ABSORPTION OF PROTEIDS. 437 
place in the large intestine. Finally, the objection that the action is due 
in 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, yel from 60-70 
per cent, of the injected proteid disappeared in 23-29 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 i/i 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-Mulheim 2 examined the contents of the stomach and intestine 
at varying periods during digestion of flesh in dogs ; he foimd that the 
amount of proteid in solution, both in the stomach and intestine, was 
small at any given tm\e,hut that the amountprest nf as albumose and peptone 
was always somewhat greater then 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 and 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 Virchon:'* Archrfv, 1874, Bd. lix. S. 174 ; see also Ewcild, Ztsehr. f. klin. Med., Berlin, 
1887, Bd. xii. S. 407 ; Hnber, TJeutschcs Arch. /. Jclin. Med., Leipzig. 1891, Bd. xlvii. 
S. 495. 
2 Arch. f. Anut. u. Physiol., Leipzig, 1879, S. 39. 
