Authors have formed very different ideas concerning the exhalants. We know the decreasing vessels of Boerhaave, and the error loci for which his imagination created these vessels. Lately all the white vessels continuous with the arteries have been rejected, and in order to explain exhalation, recourse has been had only to inorganic pores in the arterial parietes, through which the fluids transude upon the organs. Frequent observation of similar transudations upon the dead body, as those of the bile through the gall-bladder, of the marrow through the osseous texture which it discolours, &c. is one of the great supports of this method of explaining the exhalant system. But we have already many times observed, that these phenomena never take place during life, when the organic sensibility of the parts refuses to produce them. Besides, exhalation is evidently subjected to the influence of the vital forces, since it varies continually in a part, according as the vital forces of the part themselves vary. Moreover, if the exhaled fluids escaped through inorganic pores, it would be necessary that not only the vascular parietes, but also those of the serous surfaces which receive these fluids, should be perforated with small holes; why then would not these fluids, of which these surfaces are the reservoirs, transude into the neighbouring cellular texture? Let us reject then every opinion that disregards anatomical observation, and let us endeavour by this observation to ascertain what the exhalants are. It is undoubtedly difficult to form a precise idea of these vessels, their extreme tenuity constantly conceals them from us in a natural state. Yet by the aid of experiments and accurate reasoning, it appears to me that we may come at some degree of accuracy. We have seen that the existence of a capillary system terminating the arteries, is in the parts where exhalation takes place as in the others, a thing incontestably proved by experiment with injections, by inflammations which arise spontaneously, and by those that are produced at will; so that a serous, cutaneous surface, &c. on which nothing appears, is covered with an infinity of little vessels suddenly in the first case, and at the end of a longer or shorter time in the second.