Behavior of the Lower Organisms

In attempting to answer these questions, it will be best to take up first the reactions to single induction shocks. To observe the reactions accurately, the Paramecia must be placed in some viscid but not injurious substance, such as the jelly produced by allowing a few quince seeds to soak in a watch-glass of water containing the animals (Statkewitsch, 1904 a). This makes the movements so slow that they can be followed under the microscope. The reaction to induction shocks under these conditions has been studied especially by Statkewitsch (1903). When an induction shock is passed through a drop of such fluid containing Paramecia, the animals are found to react especially at that part of the body which is next the anode. Here the cilia are suddenly reversed, striking forward instead of backward ; the ectosarc contracts

sharply, and trichocysts are thrown out (Fig. 60). If the current is a very weak one, only the reversal of cilia occurs ; with a stronger current the other phenomena appear. With a very powerful current, contraction and discharge of trichocysts occur also at the cathode, and with a further increase of current, over the whole body. The animal at the same time becomes deformed and usually goes to pieces. Fig. 60. — Effect of induction shocks on Paramecia in different x .1 <r

cilia reversed, and contraction of the ectosarc, at the anodic side moderate Strength the reversal of cilia, beginning at the anode, quickly spreads over the entire body, causing the animal to swim backward. This movement is the beginning of the avoiding reaction. After swimming backward a short distance the animal turns toward the aboral side and swims forward in a new direction. Thus the reaction to an induction shock is of essentially the same character as the reaction to other strong stimuli.

Paramecium reacts to induction shocks more readily, as might be expected, when the sensitive anterior end is directed toward the anode. When in this position, it reacts to currents that are too weak to produce reaction in specimens occupying other positions. According to Roesle (1902), Paramecium reacts more readily when the oral surface is toward the anode than when in other positions, indicating that the region about the mouth is especially sensitive. While this seems probable on general principles, it was not confirmed by the thorough work of Statkewitsch (1903). In some cases an induction shock, like a weak mechanical stimulus, causes in place of the avoiding reaction a movement forward (Roesle, 1902).

Since the animal is most stimulated when the anterior end is directed toward the anode, and this stimulation causes as a rule the avoiding reaction, one would expect that if the stimulation came repeatedly from the same direction, the animal would after a time reach a position with anterior end directed away from the anode. This is exactly what occurs. If frequent induction shocks are passed in a certain direction through the water, the animals all become pointed toward the cathode and swim in that direction (Birukoff, 1899, Statkewitsch, 1903). This happens even when the current is so weak that a single induction shock causes no reaction. There is a summation of the effects of the successive shocks until a reaction is produced (Statkewitsch, 1903). As most commonly used, induction currents pass alternately in opposite directions. The induced current in one direction is due to the closing of the circuit in the primary coil, while the immediately following current induced in the opposite direction is due to the breaking of the circuit in the primary coil. The induced currents due to the breaking of the circuit are, as is well known, more powerful than those produced by the closing of the circuit. When both currents pass through the preparation alternately, Paramecia react primarily to the stronger "break" currents. They move toward the cathode of these stronger currents and are apparently not affected by the weaker "make" shocks (Birukoff, 1899, Statkewitsch, 1903 a).

If in place of induction shocks a continuous electric current is used, the result is the same as was described in the last paragraph. The Paramecia place themselves with anterior end directed toward the cathode and swim in that direction (Fig. 58). From what we know of the behavior of Paramecium under the action of other stimuli, we might suppose that the whole secret of this behavior lies in the production of the avoiding reaction when the anterior end is directed toward the anode. This reaction, continuing until a position was reached where the anterior end was no longer stimulated, would cause it to become directed toward the cathode. If the anode stimulation still continued, now at the posterior end, the animal would continue to swim forward toward the cathode, for to stimulation at the posterior end, as we have seen, the animal responds by swimming forward. If this were the method of reaction, the behavior under the electric current would be of the same character as under the stimuli which the animal meets in its natural existence.

But a study of the exact movements of the animals shows that there is present another factor which is peculiar to the action of the electric current. To detect this the precise movements of the cilia under the action of the current must be examined. The cilia themselves may be directly observed in specimens placed in some viscous medium (see Statkewitsch, 1904 a). Or the effective movements of the cilia may be determined by mingling with the fluid containing them a quantity of finely ground India ink. By its aid the direction of the currents pro-

duced by the cilia becomes evident.1 In this way we find that it is not alone at the anode that the electric current is active, but that a peculiar effect is produced also at the cathode. Here the direction of the cilia is reversed (Fig. 61) so that they point forward, and their effective stroke is forward, tending to drive the animal backward. When the electric current is weak and the animals are swimming toward the cathode, the cilia are reversed only at the anterior end (Fig. 61, 1), the reversal extending a little farther down on the oral side than elsewhere. At the anterior tip the water currents are forward instead of backward (Fig. 62, a), and the cilia themselves are clearly seen to be pointed forward (Fig. 61, 1). When the animal is swimming most rapidly toward the cathode, this effect is very slight ; almost all the cilia of the body are beating backward in the usual way.

If the current is made stronger, this cathodic effect increases. The cilia become Fig. 61. — Progressive cathodic reversed farther and farther back, till with a form in Paramecium as the concertain strength of the electric current the stant electric current is made cilia on the anterior half of the body are to he at the upper end. The curstriking forward, those on the posterior half cessive changes as the current is rents produced are 111 Opposite directions,

gradually increased. After Statkemaking the animal the centre of a sort of cyclonic disturbance in the water, which gives a most extraordinary appearance (Fig. 62, b). The two sets of cilia oppose each other, so that the animal seems to be trying to swim in two opposite directions at once. Up to a certain strength of the electric current the posterior cilia prevail over the anterior ones, so that the animal swims forward. But the movement becomes slower and more labored as the electric current is increased, until in time the two sets of cilia balance each other. Then the animal remains in place, revolving rapidly on its long axis, or it shoots first a short distance forward, then a little backward. With a still further increase of the electric current, the cathodic effect increases to such an extent that the reversed cilia gain

1 The Paramecia must be in a thin layer of fluid; this may be attained by supporting the cover-glass on thin sheets of filter paper and introducing the current through this paper. 2 This peculiar effect was first observed by Ludloff (1895). the upper hand, and the animal swims backward toward the anode. The cilia are now reversed even behind the middle (Fig. 61, 4, 5). The body is deformed, becoming short and thick, and pinched to a point at the anode end, while the cathode end is swollen. Finally the animal usually bursts and goes to pieces ; before this happens almost all the cilia have become reversed (Fig.

When a Paramecium is transverse or oblique to the direction of a current at the time the circuit is closed (Fig. 63, c, e), certain striking effects are produced. If a current of medium strength is employed, such as causes reversal of about half the cilia, the following results are observed. On the anode side the cilia strike backward, as usual. On the cathode side the cilia strike forward. As a result the animal, when in a transverse position, must turn directly toward the cathode side, both sides of the body

tending to produce this effect, as indicated by the c and e. This happens even when the oral side is directed toward the cathode (Fig. 63, e). The animal then turns toward the oral side, — a result never produced by other stimuli, and due to the peculiar cathodic effect of the current. This tendency to turn directly toward the cathodic side is complicated in certain positions of the animal by the usual strong tendency to turn, under the influence of stimuli, toward the aboral side, — that is, to respond by the typical avoiding reaction. If the anterior end is directed toward the anode at the time the circuit is closed, the animal invariably turns toward its aboral side, the cilia taking the position shown in Fig. 63, b. This method of turning is apparently due to the fact that

reversed only at cathodic tip. b, Electric currents stronger; the cilia of water currents reversed over cathodic half as far back as the backward stroke of the oral cilia is more powerful than that of the opposing aboral cilia. For the same reason the animal turns toward the aboral side even when in the position shown in Fig. 63, a, where it would be more direct to turn toward the oral side. Between this position (a) and the transverse position with oral side to the cathode (e), there is a position in which the tendencies to turn in opposite directions are exactly balanced (/). The animal tries, as it were, to turn in opposite directions at the same time, so that it remains in position, though the

Fig. 63. — Effects of the electric current on the cilia of Paramecia, and direction of turning in different positions. The oral side is marked by an oblique line. The large arrows show the direction toward which the animal turns. The small internal arrows indicate the direction in which the cilia of the corresponding quarter of the body tend to turn the animal. In all positions save c and e the cilia of different regions oppose each other. From a to d the turning is toward the aboral side; from d to /, toward the oral side. At / the impulse to turn is equal in both directions, and there is no result till by revolution on the long axis the animal comes into a position with aboral side to the cathode.

cilia are beating violently, causing complicated currents in the water. This independent and opposing activity of the cilia of different parts of the body is characteristic of the effects of the electric current, and is not found in the reactions to other stimuli. In the position shown in Fig. 63, /, the revolution on the long axis, which is a part of the normal motion of the animal, soon interchanges the position of oral and aboral sides, whereupon the infusorian of course turns at once towards the aboral side, till its anterior end is directed toward the cathode.

Thus in a considerable preponderance of all possible cases the animal turns toward the aboral side, as it does under other stimuli. But in certain positions (from d to /, Fig. 63) it turns directly toward the oral side, a result not producible by other stimuli. If the direction of the electric current is frequently reversed, certain peculiar effects are produced. If the reversal occurs at the moment when the anterior end has become directed toward the cathode, then the animal continues to turn toward the aboral side till the anterior end is pointed toward the new cathode. By repeated properly timed reversals, the animals can be caused to spin round and round, — always toward the aboral side.1 If the intervals between the reversals of the current are made less, so that the animal has not yet become pointed toward the cathode, it swings back over the space through which it has turned. Thus the animals may be made to swing back and forth or turn round and round, remaining in the same spot, like animated galvanometers, — the anterior end pointing out the direction of the current.

If the rate of reversal is much increased,2 so that the animals have scarcely time to begin swinging in a certain direction before a new reversal occurs, then certain other phenomena result; these have been described by Statkewitsch (1903, 1903 a). The Paramecia which are swimming toward one electrode when the current is closed usually continue to swim in the same direction for a time, as if reacting to only one of the current directions. Those not already pointed toward one of the electrodes usually take quickly the transverse position. Thus, soon after the beginning of the experiment, part of the animals are swimming toward the electrode at the right, part toward that at the left, while the rest are transverse. Soon those not transverse have reached the region of the electrode toward which they are swimming. Thus the Paramecia are now divided into three groups, — a group at the right swimming toward the right electrode, another at the left swimming towards the left electrode, and a central group swimming athwart the current (Fig. 64). After a time the transverse position is assumed also by those directed toward the electrodes, especially if the current is made stronger or the rate of reversal is increased. Thus at a later stage all or nearly all are transverse; they swim across the current, some toward one side of the preparation, some toward the other.

The reason for taking the transverse position when the current is rapidly reversed seems to be as follows: We have seen above that to 1 As soon as a specimen has made a half revolution on its long axis, as may happen, it of course seems to spin in the opposite direction, because the aboral side has taken up a new position. 2 The strength of the current remaining the same in both directions, not varying as in ordinary induction shocks. single electric shocks the animals react more strongly when the anterior end is directed toward the anode. Often there is no reaction when they are in the opposite position. Consider a specimen that is oblique, as in Fig. 63, b'. The current comes alternately from the right and left. To

the current coming from the left (anode at the left) the Paramecium reacts strongly, since its anterior end is directed toward the anode. It therefore turns its anterior end in the opposite direction, — to the right. To the opposite current, on the other hand, it reacts little or not at all, since the anterior end is not directed JL \^^^V\^ViU^f^£ toward the anode. Continuing thus to react to the repeated currents from the left, it must come into the transverse position. Here the anterior end has the same relation to both currents ; hence it swings as far to one side as to the other. Since it changes its position very little at any one reversal, it maintains on the whole the transverse

Fig. 64. — Positions taken by Para mecia in rapidly reversed currents, a, Posi tions in \veak currents, or in moderate direction currents at the beginning of the experiment. c and d, Positions taken in stronger curbehavior is of course to cause the amrents, or after the experiment has lasted for mals j-q pass t0 the cathode. Here they some time. After Statkevvitsch (1903 a). , . . -n t may gather in a dense mass. But it the cathode is so placed that the Paramecia can pass behind it, they do this, thus reaching a region where the current is not acting (Fig. 59, B). Here they swim about in all directions. If one comes by chance again into the field of the current, it is at once returned, by the usual reaction, to the region behind the cathode. If in any other way certain areas are left free from the action of -the current or with very little current, the animals gather in these free areas. Birukoff (1899) has described and figured many such cases, produced under induction shocks by the aid of electrodes of different forms ; his results have been extended by Statkewitsch (1903 a).

It is evident that the reaction to the electric current differs fundamentally from the known behavior under other classes of stimuli. Under other stimuli the movements are coordinated, all tending toward the same end, while in the electric current different parts of the body oppose each other. The behavior thus becomes uncoordinated, lacking unity. The animal seems to strive to perform two opposite actions at once. The anterior cilia drive the animal backward, the posterior cilia forward. In certain positions (Fig. 63, /) part of the cilia tend to turn the animal to the right, others to the left. The action of the current is more local and direct than that of other stimuli, producing opposed reactions in different parts of the body. The whole secret of this extraordinary behavior lies in the cathodic reversal of the cilia. If this cathodic effect were non-existent, the behavior under the action of the electric current would probably be the same as under other stimuli. The reaction due to the anodic stimulation is, as we have seen, the same as that due to other strong stimuli, and in the constant current the anodic cilia strike backward in the usual way. If the anodic stimulation alone existed, the animal would doubtless become directed to the cathode by the method of trial and would swim in that direction. But as the behavior actually occurs, there is nothing like a trial of different positions. The cathodic reversal of the cilia forces the animal directly into a certain orientation. The reaction is not due, like that to chemicals, to the change in conditions as the animal passes from one region to another. It is not due to a tendency to collect about the cathode, for, as we have seen, if it is possible, the animals go beyond the cathode. Moreover, in a strong current there is no movement to the cathode, and in a still stronger current the movement is away from the cathode, though the orientation remains the same in both cases. All these peculiarities in the behavior are due to the cathodic reversal of the cilia.

What is the cause of this fundamental feature of the reaction to the electric current, — the cathodic reversal? Many theories have been proposed to account for the reaction to electricity, though often these do not touch this fundamental feature in any way. It will be better to reserve an account of these theories until we have examined the behavior of other infusoria under the action of electricity (see Chapter IX). In Paramecium there are certain methods of reacting to stimuli which we have not yet described. These are, first, local contractions of the ectosarc, and second, discharge of trichocysts. Neither of these seem to play any important part in regulating the relation of the organism to the surrounding conditions.

Slight local contractions of the ectosarc occur in response to many stimuli. Since the ectosarc of Paramecium is not known to contain contractile elements, the way in which these are brought about is unknown. A discharge of trichocysts is produced by many different agents. The trichocysts are rodlike sacs in the ectosarc, perpendicular to the outer surface. Their contents are ejected, under certain conditions, into the water, forming long threads. According to some authors, these threads have a definite structure, and are probably preformed within the animal. Others suppose the threads to be formed by the coagulation of a fluid contained within the sacs. After discharge of the trichocysts the animal appears to be surrounded by a zone of radiating fibres (Fig. 65).

The discharge of trichocysts under the influence of stimuli has been studied especially by Massart (1901 a), and by Statkewitsch (1903). Crushing the animal causes discharge of trichocysts in the region injured. Weaker mechanical stimuli do not have this effect. If the animal is heated rapidly till it is killed, it discharges the trichocysts before dying; if Fig. 65. — Paramecium with trichocysts discharged, heated slowly, this effect is as a result of the application of picric acid. ^ producecL Neither Cold

nor increased osmotic pressure have any effect on the trichocysts. Many chemicals produce the discharge, particularly various acids. Saturated solution of picric acid causes a sudden discharge of all the trichocysts at once. One-fourth per cent methylene blue produces a slow and irregular discharge successively from different parts of the body.1 If any agent acts on a limited portion of the body surface, the trichocysts of only that region are discharged. Many chemicals kill the animal without discharge of the trichocysts.

A weak induction shock causes discharge of the trichocysts at the anode only (Fig. 60); a stronger shock causes discharge at both anode and cathode. A still stronger shock causes discharge of the trichocysts over the entire surface of the body (Statkewitsch, 1903). In the discharge of the trichocysts we have a phenomenon comparable to the definite reflex actions observed in various organs of higher animals. The function of the trichocysts is uncertain. They are usually supposed to be weapons of defence. If the Paramecium is seized by an animal which is attempting to prey upon it, the trichocysts will of course be discharged from the injured region. But whether they really

1 To demonstrate the discharge of the trichocysts it is convenient to use picric acid alone or picric acid to which a little aniline blue has been added. In the latter case the trichocysts become colored blue (Massart). serve for defence seems questionable. Certainly the infusorian Didinium (Fig. 113), which is the chief enemy of Paramecium, is not hindered in the least from seizing and devouring the animal by the discharge of trichocysts. It is possible that the discharge is really an expression of injury, — a purely secondary, even pathological, phenomenon, like the formation of vesicles on the surface of an injured specimen.

B. Discharge of trichocysts as a reaction : Massart, 1901 a. Behavior under Two or More Stimuli ; Variability of Be- havior ; Fission and Conjugation ; Daily Life ; General Features of the Behavior The behavior thus far described is that which takes place under the influence of but a single kind of stimulation. But normally the conditions are as a rule more complex than this ; the animal is affected by several sets of stimuli at once. What is the behavior under such conditions ? If, while the Paramecium is reacting to the stimulus a, the stimulus b acts upon it, will it react in the usual way to b ? Or will it continue to react to a? Or will its action form a compromise between the usual reactions to the two agents? Or will it, finally, react in a new way, different from the usual reactions to either a or b ?

Let us examine first the behavior under the simultaneous action of the contact stimulus and of other usual stimuli. As we have seen, the contact stimulus often causes the animal to come to rest and behave in a characteristic manner, while other classes of stimuli usually induce the avoiding reaction or a movement forward. Thus opposite reactions are induced by the two kinds of stimuli acting separately. What will be the result when the two act together?