ABSOKPTION OF FOOD 379 



The faeces in the ox and cow are more fluid than in the horse, 

 while in the sheep they contain a smaller proportion of water. 

 In the ox the average weight of the faeces per diem, is about 

 30 kilos. 



Food takes about five days to pass completely through the 

 alimentary canal of ruminants. 



III. ABSOEPTION OF FOOD 



1. State in which Food leaves the Alimentary Canal. The 

 carbohydrates generally leave the alimentary canal as mono- 

 saccharides ; but some resist the action of digestion more than 

 others. Lactose seems to be broken down in the intestine 

 only when the special lactase is present in the succus entericus, 

 but in all cases it is broken down before it reaches the liver. 

 Cane sugar when taken in large excess may also be absorbed, 

 and it is then excreted by the kidneys. 



The proteins are absorbed as peptones, possibly as proteoses, 

 and as the amino-acids and other crystalline compounds 

 formed by the action of trypsin and erepsin (p. 8). Native 

 proteins may be absorbed unchanged from the lower bowel, 

 since it has been found that when egg white is injected into 

 an isolated part of the rectum it disappears to a very con- 

 siderable extent. 



The fats are chiefly absorbed as soaps and as fatty acids. 



2. Mode of Absorption of Food. That absorption is not due 

 merely to a process of ordinary diffusion or osmosis is clearly 

 indicated by many facts. 



(1) Heidenhain has shown tliat absorption of water from the 

 intestine takes place much more rapidly than diffusion through 

 a dead membrane. 



(2) The relative rate of absorption of different substances does 

 not follow the laws of diffusion. Griibler's peptone passes 

 more easily through the intestine than glucose, but glucose 

 passes more readily through parchment paper, while sodium 

 sulphate, which is more diffusible than glucose, is absorbed 

 much less readily. Again, as shown by Reid, an animal can 

 absorb its own serum under conditions in which filtration into 



