With proteoses, however, different results are obtained, as Neumeister[156] first pointed out. These bodies introduced into the blood undergo more or less of a change prior to their excretion in the urine, the change partaking of the character of a hydrolytic cleavage in which the primary proteoses are transformed into secondary proteoses, while deuteroproteoses are changed into peptones. This is not necessarily to be interpreted as meaning that the full equivalent of the proteose injected appears in the urine, but that the portion which is eliminated through the kidneys tends to undergo a transformation somewhere _en route_, akin to the change produced in pepsin-proteolysis. As to how common or complete this transformation is under the above circumstances, we have no positive knowledge. Such a hydrolytic change certainly occurs in the case of the dog, and the experimental evidence is in favor of the view that the transformation is effected in the kidneys by the pepsin secreted through the urinary tubules, where there is momentarily a formation of free acid. In the rabbit, on the other hand, no such change occurs; the urine from this animal contains practically no pepsin, and consequently the proteoses eliminated through the kidneys are excreted unaltered. As, however, the experiments of Stadelmann[157] and others have shown that the urine of all carnivora, and of man as well, contains a ferment which, on the addition of a suitable amount of hydrochloric acid, will digest fibrin with formation of the ordinary products of pepsin-proteolysis, it is to be presumed that all proteoses passing through the kidneys will undergo at least some change prior to their excretion in the urine. [156] _Ibid._, p. 284. [157] Untersuchungen über den Pepsin-fermentgehalt des normalen und pathologischen Harnes. Zeitschr. f. Biol., Band 25, p. 208. However this may be, it is very evident that the proteoses formed in gastric digestion cannot be absorbed as such directly into the blood-current. Introduced into the blood, they behave in such a manner as to warrant the conclusion that they are truly foreign substances, and the system makes a brave endeavor to remove them as speedily as possible. The same may be said of amphopeptones, from which we may conclude that all of these products of pepsin-proteolysis undergo some transformation during the process of absorption, by which their toxicity is destroyed and their nutritive qualities rendered fully available for the needs of the body. Discussion of this question, however, will be left until the next lecture.