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

i. Vegetable nutrition, or according to Biitschli's expression, holophytic. This is the method of nutrition among animal or vegetable cellules that contain chlorophyl and that nourish themselves by forming organic nutriment from ingredients taken from the surrounding medium. It is hardly necessary to call to mind that the function of chlorophyl is that of nutrition and not of respiration. This phenomenon was formerly termed the diurnal respiration of plants. The expression involves several mistakes. Enough to say that vegetables respire as animals do, by uniting with oxygen, and that that respiration continues the same both day and night. The function of chlorophyl is by no means respiration; its office is to decompose the carbonic acid gas of the air and to seize the carbon, which serves the plant in forming ternary or quaternary substances. This chemical work is performed by all chlorophyl organisms when influenced by the radiation of light.

Chlorophyl does not belong exclusively to the vegetable kingdom. A large number of animal Microorganisms are colored green by this pigment; they are met with principally in the important group of Flagellates. Their assimilative organs, which are likewise found in all green plants, bear the name of chromatophores; they have lately formed the subject of interesting investigations. The chromatophores are small bodies of protoplasm which are distinguished from protoplasm in general by their having assumed an individual structure.

These little bodies, which in the vegetables are called leucites, have a granular and reticulate structure; they are impregnated with a coloring substance, at times green, at times yellow, and at times brown, as the case may be; in fact, several coloring substances are present, which, by intermixture in different proportions, form colors of many varieties. The best known, after green chlorophyl, is yellow chlorophyl or diatomin. The latter coloring substance can be absorbed by alcohol.

The Euglenoididae, the Chlamydomonadidae, and the Volvocinae exhibit enormous chromatophores. In the case of the Euglenae, the chromatophores are formed of small discoid plates; they are situated directly under the cuticle, so that the light can act upon them (see fig. 4). In certain species of Flagellata, they are exhibited under the cuticle in the form of two large plates which envelop the protoplasm like a cuirass formed of two pieces. The Chlamydomonadidae and the Volvocinse have green chromatophores, disc-shaped, and very small.

In the centre of the chromatophore a small bright space is observed which was formerly thought to be filled with chlorophyl; in reality, it is a minute solid globule which shows an extremely close analogy with the substance composing nuclei, or nuclein. It exhibits the same chemical reactions; it actively absorbs coloring matter and grows extremely brilliant when treated with acids. Schmitz gives this little body the name of pyrenoid (from TTI>P/> , nucleus). It is around the pyrenoid, and probably through its action, thatstarch forms; it is deposited in grains or re-unites in a ring about the pyrenoid, a fact easily ascertained by coloring them with iodine.

Production of starch has also been observed in the colorless Flagellates, as for instance in the Polytoma iivclla. These latter do not have chromatophores, but Kimstler, and after him Fisch, has noticed that every grain of starch is attached to a small mass of colorless protoplasm which is the focus of formation for the grains. This is precisely what happens in vegetable organisms where colorless starch-leucites are found. This little mass of protoplasm Always faces the hilum of the starch-grain.

As the function of the chromatophores is exercised only when subjected to the influence of light, it follows that green Micro-organisms must have light in order to nourish themselves. A quite remarkable fact may be adduced in this connection. On examining the kingdom of Protozoans as a whole, it will be seen that a striking coincidence exists between the presence of the eye and the presence of the chlorophyl pigment. Organisms having an ocular spot are in most cases provided with the chlorophyl pigment, or, in other words, nourish themselves as plants do, by generating starch through the action of light. This fact proves that sensibility to light is in some manner dependent upon the chlorophyl function. If Flagellates possessing chromatophores, that is organs generating starch, have ocular spots at the same time, it is because these rudimentary 'eyes enable them to find their way towards the light, which is the necessary agent of chlorophyl action. Accordingly, all Micro-organisms having eyes nourish themselves as plants do. In their case, the object of the eye is to direct the performance of a vegetable function.

Euglense might nourish themselves as animals do, for they have a mouth and a digestive apparatus. The buccal, or oral, aperture opens in the anterior end at the base of the flagellum, and is connected with a short gullet or esophagus (see fig. 6, the mouth and gullet of an Euglena). Nevertheless, the Euglena is never seen using its mouth for swallowing alimentary particles. A quite curious problem is involved here. If it is true, as has beefi claimed, that it is the function that makes the organ, how do we explain the existence and especially the genesis of this digestive apparatus which performs no function?

It is the presence of chromatophores that prevents certain Flagellates from feeding like animals; so much so in fact, that the digestive apparatus performs its functions in Flagellates which have no chromatophores and are not provided with chlorophyl pigment, an instance of which is seen in the Peranema. The Peranema is, further, an exceedingly voracious animal. We must note also that the Peranema does not exhibit ocular spots like the green Euglena; and moreover, it has no need of such, since it does not have to seek the light to generate starch. All these phenomena are interdependent.

The influence exerted by light upon the green organisms of both kingdoms has been ascertained by different scientists. Light at a certain degree of intensity attracts them, and at 'a greater degree, repels them. Some years ago M. Strassburger conducted a series of connected experiments upon the movements of green spores towards light. It was observed, here, that the grains of pigment in the interior of the cellules, when under the influence of

solar radiations, executed movements and set outwards in all directions. 2. Nutrition by endosmosis, or saprophytic. The organism nourishes itself by absorbing through the whole surface of its body liquids containing the products of vegetable or animal decomposition. Saprophytic beings are found in putrid waters or in infusions. This manner of nutrition may be considered, from the point of view which now engages us, as the most simple of all; it probably allows of a search for food, but it is certain that no movements are involved which are designed to draw the food into any possible digestive apparatus.

3. There is now a last mode of nutrition, of which we shall treat in minute detail; namely, animal nutrition, where the Micro-organism seizes solid alimentary particles and nourishes itself after the fashion of an animal, whether it be by means of a permanent mouth or by means of an adventitious one, improvised at the moment of need. This manner of nutrition is the process employed by higher animals. Among the lower organisms, it is met with in most of the In- fusoria, in the Sarcodines, in many of the Mastigophores, and in others. Respecting the Micro-organisms belonging to the vegetable kingdom, we find nutrition by endosmosis and chlorophyl nutrition; the Protophytes never possess a mouth and never absorb solid foods.

Animal nutrition requires very remarkable psychological faculties in the organism practicing it. These manifestations of psychic life, the progressive complexity of which we intend to trace in starting from the simplest protozoic forms and arriving at the higher — prove that these animalcula are endowed with memory and volition. We shall group our remarks under the two following heads: The Micro-organisms do not nourish themselves indiscriminately, nor do they feed blindly upon every substance that chances in their way. Also, when they ingest food through some point or other of their bodies, they understand perfectly how to make a choice of the particles they wish to absorb. This choice is sometimes quite well defined, for there are species which feed exclusively upon particular foods. Thus, there are herbivorous Infusoria and carnivorous Infusoria. Among the herbivorous ones may be classed the chilodons which feed upon small Algae, Diatomaceae, and Oscillaria. The parmecia live principally upon Bacteria. The Leucophrys is a specimen of the carnivorous class; it devours even the smaller animals of its own kind. The Cyrtostomum leucas eats everything, as do the Rotifers.

Though the fact of an exercise of choice in taking food is settled beyond question, yet the interpretation of this phenomenon is a matter of much uncertainty. Some writers, as Charlton Bastian for instance, explain this choice of food as an affinity of chemical composition existing between the organism and the nutriment. This idea does not lead to anything. Others compare the discrimination made by the Proto-organism between objects presented to it, to the action of a magnet which in some way selects particles of iron that have been mixed with particles of other substances. ' The latter interpretation is an evidence of the tendency evinced by some naturalists,

of endeavoring to identify the attributes of living organic matter with the physico-chemical properties of the mineral kingdom. In our opinion, the only question demanding consideration is whether the choice of food, in the case of Proto-organisms, does or does not result from a psychical operation, similar, for example, to that which takes place in higher organisms. We have received a noteworthy communication from M. E. Maupas, upon this subject, which tends to establish that the choice of food is not the result of individual taste in the Micro-organisms, but is determined by the organic structure of their buccal apparatus which does not allow them to receive other forms of nutriment.

We must closely examine, therefore, the mechanism for prehension of food. The following is what occurs when the Amoeba, in its rampant course, happens to meet a foreign body. In the first place, if the foreign particle is not a nutritive substance, if it be gravel for instance, the amoeba does not ingest it; it thrusts it back with its pseudopod-ia. This little performance is very significant; for it proves, as we have already said, that this microscopic cellule in some manner or other knows how to choose and distinguish alimentary substances from inert particles of sand. If the foreign substance can serve as nutriment, the Amoeba engulfs it by a very simple process. Under the influence of the irritation caused by the foreign particle, the soft and viscous protoplasm of the Amoeba projects itself forwards and spreads about the alimentary particle somewhat as an ocean-wave curves and breaks upon the beach; to carry out the simile that so well represents the process, this wave of protoplasm retreats, carrying with it the

foreign body which it has encompassed. It is in this manner that the food is enveloped and introduced into the protoplasm; there it is digested and assimilated, disappearing slowly. There are cellules found in the inner intestinal walls of lower animals which effect the prehension of solid foods in the same manner as the Amoeba cellule: they are called phagocytes. This mode of prehension is beyond contradiction the most simple imaginable; for the prehensile organ is not as yet differentiated. Every part of the protoplasm may be made to serve as a digestive cavity in enveloping the foreign substance.

From the special standpoint of prehension of food, we may place the Actinophrys sol above the Amoeba. This animalcule is a small microscopic Ileliozolarian abounding in fresh-water ooze. It casts out long, slender, filamentous pseudopodia from every part of its body. When its prey or any alimentary substance gets into the midst of this mass of filaments, the filament affected quickly draws back, carding the nutritive matter with it towards the body proper of the Actinophrys. In other instances, the filaments, anastomosing themselves, form a sort of envelope about the prey. At the instant the substance comes within a short distance of the cellule, a part of the protoplasm composing the mass projects itself forwards, and encompasses the food, which is carried back and enveloped in the midst of the protoplasm by a process analogous to that seen in Amoeba.

In the case of the Actinophrys any part of the body could serve as a way of entry for food, that is to say, could act the part of a mouth. To use the expression of W. Saville Kent, it is a pant ost ornate being. In other species of higher organization, this mode of alimentation is rendered impossible by the cutitcle which encompasses the body; the formation of a cuticle impervious to solid foods creates the necessity of a buccal orifice through which food may enter into the interior of the protoplasm.

A curious graduation in these phenomena is noticed here. Thus there are organisms destitute of a permanent and pre-existing mouth; their mouth is improvised as the occasion demands, is adventitious, so to say, and the reason that these organisms are ranked higher than the preceding ones, is that the mouth is invariably formed in the same place. In this connection we may examine a small flagellate Infusory which abounds in impure waters, the Monas vulgaris. It carries a long flagellum attached to its anterior extremity, which when not in motion, is coiled up against the body. At the base of the flagellum the protoplasm projects a pellucid substance in the shape of a lip. This protuberance is hollow, containing a vacuole filled with liquid. Cienkotvski has described how these different organs act. The Bacteria and Micrococcus, which constitute the food of the Monas , are pulled into the latter's neighborhood by strokes of the flagellum; at that instant, the animal becomes conscious of the proximity of these other bodies, for the protuberance which lies at the base of the flagellum extends towards the corpuscule, envelops it in its own substance, and pulls it back into the interior of the Monad's body. Biitschli has made an analogous observation with the Oikomonas termo.

The prehension of food comprehends, here, three phases, in two of which the organism manifests psychical activity : first, attraction of food by means of the flagellum ; second, formation of the vesicle which extends towards and enVelops the food, when the latter has come near; third, absorption of the food. The Acinetae are organisms that move about very little ; they frequently remain fixed to a pedicle their whole life long. They' have no cilia, but exhibit radiating prolongations, more or less numerous, and sparse or grouped in tufts, as the case may be. These filaments are suckers, provided at the end with a small air-hole. When a thoughtless Infusory swims into the territory of an Acineta, the latter arrests it by means of its stout filaments and fastens upon the former's body the cup-shaped extremities of its suckers, which make a vacuum. The protoplasm of the Ciliate thus captured, slips slowly through the suckers as through tubes, and is gathered together in the interior of the Acineta in the form of small drops. In the Acinetas, accordingly, particular organs are adapted to the prehension and absorption of food. Corresponding to the greater complexity of physical action, the psychical process necessary for the act of prehension has likewise become more complicated than is the case with the Amoeba. The Acineta is obliged to direct its sucker towards the Infusory which is within its reach, and consequently the animal is obliged to determine the position of its prey.

There are Acinetidse that exhibit prehensile organs more perfect than those just noticed. Such are the Hcmiophrys. They have both sucker tentacles and prehensile tentacles. The latter are filaments which the animal throws about its victim like a lasso, thus enveloping and rendering it motionless, while it proceeds to feed upon it by means of its suctorial apparatus. Now, do these Acinetidae show any preference of choice among the Infusoria that chance to fall within reach of their tentacles? M. Maupas, who has made an especial study of these organisms had at first admitted this preference in choice. But he afterwards rejected the notion. In 1885, he writes us: " I find quite another explanation of the impunity with which the Coleps hirtus can throw itself upon the terrible suckers of the Podophrys fixa. The stout shell with which this little Infusory is enveloped, serves it as a shield and guards it from the deadly grasp of the Acinetidae. The Acinetidae do not seize the Coleps because of any dislike of the latter, but because they are unable to seize them, and their inability results from the peculiar structure of the Coleps' tegumentary envelope. The Paramecia which also escape unscathed, are similarly provided with a tegument of high resisting power, which serves them as a protection in this contingency. The Stylonichia histrio, like all other Stylonichiae, has a very soft tegumentary envelope. They are accordingly seized and devoured by the Acinetidae without difficulty. The detailed knowledge of the differences of structure in the tegumentary envelopes has caused me to abandon the idea of a preference or dislike in the choice of those victims which serve as food for the Acinetidae. Of the prey that passes by, they catch what they can and not what they want to."

In a large number of species the prehension of food is preceeded by another stage, the search for food, and in the case of living prey, by its capture. We shall riot investigate these phenomena among all the Protozoa, but shall direct our attention especially to the ciliated Infusoria. Their habits are a remarkable study. If a drop of water containing Infusoria be placed under the microscope, organisms are seen swimming rapidly about and traversing the liquid medium in which they are in every direction. Their movements are not simple; the Infusory guides itself while swimming about; it avoids obstacles; often it undertakes to force them aside; its movements seem to be designed to effect an end, which in most instances is the search for food; it approaches certain particles suspended in the liquid, it feels them with its cilia, it goes away and returns, all the while describing a zigzag course similar to the paths of captive fish in aquariums; this latter comparison naturally occurs to to the mind. In short, the act of locomotion as seen in det-ached Infusoria, exhibits all the marks of voluntary movement.

It might also be mentioned that every species manifests its personality in its mode of locomotion. Thus, as a rule, the Actindtricha saltans when placed in a preparation where it finds itself at ease, remains for a few moments perfectly immovable. Then, of a sudden, it dashes forward with the rapidity of lightning and disappears from the field of vision. For a time it darts about to the right and to the left, and then once more assumes its state of immobility. It can move with the greatest agility through masses of debris, in the midst of which, bending and twisting, it slips about with wonderful nimbleness. The Lagynus crassicolis, on the other hand, moves along at a pace quite constant and uniform, neither slow nor rapid. It searches about among algae and fragmentary particles. The Peritromus Emma moves slowly. "It runs lazily over the Algae, where it seeks its nutriment, and does not stray from them to venture into the open water.

Concerning the prehension of foods and the search for nutriment on the part of Ciliates, we can do no better than to quote entire a note which M. E. Maupas has been pleased to send us upon the subject. We had put to him two questions: First, do the Ciliates hunt their food? Second, while in quest of live prey, do the Ciliates called hunters make an actual hunt, involving the espial of prey from a distance and the voluntary pursuit of the same in the circuitous paths they follow? M. E. Maupas after having once more had recourse to observation, bciefly recapitulates his opinion in the following lines:

"From the standpoint of prehension of food, the Ciliates may be divided into two great groups: "In the first group the mouth is always held wide open, and along with the nutritive particles which the current of the vortex keeps constantly sucking in, we may at will cause other, absolutely inert and indigestible, particles to take the same course; for instance, such substances as granules of carmine, indigo, and rice-starch. These granules, totally unfit for nutritive purposes, pass through the body of the Ciliates along with the genuine nutriment and are finally cast out intact with the excrement. I think, therefore, we may affirm that the species having alimentary vortices exercise no real choice in selecting their foods, and that they absorb indiscriminately all corpuscules which by reason of fheir form and density admit of being seized and drawn into the alimentary whirlpool.

" In the case of the hunter Ciliates proper, the mouth is constantly closed. The act of absorbing each object captured is accomplished by a process of deglutition comparable in every phase to the like process in higher animals. Furthermore, these species feed only upon living prey, which they capture and entrammel by means of their trichocysts (vid. Archives de Zoologie, Vol. I. 1883, p. 607 and ff.). By this very act they exercise a choice in the selection of food. But this manifestation of choice is not, in my opinion, the result of preference, or of individual taste, but is the consequence of the peculiar construction of their buccal apparatus, which does not enable them to take other and different nourishment.

"These hunter Infusoria are constantly running about in quest of prey; but this constant pursuit is not directed towards one object any more than another. They move rapidly hither and thither, changing their direction every moment, with the part of the body bearing the battery of trichocysts held in advance. When chance has brought them in contact with a victim, they let fly their darts and crush it; at this point of the action .they go through certain manoauvres that are prompted by a guiding will. It very seldom happens that the shattered victim remains motionless after direct collision with the mouth of its assailant. The hunter, accordingly, slowly makes his way about the scene of action, turning both right and left in search of his lifeless prey. This search lasts a minute at the most, after which, if not successful in finding his victim, he starts off once more to the chase and resumes his irregular and roving course. These hunters have, in my opinion, no sensofy organ whereby they are enabled to determine the presence of prey at a distance; it is only by unceasing and untiring peregrinations both day and night, that they succeed in providing themselves with sustenance. When prey

abounds, the collisions are frequent, their quest profitable, and sustenance easy; when scarce, the encounters are correspondingly less frequent, the animal fasts and keeps his Lent. The Lagynus crassicolis, accordingly, never sees its victim from a distance and in no case directs its movements more towards one object of prey than towards another. It roams about at random, now to the right and now to the left, impelled merely by its predatory instinct — an instinct developed by its peculiar organic construction, which dooms it to this incessant vagrancy to satisfy the requirements of alimentation.

"The vorticel Infusoria, when in a medium abounding in food, are almost entirely sedentary in their habits, only making slight changes of position. But if they are placed in a medium affording but little nutritive material, they become as migratory as the hunters, and are seen to race about in all directions searching for more abundant nutriment. It is hard to find a more perfect illustration of the influence exerted by the conditions of a medium upon the habits and customs of animals.