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

The first phenomena that have enabled us to conjecture as to the significance of the nucleus, have to do with the division of cellules; when a cellule divides, the nucleus comes into action, it exhibits certain movements, and passes through complicated stages which have been given the name of caryokinesis.* But these complex phenomena simply show the function of the nucleus as an histological element; they do not afford any disclosures as to the physiological role, of the nucleus in the cellule.

Other observations have enabled naturalists to surmise what phenomena are subject to the action of the nucleus. In 1881, Balbiani called attention to individuals, belonging to the species Paramacium aurelia, that were destitute of a nucleus and which nevertheless possessed the power of locomotion the same as ordinary individuals; whence, he concluded that the nuclei exerted no influence upon the phenomena of individual life. Shortly afterwards, Gruber observed small specimens of the Actinophrys sol which absorbed nutriment, changed their position in the liquid, and even fused with each other (zygosis), but which were nevertheless destitute of a nucleus. f

The idea then occurred to Gruber, and to Nussbaum likewise, to divide the Micro-organisms by artificial means into several fragments, of which some would contain a nucleus and others not, and then to watch what would come of it. Gruber, to whose experiments the most importance attaches, chose as his subject of trial the Stentor cceruleus, a ciliated Infusory of great size, which exhibits a nucleus resembling a chaplet of beads (moniliform). He afterwards continued his experiments upon other species, and his conclusion was, that the power to regenerate lost parts belonged to all Protozoans, but that this phenomenon only took place when the isolated fragment contained

t Contributions to the Biologisches Centralblatt, 1885. p. 73. some portion of the nucleus; in which case the animal reproduces all the organs it has lost in consequence of its dissection. Furthermore, the process of the formation is exactly the same as in the spontaneous division of these same Infusoria. The excitation caused by their removal is accordingly of the same character as the unknown excitation that provokes the natural division of the body.

From these experiments, the part acted by the nucleus is indicated by complete evidence. Gruber shows that in a single instance only can a fragment without a nucleus form itself anew; and that is, when the fragment contains an organ in course of formation, as happens, for example, during the spontaneous division of the animal. This amounts to saying, that the presence of a nucleus is necessary to give the impulse to the formation of the organ, but that it is not necessary to the completion of the organ when the impulse has once been given.

Lastly, if the fragment is totally destitute of a nucleus, it does not re-form itself so as to constitute a complete animal again; if the fragment possesses neither mouth nor peristome, it does not reproduce a new mouth and a new peristome; yet the fragments continue to live and to move. The absence of a nucleus does not suspend the functions of motion, sensibility, nutrition, or growth. This conclusion is, in our estimation, too sweeping, as we shall see further on.*

M. Balbiani has recently repeated these experiments of artificial division, and, while confirming in * We have taken as our guide, with the permission of M. Balbiani, the lectures delivered by that eminent authority at the College de France, in general the results of Gruber as to the function of the nucleus in the vital phenomena of ciliated Infusoria, he has endeavored to fix with more exactness a certain number of important points. His first experiments, like those of Gruber, were conducted upon the Stentor cceruleus, a species of which the size renders it better adapted to this sort of experimenting. In an observation which we shall take as a type, and which is represented by the figure sent to us by M. Balbiani, the body of the Stentor is cut by two transverse sections; three divisions are obtained, each of which contains a fragment of the nucleus. We will remember that the nucleus of the Stentor is like a long string of beads; it is not at-all rare to see a fragment of a Stentor contain one or more beads.

Fig, 12.— Artificial division of the Stentor cceruleus. (After Balbiani.) Let us follow the phenomena presented in the middle segment. This segment contains only a single grain of the nuclear chaplet; directly after severance, it assumed a globular shape; the day following, it had lengthened, had grown a tail at the posterior extremity, and upon the anterior part there had appeared, distinctly outlined, a crown of cilia longer than those upon the body; in other words, a peristome had

formed; the day after, the fragment had increased considerably in bulk, and in two days more the animal had formed a mouth. During this time, the nuclear grain had multiplied: five, in fact, were counted. The animal had the normal form; its size, however, was a little smaller than that of the ordinary Stentors. Thus, through the action of a small quantity of nuclear substance, the fragment has been completely reconstructed. It frequently happens that the artificial severing of the animal causes various deformations in the fragments. The deformation disappears with the greatest rapidity in fragments containing nuclear substance. The wound heals instantly; directly after severance, the two edges of the wound are seen to adjust themselves to each other.

In all these particulars, the experiments confirm the results obtained by Gruber. M. Balbiani desired to ascertain what would happen if the division were made during the state of conjugation. Conjugation, as we -know, aims at replacing an old, spent element, that has lost its physiological properties, by an element of new formation proceeding from an attendant nucleus (nucleolus) exchanged between the individuals in conjugation. The point in question was to ascertain whether the nucleus that was beginning to disappear, had lost its regenerative power. In the Stentors, during conjugation, this old nucleus breaks, and its nuclear globules are scattered to all parts of the protoplasm. When at this stage, the body of one of the Stentors is divided in such a manner that the fragment contains some of the scattered globules that came from the old nucleus. It is quite evident

In an experiment which we again cite as a type of many others, the fragment containing the elements of the old nucleus tends to reconstruct itself; this fragment, which represented the posterior part of the animal, presented, the day following, a rudimentary peristome; the reconstruction did not go beyond this point: it was left incomplete. Accordingly, the old nucleus loses its power of regeneration. As to the phenomena presented in fragments containing no nuclear substance, M. Balbiani has made decided advances in the question; he has completed the experiments of Gruber, he has also corrected them, and he has reached conclusions essentially different.

In order to understand more thoroughly the phenomena connected with the absence of nuclear substance, the author has directed his attention to another species, the Cyrtostomum leucas, which has the advantage that it can be kept longer alive than the Stentor can, on a glass slide holding a drop of water. The Cyrtostomum is a large ciliated Infusory of more than four-tenths of a millimeter in length. Its protoplasm is differentiated into two layers, one of which, the cortical, encloses very heavy trichocysts; the other, the endoplasm, holds alimentary substances. The animal exhibits upon one of its faces a mouth, shaped like a long narrow buttonhole, and upon the other face a contractile vesicle, from which crooked and anastomosed passages radiate. It is easy, by making a transversal division, to obtain fragments without nuclear matter; the nucleus of the Cyrtostomum being formed of a single, round mass. But it is not easy, on the other hand, to obtain fragments likely to live,

since this animalcule has a dense ectoplasm, and, when severed, this layer, which is not very retractile, does not grow together again and close the wound; the sides remain separated, the water comes in contact with the endoplasm, which swells, bulges out, and runs from the wound; the animal may thus void itself completely, dying of diffluence. It occasionally happens that the animal voids itself only in part, and that the nucleus escapes with a small piece of the protoplasm. Then, if the wound draws together, we get a fragment that has thrown out the nucleus by its own action.

We shall not speak of the actions of the fragment containing nuclear substance; they are the same as observed in the case of Stentors: the fragment rapidly reconstructs itself and re-forms a complete animal. Let us mark more closely the fragment without nucleus. Such fragments continue to live for some time; they have been kept alive as long as eight days; but they do not reconstruct themselves; they do not even assume a regular form; the part of the body facing the section retains its obliquity of truncation. At the start, for the first few days, the movements continue; a curious circumstance connected therewith is, that the fragments continue to move in the direction in which they would have moved if they were placed together to form a complete individual. The vibratile cilia are in no wise altered; they shake with the same animation as before. Only the movements of the animal are a trifle irregular; but they exhibit the same marks of volition as seen in normal individuals. The vesicle continues to contract.

fragment without nucleus contains the mouth; the mouth ingests alimentary substances. If the Cyrtostomum be given grains of potato fecula, which it is very partial to, the fragment without nucleus, but with a mouth, swallows these grains and fills itself with them. It is not known whether it digests them. This much was observed in the first stages, and Gruber was wrong in stopping at this point. At the expiration of a certain time, varying between the third and fourth day, alterations of structure are noticed in the fragment that are probably traceable to the absence of the nucleus. One of the first to take place is the disappearance of the m-arks of differentiation which we have observed to distinguish the endoplasm from the ectoplasm. The dark granules that fill the interior of the body congregate in the centre by abandoning the peripheral part; then these granules scatter and come to a position just beneath the cuticle, which denotes a deliquescence of the plasma. The layer of trichocysts undergoes changes and disappears. All these alterations result from an actual disorganization of the plasma. The contractile vesicle shrinks, its pulsations decrease, the radiating passages disappear. The body of fhe animal, which in its normal condition is elongate, becomes rounded; its movements flag and consist of nothing but a rotation of the body about its own axis; at last the animal becomes motionless and dies of difHuence.

These changes are not due to lack of sustenance, as one might suppose; for fragments that have a mouth and swallow food, pass through the same alterations as those that have no mouth.* * M. Balbiani has informed us, upon request, that the fragments of Cyrtostomum furnished with nucleus can be kept alive for a much longer time It is superfluous to insist upon the importance of these results, obtained by a method that might be called experimental physiology applied to unicellular organisms. Although the experiments have been made solely with ciliated Infusoria, the results of the same may be extended to all cellules, for the Infusoria are nothing more than autonomous cellules living an independent life.

The conclusion from the above researches of M. Balbiani, which, as we have seen,- go far beyond those of Gruber, is, that the nucleus is not necessary merely to the regeneration of the parts, as the German professor believed. The error made by Gruber arose from the fact that he did not follow the career of the fragments deprived of a nucleus long enough; if he had continued his observations, he would have seen that the fragment becomes gradually disorganized. The nucleus, accordingly, has not merely a formative power; it does not merely regulate alimentation, readjustment of form, and the healing of wounds; it has not merely a regenerative power, enabling the plasma to reconstruct complete the organs lost by artificial severance. The nucleus is, besides all this, an essential factor of the plasm's "vitality. If a fragment ot protoplasm be deprived of i^s nucleus, the fragment remains alive for some time, but afterwards undergoes disorganization.

Such are the facts, extremely complex, and consequently difficult to summarize by a formulated statement. under the same conditions (that is, in a drop of water on a glass slide kept in the moist chamber of Malassez): in this way it is possible to keep them alive for the space of a month, by introducing into the liquid a few Infusoria to serve them as food. On the other hand, the fragments deprived of nucleus by section live for only eight days at the most.

We certainly cannot regard the protoplasm as inert matter; but what appears probable is, that the protoplasm receives from the nucleus the communication, the delegation of physiological powers. The nucleus is in a certain sense the focal seat of life in all its forms. If we get rid of the nucleus by artificial section," the fragment of enucleated protoplasm continues to live for some time, having received from the nucleus an impulsion that has not yet been exhausted; but after a certain length of time, the impulsion given by the nucleus not being renewed, the protoplasm runs its

From the psychical point of view, which more particularly occupies our attention here, how are the results of these experiments in cellular vivisection to be explained? When a fragment of an organism, deprived of nuclear substance, is seen to move about freely and with the same activity as if it still possessed its nucleus, we are constrained to admit that the phenomena of the life of relation, or movement and sensibility, have their seat in the protoplasm. But it is probable that such physiological capacities as the powers of nutrition, are not inherent in protoplasm; they depend immediately upon the presence of the nucleus, for they disappear little by little and finally vanish a few days after the removal of the nucleus.*

It 'may be mentioned in passing, that there are certain psychical properties which the nucleus apparently does not transmit to the protoplasm, but which it retains for itself; this is the case with the instinct of gen- * The difficult question here, is to ascertain whether the psychical properties of the protoplasm are destroyed through the direct effect of the disorganization of the plasma, or whether they disappear a short time before the process of disorganization and in consequence of the absence of nuclear substance.

eration. We have already seen that, during the epidemic periods of conjugation, the Paramecia which have their nuclei overrun with parasites cease to conjugate with animals of the same species. The destruction of their nucleus by the Bacteria produces in the Faramecia the effect of actual castration. The removal of the nucleus, accordingly, causes the interruption of the following functions and in the following order as to time: 1. The regenerative and reproductive property of the plasma;

The psychologist will notice with interest that the psychical function of the protoplasm outlives the regenerative function for an appreciable length of time; a fragment of a cellule which, having been mutilated by the act of severance, is unable to correct its outward form, or to secrete a fresh cuticle, or to reconstruct its lost organs, is nevertheless still capable of perceiving sensations and of responding thereto by movements. Psychical life is consequently a property of living matter which appears to be less complex tKan the regenerative property, inasmuch as it ceases later.

To summarize, the nucleus plays the primordial role in the cellule; if, to use an old comparison of Ar- istotle's, we compare the protoplasm to the clay, we must compare the nucleus to the potter that fashions it. The nucleus comprehends all the physiological properties, the totality of which goes to constitute life. It is interesting to note what perfect accord prevails between these recently discovered facts and the phenomena relative to fecundation. Fecundation consists in the fusion of two nuclei, of which one proceeds from the male, and one from the female. Thus, it is through the intermediary office of the nucleus that all the faculties, all the properties possessed by the parents,— the form of their bodies as well as their psychical faculties, — are transmitted to the embryo; as we have just remarked, therefore, all these properties must be comprehended in the nucleus, in order to pass into the embryo.

We must note further, that the embryo takes from the mother something besides the nucleus. While it is connected with the father through the head of the spermatozoid, which has the morphological value of a nucleus, it receives from the mother not only the female nucleus but also the vitelline plasma of the ovule; now, as the embryo does not exhibit a greater morphological likeness to the mother than to the father, we may thence infer that the vitelline protoplasm inherited from the mother exerts no formative influence upon the development of its body.

These are not the only facts the connection of which we desire to show with the results of experiments upon the function of the nucleus. It will be well to point out here, how reproduction is effected among organisms which, besides their nucleus, possess other differentiated organs. The best known and perhaps the most general mode of reproduction is fissiparity, which consists in a division of the entire body into two equal parts. If we closely follow the course of this phenomenon in any organism whatever, we shall find that the division begins by a multiplication of the principal organs of the body. The nucleus begins by lengthening out and assuming a position perpendicu-

lar to the plane of division. The first organ that multiplies is the flagellum; it does not split into two parts, as several English authors have supposed; according to the observations of Biitschli and of Klebs, a second flagellum is formed complete. The pigmentary spot also does not divide into two parts; the old eye remains by a sort of preference with one of the parts, while the other part acquires a new eye, formed complete; this is likewise the case with the mouth and the cesophagus. There are only two elements that multiply by division: the chromatophores and the nucleus Now, when we note that the chromatophores contain a body, the pyrenoid, which exhibits the closest analogy of chemical composition with the nucleus, we may properly say that the nuclear elements of the cellule are the only ones that do not reproduce by neoformation at the expense of the protoplasm, as is the case with the cilia and the flagella.

The reason for this mode of multiplication by nuclear elements will be comprehended, if we consider the matter in the light of experiments made upon the formative properties of the nucleus. We have seen, in fact, that the nucleus can regenerate the protoplasm, but that the protoplasm cannot regenerate the nucleus. We now see that the regeneration of organs lost in consequence of the spontaneous division of cellules, is subjected to the same law as the regeneration following upon artificial division; the protoplasm cannot regenerate a nuclear element any more in the one case than in the other; in order to effect reproduction, therefore, this element must divide.

THE conclusions relative to psychological phenomena arrived at in the foregoing treatise, are in contradiction with the opinions generally received upon the psychology of the cell. Scientists have held, that cellular psychology is represented wholly and solely by the laws of irritability. In his -Essai de Psychologic Generate, a work in so many respects remarkable, M. Richet has assumed the advocacy of this view; the correctness of which we have no hesitation in disputing. In the work just mentioned, the distinguished professor has written the following:

" There exist simple beings which appear to be nothing more than a homogeneous assemblage of irritable cellules. Motory reaction, consequent upon irritation from without, constitutes their life of relation. Irritability is their life complete, but this, in effect, is psychic life; so that cellular irritability can be considered the same as elementary psychic life" From an attentive perusal of this passage it will be seen that M. Richet brings within the category of irritability, not only unicellular organisms, but also pluricellular organisms formed by the union of homogeneous cellules.