Digitized by the Internet Archive in 2007 with funding from IVIicrosoft Corporation http://www.archive.org/details/comparativephysiOOIoebrich Ube Science Series EDITED BY ptoUseov 3. »c*een Cattell, flD.B., t>b, AND COMPARATIVE PHYSIOLOGY OF THE BRAIN AND COMPARATIVE PSYCHOLOGY Comparative Physiology of the Brain and Comparative Psychology By Jacques [Loeb, M.D. Professor of Physiology in the University of Chicago Illustrated New York G. P. Putnam's Sons London: John Murray I002 Copyright, 1900 BY G. P. PUTNAM'S SONS Ube 'Rnicfierbocliec presf, flew ^tft TO PROFESSOR ERNST MACH HHi:)l PREFACE It is the purpose of this book to serve as a short introduction to the comp3.rative physiology of the brain and of the central nervous system. Physiology has thus far been essentially the physi- ology of Vertebrates. I am convinced, however, that for the establishment of the laws of life-phenomena a broader basis is necessary. Such a basis can be furnished only by a comparative physiology which includes all classes of the animal kingdom. My ex- perience in the course on comparative physiology at Wood's HoU seems to indicate that the transition from the old to the comparative physiology can be most readily accomplished through the physiology of the central nervous system. ^ The physiology of the brain has been rendered unnecessarily difficult through the fact that meta- physicians have at all times concerned themselves with the interpretation of brain functions and have introduced such metaphysical conceptions as soul, consciousness, will, etc. One part of the work of the physiologist must consist in the substitution of real physiological processes for these inadequate con- ceptions. Professor Ernst Mach, of Vienna, to whom vi PREFACE this book is dedicated, was the first to establish the general principles of an antimetaphysical science. I have added at the end of each chapter a list of the chief papers of which I have made use. Although far from complete, this may serve the beginner as a guide for the further study of the subjects touched upon. The book appeared first in German and was trans- lated by Anne Leonard Loeb. As a number of new facts have been found since the German edition ap- peared, and as it seemed desirable to formulate my antimetaphysical standpoint more precisely, I have made extensive alterations. My thanks are due to a number of friends who have offered suggestions, — most of all to my pupil, Miss Anne Moore. The University of Chicago, October i. 1900. CONTENTS CHAPTER I. PAGB Some Fundamental Facts and Conceptions Concern- ing THE Comparative Physiology of the Cen- tral Nervous System i CHAPTER II. The Central Nervous System of Medusae. Experi- ments ON Spontaneity and Coordination . . i6 CHAPTER III. The Central Nervous System of Ascidians and its Significance in the Mechanism of Reflexes . 35 CHAPTER IV. Experiments on Actinians 48 CHAPTER V. Experiments on Echinoderms 61 CHAPTER VI. Experiments on Worms 72 CHAPTER VII. Experiments on Arthropods loi CHAPTER VIII. Experiments on Mollusks 128 vii via CONTENTS CHAPTER IX. The Segmental Theory in Vertebrates CHAPTER X. Semidecussation of Fibres and Forced Movements CHAPTER XI. Relations between the Orientation and Function of Certain Elements of the Segmental Ganglia CHAPTER XII. Experiments on the Cerebellum .... CHAPTER XIII. On the Theory of Animal Instincts CHAPTER XIV. The Central Nervous System and Heredity CHAPTER XV. The Distribution of Associative Memory in the Ani MAL Kingdom CHAPTER XVI. Cerebral Hemispheres and Associative Memory . CHAPTER XVII. Anatomical and Psychic Localisation . CHAPTER XVIII. Disturbances of Associative Memory . CHAPTER XIX. On Some Starting-Points for a Future Analysis of THE Mechanics of Associative Memory Index PAGS 160 213 236 277 289 ILLUSTRATIONS IN THE TEXT FIGURE PACK 1. Hydromedusa (Gonionemus Vertens) 17 2. Diagram of the Bell of Aurelia Aurita, (After Claus.) . 18 3. Experiment in Dividing a Hydromedusa 19 4. Arrangement for Producing Automatically Pulsating Air- Bubbles 21 5. Dr. Hargitt's Experiment 27 6. Diagram of the Ascidian Heart . . . . . .28 7. Localising Reflex in Tiaropsis Indicans 31 8. Diagram for Explaining the Localising Reflex in Medusa 32 9. ClONA Intestinalis 36 10. The Ability of the Actinians to Discriminate ... 49 11. Continuation of the Experiment in Fig. 10 .... 50 12. An Actinian (Cerianthus) with a Normal Head and with an Artificially Produced Head 52 13. An Actinian (Cerianthus) that had been Placed in a Test- TuBE, Head down, Regaining its Normal Orientation . 55 14. Cerianthus Regaining its Normal Orientation . . .57 15. Actinian that has been Forced by Gravitation to Push itself through a Wire Net Three Times .... 59 16. Nervous System of a Starfish .... . . 61 17. Mechanism of the Turning of a Starfish that has been Laid ON its Back 62 18. The Same Experiment on a Starfish whose Nerve-Ring has been Severed in Two Places 63 19. Geotrgpic Reaction OF CucuM ARIA Cucumis . . . .67 ix X ILLUSTRATIONS IN THE TEXT FIGURE PAGE 20. ThysanozoOn Brocchii, a Marine Planarian .... 72 21. Thysanozoon Divided Transversely 73 22. ThysanozoOn with Transverse Incision 75 23. Fresh- Water Planarian (Planaria Torva) .... 77 24. Two-Headed Planarian Produced Artificially. (After van Duyne.) 81 25. Planarian with Two Heads that are Attempting to Move IN Opposite Directions, and in so Doing are Tearing the Common Body. (After van Duyne.) .... 82 26. The Brain and a Series of Segmental Ganglia of an An- nelid (Nereis) 83 27. Dorsal View of the Central Nervous System of an Earth- worm 84 28. Side View of the Central Nervous System of the Earth- worm 85 29. A Group of Nereis whose Brains have been Removed. They AT Last Collect in a Corner of the Aquarium and Perish in the Vain Attempt to Go through the Glass. (After Maxwell.) 93 30. Head of Nereis. (After Quatrefages.) 98 31. LiMULUs Polyphemus with the Central Nervous System Exposed 103 32. Lobster with Central Nervous System Exposed . . .115 33. Diagrammatic Representation of the Central Nervous System of a Snail (Paludina Vivipara) .... 128 34. Brain of Sepia 129 35. The Frog's Brain 139 36. Position of the Appendages of Limulus after Destruction OF the Right Half of the Brain 156 37. Attitude of an Amblystoma under the Influence of a Gal- vanic Current Passing from Head to Tail . . . 160 38. Attitude of an Amblystoma when the Galvanic Current Passes from Tail to Head 160 39. Cerebral Hemispheres of a Dog 260 COMPARATIVE PHYSIOLOGY OF THE BRAIN AND COMPARATIVE PSYCHOLOGY INTRODUCTION TO HE COMPARATIVE PHYSIOLOGY OF THE BRAIN CHAPTER I iOME FUNDAMENTAL FACTS AND CONCEPTIONS CONCERNING THE COMPARATIVE PHYSIO- LOGY OF THE CENTRAL NERVOUS SYSTEM I. The understanding of complicated phenomena lepends upon an analysis by which they are resolved into their simple elementary components. If we ask ^hat the elementary components are in the physio- logy of the central nervous system, our attention is iirected to a class of processes which are called re- lexes. A reflex is a reaction which is caused by an [external stimulus, and which results in a coordinated lovement, the closing of the eyelid, for example, ^hen the conjunctiva is touched by a foreign body, ►r the narrowing of the pupil under the influence of light. In each of these cases, changes in the sensory 2 COMPARATIVE PHYSIOLOGY OF THE BRAIN nerve-endings are produced which bring about a change of condition in the nerves. This change travels to the central nervous system, passes from there to the motor nerves, and terminates in the muscle-fibres, producing there a contraction. This passage from the stimulated part to the central nervous system, and back again to the peripheral muscles, is called a reflex. There has been a growing tendency in physiology to make reflexes the basis of the analysis of the functions of the central nervous system, consequently much importance has been at- tached to the underlying processes and the necessary mechanisms. The name reflex suggests a comparison between the spinal cord and a mirror. Sensory stimuli were supposed to be reflected from the spinal cord to the muscles ; destruction of the spinal cord would, ac- cording to this, make the reflex impossible, just as the breaking of the mirror prevents the reflection of light. This comparison, however, of the reflex pro- cess in the central nervous system with the reflection of light has, long since, become meaningless, and at present few physiologists in using the term reflex think of its original significance. Instead of this, another feature in the conception of the term reflex has gained prominence, namely, the purposeful char- acter of many reflex movements. The closing of the eyelid and the narrowing of the pupil are eminently purposeful, for the cornea is protected from hurtful contact with foreign bodies, and the retina from the FUNDAMENTAL FACTS % injurious effects of strong light. Another striking characteristic in such reflexes has also been empha- sised. The movements which are produced are so well planned and coordinated that it seems as though some intelligence were at work either in devising or in carrying them out. The fact, however, that a de- capitated frog will brush a drop of acetic acid from its skin, suggests that some other explanation is necessary. A prominent psychologist has maintained that reflexes are to be considered as the mechanicaP^ effects of acts of volition of past generations. The j ganglion-cell seems the only place where such me- chanical effects could be stored up. It has there- fore been considered the most essential element of the reflex mechanism, the nerve-fibres being regarded, and probably correctly, merely as conductors. Both the authors who emphasise the purposeful- ness of the reflex act, and those who see in it only a physical process, have invariably looked upon the ganglion-cell as the principal bearer of the structures for the complex coordinated movements in reflex action. I should have been as little inclined as any other physiologist to doubt the correctness of this concep- tion had not the establishment of the identity of the reactions of animals and plants to light proved the untenability of this view and at the same time offered a different conception of reflexes. The flight of the moth into the flame is a typical reflex process. The light stimulates the peripheral sense organs, the 4 COMPARATIVE PHYSIOLOGY OF THE BRAIN stimulus passes to the central nervous system, and from there to the muscles of the wings, and the moth is caused to fly into the flame. This reflex process agrees in every point with the heliotropic effects of light on plant organs. Since plants possess no nerves, this identity of animal with plant heliotropism can offer but one inference — these heliotropic effects must depend upon conditions which are common to both animals and plants. At the end of my book on helio- tropism I expressed this view in the following words : ** We have seen that, in the case of animals which possess nerves, the movements of orientation toward light are governed by exactly the same external con- ditions, and depend in the same way upon the external form of the body, as in the case of plants which possess no nerves. These heliotropic phenomena, conse- quently, cannot depend upon specific qualities of the central nervous system (i)." On the other hand, the objection has been raised that destruction of the ganglion-cells interrupts the reflex process. This argument, however, is not sound, for the nervous reflex arc in higher animals forms the only protoplas- mic bridge between the sensory organs of the surface of the body and the muscles. If we destroy the gan- glion-cells or the central nervous system, we interrupt the continuity of the protoplasmic conduction between the surface of the body and the muscles, and a reflex is no longer possible. Since the axis-cylinders of the nerves and the ganglion-cells are nothing more than protoplasmic formations, we are justified in seeking FUNDAMENTAL FACTS 5 in them only general protoplasmic qualities, unless we find that the phenomena cannot be explained by means of the latter alone. 2. A further objection has been raised, that al- though these reflexes occur in plants possessing no nervous system, yet in animals where ganglion-cells are present the very existence of ganglion-cells neces- sitates the presence in them of special reflex mechan- isms. It was therefore necessary to find out if there were not animals in which coordinated reflexes still ^ continued to exist after the destruction of the central nervous system. Such a phenomenon could be ex- pected only in forms in which a direct transmission of stimuli from the skin to the muscle is possible, in addition to the transmission through the reflex arc. This is the case, for instance, in worms and in Ascidi- ans. I succeeded in demonstrating in Ciona intesti- nalis that the complicated reflexes still continue after removal of the central nervous system (2). A study, then, of comparative physiology brings out the fact that irritability and conductibility are the I only qualities essential to reflexes, and these are both/ common qualities of all protoplasm. The irritable\ structures at the surface of the body, and the arrange- ) ment of the muscles, determine the character of the I reflex act. The assumption that the central nervous system or the ganglion-cells are the bearers of reflex mechanisms cannot hold. But have we now to con- clude that the nerves are superfluous and a waste ? Certainly not. Their value lies in the fact that they 6 COMPARATIVE PHYSIOLOGY OF THE BRAIN are quicker and more sensitive conductors than undif- ferentiated protoplasm. Because of these quaHties of the nerves, an animal is better able to adapt itself to changing conditions than it possibly could if it had no nerves. Such power of adaptation is absolutely necessary for free animals. 3. While some authors explain all reflexes on a psychical basis, the majority of investigators explain in this way only a certain group of reflexes — the so- called instincts. Instincts are defined in various ways, but no matter how the definition is phrased the mean- ing seems to be that they are inherited reflexes so purposeful and so complicated in character that no- thing short of intelligence and experience could have produced them. To this class of reflexes belongs the habit possessed by certain insects of laying their eggs on the material which the larvae will afterwards require for food. When we consider that the female fly pays no attention to her eggs after laying them, we cannot cease to wonder at the seeming care which nature takes for the preservation of the species. How can the action of such an insect be determined if not by mysterious structures which can only be contained in the ganglion-cells ? How can we explain the in- heritance of such instincts if we believe it to be a fact that the ganglion-cells are only the conductors of stimuli ? It was impossible either to develop a mechanics of instincts or to explain their inheritance in a simple way from the old standpoint, but our con- ception makes an explanation possible. Among the r FUNDAMENTAL FACTS 7 elements which compose these complicated instincts, the tropisms (heliotropism, chemotropism, geotropism, stereotropism) play an important part. These trop- isms are identical for animals and plants. The explanation of them depends first upon the specific irritability of certain elements of the body-surface, and, second, upon the relations of symmetry of the body. Symmetrical elements at the surface of the body have the same irritability ; unsymmetrical ele- ments have a different irritability. Those nearer the oral pole possess an irritability greater than that of those near the aboral pole. These circumstances force an animal to orient itself toward a source of stimulation in such a way that symmetrical points on the surface of the body are stimulated equally. In this way the animals are led without will of their own either toward the source of the stimulus or away from it. Thus there remains nothing for the ganglion- cell to do but to conduct the stimulus, and this may be accomplished by protoplasm in any form. For the inheritance of instincts it is only necessary that the ^gg contain certain substances — which will de- termine the different tropisms — and the conditions for producing bilateral symmetry of the embryo. The mystery with which the ganglion-cell has been sur- rounded has led not only to no definite insight into these processes, but has proved rather a hindrance in the attempt to find the explanation of them. It is evident that there is no sharp line of demarc- ation between reflexes and instincts. We find that 8 COMPARATIVE PHYSIOLOGY OF THE BRAIN authors prefer to speak of reflexes in cases where the reaction of single parts or organs of an animal to external stimuli is concerned ; while they speak of instincts where the reaction of the animal as a whole is involved (as is the case in tropisms). 4. If the mechanics of a number of instincts is explained by means of the tropisms common to ani- mals and plants, and if the significance of the gan- glion-cells is confined, as in all reflex processes, to their power of conducting stimuli, we are forced to ask what circumstances determine the coordinated move- ments in reflexes, especially in the more complicated ones. The assumption of complicated but unknown and perhaps unknowable structures in the ganglion- cells served formerly as a convenient terminus for all thought in this direction. In giving up this assump- tion, we are called upon to show what conditions are able to determine the coordinated character of reflex movements. Experiments on galvanotropism of ani- mals have proved that a simple relation must exist between the orientation of certain motor elements in the central nervous system and the direction of the movements of the body which is called forth by the activity of these elements. This perhaps creates a rational basis for the further investigation of coordi- nated movements. 5. We must also deprive the ganglion-cells of all specific significance in spontaneous movements, just as we have done in the case of simple reflexes and instincts. By spontaneous movements we mean FUNDAMENTAL FACTS 9 movements which are apparently determined by inter- nal conditions of the living system. Strictly speaking, no movements of animals are exclusively determined by internal conditions, for the atmospheric oxygen and a certain temperature or certain limits of tem- perature are always necessary in order to preserve the activity beyond a short period of time. We must discriminate between simple and conscious spontaneity. In simple spontaneity we must consider two kinds of processes, namely, aperiodic spontaneous processes and rhythmically spontaneous or automatic processes. The rhythmical processes are of import- ance for our consideration. Respiration and the heart-beat belong to this category. The respiratory movements prove without possible doubt that auto- matic activity can arise in the ganglion-cells, and from this the conclusion has been drawn that all automatic movements are due to specific structures of the ganglion-cells. Recent investigations, how- ever, have transferred the problem of rhythmical spontaneous contractions from the field of morphology into that of physical chemistry. The peculiar quali- ties of each tissue are partly due to the fact that it contains Ions (Na, K, Ca, and others) In definite proportions. By changing these proportions, we can impart to a tissue properties which it does not ord- inarily possess. If In the muscles of the skeleton the Na ions be increased and the Ca Ions be reduced, the muscles are able to contract rhythmically, like the heart. It Is only the presence of Ca ions in the 10 COMPARATIVE PHYSIOLOGY OF THE BRAIN blood which prevents the muscles of our skeleton from beating rhythmically in our body. As the mus- cles contain no ganglion-cells, it is certain that the power of rhythmical spontaneous contractions is not due to the specific morphological character of the ganglion-cells, but to definite chemical con- ditions which are not necessarily confined to gang- lion-cells (3). The coordinated character of automatic movements has often been explained by a *' centre of coordina- tion," which is supposed to keep a kind of police watch on the different elements and see that they move in the right order. Observations in lower animals, however, show that the coordination of automatic movements is caused by the fact that that element which beats most quickly forces the others to beat in its own rhythm. Aperiodic spontaneity is still less a specific function of the gang- lion-cell than rhythmical spontaneity. The swarm- spores of algae, which possess no ganglion-cells, show spontaneity equal to that of animals having ganglion-cells. 6. Thus far we have not touched upon the most important problem in physiology, namely, which mechanisms give rise to that complex of phenomena which are called psychic or conscious. Our method of procedure must be the same as in the case of in- stincts and reflexes. We must find out the ele- mentary physiological processes which underlie the complicated phenomena of consciousness. Some FUNDAMENTAL FACTS ii physiologists and psychologists consider the purpose- fulness of the psychic action as the essential element. If an animal or an organ reacts as a rational man would do under the same circumstances, these authors declare that we are dealing with a phenomenon of consciousness. In this way many reflexes, the in- stincts especially, are looked upon as psychic func- tions. Consciousness has been ascribed even to the spinal cord, because many of its functions are pur- poseful. We shall see in the following chapters that many of these reactions are merely tropisms which may occur in exactly the same form in plants. Plants must therefore have a psychic life, and, follow- ing the argument, we must ascribe it to machines also, for the tropisms depend only on simple mechan- ical arrangements. In the last analysis, then, we would arrive at molecules and atoms endowed with mental qualities. We can dispose of this view by the mere fact that the phenomena of embryological development and of organisation in general show a degree of purposeful- ness which may even surpass that of any reflex or instinctive or conscious act. And yet we do not consider the phenomena of development to be depend- ent upon consciousness. On the other hand, physiologists who have appre- ciated the untenable character of such metaphysical speculations have held that the only alternative is to drop the search for the mechanisms underlying consciousness and study exclusively the results of 12 COMPARATIVE PHYSIOLOGY OF THE BRAIN operations on the brain. This would be throw- ing out the wheat with the chaff. The mis- take made by metaphysicians is not that they devote themselves to fundamental problems, but that they employ the wrong methods of invest- igation and substitute a play on words for ex- planation by means of facts. If brain-physiology gives up its fundamental problem, namely, the dis- covery of those elementary processes which make consciousness possible, it abandons its best possi- bilities. But to obtain results, the errors of the metaphysician must be avoided and explanations must rest upon facts, not words. The method should be the same for animal psychology that it is for brain-physiology. It should consist in the right understanding of the fundamental process which re- curs in all psychic phenomena as the elemental com- ponent. This process, according to my opinion, is the activity of the associative memory, or of association. Consciousness is only a metaphysical term for phenomena which are determined by associative memory. By associative memory I mean that mechanism by which a stimulus brings about not only the effects which its nature and the specific structure of the irritable organ call for, but by which it brings about also the effects of other stimuli which formerly acted upon the organism almost or quite simultaneously with the stimulus in question (4). If an animal can be trained, if it can learn, it possesses associative memory. By means of this criterion it FUNDAMENTAL FACTS 13 can be shown that Infusoria, Coelenterates, and worms do not possess a trace of associative memory. Among certain classes of insects (for instance, wasps), the existence of associative memory can be proved. It is a comparatively easy task to find out which representatives of the various classes of ani- mals possess, and which do not possess, associative memory. Our criterion therefore might be of great assistance in the development of comparative psychology. 7. Our criterion puts an end to the metaphysical ideas that all matter, and hence the whole animal world, possesses consciousness. We are brought to the theory that only certain species of animals possess associative memory and have consciousness, and that it appears in them only after they have reached a certain stage in their ontogenetic development. This is apparent from the fact that associative memory depends upon mechanical arrangements which are present only in certain animals, and present in these only after a certain develop- ment has been reached. The fact that certain ver- tebrates lose all power of associative memory after the destruction of the cerebral hemispheres, and the fact that vertebrates in which the associative memory either is not developed at all or only slightly developed {e. g., the shark or frog) do not differ, or differ but slightly, in their reactions after losing the cerebral hemispheres, support this view. The fact that only certain animals possess the necessary 14 COMPARATIVE PHYSIOLOGY OF THE BRAIN mechanical arrangements for associative memory, and therefore for metaphysical consciousness, is not stranger than the fact that only certain animals possess the mechanical arrangements for uniting the rays from a luminous point in one point on the retina. The liquefaction of gases is an example of a sudden change of condition which may be produced when one variable is changed ; it is not surprising that there should be sudden changes in the onto- genetic and phylogenetic development of organisms when there are so many variables subject to change, and when we consider that colloids easily change their state of matter. It becomes evident that the unravelling of the mechanism of associative memory is the great dis- covery to be made in the field of brain-physiology and psychology. But at the same time it is evident that this mechanism cannot be unravelled by histo- logical methods, or by operations on the brain, or by measuring reaction times. We have to remember that all life phenomena are ultimately due to motions or changes occurring in colloidal substances. The question is. Which peculiarities of the colloidal sub- stances can make the phenomenon of associative memory possible ? For the solution of this problem the experience of physical chemistry and of the physiology of the protoplasm must be combined. From the same sources we must expect the solution of the other fundamental problems of brain-physio- logy, namely, the process of conduction of stimuli. FUNDAMENTAL FACTS 15 Bibliography. 1. LoEB, J. Der Heliotropismus der Thiere und seine Ueberein- stimmung mit dem Heliotropismus der Pflanzen. WUrzburg, 1890. A preliminary note on ihese experiments appeared January, 1888. 2. LoEB, J. Uniersuchungen zur physiologischen Morphologie der Thiere II. WUrzburg, 1892. 3. LoEB, J. American Journal of Physiology ^ vol. iii., p. 327 and p. 383, 1900. 4. LoEB, J. Bettrdge zur Gehirnphysiologie der Wiirmer, P finger's ArchiVy Band Ivi., 1894. I CHAPTER II THE CENTRAL NERVOUS SYSTEM OF MEDUSAE. EXPERIMENTS ON SPONTANEITY AND CO- ORDINATION I. Experiments on Medusae or jelly-fish afford us an excellent opportunity for analysing the con- ditions for spontaneity and coordination, and for deciding whether or not these phenomena are depend- ent upon ganglion-cells. The subumbrella of the Medusae has a very thin layer of muscle-fibres which contract rhythmically. The contraction diminishes the size of the swimming-bell, and forces the water out. By means of the recoil the animal moves for- ward. In regard to the nervous system, we must discriminate between two classes of Medusae : first, the Hydromedusae (Hydroidea, Fig. i), and, second, the Acalephae, one representative of which (Aurelza aurita, Fig. 2) is familiar to many laymen. The nervous system of the Hydromedusae consists of a double nerve-ring along the margin of the umbrella {d, Fig. i). The upper nerve-ring forms a flat layer in the ectoderm, and consists of thin fibres and gan- glion-cells. The lower nerve-ring has thicker fibres 16 EXPERIMENTS ON MEDUSAE 17 and more ganglion-cells, and is connected with the upper ring by nerve-fibres. In addition to this ring, which is called the central nervous system, there is also a peripheral nerv- ous system, a plexus, consisting of nerves and scattered ganglion cells, spread out over the whole subumbrella {b, Fig. i), between the epithelium and the muscle-layer. The convex surface of the umbrella consists of a non-contractile, gelat- inous mass, and no nervous elements are to be found in it. Acalephse (Fig. 2) have no continuous nerve-ring, but a row of separate nerve-centres {S, Fig. 2) extends around the margin of t^e umbrella, lying in the ectoderm, which covers the basis of the marginal bodies (sense organs). The number of these centres corresponds, at least in Aurelia aurita^ with the num- ber of sense organs. This nervous system contains no ganglion-cells, but processes called nerve-fibres go out from special epithelial cells. The muscle-layer of the umbrella also is said to contain a peripheral nervous plexus (i). Fig. I. (Gonionemus Hydromedusa. vertens.) a, umbrella ; b^ subumbrella with muscles ; c, man- ubrium ; d^ margin of the swimming-bell with the nerve-ring. i8 COMPARATIVE PHYSIOLOGY OF THE BRAIN Our first question is : Is the spontaneous locomo- tion of the Medusae, or the rhythmical contraction of their swimming-bell, a function of the ganglion-cells ? ©Romanes found w that if the margin of the bell of a Hydro- . . * * medusa {b, Fig. 3) be cut off, the rhythmical contraction of the centre of the bell {a, Fig. 3) ceases, while Fig. 2. Diagram of the Bell of Aurelia \\\^ marp"in b which AuRiTA, WITH Eight Sense Organs. (After Claus.) contains the nerve- ring, continues to ex- ecute rhythmical contractions (2). The wound does not even cause a decrease in the number or in the strength of the marginal contractions. The exper- iment has been repeated by other authors with the same result. Any sort of wound can be made in the umbrella without disturbing the rhythmical con- tractions so long as the nerve-ring remains intact. Thus Romanes concluded that these rhythmical con- tractions of Hydromedusse originate in the nerve- ring or its ganglia. I have found recently that this whole problem is not so much a morphological problem as a problem of physical chemistry. The osmotic pressure of the sea-water is about equal to that of a -| n NaCl solution. I found that if the centre of a swimming-bell be put into a f n NaCl or -| n NaBr solution it goes on beating rhythmically. But if a EXPERIMENTS ON MEDUSA 19 small quantity of CaCl^ or KCl, or both, be added, the centre stops beating. The centre would beat in sea-water were it not for the presence there of Ca, K, and possibly other ions (3). The centre contains some scattered ganglion-cells. It might be argued that the presence of these cells makes the rhythmical contractions in a pure NaCl solution pos- sible. It is easy to prove that such is not the case. The striped skeletal muscles of a frog do not contract rhythmically in blood or serum. I have shown that this is due to the presence of Ca ions in these liquids. If the muscle be put into a pure NaCl or NaBr solution of the same osmotic pressure as the blood, the muscles contract rhythmically (4). Yet these muscles contain no ganglion-cells. Hence it is not the presence or absence of ganglion - cells which determines the spontaneous rhythmical contractions, but the presence or absence of certai7i ions, Na ions start or increase the rate of spontaneous rhyth^nical contractions ; Ca ions diminish the rate or inhibit such contractions altogether. How can these ions have such an influence? In order to explain this we must go back to the fundamental character of protoplasmic motion. Protoplasmic Fig. 3. Experiment in Divid- ing A Hydromedusa. The amputated margin continues to contract rhythmically, while the bell no longer contracts. 20 COMPARATIVE PHYSIOLOGY OF THE BRAIN motions are due to changes in the physical character of the colloidal material in the protoplasm. These changes may consist in changes in the state of matter or in the absorption of water by these colloids, or in secondary changes derived from those before men- tioned. We know that the physical qualities of the colloids are influenced greatly by the nature and osmotic pressure of the ions in the surrounding solu- tion. For that labile equilibrium of the colloids which is required for spontaneous rhythmical contrac- tions, the Na, Ca, and K ions must be present in definite proportions in the tissues. This proportion must be different for the centre and the margin of a Hydromedusa. While for the margin the proportion in which these three ions exist in the sea-water is adequate, for the centre of a Hydromedusa more Na ions and less Ca ions are required. Hence, if we put a centre without the margin into normal sea-water it does not beat, but it will beat when put into a pure NaCl or NaBr solution of the same osmotic pressure as sea-water. In the pure NaCl solution Na ions of the solution will enter into the tissues and take the place of some of the Ca ions. This will give the col- loids of the muscles those qualities which allow rhyth- mical contractions. If too many Na ions enter the tissues of the centre it will lose its irritability. The latter will, in this case, be restored again by adding a trace of CaCl^ to the solution. It thus happens that the problem of spontaneous activity is no longer a question of the presence or absence of the ganglion- EXPERIMENTS ON MEDUSA 21 cells, but of the physical qualities of the colloidal sub- stances in the tissues. But must we conclude from this that the Na ions are the cause of the spontaneous rhythmical contractions of the Medusa? I think not. The ions only bring about a certain labile equi- V^J^ff^^7f,/f^/JJJ?/J^?}JJ/77^f Ir v/y/^//y///////?W//f////mf/,jju>)>nj,>,,,i ,jjji^jj,,j^j^,,,„„,,,,,fJ^ ^ Fig. 4. Arrangement for Producing Automatically Pulsating Air-Bubbles. (See text.) librium in the condition of the colloids of the con- tractile tissue which allows the true cause of the contractions to be effective. But what is this cause ? J. Rosenthal seems to have been the first to call attention to the fact that it is in no way essential for a rhythmical phenomenon to have a rhythmical cause, and that constant conditions can lead to rhythmical effects. If a small, constant stream of water flows into a pipette, it will pass out rhythmically in drops. The weight of the drop must be greater than the 22 COMPARATIVE PHYSIOLOGY OF THE BRAIN surface-tension in the periphery of the opening of the outlet before the drop can break off. As long as the quantity of water running into the pipette, in the unit of time, remains below a certain limit, it will be some time before the drop will be heavy enough to fall. Quincke has given a simple and elegant method by which it is easy to produce rhythmical contractions in air bubbles (5). I will describe the experiment as shown in my lectures. A glass plate P (Fig. 4) is placed in a dish B, filled with water. The lower, narrow end of the thermometer tube T is under and at the middle of the air-bubble, while the upper end rests in a dish A filled with 95 per cent, alcohol. The alcohol rises in a fine stream toward the centre of the bubble. As soon as the alcohol comes in contact with the bubble, the alcohol spreads out on the limit between the air and the water, because the sum of the surface- tensions between air and alcohol and alcohol and water is less than the surface-tension between air and water. By the decrease in the surface-tension the bubble becomes flatter and broader. In consequence of the vortex movements in the water that are pro- duced by the spreading, the flow of the alcohol to the bubble is interrupted. The layer of alcohol around the bubble diffuses rapidly into the surrounding water, and the bubble becomes again higher and narrower. The alcohol can flow to the bubble again now that the vortex-movements have ceased, and the flattening of the bubble again takes place, and so on. Under the above-mentioned conditions I obtained about EXPERIMENTS ON MEDUSA 23 eighty pulsations per minute — /. e., about the period- icity of the heart. Now, as regards the origin of the rhythmical activ- ity of Medusae, of the heart, and of respiratory activity, we can imagine that a constant fermentative produc- tion of certain compounds in the automatically active cell corresponds to the constant flow of alcohol in Quincke's experiment. These substances may be of such a nature that they occasion spreading-phenomena or some other physical change in the colloids of the muscle. But a certain quantity of these substances must be present before this change occurs, hence the periodicity of the contractions. But whether it be a constant fermentative production of some substance or not, the ultimate constant cause for the production is the heat or the intensity factor of the same — the temperature. It now can no longer surprise us that Romanes found that the centre of an Acalepha is able to beat rhythmically in normal sea-water if severed from the margin. As long as we assume that the ganglion-cells are the essential element in spontaneity, this experience on Acalephse would be difficult to ex- plain. As it is, we are only obliged to conclude that in Acalephae there is less difference between the col- loidal substances of the margin and centre than in Hydromedusae. 2. Not only the spontaneous character of locomo- tions is commonly considered to be due to ganglion- cells, but the coordinated character of these motions as well. Let us see how far this notion is correct. 24 COMPARATIVE PHYSIOLOGY OF THE BRAIN Romanes found that if the whole margin of the umbrella of a Hydromedusa be cut off, and only a tiny piece left, this is sufficient to keep up the spontane- ous activity of the jelly-fish in sea-water. From this it would appear that any element of the margin may be considered a centre for the rhythmical contractions of the whole Medusa. But if this be the case, how does it happen that the whole umbrella contracts sim- ultaneously, and why do we not find one part of the margin in systole and the other in diastole ? This coordination is by no means to be taken for granted. It is present only in healthy specimens, and is wanting in injured or dying specimens, a fact to which Roma- nes called attention. The problem of the mechanism of this coordination has been dismissed by many au- thors by the assumption of a " coordinating centre " that is supposed to control this coordination. We shall shortly be in a position to decide whether coor- dination in lower animals is controlled by a special ** centre of coordination," or whether it is not rather the result of simple laws of stimulation and conduction. Romanes found in Acalephae that coordination ceases when all direct connection between the nervous centres has been interrupted by radial incisions in the umbrella, the various sectors no longer contracting simultaneously. The same thing results in Hydrome- dusse, if conduction through the nerve-ring is inter- rupted. In such cases, the radial incision must reach well toward the centre of the bell. If, however, such incisions are made in the umbrella without injuring EXPERIMENTS ON MEDUSJE 25 the margin and the nerve-ring, no disturbance of coordination ensues. It seems that the continuity of the structures located in the marginal portions of the umbrella is necessary for the coordinated activity. Now how does it happen that so long as the continuity is preserved all the elements act synchronically, while the synchronism disappears if the continuity is inter- rupted?^ In order to answer this question, we must turn our attention to an organ which shows the phe- nomena of coordinated rhythmical activity in a strik- ing manner — namely, the heart. If the heart of a frog be divided into several pieces, they will all be rhythm- ically active, but the number of contractions will vary in the different pieces. The sinus venosus beats most rapidly, and the number of its contractions in a unit of time equals that of the heart before it was divided. Thus we see that the whole heart beats in the rhythm of the part that has the maximum nuTuber of contrac- tions per m^inute. From this we must assume that the coordination of the heart's activity is due to the fact that the part which contracts most frequently, forces the other parts to contract in the same rhythm. They will be forced to do this if the activity of the sinus venosus acts as a stimulus upon the other parts. A centre of coordination is therefore entirely unneces- sary. Porter succeeded by an ingenious method in causing ' It should be emphasised that incisions through the margin alone do not interfere with coSrdination in Gonionemus, but that it is necessary to continue the incisions to the centre of the swimming-bell. But even under such circum- stances the animal may still contract in a coordinated way. k 26 COMPARATIVE PHYSIOLOGY OF THE BRAIN strips of a mammalian heart to beat. He also draws from his observations the conclusion that there is no reason for assuming the existence of a centre of a coordination (6). In Medusae, also, a synchronical contraction of all the parts takes place if the stimulus from the portion first active can travel rapidly enough to the rest of the margin. This is only possible when the margin is uninjured. It is evident, however, that the neighbouring tissue as well as the nerve-ring is in- volved, because the radial incision must reach well toward the centre of the bell if we wish to stop the coordination. In this case the wave of stimulation must pass around the incisions, a process which in- volves so much time that the separate parts are able to contract independently, and the synchronism is lost. In injured or dying Medusae, where the contact of the cells is less close, uncoordinated, rhythmical activity occurs. In order to test this idea further, I proposed to Dr. Hargitt, who was w^orking in my laboratory, that he attempt to graft two Hydromedusae, and observe whether they continue to contract synchronically or independently after healing. For this purpose it was necessary to remove the margin of the Medusae. Two of them were then placed with their wounded surfaces in contact, and kept in this position. Figure 5 shows two Gonionemi grafted in this way. They grew together along the entire line of contact with the exception of a small part at O. New tentacles would probably have developed there in time had we not EXPERIMENTS ON MEDUSA 27 killed the animals in order to preserve them. In other experiments, the two animals did not heal together so completely. It happened in the case where the animals had grown together most completely, as represented in Figure 5, that they contracted synchronically like one animal two days after the operation. The animals, on the other hand, that had not grown together to such an ex- tent did not contract synchro- nically. I believe that if one could succeed in healing two hearts together completely, they would also beat synchro- nically. The assumption of a ** centre of coordination " situated in the ganglia of the margin of a Medusa thus becomes un- necessary. In the frog's heart, the sinus venosus beats faster than the auricle, ven- tricle, and bulbus aortae. Hence, each contraction of the sinus venosus acts as a stimulus, which causes a contraction of the auricles, and the contraction of the latter is the stimulus which causes the contraction of the ventricle and bulbus aortae. It would follow from this that if we could cause the bulbus aortae in the frog's heart to beat as fast as the sinus venosus we Fig. 5. Dr. Hargitt's Ex- periment. Two Gonionemi grafted to- gether. Two days after the operation synchronous con- tractions of both animals were observed. 28 COMPARATIVE PHYSIOLOGY OF THE BRAIN might see a reversal of the heart-beat. Nature has made this experiment for us on a large scale in the Ascidian's heart (Fig. 6). The latter has the peculiarity that the waves of contraction do not spread out con- stantly in one di- rection, as in the hearts of other an- imals, but perist- ^ ^ _^ ^ „ altic and antiperi- FiG. 6. Diagram of the Ascidian Heart. . ^ T .v A J- u _ . .• r .• staltic waves of In the Ascidian heart, contractions occur for a time in the direction from a to b, and then from b to Contraction alter- a. If the heart be cut open at c, the left half nate in it If for contracts only in the direction from a to f , the , . , right half only in the direction from b \.o c. example, it haS contracted five hundred times in succession from left to right, sending the blood to the right, this activity is followed by per- haps three hundred pulsations from right to left, which cause the blood to flow through the blood- vessels in the opposite direction. These contractions are followed again by a large number of pulsations from left to right, etc. Mr. Lingle made the follow- ing experiments on the Ascidian's heart at Wood's Holl in 1892. \{ a b (Fig. 6) be an Ascidian's heart and it be divided at ^, both pieces, a c^ and b c, con- tract uninterruptedly in a constant direction, the former in the direction from a to c, and the latter in the direction from b to c. Mr. Lingle found, further- more, that the source of the automatic activity is EXPERIMENTS ON MEDUSA 29 confined to two small regions {a and b, Fig. 6) which correspond to the sinus venosus and the bulbus aortae of the frog's heart. When we excise these two pieces from the heart they continue to beat without inter- ruption, while the long part between the two pieces no longer pulsates (in sea-water at least). These ex- periments, it seems to me, leave no room for doubt that the change in the direction of the contraction in the Ascidian's heart is determined by each of the two ends getting the upper hand alternately, and forcing the other centre to act in its rhythm for a time. This *' getting the upper hand " might possibly mean no- thing more than that one end gains the time in which to send off a wave of contraction before the other end begins to contract. For this it is only necessary that a single heart-beat of the leading end be delayed or fail entirely, a phenomenon that also appears oc- casionally in the human heart. In this way the other end of the heart gains time in which to send out a wave of contraction, and its automatic activity will continue to be the stimulus for the activity of the first end until a delay occurs in one beat or until one beat is skipped, thus allowing the first end time again to become automatically active, and so on. Last year I asked the members of the class in gen- eral physiology at Wood's Holl to find out whether the latter view was correct. Their observations were as follows : Suppose at a certain time a to be the active and b the passive end of the heart. After a short time a begins to beat more slowly or ceases to 30 COMPARATIVE PHYSIOLOGY OF THE BRAIN beat altogether. During the pause, the end b suc- ceeds in sending out a wave of contraction which reaches a before it has had time to send out a wave of its own. One sees occasionally at the time of a reversal that at first both ends send out contraction- waves which may meet in the middle of the heart. At the next heart-beat, the end which is about to stop delays the sending out of the wave a little more, and at the next heart-beat the wave starting from the other end can pass over the whole heart without being blocked. Hence the coordination of movements In Medusae (or in the heart) is not due to a hypothetical centre of coordination situated in the ganglion-cells, but to the fact that the element which is first active acts as a stimulus upon its next element, and so on. 3. It may be shown that even more specialised forms of coordination do not depend upon the pre- sence or interference of ganglia. When the back of a frog Is touched with acetic acid, the frog wipes off the acid with Its foot. If one leg Is tied. It uses the other for this purpose. The turtle acts in a similar manner when acetic acid is applied to the back of its shell. It cannot reach the stimulated spot, but the legs move dorsally under the shell as far as possible towards it. Physiology has contented Itself In regard to these phenomena by pointing to the complicated nature and Impenetrable structural secrets of the central nervous system. Yet the same reactions oc- cur In a Hydromedusa, in which case the term EXPERIMENTS ON MEDUSAE 31 *' central nervous system" has only a conventional significance. Romanes found that if we stimulate a spot a (Fig. 7) on the concave side of the umbrella of a Tiaropsis indicans with a needle, the manubrium is broug^ht to the stimulated spot y^ ^\^ ..••' (Fig. 7), as though / ^^ -^ the animal wished / /^ | \ to remove the / / I f \ I stimulating object / / \ \ \ / (2). This move- (/L^s:^====^^^^^^v?^ 1/ ment takes place 1^^^ -^^^ ^^3f' as follows: A "'''''liil^^ bending of the m a n u b r i u m as Tr ,v • . *u • • .• 1 * ^ *a. If the point a on the margin is stimulated, the well as 01 the bell manubrium is brought to the stimulated spot, ensues in that mer- somewhat as a decapitated frog tries to wipe off ... ft * ^op of acetic acid with its foot. idian of the um- brella which passes through the stimulated point a. It seems as though all the muscle-fibres cooperated in bringing the manubrium to the stimulated spot. The central nervous system has nothing to do with this reaction, for Romanes found that it continued after excision of the whole margin with the nerve- ring. On the other hand, if we make an incision in the umbrella parallel to the margin and stimulate a spot below the line of incision, movements of the manubrium, although not pronounced ones, ap- pear in the direction of the quadrant where the stimulated spot is located, but an exact localisation Fig. 7. Localising Reflex in Tiaropsis Indicans. 32 COMPARATIVE PHYSIOLOGY OF THE BRAIN Fig. 8. Diagram for Explain- ing THE Localising Reflex in Medusae. (See text.) is impossible. Romanes concludes from this that there are radial lines of differentiated tissue pass- ing through all parts of the bell and that it is their function to transmit impressions to the manu- brium. He assumes that this tissue is of a nervous character. I believe that the whole phenomenon can be explained without the as- sumption of a special differ- entiation of nervous tissue in radial directions. It seems to me that the following as- sumption is possible : Every localised stimulus leads to an increase in the muscular tension on all sides, which is most intense near the stimulated spot. Now if we decompose each of the lines of increase of tension {aa' ab' ad ad' ae\ Fig. 8) radiating from the stimul- ated spot, into a meridional component aa' dd' bb\ etc., and an equatorial component, it is evident that the lat- ter can have no influence on the manubrium. Only the meridional components can have an influence, and of these the one passing through the stimulated spot is the largest. This fact must necessarily cause a bend- ing of the manubrium toward the stimulated spot. It also shows why an incision parallel to the mar- gin of the umbrella makes an exact localisation impos- sible and only allows uncertain movements towards the stimulated quadrant. I hardly believe that the mechanisms for the EXPERMIENTS ON MEDUSA 33 analogous reflex in a frog or turtle are of a more com- plicated character. Nature works with very simple tools. The tool employed in the reflex of localisa- tion is the curvature produced by stimulation, — con- tact, for instance. We meet with this in its simplest form in plants, in which the side that comes in con- tact with a solid body becomes concave. Plants cer- tainly possess no central nervous system containing mysterious reflex structures. In their case, irritabil- ity and conductibility suffice as an explanation. In Medusae the method appears more complicated only in so far as in them the contractile tissue is real mus- cle-fibre. . In the frog, the only further complication is the fact that the conduction takes place through a special kind of tissue — namely, nerve-tissue. In its first anlage, this central nervous system is of a very simple segmental character. I believe that the cent- ral nervous system preserves this simple character better than any other tissue. The muscles undergo considerable displacement during the development, but the changes occurring in the central nervous sys- ^tem by no means equal those occurring in the mus- clar system. It seems thus possible to explain the above-men- :ioned phenomena of coordination in Medusae by leans of the simple facts of irritability and conduct- [ivity without attributing any other functions to the ;anglion-cell except those which occur in all conduct- [ing protoplasm. 34 COMPARATIVE PHYSIOLOGY OF THE BRAIN Bibliography 1. O, u. R. Hertwig. Das Nervensystem und die Sinnesorgane der Medusen. 2. Romanes, G. J. Jellyfish^ Starfish and Sea Urchins. The International Science Series, 1893. 3. LoEB, J. On the Different Effects of Ions upon Myogenic and Neurogenic Rhythmical Contractions^ etc., American Journal of Physiology^ vol. iii., 1900. 4. LoEB, J. Ueber lonen, welche rhythmische Zuckungen der Skelettmuskeln hervorrufen. Festschrift fur Fick. Braunschweig, 1899. 5. Quincke. Ueder periodische Ausbreitung an Fliissigkeits- oberfldchen^ etc. Sitzungsberichte der Berliner Akademie der Wis- sensch.y 1888, ii., S. 791. 6. Porter, W. T. The Coordination of the Ventricle, The American Journal of Physiology ^ vol. ii., 1899. CHAPTER III THE CENTRAL NERVOUS SYSTEM OF ASCIDIANS AND ITS SIGNIFICANCE IN THE MECHANISM OF REFLEXES I. If we wished to observe the order of the natural system in this book, we should not let the Ascidians follow the Medusae. We consider it more profitable, however, to discuss simple cases before taking up the more complicated ones. Having reached the con- clusion, at the end of the preceding chapter, that the spontaneous coordinated activities in Medusae are not due to specific morphological structures of the gan- glion-cells, we will now attempt to find out whether the reflex actions of animals depend upon the struct- ure of the central nervous system or of the peripheral parts. In Ascidians the central nervous system con- sists of a single ganglion {d, Fig. 9). This ganglion is situated between the oral and aboral tubes {a and b, Fig. 9). Ciona intestinalis (Fig. 9), a large, transparent Ascidian, possesses a very characteristic reflex. If either the oral or aboral opening be touched, both openings close, and the whole animal contracts so 35 ^6 COMPARATIVE PHYSIOLOGY OF THE BRAIN that it becomes small and round. This reflex is de- termined by two groups of muscles, first by ring- muscles in the oral and aboral openings, second by longitudinal muscles, which run lengthwise through the animal. By the contraction of these muscles the animal is protected from the en- trance of foreign bodies into the body cavity. This reaction is a typ- ical reflex act, and is eminently purposeful. According to the pre- vailing ideas concern- ing the decisive role that the ganglion plays in reflexes, the pro- cedure is as follows : If the oral or aboral opening be touched, the stimulation is conducted through the peripheral nerves to the ganglion, where a mysterious reflex mechanism is brought into play, which gives the muscles the command to contract in a manner corresponding to the nature of the stimulus. Ferrier, for instance, in his text-book, mentions the one ganglion of the Ascidians as illustrative of the significance of the ganglion in reflexes. I removed the ganglion from a number of Cionse. Fig. 9. CioNA Intestinalis. n oral, b aboral opening ; r , foot, d, location of ganglion. EXPERIMENTS ON ASCIDIANS 37 For some time after the operation, in most cases for about twenty-four hours, the animals remained con- tracted. At the end of this period they began to re- lax again. To my great surprise, I found that the typical reflex continued. If we let a drop of water fall on such an animal, the typical reflex act is pro- duced just as in the normal animal. Hence the reflex cannot be determined by specific structures of the ganglion. But what does determine the reflexes, and what is the function of the ganglion ? The answer to the first question must be that the reflex is determined by the structure and arrange- ment of the peripheral parts, especially the muscles. The mechanical stimulus throws the muscles directly into activity, and the stimulation is transmitted from muscle-element to muscle-element directly, as in the heart or the ureter. But is the central nervous system superfluous in this animal ? We get the answer to this question if we determine the threshold of stimul- ation. The threshold of stimulation for producing this reflex is higher in animals which have been operated upon than in normal animals. As the source of the stimulus, I used the kinetic energy of drops of water, which fell from a pipette upon the animal. Since the weight of the falling drop in the pipette is always the same, the minimum of the height from which a falling drop can produce a contraction is a convenient measure of the irritability ; the latter is of course equal to the reciprocal value of the thresh- old of stimulation. In one case there were in an 38 COMPARATIVE PHYSIOLOGY OF THE BRAIN aquarium (equally near the surface), a Ciona freshly operated upon and a normal Clona. The minimum height from which a contraction could be produced was as follows for the normal animal (a) and the animal operated upon {b) : a (normal) b (operated) 8 mm 65 mm 4 mm 75 mm 10 m.m 80 mm 80 mm In two other animals used for the experiment I obtained the following values : a (normal) b (operated) 6 mm. 22 m.m. 8 m^m 20 mm. It seems to me that the difference in the irritability arises from the fact that in the normal Ascidian the stimulation is conducted through the nerves and the ganglion, in which case less energy is required. In the Ascidian operated upon, however, the muscles are stimulated directly, and the conduction of the stim- ulation probably takes place from muscle-cell to muscle-cell, just as in the heart. We know, more- over, that the direct irritability of muscle-fibres is not so great as that of the nerves. Hence the nerves and the ganglion only play the part of a more sensitive and quicker conductor for the stimulus (i). 2. It may seem as though no conclusions could be drawn from these cases in regard to the '' reflex I EXPERIMENTS ON ASCIDIANS 39 centres " of higher animals. It is frequently stated that in higher animals the ganglia have assumed func- tions which in lower animals can be performed by the peripheral organs. It is similarly stated that the higher the animal ranks in the natural system, the more the functions ''migrate" toward the cerebral hemispheres. But how such an upward migration of functions is conceivable, none of these authors attempt to explain. It can easily be shown, however, that conditions are the same in higher and lower animals. We must only be careful to homologise a lower form with a single organ or segment of a higher animal. When the in- tensity of the light is suddenly increased, the pupil of our eye becomes narrower. The sphincter of the iris contracts, and the rays of light are excluded just as foreign bodies are shut out by the contraction of the sphincters in the Ascidians. In the eye, just as in the Ascidian, we have to deal with a typical reflex act. The increased intensity of the light stimulates the retina. The stimulation passes through the optic nerve to its centres, and is carried from there by means of the oculomotorius nerve to the sphincter of the iris, which contracts. It would nevertheless be wrong to assume that the centre for the pupillary reflex plays any other part in this process than that of a protoplasmic connection between the retina and the iris. It has been shown by Arnold, and later by Brown-Sequard and Budge, that even in the excised iris the pupil still contracts when the light strikes the former. I myself have often observed in sharks, 40 COMPARATIVE PHYSIOLOGY OF THE BRAIN whose brain I had removed, that Hght caused the pupil to contract several hours after death, when signs of decomposition had already begun to appear. Steinach has proved that in this case the muscle- elements in the iris are stimulated directly by the light (3). This reflex is therefore determined by the mus- cles of the iris, and the nervous connections serve only as quicker and more sensitive conductors. Thus we see that the eyeball behaves toward light just as the Ascidian behaves toward mechanical stimuli. Some physiologists seem to doubt that the muscles can be stimulated directly by light without the inter- vention of the ganglion-cells. But we know that phenomena of contraction are also produced by the light in the unicellular swarmspores of algae, which certainly contain no ganglia. Furthermore, no one doubts that muscles without ganglion-cells can also be stimulated chemically or mechanically. Why should there not also be muscle-fibres that can be stimulated directly by light ? There is no reason for assuming that all muscles must behave exactly like the muscles of the frog's leg, simply because the experiments on it have by chance furnished the prevailing views con- cerning muscles. The reader may believe that the pupillary reflex is an exceptional case, but this is not true. Defaecation and urination in higher animals may be considered as reflex phenomena of the spinal cord. The pressure of the faeces or of the urine acts as a stimulus, which affects the centres for the activity of the muscles of I EXPERIMENTS ON ASCIDIANS 41 these organs, and this stimulation is said to cause the contracted sphincters to relax. Goltz and Ewald have found, however, that after extirpation of the en- tire spinal cord up to the cervical part, defaecation and urination still occur normally (4). Only for a time after the operation the sphincters are relaxed. Later on everything again becomes normal. These phenomena probably belong to the same class as the one already described in the Ascidian. The processes in the normal evacuations of the bladder and rectum are not determined by the morphological structure of the so- called reflex centre, but by the muscles of the bladder and of the rectum themselves. The spinal cord serves only as a more sensitive and quicker conductor for the stimulus. Goltz and Ewald are inclined, it is true, to assume that, after all, ganglion-cells or un- known nervous structures determine these results. But the fact that the muscles of the skeleton can be caused to contract rhythmically when put in the right solution, makes this assumption unnecessary ; more- over, the facts of comparative physiology must also be taken into consideration. The Actinia mesembryan- themum of the East Sea and the Mediterranean per- haps show fewer differences morphologically than the sphincter ani and the gastrocnemius, and yet the Actinia mesembryanthemum of the Mediterranean shows a form of irritability which the Actinian of the same name from the East Sea does not show, namely, negative geotropism. I mention this illustration, to which many others might be added, in order to show 42 COMPARATIVE PHYSIOLOGY OF THE BRAIN that forms which are morphologically alike need not necessarily be alike in all their reactions. Experiments on fermentation show that a small stereochemical dif- ference of a carbohydrate or proteid can produce an entirely different physiological effect. The possibility, of course, remains that scattered ganglion-cells exist in Ascidians under the epidermis just as in Medusae. Mr. Hunter, who has studied the nervous system of Ascidians, informs us that he has found cells in certain places under the epidermis of As- cidians which he believes to be ganglion-cells. But after all that has been said about the scattered gan- glion-cells in Hydromedusae (see page 19) and their role in rhythmical contractions, it is not necessary to consider the importance of scattered ganglion-cells for reflexes. Schaper has recently made an observation which makes it seem as though in the young larvae of Amphibians conditions similar to those in Ascidians exist. He amputated the brain of the larva of a frog during the first days of development, and saw that the animal was still able to move spontaneously seven days after the operation. When sections of the animal were made, it was found that the spinal cord had also per- ished (2). This observation should be repeated and enlarged upon. It is quite possible that during the first days of development a direct transmission of the waves of stimulation may take place from the skin to the muscles in the larva of the frog, without the in- tervention of the central nervous system, as happens in the Ascidians. EXPERIMENTS ON ASCIDIANS 43 3. The objection might now be raised that the bladder and rectum are minor organs of the body. But what has been said above concerning them also holds good for larger and more important groups of organs, namely for the blood-vessels. These are able to adapt their width to external con- ditions ; the vessels of the skin become dilated when a loss of heat is desirable, and they contract in the cold when the loss of heat should be reduced. It is assumed that the mechanisms for these purposeful reflexes are contained in the central nervous system. Goltz and Ewald (4) have found, however, that dogs which have lost the spinal cord almost up to the me- dulla oblongata live for years. This alone proves that the blood-vessels can adapt themselves to the external temperature, independently of the central nervous system. Goltz had already proved that the blood-vessels regain their tonus if all the nerves of a limb be severed, the limb being connected with the animal only by means of the blood-vessels. The same thing occurs after extirpation of the spinal cord. The temperature of the hind-paws of animals whose spinal cord has been destroyed up to the thoracic part becomes normal again after the operation — that IS to say, the hind-paws have the same temperature as the fore-paws which remain connected with the central nervous system. If we hold the hand in snow for a time, we observe as a local after-effect a relaxation of the muscles of the blood-vessels and an increase in the temperature of the hand. Goltz and 44 COMPARATIVE PHYSIOLOGY OF THE BRAIN Ewald were able to show that the same phenomena may also be observed when the hind-legs of dogs whose spinal cord has been destroyed are packed for a time in snow. From the standpoint of human physiology these results seem strange, but from that of comparative physiology they are readily understood. The various reactions of plants to external stimuli are just as pur- poseful as those of animals. Why should it not be possible, then, for single organs and tissues of higher animals to react purposefully to external stimuli, and is there any reason why the purposeful character of a reaction should be dependent upon the structure of the central nervous system ? We have been able to rid ourselves of erroneous views concerning the significance of the ganglia of the central nervous system in higher animals through the help of the Ascidians ; they also help us further to determine the true role of the nervous system. Al- though the dogs experimented upon by Goltz and Ewald were able to adapt the width of their blood- vessels to the variations of temperature, it was neces- sary to shield them much more carefully from sudden changes of temperature than is necessary in the case of normal animals. The threshold of stimulation was raised and probably the rapidity of the conduction decreased. For this reason, dogs whose spinal cord is destroyed are no longer fit to live out-of-doors. As regards regulation of temperature, they are like an intoxicated person, and would perish in the cold EXPERIMENTS ON ASCIDIANS 45 much sooner than a normal animal. Hence the nervous system does not contain any regulating me- chanisms, but it serves as a quicker conductor, and allows the peripheral organs to work with greater precision. 4. Bethe has recently made a difficult experiment on Carcinus mcBuas, which, however, was successful in only two cases. If this experiment is correct, it proves that, in the conduction of a reflex in the cent- ral nervous system, the process of conduction does not of necessity pass through the ganglion-cell itself (5). An anatomical observation caused Bethe to perforni this operation. ** Almost all the ganglion- cells of Carcinus are unipolar, and often the axis-cyl- inder of the cell runs for a long distance before it gives off the first dendrites and sends out the peri- pheral fibre. It seemed very strange to me that a stimulus entering through the sensory nerves into the central organ should go through the dendrites to the far-distant motor-ganglion cells, and travel the great part of the same path before entering the peripheral motor fibre, instead of going directly to the motor fibre. It was easy to decide this question by sep- arating the ganglion-cells with their axis-cylinder process from the motor neurons without injuring the neuropiles. If the ganglion-cell were absolutely es- sential for the reflex, the muscles involved should become paralysed immediately after the operation ; if it were not essential, no paralysis should occur, at least for some time, and the stimulus could go across k 46 COMPARATIVE PHYSIOLOGY OF THE BRAIN directly from the dendrites to the peripheral fibre." It was possible to perform the operation in Carcinus on the ganglion-cells which innervate the muscles of the second antenna. The cutting of the peripheral nerves {Antennarius secundus) that go to these gan- glion-cells immediately causes a complete paralysis of the antennae, a proof that the fibres of these nerves are the only conductors of the stimulus which can call forth a reflex movement of these antennae. But when Bethe removed the ganglion-cells, without in- juring the neuropile of the second antenna, ''the second antenna retained its tonus and its reflex irrit- ability. It does not hang down limp, but remains stiff and in the normal position. When stimulated, it is withdrawn, but is stretched out again when the stimulation ceases. From this it is evident that the ganglion-cells are not necessary for reflexes. The re- flex arc either does not pass through the ganglion- cells or does not need to pass through them. It is further apparent that the ganglion-cell has nothing to do with the tonus of the muscles, and that the per- manent influence which the central nervous system exercises upon the tension of the muscles is not pro- duced in the ganglion-cells (6)." This experiment, even if it be correct, adds no- thing of importance to our conclusions. If the reflex arc acts only as a quick protoplasmic conductor, the question whether the stimulus has to pass through the ganglion itself or not becomes of secondary import- ance. EXPERIMENTS ON ASCIDIANS 47 Bibliography. 1. LoEB, J. Untersuchungen zur physiologischen Morphologie der Thiere. II. Wiirzburg, 1892, S. 37. 2. ScHAPER, A. Experimentelle Studien an Amphibienlarven. Archiv fiir Entwicklungsmechanik^ Bd. vi., 1898. 3. Steinach, E. Untersuchungen zur vergleichenden Physiolo- gie der Iris, Pfluger's Archiv, Bd. lii., 1892. 4. GoLTZ und Ewald. Der Hund mit verkUrztem RUcken- mark. Pflilgers Arch.^ Bd. Ixiii., 1896. 5. Bethe, a. Das Centralnervensystem von Carcinus manas. I. Theil, II. Mittheilung. Archiv f. mikroskop. Anatomie und EntwicklungsgeschichtCy Bd. 1., 1897. 6. Bethe, A. Das Centralnervensystem von Carcinus mcenas. II. Theil. Arch. f. mikroskop. Anatomie und Entwicklungs- geschichte, Bd. li., 1898. CHAPTER IV EXPERIMENTS ON ACTINIANS I. The two preceding chapters have furnished proof of the fact that the phenomena of purposeful reflex action, of spontaneity, and of coordination are determined, not by specific characters of the ganghon- cells, but by general peculiarities common to all pro- toplasm. These peculiarities are irritability and the power of conducting stimuli, both of which will find their explanation in the physics of colloidal sub- stances. In this chapter we wish to put the foregoing con- clusions to a test by showing that a group of animals without any true central nervous system are able to show reactions complex as those in higher animals. Without such a parallel we should be more than ready, in the case of higher animals, to attribute such reactions to the specific structure of the ganglia or the ganglion-cells. We cannot speak of a central nervous system in Actinians in the same sense as in Ascidians. Under the ectoderm there are elements which are interpreted by some authors as ganglion-cells and nerve-fibres. 48 EXPERIMENTS ON ACTINIANS 49 The unreliability of this interpretation is apparent, however, from the fact that Claus considers it uncer- tain. He mentions the possibility of a conduction of stimuli as one of the conditions that speak for the ex- istence of a nervous system in Actinians. But a con- FiG. 10. The Ability of the Actinians to Discriminate. The tentacles press the meat a into the mouth, while they drop the water-soaked paper b. duction of stimuli also occurs in plants. During the year 1888 in Kiel, and 1889-90 in Naples, I made in- vestigations on the reactions of Actinians, which show how little reason we have for concluding that compli- cated reactions need depend upon similarly compli- cated reflex centres (i). It is very obvious from these experiments that the structure and irritability of the peripheral organs determine the reactions. We will begin with the description of experiments on the Ac- tmia equina {mesembryanthemurn) of the East Sea. 50 COMPARATIVE PHYSIOLOGY OF THE BRAIN If a wad of paper soaked In sea-water be placed on the mouth of one of these Actinians it Is refused, while a piece of crab-meat, which to us does not differ in taste from the wad of paper, is usually accepted with- out delay. I tied one end of a short thread around a Fig. II. Continuation of the Experiment in Fig. id. paper wad and the other end around a piece of meat, and threw both on the outstretched tentacles of a starved Actinian. The tentacles that came in contact with the meat {a, Fig. lo) reacted at once by bend- ing in such a way as to bring the meat to the mouth, while the tentacles that were in contact with the pa- per did not react. I withdrew the thread and placed it on the oral disc in such a way that the paper rested on the tentacles where the meat had rested before, and vice versa. The meat was then drawn into the mouth and the string with It, but the paper remained outside the oral opening (Fig. 1 1). During the next twenty-four hours no change took place ; later on, the thread was ejected without the meat. The latter was EXPERIMENTS ON ACTINIANS 51 probably digested. I have often repeated the experi- ment, always obtaining the same result, except that occasionally the string was ejected sooner, in which case the meat remained on the string, partially or en- tirely undigested. These phenomena have the same explanation as the behaviour of insect-eating plants. The chemical substances diffusing from the meat, to- gether with the tactile stimuli exerted by it, cause a bending of the tentacles that are touched in such a way that they become concave and carry the meat to- ward the oral opening. The contact of the meat with the mouth causes the sphincter of the oral open- ing to relax ; the pressure of the tentacles, together with the activity of the oral disc, then pushes the meat into the interior of the digestive tract. But if these specific chemical stimuli are wanting, if we give the animal, for instance, water-soaked filter-paper, the contractions of those muscles which carry the tenta- cles to the mouth are not produced. The tentacles remain relaxed or relax still more under the stimulus, and this fact, together with the ciliary movement, causes the paper wad to fall off. 2. It is said that the nerve-elements are much more numerous in the vicinity of the mouth than in any other part of the animal. One might think that this con- centration of nerve-elements determined the reflex mechanism for these reactions. For this reason, I have made use of results obtained while carrying on investigations concerning heteromorphosis. I had found that in an Actinian of the Mediterranean, 52 COMPARATIVE PHYSIOLOGY OF THE BRAIN Cerianthus membranaceus, new tentacles could be pro- duced by a lateral incision in the body of the animal. But in some of these cases no mouth is formed. Fig. 12 shows such an ani- mal ; a is the normal, b the new head. If the incision was very small, only single tentacles were formed, without the oral disc. These new tentacles behave toward food exactly like the tentacles of the old mouth. If we offer such a new head a piece of meat, the tent- acles seize and press it against the centre of the oral disc, where the mouth should be. After pressing in vain for some min- utes the tentacles relax and the meat falls off. This experiment could be repeated for months, in fact as long as I observed the animal (2). In other cases the second head was so near the old one that it was easy to stimulate the tentacles of both simultaneously with the same piece of meat In this case a fight arose between the two tentacle systems, each attempting to draw the meat toward its own oral disc. Parker has lately shown that even a single tentacle, after being severed from the animal, grasps a piece of meat and Fig. 12. AcTiNiAN (Cerianthus) with A Normal Head {a) and an Arti- ficially Produced Head {b). Although the latter has no oral opening the ten- tacles carry the meat to the place where the mouth ought to be. EXPERIMENTS ON ACTINIANS 53 bends with it toward the place where, in relation to itself, the mouth ought to be (3). If we look at these facts without prejudice, we must conclude that the reaction of the tentacles is determined only by the irritability of the tentacle- elements themselves, and by the arrangement of their contractile elements. The following observations may also be considered in support of this conclusion. 3. If an Actinia equina be divided transversely, the oral piece, which we will call the head-piece, has the normal head, with mouth and tentacles on its oral end ; on its aboral end the body-cavity is open to the exterior, and food may pass through the opening in either direction. The old mouth of a head-piece was as particular as usual in regard to the selection of its food, while the aboral end readily swallowed pieces of paper. The old mouth often refused meat, but the aboral mouth was almost always ready to accept it,' even when it would refuse paper. I I laid a piece of an Actinian that took food in at both ends on its side, and tried to find out whether both mouths would take food simultaneously. I first placed a piece of meat on the aboral mouth, in order to cause it to open. As soon as this happened and the meat was being taken into the mouth I offered the oral mouth also a piece, and this was likewise accepted. The act of swallowing in the other mouth was interrupted at once by the contraction of the ring- muscles. After a few moments, however, when the meat in the oral mouth had been swallowed, the 54 COMPARATIVE PHYSIOLOGY OF THE BRAIN muscles of the aboral end relaxed and the meat taken in before by this mouth fell out. When I fed the mouths in succession, the mouth that was fed first ejected the food as soon as the other began to eat. It is obvious from this that a peristaltic wave is started from the end which takes up food. Thus far we have considered only the head-piece. If we turn our attention now to the foot-piece, we find that on the oral end a new oral disc with tentacles soon begins to form. Before this has occurred, how- ever, the mouth takes pieces of meat and swallows them. It seemed to me as though this new mouth, even before the regeneration of the oral disc, re- sembled the normal mouth more than the aboral mouth in the head-piece, for it did not accept paper wads and grains of sand, while It swallowed meat well. 4. In the foot of the Actinians the contact-irrita- bility is of special interest. The foot of a normal Actinia equina attaches itself to the surface of solid bodies. The character of the surface is of great im- portance for producing these processes of attachment. If it finds no other body, the Actinian attaches itself to the glass of the aquarium, and glides about on it. If, however, the shell of a Mytilus is placed in the aquarium and the animal comes in contact with it while moving about, it immediately attaches itself to the shell, and remains there, whether the shell is empty or inhabited. The surface of an ulva leaf has the same effect. While the animal upon contact with I J S-5 •«l H "o P^ '^ s ^ Z ^ Is 6 '^ ^ ^•s * c^ » « ««« -^ '?? H T3 O ffi 11 W 2"H S^ H %% ll s H . ^ <; « 73 '^ CM Z i Q H .S"5 U ■< Z •S u u ^ (1^ oi ^ t; ss o P^-5 -< 5 > eo «^ ^ o ^ K > ^ H 1^ Irt^ B a t> V V ll< ■< ?l^ pti «3 U ube sho the bot rientatic 1^ Z7zy.^ Fig. 19. Geotropic Reaction of Cucumaria Cucumis. The animals are in a battery jar (a, ^, f , er Hund mit verkiirztem Riicken- mark. Pflilger's Arch,, Bd. Ixiii., 1896. 6. Gaule, J. Der Einfluss des Trigeminus auf die Hornhaut. Physiologisches Centralblatt, Bd. v., 1891. 7. Gaule, J. Wie beherrscht der Trigeminus die Erndhrung der Hornhaut. Physiologisches Centralblatt, Bd. vi., 1892. 8. RiBBERT, H. Ueber Transplantation von Ovarium, Hoden und Mamma. Arch. f. Entwickelungsmechanik, vol. vii., 1898. CHAPTER XV THE DISTRIBUTION OF ASSOCIATIVE MEMORY IN THE ANIMAL KINGDOM I. The most important problem in the physiology of the central nervous system is the analysis of the mechanisms which give rise to the so-called psychic phenomena. The latter appear, invariably, as a func- tion of an elementary process, namely, the activity of the associative memory. By associative memory I mean the two following peculiarities of our central nervous system : First, that processes which occur there leave an impression or trace by which they can be reproduced even under different circumstances than those under which they originated. This pecu- liarity can be imitated by machines like the phono- graph. Of course, we have no right to assume that the traces of processes in the central nervous system are analogous to those in the phonograph. The sec- ond peculiarity is, that two processes which occur simultaneously or in quick succession will leave traces which fuse together, so that if later one of the pro- cesses is repeated, the other will necessarily be re- peated also. The odour of a rose will at the same 213 214 COMPARATIVE PHYSIOLOGY OF THE BRAIN time reproduce its visual image in our memory, or, even more than that, it will reproduce the recollection of scenes or persons who were present when the same odour made its first strong impression on us. By associative memory we mean, therefore, that mechan- ism by means of which a stimulus produces not only the effects which correspond to its nature and the specific structure of the stimulated organ, but which produces, in addition, such effects of other causes as at some former time may have attacked the organism almost or quite simultaneously with the given stimu- lus (2). The chief problem of the physiology of the brain is, then, evidently this : What is the physical character of the mechanism of associative memory ? As we said in the first chapter, the answer to this question will probably be found in the field of physi- cal chemistry. I think it can be shown that what the metaphys- ician calls consciousness are phenomena determined by the mechanism of associative memory. Mach has pointed out that the consciousness of self or the ego is simply a phrase for the fact that certain constitu- ents of memory are constantly or more frequently produced than others (i, 11). The complex of these elements of memory is the " ego " or the ** soul," or the personality of the metaphysicians. To a cer- tain extent we are able to enumerate these con- stituents. They are the visual image of the body so far as it lies in the field of vision, certain sensations of touch which are repeated very frequently, the DISTRIBUTION OF MEMORY 215 sound of our own voice, certain interests and cares, a certain feeling of comfort or discomfort according to temperament or state of health, etc. (i, 11). An inventory of all the memory-constituents of the ego-complex of different persons would show that the consciousness of self is not a definite unit, but, as Mach maintains, merely an artificial separation of those constituents of memory which occur most fre- quently in our perceptions. These will necessarily be subject to considerable variation in the same per- son in the different periods of life. If we speak of loss or an interruption of conscious- ness, we mean a loss or an interruption of the activity of associative memory. If a faint is caused directly by lack of oxygen or indirectly by a disturbance in the circulatory system, the activity of associative memory ceases. This was proved by Speck's experiments on the effects of a low pressure of oxygen. When he breathed air with less than eight per cent, of oxygen, he soon fainted. In these experiments, he had to count the number of respirations. Before he fainted, he became confused in his counting and forgot what happened. When this disturbance in counting began to appear, he knew it was time to discontinue the ex- periment. When a loss of consciousness is produced by narcotics or anaesthetics, we have again to deal with an interruption in the activity of the associative memory. It is the same in the case of a deep sleep. The metaphysician speaks of conscious sensations and conscious will. That the will is only a function 2i6 COMPARATIVE PHYSIOLOGY OF THE BRAIN of the mechanism of the associative memory can be proved. We speak of conscious volition if an idea of the resulting final complex of sensations is present before the movements causing it have taken place or have ceased. In volition three processes occur. The one is an innervation of some kind which may be caused directly or indirectly by an external stimulus. This process of innervation produces two kinds of effects. The one effect is the activity of the associa- tive memory which produces the sensations that in former cases accompanied or followed the same inner- vation. The second effect is a coordinated muscular activity. It happens that in such cases the reaction- time for the memory-effect of the innervation is shorter than the time for the muscular effect. When some internal process causes us to open the window, the activity of the associative memory produces the idea of sensations which will follow or accompany the opening of the window sooner than the act of opening really occurs. As we do not realise this any more than we realise the inverted character of the retina-image, we consider the memory-effect of the innervation as the cause of the muscular effect. The common cause of both effects, the innervating pro- cess, escapes our immediate observation as our senses do not perceive it. The will of the metaphysicians is then clearly the outcome of an illusion due to the necessary incompleteness of self-observation. Our conception of will harmonises with Miinsterberg's and James's views on this subject (6, 12). I think DISTRIBUTION OF MEMORY 217 that we are justified in substituting the term activity of associative memory for the phrase consciousness used by the metaphysicians. 2. We have spoken of associative memory because the word memory is often appHed in quite a different sense scientifically, namely, to signify any after-effect of external circumstances. For instance, the term memory has been used to account for the fact that a plant which had been cultivated in the tropics will often not endure low temperatures so well as a plant of the same species which was raised in the north. It is true in this case that preceding conditions influence the ability of the plant to react, but the process differs from the one which we have called associative memory in the lack of associative processes. No definite stim- ulus produces in a plant, in addition to its own effects, those of another entirely different stimulus which at some former time occurred simultaneously with the given stimulus. It is probable that the tropical plant is somewhat different chemically from the plant raised in the north. This would account for its smaller power of resistance. Further illustrations of a differ- ent use of the word memory can easily be given. Many moths sleep during the day and wake in the evening when it becomes dark. If kept for days in a dark room, they will continue at first to do the same thing. The same is true of certain plants. One might also say in this case that the moth or the plant " remembers " the difference between day and night. It is probable, however, that internal changes take 2i8 COMPARATIVE PHYSIOLOGY OF THE BRAIN place in the organism, corresponding to the periodic change of day and night, and that these changes con- tinue for a time in the same periodicity, when the ani- mal is kept in the dark. 3. We will then consider the extent of associative memory in the animal kingdom instead of the extent of consciousness among animals. How can we deter- mine whether an animal possesses the mechanism necessary for associative memory ? The criteria for the existence of associative memory must form the basis of a future comparative psychology. It will require more observations than we have made at present to give absolutely unequivocal criteria. For the present, we can say that if an animal can learn, that is, if it can be trained to react in a desired way upon certain stimuli (signs), it must possess associative memory. The only fault with this criterion lies in the fact that an animal may be able to remember (and to associate) and yet may not yield to our attempts to train it. In this case other experiments must be substituted which will prove that the animal does associate or remember. We may conclude that associative memory is pre- sent when an animal responds upon hearing its name called, or when it can be trained upon hearing a certain sound to go to the place where it is usually fed. The optical stimulus of the place where the food is to be found and the sensations of hunger and satiety are not qualitatively the same, but they occur simultaneously in the animal. The fusion or growing together of heterogeneous but by chance simultaneous k DISTRIBUTION OF MEMORY 219 processes is a sure criterion for the existence of as- sociative memory (2). Associative memory probably exists in most mam- mals. The dog which comes when its name is called, which runs away from the whip, which welcomes its master joyfully, has associative memory. In birds, it is likewise present. The parrot learns to talk ; the dove finds its way home. In lower Vertebrates, mem- ory is also occasionally found. Tree-frogs, for ex- ample, can be trained, upon hearing a sound, to go to a certain place for food. In other frogs, Rana escu- lenta, for instance, no reaction is as yet known which proves the existence of associative memory. Some fishes evidently possess memory ; in sharks, however, its existence is doubtful. With regard to the Inver- tebrates, the question is difificult to determine. The statements of enthusiasts who discover consciousness and resemblance to man on every side should not be too readily accepted. 4. In my experiments on the tropismsof animals, it became clear to me how easy it is for an observer who is inclined to think anthropomorphically to re- gard machine-like effects of external stimuli on lower animals as the expression of intelligence. He needs only to neglect the analysis of the external stimuli. I have protested against the anthropomorphisms of Romanes, Eimer, Preyer, and others in a series of ar- ticles (2, 3). Bethe has recently published a paper on the psychic qualities of ants and bees in which he took special pains not to fall into the gross anthropo- 220 COMPARATIVE PHYSIOLOGY OF THE BRAIN morphisms which have characterised this field here- tofore (4). But I am afraid that he went too far and that he overlooked the fact that bees and ants possess associative memory. Bethe assumes associa- tive memory as the criterion for the existence of con- sciousness, as I had done before. (He has evidently overlooked, or at least does not mention, my work on this subject.) According to him: '* An animal that is able to do the same things the first day of its exist- ence which it can do at the end of its life, that learns nothing, that always reacts in the same way upon the same stimulus, possesses no consciousness." This statement is not sufficient. It is possible that an ani- mal at birth, or just after hatching, may not be fully developed. In this case it may be able later to per- form actions which would have been impossible on the first day, without possessing associative mem- ory. Yet according to Bethe's definition such actions would indicate associative memory. It is a well-known fact that if an ant be removed from a nest and afterwards put back it will not be attacked, while almost invariably an ant belonging to another nest will be attacked. It has been customary to use the words memory, enmity, friendship, in de- scribing this fact. Now Bethe made the following experiment. An ant was placed in the liquids (blood and lymph) squeezed out from the bodies of nest companions and was then put back into its nest ; it was not attacked. It was then put in the juice taken from the inmates of a *' hostile " nest and was at once I DISTRIB UTION OF MEM OR Y 221 attacked and killed. Hence chemical stimuli of certain volatile substances will excite the ants. In this case we do not need to assume intelligence any more than we do in the case of the tentacles of Ac- tinians which, as we have seen, will immediately carry a piece of filter paper soaked in meat-juice to the mouth while they ignore a piece of paper soaked in sea-water. The assumption of machine-like irritable structures is quite sufficient here to explain the reaction. Mem- ory is quite unnecessary. Possibly the behaviour of the ant may be explained in the same way. Bethe was able to prove by special experiments that these reactions of ants are not learned by experience, but 'are inherited. The "knowing "of *' friend and foe " among ants is thus reduced to different reactions, depending upon the nature of the chemical stimulus and in no way depending upon memory. Memory and intellect are supposed to be responsible for the fact that an ant is able to find its way back to the nest and that when " foragers " have discovered honey or sugar the other ants of the nest soon go to it in great numbers. The ability to communicate in- formation was assumed in this case. Bethe, however, was able to determine by means of ingenious experi- ments that an ant, when taking a new direction from the nest for the first time, always returns by the same path. This shows that some trace must be left be- hind which serves as a guide back to the nest. If the ant returning by this path bear no spoils, Bethe found that no other ants try this direction. But if it 222 COMPARATIVE PHYSIOLOGY OF THE BRAIN bring back honey or sugar, other ants are sure to try the path. Hence something of the substances carried over this path by the ants must remain on the path. These substances must be strong enough to affect the ants chemically. I can prove by the following obser- vation, which must surely have been made before me by many breeders of butterflies, that Bethe is justified in the assumption that insects are affected by ex- tremely weak chemical stimuli. I placed a female butterfly of a certain species in a cigar-box, and closed the box. The box was then suspended half way be- tween the ceiling and floor of the room and then the window was opened. At first no butterfly of this species was visible far or near. I n less than half an hour a male butterfly of the same species appeared on the street. When it reached the height of the window, its flight was retarded and it came gradually toward the window. It flew into the room and soon up to the cigar-box, upon which it perched. During the afternoon, two other males of the same species came to the box. Thus we see that butterflies and certainly many other insects possess a delicacy of chemical irritability which, if possible, is finer than that of the best blood-hound. Plateau maintains that insects are attracted to the flowers by the odour rather than by the colour and marking. The dioptric apparatus of insects is very inferior to that of the human eye, while their chemical irritability is much superior to that of our olfactory epithelium. I believe that both odour and colour may influence insects. DISTRIBUTION OF MEMORY 223 One of the most remarkable conclusions of Bethe is the assumption that the roads of the ants have two paths which differ chemically from each other, one leading from and one toward the nest. Bethe tried to prove this by experiments that had been undertaken before by Lubbock, who obtained no definite results. Bethe arranged a broad ant-street so that it led over a turn-bridge. He revolved this bridge 180°, when the ants were passing to and from the nest, and found that it was impossible for the two armies to continue on their way. He again turned the bridge 180° so that the tracks had the original orientation. The ants continued in the direction they were pursuing when disturbed. An observation made by Forel also agrees with this : " An ant that is picked up from the path while moving and then put down again is al- most sure to take the same direction, no matter what orientation is given to its body." This, however, only holds good for a street which is often travelled. A weak track which leads in one direction is qualified to lead in the opposite direction, as is shown by the fact that an ant which has found a new supply returns to the nest the same way that it came. It is evidently the load and lack of load which determine which path the ant will take (that is, to or from the nest). The load causes the ant to go to the nest reflexly ; the lack of a load causes it to go from the nest. Bethe comes to the conclusion that the reactions of ants, which have always been considered psychic phenomena, are merely reflex processes comparable to the tropisms. 224 COMPARATIVE PHYSIOLOGY OF THE BRAIN 5. Although I heartily sympathise with Bethe's re- action against the anthropomorphic conception of animal instincts, I yet believe that he is mistaken in denying the existence of associative memory in ants or bees. The fact that bees find their way home through the air cannot depend upon any trace left in their path. It can only depend upon memory and, as I believe, upon visual memory. If the bee-hive be removed while the bees have swarmed out, they will return to and gather at the spot where the entrance to the hive used to be. Bethe is not willing to admit that this indicates the existence of a visual image of memory of the locality of the nest, professing to con- sider it possible that unknown forces guide the bee reflexly. I have recently had a chance to observe the activity of solitary wasps and have come to the conclusion that these animals are guided back to their nest by their memory. My observations were made on Ammophila, a spe- cies of wasps, whose habits have been carefully stud- ied and described by Mr. and Mrs. Peckham (7). Ammophila makes a small hole in the ground and then goes out to hunt for a caterpillar, which, when found, it paralyses by one or several stings. The wasp carries the caterpillar back to the nest, puts it into the hole, and covers it with sand. Before this is done. It deposits its ^g-i62, 204, 205, 231, 264 Amnesia, 277-287 Amphipyra, 184 Annelids, 82-100 Anterior roots, 113, 135 Ants, 195, 220-224 Apathy, 137 Aphasia. See Amnesia. Arbacia, 203 Arnold, 39 Arthropods, 101-127 Ascidians, 35-47 — heart of, 28-30 Association, 9 — corpuscular theory of, 277 — distribution of, 213, etc. — disturbances of, 277, etc. — dynamical theory of, 278, etc., 294 — relation to cerebral hemispheres, 236, etc., 262, etc. — relation to consciousness, 12-14, 214, etc., 236, etc. — relation to instincts, 196 Associative memory. See Associa- tion. Astacus, See Crayfish. Asterina, 69, 70 Auditory nerve, 134, 152, 155, 158, 172 Aurelia aurita, 17 Automatic processes, 9, 10, 16-30, 106, etc. Balanus perforatus, 192 Baumann, 207 Bawden, 258 Bed-sores, 209 Bee, 122, 123, 224, 227, 230 Bell, 136 Bethe, 45-49, "4-127, 131, I55, I59. 219-224, 226, 235 Bickel, 149 Blasius, 164 Blood-vessels, 43, 44, 274 Brown-Sequard, 39 Briicke, 294 Budge, 39 Burrowing of worms, 91, 96 Buttel-Reepen, v., 227, 235 Butterflies, 182, 222 — larvae of, 188 Carcinus maenas, 45, 119 Centres, in spinal cord, 134-149, 273 — in cerebral hemispheres, 259-276. See also Localisation. Cephalopods, 129 Cerebellum, 1 71-176 Cerebral hemispheres, extirpation of, in frog, 236 ; in sharks, 236 ; in birds, 238-244 ; in dogs, 246- 248, 262-276 segmental theory of, 260, etc. relation of, to reflexes, 259 Cerianthus, 52, 56-59 Changes in character after injury of the brain in worms, 92-97 ; in Crustaceans, 116 ; in Mollusks, 130 ; in frogs, 139 ; in dogs, 173 Character. See Changes of Char- acter. Chemical irritability in Actinians, 50 ; in earthworms, 88, 90 ; in crusta- ceans, iiS. See also Chemo- tropism. 305 3o6 INDEX Chemical theory of electrotonus, i6i ; of instincts, 177-199 : of heredity, 201 -212 ; of mental diseases, 207 ; of sensations, 291-294 Chemotropism, 88-90, 186-188 Christiani, 243 Chun, 193 Ciona, 35-38 Circles of touch, 211 Circus-movements. See Forced Move- ments. Claus, 49 Colour-sensations, 291 Compensatory motions, 143 Consciousness. See Associations. Contact irritability, 54. See also Stereotropism. Coordination, 10 — in dog, 86, 87, 174 — in earthworm, 84-86 — in frog, 139-143 — in Medusa, 23-27, 29-33 — of heart-beat, 25-30 — of respiratory motions, 107 — relation to cerebellum, 173 — relation to memory, 2 16 Cranial nerves, 135 Crayfish, 114, 162 Crura cerebelli, 168, 171 Cucumaria, 66 Cyon, v., 135, 274, 276 Darwinian views, 232, 253 Depth-distribution of marine animals, 69, 190 — migration of marine animals, 190- , 593 Deviation conjuguie, 151 Discrimination-power of Actinians, 50 Dog, reflexes of, 86, 137 — localisation in cerebral hemis- pheres, 260-274 — removal of spinal cord of, 43 — without cerebral hemispheres, 246- 248 Dohrn, 134 Donaldson, 258 Double-headed Actinians, 52 — Planarians, 81, 82 Duval, 258 Duyne, van, 81, 82, 100 Dynamometer, experiments with, 294-298 Ear. See Auditory Nerve. Earthworm, 84-90 Echinoderms, 61 Education, 233 Eel, 142, 164, 248 Eimer, 219 Electrical stimulation, 160-170, 173, 264, 290, 291 Electrotonus, 162, etc. Eledone, 131 Engelmann, 137 Eudendrium, 179 Exner, 250, 258 Ewald. See Goltz and Ewald. Faivre, 104, 113, 125 Falcon, 245 Fechner, 296 Ferrier, 36, 173, 176 Fish, 141, 152-154, 175 Flechsig, 275 Flourens, 104, no, 116, 139, 149, 168, 170-176, 239, 264 Fly, larvae of, 186-188 Food, taking up of, after lesions of hemispheres, 245 Forced movements, 105, 119, 150- 159, 171 Forel, 233 Free will, 234 Friedlander, 85, 86, 88, lOO Fritsch, 265 Frog, spinal cord, 139-145 — cerebral hemispheres, 139 — clasping reflex, 238 — croaking reflex, 142, 238 Frontal lobes and intelligence, 275 Fundulus, 252 Gall, 277 Galvanotropism, 178 — of Amblystoma, 160-162 — of crayfish, 163 — of Palsemonetes, 164 — theory of, 161 Gammarus, 231 Ganglion, importance of, for reflexes, 4, 36, 46 ; for coordination, 5, 20-25, 106 Ganglion, trophical functions, 136 Garrey, 160, 231 Gaule, 210, 212 Geotropism, 120 — and depth-migration, 193 INDEX 307 Geotropism in Actinians, 57 — in Cucumaria, 66 — in Echinoderms, 61-71 — in insects, 66 Geppert, 108 Golgi, 136, 137 Goltz, 43, 86, 137, 142, 145.148, 149. 193, 2CX), 205, 208, 209, 237-239, 246, 257, 262-268, 275 — and Ewald, 41-44, 47, 145, 149, 195, 209, 212, 239 Gonionemus, 17, etc., 95 Graber, 99, 229 Grafting in Medusa. See Hargitt. Grasshopper, 121 Groom, 191, 199 Hargitt, 26, 27 Heliotropism, 183, 195 — in Asterina, 69 — in Eudendrium, 179 — in caterpillars, 188 — in marine animals, 190-193 — in moths, 181 — transformation of, 189, 192 Helmholtz, 242, 290 Hemiamblyopia, 271-273 Hemianopia, 151, 270-273 Heredity, 201-212 Hering, 158, 242, 290, 301, 303 Hermann, 231, 300, 303 Hertwig, 34 Heteromorphosis, 51, 203 Hitzig, 265-267, 275 Hunter, 42 Hyde, Ida, 102, 104, 126, 155 Hydromedusse, 16, 97 Hydrophilus, 119, 123 Image of memory, 270-272, 277 Inhibition, of progressive motions, 117, 155, 171 — of reflexes, 131, 237, 289-303 Innervation, its relation to space-sen- sation, 168, 300-303 ; to wave motion, 289-303 Instincts, general remarks, 6-8 — relation to nervous system, 194 — theory of, 177-199 Intelligence, in starfish, 65 — difference in man and animals, 254 Intelligence, differences in individu- als, 254 — disturbances after injury to brain, 262, 263, 277-287 — heredity of, 211 — localisation of. See Associations. Ions and rhythmical contraction, 9, 18-20 Iris, 39, 40 Jaeger, 203 James, W., 216, 235 Janet, 230 Jelly-fish. See Medusae. Lang, 99 Langendorff, no, 126 Lea, 292 Le Gallois, no Light, effect of, on Planarians, 79-81 ; on earthworm, 89. See also Heliotropism. Limulus, 102-113 Lingle, 28 Localisation, psychic and anatomical, 259-276 — in cerebral hemispheres, 134, 259, etc. — in spinal cord, 134-149 — of images of memory, 270-272^ 277 Localising reflex, 30-33 Locomotion, centre of, 140, 157 Locy, 134 Longet, 243 Lubbock, 223 Luciani, 174, 176 Lumbricus. See Earthworm. Lyon, 176 Mach, 214, 215, 235, 291, 300-303 Magendie, 171, 175, 176, 240, 264 Mass of brain, relation to intelligence, 254 Mathews, 208, 212 Maxwell, 87, 88, 92, 93, 96, 97, 100, 164, 167 Mayer, 197 McCaskill, 96 Mechanics of brain activity, 289, etc. Medulla oblongata, no, 139, 140- 143, 152-154, 171-176 Medusae, 16, 26, 95, 97 3o8 INDEX Memory. See Associations. Mental diseases, chemical theory of, 207 Meyer, 148, 149, 212 Mollusks, 128, etc. Moth, 177-183 Motor nerves in arthropods, 113 — regions of cerebral hemispheres, 259-273. 277 MtiUer, Johannes, 290 Munk, 269-272, 276 MUnsterberg, 216, 235 Muscular activity, a measure of men- tal activity, 294, etc. Nagel, 60, 228 Nereis, 83, 87, 90-98, 116 Neuron, 45, 161 Nceud vital. See Respiratory Centre. Norman, 65, 229-232, 235 Occipital lobes, 262, 269 Optic nerve, 150 Orientation and functions of elements, 160-170 Oxygen, importance of, for associa- tions, 215, 255, 256 Pain-sensations in animal, 229-231 Palaemonetes, 164, 178 Parker, 52, 60 Pars commissuralis, 139, 140 Patten, 105 Peckham, 224, 235 Pedal ganglia of Mollusks, 131 Pfluger, 248-251, 258 Phrenic nerve, 109 Phrenology, 277 Pigeons, without cerebral hemi- spheres, 239-244 — instincts of, 196 Planarians, 72, etc., 230 Plateau, 222 Pollock, 60 Polygordius, 193 Porter, 25, 26, 34, 112, 126 Porthesia, 188 Posterior roots, 113, 135 Preyer, 64, 70, 71, 219 Progressive motion. See Spontaneity. Psychic phenomena. See Association. — blindness, 269-272 — localisation, 259-276 Pterotrachea, 128 Purposefulness, 2, etc., 177, etc. Quincke, 22, 34 Reflexes, general remarks, 1-6 — coordinate character of. See Coor- dination. — special. See various groups of ani- mals. — without ganglion, 35-46 Respiration, in relation to ganglia, 107 — in frog, 143 — in higher animals, 109 Respiratory centre, 110-112, 143, 146 Responsibility, 234 Rhythmic, innervations, 294, etc, motion in general, 9 ; in Me- dusae, 18, etc. ; in heart, 23-30 ; in respiration. See Respiration. — theory of rhythm, 21 Ribbert, 195, 206, 212 Rieger, 279, 287 Righting motion of Actinians, 56-59 ; starfish, 61-65 ; Planarians, 74 ; arthropods, 124 Rolando, 239 Rolling motions. See Forced Move- ments. Romanes, 18, 24, 31, 34, 63, 71, 219 Rosenthal, 21 Sachs, 66, 203, 290 Salamander, 142, 160, 204 Schaper, 42, 47, 206, 212 Schrader, 139, 143, 149, 157, 236-241, 258 Schweizer, 164 Segmental theory of reflexes, general remarks, 82, 147, 148 ; of worms, 82, etc. ; of Arthropods, 117; of vertebrates, 133, 145 ; rela- tion to cerebral hemispheres, 259- 276 Self-preservation, instinct of, 183 Semicircular canals, 167, 168, 176 Semi-decussation, 150-159 Sensations, 290, etc. Sexual cells, bearers of hereditary properties, 201 — — influence of nervous system upon, 204-211 INDEX 309 Shark, 40, 232 Sherrington, 158 Shock-effect, 126, 147, 298 Sleep, 243, 257 Space-sensations, 168, 242, 301 Specific energy of nerves, 290, etc. Speck, 215, 255, 258 Spencer, 211 Sphincter ani, 41 Spinal cord, reflexes of, 137 soul, 250 Spinal nerves, 134 Spontaneity, 8 — relation to central nervous system in general, 78 — relation to cerebral hemispheres, 139, 157, 239-242 — relation to ganglia in Arthropods, 108 — relation to ganglia in Medusae, 18, 21 — relation to ganglia in Planarians, 74, etc., 77 — relation to ions. See Medusae. — relation to supraoesophageal gan- glion, 106, 116, 121, 123, 128 Squilla, 119, 121 Starfish, 61, etc. Steinach, 40, 47 Steiner, 127, 128, 133, 140, 149, 156- 159, 175, 182 Stereotropism, in Actinians, 59 — in Amphipyra, 184 — in Crustaceans, 119 — in earthworm, 88 — in eel, 248-250 — in Nereis, 92, 93, 185 — in starfish, 65 — in ThysanozoOn, 74 — in Tubularia, 184 Stinging reflex of bees, 123 Suboesophageal ganglion in annelids, 82 — in Astacus, 116, 120 — in bees, 123 — in Limulus, 106 — in Mollusks, 128 Supraoesophageal ganglion in Arthro- pods, 104, etc., 114 — in bees, 123 — in Mollusks, 128 — in worms, 90, 92 Temporal lobes, 262 Thalami optici, 139 Thorndike, 286, 288 Threshold of stimulation, 46 — after loss of ganglion, 37-39 Thyroid gland, 207 ThysanozoQn, 72, etc. Tiaropsis, 31 Tone of muscles, 152-159 — after injury to cerebral hemi- spheres, 266-269. after loss of supraoesophageal ganglion, 117, 124 — after severing of posterior roots, 135 — relation to galvanotropism, 160- 169 Tornier, 203 Trigeminus, 136, 209 Trophic nerves, 208-210 Tropisms, identity of animal and plant heliotropism, 5, 179 — importance of, for instincts, 6, etc., 178-200 — importance of, for psychology, 13, 221. etc., 249 — mechanics of, 161, 179-181, 186- 190 Tubularia, 184 Turtle, 30 UexkUll, v., 130, 133, 156 Vasomotors. See Blood-vessels. Veblen, 197 Visual spheres, 269-273 Vulpian, 113, 126, 175 Ward, 116 Wasmann, 226, 235, 287, 288 Wasps, 196, 224-227 Water-beetle, 123 Wave character of innervations, 29I 303 Welch, 303 Whitman, 99, 100, 286, 288 Will, 215, 302 Wolff, 279, 288 Worms, 72, etc., 229 Yersin, 122 Zuntz, 108 PUBLICATIONS OF G. P. PUTNAM'S ^ONS, EVOLUTION OF TO-DAY. A summary of the theory of evolution as held by modern scientists, and an account of the progress made through the investigations and dis- cussions of a quarter of a century. By H. W. Conn, Ph.D., Instructor of Biology in the Wesleyan University, Middletown, Conn. Octavo, cloth . . . $i 75 Contents. — Introduction — What is Evolution? — Are Species Mutable ? — Classitication of the Organic World — Life during the Geological Ages — Embryology — Geographical Distribution — Darwin's Explanation of Evolu- tion — More Recent Attempts to Explain Evolution — The Evolution of Man. "A volume which is at once learned, scientific, ardent, independent, and devout."— yi£7«r. of Education, Boston. " A complete success on the line marked out for it — that of judicial exposition." — Boston Literary World. " The general reader can gather therefrom a very good conception of the doctrines of animal evolution and the status of the development opinions among scientific men, and of the new problems connected therewith that are arising through expanded research." — J. W. Powell, in Science. " The best general introductory work that has yet appeared in any country on the subject." — Prof. E. D. Cope. *' The first work in which American contributors to the subject are cor- rectly represented, and in which they receive due attention. It cannot fail to stimulate research, especially in America." — American Nationalist, " This book becomes a sort of dictionary of evolution, and will be a necessity for any one who would understand the evolution of to-day." — Omaha Republican. " The utmost spirit of fairness pervades every page, showing that the writer has aimed at stating truths as they are, and not as he sees them. As a contribution to the subject of evolution, it is invaluable." — Chicago Advance. " There have heen so many volumes upon evolution that an ordinary reader may be inclined to overlook this of Professor Conn. We warn him, however, that in so doing he is sure to miss a rare contribution. It is just the thing to set a layman right, and is thoroughly judicial. It sets down the general trend of thinkers as to evolution and Darwinism, finding limits to both and marking their usefulness when properly employed." — Hartford Post. ' ' Dr. Conn evidently favors the theory, but he does not write as a parti- san or to carry a point, but simply to show what has been the result of the fruitful labors of the last twenty-five years. As a devout theist, he con- siders evolution simply a method of creation, and does not believe that this derogates from the glory of the Divine Architect." — N. Y. Observer. G. P. PUTNAM'S SONS, New York : London : 27 AND 29 West 230 St. 27 King William St., Strand. [over. THE SCIENCE SERIES Edited by J. McKeen Cattell, M.A., Ph.D., and F. E. Beddard, M.A., F.R.S. I.— The Study of Man. By Professor A. C. Haddon, M.A., D.Sc, M.R.I.A. Fully illustrated. 8°, $2.00. " A timely and useful volume. . . . The author wields a pleasing pen and knows how to make the subject attractive. . , . The work is calculated to spread among its readers an attraction to the science of anthropology. The author's observations are exceedingly genuine and his descriptions are vivid." — London Athenceum. 2. — The Groundwork of Science. A Study of Epistemology. By St. George Mivart, F.R.S. $1.75. " The book is cleverly written and is one of the best works of its kind ever put before the public. It will be interesting to all readers, and especially to those interested in the study of science." — New Haven Leader, 3. — Rivers of North America. A Reading Lesson for Students of Geo- graphy and Geology. By Israel C. Russell, Professor of Geology, University of Michigan, author of " Lakes of North America," " Gla- ciers of North America," " Volcanoes of North America," etc. Fully illustrated. 8°, $2.00. "There has not been in the last few years until the present book any authoritative, broad resume on the subject, modified and deepened as it has been by modern research and reflection, which is couched in language suitable for the multitude. . . . The text is as entertaining as it is instructive." — Boston Transcript. 4. — Earth Sculpture ; or, The Origin of Land-Forms. By James Geikie, LL.D., D.C.L., F.R.S., etc., Murchison Professor of Geology and Mineralogy in the University of Edinburgh ; author of '* The Great Ice Age," etc. Fully illustrated. 8°, $2.00. " This volume is the best popular and yet scientific treatment we know of of the ori- gin and development of land-forms, and we immediately adopted it as the best available text-book for a college course in physiography. . . . The book is full of life and vigor, and shows the sympathetic touch of a man deeply in love with nature." — Science. 5. — Volcanoes. By T. G. Bonney, F.R.S., University College, London. Fully illustrated. 8°, $2.00. " It is not only a fine piece of work from a scientific point of view, but it is uncom- monly attractive to the general reader, and is likely to have a larger sale than most books of its cl^ss.^'' —Springfield Republican. 6. — Bacteria : Especially as they are related to the economy of nature, to industrial processes, and to the public health. By George Newman, M.D., F.R.S. (Edin.), D.P.H. (Camb.), etc.. Demonstrator of Bac- teriology in King's College, London. With 24 micro-photographs of actual organisms and over 70 other illustrations. 8°, $2.00. " Dr. Newman's discussions of bacteria and disease, of immunity, of antitoxins, and of methods of disinfection, are illuminating, and are to be commended to all seeking in- formation on these points. Any discussion of bacteria will seem technical to the uniniti- ated, but all such will find in this book popular treatment and scientific accuracy happily combined."— The Dial. 7.— A Book of Whales. By F. E. Beddard, M.A., F.R.S. Illustrated. 8°, $2.00. " Mr. Beddard has done well to devote a whole volume to whales. They are worthy of the biographer who has now well grouped and described these creatures. The general reader will not find the volume too technical, nor has the author failed in his attempt to produce a book that shall be acceptable to the zodlogist and the naturalist."— A''. K. Times. 8. — Comparative Physiology of the Brain and Comparative Psy- chology. With special reference to the Invertebrates. By Jacques LoEB, M.D., Professor of Physiology in the University of Chicago. Illustrated. 8°, $1.75. *' No student of this most interesting phase of the problems of life can afford to remain in ignorance of the wide range of facts and the suggestive series of interpretations which Professor Loeb has brought together in this volume." — Joseph Jastrow, in the Ckicagv Dial. 9.— The Stars. By Professor Simon Newcomb, U.S.N., Nautical Al- manac Office, and Johns Hopkins University. 8°. Illustrated. Net, $2.00. (By mail, $2.20.) 10. — The Basis of Social Relations. A Study in Ethnic Psychology. By Daniel G. Brinton, A.M., M.D., LL.D., Sc.D., Late Professor of American Archaeology and Linguistics in the University of Pennsyl- vania ; Author of "History of Primitive Religions," "Races and Peoples," " The American Race," etc. Edited by Livingston Far- rand, Columbia University. 8°. (By mail, $ .) Net, $ The following volumes are in preparation : Meteors and Comets. By Professor C. A. Young, Princeton University. The Measurement of the Earth. By Professor C. T. Mendenhall, Worcester Polytechnic Institute, formerly Superintendent of the U. S. Coast and Geodetic Survey. Earthquakes. By Major C. E. Button, U.S.A. The History of Science. By C. S. Peirce. Recent Theories of Evolution. By J. Mark Baldwin, Princeton University. The Reproduction of Living Beings. By Professor Marcus Hartog, Queen's College, Cork. Man and the Higher Apes. By Dr. A. Keith, F.R.C.S. Heredity. By J. Arthur Thompson, School of Medicine, Edinburgh. Life Areas of North America: A Study in the Distribution of Animals and Plants. By Dr. C. Hart Merriam, Chief of the Biological Survey, U. S. Department of Agriculture. Age, Growth, Sex, and Death. By Professor Charles S. Minot, Harvard Medical School. History of Botany. By Professor A. H. Green. Planetary Motion. By G. W. Hill. Infection and Immunity. By George M. Sternberg, Surgeon-General, U.S.A. The Mental Functions of the Brain An Investigation into their Localisation and their Manifestation in Health and Disease. By Bernard Hollander, M.D. (Freiburg i.B.), M.R.C.S., L.R.C.P. (London.) Illustrated with the clinical records of eight hundred cases of localised brain derangements and with several plates. 8°. (By mail, $3.75.) Net, $3.50. •* A book which should be read by every Surgeon and Physician in America." — Boston Times. " This is a work of more than ordinary importance. The author's researches and results oblige him not only to combat popular opin- ions, but to criticise rather sharply some high medical authorities. The brain is, indeed, the organ of the mind, but the various functions of the mind have their separate centres of activity in the brain. In the localisation of these centres good progress has been made and is still to be made. The great pioneer in this line of discovery was Dr. Franz Joseph Gall, a century ago. His results were long discredited but are here presented for the first time as largely confirmed by other lines of research. The phenomena of various kinds of mania are ex- hibited by Dr. Hollander in their connection with local brain-lesions, and special memories for words, numbers, music, etc., are traced to their local centres in the brain. These and cognate discussions lead on to a strenuous rehabilitation of phrenology, long discredited through quackery, and, as Dr. Hollander contends, through medical Philistinism. The ability with which Dr. Hollander pleads the case is commensurate with his courage in stemming the current of adverse prejudice. While this work is of special interest to professional men, as lawyers and physicians, it is valuable to all who are interested in the phenomena of mind and the problems of education. — Outlook. G. P. PUTNAM'S SONS New York London f lO I 9^ THE LIBRARY UNIVERSITY OF CALIFORNIA San Francisco Medical Center THIS BOOK IS DUE ON THE LAST DATE STAMPED BELOW Books not returned on time are subject to fines according to the Library Lending Code. Books not in demand may be renewed if application is made before expiration of loan period. 14 DAY APR 12^5 RETUKisic.^ MAR 3 1 '-0D 30m-10,'61(C3941s4)4128 836j