ABSORPTION OF PROTEIDS. 437 



place in the large intestine. Finally, the objection that the action is due 

 to traces of enzymes, has been disposed of by the observations of Czerny 

 and Latschenberger, 1 in a case of a fistula situated in the sigmoid flexure. 

 The rectum was thoroughly washed out from the fistula, yet from 6070 

 per cent, of the injected proteid disappeared in 2329 hours. 



Assimilable and non-assimilable proteids. Some forms of proteid, such 

 as alkali albumin, prepared from white of egg, and acid albumin, prepared 

 from muscle, myosin, fibrin, or white of egg, are directly assimilable ; that 

 is to say, when injected into the blood stream they are not removed again 

 by the kidneys ; others, such as unchanged white of egg, caseinogen, and 

 glutin, are, when injected, at once excreted in the urine. The latter forms 

 must therefore, under normal conditions, be changed during absorption, 

 before passing into the blood ; but when excess of white of egg is present 

 in the intestine, absorption oversteps the rate at which this change can 

 take place, and a portion of the egg albumin reaches the circulation 

 unchanged. Under these circumstances, this portion is promptly re- 

 moved by the kidneys, and an " alimentary albuminuria " is the result, 

 just as an excessive amount of sugar in the intestine produces " alimentary 

 glycosuria." 



Relative amounts of proteids absorbed in different forms. It is 

 evident, then, that absorption can take place, either in the form of 

 albumose or peptone, of alkali or acid albumin, or even occasionally 

 in that of native proteid ; and the question arises, to what extent does 

 absorption take place under natural conditions in each of these different 

 forms ? Such a question is exceedingly difficult to answer by experiment. 

 It is impossible to do so exactly by observation of the amount of each 

 form of proteid present in the intestinal contents during proteid absorp- 

 tion, because the absorption is selective, and a substance present only in 

 traces may be passing out of the intestine more rapidly as it is con- 

 tinuously formed than another which is present in much larger quantity. 



A rough estimate of the relative amounts of proteid absorbed as 

 albumose and peptone, and that absorbed in other forms, may be obtained 

 from analyses of the intestinal contents during proteid digestion. Thus, 

 Schmidt-Miilheim 2 examined the contents of the stomach and intestine 

 at varying periods during digestion of flesh in dogs ; he found that the 

 amount of proteid in solution, both in the stomach and intestine, was 

 small at any given time, but that the amount present as albumose and peptone 

 was always somewhat greater than that present in other forms. When it is 

 remembered that albumose and peptone are absorbed more rapidly than 

 other proteids, this points to the greater part of the proteid being absorbed 

 as albumose arid peptone. 



It is not known with certainty to what extent amido -acids are formed 

 from proteids, in the natural course of intestinal digestion. The experi- 

 mental evidence on the subject is somewhat conflicting, but the majority 

 of observers are of the opinion that but little proteid is absorbed as leucine 

 and tyrosine, being nearly all absorbed as albumose or peptone, or even 

 at a still earlier stage. 



The only positive evidence as to the formation of leucine and tyrosine 

 in natural digestion, rests on the amounts found in the intestinal contents 



1 Virckow's Archiv, 1874, Bd. lix. S. 174 ; see also Ewald, Ztschr. f. Tclin. Med., Berlin, 

 1887, Bd. xii. S. 407 ; Huber, DeutscJics Arch. f. Jclin. Meet.., Leipzig. 1891, Bd. xlvii. 

 S. 495. 



2 Arch. f. Anat. u. PhysioL, Leipzig, 1879, S. 39. 



