The Psychic Life of Micro-organisms: A Study in Experimental Psychology

that the extended pseudopod seizes some point of support with its free end, then, in contracting, draws the entire mass of the body up to this. But it is difficult to understand what the cause of the elongation of the pseudopodia is. It has been supposed that the protoplasm* is endowed with great elasticity and that the elongation is the return of this substance to its primitive form. That is not the explanation given by M. Rouget. The learned professor of the Museum has been kind enough to write out the following note for us, in which he recapitulates his opinion:

"Every time that a protoplasmic organism dies, or is subjected either to a strong electric excitation, or to a relatively high temperature (+ 45° to -f- 50°), the pseudopodia are retracted and re-enter into the mass, which assumes a globular form; the same is the case in the protoplasm of vegetable cells, the inter-cellular reticulum of which breaks in receding, or else the mass of protoplasm divides into spherical bodies. These states of retraction are the analogues of muscular rigidity, and like it represent the condition of maximum contraction in the protoplasm — nevertheless the style of the Vorticels (Carchesium) which is a protoplasmic formation, under the same conditions, remains in a state of permanent retraction. It follows from this that the emission of the pseudopodia, their elongation, cannot in any case be considered as a direct act of the contractility of the protoplasm.

"The production of the pseudopodia, one of the most difficult problems, cannot, in my opinion, be explained, except in the following manner: All protoplasmic masses, and especially the amoeba, consist of two parts, an enveloping membrane or ectosarc, viscous and elastic, and the central liquid contents holding granules in suspension. " From the time of the apparition of a pseudopod, a current of liquid is visible which penetrates into the pseudopod and which seems to contribute to its elongation. It is very evident that the liquid is passive, that it penetrates into the pseudopod only because, pressed upon from all sides, it finds less resistance there. I think that the (in appearance) homogeneous hyaline substance of the pseudopod is also a species of hernia of the estosarc, resulting from a diminution of the elastic resistance at the point where it appears, with an increase of elasticity or of contractility (to me two modalities of the same property) in those parts of the ectosarc where pseudopodia are not produced. When the contractility or the elastic tension of these parts diminishes, and returns to its original state the pseudopod re-enters into the mass. Add to this that, in an amoeba of large dimensions, Amoeba terricola, it has seemed to me that the most external membrane of the ectosarc showed striae of a granular appearance which may be identical with the striae or contractile fibrils of the ectosarc of the ciliated infusoria, Stentor,Spirostomes, Bursaria, etc." (May 20, 1887.)

The pseudopod does not represent a permanent, differentiated organ of locomotion; it is produced by a simple prolongation of the mass of the body, which can take place at any point whatever, and when the act of locomotion has been accomplished, this prolongation re-enters into the common mass without leaving any traces of its emission. In other animal species, for example the Petalobtts of Lachmann, initial traces of differentiation of the pseudopodia have been observed; they always form at the same

point of the body, on a level with the anterior part; but, in spite of this constant localization, the motor organ has only a transitory existence; it is produced at the moment it is needed, and disappears into the mass of the body, when the movement has been executed. In the Actinophrys there is a still greater progress: the numerous pseudopodia emitted by this animal, and which have the form of filaments, are permanent organs with definite functions.

The Vibratile Cilia. The vibratile cilia are short, extremely thin, homogeneous filaments which are agitated by a vibratory movement. These are distinctly differentiated organs of locomotion. They have, moreover, several functions: firstly, they enable the animal to move about in the liquid; secondly, they serve it as an organ of prehension; thirdly, they permit a renewal of the water which furnishes the necessary air for respiration to the animal; perhaps they also serve as organs of touch.

The vibratile cilia lend to the Infusoria their peculiar character and enable them to be distinguished from all the other Protozoa. Cilia are also found in vegetable species when young, and in the larvae of Coelenterates, of mollusks and of worms. But among the Protozoa, it is the Infusoria alone that are ciliated. The cilia are distributed in various manners, differing according to the species. In the holotricha, they are distributed regularly over the whole surface of the body, and almost all have the same length; in the Heterotricha, they also cover the whole surface of the body, but they are unequal in length. To this group belong the Stentors which have long cilia inserted around a circular surface, extending almost to the mouth. This surface is a rotatory organ, analo-

gous to that of the rotifers; it produces eddies in the water and thus causes the flow of foreign bodies to the mouth: these animals have the rest of their bodies covered with fine cilia. In the Hypotricha the cilia are located on the ventral surface of th£ body and aid in locomotion. In the Peritricha, they form a circular or spiral row on the anterior part of the body, and lead to the mouth. This is observed in the Vorticels, sessile species which have no other cilia than those which are used for the prehension of food; the rest of the body is bare.

Much has been said about the morphological significance of vibratile cilia; several micrographists have held that the cilia are attached to the enveloping membrane only, and have no connection whatever with the protoplasm. That was notably the opinion of Robin; it is entirely wrong. The cilia are never simple prolongations of the cuticle; they have their root in the protoplasmic substance; they pass through orifices in the cuticle, which consequently is pierced by a multitude of small holes. Engelmann, in recent observktions, has been able to trace the extremity of the vibratile cilia into the interior of the protoplasm; he made this observation on the marginal cilia of the Stylonichia; from each of these threads he has seen separate a pale fibre, which moves along almost directly beneath the cuticle in a direction perpendicular to the lateral edge of the body; towards the median line of the ventral face the fibres are often laid bare, because the body of this Infusory voids its protoplasmic substance; there the fibres have the aspect of tightened threads. Engelmann sees in this observation a confirmation of the opinion that the bodies of infusoria are formed of one single cell, because, according to

other observers, there exist also in vibratile cellules filiform striae which seems to be a continuation of the cilia, and which traverse the protoplasm of the cell throughout its whole length. We mightadd to this direct observation several other facts showing that the vibratile cilia are indeed prolongations of the plasm. Under the action of re-agents the cilia act like the cellular protoplasm; they are coagulated by the acids and dissolved by weak alkalies, while the cuticle offers a greater resistance to these same agents.

These vibratile appendices are not without analogy with the pseudopodia of naked cells; Dujardin, a French naturalist, demonstrated this in 1835, although efforts have since been made to bestow the honor of this discovery upon the Germans. Dujardin has proved that the amoeboid movement and the ciliary movement are only two manifestations of the contractile power of protoplasm. In fact, if instead of examining a pseudppod with lobed outline like that of the amoeba, we observe the slender and filamentous pseudopodia of the Foramenifera, we see that the extremity of the filament is agitated by the same vibratory movement as the vibratile cilium.

All the transitions from the fine and delicate cilia to the large cilia, tapering in form like a stilleto, which have been called cirri, have been observed; moreover these cirri are formed of agglutinated cilia; by the aid of certain re-agents they have been dissociated. An observation of a ciliated infusory, the Didinium nasutum (see the illustration further on) made by M. Balbiani, shows that the movement of the cirri is not an involuntary movement like that of the cilia of the vibratile epithelium, with which it has often been

compared, but that it is completely under the control of the will of the animal, like the organs of locomotion of animals much higher in point of organization. " The Didinium has two rows of equal, and rather strong, vibratile cilia, disposed transversely around the body, in the form of two belts or crowns. The rest of the body of this animal is entirely stripped of cilia, but its double vibratory belt suffices to enable it to execute the most rapid and most varied evolutions in the water. Not only does it swim forwards and backwards with perfect ease, but the progression in both directions is always accompanied by a rapid rotatory movementof the animal aboutits longitudinal axis, similar to that observed in other infusoria that have a cylindrical body. The two rows of cilia always act in union during the locomotion, and the direction which the animal gives to them, determines the direction in which it wishes to move. In the movement for-

Fig. i.- — Didinium nasututn (Balbiani) Figure representing movement forward. The cilia are all turned towards the front part of the body. Fig. 2. — Didinium nasutum (Balbiani). Outline of movement backwards. The cilia are all turned towards the back part of the body. Fig. 3. — Didinium ncisutum (Balbiani). A sketch of rotatory movement in one spot. The cilia of the anterior belt are directed forwards, while those of the posterior belt are directed backwards

wards, all the cilia are directed toward the anterior part of the body (fig. i); when it swims backwards, they are reversed (fig. 2). The infusory thus rapidly makes its way across the field of vision by jerks; from time to time it suddenly stops, all the time continuing to turn around rapidly on its axis on the one spot, during which movement the ciliated belts beat the water in opposite directions, the •interior ones being turned forwards, while the posterior are turned backwards (fig. 3). The result of this is that the effects of these small locomotive apparatuses neutralize each other in the same manner as two helices acting in opposite directions, and that the animal remains stationary, while all the time turning rapidly about itself, sometimes horizontally, sometimes vertically on its conical appendage, just as on a pivot."

Certain Infusoria, for example the Condylostoma patens, which has been thoroughly studied by M. Maupas, possess at the same time the two kinds of appendages, the cilia and the cirri. The former, which cover the dorsal surface of the animal, are fine, very dense and animated by a rapid and unceasing vibratile movement. The cirri, which cover the ventral surface are placed apart; furthermore they do not vibrate rapidly; their movements are slow, and when the infusory moves, one can see them move successively on the plate of glass and support themselves there, in the manner of a foot, to make the body advance. When the animal stands still, the cirri are absolutely immobile, while the cilia continue their vibratile movement. This observation which can equally well be made of the Oxytrichid, shows that the vibratile cilia are the organs of involuntary movement, and that the cirri are more directly subject to the will. The fact is demonstrated by the experiments of Rossbach, who observed that, under the influence of the falling of the temperature (from + 15 to + 4) or of the rising of the temperature (from -f 35 to 4- 40) or under the influence of various chemical substances, the large cilia, the organs of voluntary movement, are

paralysed, while the fine and delicate cilia continue their movements, which do not seem to be under the influence of the will. These movements alone cause the whole body to rotate until the vibratile cilia are in their turn paralyzed. Besides the cilia and the cirri, other appendages in the form of membranes are found among the Infusoria, appendages which are attached to the anterior part of the body or the peristome; these membranes serve the purpose of causing eddies in the water, which bring the floating alimentary particles into the mouth. They are modifications of the vibratile cilia; these membranes like the cirri are formed of agglutinated cilia.

The Flagellum. The study of the third organ of locomotion, the flagellum, brings us to speak of the class of Mastigophores and more particularly of the group Flagellata. The Flagellates are Protozoa of very small size, all in all, very much smaller than the ciliated Infusoria. They have no vibratile cilia at all, but they are always equipped with one or more filamentous appendages which have the form of a long lash. This is the flagellum. This lash, like all the organs of locomotion hitherto studied, has two functions: it is at once an organ of locomotion and an organ of prehension. The flagellum is most frequently single or double (see fig. 4, representing the Euglenadeses with its single flagellum); sometimes a person can count a much larger number of them, four, six, eight, ten, and more. As regards the insertion, the same variations are met with. Sometimes the flagella are very numerous and seem to be planted on the same point of the surface of the body, thus forming a brush or plume. In other species we find several

flagella arising in the anterior extremity of the body, directed forwards, and also posterior or caudal filaments which are turned toward the rear. This is observed in the genus Trichomonas; the anterior flagella serve for purposes of locomotion, perhaps also for the prehension of food; the posterior flagella, on the contrary, are solely organs of locomotion; they resemble a trailing tail and perform the functions of a rudder. In passing we may point out the great morphological resemblance between the Flagellata and the spermatozoa of animals, the antherozoa and -D the zoospores of plants. The organs

The Protozoan with its flagellum executes the most varied movements, moving first in one direction, then in another, and in different planes; sometimes the animal curves about entirely; but most frequently, when he uses' it as an organ of prehension, he extends \J it its whole length before himself; the basilar part remains completely immovable and rigid, while the free end alone r. c. = contractile reexecutes movements destined to drive =rdS of rheeypeirt food to the m°uth, which is generally ra;onpeh;ores;^=hnru°:situated at the base of the flagellum. Ehrenberg gives to the flagellum the name proboscis; its peculiar mobility renders it worthy of this name. The flagellum, like the vibratile cilium, is an expansion of the protoplasm through the enveloping membrane. M. Certes has observed a Proto-

zoan, the flagellum of which between whiles re-entered into the mass of the body, with which it mingled;it was replaced by a pseudopod which soon attenuated and took the form of a flagellum. Biitschli has recently made a very interesting observation on this organ of locomotion. Under certain circumstances, the Peridinia (Dinoflagellates) throw off their long flagellum and enter into a state of repose; they generate them quite as easily. In the Glenodinium cinctum, Biitschli has seen the flagellum roll itself up first like a cork-screw, and then suddenly detach itself from the animal; having become free, it stirs about in the water for several minutes before becoming motionless. This observation enables us to refute those naturalists who believe that the vibratile cilium is an appendage of the cuticle, by bringing forward the fact that when the cilia with the portion of the cuticle in which they are inserted are separated from the cell, the cilia continue to move; we have just seen that the flagellum moves even after it is separated from the cuticle; this persistence of moveme'nt is sufficiently explained by the protoplasmic nature of the cilia and of the flagellum.

From another point of view, the observation of Biitschli gives us a curious example of the phenomena of autotomy, which have recently been studied by Fredericq. The pseudopodia, the vibratile cilia, and the flagellum, constitute the three motor organs that are most frequently found in the kingdom of the Protista.' Among the Infusoria, moreover, particular differentiations of the protoplasm have been described, which may be compared to the muscular fibres of the higher animals. The Vorticellse are supported by contractile

peduncles. These are filaments capable of rolling themselves up into the form of a cork-screw, when the animal is disturbed. Certain Infusoria can modify the form of their body by a sudden contraction: they have been called metabolic; such are the Stentors, the Prorodons, the Spirostomes. In contradistinction, those which do not change their form, for example the Paramecia, have been called ametabolic. According to the observations of Lieberkiihn, which date back to 1857, the metabolic Infusoria have their bodies divided into large granulous bands, separated by bright filaments. It has been asked which is the contractile element: is it the band, or is it the filament? Oscar Schmidt, Kolliker, Stein, and Rouget think that it is the band which is the contractile element. This opinion is based on the following fact, which M. Rouget was the first to observe: at the moment at which the animal contracts, the band presents transverse striae; this appearance is due to the fact that the bands containin the state of rest small granules which, during the contraction of the animal, are disposed in transverse series, so as to recall the sarcous elements of Bowman.

Lieberkiihn, Greef, and Engelmann attribute the active part to the bright fibre. Engelmann has based his opinion on the fact that he recognized in the filament the property of double refraction, which, according to him, belongs to all contractile substances, while the substance which separates the filaments shows only single refraction. However that may be, it is one of these two elements that possesses the power of contraction, and which deserves the name of myophane, which Haeckel gave it. It is very remarkable that in the Stentors

and the Spirostomes the fibrillous striae are in intimate connection with the basilar extremity of the vijpratile cilia. In the Vorticellae one can clearly see the fibrils converge toward the axis of the style, the contractile element of which they constitute. We shall not leave the study of the motor organs without saying a word about the rhythmical movements which can be seen in the contractile vesicle of the Micro-organisms, vegetable as well as animal. This vesicle is a small cavity which is dug into the protoplasm, and which alternately increases and diminishes its capacity. Scientists by no means agree as to its exact function; Biitschli and Stein consider it to be a secretive apparatus. Its pulsations are very regular. Their number is constant in every species. In the chilodon cucullulus, a pulsation occurs every two seconds; in the Crytochium nigricans, every three seconds; in the Vorticellae, every eight seconds; in the Eiiplotes, every twenty-eight seconds; in the Acineria incurvata, every six minutes; Rossbach, whose curious experiments with the vibratile cilia and the cirri we have already cited, has made analogous experiments with the contractile vesicles. He observed especially that, under the action of alkaloids, the contractile vesicle ceased pulsating in diastole, and dilated enormously; but poisonous agents do not act all at once on the movements of the vesicle; they begin by paralyzing the larger cilia, which are under the influence of the will. The movements of the vesicle, like those of the small cilia, persist for a much longer time. M. E. Maupas has seen Paramecia, killed by a discharge of trichocysts, become completely immobile, with their vibratile cilia inert and rigid, while the contractile vesicle continued to pulsate

with the same activity; this activity continued for an hour. We have now briefly examined the morphology oi the motor organs of Micro-organisms. It is very difficult to determine the physiological process of the movements produced by these organs. The simplest movements and the ones most easily understood, are those by which a cell suddenly and strongly irritated withdraws its prolongations and assumes a spherical form; this change of form can be explained by a quick condensation of the protoplasm, which becomes the seat of a phenomenon similar to that of a contracting muscle. The sudden modifications which are observed to take .place in the form of the so-called metabolic Infusoria are in this way explained by an analogous phenomenon, so much the more evident as the Infusoria which possess this property, show in the cortical layer of their protoplasm (ectosarc) granulous bands which have with more or less justice been compared to the muscles of the higher animals. The displacements of the body determined by the pseudopodia, by the vibratile cilia, and by the flagellum are much more difficult to interpret; meanwhile it is probable that the movement proceeds from the contractions of the protoplasm which are produced either in the ectosarc or in the motor organ itself; the latter is automobile, as is seen, for example, when a flagellum separated from the rest of the body continues to move in the liquid.

It is well known that any number of discussions have been raised as to the manner in which the pedicel on which the Vorticellae are mounted, contracts. Still more obscure is the oscillatory movement of the Bacteria. These small beings are very mobile when they find themselves in a liquid; they frequently exhibit a movement of oscillation which sometimes carries them forward, sometimes backwards. An attempt has been made to explain these movements by postulating the presence of organs of locomotion, extremely slender filaments planted at one of the extremities of the Bacteria like small rods; but the existence of these organs has not been absolutely proved. Even more obscure is the movement observed in certain Gregarines." It would seem that in the case of these animals, which are often of considerable size, one ought to be able to understand the principle of their movements much more easily than in the case«of such small beings as the Bacteria; but this is not the case. The Polycystids have a very peculiar manner of moving; the motion is one of perfect translation, uniform and rectilinear; the animal seems to slide all of a piece over the object-plate; it can go to the right, to the left, stay its motion and resume it again; it is. free in directing its movements. Now, during this movement nothing can be seen to take place in the body from within or without. An analogous phenomenon is to be observed in the Diatomes. Some scientists have wished to explain the mysterious motion by translation executed by the Gregarines, as being due to an imperceptible undulation of the sarcode; but if there were any undulations whatever, one ought to observe a correlative movement in the granules inside; now this is something that is never seen.

Thus there still exists a great deal of obscurity concerning the principles determining motion among the Proto-organisms. The theories based upon muscular contraction that have been propounded from observing higher animals, are by no means sufficient to explain the phenomena of motility among certain Protozoa and Protophytes. Nervous System. Hitherto not the minutest trace of a central nervous system has been found in a single Proto-organism. The nervous function among these inferior beings devolves upon the protoplasm, which is irritable, which feels and which moves, and which, in certain species, as we shall see later on, is even capable of performing certain psychic acts, the complexity of which seems quite out of proportion to the small quantity of ponderable matter which serves as a substratum to these phenomena. There is, moreover, ng occasion to be surprised that an undifferentiated mass of protoplasm should be able to exercise the functions of a veritable nervous system. In fact every nervous element 'is nothing else than the product of protoplasmic differentiation; the protoplasm embodies in itself all the functions that, in consequence of an ulterior division of labor among the pluricellular organisms, have been assigned to distinct elements.

It has rightly been held, therefore, that if no nervous system, anatomically differentiated, existed in proto-organisms, it must be admitted that their protoplasm contains a diffused nervous system. Among all the observations that uphold this idea, we must cite one to which M. Gruber, a professor at Freiburg, in Breisgau, has recently called attention. This observation was made on a large, ciliated Infusory, the Stentor, of which mention will be made so often hereafter that it will be advantageous to give a full description of it beforehand.

The Stentor has an elongated body, broadened in front like a funnel, and able to fasten itself by its posterior extremity. The edge of its peristome is covered by a belt of vibratile cilia disposed about a spiral line. The mouth occupies the most sunken part of the peristome. The body of the animal is striated with longitudinal bands; at the plane of the peristome, these bands take a different direction: they become transversal and spiral. In the interior of the protoplasm can be observed a contractile vacuole and a nucleus like a string of beads, made up of a large number of grains. This Infusory, like all the Ciliates, multiplies by fission; a contraction is seen to take place in the middle of the body; the segment below the contraction generates a peristome similar to that of the upper segment; then a second contractile vacuole is formed, and soon the two segments represent two complete animals which possess all their organs. Nevertheless, the two Stentors continue to be united for a certain length of time by a bridge of matter, located even with the point where the contraction took place; this bridge of matter gradually grows thinner and thinner and becomes as fine as a thread. (See fig. 5.) Now, Gruber has observed that the two Stentors united by this Fis- s- stentor in probridge of protoplasm exhibit perfect harmony in their movements; they always sway in the same direction at the same time; and this harmony is necessary, because the least contrariety of motion