century students of animal behavior again returned to the problem which dominated behaviorists of the early years of the seventeenth century, namely, the reduction of reactions to mechanical principles. Prominent among these students were Engelmann, Verworn, Loeb and Jennings.

The work of the last three investigators mentioned is in a general way very well known. That of Engelmann, however, seems to have been to a considerable extent overlooked, although it is among the very best that has ever been done in behavior. I should like to refer particularly to his investigations on Euglena, published in Pflüger's Archiv in 1882, several years before any of the others mentioned began work in this line.

Engelmann finally concluded, after years of searching observations on the relation between physico-chemical phenomena and the reactions in various unicellular forms, that while many of the reactions in these forms are purely mechanical some of them can not be explained without postulating psychic processes. This conclusion may be responsible for the fact that his work has not received the attention that it deserves.

Thus we see that one problem after another has dominated the work in behavior. Reduction of reactions to mechanical principles; distribution of pain and pleasure; the evolution of reactions and psychic phenomena; and again the reduction of reactions to mechanical principles. What has become of these problems? What are the fundamental problems in behavior to-day?

DISTRIBUTION OF PLEASURE AND PAIN

It has often been said that it is impossible to ascertain whether or not animals experience pleasure and pain and that it is consequently useless to attempt to ascertain the distribution of such phenomena in the animal kingdom. In a sense this is true but in this sense it is also true in reference to human beings. Subjective states can be ascertained with certainty by the investigator only as they exist in himself. He can not be certain that your pain is like his pain. All that he can do is

to note his actions, including language, during the process of subjective experience, compare these actions with those in other individuals and base his conclusions upon the relation between them.

Precisely the same method is open to him in regard to other organisms, although it is evident that comparison of actions becomes more and more difficult as the difference between the structure of the organisms involved increases. The problem as to the nature and extent of pain and pleasure (feeling or sensation) consequently becomes more and more difficult as one descends in the organic realm.

This problem can, however, not be avoided. The behavior of every individual depends to a large extent upon his conclusion regarding the nature and extent of feelings in the creatures with which he comes in contact. Human society demands a decision of some sort or another regarding the distribution of these phenomena. Witness the work of the anti-vivisection organizations, societies for the prevention of cruelty to animals and charitable institutions everywhere, all built upon and acting upon decisions regarding this matter. The problem then resolves itself into this. Shall we permit human conduct in reference to such an important matter to rest upon judgments based upon evidence casually gained or shall we demand that it rest upon judgments based upon the results obtained in a comprehensive comparative study of the reactions of organisms under experimentally controlled conditions?

Many anti-vivisectionists and members of other anti-organizations who shed copious tears over cats and dogs in our laboratories do not hesitate to sit all day and impale earthworms, crabs and minnows on hooks, and they do not object to the practise in certain tropical regions of turning turtles and cutting steaks from them for a week or more while alive. They assume, of course, that earthworms, crabs, fishes and turtles do not suffer. Are they correct in this assumption or was Brooks correct when, after a lifetime of intimate association with animate beings of all sorts he said: "I try to treat all living things,

plants as well animals, as if they may have some small part of a sensitive life like my own"? Or are those correct who maintain that sensations in all organisms below the upper stratum of human beings are insignificant?

This question can not, at present, be defiinitely answered and it may never be definitely answered but a comprehensive comparative study of the reactions of organisms bearing directly upon it will unquestionably make it possible to answer it more nearly correctly than can be done to-day.

The field in this line is open. Practically nothing of a thorough going nature has been done in it. Among the best of the works on the lower organisms is that of Norman presented some twenty years ago. Norman showed that the squirming reactions in earthworms to violent stimulation do not constitute conclusive evidence of pain, for the simple reason that when a worm is cut in two the posterior part squirms violently while the anterior part with the brain does not. Reactions in other organisms led him to conclude that there is no satisfactory evidence of pain in any of the invertebrates. But even this work, which, as stated, is among the best, is far from comprehensive and the conclusions are consequently only meagerly supported.

ORIGIN AND EVOLUTION OF REACTIONS AND PSYCHIC PHENOMENA

It has become the fashion among certain ultra-modern psychologists to solve the problem of consciousness by contending that it does not exist. This contention is no doubt largely verbal. The term consciousness is not very specifically defined. It is used loosely by many, and the controversy as to the existence of consciousness is rooted in this fact. What is denied by some is, as I understand it, the existence of an entity capable of action and experience independent of matter. Regarding this I have nothing to say.

Practically every one who is sane, even the modern psychologist, admits that he is aware; he admits that phenomena may have a subjective as well as an objective reference or exist

ence. Whatever else the term consciousness may imply it always implies awareness (subjective experience). As to the actuality of this phenomenon, we are, I believe, more certain than we are about anything else. The origin, the evolution and the nature of awareness, the processes associated with it and its relations to objective reality constitute, in my opinion, the most fundamental problems that confront the human mind, and all available methods of attack should be brought to bear upon them.

The introspection method has been extensively used in the investigation of some of the problems mentioned. This method is, at present, in disrepute and many have abandoned it altogether in favor of the so-called behaviormethod. I do not believe that the tendency to entirely abandon introspection is wholesome, although it is of but little importance in reference to the question before us, the origin and evolution of reactions and consciousness, awareness or subjective phenomena. In the investigation of these questions two methods are promising. One might be called the comparative behavior method, the other the method of genetics.

The method of comparative behavior has been and is still being extensively employed. It consists in the comparison under given conditions of reactions in various organisms including man. It is anthropomorphic in its tendencies and owing to this it has been severely criticized both justly and unjustly. This is doubtless due largely, if not entirely, to misapprehensions as to the import of the method.

The method of comparative behavior was used almost exclusively by Lubbock, Graber, Romanes, Darwin and others interested primarily in the evolution of psychic phenomena. These investigators tried to ascertain whether or not this or that animal sees, hears, smells, tastes and feels.

The results obtained led them, as previously stated, to conclude that various animals, besides man, have subjective sensation. And since it was generally assumed that human behavior is, at least to some extent, controlled by subjective states, it was thought that the be

havior of other animals is also thus controlled. This resulted in the anthropomorphic explanations of reactions current at the time. For example, it was maintained that organisms which are photo-positive go toward the light because they hate darkness or love light, that the moth flies toward the candle-flame to satisfy its curiosity, etc. These explanations have justly been severely criticized, and yet the method is not necessarily at fault.

If human conduct is dependent upon subjective states, and if other animals have such states, is it not altogether probable that their reactions are also dependent upon subjective states? If this is true it is possible to explain in a certain sense reactions in animals on the basis of psychic phenomena. It is maintained, however, that this is putting the cart before the horse, that it consists in attempting to explain the unknown in terms of something still more unknown. With this contention I do not agree, for I hold that every individual knows his subjective sensations better than anything else. The question, then, resolves itself primarily into this. Does conduct depend upon subjective sensations? If it does then it is evident that in the study of behavior it is of the greatest importance to ascertain the distribution of such sensations. But whether conduct is dependent upon subjective phenomena or not, knowledge regarding the distribution of such phenomena is fundamental; for it seems to be the only knowledge that bears upon the problems of the origin and evolution of consciousness.

We judge as to the presence and nature of such phenomena in others almost wholly by comparing their behavior with ours. We know that conscious states in ourselves are accompanied by certain reactions and when we see these reactions in others we conclude that their subjective experience is the same as ours, and by comparing the conclusions thus reached regarding subjective experience throughout the animate kingdom, we formulate conclusions as to the origin and evolution of these phenomena. I realize full well that conclusions based upon such evidence are precarious, but this method is the only method available

in the investigations of subjective states in others, and precarious as the conclusions may be they are far more likely to be correct than those formulated without such investigations. We must consequently either abandon this profound problem altogether or proceed along the line indicated.

Aside from its bearing on consciousness the method of comparative behavior has an important bearing on the problems concerning the evolution of reactions themselves and their interrelation, their sequence. In its bearing on this problem comparative behavior is similar to comparative morphology. As comparative morphology yields results concerning the relation between structures in different organisms, so comparative behavior yields results concerning the relation between reactions. It is not primarily concerned in the relation between the environment and the reactions. primary interest lies in the relation between the reactions themselves as manifested in various organisms.

Its

In regard to the evolution of reactions, the comparative method in behavior must, however, give way to genetics just as the comparative method in morphology has. In this field we have as yet scarcely made a beginning. It is a virgin field of great promise. I should like to refer to Yerkes's work on mice and McEwen's on Drosophila.

I have pointed out a number of important problems which are dependent for their solution upon the relations between reactions and not primarily, if at all, upon the nature or the mechanics of the reactions. There are many other problems which can be greatly illuminated by a study of such relations. I shall refer to but one of these, modifiability in behavior including habit formation and learning in general.

Much of the recent work on the behavior of the higher animals centers about this problem, the work of Thorndike, Morgan, Yerkes, Watson, Carr and others. The results of this work have been of inestimable value, practical as well as theoretical, and yet it is based almost entirely upon the relation between reactions. Practically nothing is known regard

ing the mechanics of the reactions involved, and owing to their extreme complexity little is likely to be known for years to come. I should like to emphasize this point, for there are those who appear to hold that a study in behavior which does not deal with the reduction of reactions to physico-chemical principles has no practical value.

The study of modifiability in behavior should be much extended, especially in the investigation of the lower forms where it has as yet received but little attention, and closely associated with this is the problem of regulation, so clearly set forth by Jennings in the closing chapters of his book on the behavior of lower organisms.

Comparative behavior then, in spite of its anthropomorphic tendencies is valuable in certain lines of investigation, and I hope that what I have said may counteract the strong opposition that has developed against it. However, no matter what may be the immediate object of behaviorists, practically all of them desire to see reactions reduced, as far as possible, to mechanical principles. What has been accomplished in regard to this, and what are the prospects in reference to it?

THE MECHANICS OF REACTIONS

One of the foremost physiologists says in substance: Many reactions have already been reduced to physical and chemical or mechanical principles and all reactions together with all life-phenomena can be thus reduced. Another equally prominent physiologist says: "The attempt to analyze living organisms into physical and chemical mechanisms is probably the most colossal failure in the whole history of science."

How is it that the results obtained by two eminent and practical investigators in the same general field have led them to conclusions so diametrically opposed, the one maintaining that many vital phenomena have been and that all vital phenomena can be reduced to mechanics, the other apparently maintaining that no vital phenomena have been and that no vital phenomena can be thus reduced? The difference in these conclusions is in part, if not en

tirely, due to different conceptions as to what a reduction to mechanics involves.

Fundamentally all scientific knowledge is the same. It concerns the order of phenomena not the cause of the order. It is rooted in experience and founded upon the conviction that Nature is orderly, that a phenomenon that occurs under a given set of conditions will occur again whenever this set of conditions obtains. All of the scientific laws that have been formulated are merely expressions summarizing the results of experience, and their validity depends upon the extent of the experience. They are in no sense absolute; any and all of them may have to be modified as more experience is gained. To ascertain and to regulate the order of phenomena in nature is the purpose of science.

Mechanics deals with the relation between events or phenomena and changes in the configuration of material systems associated with such events. The reduction of behavior to mechanical principles consists in ascertaining the relation between reactions in animated systems and changes in material configurations within and outside of such systems. In other words, it consists in ascertaining the sequence in series of changes in material configurations ending in reactions. For example, suppose we have an alkaline medium containing paramecia and add a bit of acid, thus inducing avoiding reactions. The substance or material in the alkaline medium has a certain arrangement or configuration. When the acid is added this configuration is changed and this sets up changes in the material configuration within the paramecia which result in a response. That is, we have a series of changes in material configuration ending in a reaction, and similar series of changes precede all reactions.

Now, when the mechanist says that reactions have been reduced to mechanical principles, he probably means merely that some of the changes in material configuration in the series ending in reactions have been ascertained. And when the anti-mechanist says that the attempt to reduce reactions to mechanical principles has been a colossal failure,

he probably means merely that in no such series have all of the changes in material configuration been ascertained. If this is true then both views are doubtless corect; for it can not be disputed that some of the changes in material configuration in series ending in reactions have been discovered in numerous instances, and it can not be demonstrated that all such changes have been discovered in any instance.

Take for example, one of the very simplest, if not the simplest of all responses, changes in ameboid movement. It has been maintained that this reaction is due to changes in surface tension. Similar movements can be induced in inanimate systems. If a bit of potassium bichromate is brought near a drop of mercury in ten per cent. nitric acid the mercury will flow toward the bichromate. This is due to a local reduction in surface tension. This and numerous similar experiments, it is maintained, show that movements in Ameba are due to changes in surface tension. It has, however, recently been demonstrated that changes in surface tension can not produce the force required in certain ameboid reactions. Other factors have consequently been postulated to supply this deficiency. Now this is a perfectly legitimate procedure in scientific investigation. All that I wish to emphasize here is the fact that ameboid movement has not yet been completely reduced to mechanics. Even if it were conclusively demonstrated that every movement and every change in movement in Ameba is directly the result of changes in surface tension, it could still be maintained that the series of changes in material configurations associated with these phenomena is not completely known for such a demonstration would have no bearing upon the problem of the regulation of the movements.

Ameba can move in a homogeneous environment. Consequently, if its movements in such an environment are due to changes in surface tension, such changes are the result of internal factors concerning which practically nothing is as yet known. These factors may be purely physical and chemical, but it certainly can not be maintained that it has

been demonstrated that they are. For all that is known to the contrary there may be nonmaterial factors, entelechies and psychoids, involved in this regulation. Do not misunderstand me, I do not maintain that there are such factors involved, I merely hold that it has not been demonstrated that such factors are not involved.

In reference to regulation which constitutes the very essence of vital phenomena, we have indeed as yet traveled but a short way on the road toward reduction to mechanical principles, and it is mainly in this region that the anti-mechanist operates.

If we are correct in our analysis thus far, the essential difference between the mechanist and the antimechanist or vitalist is found in the fact that the former maintains that all reactions are completely determined by material configurations, and that all of the changes in such configurations can be ascertained, while the latter maintains that the reactions are not thus completely determined and that the changes in material configurations ending in reactions can be ascertained only in part. Which of these views is correct will be known, if it is ever known, only after every possible sequence associated with reactions has been ascertained. Thus it is evident that the mechanistic and vitalistic programs are, in so far as they pertain to experiment and observation, precisely the same. The mechanist holds that all reactions can be reduced to mechanical principles. Consequently he proceeds to ascertain by experimental methods every possible sequence of phenomena ending in reactions. The vitalists hold that some reactions or certain phases in some reactions can not be reduced to mechanical principles. He also must proceed to ascertain by experimental method every possible sequence of phenomena ending in reactions. For this is the only way he can be certain as to where mechanism breaks down and non-material factors begin to act.

But mechanists frequently maintain that faith in vitalism tends to inhibit experimentation, and that it inculcates superficiality. They maintain that when the vitalist gets into