There is certainly a very great difference between asphyxia that happens to an adult, and the state in which the fœtus is found, since, if the first is prolonged, organic life ceases, while this life is in full activity in the fœtus. Thus there is no resemblance in the composition of the black blood in the arteries in asphyxia and that in the arteries of the fœtus. These two states, however, have a sort of analogy, especially under the relation of the remarkable diminution, of even the absence of animal life, which characterize both. Now in producing asphyxia in an animal at will, by fixing a stop-cock upon the wind-pipe, I have always observed that this life is annihilated when the black blood penetrates the brain, and that when it is in part suspended, it suddenly revives and re-appears by opening the stop-cock, and permitting red blood to enter the brain, nerves, and all the parts. These experiments can, then, to a certain point, give us an idea of the part the red blood takes at birth, in the development of animal life; I say the part, for it is not, as we shall see, the only cause that puts it in action. For a long time after birth and during the whole of the growth, the nervous system and the brain, which is the centre of it, predominate in their development over the other systems; this predominance is not uniform at all the periods; it diminishes at puberty, when the nervous system is in equilibrium with the others, and the genital organs succeed it in superiority. This predominance of the nervous system in the infant has an influence on the one hand on the sensations, on the other upon the voluntary motions.