avhich this book has been written. In the first place, the developing organism is regarded as a living organism, and as such endowed with irritability and capacity of response ; con- sequently, at the outset, we must especially consider the phe- PREFACE ix nomenon of response to external stimuli. Again it is with living organisms that we have to deal, and, accordingly, no distinction should be made between animals and plants. I have, indeed, made no such distinction ; nevertheless, tastes and training have led me to lay especial stress upon animals. Even this is unfortunate, for the problem with which we are concerned is precisely the same problem in all living organisms. In the second place, much stress is laid upon the quantitative measurement of agents and effects. The lack of precision in many investigations can hardly be too strongly decried ; for it often results in confusion and useless disputes. On the other hand, there is good reason for believing that exact measure- ment is the key to many of the most puzzling of our problems, and important results are to be expected from its use. As for the aim of the book, it is twofold. I have hoped on the one hand that it might be readable to those who are inter- ested in the general matters of which it treats -- matters of importance for philosophy, for psychology, and for pedagogy,, For man is an organism, and the development of his qualities is modified by just those agents which guide the development of other organisms. My primary aim, however, has been a dif- ferent one. It is this aim to which other purposes have been made subservient, which justifies the historical treatment that has been often adopted, and justifies also the detailed descrip- tions of methods which the lay reader will, naturally, omit. This aim is so to exhibit our present knowledge in the field of experimental morphology as to indicate the directions for further research. A few words of explanation and acknowledgment are neces- sary : It was planned at the first to issue all four parts of the work at once ; but the task grew in the doing, while the need of its publication became more pressing. So it was' decided to issue the work in parts as soon as each should be done. Even under this arrangement it has not been possible to include some of the papers of the last six months ; especially I regret the omission of important papers by VERWORN and LOEB upon Galvanotaxis. In writing a book of this sort, which draws upon several sciences, I have had recourse to the kind assistance of several of my colleagues in the physical and x PREFACE chemical departments of the University. I must especially thank for favors Professor W. C. SABINE, Dr. G. W. COGGESHALL, and Dr. H. E. SAWYER. Of my zoological associates, I am greatly indebted to Dr. G. H. PARKER, who has read nearly the entire manuscript and has offered valuable criticisms on it, and to Professor E. L. MARK, who has read parts of the manuscript and proof and has made important suggestions and emendations. I am also greatly indebted to Mr. CHARLES BULLARD for his kindness in making photo- graphs of figures from which most of the illustrations of the First Part were reproduced. Finally, I cannot forbear to men- tion the painstaking work of my wife, GERTRUDE GROTTY DAVENPORT, in preparing the manuscript for the press and revising the proofs. As I send out this work I do so with the hope that it may stimulate to even greater activity in the field of experimental morphology. The subject is new, its importance hardly yet generally recognized, its needs incompletely appreciated. In its scope it embraces much of physics and chemistry, for life and development are to be studied as the physicist studies light and heat, or as the chemist studies solutions and combustion. They are phenomena which must be analyzed by the use of instruments of precision to determine the quality and quantity of the acting agents, and to measure the change in the phe- nomena resulting from a change in these agents. No other field offers a better opportunity for the utilization of a broad scientific training. The times, too, are auspicious. Biology has never before attracted so many enthusiastic workers as it does to-day. As DRIESCH has said, u Die Lust an thatsach- licher exacter biologischer Forschung ist erwacht"; and the greatest problem of morphology is ever more and more the object of this biological experimentation. CHARLES BENEDICT DAVENPORT. CAMBRIDGE, MASS., Dec. 1, 1896. vlSfc^W •^ ^--rs~ PREFACE TO PART II DEVELOPMENT consists of growth and differentiation, accom- panied in the larger organisms by nuclear- and cell-division. The present Part deals with growth. The importance of the study of growth cannot be over- estimated, and it is a cause for wonder that the treatment of the subject has been so much neglected by text-books. Indeed, it is a surprising fact that it has not been thoroughly and sys- tematically investigated. For, in last analysis, the maintenance of the human race depends upon that property which protoplasm among all substances alone displays of increasing itself for an indefinite time and to an indefinite amount. And the possibil- ity of increasing the human race be}rond limits that are not far off depends upon a better knowledge of the conditions of growth. The reader has only to consider that the world's supply of 2500 million bushels of wheat, 2000 million bushels of maize, 90 million tons of potatoes, and its untold millions of tons of beef, pork, and fish are reproduced each year by growth. The mineral matters of the soil are being washed out into the sea and are largely lost, but the capacity of growth under appropriate conditions is never lost ; it redoubles as the amount of the growing substance is increased. The only thing, then, which limits growth is the limitations in the conditions of growth. What are these conditions ? This is the important question to which attention has been directed in this Part. Aside from this practical interest, the study of growth is important as bearing on the question of the dependence of vital activities, and especially development, upon external conditions, za XJ PREFACE and the possibility of the control of development by appropri- ately altering those conditions. Growth phenomena show them- selves, indeed, particularly susceptible to this control, and are consequently especially valuable for experimental study. In the preparation of the Second Part, I have been put again under heavy obligations to my friend and colleague, Dr. G. H. PARKER, who has read most of the manuscript and made important suggestions. I am also indebted to Dr. H. E. SAW- YER for reading Chapter XI in the manuscript, and to my wife for much painstaking work on the manuscript and proofs and for compiling the index. C. B. D. CAMBKIDGK, MASS., Dec. 11, 1898. CONTENTS PAGE PREFACE • vii CHAPTER I ACTION OF CHEMICAL AGENTS UPON PROTOPLASM § 1. Modification of Vital Actions 1 1. Oxygen .......... 2 2. Hydrogen 5 3. Oxides of Carbon ......... 6 4. Ammonia .......... 6 5. Catalytic Poisons ......... 7 6. Poisons which form Salts 12 a. Acids 12 b. Soluble Mineral Bases 13 c. Salts of Heavy Metals 13 7. Substitution Poisons . . . . . • • .15 8. Sodic Fluoride ......... 21 9. Special Poisons § 2. Acclimatization to Chemical Agents .... .27 § 3. Chemotaxis 32 Summary of the Chapter .45 Appendix to Chapter I 52 Literature ............ 54 CHAPTER II EFFECT OF VARYING MOISTURE UPON PROTOPLASM § 1. On the Amount of Water in Organisms . ... 58 §2. On the Effect of Desiccation upon the Functions of Protoplasm . 59 1. Effect of Dryness on Metabolism . . .59 2. Effect of Dryness upon the Motion of Protoplasm . . 60 3. Desiccation-rigor and Death .60 § 3. On the Acclimatization of Organisms to Desiccation ... 65 § 4. The Determination of the Direction of Movement by Moisture — Hydrotaxis • 66 Literature 67 xi xii CONTENTS CHAPTER III ACTION OF THE DENSITY OF THE MEDIUM UPON PROTOPLASM PAOE § 1. Introductory Remarks upon the Structure of Protoplasm and the Physical Action of Solutions 70 § 2. Effect of Varying Density upon the Structure and General Functions of Protoplasm ....... 74 § 3. Acclimatization to Solutions of Greater or Less Density than the Normal 85 § 4. Control of the Direction of Locomotion by Density — Tonotaxis . 89 Literature 93 CHAPTER IV ACTION OF MOLAR AGENTS UPON PROTOPLASM § 1 . Effect of Molar Agents upon Lifeless Matter .... 97 § 2. Effect of Molar Agents upon the Metabolism and Movement of Protoplasm 98 § 3. Effect of Molar Agents in Determining the Direction of Locomo- tion — Thigmotaxis (Stereotaxis) and Rheotaxis . . . 105 Literature 110 CHAPTER V EFFECT OF GRAVITY UPON PROTOPLASM § 1. Methods of Study 112 § 2. Effect of Gravity upon the Structure of Protoplasm . ; .113 § 3. Control of the Direction of Locomotion by Gravity — Geotaxis . 114 Literature 124 CHAPTER VI EFFECT OF ELECTRICITY UPON PROTOPLASM § 1. Concerning Methods 126 § 2. The Effect of Electricity upon the Structure and General Func- tions of Protoplasm 129 § 3. Electrotaxis 140 Summary of the Chapter 151 Literature 152 CONTENTS xiii CHAPTER VII ACTION OP LIGHT UPON PROTOPLASM PAGE § 1. The Application and Measurement of Light .... 154 § 2. The Chemical Action of Light upon Non-living Substances . 161 1. The Synthetic Effects of Light 162 2. Analytic Effect of Light 163 3. Substitution Effects of Light 164 4. The Isomerismic and Polymerismic Changes produced by Light 164 § 3. The Effect of Light upon the General Functions of Organisms . 166 1. Effect of Light upon Metabolism .. .166 a. The Thermic Effect of Light on Metabolism . . 166 b. The Chemical Effect of Light on Metabolism . . 170 2. Vital Limits of Light Action on Protoplasm . . . 171 3. Effect of Light upon the Movement of Protoplasm . . 175 a. Effect of Low Intensity of Light on Movement — Dark- rigor 175 b. Effect of High Intensity of Light on Movement — Light-rigor ........ 178 §4. Control of the Direction of Locomotion by Light — Phototaxis and Photopathy IbO 1. False and True Phototaxis 181 2. Distribution of Phototaxis and Photopathy .... 182 a. Protista 182 b. Cells and Cell-organs 189 a. Chlorophyll Bodies . . . . . .189 /3. The Rearrangement of Pigment in Animal Cells in Response to Light 192 y. The Migration of Pigment Cells in the Metazoan Body 193 c. Metazoa 194 3. The General Laws of Phototaxis and Photopathy . . 196 a. The Sense of the Response 196 b. The Effective Rays 201 c. Phototaxis vs. Photopathy . . . . » . . 203 d. The Mechanics of Response to Light .... 207 Summary of the Chapter 210 Literature 212 xiv CONTENTS CHAPTER ACTION OF HEAT UPON PROTOPLASM PAGE § 1. Nature of Heat and the General Methods of its Application . 219 § 2. The Effect of Heat upon the General Functions of Organisms . 222 1. Effect of Heat upon Metabolism ...... 222 2. Effect of Heat upon the Movement of Protoplasm and its Irritability ......... 225 § 3. Temperature-Limits of Life ....... 231 1. Temporary Rigor and Death at the Higher Limit of Tem- perature, Maximum and Ultramaximum .... 231 2. Temporary Rigor and Death at the Lower Limit of Tempera- ture, Minimum and Ultraminimum ..... 239 § 4. Acclimatization of Organisms to Extreme Temperatures . . 249 1. Acclimatization to Heat ....... 249 2. Acclimatization to Cold ....... 257 § 5. Determination of the Direction of Locomotion by Heat — Ther- motaxis ......... . . 258 .Notes to Table XXI .......... 263 Literature ............ 267 CHAPTER IX GENERAL CONSIDERATIONS ON THE EFFECTS OF CHEMICAL AND PHYSICAL AGENTS UPON PROTOPLASM § 1. Conclusions on the Structure and Composition of Protoplasm . 274 § 2. The Limiting Conditions of Metabolism ..... 275 § 3. The Dependence of Protoplasmic Movement upon Metabolism and upon External Stimuli ....... 277 § 4. The Determination of the Direction of Locomotion . . . 278 CONTENTS CHAPTER X PAGE INTRODUCTION : ON NOKMAL GROWTH 281 CHAPTER XI EFFECT OF CHEMICAL AGENTS UPON GROWTH § 1. Effect of Chemical Agents upon the Rate of Growth . . . 293 1. The Materials of which Organisms are composed . . . 294 a. Analysis of the Entire Organism 296 b. Detailed Account of the Various Elements used as Food 304 Oxygen, 304; Hydrogen, 306; Carbon, 306; Nitro- gen, 307 ; Phosphorus, 313 ; Arsenic, Antimony, and Bismuth, 314; Sulphur, 314; Chlorine, 316; Bromine, 316 ; Iodine, 317 ; Fluorine, 317 ; Lith- ium, 318; Sodium, 318; Potassium, 318; Rubidium and Caesium, 320; Strontium, 321 ; Manganese, 321 ; Iron, 321 ; Magnesium, 323 ; Silicon, 324 ; Copper, 324. 2. The Organic Food used by Organisms in Growth . . . 324 a. Fungi 324 b. Green Plants 326 c. Animals .......... 327 Amoeba, 328; Amphibia, 329 ; Mammals, 330. 3. Growth as a Response to Stimuli 331 a. Acceleration of Growth by Chemical Stimulants . . 331 b. The Election of Organic Food 333 § 2. Effect of Chemical Agents upon the Direction of Growth — Chemo- tropism 335 1. Chemotropisrn in the Tentacles of Insectivorous Plants . 335 2. Chemotropism of Roots 336 3. Chemotropism of Pollen-tubes 337 4. Chemotropism of Hyphae 340 5. Chemotropism of Conjugation Tubes in Spirogyra . . 342 Literature 343 xv xvi CONTENTS CHAPTER XII THE EFFECT OF WATER UPON GROWTH PA6B § 1. Efect of Water upon the Rate and Quantity of Growth . 350 § 2. Effect of Water on the Direction of Growth — Hydrotropism . 355 1. Roots .... .356 2. Rhizoids of Higher Cryptogams . . 357 3. Stems 358 4. Pollen-tubes 358 5. Hyphse of Fungi 358 Literature 360 CHAPTER XIII EFFECT OF THE DENSITY OF THE MEDIUM UPON GROWTH § 1. Effect of Density upon the Rate of Growth 362 Literature 369 CHAPTER XIV EFFECT OF MOLAR AGENTS UPON GROWTH § 1. Effect of Molar Agents upon the Rate of Growth . . . 370 1. Contact ........... 370 2. Rough Movements 370 3. Deformation .......... 372 4. Local Removal of Tissue 375 § 2. Effect of Contact upon the Direction of Growth — Thigmotropism 376 1. Twining Stems 376 2. Tendrils .377 3. Roots 380 4. Cryptogams 381 5. Animals . . . . • • • • • • 382 6. The Accumulation of Contact-stimulus and Acclimatization to it .382 7. Explanation of Thigmotropism ...... 383 § 3. Effect of Wounding upon the Direction of Growth — Trauma- tropism ........ • 384 1. False Traumatropism .... . 384 2. True Traumatropism .... . . 384 § 4. Effect of Flowing Water upon the Direction of Growth — Rheo- tropism ........... 387 Summary of the Chapter ......... 388 Literature • 389 CONTENTS CHAPTER XV . EFFECT OF GRAVITY UPON GROWTH PAGE § 1. Effect of Gravity upon the Rate of Growth 391 § 2. The Effect of Gravity upon the Direction of Growth — Geotropisra 391 1. False Geotropism 392 2. True Geotropism 392 a. Roots 392 b. Stems 397 c. Rhizoma 398 d. Cryptogams 398 e. Animals 398 /. After-effect in Geotropism 401 Summary 402 Literature 403 CHAPTER XVI EFFECT OF ELECTRICITY UPON GROWTH § 1. Effect of Electricity upon the Rate of Growth .... 405 §2. Effect of Electricity upon the Direction of Growth — Electro- 409 tropism ........... 409 1. False and True Electrotropism 409 2. Electrotropism in Phanerogams ...... 411 3. Electrotropism in Other Organisms 412 4. Magnetropism 413 5. Explanation of Electrotropism and Summary . . . 413 Literature 414 CHAPTER XVII EFFECT OF LIGHT UPON GROWTH § 1. Effect of Light on the Rate of Growth 416 1. Retarding Effect of Light 416 2. Accelerating Effect of Light 423 3. The Effective Rays 427 a. The Effective Rays in the Retardation of Growth by Light 427 b. The Effective Rays in the Acceleration of Growth by Light 432 4. The Cause of the Effect of Light on the Rate of Growth . 436 § 2. Effect of Light upon the Direction of Growth — Phototropism . 437 1. Plants 437 2. Animals 442 a. Serpulidse 442 b. Hydroids 443 xviii CONTENTS PAGE 3. General Considerations 444 a. Persistence of Stimulation ...... 444 b. Acclimatization to Light .....*. 444 c. Mechanics of Phototropisni ...... 444 Literature ............ 445 CHAPTER XVIII EFFECT OF HEAT ON GROWTH § 1. Effect of Heat on the Rate of Growth 450 1. Plants 450 2. Animals 457 3. Some General Phenomena accompanying Heat Effects . . 460 a. Latent Period 460 b. Sudden Change of Temperature 460 c. Cause of Acceleration of Growth by Heat . . . 461 §2. Effect of Heat on the Direction of Growth — Thermotropism . 463 1. Effect of Radiant Heat 463 2. Conducted Heat 464 3. Causes of Thermotropism 466 Summary of the Chapter 467 Literature .... 467 CHAPTER XIX EFFECT OF COMPLEX AGENTS UPON GROWTH, AND GENERAL CONCLUSIONS § 1. The Cooperation of Geotropism and Phototropism . . . 470 § 2. Effect of Extent of Medium on Size 473 § 3. General Considerations relating to the Action upon Growth of External Agents 478 1. Modification of Rate of Growth 478 2. Modification of Direction of Growth — Tropism . . . 480 3. Adaptation in Tropisms 484 4. Critical Points in Tropism 484 Literature 486 LIST OF TABLES IN PARTS I AND II 489 INDEX TO PARTS I AND II . . .* 493 EXPERIMENTAL MORPHOLOGY EXPERIMENTAL MORPHOLOGY CHAPTER I I ACTION OF CHEMICAL AGENTS UPON PROTOPLASM IN this chapter it is proposed to consider (I) the effect of the various chemical agents upon the chemical constitution of protoplasm, as revealed by the results of their application, — death, modification of the metabolic processes, and of rate of movement ; (II) the phenomena of acclimatization to chemi- cal agents ; and (III) the effect of such agents in determining the direction of locomotion, — chemotaxis. § 1. MODIFICATION OF VITAL ACTIONS* The vital processes are chemical processes, taking place in a highly complex, very unstable, constantly changing substance, whose activities we call life. It is not easy to study this living substance chemically by the ordinary methods ; for these usually, first of all, kill the substance. That the living substance and the dead are quite different is illustrated, for example, in the action of diamid (N2H2) and hydroxylamine (NH2— O — H), which show no action upon dead protoplasm, but are powerful poisons for all living plasm. The instability of protoplasm enables us, on the other hand, to make use of * In the preparation of this section, much use has been made of the admirable work of LOEW ('93). Not only is the adopted classification of poisons for the most part his, but also, in a few cases, passages from his book have been translated in toto here. Most of the determinations of killing strengths of the various re- agents for which no other authority is given have been taken from LOEW'S book. B 1 2 CHEMICAL AGENTS AND PROTOPLASM [Cn. I certain indirect means for determining its constitution. Since death is due to chemical change, we ought to determine what substances are fatal poisons to protoplasm ; and since every activity of protoplasm is a chemical process, we ought to study the modifications of these processes by the action of various chemical reagents. In studying the behavior of protoplasm in the presence of various reagents, we shall make use especially of observa- tions upon Protista, sexual cells, and tissue cells. In cases where sufficient observations on isolated plant or animal cells are wanting, use will be made of observations upon Metazoa. At the outset, attention should be called to the necessity of a more quantitative study of the subject. A quantitative study demands, especially, a careful noting of the conditions of the experiment ; for the various physical conditions under which the reagent is applied modify the result. Thus, it has been shown, for example, by RICHET ('89, p. 212) that with various poisons the toxic dose diminishes in amount with the elevation of the temperature of the body. 1. Oxygen. — It is almost certain that no protoplasm can long survive in the absence of oxygen. Apparent exceptions are found in the case of the anaerobic bacteria, some of which are killed in the presence of free oxygen, but multiply rapidly when the oxygen supply is cut off. It has been suggested that, in the case of these and some other parasitic organisms, ox}rgen is derived from the breaking down of O-containing compounds in the nutritive medium. (Cf. LOEW, '91, p. 760.) The effect of diminished oxygen upon protoplasm is described by CLARK ('89, pp. 370, 371) and by DEMOOR ('94, p. 191). CLARK determined the minimum oxygen pressure necessary for the vital movements of the plasm odia of Myxomycetes and the protoplasm of plant hairs and tissue cells. This he found to range from 1 mm. (plasmodia of Myxomycetes) to 3 mm. (leaf hairs of Urtica) of mercury. DEMOOR * subjected Tradescantia stamen hairs, in water, to a * In studying the effect of a vacuum, DEMOOR employed a piece of apparatus constructed essentially on the plan of an ENGELMANN'S chamber. This consists of a box whose top is a centrally perforated metallic diaphragm and whose bottom is a circular glass. The vertical walls consist of an outer cylinder, at § 1] MODIFICATION OF VITAL ACTIONS 3 pressure of 6 to 8 cm. of Hg, or 0.08 to 0.1 of an atmosphere (p. 71). In one hour, on the average, the protoplasmic move- ments were affected, and in most cells ceased in 2 to 3 hours, slight oscillations only of granules occurring. Thus, not death, but arrest of activity, occurred during this period as a result of reduction of atmospheric pressure — upon which the amount of oxygen held in the water depends. That death did not occur is shown by the fact that when air was readmitted at the normal pressure the protoplasm promptly regained its nor- mal activity. Cells immobilized during 24 hours regain their movements in less than 5 minutes, and these become normal in from 10 to 20 minutes. Pure oxygen acts in an opposite fashion from diminished oxy- gen tension, exaggerating the activity of protoplasm. Under its action the protoplasmic movements are much accelerated, but preserve, meantime, their normal character. (Tradescantia hairs, leucocytes; DEMOOR, '94, pp. 192, 218.) In Ciliata the rate of the contractile vesicle does not, however, seem to be altered. (RossBACH, '72, p. 40.) Ozone and hydrogen peroxide produce atomistic "active" oxy- gen by becoming split up in the plasma. Ozone (O3) is said to kill quickly bacteria in Avater, if the latter does not contain too much organic substance ; in the dry state, however, bacte- ria are injured only slowly by it. (OHLMULLER, '92, p. 861.) Other substances which, with a greater or less degree of probability, may be said to act through oxidation of the pro- toplasm, may be treated of here. Hydrogen peroxide (H2O2). — PANETH ('89) added one part of neutralized H2O2 to 10,000 (0.01%) of hay infusion, and found that all Ciliata were dead within 15 to 30 minutes. Stronger solutions act more rapidly ; and even in a 0.005% solution, only part of the animals survived. Algte survived only 10 to 12 hours in a completely neutral 0.1% solution. A 10% solution is fatal in a few minutes. (Cf. BOKORNY, '86, p. 355.) Salts of chromic, manganic, permanganic, and hypochlorous the periphery of the diaphragm, and an inner cylinder at the inner margin of the diaphragm. An inlet and an outlet tube communicate with each of the spaces, — the central space and that between the two cylinders. 4 CHEMICAL AGENTS AND PROTOPLASM [Cn. I acids act as intense poisons, apparently by directly yielding oxygen atoms to the plasma proteins. Sodic chromate (Na2CrO4). - - Many anferobic Schizophytes are killed even by a 0.05% solution of this salt. Splenic fever bacteria do not develop in a 0.05% solution in bouillon; in an agar-agar solution, they do not cease to develop until a con- centration of 0.5% is reached, although they no longer produce spores in a 0.05% solution. Sodic chromate also acts strongly on algre. (LoEW, '93, p. 16.) Potassic dichromate (K2Cr2O7). — A 0.1% solution kills algse (Spirogyra) in a few hours. Potassic permanganate (KMnO4) is an energetic poison for alga3 and Infusoria. A 0.2% solution kills Infusoria (Para- mecium) in one minute. Chlorine, bromine, and iodine, as well as hypochlorous acid salts, act, even in very considerable dilution, fatally upon all organisms, by splitting water, forming hydro- halogen com- pounds, and leaving the oxygen to unite with the living proto- plasm. The action of bromine upon glucose may be written — C6H1206 + Br2 + H20 = CaK^O, + 2 HBr. glucose. (LoEW, '93, p. 15.) BINZ has pointed out that (on Infusoria) the poisonous action of these three halogens, like their other chemical prop- erties, diminishes with increase of atomic weight, in the series Cl, Br, I. (Compare the osmotic effects of the halogens, p. 72.) Potassic chlorate (KC1O3) — also similar salts of I and Br — oxidizes in an essentially different fashion from the permanga- nates. For the latter oxidize even dead organic matter, but the former does not. This reagent may be considered a pas- sively oxidizing one. Concerning its visible effects, we rind that bacteria in general are injured by a 2% solution; with weaker solutions in nutrient media the bacteria reduce it to KC1. The anaerobic forms are affected by a 0.5% solution; the aerobic withstand up to 3%. Algte (Spirogyra) die after a few days in a 0.01% solution of the salt. (LoEW, '93, p. 17.) Arsenious acid (H8AsO3) and to a less degree arsenic acid (H3AsO4) are poisons which BINZ and SCHULZ ('79) believe § 1] MODIFICATION OF VITAL ACTIONS 5 to act by oxidizing the protoplasm. Thus H3AsO3 can take up free oxygen as it would be found in water, and it can part with it readily to the protoplasm, thus oxidizing and eventually wholly consuming it. Such is one theory of its action. A few words as to effects upon Protista: Infusoria survive in 0.1% potassic arsenite in spring water only a short time, but live for weeks in a 0.1% solution of the potassic arsenate. (LoEW, '83, p. 112.) Algse (Spirogyra) are killed by a 0.1% solution of potassic arsenite in six days, — the protoplasm contracts and shows formation of granules, the death of the chlorophyll bands preceding that of the cytoplasm. The same solution of potassic arsenate, meantime, shows no injurious action, (LoEW, '87, p. 445.) Still other arsenious acid salts tried upon other algae (Zygnema, Diatomacea), upon Infusoria, and upon tadpoles showed themselves, uniformly, more powerful agents than the corresponding arsenic salts. The lower fungi are only slightly affected by arsenious salts ; not at all by those of arsenic acid. 2. Hydrogen. — KUHNE ('64, p. 52) subjected Amoeba to H for 24 minutes. At the end of that time, some individuals had assumed a spherical shape, others appeared unchanged in form, but were motionless. Similar results were obtained with Actinophrys, the plasmodium stage of Myxomycetes, and with the stamen hairs of Tradescantia. DEMOOR ('94, p. 190) also experimented upon t}ie latter object, and his results are worth giving in detail.* During the first moments of the passage of the gas, the protoplasmic movements are slightly accelerated. Soon the protoplasm be- comes very granular, and, after a variable time, 15 to 40 minutes, is quiet. The aspect of the protoplasm at this time varies with the character of the cell. If it is young, having a large nucleus and without a primordial utricle, the protoplasm ap- pears uniformly granular. If, on the contrary, the cell possesses a great reserve of water, with long, protoplasmic filaments, the protoplasmic granules become more refringent, increase in volume, and accumulate around the nucleus, — the peripheral * Method : The hydrogen gas may be generated in a KIPI-'S apparatus, and should pass through a series of washing flasks containing, e .CH-CH2OH CH 3>COH-CH3 amylic, norm CH3 . CH2 . CH2 . CH2 - CH2OH allylic CH2.CH-CH2OH t Ostracoda only ; the Infusoria died after 18 hours. 12 CHEMICAL AGENTS AND PROTOPLASM [Cn. I TABLE III TIME (IN HOURS) OF RESISTANCE PERIOD OF SPIROGYRA COMMDNIS TO VARIOUS ALCOHOLS STRENGTHS. 0.005% 0.01% 0.05% 0.1% 0.5% 1.0% 2.0% 3.0% 4.0% methylic 120 96 48 ethylic 72 72 48 propylic, norm. . 72 propylic, iso. . . . 48 butylic, norm. . . 72 48 butylic, iso. . . . 96 48 butylic, tertiary. 48 amylic, norm. . . 24 allylic 66 72 24 24 From these experiments it appears that allylic alcohol is more injurious than the others, so that TSUKAMOTO ('95, p. 281) believes it to attack the protoplasm directly rather than to act merely catalytically. We see also that the rule enunciated above about the greater activity of substances with more com- plex alkyls holds true in general. Of the butylic alcohols the normal is the most poisonous ; the tertiary, least. Carbonic disulphide (CS2) is one of the more powerful cata- lytic poisons. A saturated aqueous solution, which contains only a trace of CS2, nevertheless kills quickly algse, bacteria, and the lower water animals. (LoEW, '93, p. 29.) 6. Poisons which form Salts. — This is the third group recog- nized by LOEW. In this case we have to do with acids and bases which unite with the protein substances of the pro- toplasm-producing salts. Thus disturbances leading to death are produced. In addition this group comprises the poisonous metallic salts. So we may recognize three groups : a. acids; b. the soluble mineral bases ; c. salts of heavy metals. a. Acids.- -The strong inorganic acids act, in general, more powerfully than the organic. Most bacteria, alg;e, and Infusoria are very sensitive to inorganic acids (see MIGULA, '90), but splenic fever bacteria resist 1% HC1 for 24 hours, and their spores 2% HC1 for 48 hours. Mold withstands 1% phos- phoric acid. Certain tissues have gained a high resistance capacity to inorganic acids. Thus, the gland cells of marine § 1] MODIFICATION OF VITAL ACTIONS 13 Gastropoda (Dolium, Cassis, Tritonium, Natica heros) secrete 2% to 3% H2SO4. (LoEW.) To organic acids many algse are little resistant. Thus Spiro- gyra and Splueroplea die in 0.1% malic or tartaric acid after 30 minutes ; in 0.05% malic or tartaric acid after 24 hours ; in 0.01% of these same acids in a few days. Formic acid pre- vents development of bacteria even in small percents — 0.05% to 0.006%. On the other hand, some protoplasm has acquired a resistance to organic acids. The vinegar eel - - Rhabditis aceti — lives in 4% acetic acid. The protoplasm of the Dro- sera tentacle resists 0.23% tartaric, citric, and other organic acids. b. Soluble mineral bases, including those of corrosive alkalies and the alkaline earths : Ca, Ba, and Sr. The corrosive alka- lies cause a swelling of the protoplasm, but the primary effect is rather a chemical one. (Cf. FROMANN, '84, p. 90.) The lower water animals and plants are quickly killed by 0.1% potassic or sodic hydrate. Thus, the movements of Chara cease in 0.05% KOH in 35 minutes. Bacteria are more resistant ; the limit for the typhus bacilli being between 0.10% and 0.14%, and for the cholera bacillus, between 0.14% and 0.18%. Ascaris is still more resistant, living for 20 minutes in a 2% solution of NaOH. CaO is still more powerful. A 0.007% to 0.025% solution in bouillon kills bacilli. A 0.013% solution is fatal to algse like Spirogyra. K2CO3 kills bacteria in 0.8% to 1.0% solutions. Na2CO3 kills Ascaris in a 5.8% solution after 5 to 6 hours. (LoEW, '93, pp. 33, 34.) FROMANN has discussed the histo- logical changes in protoplasm after treatment in Na2CO3. It is difficult to say whether the action of some of these re- agents may not be an osmotic, rather than a chemical one. The action of Na2CO3, for example, as described by FROM ANN, is very similar to that of NaCl, whose action is probably solely osmotic. c. Salts of Heavy Metals. — The method of action of these poisons has been accounted for upon the following grounds : When amido-acids (which are found as disintegration products of all animal tissues) are treated with salts of the heavy metals, 14 CHEMICAL AGENTS AND PROTOPLASM [Cn. I the hydrogen in either the carboxyl-group or the amido- group can be replaced by the metal. Likewise the hydrogen of the amido-group in urea derivatives and many bases are replaceable by metals. In the still more complicated protein stuffs the H bound to the N or O can be replaced. Many metals, indeed, like silver or mercury replace preferably the H of the amido-groups, and on this account, perhaps, their salts are especially poisonous. (LoEW, '93, p. 34.) Salts of Hg, Ag, and Cu cause death to Spirogyra even in a dilution of 1 : 1,000,000 ; the chlorophyll bodies being first affected.* Upon the bacteria of splenic fever the double cyanides of Ag, Hg, and Au are the most injurious, next those of Cu, Pb, and Zn, and, finally, those of Pt, Ir, and Os. Tad- poles and Tubifex are killed in 24 hours by solutions of CuSO4 weaker than 0.00005%. (LoCKE, '95, p. 327.) Among mer- curic salts, splenic fever bacteria do not develop in 0.0003% HgCl2 in nutritive bouillon, nor 0.0125% in blood. Lactic acid bacteria do not reproduce in 0.0007%. Mold spores are killed in * In this connection reference must be made to the posthumous paper of NAGELI ('93), " Ueber oligodyuarnische Erscheinungen in lebenden Zellen." This author found that water distilled in copper vessels or 1 litre of water in which 12 clean copper coins had stood for four days acted fatally upon Spiro- gyra. The water was found in one such case to contain 1 part Cu in 77,000,000 of water. It was believed to be in solution in the form of the hydroxyd (CuHoOa). Similarly produced solutions of other metals, Ag, Zn, Fe, Pb, Hg, had a simi- larly fatal effect upon Spirogyra. NAGELI believed that the effect of the metals was not a chemical one, but was due to a new force — " oligodynamic." Besides the fact of the action of very dilute solutions, the only evidence he adduced for the new force was based on the difference of action on the chlorophyl bands of solutions of 1 : 1000 or 1 : 10,000 and 1 : 10,000,000. In the weaker solutions ("oligodynamic" action) the bands alone were drawn away from the cell-wall, in the stronger solution (chemical action) the whole peripheral protoplasm was shrunken away. It does not seem necessary to invoke a new force to explain the action of weak solutions: first, because the two actions are not sharply separated, according to NAGELI'S own data ; secondly, because the chlorophyll bands are in general more sensitive than the rest of the protoplasm (p. 5) ; and, thirdly, because the action of so weak a solution is not surprising in view of the fact that Spirogyra is one of the least resistant of organisms. Even in a comparatively resistant organism, like Stentor, a solution of 1 : 80,000,000 HgCl2 produces acclimatization to the poison and 1 : 10,000,000 has an injurious effect. Yet between the action of such solutions and those of 1 : 1000 there is a complete graduation in increasing effect. (See p. 30.) Even in NAGELI'S experiments solutions of less than 1 : 100,000,000 had little action. § 1] MODIFICATION OF VITAL ACTIONS 15 0.1%. NEAL and I have found that Stentor cceruleus is killed by a 0.001% solution HgCl2 in a few seconds. (Cf. p. 30.) Ascarids die in a 0.1% solution in an hour. (SCHRODER, '85.) Silver salts occasionally act upon bacteria more energetically that those of Hg. Cadmium and zinc salts are poisonous — the former more so than the latter. Thus, whereas 0.015% of cad- mium sulphate inhibits reproduction of lactic acid bacteria, 0.1% of zinc sulphate is not injurious. Many salts of thallium are likewise active. Thus LOEW ('93, p. 37) found that in 0.1% thallium sulphate Spirogyra died in 4 to 6 hours. 7. Substitution Poisons. -- In this group LOEW places cer- tain nitrogenous substances which attack the amido and alde- hyde groups of living protoplasm. These are extremely unstable substances and may therefore be transformed by agents which have no effect upon dead protoplasm. The supposed method of action of a poison upon an aldehyde may be illustrated in the case of the poison hydroxylamine (H2N--OH); which justifies at the same time the term "•substitution poisons." ,0 ^N R_C5 + H2=N-OH = R-Cf + H20. \H \H any aldehyde. hydroxylamine. an aldoxim. Hydroxylamine. - - This is a general and powerful poison. Thus, among the lower organisms, a solution of neutral hy- droxylamine of — 0.001 % kills diatoms within 24 hours. (Losw, '85a, p. 523.) 0.005% kills in 36 hours Infusoria which withstand a similar con- centration of strychnine. (LOEW.) 0.01% kills diatoms in something less than 15 hours; Planaria and leeches in 12 to 16 hours. (LoEW.) 0.1% paralyzes the muscles of Rotifera in 10 to 15 minutes ; those of Nais in 20 to 30 minutes. (HOFER, '90, pp. 324, 325.) 0.2% kills Rotifers, Copepoda, and Isopods in 1 hour (LOEW) ; stupefies Vorticella in from 2 to 10 minutes. (HoFER, '90, p. 325.) 0.25% stupefies Stentor in 10 to 20 minutes. (HOFER.) Benzenylamidoxim and acetoxim, more complex derivatives of hydroxylamine, are somewhat less poisonous. 16 CHEMICAL AGENTS AND PROTOPLASM [Cn. I Diamid, or hydrazin (H2N - - NH2) in the form of neutral solutions of the sulphate is a rapid poison. A solution of- 0.01% kills various alga species in 1 to 2 days. 0.02% is injurious to bacteria. 0.05% kills various water animals within 12 hours. (LOEW, '93.) PJienylJiydrazin , solution of — N-NIL is more powerful. A 0.0067% kills Infusoria and algae within 18 hours. 0.05% prevents the development of bacteria and mucors. As free ammonia (NH3) is a far weaker poison than diamid (H2N -- NH3), so anilin (C6H5NH2) is far weaker than phenyl- hydrazin (C6H5 . NH . NH2). ' Passing now to the more complex nitrogenous compounds, we find, first, that bodies which possess slight or no poisonous power, and contain tertiary N, can become strong poisons by addition of H and formation of imido-groups (i.e. groups which can be derived from ammonia by the substitution for two H atoms of bivalent acid radicals) ; thus, — /CH = CH\ /CH2 - CH2\ N CH/ ) \CH2 - CH/ pyridin (weaker poison). piperidin (stronger poison). /HC = HC\ /H2C - H2C\ CH2( )NH XCH2 - CH/ CH CH2 / \ I CH3 CHS CH2 collldin (weak). | CH3 coniin (violent). In the preceding and the two following cases it is seen that, in general, when there is a hydrogen atom of the amid radical (NH2) unre placed by an alkyl, the substance is poisonous. § 1] MODIFICATION OF VITAL ACTIONS 17 ONLY SLIGHTLY POISONOUS. VIOLENT POISONS. C6H5 - CH = N\ C,HB - CH - NH\ )cH-c6H5 I PC C6H5-CH = N/ C6H5-C = Nx hydrobenzaiuid. amarin. /CH = CH\ CH = CH\ CH/ > I >H ^ CH = X pyridin. pyrrol.* This increased poisonousness, correlated with the presence of H joined to N, may be accounted for by the union of this H with the O of the ketons or aldehydes of the living .substance. Likewise when one or more H atoms of the amido-group are replaced by an acid radical (e.g. that of acetic acid, CO.CH3), the poisonous qualities of the substance are con- siderably diminished ; thus, - MORE POISONOUS. LESS POISONOUS. C6HSNH . CO - CH3 anilin. antifebrin.t C6H5NH . NH2 C6H5NH . NH . CO . CH3 phenylh5rdrazin. pyrodin. /NH2 / = C HIST = C . CO . guanidin. dicyandiamidin. In like manner when, in an imido-group, the H (of the NH radical) is replaced by alkyls (e.g. CH3), the substances become less poisonous ; thus, - * While a 0.07% solution of pyrrol kills Isopods, Rotifers, Planaria, etc., in about 1 hour, these organisms withstand a solution of pyridin of the same strength. (LOEW, '87, p. 444.) t SCHURMAYER ('90, p. 445) finds that upon Ciliata (Carchesium) a 0.1% solution slightly accelerates at first the action of the cilia, diminishes the rate of succession of the phases of the contractile vacuole, and leaves the protoplasm permanently more or less paralyzed, c 18 CHEMICAL AGENTS AND PROTOPLASM [Cn. J NH-CH N.CH3-CH I II I II CO C--NH CO C-N.CH3 NH - C == N NH C = N xanthin. theobromine. N.CHg-CH I II CO C - N . CH3 ' I ^CO N . CH3 - C = N / coffein. are successively less poisonous. (LoEW, '93, p. 46.) H I Hv /C\ /H \C/ \C/ While benzol \ \ is rather inactive, 8 grammes r r / \ / \ HX \C/ \H H per day being withstood by the human organism, with the replacement of the H atoms by OH the substance becomes more poisonous in direct proportion to the number of H atoms thus replaced. (LoEW, '87, p. 440.) Thus there fol- low in order of poisonousness : - H H H I I I HC/ \C-OH HC/ \C-OH HO-C/ \C-OH II II I I HC CH HC 'CH HCV /CH \/ H OH OH phenol (rnonoxybenzole). resorcin (dioxybenzole). phloroglucin (trioxybenzole). Phenol (or carbolic acid) and its derivatives attack unstable substances, especially aldehydes, forming insoluble products. Phenol itself produces in the higher animals a paralysis of the nerve centres. Alga3 die in a 1% solution after 20 to 30 § 1] MODIFICATION OF VITAL ACTIONS 19 minutes; in a 0.1% solution after 3 days. Infusoria die quickly in a 1% solution. Ascaris lives only 3 hours in a 0.5% solution. Resorcin (0.5 g.) is hypnotic to man; 0.085 g. per kg. is fatal to dogs. Its isomer - - pyrocatechin - - is more active. 0.1% of it in spring water kills diatoms and Infusoria after a few minutes, and filamentous algte in a few hours ; while, with resorcin, Infusoria, diatoms, and green algse live several hours — even as long as 18 hours. By replacing one of the H atoms of phenol by CO OH (or carboxyl), thus producing salicylic acid, the poisonous qualities are reduced. Hydrocyanic Acid, CNH.- -The action of this substance is peculiar in that, acting on the central nervous system, it is in small quantities a more violent poison for Vertebrates than for Invertebrates. Hydrocyanic acid acts upon aldehydes - in dilute solutions upon the most unstable compounds only ; in stronger concentration upon all aldehydes. Its peculiar work- ing may be hypothetically explained by assuming the aldehydes of the ganglion cells to be more unstable than those of other cells, so that traces of CNH which do not injure other cells destroy quickly the nerve cells. (LoEW.) The action may be shown by the equation, - \ \ )C = 0 + CNHr= )C— OH. H/ H/ aldehyde. The degree and variety of its action may be inferred from the following data, taken from LOEW ('93): Infusoria die quickly in a 0.1% solution, but Ascaris resists a 3% solution for 75 minutes. The resistance of the hedgehog to CNH is remarkable ; five times the dose which killed, in 4 minutes, a cat weighing 2 kg. produced in the hedgehog only a slight sickness. A myriapod (Fontaria) excretes CNH when irri- tated. Certain salts of CNH act as poisons ; e.g. (CN)2Hg, Na2Fe(CN)5NO. Hydric sulphide acts as a poison either by deoxidizing the plasma, H2S + 0 = H,0 + S, 20 CHEMICAL AGENTS AND PROTOPLASM [1'n. I or by acting on the aldehydes, E\ Ex )c = o + H,S = ;c = s + H.,O. H/ H/ It acts rather energetically upon algse and Infusoria. In Ver- tebrates, the central nervous system is attacked and the oxy- haemoglobin of the blood is altered. Sulphurous oxide (SO2) attacks members of the aldehyde group, — Ev E\ /SO,K — OH H/ H/ \H aldehyde. 0.1% kills lower fungi in a few minutes, 0.01% in a few hours. Selenous oxide (SeO2), which acts chemically much like SO2 and has a much greater molecular weight (64 : 111), acts less energetically as a poison. A 0.1% solution kills Spirogyra and Zygnema in 3 hours, while 0.01% is scarcely injurious. Tellurous oxide (TeO2, mol. wt. = 157) is non-poisonous, although chemically closely allied to the two preceding. (BOKORNY, '93.) Aldehydes. - - The poisonous action of these substances de- rived from oxidation of alcohol is dependent upon their insta- bility. So we find that an aldehyde, which, like grape sugar, is fairly stable, is likewise non-poisonous ; while formaldehyde, which is very unstable and active, is correspondingly poisonous. Aldehydes attack especially the unstable amides, affording ni- trogenous compounds ; e.g. — C6H5 • NH2 + CH20 = C6H5NCH2 + H2O. Now, even in passive albumens, part of the N is in the form of amido-groups ; for, in treating with nitric acid, much nitro- gen is set free, which would not occur were all of the N second- arily or tertiarily bound up. (LoE\v, '93, p. 58.) Hence the poisonousness of aldehydes for living albumens. Formaldehyde. - -This substance (H -- CH : O) acts upon propeptones and upon albumen, affording compounds which are not readily soluble. An aqueous solution of — § 1] MODIFICATION OF VITAL ACTIONS 21 0.01 % is fatal to bacteria. 0.05% kills worms, molluscs, and isopods in 2 hours. (LoEW, '88, p. 40.) 1.00% kills Spirogyra very quickly. (Conx, '94, p. 5.) A weak solution seems to act ana3sthetically upon Noctiluca. (MASS ART, '93, p. 65.) When various radicals are substituted in H -- CH : O, the substance acts more like a catalytic poison. Thus, ethyl- aldehyde (CH3 — CHO) is anaesthetic; and paraldehyde (CH3-CHO)3 kills algre in a solution of 0.002% in 24 hours and causes protoplasm to become immobile either (leuco- cytes) after momentary stimulation (DEMOOR, '94, p. 218) or (Noctiluca) at once (MASS ART, '93, p. 66). Several derivatives of ethylaldehyde are poisonous. LOEW ('93, p. 60) has shown that in a 0.1% solution of the neutral sulphate of NH2 — CH2 — CH : (OC2H5)2, amidoacetal, Infu- soria, and diatoms die within 15 hours, and, somewhat later, filamentous algie. Nitrous acid, as is well known, produces, even in great dilu- tion, OH-compounds from amido-compounds (R -- NH2) ; or else, under certain conditions, especially with aromatic arnido- compounds, diazo-compounds result ; e.g. — C2H5 . NH2 + HO . NO == C2H5 . OH + N2 + H20, amine. alcohol. and C6H5 . NH2 . HN03 + HO . NO = C6H5 . N2OK02 + 2 H20. auiliue nitrate. diazobenzene nitrate. Thus a solution of 0.001% of free nitrous acid is poisonous to algce, and more so than nitric acid. The lower fungi are also very sensitive to nitrous acid. Its action as an acid is weak, so that its salts are set free in the presence of even the weaker organic acids. On this account, even neutral nitrates kill such plants (some algre, e.g. Spirogyra) as have an acid cell-sap. 8. Sodic Fluoride. — The poisonous action of the fluorides of the light metals, and especially sodium, has not hitherto been explained. A 0.2% solution of NaF kills various algas (Oscillaria, Cladophora, (Edogoniurn, diatoms) within 24 hours, 22 CHEMICAL AGENTS AND PROTOPLASM [Cii. I producing a change in size of the nucleus. (LoE\v, '92.) A 1 % solution kills the nerves of a frog in 2 hours. 9. Special Poisons. - - Toxic Protein Compounds. Little need be said here concerning the recent discoveries of poisonous albuminoids excreted by disease-producing bacteria, or of those secreted by the parasitized body (alexines). Similar compounds, highly poisonous to Vertebrates, have been extracted from the seeds of some Phanerogams, e.g. ricin, from the seeds of Rici- nus communis (castor-oil bean); abrin, from the seeds of the leguminous Abrus precatorius, L. ; and phallin, from the toad- stool Agaricus phalloides, Fr. Finally, in this group may be placed a large number of protein substances derived from animals, which are more or less poisonous to a greater or smaller number of kinds of protoplasm. The poison of the rattlesnake (Crotalus) and of the cobra (Naja) is fatal to Vertebrates in small, hypodermically injected, doses. Hydra, Turbellaria, Rotifera, and Crustacea are also affected by it ; but Infusoria and Flagellata are apparently unaffected. (HEI- DENSCHILD, '86, p. 330.) It is important that, according to the experiments of several investigators, among the earlier of whom may be mentioned DAREMBERG ('91) and BUCHNER ('92), the various species of Vertebrates possess protein substances in their blood serum which are to a certain extent injurious to other species, since the blood serum of any one species will destroy the red and white blood corpuscles of another. The poisonous action of these animal protein substances seems to be due to their un- stable character, whereby they easily form unions with the unstable groups of the protoplasm, frequently producing thereby violent poisons which work as substitution poisons. (LoEW, '93, pp. 81-84.) Alkaloids. — These basic, nitrogenous compounds have, for the most part, very complex molecules, so that their structure has, in many cases, not been determined. Consequently the nature of their chemical action upon protoplasm is, in general, unknown. LOEW suggests ('93, p. 85) the following theory of action of alkaloids. The bases unite with the active protein substances of the cell, and thereby introduce a disturbance of equilibrium § 1] MODIFICATION" OF VITAL ACTIONS 23 in the plasma body --a disturbance which is especially mani- fest in their action upon the protoplasm of ganglion cells. The capacity of this union is influenced by various factors : by the configuration and degree of dilution of the poison ; by the degree of instability of the kind of protoplasm acted upon ; by the configuration of the molecule of the active protein substance in the cells ; and by the specific (micellar) structure of the plasma body. That organic bases can unite with active albumen is known from observations upon plant cells contain- ing stored-up active protein substances. If the configuration of the albumen molecule and the general texture of the pro- toplasm favor the attack by the base, a disturbance of the equilibrium of the protoplasm will result, even in considerable dilution of the poison. The alkaloids affect chiefly the nervous tissue in the higher animals, producing, in some cases, paralysis ; in others, increased activity. Thus, curarin is paralytic in its action, while the closely allied strychnin is (in dilute solutions) stimulating upon nerve cells. Since action is almost confined to nerve tissue, additional evidence is afforded of the extraordinary instability of the nervous protoplasm. The dissimilar effect of an alkaloid upon the different sub- stances constituting nerve protoplasm gives an idea of the complexity of the latter. Thus, an alkaloid may stimulate nerves with certain functions to increased activity, and may reduce nerves in the same body, having other functions, to depression and paralysis; e.g. nicotin excites sensory nerves, and depresses the activity of the cardio-motor nerves. It is important that many of these alkaloids act also upon Protozoa and the lowest plants, in which nervous substance is still undifferentiated. Other of these alkaloids, however, do not act upon Protista. We will now proceed to an examination of the action of the principal vegetable alkaloids, arranged according to the sys- tematic position of the plants from which they are obtained. Nicotin. - - The effect produced by nicotin is directly pro- portional to the differentiation of nervous substance ; thus, it is almost inoperative on Protozoa and Actinia. Hydra is not very sensitive, 0.5% being a fatal dose. A solution of 0.05% 24 CHEMICAL AGENTS AND PROTOPLASM [Cii. I causes Medusae to become quiet in 30 minutes, and is fatal to the earthworm in a few hours ; Echinoderms are paralyzed by a 0.05% solution in 30 minutes ; Pakemon (after temporary stimulation) is paralyzed by a 0.01% solution in 30 minutes ; Sepiola is killed by 0.005% in less than a minute. (GREEN- WOOD, '90.) Veratrin, Atropin, and Cocaine act upon Vertebrates so as to excite the central nervous system at first, and then to paralyze it. All act, however, as poisons upon undifferenti- ated protoplasm (Protozoa). Thus, ROSSBACH ('72) found that when Ciliata were subjected to veratrin chloride and to atropin sulphate, a peculiar rotary movement took place about one end as a fixed axis. Then imbibition of water with great vacuolation of the protoplasm occurred. Later, the contractile vacuole fails to contract, and protoplasmic movements cease a few seconds after. (Cf. KUHNE, '64, pp. 47, 65, 100.) Cocaine is apparently a benzol derivative, closely related, chemically, to atropin. Its formula is thus given: — CH I H2C CH., CH CO . C6H5. CH Its action upon Protista has been studied by CHARPENTIER ('85), ADDUCO ('90), SCHURMAYER ('90, pp. 438-448), AL- BERTONI ('91, p. 318), DANILEWSKI ('92), and MASSART ('93, p. 66); upon sexual? cells, by O. and R. HERTWIG ('87, p. 159) and ALBERTONI ('91, p. 309); and upon tissue cells by ALBERTONI. The result has been to show that cocaine first stimulates for a very short time to excessive activity, and then stupefies and paralyzes. With the paralysis, a strong vacuolation of the protoplasm occurs, since the excretory func- tion of the contractile vacuole is inhibited (SCHURMAYER, '90, p. 439). Cocaine acts similarly upon the nerve centres and muscles of the more differentiated animals. § 1] MODIFICATION OF VITAL ACTIOXS 25 MorpJiin acts less violently upon the nervous tissue of Ver- tebrates. It has a very weak action upon Protista. Strychnin, chemically considered, is an alkaloid with the formula: C21H22N2O2 ; specific gravity, 1.359 at 18°; soluble to about 0.025% in water at 14.5°; has a very bitter taste. The nitrate is generally employed. The action of strychnin upon Protista is known through the studies of MAX SCHULTZE ('63, p. 32), BINZ ('67, pp. 384-389), ROSSBACH ('72, pp. 52-54), and SCHURMAYER ('90, pp. 423-433). KRUKENBERG ('80) has studied its effects upon higher Invertebrates. Its action upon sexual cells has been studied by the brothers HERTWIG ('87, pp. 153-156, 164), Although not fatal to bacteria and only in strong solutions fatal to the large fungi, strychnin is a nearly universal proto- plasmic poison. It kills the protoplasm of the Drosera ten- tacles and hinders the development of peas, corn, and lupines. The amount of strychnin that Protozoa can withstand has been variously stated, while all authors admit considerable individ- ual variation in this respect. Probably Protozoa cannot ordi- narily resist a saturated solution for one minute. ROSSBACH ('72, p. 52) found that no infusorian of his cultures survived a "0.1% solution" long enough to be placed under the mi- croscope. A 0.02% or 0.01% solution can be withstood for a few minutes (0.01% solution was withstood for 5 minutes, SCHURMAYER). As for the weakest solution that will kill, SCHURMAYER found that a Paramecium resisted for only 15 to 20 minutes so weak a solution as 0.0005%, while ROSSBACH found Stylonychia little affected by a 0.0055% solution. The spermatozoa of Echinoids, according to the HERTWIGS ('87, p. 164), so resist a 0.01% solution that after 180 minutes the movement is only somewhat retarded. Echinoid eggs are in- jured in a few minutes by 0.005%. The injurious action of strychnin on Protozoa varies in the different groups, the resistance capacity increasing, in general, with the height of systematic position of the group. The first effect in Ciliata is an increased activity of the cilia ; if cirri are present, these strike more powerfully; locomotion is abnormally rapid ; but the movements lack coordination, and a rotation takes place about the axis of progression. Next, 26 CHEMICAL AGENTS AND PROTOPLASM [Cu. I the movements become so disorganized that locomotion is im- possible, despite accelerated cilia-motion. Finally, the move- ments suddenly cease, death intervening. (SCHURMAYER, '90, pp. 423-4:26.) The process of excretion seems to be especially affected. Immediately after the addition of a 0.02% solution, the contractile vesicle increases to from 4 to 10 times ite normal diameter, and loses its spheroidal form. In a slightly greater dilution, 0.014%, the contractile vesicle momentarily constricts, but in diastole gains twice its normal diameter, and the time between phases of contraction is greatly increased. Thus, the normal rate of contraction for Euplotes at 15° C. is between 30 and 35 seconds; but in a 0.014% solution of strychnin this is diminished to 1 in 500 seconds. Frequently, several vacuoles are formed, and, eventually, the whole body becomes greatly vacuolated, and death intervenes. (RossBACH, '72, pp. 52, 53.) Many higher organisms are not very sensitive to strychnin. Thus, Ascaridse have a considerable resistance, which SCHRODER ('85, p. 307) ascribes to their not opening their mouths in the solution, the poison being thus obliged to pass through the skin. So, too, snails were found by KRUKENBERG ('80, p. 100) to be very resistant to strychnin. Curare, or urare, is an alkaloid, derived from Strichnos species. The commercial substance is very variable in com- position. NIKOLSKI and DOGIEL ('90) have studied the effects of this drug upon various organisms. Upon adding a few drops of a 0.8% solution of curare to water containing an amoeba, the first effect is a shrinking towards a spherical form and a cessation of all movements. Subsequent washing in water ultimately restores the normal movements. As is well known, it paralyzes also the protoplasm of the nerve endings. Quinine, or chinin (C20H24N2O2). - -The "sulphate," which is first produced in the process of extraction, is commonly employed. This is, moreover, more soluble than the pure alkaloid, 1 part dissolving at 9.5° in 788 parts of water. In- vestigations on the action of this poison upon protoplasm have been made especially by BINZ in a series of papers beginning with '67; by ROSSBACH ('72) on Protozoa; by TEN BOSCH ('80) on leucocytes; by O. and R. HERTWIG ('87) on sexual cells; and by KRTJKENBERG ('80) on higher Invertebrata. § 2] ACCLIMATIZATION TO CHEMICAL AGENTS 27 Amoeba, Actinophrys, and various Infusoria are killed by a 0.1% solution in a few minutes, and leucocytes and eggs of Ecliinoids are paralyzed even by a 0.005% solution. Its action is thus more powerful than that of strychnin. The proto- plasm at first contracts, then gradually dissolves arid streams away. Upon the higher animals, quinine so acts as to paralyze the central nervous tissue (in Mollusca, KKUKENBERG, '80, p. 10), and it affects the cerebrum and heart ganglia of mammals. Antipt/rin, or phenyldimethylpyrazolon, is an alkaloid de- rived from and belonging clearly to the benzol type, in which one atom of II is replaced by a complex atom-group, as may be seen from the formula - /\ X XHC CH HC= =C-CH3 H | C The effect of this agent upon Protozoa has been studied by SCHURMAYER ('90, pp. 434-437) and M ASSART ('93, p. 64). A solution of 0.1% acting for 80 minutes, caused Oxytricha at first to move more rapidly, but eventually to become transformed into a shapeless mass, whose protoplasm disinte- grates. Acting upon Noctiluca, a 0.25% solution causes a bright glimmer immediately after applying, followed by dark- ness again. Thus there is here a momentary hyperesthesia. § 2. ACCLIMATIZATION TO CHEMICAL AGENTS It is clear that the protoplasm of different organisms is dis- similar. We see this in the different reactions to the same chemical agent. Not only is the reaction of the various spe- cies unlike, but individuals of the same species from different localities differ widely. (Cf. LOEW, '85.) We are, naturally, most familiar with this phenomenon in the case of man. Thus, the common North American poison ivy (Rhus toxicodendron) produces, in some persons, extensive inflammation in parts which have come even indirectly in con- 28 CHEMICAL AGENTS AND PROTOPLASM [Cn. I tact with it ; while, by other persons, it may be taken into the mouth with impunity. The phenomenon shown by man is found in other animals also. Thus, among Invertebrates, although few bacteria can resist 1% Na2CO3, and even the extremely resistant Ascaris lives only 5 to 6 hours in a 5.8% solution of this salt, LOEW ('77, p. 137) has found in Owen's Lake, California (an alkaline water containing among other things 2.5% Na2CO3), numerous living Infusoria, Copepoda, larvce of Ephydra, and molds. Again, the vinegar eel, Rhabditis aceti, lives in a 4% solution of acetic acid, although this strength is usually fatal ; e.g. a 0.23% solution of acetic acid kills the tentacles of Drosera. (DARWIN, '75, p. 191.) What is true of the whole organism is true also of its parts. The gland cells of some marine Gasteropoda (Dolium, Cassis, Tritonium, Natica heros) secrete H2SO4 of a strength (2% to 3%) which is fatal to most protoplasm; the myriapod Fontaria excretes, when irritated, the extremely poisonous CHN; and, according to LOEW ('87, p. 438), the plant Oxalis produces potassic oxalate, which is a violent poison to most protoplasm. One general law of high resistance is worthy of notice: an organism which produces an albuminoid poison is strongly resistant to that poison. Thus, FAYRER ('74) has shown that venomous serpents are not destroyed by the secretion of their poison glands when it is injected into them ; and BOURNE ('87) has shown that scorpions are not injured by their own venom. An explanation of the facts of varied resistance capacity is first gained through experiment. We all know that, among men, a high resistance capacity to a poison may be acquired by taking a small quantity of it at frequent intervals. Thus, users of tobacco, alcohol, and various alkaloids become, in time, capable of taking, without apparent injury, quantities which would at first have proved fatal. Arsenic eaters may eventu- ally swallow without injury four times the ordinarily lethal dose, i.e. as much as 0.4 gramme. (BiNZ and SCHULZ, '79.) Results similar to those observed in man have been obtained by experiment upon other animals. Thus, SEWALL ('87) inoculated a pigeon hypodermically with sub-lethal doses of §2] ACCLIMATIZATION TO CHEMICAL AGENTS 29 rattlesnake poison (Crotalophorus tergeminus). While no unacclimatized pigeon could resist 1 drop of a 6.8% solution of venom in glycerine, pigeons inoculated with at first weak, then gradually increasing solutions, came at last (after 178 days) to resist 4 drops of the glycerine venom mixture. Likewise KAN- THACK ('92) succeeded in acclimatizing two rabbits and a hen to serpent's venom. Very similar are the experiments of EHRLICH ('91). This investigator fed white mice (which are killed by ^ of their weight of a 0.0005% solution of ricin, hypodermically in- jected) upon food cakes soaked in a weak solution of the poison. After feeding them for a varying length of time upon constantly increasing solutions, he determined the maximum solution which, hypodermically injected, they would withstand. If we call the maximum solution which the unacclimatized organism will withstand our unit of immunity, we can express the degree of immunity of the acclimatized organisms by the strength of solution (expressed in terms of that unit) which they can resist. The following table, taken from EHRLICH'S paper, shows the gradual increase of immunity as a result of feeding on the poison : — TABLE IV No. OF EXPERIMENT DAT. STRENGTH OF LAST DOSE GIVEN, IN MG. NUMBER OF INDI- VIDUALS EXPERI- MENTED ON. MAXIMUM IN- JECTED SOLUTION BORNE, %'8. DEGREE OF IMMUNITY. IV 4 8 ( Die in 1 v 5 16 1 0.0005 0.0007 1.3 VI 6 23 0.0066 13.3 VII 7 5 0.005 10 VIII 8 18 0.01 20 x 12 9 0.02 40 XII 20 3 0.033 66.6 XV 50 1 0.05 100 XVIII 80 4 0.1 200 XXI 80 1 0.2 400 Thus after the first 4 or 5 days the immunity rapidly in- creased ; so that, while the solution of ^o~oVo"o kills normal 30 CHEMICAL AGENTS AND PROTOPLASM [Cn. I mice, those acclimatized during 21 days resist -j-gVo to - occasionally 3"-^, corresponding to a grade of immunity of 200 to 800. By fundamentally similar procedures CALMETTE ('94) has rendered rabbits immune to the action of strong doses of the venom of Naja tripudians (cobra) and of Pelias berus. Still more recently MARMIER ('95) has isolated a toxin produced by anthrax bacteria reared in a peptone-glycerine solution. Inoculated into an animal sensitive to anthrax, this toxin produces, in certain doses, death by cachexy. By employing suitably graduated doses, however, one can obtain immunity of the organism to anthrax, as one does to the venom of serpents. Some attempts to produce acclimatization in lower organisms have been made by Dr. H. V. NEAL and myself. Stentor was employed as the object of experimentation. We reared two lots of Stentors under similar conditions except that Lot 1 was cultivated in water and Lot 2 in 0.00005% HgCl2. After the lapse of two days both were put into a killing solution of 0.001% HgCl2, and the second lot was found to survive longer than the first. The mean resistance period to the killing solu- tion of the lot reared in water was 83 seconds; of that reared in 0.00005% corrosive sublimate, 304 seconds. Similar results were obtained in other experiments. In Fig. 1 a curve is given showing the relation between strength of culture solu- tion and period of resistance. From this curve, based upon 132 determinations, it appears that the resistance period varies directly with the strength of the solution in which the protoplasm has been cultivated. This law holds good, however, only within certain limits. If the culture solution is too strong, above 0.0001%, the organism will be weakened by it so that it cannot resist the killing solution so long as those reared in water can. A similar effect of heightened resistance to quinine is ob- tained by cultivating organisms in quinine. Experiment shows that a slight increase of the resistance period follows subjection to the culture for one hour only; and that the degree of acclimatization varies directly as the time of subjection. §2] ACCLIMATIZATION TO CHEMICAL AGENTS 31 The facts obtained by us clearly indicated, then, that, without selection, — for no deaths occurred in our culture solutions, — the protoplasm may become modified merely by subjection to the poison, so as to gain an increased resistance to it. Hence the acclimatizations that we find in nature need not have been brought about by natural selection-- must have occurred, indeed, even without selection, if the organisms had been gradually subjected to their environnient. \ \ 90 sees. 80 CO Q o (0 £ ul Q. Ill O c-n 60 B LU 40 SECS. FIG. 1. STRENGTH OF CULTURE SOLUTIONS -Curve of resistance periods to a 0.00125% solution of HgCL of Stentors reared in various solutions of HgCL during 20 to 96 hours. We did not determine for how long a time the acclimatized Protozoa retained their heightened resistance capacity. The only data we have upon the subject of persistence of acclima- tization is derived from studies on Vertebrates. Thus it is the familiar experience of arsenic eaters that, after they have broken off their habit, the body does not quickly return to a normal condition. Even after a considerable period of self-denial the taking of large doses may be recommenced - must be recommenced, indeed, or illness sets in. EHELICH ('91) has studied experimentally the phenomenon 32 CHEMICAL AGENTS AND PROTOPLASM [Cn. I of acclimatization to ricin. Mice which had gained an immu- nity of over 200, and were then kept for 6.5 months on normal food, had still a resistance, although not precisely determined, certainly far above 50. It is an important question : Is an organism acclimated to one poison thereby rendered more resistant to poisons in gen- eral, or only to the specific poison to which it has been accli- mated ? EHRLICH found that mice acclimated to ricin were just as sensitive to abrin as the normal animals, and the same is true, mutatis mutandis, for mice which resist abrin. Concerning the changes in the protoplasm brought about by acclimatization little is known. EHRLICH ('91) and CALMETTE ('94) have shown that in the blood of the immunized animal a substance, antitoxic to the specific substance employed, is produced, and this apparently prevents the action of the strong poison by transforming its molecules. The antitoxic substance is of such a nature that when blood containing it (from an acclimatized animal) is injected into an unacclimatized one, the latter becomes immune to the poison. For Protista another hypothesis is admissible ; namely, that the weak solution of the poison, which is used in acclimatiza- tion, gradually destroys those compounds upon which the strong solution would have acted suddenly and, therefore, fatally. The gradual destruction is not fatal because of its slowness. At the same time it prevents the violent action of the strong poison, since it leaves it nothing to be acted upon. The parallelism between the results of experiments upon acclimatization to poisons and those upon immunization through vaccination, leads to the suspicion that, at bottom, the two processes are closely akin. § 3. CHEMOTAXIS ENGELMANN ('81) seems to have been the first to show that the direction of locomotion of simple protoplasmic masses is de- terminable by chemical agents in the environment. He found that Bacterium termo is thus acted upon by oxygen which is not uniformly distributed. Like many Infusoria, these bacteria § 3] CHEMOTAXIS 33 gather at the margin of the cover-glass, where oxygen is more abundant than elsewhere. If oxidized blood is introduced under the cover-glass, they move toward it, but not toward blood containing much CO2 in place of oxygen. If green algce are introduced, the bacteria move towards them so long as they, under the influence of sunlight, are producing oxygen. In the dark the algse have no effect. During the decade and a half which have elapsed since Ex- GELMANN'S first paper appeared, chemotactic phenomena have been observed among nearly all kinds of motile organisms and with reference to the most diverse kinds of chemical substances. ENGELMANN ('82) has studied the chemotactic movements of diatoms ; STAHL ('84), of Myxomycetes ; PFEFFER ('84, '88), of plant spermatozoids, zoospores, Flagellata, Infusoria, and bacteria ; ADERHOLD ('88), of Euglena viridis ; VERWORN ('89, p. 107), of Cryptomonas ; STANGE ('90), of zoospores and Myxomycetes ; and MASSART ('91), of Spirillum, Heteromita, and Ciliata. Within the last five years a voluminous literature has grown up on the medical side relating to chemotaxis in leucocytes and pathogenic bacteria. Into this literature we cannot penetrate deeply, but refer to some of the principal papers : LEBER, '88 ; BUCHNER, '91 ; ROEMER, '92 ; METSCHNIKOFF, '92. It thus appears that chemotactic phenomena show themselves among all the groups of lower motile organisms : Rhizopoda (Myxomycetes), Flagellata, Ciliata, bacteria, diatoms, zo- ospores, and spermatozooids. It can hardly be questioned that the phenomena shown by these organisms are of the same order as those seen in Metazoa--in those ants which LUBBOCK ('84, p. 233) has shown to move from chemical agents (essence of cloves, lavender water, and other scented stuffs), saturating a camel's-hair brush placed about ^ inch above their path ; and in the larvae of flies with which LOEB ('90, p. 79) has experi- mented. LOEB found that these crept towards a piece of flesh' brought nearer to them than the distance of 1.5 cm. Even just hatched larvre (which had therefore never been stimulated by meat) reacted in this way. Not meat only, but a trace of meat juice on glass attracted the larvse strongly. While decaying flesh and cheese allure, neither fat, asafoetida, nor ammonia do so. 34 CHEMICAL AGEXTS AXD PROTOPLASM [Cn. 1 Returning now to the simple organisms, let us consider the kinds of chemical substances which incite to a response. Oxygen is for almost all organisms a means of attraction. Various methods of demonstrating this have been used. Thus STANCE ('90, p. 1-39) filled capillary tubes with pure oxygen, under an air-pump, and brought them to the water containing zoospores, which then penetrated into them. The aggregation of zoospores and bacteria to the edges of the cover-glass, to the open end of a capillary tube (ADEKHOLD, Air bubble , v ^ . Zone of Sp irillum ,-' ;V Zone of Anophrys ..*'•: ". Ct. FIG. 2. — o. Corner of the glass slip covering a drop of liquid containing Spirillum and Anophrys, showing their aggregation with reference to the aerated bound- ing film of the drop. b. An air-bubble in the drop, showing aggregation of the organisms about it. (From MAS-SART, '91.) '88, p. 314), or to an enclosed air-bubble, are well-known phe- nomena. (Cf. MASSAKT, '91, p. 159; VERWORX, '89, p. 107; and see Fig. 2.) ENGELMANN ('94) has employed a still more refined method of studying attraction towards oxygen. A drop of foul water is put on a glass slide with an alga cell in the centre, and is covered by a cover-glass whose edges are hermetically sealed by vaseline. The bacteria are uniformly distributed in the water, moving in a lively manner, since they gain oxygen everywhere. If the slide thus prepared is kept in the dark, the oxygen is gradually consumed and the bacteria become quiescent, showing no distribution with reference to the cen- tral chlorophyllaceous body (Fig. 3). If the slide is now exposed to the light, oxygen is produced by the alga and a regular distribution of the bacteria in two distinct regions — in a mass around the central alga, and in a § 3] CHEMOTAXIS 35 peripheral zone --is apparent (Fig. 4). The peripheral zone contains bacteria which are beyond the tactic action of the oxygen. The central mass of bacteria have emigrated from what is now a clear ring between the centre and the peripheral zone. If the light be temporarily cut off, the central bacteria 0 o« « '« , ' '. . « » ' i '. ' . • .• 4 « .«•*•;*«%•.*.* ' "•' ° •• •'• •,«'.** v •*! •"• ° ' '° i I ?«•. . • . . = «.«. • . • . •• ;' . • .. - , ... -,,• ^•-•."o-..- • « .. . .•„• «.«f ,; ?„• . . -. . ,„; .„* ;. j*' '-- 5 5a FIGS. 3-5 «. — Bacteria surrounding an algal cell. Fig. 2 shows the uniform distribu- tion of the bacteria when the drop of water is kept in the dark. Fig. 3 shows the aggregation of the bacteria towards the algal cell when this has emitted oxygen rapidly in the strong light for two minutes. Fig. 4 shows the same preparation shortly after the light has been cut off. Fig. 5 shows the same preparation when a fainter light is now permitted to fall upon the green cell. Magnified about 170 diameters. (From ENGELMANN, '94.) * begin to disperse (Fig. 5). If, a minute after, a dim light be let through, the radius of its activity will be relatively small, so that a central aggregation will be found and also an inner peripheral zone, comprising those dispersing central bacteria which are not affected by the small oxygen tension resulting from the dim light (Fig. 5 a). 36 CHEMICAL AGENTS AND PROTOPLASM [Cn. I Inorganic Salts. - - PFEFFER * ('88, p. 601) tried various salts of potassium; viz. chloride, phosphates, nitrate, sulphate, car- bonates, chlorate, ferrocyanide, and tartrate, and found that all attracted various bacteria (B. termo, Spirillum undula), and the flagellate Bodo saltans with greater or less strength, when the solution in the capillary tube contained 0.1% K. So, likewise, various salts of sodium, rubidium, csesium, lithium, ammonium, calcium, strontium, barium, magnesium, especially the chlorides, were employed. All of these solutions at a concentration of 0.5% exhibited a marked attractive influ- ence upon Bacterium termo ; a weaker one, upon the two other species. STANGE ('90) experimented with the action of various phos- phates upon zoospores of a Saprolegnia belonging to the ferax group of DE BARY.f Sodic, ammonic, lithic phosphate, calcic phosphate held in solution by CO2, as well as phosphoric acid were employed and found to act attractively. Other salts, KNO3, K2SO4, KC1, HKCO3, BaClO8, SrCO3, MgSO4, had either a negative or indifferent action upon the zoospores. The attractive action of the phosphates is correlated with the fact that phosphates are abundant in the muscles of insects. The following table shows the effect of the different strengths of solutions of four phosphates upon zoospores of Saprolegnia. In this table, constructed from STANCE, the symbol r indicates repulsion ; 0, no action ; a, attraction ; al indicates a slight attraction ; «2, a strong attraction ; azrv an attraction which is partly balanced by a repulsion due to density, so that the * The method employed by PFEFFER in his experiments was as follows : Glass capillary tubes with a lumen of from 0.03 to 0.14 mm. diameter and a length of 7 to 12 mm., and sealed by fusion at one end were employed. To fill the capillary tube, it was placed in a watch-glass containing the experiment solu- tion, and the whole was placed in a vessel from which air was pumped. Under the diminished atmospheric pressure, 2 to 4 mm. of fluid entered the capillary tube ; the rest of the tube contained air, which kept the fluid oxidized. After rinsing, the free end of the tube was plunged into the drop culture, whence the solution diffused out. t The species were cultivated upon carcasses of flies thrown into glasses filled with bog water. After good colonies were obtained, the carcasses were washed, to rid of Infusoria. Such colonies may be employed to infect sterilized flies' legs placed in sterilized bog water, or they may be transferred directly to wounds in flies' legs. §3] CHEMOTAXIS 37 organisms pass only into the first part of the tube ; «3r3, such a balancing of the opposing forces that the organisms stand before the mouth of the capillary tube. STRENGTH OF SOLUTION, SODIC DIPHOS- POTASSIC MONO- AMMONIITM PHOS- PHOSPHORIC PHATE PHOSPHATE PHATE ACID %'s (HNn2PO4X (H.KP04). (H2NH4PO4?). (H8P04). 0.8 to 0.4 .... a3ra aars asr3 r 0.4 to 0.08 . . . °2ri a,?'! 0.08 to 0.04 . . . «2 a. a2 air2 0.01 to 0.02 . . . 0 ai a, airi 0.02 to 0.008 . . . 0 0 a.2 0.008 to 0.004 . . . ai 0.004 to 0.002 . . . 0 It will be noticed that the various substances produce dif- ferent effects in the same strength of solution ; arid it is interesting to observe (a point to which further reference will be made) that the strength of solution required to produce a given response is roughly proportional to the molecular weight of the substance employed. Inorganic acids and hydrides seem, in general, to act repul- sively, but phosphoric acid is an important exception to this rule. DEWITZ ('85, pp. 222, 223) states that mammalian spermatozoa are attracted by KHO. Organic Compounds. — Alcohol, in grades between 10% and 1%, acts repulsively towards bacteria. Glycerine is neutral to the same organisms and to zoospores of Saprolegnia. (STANGE, '90.) The sugars, etc., dextrose, milk sugar, dextrin, act attractively upon Bacterium termo in 10% or weaker solutions. Many or- ganic acids are among the most attractive reagents. It was with malic acid that PFEFFER ('84) tried his earlier fundamental experiments upon the spermatozoids of ferns. The attraction exerted is very great, so that a capillary tube of 0.1 to 0.14 nur. calibre, containing a 0.05% solution of malic acid, attracts from a drop of water full of spermatozoids at the rate of 100 individuals in one hour. Even a 0.001% solution acts chemo- tactically. Now, malic acid is of very wide distribution among plants, and it occurs in the fern prothalli upon which the sexual 38 CHEMICAL AGENTS AND PROTOPLASM [Cn. I organs arise, so that it seems probable that it occurs in the mouth of the archigonium, and that by its presence sperma- tozoids are attracted towards the egg cell. STANCH ('90, p. 155) has experimented much more fully with the action of organic acids upon zoospores of Saprolegnia and upon myxamceb;tj. To the former, acetic acid (0.01%) and tartaric acid (0.0125%) act attractively. Upon the latter, still other acids wrere tried ; butyric, lactic, and valeric acids cause response in concentrations between 0.2% and 4% ; malic acid, between 0.5% and 4%. Other attracting acids are : propionic, citric, tartaric, and tannic. Acetic acid repels the amrebse of TEthalium, its repellent action being about equal to the attrac- tive action of an equal amount of butyric acid. Nitrogenous Compounds. --Urea, asparagin, kreatin, taurin, hypozanthin, carnin, and peptone have been found by PFEFFEK ('88) to exert an attractive influence, especially in the case of the reagents italicized. Benzol Derivatives. — PFEFFER found that sodium salicylicate and (commercial) sulphate of morphine are clearly attractive to Bacterium termo in 1% solutions. From the foregoing list of organic compounds whose effect upon Protista has been tested by PFEFFER and STANGE, it appears that except alcohol and sometimes acetic acid, none acts repulsively, and that glycerine alone is neutral to all proto- plasm. It is further true that we do not find here any strict relation between the chemotactic action of a substance and its advantage to the organism. Substances which have a nutri- tive value for the organism, such as glycerine has for bacteria, may be wholly neutral, while solutions which act fatally, like \% sodic salicylicate and 1% morphine, attract. In the same way, many of the organic salts which act attractively cannot be considered as of importance to the organism. On the other hand, as already pointed out, the attraction of most Protista to oxygen, of Saprolegnia zoospores to phosphates, as well as the cases of attraction of bacteria (PFEFFER, '88, p. 605) and of fly larvse (LoEB, '90, p. 79) to meat extract, and of Myxomycetes to bark extract (STAHL, '84 ; STANCE, '90), is advantageous. Chemotaxis is, therefore, in some cases, a response to the stimulus afforded by substances which can be employed by § 3] CHEMOTAXIS 39 the organism as food ; under which circumstances it can be called "Trophotaxis." * In other cases it is a response to chemical substances which have no significance as food, and have no other importance for the organism. It is clear that we cannot assume that response to injurious substances is an adaptation which has been brought about by natural selection. If a response occurs in one case independent of the action of selection, we should hesitate to ascribe to this cause the origin of other, even favorable, responses. General Remarks on the Relation between Molecular Composi- tion and Response. - - PFEFFER ('88, pp. 608-612) has pointed out that the capacity of any substance to stimulate cannot be inferred from its chemical constitution and relationships. Thus, the minimum concentration of milk sugar which will produce a response is 1%, while in the case of the closely allied grape sugar it is 10% ; but in the very different kreatin it is also 1%. Also, the action of any chemical compound is determined not by the elements, such as C, H, O, which it contains, but by the entire molecule ; in other words, the atomic composition is less important than the structure - of the molecule or the arrange- ment of its atoms. Thus, malic acid and its compounds with neutral ammonium, sodium, barium, and calcium containing 0.001% parts of the acid, have an equal action upon the sperma- tozoids of ferns, which do not react to the diethylester of malic acid, even in strong solutions. (PFEFFER, '88, p. 655.) Again, nitrogenous organic compounds are, in general, more active than the non-nitrogenous ones ; but this cannot be held to be due alone to the presence of N ; for dextrin (C6H10O5) is nearly as active as the nitrogenous peptone, and, on the other hand, the nitrates of metals are not more active than their chlorides, while the ammonia salts are relatively weak. Relation between the Strength of the Stimulus and that of the Response. - - When we say that malic acid attracts sperma- tozoids we mean that under certain physical conditions of the water which we may call normal it does so. And under normal conditions of the water, it is only within certain limits * STAHL ('84, p. 164) called the attraction of plasmodiurn of myxomycetes to bark extract " Trophotropism." 40 CHEMICAL AGENTS AND PROTOPLASM [Cn. I that malic acid attracts. The strengths of solutions which attract under such conditions lie between 0.001% and 10%. The weaker solution may be designated the minimum ; the stronger, the maximum concentration which provokes a re- sponse. The minimum solution provoking response is also often called by the Germans the " Reizschwelle," or "stimula- tion threshold " ; * the optimum, the " Reizhohe," or " stimu- lation acme1'; the range, the " Reizumfang." The character of the responses observable at the two limits is very different ; at the minimum, attraction is very feeble ; thus, while a capillary tube containing 0.01% neutral sodic malate, plunged into water at 14°-20° C., swarming with spermatozoids, attracts 400 of them in 10 minutes, a 0.001% solution attracts only 10-25 individuals during the same time, and a 0.0008% exerts little attractive effect, the spermatozoids remaining undirected in their movements. At the maximum, on the contrary, repulsion is observed. The spermatozoids move from the mouth of the capillary tube. Between the two extremes lies the concentration of greatest attraction — the acme. As we pass from the acme towards the minimum, the attraction becomes less and less. As we pass towards the maximum, the attraction remains the same, or increases ; but repelling influences are now at work, which eventually entirely counteract the attractive influences. A satisfactory method of expressing quantitatively the facts just mentioned has not been invented. PFEFFER ('88, p. 599) has employed the nomenclature which we have used above (p. SG)--^ to «3 being combined with rl to r3 to indicate the coworking in varying proportions of attraction and repul- sion. Using this nomenclature, we may illustrate the state- ments made in the last paragraph with examples taken from PFEFFEU'S work: — * The following substances at the solutions named produce the threshold attraction (ai) in Bodo saltans: KC1, 0.02%; K3P04, 0.002%; KH2PO4, 0.0035%; KN03, 0.26%; K2SO4, 0.22%; KC1O3, 0.3%; K4(CN)6Fe, 0.235%; K2.C4H40G, 0.02%; RbCl, 0.14%; LiCl, 0.6%; LiN03, 3%; NH4C1, 0.3%; neutral ammonium phosphate, 0.08%; SrCl2, 0.2%; Sr(NO3)2, 0.4%; BaCl2, 0.17%; dextrin, 0.1%; urea, 1%; asparagin, 0.1%; taurin, 1%; sarkin, 0.33%; pepton, 0.01%; meat extract, 0.01%. §3] CHEMOTAXIS 41 GRADE OF SOLUTION. RESPONSE OF BACTERIUM TEEMO. SPIRILLUM. 9.53 % KC1 = 5%K as asrs 1.906 %KC1 = 1 % K «3 «3r1 0.191 % KC1 = 0.1 % K «3 «3 0.019 %KC1 = 0.01 % K a2 «i 0.0019 % KC1 = 0.001 % K a, 0 BODO SALTAN8. 3.48 % KH2PO4 = 1.0 %K a8rs 0.348 %KH2P04 = 0.1 % K asr2 0.035% KH2PO4 = 0.01 % K a2 0.0035 %KH2PO4 = 0.001 % K a\ 0.00067 % KHJPO4 = 0.0002 % K 0 Compare also the table on p. 87. For all reagents which exert an attractive influence there exists the maximum (repelling) and minimum (indifferent) limits referred to. In the case of reagents, which, like alco- hol, repel bacteria at between 1% and 10%, there is doubtless an indifferent limit, but it is not necessary that there should be a degree of concentration at which attraction takes place. In the one case, then, the phenomena of indifference, attraction, repulsion, follow each other with increasing concentration ; in the other case, only indifference and repulsion. The difference in action of the two cases is due, in part at least, to the fact that all solutions, independently of their chemical constitution, become repellent when they become concentrated enough. The repulsion, then, of high grades of chemical solutions is purely an osmotic phenomenon, and, as such, will come under discussion in the third chapter. It follows, also, from what has been said, that, in the case of those reagents which exert no attraction at any concentration, the acme and maximum coin- cide and lie at the saturation point of the solution. Finally, we may discuss the third case in which the reagent acts indifferently, as glycerine does upon bacteria between 17% and 0.86%. It is clear, that if the density of the solution can 42 CHEMICAL AGENTS AND PROTOPLASM [Cn. 1 be rendered great enough, a repulsion due to osmosis must occur. If the substance is, however, only soluble slightly or miscible, it may be that repulsion will never occur. Whether or not attraction will occur before the repulsion point is reached will have to be determined experimentally for each reagent. Thus the action of an untried substance upon any organism may be any one of three kinds : (1) It may be indifferent at all grades ; (2) it may be indifferent at lower and repellent at higher grades ; (3) it may be indifferent, attractive, and repellent at successive grades. Of two substances belonging to the second or third class, one may act upon an organism at a certain concentration with indifference, the other at the same concentration with repulsion. Likewise the same solution of a substance may attract one kind of protoplasm and repel another, under otherwise similar conditions. We have seen above that the same reagent acts upon the same kind of protoplasm similarly only when the other con- ditions of the experiment are also the same. Among the varying conditions which have been especially investigated is that of the chemical constitution of the medium. The experi- ment has generally been made as follows : A particular species, let us say Bacterium termo, is to be subjected to the action of a particular reagent, e.g. meat extract. The bacteria are reared in cultures containing a varying quantity of the meat extract, and the concentration of the capillary fluid producing the threshold stimulation is measured in each case. We may compare not only the threshold stimulations but also the concentrations necessary to produce the response indicated by ar «2, etc. The following table, from PFEFFER ('88, p. 634), gives some of such determinations: — CULTURE FLUID — MEAT EXTRACT. CAPILLARY FLUID — MEAT EXTRACT. 3 x cult. cone. 5 x cult. cone. 8 x cult. cone. 10 x cult. cone. 0.01 % 0.1% 1% 0.03 %(?) 0-3%(?) 3%(?) 0.05 %«> 0-5% (a,) 5%(«i) 0.08% (a,) 0.8% (a,) 8%(«2) 0-l%(a8) 1 % («2) 10% (a,) § 3] CHEMOTAXIS 43 From this table it appears that the strength of solution necessary to provoke a certain response depends upon the strength of solution to which the protoplasm has been pre- viously subjected and increases proportionately with it. It is clear that the capillary solution of 0.1%, which produces a marked chemotaxis in bacteria reared in a culture solution of 0.01%, would awaken no response in bacteria reared in 0.1%. We are now in a position to appreciate the importance of still another addition to our terminology of stimuli --the dif- ferential threshold stimulation (Reizunterscheidsschwelle) - which may be defined as the minimum increase of a preexisting stimulus which is capable of calling forth a just noticeable reaction. In the case just cited, the differential threshold stimulation lies just above 3 times the preexisting (culture) stimulus, and this is true whatever the degree of the preexist- ing stimulus ; and it is shown by experiment that, in general, as the preexisting stimulus increases, the differential threshold stimulation increases in the same proportion. This observa- tion is in perfect accord with the law formulated long ago by WEBER with especial reference to sight. This law runs : The smallest change in the magnitude of a stimulus which will call forth a response (differential threshold stimulation) always bears the same proportion to the whole stimulus. We may express this law mathematically, as FECHNER has done, by the following considerations : Let us take the case of a protoplas- mic body, as, for example, that of a spermatozoid, living in a stimulating medium (s) of a certain concentration and experi- encing a certain reaction r' ; then s corresponds to r'. In order just to get a chemotactic response (threshold stimulation), a solution of say 30 times the concentration must be brought to the solution affording the stimulation s. This will give a reaction which is greater than r' by a quantity which we may designate r, so that the quantity of the whole reaction may be designated as r' -f r. If the organisms are now placed in this stronger solution (31 s), the solution in the capillary tube must be 30 times stronger (30 x 31 s) in order to give the differential threshold stimulation. The reaction following this stimulation may be designated, according to FECHNER'S conception, as r' + r + r. The relation of the successive stimuli and the reac- 44 CHEMICAL AGENTS AND PROTOPLASM [Ca. I tions may be shown by the following table, following one given by PFEFFBR ('84, p. 401) : - s corresponds to r1. s-\- 30s = 31 s corresponds to r' + r. 31s-f- 30x31s = 31 x 31s corresponds to r'+r+r. 31x31s+30x31x31s = 31x31x31s corresponds to r'+r+r+r. That is to say, while the stimulation increases geometrically, the reaction increases arithmetically. In the preceding table the second term of the left-hand member of the equation is always the differential threshold stimulation. The most important objection that can be urged against this formula of FECHNER is that there is not sufficient reason for believing that the various reactions (r) to the differential threshold stimulations of various strengths are equal, nor that the stronger reaction to the strong stimulus is composed of many weak reactions. If these assumptions were true, it would follow that when the successively higher stimuli increase as a series of numbers the reactions increase as the logarithms of these numbers. If now we adopt as a unit in this phenomenon the quantity of the threshold stimulation (estimated in units of concentration of solution, of mass, light intensity, heat inten- sity, etc.), which we may call s, the strength of any stimulus ($) may be estimated in those units, and the strength of the corresponding reaction (.72) will be indicated by the equation R = c - log S, in which c is a constant to be determined empiri- cally, and S the strength of the stimulus expressed in units of the threshold stimulation.* While we are not yet in a position to understand the signifi- cance of WEBER'S law, we cannot fail to be struck with the resemblance of the phenomena with which it concerns itself to those of acclimatization referred to in the second section of this chapter. We there showed that organisms subjected for a while to a chemical agent no longer reacted as at first to that reagent. We have here shown that organisms subjected for * Since the German word for stimulus is Ileiz (initial B}, and since the re- action is usually indicated by the initial letter in Empfindung, in German text- books this formula usually runs E — c • log .R, which differs from the above equation only in the symbols employed. SUMMARY OF THE CHAPTER 45 a while to the action of a certain stimulating agent respond no longer to a concentration which would at first have provoked a reaction. In both cases it is the action of the chemical agent which modifies the subsequent action of the protoplasm, without doubt by changing the chemical constitution of the protoplasm. Mechanics of Response. - - Having considered the general relation between strength of stimulus and of reaction, it now becomes necessary to examine more in detail into the way in which the reaction takes place. A variety of kinds of locomotion exists among chemotactic organisms - - that of the Myxomycetes is amoeboid, that of Infusoria is by flagella or cilia. In all cases the first and perhaps the only effect of the acting reagent is to determine the position of the axis of the body, in the case of bodies with fixed form ; or to determine the pole of outflow in the case of amoeboid organisms. The axis lies in the line of flow of the diffusing solution or perpendicular to the isotonic lines, or lines of equal concentration. Whatever movement now occurs must be either towards or from the source of stimulus. I have said above that the axis orientation is perhaps the only effect of the acting reagent. PFEFFER ('84, p. 463 ; '88, p. 631), indeed, maintains that the stimulus does not directly cause a markedly more rapid locomotion in the case of bacteria and Flagellata ; but in the case of plasmodia it seems possible that such a hastening of movements occurs. (STAHL, '84.) However, it is necessary that measurements should be made in this matter. Further observations on the mechanics of taxis must be deferred to the general treatment of the subject in Chapter IX. SUMMARY OF THE CHAPTER We attempted in the first section to bring together observa- tions relating to the action of various chemical substances upon protoplasm with the aims of discovering the general laws of poison-action on protoplasm and of gaining an insight into the chemical structure of protoplasm and the chemical operations involved in the elementary vital processes. We ought now, therefore, to attempt to draw 'such conclusions as the imperfect and often confusing data we have collected will permit. 46 CHEMICAL AGENTS AND PROTOPLASM [Cn. I All the reagents with which we have dealt have been sub- stances capable of absorption by, mixture with, or solution in, water ; and the reason for this is that almost all proto- plasm is itself enveloped by water and largely composed of water. For the most part we have dealt with mixtures or solutions. Now the action of these is a double one. They exhibit, first, an osmotic action, and, secondly, they may attack the molecules of the protoplasm, transforming them. The osmotic action we will consider in the third chapter ; the transforming one alone concerns us now. It is not easy, without experiment, to say to which of these two categories of action the change wrought by any substance is due. To determine between the two possible causes it would be desirable in each case to treat the protoplasm to a control solution having the same osmotic action as the first, but no transforming effect. If such a solution produces no modification of the protoplasm, then the effect wrought by the first reagent is due purely to molecular trans- formations. It is not easy to find a reagent of which we may be certain that it acts only osmotically. NaCl is probably more generally useful in this way than any other substance. In the experiments which have hitherto been made, this double action of solutions has not been sufficiently considered. Hence, a doubt concerning the immediate cause hangs about many of the phenomena described in the first section. The first principle which the data collected establish is that the protoplasm of different organisms is dissimilar. This is shown by the diversity in their chemical reactions ; by the fact that whereas, in one case, a certain percent solution causes so extensive a molecular transformation as to result in death, in another, no injurious effect is produced. Thus, according to BOER ('90, p. 479), it takes of gold chloride to kill — TABLE V Anthrax bacillus 0.0125% Cholera spirillum 0.1% Diphtheria bacillus 0.1% Typhoid bacillus 0.2% Glanders bacillus 0.25% SUMMARY OF THE CHAPTER 47 Thus the weak solution, 0.0125%, of AuCl3, which is fatal to anthrax, does not injure the glanders bacillus, which requires a solution 20 times as strong ; and we conclude that the chemi- cal constitution of the glanders bacillus must be different from that of anthrax. The dissimilarity of the different protoplasms may be either a qualitative or a quantitative one. That is to say, the kinds of molecules, or the proportions of the different molecules, may differ in the two cases. If we assume that gold chloride acts upon protoplasm by the Au replacing some of the H in an amido-acid, then the diversity in action of AuCl3 upon anthrax and typhoid may be accounted for by assuming that the amido- acids are dissimilar in anthrax and typhoid or that the propor- tion of the kinds especially affected is different in the two cases. To which of these two causes the diverse reactions to AuCl3 are due cannot yet, in any given case, be determined. A second principle which we may draw from our data is this: Some kinds of protoplasm have a general high resistance to all chemical agents, while other kinds have a high or low resistance to particular agents only (specific high or low resistance). Thus, in the case of pathogenic bacteria, the experiments of BOER ('90) show that, in general, the anthrax bacillus has a low resistance, and glanders a high one. His experiments were made with 10 reagents upon five kinds of bacteria. Table VII gives in modified form the results obtained by BOER. His results are given in the form of Table V; the present table is constructed from the original by making the mean of the five observations in each column unity and reducing the sepa- rate observations proportionately. Thus Table V becomes — TABLE VI Anthrax bacillus 0.09 Cholera spirillum 0.75 Diphtheria bacillus 0.75 Typhoid bacillus 1.51 Glanders bacillus 1.88 All the other determinations have been treated in like manner. Throughout the table the numbers in each column stand for 48 CHEMICAL AGENTS AND PROTOPLASM [Cn. I relative resistance capacity. The reagents are placed with the weakest-acting first. TABLE VII CAUSTIC CARBOLIC MURIATIC SULPHURIC METHYL SUBSTANCES. SODA ACID ACID ACID VIOLET. (NaHO). (C.H60). (HC1). (H2S04). MOLECULAR WEIGHTS. 4O 94 37 98 Anthrax bacillus .... 0.46 0.95 0.40 0.37 0.07 Cholera spirillum . . . 1.38 0.71 0.32 0.37 0.33 Diphtheria bacillus . . 0.69 0.95 0.63 0.94 0.17 Typhoid bacillus .... 1.09 1.43 1.46 0.94 2.22 Glanders bacillus .... 1.38 0.95 2.19 2.36 2.22 SILVER GOLD MALACHITE OXYCTANIDE SUBSTANCES. NITRATE CHLORIDE GREEN. OF Hg. AVERAGE. (AgN03). (AuClj). MOLECULAR WEIGHTS. 17O 304 Anthrax bacillus .... 0.20 0.09 0.02 0.93 0.388 Cholera spirillum . . . 1.04 0.75 0.17 0.62 0.632 Diphtheria bacillus . . 1.67 0.75 0.11 0.93 0.760 Typhoid bacillus .... 1.04 1.51 1.75 1.25 1.415 Glanders bacillus . . '. . 1.04 1.88 2.92 1.25 1.802 From this table we see that the bacillus of glanders is more resistant than that of anthrax (except in one instance, in which the resistance is equal in the two cases) whatsoever be the poison employed. The bacillus of glanders affords, thus, a good illustration of an organism with a general high resistance capacity. The diversity in general resistance capacity which is found among bacteria exists also among other organisms. Thus, the parasitic Ascaris has shown itself highly resistant in all cases in which the action of a poison on it has been compared with that on another species; for instance (p. 10) 0.1% chloral hydrate kills Infusoria, Rotifera, and diatoms in 24 hours, but Ascaris withstands this solution. Again, while 0.1% HCN kills Infusoria quickly, Ascaris resists 3% for 75 minutes. The general higher resistance may be due to one of three causes : SUMMARY OF THE CHAPTER 49 either to the fact that the protoplasm is protected from attack, as is the case with the encysted forms of Protozoa, which are very resistant ; or to the fact that the protoplasm is not so readily acted upon by reagents brought actually in contact with it, due to diminished amount of water or other structural modifications ; or, finally, that the protoplasm has a different composition, certain unstable molecules found in other kinds of protoplasm being absent. We will now consider the phenomena of diversity in specific resistance of protoplasm. A case of specific low resistance is found in the nervous tissue. Thus many of the alkaloids, e.g. nicotine and cocaine, are almost indifferent to the protoplasm of Protista, but act towards the nervous system as powerful poisons. Hence we are led to conclude that nervous protoplasm contains especially unstable compounds, upon which its action depends. When they are subjected to the action of very weak -towards most substances, indifferent — reagents, extensive and fatal transformations occur. Cases of specific high resistance are apparently found in some glands which secrete intense poisons, or in some organisms which live in solutions of some usually poisonous agent. Ex- amples of this class are the HCl-secreting glands of the Vertebrate alimentary tract, the poison-glands of venomous serpents, and the H2SO4-secreting glands of Gasteropoda ; also the vinegar eel, which lives in 4% acetic acid. It ought to be said that it is largely an inference based upon experi- ments on acclimatization, that these glands or organisms will not show a general high resistance. Experiments are needed to determine this point. As to the cause of specific high resist- ance, I believe that much light is gained from the facts of acclimatization, and that any sufficient theory of the latter would serve also to explain the former (see p. 30). Under the general poisons we have distinguished four main groups : a. oxidizing poisons ; b. salt-forming poisons ; c. sub- stitution poisons ; d. catalytic poisons. I will comment briefly upon the action of the poisons of each of these groups. a. Oxidizing Poisons.- -The ordinary oxidation processes in living protoplasm involve the consumption not of the proto- 50 CHEMICAL AGENTS AND PROTOPLASM [Cn. I plasm itself, but of the thermogenic substances stored therein (sugar, yolk). After these have been consumed in starvation, or when the organism is subjected to the action of oxidizing poisons, the molecules of the protoplasm become oxidized. All protoplasm which is readily accessible must be injured by the direct attacks of kk active " oxygen. b. Salt-forming Poisons.- -The facility with which an acid or a base forms salts with the protein substances of the proto- plasm must depend, in large part, upon the quality of the protein molecules. It is well known that certain protein sub- stances, such as keratin, chitin, and fibrin, are not readily acted on by acids or bases, and it seems necessary to suppose that some such resistant proteids are the essential parts of glands which secrete these reagents. Into this group fall the salts of heavy metals characterized by their extraordinary fatalness. c. Substitution Poisons.- -This group comprises, besides a few sulphur compounds, almost exclusively nitrogenous sub- stances, and among these a large proportion of compounds with closed chains. As many of these are indifferent to dead albumen, but violent poisons to living protoplasm, it is clear that the latter must contain certain extremely unstable groups (amido-, aldehyde-, and keton-groups, LOEW, '80). Among these poisons the relation between molecular structure and poisonous action is very marked, especially in the nitro-com- pounds. Thus, bodies containing H united with N are poison- ous in direct proportion to the number of H atoms so combined. It seems probable that H so combined is very easily given up to the molecules of the living substance, destroying them. H in the hydroxyl radical seems also more easily parted with than H joined to C. d. Catalytic Poisons. - - Chiefly organic compounds of the fat series, which have little chemical energy and produce, for the most part, amesthesia. The poisonous action seems here proportional to the complexity and instability of the compound. Thus, in many groups, when the alkyls CH3 — , C2H5 — , etc., are successively introduced, the substance grows more poison- ous as the number of atoms in the alkyl increases. In the methan series and among sulphureted compounds the substi- tution of Cl for H increases the poisonous action. SUMMARY OF THE CHAPTER 51 The study of the action of poisons upon protoplasm gives us an insight into the extreme complexity of the living substance -its composition out of numerous kinds of compounds, many of which are extremely unstable. Not all protoplasm contains the same compounds, hence it must be a very dissimilar thing in different organisms. Not all of the compounds in any pro- toplasmic body are essential to life, for we may act upon a protoplasmic body by a weak reagent, and gradually change its composition so that it will no longer be killed by the strong solution, and all of this without perceptible injury --at least, tliis is the conclusion to which the study of acclimatization of Protista leads us. The altered chemical constitution will be transmitted in the division of the individual, and thus the composition of the protoplasm of a race will have been deter- mined by the medium in which it and its ancestors have been living. Finally, we may consider what light the action of reagents throws upon the processes involved in the elementary vital functions. The normal movement of protoplasm is profoundly modified by interfering with the oxygen supply. Thus, when the oxygen pressure is diminished, movements are retarded ; in the presence of pure oxygen they are accelerated. Some anaes- thetic or paralyzing agents — e.g. chloroform and some alka- loids, veratrin, atropin, cocaine, strychnin, and antipyrin — give rise first to acceleration, then to disappearance of movements in the protoplasm. Protoplasmic movement is, consequently, closely associated with oxidation, and it does not occur in the absence of irritability. Normal locomotion is interfered with by strychnin and co- caine. Their stimulating action produces accelerated move- ments, and these are accompanied by loss of coordination. Since many catalytic poisons (ansesthetics) destroy irrita- bility, one may conclude from the action of these chemical agents that (p. 7) stability of molecular movement is essential to the performance of this function. Disturbance of the excretory function results from the action of CO, NH3, chloroform, cocaine, strychnin ; at least, an ex- cessive vacuolation of the protoplasmic body occurs under the action of these agents. 52 CHEMICAL AGENTS AND PROTOPLASM [Cn. I Experiments on cliemotaxis show that many substances brought near to protoplasmic bodies control their locomotion. The effect upon locomotion depends both upon the kind of protoplasm and the strength of the reagent. In many cases, a certain strength of reagent attracts an organism, while a stronger solution repels, and a weaker solution is indifferent. In such a case we may speak of the protoplasm as being attuned to the attracting strength of the reagent. We find great diver- sity in the strength of solution of a reagent to which different protoplasms are attuned. This difference of attunement to chemotactic reagents is parallel to the difference in strength of the killing solution of various protoplasms. As the latter is probably due to the past action of chemical agents upon the protoplasm, so is also the former. APPENDIX TO CHAPTER I Cytotaxis ( = Cytotropism) Roux ('94) has given the latter name to a phenomenon which is probably only a special case of cliemotaxis, but which may be better considered apart. He isolated, in an indifferent medium, two or three cells from the egg of a frog (Rana fusca) at the morula or blastula stage of development. These he placed near each other upon a glass slide, and found that they moved slowly, and that the direction of the movement of any one cell was, under certain conditions, determined by the position of the other cell or cells. In order to perform the experiment a proper medium in which to study the movement of the cells must be prepared as follows : a small quantity — 5 to 10 ccm. — of fresh egg albumen (not cut up, but with the albumen threads intact) is filtered through clean wadding, and the completely clear filtrate is used. In other cases a more or less strong salt solution is employed. The cleavage cells are isolated in the filtrated albumen, on a glass plate, by means of needles. To diminish evaporation the glass plate is put into a shallow glass vessel containing several drops of water. When two cells were placed near each other (about one-fourth of their diameter apart), the distance between them diminished. The approach took place along a line joining the two cells ; APPENDIX — CYTOTAXIS 53 and when several pairs of cells were in the field, this movement took place in various directions, indicating that their move- ment was not determined by conditions outside the approaching cells. To get further light on the migration of the cells, their distance apart was meas- ured at short intervals of time. The results of two series of such meas- urements are represented graphically in Figs. 6 and 7. In both of these dia- grams the heavy lines indicate the successive positions assumed by four points ; namely, the points of the two cells which are nearest each other and those which are most distant. In the first case the cells .traverse the distance of their diameters (58 /A) in about 10.5 minutes. The rate of migration is, however, extremely variable. In some cases the cells seem even to move apart (negative cytotaxis?). Certain special cases are worthy of considera- tion. When a third cell lies near an approaching pair, the path of migra- tion of the pair may become convex towards the third cell. Two cell-complexes, each composed of three or four cells, may approach and connect. But masses composed of a larger number of cells form " closed complexes ' which show no cytotactic activity. The isolated cells of differ- FIGS. fi, 7. — Two sets of curves, showing the course of "cytotactic" movements of the cleavage cells of the frog. In each figure the dotted line represents a diameter of the cell. The full line represents the successive positions of the extremities of the diameters as the cells approach. The distances between horizontal lines = 4^ ; between vertical lines, 75 seconds. (From Roux, '94.) 54 CHEMICAL AGENTS AND PROTOPLASM [Cn. I ent eggs of the same species behave like cells from the same egg. By these important experiments it is established that, inside of the body, parts may, act upon parts, determining the direc- tion of motion. The importance of this fact will be discussed in a later Part of this book. LITERATURE ADDUCO, V. '90. Sur Pexistence et sur la nature du centre respiratoire bulbaire. Arch. Ital. de Biol. XIII, 89-123. 21 March, 1890. ADEKHOLD, R. '88. Beitrag zur Kenntnis richtender Kraf te bei der Bewe- gung niederer Organismen. Jena. Zeitschr. XXII, 310-342. ALBERTONI, P. '91. Wirkung des Cocains auf die Contractilitiit des Proto- plasma. Arch. f. d. ges. Physiol. XLVIII, 307-319. 28 Jan. 1891. BERNARD, C. '78. Lecons sur les phenomenes de la vie communs aux ani- maux et aux vegetaux. Tome I, 404 pp. Paris. BOER, O. '90. Ueber die Leistungsfahigkeit inehrerer chemischer Desin- fectionsmittel bei einiger fiir den Menschen pathogenen Bacterien. Zeitschr. f. Hygiene. IX, 479-491. BOSCH, C. TEX '80. De physiologische werking van chinamine. Onder- zoek. Physiol. Lab. Utrecht. V, 248-292. BINZ, C. '67. Ueber die Einwirkung des Chinin auf Protoplasma-Bewe- gungen. Arch. f. raik. Anat. Ill, 383-389. BINZ, C. and SCIIULZ, H. '79. Die Arsengiftwirkungen vom chemischen Standpunkt betrachtet. Arch. f. exper. Path. u. Pharm. XI, 200- 230. BOKORNY, T. '86. Das "Wasserstoffsuperoxyd und die Silberabscheidung durch actives Albumin. Jahrb. f. wiss. Bot. XVII, 347-358. '88. Ueber die Einwirkung basischer Stoffe auf das lebende Protoplasma. Jahrb. f. wiss. Bot. XIX, 206-220. '93. Ueber die physiologische Wirkung der tellurigen Saure. [Abstr. in] Bot. Centralbl. LVII, 16. BOURNE, A. G. '87. The Reputed Suicide of Scorpions. Proc. Roy. Soc. London. XLII, 17-22. BUCHNER, H. '91. Die chemische Reizbarkeit der Leukocyten und deren Beziehung zur Entziiiidung und Eiterung. Sb. Ges. Morph. u. Physiol. Munchen. VI, 148-152. '92. Die keirntodtende, die globulicide und die antitoxische Wirkung des Blutserums. Miinchener Med. Wochenschr. XXXIX, 119-123. CALMETTE, A. '94. L'immunisation artificielle des animaux centre le venom des serpentes et la therapeutique experimentale des morsures veni- meuses. C. R. Soc. de Biol. (10) I, 120-124. LITERATURE 55 CHARPENTIER, A. '85. Action de la cocaine et d'autres alcalo'ides sur cer- tains infusoires a chlorophylle. C. R. Soc. de Biol. XXXVII, 183, 184. CLARK, J. '89. Protoplasmic Movements and their Relation to Oxygen Pressure. Proc. Roy. Soc. Loud. XL VI, 370, 371. June 20, 1889. COHN, F. '94. Formaldehyd und seine Wirkung auf Bacterien. Bot. Centralbl. LVII, 3-6. DANILEWSKI, B. '92. Ueber die physiologische Wirkung des Coca'ins auf wirbellose Thiere. Arch. f. d. ges. Physiol. LI, 44(3-454. DAREMBERG, G. '91. Sur le pouvoir destructeur du serum sanguin pour les globules rouges. C. R. Soc. Biol. XLIII, 719-721. DARWIN, C. '75. Insectivorous Plants. 462pp. New York : Appleton & Co. DAVENPORT, C. B. and NEAI,, H. V., '96. On the Acclimatization of Organisms to Poisonous Chemical Substances. Arch. f. Entwick. d. Organismen. II, 564-583. 28 Jan. 1896. DEMOOR, J. '94. Contribution a 1'etude de la physiologic de la cellule (in- dependance functionnelle du protoplasma et du noyau). Arch, de Biol. XIII, 163-244, Pis. IX, X. 28 Feb. 1894. DEWITZ, J. '85. Ueber die Vereinigung der Spermatozoen mit dem Ei. Arch. f. d. ges. Physiol. XXXVII, 219-223. 29 Oct. 1885. EHRLICH, P. '91. Experimented Untersuchungen liber Immunitat. I Ueber Ricin. II Ueber Abrin. Deutsche med. Wochenschr. 976-979; 1218, 1219. ELFVING, F. '86. Ueber die Einwirkung von Ather und Chloroform auf die Pflanzen. Ofversigt af Finska Vetensk. Soc. Fbrh. XXVIII, 36-53. ENGELMAXN, T. W. '81. Neue Methode zur Untersuchung der Sauer- stoffauscheidung pflanzlicher und thierischer Organismen. Arch. f. d. ges. Physiol. XXV, 285-292. 20 June, 1881. '82. Ueber Licht- und Farbenperception niederster Organismen. Arch. f. d. ges. Physiol. XXIX, 387-400. 3 Nov. 1882. '94. L 'emission d'oxygene sous 1'influence de la lumiere, par les cellules a chromophylle, demontree au in oven de la methode bacterienne. Arch. Neerland. XXVIII, 358-371. FAYRER, J. '74. The Thanatophidia. 2d ed., 178 pp., 31 pis. London : Churchill. FROMANN, C. '84. Untersuchungen iiber Struktur, Lebenserscheinungen und Reaktionen thierischer und pflanzlicher Zellen. Jena. Zeitschr. XVII, 1-349. Taf. I-III. 19 Jan. 1884. GREENWTOOD, M. '90. On the Action of Nicotin upon Certain Invertebrates. Jour, of Physiol. XI, 573-605. Dec. 1890. HEIDENSCHILD, W. '86. Untersuchungen iiber die Wirkung des Giftes der Brillen- und der Klapperschlange. Jahresber. d. Thier-Chem. XVII, 330. [From Inaug. Diss. Dorpat. Lookmann, 1886.] HERTWIG, O. and R. '87. Ueber den Befruchtungs- und Teilungsvorgang des tierischen Eies unter dem Einfluss ausserer Agentien. Jena. Zeitschr. XX, 120-241. 8 Jan. 1887. 56 CHEMICAL AGENTS AND PROTOPLASM [Cn. I HOFER, B. '90. Ueber die lahmende Wirkung des Hydroxylamins aiif die contractilen Elemente. Zeitschr. f. wiss. Mikr. VII, 318-326. 18 Dec. 1890. KANTHACK, A. A. '92. The Nature of Cobra Poison. Jour, of Physiol. XIII, 272-299. May, 1892. KRUKENBERG, C. F. W. '80. Vergleichend-physiologische Studien. 1 Reihe. 1 Abth., 77-155. KUHXE, W. '64. Untersuchungen liber das Protoplasma und die Contrac- tilitat. 158 pp., S Taf. Leipzig: Engelmann. LEBER, T. '88. Ueber die Entstehung der Entziindung und die Wirkung der eiitziiiidungserregenden Schadlichkeiten. Fortschritte d. Medicin. VI, 460-464. LOCKE, F. S. '95. On a Supposed Action of Distilled Water as such on Cer- tain Animal Organisms. Jour, of Physiol. XVIII, 319-331. 5 Sept. 1895. LOEB, J. '90. Der Heliotropismus der Thiere und seine Uebereiustimmung mit dem Heliotropismus der Pflanzen. 118pp. Wiirzburg: Hertz. LOEW, O. '77. Lieutenant Wheeler's Expedition durch das siidliche C'ali- fornien im Jahre 1875. Petermann's Geogr. Mitth. XXIII, 134-140. '83. Sind Arsenverbindungen Gift fiir pflanzliches Protoplasma? Arch. f. d. ges. Physiol. XXXII, 111-113. 12 Sept. 1883. '85. Ueber den verschiedenen Resistenzgrad im Protoplasma. Arch. f. d. ges. Physiol. XXXV, 509-516. 30 Jan. 1885. 85a. Ueber die Giftwirkung des Hydroxylamins verglichen mit der von anderen Substanzen. Arch. f. d. ges. Physiol. XXXV, 51(3-527. 30 Jan. 1885. '87. Ueber Giftwirkung. Arch. f. d. ges. Physiol. XL, 437-447. 18 May, 1887. '88. Physiologische Notizen iiber Formaldehyd. Sb. Ges. f. Morpol. u. Physiol. Munchen. IV, 39-41. '91. Die chemischen Verhaltnisse des Bakterienlebens. Centralbl. f. Bakteriol. u. Parasitenk. IX, 659-663; 690-697; 722-726; 757-760; 789-790. May-June, 1891. '92. Ueber die Giftwirkung des Fluornatriums auf Pflanzenzellen. Miinchener Med. Wochenschr. XXXIX, 587. '93. Ein naturliches System der Gift-Wirkungen. 136 pp. Munchen, Wolff u. Liineburg, 1893. LOEW, O. and BOKORNY, T. '89. Ueber das Verhalten von Pflanzenzellen zu stark verdiinnter alkalischer Silberlbsung. Bot. Centralbl. XXXIX, 369-373 ; XL, 161-164, 193-197. LUBBOCK, J. '84. Ants, Bees, and Wasps. Internat. Sci. Ser. XLII, 448 pp. 5 pis. New York : Appleton. MARMIER, L. '95. Sur la toxine charbonneuse. Ann. de 1'Inst. Pasteur. IX, 533-574. MASSART, J. '91. La sensibilite h la concentration chez les etres unicellu- laires marins. Bull. 1'acad. roy. Belg. (3) XXII, 148-167. LITERATURE 57 MASSART, J. '93. Sur 1'irritabilite des Xoctiluques. Bull. Sci. France et Belg. XXV, 59-76. 23 Oct. 1893. MIGULA, W. '90. Ueber den Einfluss stark verdiinnter Saurelb'sungen auf Algenzellen. Inaug. Diss., Breslau, 1889. Abstract in Bot. Centralbl. XLI, 207. 12 Feb. 1890. METSCHNIKOFF, E. '92. Le9ons sur la pathologic comparee de 1'inflamma- tion. Paris. 1892. NAGELI, C. v. '93. Ueber oligoclynamische Erscheinungen in lebenden Zellen. Neue Denkschr. all. schvveiz. Ges. XXXIII, Abth. 1, 52 pp. NIKOLSKI, W. and DOGIEL, J. '90. Zur Lehre iil>er die physiologische Wirkung des Curare. Arch. f. d. ges. Physiol. XLVII, 08-115. 28 Feb. 1890. OHLMULLER, '92. Ueber die Eimvirkung des Ozons auf Bacterien. Chem. Centralbl. 1892, I, 860. [Abstr.] PANETH, J. '89. Ueber das Verbal ten von Infusorien gegen Wasserstoff- superoxyd. Centralbl. f. Physiol. Ill, 377-380. 9 Nov. 1889. PFEFFER, W. '84. Locomotorische Richtungsbewegungen durch chemische Reize. Unters. a. d. bot. Inst. Tiibingen. I, 363-482. '88. Ueber chemotaktische Bewegungeii von Bacterien, Flagellaten und Volvocineen. Untersuch. bot. Inst. Tubingen. II, 582-662. RICHET, C. '89. La chaleur animale. 307 pp. Paris : Alcan. ROEMER, F. '92. Die chemische Reizbarkeit thierischer Zellen. Arch. f. path. Anat. u. Physiol. CXXVIII, 98-131. 1 April, 1892. ROSSBACH, M. J. '72. Die rythmischen Bewegungserscheinungen der ein- fachsten Organ ismen und ihr Verhalten gegen physikalische Agentien und Arzneimittel. Verh. phys.-med. Ges. Wiirzburg. I, 179-242 ; also in Arbeiten a. d. zool.-zoot. Inst. Wiirzburg. I, 9-72. Roux, W. '94. Ueber den Cytotropismus der Furchungszellen des Gras- frpsches (Rana fusca). Arch. f. Entwick. d. Organismen I, 43-202. Taf. I-III. SCHRODER, W. v. '85. 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CHAPTER II EFFECT OF VARYING MOISTURE UPON PROTOPLASM IN this chapter it is proposed to speak (I) of the amount of water in organisms; (II) of the effect of desiccation upon the functions of protoplasm ; (III) of the acclimatization of organ- isms to desiccation, and (IV) of the control of the direction of locomotion by moisture — hydrotaxis. § 1. ON THE AMOUNT OF WATER IN ORGANISMS Any theory of the structure of protoplasm must recognize that water forms the greater part of the whole mass ; between 60% and 90%. In the case of dry seeds and grains, however, it may fall below 15%. Many determinations have been made of the proportion of water in the body of entire organisms and in their organs. I give in tabular form some of these determina- tions, which were made by BEZOLD ('57), designated by (B); KRUKENBERG ('80), designated by (K); and LIEBERMANN ('88), designated by (L). TABLE VIII SPECIES. CONDITIONS OF WEIGHING. WATER. Various sponges (K) Medusa : Rhizostoma Cuvieri (K) . Various Actinia (K) Alcyonium palmatum (K) .... Asteracanthion glacialis (K). . . Lumbricus complanatus (K) . . . In most cases, kept a short time in fresh sea water ; dried on surface and weighed. Whole animal, directly from water Piece of disc. A few minutes after removal from sea. A little water 1 ist from central cavity Weighed when fresh, 73.5 g. Weighed 850 g. 2 large specimens 58 84.0 to 74.5 95.4 95.0 87.7 to 83.2 84.3 82.3 87.8 § 2] DESICCATION AND PROTOPLASMIC FUNCTIONS 59 SPECIES. CONDITIONS OF WEIGHING. WATER. Oniscus murarius (B). Squilla mantis (K) . . Astacus liuviatilus (B) Doris tuberculata (K). . Doriopsis linibata (K) . Arion enipiricorum (B). Limax maximus (B) . . Botryllus (K) Various Vertebrates (B) Chick (L) . . 7 days old 21 days old Turnip (root) '200 young individuals 1 individual 3 individuals weighing from 16. G to 27.4 g. 3 individuals 6 individuals weighing from 4.3 to 27.1 g. 4 individuals weighing from 0.1 to 17.1 g. 4 individuals weighing from 111.2 to 35.2 g. Embryo only, yolk removed Embryo only, ready to hatch From Goodale's Physiolog. Bot., p. 236 68.1 81.9 71.1 88.4 86.5 86.8 82.1 93.6 58.4 to 80.1 92.8 80.4 91.0 These determinations suffice to show that water immensely predominates over any other substance in active organisms, and indicate that it plays an important role. The role played by water is, in fact, extremely varied. It serves to maintain that unstable, foam-like structure of the protoplasm upon which its capacity for movement depends ; it acts as a solvent for matter taken into the protoplasmic body; and it serves to transport dissolved substances from place to place in the organism. In a word, it is essential to movement and to those chemical processes which constitute metabolism. § 2. ON THE EFFECT OF DESICCATION UPON THE FUNC- TIONS OF PROTOPLASM We may consider this topic under the following heads : (1) effect upon metabolism ; (2) effect upon the motion of protoplasm; and (3) the production of desiccation-rigor and death. 1. Effect of Dryness on Metabolism. — Since water is so essential to metabolism, we should expect that a diminution of metabolism would accompany dryness. And this is clearly the case. Thus dry seeds, in which the water is reduced to only 10 60 MOISTURE AND PROTOPLASM [Cn. II to 15%, when placed under conditions of temperature favor- able to metabolism, show almost no change in the course of days. This has been indicated also by an experiment of Kocris' ('90, p. 685), who placed seeds, which had been dried in a vacuum, in a receptacle connected with a GEISSLEK'S tube, such as is used in the spectroscopic study of gases. The air was completely pumped out of both vessels, and after some months a spectroscopic study of the gases in the GEISSLER'S tube showed no trace of nitrogen or carbon, yet the seeds later germinated. This experiment can hardly be considered to demonstrate KOCHS' point, however, since the seeds were deprived of oxygen, as well as moisture. The act of drying may, on the contrary, induce the manu- facture and elimination of certain secretions. This occurs apparently in many Protista, which form cysts in the drying pools. This phenomenon is seen again in some of the higher animals, — such as our garden slugs, -- which secrete slime in large amount when kept for a short time in a dry place. In both cases the result is of immense importance for the con- tinued life of the organism, --in both cases it is to be consid- ered a response to the stimulus afforded by evaporation of water. 2. Effect of Dryness upon the Motion of Protoplasm. - - We have seen that water plays an important role in the movement of protoplasm. When by any means the water is partly with- drawn, the protoplasmic currents will be slowed. When, on the contrary, protoplasm, which is lying in an u indifferent " medium, such as blood serum, is placed in distilled water, unusually active movements occur. This has been shown by ENGELMANN ('68, p. 446) in the case of the spermatozoa of the frog, and the ciliated epithelium of the frog's oesophagus just removed from its body. Similarly, DEHNECKE ('81) found that protoplasm of the tissue cells of the higher plants exhibited abnormally rapid movements upon adding water. These obser- vations indicate that water may act as a stimulus to the move- ment of protoplasm. 3. Desiccation-rigor and Death. — It is a familiar fact which has been established by over a hundred and fifty years of experimentation, that some organisms, when gradually dried, may cease from movements. This immotile condition has § 2] DESICCATION AND PROTOPLASMIC FUNCTIONS 61 sometimes been regarded as death. By PREYER ('91) it has been called "anabiosis." I shall call it desiccation-rigor, and correlate it with phenomena, produced by various other agents, which cause the cessation of a movement that is restored again when the action of the untoward agent is withdrawn. And these are just the conditions we meet with here, — ces- sation of activity without loss of power of revival. This was very evident from the work of SPALLANZANI (1787, Tom. II, pp. 212, 213). This author showed clearly that one and the same adult rotifer can be observed in the evaporating drop, until all the water is gone, and it has lost all movement and its normal form. If, after an hour, the slide is moistened again, the rotifer reassumes, by degrees, its natural form and activities. SPALLANZANI noticed, what has been the nearly unanimous testimony of subsequent observers, that a rotifer dried for hours on clean glass does not revive ; revivification occurs only when the rotifers have crawled into sand. As for the length of time during which desiccation-rigor may persist in rotifers without death occurring, we know only that it may be considerable, extending through months, and even years. Similar phenomena to those observed in rotifers have been described for tardigrades and certain nematodes, although these organisms have not been studied in so much detail. Among the tardigrades only those species which live in moss, and are thus especially liable to desiccation, withstand drying. (LANCE, '94.) Among nematodes, Tylenchus devastatrix, KUHN, which lives in grains of wheat, is a classic object of study. Strongylus rufescens is, according to RAILLIET ('92), capable of resisting dryness for 68 days or more. We may thus conclude that adult organisms of certain species may be subjected to desiccating influences, and that those same indi- viduals may resist them so as to reexhibit activities after the return of favorable conditions.* While the results of these drying experiments are scarcely doubted, much difference of opinion has arisen concerning the interpretation of the results. The first moot point is the degree of desiccation which the protoplasm of the organisms * See in connection with this the valuable report of BROCA ('61). 62 MOISTURE AND PROTOPLASM [Cn. IT experiences. Many writers have assumed that this has been rendered in their experiments very great or nearly perfect. Thus DOYERE ('42, p. 28) says : " What is the condition of the animalcules in the dried sand of the gutters? I have never seen them, at such times, in any other condition than reduced to spangles as fragile and more deformed than when dried free on the glass. I have never discovered a single one which manifested any traces whatever of life, or which did not present all the appearances of a complete desiccation. Never- theless, I do not pretend by this to invalidate all contrary asser- tions ; the principal fact, that of the return to life after an absolute desiccation, is not affected thereby." The physicist GAVARKET ('59, p. 317) subjected, for 34 days, moss contain- ing rotifers to a vacuum having a pressure of only 4 mm. of mercury, and other experimenters have likewise employed a similar "chemically drying" device, which they believed capa- ble of extracting all water from the protoplasm. The evidence that all water is withdrawn from the body of the organism is often very slight. The fact that the seeds or plant tissues in which nematodes or tardigrades are living, have been dried until they lose no appreciable weight, is not sufficient evidence that their inhabitants are completely dried. On the other hand, there is positive evidence that one, at least, of the organisms which has been considered as having been absolutely dried, can protect itself from this condition. It is especially DAVIS ('73) who has shown this. This author has experimented with the rotifer Philodina roseata. When dried on a glass plate with sand, it assumes a spherical form. At the same time, however, it secretes a gelatinous envelope. Thus encapsuled it may rest for days until upon the addition of water it reassumes its active, adult form. That a layer of such gelatinous substance is sufficient to resist the drying action of a vacuum-chamber with sulphuric acid, was illus- trated by putting grapes varnished with gelatine in such a dry chamber for one week. They emerged in a fresh, juicy con- dition. One of the encapsuled rotifers was crushed after "desiccation" and yielded under the cover-glass a drop of fluid. In this case then the rotifer was not fully dried. DAVIS accounts for the fact that isolated rotifers dried on a clean § 2] DESICCATION AND PROTOPLASMIC FUNCTIONS 63 slide will not survive desiccation, on the ground that the sand forms a necessary retreat in which the organism can quietly encapsule itself. Of the fact of such encapsuling there can be no doubt ; it is abundantly substantiated by the testimony of HUDSON ('73 and '86). There is a doubt, however, whether this encapsuling is a phenomenon common to all organisms which can resist desiccating influences, and, therefore, whether DAVIS'S explanation is generally applicable. To sum up : I believe there is no sufficient evidence that an adult organism or active protoplasm of any sort can rapidly lose all of its " free water " without such a destruction of its finer structure as would make it incapable of exhibiting vital activities upon moistening again. A much greater capacity undoubtedly inheres in spores and seeds. Thus KOCHS ('90) subjected perforated seeds of Zea mais, Phaseolus, and Triticum vulgare to an almost perfect vacuum (made by a mercury pump) for 8 days, and they nearly all germinated. Even the small radish seed, with part of the cuticula removed, subjected to a vacuum for three weeks ger- minated perfectly. Probably there is no limit to the amount of desiccation which seeds and other masses of protoplasm especially adapted to resist desiccation can withstand. The second moot point is this : Is the protoplasm, rendered immotile by drying, living or not ? SPALLANZANI prejudiced the question by the title of his chapter on this matter, - " Observations and experiments on some marvellous animals which the observer can at his will make pass from death to life" ; and he and many of his successors argue that death has truly occurred. PREYER ('91), however, prefers to reserve the term "dead" for protoplasm which is at the same time lifeless and incapable of life ; while to protoplasm which is lifeless but capable of revivification he applies the term "anabiotic."' The question then is this, is life truly suspended during the immo- tile state ? If we think of life as the sum of the chemical changes occurring in the protoplasm, we shall realize that all degrees of vitality, even to complete cessation of activity, may occur without our being able anywhere to say at this point life becomes extinct. We can hardly hope ever to deny that mini- mum vital changes are occurring ; since the minimum changes 64 MOISTURE AND PROTOPLASM [Cn. II must be beyond our ken. That these vital changes are some- times exceedingly slight, is sufficiently indicated by the experi- ments upon seeds performed by KOCHS ('90), and referred to on p. 60. That, however, slight changes are occurring even in seeds is indicated by the fact that dessication-rigor cannot continue indefinitely without loss of the power of revivifi- cation. In the case of the rotifers, tardigrades, and nematodes, months, and even years, may elapse without complete loss of capacity for revivification. It is generally admitted, however, that in cases of long-continued drought, the chances of revitalizing upon moistening are much diminished.* In the case of seeds it has been maintained that under certain conditions, such as are realized in the mummy-graves of Egypt, life may persist for more than a thousand years. However, the experiments of MTJNTER ('47), and more especially of KOCHS ('90, p. 683), throw doubt upon this assertion, since they found that the ancient, charred seeds fell to pieces in water like lime. As for seeds preserved above ground in the ordinary way, KOCHS was assured by seedmen that they could not remain capable of germination over 10 years. These facts go to show that gradual changes occur in the dry protoplasm which are prob- ably metabolic changes, i.e. vital changes ; and that therefore life is hardly extinct in the very dryest protoplasm. The whole matter of desiccation-rigor is, after all, one with which we are familiar in nature's larger laboratory. Many Protista, when the ponds in which they live dry out, encyst themselves and enter into .a motionless condition in which they resist the hot and dry summer winds. Thus, they may lie for weeks, and, as experimentation has shown, they may be dried for several years (see BUTSCHLI, '89, p. 1663, for references) without loss of capacity for revivification. The same device * Thus KAILLIET ('92) says of Strongylus rufescens : "I have seen them regain their activity after 42 and even 68 days of desiccation. However, this activity is much slower in manifesting itself. After the course of a month a contact of 8 to 10 minutes is sufficient to bring them back to movement. . . . After 68 days at least 50 minutes are required, and certain individuals have shown activity only after 1 hour and 20 minutes. Moreover, the movements were limited, and only a small number of cases contorted themselves like ordi- nary Anguillulidse." § 3] ACCLIMATIZATION TO DESICCATION 65 for resisting desiccation is seen in the gemmules of sponges, and Bryozoa, the eggs of many animals, and the spores of many plants. Thus some protoplasm normally responds to the stimulus of drought by going into desiccation-rigor. While, as we have seen, some protoplasmic bodies may be dried as far as possible by the ordinary methods used in chem- istry without death ensuing, other bodies, especially the adult forms of higher organisms, whose cellular respiration is de- pendent upon a circulating fluid, are killed by desiccation. For loss of this fluid or desiccation-rigor in the pumping muscles will produce asphyxia. But these conditions do not militate against the belief that there is no necessary lower limit to the amount of water which must occur in quiescent protoplasm in order that it may retain vitality during a lim- ited period. § 3. ON THE ACCLIMATIZATION OF ORGANISMS TO DESICCATION We have seen in the last section that certain organisms are more capable of resisting desiccation without fatal effect than others ; e.g. rotifers, tardigrades, and Tylenchus. Now it is clear that these organisms are especially apt to become dried, so that it is possible that their high capacity for resistance has been produced by acclimatization without selection. I shall here add certain other cases of resistance to dryness which I believe, but cannot prove, to have been thus produced. LANCE ('94) has mentioned, as already stated, that only those tardi- grades which live in the moss of gutters (where they are alternately wet and dried), and not those living in water, show the phenomenon of revivification. CERTES ('92) has found that, although marine Ciliata cannot, in general, withstand desiccation, those from the chotts and saline lakes of Algeria may be dried like those from fresh-water ponds and swamps. The difference in resistance between the forms dwelling in the sea and in inland salt-water ponds is doubtless due to the fact that the former are not regularly desiccated, while the latter are ; consequently the latter alone have had a chance to become acclimated to desiccation. 66 MOISTURE AND PROTOPLASM [Cii. II § 4. THE DETERMINATION OF THE DIRECTION OF MOVE- MENT BY MOISTURE, — HYDROTAXIS This phenomenon has been described by STAHL ('84) in ^Ethalium. When this Myxomycete is placed in the dark upon a glass plate covered with several layers of moistened filter paper, it expands uniformly over the homogeneously moistened substratum. If, now, the plate be placed in a drying chamber, the paper dries slowly, and one can see that the mass of the plasmodium draws towards those places which remain longest damp. If a dilute gelatine jelly is smeared upon a glass slide supported in a horizontal position about 2 mm. above the plasmodium, still in the dark chamber, the plasmodium sends up branches, some of which may touch the gelatine and spread out over it. If the water dries still further, the entire Myxomy- cete may become transferred to the slide above. If, now, the paper be moistened again, the plasmodium sends branches down to it. STAHL'S explanation is that of the old mechanical school. He says, the peripheral protoplasmic layer lying next the dryer region is poorer in water ; while that next the damper part of the substratum contains much water. If it be assumed that the internal streaming tends to occur uniformly towards all points of the periphery, it is clear that the dryer, more consistent part will offer greater resistance than the more fluid part, and in this part, therefore, branches will tend to arise. In correspondence with the interpretations which we have hitherto placed upon similar phenomena I prefer to call this a case of response to the stimulus of excessive moisture — in any case it may be designated positive hydrotaxis. When, however, the plasmodium of JEthalium is in the fruit- ing stage, it retreats from the moister part of the substratum, and other Myxomycetes in the fruiting stage show the same negatively hydrotactic tendency. Thus the same agent, water, stimulates the same organism, at different stages, to reverse movements. I will now summarize the conclusions concerning the effect of water upon protoplasm. Water constitutes by far the larger part of protoplasm and of all active organisms. Metabolism is LITERATURE 67 directly dependent upon it, and certain excretory processes are stimulated by it. The motion of protoplasm is likewise de- pendent upon water, which determines the unstable condition of that substance. Desiccation, therefore, produces a rigor, and this may continue, in the absence of water, for months, and even years, the organism being, meanwhile, ready to awake to activity upon the return of moisture. The degree of desic- cation which organisms can resist varies. In the case of the higher organisms, it is slight ; in the case of bodies especially adapted to resist dryness (spores, seeds, statoblasts), there is, perhaps, no practicably attainable limit to the dryness which their protoplasm may undergo without loss of power of revivifi- cation. The condition of desiccation-rigor is not known to be one of death which is replaced by life upon return of moisture. It is probably rather a condition of minimum metabolism. The great resistance capacity exhibited by certain organisms is correlated with their liability to desiccation in their natural surroundings. Finally, Myxomycetes (and probably other or- ganisms) respond to inequalities in the amount of moisture in their environment, moving either towards or from greater moisture. We recognize thus that the activities of protoplasm are to a large extent dependent upon the existence of water in it ; and that protoplasm reveals itself as sensitive to differences in the amount of moisture, responding by secretions, by the assumption of a quiescent condition, and by locomotion with reference to water. LITERATURE BLAINVILLE, H. DE '26. Sur quelques petits Animaux qui, apres avoir perdu le mouvement par la dessication, le reprennent comme aupara- vant quand on vient a les mettre dans Feau. Ann. des Sci. Nat. IX, 104-110. BEZOLD, A. vox '57. Untersuchungen iiber die Vertheilung von Wasser. organischer Materie und anorganischen Verbindungen im Thierreiche, Zeitsch. f. wiss. Zool. VIII, 487-524. 26 Feb. 1857. Bos, R. '88. Untersuchung iiber Tylenchus devastatrix, KUHX. Biol. Cen- tralb. VII, 646-659. 1 Jan. 1888. BROCA, P. '61. Rapport sur la question soumise k la Societe de Biologie par MM. POUCHET, PENNETIER, TIXEL et DOYERE au sujet de la revi- viscence des animaux desseches, lu par M. PAUL BROCA au nom d'une 68 MOISTURE AND PROTOPLASM [Cn. II commission comp. de MM. BALBIANI, BERTHELOT, BROWN-SEQUARD, DARESTE, GUILLEMIN, CH. ROBIN et BROCA. Mem. Soc. de Biol. (3), 1-139. BUTSCHLI, (). '89. Protozoa (part). BRONX'S Klass. u. Ord. d. Thier-reichs. I Bd. 1585-2035. 1889. CERTES, A. '92. Sur la vitalite des germes des organismes microscopique des eaux douces et salees. Bull. Soc. Zool. France. XVII, 59-62. DAVIS, H. '73. A New Callidina: -with the Result of Experiments on the Desiccation of Rotifers. Monthly Micr. Jour. IX, 201-209. 1 May, 1873. DEHNECKE, C. '81. Einige Beobachtungen iiber den Einfluss der Prapa- rationsmethode auf die Bewegungen des Protoplasma der Pflanzenellen. Flora. -LXIV, 8-14, 24-30. 1, 11 Jan. 1881. DOYERE, M. P. L. N. '42. Me moire sur les Tardigrades. Ann. des. Sci. Nat. (2) XVIII, 5-35. ENGELMANN, T. W. '68. Ueber die Flimmerbewegung. Jena. Zeitschr. IV, 321-479. FAGGIOLI, F. '92. De la pretendu reviviscence des Rotiferes. Arch. Ital. de Biol. XVI, 360-374. 31 Jan. 1892. FROMENTEL, E. DE '77. Recherches sur la revivification des rotiferes, des anguillules et des tardigrades. C. R. Assoc. fran9- 1'avanc. des sci. VI (Le Havre), 641-657. GAVARRET, J. '59. Quelques experiences sur les rotiferes, les tardigrades et les anguillules des mousses des toits. Ann. Sci. Nat. (Zobl.). (4), XI, 315-330. HUDSON, C. T. '73. Remarks on Mr. Henry DAVIS' Paper "On the Desic- cation of Rotifers." Monthly Micr. Jour. IX, 274-276. 1 June, 1873. '86. [Desiccation of Rotifers.] Jour. Roy. Micr. Soc. (2) VI, 79. KOCHS, W. '90. Kann die Kontinuitat der Lebensvorgange zeitweilig vb'l- lig unterbrochen werden ? Biol. Centralbl. X, 673-686. 15 Dec. 1890. KRUKENBERG, C. F. W. '80. Ueber die Vertheilung des Wassers, der organ- ischen und anorganischen Verbindungen im Korper wirbelloser Thiere. Vergl.-Physiol. Stud. I, 2 Abth. 78-106. LANCE, D. '94. Sur la reviviscence des Tardigrades. Comp. Rend. CXVIII, 817, 818. 9 Apr. 1894. LIEBERMANN, L. '88. Embryochemische Untersuchungen. Arch. f. d. ges. Physiol. XLIII, 71-157. 7 Apr. 1888. MUNTER, J. '47. Flora. XXX, 478. POUCHET, F. A. '59. Recherches et experiences sur les animaux ressusci- tants. Paris : J. B. Balliere et fils. 92 pp. 1859. PREYER, AV. '91. Ueber die Anabiose. Biol. Centralbl. XI, 1-5. 1 Feb. 1891. RAILLIET, A. '92. Observations sur la resistance vitale des embryons de quelques Nematodes. C. R. Soc. de Biol. XLIV, 703, 704. LITERATURE 69 RYWOSCH, D. '89. Einige Beobachtungen an Tardigraden. Sb. Naturf. Ges. Dorpat. IX, 89-92. SPALLANZANI, L. 1787. Oeuvres : Opuscules de physique, animale et vege- tale, etc. Trans. Jean SENEBIER. 3 tomes. Pavia and Paris. STAHL, E. '84. (See Chapter I. Literature.) ZACHARIAS, O. '86. Kommen die Rotatorien und Tardigraden nach vollstan- diger Austrocknung wieder aufleben oder nicht? Biol. Centralb. VI, 230-235. 15 June, 1886. CHAPTER III ACTION OF THE DENSITY OF THE MEDIUM UPON PROTOPLASM IN this chapter we shall consider (I) the structure of proto- plasm and the physiological action of solutions ; (II) the effect of density upon the structure and general functions of proto- plasm ; (III) acclimatization to solutions of greater or less density than the normal ; and (IV) control of the direction of locomotion by density-- tonotaxis. § 1. INTRODUCTORY REMARKS UPON THE STRUCTURE OF PROTOPLASM AND THE PHYSICAL ACTION OF SOLUTIONS It is now generally recognized that protoplasm consists of two substances closely interwoven : the living plasma and a watery chylema. The relation of the plasma and the chylema is still a debated matter. Since the only theory of the struct- ure of protoplasm which has been experimentally tested is that of BUTSCHLI, his theory is especially worthy of recognition. According to this theory, the relation of plasma and chylema is that of water and air in a foam-work. The whole protoplasmic mass is bounded and penetrated through and through by plasma films which envelop watery globules. It is with membranes constructed of such protoplasm that the physical phenomena of osmosis are exhibited.* Osmosis occurs when two aqueous solutions of different density are separated by an animal membrane. f Such a mem- * Excellent treatises on the physical and chemical nature of solutions, in- cluding a discussion of osmosis, are : OSTWALD, '91, and WHETHAM, '95. t Osmosis occurs likewise when such solutions are separated by inorganic walls containing pores of extreme fineness ; e.g. a wall of porous clay in which copper ferrocyanide has been precipitated. 70 § 1] PHYSICAL ACTION OF SOLUTIONS 71 brane permits the free passage of water, but not of the dissolved substance, or rather, of the dissolved substance but slowly. Under these conditions, the water flows more rapidly towards the solution containing the greater number of molecules (per cc.). The theory of this movement is that upon the side containing the greater number of molecules of salt fewer water molecules will in a given time strike the membrane than upon the other side ; and since the number passing through is proportional to the number striking, relatively fewer molecules of water will consequently pass out, and so there will be a resultant flow of water to that side ; and if the mass of water is confined, it will exert great pressure. This phenomenon of osmosis plays an important part in organic life. Thus, under certain conditions, cells take in the surrounding water, so that their walls are put under tension (turgescence). The tension thus gained may be considerable, amounting to 6 or 7 atmospheres. Under other conditions the cells give up their water to the surrounding medium, thus losing their turgescence. This occurs when they are put into certain solutions of KNO3 or NaCl. The relation between the density of the internal and external fluids thus determines the internal pressure experienced by the cell. A quantitative method of determining this pressure in the presence of various solutions has been employed by PFEFFER ('77). Solutions of different dry salts in different proportions, enveloped by a semi-permeable membrane, were placed in pure water, and the pressure upon a column of mercury determined. It was found, for example, that with a \% solution of cane sugar a pressure of 47.1 cm. of mercury * was produced ; with a 1% solution of K2SO4, a pressure of 193 cm. of Hg. He concluded, as a result of his various experiments, (1) that the pressure is proportional to the concentration of the solution, and (2) that as the temperature rises the pressure increases. DE VBIES ('84) made a noteworthy advance, using plant cells as objects of experimentation and . subjecting them to various solutions of substances freed of water. He determined the degree of concentration which a solution of KC1 must have * The pressure of 76 cm. of mercury equals that of 1 atmosphere. 72 SOLUTIONS AND PROTOPLASM [Cn. ITT in order that no endosmosis or exosmosis should occur through the cell wall.* He next determined the same thing for some other substances, e.g. KI, and found that the degree of con- centration which produces no osmosis is, for two different solutions, proportional to the molecular weights of the salts dissolved in them. Solutions which produce the same osmotic effect DE VKIES called isotonic. A solution of 0.746% KC1 is isotonic with a solution of 1.661% of KI, for the molecular weight of KC1 is 74.6, and that of KI is 166.1. Thus the first result which DE VKIES gained was that the osmotic effect of solutions of salts of similar structure depends upon the number of their molecules in the solution. The second conclusion of DE VKIES was that salts of dis- similar structure have different osmotic properties, even when the number of molecules in the two solutions is the same. Thus, he found that with an equal number of molecules to the solution (molecular-weight solutions f ) : - (1) All salts of alkalis with one atom of metal to the molecule are isotonic (formula, R'A' [compose^ of a monad metallic radicle, R, and a monad acidic radicle, A]) ; (2) All organic compounds with no metal radicle have two-thirds the osmotic action of the first group ; e.g. cane sugar, C12H220U. $ * As is well known, when a fully developed plant cell is put into a strong saline solution the living plasma sac separates from the cell wall and contracts, eventually, into a ball, — the result of the chyleina flowing out of the protoplasm (plasmolysis). The weaker the concentration, the less marked the plasmolytic phenomena. Finally, a concentration is reached so weak that the separation of the plasma sac hardly occurs or is limited to a single corner. This concentra- tion may be regarded as equal to that of the cell-sap — as that at which no osmosis occurs. (See Fig. 8.) t I shall use the phrase "molecular-weight solution " to indicate solutions in the making up of which the molecular weight of the substance in grammes, dis- solved in 100 g. of water, is used as the unit of concentration. It will often be convenient to abbreviate it as MW% sol. Chemists frequently use as a unit solution, called "normal" solution, the molecular weight in grammes dissolved in 1000 g. of water. Our MVV % sol. is therefore equal to one-tenth of a "normal " solution. t The fact that glycerine can be absorbed by some plants has introduced a complexity into the determination of its isotonic coefficient. This determina- tion has been made the subject of a special investigation by DE VRIES ('88), who, by the use of slowly absorbing plants, has found the isotonic coefficient to be 1.78, which agrees approximately with the number given above for organic compounds. § 1] PHYSICAL ACTION OF SOLUTIONS 73 (3) All salts of alkalis with two atoms of metal to the molecule have four-thirds the osmotic action of (1) (formula, Ii2'A"') ; e.g. K2S04. (4) Salts of alkalis with three atoms of the metal to the molecule have five-thirds the osmotic action of (1) (formula, R3'A'"); e.g. K3(C6H507). In other words, the osmotic action of groups (2), (1), (3), and (4) are in the proportions of 2, 3, 4, 5. These last num- bers are the Isotonic Coefficients of DE VRIES. In addition to these substances, DE VRIES determined that the isotonic coeffi- cient is, in the case of — salts of earthy alkalis with 1 acid radicle ; e.g. MgS04 . . 2 salts of earthy alkalis with 2 acid radicles ; e.g. CaCl2 ... 4 In the third place DE VRIES established the law that each acid group and each metal has, in all compounds, the same par- tial isotonic coefficients ; the coefficient of any salt is the sum of these partial coefficients of the constituent components. These partial coefficients are : - for each atom-group of an acid 2 for each atom of an alkaline metal (Li, Na, K, Rb, Cs) . . 1 for each atom of an earthy metal (Ca, Sr, Ba, Mg) .... 0 while of the compounds the isotonic coefficients are - KC1 = 1+2 = 3, MgS04 = 0 + 2 = 2, K2S04 = 2x1 + 2 = 4, MgCl2 = 0 + 2x2 = 4, K3(C6H507) = 3x1 + 2 = 5, etc. The determination of isotonic coefficients has subsequently been extended by several authors, especially by HAMBURGER ('86 and '87) and by M ASSART ('89). The work of HAMBURGER was done upon blood corpuscles. The method employed by him was as follows : In certain weak solutions the haemoglobin passes out of the red blood corpuscles of ox blood. The concentration at which it just began to ex- trude was determined for various salts, and it was found that these concentrations were usually proportional to the molecular weights of the substances divided by certain whole numbers, which are the same as the isotonic coefficients of DE VRIES. 74 SOLUTIONS AXD PROTOPLASM [Cn. Ill The work of MASSART was done chiefly upon bacteria. He made use of the fact demonstrated by PFEFFEK (see p. 41) that substances, which at a low concentration attract bacteria chemotactically, at a higher concentration repel them. He found that, in general, the repulsions exercised by the various dissolved substances are proportional to their isotonic coef- ficients, when the solutions are made up as MW solutions. Thus, when a 10 MW % concentration of a substance with iso- tonic coefficient 2 just begins to repel bacteria, a substance which just begins to repel in a 5 MW % concentration has an isotonic coefficient of 4.* § 2. EFFECT OF VARYING DENSITY UPON THE STRUCTURE AND GENERAL FUNCTIONS OF PROTOPLASM Under this head we may consider, (a) the effect upon the general structure of protoplasm; (6) the modification of gen- eral functions, and ( n P P Acclimated to 1.8 % V V 1) V J) n P P Acclimated to 3 0 % " r " r V V 1' D P P r f TABLE XI — COLPODA HUNDREDTIIS OF MOLECULAR WEIGHT. 0.5 1.0 1.5 3.0 9.5 3.O 3.5 4.0 5.0 Unacclimated o V V V 0 V V Acclimated to 1.8 MW%. . . . 0 V V vp P P Acclimated to 3.0 MW%. . . . V P P P 88 SOLUTIONS AND PROTOPLASM [Cn. Ill If we take as our unit in Table X the concentration repre- sented by v p, and in Table XI the concentration represented by v, we may conclude that the subjection for 22 hours to a 1.8 MW % or to a 3 MW % solution of the salt has given a resistance capacity of between 2 and 3 times the normal.* The question now arises, what is the cause of this increased resistance capacity ? It is not merely apparent, resulting from the selection of the more resistant individuals, thus elevating the mean. It is clearly due to a diminution in the intensity of osmosis; and this must be due to the establishment of an equi- librium between internal and external osmotic pressures. Now, this equilibrium can only be brought about by the density of the internal fluids becoming equal to that of the external medium; and this requires that the salt held in solu- tion shall traverse the bounding protoplasmic films, gaining the interior. That such a traversing occurs has been argued by M ASSART ('89), who has himself produced new evidence for this conclusion. As is well known numerous pigments in solution penetrate to the nucleus of the living protist. Potassic nitrate (JANSE, '87, p. 22), glycerine, and urea (DE VRIES, '88 and '89) have been observed to penetrate protoplasm. f That NaCl does the same thing has been shown by many observers. Thus, EMERY ('69) found that when a frog is placed in a salt solution and is left there for some time, then rinsed in water until no salt appears in the washings, and, finally, put into pure water, salt is given forth from the epider- mis (precipitation on adding silver nitrate). Likewise PLATEAU ('71, p. 20) found that various fresh-water Arthropods reared in a salt solution excreted an unusual amount of salt ; and FREDERIC ('85) has determined that the quantity of salt in the blood of Carcinus varies from 3.1% to 1.5%, according to the * A few data concerning proper acclimatization cultures to NaCl may be found useful. To acclimate bacteria O.OOo to 0.009 MW % may be added daily ; OscSllaria, 0.01 MW %, added monthly ; Anabsena and Tetraspora, 0.018 M W %, added monthly ; Ciliata, 0.003 MW %, daily ; Hydra viridis, 0.001 MW %, daily for 6 days ; Tubifex, 0.02 MW %, daily ; tadpoles, 0.004 to 0.014 MW %, daily. t A fact observed by BERT ('71) suggests that some solids are taken into the body in acclimatization ; for, he says, fresh-water fishes acclimatized to sea water gain in weight, and when placed in fresh water fall to the bottom. The fact that they fall to the bottom indicates that their specific gravity is increased. § 4] TONOTAXTS 89 density of the salt solution in which it has been reared. Finally, MASS ART has shown, by a new method, that several soluble organic compounds can permeate the bounding cell-film of Flagellata. Thus, if after permanently plasmolyzing^ Polytoma uvella by a 0.02 MW % solution of KNO3, a 0.01 MW % solu- tion of saccharose be added to the solution, the protoplasm soon . regains its normal form, apparently by absorption of saccharose, since the cell-wall is impermeable to KNO3. By the same method, potassium acetate, calcium butyrate, calcium phosphate, glycerine, ammonium tartrate, asparagine, glycose, sodium benzoate, salicin, and phloridzin. can be shown to permeate the protoplasm of this flagellate. All these facts point to the con- clusion to which physicists had arrived concerning dead animal membranes, that protoplasm admits the slow penetration of the dissolved salts, and thus effects the eventual equilibration of internal and external densities. In conclusion, a word may be said concerning variability in capacity of acclimatization. The data afforded upon this sub- ject by RICHTER ('92) are the most valuable. He was able to acclimatize Tetraspora to 16% (0.27 MW $) NaCl, while Spirogyra would not withstand, under like treatment, 0.5% (0.0085 MW %). It is clear then that, just as the resistance capacity varies, so also does the acclimatization capacity. § 4. CONTROL OF THE DIRECTION OF LOCOMOTION BY DENSITY : TONOTAXIS Three authors only, so far as I know, have concerned them- selves with this phenomenon, — STAHL ('84), PFEFFER('84, '88), and MASSART ('89, '91). STAHL ('84) observed that plasmodia of Myxomycetes withdrew from solutions either denser or less dense than the normal, and concludes that the action is not a simple, directly explicable one, but is rather a highly compli- cated irritability phenomenon. The observations of PFEFFER were incidental to his study of chemotaxis. He found that high concentrations of many substances acted repulsively, and he was at first ('84, p. 455) inclined to attribute this repulsion to osmotic action, but later ('88, p. 624) he believed this view disproved. The disproof he considered to lie in this, that 90 SOLUTIONS AND PROTOPLASM [Cn. Ill the repulsive quality varies with the quality of the substance - may occur even in substances which are not attractive at any concentration, PFEFFER is, therefore, inclined to regard strong, repelling solutions as acting in a different fashion from attractive ones. Just as strong sunlight may repel organisms attracted by weak light, - - both phenomena being light phe- nomena,--so the repulsion and attraction of solutions may both be regarded as chemical phenomena. The work of MASSART brought evidence against PFEFFER'S conclusions, and added many important data. His studies were made chiefly upon bacteria, to a less degree upon Flagel- lata, Hydra, the frog, and the human conjunctiva. The results of the studies showed that neutral solutions of a certain con- centration repel, and that the repulsion is proportional to their isotoriic coefficients and inversely proportional to their molecu- lar weights, and, therefore, that the repulsions are purely osmotic phenomena. The conclusions of MASSART thus summarized were obtained by the use of special methods, which gave quantitative results. So they are worth detailed consideration. A drop of liquid containing bacteria is suspended from the under side of a cover-glass in a moist chamber whose side walls are formed of cardboard, and whose top is the cover-glass. Into the drop, glass capillary tubes similar to those used by PFEFFER are in- troduced, filled with the solution whose action is to be studied. In addition to this solution all the tubes should contain yo^Q-oo' MW % (0.00691 gr. %) K2CO3 for the purpose of attracting the bacteria. When a tube containing only this dilute solution of K2CO3 is put into the drop, bacteria crowd into it and liter- ally fill it in from 20 to 30 minutes. But when a series of increasing solutions of a neutral salt like NaCl is added to the K2CO3, the organisms at first do not crowd in so rapidly, then remain at the mouth, and, finally, are repelled from the tube opening. MASSART has tabulated the results obtained with Spirillum upon using tubes containing different chemical sub- stances in different degrees of concentration. One of these tables, in slightly modified form, is reproduced here. In this table, A indicates that the bacteria entered the tube readily ; «, that they merely gathered about its mouth ; excitation rest excitation Schaeurgus (octopod) excitation > excitation rest excitation Helix hortensis . . . excitation > excitation rest slight excitation Ciona intestinalis . . excitation > excitation rest rest Janus cristatus . . . excitation = excitation rest slight excitation Pleurobranchia . . . excitation = excitation* rest slight excitation Nassa reticulata . . . weak excit. rest rest rest All the species in this table (all of which, except Ciona, are Mollusca) show in their response a more or less close approach to the type of Pelomyxa (excitation, rest ; rest, excitation) ; and we may believe that with appropriate stimulus they would re- spond in precisely that way. In a second class of cases the response of the whole animal belongs to the katex type ; thus two species examined by NAGEL showed the following responses : — TABLE XIV UPON MAKING. UPON BREAKING. AT ANODE. AT KATHODE. AT ANODE. AT KATHODE. Pagurus striatus . . Triton cristatus . . . rest excitation < excitation excitation excitation rest * Inconstant in occurrence. §2] EFFECT ON STRUCTURE AND FUNCTIONS 137 These are representatives of the groups Crustacea and Ver- tebrata. Among all the species studied by NAGEL there was only one which gave results not easily assignable to either of the two types. This organism is the larva of a dragon-fly, ^Eschurea. Its formula is excitation = excitation ; rest, rest. NAGEL says, however, that these results were uncertain and variable. In some other groups studied - - Ccelenterata and Echinoder- mata--the current used provoked no response at either pole; while with Amphioxus the current employed produced excita- tion at both poles on both making and breaking the circuit. Such variations as these, are, however, easily accounted for on the ground that different species require currents of different strengths to call forth what may be termed the typical response. Not merely between different groups do we find a difference in the type of response, but even inside the group of Protozoa dissimilarity has been shown to occur. Thus VERWOKN ('89*, p. 301) has given reasons for believing that three flagellate species, the ciliate Opalina, and some bacteria belong to the katex type, although as just stated (p. 133) other Protozoa exhibit the anex type of response. Finally it appears that individuals of one and the same species subjected to different intensities of current may give rise to responses belonging to the opposite types. Thus when a medium current is " made " through Triton cristatus the exci- tation is greater at the kathode than at the anode ; but when the weakest current is employed a making response occurs at the anode only, and when a slightly greater intensity is used the continuance of the current provokes a continuance of the exci- tation at the anode. (NAGEL, '92% p. 341.) Likewise the reaction of Vertebrate muscle varies with its internal condition. Thus degenerated or over-stimulated muscle shows predominat- ing anode stimulation on making the current ; and transverse -stimulation of the muscle fibre gives the same result.* To sum up, two principal types of response to the electric current may be distinguished : the first or anex type character- izing most Protozoa, Mollusca, Vertebrates (slightly stimulated), * For a discussion of these cases see VERWORN ('89a, p. 24). 138 ELECTRICITY AND PROTOPLASM [Ca. VI and weak muscle fibres ; the second or katex type found espe- cially among some Flagellata, Arthropoda, and Vertebrata. A third possible type (katanex type) is certainly of very limited distribution. Between the two types we notice this connecting link, that in some Vertebrates a weak current produces one type of response ; a strong current the other. The reason for the existence of these two distinct types — one of which char- acterizes animals with less differentiated, the other those with more differentiated, muscular and nervous systems — is still greatly in need of investigation. The nature of the protoplasmic change wrought by the current is an important matter. We have already accounted for the effect that we see in the Protista, on the ground of re- duced cohesion. It is probable also that the current gives rise in the cytoplasm to chemical changes which are different at the two poles. It is well known that when a current is passed through a neutral solution of a salt there is produced an acid at the anode, and an alkali at the kathode. Since in the higher animals, at least, the body contains such solutions, it seems probable that acid and alkaline substances are here likewise produced by the passing current. This probability is supported by an observation of KUHNE ('64, p. 100), who found that the violet coloring matter of the stamen hairs of Tradescantia become changed by the action of a very strong induction shock. He says that a change in the violet fluid, like that which occurs at the anode, can be brought about by dilute hydrochloric acid ; while a change like that appearing at the kathode can be pro- duced by potassic hydrate. An observation of NAGEL ('92% p. 346) suggests also that the current acts by producing a chemi- cal change. He finds that that part of the body of the snail and the leech which shows most markedly the anode-making excitation is coincident with that which is most sensitive to chemical substances. So that the reaction to a galvanic, still more to a faradic, stimulation resembles that to a strong, dis- agreeable taste (quinine). In this case the response may result either from the chemical substance acting directly on the muscles or attacking first the sense organs. In the latter case the response would occur through the mediation of the nervous system. § 2] EFFECT ON STRUCTURE AND FUNCTIONS 139 So far then we have distinguished two chief effects of the current on protoplasm — a dissociation effect and a chemical effect. It may now be worth while to mention that there is good reason for believing that in the more highly differentiated animals, like Vertebrates, not all protoplasm is affected to the same degree nor in the same way. Thus a nervous and a muscular effect can be clearly distinguished in frogs, for ex- ample. The principal effect is exerted upon the central nervous system, for HERMANN ('86, p. 415) found that the tail of tadpoles is responsive only so long as it contains a piece of spinal nerve ; and upon frogs subjected to curare, which inhib- its the action of the nerve alone, the current produces a much- diminished effect, giving rise merely to muscular twitchings (BLASTUS and SCHWEIZER, '93, p. 528.) Very little progress has been made, however, upon the determination of the action of different intensities upon the different tissues of which the Vertebrate body is composed. i We have seen that the electric current provokes a response, and we have seen also that organisms vary in their responsive- ness so that a current strong enough to call forth a response in one species is not sufficient to excite another species. We may say that the one species is attuned to a different strength of current from the other. This difference in responsiveness indi- cates, of course, a corresponding difference in composition of the protoplasm. Such a difference may, moreover, be produced in a single individual by artificial means. These means are the subjection for a considerable period to the electric current. Suppose we subject an organism to a current of a strength only slightly greater than that just necessary to provoke a response. After the current has acted for some time we find that it no longer excites. This phenomenon of acclimatization to the galvanic current was first observed among the Protista, so far as I know, by KUHNE ('64, pp. 76, 78), who found that in Myxomycetes, after a few induction shocks had been sent through the plasmodium, additional shocks of the same intensity were without effect, and stronger shocks had to be sent through to cause contraction. Similar results were obtained by VER- WORN ('89a, p. 10 ; '89b, p. 272) in subjecting Actinosphterium 140 ELECTRICITY AND PROTOPLASM [Cn. VI and Amoeba to a weak constant current. At first the pseudo- podia on the anode side plainly retracted, but later ceased to do so, and, finally, the current still passing, the retracted pseudopodia began to extend again. The action of the current so modified the protoplasm as to change the attunement of the organism. § 3. ELECTROTAXIS In studying the subject of aggregation with reference to the electric current, we shall consider first the simplest case of this phenomenon as it is exhibited in Amoeba ; then pass to the more complex forms of Protista, especially the Ciliata, and after ^''•$$3^ .jMusratSI B FIG. 32. — Galvanotaxis of Amoeba diffluens. A, Amoeba creeping, unstimulated ; B, after closing of the constant current. The arrow indicates the direction of locomotion. (From VERWORN, '95.) that to the Metazoa. After dealing with the phenomena we must attempt to explain them. When such an amoeba as that shown in Fig. 32, A, is sub- jected in a drop of water to the action of a weak constant current, as already indicated (p. 129), it contracts, especially upon the face turned towards the anode. If the current is not strong enough to produce disintegration at that pole, but only repeated contraction, and if meanwhile the kathode pole retains its power of throwing out pseudopodia, the amoeba must grad- ually move from the anode (Fig. 32, J?), and if several Amoebae are under the cover-glass, they will eventually aggregate about the kathode. Here we have, then, in its simplest form, a case of electrotaxis, and, since the organism moves toward the negative electrode, we may call it negative electrotaxis. If now, instead of an amoeba, we watch a free swimming flagellate Infusorian, — Trachelomonas hispida (Fig. 33), — we § 3] ELECTKOTAXIS 141 see the long flagellum which precedes in locomotion coming to lie in the current and directed towards the kathode, so that the animal migrates in that direction. The following explanation of the observed fact that the flagellum becomes directed towards the kathode has been offered by VERWORN ('89b, p. 298). The flagellum and the pole from which it arises constitute the most sensitive end of the body. When the flagellum is stimulated it beats violently, and since it is stimulated most when turned towards the anode, it beats most violently when in this attitude. A position 180° from this is one of comparative rest. In interme- diate positions the degree of stimulation is intermediate. After a few strokes the body will "naturally" come to assume and to retain that position in which the flagellum is least stimulated. More detailed still is our knowledge of electrotaxis among FIG. 33. — Trachelomonas hispida, swimming towards the kathode (— ) upon closure of the current. The arrow shows the direction of locomotion. (From VER- WOBN, '89.) 'the ciliate Infusoria. The authors who have worked upon this group are chiefly VERWORN ('89a and '89") and LUDLOFF ('95). The work of the former shows that the phenomenon of electrotaxis is exhibited by many species, especially Para- mecium aurelia and P. bursaria, Stentor ccerulens and S. polymorpha, Pleuronema chrysalis, Opalina ranarum, Bursaria truncatella, Halteria grandinella and Stylonichia mytilus. LUDLOFF employed only Paramecium, but studied it much more completely, especially using various currents of known relative intensity.* He found that the precision with which * LUDLOFF employed a trough with wax walls, clay ends, and glass bottom, and used brush electrodes. The intensities of current given by him are the readings of the galvanometer. The cross-section of the water mass in which the Paramecia were, and over which the current spread itself, is not, exactly given, but was probably about 20 sq. mm. If we employ the unit of strength recommended by HERMANN and MATTHIAS (p. 128), namely, 1 one-millionth of 142 ELECTRICITY AND PROTOPLASM [Cn. VI the Paramecia aggregated at one pole was determined by the strength of the current, as follows : A current of 3 S caused in general a movement towards the kathode, although many individuals appeared not to be affected by it. In 20 seconds the anode end of the fluid was almost free from Infusoria. With currents of 6 S and 15 B the aggregation at one pole be- came more complete and took place in a short time. Indeed, there was a relation found between the time required for RELATIVE RATES OF MIGRATION O t-i l-S CO rf^ d O -1 r— •s 1 \ I \ I \ / \ / > r V i ^ \ \ ; x \ N --^ \ "*«•, \, 10(5 20c5 30 or (which is the same thing) multiply them by 60. That will give us the current in 5's per sq. mm. All of the numerical data given in the text have undergone this operation. §3] ELECTROTAXIS 143 rapidly for a moment, towards the opposite pole (anode), but then quickly begin to redistribute themselves throughout the water. This redistribution has occurred in about 20 seconds FIG. 35. — Apparatus for studying electrotaxis of Paramecium. A rectangular trough, whose ends are of clay and sides of wax, is built upon a glass plate. The current is applied by means of brush electrodes. The direction of the migration of the paramecia is indicated by the arrow. They move towards the kathode. (From VERWORN, '95.) after the current is broken, and the time is independent of the strength of the preexisting current. The movement of the Infusorian from one pole to the other takes place along the lines of flow of the current. If the ter- minals are two parallel plates, these lines are about parallel (Fig. 35); if they are two points near the opposite sides of A B FIG. 36. — Curves made by Paramecia in its galvanotactic response when pointed electrodes are used in the drop of water. A, beginning of migration; B, com- plete aggregation. (From VERWORN, '95.) a water drop, the lines have the direction of the lines made by iron filings scattered on a plate over the two poles of a magnet (Fig. 36). Besides this path of general migration, the form of the path followed by individuals varies with the current. Normally Paramecium moves in a long spiral. As the current is in- 144 ELECTRICITY AND PROTOPLASM [CH. VI creased, however, this spiral becomes shorter, i.e. has more turns per centimeter of progression from one pole to the other FIG. 37. — Form of the path of Paramecium under different conditions, a, when not subjected to the constant current ; 6, when subjected to a slight current ; c, when subjected to a still stronger one. (From LUDLOFF, '1)5. ) (Fig. 37), until at 60 S, in making one turn of the spiral, the organism progresses hardly more than its own length. Finally, the effect of the current upon the movement of the cilia must be considered.* In the resting Para- mecium the cilia rise perpendicularly from the surface of the body (Fig. 38). If an individual stands with its ante- rior (blunt) end towards the anode, and a current of 8 B passes through, the cilia at the posterior (kathode) end begin to vibrate. If the individ- ual lies transverse to the current and the current is closed, the cilia on the kathode side vibrate, those on the FIG. 38. -Paramecium, show- anode side being quiet. With a cur- ing position of cilia when . . . , , unstimulated. The blunt rent of 16 S one can see tliat the kath~ end is anterior. (From ode stimulation increases the forward LUDLOFF, '95.) (anteriad) phase of the cilium move- ment (the "recovery"). With an intensity of 248, vibration of cilia occurs at both kathode and anode. It is, however, more * LUDLOFF was enabled to make a careful study of the effect of the current on the cilia by making use of gelatine solutions such as have been recommended by JENSEN ('93, p. 556). § 3] ELECTROTAXIS 14 r intense at the kathode and is .also in opposite directions at the two poles. This law is important, and may be thus formulated: The current intensifies at the anode the backward movements and at the kathode the forward movements of the cilia, and the latter are more intensified than the former ; or, in other words, the anode stimulation increases the effectiveness of the normal stroke, the kathode stimulation diminishes the effectiveness of the normal stroke, and the diminishing effect is the greater of the two. On the basis of these observed facts, LUDLOFF has proposed a theory which accounts for several of the electrotactic phe- nomena in the Ciliata, especially the fact that with strong currents there is a diminution in the rate of locomotion, and that at a lower intensity the axis of the organism is placed in the axis of the current, with its anterior end towards the kathode. This theory may be stated as follows: In every com- plete swing of a cilium two phases may be distinguished — the backward "stroke" and the forward "recovery." Nor- mally the stroke is the more effective, otherwise forward loco- motion would not occur. The excess in effectiveness of the stroke may be designated by the quantity x. Let us assume a Paramecium lying in the axis of the current with its anterior end towards the kathode. Then the stimulus received at the anode or hinder end increases the effectiveness of the stroke by a quantity which we may designate m. Thus the excess energy of the stroke over recovery is for these hinder cilia x + m. The stimulus received at the kathode or anterior end diminishes the effectiveness of the stroke by a quantity which we may call n, which is larger than m. Here the excess energy of stroke over recovery is x — n. If at any intensity of cur- rent n exceeds x, the anterior cilia will work to oppose the forward motion of the individual, and when n — x =• x + m loco- motion will not occur. Such a strength of current probably occurred in the experiment given on p. 142, where locomotion ceased at above 60 8. To account for orientation of the axis and its anterior end, we have merely to apply the general law given above. Let us suppose that we are observing a Paramecium lying in the axis of a current of medium intensity, with its anterior 146 ELECTRICITY AND PROTOPLASM [CH. VI end towards the anode. Since n is here supposed to be less than x, the resultant effect is to move the animal forward. In moving forward in its spiral course, one side becomes presented to the anode. On this side the excess of energy of the stroke is x + m, while on the kathode side it is x — n. The resultant effect of the cilia on the two sides forms a couple which revolves the organism about one of its short axes until it comes again into the axis of the current, but with its anterior end towards the kathode. The beating of its cilia must now carry it towards the kathode (Fig. 39). FIG. 39. — Diagram showing the successive attitudes (a, b, c, d, and e) assumed by Paramecium when its head is turned towards the anode at the beginning (a). It rotates till its head is next the kathode (e). (From LUDLOFF, '95.) Before leaving the Protozoa, we ought to look over the whole field. We have hitherto considered only cases of migration towards the kathode - - negative galvanotaxis. VERWORN ('89b), however, has found that some Protista are positively electrotactic ; namely, the flagellata, Polytoma uvella, Crypto- monas ovata, and Chilomonas paramecium ; the ciliate, Opalina; and some bacteria. Finally, VERWORN ('95, p. 446) describes one of the elongated Ciliata — Spirostomum ambiguum — which places its long axis across that of the current and migrates towards neither pole, a condition which may be called (after VERWORN) transverse electrotaxis. Passing now to the Metazoa, we find investigations concern- ing electrotaxis among Invertebrates by NAGEL ('92 and '92a §3] ELECTROTAXIS 147 and '95), and BLASIUS and SCHWEIZER ('93); and among Vertebrates by these authors and also HERMANN ('85 and '86), EWALD ('94, '94a, and '94b), HERMANN and MATTHIAS ('94), and WALLER ('95). The number of species investigated has been considerable. I give below a table of the Invertebrate genera studied and the sense (+ or --) of their response at the given intensity of currents. Barely rough quantitative expression of strength of current can be deduced from NAGEL'S paper. Where no data are given the currents are supposed to be of intermediate strength. N. stands for NAGEL, B.S. for BLA- SIUS and SCHWEIZER. The numbers which folloAV give the year of publication and the page. TABLE XV SPECIFIC NAME. STRENGTH OF CURRENT. SENSE OF RESPONSE. At'TUORITY. Mollusca : Limnsea sta^nalis weak N. '95 Var. other Gastropoda (probably) . Annelida : Lunibricus — N. '92a; '95 N. '95, 626 Tubifex rivuloruni N. '95, 631 Hirudo niedicinalis 0.88 B.S. '92, 516 Branchiobdella parasitica B.S. '92, 516 Crustacea : Cyclops strong + N. '92, 629 Asellus aquaticus strong + N. '95, 633 Astacus fluviatilus 0.48 + B.S. '92, 518 • Insecta : Notonecta + ? N. '95, 636 Corixa striata + N. '95, 636 Dytiscus maro'inalis 1.98 -f B.S. '92, 519 Hydrophilus piceus 1.98 B.S. '92, 519 From this table it appears that Mollusca and Annelida are usually negatively electrotactic to a current of medium inten- sity, while Arthropoda are mostly positively electrotactic to such a current. It is noteworthy, however, that two quite 148 ELECTRICITY AND PROTOPLASM [Cn. VI closely allied beetles like Dytiscus and Hydrophilus should by the same observers be found to react in different ways. In addition to the species named, some have been studied which have given no results. Thus NAGEL ('95, p. 639) ob- tained no response from the larva of Libellula depressa, even with a wide range of current-intensities. Passing now to the Vertebrata, we enter a region in which, as a result of more numerous studies, the data are more volu- minous, but at the same time less in accord. Since many mat- ters are here still in dispute, we may best consider historically, i.e. in chronological sequence, what has hitherto been done in this field. The first person to describe the phenomenon of electrotaxis in Vertebrates — as, indeed, in any organism - - was HERMAN x ('85, '86). He used frog larvae 14 days old, held in a shallow rectangular porcelain trough, along the two small sides of which thick zinc wires were placed, connected with a chain of 20 small zinc-carbon elements. No mention of the strength of the cur- rent except such as can be gained from these facts was made. This omission of quantitative details is to be regretted, since had the strength of current to which the organisms were sub- jected been given, much subsequent confusion might have been avoided. With this current, then, of unknown intensity, flow- ing through the water containing the larvae, all of the latter were seen to place themselves in the axis 'of the current with their heads directed toward the anode. This orientation was the consequence of the fact that a current passing cephalad through the larva acted as a violent stimulus ; but while passing caudad it brought stupefaction or even (temporary) paralysis. The results obtained by HERMANN were now confirmed and extended by BLASIUS and SCHWEIZER ('93). They employed a wooden trough with sheet zinc electrodes of nearly the cross- section of the smaller ends of the trough, and experimented upon fishes, Salamandra, and the frog. The weakest current employed was 0.35S to 0.47 S, which merely affected the char- acter of the swimming of the fish subjected to it, without determining its direction. The next stronger current men- tioned was 1.588. With this current a marked orientation of § 3] ELECTROTAXIS 149 the fish with their heads to the anode was noticed. With Salamandra larvse currents of 2. 35 to 4. 78 were chiefly em- ployed. In the experiments of BLASIUS and SCHWEIZER the organisms sometimes migrated toward the anode, if the cur- rent was not so strong as to stupefy, but they lay stress upon the point that the migration is a secondary phenomenon --that the orientation is the primary effect of the current. Next came the observations of EWALD ('94), who used very young tadpoles (5 days) and non-polarizable points as elec- trodes. Thus he was not able to give the strength of current to which the individuals were subjected. His results seemed directly to oppose those of the two preceding authors, for with his (unknown) current, the tadpoles were stimulated when the current passed caudad and stupefied by one passing cephalad ; also they placed themselves in the axis of the cur- rent with their heads towards the kathode. The larvce did not seem to find this position as a direct response to stimulus, but whenever an individual, in its turnings to the right and left, fell into this — electrotactic — position it was no longer stimulated, but stupefied, and so came to rest. These discordant results of EWALD led HERMANN, with his student MATTHIAS, again into the discussion. By careful measurements of the strength of current, they found that between 0.38 and 1.5S frog tadpoles of from 1 to 3 weeks old did face the kathode, as EWALD found, and did move towards it. But HERMANN and MATTHIAS ('94) believed this result to be due to the fact that only cephalad-flowing currents of this intensity excite, and thus only such currents are able to pro- duce locomotion. EWALD ('94b), however, cannot accept their idea that a caudad-passing current of small intensity produces no excita- tion, for, he says, he has seen small fish, lying with face to the anode, made to move towards the kathode by the action of the weak current. Since HERMANN and others have shown that very strong currents cause paralysis even when flowing cepha- lad, EWALD concludes that we must recognize the existence of three different effects at three intensities; weakest, medium, and strongest. The medium current (which has the broadest range) is that by which the organisms are irritated as it flows 150 ELECTRICITY AND PROTOPLASM [Cn. VI cephalad, so that they come to lie with head towards anode ; the weakest current is that by which (following EWALD) the organisms are irritated as it flows caudad, so that they come to lie facing the kathode ; finally, the strongest cur- rent is that at which a violent stimulation leading to paraly- sis is produced by the cephalad-flowing current (as well as the caudad ?). In seeking for an explanation of electrotaxis in Metazoa, it is necessary, first of all, to notice that there is a close relation between response to the make-shock (as described on pp. 136, 137) and the direction of orientation of the body in electro- taxis. Thus all gastropods studied are, upon making, excited chiefly at the anode, and, correspondingly, all gastropods hitherto studied when subjected to the current face the kathode ; so on the other hand, such Crustacea as have been studied are stimu- lated at the kathode, and they accordingly come to face the anode. In regard to Vertebrates, we have apparently a double electrotactic orientation varying with the current, and corre- spondingly we have, as NAGEL has shown (p. 137), a double irritability depending on the current. A medium current pro- duces a kathode excitation and an anode orientation ; while the weakest current produces an anode excitation and a kathode orientation. So we may lay it down as a general law : Positively electrotactic organisms exhibit the katex type of irritability; and negatively electrotactic organisms exhibit the anex type or, in general, the electrotactic organism turns tail to the exciting pole. EWALD ('94, pp. 611-615) accounts for this difference of response of Vertebrates to weak and strong currents, by the aid of certain observations that he made upon the excitation of the nerve cord. We have already seen that the making of the medium constant current stimulates at the kathode, so that an animal turns tail to the kathode. EWALD found that the two parts of the dorsal nerve were differently stimulated by the current ; the brain was stimulated chiefly by a caudad- passing current ; the spinal cord chiefly by a cephalad-passing current. This conclusion was established by two experiments. First, the two electrodes, placed a few millimeters apart, are brought into contact with different parts of the body of a fish. SUMMARY OF THE CHAPTER 151 Let the current be passing through the fish from the anterior to the posterior electrode. At the tail end we get no excitation ; and, as we pass forward, the body remains quiet until, pass- ing the region of the medulla oblongata, an excitation appears. If the operation is repeated with a reverse current, we get excitation behind the head and quiet on the head. Secondly, if a frog larva be cut in two transversely at the root of the tail, the head end is irritated only by a caudad-flowing cur- rent ; the tail end only by a cephalad-flowing current ; while in both cases the opposite current quiets. (Cf. also EWALD, '94b, p. 162.) These observations were now made use of to explain the opposite orientation of the tadpole in the presence of weak and strong currents. NAGEL assumed that the weak- est currents can affect the brain only. Now if that current runs caudad, it will strongly stimulate the body so that it turns tail to the anode. The medium currents, however, stimulate the whole dorsal nerve, but the spinal cord to a preponderating degree, so that a cephalad-passing current irritates more than a caudad current, and the animal will turn tail to the kathode. Thus weaker or stronger current will determine or + electrotaxis. SUMMARY OF THE CHAPTER Electricity affects protoplasm in two principal ways : first, by causing contraction ; second, by determining orientation. We can distinguish two principal types of contraction phe- nomena and, corresponding to and dependent upon these, two types of orientation phenomena. The first type of contraction is that which is produced, upon making the constant current, chiefly at the anode ; the second is produced chiefly at the kathode. The corresponding orientation or migration types are, facing the kathode and facing the anode. Since the orien- tation phenomena are dependent upon the contraction phe- nomena, the most important causes to be investigated are, first, that of contraction, and second, that of the difference in type of contraction exhibited by different organisms. The funda- mental teaching of this chapter is that the electric current acts as a stimulus upon protoplasm, and may determine the charac- ter of its activities. 152 ELECTRICITY AND PROTOPLASM [Cn. VI LITERATURE BIEDERMANN, W. '83. Ueber rythmische Contraction quergestreifter Mus- keln unter dem Einflusse des constanten Stromes. Sitzb. Wien. Akad., Math.-Nat. Cl. LXXXVII, Abth. 3, pp. 115-136. Taf. I-II, 1883. BLASIUS, E. and SCHWEIZER, F. '93. Electrotropismus und verwandte Erscheinungen. Arch. f. d. ges. Physiol. LIU, -493-543. 10 Feb. 1893. ENGELMANN, T. W. '69. Beitrage zur Physiologie des Protoplasma. Arch. f. d. ges. Physiol. II, 307-322. '70. Beitrage zur allgemeinen Muskel- und Nervenphysiologie. Arch, f . d. ges. Physiol. Ill, 247-326. EVVALD, J. R. '94. Ueber die Wirkung des galvanischen Stroms bei der Langsdurchstromung ganzer Wirbelthiere. Arch. f. d. ges. Physiol. LV, 606-621. 10 Feb. 1894. '94s. Berichtigung. Arch. f. d. ges. Physiol. LVI, 354. 11 Apr. 1894. *94b. Ueber die Wirkung des galvanischen Stroms bei der Langsdurch- stromung ganzer Wirbelthiere. II Mitth. Arch. f. d. ges. Physiol. LIX, 153-164. 30 Nov. 1894. FICK, A. '63. Beitrage zur vergleichenden Physiologie der irritablen Sub- stanzen. Braunschweig. 1863. (Not seen.) GOLUBEW, A. '68. Ueber die Erscheinungen, welclie elektrische Schlage an den sogenannten farblosen Formbestandtheilen des Blutes hervor- bringen. Sitzb. Wien. Akad., Math.-Nat. Cl. LVII, Abth. 2, 555-572. HERMANN, L. '85. Eine Wirkung galvanischer Strbme auf Organismen. Arch. f. d. ges. Physiol. XXXVII, 457-460. 2 Dec. 1885. '86. Weitere Untersuchungen liber das Verhalten der Frochlarven im galvanischen Strorne. Arch. f. d. ges. Physiol. XXXIX, 414-419. 21 Oct. 1886. HERMANN, L. and MATTHIAS, F. '94. Der Galvanotropismus der Larven von Rana temporaria uud der Fische. Arch. f. d. ges. Physiol. LVII, 391-405. 20 July, 189 i. JENSEN, P. '93. Methode der Beobachtung und Vivisektion von Infusorien in Gelatinelbsung. Biol. Centralbl. XII, 556-560. 1 Oct. 1892. KRAFT, H. '90. Zur Physiologie des Flimmerepithels bei Wirbelthieren. Arch. f. d. ges. Physiol. XLVII, 196-235. 9 May, 1890. KUHNE, W. '64. Untersuchungen liber das Protoplasma und die Con- tractilitat. Leipzig: Engelmann. 1864. LUDLOFF, K. '95. Untersuchungen liber den Galvanotropismus. Arch. f. d. ges. Physiol. LIX, 525-554. 5 Feb. 1895. NAGEL, W. A. '92. Beobachtungen liber das Verhalten einiger wirbelloser Thiere gegen galvanische und faradische Reizung. Arch. f. d. ges. Physiol. LI, 624-631. 26 March, 1892. '92*. Fortgesetzte Beobachtungen liber polare galvanische Reizung bei Wasserthieren. Arch. f. d. ges. Physiol. LIII, 332-347. 24 Nov. 1892. LITERATURE 153 NAGEL, W. A. '95. Ueber Galvanotaxis. Arch. f. d. ges. Physiol. LIX, 603- 642. 5 Feb. 1895. OSTWALD, W. '94. Manual of Physico-chemical Measurements. Translated by J. Walker. 255 pp. London : Macmillan. 1894. VERWORN, M- '89*. Die polare Erregung der Protisten durch den galva- nischen Strom. Arch. f. d. ges. Physiol. XLV, pp. 1-36. 23 March, 1889. *89b. The same (continued). Arch. f. d. ges. Physiol. XL VI, pp. 267- 303. 18 Nov. 1889. '95. (See Chapter IV.) WALLER, A. D. '95. Galvanotropism of Tadpoles. Science Progress. IV, 96-103. Oct. 1895. CHAPTER VII ACTION OF LIGHT UPON PROTOPLASM IN this chapter it is proposed to discuss (I) the application and measurement of light; (II) its chemical action; (III) the effect of light upon the general functions of organisms ; and (IV) the control of locomotion by light - - phototaxis and photopathy. § 1. THE APPLICATION AND MEASUREMENT OF LIGHT Light, which as a form of radiant energy is closely related to radiant heat, is always accompanied by a certain quantity of heat, whose action (in at least one control experiment in every set) should be eliminated. To cut out heat without great loss of light, we must employ transparent adiathermal media. Of these, a plate of ice is the most effective, but alum, on account of its higher melting point, is more convenient. A parallel- sided vessel full of distilled water, or, still better, a saturated aqueous solution of alum, forms an inexpensive, highly adi- athermal screen. The quality of the light used in any experiment should be carefully determined. If any other light than that of the sun or incandescent solids is employed, it should be subjected to spectroscopic analysis. For biological purposes a direct-vision hand spectroscope, such as BROWNING'S, is convenient and adequate. Often monochromatic light or a definite range of the spectrum is desired. This may be obtained in various ways. The purest monochromatic light can be got by making a long spec- trum and using the desired part of it. To make such a spec- trum one may employ, in a dark room, a lamp, followed in succession by a slit and a lens to form an image of the slit 154 § 1] APPLICATION AND MEASUREMENT OF LIGHT 155 on a prism of bisulphide of carbon,* which gives very great dispersion of the rays. In defining the regions of the solar spectrum which are employed in any study, it is usual to make reference to the dark absorption bands (FRAUENHOFER'S lines) which cross the solar spectrum. The largest of these are lettered, begin- ning with A in the visible red and ending with If in the visible violet. At other times it may be more convenient to define any part of the spectrum by means of the extreme wave lengths between which it lies. Lithographs showing the spectral colors and the wave lengths corresponding thereto are given in encyclopedias and most of the text-books on physics. A crude attempt is made to show the relation be- tween color and wave length in Fig. 40. The wave lengths at Red Orange Yellow Green Blue Indigo Violet Jl 5 70 65 6 0 £ 5 i 1 1 1 1 5 0 1 5 4< i I i i i i aBCD EbF G h FIG. 40. — Diagram of the solar spectrum showing the main absorption bauds and the range of the various spectral colors. The numbers are wave lengths in hundred- thousandths of a millimeter. (From REINKE, '84.) the different absorption bands are given more exactly (in thou- sandths of a millimeter, = /A) in the following table, and also the number of waves per second in 1012ths. TABLE XVI ABSORPTION BAND. WAVE LENGTII, A. VIBRATIONS PER SECOND n x 1012. ABSORPTION BAND. WAVE LENGTH, A. VIBRATIONS PER SECOND n x 1012. A 0.760 fl 0.687 p. 0.656 ft 0.589 /A 392 433 454 506 E. . . . F. . . . G. . . . H. . . . 0.527 p. 0.486 fj. 0.431 fi 0.397 ft. 566 613 692 751 B c D * The bisulphide prism may be made as follows : Upon a thick glass plate three rectangular pieces of glass of equal size are placed perpendicularly, so as 156 LIGHT AND PROTOPLASM [Cn. VII Extreme ultra-violet \ = 0.295/*; 1010 x 1012 vibrations per second. To obtain monochromatic light from the spectrum, REINKE'S ('84) spec- trophor will be found useful (Fig. 41). In this instrument a beam of sun- light cast by a heliostat through a slit at H is converged by means of an interpolated lens, 0, upon a prism, P, set at the angle of minimum devia- tion. Passing through this prism the rays are dispersed and a spectrum is formed upon a diaphragm D. Dl composed of halves bounding a second slit whose position and width may be varied at will so as to include any desired part of the spectrum. A large lens C known as the collector brings the rays which have passed through the second slit to a focus at E. Just in FIG. 41. — Diagram showing the construction of REINKE'S spectropbor and the path of the rays in it. H, slit next to heliostat ; O, pro- jecting lens ; P, prism ; S, Si, scale marked with wave lengths ; D, D±, diaphragm, including a variable slit ; c, Cj, collecting lens ; E, posi- tion of object subjected to the rays. The spectrum ranges from A = 0.75 ^ to A = 40 F. (From REINKE, '84.) front of the diaphragm is placed a scale S, 5^ of wave lengths fitted to the spectrum obtained. Such a scale may be constructed with reference to the position of FRAUENHOFER'S lines by interpolation from Fig. 40.* To in- clude rays whose wave lengths differ by exactly 0.05 /j. the slit must be wider when at the blue end than when at the red end of the spectrum (Fig. 40). to form a hollow, triangular (60°) prism. The plates are fixed to each other and to the glass base by a pasty cement made by mixing plaster of paris and liquid glue. This cement soon hardens, and is not attacked by the carbon disulphide. The hollow prism is now filled with fluid, and a triangular glass plate is cemented on as a cover. * If artificial light is used, two points on the scale can be obtained as follows : Volatilize in a Bunsen flame, temporarily replacing the lamp, a salt of barium and one of calcium, and note the position of the extreme blue band on the former (line F) and the yellow band of the latter (line D). After determining these two points the remaining lines can be plotted upon the scale. § 1] APPLICATION AND MEASUREMENT OF LIGHT 157 A second method of getting monochromatic light is by the use of flames tinged with various volatilized metals. Of these, lithium salts give reds at A, = 0.67^, and X = 0.61/i, sodium salts give a pure yellow light of A, = 0.59//,, thallium salts (poisonous vapor) a green at about \ = 0.54/u,, and indium salts a blue and a violet, both beyond \ = 0.46/i. The number of metallic vapors which give even nearly monochromatic light is, however, not large. A third method for producing monochromatic light is found in the use of solutions of pigments. Such solutions may be held in deep glass vessels whose back and front glass surfaces are parallel and near together. In the following table are given in the first column the names which may be applied to differ- ent parts of the spectrum, following HELMHOLTZ (Handbuch, p. 251); in the second column the pigments which while dry give corresponding spectral colors in diffuse daylight and which may also be used in making solutions ; and in the third column certain pigments which in solution YUNG ('78, p. 251) found to transmit almost exclusively the part of the spectrum named in the first column. TABLE XVII From outer limit to line C, red . . . i oransre . Cinnibar, HgS (vermilion) Minium Alcoholic solution f uchsin * C' to J), ( golden yellow . . . ( vellow . Litharge, PbO Chrome yellow, Concen. Sol. potassic chromate 1) -tii I 11 / yellow-green .... to 6 green PbCXCrO, cupric arsenite, (a little red and green) Nickel nitrate, NiO2(NO2)i b F Fl G to F, transition from blue-green to blue to F\G, cyanite blue .... SCHEEL'S green Berlin blue Ultramarine Bleu de Lyon (a little V) t G to // violet Violet de Parme Solutions made up from these pigments should, however, be examined spectroscopically before using to make sure of the purity of the color. * Also a solution of iodine in carbon disulphide. (PRINGSHEIM, '80, p. 409.) t F to H is given by ammoniated copper sulphate, CuSo4-4NH3 + H20 (PRINGSHEIM). 158 LIGHT AND PROTOPLASM [Cn. VII Finally, a fourth and decidedly practical way of obtaining pure colors is by the use of transparent plates of colored glass or other transparent solids. It is very difficult to get monochro- matic glasses of certain colors in the market. A pure red is easily obtainable ; the blue is apt to contain some red also ; and the green, both blue and yellow. Lord RAYLEIGH ('81, p. 64) has used " films of gelatine or of collodion, spread upon glass and impregnated with various dyes, gelatine being chosen when the dye is soluble in water and collodion when the dye is soluble in alcohol." This method seems to me to be of wide applica- bility in our light experiments. For solid media are, after all, far less troublesome than fluids, vapors, or spectra ; and con- venience is one of the most valuable qualities of .a method. A brief statement must be made concerning the physical properties of the different light waves. An inspection of any prismatic solar spectrum shows that certain parts are brighter to our eyes than others, and a thermometer placed in different parts of the spectrum indicates a higher temperature towards the red end. Curves are given in Fig. 42 which show the relative warmth of different parts of the visible spectrum both when the spectrum is a normal one (i.e. such as is given by a diffraction grating, where all rays differing in wave length by 0.1 /A are equally distant) and when it is prismatic (in which there is a crowding of rays at the red end). Curves of relative brightness and of relative chemical (actinic) activity, so far as can be judged from the union of chlorine and hydrogen, are also given, for the prismatic spectrum. Being laid off on the " normal " scale the curves last mentioned are somewhat dis- torted. From these curves it appears that the brightest part of the spectrum lies between lines D and E, at X=0.59/i;* the warmest part is, in the normal spectrum, near X=0.60^,, but in the prismatic spectrum, beyond the visible red, at about X = 1.00/i. Finally, the chemical activity of the rays increases towards the blue end of the spectrum, but the relative activity is different for the different substances acted upon. Measured by their ability to unite chlorine and hydrogen, the rays having * MENGARINI ('89, p. 135) finds the point of maximum brightness to lie at about 0.57 /u. § 1] APPLICATION AND MEASUREMENT OF LIGHT 159 \ \ \ 1 1 1 1 III 1 « ___^_.__.__ Curve of Relative Warmth in Prismatic Spectrum. ..„_ „ Curve of Relative Brightness in Prismatic Spectrum. Curve of Relative Actinic Effect in Prismatic Spectrum. \ il— J ^f^\ •• . — m. "~~. —- . -*~~ — -^ -- • — . / X --» ,\ / i V ^, ~^, / / / i I 1 / \ / \ 1 ** / i / i \ / \ / / i / j i •-- \ / 1 i t^ -' / 1 i / f i - s \ / / i .' / / i fS / \ t i 7* / / \ ^ / V / ^ / > / ^~ i \ / \ / / i I /' / \ .' 1 V i /• \ / / X / \ .' \ \ 1 \ / .' I ,• f \ \ ^ / \ \ X / y ^* / \- \ „_ .-- • -• -- - — — — — — — ^ A \t ,'i'n/ .60^ . i II, H G F | D c B A FIG. 42. — Scale of normal solar spectrum, above which is drawn the normal curve of relative warmth ; also the curves of relative warmth, brightness, and actinism of the prismatic solar spectrum. The curves of warmth are taken from LANGLEY ('84, p. 233) ; the curve of brightness is constructed from the data of VIERORDT ('73, p. 17) ; that of actinism is taken from BUXSEN and ROSCOE ('59, p. 268) and indicates the relative efficiency of the different rays of the midday sun in caus- ing the union of chlorine and hydrogen. The absolute value of the ordiuates is entirely arbitrary. a longer wave length than 0.51yu. have feeble chemical action ; at about X = 0.42yu, this action reaches a maximum. Not only the quality but also the intensity of the light with which we experiment must be known. It is, fortunately, quite 160 LIGHT AND PROTOPLASM [Cn.VII easy to determine the intensity of white light in terms of a recognized unit ; namely, a paraffine candle burning at the rate of 7.78 grammes per hour. A paraffine candle burning at this rate has one candle power (C. P.) ; burning at twice this rate, 2 candle power, and so on. A comparison of any other light with this standard may be made by means of any of the well- known photometers, of which text-books of physics give a description. The determination of the intensity of a colored light requires an additional piece of apparatus ; namely, a spectrophotometer. The two principal types of spectrophotometer are that of VIERORDT ('73) and that of GLAN ('77), both of which have undergone important improvements. The principle in both types is the same. A spectrum of both the unmodified (standard) light and that which has passed through the colored screen are made side by side, so that their corresponding colors can be compared. Since the source of light is the same, every part of the spectrum of the unmodified light will be brighter than the corresponding part of the spectrum of the colored light. To bring the corresponding colors in the two spectra to the same intensity, the unmodified light must be made less intense to a measurable extent. In VIERORDT'S spectrophotometer this result is brought about by narrowing that half of the slit through which the unmodified light passes to get to the prism. In GLAN'S apparatus the diminution in intensity is gained by the polarization of both lights and the obscuring of the brighter by the rotation of its analyzing NICHOL prism, until equality of brightness is obtained. A modified form of VIERORDT'S convenient instrument is made by H. KRUSS of Hamburg, Germany. A modified form of GLAN'S photometer is de- scribed by VOGEL ('77). VOGEL'S apparatus (Fig. 43) consists essentially of a collimator contain- ing (1) a slit of changeable width, separated by a band q into an upper and a lower part to receive respectively the modified and the normal light; (2) a lens to render the rays parallel before they impinge ^^pon (3) a doubly refract- ing quartz prism, by which both upper and lower rays are broken into two polarized rays. Of these four rays the uppermost and the lowest are cut off by a diaphragm near F, so that only the middle two, which lie near together, pass eventually to the eye. These two rays are oppositely polar- ized and come, one from the upper, the other from the lower slit. The two §2]. CHEMICAL ACTION OF LIGHT 161 rays now pass through (4) a NICHOL prism (capable of being rotated along- side a graduated arc) set at 45°, in which position both rays pass through without changed relative intensity. The rays emerging from the collecting telescope are now dispersed by passing through the vertically placed prism, and the adjacent parallel spectra are observed through a telescope. By a rotation of the NICHOL prism through an observed number of degrees the stronger light may be brought to the intensity of the weaker. The relative intensity of two lights with reference to a third (con- stant) is as the squares of the tangent of the angle through which the NICHOL 2 prism has been rotated. Other modifications of GLAX'S photometer are those of Lord RAYLEIGH ('81) and of LEA ('H5), upon which the spectrophotometer of the- Cambridge (Eng.) Scientific Instrument Co. is based. FIG. 43. — Diagrams showing con- struction of VOGEL'S spectropho- tometer. 1. Horizontal section through the optical axis. M, mirror to reflect standard light, by aid of a totally reflecting prism p, into the optical axis. S, shutter with slit divided into an upper and a lower half hy means of a band q ; (7, colli- mating lens. D, doubly refract- ing quartz prism; m, m, the holder of the NICHOL prism N, which can be rotated through an arc that can be read off from a graduation on m, m ; P, a flint glass prism ; B, F, 0, observing telescope, in which, at the focal point, near F, is a diaphragm cutting out the two outermost of the four spectra ceming through B. 2. Front view of the shutter. (From VOGEL, 77.) M § 2. THE CHEMICAL ACTION OF- LIGHT UPON NON-LIVING SUB- STANCES The process of photography has. made us familiar with the fact that daylight acts upon the halo- gen salts of silver, gold, platinum, and other metals, although the nature of the chemical change wrought by the light is uncer- tain. It is not, perhaps, gener- ally appreciated, but it is well known to chemists, that light can produce or further very many chemical changes, particu- larly among organic compounds. The effects are mainly due to the blue and violet rays, hence are 162 LIGHT AND PROTOPLASM [Cn. VII not the results of the heat of sunlight. Most of these chemi- cal effects may be grouped under four heads. 1. Synthetic ; 2. Analytic; 3. Substitutional ; and 4. Isomerismic and Poly- inerismic. A few others may be classed (5) as fermentative. Let us now consider each of these five classes.* 1. The Synthetic Effects of Light will be considered chiefly with reference to organic compounds. All the cases I have gathered fall into three groups : addition to the organic com- pound either (a) of oxygen, (/3) of chlorine or bromine, or (y) of another organic compound. Among the compounds which take up oxygen is bilirubin, C32H36N4O6, a solution of which, in sunlight, even when air is excluded, oxidizes to biliverdin, C32H36N4O8. In the absence of sunlight this change requires air (B. Ill, 418). DUCLAUX ('87, p. 353) finds that vegetable oils, such as olive or palm oils, are rapidly oxidized if exposed to light. CHASTAIGN ('77, p. 198) believes this oxidizing action of light upon organic com- pounds to be of very wide-spread occurrence ; the bine-violet part of the spectrum being, in this respect, the most active. The direct combination by means of light of a halogen and another substance is also not rare. Thus, in daylight, hydro- gen unites with chlorine explosively. It unites with bromine also, although with difficulty. Similarly, equal volumes of chlorine and carbon monoxide unite quickly in the sunlight or magnesium light to form carbon monoxid chloride, COC12 (B. I, 546). Again, when chlorine is passed through alcohol under the influence of strong sunlight or magnesium light the two substances unite and produce chloral hydrate (STREET and FIIANZ, '70). Likewise, when chlorine is passed, in sunlight, through a solution of C3H2C12O2 in CS2, there is formed C3H2C14O2, two atoms of Cl having been added. Finally, C2C16 may be made by uniting C2C14 and C12 in sunlight (B. I, 158) ; and the compound C2H4 • FeBr2 • 2H2O may be made by passing, in sunlight, C2H4 through a concentrated aqueous solution of FeBr2 (B. I, 113). * Most of these cases were obtained by searching through BEILSTEIN ('86-'03). References to this book will be made throughout this section by the letter B, followed by the number of the volume and page upon which the statement may be found. § 2] CHEMICAL ACTION OF LIGHT 1C3 Important cases of the direct synthesis of organic compounds are given by KLINGER and STANDKE ('91). These authors have shown that in sunlight (and not in the dark) phenanthren- chinon unites directly with benzaldehyd to form a third com- pound phenanthrenhydrochinonmonobenzoat, in accordance with the formula : C14H8O2 + C6H5CHO = C14H8 (OH) (O • CO C6H5). Again, chinon (benzochinon) and benzaldehyd may unite in the sunlight to form benzohydrochinon, according to the formula : C6H4O2 + C6H5CHO = C6H5CO C6H8(OH)2. Finally, benzochinon and isovaleraldehyd may similarly unite to form isovalerochinhydron, thus : C6H4O2 + C4H9CHO = C4H9CO C6H3(HO)2. These cases, then, are examples of organic compounds which are wholly indifferent in the dark, but which, subjected to strong sunlight, lose their identity by uniting directly ; they may suffice to illustrate the important synthetic effect of sunlight on non-living, organic compounds. 2. Analytic Effect of Light. - - Cases of this effect are nu- merous, varied, and striking. I will cite a few. The organic dibasic acids CnH2n_2O4 break up in the sunlight and in the presence of a small quantity of uranium oxide, into CO2 and an acid CnH2nO2 (B. I, 63). For example, oxalic acid, C2H2O4, breaks up thus into formic acid, CH2O2 and CO2. Also an aqueous solution of butyric acid, C4H8O2, in the presence of uranyl nitrate, breaks up, in the sunlight, into CO2 and C3H8 (B. I, 422). We have seen that chlorine will unite directly with organic compounds under the influence of light ; on the other hand, compounds containing chlorine may lose it in the sunlight. Thus under these conditions the ketone (C8H17NO • HCl)2PtCl4, an ammoniacal derivative of acetone, becomes (C8H171ST6 • HCl)2PtCl2; and (C9H17NO • HCl)2PtCl4 becomes (C9H17NO - HCl)2PtCl2 (B. I, 982, 983). Again, chlo- rine acetate, Cl • O • C2H3O, undergoes slow decomposition in the light (B. I, 462) ; C5H6C12, a derivative of pentine, C5H8, does the same ; and ethylester, CIO • C2H5, explodes in sunlight. Similarly explosive in sunlight is the greenish oil distilled when absolute alcohol is poured over dry calcium chloride (B. I, 223). Finally, sugar (DucLAtrx, '86, p. 881) and oxalic acid (DowNES and BLUNT, '79, p. 209) are oxidized and break up into water, carbon dioxide, and other compounds. These cases may serve 164 LIGHT AND PROTOPLASM [Cn.VII to show the important chemical effects of sunlight in the dis- integration of organic compounds. 3. Substitution Effects of Light. — The principal substitu- tion effect of light is the replacement of hydrogen in an organic compound by either chlorine or bromine. This occurs so fre- quently that examples are superfluous. The substitution takes place most rapidly and completely in direct sunliyht, and it has been shown that the rays at the blue end of the spectrum are the most active in this process. The compounds affected belong to the most varied groups of both the fatty and aro- matic series - - carbohydrates, acids, aldehydes, ketones, and sulphides. 4. The Isomerismic and Polymerismic Changes produced by Light are among the most interesting. I will cite some exam- ples. In the first place, it may be said that the changes in the elements phosphorus and sulphur by which they assume their red form have been ascribed to sunlight. Elseomargin acid, C17H30O2, is a compound found in connection with glycerine in the oil of the seeds of Elasococca (Aleurites) vernica — Chinese oil tree — one of the Euphorbiacere. This acid crys- tallizes in rhombic plates which melt at 48°. When an alco- holic solution of this acid is placed in a bright light, leaf -like crystals of its isomere, elteostearin acid, which melt at 71°, are produced (B. I, 535). Again, thymochinon forms yellow crystals, which are soluble in alcohol. Subjected to a strong light, opaque, whitish-yellow crystals are produced, which are insoluble in alcohol. This substance, which does not arise in the dark, and is hence not merely the result of oxidation, is called polythymochinon (B. Ill, 180). Again, among the derivatives of ethylene, C2H4, is chloreth}dene, C2H3C1, a gas. When placed in the sunlight this passes into a polymere, which forms a viscous, amorphous, insoluble mass (B. I, 158). In like fashion, bromethylene, C2H3Br, a fluid, is rapidly trans- formed in the sunlight into a polymere, which is solid, amor- phous, and insoluble in water, alcohol, or ether (B. I, 181), and bromacetylen, C2HBr, a gas, is gradually transformed, in the light, into a solid polymere. Finally, very many substances undergo a gradual change of color in the sunlight, but the nature of the accompanying molecular change is unknown. §2] CHEMICAL ACTION OF LIGHT 165 5. Changes resembling those brought about by fermentation are produced by light. Thus NIEPCE DE SAINT VICTOR and CORVISART ('59) have found that a 0.1% solution of starch, exposed during 6 to 18 hours to the summer sun, becomes trans- formed into sugar, while in the dark no such change occurs. The change is favored by a small quantity of uranium nitrate. In a similar fashion glycogen is transformed into sugar more rapidly in the light than in the dark. On the other hand, GREEN ('94) finds that the ferment which normally transforms starch into sugar is destroyed by subjection to a strong light, the violet rays being especially active in this process. Like- wise, ptyalin, the ferment of saliva, is destroyed by light. To sum up, light affects organic compounds in very varied and important ways. We are, accordingly, prepared to find that light exerts a very important influence on the activities of protoplasm. Nor is the influence necessarily confined to the surface, for most protoplasmic bodies are more or less translucent. Thus SACHS ('60) found by looking through a tube with one end fitted to the eye and the other directed towards the sunlight, that considerable layers of plant tissue, for example over 32 mm. of the tissue of the potato tuber, did not cut out all the light, and that red had the greatest pene- trating power, violet the least. Even the epidermis of man permits light to pass, and ONIMUS ('95) asserts that light can pass through the hand to such an extent as to affect during 26 to 30 minutes an orthochromatic plate kept in a tight wooden box perforated only by the opening which is covered by the hand. Whether the " RONTGEN rays," which have so striking a power of penetrating organic matters, are more of the nature of light than of other physical agents, is still a subject of debate. Whether they produce any important chemical changes in protoplasm has not yet been fully determined.* * During the six months which have elapsed since the above was written, accounts of marked physiological effects of the RONTGEN rays have been pub- lished. Thus, exposure of the skin to them for an hour frequently causes loss of hair and finger nails, and produces symptoms resembling those of sunburn. AXENFELD (Centralbl. f. Physiol. X, 147) finds that many insects and a crusta- cean, Porcellius, kept in a box only one-half of which is penetrated by the rays, aggregated in this part. Several experiments upon the tropic influences of the rays have resulted negatively. 166 LIGHT AND PROTOPLASM [Ca. VII § 3. THE EFFECT OF LIGHT UPON THE GENERAL FUNCTIONS OF ORGANISMS In this section we shall consider in succession (1) the effect of light upon metabolism ; (2) the vital limits of light action on protoplasm ; and (3) the effect of light upon the movement of protoplasm. 1. Effect of Light upon Metabolism (including Assimilation). - Metabolism is a complex of chemical processes. Since, as we have already seen, light has important chemical effects, we are not surprised to find that it plays an important role in metabolism. The effects of light are, however, of two distinct kinds. One is a thermic effect, due to the heat rays of white light ; the other is a chemical effect due to the " actinic rays " of the spectrum. a. The Thermic Effect of Light on Metabolism is shown chiefly in the assimilative processes of chlorophyllaceous plants. The facts of this assimilation are chiefly these : various simple com- pounds, water, carbon dioxide, salts of ammonia and nitrates, are used as food by plants. For every volume of the gas- carbon dioxide --taken in, one volume (nearly) of oxygen is excreted. Starch (C6H10O5) is the first visible product of the water and carbon dioxide taken in. Chlorophyll is essential to the absorption of carbon dioxide, to the giving forth of oxygen, and to the formation of starch. Finally, chlorophyll can as- similate only in the presence of sunlight and at a proper tem- perature. Now, not all the rays of sunlight with their varied wave lengths are essential to this process. Just what rays are the essential ones has been a point of some dispute. The earlier studies on the subject, made chiefly by DRAPER ('44), SACHS ('64), and PFEFFER ('71), were unanimous in declaring that the most active rays in assimilation were those occupying the yellow part of the spectrum at about line D — the region of maximum brightness to our eyes (Fig. 42). But these ob- servers were at fault in that, while they carefully determined the quality of light and the corresponding quantity of assimila- tion, none of them gave, in the experiments with color screens, any adequate data upon the intensity of the diversely colored §3] EFFECT UPON GENERAL FUNCTIONS 1GT lights employed ; and this is a fundamental matter, for it has been shown, for instance by REINKE ('83 and '84), that, within certain limits, the rate of assimilation increases with the inten- sity of the light (Fig. 44). Even in experiments with the colors of prismatic spectra one must remember that the rays are crowded together at the red end, so that a given length of the spectrum contains more rays at that end than at the other (cf. Fig. 40). Later investigations with improved methods have shown quite conclusively that it is especially the rays with X = 0.68 //., or those very close to the absorption band J5, which are most 1 16 10 ~T FIG. 44. — Curve showing the relation between intensity of light (abscissae) and quan- tity of oxygen set free by Elodea canadensis. \ indicates the unit intensity of the light from the heliostat. (From REINKE, '84.) active in assimilation. The methods employed have been most diverse, but they have yielded the same result. TIMIRIAZEFF ('77) studied the assimilative power of the different parts of the solar prismatic spectrum, determining by gasometric methods the quantity of gases decomposed in a given time. REINKE ('84) also used the spectrum, but by means of his spectrophor was able to get more strictly monochromatic light, to use more nearly comparable extents of the spectrum, and, especially, to get a more exactly comparable (in this case, optimum) assimilative intensity for each part of the spectrum than his predecessors. (See p. 156.) As the measure of assimilation, REINKE usad the number of gas bubbles set free 168 LIGHT AND PROTOPLASM [Cn. VII 430 460 500 FiiO 600 660 750 per minute by the submerged, illuminated plant. As is shown in Fig. 45, the maximum of gas production occurred at about absorption line .5 --and this is the more marked of the absorption bands of chloro- phyll. A similar result was reached by ENGELMANN and set forth in a long series of papers ('81, '82, '82a, '83, '83a, '84, '86, and '87). He found that certain bacteria are extremely sensi- tive to oxygen, moving in the direction of small increments of the oxygen density. Now, by putting a thread of alga in the same water with bacteria and subjecting the thread to a "microspectrum," that part in which assimilation is pro- ceeding most rapidly, and in which, therefore, oxygen is being most rapidly excreted, will be indicated by the great- est aggregation of bacteria. The microspectrum was pro- duced by means of an appa- ratus especially designed by ENGELMANN for his work and now manufactured by the ZEISS firm in Jena. The appearances seen under the microscope when the spec- trum falls upon the alga in the bacterium - water are • shown in Fig. 46. The max- imum aggregation (hence, maximum assimilative activ- ity)^ at the red end occurs a ti c u Efo F G h FIG. 45. — Curve whose ordinates are pro- portional to the number of gas bubbles eliminated per minute by leaves illumi- nated by the various rays whose wave lengths are given at the bottom of the diagram, and whose number of vibra- tions per second are given at the top. The background of the figure is com- posed of the absorption spectra of the chlorophyll in living leaves. 1, 2, etc., at the left, indicate the number of leaves of Impatiens parvirlora, which, when superimposed, give the corresponding spectrum at the right of these numbers. The absorption at 0 is from a fern pro- thallus, that at Ale is derived from an alcoholic solution of chlorophyll. I to IV indicate absorption bands. Beyond F there is very general absorption of the highly refractive rays. (After REINKE, '84.) §3] EFFECT UPON GENERAL FUNCTIONS 169 close to the absorption band of chlorophyll. Observations upon the chlorophylls of brown, blue-green, and red cells, which, as EN GELM ANN'S microspectro-photometer indicated, have a maximum absorption at other points, showed a maxi- mum of assimilative activity at these other absorption points. In bacterio-purpurin also, in which some of the most active assimilative rays are those of the invisible red at about X = 0.85/z, most oxygen is produced at this point. (ExGEL- MANN, '83, p. 709.) Finally, by an ingeniously devised experiment, TIMIEIAZEFF ('90) has settled this matter in the most direct and indubitable a B E FIG. 46. — Piece of Cladophora with swarming bacteria in the rnicrospectrum (gas- light) . The chlorophyll grains which fill the cells very uniformly are omitted ; and, instead, the absorption band between B and C, and the tolerably pro- nounced band at the violet end between E and F, are indicated by shading. (From ENGELMANN, '82.) fashion. He kept a plant for two or three days in the dark, until the starch in its leaves had gone; then, in a dark room, a prismatic spectrum was thrown upon the leaf and the position of FBATJENHOFEB'S lines indicated on the leaf. After from three to six hours, starch had formed, under the influence of the light, only in the region of the absorption bands of chloro- phyll lying between B and D. This was determined by plung- ing the leaf into boiling alcohol, thus decolorizing it, and then staining in tincture of iodine, which combines especially with the starch. The deeply dyed places, where starch had been formed, reproduced the absorption spectra of chlorophyll. The concurrent testimony of these and other observers work- ing upon so diverse material and with such excellent methods 170 LIGHT AND PROTOPLASM [Cn. VII justifies the conclusion that it is the rays absorbed by the plant pigments which enable them to do their work in the decompo- sition of carbon dioxide. The effective absorbed rays are, moreover, chiefly those towards the red end of the spectrum, those having over 525 x 1012 vibrations per second (i.e. below the I) line).* In conclusion it may be said that the greater proportion of the radiant energy entering the plant tissue is absorbed. Thus MAYER ('93) has shown that of dark radiant heat at 100° about 80% is absorbed by a leaf through which it passes, and this proportion is about the same whether the leaf is thick or thin. Of this absorbed heat perhaps less than 10% is absorbed by the chlorophyll. The rest must be used up in the vital processes other than assimilation. b. The Chemical Effect of Light on Metabolism must now be considered ; and of this we must notice at the outset two degrees. The greater effect, which is a fatal one and the better known, will be treated of further on. The lesser effect is less striking, yet it must be included in the greater. It shows itself in a disturbance of metabolism. This disturbance of metabolism is evinced in some green plants by heightened production of carbon dioxide and the formation of chlorophyll ; and it is noteworthy that a similar result occurs among Infusoria, according to the observations of FATIGATI ('79), who finds the violet rays more active than the green in this process. Among the Metazoa light produces im- portant chemical changes in the retina of the eye, and especially in the skin, facilitating the production of pigment. That im- portant chemical changes take place in the illuminated retina follows from the experiment of placing the electrodes at oppo- site surfaces of the frog's retina. The galvanometer shows in the darkened eye a slight " current of rest " flowing from the front face to the deeper-lying part, containing the cones. If now the retina be suddenly illuminated by blue, green, yellow, red, or white light, a current, the result of chemical action, appears flowing in the opposite direction ; this continues for * Other, less important, thermal effects of light on plants are found in the formation of chlorophyll and in the quickening of transpiration, which seem chiefly due to the red and ultra-red rays. § 3] EFFECT UPON GENERAL FUNCTIONS 171 some time, slowly diminishing, however, in intensity. Certain chemical changes in the living retina may, indeed, be studied optically. These especially concern the visual purple. This is a substance lying in the outer ends of the rods of the retina, which, under the action of light, becomes bleached, but regains its color in the dark (HELMHOLTZ, Handb., pp. 265-273). These facts serve to indicate that light may influence metabo- lism even in organisms destitute of chlorophyll. 2. Vital Limits of Light Action on Protoplasm. -- We have seen above (p. 167) that the rate of assimilation diminishes in chlorophyllaceous plants with a diminution in the intensity of the light. At last a point is reached where the intensity is so low that no further assimilation can occur, and after the con- sumption of the stored-up food-stuffs, starvation and death must eventually ensue. For non-chlorophyllaceous organisms, how- ever, no such lower limit exists. Many, as parasites or cave dwellers, live in complete darkness, even through many genera- tions. A lower vital limit to the action of light exists only in the case of chlorophyllaceous plants. With the upper vital limit, it is, however, quite different. This is found in the most diverse groups. Its occurrence in bacteria being of especial hygienic importance, these organisms have been made the object of exhaustive studies. MONTE- GAZZA (see NICKLES, '65) was perhaps the first to discover that strong light kills bacteria, but DOWNES and BLUNT ('78 and '79) were the first to study the matter thoroughly. Since their time, numerous experiments have been made upon bacteria, as well as the higher fungi. For literature, see FRANKLAND and WARD (?92), and WARD ('93, p. 309). Even the earliest observers found that, while cultures of bacteria reared in the dark rapidly flourished, they not merely did not thrive when subjected to sunlight, but actually became sterilized. That the sterilization was complete was shown by the fact that when the culture was placed again in the dark, no bacteria developed in it. This result is most striking when certain bacteria, say of the species Bacillus anthracis, are mixed with gelatine or agar- agar, poured uniformly over a glass plate. If the glass plate is then covered by a black paper stencil containing some character, e.g. the letter E, and exposed to a November sun- 172 LIGHT AND PROTOPLASM [Cn. VII light for 6 hours, and if then the whole plate is placed in a dark incubator at 20° C. for 48 hours, the bacteria will be found to have developed in all parts of the plate except in the ^-shaped area sterilized by the light (Fig. 47). Compare the earlier results of BUCHXER ('92). That in these cases it is the light and not a high temperature which induces the sterilization in the illuminated region is shown by the fact that BUCHNER ('92) obtained even more striking results when parts of the culture plate were exposed under 50 cm. of water, which cuts off the heat. FIG. 47. — Appearance of a gelatine culture of Bacillus anthracis, exposed to the light over only the area E, and then incubated for 48 hours. In the area E no colonies have developed. (From WARD, '93.) Not all rays have this bactericidal property. DOWNES and BLUNT ('78) found that only the blue rays were thus active, for behind red or yellow glass the bacteria readily developed. WARD ('94) threw a solar spectrum upon an agar film in which bacteria were developing in a dark chamber. He found that the bactericidal effect was greatest in the region of the blue- violet rays (about X = 0.43 /A) and diminished towards the extreme violet arid the yellow, where it had almost disappeared. These facts were ascertained by incubating the bacteria for 48 hours after insolation, when certain parts affected by the spec- trum were found to remain clear (Fig. 48). When an electric § 3] EFFECT UPON GENERAL FUNCTIONS 173 spectrum (obtained by the use of a quartz prism) was em- ployed, a bactericidal effect was obtained (provided no glass intervened) in the ultra-violet. That the action of the light was not in these cases primarily upon the food-film was shown by the fact that a plate of sterile agar, exposed behind a stencil plate, and then laid flat on a film of dried unexposed spores, permitted the uniform growth of the spores, in the illumined as FIG. 48. — Plate of anthrax spores, exposed for 5 hours to the solar spectrum in August, ami incubated for 48 hours. The horizontal line shows the length of the spectrum. The vertical lines are not FRAUENHOFER'S lines, but serve to show the limits of the principal regions of the spectrum. The clearest area is that where fewest spores have developed in the incubation — where, consequently, the bactericidal effect was greatest. (From WARD, '9i.) well as in the unillumined region. All these observations show that the bactericidal action of light is due to the action of the chemical rays on the protoplasm. Another fact of importance, first discovered by DOWNES and BLUNT, is that light has no effect upon bacteria when they are in a vacuum. This abundantly confirmed observation indicates that death only secondarily results from light. The primar}r cause of death is an oxidation process, — a process rendered possible by the mediation of light. As we have seen (p. 162), many organic compounds undergo oxidation in the highly refracted light rays. Probably there are in bacteria such com- 174 LIGHT AND PROTOPLASM [Cn. VII pounds, the rapid oxidation of which is incompatible with life. In any case it is clear that the bactericidal effect of light is a chemical one. Concerning the range of organisms which are thus affected, it must be said that chiefly pathogenic species, such as the bacteria of anthrax, of typhus fever, and of cholera have been experimented with and have shown themselves most suscep- tible. Other bacteria are, however, likewise affected. Among the other fungi, WETTSTEIN ('85) found that the conidia of Rhodomyces Kochii, a human intestinal parasite, did not de- velop in the light. KLEIN ('85) found the same thing to be true for the conidia of Botrytis cinerea, and showed that the blue-violet rays were the most effective ones. ELVING ('90, p. 105) gained similar results with Aspergillus, although several days or weeks of insolation did not kill the fully ripe spores. WARD ('93) determined that insolated spores, cultivated on agar or gelatine plates, of Oidium lactis (5 cases), Saccharomyces pyriformis (4 cases), and " a ' Stysanus ' conidial form " found as a saprophyte on the screw-pine, Pandanus, (2 cases) became injured. These are all hyaline and colorless except Stysanus, which is nearly so. Certain colored spores which WARD experi- mented with gave negative results, and WARD concluded that this is because the blue end of the spectrum is cut off before reaching the deeper protoplasm. However this may be, we actually find that in many, but not all, fungi the metabolic processes of the spores are disturbed and even death is pro- voked by intense light. Why the spores should be especially susceptible to the action of light is an important inquiry. WARD believes the answer to be that the spores contain oily substances, which are espe- cially liable to oxidation in light, as we have already seen. Finally, we have to consider the experiments which demon- strate that a strong sunlight may be injurious even to green plants. This result follows clearly from the work of PRINGS- HEIM ('81). When strong sunlight is focussed for a short time upon cells of Spirogyra, Nitella, Mesocarpus, or Tradescantia stamen hairs in atmospheric air (5 to 15 minutes), they are killed. No result occurs, however, when the same light falls upon green cells in which the atmosphere has been replaced by §3] EFFECT UPON GENERAL FUNCTIONS 175 hydrogen (Fig. 49). That it is here also the oxygen (and not the carbon dioxide) of the air which is the destructive agent is shown by subjecting the plants to air freed of carbon dioxide, when they are killed by light as before. The most important results following from the conclusions of this sub-section are : a minimum vital limit of light action exists only in the case of those organisms (chloro- phyllaceous plants) which depend upon light for as- similation ; a maximum limit is found among the most diverse organisms, those with chlorophyll and those without. The rays which have the more rapid vibrations are the more active. They pro- duce chemical changes to which death is primarily due. 3. Effect of Light upon the Movement of Proto- plasm.--Under this head we shall consider only those protoplasmic move- ments which may not be grouped under Locomo- tion, and shall discuss three classes of cases : (a) effect of low intensity of light upon movement ; (5) effect of high intensity of light upon movement ; and (c) effect of change of intensity on contraction. a. Effect of Low Intensity of Light on Movement-- Dark-rigor. — We have already seen that chlorophyllaceous plants must eventually die if kept in the dark. Some time before death occurs the plants go into a condition of immobility, which may be called dark-rigor, since return of light brings a return of movements. Dark-rigor is very marked in the sensitive plant. •-;« FIG. 49. — Piece of a sprout of Nitella mucronata which was subjected in a gas chamber to a green light in three successive experiments A, B, C. In experiment A the insolation lasted 2 to 3 minutes, the gas chamber be- ing filled with atmospheric air. In experi- ment B the insolation lasted 20 minutes in the presence of hydrogen. In experiment C the insolation occurred again in the presence of atmospheric air and lasted 5 to 6 minutes. (From PRINGSHEIM, '81.) 176 LIGHT AND PROTOPLASM [Cn. VH If this plant is kept for several days in darkness, the usual response to touch does not occur. From some observations of BERT ('70, p. 338), it appears that it is the absence of the blue-violet and orange-red rays which brings about this dark- rigor ; for it occurs nearly as rapidly in green light as in the dark. In these cases the absence of movement in the dark might seem to be the result of diminished assimilation. O But dark-rigor occurs under conditions which destroy the general validity of this conclusion ; for example, in the reddish- purple bacteria * whose reactions have been studied chiefly by ENGELMANN ('83 and '88). It appears that in these organisms light is essential to movement ; for, after having been kept over night in the dark, they are found in the morning at first motionless ; only later, after 5 to 10 minutes of illumination, do they awaken to activity. If now, after keeping for a time in the light, the organisms are brought again into the dark, their movements gradually diminish until, in a few hours, they have ceased. We have seen above (p. 51) that oxygen is nec- essary to movement, and we know that many plants excrete oxygen in the light. We might expect that the quiescence of these organisms in the dark is a consequence of their failure to produce the oxygen necessary to locomotion, and indeed they do produce in the light a slight quantity of oxygen, by virtue of their chromophyll (bacterio-purpurin, LANKESTER). But that it is not merely oxygen which induces movement is shown by the fact that when an abundant oxygen supply is artificially furnished, no movement occurs in the dark. Thus light, in the presence of oxygen, is essential to movement ; it seems to be necessary to the irritable condition upon which locomotion depends. This irritable state of the protoplasm conditioned upon a certain intensity of light ENGELMANN calls phototonus.-f The analysis of this matter has been carried further. It has been found that a perceptible time (latent period) elapses * This term includes bacteria known as Bacterium photometricum, Bacterium roseopersicinum, rubescens, etc., Monas okeni, Spirillum violaceum, and by other names. t The term was applied to this phenomenon by ENGELMANN on account of its resemblance to that already described for the higher plants, and to which SACHS had previously given this name. §3] EFFECT UPON GENERAL FUNCTIONS 177 between the illumination of the organism and the occurrence of movement. Also, the ultra-red rays produce most rapid locomotion, next the orange-yellow, and weakest the violet-blue and violet-red. Spectrum analysis shows that the most active rays are the ones absorbed by the chromophyll (Fig. 50). This phenomenon of phototonus is not confined to the purple bacteria. Thus, FAMINTZIN ('67, pp. 29-31) has shown that the movements of the closely related Oscillaria are dimin- ished in the dark. SOKOKIN ('78) found that protoplasmic streaming in the plasmodium of Dictydium ceases at night, being awakened to movement by the light. Finally, VEK- B C D E b 80 75 TO 55 50 FIG. 50. — a. Spectrum of the chromophyll of bacterio-purpurin, showing absorption bands at \ = 0.59^ and A = 0.53^- An (invisible) absorption band has been deter- mined by means of the bolometer at A = 0.85 fi. b. The bacteria are seen aggre- gated chiefly in the regions of the absorption bands. The accumulation of bacteria in these regions of absorbed energy seems due to the fact that the moving bacteria cannot pass from a region of high energy to one of low without a violent stimulus which impels them back again. (From ENGELMANN, '83a.) WORN ('89, Nachschrift, and '95, p. 393) finds that, in the dark, the ciliate Pleuronema chrysalis rests quietly in the water, only occasionally making its peculiar spring. But when diffuse daylight is focussed upon it, for instance by the mirror of a microscope, it springs rapidly by the movement of its long cilia ; and this movement is often repeated, so long as light continues to fall. The movement is produced by blue or violet rays ; red rays have little or no effect. A latent period of from 1 to 3 seconds elapses before the response occurs. These cases serve to show that light, in the presence of other suitable conditions, is, both for some chlorophyllaceous organ- isms and plant tissues and for some organisms destitute of N 178 LIGHT AND PROTOPLASM [Cn. VII chlorophyll, nearly or quite essential to movement. Phototo- nus is a convenient name for the condition induced by light. b. Effect of High Intensity of Liyht on Movement — Light- rigor, - - We have just seen that in some organisms the most vigorous movements occur at an optimum intensity of light, which produces phototonus. At a lower intensity there is no movement. It appears, furthermore, that there is for many or- ganisms a maximum intensity of light, below that which produces death (ultramaximum), which causes a cessation of movement that may be called light-rigor. This condition is distinguished from that of death by the fact that diminished light brings return of activity. ENGELMANN ('82, p. 109) observed this condition in his Bacterium photometricum, and remarks that it is common to all bacteria. Similar light-rigor has been observed in green plants also. PRINGSHEIM ('81, p. 516) found that when, in the presence of oxygen, strong sunlight was let fall upon Nitella, the movements ceased after 1| minutes. If the insolation was now interrupted, normal move- ments were resumed. Summing up the effects of varied intensities of light, it appears that for many organisms there is an optimum, which produces a condition of phototonus, in which the organism moves and responds regularly to stimuli. As the light inten- sit}^ falls below, or rises above this optimum, the activity of movement diminishes, ceasing at certain points in the condi- tions of dark-rigor and light-rigor. Beyond each of these points, again, is the point of death. c. Contraction produced by Change in Intensity of Illumina- tion. - - We here consider a number of cases not closely related except in this, that quick movements are produced after stimu- lation by change in the intensity of the light. The cases are found both among Protista and Metazoa. Among the sulphur-bacteria ENGELMANN ('88, p. 665 ; 88a) has noticed that a sudden diminution in the intensity of the light, produced by shading the mirror of the microscope, is followed by a spring backwards, often to the distance of 10 to 20 times the organism's length. This reaction ENGEL- MANN has called " Schreckbewegung." When the light is sud- denly increased, a forward movement takes place, but this is § 3] EFFECT UPON GENERAL FUNCTIONS 179 less marked. Among the Myxomycetes, ENGELMANN ('79) has found that the amoeboid Pelomyxa, when suddenly sub- jected to a strong light, contracts into a spherical mass. Sudden darkening or gradual illumination produces no such contraction. Among swarm-spores, STRASBURGER ('78, pp. 575, 576) has noticed that a sudden diminution of the light puts the quiet Heematococcus spores again in motion, and makes the Botrydium spores start as though disturbed. Such violent movements of the protoplasm indicate that a very considerable chemical change has taken place in it. Passing, next, to the Metazoa, we find that certain smooth muscle fibres are made to contract by the direct action of light ; thus, STEINACH ('92) has offered most convincing evidence that the contraction of the iris, in the lower vertebrates at least, may occur as a direct reaction to illumination, even when the eyeball is cut out, and the iris, indeed, separated from connection with the ciliary part of the eye. Some of the higher animals react strikingly like ENGEL- MANN'S bacteria. Thus, LOEB ('93, p. 103) found that Serpula uncinata retracts into its tube when the hand is passed between it and the light ; but sudden increase of illumination has no effect. NAGEL ('96, p. 76) finds the same thing in Spirographis, and ANDREWS ('91, pp. 285, 296) has observed the same phe- nomenon in the eyeless Hydroides dianthus. In these cases the branchiae seem to be the sensitive organs. Adult barnacles show a similar sensitiveness to light; for POUCHET ('72, p. Ill) found that momentary cutting off of the light, as by the shadow of the hand, caused arrest, for several seconds, of the rhythmic movements of protrusion of the appendages from the shell. In this case, the sensitive region has not been located. Some lamellibranchs (NAGEL, '96, p. 50) react similarly to increased light. These are examples of a phenomenon which we shall meet with again in considering growth. They serve to show that there is a wide-spread irritability of protoplasm to changes in intensity of light. Let us now review the conclusions of this section. Light — especially the thermic rays --is essential to the decomposi- tion of carbon dioxide by chlorophyllaceous plants. The only effective rays are those absorbed by the chlorophyll. The rate 180 LIGHT AND PROTOPLASM [Cn. VII of assimilation is increased by increased intensity of light. The chemical rays act to increase metabolic changes, and the output of carbon dioxide. As these rays become more intense, the metabolic changes go on with abnormal rapidity, until, finally, death ensues ; thus, intense light is fatal to many, perhaps to all, organisms. Absence of light, however, is injurious only as preventing assimilation in chlorophyllaceous organisms ; but these supply the food for other organisms, so that continued darkness in any environment must likewise be eventually fatal to all life. All organisms, before succumbing to darkness or to light, enter into a condition of rigor, from which they may return to activity if favorable conditions are restored. Sudden change of intensity often produces violent protoplasmic changes, awakening quiescent organisms to activity, or causing, in the higher organisms, violent contractions. All of these effects of light, whether produced by the thermic or chemic rays, probably give rise to great chemical changes by which disturbances of metabolism, and eventually death, may be produced. Not all organisms find light immediately necessary to their existence; but very powerful light, long continued, proves fatal to most protoplasm. § 4. CONTROL OF THE DIRECTION OF LOCOMOTION BY LIGHT - - PHOTOTAXIS AND PHOTOPATHY * In this section we shall (1) distinguish between false and true phototaxis ; (2) consider the observed cases of phototaxis among Protista, the parts of higher organisms, and the Metazoa as entire organisms ; and (3) discuss the general laws of photo- taxis and photopathy. * In this section we shall deal with two sets of phenomena which very likely are different, but which, in our ignorance, we cannot always distinguish. The first includes that active migration of organisms whose direction is determined by that of the rays of light. This is phototaxis. The second includes the wandering of organisms into a more or less intensely illuminated region, the direction of locomotion being determined by a difference in intensity of illumina- tion of the two poles of the organism. This is photopathy. According as the migration is towards or from the source of light, we can distinguish positive ( + ) and negative ( — ) phototaxis. According as the migration is towards or from the more intensely illuminated area, we can distinguish positive ( + ) and negative §4] PHOTOTAXIS AXD PHOTOPATHY 181 1. False and True Phototaxis. --It must certainly be a very old observation that when small organisms are placed in a vessel in front of a window, they are soon found arranged with reference to the window ; some lying on the nearer side, some 011 the further side, and others swimming indifferently back and forth through the vessel. The conclusion is near at hand that this arrangement of the organisms is determined by the light. This conclusion is, however, not necessarily correct. Thus, SACHS ('76) showed that, under certain conditions, wholly passive substances — oil drops, in a mixture of water and alcohol -- might exhibit a similar aggregation towards the window or away from it. These conditions are that the vessel should be cooler next the window. Then, on the cooler side, there will be a descending current ; on the warmer side, an ascending current ; on the surface, a current towards the win- a FIG. 51. — Vertical section through a dish showing distribution in water of passively suspended bodies, as a result of difference of temperature at the two sides of the vessel. A, warmer side ; B, cooler side. Arrows show the direction of movement of currents in the water. The objects lighter than water are grouped at b ; those heavier than water, at a. dow ; and on the bottom, a current from the window. If the passive bodies are such as float, they will thus be carried towards the window, and will exhibit a false phototaxis (in the positive sense); if, on the contrary, they tend to sink, they will be carried from the window, and show false negative pho- totaxis. Now this appearance, due to passive transportation by currents, may likewise, under the given conditions, be exhibited by organisms - - but the phenomenon is not due to light (Fig. 51). There is at least one other kind of pseudophototaxis. This ( — ) photopathy ; and correspondingly we can in this second case speak of the organisms themselves as photophil or photophob. In this nomenclature I follow GRABER. STRASBURGER used photometry for what I here call photopathy, but OLTMANNS ('92, p. 206) has employed photometry to indicate the capacity of organisms to perceive different degrees of intensity of light. So, perhaps, the terminology here employed may lead to the least confusion. 182 LIGHT AND PROTOPLASM [Cn. VII may occur when there are in the vessel chlorophyllaceous organisms producing oxygen in the sunlight. The oxygen, more abundantly formed on the sunny side of the vessel, becomes, then, a means of attraction to other (chemotactic) organisms, whose position seems thus to be determined directly by relative brightness. A good example of this kind of pseudophototaxis is described by EXGEL- MAJSTX ('81a). He found that the Schizomycetes in a certain drop of water, partially illuminated, were aggregated toward the illuminated side. Exami- nation revealed the presence of a chlorophyllaceous schizomycete — Bacte- rium chlorinum — in the drop, and the apparent phototactic appearances were easily accounted for as follows : Under the influence of light the Bacterium chlorinum secreted oxygen, and this acted chemotactically to attract the bacteria, which thus moved, at the same time, towards the illuminated area. That it was the oxygen produced in the sunlight rather than the light itself which attracted, was evinced by the fact that, when the supply of oxygen is abundant in all parts of the drop, or if the Bacterium chlorinum is removed, no aggregation takes place at the bright point. 2. Distribution of Phototaxis and Photopathy. — a. Protista. — We now come to the consideration of the cases of true pho- totaxis and photopathy, and shall first discuss the distribution of the phenomenon in the different groups of Protista. Of the Protista we may take up first the chlorophyllaceous forms. Flac/ellata and Swarm-Spores. - - In no other group does phototaxis show itself more clearly than in this. The earliest studies were made here, but despite the ease of gaining results they were mostly fragmentary and uncritical. A simple ex- periment of NAGELI ('60) had, indeed, showed conclusively that swarm-spores are responsive to light. A glass tube three feet long and held vertically was filled with alga-water. When the upper end of the tube was enveloped by black paper the organisms moved to the lower end, and conversely. A diffi- culty was encountered, however, in the fact that when zoospores were placed in a plate by a window, the organisms gathered at the edge next the window, which, since the edge of the plate threw a shadow there, was the darkest part of the surface. In consequence some authors had concluded that swarm-spores shun the light ; whereas COHN asserted, all too briefly, that they move in the direction of the rays and toward the source of light. Finally, FAMINTZIN ("67) had discovered that swarm- § 4] PHOTOTAXIS AND PHOTOPATHY 183 spores which moved towards a light of a certain intensity would move from light of a certain greater intensity. That was the condition of knowledge on this subject when STRASBURGER'S ('78) epoch-making paper appeared. STRASBURGER worked with swarm-spores of various species of algse, and with the flagellate Chilomonas and Euglena. He observed again the phenomenon that the sense ( + or - - ) of response depends upon the intensity of the light. He also showed that the rate of movement is quicker in stronger light on account of the fact that the path taken by the organism is straighter ; and (p. 586) that phototaxis is the result of the organism putting its long axis in the axis of the infalling rays. STRASBURGER found also that, in general, the smaller species of swarm-spores and the smaller individuals are more respon- sive than the larger ones. Later studies have extended our knowledge of the distri- bution of phototaxis in this group. Swarm-spores have been studied by STAHL ('78, '80) ; Euglena, by ENGELMANN ('82% p. 396) ; and Volvox, by CIENKOWSKI ('56), VERWORN ('89, p. 45), and OLTMANNS ('92). Especially interesting is the fact that colorless swarm-spores, like those of Chytri- dlum, which are parasitic upon chloroph}rllaceous forms, respond like the green organisms. (STRASBURGER, '78, p. 568.) Desmids, especially Closterium, have been experimented with by STAHL ('78 and '79), KLEBS ('85), and ADERHOLD ('88). All are markedly phototactic in moderate, diffuse daylight. This phototaxis is the more striking since the method of loco- motion of these forms is peculiar. The crescentic Closterium moniliferum, for example, stands inclined and glides along, one extremity touching the substratum, the free extremity in ad- vance. The gliding seems to result from the secretion of a stream of mucus along the substratum. Now STAHL believed that the angle of inclination of the Closterium is dependent upon the direction of the infalling rays of light, being parallel thereto. This relation has been denied by KLEBS, but ADER- HOLD, by varying the direction of the infalling rays, has shown that the azimuthal position is determined by light. Under certain conditions Closterium moniliferum moves by a sort of head-over-heels motion, since the free end bends down to the 184 LIGHT AND PROTOPLASM [Cn. VII substratum and becomes attached, and the former attached end becomes free. STAHL explains this on the ground that the ends of Closterium periodically exchange their tendency to point towards the light. The appearances just described are found in diffuse daylight. In stronger light the azimuthal position is 90° from the infalling light. If direct sunlight falls upon desmids, they move from the light (negative pho- totaxis). Diatoms have been studied by STAHL ('80) and VERWORX ('89, p. 47). Locomotion is effected in these organisms as in desmids by the secretion of mucous threads. The movement towards diffuse daylight (Navicula, Stauroneis) takes place slowly, but it often affects nearly all the individuals. The long axis does not seem to be clearly oriented in the direction of the infalling rays, which may be partly accounted for by the normal zigzag method of locomotion. Under strong sun- light diatoms appear negatively phototactic. Occasionally a culture will be found whose individuals are separated into two groups — one next the positive side, the other next the nega- tive side of the vessel. Oscillaria. - - VERWORIST ('89, p. 50) has made experiments on the reaction of these organisms, whose method of locomotion is probably similar to that of desmids. They are markedly positively phototactic from half darkness to direct sunlight ; only in intense sunlight do they fail to accumulate at the posi- tive end of the vessel. The aggregation at the positive pole takes place by the threads assuming a direction parallel to the rays of light and creeping forward thus, side by side. VER- •yvoiix states that after all have attained the + edge, rotation of the slide or vessel through 180° does not cause a prompt transfer of all individuals towards the light side — at least during the time of his observation only a few had crawled towards the light in its new position. According to WTNO- GRADSKY ('87), Beggiatoa is generally negatively phototactic. Myxomycetes. - - In its amoeboid form and when subjected to strong sunlight JEthalium septicum retreats into the substratum, but while in the dark it comes to the surface (HOFMEISTER, '67, p. 625 ; STRASBURGER, '78, p. 620). Also, when the plasmo- dium is partially illuminated, the protoplasm tends to flow from §4] PHOTOTAXIS AND PHOTOPATHY 185 the illuminated region. (BARANETZKI, '76, p. 328, and STAHL, '84, p. 167.) BARANETZKI proceeded as follows: a glass plate was placed in a saucer so that its surface was 2 or 3 mm. below the rim. The plate was covered by filter paper which extended over the rim and here dipped into water, by which means it was kept moist. Over the saucer was laid an opaque cover, blackened below and provided with a narrow slit. The plasmodium was placed on the filter paper and diffuse daylight was thrown upon the slit by means of a plane mir- ror. In less than half an hour the illuminated threads of the plasmodium had become very thin, owing to the retreat of the protoplasm from under the slit to the darker region (Fig. 52). FIG. 52. — Plasmodium of yEthalium septicum, after having been kept in the dark for some time and then illuminated, for half an hour, over a cross-shaped area, only. The illumi- nated area is on the upper part of the figure. The protoplasm has retracted from it, leaving a partially clear region in the form of a cross. (From BARANETZKI, 75.) RTiizopoda. — Although, as we have seen, Pelo- rayxa is irritated by a sudden illumination, a phototactie or photo- pathic response has not hitherto been certainly observed in this group. VERWORX ('89, pp. 40, 41), indeed, experimented, but with negative results, upon Amoeba limax, Amoeba princeps, Actinosphoerium, and Actinophrys. Only in Polystomella crispa did he notice a slow wandering towards the source of light ; but he was uncertain whether this was due to light. VERWORN'S method was not well devised, however, for bringing out phototactie response. The Protista were placed on the slide, and, after cut- ting out heat rays by means of a plate of ice, were subjected to the light or to the ENGELMANN microspectrum, and illuminated at different intensities either over the whole body or over only a part. All disturbing influences, he says, were as far as possible eliminated : gravity, by an exact horizontal position of the microscope on a table with three screw-feet; the action of the edge of the drop, by using a very broad drop ; and, finally, the laterally 186 LIGHT AND PROTOPLASM [Cn. VII impinging rays of liyht, by means of a black cardboard box placed over the slide. Thus it is clear that all of his light fell upon the organism in perpendicular rays from below. This method of experimentation would clearly not show whether Amoeba is phototactic or not. I have experimented with Amoeba proteus, using methods resembling VERWORN'S, and likewise dissimilar ones, and have reached new results. In the first place, I have proceeded some- what after the fashion of VERWORN to determine whether the amoeba in a field illuminated from below, and separated by a sharp line into a light and dark half, showed any change of movement in passing from dark to light or from light to dark ; also, whether an arnceba moving in a uniformly illuminated field changed its direction when half of its body was dark- ened. Nearly all such experiments were negative. No effect resulting from the change from light to dark or the reverse could be detected. Thus far my results agreed with VER- WORN'S. In a second set of experiments, I proceeded differently. Usually one amoeba was isolated by means of a capillary tube. It was then introduced, with a drop of clear water, between two slips of glass, each about 25 by 50 mm., which were kept 2 mm. apart, and at the same time cemented together, by glass strips of equal thickness placed near the ends. By this means a broad field for movement with uniformity of conditions of con- tact was ensured. The whole space between the two glass plates being now filled with clear water, the entire apparatus was sub- merged in a vessel which contained water about 2 cm. deep, and which was slightly smaller than the stage of the micro- scope. Finally, the entire stage, but not the substage optical apparatus, was kept in the dark by means of a cone made of several thicknesses of dense black cloth fastened by a slip-noose to the objective, and. folded below the stage so as completely to exclude all extraneous lateral light. Light from the mirror was cut off by an interposed card. Through a slit in the cloth on the side next the window, — a west window, — a beam of direct sunlight, or ef reflected light from the morning sky, was admitted to the amoeba. The plates of glass being as nearly as possible horizontal and occasionally rotated, the directive action of gravity was eliminated. Since, so far as could be seen with § 4] PHOTOTAXIS AND PHOTOPATHY 187 the microscope, no local sources of food or oxygen occurred in the water between the plates of glass, chemotactic influences were uniformly distributed. From the conditions of the ex- periment already described, a difference in temperature or of illumination at the two poles of the amoeba is scarcely conceiv- able. The rays of radiant energy were the only directing agent. Under these conditions the amoeba nearly uniformly showed itself negatively phototactic to light of an intensity varying from strong diffuse light to direct sunlight. The absence of uniformity is to be ascribed to the accidental presence of some disturbing agent. The movements made by the amoeba were represented graphically by making at intervals a camera drawing of its outline. Two such graphic representations are repro- duced in Figs. 53 and 54. It must be said that it is difficult to get so extended a series of changes in light as is shown in Fig. 54, for the phenomenon of acclimatization conies in and the responses become irregular. But, despite such irregularities, my studies lead me unhesitatingly to conclude that Amoeba, although not at all photopathic, is strongly phototactic. This result is important, for, since Amoeba is responsive to light, it may very well be that such responsiveness is a general property of protoplasm. Ciliata.-- A double action of light must be here taken into account. ENGELMANN ('82a, pp. 391-395) states that those Ciliata which contain chlorophyll (algre) - - e.g. Paramecium bursaria, Stentor viridis, Bursaria - - move towards the light, but only when the oxygen tension in the water is low. Also when the water drop is illuminated by a microspectrum, instead of white light the organisms aggregate towards the red end. Here are the rays by which most oxygen is produced from the chlorophyll, since assimilation takes place fastest here. When the organisms are placed in excessively oxidized water they move from the light. The conclusions to which ENGELMANN arrived from these and other facts were that these species have a very delicate sensitiveness to variations in oxygen tension, and that it is through this sensitiveness that light influences move- ment. Accordingly, it would seem that the apparent photo- taxis is truly a case of chemotaxis ; but this conclusion requires better evidence. 188 LIGHT AXD PROTOPLASM [Cn. VII 11:22 11:18 <2>. 14:00 to 14:20 I 11:02 10:55 Interval not observed )' 13:57 10:44 13:O6 1O:34 ,10:28 I3:OO 12:54 12:49 (3). 14:2O to 14:34 First direction .of migration 53 Kl). 12:48 to 14:00 54 FIG. 53. — Camera drawing, showing the successive positions assumed by an amoeba subjected to light falling upon it from one side. The arrow lies in a horizontal projec- tion of the sun's rays. The amceba retreats from the source of light. The numbers to the right of the outlines of the amoeba give the observed times between 10:28 and 11 :22 A.M. Magnified 16 diameters. FIG. 54. — Camera drawing, showing the successive positions assumed by an amoeba retreating from the light. The position of the inf ailing ray was successively changed from (1) to (2), (3), and (4). The arrow labelled "First direction of migra- tion " shows the direction of loco- motion of the amoeba before the light fell upon it at the beginning of the experiment. The numbers indi- cate hours and minutes. During the interval from 13:06 (=1:06) P.M. to 13:57, the amoeba was not under di- rect observation, since I was called away. Magnified 16 diameters. Cases that can be explained only on the ground of the imme- diate effect of light upon the direction of movement are cer- tainly rare. ENTZ ('88), indeed, has intimated that Opalina flees from light, but VERWORN ('89, pp. 53-57) was not able to confirm him in this point. VERWORN'S method was here, as in the case of Amoeba, not satisfactory. Instead of having the light fall from one side only upon the drop containing the Opalinas, he let the light pass vertically from below through a small hole, and could observe no tendency to avoid the illu- §4] PHOTOTAXIS AND PHOTOPATHY 189 minated spot. The light in this case clearly did not act from one side, and the test of phototaxis can therefore hardly be said to have been critically made. Likewise, even with unilateral illumination, VERWORN was unable to gain a phototactic re- sponse with Stentor rueselii, St. cceruleus, Carchesium polypi- num, and Uroleptus musculus. On the other hand, we have often noticed here in Cambridge that our Stentor coeruleus is (rather indefinitely) negatively phototactic to diffuse daylight. Thus, an individual swimming free in a bit of glass tubing pointing horizontally towards the window only very slowly wanders away from the light. In conclusion, then, we must admit that Ciliata are not markedly phototactic, but more refined methods must be used before we can say of any of them that they exhibit no trace of this response. Let us summarize briefly the results obtained from Protista. Phototaxis is most marked among actively motile, chlorophyl- laceous forms. Many colorless forms are, however, also photo- tactic - - Beggiatoa, Annp.ba, plasmodia of Myxomycetes, and swarm-spores of Chytridium. The phenomenon is thus wide- spread, if it is not universal. b. Cells and Cell-organs. - - Under this head will be consid- ered, (a) the rearrangement of chlorophyll corpuscles, (/3) the rearrangement of pigment in animal cells, and (7) the migration of pigment cells in the metazoan body. a. That the chlorophyll bodies of the higher plants change their position in the cell according to the intensity of the light to which they are subjected has been made known chiefly through the labors of FAMINTZIN ('67), BORODIN ('69), FRANK ('72), STAHL ('80), and MOORE ('87). If one fastens a strip of black paper upon a leaf on which the sun's rays are falling, one will find, upon removing the paper after a time, that the darkened part is dark green whilst the brightly illu- minated part is considerably lighter, so that an image of the form of the dark paper is produced upon the leaf. This image is, however, only temporary. A few hours after the removal of the paper the leaf is of a uniform green again. Sections through a leaf thus affected show that in the dark green (shaded) part of the leaf the chlorophyll lies on those walls of the cells which are perpendicular to the incoming rays, 190 LIGHT AND PROTOPLASM [Cn. VII whilst in the light green (illuminated) part of the leaf the chlorophyll lies upon the walls parallel to the rays. When the grains are upon the superficial face of the cells they are said to be in epistrophe; when they have turned away from this face they are in apos- trophe. This apostrophic position is found under two opposite conditions of illumination : under intense light, as we have just seen (positive apos- trophe, MOORE), and upon prolonged standing in the dark (negative apostro- phe). (Fig. 55.) It appears, then, that epistrophe occurs only within certain limits of light intensity. The in- tensities included between these limits constitute what MOORE calls the epistrophic interval. The epistrophic interval varies in position and in extent in different species.* It has been found that in the case of plants which normally live in the bright sun the epistrophic * The limits were determined by MOORE, in a roughly quantitative way, by means of his photrum, constructed as follows. A room with a single window illuminated by the sun was chosen and 12 feet spaced off from the window back into the darkness. The intensity of the light diminished of course as one re- treated from the window. Plants of various species were allowed to stand, simultaneously, at varying distances from the window, and the distance back at which epistrophe began to appear, and, finally, at which negative apostrophe came in, were noted. Then a diagram ^ the actual scale was made (Fig. 56), showing the position of the points of beginning and ending of epistrophe (so- called positive and negative critical points). C ^ FIG. 55. — Cross-section through the leaf of Lemna trisulca. A. Position of the chlo- rophyll grains in diffuse daylight — epis- trophe. B. Position of the chlorophyll grains in intense light — positive apos- trophe. C. Position of the chlorophyll grains in darkness — negative apostrophe. (After STAHL.) §4] PHOTOTAXIS AXD PHOTOPATHY 191 interval is a region of relatively high intensity (Fig. 56, 6) ; in aquatic plants the epistrophic interval occurs in a region of low intensity (Fig. 56, 1 and 2) ; and in shade-loving aerophytes in an intermediate position (Fig. 56, 4 and 5). One may say that every species is attuned to a certain intensity and range of light, in which epistrophe occurs, just as in swarm-spores there is a certain intensity and range of light in which positive phototaxis occurs, and that attunement depends upon the conditions to which the organism has adjusted itself through living in them. FIG. 56. — A diagram of MOORE'S photrum, showing for six spaces the epistrophic interval (shaded region). 1. Anacharis (Elodea) canadensis, "water-weed." 2. Lemna trisulca. 3. Saxifraga granulata (position of positive critical point). 4. Oxalis acetosella (position of negative critical point only approximate). 5. Pteris critica (positive critical point). 0. Pyrethrum sinense (garden Chry- santhemum). + indicates the brighter end of the photrum. Concerning the question of the mechanism of the movement of the chlorophyll grains, there is much difference of opinion. It is urged on the one hand that the chlorophyll grains move actively to attain their new positions, and, on the other, that they are passively carried by the cell currents. Of these two views analogical reasons are perhaps the strongest for preferring the second. As to the question in how far these movements can lie regarded as adaptive, we may say that STAHL believed that they regulate the relation between intensity of sunlight and assimilating area, so that the quantity of assimilation shall not become too great. HIERONYMUS ('92, p. 466) considers them to be for the purpose of screening the nucleus. MOORE (p. 222), 192 LIGHT AND PROTOPLASM [Cn. VII however, chiefly from a consideration of vegetative apostro- phe, has been led to the conclusion "that the movements of chlorophyll have no relation whatever to benefit or injury experienced by the grains, nor necessarily to the well-being of the protoplasm.'' /3. The Rearrangement of Pigment in Animal Cells in Response to Light. --One of the striking cases of this effect of light is seen in the pigment cells of the skin of the chameleon, as described by KELLEK ('95, pp. 144, 162). He has found that the dark color of the (illuminated) skin is due to the rich cu. ep. FIG. 57. — Vertical section through a black dermal papilla of Chamseleo vulgaris. ep, epidermis; CM, cutis; p, black pigment cells; p', processes of the cells con- taining pigment ; y', yellow pigment cells. (After KELLER, '95.) branching at the base of the epidermis of black pigment cells lying deep in the cutis (Fig. 57). In the dark, the pigment granules stream out of the branches into the cell body, but the branches themselves are undisturbed (Fig. 58). So long as the black pigment has this central position, the skin appears whitish. The light, on the contrary, causes the pigment, which is probably carried passively in the plasma, to move centrifu- gally. Whether the direct response to light of the pigment cells of the frog, as described by STEINACH ('91), is of the same nature, or due to contractions of the pigment cells, re- mains to be determined. Again, in the retina of the compound eyes of Arthropoda, §4] PHOTOTAXTS AND PHOTOPATHY 193 we find this capacity for rearrangement of pigment granules, as EXNER ('89 and '91, p. 104), STEFANOWSKA ('90), SZCZA- WINSKA ('91), PARKER ('95), and others have shown. In the higher Crustacea, for example, the pigment granules of the pigment cells surrounding the rhabdome (or " spindle ") are, in the dark, below the level of the spindle. Upon illumination, however-, these granules migrate (or are carried) upwards, and partly envelop the rhabdomes. I believe it has not been deter- mined what rays are involved in producing this result. This response to light is considered to be an advantageous one, since cu. ep. FIG. 58. — Vertical section of a whitish-yellow dermal papilla ; lettering as in Fig. 57. p', processes of black pigment cells containing no pigment. (After KELLER, '95.) the pigment thus cuts off side rays from the perceptive organ -the rhabdome. It is interesting that we should find cells containing two so diverse kinds of pigment as chlorophyll and the retinal pig- ment responding to light in so similar a fashion. In most of the cases, if not all, this response is an adaptive one. 7. The Migration of Pigment Cells in the Metazoan Body. - It has been shown, apparently first by ENGELMANN ('85), that the pigment cells of the retina vary their movements with the light. Thus, when a strong light is thrown upon the retina of the frog, the pigment cells send out pseudopodium-like processes between the roo"s and cones, whereas in the dark the 194 LIGHT AND PROTOPLASM [Cn. VII pigment lies behind all these elements. Also, among the Crus- tacea, the protoplasm of the outer pigment cells, surrounding the cones of the compound eye, migrates centripetally in a strong light, to return again to its peripheral position in darkness. These movements may also be considered adaptive. They are, in addition, movements which are discharged only by light. c. Metazoa. - - We may treat of the control by light of the 'movements of the higher animals somewhat more summarily than we have the preceding classes. The facts will be arranged by groups in systematic order. Among radial animals, Hydra has perhaps been for the longest time an object for photopathic study. TEEMBLEY (1744, p. 66) had noticed that Hydra viridis, and even muti- lated pieces of it, came to the light side of the vessel. When the light was admitted only through a chevron-shaped slit, the Hydras were later found aggregated opposite the slit in the form of a chevron. That it was not the warmth of the sunlight that attracted was shown by turning the slit towards the cooler air, whereupon the same response occurred. The observations of TEEMBLEY showed that the Hydras did not move in as straight a line as possible towards the light (they must, of course, follow a firm substratum), but gradually wandered towards it. The response of Hydra must therefore be considered as photopathy. More extensive studies were made upon Hydra by WILSON ('91), who found that Hydra f usca is likewise responsive to light, and, indeed, photophil with reference to diffuse daylight, and photo- phob to direct sunlight. And it can be shown that it is an advantage to Hydra to be photophil, since many of the Ento- mostraca upon which it feeds are phototactic. Besides Hydra, I know of only one case of response by Cce- lenterata to light. The larvse of the sponge Reniera are said (MAESHALL, '82, p. 225) to flee from the light, — probably negative phototaxis. Among JEchinodermata, Asteracanthion rubens (GEABEE, '85, p. 155) appears to be photophil, and Asterina gibbosa (DEIESCH, '90, p. 155) to be photophob. Although, as we have seen, some radial animals may respond to light, the phenomenon is more wide -spread in the bilateral groups, --flatworms, annelids, crustaceans, insects, molluscs, PHOTOTAXIS AND PHOTOPATIIY 195 and Vertebrates. The results of experiments may here be given in tabular form. Unless otherwise stated, the light is sup- posed to be diffuse daylight, and the response to be phototactic. TABLE XVIII ORGANISM. SENSE OF RESPONSE. AUTHORITY 11 EM ARKS. Fresh-water planaria .... Polynoe sp Polygordius, larva Earthworm Leech . Daphnia Many marine copepoda Balanus, larva -(OP+) Limulus, larva Idotea tricuspidata Diastylis (Cuina) rathkii . Carcinus mamas Homarusamericanus, larva Plant lice Blatta germanica (blinded) Musca dom. (?), larva . . . Musca, adult Musca vomitoria, larva . . Musca csesar, larva Eristalis tenax, larva . . . Lepidoptera, adult Lepidoptera, larva Ants, after gaining wings . Melolontha vulgaris. (May beetle) Tenebrio molitor, larva . . Dentalium . Rissoa octona Littorina rudis Gasterosteus spinachia . Triton Fros . + LOEB, '90, p. 95 DRIESCH, '90, p. 155 LOEB, '93, p. 90 DARWIN, '81, p. 21 GRABER, '83, p. 210 HESSE, '96 LOEB, '90, p. 96 TREMBLEY, 1744, p. 96 BERT, '78, p. 989 LUBBOCK, '82, '83 DAVENPORT and CANNON LOEB, '93, p. 96 GROOM and LOEB, '90, p. 160 LOEB, '93, p. 83 GRABER, '85, p. 141 LOEB, '90, p. 91 DRIESCH, '!)0, p. 156 HERRICK, '96, p. 189 LOEB, '90, p. 55 GRABER, '83, p. 235 LOEB, '90, p. 69 LOEB, '90, p. 81 DAVIDSON, '85, p. 160 POUCHET, '72, p. 113 POUCHET, '72, p. 129 SEITZ, '90, p. 337 LOEB, '90, p. 46 LOEB, '90, p. 51 POULTON, '87, p. 315 LOEB, '00, p. 63 LOEB, '90, p. 86 LOEB, '90, p. 84 LACAZE-DUTHIERS, p. 25 GRABER, '85, p. 144 DRIESCH, '90, p. 155 GRABER, '85, p. 148 GRABER, '83, p. 221 LOEB, '90, p. 90 '57, see p. 200 > photophob 1 photophil ( ?) phototactic see p. 200 see p. 200 photophil mud-inhabiting photophob photophob see p. 197 photophob photophil photophob photophob 196 LIGHT AND PROTOPLASM [Cn. VII A study of this table reveals the fact that, in general, organ- isms which live in shady places or in the dark are negatively phototactic or photopathic, while those living in the light are positively phototactic or photopathic. Thus most fresh-water planarians and leeches are inhabitants of shady pools. Polynoe is generally found in dark retreats, the earthworm and fly larvoe are lovers of the dark, and shell-molliiscs are for the most part enclosed in cases impervious to light. On the other hand, Daphnia is found largely in open pools, larvse of Lepi- doptera and many adult insects live in the sun. Into this general rule there are some cases which do not so obviously fall. But we have little data concerning the habits of the races em- ployed and the absolute intensity of light used, so that these cases may perhaps be only apparent exceptions. One clear exception is that of the mud-inhabiting Diastylus, which is -f phototactic. 3. The General Laws of Phototaxis and Photopathy. - - Under this head we shall consider : (a) the sense of the response ; (J) the effective rays ; ( 173 Carcinus sp 38° Grapsus sp 38° Arachnida. Argyroneta aquatica . . . Hydrachna cruenta .... Insecta. Podura 38.5° 46.2° 27° Suddenly subjected Submerged (?) Suddenly subjected • PLATEAU, '72, p. 316 it i< NICOLET '-42 p 11 Agabus bipustulatiis . . . Hydaticus transversalis . Culex pipiens, larva . . . Hydrophilus caraboides . Hydroporus dorsalis . . . Nepa cinerea ] Notonecta glauca Cloe diptera, larva j Musca vom. (?) 38° 1 39° 40° 42° 42° 41° to 45° 37.5° ] died slowly. At 36° died at once Death point PLATEAU, '72, p. 316 Musca vom., larva .... Musca vom., pupa .... Silk worm larva 42.5° 43.7° 42.5° Death point SPALLANZANI, 1787, Tom I pp 56-58 "Butterfly" larva .... Culex larva 42.5° 43.7° Echinodermata. Antedou 30° Died rapidly (sud- FRENZEL '85 pp Holothuria 30D to 4CP denly subjected) Died in several hours 460-403 it ii Vertcbrata. Many fresh-water fishes . Fish 40° f 36° 33° (suddenly subjected) Survived only a few seconds In pond out of doors. Temperature elevated EDWARDS, '24, p. 114 KNAUTHE, '95, p. 752 BERT '76, p. 169 27° to 38° gradually DAVY, '63, p. 125 §3] TEMPERATURE-LIMITS OF LIFE 237 SPECIES. MAXIMUM TEMPERATURE. CONDITIONS OF EXPERIMENT. AUTHORITY. Hippocampus 30° C. Lived half an hour FRENZEL, '85, p. Salamander 44° Death point 462 SPALLANZANI, Fro" . 40° to 42° Suddenly subjected in 1787, Tom. I, p. 56 EDWARDS, '24, p. Frog, adult (summer) . . Frog adult 42° to 43° 43.8° water ; death at once Death-rigor in 1 to 14 minutes 374 MORIGGIA, '91, p. 385 SPALLANZANI, Frog, tadpoles 41° Raised in from 5 to 10 1787, p. 55 See p. 253 Rabbit 1 i L 44° to 45° minutes Death point when raised gradually * OBERNIER, '66, p. 09 Dog J Man 45° convulsions at 42° In water ; giddiness in EDWARDS, '24, p. Human spermatozoa . . . Vertebrate muscle .... Vertebrate muscle (frog) 50° 403 to 50° { 45° to 50° | 35° a few seconds Died in 10 minutes Raised in 30 seconds Raised in 18 minutes 374 MANTEGAZZA, '66, p. 186 KUHNE, '59, pp. 784-804 GOTSCHLICH, '93, p. 123 The determinations given in the above table may be compared only with caution, for diverse conditions give results which cannot be directly correlated. Thus individuals of the same species, but reared under diverse environment, have a different resistance period to heat. The lethal temperature varies accord- ing as the organisms are suddenly or gradually subjected to the high temperature. Also, the individuals of the same species will die at different temperatures according as they are rap- idly subjected to the high temperature or gradually accus- tomed to it, and, as we have seen, a lower temperature, long continued, often produces the same result as a higher tempera- ture during a brief period. Finally, too little care has been exercised in most cases to determine the temperature of the water immediately upon, and a few minutes after, placing the animals in it, — an operation which lowers the temperature of the water. In the experiments cited, unless otherwise stated, the conditions were gradual subjection continued for a short time only. The quality of the water in which the 238 HEAT AND PROTOPLASM [Cn. VIII experiments were carried on is supposed to be, except for its temperature, normal for the species. Summarizing the table, we find that the Protista have the highest maximum tempera- ture of any group, it being in extreme cases about 60° for active organisms, but generally between 40° and 45°. Among the Metazoa, the highest maxima recorded (excepting Rotifera and Tardigrada) are 44° to 45° for Turbellaria, Anguillula, Naididse, Nepa (water-scorpion), Notonecta (water-boatman), Cloe larva, Salamander, and mammals. A water-mite (Hydrachna) is said to have withstood up to 46.2°, and some vertebrate tissues resist up to 50°. For the great majority of Metazoa, the maxi- mum temperature lies below 45° and, in the case of marine species, below 40°. The low maximum temperature of marine species is probably due to the low maximum temperature of the sea as compared with ponds. We may consequently con- clude from the foregoing that the maximum temperature for protoplasm lies generally between 35° and 50°, the lower limit being characteristic of organisms living in a medium of low temperature (the sea), the latter, of organisms reared in warm pools or of organs (vertebrate muscle) in a body kept at a high temperature. The question now arises, what is the cause of the death of protoplasm at high temperatures? To get some insight into this matter, let us examine the phenomena accompanying death of protoplasm from overheating. KUHNE ('64, p. 44) thus describes the appearance of an Amreba subjected for a moment to a fatal temperature (45°). The structure is entirely altered since it has become transformed into a mass of knobbed, opal- escent, solid lumps, which, even in transferring to the slide, become easily broken apart. This appearance is clearly due to a coagulation of the protoplasm. A similar coagulation takes place in Actinophrys eichhornii ( KUHNE, '64, p. 67) at 45°. "' The sphere shrinks into a flat, hardly transparent, cake, no longer reacts to the strongest induction shocks, and breaks up after 24 hours into a heap of small granules and irregular pieces." Likewise, in muscles a change is produced by heat which is evidently a kind of coagulation. A coagulation then seems to be the immediate cause of death at high temperatures. But just what is the component of protoplasm which co- § 3] TEMPERATURE-LIMITS OF LIFE 239 agulates at the death point of organisms? As KUHNE ('64, p. 1) pointed out, it cannot be ordinary egg albumen ; for, excepting the contractile substance, we know of no native albumen which coagulates between 35° and 50° C. It was KUHNE'S great service to show that there is a substance which can be pressed out of frozen, triturated, and then thawed muscle, which becomes quickly opalescent at 40°, through the separation of the muscle plasma into myosin and a serum. This serum, in turn, contains an albuminoid which coagulates at 47° (DEMANT, '79 and '80). Now, since there are proteids in muscle which coagulate at about the point at which muscle goes into permanent heat-rigor, and since these proteids can no longer be squeezed out of rigid muscles, the conclusion seems justified that permanent heat-rigor in muscle is due to the coagulation of these proteids. Related, easily coagulable proteids occur in widely dissimilar organisms. For example, myosin has been found in vegetable protoplasm (\VEYL, '77, p. 96), and HALLIBURTON ('88) has described a globulin from blood corpuscles which coagulates at 48° to 50°. Their distribution in protoplasm is, therefore, probably general, and so we are justified in concluding that the death of protoplasm by heat is, in general, the result of the coagulation of a proteid (globulin). Death occurs because the vital machinery has been broken down.* 2. Temporary Rigor and Death at the Lower Limit of Tem- perature, Minimum and Ultraminimum. — Whilst towards the upper limit of ordinary terrestrial temperatures (35° to 40° C.) molecular changes in organic compounds are hastened, towards the lower limits (-- 40° to - 50°) molecular changes are slow, being principally confined to the transformation from the liquid or gaseous to the solid or liquid condition. This transforma- tion does occur in the water of protoplasm, but the colloids, * At this place reference may be made to the fact that protoplasm subjected to a high temperature sometimes breaks to pieces with the suddenness and com- pleteness of an explosion. Thus STRASBURGER ('78, p. 611) found that Chilo- monas curvata was uniformly killed at 45° C. by the explosion of the body, and Dr. W. E. CASTLE tells me that he has observed the same phenomenon under like conditions in Stentor. An investigation of this profound change in pro- toplasm would be sure to throw valuable light upon the nature of the living substance. 240 HEAT AND PROTOPLASM [Cn. VIII which constitute the living part, are not modified by even the lowest of the terrestrial temperatures, except that the molecular changes which they undergo are very slow. This being true, protoplasm which contains no water, or very little, ought not to be changed by low temperatures, — that is to say, the machine will not be injured. With the activities of the machine --with the vital processes -it is, however, quite different. They are essentially chemical processes, and hence we should expect them to be diminished at a low temperature. If, as PICTET ('93) maintains from an extensive and highly important series of experiments, no chemi- cal processes take place at temperatures below • - 100° C., then protoplasm ought to exhibit no vital processes at this tempera- ture, and, indeed, experience shows that, as we have already seen, as the temperature is lowered below the optimum, all manifestations of activity diminish. It is clear that at a certain point they must entirely cease. And at that point death, following the usual definition of the word, would ensue. But does the cessation of the vital processes, without injury to the mechanism, necessarily preclude the possibility of a return to activity ? Let us examine the experimental evidence on this point. SCHUMACHER ('74, p. 179) subjected yeast to cold and found that, at the lowest temperature produced (--113.7°), the yeast cells were not completely killed. More recently, PICTET ('93% cf. also C. DE CANDOLLE, '84) has sub- mitted various dry seeds and spores of bacteria to a temperature of nearly - - 200°, at which temperature the atmosphere becomes liquefied, but without fatal effects. Other results were still more remarkable : vibratile cilia from the mouth of the frog were cooled to - 90°, and recovered their movement upon raising the temperature. Some Rotifera and Infusoria were frozen in their native water at — 60°, and kept at that tem- perature, apparently, for nearly 24 hours. Most have subse- quently regained their activity. Eggs of the frog, lowered slowly to - - 60°, can revive. Eggs of the silk-worm can resist to - - 40°. Other experiments of PICTET * will be referred to * This general criticism of PICTET' s paper is, I believe, valid. He does not give us data enough upon time of subjection to the low temperature, time em- ployed in reducing the temperature, and other details. Thus, concerning his §3] TEMPERATURE-LIMITS OF LIFE 241 later. As a result of these and others' investigations we may conclude : Protoplasm may under certain circumstances, of which one of the most important is the absence of water, resist, uninjured, the lowest temperatures. There is no fatal minimum temperature for dry protoplasm. We must now turn our attention to those cases in which the phenomena of cessation of activity or death appear, and seek to determine their causes ; and first concerning temporary cold-rigor. We have already seen that as the temperature is lowered, the rate of metabolic processes and protoplasmic movements is lowered. What happens at the lower limit of activity, and where does this lie? The chlorophyll granules of Vallesneria move (according to VELTEN) only about 1 mm. per minute at 1° C. and not at all at 0°; the rotation of Nitella ceases (NAGELI, '60, p. 77) at 0°C.; in Tradescantia hairs, movement is wholly arrested on freezing the cell sap (KtJHNE, '64, p. 100, and DEMOOR, '94, p. 194). Even in seeds and bacteria, which are not killed by the lowest temperatures, all vital activities have probably ceased at 0°, for DE CANDOLLE ('65) found that in only one species out of ten could he get a seed kept at 0° to germinate, and even then germination was so retarded that it took from 11 to 17 days as opposed to 4 days at 5.7°. Likewise, bacteria do not multiply below + 5° to + 10° (BONARDI and GEROSA, '89). Among animals, KUHNE ('64, p. 46) found Amoeba cooled to near 0° almost motionless. PURKINJE and VALENTIN ('35) first noticed that the ciliated experiments on Scolopendra, he merely says: "I have frozen to —40° three Scolopendras which perfectly resisted the treatment and lived after thawing out. Submitted to — 50°, they have also resisted. Frozen a third time to — 90°, they are all three dead." Now, in the absence of further data, it is quite possible that the heat of metabolism kept the internal body temperature considerably above that of the chamber, the thick cuticula preventing rapid loss of heat, very much as a man's clothing enables him to withstand the — 40° of an arctic winter. Another experiment of PICTET'S lends greater probability to this explanation of some cases of great resistance. Three snails were subjected to a temperature of from — 110° to — 120° during several days. The operculum of two of these was not intact, so that it did not close the orifice. These two individuals died ; but the third, which was completely sealed up, survived. Those which were not sufficiently clad, so to speak, lost so much internal heat that their internal fluids were frozen. Of course this criticism cannot apply in the case of those organ- isms mentioned in the text which are without a thick cuticula. R 242 HEAT AND PROTOPLASM [Cn. VIII epithelium of the frog ceased its movements at 0°. Muscles of the frog were found by KUHNE ('64, p. 3) to become at - 3° to - - 7° a solid lump which did not, however, wholly lack irritability. The evidence of all these cases shows that activity nearly ceases in protoplasm at or near 0° C. Another effect produced on protoplasm by cold — an effect which often immediately precedes quiescence --is violent con- traction. This has been repeatedly observed. The protoplasm of Tradescantia hairs, which has been in cold-rigor, was found by KUHXE ('64, p. 101) to lie in separated rounded drops and lumps, — an appearance like that resulting from excessive stimu- lation. The rapid freezing of muscle gives rise, according to HERMANN ('71, p. 189), to violent contractions. The sciatic nerve of the frog's leg when cooled to — 4° to -- 8° causes clonic contractions of the muscle, lasting two minutes. (AFFANA- SIEFF, '65, p. 678, and others.) It is clear, then, that cold acts as a violent stimulus to protoplasm. The final result of temporary rigor is thus clearly brought about by the cooperation of two causes : (1) the diminution in the chemical processes upon which metabolism and movement depend, and (2) the directly stimulating effect of the cold, which acts like contact or excessive heat. Both causes work to produce a quiescence which may be replaced by activity when the causes are withdrawn. The fact that cold-rigor usually occurs close to the zero- point indicates that the activities of protoplasm are closely determined by the fluid state of water. This fact is not to be explained on the ground that freezing prohibits all chemical change --many chemical changes take place below the freez- ing point of water, but, apparently, few of those which are involved in metabolism. Nor is the rigor due to the change which the freezing of the protoplasmic fluids brings, because as the temperature approaches the zero-point, but while the water is still perfectly fluid, metabolism diminishes ; and it diminishes at such a rate as to cease just where water begins to freeze. The critical point for vital activity has been adjusted to this critical point of water. So, too, the composition of protoplasm is such that at a tem- perature, lying below the normal and above the freezing point § 3] TEMPERATURE-LIMITS OF LIFE 243 of water, those chemical changes rapidly occur which we desig- nate response to the stimulus of cold. This composition of protoplasm, upon which cold can work such important modifi- cations, is a quality of immense importance in the economy of the organism, as the changes of each autumn testify. Below the point of temporary cold-rigor lies that of death, if death point there be. The position of the death point is, however, very diverse in different organisms. Part of the diversity in the death points assigned by different authors is, however, due to the fact that in the methods of determining the death points there has been a lack of uniformity. Five elements ought always to be regarded in experiments on the ultraminimum temperature. (1) History of the tem- perature conditions in which the individual or its race had lived before experimentation; (2) rate at which the organ- ism has been cooled, — if possible, the temperature of the organism itself rather than that of the medium ; (3) inten- sity of cold just sufficient to kill ; (4) duration of applica- tion of the cold and the kind of medium in which the organism is subjected to the cold ; * and (5) the rate of thawing out.f These elements have been too much neg- lected in the past. I shall now present in tabular form some of the more reliable determinations of the death point of organisms, pref- acing with the caution that the results are not closely comparable. * The duration of application and intensity of the fatal cold stand in an inverse relation, so that organisms which resist a temperature — A° for X min- utes will resist a lower temperature, — (A + a)°, for a shorter time, X — x. Thus, Clepsine complana resists — 8° C. for 15 minutes ; — 5° C. for 90 minutes. So Planorbis corneus resists — 7° for 5 hours, but — 5° for 48 hours. Again, Musca domestica can resist — 12° for 5 minutes ; — 8° for 20 minutes ; and -5°C. for 40 minutes. (ROEDEL, '86.) Since many authors have little re- garded the duration of action of the cold, their determinations have little scientific value. t The importance of this is illustrated by some experiments of SACHS ('60, p. 177), who found that the leaves of the beet or cabbage frozen at from - 4° to — 6° died if they were thawed in air at 2° or 3°, or in water at 6° to 10° ; but lived when slowly thawed in water at 0°. In general, the more gradual the thawing, the lower the fatal temperature. 244 HEAT AND PROTOPLASM [Cn. VIII TABLE XX* DETERMINATIONS OK THE ULTKAMINIMUM OF ORGANISMS REARED UNDER NORMAL CONDITIONS SPECIES. MINIMI M TEMPERATI'HE. CONDITIONS OF EXPERIMENT. AUTHORITY. Plant cells. Tradescantia Hair cells -14° + — 14°- Ill water, rapidly . frozen In air, rapidly fro- [ KUHNE, '64, p. 100 • 1° zen Fully frozen, cautious- STRASBURGER, '78, Swarm-spores (Proto- coccus) 0° to — 1° ly thawed p. 612 COHN, '50, p. 720 Protozoa. Amoeba 0°- Rapidly frozen on KUHNE, '64, pp. 40-47 Animal tissues. White blood corpuscles : of Amphibia ( — 2° to — 3° <; slide over ice and salt During 8 hours; warm- ed rapidly SCHENK, '69, p. 26 of rabbit 1 -7° - 3^ For a short time ; warmed rapidly During 15 minutes " " 26 " "26 Saliva corpuscle .... Red blood corpuscle . Spermatozoa: of Amphibia - 6° to - 8° -15° + — 4° to — 7° Over 60 minutes " "27 POUCHET, '66, p. 18 SCHENK, '(if), p. 20 of Mammalia .... of frog . - 6°- - 8° to - 10° — Returned to activity on thawing Frozen in testis " 30 PREVOST, '40. of fro0" -10° to — 12D QUATREFAGES, '53, of man -17° Gradually thawed p. 353 MANTEGAZZA, '66, p. Eggs of Amphibia . . . Ciliated epithelium of Anodonta - 7° ,-. — 3° During 1 hour Subjected a very short time Subjected during 6 183 SCHENK, '69, p. 28 ROTH, '66, p. 189 " " 189 minutes * Temperatures all in degrees Centigrade. - before a number indicates below zero, - - or -f after a number indicates that the true lethal temperature lay slightly below or above that number. (.4) indicates that the organism was in air ; ( \V") , in water. §3] TEMPERATURE-LIMITS OF LIFE 245 SPECIES. MINIMUM TEMPERATURE. CONDITIONS OF EXPERIMENT. AUTHORITY. Platy helminths. Deudrocoelum lacteum Mollusca. Helix hispida 0° to — 1° - 8° Suddenly or gradually subjected, till ice forms During 30 minutes ROEDEL, '86, p. 207 " " 191 Helix pomatia — 10° Durin"1 GOO minutes « ii jy2 Helix pomatia —14° to —18°)+ Gradually frozen for POUCHET, '6(5, p. 28 Helix hortensis .... Helix aspera (— 14° to— 18°)+ (—14° to —18°)+ 180 minutes, and then thawed During 180 minutes " 180 ii u it ii Planorbis - 7° " 300 " (A) ROEDEL, '86, p. 212 Limiijea - 7° " 180 " (A?) ii u 212 Pulinoiiate embryos . Limax O3 to — 1° -17°+ " Died upon freezing " (WandA) During 2 hours (A) " " 212 POUCHET, '66, p. 26 Annelida. Aulastomum gulo . . . Clepsine complanata . "Leech" 2° - 5° - 6° During 12 to 15 hours (W) During90minutes( W) " " some min- ROEDEL, '86, p. 206 " 213 DOENHOFF/72, p.725 Insecta. Apis mellifica -1.5° utes" (W) During 210 minutes ROEDEL, '86, p. 212 Apis mellifica — 1.5° " a few minutes DOENHOFF/72, p.724 Formica rufa -1.5° " 180 minutes ROEDEL, '86, p. 196 Pelopseus (chrysalis) . Lema sp . -28° — — 6° Out-of-doors, with- stood this tempera- ture Durin0' 30 minutes WYMAN, '56, p. 157 ROEDEL, '86, p. 197 Psederus riparius . . . Phytonomus sp Melolontha - 4° -12° -18° + " 45 " 90 " " 120 " (^4) " 197 " 197 POUCHET, '66, p. 26 Melolontha (larva) . . Cetonia | -15° + 1 7'~> 1 " 180 " (A) i . -i on * * t A \ " " 26 u u OR Hydrophilus j Dytiscus 11 T - 4° l-'U (•&•) " 60 " (A) KOCHS, '90, p. 682 Vanessa cardui, larva Vanessa io, larva . . . Smerinthus populi . . Ocneria dispar -15° -17° + -10° - 4° " GOO " 120 " " 150 " 30 " ROEDEL, '86, p. 212 POUCHET, '66, p. 27 ROEDEL, '86, p. 212 " " 212 Culex pipiens, larva . Musca - 4° — 6° to — 10° " 60 " 180 " " " 212 DOENHOFF/72, p.725 Musca dom go " 20 " ROEDEL, '86, p. 201 Various insects .... 0° " 2 to 30 minutes (on ice) PLATEAU, '72, p. 98 246 HEAT AND PROTOPLASM [Ca. VIII SPECIES. MINIMUM TEMPERATURE. CONDITIONS OF EXPERIMENT. AUTHORITY. Arachnida. Phalangium opilio . . - 9° During GO minutes ROEDEL, '86, p. 201 Tegenaria domestica . - 6° " 60 " 201 Argyroneta aquatica . . 40 " 180 " " 201 llydrachna crueuta . . • 4° " 30 " " " 201 " Spider " — 2° to — 3° It 48Q .< DOENHOFF,'72,p. 724 Crustacea. Cyclops quadricornus . (P 1 "(IF) PLATEAU, '72, p. 300 Cyclops spirillum . . . - 6° " 120 " (W) ROEDEL, '86, p. 201 Daphuia pulex 0° 1 (W) •! " " 201 \ / PLATEAU, '72, p. 300 Gammarus pulex . . . 0° " 30 " (W) ROEDEL, '86, p. 205 Asellus aquaticus . . . 0° (W){ PLATEAU, '72, p. 299 ROEDEL, '86, p. 205 Astacus fluviatilus . . - 11.5° " a day (A) POUCHET, '66, p. 32 Vertebrata. Itaiia esculata — 4° to — 10° " 180 minutes (^4) " " 19 Summarizing these conditions, we find that the following- organisms, even when thawed out carefully, are killed by sub- jecting to a temperature of between 0° and -- 5° for 60 minutes: Amoeba, swarm-spores, white blood corpuscles of Amphibia, planarians, pulmonate embryos, small leeches, certain entomos- tracans, and some insects and spiders. These organisms are all either soft bodied or of small size, and, excepting animals which, like the bees, live in protected situations, they do not winter over in our northern temperate countries. The following species, on the other hand, resist - - 10° for at least 60 minutes : some snails (possibly), the beetles Melolontha (perhaps) and Phytonomus, the Vanessa larva, Pelop;eus chrysalis, and the crayfish, — all protected by a thick covering, or of rather large size. The reason why large size and thick covering should increase resistance is not far to seek, — both conditions tend to prevent the rapid loss of heat, — to defend the body from freezing through and through. Another cause of variation in resistance to cold is, doubtless, the amount of water in the protoplasm. I have already referred to this cause as explaining the fact that dry seeds and spores §3] TEMPERATURE-LIMITS OF LIFE 247 can withstand almost any temperature.* MiJLLER-THURGAU ("80) found that the "succulent labellum of Phajus freezes at - 0.56° C. ; the succulent leaf of Sempervivum, at -0.7°; the potato tuber, at — 1° ; the leaf of Tradescantia mexicana, at - - 1.16° ; the ivy leaf, at — 1.5°; the leaves of Pinus austri- aca, at -- 3.5°; young shoots of Thujopsis, at --4V (VINES.) In this series of plant tissues, we see that the more succulent the tissue, the higher its ultraminimum. Possibly the reason why spermatozoa have so low an ultramaximum, despite their small size, is on account of the denseness of their protoplasm. Not all variations in ultraminimum temperature are, however, explicable upon the ground of difference in size, body-covering, or density of plasm. The interpretation of the difference in sensitiveness to cold of the honey bee (Apis melifica) and the red ant (Formica rufa), between Bombyx on the one hand and Smerinthus and Vanessa on the other, must wait for further knowledge. The question now arises, what is the cause of death in organ- isms and protoplasm which succumb to low temperatures ? With the higher animals the immediate cause is doubtless in part asphyxia resulting from a stoppage in the flowing of the frozen blood plasma, and in part the destruction of the red blood corpuscles, as well as the white. f With the simpler organisms, like planarians, Protozoa, or Tradescantia hair-cells the case is different. An insight into the changes which pro- duce death in such organisms may be gained from KUHNE'S ('64, p. 101) description of the effect of a temperature of — 14° on Tradescantia hair-cells. The frozen hairs were placed in water and observed under the microscope. " The appearance," * Striking cases are on record of the resistance of gemmules, or "animal spores," to cold. Thus, WELTXER ('93, p. 276) saw gemmules of Spongilla fragilis frozen in an aquarium from December 26 to January 24, from the end of January to February 5, from February 20 to March 6, and from March 12 to 24 ; the intervals being occupied by thawings. Yet these gemmules produced young sponges. In other cases, a certain amount of freezing favors the subse- quent development of gemmules, e.g. those of fresh-water Bryozoa (BRAEM, '90, p. 83) and the eggs of the silk-worm (DUCLAUX, '71). t POUCHET ('66, p. 18) found that when blood of the frog was let fall into a capsule at a temperature of — 15° few of the red corpuscles were uninjured. In most the nuclei had been cast out into the plasma. 248 HEAT AND PROTOPLASM [CH.VIII says KUHNE, " was very remarkable, for there was no trace of the protoplasmic network; but the violet cavity of the cell con- tained, in addition to the naked nucleus, a large number of separate round drops and lumps." In this case, the separate pieces eventually became active again, so that the protoplasm, though nearly killed, was not quite so. The phenomena seen by KUHNE so closely resemble those produced in the same kind of cells by the galvanic current and other strong irritants as to indicate that cold acts as an intense irritant. We cannot, however, conclude that cold acts in no other way. It is clear that the expansion of forming ice in the vacuoles of the protoplasm must seriously disturb the structure, and, since the whole matter has received little attention, it is possible that a molecular change of some sort takes place when there is much water in the freezing protoplasm. To summarize: Death by freezing results in the higher animals largely from asphyxia, and in the simpler organisms from excessive irritation, mechanical rupture, and, perhaps, other causes. I shall now sum up this section on the effect of extremes of heat and cold. As the temperature is elevated above the opti- mum, molecular changes occur in the protoplasm leading to its contraction. The contraction becomes more violent as the tem- perature is still raised, until, finally, a new series of molecular changes occur by which the protoplasm begins to coagulate. At this point the protoplasm begins to lose its irritability. If this process has not proceeded far, the vital activities may, under favorable conditions, return (temporary heat-rigor). Beyond a certain point (death point) recovery is impossible. The death point varies with the species, but lies not far from the maximum natural temperature attained by the medium in which they live. On the other hand, as the temperature is diminished from the optimum, the chemical processes of metabolism decrease in vigor and come to a standstill at about the freezing point of water. Violent contractions accompany the cooling process, concomitantly with which the protoplasm breaks down. From this condition of temporary cold-rigor recovery is still possible; but a little below, at a point dependent upon the size of the body and the diathermous qualities of its §4] ACCLIMATIZATION TO EXTREME TEMPERATURES 249 covering, the water of the body begins to freeze, and in that process, or the subsequent thawings, the protoplasm undergoes a (partly mechanical) change resulting in death. If the body, however, contains no water, freezing cannot kill it. Thus the effect of high temperatures is principally chemical, involving the living plasma ; that of low temperatures is prin- cipally mechanical, involving the water of the body. Both raising and lowering the temperature act also as irritants.* Finally, the positions of the maximum and minimum stand in most intimate relation to the inorganic environment of the organism and have been molded to that environment. § 4. ACCLIMATIZATION OF ORGANISMS TO EXTREME TEMPERATURES The phenomena to be discussed in this section fall naturally into two subsections: (1) acclimatization to heat and (2) accli- matization to cold. They will be considered in that order. 1. Acclimatization to Heat. — Our study of the maximum temperature which organisms reared under ordinary circum- stances can withstand, led us to the conclusion that few active organisms can resist a temperature of over 45°, and for whole groups like Ctelenterata, marine Mollusca, and Crustacea, and the fishes, 40° is a point of death. Yet, on the other hand, it has long been known that there are organisms living in certain hot springs in waters of considerably higher temperature. I shall now give in tabular form some cases which I have collected of organisms living at or above the normally lethal temperature of the species, f * Whether sudden change of temperature has an especial effect upon the movement of protoplasm is a disputed question, which has been answered posi- tively by DCTROCHET ('37, p. 777) and HOFMEISTER ('67, p. 53) for Nitella, and DE VRIES ('70, p. 394) for root hairs of Hydrocharis, but has since, as a result of careful experiments, been denied by VELTNER ('76, p. 214) for Nitella and other plant cells. t It is desirable that accurate data concerning the temperature of organisms in hot springs should be made, and we have, in this countiy, unusually favorable conditions offered for this study, especially in Arkansas, California, and the Yellowstone National Park. It is to be hoped that persons who have had the proper training should, when contemplating a visit to hot springs, provide them- 250 HEAT AND PROTOPLASM [Cn. VIII TABLE XXI LIST OF SPECIES FOUND IN HOT SPRINGS, WITH THE CONDITIONS UNDER WHICH THEY OCCUR No.* SPECIES. TEMP. C. LOCALITY AND CONDITION or LIFE. AUTHORITY. 1 Chroococcus 51° to 57° Benton's Hot Springs, Cal. WOOD, '74, p. 34 2 Nostocs or Pro- 93° Geysers, Lake Co., Cal. ; not BREWER, 'G(J, p. 391, tococcus abundant at this tem- also WYMAN, '67, perature p. 155 3 Nostocs 51° to 57° Benton's Hot Springs, Cal. WOOD, '74, p. 34 4 Anabrena ther- 57° Dax, warm springs SERRES,'80,pp.l3-23 malis 5 Leptothrix 44° to 54° Carlsbad Springs COHN, '02, p. 539 6 Oscillaria or 54° to G8° Yellowstone Nat. Park, WEED, '89, p. 399 "Confervse" U.S.A. 7 ( i 54.4° Springs, Bernandino Sierra, BLAKE, '53, p. 83 Cal. 8 i i 57° Algeria, Constantine prov- GERVAIS, '49, p. 12 ince, waters of Hammam- Meskhoutin 9 it 57° Hot Springs, Taupo, New SPENCER, '83, p. 303 Zealand 10 ii 60° to 65° Geysers, Lake Co., Cal., BREWER, '66, p. 392 U.S.A. 11 it 60° to 65° Hot Springs, Ark., U.S.A. JAMES, '23, II, p. 291 (Long) 12 (i 9 71° Hot Springs at Banos Luzon , DANA, '38-'42, p. 543 Philippines 13 II 75.53 Soorujkoona Hot Springs HOOKER, J. D. '55, 1, p. 24 14 II 81° to 85° Ischia EHRENBERG, '59, p. 493. 15 II 98° Iceland FLOURENS, '46, p. 934 in II 9 Outlet of Lake Furnas, DYER, '74, p. 324 Azores. selves with a hand lens, bottles of alcohol for preserving organisms for further study, and an accurately calibrated thermometer. A source of error to be guarded against lies in the precise determination of the temperature of the water immediately surrounding the organism observed; for in some warm springs or their outlets the surface water is said to be much warmer than the deeper layers in which the organisms are found. Finally, if possible, it would be desirable to determine on the spot, experimentally, the maximum temperature which these organisms can withstand. For this determination some of the methods referred to on p. 220 should be used. * Notes on each of these cases will be found at the end of this-chapter, pp. 263-267. §4] ACCLIMATIZATION TO EXTREME TEMPERATURES 251 No. SPECIES. TEMP. C. LOCALITY AND CONDITION OF LIFE. AUTIIOKITY. Diatoms Frequently associated with other algre in hot springs 17 Physa acuta 33° to 35 3 Sources of Dax, St. Pierre, DUBALEN, '73, p. iv France 18 Paludina sp. 50° Thermal waters, Abano, DE BLAINVILLE, '24, Padua p. 141 19 ''Bivalve testa- 9 Hot Springs, Ark. MITCHILL, '06, p. COG ceous animal " 20 Rotifera and An- 44° to 54° Carlsbad Springs, Bohemia COHN, '62, p. 539 guillulidfe 21 Anguillulidfe 45° Aix, springs DE SAUSSURE, 179G, V, p. 13, § 1168 22 « 81° Ischia, in hot springs EHRENBERG, '59, p. 494 23 Cypris balnearia 45° to 50.5° Hammam-Meskhoutin MONIEZ, '93, p. 140 24 Stratiomys larva 69° In hot spring, Gunnison GRIFFITH, '82, p. 5C9 Co., Col. 25 i ( 9 In hot spring, Uinta Co., BRUNER, '95 Wyo. 26 " Water beetle " 44.4° In warm spring, India ; HOOKER, J. D. '55, p. abundant 24 27 ci 9 Hot spring, Port Moller, BALL, W. H. (per- Alaska sonal letter) 28 Barbels 34° 9 BERT, '77, p. 169 29 Frogs 38° "Baths of the Pise" SPALLANZANI, 1787, Tom. I, p. 55 To summarize : Protista are stated to have been found in nature in water at temperatures far above 60° C. The most striking cases are of Oscillaria and " Conferva " from several localities, which resist nearly up to the boiling point of water. The closely allied Nostocs are, perhaps, next most abundant and resistant, reaching 93° (possibly Protococcus) in the Cali- fornia geysers. Metazoa are stated to live at temperatures far above 45°. Although some doubt has been cast on No. 22 by HOPPE-SEYLER'S inability to confirm EHRENBERG'S observa- tions, the case seems established of Cypris thriving at 45° to 50.5°. Very extraordinary are the observations Nos. 24 and 25 on Stratiomys larvae, which, however, are sadly in need of confirmation by competent observers. Leaving out of account, for the moment, the less well established cases, there still remains abundant evidence that organisms can live and thrive 252 HEAT AND PROTOPLASM [Cn. VIII in hot springs at a temperature near or above that which proves fatal to their close allies. No one doubts that in all the cases cited above the individuals living in hot springs have been derived from ancestors which lived in water whose temperature rarely exceeded 40° C. The race has therefore become acclimatized, and the question arises : How has that acclimatization been effected? Now experiments have shown that organisms, when gradually accustomed thereto, may resist a temperature which would have killed them if they had been suddenly subjected to it. There- fore it seems probable that the acclimatization of organisms to hot springs has been a slow, long-continued process, during which they have become gradually accustomed to higher and higher temperatures, probably attaining the hot springs by slowly advancing up their effluent streams. This adaptation may have taken place without selection, purely by the capacity of individual adaptation which organ- isms possess. That individual adaptation is sufficient to account f >r the vitality of organisms in hot springs has been shown by experiment. DUTROCHET ('37, p. 777) observed, long ago, that an organism which at first seemed injured by a high temperature gradually regained activity while still subjected thereto. Thus, he found that the current of Nitella was at first diminished by raising it to 27° C., but it soon became rapid again ; raised, now, to 34°, the circulation began to fall off again, but in a quarter of an hour, the same temperature continuing, the circulation became very rapid. This phenome- non was repeated, also, at 40°. Similarly, HOFMEISTER ('67, p. 53) brought Xitella flexilis suddenly from + 18.5° to + 5°C. The streaming movements ceased. After staying 15 minutes in the cooler room, however, the rotation of protoplasm recovered. Much more important, however, are the remarkable experi- ments of DALLINGER ('80). He kept Flagellata in a warm oven for many months. Beginning with a temperature of 15.6° C., he employed the first four months in raising the tem- perature 5.5° ; this, however, was not necessary, since the rise to 21° can be made rapidly, but for success in higher tempera- tures it is best to proceed slowly from the beginning. When the temperature had been raised to 23°, the organisms began §4] ACCLIMATIZATION TO EXTREME TEMPERATURES 253 dying, but soon ceased, and after two months, the temperature was raised half a degree more, and eventually to 25.5°. Here the organisms began to succumb again, and it was necessary repeatedly to lower the temperature slightly, and then to advance it to 25.5°, until, after several weeks, unfavorable appearances ceased. For eight months, the temperature could not be raised from this stationary point a quarter of a degree without unfavorable appearances. During several years, pro- ceeding by slow stages, DALLINGER succeeded in rearing the organisms up to a temperature of 70° C., at which the experi- ment was ended by an accident. In this case it is plain that the high temperature acted upon the same protoplasm at the end of the experiment as it did at the beginning. But while the protoplasm at the beginning of the experiment was killed at 23° C., at the end it withstood 70°. It will be seen that, by gradual elevation of the tempera- ture, Flagellata may become acclimated to a temperature of water far above that which they can withstand when taken directly from out of doors, and approaching that of the hottest springs containing life. A series of experiments, less extensive than that of DAL- LINGER, was carried on by Dr. CASTLE and myself ('95, pp. 236-240) upon the tadpoles of our common toad, Bufo lentigi- nosus. Recently laid eggs were divided into two lots : one lot was kept in a warm oven at a constant temperature of 24° to 25°, others at about 15° C. Both lots developed normally, but the former much the more rapidly. At the end of 4 weeks the point of heat-rigor was ascertained for each lot, by gradually heating (in from 5 to 10 minutes) the water contain- ing them, until the tadpoles showed no response to stimulus, but, upon cooling, regained activity. The result was that the toad tadpoles had gained an increased capacity to heat. For when they were reared at a temperature of about 15° C., every tadpole went into heat-rigor at 41° C., or below; whereas, when they were reared at 24° to 25°, a temperature 10° higher, no tadpole died under 43°, the average increase of resistance being 3.2°. This increased capacity of resistance was not produced by the dying off of the less resistant indi- viduals, for no deaths occurred in these experiments during 254 HEAT AND PROTOPLASM [Cn. VIII the gradual elevation of the temperatures in the cultures. The increased resistance was due, therefore, to a change in the protoplasm' of the individuals. The question now arose : In how far is this change in the protoplasm permanent? Will a return of the individuals to cool water cause a return to the old point of heat-rigor ? We made a few experiments on this subject which showed that tadpoles which during 33 days in warm water have acquired an increased resistance of 3.2° lose part of that acquired resist- ance during 17 days' sojourn in cooler water. But the loss is a very slow one. The effect of the high temperature on the tadpoles is not, therefore, transitory, but persists — we have not been able to determine how long — after the cause has been removed. So we may conclude : Individual organisms have the capacity of becoming adapted to a high degree of temperature, so that a temperature which normally is fatal may be withstood. This adaptation of the individual accompanies the subjection of organisms to temperatures higher than those to which they have already become accustomed. This capacity exists among both Protozoa and Metazoa. The effect of the elevated tem- perature persists (though in diminished degree) a considerable time after the individual has been restored to a lower tempera- ture. Acclimatization may show itself not only in the change of the maximum temperature, but also in the elevation of the optimum. This is shown by the following experiments of MENDELSSOHN ('95, p. 19). When Paramecia are placed in a trough whose temperature is 24° to 28° at one end and 36° to 38° at the other, they are found to collect at the cooler end, which indicates that the temperature of that end lies nearer their optimum. If, however, the Paramecia, while uniformly distributed in the trough, are subjected to a uniform tempera- ture of 36° to 38° for from 4 to 6 hours, and then, in the same trough, to a temperature varying from 24° at one end to 36° at the other, they no longer collect at the usual optimum of 24° to 28°, but at 30° to 36°. Thus in 4 to 6 hours, by the action of a temperature of 36° to 38°, the optimum has been raised 6° to 8°. §4] ACCLIMATIZATION TO EXTREME TEMPERATURES 255 Since experiments have proved the fact of acclimatization, it now remains to determine, if possible, its cause ; to answer the question, by virtue of what property can organisms which, like Flagellata, normally perish at 45° C. come to live at 70° or even higher temperatures ? We have seen that death at high temperatures is apparently due to coagulation of certain proteids in the protoplasm which undergo a chemical change at between 45° and 50° C. Now, although the matter has not yet been studied in these proteids, it has been shown for egg albumen that in proportion as it is dried its coagulation point rises, as the following table from LEWITH ('90) shows : — EGG ALBUMEN. COAGULATION TEMPERATURE. In aqueous solution With 25 % water With 18 % water With 6 % water Without water 56° C. 74° to 80° C. 80° to 90° C. 145° C. 100° to 170° C. Since the coagulation point of egg albumen is raised by dry- ness, it is very probable that a similar cause may act to raise the coagulation point of protoplasm in organisms of hot springs. Experimental studies are much needed upon this point. Mean- while it can be said that one of the qualities which gives ca- pacity of resistance to high temperatures is dryness. I shall now cite some cases that I have collected, which prove this point. It has been found that while moist yeast is killed at a tempera- ture below 60°, dry yeast may be heated to 100° C. without losing its vitality (ScHUTZENBERGER, '79, p. 162). Damp uredo-spores are killed at 58.5° to 60° C., but dry ones with- stand up to 128° (HOFFMAN, '63); and dry spores of some molds up to 120° (PASTEUR, '61, p. 81). According to DAL- LINGER ('80, pp. 11-14), the dry spores of various Flagellata are capable of withstanding a temperature from 10° to 27° C. higher than that which these spores can resist in fluid. Accord- ing to DOYERE ('42, p. 29), various animalcules (Rotifers, Tardi grades) which cannot in water withstand a temperature of 50° C. may, after long drying, be heated in air to 120° C. 256 HEAT AND PROTOPLASM [Cn. VIII (rarely to 125°) without all dying. The foregoing cases show clearly that increased resistance capacity is frequently gained by subjecting the protoplasm of the organism to dry ness. But there are other conditions under which the living sub- stance shows extraordinary resistance capacity. In general, as is well known, the spores of organisms withstand higher tem- peratures than the motile stage, when both are in water. This rule holds for many cases : The spores of some bacteria may be heated for a time above 100° C. without killing them, although their motile stage is killed by 50° to 52° (LEWITH, '90). DALLINGER and DRYSDALE ('74, p. 101) and DALLINGER ('80, pp. 13, 14) have determined maximum temperatures for several Flagellata and their spores in water. While none in the motile stage could withstand a temperature higher than 61°, the spores in water withstood maximum temperatures varying between 65.5° and 131° for the different species. Have the high resistance capacity of dry protoplasm and that of spores a common cause ? Or, in other words, is the proto- plasm of spores especially free from water ? Many observations make it appear probable that this is so. Thus in the case of bacteria, the protoplasm of the spore stage is optically denser and occupies less space than in the motile stage. (Cf. LEWITH, '90.) In the case of the ciliate Infusoria, the larger size of the protoplasmic mass makes the comparison of the condition of the protoplasm in the two stages easier. We glean the facts -from BUTSCHLI ('89, pp. 1652-1654). As the process of encyst- ment proceeds, the contractile vacuole continues to function, the intervals between its contractions gradually increase, and finally it disappears some time after the encystment is com- pleted. Hand in hand with these changes goes a gradual con- densation of the protoplasm. This condensation BUTSCHLI believes to be due to an excretion of water from the proto- plasm. In Actinosphrerium the change from the richly vacuolated motile form to the encysted condition is even more marked. As BRAUEE ('94, p. 193) has shown, the protoplasmic mass becomes, during the process of encystment, smaller and denser. The loss of water from the protoplasm is without doubt due to §4] ACCLIMATIZATION TO EXTREME TEMPERATURES 257 the continued activity of the contractile vacuole at a time when no fluids are being taken into the protoplasmic body. From the foregoing considerations it appears probable that one of the important characters of " spores " is the diminished amount of free water held in the protoplasm; or, in other words, its dryness. This dryness of the coagulable substance would seem to be cause of its higher resistance. So far the evidence seems complete. Whether, however, loss of water is the ultimate cause of the high resistance capacity of hot-spring organisms or of those gradually acclimatized is still uncertain. Analogy renders it highly probable that such is the case. 2. Acclimatization to Cold. — Just as organisms may become acclimatized to high temperatures, so also may they live in very cold regions. I cite a few examples : Several species of Pro- tista are said to live in the Alps above the snow line, coloring the snow red. (SHUTTLEWORTH, '40.) A tardigrade is found in the same locality. Certain insects live on or in the snow or ice. Thus Desoria glacialis (or glacier flea) lives on the Swiss glaciers, and on the snow live Podura hiemalis, Trichocera brumalis (when the temperature is " below the freezing point," FITCH, '46, p. 10), and other species of Trichocera and Podura. Cf. also Boreus hiemalis and B. brumalis (FiTCH). Although swarm-spores are usually extremely sensitive to cold, STRAS- BURGER ('78, p. 613) cites a case of a marine alga in which they were being formed and thrown out when the temperature of the water was between — 1.5° and —1.8° C. Increased resistance to cold seems often the result of the action of cold on the organism. Thus, while SCHWARZ ('84r p. 69) found that Euglente gathered in the summer time were- not responsive below + 5° to + 6° C., ADERHOLD ('88, p. 320) found that Euglenae gathered in the winter would respond- even at 0°. We may say, the winter cold had in some way lowered the heat attunement of these Protista. In seeking for an explanation of acclimatization to cold we should recall that the cause of death from cold is chiefly the freez- ing of water in the protoplasm, and the irritation of excessive cold. Accustomed to great cold, protoplasm would doubtless be no longer irritated by it ; whether under these circumstances 258 HEAT AND PROTOPLASM [Cn. VIII it would contain less water is a question which lacks an experi- mental answer. The conclusion from the results offered in this section is this : protoplasm may become so modified through the action of excessive heat or cold that it is no longer killed at the ordi- nary fatal temperatures. This result is partly due to the fact that it is then not so strongly irritated by these extreme tem- peratures, and partly owing to the fact that the coagulation and freezing points have been shifted, possibly through loss of water. § 5. DETERMINATION OF THE DIRECTION OF LOCOMOTION BY HEAT- -THERMOTAXIS Our knowledge of this subject is still in its infancy and de- pends chiefly upon the observations of STAHL ('84), VER- WORN ('89, pp. 67-68), GRABER ('83 and '87), LOEB ('90, p. 43), DE WILDEMANN ('94), and MENDELSSOHN ('95). The first two and the last two mentioned have employed Protista, and we may consider their work first. STAHL'S studies were made upon Myxomycetes. He used two beakers, of which one was filled with water at 7°; the other with water at 30°. These were placed near each other, and a strip of filter-paper, on which lay the plasmodium of JEthalium septicum, was stretched between them. The two ends of the strip with the corresponding ends of the plasmo- dium hung into the two glasses. The result was that the plasmodium moved from the colder water toward the warmer, although before the experiment it was moving in the opposite direction. WORTMANN ('85) added the observation that when the warmer temperature rose above 36° a repellent action of the warmer water was discernible. VERWORN experimented chiefly with Amoeba. The difficulty in this operation depended upon the necessity of warming only a part of the body of so small an animal. He used a glass plate of 5 sq. cm. area, to the upper surface of which was glued a piece of black paper, in which had been cut a rectangular open- ing, 3 sq. mm. large, and with very sharp edges. This plate was placed on the stage of the microscope so that the hole lay § 5] THERMOTAXIS 259 in the rays of the infalling, concentrated light of midsummer, reflected from the mirror. Upon the black paper was placed the cover-glass with the amoeba in a drop of water. The light from the mirror was cut off until the amoeba, in its migrations, lay half-way over the edge of the orifice. Then concentrated light was let through the slit. A small part of the body was still moved across the line of demarcation; then for a moment movement ceased and a few seconds after the protoplasm of the amoeba began to flow backwards. In from 10 to 30 seconds the amoeba was wholly in the dark again. Similarly, when the cover-glass was moved so that the amceba was brought half-way over the open orifice it retreated into the dark. Direct measure- ment showed that the temperature at the illuminated part was 40° to 50° C., whilst over the black paper it was 15° to 20° less. That the movement was not due to the light was shown first by cutting out, by means of ice, the heat rays only. No reac- tion occurred. Secondly, by cutting out the light but not the heat, by passing the light through a solution of iodine in CS2 so that only the ultra-red rays (which act like darkness to all organisms) went through; the typical reaction occurred when the temperature over the slit was 35°. From all of these ex- periments the conclusion seems justified --Amoeba is positively thermotactic towards that temperature. Similar results were obtained by VERWORN with the shelled Rhizopod Echinopyxis aculeata, and later (see JENSEN, '93, p. 440) with Paramecium. More complete studies on the latter were, however, made by MENDELSSOHN, who worked in VERWORN'S laboratory. MENDELSSOHN devised an excellent method of study. A brass plate 20 cm. x 6 cm. and 4 mm. thick is properly supported in a horizontal position, and to its under face are affixed, transversely, tubes through which hot or cold water may be run from a reservoir placed at a high level. In the middle of the plate a space 10 cm. x 2 cm. and 2 mm. deep is cut out and into it is fitted a glass or ebonite trough. Special thermometers whose bulbs are coiled in the plane of the trough, and hence perpendicularly to the stem, serve to measure the temperature of the water in the trough at any point. By means of water running through the transverse tubes either end of the trough may be heated or cooled as 260 HEAT AND PROTOPLASM [Cn. VIII desired. Starting now with the trough filled with infusion water, the Paramecia are seen to be uniformly distributed (Fig. 71, a). Hot water is run through tubes under the right end of the trough. After 10 minutes the thermometers show the temperature of the water at the right end to be 38°, at the left end 26°. At this moment, all Paramecia are in the left third of the trough (Fig. 72, 6). If now the hot water be passed through the left tube only, the temperature rises at that end to 36° or 38°, falling to 27° or 28° at the other, and 13-° 26? 38s • " -. •"• .-. ffliPP FIG. 71. — Distribution of Paramecium in a trough of water with variable temperature at the ends. (From MENDELSSOHN, '95.) the Paramecia swim to the right end. Thus, with reference to a temperature of 38°, Paramecia are negatively thermotactic. If, now, cold water be passed through the left tube so that the temperature of the left end of the trough falls to 10°, while the right end is at 25°, the Paramecia migrate to the right end. Towards a temperature of 25° Paramecium is thus positively thermotactic (Fig. 72, -y perished after a few hours at 5° or 6°. 18. Merely the note: "On en [living mollusca] trouve aussi dans des eaux thermales : par exemple le turbo thermalis, espece de paludine sans doute, vit dans celles d'Abano, dont la temperature est de 40° R." 19. The statement is not critical: "Their heat [hot springs] is too great for the hand to bear; the highest temperature is about 15U°." "In the hot water of these springs a green plant vegetated, which seemed to be a species of conferva growing in such situations : probably the fontenalis. But what is more remarkable, a bivalve testaceous animal adhered to the plant, and lived in such a high temperature too." 20. See note 5. 21. " J'ai mesure" plusieurs fois & en diverses saisons, la chaleur de ces eaux, & je 1'ai toujours trouve'e a tres-peu pres la meme ; savoir, de 35 degre"s dans celle du sout're, & de 3(5^ ou 30.7 [R. from context] dans celle de St. Paul. Malgre la chaleur de ces eaux, on trouve des animaux vivans dans les bassins qui les reQoivent ; j'y ai reconnu des rotife"res, des anguilles & d'autre animaux des infusions. J'y ai meme de'couvert en 1790, deux nouvelles especes de tremelles doue'es d'un mouvement spontaneV 22. See note No. 14. 23. Many individuals collected by R. BLANCHARD "dans les eaux de thermes du Hamman-Meskhoutine, pres Guelma, dans les premiers jours d'avril ; 1'eau des thermes, an point de la re"colte, a une temperature de 45° et de 50.5° C. Les Cypris formaient une sorte de zone continue, de couleur chocolat, sur le bord de 1'eau." 24. Found "in a hot spring, temperature 157° F., attached to the rock by the long end at about an angle of 45° and continually moving. . . . The rocks were covered with them." 25. The note in " Insect Life " is abstracted from a longer article by BRUNER in the newspaper called the Lincoln (Nebraska) "Evening Call," for April 6, 1895. The article, through the kindness of Professor H. B. WARD of the Uni- versity of Nebraska, I have now before me. The larvse were sent to Professor BRUNER by JOHN C. HAMM, of Evanston, Wyoming, upon whom this statement of the conditions of life of the organisms depends. The larvse were found in a cup-shaped depression in the top of a small isolated cone about 20 inches high, situated about a few feet from a large sulphur mound or "dune," under which one could hear the rumbling of boiling water. Through apertures in the bottom the almost boiling water came up into the cup and ran over the edge of the pot. LITERATURE 267 The larvae were actively moving. Mr. HAMM writes to Mr. BRDNER : "I did not have a thermometer with which to take the temperature, but . . . the water was so hot when I saw them that I could not hold my hand in it. My best judgment is and was at the time that the water was not more than twenty or thirty degrees [Fahr., of course] below the boiling point." 26. " A water beetle abounded in water at 112° " [F.]. 27. Too hot for the hand to bear more than a moment or two. 28. The reference is to a discussion of a paper by BERT. " M. PAUL BERT a. vu des barbellons dans de 1'eau a 34° C." 29. " Mon ami Mr. COCCHI," says SPALLANZANI, " raconte que les Grenouilles ne souffrent point dans les bains de Pise, quoiqu'elles soient expose'es a une chaleur indique"e par le 111° du Thermometre de FAHRENHEIT qui correspond au 37° du Thermometre de REAUMUR [! sic]." LITERATURE ADERHOLD, R. '88. (See Chapter I, Literature.) AFFANASIEFF, N. '65. Untersuchungen iiber den Einfluss der Warme und der Kalte auf die Reizbarkeit der motorischen Froschnerven. Arch. f. Anat. u. Physiol. 1865. pp. 691-702. ARTAUD, J. B. L. '25. Essai sur la phosphorescence de 1'eau de la mer.. Bull. sci. nat. (FERTJSSAC). VI, 130, 13ir BERT, P. '67. Memoire sur la physiologie de la Seiche (Sepia officialis Linn.). Mem. Soc. Sci. Bordeaux. V, 115-138. '67a. Sur la mort des animaux a sang froid par 1'action de la chaleur. Mem. Soc. sc. phys. et nat. Bordeaux. Y, xxii. '76. Sur 1'influence de la chaleur sur les animaux inferieurs. C. R. Soc- de Biol. Paris. XXVIII, 168. BLAINVILLE, DE '24. Article Mollusques in Diet, des Sci. Nat. T. XXXIIf 141. BLAKE, W. P. '53. Geological Report, in Explorations and Surveys for a- Railroad Route to the Pacific Ocean. Vol. V. War Dept. U.S.A. BONARDI, E. and GEROSA, G. G. '89. Nouvelles recherches par rapport k 1'influence de certaines conditions physiques sur la vie des microorga- nismes. Arch. Ital. de Biol. XII, 89-93. 28 July, 1889. BRAEM, F. '90. Untersuchungen iiber die Bryozoen des siissen Wassers.. Biblioth. Zool. "ll. 134pp. BRAUER, A. '94. Ueber die Encystirung von Actinosphaerium Eichhornii Ehrbg. Zeitschr. f. wiss. Zool. LVIII, 189-221, Taf. x, xi. BREWER, W. H. '66. Observations on the Presence of Living Species in Hot and Saline Waters in California. Am. Jour. Sci. XLI, 391- 394. BROCA, P. '61. (See Chapter II, Literature.) BRUNER, L. '95. Animal Life in Thermal Springs. Insect Life. VII, 413- 414. 268 HEAT AND PROTOPLASM [Cn. VIII BUTSCHLI, O. '84. Protozoa. BRONN'S Klassen u. Ord. d. Thierreichs. I Bd., II Abth. 785-864. '89. The same. Ill Abth., Infusoria, pp. 1585-2035. CALLIBURCES, P. '58. Recherches experimentales sur 1'influence exercee par la chaleur sur les manifestations de la contractilite des organes. Comp. Rend. XLVII, 638-611. CAMPBELL, J. P. '88. Experiments on Tetanus and the Velocity of the Contraction Wave in Striated Muscle. Stud. Biol. Lab. Johns Hopkins Univ. IV, 123-145. Apr. 1888. CANDOLLE, A. DE '65. De la germination sous des degres divers de tem- perature constante. Arch, des sci. nat. et phys. XXIV, 243-282. CANDOLLE, A. P. DE '06. Experiences relatives a 1'influence de la lumiere sur quelques vegetaux. Mem. present, a 1'institut des sci. lett. et arts par divers savants. Sci. math, et phys. I, 329-350. CANDOLLE, C. DE '80. De 1'effet des temperatures tres-basses sur la faculte germinative des graines. (Verb.. Schweizer naturf. Ges. Jahresber. 1877-1878). Bot. Ztg. XXXVIII, 64. 23 Jan. 1880. '84. Arch. d. sci. phys. et nat. (3) XI, 325-326. 15 March, 1884. [No title.] CHMULEWITCH, J. '69. De certaines proprietes physiques et physiologiques des muscles. Comp. Rend. LXVIII, 936-938. 19 Apr. 1869. COHN, F. '50. Nachtrage zur Naturgeschichte des Protococcus pluvialis Kiitzing. Verh. d. Kais. Leop.-Car. Akad. XXII2, 607-764. '62. Ueber die Algen des Karlsbader Sprudels und deren Antheil an der Bildung des Sprudelsinters. Flora. XLV, 538-540. '71. [Das Gefrieren der Zellen von Nitella syncarpa.] Bot. Ztg. XXIX, 723. '77. Beitrage zur Biologie der Bacillen. Beitrage z. Biol. d. Pflanzen. II, 249-276. COHN, J. '94. Ueber thermogene Bakterien. Verh. Ges. deutsch. Naturf. u. Arzte. 65. Vers. Niirnberg, 1893. pp. 148-150. CORI, C. I. '93. Das Objectischaquarium. Zeitschr. f. wiss. Mikr. X, 148-151. DALLINGER, W. H. '80. On a Series of Experiments made to Determine the Thermal Death-point of Known Monad Germs when the Heat is Endured in a Fluid. Jour. Roy. Mic. Soc. Ill, 1-16. 1880. '87. The President's Address. Jour. Roy. Mic. Soc. 185-189. 1887. DALLINGER and DRYSDALE, J. '74. Further Researches into the Life His- tory of Monads. Monthly Micros. Jour. XT, 97-103. 1874. DANA, J. D. '38-'42. Geology. U. S. Explor. Exped. 1838-1842. Vol. X. 756 pp. DAVY, J. '63. Some Observations on the Vitality of Fishes as tested by Increase of Temperature. Rept. 32d Meet. Brit. Assoc. Adv. Sci. 1862. Notices, 125. DEHERAIN, P. P. and MOISSAN, H. 74. Recherches sur 1'absorptinn d'oxy- gene et 1'emission d'acide carbonique par les plantes maintenues dans 1'obscurite. Ann. Sci. Nat. (Bot.) (5). XIX, p. 321-357. LITERATURE 269 DEMANT, B. 79. Beitrage zur Chemie der Muskeln. Zeitschr. f. physiol. Chem. Ill, 241-249. '80. Ueber das Serumalbumin in den Muskeln. Zeitschr. f. physiol. Chem. IV, 384-386. 18 Aug. 1880. DEMOOK, J. '94. (See Chapter I, Literature.) DOENHOFF '72. Ueber das Verhalten kaltbliitiger Thiere gegen Frost- temperatur. Arch. f. Anat. u. Phys. Jg. 1872, pp. 724-727. DOYERE, M. P. L. N. '42. (See Chapter II, Literature.) DUBALEN '73. Note sur les Mollusques qui vivant dans les sources chaudes de Dax. Actes Soc. Linn. Bordeaux. XXIX, C. R., p. iv. DUCLAUX, E. '71. Eludes physiologiques sur la graine de vers a soie. Ann. de chim. et de physique. (4) XXIV, 290-306. DUTROCHET '37. Observation sur le Chai-a flexilis : Modifications dans la circulation de cette plante sous Pinfluence d'un changement de tempe- rature, d'une irritation mecanique, de 1'action des sels, etc. Comp. Rend. V, 775-784. 4 Dec. 1837. DYER, W. T. T. '74. Note on the Foregoing Communication [of Moseley, '74]. Jour. Linn. Soc. (Bot.) XIV, 326-327. 17 Oct. 1874. EDWARDS, W. F. '24. De Pinfluence des agens physique sur la vie. Paris : Crochard. 654 pp. 1824. EHRENBERU '59. Ueber eine auf der Insel Ischia jiingst beobachtete, zur Erlauterung einer ungarischen aus Kieselorganismene bestehenden Felsart dienende Wirkung heisser Quellen. Monatsber. Akad. Wiss. Berlin, aus d. Jahre 1858, pp. 488-495. ENGELMANN, T. W. '68. Ueber die Flimmerbewegung. Jen. Zeitschr. IV, 321-479. '77. Flimmeruhr und Flimmermiihle. Zwei Apparate zum Registriren der Flimmerbewegung. Arch. f. d. ges. Physiol. XV, 493-510. 23 Oct. 1877. '79. Physiologic der Protoplasma- und Flimmerbewegung. Handb. d. Physiol. (Hermann). I, 343-408. 1879. FITCH, A. '46. Winter Insects of Eastern New York. Amer. Quart. Jour. of Sci. and Agric. V, 274-284. Extr. by WESTWOOD, Trans. Ent. Soc. Lond. (2) I, Proc. 95-98. 1851. FLOURENS '46. ' (Note on conferva of Icelandic hot springs.) Comp. Rend. XXIII, 934. FRENZEL, J. '85. Temperaturmaxima fur Seethiere. Arch. f. d. ges. Physiol. XXXVI, 458-466. GERVAIS, P. '49. Observations sur les eaux d'Hamman-Meskhoutin. L'Institut. XVII, 11-121. GOTSCHLICH, E. '93. Ueber den Einfluss der Warme auf Lange und Dehn- barkeit des elastischen Gewebes und des quergestreiften Muskels. Arch. f. d. ges. Physiol. LIV, 109-164. 21 Apr. 1893. GRABER, V. '83. (See Chapter VII, Literature.) '87. Thermische Experimente an der Kuchenschabe. Arch. f. d. ges. Physiol. XLI, p. 240-256. 17 Oct. 1887. 270 HEAT AND PROTOPLASM [Cn. VIH GRIFFITH, H. G. '82. Larvae of a Fly in a Hot Spring in Colorado. Am. Nat. XVI, 599. HALLIBURTON, W. D. '88. On the Nature of Fibrin Ferment. Jour, of Physiol. IX, 229-286. Nov. 1888. HEINRICH, R. '71. Beitrage zur Kenntniss des Temperatur- und Lichtein- flusses auf die Sauerstoff abscheidung bei Wasserpflanzen. Land- wirthsch. Versuch-Stat. XIII, 136-154. HERMANN, L. '71. Die Erstarrung in Folge starker Kaltegrade. Arch. f. d. ges. Phys. IV, 189-192. HOFFMAN, H. '63. Neue Beobachtungen iiber Bacterien mit Riicksicht auf Generatio spontanea. Bot. Ztg. XXI, 304-307, 315-319. HOFMEISTER, W. '67. (See Chapter IV, Literature.) HOPPE-SEYLER, F. '75. Ueber die obere Temperaturgrenze des Lebens. Arch. f. d. ges. Physiol. XI, 113-121. 26 July, 1875. HOOKER, J. D. '55. Himalayan Journals. 2 vols. John Murray. London, 1855. HOOKER, W. J. '13. Journal of a Tour in Iceland in the Summer of 1809. 2d ed. 2 vols. London, 1813. JAMES, E. '23. Account of an Expedition from Pittsburgh to the Rocky Mountains under Command of Major Stephen H. Long, Philadelphia. 2 vols. 1823. JENSEN, P. '93. (See Chapter V, Literature.) KNAUTHE, K. '95. Maximaltemperaturen, bei denen Fische am Leben blei- ben. Biol. Centrallb. XV, 752. KOCHS, W. '90. Kann die Kontinuitat der Lebensvorgange zeitweilig vbllig unterbrochen werden ? Biol. Centralbl. X, 673-686. 15 Dec. 1890. KUHNE, W. '59. Untersuchungen iiber Bewegungen und Veranderungen der kontraktilen Substanzen. Arch, f . Anat. u. Phys. 1859. pp. 564- 642, 748-835. '64. (See Chapter I, Literature.) LEWITH, S. '90. Ueber die Ursache der Widerstandsfahigkeit der Sporen gegen hohe Temperaturen. Ein Beitrag zur Theorie der Desinfektion. Arch. f. exper. Pathol. XXVI, 341. LOEB, J. '90. (See Chapter VII, Literature.) MACAIRE-PRINSEP, J. '21. Memoire sur la phosphorescence des lampyres. Ann. de Chimie. XVII, 151-167. MANTEGAZZA, P. '66. Sullo sperma umano. Rendic. reale Instit. Lomb. HI, 183-196. MENDELSSOHN, M. '95. LTeber den Thermotropismus einzellige Organismen. Arch. f. d. ges. Phys. IX. 20 Feb. 1895. MITCHILL, S. L. '06. Account of a Journey up the Washita (or Ouachita) River, in Louisiana, performed by WILLIAM DUNBAR, Esq., and Dr. HUNTER. Med. Repository. New York. (2) III, 305-308. MOISSAN, H. '79. Sur les volumes d'oxygene absorbe et d'acide carbonique emis dans la respiration vegetale. Ann. des. Sci. Nat. (6) Bot. VII, 292-339. July, 1879. LITERATURE 271 MONIEZ, R. '93. Description d'une nouvelle espece de Cypris vivant dans les eux thermales du Hammam-Meskhoutine. Bull. Soc. Zool. France. XVIII, 140-142. MORIGGIA, A. '91. Die Ueberhitzung von Muskel- und Nervenfasern. Untersuch. z. Naturl. d. Mensch. u. d. Th. (MOLESCHOTT). XIV, 332- 395. MOSELY, M. N. '74. Notes on Fresh Water Algae obtained at the Boiling Springs at Furnas, St. Michael's, Azores, and their Neighborhood. Jour. Linn. Soc. (Bot.). XIV, 321-325. 17 Oct. 1874. MULLER-THURGAU '80. Landwirthsch. Jahrb. IX. [Quoted by VINES, '86.] NAGELI, C. '60. Ortsbewegungen der Pflanzenzellen und ihre Theile. (Strdmungen) Beitr. z. wiss. Bot. II, 59-108. 1860. NICHOLET, H. '42. Recherches pour servir a 1'histoire des Podurelles. Schweizer Gesell. N. Denksch. VI. 88 pp. OBERNIER '66. Versuch iiber den Einfluss hoher Warmegrade an Thieren. Verh. d. naturhist. Vereines d. preuss. Reinl. u. Westphal. XXIII, Sitzbr. 22, 23. PASTEUR, L. '61. Me moire sur les corpuscles organises qui existent dans 1'atmosphere, examen de la doctrine des generations spontanees. Ann. Sci. Nat. (4) Zool. XVI, 5-98. PEALE, A. C. '83. The Thermal Springs of Yellowstone National Park. 12 Ann. Rept. U. S. Geol. and Geog. Surv. of Territories. Pfc. II, 63- 454. PICKFORD, P. '51. Untersuchungen iiber die Lebensreize. Zeitschr, f. rat. Med. (2) I, 335-383. PICTET, R. '93. Essai d'une methode gene"rale de synthese chimique. Arch. des sci. phys. et nat. (3) XXIX, 5-27. 15 Jan. 1893. 93*. De 1'emploi methodique des basses temperatures en biologic. Arch. des sci. phys. et nat. (3) XXX, 293-314. 15 Oct. 1893. PLATEAU, F. '72. Recherches physico-chemiques sur les articules aquatiques. II Part. Resistance a 1'asphyxie par submersion, action du froid, action de la chaleur, temperature maximum. Bull. 1' Acad. roy. Belg. XXXIV, 274-321. POUCHET, F. A. '66. Recherches experimentales sur la congelation des animaux. Jour, de 1'Anat. Ill, 1-36. PREVOST '40. Recherches sur les animalcules spermatiques. Compt. Rend. XI, 907, 908. PURKINJE and VALENTIN '35. De phaenomeno generali et fundamental! motus vibratorii continui in membranis cum internis animalium plu- rimorum et superiorum et inferiorum ordinum obvii. Wratislariae. 96 pp. 1835. QUATREFAGES, A. DE '53. 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XX, 245-258. 6 Aug. 1894. WOLKOFF, VON and MAYER '74. Landwirthsch. Jahrb. III. 1874. WOOD, H. C. '74. A Contribution to the History of the Fresh-water Algae of North America. Smithsonian Contributions to Knowledge. XIX, Art. III. 1874. WORTMANN, J. '85. Der Thermotropismus der Plasmodien von Fuligo varians (Aethalium septicum d. Aut.). Ber. D. Bot. Ges. Ill, 117- 120. WYMAN, J. '56. [Observations on the Cold endured by Hibernating In- sects.] Proc. Bost. Soc. Nat. Hist. V, 157. '67. Observations and Experiments on Living Organisms in Heated Water. Am. Jour. Sci. XLIV, 152-169. YUNG, E. '85. (See Chapter III, Literature.) T CHAPTER IX GENERAL CONSIDERATIONS ON THE EFFECTS OF CHEM- ICAL AND PHYSICAL AGENTS UPON PROTOPLASM IN the present chapter it is proposed to consider certain general matters upon which the facts given in this First Part throw light : namely, (I) the structure and composition of protoplasm ; (II) the limiting conditions of metabolism ; (III) the dependence of protoplasmic movement upon metabo- lism and external stimuli ; and (IV) the determination of the direction of locomotion. § 1. CONCLUSIONS ON THE STRUCTURE AND COMPOSITION OF PROTOPLASM The question of the structure of protoplasm is preeminently a histological one. Microscopical study must eventually be re- lied upon to settle it. However, the results of experimental work seem to favor, as we have already pointed out (p. 70), BUTSCHLI'S view of a honeycomb, or foam structure, of protoplasm. The problem of the constitution of protoplasm is, on the other hand, preeminently a chemical one, and it must be solved by experimental methods. Our results can lead us to certain qualitative statements on this matter. The chemical composition of protoplasm is immensely com- plex. Just as the geologist is forced bv the facts to assume a vast, but not infinite, time for earth building, so the biologist has to recognize an almost unlimited complexity in the consti- tution of protoplasm. The evidence that protoplasm is so complex is gained partly from the results of micro-chemistry. Many staining fluids act upon only a small part of the protoplasm of a single cell, so that a mixture of stains may be used, each component of which 274 § 2] LIMITING CONDITIONS OF METABOLISM 275 attacks a different constituent of the protoplasm. In this way the dissimilar substances in protoplasm are made strikingly apparent. Not only does the protoplasm of one cell show this differentiation, but that of different cells of the body stains very diversely. Another line of evidence for the complexity of pro- toplasm is gained from the study of the effect of poisons. We have seen that the same poisonous substance acts very differently upon allied species of organisms (0.<7- of bacteria) and upon the various organs of the body, — a fact which in many cases can only be accounted for on the ground of dissimilar composition. Again, most protoplasm must contain substances which are acted upon specifically by the different agents ; for instance, certain highly explosive compounds which are set off by contact, certain others which are disturbed by light, and still others which are especially changed by heat. Each compound, again, must form an inconsiderable part of the whole, for (if the action be not too intense or prolonged) the "stimulus" of the agent results in no disturbance of the activities in general. Likewise, the facts of acclimatization, according to which, ap- parently, certain substances in the protoplasm may be destroyed without other important change in activities, give additional insight into protoplasmic complexity. Finally, the same agent acts in "varying degree on closely related protoplasm, and this indicates that, even when the general composition is the same, the proportions of the different substances vary. From the facts of protoplasmic staining and of the varied effects of poi- sons, from the diverse effects of other stimulating agents, and from the facts of acclimatization of organisms, we conclude that in dealing with protoplasm we are not always dealing with the same thing, but, on the contrary, with very diverse combi- nations, which have this in common, that they exhibit life. § 2. THE LIMITING CONDITIONS OF METABOLISM Metabolism is life. To know the limits within which it can occur is to know the vital limits. It is impossible to define these limits closely, however, for, at either extreme, metabolism graduates insensibly into inaction. It will be necessary, conse- quently, to place our limits very far out. 276 GENERAL CONSIDERATIONS [Cn. IX The limiting conditions at which inaction occurs are of two sorts. These may be termed respectively structural and dynami- cal. These two sorts of limiting conditions may be illustrated by comparing the protoplasmic mass to a factory, with many boilers and engines, much shafting and belting, and countless machines doing the most varied work. The amount of energy developed in the boilers and the efficiency of the engines and machines varies with certain conditions, such as the amount of heat applied to the former, and the friction and waste in the latter. The limiting mechanical conditions are reached when the boiler is rent by the steam pressure, a break-down is caused by friction, or a part rusts through and crumbles away. The limiting dynamical conditions are reached when the heat no longer suffices to form steam in the boiler, or the power is insufficient to run the machines. In either case, at the structu- ral, or at the dynamical limit, work ceases. It may be the work of a small part of the factory, so that the cessation is hardly noticed ; or it may involve all the machines, producing complete cessation of activity. To return to the protoplasm : the structural limiting condi- tions are of two main sorts, — mechanical and chemical. The mechanical limiting conditions are those in which the gross structure becomes broken down, while the chemical limiting conditions are those in which the composition becomes changed. To the mechanical group belongs the breaking down of the plasma films, either by drawing out the water of the protoplasm (by osmosis or by drying) or by the expansion due to the freezing of the chylenia. To the chemical group belong, for example, the reactions upon protoplasm of the halogen salts of the heavy metals, and of complex nitrogenous organic com- pounds in whose molecules hydrogen is unstably joined to nitrogen, also the coagulation of the plasma by high tempera- tures and the destruction of molecules by contact, by the electric current, or by light. The dynamical limiting condi- tions, on the other hand, are the absence of oxygen or other food-stuffs, the absence of the water necessary to the solution and circulation of the food, absence of light, in the case of chlorophyllaceous organisms, and a temperature much below 0° C. Thus, the conditions essential to metabolism are the § 3] PROTOPLASMIC MOVEMENT 277 absence of causes mechanically rupturing the machine, the absence of agents of such intense activity as to change pro- foundly its molecular constitution, and the presence of those agents --food, heat, light, and water — which supply or dis- tribute the energy of metabolism. Given protoplasm under these conditions, and normal me- tabolism must occur ; without them, there is no metabolism. Vary the dynamical conditions quantitatively, and a quantita- tive variation in metabolism will ensue. Approach a struct- ural limiting condition, and metabolism begins to cease. This conclusion, important for experimental morphology, is now reached : A vital phenomenon occurring in a given proto- plasmic mass can be reproduced only when the dynamical condi- tions are reproduced, and the structural limiting conditions are in no wise closely approached. § 3. THE DEPENDENCE OF PROTOPLASMIC MOVEMENT UPON METABOLISM AND UPON EXTERNAL STIMULI I do not propose to enter the debated ground of the cause of protoplasmic motion; but shall merely summarize the re- sults of our studies on this subject. First, protoplasmic movement is closely related to metabolism and is probably dependent upon it. This is indicated by the fact that ces- sation of movement always occurs before the vital limit is reached. Rigor always precedes death. A second series of facts indicating the same thing is found in the closeness with which the optimum for metabolism agrees with the optimum for movement. Thus at about 35° C. both the metabolic processes and the movements of protoplasm find their optimum. These two results, then, that movement is impossible in dead protoplasm even when its structure is seemingly unaltered, and the close approximation of the optimum points for metabolism and for movement, are the best justification for the belief that movement is dependent upon metabolism. But are the conditions essential to metabolism the only con- ditions necessary for movement? In other words, will move- ment always accompany metabolism, or are external stimuli 278 GENERAL CONSIDERATIONS [Cn. IX essential to its production? There is in biology no question more important than this, and the answer is not so certain as it ought to be. The fact that rigor occurs at a point at which recovery of movement is still possible is not sufficient evidence that metabolism has not ceased with the motion ; for I think it has not been shown that with rigor "latent life" does not come in. On the other hand, the fact that some bacteria are motion- less in the absence of light (which can hardly be essential to metabolism) would seem to indicate that conditions other than those of metabolism are necessary to movement. This single fact cannot, however, lead us to a definite answer, and our inquiry, whether or not "stimuli" are essential to protoplasmic movement, must still be regarded as unanswered. § 4. THE DETERMINATION OF THE DIRECTION OF LOCOMOTION As we watch an animalcule swimming across the field of view, or as we see a larger organism moving, perhaps in a broken line, towards any point, we think of its movements as controlled from inside. Yet it is clear that if an organism is moving definitely towards a point, it must be on account of some influ- ence emanating from that point and falling upon the organism. Without external directive influences of some sort there can be no directed movements. This conclusion is confirmed by experiment. I have put an amceba into the apparatus already described (p. 186), so that the chemical conditions of its environment were uniform ; con- tact and temperature were also similar on all sides ; the direc- tive action of gravity was annulled and all light was cut off. At intervals the position of the amosba was platted by the aid of light reflected momentarily from below the stage of the microscope and by means of a camera. Thus the path of the amoeba was traced. A typical tracing made in this way is reproduced in Fig. 72. Compare the devious path made under these conditions with the straight path taken in response to light (Fig. 53). The curious spiral twists and the turning of the line upon itself are characteristic of all the tracings which I have made under these conditions. Important also is the DIRECTION OF LOCOMOTION 279 1O:58 11:02 13:10 :2O 13:OO :4O :56 \ :52 FIG. 72. — Camera drawing, showing the successive positions assumed by Amoaba proteus when acted upon by external agents uniformly in all directions. Mag- nified 1() dianis. FIG. 73. — Tracks made on paper by larvae of Musca caesar moving in the dark from a central spot of colored fluid. (From POUCHET, '72. Revue et Mag. de Zool. (2) XXIII.) 280 GENERAL CONSIDERATIONS [Cn. IX fact that whereas the amoeba responding to light is constantly elongated in the direction of the infalling ray, the amoeba which is not stimulated from one direction exhibits, most of the time, a stellate appearance. The wandering of the undi- rected organism is illustrated again in the experiment of Pouchet on the larv;e of Musca (Lucilia) ctesar, kept in the dark (Fig. 73 ; compare Fig. 74, where the same larvse are migrating under the directive influence of light). From these experiments we make the deduction that external agents play a role of the utmost importance for morphology, — of the utmost importance because by them alone is determined the direction of migration of the motile cells or the migrating FIG. 74. —Tracing made like that of Fig. 73 by fly larvae, when the light falls upon them in the direction of the arrow. A, the first direction of the light; B, the second direction. To be compared with the undirected movements of Fig. 73. (From POUCHET, '72.) protoplasm of whatever sort in the organism. The sense of that migration depends in part upon the internal condition of the protoplasm. The mechanism by which locomotion is effected -that is wholly internal. The mechanism and the energy necessary to make it go are alone impotent to determine any adaptive movement or any other predictable result. To mech- anism and energy must be added a stimulus external to the responding protoplasm in order that an adaptive or orderly result should occur.* * There are several other important matters upon which the results of this First Part throw light, such as the Mechanics of Response and the Origin of Adaptation in Response. Since additional facts for the discussion of these topics will be gained from the succeeding Parts, that discussion will be deferred. PART II THE EFFECT OF CHEMICAL AND PHYSICAL AGENTS UPON GROWTH CHAPTER X INTRODUCTION: ON NORMAL GROWTH ORGANIC growth is increase in volume.* It is not develop- ment ; it is not differentiation ; it is not increase in mass, although the latter may often serve as a convenient measure of growth. In analyzing the processes of growth in organisms we must recognize at the outset that organisms are composed of living matter and formed substance, and that growth may therefore result from the increase in volume of either of these. The living matter, in turn, is composed of two principal substances : the plasma and the enchylema or cell sap ; so growth may be due to the increase of either of these substances, -- may result either from assimilation, or more strictly from the excess of * Growth has been variously defined. Thus HUXLEY has called growth " increase in size," which is essentially the same as my definition. SACHS ('87, p. 404) defines growth as an increase in volume intimately bound up with change of form (" eine mit Gestaltveranderung innig verkniipfte Volumen- zunahme") ; and he illustrates the definition by the example of the growth of a sprout from its beginning to its full development. In this case two phenom- ena are distinguishable : first, increase in volume, and, second, the filling out of the details of form. As SACHS says, these phenomena taken together are gen- erally denominated " development "; and it seems decidedly advantageous to retain this word with its usual signification, and to distinguish the two compo- nent processes by the terms growth and differentiation. PFEFFER'S ('81, p. 46) definition differs still more widely from the one pro- posed above. He defines growth as change in form in the protoplasmic body ("die gestaltliche Aenderung im Protoplasniakorper " ) ; and he goes on to say that increments of volume and mass are not proper criteria of growth. PFEFFER illustrates this statement by the following example : A plant stem or a cell mem- 281 282 INTRODUCTION [Cn. X. the constructive over the excretory processes of the plasma, or from the taking in of water.* Of the three factors involved in growth — increase of formed substance, of plasma, and of enchylema — the part played by the last seems to me to have been underestimated. Plant physiol- ogists have been in the best position to acquire the facts. brane can be permanently elongated by extension beyond the limits of elasticity without the volume necessarily increasing; — and he apparently means to include such an artificial deformation in his definition of growth. "And," he continues, " under certain circumstances a diminution of volume of a plant seg- ment can indeed occur as a result of growth, when, for example, the elasticity of the wall is increased by growth and water is pressed from the cell until equi- librium is restored." It may be doubted, however, if PFEFFER would say that in this case the cell, as a whole, had grown ; but if he would, then his definition is a wide departure from ordinary usage. Also, VINES ('86, p. 291) offers a definition, which is intermediate between that of SACHS and that of PFEFFER. "By growth," he says, " we mean per- manent change of form, accompanied usually by increase in bulk." But then he goes on to say, "Nor does this increase even of the organized structures of an organ, that is of the protoplasm and the cell wall, necessarily imply that it is growing. Thus, an increase of the cell wall may take place without any appre- ciable enlargement of the cell, as, for instance, when a cell wall thickens." But since the thickening is a "permanent change of form," it should be consid- ered by the author a growth process were not increase in size of the cell after all, in the author's mind, the most important criterion of its growth. Finally, FRANK ('92, p. 355) finds no other criterion for growth than an increase in vol- ume (dependent, however, upon the increase of a particular substance). Thus, with these different plant physiologists, we see the word growth bearing the ideas of increase of volume and differentiation, then of differentiation alone, and, finally, of increase of volume alone. * Various analyses of the process of growth have been made by different authors. Let us look at a few of these opinions. Says HUXLEY ('77, p. 2), " growth is the result of a process of molecular intussusception." According to N. J. C. MULLER ('80, p. 100), "all phenomena of growth depend, in last analy- sis, upon this, that the molecule of the solid substance is introduced into the region of growth." FRANK ('92, p. 355) understands by growth that increase of volume which consists of the apposition or intussusception of new solid mole- cules of similar matter ("welche auf der An- oder Einlagerung neuer fester Molekule gleichartigen Stoffes beruhen "). According to VERWORN ('95, p. 475), growth is due to the excess of assimilation over disassimilation. These defi- nitions include what I regard as only half the process of growth. On the other hand, DRIESCH ('94, p. 37) distinguishes two kinds of cell growth: (1) passive growth, due to imbibition of water, and (2) active growth, resulting from assimilation. This classification agrees with the one I have pro- posed, but I think the term passive growth very inapt, since the imbibition of water is as truly an active process as any other vital activity. INT.] ON NORMAL GROWTH 283 MM. 10 MM. 5 MM. They have recognized in the tip of the plant three growth regions. At the extreme tip of the stem (or radicle) is the region of rapid cell division but comparatively slow growth ; next below is the zone exhibiting the Grand Period of growth ; and still below is the zone of histological differ- entiation (Fig. 75). In the lirst zone growth of plasma 100AYS is occurring ; in the FIG. 75.— Curve of daily growth in length of a disc, geconcl zone growth originally 1 mm. long, and taken immediately behind the vegetation point of a radicle of Phaseolus. It OI the enchylema IS comes to occupy in successive days the three zones chiefly taking place; referred to in the text. From SACHS, Lectures on . , , • i Plant Physiology. m the third ZOne there is growth of formed substance. The immense preponderance of the growth of the second period (at 7 days) is an index to the preponderat- ing influence in growth of the imbibition of water. \ 3.0 2.8 2.6 2.1 2.2 2.0 1.6 1.1 l.« 1.0 0.8 0.6 U.I 0.2 _ X \ \ V \ 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0 6.5 7.0 FIG. 76. — Curve representing the intensity of growth of roots of Pisum sativum, ; Vicia sativa, ; and Lens esculenta, , the time being assumed to be constant. The length of the abscissas in the direction from left to right corresponds to the distance, in millimeters, of the marked spaces on the root from the root apex. The ordinates correspond to the amount of growth, in milli- meters, of the corresponding piece of the root after 20 hours. From CIESIELSKI ('72.) That which occurs with one and the same piece of the stem on successive days takes place simultaneously at the different zones of the growing organ. Thus in the radicle (Fig. 76) 284 INTRODUCTION [Cn. X. 80 70 „ II III IV we find during a period of 20 hours little growth occurring at the root tip, a maximum of growth at 3 or 4 millimeters from the tip, and further up less growth, until a zone of almost no growth is reached. An analysis of the substance of the stem at different levels below the tip reveals the same thing — a sudden increase in the amount of water from 73% at the tip to 88% at the first internode (II), reaching a maxi- mum at 93% in the second internode (III), then falling slightly (92.7) to FIG. 77. — Curve showing the percentage of water in sue- +1 p fifth internode cessive internodes of hothouse plants of Heterocen- tron roseum Hook, et Arm., about 4 decimeters high. ( » 1, r Ig. 77). 1 he The ordinates indicate the percentage of water at experiments and ob- each internode from the terminal bud (I) to the fifth , . (VI). (From KKAUS, '79.) servations upon which these conclu- sions rest thus agree in assigning the chief role to water in the growth of plants. While the fact that water constitutes a large proportion of the growing animal was made known by the classical researches of BAUDRIMONT and MARTIN SAINT-ANGE ('51), the impor- tance of the part which it plays in the growth of animals seems first to have been appreciated by LOEB ('92, p. 42), who showed how in the withdrawal of water by plasmolytic meth- ods growth was interfered with. Later I made a series of determinations of the relative part played by water and dry substance in the growth of an animal (tadpole). Eggs and embryos at various ages were weighed after removal of super- ficial water. Then they were kept in a desiccator from which air had been pumped and which contained a layer of sulphuric acid to absorb moisture. After repeated weighings a condition was found in which the drying mass lost no more water (con- stant weight). The total diminution in weight indicated the mass or volume of free water contained in the organism at the beginning of the experiment. Numerous weighings were INT.] ON NORMAL GROWTH 285 made during two seasons upon Amblystoma, toads, and frogs. All series showed the same thing ; the most complete series is that given in the following table : — TABLE XXII EMBRYOS OF FROGS. 1895* DATE. DAYS AFTER HATCHING. AVERAGE WEIGHT, IN MG. WEIGHT or DRY SUBSTANCK, IN Me. WEIGHT OF WATER IN MG. %OF WATER. May 2 1 1.83 .80 1.03 56 " 3 2 2.00 .83 1.17 59 " 6 5 3.43 •80 2.63 77 " 8 7 5.05 .54 4.51 89 " 10 9 10.40 .72 9.68 93 " 15 14 23.52 1.16 22.36 96 June 10 41 101.0 9.9 91.1 90 July 23 84 1989.9 247.9 1742.0 88 These results are graphically represented in Fig. 78. The curve and table show that, exactly as in plants, there is a too'/. Sor. 70% 60* So-* Day*. 10 20 30 40 SO GO JO QO 9o FIG. 78. — Graphic representation of last column of Table, showing percentage of water in frog embryos from 1 to 84 days after hatching. Compare with Fig. 77. period of slow growth accompanied by abundant cell division — the earliest stages of the egg. Then follows, after the first * Compare with the less complete table of BAUDRIMONT and MARTIN SAINT- ANGE, '51, p. 532. 286 INTRODUCTION [Cn. X few hours, a period of rapid growth due almost exclusively to imbibed water, during which the percentage of water rises from 56 to 96 ; lastly comes the period of histological differen- tiation and deposition of formed substance, during which the amount of dry substance increases enormously, so that the per- centage of water falls to 88 and below. But the growth is due chiefly to imbibed water. The foregoing facts thus unite in sustaining the conclusion that at the period of most rapid growth of organisms growth is effected by water more than by assimilation. In later development the proportion of water slowly falls. This fact is well brought out in the following tables : — TABLE XXIII SHOWING THE PERCENTAGE OF WATER IN CHICK EMBRYOS AT VARIOUS STAGES UP TO HATCHING, FROM POTTS, '79 HOURS OF BROODING. ABSOLUTE WEIGHT IN GRAM. % WATER. 48 0.06 83 54 0.20 90 58 0.33 88 91 1.20 83 96 1.30 68 124 2.03 69 264 6.72 59 TABLE XXIV SHOWING THE PERCENTAGE OF WATER IN THE HUMAN EMBRYO AT VARIOUS STAGES UP TO BIRTH, FROM FEHLING, '77 AGE IN WEEKS. ABSOLUTE WEIGHT IN GRAM. % WATER. 6 0.975 97.5 17 36.5 91.8 22 100.0 92.0 24 242.0 89.9 26 569.0 80.4 30 924.0 83.7 35 928.0 82.9 39 1640.0 74.2 INT.] ON NORMAL GROWTH 287 These results indicate that during later development growth is largely effected by excessive assimilation or by storing up formed substance. From another standpoint we can recognize two kinds of growth : one a transitory growth, after which the enlarged organ may return again to its former size, and the other a per- manent or developmental growth, which is a persisting enlarge- ment, and plays an important part in development. As an example of transitory growth may be cited the case of the Sen- sitive Plant, whose leaflets when touched turn upwards as a result of the growth of cells on the convex side ; but this enlargement is only temporary -- it is transitory growth. This phenomenon is indeed usually not included in the idea of growth ; yet it is well-nigh impossible to draw a sharp line of distinction between it and permanent growth. For example, when a tendril of the Passion Flower is touched it may curve as a result of growth of the cells on the convex side, and this curvature may later become obliterated, as in the case of the Sensitive Plant ; but the longer the contact is continued the more the cells enlarge, and the more their walls become perma- nently modified. Thus the condition of temporary growth shades insensibly into that of permanent growth. So far as possible we shall consider in this book only developmental growth. Still another classification may be made of the phenomena of growth. We may distinguish between diffused and localized growth. In diffused growth the entire individual or many of its parts are involved. In localized growth the process is con- fined to a limited region. Thus in the early development of the frog diffused growth occurs, while in the formation of the appendages we have an example of localized growth. Since localized growth is an important factor in differentiation, many of the data concerning this phenomenon will be first considered in the Part dealing with Differentiation. Normal growth may or may not be accompanied by cell-divi- sion. But usually cell-division occurs sooner or later- in the growing mass. The act of cell-division seems to retard the process of growth. This conclusion follows from some experi- ments of WARD ('95, p. 300) on the growth of bacteria, which INTRODUCTION [Cn. X are summarized in the curve, Fig. 79. This shows how the growth in length of the bacterial rods is delayed at intervals 70 fl 60/1 SO fl 10 /i 30 IJL 20 [I MOMENT WHEN 4TH SEPTUM WAS CLEARLY VISIBLE, GROWTH AT MAXM. 1 MOMENT V 6RI WHEN *AS VIS >WTH A 3D B SEPTUM £• MAXM. J 70-03 MOMENT WHEN 20 SEP FUM .s WAS FIRST; VISIBLE, ^fC 3ROWTH , T MAXM. . ' MOMENT WHEN 1ST SEPTUM ^-^5 )-86 WAS DISTINCTLY VISIBLE, s ': 6-22 5ROWTH *T MAXM. 1 ' i t .-—"Su •3. •76 f x^ 13-48 PERIOD OF MINM GROWTH .*-- "*39 -84 d 4TH CELL D VISION. 36-2 1 ^--^ [3256 34-38 i THI RD PERIO 3 OF MINM. GROWT I, ""29-12 WHEN 3D DIVISION 27-30 t Td >OK PLAC 0 !-, •? S !=| S " 9 3-^2 a ci . *7* V *? 5 7 S S 9 PERIOD OF"M,NM. OROWT'H, «co~ ^^^D^N0"™^ * * d WHEN FIRST CELL DIVISION OCCURRED. OCCURRED. FIG. 79. — Curve of growth of a bit of a filament of Bacillus ramosus, 27.30 M long at the beginning and 70.88 M at the end of the period of observation. The curve shows certain periods of diminished growth (indicated by the arrows below the curve), which correspond to cell-division. From WARD ('95, p. 300). by the nuclear divisions and the accompanying formation of transverse septa.* The course of normal growth may now be studied 20 MM. 10 MM. * Attention may here be called to a phenomenon which has repeatedly been observed when a single growing mammal has been weighed at regular intervals. This is a sort of alternation of periods of unusually rapid growth with periods of diminished growth, the interval being a day or two. There is an irregu- 20 40 co so 100 larity in the length of FIG. 80. - Curve of length of shell of Lymnfea stagnalis these Periods. See SAINT- at intervals from hatching up to 85 days. From LOUP, '93 ; compare also SEMPER, Animal Life, p. 163. MINOT, '91, Table XIV. in INT.] ON NORMAL GROWTH 289 the case of certain selected, typical organisms. This may be most quickly done by the use of curves whose abscissae represent time intervals and whose ordinates represent size or weight. Figures 80, 81, and 82 are such curves. In all cases excepting that of guinea pig (in which the curve represents the growth of only a comparatively late developmental period, namely, from birth onward) the curves exhibit one characteristic shape. The absolute increments are not, however, shown directly by these curves. To obtain them one must transform the curves into others in which the successive ordinates shall represent the absolute incre- ment of weight over the last preceding. Under these » circumstances the absolute increments rapidly reach a maximum from which they decline to zero.* Why does the growth de- cline to zero ? The theory has been suggested f that there is a " certain impulse given at the time of im- pregnation which gradually fades out, so that from the beginning of the new growth there occurs a diminution in the rate of growth." The facts of a 5 10 MOS. FIG. 81. — The continuous line (a) represents the weights in fractions of a kilogramme attained by guinea pigs from birth until 12 months old. The broken line (6) rep- resents the daily percentage increments (% 's at the right) of the same guinea pigs up to 7 months. After MINOT ('91). * Another method of representing curves of growth has been proposed by Professor MINOT ('91, p. 148), who argues that for a given period the rate of growth should be expressed as the fraction of weight added during that period ; for, he says, "the increase in weight depends on two factors: first, upon the amount of body substance, or, in other words, of growing material present at a given time ; second, upon the rapidity with which that amount increases itself." Such a curve of percentage daily increments is given for the guinea pig in Fig. 81. Since, however, the greater part of the " body substance " at its period of greatest growth is not " growing material," as assumed, but water, the peculiar value of the curve of percentage increments is doubtful. t By MINOT, '91, p. 151. u 290 INTRODUCTION [Cii X 60 MM. BO 20 10 growth in the tip of the plant do not, however, support this theory, for the protoplasm at this point may go on growing for centuries, as we see in the case of trees. Some of the protoplasm at the tip is, how- ever, constantly falling back to form part of the stalk : this part soon ceases to grow, undergoing histological dif- ferentiation. The reason why the animal ceases at length to grow is the same as the reason why the differ- entiated tissue below the tip of the epicotyl ceases to grow — not because there is a nec- essary limit to growth force at a certain distance from impregnation, but because it is in the nature of the species that the individual should cease to grow at this point. The indefinite growth of this part, the limited growth of that, are as much group characters as any structural quality. To recapitulate briefly : Growth is increase in size, and may result from increment of either the formed substance through secretion, the plasma through assimilation, or the enchylema through imbibition. This increment may be either transitory or permanent ; the latter class chiefly concerns us here. Growth may be either diffused throughout the entire organism, or local, forming a factor of differentiation. In normal growth the increase is at first slow, then rapidly increases to a maxi- mum, and, finally, in most animals, diminishes to zero. This final cessation is a special quality of certain organisms, to be explained like structural qualities, on special grounds. DAYS 24 C 8 10 FIG. 82. — Curves of growth of Phaseolus multiflorus (continuous line) and Vicia faba (broken line). The ordinates rep- iresent actual lengths attained on the respective days by a bit of stem origi- nally 1 mm. long. After SACHS, Lect- ures on Plant Physiology. INT.] ON NORMAL GROWTH 13456 291 KG. 22 21 20 19 18 17 1C 15 14 13 12 11 10 9 8 7 6 5 4 3 o 1 n / / 22 21 20 10 18 17 10 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0 / s / / / s / s / / / / / / s A / / / / / / / / / | I / ^X | 01234567 FIG. 83. — Curve of growth of man. The ordinates represent weight in kilogrammes. The prenatal part of the curve is constructed from the data of FEHLING ('77) ; the postnatal part from QUETELET ('71) for the male. The curve of the first twelve months of postnatal life is adapted from GALTON ('84). LITERATURE BAUDRIMONT, A., and G. T. MARTIN SAIXT-ANGE, '51. Recherches anato- miques et physiologiques sur le developpement du foetus et en parti- culier sur 1'evolution embryonnaire des oiseaux et des batrachiens. Mem. presentes par divers savants k 1'Acad. des Sci. de 1'Inst. Nat. de France. XI, 469-692. 18 pis. 292 INTRODUCTION [Cn. X DRIESCII, H. '94. Analytische Theorie der organischen Entwicklung. Leip- zig. Engelmann, 185 pp. 1894. FEHLING, H. '77. Beitriige zur Physiologie der placentaren Stoffverkehrs. Arch. f. Gynakologie. XI, 523-557. FRANK, A. B. '92. Lehrbuch der Botanik nach dem gegeivwartigen Stand der VVissenschaft bearbeitet. I. Band. Leipzig. 1892. GALTON, F. '84. Life History Album. 172 pp. London. 1884. HUXLEY, T. H. '77. A Manual of the Anatomy of Invertebrated Animals. 698 pp. London. 1877. KRAUS, G. '79. Ueber die Wasservertheilung in der Pflanze. Festschr. z. Feier des Hundertjahrigen Bestehens d. Naturf. Ges. in Halle, pp. 187-257. LOEB, J. '92. Untersuchungen zur physiologisclien Morphologie der Thiere. II. Organbildung und Wachsthum. 82 pp. 2 Taf. Wiirzburg. 1892. MINOT, C. S. '91. Senescence and Rejuvenation. Jour, of Physiol. XII, 97-153. Plates 2-4. MULLER, N. J. C. '80. Handbuch der allgemeinen Botanik. I. Theil. Heidelberg. 1880. PFEFFER, W. '81. Pflanzenphysiologie. Engelmann. Leipzig. 2 Bde. 383 + 474 pp. POLL, R. '79. Untersuchungen liber die chemischen Veranderungen im Hiihnerei wahrend der Bebriitung. Landwirth. Versuchs-Stat. XXIII, 203-247. QUETELET, A. '71. Anthropometrie ou mesure des differentes facultes de 1'homme. 479 pp. 2 pis. Bruxelles and Paris. 1871. SACHS, J. '87. Vorlesungen iiber Pflanzenphysiologie. Leipzig. Engel- mann. 884 pp. 1887. SAINT-LOUP, R. '93. Sur la vitesse de croissance chez les Souris. Bull. Soc. Zool. de France. XVIII, 242-245. VERWORN, M. '95. Allgemeine Physiologie. 584 pp. Jena : Fischer. 1895. VINES, S. H. '86. Lectures on the Physiology of Plants. Cambridge [Eng.] Univ. Press. 710 pp. 1886. WARD, H. M. '95. (See Chapter XVII, Literature.) CHAPTER XI EFFECT OF CHEMICAL AGENTS UPON GROWTH WE shall consider this subject under two heads : (1) Effect upon the rate of growth, and (2) Effect upon the direction of growth. § 1. EFFECT OF CHEMICAL AGENTS UPON THE RATE OF GROWTH Organic growth, occurring in a material composed of water, plasma, and formed substance, consists in the increment of each of these components. The means and results of varying the quantity of water in the organism will be discussed in the next chapter ; here we are to consider the results of assimilation, including the production of formed substance. The scope of our work may be more precisely denned as the answer to the question, What role do the various chemical substances (exclud- ing water) play in the metabolic changes involved in growth ? There are two roles played by chemical substances in the body ; and, accordingly, we may distinguish two kinds of chemical agents having diverse effects upon growth. These agents - - foods, in the widest sense of the word — must supply the material — the atoms — from which the molecules of the plasma, or of its formed substance, are made up ; and, sec- ondly, they must supply energy for metabolism. Foods, then, yield to the organisms matter and motion ; they are hylogenic (plastic) and thermogenic (respiratory). These two offices of chemical agents in growth are only in certain cases exerted by distinct kinds of food. In the case of animals, sodium chloride and iron compounds are examples of wholly plastic foods, while the free oxygen taken into the body is chiefly thermogenic. In the case of the free oxygen, how- ever, it is quite probable that it is sometimes used in the con- struction of the molecule of active albumen which, according 293 294 EFFECT OF CHEMICAL AGENTS [Cn. XI to LOEW, constitutes the essential living substance. For exam- ple, oxygen performs this office in LOEW'S ('96, p. 39) hypoth- esis of the formation of albumen in plants from the nitroge- nous products which result from the action of an enzyme upon the reserve proteids, i.e. leucine. Thus leucine formaldehyd C6H13N02 + 7 0 = 2 C02 + H20 + 4 CH20 + NH3. formaldehyd asparagin 4 CH20 + 2 NH3+ 02 = C4H3N203+ 3 H20. Now since, as LOEW makes probable, asparagin is a stage in the production of albumen, the free oxygen molecule may be essential to the synthesis of the living substance. The facts indicate that the plastic and thermogenic functions of foods are inextricably intermingled -- that both are exhib- ited in the mutations of the living substance as well as in the respiratory processes. Thus, on the one hand, assimilation is accompanied not only by endothermic (energy-storing) but also by exothermic (energy-releasing) processes ; while, on the other hand, the partial oxidation of the food proteids may be a necessary step towards assimilation. It is because the net result is the storing or the release of energy that we may speak of any complex of processes as enthodermic or exothermic, and certain foods as plastic or thermogenic. The source of energy in organisms is not, however, solely food. Energy may likewise be derived directly from energy in the environment. This source is of greatest importance in the case of chlorophyllaceous organisms, but it is probably not of importance for them alone. For the heat and light of the environment aid, as we have seen (pp. 166-171, 222-225), various metabolic processes in all kinds of protoplasm. 1. The Materials of which Organisms are Composed. — To determine the sorts of materials which plastic food must supply to the body, it will be instructive to consider the proportional composition of the body out of water and dry substance, both organic and inorganic. Such data, gathered from various animals and plants, are given in the following table : — §1] UPON THE RATE OF GROWTH 295 TABLE XXV ANIMALS « S H s » K £ 3 O e g CD . * 5 s ej < < > Ofl SPECIES. $8 J^OP: ^£ H a SH *S> O S S5- 0 H g a ti AUTHORITY. > z 3 H >J X M 2 £ ^ •< c « r* "* >• a s a K. 0 f QQ I 1 00 Sponges, average .... 79.4 11.0 9.7 54.1 45.9 KKUKENBERG, 'SO Medusae : Rhizostoma cuvieri . . . 95.4 1.6 3.0 34.8 65.2 " Actiniaria : Anthea cereus 87.6 10.7 1.6 87.0 13.0 (t Actinia mesembryanth. 83.0 15.4 1.7 90.0 10.0 " Sagartia troglodytes . . 76.8 20.9 2.3 81.1 18.9 it Cerianthus membran. . 87.7 11.6 1.7 87.2 12.8 " Alcyoniurn palmatum . 84.3 10.8 4.9 68.8 31.2 " Asteroidea : Astercanthion glacialis . 82.3 14.1 3.6 79.6 20.4 " Annelida : Luinbricus complanatus 87.8 9.7 2.4 80.2 19.8 " Crustacea : Oniscus murarius .... 68.1 21.2 10.6 66.6 33.4 BEZOLD, '57 Squilla mantis 72.0 22.1 5.9 78.9 21.1 KRUKENBERG, 'SO Astacus fluviatilus . . . 74.1 16.8 9.1 64.9 35.1 BEZOLD, '57 Mollusca : Doris tuberculata .... 88.4 9.0 2.6 77.6 22.4 KRUKENBERG, 'SO Doriopsis limbata .... 86.5 12.4 1.1 91.9 8.1 11 Arion empiricorum . . . 86.8 10.1 3.1 76.5 23.5 BEZOLD, '57 Limax maximus .... 82.1 16.4 1.5 91.6 8.4 11 Ostrea virginiana .... 88.3 10.8 0.9 92.3 7.7 (without shell) Tunicata : Botryllus . . . 93.6 3.1 3.3 48.4 51.6 KRUKENBERG, 'SO Vertebrata : Cyprinus auratus .... 77.8 17.6 4.6 79.1 20.9 BEZOLD, '57 Triton igneus 80.2 16.1 3.7 81.1 18.9 1 1 Triton cristatus 79.6 17.0 3.4 82.9 17.1 1 1 Bombinator igneus . . . 77.3 19.4 3.3 85.2 14.8 1 1 Biifo cinereus . ... 79.2 14.8 6.0 71.1 28.9 ti Rana esculenta 82.7 14.2 3.0 82.2 17.8 11 Angius fra°ilis 55.0 32.1 12.9 71.5 28.5 11 Ijacerta viridis 71.4 23.2 5.4 81.3 18.7 u Sparrow 67.0 27.8 5.2 84.3 15.7 it Bat 67.5 27.4 5.0 85.2 14.8 11 Mouse 70.8 25.7 3.5 88.0 12.0 ti Man 65.7 29.6 4.7 86.3 13.7 VOLKMANN, '7-i 296 EFFECT OF CHEMICAL AGENTS [Cn. XI PLANTS ( >ats, in blossom .... 77.0 6.4 16.6 27.8 72.2 WOLFF, '65 Wheat, in blossom . . . 69.0 9.3 21.7 30.0 70.0 tc 1'ea vines, green .... 81.5 4.8 13.7 26.0 74.0 u a. Analysis of the Entire Organism. — We are now ready to consider the atomic composition of the dry substance of organ- isms. VOLKMANN ('74) has contributed data on this subject in the case of man. Thus the dry substance gives : — c 52.9% o 18.5% H 7.7% N 7-4% ASH 13.4% In the case of a plant (stems and leaves of dry clover) we have, according to JOHNSON : — C O H N S P REMAINING ASH 47.4% 37.8% 5.0% 2.1% 0.12% 0.30% 2.0% These two determinations, fairly typical of the higher plants and the higher animals respectively, run nearly parallel. The greatest difference is shown by the nitrogen, which is more than three times as abundant in animals as in plants. Oxygen, on the other hand, is more abundant in plants. The ash, in turn, must be further analyzed. The following table gives the percentage composition of the ash of various organisms : - TABLE XXVI ANIMAL. NEW-BORN DOG. MENHADEN (Fisn). OAT PLANT. AUTHORITY. BUNGB, '89. COOK, '68, p. 498. AVENDT (VINES, '86, p. 129). CaO 29.6 40.0 12.1 P205 39.4 35.8 8.8 K20 11.4 7.1 45.9 Cl 8.4 3.1 6.1 Na2O 10.6 4.7 2.32 MgO 1.82 3.1 4.12 Fe2O3 0.72 0.54 SiO2 6.1 17.2 S03 2.86 §1] UPON THE RATE OF GROWTH 297 It would be valuable to know the relative number of atoms of each of the metalloids and metals named in the preceding table. This may be determined in the following way : Find the proportion by weight of each metallic radical (excluding the oxygen) in the entire ash and divide this percentage by the molecular weight of the metal. The varying weights of the elements are thus eliminated, and a set of numbers which indi- cate relative abundance of atoms is obtained. We multiply these small fractions by 1000 for convenience. The results are as follows : — TABLE XXVII NEW-BOKN Doo. MENHADEN (Fisn). OAT PLANT. Ca 528 715 216 P 555 506 124 K 243 151 974 Cl 24 174 173 Na 343 150 60 Mg 45 77 114 Fe 9 — 6 Si — 101 287 S — — 36 These examples may suffice to show how diverse is the com- position of different organisms and how diverse therefore must be their requirements in the way of food to build up the adult body. The examples serve also to indicate what are the important elements for organisms. They appear to be the same for animals and plants, and are : — *Carbon *Calcium Sodium *Sulphur *0xygen *Potassium Chlorine Silicon *Hydrogen *Phosphorus *Magnesium *Iron *Mtrogen While this list does not pretend to exhaust the elements found in organisms, it contains those which are usually present. In the organism the atoms just named are, of course, found in combination. The carbon, oxygen, hydrogen, and nitrogen are contained in the organic matter of the organism - - the * Those elements which are starred (*) are essential to all organisms. 298 EFFECT OF CHEMICAL AGENTS [Cn. XI greater part of the entire dry matter. The relations of the remaining elements are largely obscure. Some of them form inorganic acids in the body, such as hydrochloric and sulphuric acids. Others form inorganic compounds deposited in the body as supporting or protective substances, such as the calcic phos- phate and calcic carbonate of bone and spicules and the silicic oxide of plants. But there can be little doubt that a large and highly important part of these elements is built up into organic molecules and in this position plays a weighty and varied part in metabolism and growth. As examples of the way in which the metals and metalloids occur in the organic molecule I may cite a few cases in which the molecular structure has been deter- mined more or less satisfactorily. Thus we have sulphur in albu- men, C72H112N18SO22 ; iron in hematin, C34H35N4FeO5 ; phos- phorus in lecithin, C42H84NPO9, and nuclein, C29H49N9P3O22, magnesium in chlorophyllan, and various halogens in the urates of sodium, calcium, and lithium. In discussing as we shall immediately the importance of each of these elements for the formation of the body we shall find additional facts con- cerning the importance of the metallic atoms in the organic molecules. There is good reason for believing that the pecul- iar properties of haemoglobin depend upon its iron and that the characteristic properties of nuclein depend largely upon its phosphorus and (as the later investigations indicate) its iron also. As our knowledge develops, the importance to many organic molcules in the living body of metallic or metalloid elements becomes clearer; the "ash" of the body is not some- thing accidental, secondary, or superfluous, but is an essential part of the organism. We must now consider the source of the various elements necessary to nutrition. Botanists early determined that C, H, and O enter the organism through the carbonic acid and water which green plants absorb. Concerning the source of nitrogen there has been less certainty ; it is generally believed to come from nitrates in the soil, but that matter will be considered later in more detail. Another source of the more characteris- tically organic elements, C, H, N, and O, is, without doubt, organic compounds of various sorts. Although it has long been known that insectivorous plants absorb the organic mat- § 1] UPON THE RATE OF GROWTH 299 ters they digest, still it is only recently that the fact that green plants in general can make use of organic compounds has been recognized. BOKORNY (n97 ) has lately brought together the evidence which makes this conclusion certain. It appears that in the presence of organic solutions some algre may grow for half a year in the absence of carbon dioxide ; and the potato plant may, even in the dark, store up starch in its tubers in the presence of rich organic food. Nitrogen may also be gained from amido-bodies ; thus, BASSLER ('87) found that his maize cultures grew better in asparagin, CO2H - CH(NH2) . CH2 • CO(NH2), than in potassium nitrate. Tims plants may gain their C, H, O, and N from either organic or inorganic sources. Non-chlorophyllaceous organisms, on the other hand, have long been known to gain their C, H, N, and O from organic •» compounds ; indeed, it has gen- P prallv bppn Viplipvprl fliat. tlipv f erally been believed that they can gain those elements from organic compounds only. Cer- tain observations, however, Fio.84.-a, Nitrosomonas europ»a(ni- throw doubt Upon the entire trite bacteria from Zurich) ; 6, Nitro- f . i • , i. - .-, somonas javensis (nitrite bacteria correctness of this belief ; these from JavaJ} . c> Nitrobacter (nitrate are especially the remarkable bacteria from Quito). Magnified ioso. results gained by WINOGRAD- After WINOGRADSKT, from FISCHBK, . . . Vorlesungen iiber Bakterien, 1897. SKY ( 90) from nitrifying bacte- ria (Fig. 84). This author found that the bacteria could grow in a mixture of inorganic salts free of organic matters. Solutions free from organic matter were prepared by the following means : The culture vessels were cleaned by boiling in them sulphuric acid and potassium permanganate. The water used in the cultures and in washing the vessels was twice distilled in vessels without joints of organic material — the second time with the addition of sulphuric acid and potassium permanganate. The magnesium sulphate and potassium phosphate, used as food, were calcined ; the calcium carbonate, used in excess, was likewise- calcined and saturated with carbon dioxide; finally, the ammonium sul- phate was especially prepared to avoid organic impurities. The culture flasks were plugged with calcined amianthus, not with cotton. The solu- tions were inoculated with a mere trace of the culture containing nitrifying 300 EFFECT OF CHEMICAL AGENTS [Cn. XI organisms. The cultures were then reared either in complete darkness or in dim light. The precautions taken to eliminate organic matters would seem to be complete; but those who know the difficulties of such experi- irients seem willing to admit the possibility "that exceedingly minute quan- tities of organic nitrogen and carbon are actually present " (JORDAN and RICHARDS, '91, p. 880). On the other hand, "exceedingly minute quanti- ties" of organic matter could hardly account for the vigorous growth of bac- teria ; and, in general, a priori objections cannot be permitted to overthrow results gained by the use of methods which are beyond reproach. The organisms placed in this water, deprived of the last traces of organic matter, developed rapidly, but not quite so rapidly as organisms placed in natural water to which the necessary salts had been added. Analysis showed that not only nitrates but also organic carbon compounds had been formed. Thus the careful experiments of WINOGRADSKY demonstrate what the less critical experiments of HER.EUS ('86) had already rendered probable, that a complete synthesis of organic matter may take place through the action of living beings and independently of the solar rays. These noteworthy observa- tions, then, obliterate the last sharp line of distinction between the nutritive processes of chlorophyllaceous and non-chloro- phyllaceous organisms. We may now state that the elements C, H, N, and O may be gained from complex organic food materials by all organisms, and from simple compounds, such as carbonic acids, ammonia, and water, by all chlorophyllaceous organisms, and, very probably, by certain non-chlorophylla- ceous ones also. The elements other than C, H, N, and O are probably gained by chlorophyllaceous and non-chlorophyllaceous organ- isms alike, from either inorganic or organic compounds con- taining the necessary elements ; although, possibly, animals make use of the metals more readily when they are in organic compounds. Suitable proportions of the different metals in a nutritive solution for green plants are given in the following tables, showing various standard solutions employed by differ- ent experimenters : — § 1] UPON THE RATE OF GROWTH 301 TABLE XXVIII NUTRITIVE SOLUTIONS FOR PHANEROGAMS SACHS' Solution GRAMMES. Distilled water 1,000.0 Potassium nitrate, KN03 1.0 Calcium sulphate, CaS04 0.5 Magnesium sulphate, MgS04 0.5 Calcium phosphate, CaHP04 0.5 Ferrous sulphate, FeS04 trace SCHIMPER'S Solution ('90) Distilled water 600.0 Calcium nitrate, Ca(N03)2 6.0 Potassium nitrate, KN03 1.5 Magnesium sulphate, MgS04 1.5 Neutral potassium phosphate, K3P04 . . . 1.5 Sodium chloride, NaCl 1.5 FRANK'S Solution Water, ^T distilled ; ff Berlin reservoir water . 1,000,000.0 Calcium nitrate, Ca(N03)2 267.4 Potassium chloride, KC1 121.5 Potassium phosphate, K3P04 101.9 Magnesium sulphate, MgS04 . 7 H20 .... 100.2 Ferric chloride, Fe,Cl6 trace The first differs from the others chiefly in the absence of chlo- rine. How fit ordinary waters may be to provide all these salts is shown by this analysis of the ordinary drinking water of Bos- ton (JOKDAN and RICHARDS, '91) : — TABLE XXIX PARTS BY WEIGHT OF INORGANIC MATTERS IN 1,000,000 PARTS OF POTABLE WATER Sulphuric acid 4.58 Chlorine 4.00 Alumina and oxide of iron 0.75 Calcium oxide 6.45 Magnesia 1-60 Potash 0.92 Soda 5.00 Silica 3.04 Nitrates . .... 0.25 302 EFFECT OF CHEMICAL AGENTS [Cn. XI All of the elements mentioned above, except phosphorus, appear in this list. Thus, ordinary drinking water is clearly well adapted to the nutrition of plants. t For algce, MOLISCH ('95) used the solution given in the fol- lowing table : — TABLE XXX NUTRITIVE SOLUTION FOR ALGM GRAMMES. Water 1,000.0 (NH4)2HP04 0.8 (KH2)P04 0.4 MgS04 0.4 FeS04 trace (2 drops of a 1% sol.) Here we note an absence of the calcium used in the solutions for phanerogams. Fungi likewise require a mixture of salts, according to NAGELI ('80, p. 354) and BENECKE ('95), in the following proportions : — TABLE XXXI NUTRITIVE SOLUTIONS FOR FDNGI NAGELI'S Solution GRAMMES. Water 1,000.0 (NH4)H2P04 .... 0.5 MgS04 + 7H20 ... 0.5 KC12 0.5 FeS04 0.05 Organic Compounds BENECKE'S Solution GRAMMES. Water 1,000.0 KH2P04 5.0 MgS04 + 7H,0 . . . 0.01 K2S04 0.5 NH4C1 10.0 FeS04 trace Glycerine 50.0 The solutions differ principally in the proportion of the salts. Finally, all animals likewise require a certain quantity of salts. What the proportions are can be shown in the case of young mammals, which live during part of their growing period exclusively upon milk. A wonderfully close relation exists, indeed, between the proportions of the mineral con- stituents of milk and of the young mammal before it has begun to suck. This is shown in the analyses made by BUNGE ('89) upon the milk of a dog and the body of its newly-born pup. §1] UPON THE RATE OF GROWTH 303 TABLE XXXII COMPARISON OF ASH IN NEW-BORN DOG AND IN THE MILK OF ITS MOTHER Asa. IN MILK.: % or Asir. IN NEW-BORN DOG: % OF ASH. P205 34.2 39.4 CaO 27.2 29.5 Cl 16.9 8.4 K20 15.0 11.4 Na2O 8.8 10.6 MgO 1.5 1.8 Fe203 0.12 0.72 The quantities in the two columns are fairly similar. The greatest proportional difference occurs in the case of iron, and this fact requires a special explanation, which is briefly this, that iron is more important for the rapidly growing embryonic stages than for later life. So likewise in the eggs of birds we find stored up all the mineral matters which are necessary for their development. Thus the yoke of the hen's egg contains phosphoric acid, lime, chlorine, potassa, soda, magnesia, iron oxide, and silica in the relative abundance indicated in this descending series. This series closely agrees with that given for milk. In the case of marine animals, also, certain inorganic elements are a necessary food. The following list of such elements is based upon the results of thorough experiments by HERBST ('97) upon developing eggs of sea-urchins, starfishes, hydroids, ctenophores, and tunicates ; the most favorable proportions of the elements were not, however, determined : calcium (in the form of carbonate, sulphate, or chloride), chlorine, iron (trace), magnesium, phosphorus (as Ca3P.2O8 or CaHPO4), potassium, sodium, and sulphur. Now all these elements are found in sea water, which in the Mediterranean Sea near Naples contains in 1000 parts of water * * After FORCHHAMMER ('61), p. 383. 304 EFFECT OF CHEMICAL AGENTS [Cn. XI 30.292 parts NaCl 3.240 « MgCl2 2.638 " MgSO, 1.605 « CaS04 0.779 " KC1 0.080 " silicic acid, calcium phosphate, and insolu- Total . 38.634 ble residue, including CaC03 and Fe203. From the foregoing tables it appears that mineral substances, and essentially the same mineral substances, are required by all organisms. The differences in this respect between the different organisms are slight. Thus while sodium is not included among the necessary elements of either chlorophyl- laceous plants or fungi, its occurrence in considerable quantity in milk, probably associated with chlorine as common salt, indi- cates that it is important for some animals. The important conclusion seems warranted that all organisms may use as hylogenic food any sort of compound which will furnish the appropriate elements, but that among animals, and to a less degree among fungi, organic combinations have the preference because they fulfil at the same time the thermogenic function. b. Detailed Account of the Various Elements used as Food. — We may now consider the part which each element plays in the growth of the body as a whole, reserving for the Fourth Part a consideration of the specific role which the element plays in organs of the body. We may, in general, consider first the share taken by the element in the constitution of the body, then the form in which the element gains access to the body, and finally what general effect it has upon the growth of the organism. Oxygen. — Excepting carbon, oxygen constitutes a greater part of the body, by weight, than any other element. Between 20% and 25% of the dry substance of the human body and between 35% and 45% of that of green plants is oxygen. The oxygen used as hylogenic food comes to land-animals from the organic compounds and the air consumed by the developing young ; the oxygen of water-animals may come from their food or from the oxygen dissolved in water ; finally, § 1] UPON THE RATE OF GROWTH 305 that of phanerogams is believed to be gained chiefly from the air at all parts of the body, roots as well as stems and leaves. Since oxygen is of great importance for metabolism (p. 2), it is naturally essential to growth. It is well known that the lower the oxygen tension is, the more slowly do seeds germinate and pass through their early stages of growth. Thus in an experiment performed by BERT ('78, pp. 848-853) barley grains which germinated and were reared at various pressures had in six days the following dry weights : — ATMOSPHERIC PRESSURE. RESULTING WEIGHT. 76 cm. mercury (normal atmosphere) 50 " (0.66 " ) 25 " (0.33 " ) 7 " (0.1 " ) 8.8 mg. 7.1 6.2 No growth On the contrary, as the oxygen pressure increases up to about twice the normal, growth is accelerated, but beyond that point growth is retarded until at about 7 atmospheres growth hardly occurs. In older seedlings, observations upon which have been made by WIELER ('83), JENTYS ('88), and JACCARD ('93), atmos- pheric pressure below the normal, even down to one-fourth or one-eighth of the normal, appears to induce accelerated growth ; likewise in pure oxygen at the atmospheric pressure growth is as rapid as or somewhat more rapid than in the ordinary at- mosphere. When, however, the oxygen tension is above the atmospheric pressure or below one-eighth of the normal, growth is retarded. It thus appears that an abnormal oxygen pressure may accelerate growth, and as we shall see later, the same effect is produced by other abnormal conditions. Among animals, also, the oxygen tension exerts an important effect upon growth. This is shown by the experiments of RAUBER ('84, pp. 57-65) upon the eggs of the frog. To get a variable atmospheric pressure RAUBER used champagne flasks in which were put the eggs and a little water. Through the air-tight cork of the inverted flask one end of a U-shaped glass tube of proper length and strength was passed. To the other end was fixed a funnel through which 306 EFFECT OF CHEMICAL AGENTS [Cn. XI mercury could be poured into the tube. The column of mercury produced the increased pressure in the flask, and the difference iu height of the mercury in the two arms of the tube was a measure of this pressure. To get a pressure below the normal a partial vacuum was produced by a water- pump and the flask was then sealed. We assume (with BERT, '78, p. 1153) that the chief effect of the variation in the atmospheric pressure was the variation in the amount of oxygen absorbed by the water. Pure oxygen was also used in the flask. At a pressure of three atmospheres no growth occurred. At a pressure of two atmospheres growth was slower than at the normal pressure. At three-fourths of an atmosphere also growth was retarded and at one-half an atmosphere death generally occurred. Thus the optimum condition of oxygen tension is near the normal for the atmosphere. The same thing is indicated in a qualitative way by the experiments of LOEB ('92). The stems of the hydroid Tubu- laria possess in ordinary water a high regenerative capacity, but in water deprived of oxygen by boiling no regeneration takes place, although, after the water has been aerated again by shaking, rapid growth occurs. Hydrogen. — This element forms, in its various compounds, between 5% and 10%, by weight, of the dry substance of organisms. How is it acquired? In the case of plants it is believed that it is taken into the organism as a constituent of water, which combines with carbon or carbonic acid in the plant, forming either starch directly or some other compound from which starch is later derived. Other possible sources of hydrogen are ammonia and its compounds, also the organic compounds absorbed. The hydrogen of fungi and animals has clearly been derived from the latter compounds alone. The effect of hydrogen gas upon growth seems to be merely that due to the replacement of oxygen; it has no active effect. Carbon is the largest constituent of dry organic matter, of which it forms between about 44% and 60%. In green plants it is obtained for the most part from the carbon dioxide or carbonic acid of the air which is absorbed by the leaves. Other sources of carbon for green plants are found in many organic compounds, such as urea, uric acid, hippuric acid, glycocoll, kreatin, guanin, asparagin, lucin, tyrosin, and acetamid. These afford nitrogen also. Certain green plants make use of animal §1] UPON THE RATE OF GROWTH 307 matter, e.g. insects, as food. Fungi and animals obtain their carbon from carbon compounds elaborated by plants. The indispensableness of carbon for the life of all organisms as well as for their growth requires no illustration. Nitrogen. - - Of the importance of nitrogen as a hylogenic food nothing more need be said than that it is essential to the formation of albumen. The ordinary form in which nitrogen is / — -^r fcX" £C— I ;%r '""' 1*1^. ^-i - f&imz r$^& FIG. 85. — Cultures of Sinapis alba in pure quartz sand, to which have been added equal amounts of a nutritive solution, but unequal quantities of 'nitrogen in the form of calcic nitrate, as follows: A, without nitrogen ; B, 0.1 gramme calcic nitrate in each vessel ; C, 0.(5 gramme calcic nitrate in each vessel. After a photo- graph. From FRANK ('92). obtained by the seedling is, as already stated (p. 298), that of the nitrates or ammonia in the soil (Fig. 85). Growing fungi gain it chiefly from nitrogenous organic compounds, but many fungi can make use of ammonium nitrate for this purpose. Growing animals gain nitrogen chiefly, if not exclusively, from organic compounds, especially albumen and allied substances. Free nitrogen is found wide-spread in nature. It forms about 79% of the volume of the air; penetrates into water, though in a smaller proportion than in the air, and even into the soil. Thus for organisms living in any of these media free 308 EFFECT OF CHEMICAL AGENTS [Cn. XI nitrogen is a possible food. Is it actually made use of ? This question has until recently usually been answered in the nega- tive, and this conclusion was the more readily accepted since nitrogen is a notoriously inert gas. Another view, however, has within recent years come to obtain. It developed in this wise. It had long been known that land which has lain fallow or on which clover or other leguminous crops have been reared is in a way strengthened as if fertilized, and it was also known that this strengthening is due to the fact that the soil acquires nitrogen from the air and " fixes " it in the form of nitrates. While the studies of PASTEUR on fermentation, since 1862, had paved the way for the interpretation of the process, the fact that it is due to organ- isms was first proved by SCHLOSING and MiixTZ ('77, '79). This proof they made by chloroforming a certain mass of nitri- fying earth and finding that the nitrifying process thereupon ceased. Later, they isolated a form of bacteria which had the nitrifying property. Their results were quickly confirmed and extended by others, notably BERTHELOT ('85, '92, etc.), in a long series of investigations, so that there is now no question that the nitrification of the earth is brought about by the activity of bacteria, perhaps of several species. The results thus gained were extended to some of the higher fungi by FRANK ('92, p. 596). Spores of Penicillium cladosporioides were sown in a nutritive solution of pure grape sugar and mineral salts, completely free of nitrogen, and in the presence of air which had been freed from ammonia by passing through sulphuric acid. The fungi grew, but not so rapidly as those in a solution containing nitrogenous compounds, and produced a mass of hyphpe. These hyphse, when tested, yielded ammonia. One such culture solution of 65 cc. volume became rilled with the fungus mass in ten months and yielded 0.0035 gramme of nitrogen, which must have been derived from the air. As similar results have been gained for other molds by BERTHELOT ('93) and for Aspergillus and Penicillium glau- cum by PURIEWITSCH ('95), we seem almost justified in pre- dicting that the capacity for assimilating free, atmospheric nitrogen will prove to be a characteristic of all fungi. Now if it is conceded that some organisms can make use of the nitrogen of the air, it is clear that the a priori objection to § 1] UPON THE RATE OF GROWTH 309 all organisms doing so, the objection, that is, on the ground of the inertness of nitrogen, is disposed of. The question is now merely one of fact. Do the algte, the higher plants, and the animals make nitrogenous compounds out of free atmospheric nitrogen ? Of these groups, the algae first claim our attention because of the inherent probability that they will act more like bacteria than any other group, since they pass over into the bacteria through such connecting forms as the Oscillariae and Nostocs. SCHLOSING and LAURENT ('92), FRANK ('93), KOCH and KOSSOWITSCH ('93), experimented with various species of Nos- toc, Oscillaria, Lyngbya, Tetraspora, Protococcus, Pleurococ- cus, Cystococcus, Ulothrix, etc., and found that, when supplied with a non-nitrogenous food, these plants produced nitrogenous compounds in the substratum, evidently gaining their nitrogen, from the previously purified air. Doubt exists, however, as to whether the free nitrogen is taken in directly by the algae or only after having been assimi- lated by bacteria associated with the algae and by them made into nitrogenous compounds. For the latter alternative speak the experiments of KOSSOWITSCH ('94) and MOLISCH ('95). KOSSOWITSCH, who with KOCH had previously found that algse gain nitrogen from the air when reared in impure cultures, now took special pains to get algal cultures free from bacteria. To this end he reared algse on potassium silicate permeated by a nutritive solution. The pure cultures thus gained were then grown in a sterilized tiask to which air, freed from ammonia, was admitted. The nutritive solution was made of salts free from nitrosren but containing1 the other essential elements. O O The results of this experiment were striking. The pure cult- ures of algae grew for a time, but then ceased. New non- nitrogenous food did not revive them, but the addition of nitrates caused rapid growth. Other evidence was gained from analyses. When the cult- ures of algae were pure there was no increase in the amount of nitrogen in the dry matter of the algse. But when bacteria were mingled with the algce, the quantity of nitrogen was increased. This is shown in the following typical analy- sis:— 310 EFFECT OF CHEMICAL AGENTS [Cn. XI MILLIGRAMMES OF N IN CULTUEE. AT THE BEGINNING. AT THE END. Cystococcus, pure culture 2.6 2.7 Cystococcus, with ( no sugar bacteria < . , I with sugar 2.6 2.6 3.1 8.1 These results, abundantly confirmed by MOLISCH ('95), seem to show that unless bacteria are present algre can build up free N into nitrogenous compounds only slowly, if at all.* While SCHLOSIXG and MUNTZ, BERTHELOT, and others were gaining an explanation of the enrichment of fallow ground, HELLRIEGEL ('86) and WILFAIITH were making their investi- gations upon the cause of the enriching action of leguminous crops, which led them to the conclusion that it was due to the iixation of nitrogen in plants with root-nodosities containing bacteria, the compounds thus formed by the symbiotic bacteria being directly assimilated by the plant. This conclusion has been repeatedly sustained for leguminous plants (Fig. 86). The question whether green phanerogamous plants other than legumes can make use of free atmospheric nitrogen is one which is still in hot debate, and it is not an easy one to answer. The calm conviction, based chiefly upon the excellent work of BOUSSINGAULT ('60), and LAWES, GILBERT, and PUGH ('61), that nitrogen is not thus obtained was rudely shaken by the paper of FRANK ('93) in which that author stated that he finds that nitrogen is removed from the air by non-leguminous plants — plants, moreover, which are not known to have bacteria living in their roots. Consequently he is of opinion that perhaps the fixation of free nitrogen may be carried on by any living plant cell. The difficulties in the solution of the problem may thus be set forth. It is recognized that all growing plants make use * One "crucial test" of FRANK still requires an explanation. If the free nitrogen is "fixed" by the aid of bacteria, the process should go on in the dark. Experiment shows that it does not do so. This difficulty KOSSOWITSCH over- comes by the assumption that the activities of the bacteria are dependent upon certain carbohydrates which the plant can afford them only in the light. §1] UPON THE RATE OF GROWTH 311 of nitrogen, but the nitrogen is usually obtained from the soil in the form of nitrates. It is feasible to determine by analysis the amount of nitrogen in the soil at the beginning of the ex- periment and the amount in the seed planted, and then after the experiment to determine the quantity in the soil and in the plant. But the difficulty comes in interpreting the results FIG. 86. — Parallel cultures of peas in the symbiotic and the non-symbiotic conditions. Each series comprises three culture vessels: B, the symbiotic plants in soil with- out nitrogen; C, the non-symbiotic plants in like soil; A, for comparison, non- symbiotic plants after addition of nitrate to the soil. After a photograph. (From FRANK, '92.) of the analyses. Thus the fact that the sum of nitrogen in the plant and the soil is greater at the end than at the beginning of the experiment does not prove that the plant has taken in free nitrogen ; for, as we have seen, the soil contains nitrifying bacteria, which intermediate between the free nitrogen of the air and the nitrates absorbed by the green plants. This diffi- 812 EFFECT OF CHEMICAL AGENTS [Cn. XI culty may be partly met by sterilizing the soil, but this prob- ably produces also other changes than the death of the bacteria. The most careful observations of the last five years have not supported FRANK'S generalization. Here and there there have been observers who, like LIEBSCHER ('92) and STOKLASA ('96), believe they have evidence for the direct assimilation of free nitrogen by the cells of phanerogams. But the evidence for the contrary opinion is predominant. The experiments which speak for the theory that green plants cannot directly make use of free nitrogen are not in unison. Thus, some indicate that in non-leguminous as well as leguminous plants nitrogen of the air is indirectly made use of through the action of the bacteria of the soil, while accord- ing to others it would seem not to be made use of at all. To the first class belong the experiments of PETERMANN ('91, '92, and '93) with barley, of NOBBE and HILTNER ('95) with mustard, oats, and buckwheat, and of PFEIFFER and FRANKE ('96) with mustard. To the second class belong the experi- ments of SCHLOSING and LAURENT ('92 and '92a) with various plants, DAY ('94) with barley, and AEBY ('96) with mustard. In the second class, however, the experimental con- ditions did not favor the development of the bacteria of the soil. The experiments of PETERMANN were, however, carried out upon a very large scale and under practically normal con- ditions and showed a marked difference between the acquisi- tion of nitrogen by barley growing in an unsterilized soil and in a sterilized one. Likewise NOBBE and HILTNER, and PFEIFFER and FRANKE, were careful to rear plants under normal conditions, so that their results are worthy of especial consideration. They agree that there is an acquisition of nitrogen by the -plant growing in normal soil and that this occurs only when the soil is unsterilized. We conclude then that probably phanerogams, like algae, can use the free nitro- gen of the air as food only after it has been converted into nitrates by the action of the nitrifying organisms — the bac- teria of the soil. Turning now to animals, whose nutrition is often compared with that of fungi, we find an absence of knowledge on the subject of the nutritiveness of free nitrogen. It is clear that § 1] UPON THE RATE OF GROWTH 313 land animals are in a favorable position for making use of it, since it penetrates with the oxygen to all parts of the body. It is found in the blood of mammals, but still as free nitrogen. Whether it eventually becomes fixed in the body is entirely unknown. The a priori argument against such fixation --the argument of inertness-- has lost much of its force since the discovery of the nitrifying organisms. Phosphorus. — This element is of constant occurrence in organisms. It has been found in yeast, mucors of the most diverse kinds, seeds, plant tissues, and animal tissues of all kinds. It is indeed one of the first among the mineral ele- ments of most organisms, as shown on pages 296 and 297= Of the dry substance of a fish, about 7% is phosphoric acid, and the dry substance of many seeds yields 15%. Phosphorus occurs in organisms as phosphoric acid compounds. Of these the most important organic compounds are nuclein, which has albuminoid properties, and occurs chiefly in all nuclei and in deutoplasm ; lecithin, of a fatty nature, occurring in yeast, plasmodium of JEthalium, seeds, milk, yolk of eggs, and nervous tissue ; and glycerin-phosphoric acid, a product of decomposition of lecithin and found wherever the latter occurs. As examples of inorganic salts we have the sodium and potas- sium phosphates of the blood and tissues and the calcium phos- phate deposited in bone. So important an element as phosphorus would naturally form an essential part of the food of all growing organisms. It is supplied at first in the germ, — seed or egg, --but later must come from without. Plants gain phosphorus from the disinte- grating rocks. Animals derive it chiefly from plants, directly or indirectly, or from the calcic phosphate of the sea; in mam- mals it is supplied to the developing young through the milk, which, as we have seen on page 303, is rich in phosphates. The abundance of phosphorus in the body indicates that its office in the organism is an important one, and its peculiar abundance in seeds, yolk, and milk indicates that it is especially important in growth. Experiments have been directed towards this point. The fact has long been established that plant growth cannot occur in the absence of phosphates, and this is true not only for green plants, but also for molds and yeast 314 EFFECT OF CHEMICAL AGENTS [Cn. XI (R.AULIN, '69). Embryos of various marine animals also will not develop in the absence of phosphorus (HERBST, '97). The peculiar importance of phosphorus for growth is also indicated by the fact that HARTIG and WEBER ('88) found more phos- phoric acid in the ash of the growing ends of the plant than in its fully differentiated parts. Again, LOEW ('91a) found that Spirogyra kept in a nutritive solution of salts in which phos- phorus alone was lacking, continued to live and, indeed, to form starch and albumen, but its cells did not grow or divide ; so that LOEW concludes that an important use of phosphorus is to nourish the cell-nucleus, and this fact is easily understood from the known importance of the phosphorus-containing nuclein of chromatin in cell-division. All these facts go to show that phosphorus is of prime importance in the growth of organisms. Arsenic, Antimony, Boron, and Bismuth, and their compounds, are apparently all injurious to organisms, so that sublethal solutions strong enough to be active, interfere with or even inhibit growth. Sulphur. - - This element is, without doubt, of constant oc- currence in organisms of all sorts, for it constitutes between 0.3% and 2% of all proteids, out of which organic bodies are largely composed. Sulphur forms between 0.6% and 1% of various (dry) organs of man, and nearly 1% of the dry sub- stance of a month-old seedling of Sinapis alba. In the growth of a plant (Sinapis alba) the amount of its sulphur increases from 0.02 ing. in the seed to 84.4mg. in the adult plant, and, indeed, it has been shown in one case (ARENDT, '59, for the oat plant) that the percentage of sul- phuric acid in the ash increases from 2.9 to 4.2 as the plant develops from a seedling to maturity. Since the sulphur goes chiefly into the composition of the living substance, its hylo- genic importance for growth is evident. The form in which sulphur may be taken into the body is very varied. It is well known that green plants usually absorb it in the form of sulphates, especially sulphates of potassium, calcium, and magnesium ; marine animals take it chiefly from the calcic sulphate of sea water, and land animals gain it largely from organic sulphur compounds produced in §1] UPON THE RATE OF GROWTH 315 plants. Whether non-chlorophyllaceous plants can make use of it has been much discussed, and is worthy of further inves- tigation. WINOGRADSKY ('88, '89) has, indeed, shown that the sulpho-bacteria store up pure sulphur from sulphuretted hydrogen (H2S), and PRESCH ('90) has concluded, as a result of feeding himself with pure sulphur and analyzing the sulphur of the urine, that about one-fourth of the sulphur taken into the body in an elementary form becomes built up into organic molecules. Recently HERBST ('97) has shown that embryos lays No 3 days FIG. 87. — Right, Larva of Echinus reared for 72 hours in water containing all the necessary salts ; the sulphur being in the form of 0.26% magnesium sulphate and 0.1% calcic sulphate, and the phosphate in the form of CaHPO4. The larva is normal. Left, Larva reared for fi8 hours in a solution containing no sulphur nor CaCl2. The typical larva without sulphur, but with CaC1.2, differs from this chiefly in the presence of rudimentary spicules ; kr, spicule-formiug cells. (From HERBST, '97.) of sea-urchins and other marine animals do not develop in the absence of sulphur (Fig. 87). These facts indicate that not green plants merely, but all organisms, can use elementary sulphur as a hylogenic food. Tlie Halogens, chlorine, bromine, iodine, and fluorine, are elements which are closely similar in their chemical reactions 316 EFFECT OF CHEMICAL AGENTS [Cn. XI outside of organisms, and carry a part of that peculiarity with them into organisms. All of them are of physiological interest ; but so far as we know chlorine and iodine are most important. Chlorine. - -This element is probably of constant occurrence in organisms, and indeed in rather large quantities, as Table XXVII, p. 297, shows. It is not strange that it should be so, since this element is very widely distributed in all waters. This very fact, however, renders it possible that chlorine is merely an accidental constituent of organisms, being unessential to growth, and precisely this conclusion has been maintained. Of green plants it was early asserted that growth occurs as readily in solutions containing no chlorine as in ordinary potable water, but of late years evidence opposed to this view has been accumulating. Thus, while it appears that growth may occur in the absence of chlorine, ASCHOFF ('90) and others have found that growth is not so vigorous as in solutions containing this element. It has been thought that chlorine makes an advantageous combination with the potassium neces- sary for the plant, but the true significance of the favorable properties of chlorine remains undetermined. Turning to animals, we find that chlorine occurs in the milk of mammals, and is therefore probably necessary to them. According to HERBST ('97, p. 709) it is a necessary food for young echinoids. Certainly in the form of sodium chloride it is an essential food of the higher animals, and some of them, especially the herbivora, require large quantities of it, as " salt- licks" testify. The function of chlorine is not altogether plain. It must be used in the production of the hydrochloric acid of the digestive juices. In addition, sodium chloride is found widely distributed in the tissues. It has often been asserted that it goes through the tissues unchanged ; but NENCKI and SCHOUMOW-SIMAXOWSKY ('94) believe that it is probably disintegrated and the chlorine built up into organic molecules. Bromine. - - The normal occurrence of traces of this element has lately been demonstrated by HOTTER ('90) for a great variety of plants. It occurs most abundantly in various fruits, apple, pear, peach, and also in the leaves and twigs of many plants, as well as in various berries. Its normal occur- § 1] UPON THE RATE OF GROWTH 317 rence permits us to believe that it has an importance, if not for growth, at least for development ; there is, however, no direct evidence that it is generally necessary to organisms. Since it is closely allied to chlorine, the question whether it may replace chlorine in growth has been tested. NENCKI and SCHOUMOW- SIMANOWSKY ('94) have found that in the higher animals the bromides can replace the chlorides to a limited extent, but are clearly less advantageous. Altogether the importance of bromine for growth is slight. Iodine. — This element is of wide-spread occurrence in organ- isms, probably as a constituent of organic molecules, for it is found in plants, especially in some species of Fucus and Lami- naria (cf. ESCHLE, '97); in invertebrates, especially in sponges and the stem of Gorgonia; and in vertebrates, especially in mammals, where it has recently been shown to be most im- portant for growth. It has long been known that mammals which have been deprived of the thyroid gland acquire a weak condition of body known as myxcedema. This effect has been accounted for by the loss, to the organism, of a substance elaborated in the thyroid gland ; for when the thyroid gland, or a docoction of it, is fed to the animal it recovers to a certain extent its normal condition. The nature of this substance has been investigated by BAUMANN and Roos ('96), who find that it is a compound of iodine — thyroiodine ; for when thyro- iodine is fed to the myxcedema patient, the same favorable result ensues as follows feeding upon the gland. Fluorine is found rather widely distributed among verte- brates in very minute quantities. It forms about 1.3% of the total ash of bone. It is present also in the hen's egg, being more abundant in the yolk than in the albumen (TAMMANN, '88). Since it is chiefly found in the body as a constituent of bone, possibly in the form of the mineral apatite, Ca10F2 (PO4)6, it may very well be that its chief importance is in the consti- tution of this formed substance. According to BRANDL and TAPPEINER ('92) the normal amount in the body may be greatly increased by feeding small quantities of sodium fluoride during a long period. Altogether, we have no reason for thinking that fluorine is essential to the growth of organisms in general. 318 EFFECT OF CHEMICAL AGENTS [Cn. XI Salts of Alkalis. - - This group contains one or two of the most important elements of which organisms are composed. The elements are only slightly replaceable by one another. Lithium seems normally to have little importance for growth, although slight traces of it have been found spectroscopically in the blood (HOPPE-SEYLER, '81, p. 453J). Sodium is probably of constant occurrence in organisms. The quantity of it in the body is widely different in different species ; and as our table on page 297 shows, it may vary in its position from one of the most abundant of the elements to one of the least. Whereas sodium is not essential to the nutrition of plants, it is necessary in the form of sodium chloride to certain higher animals. Sodium is also found in all the tissues of the body, and perhaps enters into the albuminoid molecule (NENCKI, '94). The fact that, as we have seen on page 303, soda is a prominent constituent of milk, indicates its impor- tance in the growth of mammals. Finally, HEEBST ('97) has been able to demonstrate its indispensability for the growth of marine animals. Potassium constitutes an important part of all organisms. It forms the largest part of the ash of nearly all phanerogams (see page 297) and is markedly abundant in yeast and in many invertebrates. It occurs in the body as chloride and as sul- phate, and probably also in combination with albumen and various organic acids ( VINES, p. 134). That it is an essential and unreplaceable food for all organ- isms is indicated by trustworthy experiments upon fungi, algae, phanerogams, invertebrates, and vertebrates. RAULIN ('69) first showed that only culture-solutions containing this metal permit the growth of fungi. The experiments of BENECKE ('96) upon the growth of certain molds, e.g. Aspergillus, are worth citing in detail as an illustration of the method. He sowed spores in culture-vessels made of a glass which analysis had shown to be free from potassium. Two of these vessels contained a nutri- tive aqueous solution consisting of 3% cane sugar and 0.25% magnesium sulphate. To the one of these solutions was added 1.2% potassium nitrate, and 0.26% potassium phosphate; and to the other 1% sodium nitrate and 0.5% sodium phosphate. After four days the first culture was covered by a sheet of fungi and in five weeks the whole surface was black with spores ; in § 1] UPON THE RATE OF GROWTH 319 the second culture, on the other hand, little growth had- occurred even at the end of five weeks. The crop from each of the cultures was then harvested and its dry weight determined. That of the first culture was 0.3 gramme, that of the second 0.03 gramme. By a somewhat similar procedure MOLISCH ('95) has been able to show that potassium is essential to the growth of algae ; and NOBBE and others ('71) that it is necessary for the growth of phanerogams. The experiments upon animals have been rather less satisfac- tory on account of the greater difficulties in experimentation. FIG. 88. — Two embryos of Sphserechinus from parallel cultures, a, reared in a solu- tion containing all the necessary salts ; embryo normal, b, reared in the same solution, but without potassium; blastula wall abnormally dense, and embryo of small size. (From HEEBST, '97.) Nevertheless we have some trustworthy data upon this matter. On the side of the invertebrates we have the experiments of LOEB ('92), who placed a hydroid, Tubularia, in fresh water to which solutions of various combinations of the salts found in sea water were added so as to give approximately the nor- mal osmotic effect. Under these circumstances regeneration of the hydroids occurred only in the solutions containing potassium. Again, HERBST ('97) finds potassium essential to the growth of embryos of echinoids (Fig. 88). Thus the potassium compounds seem necessary to the processes upon which growth depends. On the side of vertebrates we have the somewhat inconclusive results of KEMMERICH ('09), who fed two young dogs of the same age and of nearly the same size upon meat boiled until a large portion of its salts was extracted. To the food of one dog he added only sodium chlo- 320 EFFECT OF CHEMICAL AGENTS [Cn. XI ride ; to that of the other, both sodium chloride and potassium salts. After 26 days the dog fed on the potassium salts as well as the sodium chloride was about 30% heavier than the other, and this difference was reasonably ascribed to the beneficial effects of the potassium. The particular part which potassium takes in growth is still somewhat doubtful. The recent observations of COPELAND ('97) with seedlings reared in water cultures in which sodium replaces potassium, lead him to the conclusion that potassium is necessary to turgescence. The potassium salts become lodged in the cell-sap, as analysis shows, and are therefore, perhaps, one of the principal causes of imbibition. Rubidium and Ccesium. — These rather rare metals are important only because of the fact that they may replace potassium in the growth of some fungi. WINOGBADSKY ('84) recognized this to be the case with rubidium in yeast cultures. NAGELI ('80) found that in molds rubidium and caesium gave even greater growth of dry substance than potassium cultures, a conclusion abundantly confirmed by the studies of BENECKE ('95). Whatever, therefore, is the significance of potassium for growth, rubidium and caesium seem to have the same significance. Earthy Metals. - - Under this head are included the elements calcium, strontium, and barium, which form compounds having closely similar molecular structure and properties. We might therefore expect them to be in some degree mutually replace- able. Calcium shares with potassium and phosphorus the position of one of the most abundant elements of organisms. It is found in every tissue and seems to be a constant accompaniment of protoplasm. Its constant occurrence is indicative of its importance as food for both plants and animals. It is apparently indispensa- ble and unreplaceable by any other element in phanerogams ; but MOLISCH ('94) finds that growth can take place in certain molds (Penicillium, Aspergillus) as well in its absence as in its presence, and jn some algse, but not in all (MOLISCH, '95), calcium is apparently of little importance. In animals, calcium can be replaced by other elements only to a very slight extent. § 1] UPON THE RATE OF GROWTH 321 Its absence from the water in which echinoid larvae are developing produces dwarfs. In vertebrates, owing to the need of this metal for the skeleton, large quantities of calcium are taken in by the growing organism. In normal growth, then, the food of animals and phanerogams must contain calcium. Strontium, although closely allied to calcium, is rather rarely found in considerable amount in organisms. In certain plants,, as e.g. Fucus, it is constantly present. It can be stored up in the animal organism when supplied abundantly in the food, but in general is believed to be of little importance for growth. Manganese, likewise, is not of general importance, although it is found abundantly in certain plants, e.g. Trapa natans, Quercus robur, and Castanea vesca, and in the excretory organ of the mollusc Pinna squamosa (KRTJKENBERG, '78). Iron. - - This most abundant of the heavy metals occurs so frequently in organic substances, especially those related to the compounds found in protoplasm, that it is little wonder that iron has been found to be an essential ingredient of all proto- plasm, hardly less important than oxygen itself. Although its occurrence has been demonstrated, especially by SCHNEIDER ('89), in all the large groups of animals, its amount in any individual or organ is always very small. Iron oxide (Fe2O3) forms between 1% and 2% of the ash of muscle, about 5% of the ash of blood, and rarely rises to 5% in plants. It is found in the body, for the most part, as in yolk (BuNGE, '85), in organic union. It occurs thus in the chro- matin of the nucleus of all cells (MACALLUM, '92, '94 ; SCHNEIDER, '95). That chromatin contains iron has been demonstrated by MACALLTJJT ('91) by means of a microchemical method whose general validity has never,, so far as I know, been questioned. It was shown by BUNGE, in 1885, that when tissue is put into ammonium sulphide the iron, even in an organic molecule, is separated from its compound, and uniting with the sulphur forms ferrous sulphide (FeS). This ferrous sulphide appears in the proto- plasm as green granules (black in large quantity) ; and the fact that these granules appear abundantly in the nucleus shows that iron is especially abundant there. Additional evidence is given if after several weeks the chromatin loses its stained appearance and becomes rusty. This result is interpreted as due to the formation of ferric oxide, Fe2O3; for when the 322 EFFECT OF CHEMICAL AGENTS [Cn. XI nuclei are subjected to hydrochloric acid and potassium ferricyanide they immediately assume a deep azure-blue color, clearly due to the formation of "Prussian blue" or Fe4(Fe C6X6)r This series of reactions can only be explained on the ground that there is iron in the nucleus. Iron has shown itself to be essential to the growth of all organisms. Its importance for growth is indicated by its rela- tive abundance in the yolk of birds' eggs, and by the fact of its occurrence in larger proportion in a mammal just born than JV'o We FIG. 89. — Echinus larvae from parallel cultures, all 5£ days old. «, reared in a solu- tion containing all salts, including iron as FeCl3 ; b and c, from solutions contain- ing all salts excepting iron. (From HERBST, '97.) in later stages. When excluded from a nutritive solution which is otherwise complete, growth is imperfect (Fig. 89). This may be associated with the facts that in plants the chloro- phyll granules are not developed in its absence, that in the higher animals haemoglobin cannot be formed, and that the chromatic substance of all cells requires it. The question in what form iron is absorbed by the organism has been the subject of an extensive discussion. Although doses of metallic iron have long been used wit?h favorable § 1J UPON THE RATE OF GROWTH 323 results in medical practice, BUNGE ('85) concluded that only organic iron compounds are assimilable. The studies of KUNKEL ('91 and '95) and WOLTEKING ('95) have, however, shown in the clearest manner that inorganic iron is assimilated, stored in the liver, and made use of in the construction of such organic compounds as the haemoglobin of the blood. At the same time, as SOCIN ('91) and others have shown, iron may be gained from organic compounds. Apparently, iron com- pounds of any sort may be made use of by the organism. Magnesium, — This metal is closely associated with calcium, the two usually occurring together in organisms just as they do in the inorganic world. As the table on page 297 shows, magnesium is of constant occurrence among organisms, although never present in great quantity. The magnesium is gained by green plants at the same time with the calcium from mineral salts (chiefly magnesium carbonate and sulphate) derived from disintegrating rocks. Fungi can also make direct use of the salts of magnesium (excepting always the chloride) ; and ani- mals, although no doubt chiefly gaining their magnesium from plants or the waters in which they live, may make use of min- eral salts, especially in the construction of the mineral parts of various formed substances, such as those of bone. So constant an element is presumably necessary to the organ- ism, and numerous observations make it quite certain that this is true for green plants in general. Indeed, the fact that mag- nesium occurs in chlorophyllan of chlorophyll makes it prob- able that it functions in assimilation. Concerning its iiidis- pensableness for fungi there can likewise be no doubt, since BENKCKE'S ('95, p. 519) experiments show it to be replaceable neither by calcium, barium, or strontium. While some investi- gators, like HOPPE-SEYLER, believed it to have little signifi- cance for the animal body, — to be an accidental accompaniment of calcium, — later study has shown that it is of importance for regeneration of hydroids (LoEB, '92), and, according to HERBST ('97), a constituent of the sea water which is necessary to the normal growth of various marine larvse. Also its occur- rence, although slight, in milk, as well as its very abundant occurrence in seeds, indicate that it plays an important, if an unknown, part in growth. 324 EFFECT OF CHEMICAL AGENTS [Cn. XI Silicon. - - This element is of wide occurrence among organ- isms. In many plants, especially the grains and grasses, it is exceeded in abundance only by potassium. Among the lower organisms whole groups, e.g. diatoms, Radiolaria, and glass sponges, are characterized by the great amount of silica made use of. Even in vertebrates it is found wide-spread in the blood, gall, bones, feathers, and hair. The silicon required for the body is gained by plants and lower organisms from the soluble silicates or silicic acid of the soil and waters ; by verte- brates, probably from plants. Although SACHS ('87, p. 271) was able in 1862 to show that growth even of maize (about one-third of whose ash is silica) continues in the absence of silicon, yet some grains do better, according to WOLFF ('81), when that element is abundant. It is significant, likewise, that, as POLECK ('50) found, 1% of the ash in the albumen of the hen's egg is silicon. Copper. - - Brief mention may be made of the fact that this metal occurs in a great variety of organisms, but usually in minute quantity. It occurs as a physiologically important con- stituent of the hsemocyanine of the blood of the squid (FRED- ERICQ, '78, p. 721), of crabs and lobsters, and of certain gas- tropods and lamellibranchs (FREDERTCQ, '79). 2. The Organic Food used by Organisms in Growth. - - All organisms may use organic compounds as food ; all organisms which contain no chlorophyll, certain bacteria excepted, must do so. This organic food may consist of solutions of definite composition or it may consist of solid masses of plant and animal tissue composed of varied and indeterminate kinds of organic molecules. The former are made use of chiefly by plants ; the latter, by the higher animals. This distinction is, however, not a necessary and constant one, for on the one hand insectivorous plants and many fungi live upon solid masses which they digest, and on the other hand some of the Protozoa can be fed upon known solutions, and doubtless some of the higher animals could be likewise fed, although few experiments seem to have been made in this direction. Even in methods of nutrition there is no sharp line to be drawn between the different groups of organisms. a. Fungi. --Our knowledge of the effect of known chemi- § 1] UPON THE RATE OF GROWTH 325 cal compounds used as food has been much more advanced by studies upon this group than upon any other. Yeast and bacteria have been especially investigated, but valuable results have been obtained upon the higher fungi also. Con- sidering all these results together, it appears that the nutritive value of an organic compound is perhaps chiefly determined by its assimilability; that is, the less the energy required to attack and transform the compound by the various chemical means at hand, the more favorable it is as a food. This assimilability depends in turn upon the molecular structure - - upon a certain molecular instability or lability - - upon the possession of that quality which is found in its extreme expression in many organic poisons. As LOEAV ('91, p. 761) has expressed it: Poison action, like nutritive action, is a relative conception. An indifferent body can become, by entrance of one atom-group, a nutritive substance ; by entrance of an additional atom group, a poison. While a certain lability — that is, a certain degree of ease of decomposition — is a condition of the nutritive quality of a substance, a slight increase of this lability can give it a poisonous character, especially when the loosely arranged atoms can link into that atom-grouping upon which the vital movement in the protoplasm depends. Thus methan is indifferent for bacteria, methylalcohol is a nutritive sub- stance, formaldehyd is a poison, and its combination with sodic sulphate again a nutritive material.* Additional laws of nutritive value which hold true in many cases are as follows : The assimilable carbon compounds con- tain the group CH2 or at least CH. Under otherwise similar conditions, compounds with one carbon atom are assimilated with great difficulty (methylamin) or not at all (formic acid, chloral) ; and, in general, but with important exceptions in the case of certain classes of substances, the assimilability increases as the number of carbon atoms in the molecule increases. The * The graphic formulas of these substances are : — OH OH CH4 CH3-OH CH2 CH2 OH S03Na. methan. methylalcohol. formaldehyd. formaldehyd-sodic sulphate. 326 EFFECT OF CHEMICAL AGENTS [Cn. XI radical HO- is usually easily released, consequently we find compounds containing this radical in general more assimilable than allied compounds in which the HO- is replaced by H. Especially is this true when the HO- is joined with radicals containing carbon and hydrogen atoms. For example, foods with the radical -CH2 • OH are more nutritive than those with -CH3. Hydroxylized acids are better food for bacteria than non-hydroxylized - -lactic acid, C3H6O3, is better than pro- pionic acid, C3H6O2. It is, perhaps, a special case under this rule that multivalent alcohols — i.e. those containing several HO groups — are better foods than the univalent ones; for instance, glycerine, CH2OH-CHOH-CH2OH, is better than propylalcohol, CH3 • CH2 • CH2OH. Finally, the entrance of the extremely unstable aldehyd (-CH:O) and keton (-CO-) groups increases the nutritive capacity of the food ; for example, glucose, CH2OH • (CH • OH)4CHO, or fructose, CH2OH . (CH . OH)3 • CO . CH2OH, is better than mannit, CH2OH . (CH • OH)4- CH2OH. But all substances containing the group CHOH are good foods, since this compound can be used directly in the construction of carbohydrates, and eventu- ally of albumen. As an example of the application of these general principles may be given this series of substances arranged in the order of their decreasing nutritive value for yeast and molds (NAGELI and LOEW, '80) : 1, sugars ; 2, mannit, glycerine, the carbon groups in leucin ; 3, tartaric acid, citric acid, succinic acid, the carbon groups in asparagin ; 4, acetic acid, ethylalcohol, kinic acid; 5, benzoic acid, salicylic acid, the carbon groups in pro- pylamine; 6, the carbon groups in methylamin, phenol. In conclusion may be mentioned a food for bacteria which, although inorganic, resembles organic compounds in that it may serve as a source of energy. This is the hydrogen disul- phicle employed by the sulphur bacteria and allied forms (WlNOGRADSKY, '87, '89). b. Green Plants. — It has already been shown that organic compounds can be assimilated by green plants. The experi- ments which have shown this have been made upon both algse and phanerogams, especially by BOKORNY, LOEW, A. MEYER, and LAURENT. It appears that, in the absence of carbon § 1] UPON THE RATE OF GROWTH 327 dioxide, Spirogyra may form starch from methylalcohol, for- maldehyd, glycol, methylal, acetylethylesteracetat, acetic acid, lactic acid, butyric acid, succinic acid, phenol, asparaginic acid, citric acid, acid calcium tart rate, ammonium tartrate, calcium bimalate, glycocoll, tyrosin, leucin, urea, hydantoin, kreatin, and peptones.* Phanerogams form starch from glycerine, cane sugar, levulose, dextrose, lactose, maltose, mannit, dulcit, and lecithin. While daylight favors assimilation it can be in some cases dispensed with. Thus the potato plant can accumulate starch in the dark when glycerine is used as food. An attempt to gain a deeper insight into the conditions of formation of albumen from organic matter has been made by HANSTEEN ('96), who reared Lemna in solutions of grape sugar or cane sugar, on the one hand, and amids, like asparagiu, urea, glycocoll, leucin, alanin, or kreatin, on the other; also on grape sugar and inorganic nitrogenous bodies such as potassium nitrate, sodium nitrate, ammonium sulphide, and ammonium sulphate. As a result of feeding on grape sugar alone at 20° C. during 24 hours, much starch was stored in the cells ; when grape sugar and inorganic nitrogenous bodies were combined little starch and much albumen were produced. Much albumen was also gained when the nutritive solution contained cane sugar and urea, or asparagin and ammonium chloride, or asparagin and ammonium sulphate. The production of albu- men in green plants is favored by nitrogenous organic com- pounds. c. Animals. — These organisms are distinguished from the foregoing by an immense requirement of energy for their muscular processes, much of which is continually lost to the organism in the form of motion communicated to the environ- ment. On the other hand, growth is generally slower than in plants. Consequently in animal nutrition thermogenic foods are the more important and the nutritive processes are prevail- ingly exothermic. The plastic processes are the less striking ; nevertheless, it is they which chiefly concern us in our study of growth. Among the organic compounds ingested, carbohydrates are * The reagents were employed in about 0.1% solution, and whenever acid were neutralized with lime-water. 328 EFFECT OF CHEMICAL AGENTS [Cn. XI believed to have little importance as plastic foods --we have chiefly to consider the use of the complex fats, albuminoids, and other organic compounds. We can make little use of the extensive tables of calorific properties of foods which, however important for determining capacity for supplying energy, afford little insight into the plastic properties of the food- its importance for the growth of dry substance or the imbi- bition of water. The difficulties in the way of feeding animals upon known nutritive solutions are great, both because solutions are not their normal food, and because, in the case of water organisms, the bacteria introduced with the animals thrive better than they. Consequently the observations on nutritive compounds for animals are meagre. It will be best to consider them under the types upon which they have been made. Amoeba. - -We owe important studies on the foods of Amoeba to the fact that some species have a pathogenic importance. Cultures of them have therefore been made by bacterio- logical methods. It is found that various, even innocuous kinds, will grow upon egg albumen in distilled or phenylated water kept at about 15° C. (CftiVELLi et MAGGI, '70, '71 ; MONTI, '95), upon agar-agar sheets from which the soluble substances have been removed by repeated washing in distilled water (BEYERINCK, '96), upon " Fucus [Chondrus?] crispus" (CELLI, '96), or upon slices of potato (GoniNi, '96). It is thus clear that, in addition to salts, Amoeba needs only a very simple nitrogenous diet. It is, however, uncertain whether the amceba feeds directly from the organic food stuff, or indi- rectly upon the bacteria which grow upon the food supplied. Infusoria.-- A. beginning has been made in the study of this group by FIG. 90. — Poiytoma nveila, OGATA ('93), who reared pure cultures a flagellate infusorian. Qf ^ flagellate Poiytoma UVella (Fig. (From VERWORN, 95.) rt J . \.e 90) on plates 01 nutrient gelatine (which is extremely rich in protein) and also upon a medium composed of 500 ccm. meat bouillon, 12.5 grammes grape sugar, and 250 grammes of a Japanese mixture of algte called " riori," derived mostly from the species Porphyra vulgaris. §1] UPON THE RATE OF GROWTH 329 The mixture was cooked, neutralized, filtered, sterilized, and infected with the flagellates, which had been isolated by means of capillary tubes. Here again growth was supported by simple, definite foods. Amphibia. - - It is a great leap from Protozoa to vertebrates, but precise feeding experiments are almost lacking in the invertebrate Metazoa. In the present group come the pioneer experiments of YUNG ('83). This author fed a number of tadpoles derived from the same batch of eggs upon foods of various kinds in unlimited quantity and under otherwise similar conditions. After forty-two days the size of the tad- poles in each lot was measured and the following results were obtained : — TABLE XXXIII RESULTS OF FEEDING TADPOLES ON VARIOUS SUBSTANCES No. OF VESSEL. l o 3 4 5 6 \ KINDS OF I FOOD. I 1 I AQUATIC PLANTS : ANACHARIB AND SPIROGYRA. ALBUMINOUS EGG ENVE- LOI'E OP FROG. PIECES OP YOLK OP HEN'S EGG. ALBUMEN OF HEN'S EGG. PIECES OF FISH FLESII. PIECES OF BEEP FLESH. Length of tadpole 18.3 23.2 26.0 33.0 38.0 43.5 Breadth of tadpole 4.2 5.0 5.8 6.6 8.8 9.2 It will be observed that the importance for growth was not proportional to the calorific properties of the respective foods, for the yolk of the hen's egg has about 40% higher fuel value than dry egg albumen or dry flesh. The least growth occurred with a plant food which is relatively rich in carbohydrates, and has some protein and little fat ; the third greatest growth occurred with the yolk, which has more fat than protein ; next comes egg albumen, with more protein than fat ; and, finally, fish and beef flesh, characterized by their high percentage of nitrogenous matter. The tadpole grows fastest on a highly nitrogenous diet. 330 EFFECT OF CHEMICAL AGENTS [Cn. XI Additional experiments upon the frog's egg have been made by D ANILE WSKY ('95), who found that such eggs placed in water containing -15^0 of lecithin gained in 54 days 300% greater weight than those reared in pure water. The author believes, however, that this small quantity cannot act in a directly nutritive manner but, rather, that it favors in some way the assimilation of food. Mammals. - - The requirements of agriculture have led to numberless experiments upon the feeding of domesticated mam- mals. Yet they are for the most part of little value for our purpose. A few of the better class of experiments from our point of view may be given, together with such conclusions as they permit. Years ago, LAWES and GILBERT ('53), from extensive feed- ings of sheep and pigs, upon diverse foods, reached the conclu- sion that those "apparently grew more where, with no defi- ciency of other matters, the nitrogenous constituents were very liberally supplied. Hence, the gross increase obtained might be somewhat more nitrogenous with the large supply of nitrog- enous food ; but it would in that case, according to some experiments of our own, contain a larger proportion of water, and less of solid matter, than where more fat had been pro- duced." More recent studies made on various domesticated animals tend to confirm these results. A mixed diet with an abundance of nitrogenous food permits of greater growth than an equal quantity of food of one kind, or mixed food in which the nitrogenous constituent is scant. Growth tends to increase with the quantity of nitrogenous food rather more closely than with that of the non-nitrogenous food devoured. This conclusion is sustained by the striking results gained by PROSHER ('97) in investigating the cause of the varying percentage rate of growth of different mammals. The rela- tion between growth and the percentage of the different organic and certain mineral constituents of milk is given in the following table : — §1] UPON THE RATE OF GROWTH 331 TABLE XXXIV SHOWING FOR VARIOUS MAMMALS THE TIME REQUIRED TO DOUBLE THE BIRTH- WEIGHT, THE PERCENTAGE OF DIFFERENT ORGANIC CONSTITUENTS IN THE MILK, AND THE RELATIVE QUANTITY OF ALBUMEN, CALCIUM OXIDE, AND PHOSPHORIC ACID IN THE MILK OF THE DIFFERENT SPECIES — THE QUAN- TITY IN MAN BEING TAKEN AS THE STANDARD 1 3 3 4 5 0 7 8 SPECIES. RELATIVE TIME TO DOUBLE WEIGHT. % FAT. % SUGAR. % ALBUMEN. RELATIVE QUANTITY ALBUMEN. RELATIVE QUANTITY CaO. RELATIVE QUANTITY P206. Man 1 3.5 6.6 1.9 1.0 1 1 Horse .... Ox l 3 1 1.1 4.5 6.1 4.5 2.3 4.0 1.2 2.2 4 5 3 4 Piff A 6.9 2.0 6.9 3.7 _ Sheep .... Dog TV A 10.4 10.6 4.2 3.1 7.0 8.3 3.8 4.46 8 14 9 10 Cat *v 3.3 4.9 9.5 5.1 From this table it is clear that there is a close relation between rate of growth and the percentage of albumen only among the organic substances of milk. This relation is best brought out by comparing columns 2 and 5. The last two col- umns show a close relation between growth and the quantity of calcium and phosphorus in the milk. But of the organic substances the quantity of the nitrogenous compound deter- mines the rate of growth. 3. Growth as a Response to Stimuli. — Hitherto we have regarded the process of growth in too mechanical a way, as though certain nutritive compounds, passing into a chemical mill, were inevitably transformed, at a certain rate, into proto- plasm or formed substance. We have now to recognize that the growth processes are essentially vital processes, and, as such, characterized by all that complexity which we find in such a vital process as response to stimuli. a. Acceleration of Growth by Chemical Stimulants. - - Many chemical agents which are not themselves food may stimulate the growth processes. We have already seen (p. 51) how certain poisons cause, in dilute solutions, accelerated move- 332 EFFECT OF CHEMICAL AGENTS [Cn. XI ments and heightened metabolism. To the cases previously given may be added the experiments of SCHULZ ('88), who found that various poisons, such as corrosive sublimate, iodine, bromine, and arsenious acid, increase the activities of yeast in fermentation. It is not strange, therefore, to find that poisons ma}r, at a certain concentration, accelerate growth. That they do so follows from the experiments of RICHARDS ('97), who reared the molds Aspergillus, Penicillium, and Botrytis in nutritive solutions to which had been added small quantities of zinc sulphate, other metallic salts, cocaine, morphine, and other alkaloids. After five to seven days Aspergillus, reared in nutritive solutions in which sugar was the organic compound, had gained the following dry weights (in milligrammes). In all the experiments, except those in the column headed " Control," the solution contained certain non-nutritious sub- stances in from 0.002% to 0.033% concentration. TABLE XXXV SHOWING THE TOTAL DRY WEIGHT IN MILLIGRAMMES OF A CROP OF ASPER- GILLUS REARED IN THE ABSENCE AND IN THE PRESENCE OF VARYING QUANTITIES OF IRRITATING SUBSTANCES SUBSTANCE. CONTROL. 0.002% O.004% 0.008% 0.01C% 0.033% ZnS04 335 730 760 765 770 715 NaFl 250 565 405 340 270 245 Na2SiO3 350 520 575 450 435 380 CoS04 245 405 350 235 170 75 Cocaine 280 410 320 350 390 540 Morphine 160 155 170 140 210 216 It is clear from this table that the addition of even small quan- tities of innutritions and poisonous substances may so excite the hylogenic processes as to cause twice or even far more than twice the normal formation of dry substance in a given time, and that this excessive growth increases with the concentration of the salt up to a certain optimum, beyond which growth declines again to below the normal. Similarly TOWNSEND ('97) has observed that a seedling living under a bell jar whose atmosphere contains a small quantity of ether grows §1] UPON THE RATE OF GROWTH 333 faster than one under similar conditions but without ether. If the plant is subjected to an increased quantity of ether, growth is retarded. The effect of these poisons is thus very different from that of nutritive substances ; it is due to the irritating properties of the poison. b. The ^Election of Organic Food. — Not all of the food-stuff presented to the organism is utilized by it — neither, on the one hand, all of the kinds of food, nor, on the other, all of the food of the most acceptable kind if offered beyond a certain amount. There is an election of kind and of amount. A study of an election of kind has been made by DUCLAUX ('89), and, especially, PFEFFER ('95). The method employed was this : To the organisms (various molds, Aspergillus, Penicil- lium, etc.) were offered two compounds ; one more nutritious, the other less so. Under these circumstances, the more nutri- tious compound was usually taken by the organism, while the less nutritious was often left entirely alone ; thus, dextrose was preferred to glycerine, peptone to glycerine, and dextrose to lactic acid, even when, in each case, the quantity of the latter substance was in excess of the former. The election was not, however, always of the more nutritious material, so far as we can judge of relative nutritiveness. Thus, when Aspergillus was sown on a nutritive fluid, containing 8% dex- trose and ~L% acetic acid, proportionally far more of the latter was assimilated than of the former, although the latter is of less value as food, as was shown by the fact that the plant had also to devour a considerable quantity of the dextrose. This extensive assimilation of a slightly nutritive substance is not, so far as we can see, an adaptive process. The character of the election may change with age, so that what is favorable for growth at one time is not at another. Thus DUCLAUX ('89) found that alcohol restrains or arrests the germination of the spores of molds, whereas it is made use of almost as abundantly as sugar by the adult plant ; so, like- wise, lactose and mannit cannot nourish young plants when they replace sugar in the nutritive solution, whereas they are a good food for the older plants. So, also, among vertebrates, the food of the young, supplied in the egg or in the milk of the parent, is very unlike that 334 EFFECT OF CHEMICAL AGENTS [Cn. XI which is most favorable for growth in later stages. So impor- tant is this difference of food at different ages that agriculturists persistently change the ratio of the different foods supplied as their animals increase in age. The reason for this change in food required lies doubtless in this, that the chemical processes of growth change with the age of the animal ; at first imbi- bition of water predominates, then comes the secretion of the various formed substances of the organism and the constant maintenance and increase of the plasma. The most favorable food of an organism at any time is dependent upon the metabolic processes going on at that time. The election of quantity is not less striking. It is well known that an increase above a certain limit in the amount of food presented to an organism or even actually taken into its body does not result in any increase in growth. There is a certain amount, fixed within broad limits, which corresponds to a maximum of nutritiveness. This amount, this feeding capacity, is not, however, necessarily constant at all stages of the adult growth of the organism. For it has been observed in certain animals, e.g. pigs, that as they grow older there is a steady increase in the amount of food required to produce a pound of gain in weight. Such facts serve to indicate that the rate of growth is largely determined by internal factors. Let us now summarize the results of this study of the effect of chemical agents upon the rate of growth. Of foods, those used in the plastic processes are chiefly to be considered. The substances serving as plastic food must contain all the elements normally occurring in the organism. These are found in di- verse proportions in different organisms, and hence the neces- sity of dissimilar foods. Not only carbon, oxygen, hydrogen, and nitrogen are necessary, but a whole series of other elements, such as phosphorus, sulphur, chlorine, iodine, sodium, potas- sium, calcium, iron, and magnesium are more or less essential. The organic plastic food varies with the group of organisms. Of relatively little importance for green plants, it becomes essential to fungi. In this group we find the most important character of a nutritive substance to be a certain degree of lability. Among animals a mixed diet is especially beneficial, but nitrogenous food favors growth more than non-nitrogenous §2] UPON THE DIRECTION OF GROWTH 335 food. Finally, growth must be studied as a response to chem- ical agents which may stimulate the protoplasm to absorb and assimilate them to the degree required by the organism, or which may stimulate the protoplasm to absorb some other sub- stances, as we have seen in the case of zinc sulphate. The quantity and quality of food needed will, moreover, vary with the age and other qualities of the organism. The consumption of food both in quantity and in quality will be closely deter- mined by the demand. All these complexities in the process of nutrition indicate that it, like other processes in organisms, can only be explained on the assumption of a vastly complex molecular organization of the protoplasm. § 2. EFFECT OF CHEMICAL AGENTS UPON THE DIRECTION OF GROWTH — CHEMOTROPISM One of the most common processes in the early development of organisms is the turning or bending of a filament, tubule, or lamella. The cause of this turning is clearly an unequal growth of the two sides of the organ. When the bending organs are internal, their movements are largely removed from experimental study ; when external, as in plants, they more easily lend themselves to our investigation. The object of this investigation is always to find in how far the direction of these tropic movements is determined or is determinable by external agents. In the present section it is proposed to consider in how far tropic movements are determined by chemical agents. At the outset it must be said that the growth which gives rise to these bendings is frequently due to imbibition of water ; and in such cases it may be only temporary. Yet these temporary bendings pass by such insensible gradations into permanent ones that a sharp distinction between the two is impracticable and unim- portant. Rejecting such a classification of the subject, we may adopt one based on the tropic organ. 1. Chemotropism in the Tentacles of Insectivorous Plants. - This case of chemotropism was the earliest to be observed ; it was DARWIN ('75, p. 76) who first called attention to it, He found that when drops of water or solutions of non-nitrogenous 336 EFFECT OF CHEMICAL AGENTS [Cn. XI compounds are placed upon the leaves of the sundew, Drosera, the tentacles remain uniuflected; but when a drop of a nitroge- nous fluid, such as milk, urine, albumen, infusion of raw meat, saliva, or isinglass, is placed on the leaf, the tentacles quickly bend inwards over the drop. DARWIN now set to work sys- tematically to determine which salts and acids cause and which do not cause inflection. Of nine salts of ammonia tried, all caused inflection of the tentacles, and of these the phosphate of ammonia was the most powerful. Sodium salts in general cause inflection while potassium salts do not. The earthy salts are in general inoperative, as are likewise those of lead, manganese, and cobalt. The more or less poisonous salts of silver, mercury, gold, copper, nickel, platinum, and chromic and arsenious acids produce great inflection with extreme quick- ness. Other substances which caused inflection were nitric, hydrochloric, iodic, sulphuric, phosphoric, boracic, and many organic acids ; gallic, tannic, tartaric, citric, and uric acids alone being inoperative. In all these cases, where a bending of the tentacles over the drop occurs, the turning must be regarded as a response to the stimulus of the chemical sub- stance. An excitation proceeds from the irritated region to the protoplasm upon whose imbibitory activity the turning of the tentacles depends. 2. Chemotropism of Roots. -- - Attention was directed to the fact that roots turn towards or from chemical substances by MOLISCH ('84), who experimented with gases. When grains of maize or peas are sprouted in water, their roots will turn FIG. 91. — Seedling of Zea, whose radicle originally was just touching the water obliquely with its apex and thereafter nutated in characteristic fashion, keeping close to the air. (From MOLISCH, '84.) § 2] UPON THE DIRECTION OF GROWTH 337 upwards towards the surface of the water — in response to the more abundant oxygen supply there (Fig. 91), and will grow along the surface of the water. MOLISCH undertook a .sys- tematic investigation of the action of various gases in con- trolling this growth. The method employed was as follows : The gases were enclosed in glass vessels whose mouth was closed by a plate of hard rubber perforated by slits, 'J cm. long by 2 mm. broad. The vessel being laid on its side so that the slits were vertical, the rootlet of a germinating grain was placed in front of it. As the gas diffused from the vessel, it was for some time in excess upon one side of the rootlet. The gases experimented with were pure oxygen, pyrogallic acid, nitrogen, carbon dioxide, chlorine, hydrochloric acid gas, illuminating gas, ammonia, nitrous oxide* ether, chloroform, and oil of turpentine. In all cases there occurred, generally after about an hour, a turning of the root towards the gas (positive aerotropism, MOLISCH), followed by a marked curvature from the slit (neg- ative aerotropism). Since decapitated roots respond in the same way as intact ones, but in less degree, MOLISCH con- cluded that the gases affect the growing region directly and do not require the intervention of the root-tip. 3. Chemotropism of Pollen-tubes. --The suggestion was early made by PFEFFER ('83), as a consequence of his discovery of chemotaxis in swarm-spores, that perhaps the bending of the antheridium-tube of Saprolegnia towards the oogonium was a case of response to a chemical agent. STRASBURGER ('86) offered a similar suggestion for phanerogams. PFEFFER ('88) then made experiments, but was unable to control the direction of growth of pollen-tubes. MOLISCH ('89 and '93) was next led to undertake further study in this direction by the obser- vation that, when various pollen-grains are germinating in a nutritive drop and a cover-glass is placed over them, the pollen- tubes, after approaching near to the edge of the cover-glass, turn away towards the centre again (Fig. 92, a, 6). The move- ment from the margin of the cover-glass cannot be ascribed to a difference of density produced by evaporation at the margin, for it occurred in a saturated atmosphere ; nor can it be due to surface tension of the bounding film of water, for the turning occurred before the surface film was reached. These results 338 EFFECT OF CHEMICAL AGENTS [Cn. XI were abundantly confirmed by MIYOSHI ('94a), so we must conclude that the pollen tube is negatively aerotropic to oxy- gen. However, this negative aerotropism does not occur in all pollen, for that of Orobus vernus and various other legumes, of Primula acaulis, Viola odorata, V. hirta, etc., were indifferent. a FIG. 92. — Illustrates chemotropism of pollen-tubes, a. Negative chemotropism with reference to the air (aerotropism) of pollen-tubes of Narcissus tazetta ; the tubes are growing under a cover-glass in a 7% sugar solution and turn at the edge, a, b, from the air; magnified about 20. 6. Negative aerotropism of pollen-tubes of Cephalanthera pallens, after 20 hours; a, b, edge of cover-glass. c. Stigma of Narcissus tazetta in 1% sugar solution ; pollen-tubes grow towards the stigma ; magnified about 10. (From MOLISCH, '93). A second class of chemotropisms is seen in the turning of pollen-tubes towards the stigma of a flower.* When pollen is sown upon a plate of agar-agar or gelatine on which the upper end of a ripe pistil has been placed, the tubes are sent out in * MOLISCH accounts for the failure of some of the earlier experiments with pollen-tubes on the ground that certain pollen-tubes do not exhibit this class of chemotropism. Among these are Viola odorata, V. hirta, Orobus vernus, etc. — species which are likewise not aerotropic. §2] UPON THE DIRECTION OF GROWTH 339 all directions at first, but quickly grow towards the pistil (Fig. 92, 2 •f. TION. o . i g O n i. M O 6 ^ 6 'ti. 3 rt O be O 5 to to z, ^ K ^i 2 ^ M MOLEC. WEIGHTS, 58.5 12O 111 95 74.6 Control : water 787 113.0% 75 134.0% 0.05% 100 85.2 50 22.0 50 40% 25 12 % 50 12% 0.10 350 77.0 75 -10.6 50 -12 50 -64 0.15 100 58.0 75 - 2.6 25 -36 25 -28 25 -92 0.20 350 40.8 75 -35.3 50 -58 25 -68 0.25 100 21.5 75 -65.3 25 -72 0.30 350 3.2 75 -84.0 25 -84 0.35 25 -24.0 25 -92 0.40 375 -18.1 25 -100 0.50 150 -35.0 These columns, and especially the first one, show a close relation between concentration and growth (as tested by mul- tiplication of individuals). They show also that the diminished growth falls off rapidly at first with slight increments of con- centration, then less slowly at the higher grades (Fig. 99). Finally they show that different salts have diverse osmotic effects, for sodium chloride is less retarding than any other salt at the same percentage of concentration. The effect of the remaining salts is seen to increase as the molecular weight diminishes, and therefore the osmotic effect increases (Fig. 99). The fact that magnesium sulphate dissociates at these weak concentrations only about two-thirds as much as calcium chlo- ride does, would lead us to expect even a relatively smaller effect as compared with calcium chloride than we find (see p. 74, note) -, perhaps further experimentation would give facts §1] UPON THE RATE OF GROWTH 367 agreeing closer with theory. On the whole, Table XL indi- cates that it is the osmotic effect which retards growth. In tadpoles a similar retarding effect of solutions has been observed by YUNG ('85), who made solutions of 0, 2, 4, 6, and 8 grammes of sea salt in 1000 grammes of water, and reared frog's embryos in them. Other conditions excepting concentration were believed to be alike in all experiments. In the 0.2% solution the tadpoles developed at nearly the same rate as in pure water. In the denser solutions there was a retardation in development which in- creased with the density of the solution, so that in the 0.8% solution the lar- vse hatched out seventeen days behind the normal time. The effect of a sudden change in the density of the solution has been es- pecially studied by TRUE ('95). Beans, Vicia faba, which had radicles from 17 to 35 mm. long, were placed directly in the solu- tions and held there so that the cotyledons alone were free. The cultures were kept in the dark. When the transfer was made sud- denly to a 1% solution of potassium nitrate, it was observed that a mechanical contraction occurred, followed by a more or less prolonged period of retar- -80 -90 -100 .05 .10 .15 .30 .25 .30 .35 .40 .45 .50 FIG. 99. — Curves of average increase per cent of individuals (ordinates) of Dero vaga re- producing, during 10 days, in solutions of different salts, whose strengths are laid off as abscissae. The data are taken from Table XL. 368 EFFECT OF DENSITY OF THE MEDIUM [Cn. XIII elation in the rate of growth. When, on the other hand, the plant was transferred from a salt solution to which it had become accustomed to pure water, a mechanical elongation quickly occurred, but this too was followed by a retardation in the rate of growth. Thus the reduction in the rate of growth is not a mechanical result of change of medium, but is a response to the stimulus of changed environment. We have hitherto considered almost exclusively the effect of aqueous solutions. We must now consider how a variation in the pressure of the atmosphere affects the growth of plants. Upon this subject experiments have been made by JACCARD ('93), who found that when the pressure of the air was reduced from 78 cm. to between 10 cm. and 40 cm. of mercury, growth is two or three or even six times as rapid as in ordinary air. Likewise when the air is compressed to between three and six atmospheres acceleration in growth occurs, although not to the same extent as in the depressed air. If, however, the rarefac- tion is very great (below 10 cm.) or the pressure excessive (over 8 atmospheres), growth is retarded. Experiments indi- cate that this result is not wholly due to the concentration of the oxygen in the air. We may therefore conclude that a change in pressure from the normal accelerates growth by irritating the growing plasma up to a certain limit, beyond which its injurious effects counterbalance its favorable ones. Summing up this account of the effect of concentrated solu- tions upon the growth of organisms, we find that in general as the density increases beyond the normal the rate of growth diminishes until, at a certain concentration, it ceases. In the particular case of marine organisms a reduction in concentration to a certain point causes excess of growth ; below that point, diminution. It is probable that the diminution in growth is proportional to the osmotic action of the medium (Chapter III). An explanation of the foregoing phenomena may be attained by reference to the principles laid down in preceding chapters. In Chapter X it has been shown that growth depends very largely upon the specific imbibition of water. We do not know the cause of the difference in imbibitory properties at different times ; but if, as has been suggested, it is purely an endosmotic phenomenon resulting from the secretion of plant § 1] UPON THE RATE OF GROWTH 369 acids or salts in the cell sap, then we can understand how a denser medium should diminish or destroy the imbibitory tendency. On the other hand, a change in concentration may act in a more indirect fashion to cause increased growth ; namely, by calling forth a response to the irritation of changed conditions of pressure. LITERATURE ESCHEXHAGEN, F. '89. Ueber den Einfluss von Losungen verschiedener Concentration auf das Wachsthum von Schimmelpilze. Stolp, 1889. JACCARD, P. '93. Influence de la pression des gaz sur le developpement des vegetaux. Coinp. Rend. CXVI, 830-833. 17 April, 1893. JARIUS, M. '86. Ueber die Eimvirkung an Salzlosuugen auf den Keimungs- process der Sanien einiger einheimiseher Culturgewachse. Landwirths- schaft. Versuchs-Stat, XXXII, 149-178. Taf. IT. JENTYS, S. '88. Ueber den Einfluss lioher Sauerstoffpressungen auf das Wachsthum der Pflanzen. Unters. a. d. bot. Inst. Tubingen. II, 419-404. LOEB, J. '92. (See Chapter X, Literature.) RACIBORSKI, M. '96. Ueber den Einfluss ausserer Bedingungen auf die Wachsthurasweise des Basidiobolus ranarum. Flora. LXXXIII, 110-115. STANCE, B. '92. Beziehungen zwischen Substratconcentration, Turgor und Wachsthum bei einigen phanerogamen Pflanzen. Bot. Ztg. L, 253 et seq. TRUE, R. H. '95. On the Influence of Sudden Changes of Turgor and of Temperature on Growth. Ann. of Bot. IX, 365-402. Sept. 1895. VANDEVELDE, A. J. J. '97. Ueber den Einfluss des chemischen Reagentien und des Lichtes auf die Keimung der Samen. Bot. Centralbl. LXIX, 337-342. 11 March, 1897. DE VRIES, H. '77. Ueber die Ausdehung wachseuden Pflanzen-zellen durch ihren Turgor. Bot. Ztg. XXXV," 1-10. WIELER, A. '83. Die Beeinfliissung des Wachsens durch verminderte Par- tiarpressung des Sauerstoffs. Unters. a. d. Bot. Inst. Tubingen. I, 189-232. TUNG, E\ '85. De 1'influence des variations du milieu physico-chimique sur le developpement des animaux. Arch, des Sci. Phys. et Nat.* XIV, 502-522. 15 Dec. 1885. 2s CHAPTER XIV EFFECT OF MOLAR AGENTS UPON GROWTH IT is proposed in this chapter to consider, first, the effect of contact, rough movements, deformations, and associated molar agents upon the rate of growth, and, secondly, the effect of such agents upon the direction of growth. § 1. EFFECT OF MOLAR AGENTS UPON THE RATE OF GROWTH We have already (Chapter IV) seen that profound changes in metabolism and the motion of protoplasm are induced by various sorts of contact. We shall here consider how those changes result in modifications of growth. 1. Contact. --In the case of organs which normally grow upon a solid substratum the growth may take place more rapidly after coming in contact than before. Thus LOEB ('91, p. 29) says of the stolons of the hydroid Aglaophenia pluma, that when they reach a solid surface they begin to grow more rapidly than stolons which develop free in the water. Evidently the stimulus of contact excites to extraordinary growth. 2. Rough Movements. — Experiments with this agent have been almost confined to bacteria, and have been made by shak- ing. The first experimenter in this direction was HORVATH ('78), whose method of work is worth giving in some detail. Glass tubes about 20 cm. long and 2 cm. wide were half filled by a nutri- tive fluid, inoculated with an infusion full of various bacteria, and sealed. The tubes were then fixed on a board •which was made to swing horizontally to and fro by means of a motor through an arc of about 25 cm. length at the rate of 100 to 110 times per minute. At the end of each excursion the board received, by means of a special device, an extra blow. The resulting agitation was like that made in shaking a test-tube. 370 § 1] EFFECT OF MOLAR AGENTS UPON GROWTH 371 The results of HORVATH'S experiments were these. Tubes which were shaken for 24 hours were clear at the end of that period, while similar tubes kept at rest had become muddy with bacteria in. the same time. If, now, the shaken tubes were kept at rest during a day in a warm oven, they, too, produced a rich growth of bacteria. When, however, the tubes had been shaken for 48 hours they not only were found clear, but they did not become cloudy upon subsequent warming (I, p. 99). The shaking during the briefer period had thus merely interfered with the normal growth processes, but the more prolonged shaking had resulted in the death of the bacteria. Subsequent attempts by other workers to reproduce these results, by the use, however, of other methods, partially or completely failed. REINKE ('80), indeed, found that in water agitated for 24 hours bacteria had ceased to grow, but had not been killed ; in so far a confirmation of HORVATH. Other investigators, however (BUCHNER, '80 ; TUMAS, '81 ; LEONE, '85 ; SCHMIDT, '91 ; RUSSELL, '92 ; and others), have either obtained no effect upon the growth of bacteria, or have found it increased by motion. The results seemed hopelessly dis- cordant. The more recent work of MELTZER ('94) has, however, brought these conflicting observations under one general law, and has thus offered an interpretation of the varied results. He pointed out first that the diverse results of previous investi- gators were due to the use of different species of bacteria and of different kinds and degrees of shaking ; in a word, to dis- similar methods. MELTZER employed pure cultures of bacteria of ascertained species, and counted the colonies by the well- known bacteriological methods. Shaking was either violent, being done in a machine somewhat like HORVATH'S ; or slight, being done by hand. The media used were neutral salt solu- tions, KOCH'S bouillon, or pure water. The results showed that a slight shaking is advantageous to the metabolism of Bacterium ruber in water. Thus, while a culture containing 950 colonies, left quiet, was reduced after 8 days to 259 colonies ; shaken, it had at the end of the same, period 1366 colonies ; and shaken with glass drops rolling loose in the tube, 372 EFFECT OF MOLAR AGENTS [Cn. XIV it had attained 16,200 colonies. When, however, the shaking was longer continued the number of colonies began to fall off, so that after 21 days the medium shaken with glass drops exhibited only 5 colonies. These facts enable us to distinguish a minimum degree of movement which will permit of growth (shaking for 6 days without glass drops); an optimum (shaking for 8 days with glass drops) ; and a maximum (shak- ing for 21 days with glass drops). The optimum is very diverse in different species. Thus in Bacterium megaterium it is so low that shaking for a little over 1.5 days results fatally. It is probable that the growth of every race of bacteria is attuned to a particular optimum of movement.* 3. Deformation. - - Under this head we may consider the effects of pulling and bending upon the growth of an elongated body. Data upon this subject have been obtained only from plants. The effect of pulling upon the growth in length of a plant stem has been studied by BARANETZKY ('79), SCHOLTZ ('87), and HEGLER ('93). The results obtained are concordant and important. It appears that when a weight is attached, by means of a cord running over a pulley, to the epicotyl of various seedlings — such as Helianthus, Tropteolum, Cannabis, Linum, etc., --the growth in length of the stem is, under appropriate conditions, not accelerated but retarded. When, for example, a pull of 13 grammes is exerted upon the epicotyl * Concerning the cause of the increase of growth accompanying a slight molar disturbance and the diminished growth and death accompanying a violent one, MELTZER has something to say. He finds in those cultures in which no growth of bacteria occurs, no fragment of cells but on the contrary nothing except a fine "dust" — the bacteria have experienced a molecular disintegration. In order to explain this disintegration, MELTZER accepts NAGELI'S conception of the structure of protoplasm, — micellae enveloped by water, — and supposes that a molar disturbance modifies the normal movements of these micellae. A very violent movement causes the micellee to separate completely ; a much less tur- bulent movement causes an increase in the vibrations of the micellae by which they are brought into more intimate contact with food material including oxygen, and more easily get rid of the metabolic products. Without accepting NAGELI'S micellar hypothesis, we may account for the beneficial effects of slight movement upon the ground of an increased supply of oxygen afforded by it; and we may regard the fatal effect as the result of disturbed metabolism or of protoplasmic disintegration. §1] UPON THE RATE OF GROWTH 373 of a Cannabis seedling there is a momentary elongation followed for six hours by no growth whatever ; then periods of growth alternating with periods of retardation occur until, after perhaps 24 hoars, the hourly growth is nearly equal to that of the unweighted plant. The least weight which will cause a retardation is different for different plants. In the case of Cannabis and Linum it is below 1.3 grammes, a result which indicates that the weight of the index used in self-recording auxanometers is sufficient to retard the growth of the plant and thus to give an abnormal growth curve. The diminution of growth is not the same at all periods of the plant's development. Thus the retarding effect is greatest at the commencement of the grand period of growth, but begins quickly to diminish until at the maximum of growth there is no retarding effect. Then, as the rate of growth decreases, the retardation becomes more evident. The effect of the pull is best seen in comparing the curves of daily fluctuation of growth of the weighted and unweighted plants. The early morning is the period of rapid growth, and at this time the growth of the stretched plant is quite equal to or exceeds that of the.un- I 8 8 4 58 7 8 010111S1S 8 4 68 7 8 910111S1* 8 * id 7 S 910U121S 34 6 6 7 8 9 lull 12 12 3 4667 FIG. 100. — Curves of hourly growth, measured in hundredths of a millimetre, — ver- tical scale at the left. The full line gives the course of growth of a Cannabis seed- ling subjected to a pull of 13 grammes. The dotted line gives, for comparison, the course of nearly normal growth, the plant being subjected to a pull of only 3 grammes. The numbers at the bottom indicate hours of the day; the broken line at the bottom indicates night-time. (From HEGLER, '93.) weighted one. During the early night, on the contrary, when growth is feeble, the stretched stem grows slowly (Fig. 100). If an etiolated plant is used, the daily growth fluctuations are eliminated and the effect of the larger growth cycle becomes 374 EFFECT OF MOLAR AGENTS [Cn. XIV evident. Thus, in general, the more rapid the growth, the less is the retardation provoked by pulling. The direction in which we must look for an explanation of these facts is indicated by the circumstance that, in the most rapid period, growth is chiefly due to imbibition of water, while in the preceding and succeeding periods it is due more to an increase in the plasma. Thus not all kinds of growth are equally affected by the irritation of pulling, but principally that growth which is due to assimilation. Further insight into this matter is gained from the circumstance that despite the fact that growth is slower in the plant under tension the tur- gescence in the stretching zone is greater in such a plant than in a normal one. This indicates again that it is not the imbib- itory process which is interfered with but rather the assimila- tive one. All these facts thus lead to one conclusion, that, under tension, the plasma, especially that of the cell-wall, grows in length less rapidly than under normal circumstances. This diminution of growth can hardly be explained in a direct mechanical way ; we must consider it a response to the stimulus of pulling. A confirmation of this conclusion is found in the fact that the effect of the pulling gradually wears off. Thus when one of a pair of seedlings of Cannabis sativa is subjected to a pull of 20 grammes, there is a retardation during the first day of 61% in the stretched plant as compared with the control plant; during the second day of 51% ; during the third day of only 9%. (HEGLER, '93, p. 389.) In order that the retardation should continue, additional weight must be imposed ; then an increased retardation occurs. Thus in one case HEGLER sub- jected one of two Helianthus seedlings to a pull of 50 grammes. During the first day the retardation of the pulled plant was 20% ; during the second there was an excess of growth over the control of 17%; then 150 grammes were added; on the third day the retardation was 18% ; on the fourth there was an acceleration of 2%. This series of phenomena is clearly like that which we have observed in locomotion — there is an accommodation of the growing protoplasm to the stimulus. There can be little doubt that in the cases of diminished growth in length there is a thickening of the cell-walls and §1] UPON THE RATE OF GROWTH 375 probably an increase in cross-section of the whole stem. There is indeed considerable experimental evidence for this con- clusion. Thus SCHENCK ('93) found that when stems are irritated by twisting or bending, an excessive growth both of cell-walls and of the wood as a whole follows. So, too, NEWCOMBE ('95) finds that roots become strengthened by attaching weights to them. In fact, if stems are deprived of their normal swaying movements, for instance by enclosing internodes in plaster casts which inhibit lateral movements and partly support the weight of the superior part of the plant, their walls remain abnormally thin. These effects of deformation are of especial importance because they are so clearly not at all directly mechanical but- adaptive ; they are, indeed, rather opposed to the direct mechanical effects which would tend to stretch the cells, and thus to diminish the thickness of their walls. Here again the organism shows itself a highly irritable thing, capable of responding in an adaptive fashion. 4. Local Removal of Tissue. --When a protist, for instance a Stentor, is transsected, certain changes take place along the cut surface. First, there is a warping of the edges towards each other ; secondly, rapid growth (differential growth, page 287) occurs. Similarly, if a Hydra be cut lengthwise, the free edges may fold towards each other so as to form a smaller cyl- inder, and the seam, by growth, will be healed over. So, too, in the higher animals, the removal of a bit of tissue results usu- ally in the closure of the wound and growth to fill the gap. We may call these two processes warping and regenerative growth. The causes of these two processes are probably different. The warping seems to result from the presence of tensions and pressures in the tissues whose equilibrium is disturbed by the cut. This process is probably grossly mechanical. The regen- erative growth, however, must have a less direct explanation. It is apparently a typical response to the stimulus of cutting, or of the new environment presented at the cut edge. Here, too, may be mentioned an experiment by LOEB ('92, p. 51), which throws light upon the cause of these internal tensions. Below the crown of tentacles of a Cerianthus a 376 EFFECT OF MOLAR AGENTS UPOX GROWTH [Cn. XIV horizontal slit was made in the side of the body-wall. The tentacles over the slit contracted - - there was a sort of negative growth. The shortening was doubtless due, as LOEB says, to the loss of water and con- sequently of turgescence in this part of the body-wall (Fig. 101). I have cut the body- wall of a hydroid immediately below an incipient bud, whereupon the bud at once flattened out. These experiments show how important water pressure is for the maintenance of the size of the body and for growth, and in so far explain the mechanical effect of a cut or other similar wound. 2. EFFECT OF CONTACT UPON THE DIREC- TION OF GROWTH — THIGMOTEOPISM FIG. 101. — Ceriauthus, from which a piece, a,b, c, has been cut, causing a loss of tur- gescence and conse- quent shrinking of tentacles on the cut side. (From LOEB, '92.) Having seen that molar agents can affect the rate of growth, we are in a position to understand how a molar agent, acting upon one side only of an elongated organ or plate of tissue, may induce a less or greater growth upon that side, and, con- sequently, a bending towards or from it. This turning phenomenon may now be considered. Before taking up the permanent growth turnings, however, we may consider a case of transitory growth, which throws valuable light upon the true nature of thigmotropism, and serves to connect it with thigmo- taxis. This is the case of the pseudopodia of Orbitolites, which, according to VERWORN ('95, p. 429), float at first free in the water after being protruded through holes in the shell; but as soon as they grow longer and heavier they sink in the water, until their distal ends touch the substratum. To this they become attached by a delicate secretion, and grow out along it by the streaming of the protoplasm. The persistent clinging to the substratum is a thigmotropic reaction, and one which belongs clearly to the category of response. 1. Twining Stems. — The characteristic form of twining plants, like the bean, has long excited the interest of natural- § 2] THIGMOTROPISM 377 ists. A study of the cause of this form was made by PALM ('27), by MOHL ('27), and by DUTROCHET ('43, '44) ; and from this early period to the present there have existed on this matter great differences of opinion. On the one hand, there has been maintained a view that had great inherent probability, the view, namely, that the twining of plants is a response to the contact-stimulus of the object about which they are coiled. Against the general validity of this view certain experiments of DARWIN ('82, p. 16) seem conclusive. For he found that even the hard rubbing of the stalk caused no modification of the normal spiral growth. Accordingly, the conclusion seems generally accepted to-day that the peculiar form of growth of most twining plants is the combined result of geotropism, by which the stem grows upwards, and a special form of nutation, by which it impinges against the supporting stick and bends round it. The twining is thus mechanical, — depending upon the structure of the stem, -- rather than responsive. An exception among twining plants is found in the dodder, Cuscuta. This plant is a parasite, belonging to the Convol- vulus family, and lives upon the flax and other plants. It is leafless, and twines closely about its host, into which it sends the feeding organs --the haustoria. According to the careful studies of PEIRCE ('94), the stem, when not in contact with any solid body, makes long, steep turns about the axis of the spiral, as is the case with other twiners. If now the free stem, during a period of slow growth, be brought into contact with a wooden or glass rod or a thread at about 3 cm. from the tip, the stem bends sharply, and in the course of 15 hours makes two or three close turns around the vertical support. If the con- tact be made at a distance of only about 1 cm. below the tip, there will be little or no change in the character of the twining. If the point of contact be too far below the tip, — 6 to 7 cm.,- there will also be no effect. The result is thus clearly depend- ent upon a stimulus applied at a definite sensitive point ; it is a typical response. 2. Tendrils. - - Very similar to the phenomena of close twin- ing in Cuscuta is that of coiling in the tendrils of phanero- gams— those most marvellously sensitive of all plant struct- ures. DARWIN ('82) and PFEFFER ('85), particularly, have 378 EFFECT OF MOLAR AGENTS UPON GROWTH [Cn. XIV studied by experimental methods the movements of these organs. The conditions which induce the twining of tendrils are peculiar. It appears that tendrils are not irritated by mechanical shaking, such as is produced by a powerful current of air issuing from a narrow tube ; nor by a drop or strong cur- rent of water, provided it contains no hard particles ; nor even by a stream of mercury, or the surface of pure mercury or oil. All solid bodies, however, with the exception of moist gelatine, when rubbed against the stem stimulate it so as to produce a bending at the irritated point. The behavior of moist gelatine is instructive. PFEFFER first observed that it was exceptional, and PEIRCE has found the same exception to hold for Cuscuta. PFEFFER'S experi- ments showed that, no matter how great the pressure or strokes made by drops of 5 to 14% gelatine, or by glass rods covered by a layer of moist gelatine, no response occurred ; and PEIRCE ('94, p. 66) found that when the Cuscuta stem came in contact with a rod covered with wet gelatine it made only the long, steep turns characteristic of the free-growing stem. Later, when it reached the part of the rod not covered with gelatine, it formed at once a close, tight coil. That it is not the chemical composition of gelatine which prevents the twining is shown by the fact that dry gelatine, even to 25%, irritates ; also, if some sand is mingled with the moist gelatine, tropism occurs. The fact that wet gelatine does not irritate is explained by PFEFFER upon the ground that the stimulus is not given by mere contact, for a blow does not produce it. A certain degree of adhesion between the tendrils and the irritat- ing substance is necessary. The moist surface of the gelatine prevents such adhesion taking place. The effective irritation is a sort of tickling. The degree of this tickling may, however, be extremely slight. Thus PFEFFER ('85, p. 506) placed a rider of cotton thread, weighing 0.00025 milligramme, on a tendril, and found that no effect was produced so long as it was quiet ; whereas, when the rider was put in motion by a current of air, a considerable bending occurred. Under similar conditions, a thread weighing 0.00012 milligramme produced no reaction. MAcDouGAL ('96, p. 376) finds that a spider's web, 43 cm. §2] THIGMOTROPISM 379 long, suspended above a tendril of Echinocystis, caused such a reaction that the tendril coiled around and fastened to it. Concerning the irritable region, it appears that in most ten- drils there is an especially sensitive side and an especially sensitive zone. The presence of a more irritable side is not a constant character of all tendrils, however. Thus, Cobsea scandens, Cissus discolor, and others, are irritable on all sides. When a differentiation in this respect occurs, however, a bend- ing takes place towards the more irritable side. The sensitive zone lies either at the tip or immediately below. - The period of development at which the tendril is most irri- table must also be considered. Thus, DARWIX ('82, p. 174) says : " Tendrils which are only three-fourths grown, and, per- haps, even at an earlier age, but not whilst extremely young, have the power of revolving and grasping any object which they may touch. These two capacities . . . both fail when the tendril is full grown." PFEFFER ('85, p. 485) and MUL- LER ('86, p. 104) likewise find tendrils irritable only in the latter part of their growth-period. f There are four periods in the response to a momentary stimulus : (1) a latent period elapsing before the curvature begins to take place ; (2) a period of bending; (3) a period of quiescence in the bent condition ; and, finally, (4) a period of 7 FIG. 102. — Curve of contraction of a tendril. The distance of the curve from the base represents the amount of displacement of the tip ; one unit on the base-line represents five minutes of time ; 1 to 2, latent period and period of contraction ; 2 to 3, period of maintenance ; 3 to 4, period of relaxation. (From MACDOUGAL, '95.) * In Cuscuta, according to PEIRCE ('94, p. 64), the tip is non-irritable ; the most sensitive zone is 3 cin. below the tip. t In Cuscuta, PEIRCE ('94, pp. 63, 64) found that neither the stalk of seed- lings nor of older plants, during the period of rapid growth which follows the formation of haustoria, are sensitive. Irritability shows itself only when growth becomes less rapid, as it does some time after forming haustoria. 380 EFFECT OF MOLAR AGENTS UPON GROWTH [Cn. XIV straightening again. These periods are represented graphically in Fig. 102. The latent period is of variable length in differ- ent species. Perhaps the shortest period is that of Cyclan- thera, which MULLER ('86, p. 103) found to vary in the most sensitive condition of the plant from 5 to 9 seconds. DARWIN ('82, p. 172) found a latent period in Passiflora tendrils of. 25 to 30 seconds, while in other cases (Dicentra smilax, Ampe- lopsis) this period may be 30 to 90 minutes or more in length. The entire time required for the plant to straighten completely again is, according to MULLER ('86, p. 104), for Cyclanthera about 20 minutes. These times depend, however, to a large extent upon various external agents. Thus a quick response is favored by a temperature between 17° and 33° C., sunlight rather than shade, considerable humidity, and small size of ten- dril. Thus this growth response resembles, in its dependence upon various conditions, other responses, e.g. those of muscle, to stimuli. 3. Roots. - - Thigmotropism in roots was apparently first investigated by SACHS ('73, pp. 437-439). He fastened ger- minating seeds of various species in a moist chamber so that their radicles, of about 10 to 30 mm. length, were horizontal. A pin was now placed against the root near its tip so as to exert considerable pressure. Usually within eight or ten hours a turning of the root in the growing region occurred so that it became concave towards the pin and finally made a complete loop about it, or, if the needle was vertical, descended along it in a spiral - - a result of the double action of thigmo- tropism and geotropism. This response was, however, rather inconstant and appeared not to be very powerful. The sense of the thigmotropic response was, in the foregoing example, positive ; that is, the turning was towards the solid ( body. DARWIN ('81, p. 131) believed that he had evidence that the response is sometimes negative. Thus he says that the radicle of a germinating bean, coming in contact with a sheet of extremely thin tinfoil (0.003 to 0.02 mm. in thick- ness), was in one experiment deflected without making a groove upon it ; also, when a piece of paper was gummed to the root near the tip, the root usually turned so that it became convex to the gummed paper. But DARWIN'S conclusion has not been § 2] THIGMOTROPISM 381 sustained by later work. Thus DETLEFSEN ('82) found that bean radicles plunged right through tinfoil 0.0074 mm. in thickness, and WIESNER ('84) and SPAULDING ('94) have shown that the turning from the gummed paper is the result of the injurious action of the gum. Indeed, it is difficult to see how a root, which must force its way through the earth, should turn from a solid surface. Experience shows rather that it turns towards it and tends to grow along it or through it. 4. Cryptogams. — Among Fungi a thigmotropic response has been observed and studied in the mold Phy corny ces nitens by ERRARA ('84) and WORTMANN ('87). They find that rub- bing the sporangiferous hypha lightly with a bristle or glass thread for from three to six minutes will produce a response more powerful even than that to light. As with tendrils, 1% to 14% gelatine, almond oil, and water drops provoke no bend- ing ; but, on the other hand, even the mutual rubbing of two adjacent sporangiferous hyphte may incite a response. The response will, however, appear only when the growing region of the hypha is irritated ; if the hypha is fully grown, no thig- motropism will take place. The sharpest part of the bend will occur at the region of greatest growth, not necessarily at the point of contact. However, WORTMANN finds that the turn- ing commences at the point of contact, but becomes more and more pronounced as the bend approaches the most rapidly growing part of the hypha. The response to a brief contact is only temporary. Thus when a sporangiferous hypha 2.3 cm. long was touched for one minute with a glass thread a bending began to appear after 15 minutes and disappeared 10 minutes later. Thus Phycomyces follows closely the laws of response of tendrils. The rhizoids of the hepatic Marchantia and its allies have been found by MOLISCH ('84, p. 933) to behave in a similar way to the foregoing. When the hepatics are placed on damp filter-paper, over a watch-glass, in a moist chamber and in the light, one finds after 48 hours that rhizoids have penetrated through the filter-paper. Since the paper reveals, even to the microscope, no pores, and since grains of corn starch, of from 2 to 24 microns diameter, will not pass through it, we must con- clude that the root hairs of 10 to 25 microns diameter, although 382 EFFECT OF MOLAR AGENTS UPON GROWTH [Cn. XIV consisting of only a single cell, have the power of forcibly boring their way between the fibres of the paper. This phe- nomenon is most easily accounted for on the ground of response to contact. 5. Animals.- -The phenomenon of thigmotropism is exhib- ited among animals in the power of growing along an irregular substratum. Thus the stolons of hydroids, Bryozoa, and some compound ascidians, upon once gaining the surface of an appro- priate substratum, cling closely to it without reference to the direction, up or down, which the substratum may take. It is not necessary that the surface should be a rough one ; the sur- face film of water may incite the response. More striking is the direction of growth of regenerating hydroid steins, accord- ing to the observations of LOEB ('91, p. 18). This experi- menter found that when pieces are cut from a stem of Tubularia and are so placed in a cylindrical glass vessel that the lower end lies buried in the sand while the upper end is in contact with the side of the vessel, then, regeneration of the hydranth occurring, the new growth is perpendicular to the surface of the vessel, i.e. horizontal. This direction is independent of the direction of light rays, since it occurs at all parts of the circum- ference of the vessel ; nor is it a response to gravity, since the stems normally assume a vertical position. The phenomena are, in so far, exactly like those in plants. The experiments made upon plants suggest a series which might be made upon animals. Do stolons exhibit nutations to aid in the finding of the solid substratum ? What substances call forth the thigmotactic response? Will a momentary irri- tation cause turning? The field of thigmotropism, like that of the other tropic phenomena of sessile animals, is an imperfectly worked one. 6. The Accumulation of Contact-Stimulus and Acclimatization to it. — These two phenomena accompanying contact-stimu- lation must be alluded to. PFEFFER ('85, p. 506) pointed out that a soft blow which calls forth no response when given once, will produce bending when given repeatedly for several minutes. The basis for an explanation of this phenomenon is given by an observation of DE VRIES ('73, p. 307), who with- drew the support from a tendril which had already turned § 2] THIGMOTROPISM 383 through 45° as a result of contact irritation. The tendril tinned to bend at the previously irritated point even after the irritant had been removed. Thus a stimulated condition per- sists after the removal of its inciting cause, and this gives a chance for the building up of a powerfully stimulated condition by the accumulation of slight stimuli. The persistence of the stimulated condition is revealed by another set of changes. PFEFFER found that the tendrils of Sicyos when repeatedly rubbed at short and regular intervals first coil and then gradually straighten out. DARWIN" ('82, p. 155), who had previously shown this same thing, found also that after a tendril of Passiflora gracilis had been stimulated 21 times in 54 hours it finally hardly responded at all. Similar results have been obtained with Drosera hairs (PFEFFER, '85, p. 514). Thus the constantly repeated stimulation produces such a modification of the protoplasm that it eventually fails to respond. On the one hand, this phenomenon is the same as that of fatigue ; on the other, it resembles closely the condition seen in stimulated Protista referred to in Chapter IV, § 3, and there designated as acclimatization. 7. Explanation of Thigmotropism. — Concerning the cause of the bending of plants as a result of contact, I know of no better explanation than that offered by SACHS ('87, pp. 697-699). He ascribes the bending to a difference in the rate of growth on the two sides of the bending cylindrical organ. This is indicated by the fact that it is chiefly in the region of "stretching" that the response occurs ; i.e. shortly behind the apex. At the very tip, growth by assimilation is chiefly occur- ring ; below the region of stretching, growth is occurring only slowly. The measurements of DE VRIES ('73) have, however, shown directly that the convex side of the tendril grows faster than the straight tendril and the concave side less rapidly. The convex side thus pushes still farther over the concave, pro- ducing the coiling. As the region of stretching is one of imbibition of water, we conclude that more water is taken in on the convex side than on the concave, where even a loss of water may occur ; or perhaps there is a movement of water from the irritated towards the opposite side. The irritant then produces a chemical change on one side of the organism such as to cause 384 EFFECT OF MOLAR AGENTS UPON GROWTH [Cn. XIV a movement towards that side or from that side according as the organ is positively or negatively thigmotropic. § 3. EFFECT OF WOUNDING UPON THE DIRECTION OF GROWTH — TRAUMATROPISM * Under this head may be considered the effect of a special class of molar agents, namely, those which produce a wound, upon the direction of growth of roots. We may consider first false and then true traumatropism. 1. False Traumatropism. - - When the growing tissue of the radicle of a seedling is destroyed on one side by caustic or heat, the radicle turns towards that side (CiE- SIELSKI, '72 ; DARWIN, '81 ; SPAULDING, '94). This result is satisfactorily ex- plained on the ground that the killing of the growing tissue on one side causes a retardation or cessation of growth on that side ; so that, while the points re, y (Fig. 103), remain nearly stationary, the points x\y\ opposite to them, grow widely apart. It will be seen at once that this bending belongs to a wholly different category from the thigmotropic curva- tures described in the last section. It is, as DARWIN called it, a mechanical bending ; it is a false traumatropism. f 2. True Traumatropism. -- Of widely different cause from the foregoing is the turning due to slight wounding which has been investigated by CIESIELSKI ('72), DARWIN ('81), DET- LEFSEN ('82), WIESNER ('84), and SPAULDING ('94). DAR- WIN irritated the radicle of a bean by touching it near the apex with dry caustic (nitrate of silver). The point of wound- FIG. 103. — Diagram of a root tip, illustrating false traumatropism : ce?/,region of wounding. The line y-y' ran orig- inally parallel to the line x-x', but by growth has been brought to make an angle of 90° with it. * From Greek, rpaC/ua, a wound. f A phenomenon allied to this is seen when at an early stage one half of a frog embryo is killed and, consequently, remains of small size ; the larger, growing, side soon comes to bend around the smaller, dead, side. A fuller account of these experiments, made by Roux and others, upon the frog's egg, must be postponed to the next Part of this work, since it is complicated by the phenomenon of regeneration. §3] TRAUMATROPISM 385 ing appeared as a small, dark spot on one side of the radicle. The seedlings were then suspended in a moist chamber, over water, and at a temperature of 14.4° C. After 24 hours almost all of the radicles showed a marked curvature from- the wounded side. Other means can be used to produce this result : a thin slice cut off obliquely from the tip of the radicle, a drop of shellac, of copper sulphate, of potassium hydrate, or steam at about 95° C. (SpAULDixo) --in general, any agent which irritates strongly without killing. Concerning the place on the root where the injury must be made in order that a response should appear, SPAULDING finds that if the branding is made further from the apex than 1.5 mm. no traumatic curva- ture will occur ; or if an oblique cut at the apex should not involve the growing root tip, as at «6, Fig. 104, it is without effect. So it seems that the pro- liferating root tip is the sensitive part. The point of maxi- mum curvature is, how- ever, not at the root tip, but lies in the region of most rapid growth. The length of time elapsing between injury and response varies with the species and with the tem- perature. Thus, at a temperature of 18° C. the curvature begins in from 45 to 55 minutes, and reaches a maximum within 24 hours (WiESNER). The long, latent period and the slowness of complete response give an insight into' the reason for this separation of the per- ceiving and responding zones. During the . 7 , . . , latent period the irritated tissue is be- coming stretching tissue through the im- i -i •,- c -\ ••> ,1 ,- kibition of wat«r, ^hlle the.root tip IS becoming generated in advance, leaving FIG. 104. — Diagram showing the rela- tions of the root tip, r.t, and the root cap, r.c. ; a,b, line of a cut which involves only the root cap. FIG. 105.- Median longi- tudmal section through a gypsum cast, b, sur- rounding and repress- inga root of Viciafaba. Natural size. (From PFEFFER, '93.) 2c 386 EFFECT OF MOLAR AGENTS UPON GROWTH [Cn. XIV the irritated protoplasm behind. This can be demonstrated if (following PFEFFER, '93) the freshly irritated radicle is con- rined in a plaster cast (Fig. 105). The growth of the tip is slackened so that it does not leave the irritated tissue far behind ; at the same time, the zone of stretching encroaches upon the root tip, so that, if the radicle is released after several days, the curvature, although taking place, occurs abnormally near the tip. If the response were transmitted a fixed dis- tance backward from the tip, we should expect that in the confined plant either the turning would take place at the normal position or would altogether fail to occur. Since neither of these effects follows, the conclusion is strengthened that the identical plasm which is irritated responds, producing the traumatic curvature. Temperature, controlling as it does the rate of growth, con- trols the length of the latent period. According to the obser- vations of WIESNER, this is at — TEMPERATURE. IN DAMP CHAMBER. IN WATER. 8.0° C. 438 min. 393 min. 17.5° C. 87 52 25.0° C. 37 28 33.0° C. 58 70 Thus, 25° C. seems to be about the optimum temperature for the traumatropic response ; and this is a temperature 10° to 12° below the optimum for protoplasmic movements (Chap. VIII, § 2). The true explanation of traumatropism remains, after pro- longed discussion, uncertain. DARWIN regarded it as a response to stimulation, but DETLEFSEN and WIESNER sought to show that it is the immediate mechanical result of the injury. Thus, DETLEFSEN assumed tensions in the root cap, which caused the root when cut on one side to shorten on the other ; but this conclusion was disproved by SPAULDING, who found that the usual results do not follow when the root cap is injured without injuring the root tip. WEISNER'S explanation was based on the observation that decapitated roots grow more § 4] RHEOTROPISM 387 rapidly in water than normal ones. In like manner, if the root is, as it were, half decapitated, by cutting the tissue on one side, an abnormally rapid growth will take place on that side, proximal to the injury. The reason for this more rapid growth, continues WIESNER, is that the nutritive fluids intended for the tip are prevented by the injury from attaining the tip, and, consequently, go to build up the cell-walls above the wound. While the possibility of this explanation cannot be denied, the facts are not opposed to another interpretation, such as is offered by SPAULDING, and which is more in accord with the explanations of other tropic phenomena. This expla- nation is that the wounding produces a chemical change in the protoplasm of one side of the root, such that growth occurs more rapidly upon that side, either as a result of increased upbuilding of cell-walls or of increased imbibition of water, or of both. § 4. EFFECT OF FLOWING WATER UPON THE DIRECTION OF GROWTH - - RHEOTROPISM When the radicle of a bean is suspended by the cotyledons above a stream of flowing water, so that it lies in the axis of the current and points down stream, the free end, as it grows, gradually turns, and becomes directed up stream. It turns against the current. This remarkable phenomenon, named rheotropism by its dis- coverer, JONSSON ('83, p. 518), has been carefully studied by him by the following method : The stream, whose rate could be controlled at will, flowed in a trough. Over the current, seedlings of maize and other grains, with well-developed rad- icles, were suspended so that the radicles lay in the axis of the current, and were directed either up stream or down as desired. When the rootlets were directed down stream, a turning began, after a latent period of several hours, and reached its final posi- tion in the current in about twenty hours. If the rootlet was originally directed up stream, it simply grew straight ahead until mechanically bent out of position by the impact of the water. By directing a rootlet alternately down stream and up stream after each rheotropism has occurred, the whole root may become very zigzag. These facts show clearly that cer- 388 EFFECT OF MOLAR AGENTS UPON GROWTH [Cn. XIV tain radicles are sensitive to the impact of water, so that they turn in such a way that the irritant shall affect their two sides equally, and shall be directed against the tip. While the pre- cise part of the radicle which is sensitive to the current has not been determined, the responding part is in the region of greatest growth, and the response is such that the root becomes concave towards the irritant. Among animals, a response which probably belongs to this category has been observed by LOEB ('91, p. 36) in the grow- ing stem of the hydroid Eudendrium. In a vessel of water in which all other hydranths turned towards the light, there was one which rose near the cloacal opening of an ascidian, from which strong currents of water passed. This individual was turned with its concave side towards the impinging current. It is probable that the current had induced a rheotropic response. SUMMARY OF THE CHAPTER The rate of growth of the entire organism or of its organs is accelerated by contact, as in the stolons of hydroids ; by rough movement, as in bacteria ; by cutting — when accelerated growth occurs along the cut surface. Growth in length may be retarded by pulling, as in steins and roots. Many organisms show themselves very sensitive in their growth to mechanical irritation. The direction of growth is determined by external agents, acting as irritants, in the cases of the twining dodder, tendrils in general, roots, the hyphee of Phycomyces, the rhizoids of hepatics, and the hydranths of various hydroids. Wounding may cause a turning from the wounded side in the radicle of a seedling, and radicles and hydroids may even grow so as to face the current. The sensitiveness to contact may be excessively great, a swinging cotton rider weighing 0.00025 mg. causing a tendril to bend. This sensitive region varies from near the tip in roots to some distance behind the tip in the case of tendrils. The response may occur after seconds, as in Cuscuta, or after hours, as in traumatropism of radicles. The bending usually reaches a maximum at the region of greatest growth. The LITERATURE 389 stimulated condition persists for some time after irritation, so that a summation of effects may occur. An acclimatization to contact may appear, when no response is invoked by the irrita- tion. The thigmotropic response may be explained, in general, as due to a chemical change, wrought by the one-sided impact, such as to cause a disturbance in the equality of the growth processes — assimilation, secretion, or imbibition — on the two sides of the organ. LITERATURE BARANETZKY, J. 79. Die tagliche Periodizitat im Langenwachsthum der Stengel. Mem. de 1'Acad. de St. Petersb. XXVII. 91 pp. BUCHNEH, II. '80. Ueber die experimentelle Erzeugung des Milzbrand- contagiums aus den Heupilzen. Sb. k. bayer. Akad. Miinchen. X, 368-413. CIESIELSKI, T. 72. Untersuchuugen liber die Abwartskriimmung der Wurzel. Beitrage zur Biologic der Pflanzen. Band I, Heft II. pp. 1-30. Taf . I. DARWIN, C. '65. On the Movements and Habits of Climbing Plants. Jour. Linn. Soc. (Bot.). IX, 1-118. '82. The Movements and Habits of Climbing Plants. 208 pp. 3d thousand. London, 1882. [Date of first edition, 1875.] DARWIN, C. and F. '81. The Power of Movement in Plants. 592 pp. New York, 1881. DETLEFSEN, E. '82. (See Chapter XII, Literature.) DUTROCHET, H. '43. Des mouvements revolutifs spontanes qui s'observent chez les vegetaux. Ann. Sci. Nat. XX (Bot.), 306-329. '44. Recherches sur la volubilite des tiges de certains vegetaux et sur la cause de ce phenomene. Ann. Sci. Nat. II (Bot.), 156-167. ERRARA, L. '84. Die grosse Wachsthumsperiode bei den Fruchttragern von Phycomyces. Bot. Ztg. XLII, Nos. 32 to 36. Aug., Sept. 1884. HEGLER, R. '93. Ueber den Einfluss des mechanischen Zugs auf das Wachsthum der Pflanze. Beitrage z. Biol. d. Pflanzen. VI, 383-432. HORVATH, A. 78. (See Chapter IV, Literature.) JONSSON, B. '83. (See Chapter IV, Literature.) LEONE, T. '85. Sui microorganism! delle acque potabili. Atti della R. Accad. Lincei (4) Rencond. I. LOEB, J. '91. Untersuchungen zur physiologischen Morphologic der Thiere. I. Ueber Heteromorphose. Wiirzburg, 1891. '92. (See Chapter X, Literature.) MACDOUGAL, D. T. '96. The Mechanism of Curvature of Tendrils. Ann. of Bot. X, 373-402. April, 1896. MELTZER, S. J. '94. (See Chapter IV, Literature.) 390 EFFECT OF MOLAR AGENTS UPON GROWTH [Cn. XIV MOHL, II. v. '27. Ueber den Ban und das Winden der Ranken und Schling- pflanzen. Tubingen, 1827. MOLISCH, II. '84. (See Chapter XII, Literature.) MULLER, O. '86. Untersuchungen iiber die Ranken der Cucurbitaceen. Beitviige z. Biol. d. Pflanzen. IV, 97-144. NEWCOMHE, F. C. '95. The Regulatory Formation of Mechanical Tissue. Bot. Gazette. XX, 441-448. Oct. 1895. PALM, L. II. '27. Ueber das Winden der Pflanzen. 101 pp. 3 Tab. Stutt- gart, 1827. PEIRCE, G. J. '94. A Contribution to the Physiology of the Genus Cuscuta. Ann. of Bot. VIII, 53-117. - PI. VIII. March, 1894. PFEFFER, W. '85. Zur Kenntniss der Kontaktreize. Unters. a. d. bot. Inst. Tubingen. I, 483-535. '93. Druck und Arbeitsleistung durch wachsende Pflanzen. Abh. sachs. Ges. d. Wiss., Leipzig. XX, 235-474. REIXKE, J. '80. Ueber den Einfluss mechanischer Erschiitterung auf die Entwickektng der Spaltpilze. Arch. f. d. ges. Physiol. XXIII, 434-446. RUSSELL, H. S. '92. The Effect of Mechanical Movement upon the Growth of Certain Lower Organisms. Bot. Gazette. XVII, 8-15. Jan. 1892. SACHS, J. '73. Ueber das Wachsthum der Haupt- und Nebenwurzeln. Arb. Bot. Inst. Wurzburg. I, 385-474. '87. (See Chapter X, Literature.) SCHENCK, H. '93. Ueber den Einfluss von Torsionen und Biegungen auf das Dickenwachsthum einiger Lianen-Stamme. Flora. LXXVII, 313-326. SCHMIDT, B. '91. Ueber den Einfluss der Bewegung auf das Wachsthum und die Virulenz der Mikroben. Arch. f. Hygiene. XIII, 247. SCHOLTZ, M. '87. Ueber den Einfluss von Dehnung auf das Langenwachs- thum der Pflanzen. Beitr. z. Biol. d. Pflanzen. IV, 365-408. SPAULDING, V. M. '94. The Traumatropic Curvature of Roots. Ann. of Bot. 423-452. PL XXII. Dec. 1894. TUMAS, L. '82. Ueber die Bedeutung der Bewegung fur das Leben der niederen Organismen. Medic. Wochenschr. 1882. No. 18. St. Peters- burg. VERWORN, M. '95. Allgemeine Physiologic [1st Aufl.]. 584pp. Jena, 1895. DE VRIES, H. "73. Langenwachsthum der Ober- und Unterseite sich kriim- mender Ranken. Arb. Bot. Inst. Wurzburg. I, 302-316. WIESNEK, J. '84. Untersuchungen iiber die AVachsthumsbewegungen der Wurzeln. Sb. k. Akad. Wiss. Wien. LXXXIX1, 223-302. WORTMANN, J. '87. Zur Kenntniss der lleizbewegungen. Bot. Ztg. XLV, 785 et seq. Dec. 1887. CHAPTER XV EFFECT OF GRAVITY UPON GROWTH § 1. EFFECT OF GRAVITY UPON THE RATE OF GROWTH IT is a result of the sessility of the higher plants that they and their parts are acted upon continuously in one direction by gravity. It might consequently be suspected that the rate of their growth would be affected if they were placed in an abnormal position with respect to this agent. In the experi- ments which have been made to test the correctness of this suspicion various methods have been employed. When the growth of Penicillium which is removed from gravity's action by being slowly revolved on a klinostat is compared with that of a plant under normal conditions, the former is found to be more rapid. The plant seems to reap an advantage from not hav- ing to sustain its own weight (RAY, '97). When Phycomyces is inverted, its growth is slower than in the normal position (ELFVING, '80). These two experiments upon fungi indicate a considerable sensitiveness on their part to gravity. Experi- ments made by ELFVING ('80) and SCHWAEZ ('81). upon the growth of inverted phanerogams and those from which the action of gravity had been eliminated by the slowly rotating klinostat, as well as those which had been subjected to exces- sive pressure by the centrifugal machine, yielded for the most part only negative results. Upon the rate of growth of seed- lings gravity has little effect. § 2. THE EFFECT OF GRAVITY UPON THE DIRECTION OF GROWTH - - GEOTROPISM As with contact so with gravity two classes of effects may be distinguished, which, while often producing similar results, bring them about through very dissimilar processes. The first of these is a mechanical effect due to gravity acting upon the 391 392 EFFECT OF GRAVITY UPON GROWTH [Cn. XV growing organ as it might upon any other heavy body. The second is a vital effect, having no immediate, direct, physical relation to the cause. The first may be called false geotro- pism ; the second, true geotropism. 1. False geotropism may be treated very briefly, since it is not a true growth phenomenon. As an example of such geotro- pism may be cited the downward bending of the top of a stem heavily laden with a head of seed or with fruit, or the upward growth of the long fronds of kelp in the sea on account of the buoyant effect of the dense sea water. In such cases the direction of the growth can be accounted for upon well-known principles of hydrostatics. 2. True Geotropism. — The biological effect, on the other hand, which is seen in true geotropism is often opposed to the gross physical one. It shows itself especially in various groups of sessile plants and animals. Since, unfortunately, com- paratively few experiments have been made upon geotropism in animals, the great mass of our knowledge on this subject is derived from studies on plants. The general fact of geotropism strongly impresses one who stands on the shore of a lake in our northern country and looks across to the dense pine forest on the opposite side. The landscape is composed of vertical and horizontal lines - vertical lines below formed of close-set trunks of trees, hori- zontal lines above formed of the great branches. If at one side a steep slope ascends, its outline is obscured by the grill-work of perpendicular lines formed by the vegetation which clothes it. Here the effect — the dissimilar effect — of gravity in determining the direction of growth of two organs, trunk and branch, is seen. There are, however, still other organs which may respond to the same stimulus. Among these are the roots, flower stalks, and leaves of phanerogams ; the vertical parts of many vascular cryptogams ; the sporiferous hyphoe of fungi and some vertical algre, e.g. Chara. There is no need to examine all these cases of geotropism, but only such of them as will help us to get at the principles of the action of gravity in determining the direction of growth. a. Roots. - - When a seedling is so placed that its radicle is horizontal, the radicle does not continue to grow out in the §2] GEOTROPISM 393 same direction ; but all additional growth is vertical so that the radicle bends sharply downwards — it is positively geotropic. The curvature does not take place at the very tip of the root, — in the region of growth by assimilation, -- but immediately behind in the region of stretching or of growth by imbibition. The precise region at which the curvature occurs was deter- mined by CIESIELSKI ('72), by means of a method illustrated in Fig. 106. It is here seen that the maximum bending occurs in this radicle at between 3 and 4 mm. from the tip. It is also plain that the geotropic curvature is in some way connected with growth — could not occur without growth. To show that the normal vertical growth of a root is due to the press- ure of gravity, KNIGHT, in 1806, determined experimentally that the direction of its growth can be deter- mined by other pressures replacing gravity, such as centrifugal force. Thus when seedlings were attached to the rim of a wheel and this was made to rotate rapidly about a hori- zontal axis the radicles grew straight outward from the axis ; thus in the sense in which the centrifugal press- ure acted, as before they had grown in the sense of the pull of gravity. A second method of proof, employed by SACHS ('79), consisted in eliminating the effect of gravity by means of the klinostat (Chapter V, § 1), under which circumstances the root grew irregularly. Such results leave no room for doubt that it is gravity which determines the verticality of the root. The question now arises, in what way does gravity control the direction of growth of this organ ? An early suggestion was that the action was direct, due to the relatively great specific gravity of the root tip ; but this idea was easily refuted by a mass of evidence. Thus it is not, a priori, easy to see FIG. 100. — An originally straight radicle of the pea, graduated in 0.5 nun. spaces and placed nearly vertically with its apex directed upwards in the direc- tion of a, has turned down- wards in the zone of greatest growth at between 3.5 and 4 mm. from the tip. (From CIE- SIELSKI, '72.) 394 EFFECT OF GRAVITY UPON GROWTH [Cn. XV how the mere weight of the tip of the plant, supported as it is by the firm soil, should enable it to find its way down. Experiments, also, have shown that the radicle will curve downwards against considerable resistance such as is afforded by the surface of a cup of mercury, by a weight which is lifted by means of a thread passing over a pulley ( JOHNSON, '29), or by a delicate spring which is compressed by the down-curv- ing radicle (WACHTEL, '95). By these various methods it has been demonstrated that the down-curving of the geotropic radicle is an active process capable of overcoming resistance amounting, in one case, to 150 milligrammes. Consequently gravity does not act in a grossly mechanical way, but as a stimulus inciting a growth response. If now the down-curving of the root is a response the question arises, where is the stimulus received ; at the region of curvature or at some other point ? This is a question which has excited much discussion, owing to apparent contradictions in the experimental evidence. The first attempt to answer this question was made by CIESIELSKI * ('72), who cut off the terminal one-half millimeter of the radicle, placed the rootlet in a horizontal position, and found that, although growth con- tinued, no down-curving occurred until, after several days, the root tip had regenerated. He concluded that the root tip is useful or necessary in geotropism. SACHS ('73, p. 433) repeated CIESIELSKI'S experiments and likewise found an incomplete exhibition of geotropism. But this he attributed to the excessive irritation of the cutting, which led to exagger- ated movements of nutation, tending to obscure geotropism. DARWIN ('80) confirmed CIESIELSKI'S results after both cutting off the root apex and cauterizing it, and explained SACHS' partial failure to get like results on the ground that he did not amputate the radicles in a strictly transverse direction. DARWIN concluded that the "tip of the radicle is alone sensi- tive to geotropism, and that when thus excited it causes the ad- joining parts to bend." The exact length of the sensitive part seems to vary with certain conditions, but it is generally less * HARTIG ('66, p. 63) had already stated that the decapitated root was not geotropic. § 2] GEOTROPISM 395 than 1 to 1.5 mm. This terminal millimeter or so, then, acts like a sense organ in a vertebrate, which receives the sensation at some distance, it may be, from the responding organ. From this time on, two schools may be distinguished, of which the first, following DARWIN, regarded the stimulus as received at the root tip and transmitted to the region of Growth : while the second conceived the stimulus to act di- j? rectly upon the root in the bending region and to arise from the difference in the pressures on the upper and lower surfaces of the radicle. The second school persistently denied the validity of the decapitation experiments, WIESNER ('81) in particular maintaining that decapitation inhibited growth and consequently growth curvatures, but did not necessarily remove the sensitive organ. The first school was forced to new experi- ments. FRANCIS DARWIN ('82) maintained on the basis of such experiments that it is not the cutting per se which inhibits geotropism ; for the cutting of the root tip, as for example, lengthwise, without its removal, permits the normal response. But it was easy to reply to this that a transverse cut might well affect growth more seriously than a longitudinal one. The satisfactory solution of this difficulty required a method by which, without mutilating the root, gravity should act horizontally upon the chief growing part of the root without so acting upon the root tip. A method for accomplishing this- was invented by PFEFFER ('94). A radicle of a bean or other species, fixed to a klinostat, was made to grow into a small glass tube, closed at its further end and bent so as to form two arms, at right angles to each other, and each about 1.5 to- 2.0 mm. long. The preparation was now turned until the root tip was directed ver- tically downwards, while the rest of the root, and especially its chief growing re- gion, was horizontal (Fig. 107). This region FIG. 107. — Diagram il- was then subjected to the full transverse gating the method J employed m PFEF- action of gravity, while the tip was not so FER'S. experiment, acted upon. Meanwhile the normal growth processes were not interfered with, for as the root lengthened it backed out, so to speak, from the bent tube, the apex remain- 396 EFFECT OF GRAVITY UPON GROWTH [Cn. XV ing at the blind end. Under these conditions no geotropic cur- vature occurred ; but such curvature always took place when the root tip was placed horizontally or at any acute angle with the horizon. This experiment seems, then, better fitted than any previous one to prove that the geotropic sensitiveness of the root resides in the apex.* Consequently, since, as an in- spection of Fig. 106 will show, the curving part of the root can contain none of the originally irritated cells, there must be a transmission of stimuli from the root tip to the curving region. Two associated phenomena remain to be considered. First, geotropic response is more powerful, the bending becomes stronger, as the angle made by the root with the vertical in- creases, reaching a maximum when the root is horizontal (SACHS, '73, p. 454). Secondly, as already indicated, response does not take place immediately after the root is placed hori- zontally. In one experiment of SACHS' ('73, p. 440) a bean radicle placed horizontally and growing in loose earth at 20° C. began to turn downwards in the second hour. There is thus a considerable latent period. The cause of geotropism in roots is indicated by the con- ditions of its occurrence already mentioned. It is intimately associated with growth, yet, as KLRCHXER ('82) has shown, it may occur at a temperature (2° to 3.5° C.) at which growth is extremely slow. The turning is clearly due to unequal growth upon the convex and concave sides of the root. But is it due to acceleration on the convex side over the normal, to retarda- tion on the concave side, or to both ? Measurements have been made upon plants to decide this question. In one set of such measurements made upon the bean radicle by SACHS ('73, p. 463) the growth was hastened about 3% on the convex side and retarded 42% on the concave side, so that both accelera- tion and retardation occur. Finally, lateral roots which run more or less obliquely down- wards have been shown by SACHS ('74) and others to be influenced by gravity; for, if the plant be inverted, the roots will turn until they assume their normal inclination to the horizontal plane. * But species may differ in this respect as in phototropism (see page 441). §2] GEOTROPISM 397 b. Stems. - - The central fact that the upward growth of stems is determined by gravity is established by the observa- tions that on the klinostat no definitely directed growth occurs, and that on the centrifugal machine the stem turns in the opposite sense to that of the cen- trifugal pressure. The stem is nega- tively geotropic. As with roots, so with stems, a number of questions now arise : Where is the sensitive region and where the response? At what inclination of the stem is the strongest geotropic cur- vature called forth? What is the im- mediate cause of the curvature ? As Fig. 108 shows, the response of the stem of a seedling is fundamentally different from that of the radicle. In- stead of the tropism beginning at one point, and continuing there as in the root (Fig. 106), it begins close below the cotyledons of the seedling and passes downwards towards the base as far as growth is still occurring. Response, consequently, takes place along the whole , , . „ • rpi -,• FIG. 108. — Course of geotro- "stretching" region. The sensitive re- pism in a plumu]eg The gion also, unlike that of the root, is not successive figures i to IG confined to the tip, but extends along the entire bending stem. The position in which the strongest response is incited was believed by SACHS ('79a, p. 240) to be the horizontal one, and BATESON and DARWIN ('88) have confirmed this conclusion. Their method depends upon the fact that a stem placed horizontally and restrained for several hours from taking the verti- cal position will, upon being released, suddenly spring upwards. In using this method it was found that the stem springs through a greater arc after having been indicate successive stages in the geotropic turning of a seedliug growing in half darkness. Placed at first horizontal as at 1, the plant has become completely erect at 16. The most rapid growth is just behind the cotyle- dons and diminishes toward the base. The temporary bending beyond the vertical is to be noted. (FromSTRAS- BURGER, NOLL, SCHENCK, and SCHIMPER, Textbook of Botany, Macmillan.) 398 EFFECT OF GRAVITY UPOX GROWTH [Cn. XV restrained for two hours in a horizontal position than if re- strained in any oblique position, whether the tip be directed up or down. Concerning the cause of the curvature there is little to add to what was said under " Roots." The remote cause is appar- ently the dissimilar action of gravity on the upper and the under sides of the stem ; the immediate cause is the difference in growth on the two sides of the stem. In the special case of stems with knots, the knots show themselves especially respon- sive to the geotropic stimulus. c. Rhizoma. - - These horizontally running, root-like, subter- ranean stems are strikingly responsive to gravity, as ELFVING ('80), especially, has shown. He has reared various rushes in a glass box with their axes making various angles with the vertical. In their subsequent growth all the rhizomes of the plants extended in a strictly horizontal direction. In this case any component of gravity, however small, running in the direc- tion of the axis of the rhizome seems to irritate. The curving into a horizontal plane may be called transverse geotropism (diageotropism, FRANK). d. Cryptogams. --We, have already seen (p. 391) that the sporangiferous hyphse of Phycomyces nitens are negatively geotropic. The same is true of certain algfe. Thus RICHTER ('94) has found that when the stem of Chara is inverted the youngest two or three internodes curve upwards in their further growth so that the apex of the stem is now directed zenithwards. On the other hand the rhizoids of this species are positively geotropic. Rotation experiments show that in the absence of the directive pressure of gravity there is no definite orientation. Finally, some mosses are slightly geo- tropic. Thus, BASTIT ('91) reared Polytrichum juniperinum in the dark in both air and water, some plants being placed right side up, others inverted. In both cases new branches budded from the roots and, although etiolated, grew irregularly up- wards— there was a feeble negative geotropism. e. Animals. --Since only sessile organisms can be expected to show marked geotropism, this phenomenon among animals must be confined to rather few groups. It has been studied hitherto exclusively in the group of hydroids. Many repre- §2] GEOTROPISM 399 sentatives of this group show themselves, however, markedly responsive. The first observations upon geotropism in hydroids seem to have been made by LOEB ('91a, pp. 27, 28). He says : "When a stolon was formed at the cut end of a vertical stem (of Ag- laophenia) it grew (in case it did not come in contact with a solid body) first a short distance horizontally, and then down- wards. In horizontal stems the stolon grew directly down- Wi— \ / \ no FIG. 109. — Positive geotropism of regenerated stolons (TFj, TF2) and negative geotro- pism of regenerated hydranths of Aglaophenia plunia. The original piece of the stem is included between b and c. This piece was placed vertically, right end up, in the aquarium. At the cut end, 6, the stolon (Wi) has arisen, but has soon begun to grow downwards. It has produced a vertical hydrauth at s. W», an adventi- tious stolon. (From LOEB, '91'.) FIG. 110. — Two bits of regenerating stems of Antennnlaria antennina. The one at the left is in the normal position ; that at the right is inverted. From both, new hydranths (S) have developed at the upper end, and new stolons (W) at the lower end. (From LOEB, '92.) 400 EFFECT OF GRAVITY UPON GROWTH [On. XV wards." "Adventitious stolons grew directly downwards towards the earth. This was most noteworthy when such adventitious stolons arose from a reversed stem (with the apex down) sticking in the sand ; under these circumstances the stolon grew towards the apex. These descending stolons showed occasionally twistings and curlings, such as are found in tendrils. The newly arising sprouts [hydranths] behaved in the reverse fashion from the stolons : they grew vertically upwards" (Fig. 109). Subsequently, LOEB ('92, p. 8, '94) FIG. 111. — A bit of regenerating stem of Antennularia antennina placed in the water obliquely, with the basal end downwards. The new hydranths (S) and stolons (W) arise vertically. (From LOEB, '92.) FIG. 112. — A piece of the stem of Antennularia placed horizontally, and regenerating stolons (r, r) downwards, and hydranths (6, c) upwards. (From LOEB, '94.) found another hydroid, Antennularia, which, whether the stem was held inverted, oblique, or horizontal, sent out new stems, which grew vertically upwards, and stolons, which grew verti- cally downwards (Figs. 110, 111, 112). The growing stolon, if moved out of its first position, will curve until it acquires again its vertical direction. The geotropism of stolons has been likewise carefully studied by DR'IESCH ('92). This author found in a species of Sertularella that, although the main stolons are not geotropic, the daughter (secondary) sto- §2] GEOTROPISM 401 Ions are markedly negatively geotropic. As the following figure shows (l^ig- US), it is only the newly growing part which exhibits this geotropism. These geotropic movements FIG. 113. — Diagrams of a Sertularella stock, showing how the direction of growth is determined by gravity. The arrow points towards the earth's centre. The stock originally placed in the position « is subsequently reversed as at b, and again as at d. The asterisk indicates a hydranth. (From DRIESCH, '92.) in animals, which occur near the growing apex, are clearly due to unequal growth on the two sides of the inclined stem or stolon. Many untouched questions on geotropism in animals arise for solution — questions about the location of the perceiving and the responding portions of the stem, latent period and after effect, and others. Especially is it desirable to find how wide-spread the geotropic phenomena are in sessile animals. /. After-effect in Creotropism. - - When a root or stem is placed horizontally, and retained in that position for a part of its latent period, and then, before the curving has appeared, is rotated on its long axis through 180°, the turning takes place at about the time and towards the same side as it would had the organ been left undisturbed ; in its new position the root turns up, and the stem, for the moment, down. The response, once set in motion, works itself out, until finally annihilated by an opposing response (HOFMEISTEK, '63 ; CIESIELSKI, '72). This experiment has been variously modified in ways which throw light on the meaning of the after-effect. It has repeat- edly been observed that if the root tip be decapitated before 2D 402 EFFECT OF GRAVITY UPON GROWTH [Cn. XV the end of the latent period the geotropism will occur in the normal manner. The impulse once transmitted, the geotropic function of the root tip is finished. Again, SACHS ('74a) laid a stem in a horizontal position for an hour or two, until up- curving had commenced near the tip. The tip was now held horizontal, and for from one to three hours, during which stretching took place, the horizontal part grew horizontally, while the new tip turned zenithwards. The tip in turning de- termines the direction of the incipient stretching zone, and the stretching continues in this direction without regard to subse- quent changes in position of the stem. The stretching is inde- pendent of an}7- control on the part of the tip. Other conditions of geotropic after-effect have been deter- mined by WOUTMANN ('84). He treated a stem according to SACHS' method, and placed it in a chamber filled with hydro- gen. Growth ceased. After oxygen was readmitted the tip turned up at once, but no after-effect appeared. This had been annihilated by the absence of oxygen. If, however, the stimulated sprout was placed vertically in de-aerated water, there was an after-effect, but no geotropic response. So we may conclude that, in the absence of oxygen, the geotropic response will not occur : and that an after-effect may occur if the stretching tissue is bathed with water for imbibition, but not under other conditions. SUMMARY The rate of growth seems to be little affected by the absence of gravity or the abnormal condition of its action, except in some of the higher fungi, where the removal of gravity hastens growth, and its abnormal direction retards. Geotropism is found only in sessile organisms. In roots the turning occurs in the region of greatest growth, and the tip alone is sensitive to gravity's action. The response is preceded by a latent period, and is strongest after the root has been placed hori- zontal ; it is due, in the case of both roots and stems, to an acceleration of growth on one side and its retardation on the other. In plumules the turning begins near the tip and pro- ceeds towards its base ; the whole bending region is responsive LITERATURE 403 as well as sensitive. Many cryptogams show negative geo- tropism. Many branches and rhizomes show transverse geotro- pism. Among animals, hydroids show negative geotropism. A marked after-effect follows negative stimulation, by means of it we can show that stretching or the geotropic curvature are independent of any control from the tip after once the stimulus has been transmitted to the stretching region. Like other responses to stimuli, geotropism does not occur in the absence of oxygen. LITERATURE BASTIT, E. '91. Recherches anatomiques et physiologiques sur la tige et la feuille des mousses. Rev. Gen. de Bot. Ill, 255 et seq. BATESON, ANNA, and DARWIN, F. '88. On a Method of Studying Geotro- pism. Ann. of Bot. II, 65-68. June, 1888. CIESIELSKI, T. '72. (See Chapter XIV, Literature.) DARWIN, C. '80. (See Chapter XII, Literature.) DAHWIN, F. '82. On the Connection between Geotropism and Growth. Jour. Linn. Soc. XIX, 218-230. DRIESCH, H. '92. Kritische Erorterungen neuerer Beitrage zur theoretischen Morphologic. II. Zur Heteromorphose der Hydroidpolypen. Biol. Centralb. XII, 545-556. 1 Oct. 1892. ELFVING, F. '80. Beitrag zur Kenntniss der physiologischen Einwirkung der Schwerkraft auf die Pflanzen. Acta Soc. Scient. Fennicse, Helsing- fors. XII, 25-58. '80a. Ueber einige horizontal wachsende Rhizome. Arb. Bot. List. Wiirz- burg. II, 489-494. HARTIG, T. '66. Ueber das Eindringung der Wurzeln in den Boden. Bot. Ztg. XXIV, 49-54. 16 Feb. 1866. HOFMEISTER, W. '63. Ueber die durch die Schwerkraft bestimmten Richt- ungen von Pflanzentheileu. Jahrb. f. wiss. Bot. Ill, 77-114. JOHNSON, H. '29. The Unsatisfactory Nature of the Theories proposed to account for the Descent of the Radicles in the Germination of Seeds shewn by Experiments. Edinb. New Pliilos. Jour. April, 1829. 312-317. KIRCHNER, O. '82. Ueber die Empfindlichkeit der Wurzelspitze fur die Einwirkung der Schwerkraft. Prog, zur 64. Jahresfeier d. k. Wiirt- temb. Landwirths. Akad., Hohenheim. 53 pp. Abstr. Bot. Centralb. XIII, 180-183. KNIGHT, T. A. '06. On the Direction of the Radicle and Germen during the Vegetation of Seeds. Phil. Trans. London for 1806. pp. 99-108. LOKB, J. '91. Ueber Geotropismus bei Thieren. Arch. f. d. ges. Physiol. XL IX, 175-189. 404 EFFECT OF GRAVITY UPON GROWTH [Cn. XV '91a. Untersuchungen zur pbysiologischen Morphologie der Thiere. I. Ueber Heteromorphose. 80 pp. Taf. Wiirzburg, 1891. '92. Untersuchungen zur physiologischen Morphologie der Thiere. II. Organbildung und Wachsthuin. Wiirzburg : G. Hertz. 81 pp. '94. On Some Facts and Principles of Physiological Morphology. Biol. Lectures, Wood's Holl Laboratory, 1893. pp. 37-61. PFKFFEK, W. '94. Geotropic Sensitiveness of the Root-tip. Ann. of Bot. VIII, 317-320. Sept. 1894. RAY, J. '97. Variations des champignons inferieurs sous 1'influence du milieu. Rev. Gen. de Bot. IX, 193-212, 245-259, 282-304. June- Aug. 1897. RICHTER, J. '94. Ueber Reaction der Characeen auf aussere Einfliisse. Flora. LXXVIIT, 399-423. SACHS, J. '73. Ueber das Wachsthum der Haupt- und Nebenwurzel. Arb. Bot. Inst. Wiirzburg. I, 385-474. 74. The same, continued. Arb. Bot. Inst. Wiirzburg. I, 584-634. '74a. Ueber Wachsthuin und Geotropismus aufrechter Stengel. Flora. LVI, 320-331. 79. Ueber AusscMiessung der geotropischen und heliotropischen Kriim- mungen wiihrend des Wachsens. Arb. Bot. Inst. Wiirzburg. II, 209- 225. 79a. Ueber orthotrope und plagiotrope Pflanzentheile. Ibid. pp. 226- 284. '87. Vorlesungen iiber Pflanzen-Physiologie. 2 Aufl. Leipzig : Engel- mann. 884 pp. 1887. SCHWARZ '81. Der Einfluss der Schwerkraft auf das Langenwachsthum der Pflanzen. Unters. Bot. Inst. Tubingen. I, 53-96. WACHTEL, M. '95. Einige Versuche betreffend die Frage uber die geotrop- ischen Krummungen der Wurzeln. Abstr. in Bot. Centralb. LXIII, 309, 310. WIESNER, J. '81. Bewegungsvermogen der Pflanzen. Wien, 1887. WORTMANN, J. '84. Studien Uber geotropische Nachwirkungserscheinungen. Bot. Ztg. XLII, 705-713. 7 Nov. 1884. CHAPTER XVI EFFECT OF ELECTRICITY ON GROWTH § 1. EFFECT OF ELECTRICITY UPON THE RATE OF GROWTH ELECTRICAL changes are so intimately associated with chem- ical changes that we may reasonably expect not only to find that the metabolic processes of growth are accompanied by the development of electricity, but also to find that an electric current disturbs growth. It is indeed known that electricity is produced in seedlings, for MULLER-HETTLINGEN ('83) has obtained from a seedling of Vicia faba by connecting the two extremities a maximum electro- motive force of about one-tenth of a volt. (Fig. 114.) There is thus in the living plant an elec- tric stress. Will an outside cur- rent, which must affect that of the organism, disturb also its growth? In the case of the growing animal even a slight current of electricity is usually injurious. Thus LOMBARDLNI ('68) and WlNDLE ('93 and ?95) have sub- FIG. 114. — Vicia seedling. jected the egg of the chick to such a current running trans- versely through the embryo, with the result that the embryo either soon ceased to develop or devel- oped abnormally. RUSCONI ('40), on the other hand, believed that a slight current accelerated the development of the frog's egg. More extended experiments with known strengths of currents are much to be desired.* * Certain unconfirmed results with a powerful magnet deserve to be noted. MAGGIORINI ('84) found that developing hens' eggs subjected to this agent pro- duced four times the normal number of cases of arrested development. 405 *»— > The lines uniting different points of the seed- ling may represent the wires run- ning to the galvanometer ; the points themselves are those from which the current was led off ; the arrows go with the currents in the wires. (From MULLER-HETTLINGEN, '83.) 406 EFFECT OF ELECTRICITY [Ca. XVI Upon growing plants, on the other hand, numerous experi- ments have been made. Nevertheless there is still a difference of opinion even as to the occurrence of any effect. During the middle of the last century much attention was paid to this subject. BERTHELON (1783) and several others concluded from extended researches that electricity favors plant growth ; but their results, apparently having no practical value, were largely forgotten. A century later GRANDEAU ('79) revived the idea of the beneficial effect for plants, not merely of cur- rents of electricity, but also of those of the atmosphere. This paper seems to have been the starting-point of the modern discussion. The methods employed in studying the action of electricity FIG. 115. — The effect of atmospheric electricity upon the growth of plants. A, To- bacco plant reared under normal conditions. B, Similar plant reared under a wire cage, by means of which it is isolated from the action of atmospheric elec- tricity. (From GRANDEAU, '79.) § l] UPON THE RATE OF GROWTH 407 have been of two general kinds. On the one hand the seedling is electrified by passing a current through the soil in which it is growing and after several days comparing it with an untreated seedling. On the other hand the tension of the atmospheric electricity is altered either by electrifying the air of the chamber in which a plant is growing, or by isolating a plant from the action of atmospheric electricity by means of a cage made of fine wire and with meshes so wide that a minimum amount of light is cut out (Fig. 115 A and B). The method of passing a current through the soil has been employed by WARREN ('89), CHODAT ('92), McLsoD ('93 and '94), and by other investigators with results favorable to the plants. McLEOD passed the current transversely. He sunk plates of metal on either side of the pea seeds employed in the experiment and used a current from a single cell. While the control seedlings germinated somewhat earlier than the electrified ones, at the end of 45 days the latter had outstripped the former. Again, a coil of wire, partly stripped of its insula- tion, was imbedded in the ground, and from a lot of similar mustard seeds some were placed next to the uncovered wire and others about one inch away from the insulated part of the wire. A constant current was sent through, and at the end of seven days the seedlings planted near the uncovered wire were one-third larger than the others. CHODAT used a current passing lengthwise through the plant. Similar beans were di- vided into two equal lots and each was reared in glass cylinders under similar conditions, except that one was unelectrified while the other was electrified by the following method. The cylinder rested on one armature of tin-foil while the other was suspended 1.8 meters over the first. The armatures were connected with a Holtz machine and a current was passed through the cylinder for about three hours each day. The result was that on the fourth day leaves began to show on the electrified seedlings but not on the control ones, and on the seventh day all the electrified seedlings had attained considerable size, whereas the control ones were just making their appearance. The electrified seedlings were spindling, however, much as if reared in the dark. WARREN'S experi- ments are noteworthy in that he found the seedlings which 408 EFFECT OF ELECTRICITY [Cn. XVI were nearer the positive electrode more advanced than those which were nearer the negative electrode. The method of electrifying the air over the plants was employed by CELT ('78), FREDA ('88, on Penicillium), and LEMSTROM ('90). Their methods were somewhat dissimilar: CELI discharged static electricity through a wire breaking up into fine points over the growing seedlings and got increased growth 5 FREDA used a similar method with Penicillium reared on bread but obtained no favorable effect , LEMSTROM conducted his experiments upon a larger scale, since he covered a small part of a field of germinating barley with fine parallel wires about a meter apart, provided with metal points at intervals, and supplied with a current from a Holtz machine during eight hours a day for over two months. In LEM- STRUM'S experiments the yield of the electrified field was 35% in excess of that of the unelectrified, and the quality of the grain was better. These experiments, which extended through several years, were carried on in various parts of Scandinavia and in France, and generally resulted in a favor- able effect upon the growth of malt crops. The method of eliminating atmospheric electricity was used with success by GRANDEAU ('79), who employed the method of isolating seedlings in a wire cage referred to on p. 407. The plants reared in the wire cage grew uniformly less rapidly than similar plants reared outside. ALOI ('95) has confirmed these results with the same method, using maize and bean seedlings. On the other hand other investigators, preeminently WOLLNY ('93), who used the methods both of increasing and of eliminating atmospheric electricity, obtain only negative results. Thus the whole matter stands, rejected on a priori grounds by many, denied as a result of negative experiments by others, but still apparently demonstrated by three lines of experimentation, none of them, However, free from criticism. There prevails a cautious scepticism concerning the validity of the positive results obtained. Various explanations have been offered by those who accept the positive results. FREDA, who found that Penicillium is injured by the increased atmospheric electricity, attributed that § 2] UPON THE DIRECTION OF GROWTH 409 injury to the greatly increased amount of ozone that appeared in his vessels. In the open air, on the other hand, the increase of ozone would be relatively so slight that it might well be advantageous to growth. WARREN'S results would then be accounted for by the fact that the ozone is especially produced at the positive pole, thus favoring for a time the excessive growth at that pole. On this explanation the electricity would act only indirectly. Somewhat similar is the conclusion of THOUVENIN ('96), that the electric current aids the plant in its decomposition of carbon dioxide. On the other hand there is reason for believing that since plants are adjusted to an (internal) electrical condition, a slight external one might be advantageous rather than injurious. § 2. EFFECT OF ELECTRICITY UPON THE DIRECTION OF GROWTH - - ELECTROTROPISM In 1882 the Finnish botanist ELFVING announced his dis- covery that when the radicle of the seedling of a bean or of certain other species was subjected in water to a transverse current of electricity, it grew towards the anode. This was the introduction to a series of interesting studies on what has been called electrotropism. In classifying the data which have been acquired we may make use of the following heads : 1. False and True Electrotropism ; 2. Electrotropism in Phanerogams ; 3. Electrotropism in Other Organisms ; 4. Magnetropism ; and 5. Explanation of Electrotropism and Summary. 1. False and True Electrotropism. — ELFVING himself ob- served two opposing phenomena in the seedlings which he subjected to the current. In most cases the radicles grew towards the anode, but in one species, Brassica oleracea — the wild cabbage --the radicle grew towards the kathode. ELF- VING was inclined, in consequence, to believe that some species respond by growth in one direction and other species by the opposite growth ; that these are diverse responses to the same agent, just as negative and positive chemotropism are. Gradu- ally, however, it became evident, chiefly through the work of MULLER-HETTLINGEN ('83) and especially BRUNCHORST ('84, '89), that these results are due to dissimilar causes. Thus 410 EFFECT OF ELECTRICITY [Cn. XVI BRUNCHORST ('84, p. 209) found that the radicles of seedlings of Brussica grow, under otherwise similar conditions, at a cur- rent intensity* of 0.03 8 to 0.05 8, towards the kathode, and at a current intensity of 3.0 8 towards the anode (Fig. 116). BRASSiCA FIG. llfi. — Effect of different strengths of electric current on the radicle of Brassica. At the right : strength of current, 1.1 S ; all strongly negative and growing well. At the middle : strength of current, 1.8 5; after a few hours negative at the apex but positive higher up. At the left : strength of current, 3.1 5 ; all positive, weak, and dead. (From BRUNCHORST, '84.) If decapitation has occurred the kathode turning does not follow, whereas the anode turning does occur as in the intact root. A similar result having been obtained with seedlings of various species, the conclusion was drawn that "the positive galvanotropic curving is a simple chemico-pathological phenom- enon which has only a superficial analogy with the directive movements of roots, and therefore does not deserve the name galvanotropism " [electrotropism]. The cause of the positive turning effect, it has been sug- gested, lies in the fact that certain substances, perhaps hydrogen peroxide and ozone, produced in electrolysis act more injuriously upon the positive than upon the negative side. According to another explanation, offered by RlSGHAWl ('85), the positive curvature is due to the kathophoric action *The current density (see Chapter VI, § 1) is calculated from the following data : The amount of copper deposited in a voltameter was 0.14 mg. to 35 mg. per hour during the course of experimentation. A current of one ampere intensity deposits 0.000326 gramme of copper per second or 1.17 mg. per hour per milliampere. Thus the strength of current varied from 0.12 to 30 milliamperes. The determination of the density requires a knowledge of the cross-section over which the current spread itself. For this we may take the given area of the electrodes, 6499 sq. mm., which is not far from the cross- section of the trough. §2] UPON THE DIRECTION OF GROWTH 411 T •••• of the current.* DuBois-REYMOND had found that when a current was passed through a cylinder of hard-boiled albumen it became concave towards the anode owing to the passage of water into the plant and its aggregation at the kathode side. RISCHAWI found that a cylinder of plant tissue did the same, and he attributed this result as well as that seen in the living radicle to the accumulation of water at the kathode side. But, 'as BRUNCHORST points out, this is not the whole explana- tion, for the positive curving is generally accompanied by death of the tissue, and death would not necessarily result from the kathophoric action. By the use of a transverse partition of porous clay BRUNCHORST ('89) has been able to show that the radicles in the positive half of the vessel are much more seriously affected than those in the negative half, which fact the kathophoric theory will not explain, but the chemical theory will (Fig. 117). In accordance with the view that the positive reaction is not a reaction to stimulus, but is a false electrotropism, it will be henceforth neg- lected. The negative reaction, on the contrary, is a response to stimulus — a true electro- tropism. 2. Electrotropism in Phane- rogams.--We have seen that the transverse electric cur- rent, when not too strong, causes a turning of the tip of the seedling from the anode. That this turning is a growth phenomenon is indicated by the fact that it takes place a few millimeters behind the tip in the region of maximum growth. This is then the region of response. * The kathophoric action is seen when an electric current passes perpendicu- larly through a porous partition submerged in water. The liquid moves through the partition towards the kathode (hence called also electrical endosmosis). FIG. 117. — Radicles of Phaseolus on opposite sides of a partition, T, subjected to a transverse electric current, of K.5 5 inten- sity, for two hours. On the positive side of the partition all the roots are strongly positive ; on the negative side, where tlie water is being continually renewed, the roots are slightly positive, being bent less than 40°. (From BRUNCHORST, '89.) 412 EFFECT OF ELECTRICITY [Cn. XVI The location of the sensitive region has been demonstrated by various methods. MULLER-HETTLINGEN placed the tip only of a radicle in contact with moist flannel through which the current was passing ; the radicle turned from the anode. Also BRTJNCHOEST ('84) found that when merely the apex was in contact with the electrified water there was a marked turning from the anode, even when the current was so powerful as to cause the submerged root to turn towards the anode. The tip is sensitive. Next BRUNCHORST cut off the tip and found that no response occurred when the current traversed the radicle. Hence the tip is necessary to response, and it may be con- cluded provisionally that as in geotropism so in galvanotropism the root tip is the only sensitive part of the radicle. The critical point at which the electrotropic effect passes into the mechanical one is indicated by a sigmoid turning of the radicle. According to BRUNCHORST'S observations this critical point lies, at a temperature of 20°, for Phaseolus seed- lings near 1.28; for Helianthus near 1.38; for Lupinus, 2.58; for Brassica, 38; for Lepidium, 3.58. These results indicate that the different species have a diverse sensitiveness to the electric current, so that an intensity which causes the radicle of one species to turn from the anode will cause the other to turn towards it (false electrotropism).* 3. Electrotropism in Other Organisms. -- While the stolons of hydroids, Bryozoa, and tunicates offer an excellent oppor- tunity for experiments on electrotropism in animals, results have been obtained, so far as I know, outside the group of phanerogams only in the mold Phycomyces. HEGLER ('92) has subjected this organism not to the ordinary electric current, but to HERTZ' electric waves.f The result was that, after exposing to the radiant electricity for from three to six hours, the sporangiferous hyphse curved markedly from the source of * We can now easily understand why ELFVING obtained, with approximately the same current, a positive curvature in many species, but a negative one with Brassica. As the list just given shows, the critical point in Brassica lies high. t These were obtained by reflecting, by means of a parabolic tin reflector, the radiant energy upon the stems of the fungi. The latter were covered with a pasteboard box, to keep out light, and the whole experiment was performed in a darkened room. The fungi were experimented with when about 8 to 10 cm. long, a period when they are most sensitive to light. § 2] UPON THE DIRECTION OF GROWTH 413 the rays in the same fashion, but not so powerfully, as they would have curved from light. Thus, electric waves produce in Phy corny ces a negative electro tropism. 4. Magnetropism. --It was stated in an earlier chapter* that magnetism has no clearly established effect upon proto- plasm. The alleged effect on growth is, consequently, worthy of attention. TOLOMEI ('93) placed over a glass vessel con- taining germinating peas a large horseshoe magnet, connected with a battery composed of eight Daniell cells. The germi- nating organs bent away from the centre of the magnetic field ; by an appropriate position of the magnet the roots might be forced to grow upwards. TOLOMEI also asserts that young plants are diamagnetic, i.e. tend to place their long axes at right angles to the lines of force of the magnet. These results are interesting enough to deserve confirmation. 5. Explanation of Electrotropism and Summary. — Is elec- trotropism the direct result of the current, or is it, like the effect upon the rate of growth, an indirect result, due, for instance, to chemical agents produced by the current ? If the action is indirect, it may be either of a mechanical or of a chemical nature. Risen A wi, who proposed the very clever explanation of positive curvature on the ground of katophoric action, offered a similar explanation for negative electrotro- pism. He finds that a cylinder made of coagulated yolk, and placed in the water transverse to the current, bends at first convex to the anode, owing to the more rapid diffusion at first of water into that side ; but, later, when the whole mass becomes permeated, it bends so as to be concave towards the anode. So, in the root, a weak current can induce a weak dif- fusion of the external water into the cells on the anode side. This theory does not, however, meet the conditions ; for, first, a long-continued weak current does not induce the positive curvature, and, secondly, because the decapitated root does not turn from the anode, and the irritation of the tip alone can induce the result. The mechanical theory must be rejected. There remains only the other theory, that the negative tro- pism is a response to a stimulus of some sort applied at the tip. * Chapter VI, § 1. 414 EFFECT OF ELECTRICITY UPON GROWTH [Cn. XVI It is possible that the stimulus is due to a chemical agent pro- duced by the current, or directly to the current itself. The first alternative is opposed by the fact that the reflected HERTZ waves, which have little or no gross chemical effect, still incite a response. There is every reason for concluding that the electric current, like gravity, and, as we shall see, light, acts in determining the direction of growth immediately. The electric current appears to affect the rate of growth of some plants, so that they grow more rapidly when lying in the magnetic field or in a highly electrified atmosphere than other- wise ; but this effect is often slight and uncertain. The direc- tive effect on the growth of elongated organs is more marked. Apart from a false electrotropic effect produced by the injury of the positive side of the root, so that growth ceases on that side, there is a true electrotropic effect, which shows itself in a turning of the root from the anode. This is a true response to stimulus, depending for its consummation upon the presence of the root tip. The HERTZ waves produce this effect in Phyco- niyces. Magnetism has an uncertain effect. The whole phe- nomenon is closely like that of response to gravity and light. LITERATURE ALOI, A. '91. Del? influenza dell' elettricitk atmosferica. Malpighia. V, 116-125. '95. Dell' influenza dell' elettricita atmosferica sulla vegetazione delle piante. Bull. Soc. Bot. Italiana. Oct. 1895. pp. 188-195. BERTHEJ.ON DE ST. LAZARE 1783. De 1'electricite des vegetaux, ouvrage dans lequel ou traite de 1'electricite de I'atniosphere sur les plantes, etc. Paris et Lyon : Didot. 468 pp. 3 Tab. BRUNCHORST, J. '84. Die Funktion der Spitze bei den Richtungsbewegungen der Wurzeln. II. Galvanotropismus. Ber. D. Bot. Ges. II, 204-219. '89. Notizen iiber den Galvanotropismus. Bergens Mus. Aarsberetning for 1888. No. 5. 35 pp. CELI '78. Appareil pour experimenter 1'action de 1'electricite sur les plantes vivantes. Comp. Rend. LXXXVII, 611-612. 22 Oct. 1878. CHODAT, R. '92. Quelques effets de 1'electricite statique sur la vegetation. Arch. Physiq. et Nat. (3), XXVIII, 478-481. DuBois-REYMOND, E\ '60. Ueber den secundaren Widerstand, ein durch den Strom bewirktes Widerstandsphanomen an feuchten porosen Korpern. Monatsber. Berlin Ak. 1860. pp. 846-906. LITERATURE 415 ELFVING, F. '82. Ueber eine Wirkung des galvanischen Stroms auf wachs- ende Keimlinge. Bot. Ztg. XL, 257-264, 273-278. Apr. 1882. FREDA, P. '88. Sulla influenza del flusso elettrico nello sviluppo dei vegetal! aclorofillici. Le stazioni sperimentali agrarie ital. Roma. XIV, 39- 56. [Abstr. iu Just's Jahresber. XVI, 93, 94.] GAUTIER, A. '95. [Comments on paper of FLAMMARION.] Comp. Rend. CXXI, 960, 961. 16 Dec. 1895. GRANDEAU, L. '79. De 1'influence de 1'electricite atmospherique sur la nutrition des vegetaux. Ann. de Cliim. et de Physiq. (5), XVI, 145- 226. Feb. 1879. HEGLER, R. '92. Ueber den Einfluss des mechanischen Zugs auf das Wachs- thum der Pflanze. Beitrage zur Biologie der Pflanzen. Band VI. Heft. Ill, 383-432. Taf. XII-XV. LEMSTROM, S. '90. Om elektricitetens inflytande pa vaxterna. Helsingfors, 1890. 67 pp. 4°. [Abstr. in BAILEY. Trans. Mass. Horticult. Soc. for 1894. 54-79.] LOMBARDINI '68. Forme Organiche Irregolari negli Ucelli e ne' Batrachida. Pisa, 1868. MAGGIORINI, C. '84. Influenza del magnetismo sulla embriogenesi e sterili- mento degli uovi. Atti Acad. Lincei. (3), Transmit!, VIII, 274-279. McLEOD, H. M. '93. The Effect of Current Electricity upon Plant Growth. Trans, and Proc. New Zealand Inst. XXV, 479-482. May, 1893. '94. The same. Ibid. XXVI, 463, 464. MULLER-HETTLINGEN, J. '83. Ueber galvanische Erscheinungen an kei- menden Samen. Arch. f. d. ges. Physiol. XXXI, 193-214. 2 May, 1883. RISCHAWI, L. '85. Zur Frage iiber den sogenannten Galvanotropismus. Bot. Centralb. XXII, 121-126. RUSCONI, M. '40. Ueber kiinstliche Befruchtungen von Fische und iiber einige neue Versuche in Betreff kiinstlicher Befruchtung an Froschen. Arch. f. Anat. Physiol. und wiss. Medicin (Miiller). 1840. 185-193. THOUVENIN, M. '96. De 1'influence des courants electrique continues sur la decomposition de 1'acide carbonique chez les vegetaux aquatique. Rev. Gen. de Bot. VIII, 433-450. TOLOMEI, G. '93. Azione del magnetismo sulla germinazione. Malpighia. VII, 470-482. [Abst. Just's Jahresber. XXI, 37.] WARREN, H. N. '89. The Effects of Voltaic Electricity toward Germina- tion. Chem. News. LIX, 174. WINDLE, B. C. A. '93. On Certain Early Transformations of the Embryo. Jour, of Anat. and Physiol. XXVII. 436-453. July, 1893. '95. On the Effects of Electricity and Magnetism on Development. Jour. of Anat. and Physiol. XXIX, 346-351. April, 1895. WOLLNY, E. '93. Electrische Culturversuche. Forsch. Agr. XVI, 243- 267. [Abstr. in Just's Jahresber. XXI, 36.] CHAPTER XVII EFFECT OF LIGHT UPON GROWTH WE have seen in Chapter VII that light profoundly affects metabolism, not only by its heat rays, which are essential to the process of starch formation in green plants, but also by its more chemically active rays, which produce chemical changes in organisms of all classes. We have now to see how, as a result of these effects, light has an influence upon growth. § 1. EFFECT OF LIGHT ON THE RATE OF GROWTH Two fundamental principles, established in the First Part of this work, must be recognized at the outset of this discussion, or else the data which have been accumulated will appear con- fused and meaningless. The first principle is that white light is not a constant, definitely determined thing, but varies in its intensity, and, as we saw in the case of phototaxis (I, p. 201), at the different intensities produces diverse, even opposing, effects. The second principle is that not all organisms are sim- ilarly affected by the same intensity of white light. This is because they are attuned to diverse intensities of light, so that the same intensity will call forth a dissimilar response in differ- ent organisms (I, p. 196). It is a consequence of these two principles that, when we classify our data on the basis of the intensity of the light, we shall find dissimilar effects in each class ; or when, on the other hand, we classify on the basis of results, we shall have to consider in each class apparently diverse causes. Since, however, results are always more cer- tain than causes, we adopt the method of treatment on the basis of results. 1. Retarding Effect of Light. --We have already in the First Part of this work seen that Protista are injuriously affected by strong sunlight, cultures of bacteria becoming 416 § 1] EFFECT OF LIGHT UPON GROWTH 417 sterilized and ordinary aquaria being quickly deprived of living occupants. To the higher organisms, on the other hand, sunlight is generally not fatal, but is usually unfavorable to growth. This result is most clearly seen in seedlings. Thus WIESNER ('79, p. 181) exposed seedlings of the vetch Vicia sativa under a clear glass globe to sunlight, after having marked off a centimeter's distance upon its zone of strongest growth, and having placed it in a horizontal position so that it should get the full force of the sun's rays. No growth occurred during seven and a half hours, although the control, in a dark- ened globe, turned its tip upwards and grew from 2.5 to 8.1 mm. during that period. A vertical seedling of the same age was so protected by its foliage that in the sunlight it grew from 0.5 to 1.2 mm. on the different sides. Thus, when the growing part of a seedling is exposed to sunlight, little or no- growth occurs, and accordingly we find, as SACHS ('63) first pointed out, that the growing tissue of vegetative points is usually protected from the sun's rays. In animals, likewise, it is noteworthy that embryonic tissue, and indeed the entire embryonic individual, is usually sheltered from sunlight. In animals the embryo is sheltered in the dark- ness of the maternal body ; in birds and reptiles the egg shells are not merely mechanically resistant, but more or less opaque, and, moreover, the whole egg is usually hidden from light.* The delicate, often externally pigmented, embryos of Amphibia are often buried by one of the parents or else develop among weeds in the water. More rarely, as sometimes in the case of frogs, they occur in open ponds, but then imbedded in a thick envelope of albumen. Fishes usually bury their eggsf or affix them to the under side of stones or place them in other shady retreats. To the general rule, however, pelagic fish eggs seem to constitute an important exception ; but some of these, per- haps all, can change their level in the water (HEXSEN and APSTEIN, '97, p. 63). Among molluscs, embryos are often retained in the shell of the parent or laid in capsules and then * BLANC ('02) has indeed shown that the development of the hen's egg is much retarded when subjected in the incubator to daylight. t MILLET ('35) has shown that exclusion of light is the chief advantage gained in this habit. 2E 418 EFFECT OF LIGHT [Cn. XVII \ attached to the under side of rocks, hidden in sand or secreted in other shady places. Insects affix their eggs to the under side of leaves, provide nests for them, bury them in the earth, in masses of food, in a hundred places hidden from direct sun- light. Even the larvae, which swarm on the surface of seas and lakes, sink before the rising sun and find protection beneath the superin- cumbent strata of water.* From these facts we may conclude that, in general, growth does not take placs in nature in full exposure to sunlight. Diffuse daylight, even the light which is essential to all healthy green plants, markedly affects their growth. This is a matter of every-day observation. Who has not observed the contrast be- tween the elongated, scraggy form of plants grown in the dark and the re- pressed, compact form characteristic of the light? (Fig. 118.) Experiments and comparative measurements give us an insight into the degree of this difference. Take, for example, the case of tubers. SACHS ('63) planted similar potato tubers in flower-pots. One pot was covered with a clear bell- jar and placed in the window ; the other, which served as a control, was covered by a large flower-pot, thus re- maining in the dark. Both pots were kept equally moist. At the end of a period of 53 days, while the control tubers had produced sprouts from 150 to 200 mm. high,' those which had been FIG. 118. — Two seedlings of Sinapis alba of equal age. E, reared in the dark, etio- lated. N, reared in ordi- nary daylight, normal. Root hairs arising from the roots. (From STRAS- BURGER, NOLL, SCHENCK, and SCHIMFEK, Textbook of Botany.) * The degree of protection from light afforded by layers of water is indicated by certain calculations of WHIFFLE ('96), who finds that in a reservoir whose color is slight (0.38, platinum standard), a layer of water one foot thick absorbs 25% of the light falling upon it, so that only 0.762, or 56%, of the light at the sur- face gets below two feet ; 0.753, or 42%, below three feet, and so on. § 1] UPON THE RATE OF GROWTH 419 exposed to the spring sunlight were only 10 to 13 mm. high — a reduction to one-fifteenth the height in the dark. Many seedlings show the same thing ; thus SACHS found that the hypocotyl of the buckwheat (Fagopyrum), which attains a height of 35 to 40 cm. in the dark, reaches only 2 to 3 cm. when freely exposed on a sunny day - - here again a reduction in height of about 94%. This diminution in length is accompanied for a while by a diminution in size of the plant as a whole. This is shown by the measurements of KARSTEN ('71), who raised kidney beans in the dark and in the light for a month or two, and found that the entire individual reared during this period in the light weighed less than that reared in the dark. The proportionate weight in dark and light was as 12 to 10, fresh weight. The only organs which were heavier in the seedlings grown in the light were the roots (slightly) and the leaves (as 5.4 to 1). This excess in the growth of illuminated leaves as compared with those developed in the dark is characteristic only of such as have broadly expanded blades. Such leaves seem to require the light for their full development ; they constitute a special case, the peculiarities of whose development will be considered together with that of other special cases in the last Part of this work. The growth of leaves, like that of the rest of the plant, is relatively retarded in the daytime, but this is probably due to the increased transpiration of that period (PRANTL, 73). The effect of daylight upon the growth of stems is, as SACHS has pointed out, unequal in the different plants. In extreme cases (internodes of Bryonia, a wild gourd ; of Dioscorea, the yam; etc.) daylight has no evident effect, for the stems have the scrawny, " etiolated " habit characteristic of plants grown in the dark. Plants which are little repressed by light are said by SACHS to be chiefly those whose rapidly growing parts are sheltered from the sun's rays by protecting coverings. We may conclude that the growth processes of such plants are little interfered with by strong light, because their protoplasm has through long experience become attuned to it. Except where such attunement has occurred, light tends to retard the growth of phanerogams. The germination of seeds and spores of fungi is accompanied by processes akin to those of growth, and so may be treated here. The germinating protoplasm of seeds is partly shielded from light by a thick coat ; nevertheless a series of careful 420 EFFECT OF LIGHT [Cn. XVII Fig. 1 observers in the early half of the century, and, more recently, NOBBE ('82), ADRIANOWSKY ('83), and others, have shown that germination of seeds takes place slightly earlier in the dark than in daylight. Among fungi, also, we have the assur- ances of HOFFMANN ('60, p. 321) that the spores of the mush- room Agaricus campestris germinate more slowly in the light ; and of DB BARY ('63, p. 40) that the spores of the potato fungus, Peronospora infestans, and its allies do germinate with difficulty in the daylight, and not at all in the sunlight. Thus the germination of spores even more than of seeds is retarded by light (p. 174). Passing now to the growth of fungi, we find numerous and harmonious observations on the effect of light. FRIES ('21, p. 502) first noticed that the growth of fungi is retarded in the light, and ScHMiTz('43, p. 512), KRAUS ('76, p. 6), VINES ('78), STA- MEROFF ('97), and others have confirmed this result for hymenomycetes, the er- got fungus, and molds.* BREFELD (77, p. 90 ; '89, p. 275) found that the toad- stool Coprinus stercorarius reared in the dark attains a length of two feet or more, while in the daylight it is only an inch long (Fig. 119). Again, the sporangiferous hypha of the dung mold Pi- lobolus microsporus, which is eight or ten inches long 5, roots; 6,hyphse. (From BREFELD, '77.) in the dark, gl'OWS only half FIG. 119. — Coprinus stercorarius in reduced size. Fig. 1, typical young fruiting fungus reared in the light. Fig. 2, a, b, c, d, fungus reared in weak illumination. Fig. 5, Coprinus reared in darkness. 1, sclerotium ; 2, 6, stalk ; 3, 4, fruit ; * But BULLOT ('97) denies it in the case of Phycomyces nitens. His experi- ments are not, however, convincing. §1] UPON THE RATE OF GROWTH 421 an. inch long in the daylight. Bacillus ramosus, in one case, grew during five hours, in the dark, 540 /* ; in the light, 200 /i (WARD, '95). These results demonstrate that the inhibiting or retarding effect of sunlight, and even of diffuse daylight, is probably unconnected with the chlorophyll function, but is due to a more general effect of light upon growing protoplasm. Even brief illumination has its marked effect. Thus VINES ('78, p. 137), who has made exact measurements of the hourly growth of the sporangiferous hyphte of the mold Phycomyces nitens, found that growth was diminished whenever the plant was subjected for only s 9 10 11 an hour to sunlight (Fig. 120). The same is true for phanero- gams (GODLEWSKI, '93). The great diurnal period of darkness and illumination to which plants are subjected in nature likewise has its effect on growth. The first studies made Upon this subiect were FlG> 120- — Diagram illustrating the retarding influence by TREW in 1727. Numerous observers followed, but it was left to SACHS ('72), by the aid of his aux- anometer, to obtain a continuous curve of growth. This showed at a glance that dur- ing the night the rate of growth gradually increases, reaches a maximum at about daybreak, diminishes to a minimum a little before sunset, and then begins to rise again.* This variation in the rate of growth is opposed to the diurnal fluctuation of temperature, since this is low at night and high during the day. It is favored, on the other hand, by the circumstance that heat 0 23° of light upon the growth of a sub-aerial hypha of Phycomyces. The thick line represents the course of growth, the thin line that of temperatures ; the unshaded spaces, periods of exposure to light ; the shaded spaces, periods of darkness. The figures at the left indicate tenths of millimeters, those at the right, degrees of temperature; those at the top, hours. (After VINES, 78.) * A similar periodicity has been detected among toadstools and puffballs by KRAUS ('83, p. 97). 422 EFFECT OF LIGHT [Cn. XVU and light favor transpiration ; and this means loss of water and, consequently, of growth. Just how far these opposing effects neutralize each other cannot be said, but our compara- tive study gives assurance that the effect may well be pro- duced by light acting alone. While the diurnal periodicity in growth can clearly be ascribed to no other cause than the alter- nation of day and night, it is an important fact that this perio- dicity may be exhibited for several days after the plant has been placed in a room kept constantly dark. There is apparently a persistence of an effect impressed by environment. Among animals the evidence of a retarding effect upon growth is not so clear. MAUPAS ('87, p. 1008), indeed, con- cludes from actual experiment that various ciliate Infusoria multiply with equal rapidity in the presence or the absence of light. In the higher vertebrates, on the other hand, light, acting through the retina, increases destructive metabolism, as MOLESCHOTT ('55) first pointed out, so that many vertebrates undergo a greater loss of weight in the light than in the dark. Indeed, a diurnal periodicity in the weight of animals was described as long ago as 1852, by BIDDER and SCHMIDT, who found that starving cats lost weight much faster in the day than at night. These facts constitute a not unimportant par- allel with the conditions in plant growth. In summarizing the foregoing facts on the retardation of growth by light, we see that strong sunlight usually com- pletely inhibits growth, so that the growing parts of organ- isms, or entire organisms during the period of growth, are usu- ally concealed. Even diffuse light retards growth, especially in the following organisms : most seedlings, many of the higher aerial fungi, germinating seeds in general, and spores of fungi. Also, light hastens destructive metabolism in the higher vertebrates so as to diminish weight rapidly. The organisms thus brought together are without exception aerial. This fact suggests that in plants, at least, the restraint of growth by light may be due to the rapid loss of water which accompanies illumination. The illumination of seedlings and fungi for only a brief period — an hour or so — retards their growth. These organisms likewise exhibit a diurnal perio- dicity in growth corresponding to the alternation of day and §1] UPON THE RATE OF GROWTH 423 night. Not all seedlings and fungi are equally affected by light ; the effect depends upon their normal conditions of illu- mination — the conditions to which they have become attuned. 2. Accelerating Effect of Light. -- Although certain species of phanerogams are little affected in their growth by light, actual acceleration probably rarely occurs in this group. The parasitic mistletoe (Viscum album) seems to form an impor- tant exception, however, since, according to WIESNER ('79, p. 183 ; '98, p. 506), it neither grows nor germinates in the dark. This fact is correlated with a peculiarity in its phototropic response, as we shall see later (p. 438). Among aquatic algte several cases of acceleration of growth by light have been 0 1( NU 00 MBER PER C. 2000 C. 30 )0 40 JO 0 ( INTENSITY OF 20 40 C LIGHT) 0 80 1( 0 2 -^ f\ £,£•- -"""" 1 A ^ G OIAGF GROW! INTEN AT VAF AM SHOWING THE H OF DIATOMS AND THE SITY OF LIGHT UOUS DEPTHS 1- o UJ 0 // u. I10 H a. a 12 / H 1 1 Is LAKE COCHITUATE WATER LOCATED IN LAKE COCHITUATE NOV. 29,1895. EXAMINED DEC. 9, 1895. TEMPERATURE 4O- 44? COLOR 0.33 THE DIATOMS WERE CHIEFLY ASTERIONELLA AND MELOSIRA. THE INTENSITY OF LIGHT AT DIFFERENT DEPTHS WAS CALCULATED ON THE ASSUMPTION THAT A LAYER OF WATER ONE FOOT IN DEPTH ABSORBS 26°/o OF THE LIGHT FALLING UPON IT. 1C IS 26 I ^IG. 121. recorded. The flat, circular, green thallus of Coleochsete scu- tata, when obliquely illuminated, grows, according to KNY ('84), faster on the side next to the light. Again, Spirogyra which has been kept in the dark until all of its starch has been consumed grows when placed in the light, but does not grow in darkness (FAMINTZDST, '67). Lately WHIPPLE ('96) has given quantitative data on the relation between intensity of light and of growth in diatoms. A known quantity of dia- toms of one or two species was placed in a bottle of water, 424 EFFECT OF LIGHT [Cn. XVII covered with bolting cloth, and suspended in the water of a reservoir, at the surface and at various depths below the sur- face down to 20 feet. Experiments were made at a time when the temperature of the reservoir water was almost the same at all depths. After several days the bottles were col- lected and the number of diatoms in each determined. The results of one series of experiments, shown graphically in Fig. 121, demonstrated that the growth of diatoms is directly pro- portional to the intensity of light received by them.* We may conclude that in general, excepting perhaps the mistle- toe, those plants whose growth is accelerated by light normally have the'ir growing parts fully exposed to sunlight. Their pro- toplasm is attuned to a high intensity of light — is not retarded by it ; indeed, demands it for the normal exercise of its func- tions. Passing now to the subject of germination, we find that the first development of the spores of the higher cryptogams usu- ally requires or is favored by light (HOFFMANN, '60, p. 321, and others). The spores of many ferns, of the moss Poly- trichum commune (BORODIN, '68), of the hepatics Duvalia and Preissia (LEITGEB, '77), and of Vaucheria do not germinate at all in the dark. However, this result is not universal among the higher green cryptogams, for MILDE ('52, p. 627) observed that spores of Equisetum germinated in the dark as well as in the light ; and it is clear that certain fern spores (Ophioglos- sum) can do so, for they germinate when covered by soil to a depth of 3 to 5 cm. It is somewhat unexpected to find the spores of such dark-lovers as ferns and hepatics nor- mally dependent for their germination upon light. One calls to mind, however, the fact that it is the habit of such spores to germinate on the surface, where their prothalli are found - hence at such times always subjected at least to a diffuse light. Certain seeds, also, are said to germinate more readily in the light than in the dark. We have already cited the case of the mistletoe ; the same seems to be true of the meadow grass, Poa, as is shown by the following experiments of STEBLER ('81). Two species were experimented with, and two experi- * However, WHIPPLE found that growth at the surface, where full sunlight fell upon the bottle, was less than at a few inches below the surface. §1] UPON THE RATE OF GROWTH 425 ments were made upon each species. In each experiment two lots of seeds were placed together in a thermostat ; the one being subjected to daylight, the other being kept in darkness. The percentage of germination in the eight lots was as fol- lows : — POA NEMORAL1S. POA PRATENSIS. LIGHT. DARK. LlOIIT. DARK. Experiment Xo 1 C2 53 3 1 59 61 7 0 Experiment No 2 The result seems decisive and has been fully confirmed by LIEBEXBERG ('8-1) and JOXSSON ('93), not only for Poa but certain other small seeds. According to LIEBENBERG the favorable action of daylight is due rather to the alternation of high and low temperature on the seed. Thus, while about 3% of Poa seeds germinate in a dark chamber kept constantly either at 20° or 28° C., 91% are germinated after 34 days in a dark chamber kept for 19 hours at 20° C. and for 5 hours at 28° C. In this case we have to do clearly with a response to a particular stimulus of the heat rays reminding us of the stimulus of alternating heat and cold necessary for the germination of certain animal statoblasts or gemmules (BBAEM, '95). Among growing animals, studies on the effect of light were early made by EDWARDS ('21), who concluded that tadpoles would not develop at all in the dark. In this he went as far from the truth in one direction as HIGGEXBOTTOM ('50 and '63) and MACDOXXELL ('59), who denied any difference of growth in the light and in the dark, did in the other. The work of YUNG ('78) first revealed the exact "truth of the matter. This naturalist placed freshly laid frogs' eggs in vessels, each containing 4 liters of water and 60 eggs. One lot was placed in front of a window, where, however, it never received the direct rays of the sun. The other lot was kept constantly in the dark. Otherwise the conditions of the 426 EFFECT OF LIGHT [Cn. XVII two lots were very similar. After 30 days, and again after 60, 3 typical tadpoles of each lot were measured. Their averages, together with those from a second series, are given below : - TABLE XLI SHOWING FOR Two LOTS OF TADPOLES THE RELATIVE SIZES ATTAINED IN THE LIGHT AND IN THE DARK REARED IN THE UKLATIVK SIZE OF "Litiirr" TADPOLES COMPARED WITH "DARK." LIGHT. DARK. Lot 1 : 30 days { Jfng^ • • • • I Breadth .... 23.10 mm. 5.50 19.66 mm. 4.66 1170/0 118 Lot 1 : 60 days ( Len§* .... I Breadth .... 32.16 7.66 30.30 7.16 106 107 Lot 2 : 25 days •< >en^ '..''"' I Breadth .... 19.83 4.33 15.83 3.50 125 124 This table clearly shows that tadpoles grow faster in the light than in the dark, and that the difference in the rate of growth is more marked during the first than during the second month of development.* Other animals have been experimented upon by YUNG. He placed recently fecundated eggs of the sea trout, Salmo trutta, in 4-liter vessels, each of which contained 200 eggs. Those lots which were reared in the light hatched a day earlier than those reared in the dark. Also, the pond snails, Lymnsea stag- nalis, reared in the light hatched in 27 days, whereas those reared in the dark required 33 days. Perhaps less weight is to be given to the observation of HAMMOND ('73), who found that 20-day-old cats, reared under similar conditions except as concerns daylight, grew faster in the light than in the dark. * With these experiments agree certain experiments of LESSONA ('77) and CAMEUANO ('93) upon the size of tadpoles taken from ponds so thickly covered with vegetation as to shut out the light, as compared with tadpoles from fully exposed ponds. CAMERANO finds that, at the same stage of development, the sizes are as 9 to 14, or the tadpoles reared in the light are 156% of the size of those reared in the darker ponds. Such observations in which the other con- ditions are not controlled are not, however, altogether satisfactory. § 1] UPOX THE RATE OF GROWTH 427 There is thus a considerable body of evidence that a not too intense light accelerates the growth of animals in general. To sum up, we find that diffuse light accelerates growth in the following organisms : Mistletoe seedlings, Coleochteta, etio- lated Spirogyra, diatoms, germinating spores of many ferns, mosses, hepatics, and Vaucheria, germinating seeds of Viscum and small-seeded grasses, tadpoles, embryo snails, trout, and, perhaps, young kittens; in brief, of a parasitic seedling, of algre, of germinating spores in many higher cryptogams, of a few germinating seeds, and of some animals. The collection seems like a heterogeneous one ; yet omitting germination phenomena, the case of the parasitic mistletoe, and the doubtful cat, all the organisms concerned are aquatic. The reason why the growth of aquatic organisms is not restrained by light may be that with them light does not produce increased trans- piration. 3. The Effective Rays. - - As we have seen in the First Part the various rays of which white light is composed affect proto- plasm diversely. The question now arises, What part do the separate kinds of rays play in the retarding and accelerating effect of light on growth - - what are the rays upon which these effects especially depend? At the outset it must be stated that a large part of the recorded observa- tions upon this subject is \vorthless because the methods were not quantita- tive. Let us suppose we have a white light of known intensity which in- hibits growth, and that we desire to know which of the component rays are most effective in imbibition. The different component rays should have the same intensity as they have in the given white light. For a more effective ray of weak intensity will produce a smaller result than a less effective ray of great intensity; because not only quality but intensity of the light deter- mines its effect. Now, insufficient care has been taken to measure, by the methods given in Chapter VII, the intensity of the colored light employed;, consequently it is little wonder that most contradictory statements are given as to the effect of red, green, and violet light upon related organisms, and that great caution is demanded in drawing conclusions from the data at hand. a. The Effective Rays in the Retardation of Growth by Light. - We have already seen (p. 166) that experiments upon the effect of the different rays upon metabolism occupied the atten- tion of naturalists in the first half of the century. It was but 428 EFFECT OF LIGHT [Cn. XVII a step to the study of the effect of these rays upon growth, and this step was taken by SACHS in 1864. The method of subjecting the plant to particular rays was as follows : The apparatus consisted of a glass jar, placed inside of a larger glass jar, the interspace being filled with a colored fluid. This apparatus stood behind a southeast window. Orange light was obtained by 12 to 13 mm. of a satu- rated solution of potassium dichromate, which transmitted red, orange, and yellow, but no blue or violet; and blue light, by the same thickness of ammoniated copper sulphate, which excluded all rays of shorter vibration than the green, but, likewise, reduced the intensity of the violet end of the spectrum. The relative chemical intensity of the light passing through the solutions was determined by noting the time required to blacken photo- graphic paper held in the inner jar. Under the conditions of the experiment young seedlings of the white mustard, Brassica alba, and of flax, Linum usitatis- simum, grew more rapidly and vigorously in the orange rays, which act thus like darkness, than in the blue, which act thus like daylight. In orange light the leaves, although differen- tiated, remain small, while the internodes are elongated ; in both of which respects the plants show themselves etiolated. In the blue rays the cotyledons, unlike the leaves, remain small; vsince, in the absence of assimilation, which requires red rays, they are drawn upon for food. Throughout, the less intense blue rays acted more like white light than the more intense •orange rays. Several confirmatory experiments upon other plants may now be briefly considered. BERT ('78, p. 986) cultivated a Sensitive Plant in a lantern made of red glass. It lived for months, elongated considerably, and had small leaves ; one might have called it etiolated but for its remaining green, owing to the formation of chlorophyll in the red rays (p. 170, note). Behind blue glass it had the general form character- istic of white light, but it did not grow as large as in day- light - - which includes also the warmer rays. The whole habit of the plants in the red rays indicated greater turges- cence than in the blue : a result which BERT suggests may be due to the manufacture in the presence of the red-yellow rays of a material (glucose) causing an endosmotic flow. This explanation, however, seems negatived by the fact that plants o-rown in darkness exhibit this same condition. WEISNEK §1] UPOX THE RATE OF GROWTH 429 ('93) finds that the stems of seedlings of Vicia faba grow behind SACHS' blue solution, which reduces the intensity from one-third to one-half that of daylight, nearly as slowly as in daylight, and much more slowly than in darkness, in the ratio of : daylight, 141 ; blue, 155 ; darkness, 185. Again, FLAM- MAKION ('95) cultivated the Sensitive Plant in little conserva- tories behind clear and colored glass.* From a lot of seedlings reared under normal conditions those were selected which were most alike (all 27 mm. high), and placed, July 4th, in the various conservatories. On October 22d the plants had the following average heights : hi the red, 420 mm. ; green, 152 mm.; white, 100 mm. j blue, 27 mm. (Fig. 122). Thus, under Red Green White Blue FIG. 122. — Action of different solar rays upon the growth of the Sensitive Plant. On August 1st, placed as seedlings each 27 mm. high behind diversely colored glass screens. Photographed Oct. 22. (From FLAMMARION, '95.) * The data concerning methods are as follows : The blue glass used trans- mitted only the more highly refracting rays ; the red was almost strictly mono- chromatic ; the green was less satisfactory, but let through no red. The inten- sity of illumination decreased considerably in the order : white, red, green, blue. The conservatories were placed side by side, under similar conditions, and a current of air was passed through, from one to the other, to maintain a uniform temperature. 430 EFFECT OF LIGHT [Cn. XVII red light, as in darkness, the greatest growth occurred ; under the blue light no growth had occurred, i.e. less than under the clear glass. The order of height was thus : blue, white, green, red ; that of the vigor of vegetation was : blue, green, white, red. The peculiarly injurious effect of the violet and ultra-violet rays is shown also in the deleterious action of electric light, which is rich in these rays (SIEMENS, '80, '80a, '82). All the foregoing observations are thus in accord, and indicate that the retarding action of white light upon seedlings is the resultant of the accelerating and the inhibiting actions of the different rays. Among fungi we have observations by VINES ('78) which show that Phycomyces nitens, subjected intermittently to the action of darkness on the one hand, and of white light, blue light, or yellow light, on the other, suffered a similar retarda- tion in white and blue light, while in yellow light no marked retardation occurred.* Bacillus ramosus (Fig. 123) grows behind a red screen as in darkness ; behind a blue screen (of CuSO4) its growth is retarded as in daylight (WARD, '95, p. 381). Among algas FAMINTZIN ('67) has found that Spirogyra which has been kept in the dark until all of the starch is con- sumed grows more rapidly in the successive members of this series: darkness (no growth), blue light, full lamplight, yellow light. Here we see that, while a certain amount of light is necessary to the metabolism of the etiolated alga, growth, as a whole, is favored by the absence of blue rays. Animals which are symbiotic with algre flourish or decline with the latter. Accordingly, YUNG ('92) has found that Hydra viridis,f which has this kind of symbiosis, grows more rapidly in the successive members of the series : darkness (fatal), violet, green, white, and red. This series is essen- tially that just given for algre living alone. * KRADS ('76) says that Claviceps growing in daylight attains a length of only 4 to 6 mm. ; in green rays, 17 mm. ; in yellow and blue, each, 30 mm. ; and, in. the dark, 36 mm. Not much weight can be given to this statement, since an account of methods is lacking. t A similar result was obtained with the green turbellarian Convoluta Schultzii. §1] UPON THE RATE OF GROWTH 431 The foregoing concordant observations may be summed up in the statements that the action of white light upon seedlings is the resultant of the action of the component rays ; that, of these, the red tends to favor growth by rendering possible starch formation ; the blue, on the other hand, tends to 320 300 280 260 210 220 200 180 160 liO 120 100 80 60 10 /Z20 0 75 ft/ 231 0 7 9 10 11 12 1 3 15 FIG. 123. — Curves of growth of threads of Bacillus ramosus in hlue light (Experi- ment No. 75, of WARD) and in red light (Experiment No. 74). The numbers at the left indicate microns ; at the bottom, hours. The retardation due to blue light is evident. (From WARD, '95.) restrain growth, probably by introducing certain destructive (or controlling) chemical changes ; that, in the dark, seedlings being freed from the restraining action of the chemical rays, grow rapidly so long as the stored food products permit ; that, in daylight, although the means of nutrition is provided, the presence of the inhibiting blue rays tends to cause slow growth. Upon other organisms whose growth is retarded by light, the effect of white and blue light must be quite the same ; and the experiments of VINES and of WARD upon fungi show that this is the case. The effective rays in retardation of growth are clearly those at the blue end of the spectrum. 432 EFFECT OF LIGHT [Cn. XVII b. The Effective Rays in the Acceleration of Grrowth by Light. - - We have seen that the effective rays in retardation are the blue ; the question now arises : Will the same rays serve, in other cases, for acceleration, or must the latter be due to the red rays ? As concerns the germination of ferns we have the observa- tions of BORODIN ('68, p. 435), in the case of Aspidium, that germination did not take place in the blue any more than it did in darkness, while the red rays produced nearly the whole effect of white light. Germination in this case seems to demand the red rays for its processes --processes consisting largely of certain chemical changes favoring imbibition of water. Probably those seeds which germinate more rapidly in the light than in the dark make similar use of the red rays, as JONSSON ('93) has, indeed, found they do in the case of Poa. Passing now to animals, we find the first critical work on these organisms is that of BECLARD ('58). This experimenter placed at one and the same time, under diversely colored glass bells, eggs of the flesh-fly, Musca carnivora, taken from a single laying. All the eggs produced larva? ; of these, the largest were formed under the violet or blue glass, the small- est under the green. The effect of the other colors was inter- mediate and fell in the following order : violet, blue, red, yellow, white, green. The larvce reared under the violet rays were three-fourths greater than those reared under the green.* The apparent acceleration in violet, as compared with white light, indicates that the green rays of white light retard. This was the result actually obtained by SCHNETZLER ('74, p. 251), who found that tadpoles developed more slowly behind green glass (from which red and violet rays chiefly were cut out) than behind clear glass. YUNG ('78) made more critical experiments upon tadpoles. Screens of nearly monochromatic solutions were used (p. 157). The size of the vessels and the number of tadpoles in each * Exactly opposite results for blow-flies are given by DAVIDSON ('85), whose work, however, strikes one as crude. Fly larvae reared in a bottle made of blue glass had at the end of nine days only half the weight, on the average, of larvre reared either behind clear glass or in the dark. This subject needs careful investigation. §1] UPON THE RATE OF GROWTH 433 were the same. At the end of one month * three tadpoles were taken at random from each vessel and measured. In the following tables are given the average length and breadth of these tadpoles (from series of 1876 and 1877), and also the lengths compared with that in white light : - TABLE XLII AVERAGE DIMENSIONS OF TADPOLES REARED BEHIND CLEAR AND COLORED SCREENS DURING ONE MONTH COLOR OF LIGHT. AVERAGE LENGTH. AVERAGE BREADTH. LENGTH COMPARED WITH WHITE LIGHT. White 24.43 mm. 5.37 mm. 100 Violet 28.58 6.75 117 Blue 25.66 5.70 105 Yellow .... 24.37 5.46 99 Red 20.37 4.66 83 Green 16.99 3.91 70 Similarly, averaging the dimensions of the tadpoles at the expiration of two months, we obtain : — TABLE XLII a AVERAGE DIMENSIONS OF TADPOLES REARED BEHIND CLEAR AND COLORED SCREENS DURING Two MONTHS COLOR OF LIGHT. AVERAGE LENGTH. AVERAGE BREADTH. LENGTH COMPARED WITH WHITE LIGHT. White 31.58 mm. 7.50 inm. 100 Violet 42.32 10.41 134 Blue 33.92 8.00 107 Yellow 32.24 7.50 102 Red 27.17 6.50 86 Green All died before two months Tadpoles reared in the dark were uniformly slightly larger than those reared in red light, while violet and blue light show themselves especially favorable to the growth of the frog. * During the first days of development in the cases of the frog, the snail Pla- norbis, and the sea-urchin Echinus, there is, according to DRIESCH ('91), no difference in the rate of growth behind various colored glasses. The diverse effects of different rays appear only in later stages. 2F 484 EFFECT OF LIGHT [Cn. XVII Upon Echinoderm larvre VERNON ('95) has made some important experiments. He used YUNG'S methods of getting colors ; but relative intensity is not indicated. The following table gives his results : - TABLE XLIII PERCENTAGE DEVIATIONS IN LENGTH OK LARVAE OF STRONGTLOCENTROTUS LIVIDUS REARED BEHIND VARIOUS COLORED SCREENS, FROM LENGTH OF LARVAE REARED IN WHITE LIGHT COLOK. NUMBER or SETS OF EXPERIMENTS. MEAN CHANGE. Semi-darkness 3 + 2.5% Complete darkness 4 - 1.3 Blue (copper sulphate) 2 - 4.5 Green 4 - 4.8 Red 2 - 6.9 Blue (Lyon's blue) 2 - 7.4 Yellow 2 - 8.9 All larvre reared in violet light soon died on account of the development of bacteria. In this case the order of growth followed the series : white, blue (of copper sulphate solution), green, red, blue (of Lyon's blue), yellow. This series differs so much from BECLARD'S that the experiment demands confirmation. Certain experiments of YUNG on the relative time of hatch- ing may be given here, since the time of hatching depends upon rate of growth : — TABLE XLIV RELATIVE TIME OF HATCHING OF ORGANISMS REARED BEHIND COLORED SCREENS LOLIGO VULGARIS. SALMO TRUTTA. LYMN.EA STAGNALIS. AVERAGE. Violet, 50 days Violet, 32 days Violet, 17 days Violet Blue, 53 " Yellow, 34 " Blue, 19 " Blue Yellow, •) 5g t, Blue, |35 4t Yellow, 25 " Yellow Red, / White, ) White, 27 " White Green, — * Green, 36 " Red, 36 " Red White, all died Green, all died Green * Had not hatched by 62 days. § 1] UPON THE RATE OF GROWTH 435 These series run then in order of effect on growth exactly par- allel to the series obtained from the growing tadpole, and are very similar to the series obtained by BECLARD for the blow- fly- There are certain a priori grounds for believing that BECLARD'S series is the more correct, not only for growing flies, but for all animals. We would then get for a curve of relative effect of the different parts of the spectrum upon growth something like Fig. 126, I. * The conclusion to which all these experiments point is this : the accelerating effect of weak white light upon the growth of animals, contrary to the case in plants, is due to the short-waved rays. The alleged peculiar effects of the green rays cannot go unnoticed. These seem to have been first insisted upon by BERT ('72, '78), who found that in the green lantern the young sensitive plant lost sensibility and died in three or four days, which is about the time in which they would have died in complete darkness. This observation has been confirmed by several experimenters ; for example, by KRAUS ('76, p. 8), ADRIANOWSKY ('83), VILLON ('94, p. 461), and GAUTIER ('95) for plants, and by SCHNETZLER and by YUNG for tad- poles. Yet, on the other hand, FLAMMARION ('95) found no peculiar action of green light upon the sensitive plant. In the absence of precision in the opposing statements, we may doubt whether green rays, as such, produce any positive harm. It is probable that they are neutral in growth. Summing up the results of our study on the effective rays in the modification of growth by light, we find that retardation, as it occurs in most aerial plants, is due to the chemically active rays ; that acceleration, as it occurs in animals, is like- wise due to the same rays. Both effects must be due to chem- ical, metabolic changes, induced by light : in the first class, * The favorable effect of violet or blue rays was noticed also by VILLON ('94, p. 463) upon silkworms. Here may be mentioned the "blue glass" rage of twenty years ago, which was largely due to the writings of General A. J. PLEASONTON ('70), which, while containing a basis of truth experimentally obtained by the author, were of a highly uncritical and even sensational char- acter. 436 EFFECT OF LIGHT [Ca. XVII these are of an injurious character ; in the second, they favor the metabolic growth processes. Long-waved light, on the other hand, has usually no more effect than darkness, or the absence of light. However, upon germinating ferns and grasses long-waved light has a decided accelerating effect. Since even in daylight growth occurs faster than in the dark we must conclude that upon these organisms the blue rays do not seem to exert an injurious effect ; they are, as it were, blind to the blue rays, and hence experience no freedom from restraint in the dark, and, unlike seedlings, no excessive growth there. 4. The Cause of the Effect of Light on the Rate of Growth. — The action of red rays upon growing phanerogams requires no special explanation here. It is clear, from what we already know, that an etiolated seedling, or alga, can develop only in the presence of the red rays, which are ordinarily essential to its nutrition. Consequently, we find that red rays do not hinder the growth of ordinary seedlings, but cause etiolated green plants as well as seedlings of ferns and grasses to grow faster than they would in the dark. The action of the blue ray does, on the other hand, demand more detailed consideration, for it seems at first as if its diverse effects upon plants and animals constitute a great diffi- culty. Why should the same rays retard the growth of aerial organisms and accelerate that of water animals ? In inventing an hypothesis to fit the case, we have first to recognize that the action of the blue ray is a chemical one, and is probably of the same kind upon all organisms. It must, consequently, be that the degree of the effect is different. This difference may be due either to a difference in the quality of the different proto- plasms or to a dissimilarity of the external conditions under which the effect is produced. We may say that, either on account of the presence of abundant free oxygen in the air, or, perhaps, on account of a greater lability of plant protoplasm, the blue rays effect such extensive transformations (oxidations, QUINCKE, '94) in aerial plants as to interfere with growth, possibly, by promoting loss of water. Upon water organisms, on the other hand, only slight metabolic changes occur, Avhich, on the whole, favor the imbibitory or assimilative processes. §2] UPOX THE DIRECTION OF GROWTH 437 § 2. EFFECT OF LIGHT UPON THE DIRECTION OF GROWTH -PHOTOTROPISM * Under this topic will be considered, first, the effect upon plants ; secondly, upon animals ; and, after that, certain gen- eral matters concerning phototropism. 1. Plants. - - The fact that seedlings reared in a room near a window all have their tops directed towards the source of light instead of vertically can scarcely have escaped any one's notice. References to the phenomenon are found in the literature of the an- cients ; its scientific study was begun in the early part of the last century by HALES (1727). Not only the stems of seedlings but many other plant-organs show this growth with reference to the direction of the infalling rays of light. Among these are tips of many stems, many leaves, cotyledons, roots (es- pecially aerial ones), tendrils, the fruit-bearing hyplue of cryptogams, and certain or- gans of the bryophytes and pteridophytes. The sense of the turning d ,. , T i, • FIG. 124. — Seedling of Sinapis alba exhibiting in ordinary daylight is not positive phototropism of the 8tenif ab> and negative phototropism of the root, de. nn, surface of the water iu which the plant is germinating. The arrow indicates the di- rection of the infalling light rays. (From FRANK, '92.) always the same. While the stems of most seedlings of phanerogams turn towards the light (positive photo- * On some accounts it is unfortunate to accept this word rather than the older, more familiar term " heliotropism "; but as the latter is obviously unfitted to our broader view of the subject, and encourages the introduction of new special terms, such as selenetropism or turning towards the moon (MussET, '90), I think it is desirable to adopt the newer term. 438 EFFECT OF LIGHT [Cn. XVII tropism), the following turn from it (negative phototropism): the hypocotyl of the seedling mistletoe ; the roots of many plants, e.g, Sinapis (Fig. 124), Helianthus, Vicia faba, Zea mais, etc.; stems of some recumbent dicotyledons, e.g. the moneywort ; the root hairs of the prothalli of ferns and hepat- ics ; the tendrils of the vines Vitis and Ampelopsis. As we shall see later, however, the sense of turning is, within limits, dependent upon the intensity of the light. Finally, we observe that plants differ greatly in the degree of their phototropism. Thus aquatic plants and non-chloro- phyllaceous phanerogams are only very slightly phototropic (compare HOCHREUTIKER, '96). The general phenomena of positive phototropism are seen when a seedling which has been growing in the dark is illu- minated upon one side by a horizontal ray. The tip of the seedling, which is normally constantly "nutating" about the vertical line passing through its axis, now begins to move towards the light side of the vertical. The quickness with which it does so seems to vary with the species and with the intensity of illumination of the plant and other conditions of the environment ; the turning may be evident in 15 minutes * or it may be delayed for several hours. There is apparently a certain, not precisely determined, latent period elapsing be- tween illumination and response. The curvature first appears just behind the tip of the seedling, but later almost the whole stem above the ground becomes in- volved, so that after several hours it points straight towards the source of light (Fig. 125). The intensity of light necessary to provoke the maximum response varies with the species. WIESNER ('93) especially has made accurate determinations on this subject. The unit of measurement is a normal candle (p. 160) burning at a distance a FIG. 125. — Course of phototropic curving of the cotyledon of Avena sativa. a, before illu- mination; b, after H hours; c, after 3j hours ; d, after 7j hours. (From ROTHERT, '94.) * DARWIN ('81, Chapter IX) found with the aid of a microscope that the tip may begin to turn in from 3 to 10 minutes. § 2] UPON THE DIRECTION OF GROWTH 439 of one meter from the organism (meter-candle). A flame of one candle power at a distance of five 7iieters has, therefore, an effective intensity of 1 H- 52 = 0.04 " meter-candles." An ordinary flame of gas, kept at constant pressure by means of a manometer, was employed in the earlier experiments; a " microburner " in the later ones. The following table gives the optimum intensity in the case of various seedlings, in units of the meter-candle, at a tempera- ture of 20° to 27° C. and at a humidity of 75 to 77% : - TABLE XLV THE OPTIMUM INTENSITY FOR PHOTOTROPISM IN VARIOUS SPECIES OF PLANTS Lepidium sativum, hypocotyl .... 0.25-0.11 Pisum sativum, epicotyl 0.11 Phaseolus multiflorus, epicotyl .... 0.11 Vicia faba, epicotyl 0.16 Helianthus animus, hypocotyl .... 0.16 Vicia sativa, epicotyl , 0.44 Salix alba, etiolated sprout 6.25 This table shows also the effect of preceding conditions of illu- mination ; the etiolated plant has a very high optimum. At an intensity of light above the optimum the phototropic response is less pronounced until, finally, at between 100 and 800 meter-candles it disappears. At an intensity below the optimum a similar diminution in response occurs ; but the minimum lies often remarkably low. Thus FIGDOR ('93) has found the minimum to lie for the different species at or just below the following intensities (in meter-candles). The tem- perature was 15° to 24° C., and the humidity between 58 and 80%. TABLE XLVI THE MINIMUM INTENSITY FOR PHOTOTROPIC RESPONSE IN VARIOUS SPECIES OF PLANTS Lepidium sativum, Amaranthus melancholic us ruber, *Papa- ver pseoniflorum, and fLunularia biennis . limit below 0.00033 *Vicia sa,tiva 0.0026 Salpiglossus sinuata, Keseda odorata, Iberis forestieri 0.004 to 0.16 Mirabilis jalappa, * Helianthus animus, *Dianthus chinensis 0.016 * Xeranthemum aimuum, *Raphanus sativus, * Helichrysum monstrosum, * Capsicum annuum, Cynoglossum offici- nale 0.016 to O.OG 440 EFFECT OF LIGHT [Cn. XVII This list shows that different plants have diverse photo- tropic sensitiveness. Since in this list species preceded by an asterisk (*) live in the sunlight, that preceded by a dagger (f ) is a shade-loving plant, while the others live in an intermediate habitat, we may conclude that, in general, sun-loving plants are less sensitive to light than those not markedly sun loving. The former exhibit a sort of acclimatization to light.* The effective rays have been determined by WIESNER ('79, p. 191) for seedlings of several species as a result of experi- ments in which colored solutions were employed. His results are summarized in Fig. 126, which shows that the phototropic effect is greatest at the violet end of the spectrum, and that as we pass towards the D line, lying between the yellow and the orange, the effect diminishes, becoming null at D. In the red, again, there is a considerable effect. Beyond the visible red, FIG. 12;j. — A-H, positions of FRAUENHOFER'S lines in the spectrum. ,• curves of phototropic effect of the various rays; the ordinates have only relative values. 1, I, curve for the seedling of the vetch, Vicia; II, II, for cress seedlings ; III, for etiolated willow shoots, upon which latter the more strongly refractive rays only act phototropically. - -, curve of retardation of growth in length of Helianthus seedlings reared in the various rays. The ordinates give the increment in length of the seedling subjected to the ray under consideration ; thus the retardation is least at ?, and is greatest at y. (From WIESNER, '81.) * Certain plants are so sensitive to differences of illumination on their two sides as to make very delicate photometers. Thus WIESNER determined as nearly as 'possible by BCNSEN'S photometer the point of equal illumination between two flames, but a seedling still detected a difference between their intensities. MASSART ('88) has made use of this method to demonstrate for phototropism the validity of WEBER'S law. He found that in Phycomyces a difference of intensity of 18% between two sources of light could be detected ; and this held true for all intensities of light. §2] UPON THE DIRECTION OF GROWTH 441 in the region of the dark heat rays, we find an effect still pro- duced. This effect of dark heat rays will be referred to again in the next chapter. TJie Responding Region. - - We have already seen that the curvature begins a short way below the tip of the stem of the seedling. Further study shows that this region of first curva- ture is also that of maximum growth. The response does not, however, end here, but passes basalwards even after the seed- ling is transferred to the dark. Also in roots, the region of maximum negative curvature is that of most rapid growth (MULLER, '76). The Perceptive Region. — In most cases the region of re- sponse is also that of perception. But DARWIN ('81) found that in some organs this is not the case. When, for example, the phototropic cotyledons of the seedlings of grasses and grains were deprived of their tips for a distance of 2.5 to 4 mm., they exhibited no phototropism ; but when only 1.3 mm. of the tip was cut off, the curving occurred, although in diminished degree. Again, when the tips of some of the cotyledons were covered with opaque caps made of glass thickly painted with India ink, while others were covered with transparent glass, the first lot remained straight or nearly so, whereas the second curved normally. From such results DAR- WIN concluded that the tip of the cotyledon is the chief per- ceptive region. That it is not the only perceptive part, even in cotyledons, follows from the observations of ROTHERT ('94), who finds that a slight curvature succeeds the illumination of the basal part alone of the cotyledon. In some seedlings of dicotyledons, indeed, the perceptive region exists nearly equally developed along the whole stem. In those ca.ses where the tip of the plant is alone percep- tive there must be the transmission of an impulse from the per- ceptive to the bending region. The rate of this transmission is variable ; in favorable cases it is about 2 cm. per hour (ROTHERT, '94, p. 209). If we define "irritation" or "stimu- lation " as the condition of the protoplasm immediately ante- cedent to its response, — as the chemical transformation lying behind the visible result, - - then, since in these plants the response occurs some distance from the perceptive region, we 442 EFFECT OF LIGHT [Cn. XVII must conclude, with ROTHERT, that here, as in animals, stimu- lation is a process distinct from perception. 2. Animals. - - Phototropism among animals will naturally be limited to elongated, sessile forms. It has hitherto been detected only among hydroids and worms of the family Serpu- lidse. a. SerpulidcB. - - A type of response to light intermediate between phototaxis and phototropism is described by LOEB ('90) for Spirographis spallanzanii. This worm (Fig. 127; b FIG. 127. — Persistent phototropic curvature in Spirographis spallanzanii. The ani- mals were originally placed horizontally on the bottom of the aquarium, the majority with their heads towards the side, efgh, of the aquarium away from the window. In their further growth the animals curve until their heads are turned towards the light side, abed, of the aquarium, and the axes of their gills stand in the direction of the rays of daylight. (From LOEB, '90.) builds, from a secretion of the body, cylindrical tubes of some- what elastic nature which are attached at their base to a solid substratum. When these worms, in their tubes, are illumi- nated from one side by a pencil of rays, the upper part of the tube comes, within a few hours, to lie in the axis of the pencil, and the gills, which surround the head, are stretched out towards the source of light. This result seems to be due to a sort of phototactic response modified by the sessile habit of §2] UPON THE DIRECTION OF GROWTH 443 the organism. Since the tube is tough and elastic, its bending towards the light must be due, at first, to muscular action of the animal inhabiting it. Additional secretions are, however, constantly poured forth so that the new position soon becomes in turn the permanent one. Serpula, which has a tube con- taining lime, likewise turns its head end towards the light ; but, since its tube is firm and inelastic, the bending which it finally exhibits must be ascribed alone to growth of the shell by additions to its free upper margin. b. Hydroids. - These have been made the object of study by DRIESCH ('90) and LOEB ('90 and '91, p. 36). In stocks of Sertularella polyzonias, reared in an aquarium, one often finds a stolon (primary stolon) growing out from the distal end, at first straight, so as to prolong the axis of the stock, then turning and growing from the source of light. From the convexity • of this primary stolon a secondary one a buds forth. It grows towards the FIG. 128.— Phototropism in re- light for a time, until it in turn buds off a (tertiary) stolon; then it becomes negatively phototropic. Tertiary and succeeding generations of stolons fol- low the same law. We have here the remarkable phenomenon of change in the sense of response depending upon the condition of development of the sto- lon (DRIESCH). In Eudendrium the hydranths, in contradistinction to the stolons, grow towards the light — they are positively phototropic (Fig. 128). The effective rays in animal phototropism have not been determined. It is highly probable that, as in plants, they are the more highly refractive ones. The responding region in hydroids is the growing region. The fully formed stolon does not turn in response to light. The perceiving region is still generation of Sertularia (poly- zonias?). The stock was cut near the stolon at b and in- serted reversed in the sand, being buried from a to c. From the upper end b, both a stolon, Wi, and Lydranths, S, regenerated, and both grew in the axis of the infalling ray of light, indicated by the arrow. The hydranths are di- rected toward the source of light ; the stolon tip in the opposite direction. Magnified 2 diameters. (From LOEB, '90.) 444 EFFECT OF LIGHT UPON GROWTH [Ca. XVII unknown ; the subject has not been investigated. Is it at the tip or at the responding region, or do these regions exactly coincide ? The essential identity of phototropism in sessile animals and plants is striking, and indicates how closely simi- lar needs are met by similar capacity for response in the two groups. 3. General Considerations. - - a. Persistence of Stimulation. If a seedling, after momentary illumination on one side, be placed in the dark before any turning has occurred, phototro- pism will follow after the same interval as would have elapsed had the plant remained in the light. Even if the irritated seedling be placed in the dark in a horizontal position, no geo- tropic curvature will interfere with the working out of the stimulus already given. This persistence of an effect wrought by light has been called by WIESNER photomechanical induc- tion : it is, however, only a particular case of persistence of an effect, of which we have seen other examples. As a result of this phenomenon a seedling, intermittently illuminated for one second and kept in the dark for two seconds, will respond phototropically as completely and as quickly as if it had been kept continuously in the light. b. Acclimatization to light is a process closely related to the foregoing. As early as 1827 MOHL observed that plants reared in a weak light, or in the dark, became, after a time, phototropically more sensitive than plants which had been con- stantly exposed to full daylight. The observation has been several times confirmed (cf. DARWIN, '81, Chapter IX) ; so we may conclude that the constant subjection to light diminishes the sensitiveness towards light. c. Mechanics of Phototropism. — It is clear that phototropic curvature, as seen in the seedling, the mold, or the hydroid, is the result of unequal growth upon the two sides of the cylin- drical organ ; and, indeed, that the positive phototropism is due to a relative diminution of growth on the side next the source of light, and the negative phototropism to a relative increase of growth on that side. Experiments have shown that in positive phototropism growth is excessively rapid upon the convex side of the organ, and excessively slow upon the concave side. These results are reasonably attributed to an LITERATURE 445 increased turgescence on the one side and a decreased turges- cence on the other. In unicellular organisms, on the other hand, this mechanism cannot be called upon ; and great difficulty has been met with in explaining how an elongated cell, for instance, of a hypha, can curve itself. Some authors have suggested that the cell-wall on the convex side becomes excessively extensible, on the concave side excessively rigid. Again, it has been sug- gested that this change takes place rather in the protoplasm inside the wall than within the wall itself. If, however, with many plant physiologists we regard the cell-wall as the truly living, only considerably modified, protoplasm, then we may accept both of these views, and, uniting with them the expla- nation advanced for phototropism in multicellular organs, say : The curving of the unicellular organ is probably due to the increased extensibility, gained through imbibition of water, of the whole protoplasm (including cell-wall) of the convex side, together with a corresponding diminution on the concave side. In a word, then, the mechanism of phototropism may be stated to be the excessively rapid imbibition of water by the proto- plasm on the convex side. But what starts the mechanism ? This is the same question that arises with other growth responses. Its answer must be deferred to a later chapter. LITERATURE ADRIANOWSKY, A. '83. Wirkungdes Lichtes auf daserste Keimungsstadium der Samen. [Russian.] Abstr. in Bot. Centr. XIX, 73-75. ADUCCO, V. '89. Action de la lumiere sur la duree de la vie, la perte de poids, la temperature et la quantite de glycogene hepatique et muscu- laire chez les pigeons soumis au jeune. Arch. Ital. de Biol. XII. 208-214. 28 July, 1889. BARY, A. DE, '63. Recherches sur le developpement de quelques cham- pignons parasites. Ann. d. Sci. Nat. (Bot.). (4), XX, 5-148. BECLARD, J. '58. Influence de la lumiere sur les animaux. Comp. Rend. XLVI, 441-453. BERT, P. '72. Influence des divers rayons colores sur la ve'getation. C. II. Soc. Biol. Paris. XXIII, 67-69. '78. Influence de la lumiere sur les etres vivants. Revue Sci. (2), VII, 981-990. 20 Apr. 1878. 446 EFFECT OF LIGHT UPOX GROWTH [Cn. XVII BIDDER, F. H., and SCHMIDT, K. '52. Die Verdauungssafte und der Stoff- wechsel. 413 pp. Mitau and Leipzig, 1852. BLANC, L. '92. Note sur les effets teratogeniques de la lumiere blanche sur 1'oeuf de poule. C. R. Soc. de Biol. Paris. XL IV, 9G9-971. BORODIN, J. '68. Ueber die Wirkung des Lichtes auf einige hohere Krypto- gamen. Bull. Acad. Sci. St. Petersburg. XII, 432-147. 1 Taf. 13 Jan. 1868. BRAEM, F. '95. Mittheilung iiber den Einfluss des Gefrierens auf die Ent- wickelung thierischer Keime. Jahresber. der Schlesischen Gesellsch. f. Vaterland. Cultur. LXXII2. Zool. Bot. Sect. 2-3. BREFELD, O. '77. Botanische Untersuchungen iiber Schimmelpilze. III. Hft. Leipzig : Arthur Felix. 1877. '89. Untersuchungen aus dem Gesainmtgebiete der Mykologie. Fort- setzung der Schimmel und Hefenpilze. VIII. Hft. Leipzig : Arthur Felix. BULLOT, G. '97. Sur la croissance et les courbures du Phycomyces nitens. Ann. Soc. Belg. de Micros. XXI, 69-93. 1897. CAMERANO, L. '93. Dell' azione dell' acqua corrente e della luce sullo svi- luppo degli Anfibi anuri. Boll. Mus. Zool. ed Anat. Comp. Torino. VIII, 3-12. 20 Jan. 1893. DARWIN, C. and F. '81. (See Chapter XIV, Literature.) DAVIDSON, J. '85. On the Influences of Some Conditions on the Metamor- phosis of the Blow-fly (Mmca vomitoria). Jour, of Anat. and Physiol. XIX, 150-165. Jan. 1885. DRIESCH, H. '90. Heliotropismus bei Hydroidenpolypen. Zool. Jahrb., System. Abth. V, 147-156. 3 May, 1890. '91. Entwickelungsmechanische Studien, II. tiber die Beziehungen des Lichtes zur ersten Etappe der thierischen Formbildung. Zeitschr. f. wiss. Zool. LIII, 160-184. 10 Nov. 1891. EDWARDS, W. F. '24. De 1'inflnence des agens physiques sur la vie. Paris, 1824. Also, On the Influences of Physical Agents on Life. Translated from the French by Dr. HODGKINS and Dr. FISCHER. London, 1832. FAMINTZIN, A. '65. Die Wirkung des Lichtes auf das Wachsen der Kei- menden Kresse. Mem. Acad. St. Petersb. (7), VIII. No. 15. 16 pp. '67. Die Wirkung des Lichtes auf Algen und einige ihnen nahe ver- wandte Organismen. Jahrb. f. wiss. Bot. VI, 1-44. FIGDOR, W. '93. Versuche iiber die Heliotropische Empfindlichkeit der Pflanzen. Sitzungsber. Akad. Wiss. Wien. CII1, 45-59. FLAMMARION, C. '95. Etude de Paction des diverses radiations die spectre solaire sur la vegetation. Comp. Rend. CXXI, 957-960. 16 Dec. 1895. FRIES, E. M. '21. Systema Mycologicum, etc. I. 520 pp. GAUTIER, A. '95. Discussion on FLAMMARION, '95. Comp. Rend. CXXI, 960-961. GODLEWSKI, E. '90. Die Art und Weise der wachsthumretardirenden Licht- wirkung und die Wachsthumstheorien. Anz. d. Akad. d. Wiss. Kra- kau, July, 1890, p. 286. [Abstr. Naturw. Rundschau. VI, 150, 151. 21 March, 1891.] LITERATURE 447 GODLKWSKI, E. '93. Studien iiber das Wachsen der Pflanzen. Abh. Krakauer Akad.d.Wiss. XXIII, 1-1 57. [Polish.] Abstr. in Bot. Centr. LV, 34-40. HALES, S. 1727. Statical Essays. Volumen I : Vegetable Staticks, or an Account of Some Statical Experiments on the Sap in Vegetables. 376 pp. 19 Tab. London. HAMMOND, '73. Some Points relative to the Sanitary Influence of Light. The Sanitarian, II. HENSEN, V. and APSTEIN, C. '97. Ueber die Eimenge der im Winter laichenden Fische. Wiss. Meeresuntersuch. deutsch. Meere. II, Heft 2, pp. 1-98. HIGGENBOTTOM, J. '50. Influence of Physical Agents on the Development of the Tadpole, of the Triton, and the Frog. Phil. Trans. Roy. Soc. London for 1850. 431-436. PI. XXXII. '63. Influence des agents physiques sur le developpement du tetard dela grenouille. Jour, de la Physiol. VI, 204-210. HOCHREUTINER, G. '96. Physiologic des plantes aquatiques du Rhone et du Port de Geneve. Rev. Gen. de Bot. VIII, 148-167, 188-200, 249-265. 15 Apr.-15 June, 1896. HOFFMANN, H. '60. Untersuchungen iiber die Keimung der Pilzsporen. Jahrb. f. w. Botanik. II, 267-337. JONSSON, B. '93. lakttogelsen ofver ljusets betydelse for frons groning. Lunds Universitets Ars-skrift. XXIX, 47 pp. KARSTEN, H. '71. Die Eimvirkung des Lichts auf das Wachsthum der Pflanzen, beobachtet bei Keimung der Schminkbohnen. Landw. ATer- suchs-Stat. XIII, 176-195. KNY, L. '84. Das Wachsthum des Thallus von Coleochsete scutata in seinen Beziehungen zur Schwerkraft und zum Lichte. Ber. Bot. Ges. II, 93-96. KRAUS, G. '76. Versuche mit Pflanzen im farbigen Licht. Ber. Sitzungs d. Naturf. Ges. Halle. Jahre 1876. 4-8. '83. Ueber das tagliche Wachsthum der Friichte. Ber. d. Naturf. Ges. zu Halle. 1883. 92-121. LEITGEB, H. '77. Die Keimung der Lebermoossporen in ihrer Beziehung zum Lichte. Sb. Wien. Akad. LXXIV, 1 Abth. 425-436. 1 Taf. LESSONA, '77. Stude sugli amfibi anuri del Piemonte. R. Accad. dei Lincei Atti. (3) Mem. Sci. I, 1019-1098. 5 Tav. LIEBENBERG, A. RiTTER VON, '84. Upber den Einfluss intermittender Erwarmung auf die Keimung der Samen. Bot. Centralb. XVIII, 21-26. LOEB, J. '90. Weitere Untersuchungen iiber den Heliotropismus der Thiere und seine Uebereinstimmung mit dem Heliotropismus der Pflanzen. Arch. f. d. Ges. Physiol. XL VII, 391-416. Taf. IX. 9 May, 1890. '91. Untersuchung zur physiologischen Morphologic der Thiere. I. Ueber Heteromorphose. Wiirzburg : G. Hertz. 1891. MCDONNELL, R. '59. Expose de quelques experiences concernant 1'influence des agents physiques sur le developpement du tetard de la grenouille commune. Jour, de la Physiol. II, 625-632. 448 EFFECT OF LIGHT UPON GROWTH [Cn. XVII MASSART, J. '88. Recherches sur les organismes inferieurs. 1. La loi de Weber verifiee pour 1'heliotropisme du champignon. Bull. Belg. Acad. (3), XVI, 590-597. MAUPAS, 1C. '87. Sur la puissance de multiplication des Infusoires cilies. Comp. Rend. CIV, 1006-1008. 4 Apr. 1887. MILDE, J. '52. Zur Entwicklungsgeschichte der Equiseten und Rhizokarpen. Verb. d. Kais. Leop.-Car. Ak. d. Naturf. XV, 2 Abth. 613-646. Taf. 57-59. MILLET, C. '55. Influence nuisible de la lumiere sur les oeufs de certaines especes de Poissons. L'lnstitut. XXIII1, 55. 14 Feb. 1855. MOHL, H. v. '27. Ueber den Bau und das Winden der Ranken-und Schling- pflanzen. 152 pp. 13 Tab. Tubingen, 1827. MOLESCHOTT, J. '55. Recherches sur 1'influence de la lumiere sur la pro- duction de 1'acide carbonique par les animaux. Ann. d. Sci. Nat. (Zool.). (4), IV, 209-224. MULLER, H. '76. Ueber Heliotropismus. Flora. LIX, 65-70, 88-95. MUSSET, C. '90. Selenetropisme. Comp. Rend. CX, 201-202. 27 Jan. 1890. NOBBE, F. '82. Uebt das Licht einen vortheilhaften Einfluss auf die Kei- mung der Grassamen ? Landw. Versuchs-Stat. XXVII, 347-355. PLEASONTON, A. J. '76. The Influence of the Blue Ray of the Sunlight and of the Blue Color of the Sky in developing Animal and Vegetable Life, in arresting, and in restoring Health in Acute and Chronic Disorders to Human and Domestic Animals. Philadelphia, 1876. PRANTL, K. '73. Ueber den Einfluss des Lichts auf das Wachsthum der Blatter. Arb. a. d. Bot. Inst. Wurzburg. I, 371-384. QUINCKE, H. '94. Ueber den Einfluss des Lichtes auf den Thierkorper. Arch. f. d. ges. Physiol. LVII, 123-148. 1 June, 1894. ROTHERT, W. '94. Ueber Heliotropismus. Beitrage zur Biol. der Pflanzen. VII, 1-212. SACHS, J. '63. Ueber den Einfluss des Tageslichts auf Neubildung und Entfaltung verschiedener Pflanzenorgane. Bot. Ztg. XXI, Suppl. 30pp. '64. Wirkungen farbigen Lichts auf Pflanzen. Bot. Ztg. XXII, 353 et seq. 72. Ueber den Einfluss der Lufttemperatur und des Tageslichts auf die stundlichen und taglichen Aenderung des Langenwachsthums (Streck- ung) der Internodien. Arb. a. d. Bot. Inst. Wurzburg. I, 99-192. SCHMITZ, J. '43. Beitrage zur Anatomic und Physiologie der Schwanime. Linnaea. XVII, 417-548. SCHNETZLER, J. B. '74. De 1'influence de la lumiere sur le ddveloppement des larves de grenouilles. Arch. Sci. Phys. et Nat. LI, 247-258. SIEMENS, C. W. '80. On the Influence of Electric Light upon Vegetation, and on Certain Physical Principles involved. Proc. Roy. Soc. XXX, 210-219. '80*. Some Further Observations on the Influence of Electric Light upon Vegetation. Proc. Roy. Soc. XXX, 293-295. LITERATURE 449 SIEMENS, C. W. '82. On Some Applications of Electric Energy to Horticultural and Agricultural Purposes. Rept. Brit. Assoc. Adv. Sci. LI, 474-480. STAMEROFF, K. '97. Zur Frage iiber den Einfluss des Lichtes auf das Wachsthum der Pflanzen. Flora. LXXXIII, 135-150. 22 Feb. 1897. STEBLER, '81. Ueber den Einfluss des Lichtes auf die Keimung. Viertel- jahrs. Naturf. Ges. Zurich. XXVI, 102-104. TREW, C. T. 1727. Beschreibung der grossen Amerikanischen Aloe, wobei das tagliche Wachsthum des Stengels der im Jahr 1726, zu Niirnberg verbllihten Aloe erlautert wird. 36 pp. 1 Tab. Niirnberg, 1727. VERNON, H. M. '95. The Effect of Environment on the Development of Echinoderm Larvae : An Experimental Inquiry into the Causes of Variation. Phil. Trans. Roy. Soc. London. CLXXXVI3, 577-632. 14 Oct. 1895. VILLON, A. M. '94. La culture sous verres colores. Rev. Sci. (4), I, 460- 463. 14 Apr. 1894. VINES, S. H. '78. The Influence of Light upon the Growth of Unicellular Organs. Arb. Bot. lust. Wiirzburg. II, 133-147. WARD, H. M. '95. On the Biology of Bacillus ramosus (Fraenkel),a Schizo- mycete of the River Thames. Proc. Roy. Soc. LVIII, 265-468. WHIFFLE, G. C. '96. Some Experiments on the Growth of Diatoms. Tech- nology Quarterly. IX, 145-168. WIESNER, J. '79. Die heliotropischen Erscheinungen im Pflanzenreiche. Eine physiologische Monographic. Theil I. Denkschr. Wien. Akad. XXXIX, 143-209. •81. The same. Theil II. Denkschr. Wien. Akad. XLIII, 1-92. '93. Photometrische Untersuchungen auf Pflanzenphysiologischen Ge- biete. Erste Abhandlung. Orientierende Versuche iiber den Einfluss der sogenannten chemischen Lichtintensitat auf den Gestaltungsprocess der Pflanzenorgane. Sb. Wien. Ak. GIF, 291-350. '98. Ueber die Ruheperiode und iiber einige Keimungsbedingungen der Samen von Viscum album. Ber. Deut. Bot. Ges. XV, 503-516. YUNG, E\ '78. Contributions a 1'histoire de 1'influence des milieux physiques sur les etres vivants. Arch. Zool. Exper. et Gen. VII, 251-282. '80. De 1'influence des lumieres colorees sur le developpement des ani- maux. Mitth. a. d. Zool. Stat. zu Neapel. II, 233-237. '92. De 1'influence des lumieres colorees sur le developpement des ani- maux. Comp. Rend. CXV, 620, 621. 24 Oct. 1892. CHAPTER XVIII EFFECT OF HEAT ON GROWTH As in other cases, so in describing the effect of heat we shall consider separately its effect on the rate and on the direction of growth.* § 1. EFFECT OF HEAT ON THE RATE OF GKOWTH The descriptive fact that the rate of growth --of develop- ment in general --in both animals and plants is dependent upon temperature, has long been known. The work upon plants was begun earlier than that upon animals, and has been carried further. We may consider, first, the results gained in that group. 1. Plants. --As an introduction to the study of the effect of heat upon growing plants, we may consider the results of measurements made upon phanerogams, showing, for various temperatures, the increase in length of the plant after 48 hours : — * The methods to be employed in subjecting organisms to heat have already been discussed on pp. 219-222. The constant-temperature oven, of the kind employed in bacteriological laboratories, may be used for rearing growing plants or aquatic animals at a high temperature. An ordinary refrigerator will serve for temperatures from near 0° to 8° or 10° C. The methods employed in thermo- tropic experimentation are referred to on p. 464. To test the question of the dependence of the optimum for growth upon the temperature to which the organism is normally subjected it would be necessary to rear a species attuned to a warm climate at a constantly low temperature for several generations, or the reverse, and then compare the optimum of the normal race with that subjected to the new conditions. To test the question of the dependence of the range of the growing temperatures upon the range of tem- peratures in the environment, one lot of individuals of a species should be reared in a constant-temperature room, and another in a very fluctuating temperature. 450 §1] EFFECT OF HEAT UPON GROWTH 451 TABLE XLVII SHOWING THE AVERAGE TOTAL INCREMENTS IN LENGTH (IN MILLIMETERS) OP THE Plumules OF SEEDLINGS SUBJECTED TO DIFFERENT TEMPERATURES (EXPRESSED IN DEGREES CENTIGRADE). THE OBSERVATIONS MARKED S WERE MADE BY SACHS ('00) ; THOSE MARKED K, BY KoPPEN ('71) J AND THOSE MARKED V, BY DE VRIES ('70). THE TlME INTERVAL IS 48 HOURS TEMPERATURE. PIIASEOI.US MULTIF. (S). £- «j 2 a <: N S % < 2 - ' N a PISUM 6ATIVUM (S). £ s 5 _ — to H £ 5 g£ z — ' hi SINAPIS ALBA (V). LEPIDIUM 8ATIVUM (V). *b 1 B' 3 S 14-15.9 5.0 9.1 3.8 5.9 1.5 16-17.9 7.4* 4.6* 3.0* 18-19.9 1.1 8.3 11.6 20-21.9 9.3 25.5 25.0 24.9 38.0 20.5 22-23.9 10.8 30.0 31.0 24-25.9 20.1 45.8 33.9 26-27.9 11.0 5.6 29.6 10.0 53.9 54.1 52.0 71.9 44.8 28-29.9 26.5? 40.4 50.1 30-31.9 64.6 38.5 43.8 44.1 44.6 39.9 32-33.9 10.5 11.0 69.5 5.7 23.0 14.2 34-35.9 15.0 13.0 5.0 30.2 26.9 28.1 36-37.9 20.7 8.7 12.6 10.0 0.0 9.2 38-39.9 10.2 9.1 5.5 42.5 7.5 4.6 TABLE XLVIII SHOWING THE AVERAGE INCREMENTS IN LENGTH IN MILLIMETERS OF THE Radicle OF VARIOUS SEEDLING PLANTS SUBJECTED TO DIFFERENT TEM- PERATURES. TEMPERATURES IN DEGREES CENTIGRADE. ALL FROM SACHS ('60). THE TIME INTERVAL is 48 HOURS. °c. ZEA MAIS. PHASEOLfS MULTIFLORUS. Cl'CrRIitTA PEPO. PlSTJM 8ATIVUM. 17.0 2.5* 4.0* 25.7 39 26.3 24.5 47 28.5 34 41.0 33.2 39.0 30 17.0 34.0 55.0 28 30 38.2 25.2 22 14 12.2 42.5 5.9 7 11 * Growth during 96 hours. 452 EFFECT OF HEAT [Cn. XVI II Data from the higher fungi have been afforded by the studies of WIESNER ('73) upon Penicillium. I give all of WIESNER'S data, although not all are strictly concerned with growth. These data show the relation between temperature, on the one hand, and the interval, in days, between sowing and (1) germination, (2) formation of visible mycelium, and (3) spore formation, on the other : — TABLE XLIX TIME, ix DAYS, REQUIRED FOR SPORES or PENICILLIUM TO GERMINATE, PRODUCE VISIBLE MYCELIUM, AND TO FORM SPORES, AT VARIOUS TEMPERATURES TEMPERATURE ° C. TIME TO GERMINATION. TIME TO PRODUCTION OF VISIBLE MYCELIUM. TIME TO SPORE FORMATION. 1.5 5.80 2.0 5.50 2.5 3.00 6.00 3.0 2.50 4.00 9.00 3.6 2.25 3.50 8.00 4.0 2.00 3.00 7.75 5.0 1.50 2.90 7.00 7.0 1.20 3.00 6.25 11.0 1.00 2.30 4.00 14.0 0.75 2.00 3.00 17.0 0.75 2.00 3.00 22.0 (Opt.) 0.25 1.00 1.50 26.0 0.50 0.99 2.00 32.0 0.70 1.01 2.10 38.0 0.55 2.25 2.60 40.0 0.70 2.50 3.50 The law of growth of bacteria at various temperatures is illustrated in the observations of WARD ('95, p. 458). His results are epitomized in the curves of Fig. 129. The curve (Fig. 130) of the phanerogams Zea mais and Pisum sativum, which is constructed somewhat differently from that of FIG. 129. — Curve of relation between rate of growth of Bacillus ramosus and the temperature. The growth is measured by the period, expressed in minutes (/*), required for the bacillus to double its length. The relative duration of these periods is expressed by the ordinates. The abscissae are temperatures. (From WARD, '95.) FIG. 130. — Curves of absolute growth in 48 hours of Zea mais and Pisum sativum at different temperatures. (Data from Table XLVII.) §1] UPON THE RATE OF GROWTH 453 280 260 210 13' li' 15° 16° 17° 18° 19 "JilT 21° 2a° 23° 21° 25° 26° 27° 28° 29° 30° 31° 32° 33° 31° 35° 36° 3', " 3S° 3»° 10° il" FIG. 129 MM. 15 17 19 21 23 25 27 29 31 33 35 37 39 454 EFFECT OF HEAT [Cn. XVIII Fig. 129, shows, more graphically than the tables from which they are drawn, that, as the temperature rises, growth increases up to a certain point, and then diminishes again. The falling off is more rapid than the increase — a condition which we found also in the curves (Fig. 68 ; p. 226) giving the rate of movement of protoplasm at different temperatures. We have thus three critical points to distinguish : the minimum, or lowest temperature at which growth occurs ; the optimum, or the temperature of greatest growth ; and the maximum, or the highest temperature at which growth can take place. These critical points, then, are to be considered comparatively ; and as an introduction to this consideration I present, in a table, the points as they have been determined for various species : — TABLE L SHOWING CRITICAL POINTS FOR VARIOUS PLANT ORGANISMS, ARRANGED ACCORDING TO THE OPTIMUM NAME OF PLANT. TEMPERATURE FOE GROWTH. AUTHORITY. OPTIMUM. MINIMUM. MAXIMUM. Bacillus phosphorescens . . . 20.0° 0.0° 37.0° FORSTER, ' 87 Penicillium 22.0 1.6 43.0 WlESNER, ' 73 Phaseolus inultiflorus (Radicle) . 26.3 SACHS Pisura sativum (Plumule) . . 26.6 6.5 — KOPPEN Sinapis alba (Plum.) .... 27.4 0.0 37.2 + DE VRIES Lepidium sativum (Plum.) . . 27.4 1.8 37.2 + « Linum usitatissimum (Plum.) . 27.4 1.8 37.2 + it Lupinus albus (Plum.) .... 28.0 7.5 — KOPPEN Hordeum vulgare (Plum.) . . 28.7 6.0 37.7 SACHS Triticum vulgare (Plum.) . . -j 28.7 29.7 6.0 7.5 42.5 n KOPPEN Yeast 28-34 0.0 + 38.0 Bacillus subtilis ..... 30.0 6.0 60.0 Bacterium termo 30-35 5.0 40.0+ EIDAM, '75 Zea mais (Plum.) . . . . j 32.4 33.7 9.6 9.5 46.2 KOPPEN SACHS Phaseolus niultiflorus (Plum.) . 33.7 9.5 4G.2 « Cucurbita pepo (Plum.) . . . 33.7 13.7 46.2 u Zea mais (Rad.) 34.0 14 Bacillus ramosus 37.0 13.0 40.0 WARD, '95 " anthracis 37.0 14.0 45.0 FISCHER, '97 " tuberculosis .... 38.0 30.0 42.0 1 1 " thermophilus .... 63-70 4-2.0 72.0 u § 1] UPON THE RATE OF GROWTH 455 This table shows, first, that the optimum, minimum, and maximum are correlated ; that when one is high or low the others are, in general, high or low also. It shows, moreover, that the position of the optimum varies greatly ; so that the minimum of one species, Bacillus thermophilus, lies higher than the maximum of another, Bacillus phosphorescens. We see, also, that the bacteria have, among all organisms, the great- est variation in the optimum, for this ranges from 20° to 63°- 70° C., or through 43°-50° C. In the various phanerogams the extreme range of the optimum is from 26.6° to 33. 7° C., or through 7°. Again, the range of temperatures at which growth occurs in any one species varies greatly. The most striking feature of this table — the one which most needs accounting for — is its variety. In respect to the optimum we find a certain relation between the degree of temperature of most rapid growth and that to which the organism is normally subjected. Taking the case of an organism with a low optimum, we find Bacillus phosphores- cens living in the North Sea, and normally subjected to a low temperature ; for, even in its southern part, the mean temper- ature of the North Sea is 17.5° at the surface. Taking the case of organisms with a high optimum, we find Bacillus an- thracis and Bacillus tuberculosis living in the mammalian body at a normal temperature of 35° to 38° C. These numbers lie near the optima of the species. Bacillus thermophilus lives in fer- menting manure and in other situations attaining a temper- ature of 60° to 70°. Likewise, among phanerogams, we find a relation between the optimum and the normal temperature — the maize and gourd are of tropical origin, while the white mustard (Sinapis) belongs to the temperate zone. That this agreement between optimum and normal temperature is not always close may be partly ascribed to the fact that many spe- cies of plants, especially cultivated plants which are usually employed in experimentation, have lived at different times under dissimilar environmental conditions. What, now, is the reason for this general parallelism between the optimum and the normal temperature ? As in other cases, it can clearly be ascribed only to an attunement gained by the organism as a result of its subjection to the temperature. 456 EFFECT OF HEAT [Cn. XVIII As for the minimum we find that, while it varies somewhat with the optimum, it never falls below 0° C. The reason for this is clear ; for, as we have already seen (p. 241), 0° C. is the minimum for most vital activities. The fact that the minimum for phanerogams is given some distance above 0° is partly due to the fact that, since growth becomes very slow towards 0°, the absolute minimum for growth is hard to find. KIRCHNER ('83), who paid particular attention to this matter, concluded that, the minimum temperature of both radicles and plumules of many seedlings lies between 0° and 1° C. However, we cannot ignore the fact that Cucurbita, for example, has a minimum for growth considerably above the point of cold-rigor , nor that, in pathogenic bacteria, the minimum is near the optimum of some free-living organisms. These facts teach us that the con- ditions for growth may be surpassed before metabolism has wholly ceased. The maximum temperature tends to be rather constant ; inside of the group of phanerogams the range is only from 37° to 46°, or 9°. But 45° to 46° is a fatal temperature for most plant protoplasm (p. 234), and 50° is the outside limit ; hence the death-point (ultra-maximum) lies very close to- only slightly beyond — the maximum temperature for growth. It is probable that growth ceases where heat-rigor comes in. The extraordinarily high resistance of Bacillus thermophilus can create no surprise after our study of the capacity of organ- isms for acclimatization to temperatures near the boiling-point of water (p. 250). It is merely another striking case of the capacity of protoplasm for self-adjustment. The range of growing temperatures varies, as we have seen, with the species. The greatest range in our table is that of Bacillus subtilis, 44°. It is tolerably uniform for phanerogams (37° to 32°); but in bacteria We have a range of 38° in the case of Bacillus phosphorescens to only 12° in the case of Bacillus tuberculosis. Here, again, we see a relation between the vital peculiarities and the environment of the organism. B. phosphorescens lives on the surface of the sea, whose tem- perature varies with that of the air ; whereas B. tuberculosis lives in the mammalian body, whose temperature is nearly con- stant. It is interesting that the temperature of 42°, which is §1] UPON THE RATE OF GROWTH 457 the maximum for B. tuberculosis of man, is likewise about the human ultra-maximum ; and 30°, the minimum for B. tubercu- losis, is just below the human ultra-minimum. Thus the range of vital temperatures of this parasite is practically the same as that of its host. To sum up, the critical temperatures of plants are wonder- fully adjusted to their environment, not only in respect to the optimum for growth, but also in respect to the range within which growth is possible. The origin of this adjust- ment is, as the phenomena of acclimatization show, not to be sought in any process of selection, but in the modification wrought on the protoplasm by the temperature itself. 2. Animals. - - We may begin our account of the effect of heat on the rate of growth of animals by a table, necessarily drawn from more limited data, but otherwise resembling Table XLVII. TABLE LI SHOWING FOR DIFFERENT TEMPERATURES THE ABSOLUTE INCREASE IN LENGTH, MEASURED IN MILLIMETERS, FROM THE 24TH TO THE 48TH HOUR AFTER HATCHING. MEASUREMENTS MADE ON YOUNG TADPOLES OF THE FROG, RANA VIRESCENS, AND THE TOAD, BUFO LENTIGINOSUS, BY LILLIE AND KNOWLTON, '98 AVERAGE GROWTH. AVERAGE GROWTH. FROG. TOAD. FROG. TOAD. 9-10.9° 4.5 3.0 23-24.9° 41.3 11-12.9 5.3 5.3 25-26.9 31.5 39.0 13-14.9 4.3? 15.5 27-28.9 40.0 15-16.9 16.3 29-30.9 47.5 56.8 17-18.9 9.5 31-32.9 40.2 55.3 19-20.9 19.8 21.2 33-34.9 43.5 21-22.9 OSCAR HERTWIG ('98) has determined the curves of growth for Rana fusca, and these are given in Fig. 131. These curves have not been carried beyond the optimum. (Compare Fig. 129.) This table and the curves show plainly that the growth of organisms so remote as the maize plant and -tadpoles are simi- larly affected by heat. In both cases there is a slow and con- 458 EFFECT OF HEAT [Cn. XVIII stantly diminishing increment to the optimum, and then a rapid decline to the maximum. Although many ob- T HI servations upon the effect of heat on the growth of animals have been made, they have been mostly fragmen- tary. 1 have gathered certain cases from the literature which it may not be useless to repro- duce here. Echinodermata. — According to VERNON ('95) the optimum for the development of Echinoid larvae is 7°- 22°. Crustacea. — Nauplii of Branchipus and Apus hatch out at a temperature of 30° in less than 24 hours, whereas at 16°-20° they require some weeks (SEMPER, '81, p. 129). Lobster larvae reared at 23° to 27° C. passed the fourth molt in about 10 days, or 3 days earlier than lar- vae reared at 19° C. (HERKICK, '96, p. 190). Jnsecta. — The mi- gratory locust is as- serted to require at different temperatures the following times for hatching. The figures are suspiciously regular. (From CUENOT, '94, p. 18, after "CLEVELAND.") FIG. 131. — Curves showing the relation between the num- ber of days (ordinates, indicated at left) required for the frog tadpole to reach a certain definite stage, and the temperature to which it is subjected during devel- opment. Stage I is that of a gastrula whose blastopore is just closing; II, edges of medullary plate rising; III, medullary tube completely closed ; IV, tail evi- dent, but gills not formed; V, embryo 5 mm. long; VI, embryo 7.5 mm. long; VII, 9 mm. long; VIII, 11 mm. long; IX, 11.5 mm. long. (From HERTWIG, '98.) Degrees Days 25 50 20 55 15 60 10 65 Fishes. — Many experiments have been made with these animals for com- mercial reasons, as it is sometimes desirable to retard growth during trans- portation or to delay hatching until the season of the natural enemies shall have been passed. Some of the results are summarized in §1] UPON THE RATE OF GROWTH 459 TABLE LIT SHOWING FOR THREE SPECIES OF FISH THE INTERVAL, IN DAYS, ELAPSING BETWEEN FERTILIZATION AND HATCHING, AT VARIOUS TEMPERATURES TEMPERATURE OF WATER. COD (EARLL, 'SO). HERRING (MEYER, '78). SHAD (KiCE, '84). -2- 0.0 30.0 0- 1.9 32.5 2- 3.9 22.0 40 4- 5.9 16.0 6- 7.9 13.0 15 8- 9.9 10-11.9 11 13.5 11 20-23.0 3-5 RAUBER ('83) states that eggs of minnows and salmon, which develop during the winter season, will not grow at much above 12°-15°, but will do so at 0°. On the contrary, eggs which normally develop during the summer- grow better at the higher temperatures. Amphibia. — The European Ran a is said not to develop at 0° (SCHULTZE, ',04), and the same is true of the Amblystoma tigrinumof the United States. (LiLLiE and KNOWLTON, '98). The time required to attain a definite stage, at which the chorda is well developed and head and tail are sharply marked, is for Rana temporaria: at 15°, 6 days; at 33°, 1 day (HERTWIG, '96). If brought gradually to it tadpoles may develop at 37°, or even for a few hours at 40°, but they do not thrive long at this temperature. The great effects of temperature on rate of development of the frog are illustrated by Fig. 132. Birds develop only at a high temperature and within narrow limits. The normal for the chick is 38°, the minimum is 25°, the maximum near 42° (RAUBER, '84). FERE ('94) has determined the rate of development of the chick's egg incubated at different temperatures. One lot at an abnor- mal temperature and a second at 38° were reared synchronously ; after a time the eggs were opened and the average stage of development (in hours of a standard series) determined. The following numbers express the ratio of the stage of development at the abnormal temperature to the stage at the normal temperature of 38°: — Temperature .... 34° 35° 36° 37° 38° 39° 40° 41° Index of Development 0.65 0.80 0.72 ?* (1.00) 1.06 1.25 1.51 In summarizing these scattered observations on growing animals we may exhibit in one table their critical temperatures. *The stage at 37° is taken from too few observations to be trustworthy. The stages at 35° and 36° are irregular, doubtless because of too few observations. As we go beyond 41° the ratio must decline again with great suddenness to 0. 400 EFFECT OF HEAT [Cn. XVIII TABLE LIII CRITICAL POINTS FOR VARIOUS ANIMALS, ARRANGED ACCORDING TO THE OPTIMUM SPECIES. OPTIMUM. MINIMUM. MAXIMUM. AUTHORITY. Minnows) 0° 12°-15° RAUBER, '84 Salmon / Echinus ....... 17°-22° VERNON, '95 Rana virescens .... 30 3 Li 1.1.1 1. and K '98 Bufo lentiginosus .... Gallus doinesticus .... 32 38 6 25 42 it It tt RAUBER, '84 These critical points for animals show the same variations with reference to optima, minima, maxima, and range that those of plants do, and here also these variations are cleai'ly adjusted to the temperatures normally experienced by the species. 3. Some General Phenomena accompanying Heat Effects. — a. Latent Period. - - We have seen that a change in the rate of growth is produced lay a change in temperature. If, how- ever, the times of the two changes be carefully noted, it will be found that a considerable interval elapses between them. This interval, the latent period, varies with the temperature. Thus ASKENASY ('90, p. 75) found that, in the case of maize seedlings cooled to l°-5°, two or three hours elapsed before decreased growth occurred ; whereas, when the seedling was cooled to 0°, five hours elapsed. A similar effect follows a change in the reverse direction. b. /Sudden Change of Temperature. — If the radicle of a seedling is suddenly transferred from water at or near 0° C. to water at between 18° and 21°, two effects follow. The first appears immediately after the transference, and consists in the sudden elongation of the radicle. The second appears later, and consists in a growth which is slower than that of the normal radicle. These facts have been determined by TRUE ('95), who concludes that the first effect is of a physical nature, and is due to the fact that, at the higher temperature, osmotic pressure is greater ; hence the tension in the tissues is greater and, consequently, they become stretched. The second effect TRUE regards as a response to the stimulus of the change, since §1] UPON THE RATE OF GROWTH 461 it is not constant for a given difference between the two tem- peratures, but is greater in raising the temperature from 5° to 18° than in raising from 17° to 30°. The more abnormal one of the pair of temperatures is, the greater is the response. c. Cause of Acceleration of Crrowth by Heat. — The accel- eration of growth may be due either to increased assimilation, imbibition, or production of formed substance. Is it princi- pally due to any one of these or are all increased in the same proportion? Data on this subject are afforded by certain measurements made by BIALOBLOCKI ('71). Seeds of rye, barley, and wheat were planted in soil which was fertilized by nutritive solutions and heated by a surrounding bath of water. The average absolute weight of the whole plant of each species was determined after the lapse of twenty days. The proportions of water, organic matter, and ash in the entire plant were likewise determined. Some of the results are given in Table LIV. It is to be noted that the high temperature was applied only to the soil in which the roots of the plant were imbedded. TABLE LIV GIVING THE AVERAGE WEIGHT (IN MILLIGRAMMES) AND THE PERCENTAGE OF WATER IN PLANTS WHOSE ROOTS ARE MAINTAINED IN SOIL, AT VARIOUS TEMPERATURES, FOR 20 DAYS (BIALOBLOCKI) EYE. BARLEY. WHEAT. TEMPERATURE. FRESH FRESH FRESH WEIGHT % WATER. WEIGHT % WATER. WEIGHT % WATER. IN MG. IN Mo. IN Mo. 10° 176 87.1 156 88.4 131 84.1 15 269 87.9 383 91.0 241 87.8 20 459 89.1 409 91.0 261 88.2 25 376 88.7 485 90.4 342 87.2 30 408 88.4 365 90.0 402 88.3 40 240 87.0 231 88.6 296 86.4 88 192 87.5 152 88.7 98 83.9 This table shows that the percentage of water increases slightly but constantly as the growth is accelerated by increased tem- perature, reaching a maximum near the optimum temperature. Other data (not reproduced here) show that the percentage of ash remains about constant, while that of dry organic sub- 462 EFFECT OF HEAT [Cn. XVIII MEAT) TEMPERATURE 66°FAHR. S3°FAHR. T84S HARCH ms 20M 23 D <§> 27tH stance diminishes slightly towards the optimum temperature for growth. We conclude, consequently, that in the acceleration of growth by heat all three processes are accelerated, but the im- bibitory process more than the others. Apparently con- tradictory are the results gained by COPELAND ('96), who found that the cells in the foliage of a moss which was trans- ferred from a cold room at 2° to a room at 18° to 20° lost, in from one to two weeks, a degree of turges- cence measured by a 1 to 3% so- lution of potassic nitrate (p. 72). When returned to the cold room the cells gained an increased turges- cence. The nearer the temperature lay to the optimum, the more rapid therefore the plant growth, the lower was the turgescence. This seeming paradox can be explained upon the hypothesis that just because the whole tissue is expanding, just because the superficial increase of the organic walls keeps pace, or more than keeps pace, with that of the included water, there is less osmotic pressure in the rapidly growing plants than in the slow-growing ones where the plasma walls are not expanding as fast as the imbibitory process would demand. APRIL *TH 8TH 10T.H MA? 22P AUQ. 1 BTh 98TH OCT. a 1ST FIG. 132. — A chart showing the correlation between the stage of development of the frog on successive clays and the temperature at which it has developed. (From HlGGENBOTTOM, '50.) § 2] UPON THE DIRECTION OF GROWTH 463 We may now gather together the results of our study of the effect of heat on the rate of growth of organisms. The relation between temperature and rate of growth may be expressed by a curve which, starting near 0°, reaches its highest point at a temperature varying with the species, and falls to a maximum temperature generally not far from the lethal temperature for the race. Three critical points are thus distinguishable, — the minimum, the optimum, and the maximum. In both animals and plants these points are correlated. The optimum lies close to the normal temperature for the species, the minimum lies usually only a little above the point of cold-rigor, and the maximum only slightly below the point of heat-rigor. The optimum lies nearer the maximum than the minimum, but the curve is not so unsymmetrical as that of metabolism. Any change in temperature leads to a change in the rate of growth, but this does not take place completely at once : there is a latent period of an hour or so. A sudden rise in temperature, especially from 0° to the ordinary summer temperature, is accompanied not only by a mechanical (elongating) effect, but also by a physiological response, showing itself in accelerated growth. Finally, in the acceleration of growth by heat, the imbibition of water is slightly more accelerated than the other growth processes. § 2. EFFECT OF HEAT ON THE DIRECTION OF GROWTH — THERMOTROPISM * Two sorts of heat are to be here distinguished — radiant and conducted. The former is a form of radiant energy and allied to light, consisting, indeed, of the rays lying beyond the visible red of the spectrum. The latter is due to molecular vibrations of the medium. 1. Effect of Radiant Heat.- -When Phycomyces nitens or seedlings of Lepidium sativum, Zea mais, etc., are reared on a * The first suggestion of this phenomenon was based upon an analogy with the action of light and was made by VAN TIEGHEM ('82), who gave it the name Thermotropism. WORTMANN ('83 and '85) first published extensive critical studies on the subject. Others who have contributed data are BARTHELEMY ('84), working on the roots of bulbous plants ; VOCHTING ('88), upon flower buds : and AF KLERCKER ('91) upon radicles. 464 EFFECT OF HEAT [Cn. XVIII klinostat whose axis of rotation is parallel to the window, and are subjected to rays of heat from a warmed plate of iron held in the axis of rotation, they turn with reference to the source of heat. Thus WORTMANN found that, at a distance from the iron plate of 10 cm., corresponding to a temperature of 27° C., all the spore-bearing hyphee of Phy corny ces turned in seven hours from the source of heat; they were negatively thermotropic. Under the same conditions the plumule of a seedling maize was positively thermotropic. The roots of the hyacinth when growing in water turn towards the adjacent stove-pipe. The flower-buds of Magnolia turn, in the field, from the dark heat-rays of the sun (VOCHTING). 2. Conducted Heat. - - The methods employed in working with this agent have been as follows : WORTMANN used a box divided into two compartments by a diathermous partition. Through one compartment there passed a constant current of cold water ; the second was filled with sawdust in which seeds were imbedded. In front of this second compartment, on the opposite side from the cold-water chamber, was a gas flame, the source of energy. The seeds were scattered through the saw- dust, so that some were nearer the flame, others nearer the cold hinder wall. The temperature of the sawdust near each seedling was determined. KLERCKER used essentially the same apparatus, excepting that a box of hot water replaced the flame. The results of the experiments are summarized in TABLE LV SHOWING FOR THE RADICLES OF SEEDLINGS OF VARIOUS SPECIES THE RELATION BETWEEN THE TEMPERATURE AND THE SENSE OF THERMOTROPIC RESPONSE TEMPERATURE. ZEA MAIS. ERVUM LENS. PHASEOLPS MULTIFLORU8. 50.0° — — — 40.0 — — — 37.5 -, + — — 35.0 + — — 30.0 + — — 27.5 + -, + — 25.0 + + — 22.5 + + -1 + 20.0 + + + 15.0 . + + 4- §2] UPON THE DIRECTION OF GROWTH 465 N This table shows that the sense of thermotropism is not con- stant for all temperatures, but is positive at the lower tempera- tures, negative at the higher ones, and neutral at a certain intermediate one. Also, just as different species vary in their optimum so also do they vary in the temperature of neutrality. As the optimum for growth is high in maize radicles (34°), and low in the pea radicle (26°. 3), so also is the neutral point. The neutral temperature is thus 3 +10 also probably related to | the attunement of the or- ganism and is an advan- tageous response. Within the range of positive or of negative turning there is a correla- tion between the temper- ature and the angle of inclination of the organ. KLERCKER has paid par- ticular attention to this fact. His results are summarized in the following table and curves, showing for each species the average inclination at each range of temperature : — 20° 25° C. FIG. 133. — Caloritropic curve of Sinapis alba, showing the relation between the inclination of the radicle and the surrounding tempera- ture. The numbers on the left give the in- clination in degrees ; the horizontal series of numbers are the temperatures to which the plant is subjected, the temperature diminish- ing 4° for every centimeter of departure from the source of heat. (After AF KLERCKER, '91.) TABLE LVI THE SENSE (+ or — ) AND THE AVERAGE EXTENT (EXPRESSED IN DEGREES OP ANGULAR DEVIATION FROM VERTICALITY) OF THERMOTROPISM AT DIFFER- ENT TEMPERATURES Pisuni sativuin | -8.9 | -12.9| -27.2J -38.4| -43.9| Sinapis alba | +10.5 | +19.0 | +2.4 | (See Fig. 133.) Fabavulgaris | - 4.3 | - 6.5 | -9.8 | -19.1 | -28.9 | °C. . . . 13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41 We see here that the angle of inclination (whether + or— ) increases regularly as we depart from the temperature of neutrality or that of 0° curvature. 2H 466 EFFECT OF HEAT UPON GROWTH [Cn. XVIII 3. Causes of Thermotropism. --VAN TIEGHEM suggested, in his a priori account of thermotropism, that it was due to an unequal growth on the two unequally heated sides of the organ, the side whose temperature was nearest the optimum making the greater growth. This explanation is not a direct mechanical one, the turning stem does not act merely like a metallic rod. The curvature is rather the result of unequal growth at unequal temperatures. In accordance with the theory just outlined we should find organs subjected on one side to the optimum temperature growing on that side faster than on the other, and hence turning from the optimum — but they turn towards it. Again, plants subjected on one side to a temperature slightly below the optimum will have a still lower temperature on the opposite side, and should be negatively thermotropic — but they are positive. Finally, plants subjected on one side to a temperature above the opti- mum will have a lower temperature, one nearer the optimum, on the opposite side, and should be positively thermotropic — but they are negative. In a word, according to the theory, plants should turn from the optimum ; they turn, however, towards the optimum, hence VAN TIEGHEM'S theory is exactly opposed to the facts. WORTMANN, on the other hand, believed that the sense of thermotropism is due to a self-regulation of growth in the organism leading it to make this advantageous turning. The stem tends to place itself in the axis of the heat rays just as in phototropism it places itself in the axis of the ra}rs of light. To this theory we must, however, add that plant organs may respond to conducted heat as well as to radiant heat, since they turn in a direction which, although opposed to the ordi- nary law of growth, tends to bring the tip into its optimum temperature. Such a result indicates clearly that thermotro- pism is a response to stimulus. If thermotropism is a response, where is the perceptive region? Suspecting that it was at the apex, WORTMANN de- capitated the root tip, but the response occurred as before. Evidently the whole growing part is sensitive to temperature. Thermotropism is thus seen to be such a response to the stimu- lus of either radiant or conducted heat that the organ — plumule, LITERATURE 467 radicle, flower-bud or sporangiferous hypha -- tends to place itself in the axis of the heat rays, if there are any, or to bend towards or from the source of heat. Whether the organ shall bend towards or from the source of heat depends both upon the external temperature and the protoplasm of the plant. The turning is such that it will tend to keep the organ at the opti- mum temperature for its protoplasm, or bring it into such a temperature. The response is thus, on the whole, an advan- tageous one. SUMMARY OF THE CHAPTER There is in all organisms a close relation between tempera- ture and rate of growth, such that growth is most rapid at that temperature at which the chemical changes of metabolism pro- ceed most quickly. The position of this optimum varies with the normal thermal environment of the race ; it is attuned, we may say, to that normal temperature. Certain organisms or their parts grow in a definite direction with reference to the source of heat : away from the source when its temperature is too high ; towards the source when the temperature is low. The neutral point varies in the different species in much the same way as the optimum for growth varies. We may say that the different attunements of organisms determine their different neutral points. At the same time these responses are advantageous. In some way the advantageous response of the organism is bound up with its attunement. LITERATURE ASKENASY, E. '90. Ueber einige Beziehungen zwischen Wachsthum und Temperatur. Ber. deut. Bot. Ges. VIII, 61-94. 23 April, 1890. BARTHELEMY, A. '84. De Faction de la chaleur sur les phenoinenes de vegetation. Comp. Rend. CXVIIT, 1006, 1007. 21 April, 1884. BIALOBLOCKI, J. 71. Ueber den Einfluss der Bodenwarme auf die Ent wick- lung einiger Culturpflanzen. Landw. Versuchs-Stat. XIII, 424-472. COPELAND, E. B. '96. Ueber den Einfluss von Licht und Temperatur auf den Turgor. Inaug. Diss., 59 pp. Halle. Bot. Centralb. LXVIII, 177-180. 4 Nov. 1896. CUENOT, L. '94. L'influence du milieu sur les animaux. Encyclopedic scientifique des Aide-Memoire. Paris: [1894]. 468 EFFECT OF HEAT UPON GROWTH [Cn. XVIII EARLL, R. E. '80. A Report on the History and Present Condition of the Shore Cod-fisheries of Cape Ann, Mass., etc. Rept. U. S. Fish Com. for 1878. 685-740. EIDAM, E. '75. Untersuchungen iiber Bacterien, III. Beitrage zur Biologie der Bacterien. 1. Die Einwirkung verschiedener Temperaturen und des Eintrocknens auf die Entwicklung von Bacterium Termo, Duj. Beitrage z. Biol. d. Pflanzen. I, 208-224. FERE, C. '94. Note sur 1'influence de la temperature sur 1'incubation de 1'oeuf de poule. Jour, de 1'Anat. et de la Physiol. XXX, 352-365. FISCHER, A. '97. Vorlesungen iiber Bakterien. Jena : Fischer, 1897. FORSTER, J. '87. Ueber einige Eigenschaften leuchtender Bakterien. Cen- tralb. f. Bacteriol. u. Parasitenk. II, 337-340. HERRICK, F. H. '96. The American Lobster. Bull. U. S. Fish Com. XV, 1-252. 64 plates. HERTWIG, O. '96. Ueber den Einfluss verschiedener Temperaturen auf die Entwicklung der Froscheier. Sitzungsb. Berlin Akad. Jan. 1896. 105-108. 6 Feb. 1896. '98. Ueber den Einfluss der Temperatur auf die Entwicklung von Rana fusca und Rana esculenta. Arch, f . mik. Anat. LI, 319-381. 8 Jan. 1898. HIGGENBOTTOM, J. '50. (See Chapter XVII, Literature.) KIRCHNER, O. '83. Ueber das Langenwachsthum von Pflanzenorganen bei niederen Temperaturen. Beitrage z. Biol. d. Pflanzen. Ill, 335-364. KLERCKER, JOHN AF, '91. Ueber caloritropische Erscheinungen bei einigen Keirnwurzeln. Ofversigt af Kongl. Vetenskaps. Akad. Forh. XLVIII, 765-790. KOPPEN, W. '71. Waerme und Pflanzenwachsthum. Bull. Soc. Imper. des Naturalists, Moscow. XLIII, Part 2, 41-110. LILLIE, F. R., and KNOWLTON, F. P. '97. On the Effect of Temperature on the Development of Animals. Zoological Bulletin. I, 179-193. Dec. 1897. MEYER, H. A. '78. Beobachtungen iiber das Wachsthum des Herings im westlichen Theile der Ostsee. Jahresber. der Commission zur wiss. Unters. d. Deutschen Meere in Kiel. IV-VI, 227-251. RAUBER, A. '84. Ueber den Einfluss der Temperatur, des atmosphiirischen Drucks und verschiedener Stoffe auf die Entwicklung thierischer Eier. Sb. Naturf. Ges. Leipzig. X. 55-70. RICE, H. J. '84. Experiments upon Retarding the Development of Eggs of the Shad, made during 1879, at the U. S. Shad Hatching Station at Havre de Grace, Md. Report U. S. Fish Com. for 1881. 787-794. SACHS, J. '60. Physiologische Untersuchungen u'ber die Abh'angigkeit der Keimung von der Temperatur. Jahrb. f. wiss. Bot. II, 338-377. SCHULTZE, O. '94. Ueber die Einwirkung niederer Temperatur auf die Entwicklung des Frosches. Anat. Anz. X, 291-294. 19 Dec. 1894. SEMPER, C. '81. Animal Life as affected by the Natural Conditions of Existence. 472pp. New York, 1881. TIEGHEM, P. VAN, '82. Traite de Botanique. Paris, 1884. [First part- issued in 1882.] LITERATURE 469 TKUE, R. H. '95. On the Influence of Sudden Changes of Turgor and of Temperature on Growth. Ann. of Bot. IX, 365-402. VERNON, H. M. '95. (See Chapter XVII, Literature.) VOCHTING, H. '88. Ueber den Einfluss der strahlenden Warme auf die Bluthenentfaltuug der Magnolia. Ber. deut. Bot. Ges. VI, 167-178. VRIES, H. DE, '70. Materiaux pour la connaissance de 1'influence de la temperature sur les plantes. Arch. Neerlandais. V, 385-401. WARD, II. M. '95. (See Chapter XVII, Literature.) WIESNER, J. '73. Untersuchungen iiber den Einfluss der Temperatur auf die Entwicklung des Penicillium giaucum. Sb. Wien. Akad. LXVIII1, 5-16. WORTMANN, J. '83. Ueber den Einfluss der strahlenden Warme auf wachs- ende Pflanzentheile. XLI, 457-470, 473-479. July, 1883. '85. Ueber den Thermotropismus der Wurzeln. Bot. Ztg. XLIII, 193 et seq. CHAPTER XIX EFFECT OF COMPLEX AGENTS UPON GROWTH, AND GENERAL CONCLUSIONS IN the foregoing chapters we have examined the effect upon growth of various agents considered as acting separately. This treatment has been necessary for purposes of analysis, but it has the disadvantage that it does not reveal the normal action of these agents. For, in nature, we find many agents working together upon the growing organism. For example, gravity is constantly acting in one direction, upon sessile organisms at least, and at the same time the chemical character and the density of the surrounding medium, contact and im- pact, light and heat, are exerting their specific influences. The rate of growth of an organism and the direction of growth of its organs are determined by the resultant of some half dozen controlling factors which, in their totality, constitute environ- ment. Again, some of the factors influencing growth are so complex that they are not yet amenable to analysis into the chemical, molar, and physical agents whose effects we have considered in foregoing chapters. For instance, the reaction of an organism to its own activity is still too complex an effect for us to be able to resolve it into its elemental reactions to pressure, chem- ical change, etc. The effect of exercise upon growth may con- sequently form a subject for special consideration. § 1. THE COOPERATION OF GEOTROPISM AND PHOTOTROPISM When light falls from one side upon a seedling in the ground, the seedling is influenced by both gravity and light, and tends to respond to both. In responding to both, the apex of the seedling tends to point upwards on account of gravity's action, and laterally towards the source of illumination on account of 470 §1] GEOTROPISM AND PHOTOTROPISM 471 the light. As a result of this combined response the plant comes to occupy an oblique position. The exact angle assumed by the plant is variable. It varies in a given species with the intensity of the light, and, the in- tensity of the light remaining constant, the angle varies with the species. For example, seedlings of Lepidium sativum sub- jected to a unilateral horizontal illumination for 48 hours showed at different intensities of the light the following inclinations from the vertical (WiESNER, '79, p. 196) : - DISTANCE OF SEEDLING FROM FLAME. 0.25 meter 0.30 " 0.75 " 1.25 " 2.50 " (optimum) 3.00 " 3.75 " INCLINATION FROM VERTICALITT. 30° 35 55 70 80 65 35 This table shows that the inclination from verticality in- creases with the intensity of illumination to a certain maximum degree, beyond which it diminishes again. This maximum inclination is called the phototropic limiting angle. More extended determinations of the limiting angle have been made by CZAPEK ('95), who finds that it is the same for a given intensity of horizontal light whether the plant is verti- cal or horizontal, having its apex directed towards the source of light. TABLE LVII GIVING THE PHOTOTROPIC LIMITING ANGLE FOR VARIOUS SPECIES OF PLANTS Phycomyces nitens . . . 90° Pilobolus crystallinus . . 90 Vicia sativa 70 Avena sativa 70 Phalaris canariensis ... 70 Linum usitatissimum . . 70 Brassica napus 70 Datura stramonium ... 70 Lepidium sativum ... 60 Sinapus alba (plumule) . . 60° Pisurn sativum 60 Vicia faba 60 Phaseolus multiflorus . . -60 Sinapis alba (radicle) . . 50 Helianthus annus .... 45 Kicinus communis ... 45 Cucurbita pepo 40 472 EFFECT OF COMPLEX AGENTS ON GROWTH [Cn. XIX The phototropic limiting angle is constant for all cases in which gravity and light act at a right angle, whether .the plant axis be originally placed vertically upright, inverted, or hori- zontal. When the direction of the light ray makes some other angle with that of gravity, the resulting position of the plant may be quite different, as CZAPEK ('95) has shown. If the light falls upon the plant vertically from below, in such a way therefore as directly to oppose gravity, the resulting position of the plant varies according to its original position, in a way generally explicable on the ground that one of the two tropic influences has come to prevail, but with diminished power. Thus, when the axis of the seedling is horizontal it will, if like Avena it is very sensitive to light, turn its tip slightly upwards for a time, and then definitely down. A slightly phototropic plant, like Helianthus, assumes its limiting angle of 45° from the zenith. When the seedling is exactly inverted, plants highly sensitive to light grow down, but Helianthus places itself at 135° from the zenith, hence no longer at the limiting angle. When the axis of Helianthus is placed obliquely downwards its tip becomes inclined at 45° from the zenith. If the ray of light falls upon the plant obliquely from below, the result on the erect, horizontal, or inverted seedling is a response to the active component of the light ray. The erect seedling is affected in the same way as by the horizontal ray; the horizontal seedling responds as though the light came verti- cally from below, and all inverted plants place themselves in the axis of the infalling ray. If the ray of light falls obliquely from above, all plants, even Helianthus, place themselves in the axis of the ray. This is what might have been anticipated, since gravity affects the inclined plant much less than the horizontal one, and so the active component of the light ray is relatively more effective in this oblique position than in the horizontal one. The foregoing experiments show that, in general, the geo- tropic reaction is modified by the simultaneous action of light. I have hitherto assumed that the final position of the plant is the resultant of the action of two tropic agents ; that the pho- totropic and geotropic reactions interlock. Another cause of § 2] EFFECT OF EXTENT OF MEDIUM ON SIZE 473 the modified position is, however, possible. The stimulating action of light may interfere with the sensibility of the plant to gravity. An early experiment made by CZAPEK seemed to indicate that this is the case. A vertical plant was illumined upon one side and then placed horizontally with the former illumined side facing the nadir. The geotropic curvature was, as might be inferred from the experiment described on p. 444, greatly retarded. The retardation of geotropism by a pre- vious photic stimulation occurs, however, only in species which are much more phototropic than geotropic. That the result just described is not due to a diminution in geotropic sensitive- ness follows from two considerations : first, a plant previously geotropically stimulated is not retarded in its subsequent pho- totropic response, as we should expect if the irritated state interfered with the reception of a new stimulus ; secondly, the retardation in response to light after geotropic stimulation is most directly explained on the ground that a response which is being actually worked out interferes with an incipient response. The conclusion may, consequently, be drawn that there is no reason for believing that the modified response resulting either from the simultaneous or successive action of two tropic agents is due to an alternation of geotropic or phototropic sensitive- ness, but rather to a modification of the response. The modifi- cation of the response is due to the interlocking effect or the mutual interference of the phototropic and geotropic reactions to stimuli. § 2. EFFECT OF EXTENT OF MEDIUM ON SIZE The quantity to which an organism shall grow — the size that it shall attain — is a specific character which is, within limits, independent of the amount of food consumed by the organism. In how far this character is dependent upon other environmental conditions is an interesting question. It is clear that size is relative, and among other things it is related to the extent of the space in which the organism can move. An ant can lose its way in a cage in which an elephant can hardly find room to move. The ant is small, the elephant large, in relation to their common room. 474 EFFECT OF COMPLEX AGENTS ON GROWTH [Cn. XIX Now it is a common observation of naturalists that there is frequently a relation between the size attained by a developing organism and the extent of the medium in which it is develop- ing. Animals reared in aquaria rarely attain the size of their fellows developing in out-of-door ponds. Even in nature, fishes of a given species living in small or densely inhabited ponds are smaller than fishes of the same species inhabiting large or sparsely populated ponds. According to SEMPER ('74) the experiment was tried of transplanting the very small chars from a small lake in the Maltathal, Carinthia, Austria, where they were very abundant, to another lake where there were few fish. The transplanted chars soon became three times the size of the parent stock. In other experiments it has often been observed that tadpoles reared in the laboratory, although well fed, never attain the size of those living free. SIEBOLD * found that Apus reared in a small vessel grew no longer than 7 or 8 mm. instead of 50 or more. The pond-snail, Limmea stagnalis, has been made the special object of experimental dwarfing. HOGG ('54) found that when confined to a small, narrow cell they ac- quire, even after six months, only the size of normal animals two or three weeks old. HOGG'S conclusions no doubt ap- peared crude to the physiologist of the last decade. He said that the snail grows "to such a size only as will enable it to move about freely, thus adapting itself to the necessities of its existence." SEMPER ('74) next undertook a more thorough set of experi- ments upon these animals. He kept the snails in vessels con- taining different quantities of water to each individual, and found that as the quantity of water is diminished from 4000 cc. or 2000 cc. to 100 cc., a diminution in the rate of growth occurs. Increasing the number of individuals in a vessel has the same effect as diminishing the volume of water. The relation of volume of water per individual to length of shell at the end of eight or nine weeks is given in Fig. 134. This curve shows that as the volume increases from 100 cc. to 800 cc., the average length of the shell of the snail doubles. The result SEMPER * Cited from SEMPER ('74). §2] EFFECT OF EXTENT OF MEDIUM ON SIZE 475 explains on the hypothesis that water contains some substance necessary to the growth of the snails, which becomes used up before full size is acquired : the more quickly, of course, the smaller the amount of water. Instigated by SEMPER'S experiments YUNG ('85) now under- took similar ones upon tadpoles. Twenty-five just-hatched tadpoles were put into each of three vessels, A, B, and C, contain- ing about 1200 cc. of water, but of different forms, so that A, which measured 7 cm. diameter, had a depth of 30 cm. of water ; 200 400 600 800 1UOO 1200 liOO 1000 1800 2000 CUBIC CENTIMETRES OF WATER FIG. 134. — Curve of relation between length of shell of Limnrea stagnalis and quantity of water in which it is reared. (From SEMPER, '74.) B, whose diameter was 11 cm., had 13 cm. of water; and C, whose diameter was 14.5 cm., had 6.5 cm. of water. At the end of one and a half months measurements were made of the length and the breadth of each tadpole with the following average results : - VESSI.L A. VESSEL B. VESSEL C. Length 26.20 34 2 41.2 Breadth 6.15 7.8 8.8 Date of first metamorphosis. . August 4 July 22 June 18 YUNG concluded that the larger size of the animals in the shallower water (C) was due to its absorbing oxygen more thoroughly. Finally, DE VARIGNY ('94) has attacked even more system- atically this problem of effect of extent of medium on size. He has found that Limnaeas kept for eight months in similar vessels, each containing 550 cc. of water and about 500 cc. of 476 EFFECT OF COMPLEX AGENTS OX GROWTH [Cn. XIX air, but differing in that one was stoppered and the other not, had attained about the same size (Fig. 135). Since the oxygen supply of the snails in the two vessels was evidently very dis- similar, YUNG'S explanation is shown to be inadequate. Next DE VARIGNY tested the effect of differences in volume. He reared Limn seas in different quantities of water, in vessels of dissimilar proportions, such that in all there was the same free surface area of water. The differences in volume had only a slight effect on the size of the snails (Fig. 136). On the other hand differences in surface, with constant volume of water, have an important influence on size. The greatest growth occurs in the broader vessel (Figs. 137, 138). The number of individuals in the vessel influences the average size, as SEMPER found. To test SEMPER'S theory that the small size of the animals in the small vessel is due to its having exhausted the necessary substance in the water, DE VARIGNY partitioned a vessel of water into two unequal compartments and reared a Lymnea in each. One of the compartments was made by partly submerg- ing a test-tube, from which the bottom had been removed, in a beaker of water. A piece of muslin, tied over the bottom of the test-tube, permitted an interchange of water, but not the intermigration of the Limnjeas between the test-tube and the main vessel of water. The latter constitutes the second com- partment in which the snails lived. After several months the individuals kept in the two vessels usually showed a marked difference in size, those reared in the roomier vessel being the larger (Fig. 139). When, however, the two similar snails were kept in similar tubes plunged in beakers of water of unequal volume, they attained about the same size. A second test of SEMPER'S theory applied by DE VARIGNY consisted in comparing the growth of Limmeas in fresh water with their growth in water in which snails had for some time been developing. The snails in the latter showed a slight but nearly constant inferiority in size. It may well be that some of the salts necessary to growth had been extracted from the water by the development of snails therein, making it less fit for growth. Nevertheless, even the most mai^ked differences in the size of the snails in the two kinds of water was not sufficient fully to account for SEMPER'S result by means of SEMPER'S theory. §2] EFFECT OF EXTENT OF MEDIUM OX SIZE 477 135 13G FIG. 1:35. —Two individuals of Limnsea stagnalis, which have lived from May, 1891, to January, 1892, in two flasks nearly alike in respect to surface and volume of water. In the one case (shell at left) the flask, enclosing 500 cc. of air, was sealed ; in the other case (shell at right) the flask remained unsealed throughout the 8 months of experimentation. (From DE VAKIGNY, '94.) FIG. 130. — Limusea auri- cularis, reared in dif- ferent masses of water having the same sur- faces but different volumes. The speci- mens, taken in order from left to right, were reared in vessels having surface areas of 100, 200, 400, and 500 cc. respectively. Experiments extended from 15 November to 5 April. (From DE VARIGNY, '94.) FIG. 137. — Limnrea stag- nalis. The individual at the left lived from 18 November to 20 April in a liter of water having a sur- face of only 2 cm. diam- eter; that at the right lived during the same period in an equal vol- ume of water having a surface of 18 cm. diameter. (From DE VARIGNY, '94.) FIG. 138. — The Limnsea stagnalis at the left lived from 21 Novem- ber to 6 January in 1350 cc. of water hav- ing a surface of 3.5 cm. diameter ; that at the left, somewhat larger, lived during this pe- riod in 600 cc. of water having a surface of 16 cm. diameter. (From DE VARIGNY, '94.) FIG. 139. — Limnsea 1 lived from 18 November to 5 April in a glass without a bottom (capacity 250 cc.), suspended in the beaker (capacity 4200 cc.), in which 2 lived. Limnsea 3 lived from 20 November to 7 February in a tube, suspended in a vessel in which 4 was reared. Limnaea 5 lived from 9 April to 24 June in a tube, sus- pended in the vessel in which 6 lived. (From DE VARIGNY, '94.) 478 GENERAL CONSIDERATIONS [Cn. XIX The conclusion to which DE VARIGNY arrived was that the nanism provoked in the small vessels is caused by a diminution of movement and consequently of exercise, for in the restricted medium the movements are fewer and slighter, since the food is near at hand. Also, the snails will exercise more in a body of water with a broad, exposed surface than in a narrower one, because they crawl so much on the surface films. This interpretation is sustained by all the results excepting those obtained from a varying number of individuals in masses of water of the same volume and form. The fact that the individuals grow larger the fewer they are, may be accounted for, thinks DE VAEIGNY, on psychological grounds ; for, in the crowded room, movements will be restricted from very much the same cause that makes one move less rapidly in a street containing impediments than in one which is quite clear. It may well be doubted whether the bottom of this matter has yet been reached. Probably nanism is produced by several causes : such as insufficient supply of mineral constituents in the water, especially of calcium salts, products of excretion in the water, and exercise. There is, however, much reason for believing that HOGG'S conclusion is one which, with our fuller knowledge, we can hardly improve upon --that, in respect to the size attained as in other qualities, the snail has the power of "adapting itself to the necessities of its existence." § 3. GENERAL CONSIDERATIONS RELATING TO THE ACTION UPON GROWTH OF EXTERNAL AGENTS 1. Modification of Rate of Growth. — Protoplasm is composed of three kinds of substances: the living plasma, the formed sub- stance, and the watery chylema. Accordingly, growth involves three processes : that of the formation of new plasms, assimila- tion; that of the manufacture of formed substance, secretion; and that of the absorption of water, imbibition. Anything which affects these three processes will affect the rate of growth. The action of external agents upon the rate of growth is of two general kinds. There is, first, the general effect ; and, secondly, the specific effect. The general effect is more or less similar in all protoplasmic masses (organisms) subjected to the agent ; it is the result of some immediate and necessary modifi- § 3] EFFECT OF EXTERNAL AGENTS UPON GROWTH 479 cation of the protoplasm depending upon its very structure. This general effect may be of two sorts : a grosser mechanical one and a more refined. The grosser general effect is seen in the osmotic action of dense solutions; in the elongation of an organ consequent upon pulling it with a considerable force ; in the interference with vital actions by poisons, by intense light, or by high temperatures. The more refined general effect is due to the acceleration of growth by the acceleration of the essen- tial metabolic processes involved in growth ; hence come the effects, within limits, of favorable foods, of electricity, of radiant energy, and of warmth. We can explain the effect of such refined agents by known chemical laws. The grosser and the finer effects pass over into each other at certain intensities. Thus the acceleration of growth produced by summer temperature passes over at a higher temperature into the gross retardation due to coagulation. The specific effects, in contradistinction to the general, appear only in certain organisms or their parts, and have no such evi- dent and explicable relation to the cause as the general effects have to their causes. Such is the increased growth resulting from certain slight poisons, from the deformations of the stems of certain plants, from a wound which leaves a defect to be filled by growth. These effects cannot at present be accounted for satisfactorily by known chemical processes ; they result from peculiarities of the specific protoplasms which depend largely upon the past history of each kind of protoplasm. The same agent may have at different intensities, at one time, the specific ; at another, the general effect. Thus the slight pull- ing of the stem of a seedling may induce the specific shortening effect, whereas a stronger pull will cause a gross elongation. The gross general effect, the refined general effect, and the specific effect form a series of results brought about by pro- cesses which are quite intelligible in the first case, much more complex in the second, and still further removed from our ken in the last ; we might speak roughly of these effects as due to physical, chemical, and vital processes respectively, without meaning to imply a qualitative difference between these pro- cesses. The most complex of these three processes may also be designated as response to stimulus. 480 GENERAL CONSIDERATIONS [Cn. XIX Let us now consider the mechanics of the acceleration of growth by various agents. The mechanics of the effect of food on growth varies of course with the food ; some supply- ing the energy or the material for assimilation, other kinds furthering secretion, and still others going to build up the molecules which do the work of vital imbibition. Whether the poisons which, like zinc sulphate, stimulate growth affect chiefly the assimilatory or the imbibitory process, is unknown; but the slowness of the result suggests a modification of assimi- lation. The effects of water and of solutions seem to be chiefly upon imbibition ; that of deformation and wounding chiefly upon assimilation ; that of electricity is uncertain ; that of light is probably chiefly upon assimilation; and that of heat upon imbibition. These conclusions are, however, tentative; experiments are needed to test them further : this is one of the next tasks in the investigation of growth. 2. Modification of Direction of Growth — Tropism. — The tropic effect of an external agent occurs only when the agent does not act uniformly from all sides upon the growing organ- ism, but constantly from one side. Hence this effect will be marked only in organisms which for a considerable period present the same surface to the action of the agent. Such an effect is characteristic therefore of sessile plants and animals. The turning of an organ with reference to an external agent may be either a gross effect or a specific response effect of the agent. As examples of the gross effect may be cited the cases of false traumatropism and false electrotropism, in which the turning is due to the death or injury of the tissue on the con- cave side of the organ. All cases of true tropism are cases of response to stimuli : such are, chemotropism, hydrotropism, thigmotropism, traumatropism, rheotropism, geotropism, elec- trotropism, phototropism, and thermotropism. The mechanics of these tropic responses may now be briefly considered. In general the tropisms are growth phenomena, for they are due to enlargement of the bending organ on one side. The growth seems to be due either to assimilation or imbibition, or both, secretion playing no part. It is not easy to say whether in any case assimilation or imbibition is the more important. An inference can be drawn, however, from § 3] EFFECT OF EXTERNAL AGENTS UPON GROWTH 481 the quickness of response, for growth by imbibition is more rapid than that by assimilation. Also a histological study of the curving region should throw light upon this question. Among the rapid tropisms are chemotropism, especially as seen in the tentacles of Drosera and in pollen-tubes, and thig- motropism, as exhibited in tendrils. Such are probably due to differential imbibition. Among slow tropisms are hydro- tropism and rheotropism, which are probably due largely to differential as- ep similation. Traumatro- pism, geotropism, and the response to radiant en- ergy, namely, electrotro- pism, thermotropism, and phototropism, are inter- mediate in their rate, and are probably due to the combined action of assim- ilation and imbibition. Sections through the responding region show the importance of imbi- bition in certain tropisms, as, for example, geotro- pism. In such sections it is seen that the cells on the convex side are en- larged in all axes and full Of water, while those of FlG. 140. - A section of a tropic radicle taken in the concave side are com- pressed so that the cells are shoved into one an- other, are diminished in size, and have a dense plasma (Fig. 140) . A typ- ical set of measurements of the dimension of the cells in the curving region, compared with normal cells, is given by CIESIELSKI ('72) as follows : — the plane of curvature, at the region sy, Fig. 10(). ep, epidermis ; rp, parenchyma ; gbs, sheath of the fibro-vascular bundle ; Izb, fibro- vascular bundle ; h, wood-cells ; .(/, vessels. Those cells which lie next the nadir («) are smaller than those turned toward the zenith (6). The latter appear stretched with water, while the former are dense and of small size. (From CIESIELSKI, 72.) 482 GENERAL CONSIDERATIONS [Cn. XIX LKNGTH. BREADTH. THICKNESS. 0 1 2-3 mill. 0.045 mm. 0.042 mm. Cells of concave side 0.020 0.025 0.026 Cells in normal condition .... 0.099 0.035 0.032 The importance of imbibition for geotropism is also shown by the experiment of cutting a slice off from the upper part of the horizontal root, which then curves only slowly ; whereas, if the cut surface is placed down, the curving takes place with abnormal rapidity. It being admitted that tropisms are, for the most part, largely, if not chiefly, due to differential imbibition, the ques- tion arises, How can this produce a turning ? It is easy to see how it might be possible in the case of a multicellular plant, but tropism also occurs in animals and unicellular organs, as e.g. the hyphse of Mucor. It has been suggested, to meet this difficulty, that the unequal growth affects primarily the cell- walls ; but this explanation does not quite meet the case of hydroids. A general statement, applicable to multicellular plants and animals and to unicellular organs, may be made, if the cell-wall be recognized as living, as follows : The imbibi- tion distends the living substance on the convex side, the water probably being in part drawn from the concave side. Going a step farther, the tropic agent produces such a change in the molecules of the curving region as to cause them to imbibe water with abnormal rapidity. This change may, however, be produced by the agent either directly or indi- rectly. In all cases in which the sensitive part of the organ becomes the curving part, the action of the agent is direct. Examples are found in the thigmotropism of tendrils, in the phototropism and thigmotropism of stems, and, probably, in traumatropism. In cases in which the curving part is remote from the sensitive part, as in geotropism, the action of the agent is indirect. In these cases there must be a transmission of a stimulus from the sensitive part (the tip) to the respond- ing part, producing the required molecular change there. Concerning the nature of the changes induced by the tropi- § 3] EFFECT OF EXTERNAL AGENTS UPON GROWTH 483 cally stimulating agent, we have recently gained valuable data from the studies of CZAPEK ('98). He has found that the stimulated protoplasm, for instance, of a geotropic radicle exhibits no visible movements or negative electrical variation, as in the nerve cells of animals, but does exhibit a chemical change. Thus, when the root tip of the seedling of a bean or other species is boiled in a solution of ammoniacal silver nitrate, there is a marked reduction of the silver, especially in the cells of the periblem. This reduction is stronger in the cells of stimulated root tips than in those of unstiraulated ones. A second change consists in the diminution in the amount of a substance of the root tip which easily loses oxy- gen. Such a substance is indicated by such changes as these in the normal root tip : blue coloration (oxidation) of a sec- tion of the tip when placed in an emulsion of guaiac gum in water ; deep blue coloration of sections by indigo white * ; strong violet reaction (indophenal reaction) in sections sub- jected to an aqueous solution of a-naphthol to which paraphe- nylendiamin has been added. Now all such reactions are less marked in the root after stimulation. We conclude that stim- ulation results in increased capacity for reduction and dimin- ished capacity for oxidation - - an increase in the avidity for oxygen. These changes occur long before the response of turning shows itself ; they occur earlier in the non-sensitive roots, and they are less marked after a slight stimulus, such as results from a slight inclination of the root from the vertical position. The isolation of the two substances, the reducing and the oxidizing, was now attempted. The former is not changed by boiling or by the action of chloroform, and is soluble in alcohol; the latter is destroyed by heat, is unchanged by chloroform, is insoluble in alcohol, and may be extracted from the triturated cells by water. A large number of root tips of Vicia faba were rubbed up with water until no fragments remained This aque- ous extract was filtered, and to the filtrate alcohol was added. A precipi- tate occurred, which had all the properties of the oxidizing substance. It is highly probable that it belongs to the category of oxidation ferments. * This is made by the cautious reduction of indigo carmine by dilute hydro- chloric acid and zinc. 484 GENERAL CONSIDERATIONS [Cn. XIX To get the reducing substance, the preceding solution was filtered to eliminate the alcoholic precipitate. The filtrate had all of the qualities of the reducing substance. A further study of its properties indicated that it belongs to the aromatic organic substances, many of which have an intense reducing action and are hence used in photography. We may conclude that geotropic stimulation of the root tip induces chemical changes leading to the increase of a reducing substance of aromatic nature, and to the diminution in amount of an oxidizing ferment. 3. Adaptation in Tropisms. - - The capacity for bending is usually associated with an advantage accruing to the part by that bending. Thus, the upward tropism of the stem and the downward tropism of the root ; the positive phototropism of the stem and the positive thigmotropism of the root and of the climbing Dodder; negative traumatropism ; and positive and negative thermotropism, depending upon whether the source of heat is of a less or greater temperature than the opti- mum— all these responses tend to preserve the normal envi- ronment for the organism ; they are adaptive. At least one tropic response cannot be shown to be advantageous, namely, electrotropism. Electric currents of such intensity as roots respond to certainly do not exist in the soil. The response has no conceivable advantage in the ordinary life of the plant, and yet it occurs with as much precision as does a response to light or heat. If only there were, in the ground, such electric cur- rents as we apply to the plant, we might be able to show an advantage of the response in this case also ! 4. Critical Points in Tropism. — It has been shown repeat- edly in the foregoing chapters that the sense of tropism depends upon the degree of the stimulating agent. , Thus Mucor stolonifer is strongly positively chemotropic with refer- ence to 2% cane sugar ; becomes less so as the concentration approaches 30% ; and is negatively chemotropic to a 50% solu- tion. So, likewise, the radicle of Zea mais is + thermotropic at 12°- 36° ± thermotropic at 37°- 38° — thermotropic at 40°- 49°. In these cases, as in the tactic phenomena, there is recognizable an optimum intensity of the agent, to which the organism is § 3] EFFECT OF EXTERNAL AGENTS UPON GROWTH 485 attuned, so that, if the intensity rises above that optimum, neg- ative tropism will occur, and, if the intensity falls below that optimum, positive tropism may be expected. This optimum - this intensity to which the organism is attuned -- differs, how- ever, in different species. Thus, according to WORTMANN, as we have seen, the turning-point of the radicle is for — Zea mais, 37°; Ervum lens, 27°; Phaseolus multiflorus, below 22°. But why is the turning-point so different in different species, or why are species attuned to different intensities ? This dif- ference is for the most part more or less closely correlated with the usual intensity of the agent to which the growing organ- ism is subjected. To certain minds the phrase "Natural Selec- tion " will be considered sufficient to stifle further inquiry ; the known facts of self-adjustment, however, have thrown the burden of proof that Natural Selection has acted in any case upon those who assert it. Meanwhile we may seek for a cause more consistent with sound physiology. In the first place, the facts of " after-effect " may be consid- ered. It has been shown, with reference to the effect of many of the agents considered, that this effect does not endure only so long as the agent acts, but that it persists for a longer or shorter period after the stimulus has ceased to be applied. Thus, if a stem is placed horizontally, so that gravity stimu- lates it and causes it to grow up, and it is then placed verti- cally, the growth continues for a time in the former (now hori- zontal) direction ; or, a horizontally placed root, decapitated after the lapse of one hour, curves geotropically, whereas a root placed horizontally and decapitated at once does not do so. • Again, if a tendril is irritated by contact and the irri- tating body is then removed, a thigmotropic curvature of as much as 45° may occur. Still again, in an experiment of DARWIN ('81, p. 463), a seedling of canary grass was placed before a window for nearly two hours, during which the coty- ledon turned towards the glass ; the light was now cut off, but the cotyledon continued to bend in the same direction for one- fourth to one-half an hour. It was kept in the dark for an 486 GENERAL CONSIDERATIONS [Cn. XIX hour and forty minutes (during which time it acquired an upright position through the action of gravity), and then exposed again to diffuse light from one side for an hour, show- ing the phototropic curvature. Light was now excluded, but the cotyledon continued to bend for 14 minutes towards the window. In these experiments there was a persistence of the response to light after light had been cut off. Finally, if a plant organ, which has been growing slowly at a low temper- ature, is quite rapidly subjected to the optimum, the increased growth is slow in making its appearance ; it may be delayed for an hour or two. What is the significance of this after-effect ? It seems clearly to show that an agent acting on protoplasm not merely modifies the constitution of the protoplasm, but produces a change which is more or less permanent, and is only slowly obliterated upon removal of the agent, or becomes only slowly overshadowed by a new stimulus. This permanency of the change wrought permits the accumulation of extremely slight effects. An instance of such accumulation is seen in tendrils, which exhibit no response to a single soft blow but show evi- dent thigmotropism to a series of such blows. When, however, the repeated stimuli are each great, it is not an accumulation of effect which is noticed, but rather an absence of any response whatever. Then appears the phe- nomenon of acclimatization, or accustoming to the stimulus. Examples of this have been given in the foregoing chapters. Thus, in the case of thigmotropism, DARWIN found that after repeatedly stimulating the tendril of the passion flower (twenty-one times in 54 hours), it responded only slightly. In the case of traumatropism, DARWHST ('81, p. 193) observed that the radicle, to one side of which a card had been fixed by shellac, eventually became so accustomed to the stimulus that it no longer bent away from it, but grew vertically downwards. In the case of phototropism, WIESNER noticed that after a growing organ had been for some time subjected to daylighl, its growth was less markedly controlled by a unilateral ilium; nation. Any general explanation of acclimatization, whether of meta- bolic or of growth processes, to repeated irritants must, at the § 3] EFFECT OF EXTERNAL AGENTS UPON GROWTH 487 present time, be hypothetical. The attempt to picture to our- selves the probable processes which bring about this condition should, nevertheless, be undertaken. It is generally accepted that a stimulus of any kind produces a chemical change in the protoplasm, and this leads to a change in the activity of the protoplasm - - the response. The different kinds of stimuli usually induce different kinds of responses, and this is probably because each kind of stimulus affects a particular kind of mole- cule — a kind capable of being transformed by the stimulus in question. If we assume that the reception of any stimulus is due to the transformation of a specific kind of molecule capable of being acted upon by the stimulus in question, then it is not difficult to see how, by repeated, violent stimulations of the same kind, nearly all of the molecules upon which sensation depends should become transformed, so that, thenceforth, the protoplasm should be incapable of receiving that kind of stimulus until such time as the sensitive substance shall have been reproduced. Let us imagine 100 molecules (ar a2, a3, a4 -«98, «99, a100) iR tne root t'lPs which are capable of being decomposed by daylight and as a result setting in motion a series of changes resulting in the phototropic response. Let us imagine that the irritation of light during the first half hour decomposes 50 of them ; during the second, 25 of the remain- der ; during the third, 12 of the remainder, and so on ; then, eventually, the sensation will grow weaker if the substance is not renewed, so that the response will diminish in intensity and finally fail altogether. • Then we say the organ is accli- mated to the reagent, for the application of the agent produces no response. This explanation of acclimatization to violent agents may now be easily extended to cover the case of attunement. Let us imagine a plant which, living in the dark, is negatively pho- totropic to ordinary daylight. It is attuned to a low intensity of light. If, however, the plant comes gradually to change its habitat so that it is repeatedly subjected to the sunlight, then, as a result of repeated stimulation, those sensitive molecules which are affected by the light are destroyed, so that the plant no longer turns from the light. It is attuned to it. The same theory, mutatis mutandis, will account for attunement to tern- 488 GENERAL CONSIDERATIONS [Cn. XIX perature or to chemical agents. It is to be observed that this hypothesis is not an hypothesis to account for response to stimuli or of the usual adaptive nature of that response ; but to account only for that phase of "adaptation" which is seen in attunement. The hypothesis is an attempt to explain an adaptive result independently of selection, but rather as a necessary result of the constitution of protoplasm. The adaptive acclimatized or attuned condition may be in- herited. It has been shown that the acclimated condition may long persist, only eventually apparently disappearing. It may well be doubted, however, if the acclimated protoplasm ever returns exactly to its primitive condition. If it does not, progeny developed from the acclimated protoplasm will neces- sarily be different and respond differently from their parents. Individual attunement will initiate a race attunement. LITERATURE CIESIELSKI, '72. (See Chapter XIV, Literature.) CZAPEK, F. '95. Ueber Zusammenwirkung von Heliotropismus und Geotro- pismus. Sb. Wien. Akad. CIV1, 337-375. '98. Ueber einen Befund an geotropisch gereizten "VVurzeln. Ber. deut. Bot. Ges. XV, 516-520. Jan. 1898. DARWIN, C. and F. '81. (See Chapter XIV, Literature.) HOGG, J. '54. Observations on the Development and Growth of the Water- snail (Limneus stagnalis). Trans. Micr. Soc. London. II, 91-103. SEMPER, C. '74. Ueber die Wachsthums-Bedingungen des Lymnseus stag- nalis. Arb. Zool.-Zoot. Inst. Wurzburg. I, 138-167. VARIGNY, H. DE. '94. Recherches sur le nanisnie experimentale. Contribu- tion a 1'etude de 1'innuence du milieu sur les organismes. Jour, de 1'Anat. et Physiol. XXX, 147-188. WIESNER, J. '79. (See Chapter XVII, Literature.) YUNG, E. '85. (See Chapter XIII, Literature.) LIST OF TABLES IN PARTS I AND II TABLE NO. PAGE I. Time of Resistance of Tadpoles to Various Alcohols . . 11 II. Time of Resistance of Infusoria and Ostracoda to Various Alcohols 11 III. Time of Resistance Period of Spirogyra communis to Vari- ous Alcohols ......... 12 IV. Increase of Immunity resulting from feeding on Ricin . 29 V. Lethal Solutions of Gold Chloride for Various Bacteria . 46 VI. Relative Resistance Periods of Various Bacteria to Gold Chloride .......... 47 VII. Relative Resistance Period of Various Bacteria to Various Poisons 48 VIII. Percentage of Water in Organisms ..... 58 IX. Resistance Periods of Fresh-water Crustacea to Various Constituents of Sea Salt 81 X. Plasmolysis of Vorticella by Solutions .... 87 XT. Plasmolysis of Colpoda by Solutions 87 XII. Tonotaxis of Spirillum to Various Solutions ... 91 XIII. List of Animals showing the Anex Type of Irritability . 136 XIV. List of Animals showing the Katex Type of Irritability . 136 XV. Electrotactic Response of Various Invertebrates . . . 147 XVI. Wave Lengths and Vibration Times of Different Parts of Spectrum ......... 155 XVII. List of Solutions giving nearly Monochromatic Colors . 157 XVIII. Phototactic Response of Various Animals . . . .195 XIX. Results of Experiments to determine the Ultramaximum Temperature of Organisms in Water .... 234 XX. Determinations of the Ultraminimum of Organisms reared under Normal Conditions 244 XXI. List of Species found in Hot Springs, with the Conditions under which they occur 250 XXII. Percentage of Water and Dry Substance in Frog Embryos at Various Ages 285 XXIII. The Percentage of Water in Chick Embryos at Various Stages up to Hatching 286 XXIV. The Percentage of Water in the Human Embryo at Various Stages up to Birth ....... 286 XXV. Percentage Composition of Animals and Plants . . . 295 489 490 LIST OF TABLES TABLE NO. r*r.v, XXVI. Percentage Composition of the Ash of Various Organisms 296 XXVII. Relative Abundance of Various Elements in the Ash of Organisms 297 XXVIII. Nutritive Solutions for Phanerogams .... 301 XXIX. Inorganic Matters in Potable Water 301 XXX. Nutritive Solutions t'cr Algae 302 XXXI. Nutritive Solutions for Fungi 302 XXXII. Comparison of Ash in New-born Dog- and iu the Milk of its Mother 303 XXXIII. Results of feeding Tadpoles on Various Substances . . 329 XXXIV. Showing for Various Mammals the Time required to double the Birth-weight correlated with the Chemi- cal Composition of the Milk of the Species . . 331 XXXV. The Total Dry Weight of a Crop of Aspergillus reared in the Absence and in the Presence of Various Quan- tities of Irritating Substances ..... 332 XXXVI. Interval elapsing before Germination when Spores of Penicillium are kept in Moist Chambers over Vari- ous Solutions of Sodium Chloride .... 351 XXXVII. Relation between the Humidity of the Soil and the Amount of Dry Substance produced 353 XXXVIII. Relation between Concentration of the Solution and Ger- mination of Peas ....... 363 XXXIX. Relation of Regeneration of Nais to Strength of Solution 365 XL. Relation of Reproduction by Fission of Dero to the Strength of the Solution 366 XLI. Relative Size of Tadpoles reared in the Light and in the Dark 426 XLII. Average Dimensions of Tadpoles reared behind Clear and Colored Screens ........ 433 XLIII. Percentage Deviations in Length of Larvae of Strongylo- centrotus reared behind Various Colored Screens, from Length of Larvae reared in White Light . . 434 XLIV. Relative Time of Hatching of Organisms reared behind Colored Screens ........ 434 XLV. The Optimum Intensity for Phototropism in Various Species of Plants ....... 439 XLVI. Minimum Intensity for Phototropic Response in Various Species of Plants ....... 439 XLVII. Average Total Increments in Length of the Plumules of Seedlings subjected to Different Temperatures . . 451 XLVIII. Average Increments in Length of the Radicle* of Various Seedlings subjected to Different Temperatures . . 451 XLIX. Time required for Spores of Penicillium to germinate, produce Visible Mycelium, and to form Spores, at Various Temperatures ...... 452 LIST OF TABLES 491 TABLE NO. ' PAGE L. Critical Points for Various Plants ...... 454 LI. The Absolute Increase in Length of Tadpoles at Different Temperatures ......... 457 LIT. The Time Required for Various Species of Fish to hatch at Various Temperatures . 459 LIIL Critical Temperature Points for Various Animals . . . 460 LIV. Average Weight and Percentage of Water in Plants reared at Various Temperatures 461 LV. The Relation between the Temperature and the Sense of Thermotropic Response in Various Seedlings . . . 464 LVI. The Sense and the Average Extent of Thermotropism at Different Temperatures ....... 465 LVII. Phototropic Limiting Angles for Various Plants . . . 471 INDEX Acclimatization to solutions, 87 ; to heat and cold, 249, 255, 257 ; to contact-irritation, 382 ; to stimuli, 484. Acetic acid, attracts zoospores, 88 ; re- pels amoeba, 38. Acetoxim, 15. Acids, inorganic, as poisons, 12 ; pro- voking response, 37. Acids, organic, as poisons, 13; chemo- taxis towards, 37. Actinia, action of nicotin on, 23. Actinophrys, action of hydrogen on, 5 ; of quinine, 27 ; of varying den- sity, 76 ; heat-rigor of, 232. Actinospherium, response to density, 86 ; contact, 98, 102 ; alternating current, 131 ; galvanic current, 139. ADDUCO, action of cocaine, 24. ADERHOLD, chemotaxis, 33, 34 ; grav- ity, 114 ; phototaxis, 183 ; acclima- tization to cold, 257. ADRIANOWSKY, light and seed germi- nation, 420 ; green rays on plants, 435. AEBY, free nitrogen as food, 312. ^Ethalium, rheotaxis of, 108 ; photo- taxis, 185. AFFANASIEFF, cold on muscle, 242. Agaricus, light on germination of, 420 ALBERTONI, cocaine on protoplasm, 24. ALCOHOL, on protoplasm, 10 ; struct- ural formulas, 11 ; resistance of or- ganisms to, 11 ; chemotactic action, 37. Aldehydes, 20. Alg?e, effect on, of hydrogen peroxide, 3 ; sodic-chromate, 4 ; potassic per- manganate, 4 ; potassic chlorate, 4 ; potassic dichromate, 4 ; potassic ar- senite and arsenate, 5 ; arsenious acid, 5 ; azoimid, 7 ; chloral hydrate, 10 ; carbonic disulphide, 12 ; organic acids, 13 ; calcic oxide, 13 ; diamid, phenylhydrazin, 16 ; nitrous acid, 21 ; paraldehyd, 21 ; sodic fluoride, 21 ; oxygen, 34 ; changing density, 86 ; molar agents, 100 ; growth of A. and salts, 302 ; nitrogen, 309 ; potassium, 318, 319. Alkaline salts and growth, 318. Alkaloids, as poisons, 22. Ammonia, effect on Tradescantia and Spirogyra, 6. Amoeba, effect on, of hydrogen, 5 ; curare, 26 ; quinine, 27 ; chemotaxis, 38 ; varying density, 75, 86 ; molar agents, 99 ; thigmotaxis, 105 ; elec- tric irritation, 130, 132 ; electric ac- climatization, 139; electrotaxis, 148 ; phototaxis, 186 ; heat-rigor, 232 ; coagulation, 238 ; cold, 241 ; thermo- taxis, 258 ; foods of A., 328. Ampelopsis, phototropism, 438. Amphibia, foods of, 329 ; temperature and growth, 459. Amphioxus, electric excitation, 137. Ancylus, acclimatization to changed density, 85. ANDREWS, photic irritability of Hy- droids, 179. Anex type of electric response, 137. Animals, toxic protein compounds, 22 ; salts necessary for, 302; organic foods of, 327 ; thigmotropism, 382 ; geotro- pism, 398; phototropism, 442; growth of, at various temperatures, 457. Anisonema, change of structure with density of solution, 77. Annelida, negatively electrotactic, 147 ; ultramaximum, 234, 246. Antimony, effect on growth, 314. Antipyrin, on protoplasm, 27. Ants, chemotaxis, 33 ; phototaxis, 198; thermotaxis, 261. Apostrophe, conditions of, 190. 494 INDEX AI-STI.IX, lighten pelagic eggs, 417. A pus, heat on growth of, 458. Area, acclimatization to changed den- sity, si>. ARENDT, sulphur and growth, 314. Arsenic and growth, 314. Arsenic acid, oxidization by, 5. Arsenious acid, oxidization by, 5. Ai:T\ri), temperature and metabolism, 222. Arthropoda, effect of varying density, 81, 82 ; salt absorption by, 88 ; posi- tively electrotactic, 147. Ascaridre, strychnin, 26. Ascaris, sodh; carbonate, 13 ; sodic hy- drate, 13 ; phenol, 19 ; hydrocyanic acid, 19. Ascidia, thigmotropism, 382. Asellus aquaticus, acclimatization to changing density, 86. Ash, of organisms, 295, 296 ; of dog and dog's milk, 303. ASKENASY, latent period, 460. Asparagin, chemotaxis towards, 38. Aspergillus, nitrogen food, 308. Atmospheric pressure and growth, 368 ; electricity, 408. Atropin and protoplasm, 24. Azoimid, effect on protoplasm, 7. Bacilli, calcic oxide and caustic potash poisonous to, 13. Bacillus ramosus, growth in colored light, 430 ; critical points, 454. Bacteria, effect on, of oxygen, 2, 168 ; ozone, 3 ; potassic chlorate, 4 ; sodic chromate, 4 ; carbonic disulphide, 12 ; organic acids, 13 ; potassic car- bonate, 13 ; salts of heavy metals, 14; diamid, 16; formaldehyde, 21; chemotactic, 33, 45 ; towards oxy- gen, 34 ; inorganic salts, 36 ; alcohol and glycerine, 37 ; to determine iso- tonic coefficients, 74 ; acclimatiza- tion to density, 86 ; tonotaxis, 90 ; effect of violent shaking, 99, 371 ; of light, 169, 171, 174; dark-rigor, 175; change of light intensity, 178; light-rigor, 178 ; cold, 241 ; growth, 288 ; nitrifying, 299, 308-312 ; food, 324, 325 ; growth in light, 430 ; heat and growth, 462 ; critical tempera- tures, 454-457. Bacterium termo, chemotaxis, 32, 38. Balanus larvae, chemotaxis, 198. BAKANET/KI. negative phototaxis, 185; response of Myxomycetes to light, -Mi.! ; effect of pulling on growth, 372. Bark extract, attracts Myxomycetes, 38. Barnacles, respond to shadow, 179. DE BARY, light and seed germination, 420. Bases, effect on protoplasm, 13. BASSLER, nutrition of plants, 299. BASTIT, geotropism, 398. BATESOX, geotropism, 397. BAUDRIMONT, role of water in growth, 284. BAUMANN, iodine and growth, 367. Bean, effect of changing density, 367 ; traumatropisrn, 384. BECLARD, colors and growth of fly, 432. Beetles, geotaxis, 118. Beggiatoa, negative phototaxis, 184. BENECKE, solutions for fungi, 302 ; po- tassium and growth, 318 ; rubidium and caesium and growth, 320 ; mag- nesium and growth, 323. Benzenylamidoxim, poison, 15. Benzol derivatives, chemotaxis towards, 38. BERNARD, chloroform on protoplasm, 9. BERT, effect of dense solutions on fish, 79. 80, 82 ; acclimatization to den- sity, 86 ; dark-rigor, 176 ; range of visible spectrum in animals, 203 ; effective rays in phototaxis, 203 ; oxygen and plants, 305 ; effective rays in plant growth, 428 ; green rays and growth, 435. BERTHELON, electricity and plant growth, 406. BERTHELOT, nitrifying organisms, 308 ; enrichment of fallow ground, 310. BEUDANT, acclimatization to density, 85.. BEYERINCK, food of Amoeba, 328. BEZOLD, water in animals, 58, 295. BIALOBLOCKI, heat and growth, 461. BIEDERMANN, electric response of muscle, 133. BINZ, theory of arsenical poisoning, 4, 5; effects on protoplasm of halo- INDEX 495 gens. 4 ; strychnin, 25 ; quinine, 26 ; acclimatization to arsenic, 28. Birds, effect of temperature on growth, 459. Bismuth, effect on growth, 314. BLASIUS, compression-rheostat, 127 ; electric irritation, 139 ; electrotaxis, 147-149. Blood-corpuscles, to determine isotonic coefficients, 73 ; effect on, of density, 7G ; and molar agents, 99. BLUNT. See DOWSES. Body, composition, 294. BOER, gold chloride, 46. BOKORNY, hydrogen peroxide a poison, 3 ; ammonia, 6 ; nutrition of plants, 299. BONAKDI, minimum temperature for bacteria, 241. BORODIN, light and chlorophyll arrange- ment, 187 ; light on spores, 424 ; effective rays in fern growth, 432. Boron, and growth, 314. TEN BOSCH, quinine and protoplasm, 26. BOURNE, scorpions acclimated to own poison, 28. BOUSSINGAULT, free nitrogen as food, 310. BRAEM, heat and cold on statoblasts, 425. Branchipus, heat and growth, 458. BRANDL, fluorine and growth, 317. Brassica, light on growth, 428. BRAUER, encystment, 256. BREFELD, light and growth of toad- stools, 420. Bromine, and protoplasm, 4 ; and growth, 316. BRUNCHORST, electrotropism, 409-412. Bryonia, light and growth, 419. Bryozoa, desiccation of, 65 ; thigmo- tropism, 382. BUCHNER, toxic protein compounds, 22 ; chemotaxis, 33 ; light and bac- teria, 172 ; movement and growth, 371. Bufo lentiginosus, acclimatization to heat, 253 ; heat and growth, 457-4uO. BUNGE, iron and growth, 321-323. BUTSCHLI, encystment, 256. Butyric acid, chemotaxis towards, 38. BUXTON. See RINGER. Caesium and growth, 320. Calcium and growth, 320. CALDANI, frictional electricity and growth, 132. CALLIBURCES, heat and protoplasmic movement, 227. CALMETTE, immunization, 30. See also EHRLICH. CAMPBELL, temperature and proto- plasmic irritability, 230. DE CANDOLLE, heat-rigor, 231 ; cold- rigor, 240, 241. CANNON, phototaxis of Daphnia, 203, 204. Carbon, as food, 306 ; oxide of, and protoplasm, 6. Carbonic disulphide, and protoplasm, 12. Carcinus, absorption of salt, 88. Cardium edule, acclimatization to density, 86. Carnin, chemotaxis towards, 38. Cassis, acclimated to sulphuric acid, 28. CASTLE, acclimatization to contact, 108; to heat, 253. Cat, light on growth of, 420. Catalytic poison, action of, 7-9. CELI, electrified air and plant growth, 408. Cell-division and growth, 287. CELLI, food of Amoeba, 328. CERTES, desiccation of Ciliata, 65. Chameleon, pigment response to light, 192. Chara, and caustic potash, 13. CIIARPENTIER, cocaine and protoplasm, 24. CIIASTAIGN, oxidizing action of light, 162. Chemical agents, effect on vital ac- tions, 1 ; acclimatization to, 27 ; and growth, 293. Chemotaxis, 32-54. Chemotropism, 335 ; in insectivorous plants, 335 ; of roots, 336 ; of pollen- tubes, 337 ; of hyphfe, 340 ; of con- jugation tubes of Spirogyra, 342. Chick, water in growth of, 286 ; elec- tricity and growth of, 405 ; heat and growth, 459. Chilomonas, phototaxis and photo- pathy, 183. Chlamydomonas, thigmotaxis of, 106. 496 INDEX Chloral hydrate, poison, 10. Chlorine, poison, 4 ; effect on growth, 310. Chloroform, action on protoplasm, 9, 10. Chlorophyll, effect of light on position, 189 ; temperature and movements, 226. CHMULEVITCH, heat-rigor, 232. CHODAT, electricity and plants, 407. Chromic acid, as poison, 3, 4. Chytriclium, phototaxis, 183. CIENKOWSKI, phototaxis, 183. CIESIELSKI, traumatropism, 384 ; geo- tropism, 393, 394 ; after-effect, 401 ; tropism, 481. Cilia, effect of density on movement, 77 ; electric stimulation, 145 ; tem- perature, 227. Ciliata, effect on, of oxygen, 3 ; hydro- gen peroxide, 3 ; chloroform and ether, 10 ; strychnin, 26 ; chemotaxis, 33 ; of saline lakes, 65 ; density ef- fect, 76, 78, 86 ; phototaxis, 187. CLARK, oxygen, 2. Cobra poison, 30. Cocaine, effect on protoplasm, 24. Cockroach, geotaxis, 118 ; thermotaxis, 261. Coelenterata, electric response, 137 ; phototaxis, 194. COHN, phototaxis, 202 ; heat and proto- plasm, 225. Cold, 242 ; resistance to, 246 ; extreme, 248 ; acclimatization, 257. Cold-rigor, 239. Colored light, 432-436, 440, 441. Crab, copper in blood of, 324. Critical temperatures, 460. CRIVELLI, food of Amoeba, 328. Crustacea, density, 79, 81 ; optimum temperature, 458. Cryptogams, water and growth, 350 ; geotropism, 378; thigmotropism, 381. Cryptomonas, chemotaxis, 33. Ctenophora, inorganic food, 303. Cucurbita, moisture, 352. CUENOT, temperature and growth, 458. Curare, Amceba, 26. Cyphoderia, molar agents, 100. Cytotaxis, 52. CZAPEK, phototropism, 471; tropism, 482, 483. CZERNY, density, 75, 76, 78, 86. DALLINGER, heat and Infusoria, 252- 256. DANILEWSKY, cocaine, 24; lecithin, 330. Daphnia, phototaxis, 203-206. DAREMBRAY, blood serum, 22. Dark-rigor, 175, 176. DARWIN, C. , insectivorous plants, 99; chemotropism, 335 ; hydrotropism, 357; tendrils and twining, 377; thig- motropism, 379, 380, 383 ; trauma- tropism, 384-386 ; geotropism, 394 ; phototropism, 441, 485. DARWIN, F., moisture and growth, 252, geotropism, 397. DAVIS, desiccation of rotifers, 62, 63. DAY, nitrogen, 312. Death, 1 ; by poisons, 2-24 ; desicca- tion, 60-65; density, 80-83; light, 171-175; heat, 231-249; limits, 275- 277. DEHNECKE, gravity, 113. DEHERAIN, temperature and secretion, 223. DEMOOR, oxygen, 2, 3 ; hydrogen, 5, 6 ; ammonia, 6 ; oxides of carbon, 6 ; chloroform, 9; paraldehyde, 21; cold-rigor, 241. Density of the medium, effect on pro- toplasm, 70-93 ; on growth, 362- 369. DERM ANT, heat-rigor, 239. Dero, fission and density, 365, 366. Desiccation, protoplasm, 59 ; rigor and death, 60, 61; acclimatization to, 65. Desmids, phototaxis, 183. DETLEFSEN, hydrotropism, 257 ; trau- matropism, 384. DEWITZ, chemotaxis, 37; thigmotaxis, 106, 107. Diamid, poison, 1, 16. Diatoms, effect on, of chloral hydrate, 10 ; hydroxylamine, 15 ; ethylalde- hyde, 21; phototaxis of, 184, 199; silicon food of, 324. Differential threshold stimulation, 43. Difflugia, molar agents, 101. Diontea, response to contact, 99. Dioscorea, light, 419. Dodder, twining, 377, 484. DOGIEL, curare, 26. INDEX 497 Dogs, potassium and growth of, 319. Doliuiu, and sulphuric acid, 28. DOWNES, analytic effect of light, 163 ; bactericidal effect of light, 171-173. DOVERE, desiccation, 62 ; heat on Rotifera, 255. Dragon-fly larvse, electric stimulation, 137. DRAPER, assimilation in plants, 166. DRIESCH, phototaxis, 202 ; growth, 282 ; geotropism, 400 ; phototropism, 443. Drosera, organic acids, 13 ; thigmo- taxis, 99 ; thigmotropism, 383, 481. Drosophyllum, and contact, 99. Dryness and protoplasm, 59, 60. DRYSDALE, heat and protoplasm, 256. DITBOIS, response to light, 207. DUCHARTRE, hydrotropism, 256. DUCLAUX, chemical effect of light, 162, 163 ; election of food, 333. DUTROCHET, molar agents, 100 ; tem- perature on protoplasm, 225 j accli- matization to heat, 252 ; twining, 377. Duvalia, germination, 424. Earthworm, nicotin, 24 ; phototaxis, 203. Echinodermata, nicotin, 24 ; density, 79; electric current, 137 ; phototaxis, 194 ; light on growth, 434 ; optimum temperature for growth, 458. Echinoids, strychnin, 26. EDWARD1;, light on growth, 425. Effective rays in growth, 427-436 ; in phototropism, 440. Egg, food materials in, 303 ; phospho- rus, 313 ; iron, 322 ; electricity, 403. EHRENBERG, heat, 251. EHRLICH, ricin, 31 ; acclimatization to poison, 32. Electricity, 126 ; protoplasm, 129-153 ; electrotaxis, 140-151 ; growth, 405- 414 ; electrotropism, 409-414. Electrotaxis, 140-151. ELFVING, chloroform, 9 ; light, 174 ; gravity and growth, 391 ; geotro- pism, 398. Embryos, phosphorus, 314 ; light, 417, 418. EMERY, salt absorption, 88. Encystment, 256. ENGELMANN, chemotaxis, 32, 34 ; den- sity, 86 ; electricity, 130, 132, 135 ; bacteria and spectrum, 168 ; dark- and light-rigor, 176, 178; changing light intensity, 179 ; phototaxis, 182, 183, 187, 202, 207; retinal move- ments, 193 ; photopatliy and chem- ical agents, 201 ; temperature, 227, 231. Entomostraca, density, 81. ENTZ, photopatliy, 188. Ephydra, acclimatization, 28. Epistrophe, 190. Epithelium, ciliated, 129, 227. ERLACH, acclimatization, 29, 30. ERRARA, hydrotropism, 359 ; thigmo- tropism, 381. ESCHENHAGEN, growth and density, 362. ESCHLE, iodine and growth, 317. Ether, 9, 10. Ethylaldehyde, protoplasm, 21. Euglena, chemotaxis, 33 ; phototaxis, 183 ; acclimatization to cold, 257 ; therrnotaxis, 261. EWALD, electrotaxis, 147-150. Excretion and poisons, 51. EXNER, pigment and light, 193. Extent of medium and size, 473. FABRE-DOMERGUE, density, 76, 86. Fallow ground, enrichment, 310. False, phototaxis, 181 ; traumatro- pism, 384 ; geotropism, 392 ; electro- tropism, 409. FAMINTZIN, phototonus, 177 ; photo- taxis, 182 ; chlorophyll position, 189 ; light and growth, 430. FATIGATI, rays which disturb metabo- lism, 170. FAYRER, serpent poison, 28. FECHNER, threshold stimulation, 434. FERE, temperature and chick's growth, 459. FICK, electric stimulation, 133. FIGDOR, phototropic limit, 439. Fish, density-effects, 79-82 ; rheotaxis, 109 ; temperature and growth, 458, 459 ; medium and size, 474. See also Gold-fish. Flagellata, chemotaxis, 33, 36, 45 ; salt-absorption, 86, 89 ; phototaxis, 182; acclimatization to heat, 252, 255. 2 K 498 INDEX FUMMARION, effective rays in growth, 429. Fly larvse, chemotactic, 38 ; geotactic, 118. Fluorine, and growth, 317. Food, 309-330 ; response to, 39 ; elec- tion, 334. Formaldehyde, poison, 20, 21. FKANK, chlorophyll position, 189 ; growth definition, 282 ; nitrogen as food, 308-310. FRANKE. See PFEIFFER. FKANKLAND, light and bacteria, 171. FKAZEUK, regeneration and density, 365. FREDA, electricity and growth, 408. FREDERICQ, salt-absorption, 88 ; cop- per and growth, 324. Fresh water absorbed by marine or- ganisms, 79, 80. FRIES, light and fungi, 420. Frog, sodic fluoride, 22 ; density, 82 ; salt-absorption, 88 ; electric stimu- lus, 132, 139 ; pigment and light, 192 ; water in developing, 285 ; size and medium, 474, 475. Frog's egg, cytotaxis, 52 ; cold-rigor, 240 ; oxygen and growth, 305 ; elec- tricity, 405. FROMANN, soluble mineral bases as poisons, 13. Fungi, salts of arsenic, 5 ; sulphurous oxide, 20 ; nitrous acids, 21 ; nutri- tive solutions, 302 ; hydrogen as food, 306; potassium, 318; iron, 323; organic foods, 324-326 ; water and growth, 350; hydrotropism, 358; light and growth, 420 ; colored light, 430. GAIN, water and growth, 254. Galvanic current, acclimatization to, 139. Gastropoda, copper in blood, 324. GAUTIER, green rays and plants, 435. GAVARRET, desiccated rotifers, 62. Geotaxis, 114-124. Geotropism, 391-403 ; and phototro- pism, 470. GEROSA, cold, 241. Germination, and solutions, 363 ; and light, 424. GILBERT. See LAWES. GLAN, spectrophotometer, 160. Glucose, reaction, 4. Glycerine, chemotactic, 37. GOGORZA, density, 79-83 ; acclimatiza- tion, 86, 87. Gold chloride, poison, 46, 47. Gold-fish, density, 77, 79. GOLUBEW, electricity stimulus, 130. GORINI, Ainceba, 328. GOTSCHLICH, heat-rigor, 232, 233. GRADER, phototaxis, 203, 205, 207 ; thermotaxis, 258, 261. GRANDEAU, electricity, 406, 408. Gravity, methods, 112 ; protoplasm, 113, 114 ; direction of locomotion, 114-124 ; growth, 391-403. Green plants, light, 174 ; organic food, 326, 327. GREENWOOD, nicotin as poison, 24. GROOM, phototaxis and temperature, 200. Growth, analysis of processes, 281 ; three factors, 282 ; regions in plants, 283 ; cell-division, 287 ; kinds of, 287 ; normal, 288, 289 ; chemical agents on, 293 ; as response to stim- ulus, 331 ; directed, 335, 355, 376, 384, 387, 391, 409, 437, 460; water, 350 ; density, 362 ; molar agents, 370 ; wounding, 384 ; gravity, 391 ; electricity, 405 ; light, 416 ; heat, 450 ; optimum, 454 ; maximum tem- perature, 456 ; range, 456 ; modifi- cation of rate, 478-480 ; modification of direction, 480-483. GRUBER, density, 76. HABERLAND, chemotropism, 242. Haemoglobin, properties, 298. HALES, phototropism, 437. HALLIBURTON, heat-rigor, 239. Halogens and growth, 315. HAMBURGER, isotonic coefficient, 73; density, 76. HAMMOND, light and growth, 426. HAXSTEEN, organic food of plants, 327. HAHTIG, phosphorus and growth, 314. Heat, absorption by plants, 170 ; nat- ure of, 219 ; action on protoplasm, 222-263 ; chlorophyll formation, 224 ; irritability, 225 ; acclimatization to, 249, 251 ; extremes, 248 ; direction of locomotion, 258 ; growth, 450- 467 ; latent period, 460. INDEX 499 Heat-rigor, 2:11, 239. Hedgehog, hydrocyanic acid, 19. HEGLEH, pulling and growth, 372, 374; electrotropism, 412. HEIDENSCHILP, toxic proteids, 22. Helianthus, pulling, 374 ; phototro- pism, 438 ; phototropic angle, 471. HELLRIEGEL, nitrogen fixation, 310. HELMHOLTZ, light on retina, 171. Hen, mineral matter in egg, 303 ; flu- orine, 317. HENSEN, light and pelagic eggs, 417. Hepatics, thigmotropism, 381. HER.EUS, nutrition, 300. Herbivora, chlorine, 316. HERBST, salts of marine animals, 303 ; phosphorus and growth. 314 ; sul- •phur, 315 ; chlorine, 316 , potassium, 319 ; magnesium, 323. HERMANN, electrical measurements, 128 ; electric stimulation, 139 ; elec- trotaxis, 147-149; cold, 242. HERRICK, gravity and nucleus, 114 ; temperature and growth, 458. HERTWIG, O., growth of frogs, 458, 459. HERTWIG, O. and 11., cocaine, 24 ; strychnin, 25 ; quinine, 26; chemo- taxis, 33. HIERONYMUS, chlorophyll movements, 191. HIGGENBOTTOM, light and growth, 425. HILTNER, nitrogen and growth, 312. HOFER, hydroxylamine, 15. HOFFMANN, water and growth, 250 ; dryness and resistance to heat, 255 ; light and termination, 420, 424. HOFMEISTEK, molar agents and proto- plasm, 100, 102; phototaxis, 184; temperature and protoplasm, 225 ; heat-rigor, 232; geotropism, 401. Holothuroidea, geotaxis, 118. Honey bee, temperature and metab- olism, 223. HOPPE-SEYLER, acclimatization to heat, 251 ; lithium on growth, 318 ; mag- nesium, 323. HORVATH, shaking protoplasm, 99 ; bro- mine and growth, 316 ; rough move- ment on growth, 370. HUDSON, desiccation, 63. Human embryo, water in growth, 286. Humidity of soil and growth, 253. HUXLEY, definition of growth, 282. Hydra, nicotin, 23 ; density, 81, 86 ; phototaxis, 194, 202 ; light waves and growth, 430. Hydrachna, maximum temperature, 238. Hydrazin and protoplasm, 16. Hydric sulphide, protoplasm, 19, 20. Hydrides, chemotactic, 37. Hydrocyanic acid, poison, 19. Hydrogen on protoplasm, 5 ; in organ- isms, 306. Hydrogen peroxide, poison, 3. Hydroidea, inorganic food, 303 ; iron, 323 ; density and regeneration, 364 ; thigmotropism, 382 ; geotropism, 398, 399; phototropism, 443. Hydro ides dianthus, responds to shadow, 179. Hydrotaxis, 66. Hydrotropism, 255. Hydroxylamine, poison, 1, 15. Hyphse, chemotropisin, 340 ; hydro- tropism, 358. Hypochlorous acid, poison, 3, 4. Hypozanthin, chemotactic stimulus, Indifferent chemical agents and proto- plasm, 41, 42. Induction apparatus, 127. Infusoria, and potassic permanganate, 4; halogens, 4; arsenious acid salts, 5; azoimid, 7; chloral hydrate, 10; hydroxylamine, 15 ; phenylhydrazin, 16; hydrocyanic acid, 19; ethylalde- hyde, 21; quinine, 27; acclimatiza- tion, 28; chemotaxis, 33; thigmotaxis, 106 ; katex response, 137 ; electro- taxis, 140; wave-lengths which dis- turb metabolism, 170; heat and movement, 228 ; cold-rigor, 240 ; or- ganic foods, 328 ; multiplication and light, 422. Injurious substances, response to, 39. Inorganic salts and protoplasm, 37. Insecta, hatching and temperature, 458. Insectivorous plants, chemotropism, 335. Invertebrates, quinine, 26 ; sodic car- bonate, 28; water in, 58, 59; elec- tric response, 136 ; electrotaxis, 147 ; ultramaxinium temperatures, 234- 237; ultraminimum, 244-246 ; in hot 500 INDEX springs, 250, 251; potassium as food, 318. Iodine, protoplasm, 4; growth, 317. Iron, and growth, 321-323. Irritable period in development, 379 ; region in tendrils, 379. Isopoda, hydroxylauiine, 15 ; formalde- hyde, 21. Isotonic coefficients, 23. JACCARD. oxygen on plant growth, 305; pressure and growth, 368. JANSE, salt-absorption, 88. JAKIUS, growth and density, 302. JENSEN, geotaxis, 114-118, 121-124. JENTYS, oxygen and growth, 305; den- sity and growth, 302. JOHNSON, hydrotropism, 256 ; geotro- pism, 394. JONSSON, rheotaxis, 108 ; rheotropism, 387; light and germination, 425. JORDAN, analysis of water, 301. JUMELLE, water and growth, 253. KARSTEN, light and plants, 419. Katex type of electric response, 138. KELLER, retinal pigment and light, 192. KLEBS, phototaxis, 183. KLEIN, light fatal to fungi, 174. KLINGER, synthesis of organic com- pounds, 1(>3. KNIGHT, hydrotropism in roots, 256 ; geotropism, 393. KNOVVLTON, temperature and growth, 459. KNY, light and growth, 423. KOCH, free nitrogen as algse food, 309. KOCHS, desiccation and seed vitality, 63, 64. KOFOID, blastula cavity, 78, 79. KOSSOWITSCH. See KOCH. KRAFT, electricity on epithelium, 129. KRAUS, light on growth, 420 ; green rays and growth, 430. Kreatin, chemotactic, 38. KRUKENBERG, strychnin, 25 ; quinine, 26 ; water in organism, 58, 295 ; iron and growth, 321. KUHV, desiccation of nematodes, 61. KUHNE, effect on protoplasm of hydro- gen, 5 ; chloroform, 9 ; veratrin, 24 ; varying density, 75-77 ; electric cur- rent, 129, 132, 138, 139 ; tempera- ture and movement, 225 ; heat-rigor, 231, 232 ; fatal temperature, 238 ; cold-rigor, 241 ; cold, 242, 247, 248. KUNKEL, iron as food, 323. Lactic acid, chemotactic, 38. Lamellibrauclriata. electric stimula- tion, 133 ; light reaction, 179. LANCE, desiccation of tardigrades, 61, 65. Land animals, acquisition of oxygen, 304 ; sulphur, 314. Larvae, food, 323 ; light, 418. LAURENT, nitrogen food of plants, 309, 312. LAWES, nitrogen as plant food, 310 ; food of mammals, 330. LEBER, chemotaxis, 33. LE DANTEC, thigmotaxis, 105, 107. Leeches, poison, 15. Legumes, enriching action of, 310. LEITGEB, light and spores, 424. Lemna, organic food of, 327. LEMSTROM, electricity favors plant growth, 408. LEONE, agitation of water and growth, 371. LESAGE, moisture and germination, 350, 351. Leucocytes, oxygen and protoplasm, 3 ; chloroform, 10 ; quinine, 26 ; chemo- taxis, 33 ; electric stimulation, 130. LEWITH, heat and coagulation, 255, 256. LIEBENBERG, light and germination, 425. LIEBERMANN, water of organism, 58. LIEBSCHER, free nitrogen as plant food, 312. Life, temperature-limits, 231. Light, methods, 154 ; monochromatic, 156-158 ; physical properties of dif- ferent wave-lengths, 158, 159 ; in- tensity, 160 ; chemical action, 161- 165 ; thermic effect on metabolism, 166-170 ; chemical effect, 170, 171 ; vital limits, 171 ; and movement, 175 ; light-rigor, 178 ; and carbon dioxide production in plants, 179; phototaxis and photopathy, 180-210 ; of chlorophyll, 189 ; of pigment, 192 ; racial attunement, 197 ; period of life, 197, 198 ; mechanics of response INDEX 501 to, 207-209 ; retarding effect on growth, 416-423 ; accelerating effect, 423-427 ; phototropism, 436-445. LILLE, temperature and growth of tadpoles, 459. Limax, geotaxis, 118-120. Limnsea, poisoned by azoimid, 7 ; ac- climatization to density, 85 ; light on growth of, 426 ; extent of medium and size, 474. Linuni, light and growth, 428. Lithium and growth, 318. Lobster, copper in blood, 324 ; heat and growth, 458. LOCKE, metallic salts as poisons, 14, 15.' Locomotion, interference with normal, 51 ; determination of direction, 32. 66, 89, 105, 114, 140, 180,258. Locust, heat and growth of, 458. LOEB, chemotaxis, 33 ; oxygen attracts fly larvae, 38 ; gravity and inverte- brates, 118 ; effect of light intensity, 179, 197 ; phototaxis, 198 ; photo- taxis and temperature, 200 ; light attunement, 200 ; phototaxis, 204, 206, 208 ; temperature and irritabil- ity, 230 ; thermotaxis, 258-261 ; r61e of water in growth, 304 ; oxygen and growth, 306 ; potassium and re- generation, 319 ; magnesium and growth, 323 ; growth and density, 364 ; contact and growth of stolons, 370; cutting and rate of growth, 376 ; thigmotropism in hydroids, 382 ; rheotropism, 388 ; geotropism in hy- droids, 399, 400 ; phototropism in animals, 442, 443. LOEW, effect on protoplasm of oxy- gen, 2 ; potassic chlorate, halogens and sodic chromate, 4 ; arsenical salts, 5 ; catalytic poisons, and azoi- mid, 7 ; sulphonal, 10 ; carbonic di- sulphide and inorganic acids, 12 ; soluble mineral bases, 13 ; salts of heavy metals, 14, 15 ; hydroxyla- mine, substitution poisons, 15 ; com- plex nitrogenous compounds, 16 ; hy- drocyanic acid, 19 ; aldehydes, 20 ; ethylaklehydes, 21 ; sodic fluoride, 21, 22 ; alkaloids, 22, 23 ; acclimati- zation to poisons, 27 ; oxygen and growth, 294 ; phosphorus and growth, 314. LOMBARDINI, effect of electricity on development of chick, 405. LUBBOCK, chemotaxis, 33 ; effective wave-lengths in phototaxis, 203, 205. LUDLOFF, electrotaxis, 141 ; theory of electrotaxis in Ciliata. 145. MACAIRE, heat and metabolism, 222. MACALLUM, iron in growth, 321. MAcDoNNELL, light on frog's growth, 425. MACDODGAL, contact response of ten- dril, 378, 379. McLEOD, electricity and plant growth, 407. MAGGI, food of Amceba, 328. Magnesium, and growth, 323. Magnetropism, 413. Maize, silicon in, 324. See, Zea. Malic acid, chemotactic, 37, 38. Mammals, quinine, 27 ; foods of, 330. Man, acclimatization to poisons, 28 ; sulphur as food, 315. Manganese, and growth, 321. Manganic acid, poison, 3, 4. Marine organisms, effect of fresh water on, 79 ; foods of, 303. MARMIER, immunity, 30. MARSHALL, phototaxis, 194. MARTIN SAINT-ANGE, role of water in growth, 284. MASSART, effect on protoplasm of par- aldehyde and formaldehyde, 21 ; cocaine, 24 ; antipyrin, 27 ; chemo- taxis, 33, 34 ; isotonic coefficients, 73, 74 ; density and protoplasmic structure, 76, 80 ; acclimatization to density, 8(i-88 ; tonotaxis, 89-92 ; phosphorescence, 98 ; thigmotaxis, 106, 107 ; gravity and Protista, 114- 116, 121 ; phototaxis, 200. MATTHIAS. See HERMANN. MAUPAS, light and growth of Infuso- ria, 422. MAYER, absorption of heat by plants, 170 ; temperature and metabolism, 222. Mechanics of response, 45. MELTZER, shaking bacteria, 99, 371. MENDELSSOHN, change of optimum, 254 ; thermotaxis, 258, 259. Metabolism, modification by poisons, 1-27 ; by dryness, 59 ; molar agents, 502 INDEX 98 ; by light, 16G-175 ; by heat, 222- 22-5 ; limiting conditions of, 275. METSCHNIKOFF, cheinotaxis in bacte- ria, 33. Mice, acclimatized to ricin, 29-32. MIGULA, inorganic acids on protoplasm, 12. MILIH:, light and spores, 424. Mi NOT, growth, 289. Mistletoe, light and growth, 423, 438. MIYOSHI, chemotropism, 338, 340 ; hy- drotropisin, 358. MOIIL, twining stems, 377 ; acclimati- zation to light, 444. MOISSAN, temperature and metabolism in plants, 223. Moist gelatine, no thigmotropic re- sponse to, 278. Moisture and protoplasm, 58. Molar agents, and lifeless matter, 97 ; and protoplasm, 97 ; movement, 98, 99 ; metabolism, 98 ; direction of locomotion, 105 ; and growth, 370. Molds, and sodic carbonate, 28 ; nutri- tive solutions for, 302 ; and free nitrogen, 308 ; potassium and growth, 318 ; rubidium, 320 ; election of or- ganic foods, 333 ; thigmotropism, 381 ; electrotropism, 412 ; light, 420. Molecular composition and effect on metabolism, 3'.). MOLESCHOTT, effect of light on verte- brates, 422. MOLISCH, hydrotropism, 257 ; potas- sium and calcium in growth, 319, 320 ; chemotropism, 336, 337 ; hy- drotropism, 359 ; thigmotropism, 381. Mollusca, formaldehyde, 21 ; quinine, 27 ; changed density, 79 ; electro- taxis, 147; phototaxis, 202, 207; ultramaximum temperature, 235 ; ultraminiinum, 245 ; species living in hot springs, 251 ; composition, 295 ; light and growth, 426. MONTEGAZZA, effect of strong light on bacteria, 171. MONTI, food of Amoeba, 328. MOORE, light and chlorophyll arrange- ment, 189, 191, 192. MORIGGIA, heat-rigor, 232. Morphine, and protoplasm, 25. Moths, phototaxis, 197. Mucor, phenylhydrazin a poison, 10 ; tropisms in, 482. MULLER, H., responding region in phototropism, 441. Mri.LKit, X. .1. C., definition of growth, 282. MILLER, 0., thigmotropism, 379, 380. MULLEK-HETTLINGEN, electric stiv.-s in seedlings, 405; tlectrotropisin, 40! ». MULLER-THURGAU, freezing-point in plants, 247. MTNTER, vitality of drkd seeds, 64. Mi'NT/, nitrifying organisms. 301S, 310. Musca, light and growth, 432. See also Fly. Muscle, electric stimulus, 133, 135 ; cold-effect, 242. Myriapoda, hydrocyanic acid secreted, 19. Mytilus, acclimatization to density, 85, 86. Myxomycetes, hydrogen, 5 ; cheino- taxis, 33, 38, 45 ; varying density, 75, 86 ; molar agents, 100 ; electric stimulation, 129 ; light stimulus, 179 ; phototaxis, 184, 202. NAGEL, electric stimulus, 135-138 ; electrotaxis in invertebrates, 146, 150, 151; light stimulus, 179; me- chanics of light response, 207. NA<, ELI, catalytic poisons, 7-; salts of metals as poisons, 14 ; phototaxis, 182 ; temperature and movement, 225 ; cold-rigor, 241 ; nutritive solu- tion for fungi, 302 ; caesium and growth, 320. Nais, regeneration and solutions, 365. Naja tripudians, acclimatization to poison of, 30. Natica, acclimated to sulphuric acid, 28. NEAL, corrosive sublimates as poison, 15 ; acclimatization to poison, 30, 31. Nematoda, azoimid, 7 ; chloral hydrate, 10 ; desiccation, 61. NENCKI, chlorine and growth, 316 ; sodium and growth, 318. Nephelis, effect of varying density, 81. Nereis, effect of cocaine, 24. Nerve, electric stimulation, 133, 135. Nicotin, and protoplasm, 23, 24. INDEX 503 NIEPCE r>E SAINT VICTOR, chemical action of light on starch, 105. NIKOLSKI, curare and protoplasm, 26. Nitella, cold-rigor, 241. Nitrogen, source of, in organisms, 307 ; free N. as food, 308, 313. Nitrogenous compounds, as poisons, 16-21 ; chemotactic, 38. Nitrous acids, and protoplasm, 21. NOBBE, free nitrogen as plant food, 312 ; potassium as food, 319. Noctiluca, effect of paraldehyde, 21 ; formaldehyde, 21 ; antipyrin, 27 ; deformation, 98. Nuclein, composition, 298. Nutritive solutions, for algae, 302 ; for fungi, 302 ; light and seed germina- tion, 420. Nutritive values, laws of, 325. OGATA, food of Infusoria, 328. OHLMULLER, ozone and bacteria, 3. OLTMANNS, phototaxis, 183, 205, 20(5. ONIMUS, penetrability of tissues by light, 165. Optimum, 40 ; change of, 254 ; con- centration for growth, 364 ; move- ment for growth, 372 ; temperature for growth, 454-456, 460, 401. Orbitolites, molar agents, 100 ; thig- motaxis, 106 ; thigmotropism, 376. Organic, compounds chemotactic, 37 ; food used in growth, 324 ; food, election of, 333. Organisms, atomic composition of dry substance, 296 ; elements important for, 297, 298 ; food of non-chloro- phyllaceous O. , 299. Oscillaria, phototaxis, 184. Osmosis, role in organic life, 71 ; quantitative measure of, 71-73. Osmotic index, 82. Ostracoda, azoimid, 7. Ostrea, acclimatization to changed density, 85. OSTWALD, temperature and osmosis, 83 ; electrical methods, 126. OVERTON, chemotropism, 242. Oxygen, effect on anaerobic bacteria, 2 ; on protoplasm, 2-5 ; antipyrin, 27 ; chemotactic, 34 ; thigrnotactic, 106 ; as food, 304 ; and growth, 305. Ozone, and bacteria, 3. Palaemon, nicotin, 24. PALM, cause of twining, 377. Paludina, changing density, 85. PANETH, hydrogen peroxide and Cili- ata, :>. Paraldehyde, protoplasm, 21. Pararnecium, strychnin, 20 ; electro- taxis, 142, 144, 145 ; change of optimum, 204 ; thermotaxis, 259, 260. Parasites, oxygen, 2. PARKER, response of pigment to light, 193. PASTEUR, ultrainaximum of dry spores, 255. Patella, acclimated to diminished tem- perature. 85. Pathogenic bacteria, chemotaxis, 33. PEIRCE, twining in dodder, 377. Pelias berus, rabbits acclimated to poison of, 30. Peloinyxa, electric stimulus, 129, 133, 134. Penicillium, fixes free nitrogen, 308. Peptone, chemotactic, 38. Peranema, electric response, 130. Perceptive region, in phototropism, 441. PERKINS, gravity and Limax, 118-120. Permanganic acid, poison, 3, 4. Peronospora, does not germinate in light, 420. PETERMAXN, free nitrogen as plant food, 312. PFEFFER, chemotaxis, 33, 36-45 ; measure of osmosis, 71 ; tonotaxis, 89, 90 ; thigmotaxis, 106, 108 ; wave- length active in assimilation, 166; growth, 281 ; election of food, 333 ; chemotropism, 337 ; method of iso- lating the root tip, 395 ; cause of twining, 377 ; irritable period in thigmotaxis, 379 ; contact stimulus, 382, 383, 386. PFEIFFER, free nitrogen and plants, 312. Phanerogamia, free nitrogen as food, 312 ; potassium, 318 ; calcium, 320 ; electrotropism, 411 ; red rays and growth, 436. Phenol, as poison, 18. Phenylhydrazin, poison, 16. Phosphorescence, 98. 504 INDEX Phosphorus, and growth, 313. Photopathy, 180 ; distribution, 182 ; laws of, 190 ; and chemical constitu- tion of medium, 201. Phototaxis, 180, 195 ; true and false, 181 ; distribution, 182 ; effect on P. of strong light, 1(J6 ; laws of, 196 ; effective rays, 201 ; P. vs. photo- pathy, 203. Phototonus, 177. Phototropism, 437, 438 ; optimum in- tensity in, 439 ; effective rays, 443 ; mechanics of, 444 ; limiting angle, 471, 472; after-effect, 484. Phy corny ces, water and spores, 358 ; heat and growth, 464. PICKFORD, heat-rigor, 231. PICTET, cold-rigor, 240. Pigeon, acclimatization to poison, 29. Pigs, food of growing, 330. Planaria, azoimid, 7 ; hydroxylamine, 15 ; density, 81 ; thigmotaxis, 105 ; photopathy, 206. Planorbis, azoimid, 7 ; density, 85. Plastic foods, 293. PLATEAU, density, 80-82, 86 ; absorp- tion of salt, 88. PL ATT, geotaxis, 124. Poa, light on seeds, 424. Poisons, oxidizing, 3, 49 ; catalytic, 7, 50 ; salt-forming, 12, 50 ; substitu- tion, 15, 50 ; acclimatization to, 29. POLECK, silicon in hen's egg, 324. Pollen-tubes, chemotropism, 337, 338 ; hydrotropism, 358. Polygordius, phototaxis, 200. Polyphemus, density effect, 76. Polystoma, salt-absorption in, 89. Polystomella, electric stimulus, 129. 1'olytrichum, light and germination, 424. Porthesia, thermotaxis, 261. Potassium, growth, 318 ; regeneration, 319. Potassium salts, poisons, 4, 5. PorcHET, light-stimulus, 179. Preissia, light and germination, 424. PRESCH, sulphur and growth, 315. PREYER, anabiosis, 61, 63. PRINGSHEIM, light on green plants, 174; light-rigor, 178. Propionic acid, 38. PROSHER, growth of mammals, 330, 331. Protein poison compounds, 22. Protista, cocaine, 24 ; morphine, 25 ; desiccation, 64; contact response, 99 ; geotaxis, 114, 115, 118, 121-123; electric stimulus, 134 ; acclimatiza- tion to electricity, 139 ; electrotaxis, 146; photopathy and phototaxis, 182, 203; heat, 224, 228; thermo- taxis, 258, 261 ; growth of P. and light, 410. Protoplasm, hydroxylamine, 1 ; oxy- gen, 2, 3; substitution poisons, 15; nicotin, 23 ; strychnin, 25 ; quinine, 26 ; antipyrin, 27 ; acclimatization to poisons, 32 ; specific resistance of, 49 ; structure of, 70 ; varying den- sity, 74 ; acclimatization to change of density, 86 ; contact, 97 ; periodic disturbances, 98 ; electric stimulus, 138 ; temperature, 241 ; chemical agents and growth, 274 ; structure and composition, 274, 275 ; struct- ural limiting conditions, 276. Pseudophototaxis, 181, 182. PUGH, free nitrogen, 310. Pulnionates, fresh-water, varying den- sity, 78. PURIEWITSCH, free nitrogen, 308. PURKINJE, cold, 241. Pyrocatechin, poison, 19. QOINCKE, effect of blue rays on growth, 436. Quinine on protoplasm, 26, 27. Rabbit, acclimatization to snake poi- sons, 30. RACIBORSKI, growth and density, 363. Kadiant heat and growth, 463. Radiolaria and silicon, 324. RAILLET, desiccation-rigor, 61. Rana, heat and growth, 457-459. RADBER, oxygen on frog's eggs, 305 ; temperature and growth, 459. RAULIN, phosphorus and growth, 314. RAY, gravity and growth, 391. RAYLEIGH, monochromatic light, 158. Regeneration and potassium, 319 ; density, 364, 365. REINHARDT, chemotropism, 340. REINKE, light and plant assimilation, 167 ; moisture and growth, 251 ; agitation of water and growth, 371. IXDEX 505 Removal of tissue, and growth, 375. Repulsion, by chemical agents, 38 ; by dense solutions, 91. Resistance capacity, to poisons, 48 ; to dense solutions, 83 ; to heat, 249. Resorcin, poison, 19. Response to injurious substances, 39; mechanics of R., 45, 277 ; 480-484. Rheostat, 127. Rheotaxis, 105-108. Rheotropism, 387, 388. Rhizoids, hydrotropism of, 257. Rhizoma, geotropism, 398. Rhizopoda, thigmotaxis, 106; electric stimulus, 129 ; phototaxis, 185; ther- motaxis, 259. RICHARDS, E. See JORDAN. RICHARDS, H. M., growth and chemi- cal irritation, 332. RICHET, toxic dose and temperature, 2. RICHTER, varying density, 78, 80, 86, 89 ; geotropism, 398. Rigor, cold-R., 242; dark-R., 175; desiccation-R., 61; heat-R., 231; light-R., 178. RINGER, density, 80. RISCHAWI, temperature and excretion, 223; electrotropism, 410. ROEMER, chemotaxis, 33. Roos, iodine and growth, 317. Roots, chemotropism, 336 ; hydrotro- pism, 256 ; thigmotropism, 380 ; geo- tropism, 393. ROSANOFF, chemotaxis, 108. ROSSBACH, 24; strychnin, 25, 26; qui- nine, 2(5; varying density, 78; heat and excretion, 224 ; heat and cilia movement, 228. ROTH, temperature and cilia move- ment, 227. ROTHERT, transmission of light stimu- lus, 441. Rotifera, chloral hydrate, 10; hydroxyl- amine, 15 ; desiccation-rigor, 61, 62 ; cold-rigor, 240 ; heat and dryness, 255. Rough movements and growth, 370. Roux, cytotropism, 52, 53. Rubidium, effect on growth, 320. RUSCONI, electricity on frog's egg, 405. RUSSELL, movements and growth, 371. SACHS, penetration of light into plant tissue, 165 ; active rays in plant as- similation, 166 ; false phototaxis, 181 ; temperature and protoplasmic movement, 225 ; hydrotropism, 256 ; growth, 281 ; silicon and growth, 324; hydrotropism, 358; thigmotro- pism, 380, 383 ; geotropism, 393- 397, 402 ; light and growth, 417, 418 ; curve of growth, 421; effective rays in growth, 428. Salmo trutta, light on eggs of, 426. Salts as poisons, 14, 15; chemotactic, 36. SAMKOWT, heat-rigor, 232. SARGENT, fission and density, 365, 366. Schizomycetes, pseudotaxis, 182. SCHENCK, effect of twisting on plant growth, 375. SCHLOSING, nitrifying organism, 308, 310 ; algse and nitrogen, 309 ; free nitrogen and phanerogams, 312. SCHMANKEWITSCH, changed density on Flagellata, 76, 77, 86. SCHMIDT, movements and growth, 371. SCHMITZ, light and growth, 420. SCHNEIDER, iron and growth, 321. SCHNETZLER, rays affecting growth of tadpoles, 432, 435. SCHOLTZ, pulling on plant growth, 372. ScHOUMOw-SiMANOwsKY. See NENCKI. SCHRODER, strychnin, 26. SCHULTZE, M., strychnin, 25 ; temper- ature and protoplasmic movement, 225 ; heat-rigor, 232. SCHULTZE, 0., temperature and growth, 459. SCHULZ, salts of arsenic, 4, 5 ; acclima- tization to poison, 28 ; poisons and cell activity, 332. SCHURMAYER, chloroform and ether, 10 ; cocaine, 24 ; strychnin, 25, 26 ; antipyrin, 27 ; heat and cilia move- ments, 228 ; cold-rigor, 240. SCHUTZENBERGER, dry protoplasm re- sists heat, 255. SCHWARZ, gravity and Protista, 114- 116, 121 ; temperature and irritabil- ity, 230 ; acclimatization to cold, 257 ; gravity and growth, 391. SCHWEIZER, compression rheostat, 127 ; electric current, 139 ; electrotaxis, 147-149. Scyllium, effect of changed solution on, 80. 506 INDEX Sea-urchin, inorganic food, 303. Secretion, contact stimulus, 99. Seed, vitality, 04 ; phosphorus in, 303 ; light on germination, 419, 422. Seedling, oxygen and growth, 305 ; ether and growth, 333 ; pulling stim- ulus, 372, 373 ; rheotropism, 387 ; electricity and growth, 405-410. Selenous oxide and Spirogyra, 20. SEMPER, extent of medium on size of snails and lish, 474. Sensitive plant, light on growth, 429 ; temperature and growth, 458. Sepolia, nicotin, 24. Serpula uncinata, sudden change of intensity, 17i>. Serpulidte, phototropism, 442. SKWALL, acclimatization to poison, 29. Sexual cells, cocaine, 24 ; quinine, 26. Sheep, food of growing, 330. SiirTTi.EwoRTH, acclimatization to cold, 257. Silkworm, cold- rigor in eggs, 240. Silicon and growth, 324. Sinapis, phototropic, 438. Slug, thigmotaxis, 105. Snails, strychnin, 26; extent of me- dium on size, 474, 475. SOCIN, iron and growth, 323. Sodium, salts on protoplasm, 4, 21, 22 ; and growth, 318. Solutions, physical action of, 70. SOROKIN, phototonus, 177. SPALLANZANI, desiccation-rigor in roti- fers, 61, 63. SPAULDING, false and true thigmotro-^ pism, 384, 385. Specific rate of vibration, 98. Spectrophor, Reinke's, 156. Spectrophotometer, 160. Spermatozoa, chemotaxis, 37 ; thigmo- taxis, 10(5, 107. Spermatozoids, chemotaxis, 33. Spirillum, chemotaxis, 33. Spirographis, sudden change of light, 179! Spirogyra, ammonia, 6 ; salts of heavy metals, 14 ; selenous oxide, 20 ; formaldehyde, 21 ; phosphorus on growth of, 314 ; effective rays in growth, 430. Sponge, silicon and growth, 324. Sponge gemmules, 65. Spores, desiccation of, 65 ; heat, 256 •, chemotropism, 341 ; light and germi- nation, 419, 422, 424 ; heat and ger- mination, 452. Squid, copper in blood of, 324. STAHL, chemotaxis, 33. 38. 45 ; hydro- taxis, 66 ; acclimatization to changed density, 86 ; tonotaxis, 811 ; rheotaxis, 108 ; light and chlorophyll arrange- ment, 181, 191 ; phototaxis, 183- 185 ; thermotaxis, 250. STAMEROFF, light and growth, 420. STANDKE. See KLINGEII. STANGE, chemotaxis, 33-38 ; growth and density, 362. Starfish, geotaxis, 118 ; phototaxis, 202 ; inorganic food and growth, 303. Statoblasts, changing temperature necessary to development of, 425. STEBLER, light and germination, 424. STEFANOWSKA, light response of pig- ment, 193. STEINACH, direct action of light on iris movements, 179 ; light response of pigment, 192. Stems, hydrotropism, 358 ; gravity on growth, 397 ; curvature, 398 ; day- light and growth, 419. Stentor, salts as poisons, 15 ; accli- matization, 30, 31 ; photopathy, 189 ; thigmotropism, 375. Stimulus, relation between intensity and response, 39, 40. STOKLASA, free nitrogen and plants, 312. Stolons, geotropism, 400 ; phototro- pism, 44o. STRASBURGER, rheotaxis, 108 ; light- response, 179 ; phototaxis, 183, 184, 199, 202, 208 ; light and temperature on locomotion, 199 ; temperature and irritability, 230 ; high temperature, 239 ; acclimatization to cold, 257 ; chemotropism, 337. Strongylus rufescens, desiccation-rigor, 61. Strontium, growth, 321. Structure of protoplasm, 70. Strychnin, 25, 26. Sugar, attracts Bacterium termo, 37. Sulphonal, 10. Sulphur, on growth, 314 ; oxide and growth, 20. INDEX 507 Swarm spores, protoplasm, 10; photo- taxis, 182, 183. SZCZAWINSKA, light response of pig- ment, 193. Tadpoles, salts of arsenic, 5 ; of heavy metals, 14 ; varying density, 86 ; geotaxis, 124 ; electrotaxis, 149 ; growth and density, 367 ; light and growth, 425, 4_:6, 432, 433 ; extent of medium and size, 475, 478. TAMMANN, fluorine and growth, 317. Tannic acid, chemotaxis, 38. TAPPEIXER, fluorine and growth, 317. Tardigrades, desiccation, 61, 65; dry- ing and heat resistance, 255. Tartaric acid, chemotactic, 38. Taurin, chemotactic, 38. Temperature, effect on toxic dose, 2 ; increases osmosis, 83 ; T. and metab- olism, 222, 223 ; and protoplasmic activity, 229, 230 ; ultromaximum, 231, 234-237 ; ultraminimum, 239 ; sudden change of, 460, 461 ; thermo- tropism, 464. Temporary rigor, 242. Tendrils, twining, 377. Tension, effect on plasma, 374. Tetraspora, and density, 78, 89. Thalassicola, contact-response, 98, 99. Thermogenic food, 293. Thermotaxis, 105, 258, 261. Thigmotropism, 376, 383, 463, 465, 466. THOUVENIN, electricity and plants, 409. Threshold stimulus to chemical agents, 42. TIMIRIAZEFF, plant assimilation and wave-lengths, 167, 169. TOLOMEI, magnetropism, 413. Tonotaxis, 89-91. Tradescantia hairs, oxygen, 2, 3 ; hy- drogen, 5 ; ammonia, 6 ; chloro- form, 9 ; molar agents, 102 ; electric current, 132; cold-rigor, 241, 242; cold, 247. Traumatropism, 384, 386. TREMBLET, phototaxis, 194. TREVIRANUS, temperature and metab- olism, 223. TREW, light and growth, 421. Triton, electric stimulation, 137 ; ther- motaxis, 261. Tritonium and sulphuric acid, 28. Trophotaxis, 39. Tropism, 484, Trout, light and growth, 426. TRUE, traumatropism, 384 ; electro- tropism, 410. TSCHAPLOWITZ, moisture and growth, 253. TSUKAMOTO, alcohols, 10-12. Tubers, light and growth, 418. Tubifex, poisons, 14. Tubularia, oxygen and regeneration, 306 ; potassium and regeneration, 319. TUMAS, molar agents and growth, 371. Tunicates, inorganic food of, 303. Turbo, acclimatization to changed density, 56. Twining stems, 376. Ulothrix, prototaxis of spores, 199. Ultramaximum temperature, 234. Ultraminimum temperature, 244. Urea, attractive, 38. Urostyla, thigmotaxis, 106. VALENTIN, cold, 241. Valeric acid, chemical response, 38. Vallisneria, cold-rigor, 241. VANDEVELDE, germination and con- centration, 363. DE VARIGNY, varying density, 80 ; ac- climatization to density, 85, 86 ; ex- tent of medium and size of Limnsa, 475-478. VELTEN, cold-rigor, 241 ; temperature and chlorophyll movements, 226, 227. Veratrin, poison, 24. VERNON, temperature and growth of Echinoidea, 458. Vertebrates, chemicals, 25 ; electro- taxis, 150 ; potassium on growth, 318 ; calcium as food, 321 ; organic foods of, 334. VERWORN, chemotaxis, 33, 34 ; accli- matization to changed density, 86; phosphorescence, 98, 99 ; molar agents, 100 ; thigmotaxis, 106 ; geo- taxis, 121-123 ; electrical apparatus, 126; electric stimulation, 129-131, 134, 137 ; acclimatization to electric current, 139, 140; electrotaxis, 141, 508 INDEX 146, 148 ; phototaxis, 183-185, 188, 199, 202 ; growth, 282 ; thermotaxis, 258, 259. Vicia, phototropism, 438. VIERORDT, spectrophotometer, 160. VILLON, green rays and light, 435. Vinegar eel, organic acids, 13 ; accli- mated to sodic carbonate, 28. VINES, temperature and metabolism, 222 ; freezing point for plants, 247 ; growth, 282 ; potassium and growth, 318 ; light and growth, 420, 421, 423 ; effective rays in' growth, 430. Vitis, phototropism, 438. Volvox, phototaxis, 183 ; light attune- ment, 206. DE VRIES, quantitative studies in os- mosis, 71-73 ; salt-absorption, 88 ; growth and density, 362 ; contact stimulus, 382 ; thigmotropism, 383. WACHTEL, geotropism, 394. WALLER, electric response, 128 ; elec- trotaxis, 147. WARD, bactericidal effect of strong light, 171-174 ; cell division and growth, 287 ; light and growth, 421. WARREN, electric current on plant growth, 407. WASMANN, thermotaxis, 261. Water, amount in organisms, 58 ; role in organisms, 59 ; effect on proto- plasm, 67 ; analysis of, 301 ; effect on growth, 360. Water animals, hydrazin a poison, 16 ; source of oxygen for, 304. WEBER, phosphorus and growth, 314. WEBER'S law, 43-45, 440. WETTSTEIN, light on development, 174. WEYL, heat-rigor, 239. WHIFFLE, light accelerating growth, 423. WIELER, oxygen and plant growth, 305 ; growth and density, 362. WIESNER, hydrotropism, 257 ; trau- matropism, 384, 385 ; light and seedlings, 417 ; mistletoe, 423 ; Vicia faba, 429 ; intensity of light and response, 438 ; effective rays for seedlings, 440 ; heat and spore germination, 452 ; phototropism and geotropism, 471. DE WILDEMANN, thermotaxis, 268, 261. WILFARTH, enriching action of le- gumes, 310. WILLEM, light response, 207. WILSON, phototropism of Hydra, 202. WINDLE, electricity and development of chick, 405. WINOGRADSKY, phototaxis, 184 ; nu- trition of bacteria, 299 ; sulphur and bacteria, 315 ; rubidium and growth, 320 ; hydrogen disulphide and bacteria, 326. WOLFF, silicon and growth, 324. v. WOLKOFF, temperature on metabo- lism, 222. WOLLNY, atmospheric electricity, 408. WOLTERING, iron and growth, 323. Worms, formaldehyde, 21 ; electro- taxis, 147; phototaxis, 195; ultra- maximum, 2>!5 ; ultraminimum, 245 ; acclimatization to high temperatures. 251. WORTMANN, chemotropism, 340; hydro- tropism, 358, 360; thigmotropism, 381 ; geotropism, 402. Wounding, and traumatropism, 384. Yeast, phosphorus and growth, 313; potassium and growth, 318. YUNG, acclimatization to changed den- sity, 86 ; food of Amphibia, 329, 330 ; density and growth, 367; light and growth, 425, 426 ; light and growth of hydra, 430 ; different wave-lengths on growth of tadpoles, 433-435 ; ex- tent of medium and size of tadpoles, 475. ZACHARIAS, varying density on proto- plasm, 76. Zea, silicon and growth, 324; phototro- pism, 438 ; temperature and growth, 451-455 ; thermotropism, 463-405. Zoospores, chemotaxis, 34, 36, 37. ERRATA AND ADDENDA PAGB 10, note, ELFING should read ELFVING. 21, last sentence in next to last paragraph, should read : " On this account even neutral nitrites kill such plants as have an acid cell-sap, but not such as have a neutral cell-sap (some algse, e.g. Spirogyra)." 35. See the valuable paper of H. S. JENNINGS, Jour, of Physiology, XXI, 258-322, 1897, where it is shown that carbon dioxide in weak solu- tions is attractive ; in strong solutions, repellent. 59, line 3, 81.9% water should be 71.9%; line 4, 71.1% water should be 74.1%. 64. See WILL, Ceutralbl. f. Bakteriol. (2), III, 17; latent life of yeast. 72, second note, next to last line, one-tenth of should read ten times. 88, second line from bottom, FREDERIC should read FREDEKICQ. 108, fifth line from bottom, JONNSON should read JONSSON. 113, line 9, should read, "cannot be affected, as a whole, by gravity." 127, fourth line from the bottom, electrometer should read electrodynamometer. 146, line 13, galvanotaxis should read electrolaxis. 157, Table XVII. Other solutions are suggested by WIESNER, '79, Wien. Denkschrift, XXXIX, 187. 160. For measurement of chemical intensity see WIESNER, '93. Sitzungsber. Wien. Akad. CJI, 298. 170, line 5, over should read under. 174, line 13, ELVING should read ELFVING ; so, too, on p. 213. 191, description of Fig. 56, line 1, spaces should be species. 196, first paragraph. Dr. A. D. MEAD informs me that at Wood's Holl Diastylus swims free at night so that it is taken in the tow. Con- sequently these crustaceans are not exclusively mud-inhabiting, and may constitute no exception to the rule. 209, first two lines should read, "migrated in travelling 18 cm. in full light, 15% faster than the same individual migrated in light \ as strong." 224. A fuller table than that of RISCHAWI is given by CLAUSEN, '89, Landw. Jahrbiicher, XIX, 907, 911. 230. Compare with Campbell's table the similar results of EDWARDS, Studies Biol. Lab., Johns Hopkins Univ., July, 1887; and those of HUNT, '97, Science, V, 907. 247, line 15, dele words " between Bombyx." 251. 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From the beginning it was regarded as a masterpiece, and at once took a prominent place among text-books of physiology. . . . If one seeks for the reason of the high estimate in which this work is held on both sides of the Atlantic, by the most advanced students as well as by general readers, it may be found in the beauty and simplicity of the style, in the lack of personal prejudice on the part of the author, in his thorough familiarity with the progress of physiological knowledge, and in the rare judgment with which purely hypothetical ideas and those founded on sufficient evidence are discriminated. The work is therefore a most admirable guide to physiological progress as well as general physiological knowledge." — The Nation. FOSTER'S TEXT-BOOK OF PHYSIOLOGY. IN ONE VOLUME. 8vo. Cloth, $5.00. Sheep, $6.00. Abridged and revised from the Sixth Edition of the Author's larger Work published in five octavo volumes. This new Edition contains all the Illustrations included in the larger work, and is published in one octavo volume of about 1400 pages. It contains all of the author's more important additions to the complete work, and is like the sixth edition of that copyrighted in this country. NOW READY. i6mo. Price, 75 cents. PHYSIOLOGY FOR BEGINNERS. New Edition, with an Additional Chapter on Alcohol and Food. By MICHAEL FOSTER and L. E. SHORE. THE MACMILLAN COMPANY, 66 FIFTH AVENUE, NEW YORK. EXPERIMENTAL MORPHOLOGY. BY CHARLES BENEDICT DAVENPORT, Ph.D., Instructor in Zoology in Harvard University. PART I. EFFECT OF CHEMICAL AND PHYSICAL AGENTS UPON PROTOPLASM. 8vo. Cloth. Price $2.60, net. It is intended to serve as an introduction and guide to the study and development of the individual regarded as a complex of processes rather than a mere succession of different forms. It brings together under appropriate heads the published observations hitherto made on the subject, laying special stress upon the results and methods of those investigations \\hich have a quantitative value. The central idea of the work is that ontogeny is a series of reactions to chemical and physical agents. This determines the scope of the work, and the division of the effects of agents under the heads : I. Proto- plasmic Movements ; II. Growth; III. Cell Division ; IV, Differentiation. "The thoroughness which characterizes this important treatise renders it the most useful annotated bibliography of the subject which has appeared. But it is far more than an expanded bibliography. With a good sense of proportion, Dr. Davenport has placed at the command of biologists, not merely the results which have already been secured in this fascinating field, but he has pointed out certain directions which new investigations ought to pursue if they are to be fruitful. The sequence of sub- jects does not commend itself to us as in all respects the best, for it appears as if the effect of molar agents and of varying moisture upon protoplasm might well precede instead of follow the action of chemical agents and the molecular forces, but, aside from this, one can go with the author along a straight path, until he comes to the end of this part now before us; namely, the action of light and heat upon protoplasm. The general considerations of the effects of chemical and physical agents upon proto- plasm, which constitute the closing chapter of this part, are carefully stated, and kept on relatively safe ground; they are at the same time of a distinctly suggestive character, which must aid in carrying out the chief wish of the author; namely, the stimulation of further inquiries in this attractive and fertile iield. Botanists owe to Dr. Davenport very sincere thanks for the exhaustive manner in which he has pre- sented the botanical side of his subject." — American Journal of Science. " The material which is discussed has been well digested and is well arranged, and the style is on the whole clear and concise. The book is a readable one, and the descriptions and criticisms employed in experimentation, and the bibliographical lists at the conclusion of each chapter, contribute materially to the value the book pos- sesses for both the morphologist and the physiologist." — Science. THE MACMILLAN COMPANY, 66 FIFTH AVENUE, NEW YORK. m m