But in some instances, when no lymph is previously effused, and no cyst is formed, the matter is not confined, but pervades the cellular substance extensively, and is generally followed by more or less sloughing of that tissue, and by great constitutional disturbance. This most frequently occurs in patients of a debilitated habit, in whom the incited action has been so slight as not to cause the effusion of lymph, by which nature usually sets bounds to the suppurating process. M. Gendrin advanced the opinion that pus was nothing but transformed blood; but his experiments on frogs are at least doubtful, since Mr. Gulliver, on repeating them, could not by any means induce the process of suppuration in these animals. It has been rendered probable by this gentleman’s observations that suppuration is a sort of proximate analysis of the blood, the fibrin being added to the contiguous parts, as in causing them to swell, forming the cysts of abscesses; the blood globules altered into pus being discharged as useless and excrementitious matter. Pure pus is heavier than water, of a yellowish-white colour, somewhat of the consistence of cream. It is very little inclined to putrefaction, less so, perhaps, than any animal fluid not oily. It is composed of globules, and a clear transparent fluid, coagulable, it has been said, by the muriate of ammonia. When a solution of this salt produces any change, it is by rendering the pus more ropy; not coagulation, but a sort of gelatinisation follows. It is said also to be sweet and “mawkish to the taste.” In unhealthy pus, such as already noticed, or in vitiated muco-puriform secretion, the colour and consistence are different, and flakes, resembling portions of lymph, are seen floating in it: they consist of fibrin thrown off with the pus, instead of being used for reparation and bounding the extent of the abscess; and by this latter circumstance such fluid is distinguished from the pure or laudable pus. In purulent matter also, especially that of an unhealthy character, the existence of a quantity of sulphureted hydrogen is indicated by the blackening of silver probes, and of various substances applied to the sore. It is necessary to bear in mind, that a matter resembling pus in many particulars, but in reality differing essentially from it, has generally been regarded as true purulent fluid; for it results, from some observations of Mr. Gulliver, that the pulpy matter, so frequently found in the substance of fibrinous clots of the heart and veins, is simply fibrin which has coagulated and passed into the state of softening, which he regards as a very frequent elementary disease. The subject is one of great interest, because it is connected with the theory of suppuration, and tends to modify materially our views on the pathology of the veins.