Throuo^h the humblest, as well as throuo:h the hisrhest, ve- getal organisms, there are ever going on certain re-distribu- tions of matter. In protophytes the microscope shows us an internal transposition of parts, wliicli when not active enough to be immediately visible, is proved to exist by the changes of arrangement that become manifest in the course of hours and days. In the individual cells of many higher plants, an active movement among the contained granules may be wit- nessed. And well- developed cryptogams in common with all phanerogams, exhibit this genesis of mechanical motion still more conspicuously in the circulation of sap. It might, in- deed, be concluded a priori^ that through plants displaying much differentiation of parts, an internal movement must be going on; since, without it, the mutual dependence of organs having unlike functions would seem impossible. Besides these motions of fluids kept up internally, plants, espe- 5-1 THE DATA OF BIOLOGY.
dally of tlie lower orders, are able to move tlieir external parts in relation to each other, and also to move about from place to place. Illustrations in abundance will occur to all students of recent Natural History — such illustrations as the active locomotion of the zoospores of many Algae, the rhyth- mical bendings of the OscillatoricB, the rambling progression of the Diatoinacece. In fact many of these smallest vegetals, and many of the larger ones in their early stages, display a mechanical activity not distinguishable from that of the simplest animals. Among well- organized plants, which are never locomotive in their adult states, we still not unfre- quently meet with relative motions of parts. To such fami- liar cases as those of the Sensitive plant and the Yenus' fly-trap, many others may be added. When its base is irritated, the stamen of the Berberry flower leans over and touches the pistil. If the stamens of the common wild Cistus be gently brushed with the finger, they spread themselves — bending away from the seed-vessel. And some of the orchid- flowers, as Mr Darwin has recently shown, shoot out masses of pollen on to the entering bee, when its trunk is thrust down in search of honey.
Though the power of moving is not, as we see, a character- istic of animals alone, yet in them, considered as a class, it is manifested to an extent so marked, as practically to become one of their distinctive characters — indeed, we may say, their most distinctive character. For it is by their immensely greater ability to generate mechanical motion, that animals are enabled to perform those actions which constitute their visible lives; and it is by their immensely greater abilitj^ to generate mechanical motion, that the higher orders of animals are most obviously distinguished from the lower orders. Though, on remembering the seemingly active movements of infusoria, some will perhaps question this last-named con- trast; yet, on comparing the quantities of matter propelled through given spaces in given times, they will see that the momentum evolved is far less in the protozoa than in the THE RE-ACTIONS OF ORGANIC MATTER ON FORCES. 55 teleozoa. Those sensible motions of animals are cfFectcd by various organs under various stimuli. In the humblest forms, and even in some of the more developed ones which. • inhabit tlie water, locomotion results from the vibrations of cilia: the contractility resides in these waving hairs that grow from the surface. Some of the AcalephcB^ and their allies the Polypes, move when mechanically irritated: the long pendant tentacle of a PhysaUa is suddenly drawn up if touched; and, as well as its tentacles, the whole body of a Hydra collapses if roughly handled, or jarred by some shock in its neighbourhood. In all the higher animals how- ever, and to a smaller degree in many of the lower, sensible motion is generated by a special tissue, under the special ex- citement of a neural discharge. Though it is not strictly true that such animals show no sensible motions otherwise caused; since all of them have certain ciliated membranes, and since the circulation of fluid in them is partially due to osmotic and capillary actions; yet, generally speaking, we may say that their movements are effected only by muscles that contract only through the agency of nerves.
What special transformations offeree generate these various mechanical changes, we do not, in most cases, know. Those re-distributions of fluid, with the alterations of form sometimes caused by them, that result from osmose, are not, indeed, quite incomprehensible. Certain motions of plants which, like those of the " animated oat," follow contact with water, are easily interpreted; as are also such other vegetal motions as those of the Touch-me-not, the Squirting Cucumber, and the Carpoholus. But we have as yet no clue to the mode in which molecular movement is transformed into the movement of masses, in animals. We cannot refer to known causes the rhythmical action of a Medusa's disc, or that slow decrease of bulk that spreads throughout the mass of an Alcyonium, when one of its component individuals has been irritated. 'Hov are we any better able to say how the insensible motion transmitted through a nerve, gives rise to sensible motion in 56 THE DATA OF BIOLOGY.
a muscle. It is true tliat Science lias given to Art, several methods of changing insensible into sensible motion. By ap- plying heat to water we vaporize it; and the movement of its expanding vapour, we transfer to solid matter; but it is clear that the genesis of muscular movement is in no way analogous to this. The force evolved during chemical transformations in a galvanic battery, w^e communicate to a soft iron magnet through a wire coiled round it; and it would be quite possi- ble, by placing near to each other several magnets thus excited, to obtain, through the attraction of each for its neighbours, an accumulated movement made up of their separate movements, and thus to mechanically imitate a mus- cular contraction; but from what we know of organic mat- ter, and the structure of muscle, there is no reason to suppose that anything analogous to this takes place in it. We can, however, through one kind of molecular change, produce sensible changes of aggregation such as possibly might, when occurring in organic substance, cause sensible motion in it: I refer to allotropic change. Sulphur, for example, as- sumes different crystalline and non-crystalline forms at dif- ferent temperatures; and may be made to pass backwards and forwards from one form to another, by slight variations of temperature: undergoing each time an alteration of bulk. We know that this allotropisra, or rather its analogue iso- merism, prevails among colloids — inorganic and organic. We also know that some of these metamorphoses among col- loids, are accompanied by visible re-arrangements: instance hydrated silicic acid, which, after passing from its soluble state to the state of an insoluble jelly, begins, in a few days, to contract, and to give out part of its contained water. Now, considering that such isomeric changes of organic as well as inorganic colloids, are often very rapidly produced by very slio-ht causes, it seems not impossible that some of the colloids constituting muscle, may be thus changed by a nervous dis- charge— resuming their previous condition when the dis- charge ceases. And it is conceivable that by structural THE RE-ACTIONS OF ORGANIC MATTER ON FORCES. 57 arrangements, minute sensible motions so caused, may be ac- cumulated into largo sensible motions. There is, however, no evidence to support this supposition.
§ 23. But the truths which it is here our business espe- cially to note, are quite independent of hypotheses or inter- pretations. It is sufficient for the ends we have in view, to observe that organic matter docs exhibit these several conspi- cuous re- actions, when acted on by incident forces: it is not requisite that we should know Jiow these re- actions originate.
In the last chapter were set forth the several modes ia whicb incident forces cause re -distributions of organic mat- ter; and in this chapter have been set forth the several modes in which is manifested the motion accompanying this re-dis- tribution. There we contemplated under its several aspects, the general fact, that in consequence of its extreme instability, organic matter undergoes extensive molecular re-arrange- ments, on very slight changes of conditions. And here we have contemplated under its several aspects, the correlative general fact, that during these extensive molecular re-arrange- ments, there are necessarily evolved large amounts of force. In the one case the atoms of which organic matter consists, are regarded as changing from positions of unstable equili- brium to positions of stable equilibrium; and in the other case they are regarded as giving out in their falls from unstable to stable equilibrium, certain momenta — momenta that may be manifested as heat, light, electricity, nerve- force or mechanical motion, according as the conditions determine.
I will add only that these evolutions of force are rigor- ously dependent on these changes of matter. It is a corol- lary from that primordial truth which, as we have seen, underlies all other truths, {First Principles, §§ 76, 141,) that w^hatever amount of power an organism expends in any shape, is the correlate and equivalent of a power that was taken into it from without. On the one hand, it 58 THE DATA OF BIOLOGY.
follows from the persistence of force, that each portion of mechanical or other energy which an organism exerts, im- plies the transformation of as much organic matter as con- tained this energy in a latent state. And on the other hand, it follows from the persistence of force that no such trans- formation of organic matter containing this latent energy can take place, without the energy being in one shape or other manifested.
CHAPTER lY.* PROXIMATE DEFINITION OF LIFE.
§ 24. To those wlio accept the general doctrine of Evolu- tion, it needs scarcely be pointed out that classifications are subjective conceptions, which have no absolute demarcations in Nature corresponding to them. They are applianCes by which we limit and arrange the matters under investigation; and so facilitate our thinking. Consequently, when we at- tempt to define anything complex, or make a generalization of facts other than the most simple, we can scarcely ever avoid including more than we intended, or leaving out some- thing that should be taken in. Thus it happens that on seeking a definition of Life, we have great difficulty in find- ing one that is neither more nor less than sufficient. Let us look at a few of the most tenable definitions that have been given. While recognizing the respects in which they are defective, we shall see what requirements a more com- plete one must fulfil.
* This chapter and the following two chapters originally appeared in Part III. of the Principles of Psychology: forming a preliminary which, though indis- pensahle to the argument there developed, was somewhat parenthetical. Having now to deal with the general science of Biology before the more special one of Psychology, it becomes possible to transfer these chapters to their proper place. They have been carefully revised.
60 THE DATA OF BIOLOGY.
Sclielling said that Life is the tendency to individuation. This formula, until studied, convej^s little meaning. But it needs only to consider it as illustrated by the facts of develop- ment, or by the contrasts between lower and higher forms of life, to recognize its value; especially in respect of compre- hensiveness. As before shown, however, {First Princij^les, § 56), it is objectionable, partly on the ground that it refers, not so much to the functional changes constituting Life, as to the structural changes of those aggregations of matter which manifest Life; and partly on the ground that it includes under the idea Life, much that we usually exclude from it: for instance — crystallization.
The definition of Richerand, — " Life is a collection of phenomena which succeed each other during a limited time in an organized body," — is liable to the fatal criticism, that it equally applies to the decay which goes on after death. For this, too, is " a collection of phenomena which succeed each other during a limited time in an organized body."
" Life," according to De Blainville, " is the two-fold internal movement of composition and decomposition, at once general and continuous." This conception is in some re- spects too narrow, and in other respects too wide. On the one hand, while it expresses what physiologists distinguish as vegetative life, it excludes those nervous and muscular functions which form the most conspicuous and distinctive classes of vital phenomena. On the other hand, it describes not only the integrating and disintegrating processes going on in a living body, but it equally well describes those going on in a galvanic battery; which also exhibits a " two-fold in- ternal movement of composition and decomposition, at once general and continuous."
Elsewhere, I have myself proposed to define Life as " the co-ordination of actions; "* and I still incline towards this de- finition as one answering to the facts with tolerable precision, * See Westminster Eevieio for April, 1852. — Art. IV. "A Theory of Popu- lation."
PROXIMATE DEFINITION OF LIFE. Gi It includes all organic changes, alike of the viscera, the limbs, and the brain. It excludes the great mass of inor- ganic changes; which display little or no co-ordination. By making co-ordination the specific characteristic of vitality, it involves the truths, that an arrest of co-ordination is death, and that imperfect co-ordination is disease. More- over, it harmonizes with our ordinary ideas of life in its dif- ferent gradations: seeing that the organisms which we rank as low in their degree of life, are those which display but little co-ordination of actions; and seeing that from t?iese up to man, the recognized increase in degree of life corresponds with an increase in the extent and complexity of co-ordina- tion. But, like the others, this definition includes too much; for it may be said of the Solar System, with its regularly- recurring movements and its self-balancing perturbations, that it, also, exhibits co-ordination of actions. And how- ever plausibly it may be argued that, in the abstract, the motions of the planets and satellites are as properly compre- hended in the idea of life, as the changes going on in a motionless, unsensitive seed; yet, it must be admitted that they are foreign to that idea as commonly received, and as here to be formulated.
It remains to add the definition since suggested by Mr G. H. Lewes — '' Life is a series of definite and successive changes, both of structure and composition, which take place within an individual without destroying its identity." The last fact which this statement has the merit of bringing into view — the persistence of a living organism as a whole, in spite of the continuous removal and replacement of its parts — is important. But otherwise it may be argued, that since changes of structure and composition, though probably the causes of muscular and nervous actions, are not the muscular and nervous actions themselves, the definition excludes the more visible movements Avith which our idea of life is most associated; and further, that in describing vital changes as a serieSy it scarcelv includes the fact that manv of them, as 62 THE DATA OF BIOLOGY.
Nutrition, Circulation, Kespiration, and Secretion, in their many subdivisions, go on simultaneously.
Thus, however well each of these definitions expresses the phenomena of life under some of its aspects, no one of them is more than approximately true. It may turn out, that to find a formula which will bear every test is impossible. Meanwhile, it is possible to frame a more adequate formula than any of the foregoing. As we shall presently find, these all omit an essential peculiarity of vital changes in general — a peculiarity which, perhaps more than any other, distinguishes them from non- vital changes. Before specify- ing this peculiarity, however, it wdll be well to trace our way, step by step, to as complete an idea of Life as may be reached from our present stand- point: by doing which, we shall both see the necessity for each limitation as it is made, and ulti- mately be led to feel the need for a further limitation.
And here, as the best mode of determining what are those general characteristics which distinguish vitality from non- vitality, we shall do well to compare the two most unlike kinds of vitality, and see in what they agree. Manifestly, that which is essential to Life must be that which is common to Life of all orders. And manifestly, that which is common to all forms of Life, will most readily be seen on contrasting those forms of Life which have the least in common, or are the most uAlike.* § 25. Choosing assimilation, then, for our example of bodily life, and reasoning for our example of that life known as intelligence; it is first to be observed, that they are both processes of change. Without change, food cannot be taken into the blood nor transformed into tissue: without * This paragraph replaces a sentence that, in The Frinciples of Fsi/choloffi/, referred to a preceding chapter on "Method;" in which the mode of procedure here indicated, was set forth as a mode to be systematically pursued in the choice of hypotheses. Should opportunity ever permit, this chapter on Method will be embodied, along with other matter on the same topic, in a General Introduction to lu-iit Frinci2)lcs.
niOXIMATE DEFINITION OF LIFE. 63 change, there can be no getting from premisses to conclusion. And it is this conspicuous manifestation of change, which forms the substratum of our idea of Life in generah Doubt- less we see innumerable changes to which no notion of vital- ity attaches: inorganic bodies are ever undergoing changes of temperature, changes of colour, changes of aggregation. But it will be admitted that the great majority of the phe- nomena displaj^ed by inorganic bodies, are statical and not dynamical; that the modifications of inorganic bodies are mostly slow and unobtrusive; that on the one hand, when we see sudden movements in inorganic bodies, we are apt to assume living agencj^, and on the other hand, when we see no movements in organic bodies, we are apt to assume death. From all which considerations it is manifest, that be the requisite qualifications what they may, a definition of Life must be a definition of some kind of change or changes.
On further comparing assimilation and reasoning, with a view of seeing in what respect the change displayed in both differs from non- vital change, we find that it differs in being not simple change, but change made up of successive changes. The transformation of food into tissue, involves mastication, deglutition, chj^mification, chylification, absorption, and those various actions gone through after the lacteal ducts have poured their contents into the blood. Carrying on an argu- ment necessitates a long chain of states of consciousness; each implying a change of the preceding state. Inorganic changes, however, do not in any considerable degree exhibit this peculiarity. It is true that from meteorologic causes, inanimate objects are daily, sometimes hourty, undergoing modifications of temperature, of bulk, of hygrometric and electric condition. Not only, however, do these modifications lack that conspicuousness and that rapidity of succession which vital ones possess, but vital ones form an additional series. Living as well as not-living bodies are affected by atmospheric influences; and beyond the changes which these produce, living bodies exhibit other changes, more nu- 64 THE DATA OF BIOLOGY.
merous and more marked. So that though organic change is not rigorously distinguished from inorganic change by presenting successive phases — though some inanimate objects, as watches, display phases of change both quick and nu- merous— though all objects are ever undergoing change of some kind, visible or invisible — though there is scarcely any object which does not, in the lapse of time, undergo a con- siderable amount of change that is fairly divisible into phases; yet, vital change so greatly exceeds other change in its dis- play of varying phases, that we may consider this as prac- tically one of its characteristics. Life, then, as thus roughly differentiated, may be regarded as change presenting succes- sive phases; or otherwise, as a series of changes. And it should be observed, as a fact in harmony with this concep- tion, that the higher the life the more conspicuous the varia- tions. On comparing inferior with superior organisms, these last will be seen to display more rapid changes, or a more lenorthened series of them, or both.
Contemplating afresh our two typical phenomena, we may see that vital change is further distinguished from non- vital change, by being made up of many simultaneous changes. Assimilation is not simply a series of actions, but includes many actions going on together. During mastication the stomach is busy with the food already swallowed; on which it is both pouring out solvent fluids and expending muscular efforts. While the stomach is still active, the intestines are performing their secretive, contractile, and absorbent func- tions; and at the same time that one meal is being digested, the nutriment obtained from a previous meal is undergoing that transformation into tissue which constitutes the final act of assimilation. So also is it, in a certain sense, with mental changes. Though the states of consciousness which make up an argument occur in series, yet, as each of these states is complex — implies the simultaneous excitement of those many faculties by which the perception of any object or relation has been effected; it is obvious that each such change in niOXlMATE DEFINITION OF LIFE. 65 consciousness implies many component ch-anges. In this respect too, however, it must be admitted that the distinction between animate and inanimate is not precise. No mass of dead matter can have its temperature altered, without at the same time undergoing an alteration in bulk, and sometimes also in hygrometric state. An inorganic body cannot be oxidized, without being at the same time changed in weight, colour, atomic arrangement, temperature, and electric condition. And in some vast and mobile aggre- gates like the sea, the simultaneous as well as the successive changes displayed, outnumber those going on in an animal. Nevertheless, speaking generally, a living thing is distin- guished from a dead thing, by the multiplicity of the changes at any moment taking place in it. Add to which, that by this peculiarity, as by the previous one, not only is the vital more or less clearly marked off from the non- vital; but creatures possessing high vitality are marked off from those possessing low vitality. It needs but to contrast the many organs co-operating in a mammal, with the few in a polype, to see that the actions which are progressing together in the body of the first, as much exceed in number the actions pro* gressing together in the body of the last, as these do those in a stone. As at present analyzed, then, Life consists of simultaneous and successive changes.
Continuing the comparison, we next find that vital changes, both visceral and cerebral, differ from other changes in their heterogeneity. Neither the simultaneous acts nor the serial acts, which together constitute the process of digestion, are at all alike. The states of consciousness comprised in any ratiocination are not repetitions of each other, either in com- position or in modes of dependence. Inorganic processes, on the other hand, even when like organic ones in the number of the simultaneous and successive changes they involve, are unlike them in the homogeneity of these changes. In the case of the sea, just referred to, it is observable that count- less as are the actions at any moment going on, they are 5 66 THE DATA OF BIOLOGY.
mostly mechanical actions tliat are to a great degree similar; and in this respect widely differ from the actions at any mo- ment taking place in an organism: which not only belong to the several classes, mechanical, chemical, thermal, electric, but present under each of these classes, innumerable unlike actions. Even where life is nearly simulated, as by the working of a steam-engine, we may see that considerable as is the number of simultaneous changes, and rapid as are the successive ones, the regularity with which they soon recur in the same order and degree, renders them unlike those varied changes exhi- bited by a living creature. Still, it will be found that this peculiarity, like the foregoing ones, does not divide the two classes of changes with precision; inasmuch as there are inanimate things which exhibit considerable heterogeneity of change: for instance, a cloud. The variations of state which this undergoes, both simultaneous and successive, are many and quick; and they differ widely from each other both in quality and quantity. At the same instant there may occur in a cloud, change of position, change of form, change of size, change of density, change of colour, change of tem- perature, change of electric state; and these several kinds of change are continuously displayed in different degrees and combinations. Yet notwithstanding this, when we consider that very few inorganic objects manifest heterogeneity of change in a marked manner, while all organic objects mani- fest it; and further, that in ascending from low to high forms of life, we meet with an increasing variety in the kinds and amounts of changes displaj^ed; we see that there is here a further leading distinction between organic and inorganic actions. According to this modified conception, then. Life is made up of heterogeneous changes both simultaneous and successive.
If now we look for some point of agreement between the assimilative and logical processes, by which they are distin- guished from those inorganic processes that are most like them iu the heterogeneity of the simultaneous and successive PROXIMATE DEFINITION OF LIFE. 07 cluanges they comprise, we discover that they are distinguish- ed by the combination subsisting among their constituent changes. The acts that make up digestion are mutually de- pendent. Tliose composing a train of reasoning are in close connection. And generally, it is to be remarked of vital changes, that each is made possible by all, and all are affected b}^ each. Respiration, circulation, absorption, secretion, in their many sub-divisions, are bound up together. Muscular contraction involves chemical change, change of temperature, and change in the excretions. Active thought influences the operations of the stomach, of the heart, of the kidneys. But we miss this union among inorganic processes. Life-like as may seem the action of a volcano in respect of the heterogeneity of its many simultaneous and successive changes, it is not life- like in respect of their combination. Though the chemical, mechanical, thermal, and electric phenomena exhibited, have some inter-dependence; yet the emission of stones, mud, lava, flame, ashes, smoke, steam, usually takes place irregularly in quantity, order, intervals, and mode of conjunction. Even here, however, it cannot be said that inanimate things pre- sent no parallels to animate ones. A glacier may be instanced as showing nearly as much combination in its changes as a plant of the lowest organization. It is ever growing and ever decaying; and the rates of its composition and decom- position preserve a tolerably constant ratio. It moves; and its motion is in immediate dependence on its thawing. It emits a torrent of water, which, in common with its motion, undergoes annual variations, as plants do. During part of the year the surface melts and freezes alternately; and on these changes are dependent the variations in movement, and in efflux of water. Thus we have growth, decay, changes of temperature, changes of consistence, changes of velocity, changes of excretion, all going on in connexion; and it may be as truly said of a glacier as of an animal, that by cease- less integration and disintegration it gradually undergoes an entire change of substance without losing its individuality.
68 THE DATA OF BIOLOGY.