4thly. The division into acute and chronic, ought not to be neglected in resolving the problem. 5thly. In fine, it would be necessary to make another distinction not less important, viz. that of diseases which are independent of every principle inherent in the economy and of those which proceed from a similar principle, as when the virus of the venereal, the tetters, scrofula or scurvy predominates in the whole system, and alternately attacks the different organs. How little soever you may examine diseases under different points of view, you will perceive that what is true of one class cannot be so of another. It is evident from this, that it is improper to resolve this question in a general manner, as it has been too often done, and that a theory of diseases founded upon the principle of the affection of the solids or fluids alone, is a pathological absurdity, equal to that in physiology which would place in action the fluids or solids only. I think there are two errors that should be equally feared, that of particularizing and that of generalizing too much. The second leads us to false conclusions as well as the first. Though the vital properties reside especially in the solids, it is not necessary to consider the fluids as entirely inert. It is undeniable, that those of them which form the composition of the body, increase in vitality as they advance from the aliments of which they are formed, to the solids which they compose. The alimentary mass is less animalized than the chyle, and this is less so than the blood. It would undoubtedly be a subject of very curious research, to determine, how the particles, from being foreign to the vital properties, and enjoying only physical ones, become by degrees possessed of the rudiments of the first. I say the rudiments, for certainly the vital elaboration that the fluids experience in circulating as such in the body, and before they penetrate the solids to become a part of them, is the first degree of their vital properties. In the same manner, if you should inject into this fluid the materials of those that are exhaled or secreted, the exhalant and secretory organs would repulse these materials, if life had not made them undergo a previous elaboration.