Such relations do not exist only between the different sensibility of the organs, and the different fluids of the body; but they may be exercised also between exterior substances, and the various parts of the living system. The sum of sensibility in the bladder, the kidneys and the salivary glands has a peculiar analogy with cantharides and mercury. It might be thought that the sensibility of each organ is modified, that it assumes a peculiar nature, and that it is this diversity of nature, which constitutes the difference of the relations of the organs with regard to bodies in contact with them; but a number of considerations tend to prove that such difference is occasioned, not by any difference in the nature, but in that of the sum, the dose, the quantity of the sensibility, if such words may be applied to a living property. I shall adduce the following instances:-- The absorbent orifices of the serous surfaces, are sometimes bathed for months together in the fluid of dropsies, and take up nothing. But if the sensibility of these orifices be exalted by tonics, or an effort of nature, in such case it will place itself, if I may so say, in equilibrium with the fluid, and absorption will be made. The resolution of tumours presents us with the same phenomena; as long as the powers of the parts are weakened, the lymphatics refuse admittance to the extravasated substances; but if the sum of these powers be augmented by the use of resolvents, in a short time, from the action of the lymphatics, the tumour will disappear: from the same cause the blood, and other fluids are taken up with a sort of avidity at times, and at others, not at all.[27] The art of the physician, then, in the use of resolvents, must consist in ascertaining the degree of sensibility which he requires in the vessels for the purpose which he has in view; and in exalting or depressing this power accordingly. In this way, in different circumstances, resolvents may be taken from the class of the debilitating or stimulating remedies.