PROTEIN METABOLISM 33 
of increase at all was obtained in the comparatively small amount 
of blood which could be examined. Abderhalden (/.c.) attempted 
to prove the presence of amino acids in the blood after a full 
proteid meal, but without success. The method which he 
employed was the very excellent one devised by Fischer, in 
which the amino acids, even when present in small amount, 
form crystalline compounds with §-naphthalinsulphochloride. 
Howell (Zc.), by using this same method in conjunction with 
a process of dialysis, has reported that he has been able to 
detect small amounts of amino acids in the blood taken from 
dogs at the height of digestion; more, further, in the portal 
blood than in blood taken from the general systemic circula- 
tion. Even in the blood of dogs which had fasted for a 
considerable number of hours, a positive reaction could still 
be obtained. 
A point in favour of the full breakdown of the protein 
molecule was given in a piece of work by Abderhalden and 
Samuely,! in which an attempt was made to affect the con- 
stitution of serum protein. A horse was bled to an extreme 
degree, and then was fed with a protein obtained from wheat— 
gliadin. This protein differed very markedly from the con- 
stitution of the serum protein, especially in its content of 
glutaminic acid (gliadin has 36°5 per cent. glutaminic acid, whereas 
serum albumen has only 77, and serum globulin 8°5). When the 
horse on the gliadin diet had regenerated its blood to a large 
extent, it was again bled, and the constitution of the newly 
formed serum proteid investigated. Results, as regards the 
alteration of the internal constitution of the body protein by 
the nature of the food protein, were quite negative. The serum 
protein obtained resembled that formerly present in every 
respect. The fact, too, that Howell (/.c.) was able to detect 
amino acids, but no trace of albumoses or peptones in the blood, 
seems to lend support to the view that the hydrolytic changes 
in the intestine are pretty thorough. 
In what form, then, does the absorbed protein reach the 
tissues proper? Is it absorbed as simple amino acids in solution 
absolutely unchanged? In all probability not to any great 
extent, as is shown by the slight increase of the nitrogen in 
the blood. Of course, it might be absorbed by means of the 
leucocytes, as suggested by Hofmeister, and that owing to 
' Abderhalden and Samuely, Zezt. f. physiol. Chem. 46, 1905, 193. 
