THE ABSORPTION OF THE FOOD-STUFFS 847 



by Leathes and Folin, a large proportion of the amino-acids undergo 

 deamination in the wall of the gut, so that the products that are 

 actually absorbed are ammonia and a fatty acid or its oxy-derivative. 

 The ammonia passes through the liver and is at once converted into 

 urea, so that the post-prandial rise in urea excretion is due to this 

 immediate deamination of the ingested protein. What happens 

 to the non-nitrogenous moiety of the protein we do not know. It is 

 apparently oxidised fairly rapidly, since excessive protein ingestion 

 does not give rise to any formation of fat, but produces in every 

 case an increase in the respiratory exchanges and in the output of 

 C0 2 . At the present time it is impossible to decide with any certainty 

 as to which of these views of the fate of the ingested protein is correct. 

 It is possible that all three processes may take place, viz. that a 

 proportion of the protein may be built up in the cells lining the 

 alimentary canal to form blood protein, so that this organ would 

 have to be regarded as an important blood-forming organ, and that 

 another portion, representing the amount required to replace the 

 tissue waste of the body, is absorbed into the blood stream as amino- 

 acids, in which form it is carried to the tissues and reintegrated 

 into the protein characteristic of each tissue. A third portion, 

 probably the major part of the protein, does not reach the tissues 

 at all as a nitrogenous compound, but undergoes deamination 

 in the intestinal wall, the nitrogen being rapidly carried to the liver 

 and converted into urea, and then excreted by the kidneys, while 

 the non- nitrogenous moiety is carried to the tissues, to which it serves 

 as a ready and important source of energy. Further investigation on 

 all these points is required. 



THE ACTUAL COURSE OF DIGESTION 



In a recent series of papers London describes the course of digestion 

 of meals of various characters in dogs which had been provided 

 with fistulse in one of the following places : (a) gastric fistula (into 

 the fundus of the stomach) ; (6) pyloric fistula (on the duodenal side 

 of the pylorus) ; (c) duodenal fistula (about one foot below the pylorus) ; 

 (d) jejunal fistula (about the middle of the small intestine) ; (e) ileum 

 fistula (just above the caecum). 



We may take as an example the course of digestion of a meal 

 composed of 200 grm. of bread. This is eaten by the animal, 

 mixed with saliva and swallowed. On arriving at the stomach it 

 gives rise to the secretion of gastric juice. In a series of special 

 experiments London found that on the average 200 grm. of bread 

 evoked the secretion of 20 grm. of saliva, about 10 grm. of mucus 

 from the coats of the stomach, and about 315 grm. of gastric juice. 

 The secretion of gastric juice is continuous during the whole time 



