PROTEIN METABOLISM 77 
mere trace is excreted through the kidney. How and where 
this utilisation takes place is as yet unknown. 
The classical work of Miescher on the Rhine salmon demon- 
strated the fact that the body can change one protein substance 
into another without the intervention of the intestinal wall. 
This observer stated that after the fish entered the fresh water 
they ceased to take food, and yet in spite of this, great anabolic 
changes took place in the salmon body. These changes con- 
sisted in the marked growth of the generative organs, which 
was shown to take place at the expense of the muscular 
system. 
As regards the absorption of native proteins from the 
intestine, the old work of Voit and Bauer,! which showed 
that absorption of undigested proteins such as serum and egg 
albumen could take place, has been extended and confirmed 
by Heidenhain,? Friedlander, Waymouth Reid,* and others. 
Ascoli,’ with the newly introduced biological methods of testing 
for the presence of proteins, has been able to prove that the 
protein taken up is unchanged, and can give the precipitin 
reactions significant of the protein introduced. The absorption 
of unchanged protein can hardly, however, be said to occur 
under normal conditions. In the experiments referred to the 
protein was introduced in excess into the intestine. This 
absorption would seem also to be dependent to some extent 
on an increased permeability of the intestinal wall, such as 
is found in the very young. Another factor which plays an 
important part in this form of absorption is the presence of 
water, or salt solution. Friedlander (/c.) has shown that after 
all the water or salt solution has been taken up, absorption 
of the protein, to all intents and purposes, comes to a 
standstill. 
The objection which has naturally been raised to these 
various experiments is that, although the observers say that 
the intestine used in the experiment was thoroughly washed 
out previous to the introduction of the protein, yet there may 
have been sufficient trypsin left to act on the protein, and 
1 Voit and Bauer, Zeit. f. Biol. v. 536, 1869. 
? Heidenhain, Pfliiger’s Archiv, 56, 1894, 579. 
3 Friedlander, Zezt. f. Biol. 33, 1896, 264. 
* Waymouth Reid, PAz/. Trans. Ser. B. 192, 1900, 21. 
° Ascoli and Vigan, Zezt. f. physiol. Chem. 39, 1903, 283. 
