is convulsed; for if in an experiment this phenomenon takes place, open the abdominal parietes, in an instant the flow of urine ceases, because on the one hand the muscles of these parietes cannot act upon the intestines and press them against the bladder, and because on the other the levator ani which contracts and raises this organ, has no resisting point against which it can compress it above. Observe in fact that in strong jets of urine, the bladder is placed between two opposite efforts, one superior, which is the gastric viscera pressed by the diaphragm and the abdominal muscles, the other inferior, which is especially the levator ani which acts by contracting from below above, whilst the opposite effort acts from above below; now these two efforts are evidently under the cerebral influence. I have very frequently had occasion to observe the bladder full of urine in a living animal whose abdomen was opened; I have never seen it contract with sufficient violence to expel the fluid. I do not deny but that the bladder, by the nerves it receives from the sacral plexuses, is to a certain extent a voluntary muscle; but I say that it is principally by forces accessory to its own and necessary to its functions, that it is subjected to the will; that the animal contractility is much greater in its functions than the sensible organic contractility. How then is the urine retained in this organ, or expelled from its cavity at will? In this way; when the urine falls into the bladder, and is there on the one hand but a short time, and on the other only in small quantity, it is not then an irritant sufficiently powerful to produce the exercise of the sensible organic contractility. The effort which the bladder makes is so small, that it cannot overcome the resistance of the urethra, which being shut by the contractility of texture, must be dilated by the impulse communicated to the urine. In order to void this fluid, there must then be added to the contraction of the bladder that of the surrounding voluntary muscles; now the least effort of these muscles is sufficient to overcome the resistance of the urethra. But if the urine is in great quantity in the bladder, and it has acquired by remaining in it a long time that deep colour which indicates the concentration of its principles, then the irritation that it produces on the organ brings powerfully into action the sensible organic contractility; the bladder contracts, and in spite of the animal, there is an evacuation of urine.