I 



THE ABSORPTION OF THE FOODSTUFFS 797 



appreciably increase the amino-acid content of the tissues, shows that any 

 storage of nitrogen in the organism must take place, not in the form of 

 ammo-acids, but as body protein. 



It was formerly thought that the deamination of amino-acids occurred on a large 

 scale in the wall of the alimentary canal, on the grounds that a larger amount of 

 ammonia was present in the portal blood than in the arterial blood. It seems probable 

 however that the source of this excess of ammonia is to be found in intestinal bacterial 

 changes, and that the major portion of the amino-acids is actually absorbed unchanged. 

 The view of Abderhalden that the amino-acids are synthetised in the intestinal wall 

 to serum proteins, and absorbed in that form into the blood stream, need here only 

 be mentioned, since it lacks experimental support. 



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 fistulas in one of the following 

 places : (a) gastric fistula (into the fundus of the stomach); (b) 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 the saliva and swallowed. On 

 arriving in 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 that the food remains in the stomach. In the animal with a pyloric 

 fistula, one to two minutes after the meal had been taken, a few drops of alkaline fluid 

 were extruded from the opening. From three to eight minutes after the conclusion 

 of the meal small quantities of clear acid gastric juice were repeatedly extruded. The 

 first admixture of the food with the outflow from the fistula occurred at eight to twelve 

 minutes after the completion of the meal, and after this time the pylorus continued 

 to open at regular intervals of ten to forty seconds, discharging each time a small 

 amount of fluid composed of particles of undigested bread mixed with gastric juice. 

 One and a half hours later the pylorus began to open less regularly and the fluid became 

 of a more pasty consistence, devoid of lumps of undigested bread. In the fourth, 

 fifth, and sixth hours after the meal the pylorus opened only once every one or two 

 minutes, and towards the end of this period the fluid extruded was clear. The following 

 Table shows the percentage amount of food taken which had left the stomach at 

 the end of each hour after the meal : 



First hour . . 32-6 per cent. 



Second hour . . . . . : 17-9 



Third hour . ... 29-5 



Fourth hour 1-87 



Fifth hour 6-66 



Sixth hour . .... 4-21 



The large proportion of the ingested food leaving the stomach during the first two 

 % or three hours can hardly be regarded as normal. Since in these experiments there was 

 a free outflow from the pylorus and the food was not allowed to enter the duodenum, 

 the local reflex, evoked by the presence of acid in the duodenum, was absent. The 

 gastric contents obtained in this way were analysed in order to find what changes 

 had been wrought on the food by the gastric juice. It was found that 32 per cent, 

 of the bread had been brought into solution. This solution had affected the proteins 

 more than the carbohydrates. Thus 67 per cent, of the nitrogen had been brought 

 into soluble form, consisting chiefly of proteoses and peptones. No amino-acids weie 



