220 THE HUMAN SPECIES 



die with severe diabetes, and many cases of diabetes in man 

 are associated with degenerative changes in the pancreas. 



As the chyme passes down the intestine its various con- 

 stituents are absorbed by means of a series of changes in the 

 mechanical affinity of the intestinal villi, not merely as fats 

 converted into alkalis of the fatty acids, but as albumoses and 

 peptones, carbohydrates, salts and water. During these pro- 

 cesses the fat enters the lacteals of the intestinal mucosa, and as 

 " chyle " runs in the lymphatic vessels of the intestine to be ulti- 

 mately applied to the use of the body. 



The excellent work of Ludwig, Zawilkski, von Mering, 

 Munk and Rosenstein has shown that only a small fraction 

 (A"i) f * ne soluble matter (water, salt, sugar and proteid) 

 travels by way of the axial chyle vessel (lacteal radicle) of the 

 villi, which is devoted almost exclusively to the passage of fats, 

 the remainder being absorbed by the superficial capillary net- 

 work of the villi into the portal system. 



The chyle contains 7-10 per cent, of solids, some 3-4 per 

 cent, more than lymph, the difference being made up almost 

 entirely of fat. The chyle of dogs contains the maximum 

 amount of fat (6-8 per cent.); that of man contains only 5 

 per cent. 



In man and animals the intestinal digestion is associated 

 with certain special fermentation processes which are of greater 

 importance in herbivora than in carnivora and omnivora. 

 They depend in all cases upon the presence of micro-organisms 

 (organised ferments) which enter the gut with the food ; they 

 do not occur in the foetus during intra-uterine life. 



The fermentation of carbohydrates begins in carnivora and 

 omnivora in the small intestine ; the chief seat of decomposition 

 fermentation with formation of abundant gases (especially in 

 herbivora) is in the large intestine, particularly the caecum, as- 

 cending and transverse colon. Here again we see the effect of 

 the bile in transforming the poisonous decomposition products 

 into harmless aethereal sulphates. 



The relative proportion of useless waste material to assimil- 

 able nourishment derived from the food is always greatest in 

 herbivora and least in carnivora, the faecal residue in omnivora 

 varying according to the predominance of the vegetable or flesh 



