Physiologists at one time were much engaged with the introduction of medicinal infusions into the veins of living animals. They circulated by these infusions purgatives, emetics and a thousand other foreign substances, the contact of which the blood bore, without occasioning any other accident to the animal than that of vomiting or alvine evacuations if they were emetics or purgatives, and a greater or less general derangement if they were other foreign substances which had no affinity with any particular organ. The caustics, as the nitric and sulphuric acids and other very irritating substances, have alone caused death in these curious experiments of which Haller has given us a sketch, and which prove that various substances wholly foreign to the blood can circulate in it, and that it is a common mass in which are found many principles differing from each other, and which cannot be always essentially the same. In these experiments the most important part has been neglected, that of the infusion of the different animal fluids, particularly the secreted ones, and those also which are preternaturally produced in diseases. I think that the different reabsorptions would be much elucidated by the infusion of the various kinds of pus, sanies, &c. But we have already sufficient facts to convince us that the fluids and especially the blood can be diseased; that the various foreign substances mixed with it can act in a fatal manner upon the solids. In fact, every acrid, irritating matter, without being mortal, accelerates the action of the heart and produces a true fever, if injected into the veins. In all these cases, it is always necessary that the solids should act; for all the morbid phenomena suppose their alterations; but the principle of these alterations is in the fluids. They are the excitants, and the solids the organs excited. Now if there are no excitants, there is no excitement, and the solids remain unaffected. Finally there are cases in which the whole economy both solids and fluids seem to be simultaneously affected; such are adynamic fevers, in which at the same time that there is a general prostration of the first, the second appear to be really decomposed.