Such is the classification that I made in my Lectures on Physiology; it has evidently nothing in common with any of those that are found in physiological works; and if you reflect upon it a little, it will appear I think infinitely preferable to any of them. Observe in fine, that each class and each order have general and characteristic attributes that particularly distinguish them, and which being applicable to all the functions of that order, mark a difference between them and all the functions of any other order. I have pointed out moreover the distinctive attributes of animal and of organic life; I have shown that the organs of one are symmetrical, those of the other irregular; that there is a harmony in the functions of the first, a discordance in those of the second; that one commences sooner and terminates later, &c.
I have demonstrated, that the cerebral nerves belong especially to animal life, the nerves of the ganglions to the organic, which appears to me to be a remarkable difference, and which has induced me to make two systems of the nerves, that anatomists have united in one. The first, belonging to animal life, is composed of the cerebral nerves, the other to organic, is formed of the nerves of the ganglions, or what is commonly called the great sympathetic.
But it is the vital powers especially that distinguish one life from another. I have shown that one kind of sensibility and contractility belongs to animal life, and another to organic. Now as these vital properties are the principle of the functions, it is evident that the division of these properties demonstrates that that of the two lives is not an abstraction, but that it is nature herself that has fixed the limits, since she has made particular properties for each.
It is impossible to form a precise idea of the vital properties, without admitting the division I have made. How many disputes there have been, upon the subject of sensibility! Not one of them would have taken place, if the attributes of animal life had been properly distinguished from those of the organic. Certainly no one will hereafter confound in one view, as frequently has been done, the faculty that the heart has of being sensible to the entrance of the blood, without transmitting that impression, and the faculty that the skin, the other senses, the nerves, &c. have, not only of feeling the impression of external bodies, but of transmitting it to the brain, so that the sensation may be perceived.
If you include under one common name of irritability, the motions of muscles that contract only by stimuli, and those which the cerebral influence puts in action, it is impossible that you should be understood.
There has been much discussion during the last age, upon the point, whether sensibility is the same as contractility, or if these two properties can be separated. Each of the two opinions seem to have rested upon an equally solid foundation. But all these disputes will be done away, by admitting the distinction I have made in the vital properties. 1st. In animal life, then, it is evident, that contractility is not a necessary consequence of sensibility; thus frequently external objects make for a long time an impression upon us, and yet the voluntary muscles remain unmoved. 2d. On the other hand, in organic life, these two properties are never separated. In the involuntary motions of the heart, the stomach, the intestines, &c. there is first an excitement of the organic sensibility, and then an action of the sensible organic contractility. In the same manner, in the motions necessary to secretion, exhalation, &c. when the organic sensibility has been brought into action, immediately insensible organic contractility takes place. It is that they may be studied better, and appreciated more accurately, that in organic life, I separate these two kinds of contractility from sensibility. In the natural state they are inseparable. Hence why the passive sympathies of animal sensibility are very different from those of animal contractility, and make two distinct classes, whilst the passive sympathies of organic sensibility can never be separated from the corresponding contractilities. We suffer by sympathy, and are sympathetically convulsed in a distinct manner; these two things are almost always separate. On the contrary, sensation and motion in the organic sympathies are inseparable.
I could prove by many examples, that all the disputes, and all the diversities of opinion, upon the subject of the vital properties, proceed only from this cause, that those which preside over the functions of one life, have not been distinguished from those which put into action the functions of the other.
Let us return to my physiological division; I will now give a table of it, which, presenting it under one point of view, will give a more precise idea of the classification. This table comprehends, 1st. the prolegomena of the science; 2d. the exposition of the functions. In the prolegomena, every thing is referred to two great considerations; on the one hand to organic texture, described in a general manner, and on the other to life, considered in relation to its great attributes.