Behavior of the Lower Organisms

(9) The Behavior 0} the Organism at any Moment depends upon its Physiological State at that Moment. — This follows immediately from the principles already developed. We have seen that both in "spontaneous" movements and in reactions to stimuli the behavior depends on the physiological condition of the animal. The behavior must then depend, secondarily, not only upon the present external stimulus, but upon all the conditions which affect the physiological states. This point will be developed under the two succeeding heads.

(10) Physiological Slates change in Accordance with Certain Laws. — It is evident that we may distinguish at least two great classes of physiological states, — those depending on the progress of the metabolic processes of the organism, and those otherwise determined. The changes in the metabolic states, as we may call the former, of course depend largely upon the laws of metabolism. In the physiological states not directly dependent on metabolism, but rather upon stimulation and upon the activity of the organism, such as we have seen in Stentor, we find certain fairly well-defined laws of change, of a peculiar character.

In a number of organisms we have found the following phenomenon : Under certain conditions the organism reacts in a certain way. These conditions continuing, the organism changes its first reaction for a second or third or fourth. Later the same external conditions recur, and now the organism at once responds, not by its first reaction, but by its final one. This is illustrated for unicellular organisms by the case of Stentor (Chapter X); for higher Metazoa it is well seen in the behavior of certain Crustacea, as described by Yerkes and Spaulding (Chapter XII). There are certain differences in these two cases that will be taken up later.

How does this state of affairs come about? The "physiological state " is evidently to be looked upon as a dynamic condition, not as a static one. It is a certain way in which bodily processes are taking place, and tends directly to the production of some change. In this respect the "law of dynamogenesis," propounded for ideas of movement in man, applies to it directly (see Baldwin, 1897, p. 167); ideas must indeed be considered, so far as their objective accompaniments are concerned, as certain physiological states in higher organisms. The changes toward which the physiological state tends are of two kinds. First the physiological state (like the idea) tends to produce movement. This movement often results in such a change of conditions as destroys the physiological state under consideration. But in case it does not, then the second tendency of the physiological state shows itself. It tends to resolve itself into another and different state. Condition 1 passes to condition 2, and this again to condition 3. This tendency shows itself even when the externaL conditions remain uniform.

In this second tendency a most important law manifests itself. When a certain physiological state has been resolved, through the continued action of an external agent or otherwise, into a second physiological state, this resolution becomes easier, so that in the course of time it takes place quickly and spontaneously. This may be illustrated from the behavior of Stentor, as described in Chapter X as follows : When the organism is stimulated by the flood

of carmine grains (or in any other way), this produces immediately a certain physiological state (corresponding to that accompanying a sensation in ourselves) ; this state we may call A. This state at first produces no reaction. As the carmine continues or is repeated, this state A passes to a second state B, producing a bending to one side. (The two may differ only slightly, but a difference must exist, otherwise B would not produce a reaction while A does not.) After several repetitions of the stimulus, the condition B passes to the condition C, producing a reversal of the cilia, and this finally passes to D, resulting in a contraction of the body. The course of the changes in physiological states may then be represented as follows : —

Now we find that after many repetitions of the stimulation the organism contracts at once as soon as the carmine comes in contact with it. In other words, the first condition A passes at once to the condition D, and this results in immediate contraction. It seems probable that the same series occurs as before, save that conditions B and C are now passed rapidly and in a modified way, so that they do not result in a reaction, but are resolved directly into D. The process would then be represented as follows : —

But whatever the intermediate conditions, it is clear that after the state A has become resolved, through pressure of external conditions, into state D, this resolution takes place more readily, occurring at once after the state A is reached. The same law is illustrated in the experiments of Yerkes and Spaulding on much higher organisms. In the experiments of Spaulding with the hermit crabs (Chapter XII), the introduction of the screen and the diffusion of the juices of the fish cause the animals to move about. In so doing they reach the dark screen, which induces, let us say, the physiological condition A. This leads to no special reaction. But this is followed regularly by contact with food, inducing the physiological condition B, which is concomitant with a positive reaction. The physiological condition A is thus regularly resolved into the condition B. In the course of time this resolution becomes automatic, so that as soon as the condition A is reached it passes at once to B. The positive reaction concomitant with B is therefore given even though the original cause of B is absent.

In the experiments of Yerkes, using the two passages to the water, described in Chapter XII, the following are the conditions. The presence of the investigator or the drying of the animal at T, Fig. 139, acts as a stimulus to cause movement away from T. A turn to the right is accompanied, let us say, by the physiological condition A. This is soon followed by contact with the glass plate G, inducing the condition B, which involves inhibition of movement and a turn in another direction. In the course of time the condition A comes to be resolved immediately into B, so that movement is inhibited at the start. On the other hand, the physiological condition C, concomitant with a turn to the left, is regularly resolved into the condition D, concomitant with reaching the water, and inducing a positive reaction. This resolution becomes automatic, so that the turn to the left is followed at once by forward motion to the water. In these cases the actual number of physiological states that could be distinguished is, of course, greater than what we have set forth above. But this does not alter in any way the general principle involved.

The law of the resolution of physiological states illustrated in the foregoing examples is of the highest importance for the understanding of behavior. With selection from among varied movements, it forms one of the corner-stones for the development of behavior. The law may be expressed briefly as follows : — The resolution oj one physiological state into another becomes easier and more rapid after it has taken place a number 0} times. Hence the behavior primarily characteristic for the second state comes to follow immediately upon the first state.

The operations of this law are, of course, seen on a vast scale in higher organisms, in the phenomena which we commonly call memory, association, habit formation, and learning. In the lower organisms the manifestations of this law are comparatively little known. This is probably due largely to difficulties of experimentation. Since the law has been demonstrated to hold in unicellular organisms (Stentor and Vorticella), there is much reason to suppose that it is general, and that it will be demonstrated in one form or another for other lower organisms. There seems to be no theoretical reason for supposing it to be limited to higher animals. Very great differences exist among different organisms as to the ease with which the quick resolution of one physiological state into another is established. There are likewise great differences in the permanency of existing connections among the present reaction methods. Hence it does not follow, as Yerkes (1902) has well pointed out, that because a few experiments do not demonstrate this law in a given case, the law, therefore, does not hold. In his experiments with crustaceans,

Yerkes found that a very large number of repetitions were necessary before a given resolution was established. (n) Different Factors on which Behavior Depends. — We have seen that the behavior of the organism at a given moment depends on its physiological state, and that it therefore secondarily depends upon all the factors upon which the physiological state depends. Hence we cannot expect the behavior to be determined alone by the present external stimulus, as is sometimes maintained, for this is only one factor in determining the physiological state. The behavior at a given moment may depend on the following factors, since these all affect the physiological state of the organism : —

4. Progressive internal changes (due to metabolic processes, etc.). 5. The laws of the resolution of physiological states one into another. All these factors have been strictly demonstrated by observation and experiment, even in unicellular organisms. Any one of these alone, or any combination of these, may determine the activity at a given moment. (i) As we have seen in the foregoing chapter, external agents produce reactions through the intermediation of changes in the internal physiological condition of the organism. This proposition is, perhaps, a truism, yet it needs to be kept in mind if behavior is to be understood. In the following discussion it will be unnecessary to mention specifically in each case the intermediate step in the process.

(2) The most general external cause of a reaction is a change in the conditions affecting the organism. This has been illustrated in detail in the descriptive portions of the present work. In most cases the change which induces a reaction is brought about by the organism's own movements. These cause a change in the relation of the organism to the environment; to these changes the organism reacts. The whole behavior of free-moving organisms is based on the principle that it is the movements of the organism that have brought about stimulation; the regulatory character of the reactions induced is intelligible only on this basis. Reactions due to stimulation produced in this manner are seen when an organism progresses from a cooler to a warmer region, or vice verscL; when it moves into or out of a chemical in solution; when it strikes in its course against a hard object ; when the unoriented infusorian shows lateral movements while subjected to light coming from one side. In all these cases it is the movement of the organism which causes a change in its relation to the external agent, and this change produces reaction. In most, if not all, cases the change is one in the intensity of some agent acting on the organism.

But an active change in the environmental conditions, not produced by movement of the organism, may likewise produce reaction ; this is, of course, most frequently the case in fixed organisms, such as the sea anemone. Responses produced in this way are seen in the reactions of organisms when heated or cooled from outside, or when a chemical or a solid object is brought in contact with them, or when the source of light changes in intensity or position, or when the direction of a water

current changes. The general fact is that a change in the environment produces a change in behavior. A. Change of conditions often produces a change of movement when neither the preceding nor the following condition would, acting continuously, produce any such effect. Thus when Euglena is swimming toward the source of light, if the light is suddenly diminished, the organism reacts by a change in its course ; it then returns to its course and continues to swim toward the light as before. Its behavior before and after the change is the same; but at the moment of change there is a reaction. Paramecium may live and behave normally in water at 20 degrees or at 30 degrees, yet a change from one to the other, or a much less marked change, produces a definite reaction. This relation could be illustrated by many cases from the behavior of any of the organisms described in the foregoing pages. Thus change simply as change may produce reaction.

To constant conditions, on the other hand, unless differing very greatly from the normal, the organism usually does not react. The Paramecium placed in A^ per cent sodium chloride reacts at first, but soon resumes its normal behavior. Euglena or Stentor when subjected to changes in the illumination of the anterior end react till they come into a position of orientation where these changes cease ; they then swim forward in the normal manner. As a general rule, organisms soon become acclimatized to a continuous condition, if it is not too intense. Exceptions to this rule will be considered later.

Of course a change must reach a certain amount before reaction is produced; that is, there is a certain necessary threshold of stimulation. In the best-known cases the amount of the change which produces reaction is proportional to the intensity of the original condition ; in other words, the relation of stimulus to reaction follows Weber's law (see pp. 38, 123). That is, it is relative change, not absolute change, that causes reaction. B. But not every change, even if sufficiently marked, produces reaction. It is usually not change alone that determines reaction, but change in a certain direction. Of two opposite changes, one usually produces a certain reaction, while the other either produces none or brings about a reaction of opposite character. This point is one that is of fundamental importance for an understanding of behavior. It may be illustrated in its simplest aspect from the behavior of the infusoria, where any reaction that is produced is usually of such a character as to remove the organism from the source of stimulation (the "avoiding reaction"). Paramecium at a temperature of 28 degrees reacts thus negatively to a change to a higher temperature, not to the opposite change. Paramecium at 22 degrees reacts to a decrease of temperature, not to

an increase. Stentor reacts to an increase of illumination, not to a decrease. Euglena when moderately lighted reacts negatively to a decrease of illumination, not to an increase ; if strongly lighted, it shows the opposite relations. Paramecium reacts at passing into an alkaline solution, but not at passing out ; it reacts at passing out of a weak acid solution, not at passing in. Hydra at 24 degrees reacts to an increase of 2 degrees in temperature, not to an equivalent decrease. Innumerable instances of this fact could be given from the behavior of the lower organisms.

What decides whether a given change or its opposite shall produce this negative reaction? Examination of the facts brings out the following relations : The organism generally reacts by a change in its behavior when the change is of such a nature as to lead away from the optimum. By optimum we mean here the conditions most favorable to the life processes of the organism in question. Changes leading toward this optimum produce in many animals no reaction; the organisms simply continue the activity which has brought about this change. Changes leading away from the optimum produce a negative reaction, by which the organism is removed from the operation of this change. There are undoubtedly some limitations and exceptions to this, and with these we shall have to deal later, but, as we have seen for Paramecium, it is unquestionably the rule. Cases where this rule does not hold are striking because exceptional. Reaction in this manner keeps the infusoria in regions of moderate temperature, prevents them from entering injurious chemical substances, brings green organisms such as Euglena into the light, where their metabolic activities are aided, and in general keeps the organisms in regions where the conditions are favorable. In these organisms the chief cause of reaction to a change is its interference with the normal life activities, and the reaction if successful serves to remove the interference.

C. But in many cases changes which favor the normal activities produce reaction. The response is then of such a character as to retain the organism under the conditions producing the change. Such responses we usually call positive reactions. In many cases it is clear that such reactions are determined by a previously existing unfavorable state of metabolism or of other processes. The Hydra or the sea anemone does not react positively to food substances unless metabolism is in such a state as to require more material; and parallel relations exist in the behavior of many if not all organisms. In unicellular organisms definite positive reactions play a comparatively small part, favorable conditions being secured primarily by a negative reaction to less favorable conditions. It is possible that all positive reactions are

to be traced to this as the primitive type (see the following chapter). That is, while the negative reaction is impelled by new unfavorable conditions, tending to retain the more favorable old condition, the positive reaction is impelled by the old unfavorable condition, tending to retain the new more favorable one. (3) Sometimes change of behavior occurs without change in the environment, the external conditions remaining uniform. As a rule, we have found that change of behavior occurs under uniform conditions only when these are decidedly injurious to the organism. If the water containing infusoria or the flat worm is heated to about 37 degrees, the animals react not merely to the change in temperature; they continue to react violently, with frequent alternations in the behavior, until they die. Many examples could be given of such reactions. Under uniform conditions a change in behavior also occurs at times owing to internal changes. The commonest cases of this sort are the changes in behavior due to hunger. In almost all cases of reaction under uniform conditions we find that the reaction is due to some interference with the normal life processes. But reactions under uniform conditions play only a small part in the behavior, as compared with reactions to changes.

We have then two main results as regards the external causes of changes in behavior: (1) change alone may produce reaction; (2) interference with the normal life processes or release from such interference may produce reaction. The usual cause of a change in behavior is a combination of both these factors — a change that hinders or helps the normal life processes. In the lowest organisms it is chiefly interfering changes that cause reaction. (4) Reactions to Representative Stimuli. — In the reactions due to change, one further point is of much importance. The organism may react to changes that in themselves neither favor nor interfere with the normal life activities, but which do lead to such favor or interference. The reaction given is then positive or negative in correspondence with the benefit or injury to which the change leads. Thus, Stentor may bend toward a small solid body when touched by it (Fig. 83), this reaction aiding it to procure food, though there is no indication that the touch itself is directly beneficial. Or it may contract away from a light touch, this enabling it to escape from a possible approaching enemy, though the touch itself is not injurious. Euglena reacts negatively when its colorless anterior end alone is shaded, yet it is only when the shadow affects its chlorophyll bodies that it interferes with metabolism. The flatworm may turn toward a weak stimulus of any sort. This leads in the long run to its obtaining food, though sometimes the stimulus does not come from a food body. In such cases the animal

reacts positively merely to the localized change, not to the nature of the change. Certain colorless infusoria, and the white Hydra, react to light in such a way as to gather at the lightest side of the vessel containing them. There is no evidence that the light itself is beneficial to them, but their reaction does aid them in obtaining food, since their prey gathers on the lightest side of the vessel. The collecting of Paramecia in C02 can hardly be considered to favor directly the life processes of the animals, but it apparently aids them to obtain food. The sea urchin tends to remain in dark places, and light is apparently injurious to it. Yet it responds to a sudden shadow falling upon it by pointing its spines in the direction from which the shadow comes. This action is defensive, serving to protect it from enemies that in approaching may have cast the shadow. The reaction is produced by the shadow, but it refers, in its biological value, to something behind the shadow.

In all these cases the reaction to the change cannot be considered due to any direct injurious or beneficial effect of the actual change itself. The actual change merely represents a possible change behind it, which is injurious or beneficial. The organism reacts as if to something else than the change actually occurring; the change has the function of a sign. We may appropriately call stimuli of this sort representative stimuli. This reaction to representative stimuli is evidently of the greatest value, from the biological standpoint. It enables organisms to flee from injury even before the injury occurs, or to go toward a beneficial agent that is at a distance. Such reactions reach an immense development in higher animals ; most of our own reactions, for example, are to such representative stimuli. Only as we react to actual physical pain or pleasure do we share with lower organisms the fundamental reaction to direct injury or benefit. Practically all our reactions to things seen or heard are such reactions to representative stimuli. While such behavior plays a much larger part in higher than in lower organisms, the existence of reactions to representative stimuli even in the low organisms considered in the present work is an evident fact.

How can we account for such reactions ? It is perhaps worth while to point out that the operation of the law of the resolution of physiological states, set forth on page 291, would result naturally in the production of such reactions. Let us take as the simplest possible case the reaction of Euglena when its colorless anterior tip is shaded. Since it is only the metabolism of the chlorophyll bodies that is blocked by shade, we cannot suppose that the shading of the colorless tip actually interferes with the life processes. Yet to this change Euglena reacts negatively. We may suppose that the shading of this colorless part induces the indif-

ferent physiological state A, which of itself produces no reaction. But this is invariably followed by the shading of the chlorophyll bodies, interfering with metabolism and inducing the physiological state B, resulting in a negative reaction. Thus the state A is regularly resolved into the state B. In accordance with the law of the resolution of physiological states, this resolution in the course of time becomes spontaneous. A passes at once to B and a negative reaction occurs, even when the colorless anterior tip alone is shaded. In unicellular organisms a condition so reached would naturally continue to succeeding generations, since the organisms in reproducing merely divide.

In the same way the defensive reaction of the sea urchin when shaded could be produced. The condition A, induced by the shade, is usually resolved into the condition B, induced by the attack of an enemy, and resulting in the defensive movement. This resolution in the course of time may then become spontaneous, so that the sea urchin now reacts defensively even when a cloud passes over the sun. This condition could be continued to succeeding generations only if acquired characters are inherited.

Thus through the operation of the law of the resolution of physiological states the following general result will be produced : If a given agent induces a physiological state A, and this is usually followed by a second state B, then in time the given agent will produce at once the response due primarily to B. The organism will have come to react to A as representative of B. We do not know whether the development of reactions to representative stimuli has actually taken place in this way, or not. But the fact that there is a factor, whose existence is demonstrated, that would produce exactly these results, certainly suggests strongly the probability that they have been at least partly brought about in the way above set forth. If the law of the resolution of physiological states is actually operative throughout behavior, the effect would be to make behavior depend on the results of the animal's own action. This would produce behavior that is regulatory, such as we actually find to exist.

(5) The reaction to a given external stimulus depends, as we have previously seen, on the physiological condition of the organism, not alone on the nature of the external change. The physiological condition depends partly on whether the normal stream of life activities is proceeding uninterruptedly. In certain physiological states, such as hunger, the processes are not proceeding normally. This impels the organism to a change, so that to almost any external stimulus it may react in a way that tends to bring about a change. The hungry sea anemone in this condition reacts positively to all sorts of neutral bodies;