This exceptional instance, however, will scarcely be held to obscure that broad distinction from inorganic processes, which organic processes derive from the combination among their constituent changes. And the reality of this distinctiou becomes yet more manifest when we find that, in common with previous ones, it not only marks off the living from the not-living, but also things which live little from things which, live much. For while the changes going on in a plant or a zoophyte are so imperfectly combined that they can continue after it has been divided into two or more pieces, the com- bination among the changes going on in a mammal is so close that no part cut off from the rest can live, and any con- siderable disturbance of one function causes a cessation of the others. Life, therefore, as we now regard it, is a com- bination of heterogeneous changes, both simultaneous and successive.
Once more looking for a characteristic common to these two kinds of vital action, we perceive that the combinations of heterogeneous changes which constitute them, differ from the few combinations which they otherwise resemble, in re- spect of dcfiniteness. The associated changes going on in a glacier, admit of indefinite variation. Under a conceivable alteration of climate, its thawing and its progression may be stopped for myriads of years, without disabling it from again displaying these phenomena under appropriate conditions. By a geological convulsion, its motion may be arrested with- out an arrest of its thawing; or by an increase in the in- clination of the surface it slides over, its motion may be accelerated without accelerating its rate of dissolution. Other things remaining the same, a more rapid deposit of snow may cause an indefinite increase of bulk; or, conversely the accretion may entirely cease, and yet all the other actions continue until the mass disappears. Here, then, the combina- tion has none of that dcfiniteness which, in a plant, marks the mutual dependence of assimilation, respiration, and cir- culation; mucli less has it that dcfiniteness seen in the I PllOXIMATF- DEFLNITION OF MFE. 69 mutual (lopcndence of the chief animal functions: no one of which can be varied without varying the rest: no one of which can go on unless the rest go on. It is this definitcness of combination which distinguishes the changes occurring in a living body from those occurring in a dead one. Decom- position exhibits both simultaneous and successive changes, which are to some extent heterogeneous, and in a sense com- bined; but they are not combined in a definite manner. They vary according as the surrounding medium is air, water, or earth. They alter in nature with the temperature. If the local conditions are unlike, they progress differentlj^ in difTerent parts of the mass, without mutual influence. They may end in producing gases, or adipocire, or the dry substance of which mummies consist. They may occupy a few days, or thousands of years. Thus, neither in their simultaneous nor in their suc- cessive changes, do dead bodies display that definiteness of combination which characterizes living ones. It is true that in some inferior creatures the cycle of successive changes admits of a certain indefiniteness — that it may be apparently suspended for a long period by desiccation or freezing; and may afterwards go on as though there had been no breach in its continuity. But the circumstance that only a low order of life permits the cycle of its changes to be thus modified, serves but to suggest that, like the pre^ vious characteristics, this characteristic of definiteness in its combined changes, distinguishes high vitality from low vital- ity, as it distinguishes low vitality from inorganic processes. Hence, our formula as further amended reads thus: — life is a definite combination of heterogeneous changes, both simul- taneous and successive.
Finally, we shall still better express the facts, if, instead of saying a definite combination of heterogeneous changes, we say the definite combination of heterogeneous changes. As it at present stands, the definition is defective both in allow- ing that there may be other definite combinations of hetero- geneous changes, and in directing attention to the heteroro THE DATA OF BIOLOGY.
geneous changes rather than to the definiteness of their combination. Just as it is not so much its chemical elements which constitute an organism, as it is the arrangement of them into special tissues and organs; so it is not so much its heterogeneous changes which constitute Life, as it is the de- finite combination of them. Observe what it is that ceases when life ceases. In a dead bod}^ there are going on hetero- geneous changes, both simultaneous and successive. What then has disappeared? The definite combination has dis- appeared. Mark, too, that however heterogeneous the simul- taneous and successive changes exhibited by an inorganic object, as a volcano, we much less tend to think of it as living, than we do a watch or a steam-engine, which, though displaying homogeneous changes, displays them definitely combined. So dominant an element is this in our idea of Life, that even when an object is motionless, yet, if its parts be definitely combined, we conclude either that it has had life, or has been made by something having life. Thus then, we conclude that Life is — the definite combination of hetero- geneous changes, both simultaneous and successive.
§ 26. Sucli is the conception at which we arrive without changing our stand-point. It is, liowever, an incomplete conception. This ultimate formula (which is to a consider- able extent identical with one above given — " the co-ordina- tion of actions; *' seeing that " definite combination " is synonymous with " co-ordination," and " changes both si- multaneous and successive" are comprehended under the term " actions; " but which differs from it in specifying the fact, that the actions or changes are " heterogeneous ") — this ultimate formula, I say, is after all but proximately correct. It is true that it does not fail by including the growth of a crystal; for the successive changes this implies cannot be called heterogeneous. It is true that the action of a galvanic battery is not comprised in it; since liere, too, heterogeneity is not exhibited by the successive changes. It is true that by rilOXlMATE DEFINITION OF I.IFK. 71 this same qualification the motions of the Solar System are excluded; as are also those of a watch and a steam-engine. It is true, moreover, that while, in virtue of their heteroge- neity, the actions going on in a cloud, in a volcano, in a glacier, fulfil the definition; they fall short of it in lacking definiteness of combination. It is further true that this de- finiteness of combination, distinguishes the changes taking place in an organism during life, from those which commence at death. And beyond all this it is true that, as well as serving to mark off, more or less clearly, organic actions from inorganic actions, each member of the definition serves to mark off the actions constituting high vitality from those constituting low vitality; seeing that life is high in propor- tion to the number of successive changes occurring between birth and death; in proportion to the number of simultaneous changes; in proportion to the heterogeneity of the changes; in proportion to the combination subsisting among the changes; and in proportion to the definiteness of their com- bination. Nevertheless, answering though it does to so many requirements, this definition is essentially defective. It does not convey a complete idea of the thing contemplated. The definite combination of heterogeneous changes, both simtdtaneous and successive^ is a formula which fails to call up an adequate conception. And it fails from omitting the most distinctive peculiarity — the peculiarity of which we have the most familiar experience, and with which our notion of Life is, more than with any other, associated. It remains now to supplement the definition by the addition of this peculiarity.
CHAPTEE V.
THE CORRESPONDENCE BETWEEN LIFE AND ITS CIRCUMSTANCES.
§ 27. We habitually distinguish between a live object and a dead one, by observing whether a change w^hich we make in the surrounding conditions, or one w^hich Nature makes in them, is or is not followed by some perceptible change in the object. By discovering that certain things shrink when touched, or fly away when approached, or start when a noise is made, the child first roughly discriminates between the living and the not-living; and the man when in doubt whether an animal he is looking at is dead or not, stirs it wijth his stick; or if it be at a distance, shouts, or throws a stone at it. Vegetal and animal life are alike primarily recognized by this process. The tree that puts out leaves when the spring brings a change of temperature, the flower which opens and closes with the rising and setting of the sun, the plant that droops when the soil is dry, and re-erects itself when watered, are considered alive because of these in- duced changes; in common with the zoophyte which contracts on the passing of a cloud over the sun, the worm that comes to the surface when the ground is continuously shaken, and the hedgehog that rolls itself up when attacked.
Not only, however, do we habitually look for some response when an external stimulus is applied to a living organism, but we perceive a fitness in the response. Dead as well as living things display changes under certain changes of con- CORRESroXDENCF. BETWEEN LIFE AND IT."=; CIRCUMSTANCES. 73 dition: instance, a lump of carbonate of soda that effervesces when dropped into sulphuric acid; a cord that contracts when wetted; a piece of bread that turns brown when hold near the fire. But in these cases, we do not see a connexion between the changes undergone, and the preservation of the things that undergo them; or, to avoid any teleological im- plication— the changes have no apparent relations to future external events which are sure or likely to take place. In vital changes, however, such relations are manifest. Light being necessary to vegetal life, we see in the action of a plant which, when much shaded, grows towards the unshaded side, an appropriateness which we should not see did it grow otherwise. Evidently the proceedings of a spider, which rushes out when its web is gently shaken and stays within when the shaking is violent, conduce better to the obtain ment of food and the avoidance of danger than were they reversed. The fact that we feel surprise when, as in the case of a bird fas- cinated by a snake, the conduct tends towards self-destruction, at once shows how generally we have observed an adaptation of living changes to changes in surrounding circumstances.
Note further the kindred truth, rendered so familiar by infinite repetition that we forget its significance, that there is invariably, and necessarily, a conformity between the vital functions of any organism, and the conditions in which it is placed — between the processes going on inside of it, and the processes going on outside of it. We know that a fish can- not live in air, or a man in water. An oak growing in the ocean, and a seaweed on the top of a hill, are incredible combinations of ideas. We find that every animal is limited to a certain range of climate; every plant to certain zones of latitude and elevation. Of the marine flora and fauna, each species is found exclusively between such and such depths. Some blind creatures flourish only in dark caves; the limpet only where it is alternately covered and uncovered by the tide; the red-snow alga rarely elsewhere than in the arctic regions or among alpine peaks.
74 THE DATA OF I^IOLOGY.
Grouping together the cases first named, in which a parti- cular change in the circumstances of an organism is followed by a particular change in it, and the cases last named, in which the constant actions occurring within an organism im- ply some constant actions occurring without it; we see that in both, the changes or processes displayed by a living body are specially related to the changes or processes in its en- vironment. And here we have the needful supplement to our conception of Life. Adding this all-important charac- teristic, our conception of Life becomes — The definite com- bination of heterogeneous changes, both simultaneous and successive, in correspondence with external co-existences and sequences. That the full significance of this addition may be seen, it will be necessary to glance at the correspondence under some of its leading aspects.* § 28. Neglecting minor requirements, tne actions going * Speaking of "the general idea of /*/<?," M. Comte says: — " Cette idee sup- pose, en effct, non-seulement celle d'un etre organise de maniere a comporter I'etat vital, mais aiissi celle, non moins indispensable, d'un certain ensemble d'inflaences exterieure propres a son accomplissement. Une telle harmonie entre I'etre vivant et le milieu correspondant, caracterise evidemment la condition fon- damentale de la vie." Commenting on de Blainville's definition of life, which he adopts, he says: — ** Cette lumineuse definition ne me parait laisser rien d'impor- tant a desirer, si ce n'est une indication plus directe et plus explicite de ces deux conditions fondamentales co-relatives, necessairement inseparables de I'etat vivant, un organisme determine et un milieu convenable." It is strange that M. Comte should have thus recognized the necessity of a harmony between an organism and its environment, as a condition essential to life, and should not have seen that the continuous maintenance of such inner actions as will counterbalance outer actions, constitutes life. It is the more strange that he should have been so near this truth and yet missed it, since, besides his wide range of thought, M. Comte is often remarkable for his clear intuitions. Lest by saying this, I should deepen a misconception into which some have fallen, let me take the opportunity of stating, that though I believe some of M. Comte's minor generalizations to be true, and thouo-h I recognize the profundity of many incidental observations he makes, I by no means accept his system. Those general doctrines in which I agree with him, are those which he holds in common with sundry other thinkers. With all those general doctrines which are distinctive of his philosophy, I disagree — with all those at least that I have definite knowledge of; for beyond the first half of his " Course of Positive Philosophy," I know his opinions only by hearsay.
COlUlKSro^^DHXCE BETVVEKN LIFE AND ITS CIRCUMSTANCES. 75 on ill II plant pre-suppose a surrounding medium containing at least carbonic acid and water, together with a due supply of light and a certain temperature. Within the leaves carbon is being assimilated and oxygen given off; without them, is the gas from which the carbon is abstracted, and the imponderable agents that aid the abstraction. Be the nature of the process what it may, it is clear that there are external elements prone to undergo special re-arrangements under special conditions. It is clear that the plant in sunshine presents these conditions and so effects these re-arrange- ments. And thus it is clear that the changes which consti- tute the plant's life, are in correspondence with co-existences in its environment.
If, again, we ask respecting the lowest protozoon, how it lives; the answer is, that while on the one hand its sub- stance is ever undergoing oxidation, it is on the other hand ever absorbing nutriment; and that it may continue to exist, the assimilation must keep pace with, or exceed, the oxidation. If further we ask under what circumstances these combined changes are possible; there is the obvious reply, that the medium in which the protozoon is placed, must contain oxy- gen and food — oxygen in such quantity as to produce some disintegration; food in such quantity as to permit that dis- integration to be made good. In other words — the two antagonistic processes taking place internally, imply the pre- sence externally of materials having affinities that can give rise to these processes.
Leaving those lowest animal forms revealed by the mi- croscope, which simply take in through their surfaces the nutriment and oxygenated fluids coming in contact with them, we pass to those somewhat higher forms which have their tissues partially specialized into assimilative and re- spiratory. In these we see a correspondence between certain actions in the digestive sac, and the properties of certain sur- rounding bodies. That a creature of this order may continue to live, it is necessary not only that there be masses of sub- 76 THE DATA OF BIOLOGY.
stance in. tlie environment capable of transformation into its own tissue; but that the introduction of these masses into its stomach, shall be followed by the secretion of a solvent fluid that will reduce them to a fit state for absorption. Special outer properties must be met by special inner properties.
When, from the process by which food is digested, we turn to the processes by which it is seized, we perceive the same general truth. The stinging and contractile power of a polype's tentacle, correspond to the sensitiveness and strength of the creatures serving it for prey. Unless that external chanofe which brino:s one of these creatures in con- tact with the tentacle, were quickly followed by those inter- nal changes which result in the coiling and drawing up of the tentacle, the polype would die of inanition. The funda- mental processes of integration and disintegration within it, would get out of correspondence with the agencies and pro- cesses without it; and the life would cease.
Similarly, it may be shown that when the creature be- comes so large that its tissue cannot be eificiently supplied with nutriment by mere absorption through its limiting membranes, or duly oxygenated by contact with the fluid that bathes its surface, there arises a necessity for a circu- latory system by which nutriment. and ox3^gen maybe dis- tributed throughout the mass; and the functions of this sys- tem, being subsidiary to the two primary functions, form links in the correspondence between internal and external ac- tions. The like is obviously true of all those subordinate functions, secretory and excretory, that facilitate oxidation and assimilation — functions in which we may trace, both co- temporaneous changes answering to co-existences in the en- vironment, and successive changes answering to those changes of composition, of temperature, of light, of moisture, of pres- sure, which the environment undergoes.
Ascending from the visceral actions to the muscular and nervous actions, we find the correspondence displayed in a manner still more obvious. Every act of locomotion implies CORJIESPONDENCE BETWEEN LIFE AND ITS C1KCUMSTA^'CES. 77 the expenditure of certain internal mechanical forces, adapted in amounts and directions to balance or out- balance certain external ones. The recognition of an object is impossible without a harmony between the changes constituting per- ception, and particular properties co-existing in the environ- ment. Escape from enemies supposes motions within the organism, related in kind and rapidity to motions without it. Destruction of prey requires a particular combination of sub- jective actions, fitted in degree and succession to overcome a group of objective ones. And so with those countless au- tomatic processes exemplified in works on animal instinct.
In the highest order of vital changes, the same fact is equally manifest. The empirical generalization that guides the farmer in his rotation of crops, serves to bring his actions into concord with certain of the actions going on in plants and soil. The rational deductions of the educated navisrator who calculates his position at sea, constitute a series of mental acts by which, his proceedings are conformed to surrounding circumstances. Alike in the simplest inferences of the child, and the most complex ones of the man of science, we find a correspondence between simultaneous and successive changes in the organism, and co-existences and sequences in its envi- ronment.
§ 29. This general formula, which thus includes the lowest vegetal processes as well as the highest manifestations of hu- man intelligence, will perhaps call forth some criticisms which it is desirable here to meet.
It may be thought that there are still a few inorganic ac- tions included in the definition; as for example that displayed by the mis-named storm -glass. The feathery crystallization which, on a certain change of temperature, takes place in the solution contained by this instrument, and which afterwards dissolves to reappear in new forms under new conditions, may be held to present simultaneous and successive changes that are to some extent heterogeneous, that occur with" some de- 78 THE DATA OF BIOLOGY.
fiiiiteness of combination, and, above all, occur in correspond- ence with external changes. In this case vegetal life is sim- ulated to a considerable extent; but it is merely simulated. The relation between the phenomena occurring in the storm- glass and in the atmosphere respectively, is really not a cor- respondence at all, in the proper sense of the word. Outside there is a certain change; inside there is a change of atomic arrangement. Outside there is another certain change; in- side there is another change of atomic arrangement. But subtle as is the dependence of each internal ujDon each ex- ternal change, the connexion between them does not, in the abstract, differ from the connexion between the motion of a straw and the motion of the wind that disturbs it. In either case a change produces a change, and there it ends. The alteration wrought by some environing agency on an inani- mate object, does not tend to induce in it a secondary altera- tion, that anticipates some secondary alteration in the en- vironment. But in every living body there is a tendency towards secondary alterations of this nature; and it is in their production that the correspondence consists. The dif- ference may be best expressed by symbols. Let A be a change in the environment; and B some resulting change in an inorganic mass. Then A having produced B, the ac- tion ceases. Though the change A in the environment, is followed by some consequent change a in it; no parallel se- quence in the inorganic mass simultaneously generates in it some change h that has reference to the change a. But if we take a living body of the requisite organization, and let the change A impress on it some change C; then, while in the environment A is occasioning a, in the living body C will be occasioning c: of which a and c will show a certain con- cord in time, place, or intensity. And while it is in the con- tinuous production of suoh concords or correspondences that Life consists, it is by the continuous production of them that Life is maintained.
The further criticism that may be expected, concerns cer- CORRESPONDENCE BETWEEN LIFE AND ITS CIRCUMSTANCES. 70 tain verbal imperfections in the definition, which it seems impossible to avoid. It may bo fairly urged that the word correspondence will not include, without straining, the various relations to be expressed by it. It may be asked: — How can the continuous processes of assimilation and respiration, cor- respond with the co-existence of food and oxygon in the en- vironment? or again: — How can the act of secreting some defensive fluid, correspond with some external danger which may never occur? or again: — How can the dijnamical phe- nomena constituting perception, correspond with the statical phenomena of the solid body perceived? The only reply to these questions, is, that we have no word sufficiently general to comprehend all forms of this relation between the organ- ism and its medium, and yet sufficiently specific to convey an adequate idea of the relation; and that the word correspond- ence seems the least objectionable. The fact to be expressed in all cases, is, that certain changes, continuous or discon- tinuous, in the organism, are connected after such a manner that, in their amounts, or variations, or periods of occurrence, or modes of succession, they have a reference to external ac- tions, constant or serial, actual or potential — a reference such that a definite relation among any members of the one group, implies a definite relation among certain members of the other group; and the word correspondence appears the best fitted to express this fact.
§ 30. The presentation of the phenomena under this ge- neral form, suggests how our definition of Life may be reduced to its most abstract shape; and perhaps its best shape. By regarding the respective elements of the definition as relations, we avoid both the circumlocution and the verbal inaccuracy; and that we may so regard them with propriety is obvious. If a creature's rate of assimilation is increased in consequence of a decrease of temperature in the environment; it is that the relation between the food consumed and heat produced, is so re-adjusted by multiplying both its members, that the 80 THE DATA OF BIOLOGY.
altered relation in the surrounding medium between the quantity of heat absorbed from, and radiated to, bodies of a given temperature, is counterbalanced. If a sound or a scent wafted to it on the breeze, prompts the stag to dart away from the deer-stalker; it is that there exists in its neighbour- hood a relation between a certain sensible property and cer- tain actions dangerous to the stag, while in its organism there exists an adapted relation between the impression this sensible property produces, and the actions by which danger is escaped. If inquiry has led the chemist to a law, enabling him to tell how much of any one element will combine with so much of another; it is that there has been established in him specific mental relations, which accord with specific chemical relations in the things around. Seeing, then, that in all cases we may consider the external phenomena as simply in relation, and the internal phenomena also as simply in re- lation; the broadest and most complete definition of Life will be — The continuous adjustment of internal relations to external relations*