At birth and some time after, the great quantity of sub-cutaneous fat makes artificial emphysema very difficult; it does not appear that the fœtus ever has a natural one. The delicacy of the cellular layers and filaments is such at this period, that the imagination cannot represent it; the texture of the hair is gross in comparison with it. I presume that the ball of fat, which I have said almost always exists in the cheek of the fœtus, arises from a rupture of several layers, a rupture from which is produced a great cell, that is filled with fat. Sometime before birth, at that period and in the subsequent years, the cellular humour constantly diminishes; the cells become dryer, consequently more apparent; the whole mass of the cellular system diminishes, because as the organs increase, the interstices are contracted. This system however predominates for a long time over the others; hence the roundness of form that characterizes the infant, the want of prominence of its organs, that are almost concealed by it; hence in part the suppleness and multiplicity of its movements; hence also the frequent diseases of which it is the seat at that age. The layers still preserve an extreme delicacy; they are still easily broken. In producing emphysema, upon very lean children, I have observed that often it forms in places very considerable dilatations, a kind of sacs in which the air accumulates in large quantity, and which arises from this rupture; whilst in the same experiment upon an adult, the air is propagated in an uniform manner and constantly infiltrates the cells without destroying them. By comparing in our slaughter-houses, the flesh of calves blown, and that of oxen in the same state, I have sometimes made an analogous observation.