This example gives an idea of what occurs in diseases, in all of which the solids are especially in action; but the cause of this action, sometimes exists in them, and sometimes not. It is no doubt essentially necessary to seek the distinction of these cases. The following reflections are made with this view. 1st. I distinguish, in the present question, diseases into two classes; 1st. into those which especially affect animal life; 2d. into those that particularly disorder organic life. I say particularly, for such is the connexion of these two lives, that the one can hardly be altered without the other; thus fevers that affect organic life, produce cerebral effects that agitate the animal: thus also primitive cerebral affections influence sympathetically the circulation, respiration, &c. But certainly we cannot deny, that there are some affections, whose principal and primitive character is a disorder of the animal life; such are convulsions, spasms, paralysis, mania, epilepsy, catalepsy, &c. But it appears that the cause of these diseases is almost always in the solids, and that the fluids most commonly are not affected. Therefore you see that crises, in every case are foreign to these diseases. Hypochondria, hysteria, melancholia, &c. though they appear to reside more particularly in the solids, can yet be in a degree dependant on the fluids, as different examples will prove. Diseases, on the other hand, that particularly affect organic life, as fevers, inflammations, &c. may have their principle as well in the fluids as in the solids. Hence the reason, that these diseases are subject to crisis, and are cured by evacuants, alteratives, &c. 2dly. It is necessary in order to resolve the question of the affection of the solids or the fluids in diseases, to distinguish their phenomena into those which are sympathetic, and those that are the product of a direct excitement. Every sympathetic phenomenon has its seat essentially and necessarily inherent in the solids. In fine, the solids alone act upon each other and correspond together by means yet unknown. All sympathetic vomiting, febrile agitation of the heart, exhalation, secretion, and absorption, arise from a change effected, by the influence of a part more or less remote, in the solids of those which are the seats of these phenomena. When cold acts upon the skin covered with sweat, immediately the pleura becomes affected. If cold water is conveyed into the stomach while the body is hot, an effect is oftentimes produced upon a distant organ. This is sympathy, and not the repercussion of the humours. In this work I have cited a great number of examples of sympathy under each system; but in none of them I think is it possible to conceive of an affection of the fluids. 3dly. The division of diseases into organic, or those which alter the texture of the organs, and into those which leave this texture untouched, is still essential here. The first have their seat evidently in the solids.