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

would suffice to break the feeble bond that unites them. Moreover, their vibratile cilia beat in unison. To explain this concordance in the movements of the two animals, Gruber assumes that the entire mass of their protoplasm performs the function of a diffused nervous system, which has the effect of regulating their movements and of making them harmonize. We might add that the Infusoria possess not only a diffused nervous system, but that they must of necessity possess special nerve centres, endowed with different functions.

It will be remembered in fact that, under the influence of certain poisonous agents, death is not simultaneous throughout all parts of the organism. What ceases first are the voluntary movements of the large cilia; the movements of the small cilia are able to persist much longer; and finally, when all the cilia have become immobile and rigid, the vesicle has still been seen to pulsate for an hour. This gradual death recalls what we remark among the Vertebrates; under the influence of poisonous agents, the brain dies first, then follows the marrow, and lastly the bulb, which is the ultimum moriens.

The Organs of Sense. All the Micro-organisms are endowed with sensibility; some, like the Infusoria, have exceedingly sensitive powers. But, hitherto, organs of sense anatomically differentiated have been found in only a very small number of species. Generally, the protoplasmic expansions which we have above described under the name of pseudopodia are regarded as fulfilling the function of rudimentary organs of touch which advise the micro-organism of the presence of objects which happen in its path; but these pseudopodia, which at the same time serve as

motor apparatus, do not exhibit any structure which especially fits them for the reception of sensory impressions. Similarly, Stein considers the vibratile cilia as organs of touch. As these are organs which have not undergone any differentiation, we shall not stop to consider them. The Infusoria belonging to the genus Cryptochilum (Maupas) carry at their posterior extremity a long rigid bristle, which M. Maupas regards as an organ of touch, intended to advise the animal of the approach of other Infusoria.

We shall speak more at length of the organ of sight: this has been the subject of numerous treatises, some of which are quite recent and of the greatest interest to general physiology and psychology. Of all the organs of sense the eye is the one which is first differentiated. It is found in the organisms belonging to the vegetable kingdom as well as in those belonging to the animal kingdom. While these small beings do not seem to possess any organ especially adapted by its structure for the reception of tactile, olfactory, or gustatory impressions, a large number already exhibit an ocular spot, that is to say a differentiated organ, for the purpose of sight and for no other purpose.

It is chiefly in the group of Flagellates, and principally in the species that are colored green by chlorophyl (for example the Euglenae), that ocular spots are found; these spots which are colored a bright red, present themselves very clearly to the observation, for they are set off by the uncolored plasma of the anterior part of the body where they are generally located. Oculiform spots are also found in the species colored by yellow chlorophyl (Uroglena volvox, etc.). Generally, there is only one spot, situated at the base of the flagellum. This is seen especially in the Euglena viridis, a small flagellate infusory, which is veryabundant in fresh waters, which it often covers with a thick green coating.

In the Synura uvella, a colony-forming flagellate, there exist in each individual, in the anterior part of the body, numerous spots, varying from two to ten. Below we give an illustration representing the anterior extremity of the Euglena Ehrenbergii, according to Klebs. A large ocular spot is noticeable, in contiguity with the contractile reservoir. Ehrenberg, deceived by the appearance of these two organs, had taken the contractile reservoir for a nerve ganglion.

It is not only in the large group of Protozoans that the red spots are met with; they are found also among thevegetable Micro-organisms. A large number of green-colored zoospores exhibit at the anterior, and /?£,6.— Anterior extremity of usually colorless, extremity of their bodies, a small red point same structure as the red spot of the Euglenae. It was on this fact that Stein based his opinion that the spot of Euglena is not an eye; to him it seemed impossible to admit that the vegetable Proto-organisms could possess a visual organ. This is an excellent instance of a priori reasoning. Later on we shall see that Stein's view has now been completely abandoned; the very opposite view is taken, for the

eye of the Protista is considered as being destined to perform chiefly a vegetable function. Klebs was able to study the structure of the ocular spots, by employing a very ingenious artifice. When the Euglenae are treated with a solution of sea salt, in the proportion of one part to one hundred, an enormous dilatation of the contractile vesicle, which forms a hollow in the protoplasm of the animal, is induced; now, as the red spot is, so to speak, glued to the vesicle, it undergoes the same dilatation as the latter does, thus greatly facilitating observation. By this treatment it has been observed that the spot is a small discoid or triangular mass, of jagged and irregular outline; it is formed of two material parts; for a base it has a small mass of reticulated protoplasm, and in the meshes of the protoplasm there are small drops of an oily substance, colored red.

This red pigment, which has received the name of hematochrome, is not without its analogy with the green pigment of the chlorophyl, because this latter becomes red under certain conditions. For example, the chlorophyl pigment which fills the entire body of the Hematococcus pluvialis becomes red, when the animal enters into a state of rest; the stagnant spores of the algae alsf) assume a red tint. So, also, in numerous plants, the parts of the flower destined to become red are green as long as they are enclosed in the bud. It is thus probable that the red pigment of the Euglenoids is derived from a green pigment.

What is the physiological significance of these spots? Ehrenberg considered them as eyes; hence the name Euglena (word for word, pretty eye), which he had given to a species of Flagellates provided with ocular spots. This interpretation had been questioned by all the authors of his time, especially by Dujardin. At the present day, however, naturalists have come back to it, in consequence of observations which have been made on other Micro-organisms that possess a more perfectly developed eye.

M. Pouchet has discovered in the Glenodinium polyphemus, which belongs to the group of Peridinia (or Dinoflagellates, according to the classification of Biitschli), an eye about the function of which there can be no mistake. This eye occupies a fixed place in the cellule of the Peridinium; it has a uniform location and position. It consists of two parts, the one a veritable crystalline humor, and the other a veritable choroid. The crystalline is a strongly refracting, hyalin, club-shaped body, rounded at its free end, which is always directed forwards, while the other end is immersed in the mass of pigment which represents the choroid. This latter is clearly determined; it forms a sort of hemispherical cap, enveloping the posterior extremity of the crystalline. In one of the two forms of Glenodinium polyphcmus, the choroid pigment is red; in the other it is black.

M. Pouchet has been able to establish that in the young animals the crystalline is first*formed of six to eight refracting globes, which are merged into each other in order finally to constitute one unified mass. Also, the choroid is the result of a combination of the pigmentary granules which, at first sparse, group together and finally form the hemispheric cap that covers the posterior extremity of the crystalline. In fact, the visual organ of this Peridinium is composed of exactly the same parts as the eye of a metazoon with one exception, the absence of the nerve

element. This is not at all differentiated, but remains diffused, like the whole nervous system. M. Pouchet calls attention to the interest which his observation affords from a taxonomic point of view. The Peridinia have sometimes been classed among the vegetables; the presence of starch and of cellulose in their protoplasm has induced Warming to classify them among the Diatomaceae and Desmidiaceae. It is admitted to-day that certain Peridinia possess an eye, an organ which has hitherto been considered as the exclusive attribute of animals. Nothing more clearly emphasizes the altogether artificial character of the distinction between animals and vegetables than the results of dealing with Micro-organisms.

Before leaving the Peridinia, we would remark that these small beings afford an interesting fact from the point of view of the history of the Protozoa; they are provided with a long flagellum; they exhibit in addition an equatorial line on which formerly a crown of vibratile cilia was thought to be recognizable: this supposed coexistence of a flagellum and of cilia had determined the naturalists to form a group of Cilioflagellates, serving as a transition between the Flagellates, properly so-called, and the Ciliates. Since then it has been discovered that the Peridinia do not possess vibratile cilia; what had given rise to this error is the presence of a second flagellum on the level of the transverse line which we have just described; the movements of this flagellum have the appearance of vibratile cilia in motion.

Some time before the investigations of M. Pouchet, M. Kimstler (of Bordeaux) had discovered, in a Flagellate of the genus Phacus, a red eye which is also formed ^{ two parts; it is composed of a homogenous globule, acting as a crystalline humor, and surrounded by a red pigment, acting the part of the choroid. Before M. Kiinstler, Claparede and Lachmann, in their important work on Infusoria and Rhizopods, had described a similar visual organ in the Freia elegans, a ciliated infusory of the family of Stentorines. " Immediately behind the point of truncation," say they, " there is found a lunate spot of intense black, evidently belonging to the category -of those phenomena which M. Ehrenberg, in the Ophryoglenae, for example, calls an eye or an ocular spot. The significance of this spot has never been known. It was often very much denser than that of the Ophryoglenae, and sometimes there was discovered behind it a very transparent corpuscle, which involuntarily gave rise in the mind to the idea of a crystalline humor. We cannot, however, add much of importance to this idea, since the functions of a refracting apparatus must necessarily remain problematic, as long as we do not discover behind it a nervous apparatus fitted to perceive the impressions received."

This last conclusion seems to us excessively cautious. The co-existence of a pigment and of a crystalline humor amply suffices to characterize a visual organ. As to the nerve apparatus susceptible of perceiving impressions, it is replaced by the protoplasm, which, as is well known, is sensitive to light. Even before that, in 1856, Lieberkiihn had discovered in a ciliated infusory, the Panophrys flavicans, an ocular spot, composed of a convex crystalline humor, having the form of a watch-crystal enveloped by pigment and placed on the convex side of the oral fosse. In another species, the Ophryoglena atra, he found black pigment, but no crystalline humor.

It is impossible to believe that these organs are not eyes, for -they have the same structure as the eyes of comparatively higher classes of animals, such as certain worms, turbellaria, rotifers, lower-class crustaceans, etc; all these organs are similarly formed of a small crystalline globule enclosed in a small mass of pigmentary matter. The identity of structure naturally leads to the assumption of the identity of functions. The eye of the Euglena is the simplest of all; it is even reduced to the maximum point of simplicity, as it is composed of a spot of pigment. What induces us to believe that this spot is a visual organ, is the presence of this pigment. In fact this pigment is found in the most elementary visual organs. A second argument might be advanced; the red pigment of the Euglena exhibits the same re-actions as the coloring matter that fills the rods of the retina in the Vertebrates. From among these re-actions common to both, we cite the decoloration under the influence of light (Capranica).

Whatever the case may be, one thing is certain, namely that the Euglena is very sensitive to the light. When they are kept in a vessel, they are invariably seen to cover the side exposed to the light. M. Engelmann has observed that light acts very strongly upon this small animal; it does not act directly on the spot of pigment, nor, as was formerly thought, on the flagellum, but on the protoplasm which is located in front of the spot. The special microspectral object-glass that M. Engelmann constructed, enables us to see that the Euglenae always congregate in the band F to G of the spectrum.

cerned, we have already mentioned that a large number of the algae zoospores exhibit, in the anterior part of their body, ocular spots of a beautiful ruby color: these are organs that probably have the same structure as the red spots of the Euglenae. Moreover, it is probable that certain Microphytes possess more complex visual organs, composed of red pigment and of a crystalline humor. M. Balbiani has recently testified to this fact • in the case of the Pandorina morum, a spherical colony of green micro-organisms; in each colony there exists a certain number of individuals which possess a red spot, the shape of which is perfectly circular; if this spot be examined under a glass of very high magnifying power, one can readily see that it is formed of a small spherical globule, covered, on a portion of its surface, by a cap of red matter. This observation is all the more interesting because it is made on a being, the vegetable nature of which is to-day no longer doubted; the Pandorina are Volvocina3 which modern botanists place among the algae. (We are glad to give our readers the earliest communication concerning this fact.)

In describing the eye of the Protista, we said that the eye is the only organ of sense which is distinctly differentiated in these lower beings. But, perhaps, this assertion is too sweeping. Some species appear armed with small organs which could easily be invested with a sensory function. In this respect, we may cite the Loxodes rostrum, a beautiful ciliated infusory, remarkable for its proboscis and for the muscular sheath which closes its mouth. This animal exhibits along the dorsal surface a row of small organs which, by their structure, seem destined to act a part in performing the function of hearing. They are

formed of a vesicle, the centre of which is occupied by a refracting globule; they are called the vesicles of Miiller, after Johannes Miiller, who discovered them. The auditory organs which have been observed in Worms and the Ccelenterata are apparently composed of a vesiculiform capsule enclosing a solid concretion, called otolith. Thus it is possible that the vesicles of Miiller may be auditory vesicles. Up to the present time this organ has not been met with in any other species of Protozoa.

After studying the organs, let us pass to a study of their functions. It is not our intention to devote special chapters to irritability, instinct, memory, reasoning, and thepowers of volition in Micro-organisms. This would lead to diffuseness of treatment. Our method will be quite different. We shall describe as a whole all the different manifestations of psychical activity attendant upon the actions of Micro-organisms in the exercise of the important functions of their existence. The present chapter will be devoted to psychical phenomena connected with the act of nutrition.

All living matter possesses the power of continually increasing its mass by the inward reception of materials, and of simultaneously decreasing the same through the combustion of its substance with the oxygen of the atmosphere. The first of these processes is called nutrition, and the second, respiration. We shall first examine the psychical phenomena which precede and determine the act of respiration. These phenomena are often very simple and of little

significance. If the Micro-organism lives in the water, which is most frequently the case, the oxygen contained in solution therein passes directly through the cellular cuticle by dialysis and comes in contact with the body of the protoplasm; in which case the process of respiration is solely a chemical phenomenon. But it may happen that a minute organism chances into a medium containing little or no oxygengas; amid these new conditions where it becomes necessary to move towards sources emitting oxygen by voluntary effort and directed motion, it has been discovered that a great number of Micro-organisms, and particularly Bacteria, are capable of detecting the expansive power exerted by oxygen in the liquids in which they are found. When bacteria of putrefied matter are put in a drop of water containing no oxygen but in which have been placed chlorophyl algae, or green Euglenae, or grains of chlorophyl obtained by crushing green cellules, nothing happens in the first instant; but if the preparation be illuminated so as to allow the chlorophyl to act, the bacteria are seen to exhibit very rapid movements and to proceed, altogether, towards the points of the preparation where the generation of oxygen is taking place, that is to say, about the grains of chlorophyl. Under these conditions a chemical exchange is instituted -between the chlorophyl and the aerobious Bacteria: the Bacteria disengage carbonic acid gas and absorb oxygen; the chlorophyl fastens upon the carbon of the acid and sets the oxygen at liberty. If the preparation be darkened the Bacteria cease assembling about the chlorophyl grains, which, hid from the light, cease to disengage oxygen. The clustering begins anew, if a ray of sunlight is again let touch the chlorophyl.

Analogous facts have been observed under circumstances somewhat different. In a preparation from the intestines of a silk-worm, M. Balbiani has seen Bacteria which were uniformly distributed throughout all points of the preparation, gather about the green and undigested cellules of the leaves contained in the intestines, and bury themselves in them as if to partake of them. In other instances, the same naturalist has observed that Bacteria developed in a drop of silk-worm's blood, would gather, after a while, about the globules of the blood; undoubtedly for the purpose of seizing the oxygen being absorbed by them.

Upon the basis of these facts M. Engelmann has established the method called the Bacteria method. He regards bacteria as a living reagent which enable us to reveal the trillionth part of a milligram of oxygen, that is to say, a quantity scarcely greater, according to the calculations of physicists, than a molecule. This curious method enables us to explain biological problems which had hitherto remained unsolved. Before this, it was not known whether the colorless protoplasm of green plants could or could not disengage oxygen. It is now known, thanks to the bacteria, that grains of chlorophyl are the only points about which the liberation of oxygen takes place. The same method has enabled us to prove, in the variegated plants, that the maximum liberation of oxygen coincides with the maximum absorption of light. Thus, in the case of green algae, the red and the violet colors of the spectrum are the spots where the bacteria accumulate the thickest; consequently here is where the liberation of oxygen is greatest. Now, these colors correspond to the lines of greatest absorption in the spectrum of chlorophyl. In the case of brownish yel-

low cellules, the maximum action is in the green; in the case of bluish green cellules, in the yellow; in the case of red cellules, in the green. The author has concluded from this that there exists a series of coloring substances which, like chlorophyl, have the power of resolving carbonic acid gas; he calls them chromophyls. In the same way, moreover, this method enables us to solve the question of the distribution of energy in the solar spectrum. As M. Engelmann has remarked, it is interesting to see the Bacteria come to confirm our theories as to the composition of solar light.

Bacteria are not the only organisms that eagerly make towards points where oxygen is to be found. A large number of other Micro-organisms act in the same way when they happen into a medium lacking oxygen. M. Ranvier has noticed that if a preparation containing leucocytes, screened from air, be examined for a certain length of time the cellules will be seen to throw out long filaments towards the part that faces the air-side of the preparation. It appears, then, that a rudimentary oxygen-sense exists in the protoplasm of Proto-organisms.

This sense does not merely apprise the organism of the presence of oxygen; it enables it, further, to gauge the tension (expansive power) of the gas. So that, when the tension becomes too powerful, the organisms are seen to flee before it. The mode of nutrition among Micro-organisms is not uniform — a fact which ought not to appear remarkable when we bear in mind that this immense group is made up of all manner of heterogeneous beings that have nothing in common save the microscopic littleness of their bodies and the simplicity of their structure. Three main types of nutrition may be briefly distinguished.