9 oo METABOLISM. 



other syntheses which accompany assimilation, such as the formation of 

 proteids from peptones, must also occur within them. Hofmeister l has 

 suggested that the leucocytes may also take an important part in determining 

 the assimilation of the foodstuffs. They are present in great abundance in 

 the intestinal mucous membrane, and especially those parts of that membrane 

 where absorption proceeds most extensively ; and they are also, it has been 

 shown, greatly increased in number during the process of absorption. It is, 

 however, difficult to obtain affirmative evidence upon this point, and since 

 leucocytes elsewhere do not possess this power, it is improbable that they are 

 the agents for such conversion in the intestine. 



After assimilation the proteids are absorbed by the blood vessels of 

 the intestinal mucous membrane. *The evidence for this has been 

 already given in the article on " Digestion and Absorption " (p. 433). 

 If any proteids are taken up by the lacteals of the small intestine, they 

 do not get into the thoracic duct, 2 but must be transferred to the blood 

 vessels in passing through the mesenteric glands. At any rate we may 

 assume that nearly the whole of the proteids are ultimately taken by the 

 portal vein to the liver. The portal vein, therefore, contains the absorbed 

 material derived from digestion and assimilation of proteid food; it 

 must have, therefore (besides the ordinary constituents of blood plasma), 

 an additional amount of serum albumin or of serum globulin, obtained by 

 the transformation of the peptones into these materials ; also extractives 

 of the meat or other forms of proteid diet (which are absorbed equally 

 by the blood vessels of the intestine), and in addition any products 

 of further decomposition of peptones, such as the amido-acids, the 

 possibility of the presence of which we have already discussed. But it 

 must be borne in mind that the blood flow through the portal system is 

 so large and rapid, that one could hardly expect these substances to be 

 absorbed into it in such a proportion that it would be possible to detect 

 by chemical means any appreciable difference of composition between 

 the blood of the portal vein and that of the system generally, nor are 

 there any satisfactory analyses directly showing such difference. Never- 

 theless there is a distinct physiological difference between the portal 

 blood collected during absorption of food, and especially of proteid food, 

 and the same blood collected during the intervals of digestion ; for it has 

 been shown that in the former case such blood, on being passed through 

 the liver, shows an increased amount of urea, whereas in the latter case 

 such an increase is not noticed. It is certain, at any rate, that the 

 products of absorption and assimilation of proteid foods are carried 

 to the liver, and, having traced them to this organ, we have next to 

 consider (1) Whether they are stored at all within it; (2) whether 

 they undergo any change in passing through it. 



Influence of the liver on proteid metabolism. With regard to the 

 possible storage of proteid in the liver, it is open to us to suppose 

 that an excess of proteid material which is present in the portal blood 

 as the result of the absorption of proteid food, might be temporarily 

 taken up, at least in some measure, by the hepatic cells, and, after being 



1 Arch. f. exper. Path. u. PharmakoL, Leipzig, 1884-7, Bde. xix. S. 1 ; xx. S. 29 ; xxii. 

 S. 306. 



2 Asher and Barbera found, however, in a dog a marked rise both in the amount of 

 chyle and of the nitrogen of the chyle (estimated by Kjeldahl's method) during digestion 

 of purely proteid food, given by a gastric fistula. The rise was greatest at the sixth hour 

 after feeding, but there Avas a primary culmination at the second hour (CentralbL f. 

 PhysioL, Leipzig u. Wien, 1897, Bd. xi. S. 403). 



