250 DIGESTION AND ASSIMILATION OF THE FOODSTUFFS 



THE TIME- AND MASS-RELATIONS OF DIGESTION AND 

 ABSORPTION. 



The Intestine is an extraordinarily efficient organ of absorption. 

 As much as seventy or eighty per cent, of the total length of the 

 jejunum and ileum may be removed and, provided fats be not too 

 abundant in the diet, absorption still remains practically complete. 

 If the food contains a large proportion of fat, however, over twenty- 

 five per cent, of the fat may, under these conditions, be discharged 

 unabsorbed in the feces as contrasted with four or five per cent, in 

 normal animals of similar kind and dimensions. 



The greater part of absorption takes place in the upper part of the 

 small intestine and absorption is practically complete before the 

 contents of the small intestine are discharged into the cecum. There 

 are, however, certain exceptions to this rule, mainly furnished by dif- 

 ficultly digestible foodstuffs. Thus uncooked white of egg is digested 

 with great difficulty and as much as seventy per cent, of this protein 

 may pass undigested and unabsorbed into the large intestine where it 

 may be presumed to afford a favorable culture medium for putrefactive 

 bacteria. Then, also, when proteins very diverse in composition from 

 the normal tissue-proteins of animals, such as certain vegetable pro- 

 teins, are partaken of, the selective absorption which occurs may result 

 in a proportion of an amino-acid which is present in undue excess 

 remaining unabsorbed until its passage into the large intestine. 



The Stomach, as might be imagined from the nature of the part it 

 plays in digestion, is not essential to the absorption of foodstuffs. 

 Excision of the stomach is followed by a good utilization even of 

 proteins, the digestion being accomplished by the trypsin of the pan- 

 creatic juice and the erepsin of the succus entericus. Provided the 

 stomach be left in situ, moreover, efficient digestion and absorption of 

 proteins may still continue when the pancreatic duct is ligated, so 

 that pancreatic juice cannot enter the intestine. In this case digestion 

 is effected by erepsin after preliminary cleavage by the pepsin in the 

 gastric juice. The absorption of Fats, however, is very seriously 

 interfered with by the exclusion of pancreatic juice from the intestine. 



An important relationship subsists between the amount of food 

 which is partaken of at a meal and the quantity of digestive juices 

 secreted on the one hand, and the time occupied in digestion on the 

 other hand. In the case of the Gastric Juice the quantity of the 

 digestive fluid secreted may be estimated by forming a diverticulum 

 or pocket in the stomach which is connected with the exterior by 

 means of a fistula. The juice secreted by this diverticulum is found 

 to be a constant proportion of the fluid which is secreted by the whole 

 area of the gastric mucosa and the total secretion of gastric juice during 

 digestion may therefore be estimated in terms of the volume of the 

 secretion furnished by the diverticulum. It has been observed that 

 the quantity of gastric juice which is secreted during the digestion 



