Transition

from the in

Primitive

sufficient knowledge; and it must be by this time evident that this is the link between the organic to the inorganic and the biological philosophy, by organic. which we are enabled to regard the whole of natural philosophy as forming a homogeneous and continuous body of doctrine. By a natural consequence, a wholly different view must be taken of the rational theories of animal life: that is, of the phenomena of irritability and sensibility, which offer no basis of analogy with inorganic phenomena. With regard to sensibility, no one will question this: and, as to irritability,-though contraction may be seen as a movement occasioned by heat, and, yet more, by electricity, these phenomena must be carefully separated from the contractile effect of the irritable fibre which is a product of the nervous action; and especially when it is voluntary. Irritability is as radically foreign to the inorganic world as sensibility; with which, too, it is inseparably connected. This double property is, then, nervous pro- strictly primitive in the secondary tissues, perties. and therefore no more a subject of explanation than weight, heat, or any other fundamental physical property. Whenever we have a true theory of animal life, it will be by comparing all the general phenomena which are connected with this double property, according to their preparatory analysis, in order to discover their laws; that is, as in all other cases, their constant relations, both of succession and similitude. This will be done in order to the usual end of obtaining a rational prevision; the subject here being the mode of action of a given animal organism, placed in determinate circumstances; or, reciprocally, the animal arrangement that may be induced by any given act of animality. All attempts to explore the nature of sensibility and irritability are mere hindrances in the way of this final aim, by drawing off our attention from the laws. of animality in a vain search after what can never be found.

Relation of the animal to the organic

The true relation of the animal to the organic life must throughout be carefully kept in mind. This relation is double. The organic life first serves as the basis of the animal; and then as its general end and object. We have

life.

RELATION OF THE ANIMAL TO THE ORGANIC LIFE. 99

dwelt enough on the first, if even any one would think of contesting that, in order to move and feel, the animal must first live; and that the fundamental vegetative life could not cease without extinguishing the other. As for the second relation, it is evident that the phenomena of irritability and sensibility are directed by the general needs of the organic life, which they serve by procuring better materials, and by guarding against unfavourable influences. Even the intellectual and moral functions have usually no other primitive office. Without such a destination, these properties would either destroy the organism or themselves perish. It is only in the human species, and even there only under a high degree of civilization, that any kind of inversion of this order can be conceived of. In that case, the vegetative life is essentially subordinated to the animal, the development of which it is alone destined to aid; and this, it seems to me, is the noblest scientific notion that we can form of humanity, distinct from animality:-a transformation which can be safely considered as possible only by transferring to the whole species, or at least to society, the primitive end which, in the case of animals, is limited to the individual, or, at the utmost, to the family, as we shall see hereafter. It is only among a small number of men, and it is very far indeed from being a just matter of expectation from the whole species, that the intellect can acquire such a preponderance in the whole of the organism as to become the end and object of human existence. An exception so special, and so easy to explain in the case of Man, cannot alter the universality of a consideration verified by the whole animal kingdom, wherein the animal life is seen to be always destined to perfect the organic. It is only by a scientific abstraction, necessary for purposes of progress. that we can provisionally conceive of the first as isolated from the second, which is, strictly speaking, inseparable from it under the double aspect just exhibited. Thus, as the positive theory of animality must continually rest on that of general vitality, it is indissolubly combined with the whole of inorganic philosophy, which furnishes the basis of organic physiology. In a secondary sense, the same dependence exists. We admitted, while reviewing mathematical philosophy, that the laws of

To inorganic philosophy.

equilibrium and motion operate among all orders of phenomena, being absolutely universal. Among physiological phenomena we find them accordingly; and, when contraction is produced by the irritability of the muscular fibre, all the phenomena of animal mechanics which result, whether for rest or locomotion, are dependent on the general laws of mechanics. In an inverse way the same thing takes place with regard to the functions of sensibility, in which the inorganic philosophy must intervene in connection with the primitive impression on the sentient extremities, carefully distinguished from its transmission by the nervous filament, and its perception by the cerebral organ. This impression acts through an intermediate physical apparatus, optical, acoustic, or other, the study of which according to appropriate physical laws, constitutes a chief element of the positive analysis of the phenomenon. Not only must we use the knowledge already established, but we want, for our analysis, further progress in it, and even the creation of new doctrines, as the theory of flavours, and yet more of odours, in regard to the mode of propagation of which there are doubtless several general laws, of a purely inorganic character, remaining to be established. In investigating these connections between biology and inorganic science, we find again what we saw before, that chemistry is spontaneously related to vegetable physiology, and physics especially to animal physiology; though neither could be altogether dispensed with in either department, where they are required, more or less, in combination.

Properties of tissue.

Our ideas of the double properties of irritability and sensibility cannot be truly scientific till each is irreversibly assigned to a corresponding tissue. Bichat conceived of all tissues as necessarily sensitive and irritable, but in different degrees ;—an error which was natural or inevitable at a time when so little was known of tissue in the way of anatomical analysis, but one which, if maintained now, would hand over the whole science to the physico-chemical school, and efface all real distinction between the inorganic and organic departments of natural philosophy. Rational biology requires that the two properties should be inherent in determinate tissues, themselves modifications, profound and distinctly

PROPERTIES OF TISSUE.

101

Sensibility.

but

marked, of the primitive cellular tissue, that our anatomical data may be in harmony with the physiological; in other words, that the elementary ideas of tissue and of property should be in perfect correspondence. The scientific character of physiology in this direction is essentially defective among biologists in general. But the new explorations continually made show us how it was that Bichat was misled. He considered it proved that sensibility existed where there were no nerves: further investigation proves that the systems of sensibility were erroneously attributed to an organ deprived of nerves, instead of being referred to the simultaneous injury of neighbouring nerves; or that the nervous tissue existed, though it was difficult to find. If cases apparently contradictory still remain, it would be obviously absurd to reject on their account a conception required by the principles of rational physiology, and founded on unquestionable cases, by far more numerous and decisive than those which still seem to be exceptional. This consideration should be applied to different organisms, as well as to the different tissues of the human organism. The animals supposed to be without nerves, on which the metaphysical school has insisted so much, disappear as comparative anatomy enables us to generalize more and more the idea of nervous tissue, and to detect it in the inferior organisms. It is thus, for instance, that it has been recently found in several radiated animals. The time has come for its being established as a philosophical axiom that nerves are necessary for any degree of sensibility, the apparent exceptions being left as so many anomalies to be resolved by the future progress of anatomical analysis.

Irritability.

The same process must be instituted with the common notions of irritability, which are still ruled by Bichat's theory. He supposed, for instance, that the contractions of the heart were determined, independently of all nervous action, by the immediate stimulus of the flow of the blood towards it; whereas, it is now established that a provision of nerves is as indispensable to the irritability of this muscle as of any other; and generally, that the great distinction laid down by Bichat, between organic and animal contractility, must be abandoned.

All irritability is then necessarily animal; that is, it requires a corresponding nervous provision, whatever may be the immediate centre from which the nervous action proceeds. Much illustration of this subject is needed for its scientific use, though not for the logical sanction of a principle already placed beyond dispute. We need this further enlightenment, not only in regard to the use of the modern distinction made by many physiologists between the sensory and the motory nerves, though such a question has considerable philosophical importance; but much more in regard to another consideration, more direct and more eminent, in regard to which we are in a state of most inconvenient uncertainty and obscurity: I mean the scientific distinction which must be maintained, sooner or later, between the voluntary and involuntary motions. The doctrine of Bichat had the advantage of representing this difference, which we see, in fact, to have furnished him with his chief arguments; whereas, now that we insist on irritability being of one kind only, and dependent on a nervous provision, we find ourselves involved in a very delicate fundamental difficulty, the solution of which is however indispensable, to enable us to understand how all motions must not be indistinctly voluntary. For this solution we must obtain-what we certainly have not as yetan exact co-ordination of anatomical differences with incontestable physiological differences. There can be no question that such a phenomenon as the voluntary movements of the locomotive muscles while that of the cardiac muscle remains absolutely involuntary, must admit of analysis, however difficult it may be. Here then we find a chasm among the very principles of the science, by which the positive theory of irritability is much perplexed, certain as is its principle. In almost all cases the ablest anatomist is unable to decide otherwise than by the fact itself, if any definite motion is necessarily voluntary or involuntary; which affords sufficient proof of the absence of any real law in the case. The solution will probably be obtained by an analysis of the intermediate motions, as we may call them, those which, involuntary at first, end in becoming voluntary; or the reverse. These cases, which are very common, appear to me eminently fit to prove that the dis