[30] In deducing general conclusions from experiments upon animals, it must be borne in mind, that in them suppuration is induced with great difficulty. Many of the appearances produced by the injection of putrid fluids (as in Experiment XIV) would, in man, probably have terminated in suppuration. Dr. Sédillot has nevertheless established the fact, that, generally speaking, a different class of post-mortem appearances may be expected from the introduction of decomposed serum, to those produced from fluids containing solid particles. Another class of cases, in which there would be difficulty in admitting the doctrine of the introduction of pus in substance into the circulation, presents itself, where, in the primary affections (as in Case VI), no evidence can be obtained of the original lesion having suppurated. The fluids effused in such cases may be serum, lymph, or blood, mixed in different proportions; and yet the constitutional symptoms will be exactly similar to those which follow the formation of pus in other instances. There may exist, both in the primary and in the secondary affection, every intermediate gradation between the healthy secretion of a part, and the formation of pure pus, or pus mixed with blood or lymph, without any of the essential characters of the disease being absent. An inflamed bursa, or a punctured wound, without the formation of pus, (Cases IV and V), may give rise to symptoms as severe, and consequences as fatal, as any that arise from the direct introduction of pus into the system. The secondary affections, in such cases, may run their course and prove as speedily fatal, as where well-formed purulent deposits have taken place. The most severe constitutional symptoms will sometimes be followed by the effusion of bloody fluid only, in one of the serous cavities (Case XXX). It would be unphilosophical, even were it practicable, to refer such cases to a different disease, merely because the accidental circumstance of the formation of pus is wanting. The origin of the affection in such instances may be as well-marked, the poison can often be traced as distinctly into the system, and the secondary disease may be as clearly connected with the primary, as in any case where pus has been originally formed. In some cases again, the constitutional symptoms which accompany, or are followed by, effusions into distant parts of the body, begin before sufficient time has elapsed to allow the supposition that pus can have been fully formed at the original seat of injury. Such instances occasionally, although rarely, present themselves in extensive burns and scalds, occurring in enfeebled habits, and after amputation of the limbs in scrofulous children.