Problems of Life and Mind. Second series, George Henry Lewes [e book reading free TXT] 📗

processes of its body into the opening already made, and drags out the remains of the chlorophyll left there by its predecessor; while a third Monad leads a predatory life, falling upon other Monads that have filled themselves with food. Here, as he says, we stand on the threshold of that dark region where Animal Will begins; and yet there is here only the simplest form of organization.15

51. Now let our glance pass on to the second stage—the Cell. Here we have a recognized differentiation in the appearance of a nucleus amid the protoplasm. The nucleus is chemically different from the substance which surrounds it; and although perhaps exaggerated importance has been attributed to this nucleus, and mysterious powers have been ascribed to it, yet as an essential constituent of the cell it commands attention. Indeed, according to the most recent investigations, the definition of a cell is “a nucleus with surrounding protoplasm.” The cell-wall, or delicate investing membrane—that which makes the cell a closed sac—is no longer to be regarded as a necessary constituent, but only as an accessory.16

52. The cell may be either an organism or an organite. It may lead an isolated life as plant or animal, or it may be united with others and lead a more or less corporate existence; but always, even as an element of a higher organism, it preserves its own individuality. At first we see that the corporate union is very slight, merely the contact of one cell with another of its own kind, as in the filament of a Conferva. Rising higher, we see the cell united with others different from it; plants and animals appear, having structures composed of masses of various cells. Rising still higher, we see animal forms of which the web is woven out of myriads upon myriads of cells, with various cell-products, processes, fibres, tubes.

ORGANISM AND MEDIUM.

53. But we have only one half of the great problem of life, when we have the organism; and it is to this half that the chief researches have been devoted, the other falling into neglect. What is that other? The Medium in which the organism lives. Every individual object, organic or inorganic, is the product of two factors:—first, the relation of its constituent molecules to each other; secondly, the relation of its substance to all surrounding objects. Its properties, as an object or an organism, are the results of its constituent molecules, and of its relation to external conditions. Organisms are the results of a peculiar group of forces, exhibiting a peculiar group of phenomena. Viewing these in the abstract, we may say that there are three regulative laws of life:—(1) The Lex Formationis—the so-called nisus formativus, or “organizing force”; (2) the Lex Adaptationis, or adaptive tendency; (3) the Lex Hereditatis, or tendency to reproduce both the original form and its acquired modifications. We have always to consider the organizing force in relation to all surrounding forces—a relation succinctly expressed in the word Adaptation. Just as water is water only under a certain relation of its constituent molecules to the temperature and atmospheric pressure—just as it passes into other forms (ice or steam) in adapting itself to other conditions; so, likewise, the organism only preserves its individuality by the adjustment of its forces with the forces which environ it.

54. This relation of Organism and Medium, the most fundamental of biological data, has had a peculiar fortune: never wholly unrecognized, for it obtrudes itself incessantly in the facts of daily experience, it was very late in gaining recognition as a principle of supreme importance; and is even now often so imperfectly apprehended that one school of philosophers indignantly rejects the idea of the Organism and Medium being the two factors of which Life is the product. Not only is there a school of vitalists maintaining the doctrine of Life as an entity independent both of Organism and Medium, and using these as its instruments; but there is also a majority among other biologists, who betray by their arguments that they fail to keep steadily before them the fundamental nature of the relation. Something of this is doubtless due to the imperfect conception they have formed of what constitutes the Medium; instead of recognizing in it the sum of external conditions affecting the organism—i. e. the sum of the relations which the organism maintains with external agencies,—they restrict, or enlarge it, so as to misapprehend its significance—restrict it to only a few of the conditions, such as climate, soil, temperature, etc., or enlarge it to embrace a vast array of conditions which stand in no directly appreciable relation to the organism. Every one understands that an organism is dependent on proper food, on oxygen, etc., and will perish if these are withheld, or be affected by every variation in such conditions. Every one understands that an animal which can devour or be devoured by another, will flourish or perish according to the presence of its prey or its enemy. But it is often forgotten that among external existences, all those which stand in no appreciable relation to the organism are not properly to be included in its Medium. In consequence of this oversight we frequently hear it urged as an objection to the Evolution Hypothesis, that manifold organisms exist under the same external conditions, and that organisms persist unchanged amid a great variety of conditions. The objection is beside the question. In the general sum of external forces there are certain items which are nearly related to particular organisms, and constitute their Medium; those items which are so distantly related to these organisms as to cause no reactions in them, are, for them, as if non-existent.17 Of the manifold vibrations which the ether is supposed to be incessantly undergoing, only certain vibrations affect the eye as light; these constitute the Medium of Sight; the others are as if they were not. Only certain vibrations of the air affect the ear as Sound; to all other vibrations we are deaf; though ears of finer sensibility may detect them and be deaf to those which affect us.

55. “The external conditions of existence” is therefore the correct definition of the Medium. An animal may be surrounded with various foods and poisons, but if its organism is not directly affected by them they cannot be food or poison to it. An animal may be surrounded with carnivorous rivals, but if it is not adapted to serve them as food, or is too powerful to be attacked by them, they only indirectly enter into its Medium, by eating the food it would eat. The analogy is similar with anorganisms and their relation to their media. Every physical or chemical phenomenon depends on the concurrence of definite conditions: namely, the substance which manifests the change, and the medium in which the change is manifested. Alter the medium, solid, liquid, or gaseous, change its thermal or electrical state, and the phenomenon is altered. But although similar alterations in the medium notoriously influence the organism, yet, because a great many variations in external conditions are unaccompanied by appreciable changes in the organism, there are biologists who regard this as a proof of Life being independent of physical and chemical laws; an error arising from their not recognizing the precise nature of organic conditions.

56. To give greater precision to the conception of a Medium it will be desirable to adopt the distinction much insisted on by Claude Bernard, namely, 1°, an External or Cosmical Medium, embracing the whole of the circumstances outside the organism, capable of directly affecting it, and 2°, an Internal or Physiological Medium, embracing the conditions inside the organism, and in direct relation with it—that is to say, the plasma in which its tissues are bathed, by which they are nourished. To these add its temperature and electrical conditions. Bernard only includes the nutritive fluid; but inasmuch as each organism possesses a temperature and electrical state of its own, and these are only indirectly dependent on the external temperature and electricity, and as it is with these internal conditions that the organism is in direct relation, I include them with the plasma among the constituents of the Physiological Medium. Any change in the External Medium, whether of temperature or electricity, of food or light, which does not disturb the Internal Medium, will of course leave the organism undisturbed; and for the most part all the changes in the External Medium which do affect the organism, affect it by first changing the Internal Medium. External heat or cold raises or depresses the internal temperature indirectly by affecting the organic processes on which the internal temperature depends. We see here the rationale of acclimatization. Unless the organism can adapt itself to the new External Medium by the readjustment of its Internal Medium, it perishes.

57. We are now enabled to furnish an answer to the very common objection respecting the apparent absence of any direct influence of external conditions. Let the objection first be stated in the words of a celebrated naturalist, Agassiz: “It is a fact which seems to be entirely overlooked by those who assume an extensive influence of physical causes upon the very existence of organized beings, that the most diversified types of animals and plants are everywhere found under identical circumstances. The smallest sheet of fresh water, every point of the sea-shore, every acre of dry land, teems with a variety of animals and plants. The narrower the boundaries which are assigned as the primitive home of all these beings, the more uniform must be the conditions under which they must be assumed to have originated; so uniform indeed that in the end the inference would be that the same physical causes can produce the most diversified effects.”

Obviously there is a complete misstatement of the argument here; and the excess of the misstatement appears in the following passage: “The action of physical agents upon organized beings presupposes the very existence of those beings.” Who ever doubted it? “The simple fact that there has been a period in the history of our earth when none of these organized beings as yet existed, and when, nevertheless, the material constitution of our globe and the physical forces acting upon it were essentially the same as they are now, shows that these influences are insufficient to call into existence any living being.”18 Although most readers will demur to the statement that because the material constitution of our globe was “essentially the same” before and after animal life appeared, therefore there could have been no special conditions determining the appearance of Life, the hypothesis of Evolution entirely rejects the notion of organic forms having been diversified by diversities in the few physical conditions commonly understood as representing the Medium. Mr. Darwin has the incomparable merit of having enlarged our conception of the conditions of existence so as to embrace all the factors which conduce to the result. In his luminous principle of the Struggle for Existence, and the Natural Selection which such a struggle determines, we have the key to most of the problems presented by the diversities of organisms; and the Law of Adaptation, rightly conceived, furnishes the key to all organic change.

58. In consequence of the defective precision with which the phrase “Medium,” or its usual equivalent “physical conditions,” is employed, several biological errors pass undetected. Haeckel19 calls attention to the common mistake of supposing the organism to be passive under the influence of external conditions, whereas every action, be it of light or heat, of water or food, necessarily calls forth a corresponding reaction, which manifests itself in a modification of the nutritive process. He points out the obverse of this error in the current notion