We see then what should be thought of the disputes of anatomists respecting the origin of this pretended nerve, placed in the fifth, sixth pair, &c. in those of the neck, back, &c. Many physiologists have entertained concerning the ganglions opinions similar to those which I have now offered, by considering these bodies as small brains; but it is essential that these opinions should enter into the description, which, as it is now made, gives a very inaccurate idea both of these nervous centres and of the nerves which go off from them. The expression of _nervous branches giving origin to such or such a ganglion_, &c. resembles that in which we should consider the brain as arising from the nerves of which it is itself the origin. CHAPTER VII. GENERAL DIFFERENCES OF THE TWO LIVES WITH RESPECT TO VITAL POWER. The greater number of Physicians, who have written upon the vital properties, have begun by researches on their principle, have endeavoured to descend from the knowledge of the nature of this principle to that of its phenomena, instead of ascending from observation to theory. The Archæus of Van Helmont, the soul of Stahl, the vital principle of Barthez, the vital power of others, have each in their turn been considered as the sole centre of every action possessing the character of vitality, have each in their turn been made the common base of every physiological explanation. But these bases have every one of them been sapped, and in the midst of their wrecks have remained the facts alone which rigorous experiment has furnished upon the subject of sensibility and motility. So narrow indeed are the limits of the human understanding, that the knowledge of first causes has almost always been interdicted. The veil, which covers them envelops with its innumerable folds whoever attempts to rend it. In the study of nature, principles are certain general results of first causes, from whence proceed innumerable secondary results. The art of finding the connexion of the first with the second is that of every judicious mind. To seek the connexion of first causes with their general effects is to walk blindfold in a road from whence a thousand paths diverge. Of what importance besides to us are these causes? Is it necessary to know the nature of light, of oxygen and caloric to study their phenomena? Without the knowledge of the principle of life, cannot we analyze its properties? In the study of animals let us proceed as modern metaphysicians have done in that of the understanding. Let us suppose causes, and attach ourselves to their general results. I. _Difference between vital power and physical law._