§ 34. To make yet more manifest the fact, that the degree of life varies as the degree of correspondence, I may here point out, that those other distinctions successively noted when contrasting vital changes with non-vital changes, are all implied in this last distinction — their correspondence with external coexistences and sequences. And to this may be added the supplementary fact, that the increasing fulfilment of those other distinctions which we found to accompany increasing life, is involved in the increasing fulfilment of this last distinction. To descend to particulars: — We saw that living organisms are characterized by successive changes; and that as the life becomes higher, the successive changes become more numerous. Well, the environment is full of successive changes, both positive and relative; and the greater the correspondence, the greater the number of successive changes an organism must display. We saw that life presents simultaneous changes; and that the more elevated it is, the more marked the multiplicity of them. Well, besides countless phenomena of coexistence in the environment, there are often many changes occurring in it at the same moment; and hence increased correspondence with it, supposes an increased display of simultaneous changes in the organism. Similarly with the heterogeneity of the changes. In the environment the relations are very varied in their kinds; and hence, as the organic actions come more and more into correspondence with them, they also must become very varied in their kinds. So again is it, even with definiteness of combination. For though the inorganic bodies of which the environment mainly consists, do not present definitelycombined changes, yet they present definitely-combined properties; and though the minor meteorologic variations of the environment, do not show much definiteness of combination, yet those resulting from day and night and the seasons do. Add to which, that as the environment of each organism comprehends all those other organisms existing within its sphere of life — as the most important and most numerous surrounding changes with which each animal has to deal, are the definitely- combined changes exhibited by other animals, whether prey or enemies; it results that definiteness of combination is a general characteristic of the external changes with which internal ones have to correspond. Hence, increase of correspondence involves increased definiteness of combination. So that throughout, the correspondence of the internal relations with the external ones, is the essential thing; and all the special characteristics of the internal relations, are but the collateral results of this correspondence.
§ 35. As affording the simplest and most conclusive proof that the degree of life varies as the degree of correspondence, it remains to point out that perfect correspondence would be perfect life. Were there no changes in the environment but such as the organism had adapted changes to meet; and were it never to fail in the efficiency with which it met them; there would be eternal existence and universal knowledge. Death by natural decay, occurs because in old age the relations between assimilation, oxidation, and genesis of force going on in the organism, gradually fall out of correspondence with the relations between oxygen and food and absorption of heat by THE LIFE VARIES AS THE CORRESPONDENCE. 89 the environment. Death from disease, arises either when the organism is congenitally defective in its power to balance the ordinary external actions by the ordinary internal actions, or when there has taken place some unusual external action to which there was no answering internal action. Death by accident, implies some neighbouring mechanical changes of which the causes are either unobserved from inattention, or are so intricate that their results cannot be foreseen; and consequently certain relations in the organism are not adjusted to the relations in the environment. Manifestly, if, to every outer coexistence and sequence by which it was ever in any degree affected, the organism presented an answering process or act; the simultaneous changes would be indefinitely numerous and complex, and the successive ones endless — the correspondence would be the greatest conceivable, and the life the highest conceivable, both in degree and in length.
§ 36. Before closing the chapter, it will be useful to compare the definition of Life here set forth, with the definition of Evolution set forth in First Trinciples. Living bodies being bodies which display in the highest degree the structural changes constituting Evolution; and Life being made up of the functional changes that accompany these structural changes; we ought to find a certain harmony between the definitions of Evolution and of Life. Such a harmony is not wanting.
The first distinction we noted between the kind of change shown in Life, and other kinds of change, was its serial character: we saw that vital change is substantially unlike non-vital change, in being made up of successive changes. Now since organic bodies display in so much higher a degree than inorganic bodies, those continuous difierentiations and integrations which constitute Evolution; and since the re- distributions of matter thus carried so far in a comparatively short period, imply concomitant re -distributions of motion; it is clear that in a given time, organic bodies must undergo changes so comparatively numerous as to render the successiveness of their changes a marked characteristic. And it will follow a priori, as we found it to do a ^posteriorly that the organisms exhibiting Evolution in the highest degree, exhibit the longest or the most rapid successions of changes, or both. Again, it was shown that vital change is distinguished from non- vital change by being made up of many simultaneous changes; and also that creatures possessing high vitality are marked off from those possessing low vitality, by the far greater number of their simultaneous changes. Here too there is entire congruity. In First Principles, § 116, we reached the conclusion, that a force falling on any aggregate is divided into several forces; that when the aggregate consists of parts that are unlike, each part becomes a centre of unlike differentiations of the incident force; and that thus the multiplicity of such differentiations must increase with the multiplicity of the unlike parts. It follows necessarily, therefore, that organic aggregates, which as a class are distinguished from inorganic aggregates by the greater number of their unlike parts, must be also distinguished from them by the greater number of simultaneous changes they display; and further that the higher organic aggregates, having more numerous unlike parts than the lower, must undergo more numerous simultaneous changes. We next found that the changes occurring in living bodies, are contrasted with those occurring in other bodies, as being much more heterogeneous; and that the changes occurring in the superior living bodies, are similarly contrasted with those occurring in inferior ones.
Well, heterogeneity of function is the correlate of heterogeneity of structure; and heterogeneity of structure is the leading distinction between organic and inorganic aggregates, as well as between the more highly organized and the more lowly organized. By reaction, an incident force must be rendered multiform in proportion to the multiformity of the aggregate on which it falls; and hence those most mul- THE LIFE VATITES AS THE CORRESPONDENCE. 91 tiform aggregates which display in the highest degree the phenomena of Evolution structurally considered, must at the same time be aggregates which display in the highest degree the multiform actions which constitute Evolution functionally considered. These heterogeneous changes, exhibited simultaneously and in succession by a living organism, prove, on further inquiry, to be distinguished by their combination from certain non-vital changes which simulate them. Here, too, the parallelism is maintained. It was shown in § 56 of First Princii^les, that an essential characteristic of Evolution is the integration of parts, which accompanies their differentiation — an integration that is shown both in the consolidation of each part, and in the consolidation of all the parts into a whole. Now, nianifestl}^ combination among the changes going on in different combined parts, must be proportionate to the degree of combination among these parts: the more mutually-dependent the parts, the more mutually- dependent must be their actions. Hence, animate bodies having greater co-ordination of parts than inanimate ones, must exhibit greater co-ordination of changes. And this greater co-ordination of their changes must not only distinguish organic from inorganic aggregates; but must, for the same reason, distinguish higher organisms from lower ones, as we found that it did. Yet once more, it was pointed out that the changes constituting Life, differ from other changes in the dcfiniteness of their combination; and that a distinction like in kind, though less in degree, holds between the vital changes of superior creatures and those of inferior creatures. Thes9, also, are contrasts in harmony with the contrasts disclosed by the analysis of Evolution. We saw [First Principles^ §§ 54, 55) that during Evolution, there is an increase of definiteness as well as an increase of heterogeneity. We saw that the integration accompanying differentiation, has necessarily the effect of increasing the distinctness with which the parts are marked off from each other; and that so, out of the incoherent and indefinite, there arises the coherent and definite.
But a coherent whole made up of definite parts definitely combined, must exhibit more definitely combined changes than a whole made up of parts that are neither definite in themselves nor in their combination. Hence, if living bodies display more than other bodies this structural definiteness, then, definiteness of combination must be a characteristic of the changes constituting Life; and must also distinguish the vital changes of higher organisms from those of lower organisms. Finally, however, we discovered that all these peculiarities are subordinate to the one fundamental peculiarity, that vital changes take place in correspondence with external co- existences and sequences; and that the highest possible Life is reached, when there is some inner relation of actions fitted to meet every outer relation of actions by which the organism can be affected. But this conception of the highest possible Life, is in perfect harmony with the conception, before arrived at, of the ultimate limit of Evolution.
When treating of equilibration as exhibited in organic phenomena {First Principles, |§ 133, 134), it was pointed out, that the continual tendency is towards the establishment of a balance between inner and outer changes. It was shown that " the final structural arrangements must be such as will meet all the forces acting on the aggregate, by equivalent antagonistic forces,'^ and that " the maintenance of such a moving equilibrium " as an organism displays, *•' requires the habitual genesis of internal forces corresponding in number, directions, and amounts, to the external incident forces — as many inner functions, single or combined, as there are single or combined outer actions to be met." It was shown, too, that the relations among conceptions and ideas, are ever in progress towards a better balance between mental actions and those actions in the environment to which conduct must be adjusted. So that that maintenance of a correspondence between inner and outer relations, which we have here found to constitute Life, and the THE LIFE VAKTES AS THE CORRESPONDENCE. 93 perfection of whicli is the perfection of Life, answers completely to that state of organic moving equilibrium which we saw arises in the course of Evolution, and tends ever to become more complete.
There is much significance in this complete parallelism. That two inquiries starting from different points and carried on in different ways, should lead to conclusions so entirely harmonizing with each other, cannot fail further to confirm these conclusions; if further confirmation of them be needed.
CHAPTER YII.
THE SCOPE OF BIOLOGY.
§ 37. "We are now in a position to map-out the boundaries and divisions of our subject. Grouping together the general results arrived at in the first three chapters, and joining with them the results which the last three chapters have brought us to, we shall be prepared to comprehend the science of Biology as a whole; and to see how its truths may best be classified.
In the chapters treating of Organic Matter, the Actions of Forces on it, and its Eeactions on Forces, the generalizations reached were these: — that organic matter is specially sensitive to surrounding agencies; that in consequence of the extreme instability of the compounds it contains, minute disturbances can cause in it large amounts of re- distribution; and that during the fall of its unstably-arranged atoms into stable arrangements, there are given out proportionately large amounts of motion. We saw that organic matter is so constituted, that small incident actions are capable of initiating great reactions — setting up extensive structural modifications, and liberating large quantities of power. In the chapters just concluded, the changes of which Life is made up, were shown to be so adjusted as to balance outer changes. And the general process of the adjustment we found resolves itself into this; that if in the environment there are any related actions, A and B, by which the or- THE SCOrK OF IIIOLOGY. 95 ganism is affected, then if A produces in the organism some change a, there follows in the organism some change h, fitted in time, direction, and amount to meet the action B — a change which is often required to be much larger than its antecedent. Mark, now, the relation between these two final results. On the one hand, for the maintenance of that correspondence between inner and outer actions which constitutes Life, an organism must be susceptible to small changes from small external forces (as in sensation), and must be able to initiate large changes in opposition to large external forces (as in muscular action). On the other hand, organic matter is at once extremely sensitive to disturbing agencies of all kinds, and is capable of suddenly evolving motion in great amounts. That is to say, the constitution of organic matter specially adapts it to receive and produce the internal changes required to balance external changes.
This being the general character of the vital Functions, and of the Matter in which they are performed, the science of Biology becomes an account of all the phenomena attendant on the performance of such Functions by such Matter — an account of all the conditions, concomitants, and consequences, under the various circumstances fallen into by living bodies. If all the functional phenomena which living bodies present, are, as we have concluded, incidents in the maintenance of a correspondence between inner and outer actions; and if all the structural phenomena ^vhich living bodies present, are direct or indirect concomitants of functional phenomena; then the entire Science of Life, must consist in a detailed interpretation of all these functional and structural phenomena in their relations to the phenomena of the environment. Immediately or mediately, proximately or remotely, every trait exhibited by organic bodies, as distinguished from inorganic bodies, must be referable to this continuous adjustment between their actions and the actions going on around them. Such being the extent and nature of our subject-matter, it may be thus divided.
1. An account of tlie structural phenomena presented by organisms. And this subdivides into: — a. The structural phenomena presented by individual organisms. h. The structural phenomena presented by successions of organisms.
2. An account of the functional phenomena which organisms present. And this, too, admits of sub- division into: — a. The functional phenomena of individual organisms. h. The functional phenomena of successions of organisms.
3. An account of the actions of Structure on Function, and the re- actions of Function on Structure. And like the others, this is divisible into: — a. The actions and re-actions as exhibited in individual organisms. h. The actions and re-actions as exhibited in successions of organisms.
4. An account of the phenomena attending the production of successions of organisms: in other words — the phenomena of Genesis.
There is, indeed, another mode of grouping the facts of Biology, with which all are familiar. According as they are facts of animal or vegetal life, they may be classed under the heads of Zoology and Botany. But this division, though convenient and indeed necessary for practical purposes, is one that does not here concern us. Dealing with organic structures and functions in connexion with their causes, conditions, concomitants, and consequences, Biology cannot divide itself into Animal-Biology and Vegetal-Biology; since the same fundamental classes of phenomena are common to both. Recognizing this familiar distinction only as much as convenience obliges us to do, let us now pass on to consider, more in detail, the classification of biologic phenomena, above set down in its leading outlines.
§ 38. The facts of structure which an individual or- THE SCOPE OF BIOLOGY. 97 ganism exhibits, are of two chief kinds. In order of conspicuousness, though not in order of time, there come first those ultimate arrangements of parts which characterize the organism in its mature state — an account of which, commonly called Anatomy, is more properly called Morphology. And second, there come those successive modifications through which the organism passes in its development from the germ to the adult form— an account of which is called Embryology.
The facts of structure which any succession of individual organisms exhibits, admit of similar classification. On the one hand, we have those inner and outer differences of shape, that are liable to arise between the adult members of successive generations descended from a common stock — differences which, though usually not marked between adjacent generations, may in course of many generations become great. And on the other hand, we have those developmental modifications through which such modifications of the descended forms are reached.
The interpretation of structure, as exhibited in individual organisms and successions of organisms, is aided by two subsidiary divisions of biologic inquiry, named Comparative Anatomy (properly Comparative Morphology) and Comparative Embryology. These cannot properly be regarded as in themselves parts of Biology; since the facts embraced under them are not substantive phenomena, but are simply incidental to substantive phenomena. All the facts of structural Biology are comprehended under the two foregoing subdivisions; and the comparison of these facts as presented in different classes of organisms, is simply a method of interpreting the real relations and dependencies of the facts compared.
Nevertheless, though Comparative Morphology and Comparative Embryology do not disclose additional series of concrete or special facts, they lead to the establishment of certain abstract or general facts. By them it is made manifest that underneath the superficial differences of groups and classes and types of organisms, there are hidden fundamental similarities; and that the courses of development in such groups and classes and types, though in many respects divergent, are in some essential respects, coincident. The wide truths thus disclosed, come under the heads of General Morphology and General Embryology.
By contrasting the structures of organisms, there is also achieved that grouping of the like and separation of the unlike, called Classification. First by observation of external characters; second by observation of internal characters; and third by observation of the phases of development; it is ascertained what organisms are most similar in all particulars; what organisms are like each other in every important attribute; what organisms have common primordial characters. Whence there finally results such an arrangement of organisms, that if certain structural attributes of any one be given, its other structural attributes may be empirically predicted; and which prepares the way for that interpretation of their relations and genesis, which forms an important part of rational Biology.
§ 39. The second main division of Biology, above described as embracing the functional phenomena of organisms, is that which is in part signified by Physiology: the remainder being what we distinguish as Psychology. Both of these fall into subdivisions that may best be treated separately. That part of Physiology w^hich is concerned with the molecular changes going on in organisms, is known as Organic Chemistry. An account of the modes in which the force generated in organisms by chemical change, is transformed into other forces, and made to work the various organs that carry on the functions of Life, comes under the head of Organic Physics. Psychology, which is mainly concerned with the adjustment of vital actions to actions in the environment (in contrast with Physiology, which is mainly concerned with vital actions apart from THE SCOPE OF lUOLOGY. 99 actions in the environment) consists of two quite distinct portions. Objective Psychology deals with those functions of the nervo-muscular apparatus by which such organisms as possess it, are enabled to adjust inner to outer relations; and includes also, the study of the same functions as externally manifested in conduct. Subjective Psychology deals with the sensations, perception's, ideas, emotions, and volitions that are the direct or indirect concomitants of this visible adjustment of inner to outer relations — considers these several kinds of consciousness in their genesis, and their connexions of co-existence and succession. Consciousness under its different modes and forms, being a subject-matter radically distinct in nature from the subject-matter of Biology in general; and the method of self- analysis, by which alone the laws of dependence among changes of consciousness can be found, being a method unparalleled by anything in the rest of Biology; we are obliged to regard Subjective Psychology as a separate study —not absolutely, of course, but relatively to the mind of each student. And since it would be very inconvenient to dissociate Objective Psychology from Subjective Psychology, we are practically compelled to deal with the two as forming an independent sub-science, to be treated apart from the lower diA^sions of Biology.
Obviously, the functional phenomena presented in successions of organisms, similarly divide into physiological and psychological. Under the physiological, come the modifications of bodily actions that arise in the course of generations, as concomitants of structural modifications; and these may be modifications, qualitative or quantitative, in the molecular changes classed as chemical, or in the organic actions classed as physical, or in both. Under the psychological, come the qualitative and quantitative modifications of instincts, feelings, conceptions, and mental changes in general, that occur in creatures having more or less intelligence, when certain of their conditions are changed. This, like the preceding department of Psychology, has in the abstract two different aspects — the objective and the subjective. Practically, however, the objective, which deals with these mental modifications as exhibited in the changing habits and abilities of successive generations of creatures, is the only one that admits of scientific investigation; since the corresponding alterations in consciousness, cannot be immediately known to any but the subjects of them. Evidently, convenience requires us to class this part of Psychology along with the other parts, in a distinct sub-science.
Light is thrown on functions, as well as on structures, by comparing organisms of different kinds. Comparative Physiology and Comparative Psychology, are the names given to those collections of facts respecting the homologies and analogies, bodily and mental, that are brought to light by this kind of inquiry. These classified observations concerning likenesses and differences of functions, are helpers to interpret functions in their essential natures and relations. Hence Comparative Physiology and Comparative Psychology are names of methods, rather than names of true subdivisions of Biology.
Here, however, as before, the comparison of special truths, besides facilitating their interpretation, brings to light certain general truths. Contrasting bodily and mental functions as exhibited in various orders of organisms, shows that there exists, more or less extensively, a community of processes and methods. Hence result two groups of abstract propositions, constituting General Physiology and General Psychology.
§ 40. In these various divisions and sub- divisions of the first two great departments of Biology, the phenomena of Structure are considered separately from the phenomena of Function, so far as separate treatment of them is possible. The third great department of Biology deals with them in their necessary connexions. It comprehends the determin- THE SCOPE OF inOLOGY. 101 ation of functions by structures, and the determination of structures by functions.
As displayed in individual organisms, the action of structures on functions is to be studied, not only in the broad and familiar fact that the general kind of life an organism leads is necessitated by the main characters of its organization, but in the more special and less conspicuous fact, that between members of the same species, minor differences of structure lead to minor differences of power to perform certain kinds of action, and of tendency to perform such kinds of action. Conversely, under the re- actions of function on structure as displayed in individual organisms, come the facts showing that functions, when fulfilled to their normal extents, maintain integrit}^ of structure in their respective organs; and that within certain limits, the increase of functions is followed by such structural changes in their respective organs, as enables the organs to discharge better their extra functions.
Inquiry into the action of structure on function as displayed in successions of organisms, introduces us to such phenomena as Mr Darwin's "Origin of Species" deals with.
In this category come all proofs of the general truth, that when an individual is enabled by a certain structural peculiarity, to perform better than others of its species some advantageous action; and when it bequeaths more or less of its structural peculiarity to descendants, among whom those which have it most markedly, are best able to thrive and propagate; there arises through this continuous action of structure on function, a visibly modified type of structure, having a more or less distinct function. In the correlative class of facts, which come under the category of reactions of function on structure as exhibited in successions of organisms, are to be placed all those modifications of structure which arise in races, when changes of conditions entail changes in the balance of their functions. Here is to be studied the way in w^hich altered function externally necessitated, works, by re-action, altered structure; and how in succeeding generations, this altered structure may be made continually more marked by this altered function. Though logically distinct, these two sub-divisions of biologic inquiry cannot in practice be carried on apart. A speciality of structure which leads to an excess of function in any direction, is, by the perpetual re-action of function, rendered ever more decided. A speciality of function, by calling forth a corresponding speciality of structure, produces an increasingly efficient discharge of such function. Whichever of the two initiates the change, there goes on between them an unceasing action and re-action, producing in them co-ordinate modifications.
§ 41. The fourth great division of Biology, comprehending the phenomena of Gfenesis, may be conveniently separated into three sub-divisions.
Under the first, comes a description of all the special modes whereby the multiplication of organisms is carried on; which modes range themselves under the two chief heads of sexual and asexual. An account of Sexual Multiplication includes the various methods by which germs and ova are fertilized, and by which, after fertilization, they are furnished with the materials, and maintained in the conditions, needful for their development. An account of Asexual Multiplication includes the various methods by which, from the same fertilized germ or ovum, there are produced many organisms that are partially or totally independent of each other.
The second of these sub-divisions deals with the phenomena of Genesis in the abstract. It takes for its subject-matter, such general questions as — What is the end subserved by the union of sperm-cell and germ -cell? Why cannot all multiplication be carried on after the asexual method? What are the laws of hereditary transmission? What are the causes of variation?
The third sub-division is devoted to still more abstract THE SCOPE OF BIOLOGY. 103 aspects of the plienomcna. Recognizing the general facts of multiplication, without reference to their modes or immediate causes, it concerns itself simply with the different rates of multiplication in different kinds of organisms, and different individuals of the same kind.. Generalizing the numerous contrasts and variations of fertility, it seeks a rationale of them in their relations to other organic phenomena.
§ 42. Such appears to be the natural arrangement of divisions and sub-divisions which Biology presents, when regarded from the highest point of view, as the Science of Life — the science which has for its subject-matter, the correspondence of organic relations, with the relations amid which organisms exist. This, however, is a classification of the parts of Biology when fully developed; rather than a classification of the parts of Biology as it now stands. Several of the sub-divisions above named have no recognized existence; and sundry of the others are in quite rudimentary states. It is therefore impossible now to fill in, even in the roughest way, more than a part of the outlines here sketched.