I08 NUTRITION OF FARM ANIMALS 



from the intestines even during the height of protein resorption. 

 Folin and Denis and also Van Slyke and Meyer have recently 

 demonstrated, however, that sufficiently delicate tests show 

 the presence of such products in the portal blood in amounts 

 as large as could be expected in view of the gradual nature of 

 digestion and resorption and of the large volume of blood pass- 

 ing through the intestinal capillaries. The prevailing opinion 

 seems to be at present that the digestive products of the pro- 

 teins undergo relatively little modification before entering into 

 the circulation. 



Fats. The mechanism of fat resorption has been the subject 

 of heated controversy. Some physiologists have maintained 

 that it is chiefly a physical process ; that globules of emulsified 

 feed fat are taken up bodily by the epithelial cells and excreted 

 again by them into the lacteals. This view is based largely 

 on microscopical observations which show the presence of ap- 

 parently unaltered fat globules of the intestinal emulsion in 

 the protoplasm of the epithelial cells and in the lymph of the 

 lacteals after the ingestion of fat. Other no less eminent physi- 

 ologists, however, have as stoutly held that fats are not resorbed 

 unaltered but only after cleavage into glycerol and fatty acids 

 (or their salts), which are soluble in bile (135), and that the fat 

 globules observed in the epithelial cells are the product of a 

 resynthesis. At present the weight of scientific opinion is 

 strongly in favor of this latter view. It is perhaps true that 

 unaltered fat droplets may be taken up by the epithelial cells 

 but that any considerable amount of fat is resorbed in this 

 fashion is to say the least very questionable. 



At any rate, the digested fat reaches the lacteals almost en- 

 tirely in the form of fat, so that after a meal containing much 

 fat the lacteals are filled with a milky fluid and the lymph is 

 found to contain relatively large amounts of neutral fats. It 

 is clear, then, that the resorbed soaps and fatty acids are speedily 

 synthesized to fat again. This synthetic power is still further 

 and strikingly demonstrated by the fact that free fatty acids 

 are readily digested but are transmitted to the lacteals in the 

 form of the corresponding neutral fats, having evidently been 

 combined with glycerol in the process of resorption, although 

 the source from which the body derives its glycerol is still un- 

 certain. Evidently, then, from this point of view, nothing 



