264 ABSORPTION OF THE FOOD. 



either depositing it while still maintaining their integrity, or set- 

 ting it free by themselves breaking up and disintegrating. Some 

 authorities hold the opinion that the contractions of the proto- 

 plasm of the columnar epithelial cells forces out the fat, and that 

 the particles pass through the spaces between the cells and thus 

 reach the lacteals. 



Final Disposition of the Absorbed Fat. Inasmuch as no more 

 than 60 per cent, of the fat absorbed finds its way into the thoracic 

 duct, it might be inferred that the lacteals were not the only 

 channels of absorption, and that the capillary blood-vessels of the 

 villi had a part in this process, but there is no more fat found in 

 the blood of the portal vein during the period of fat absorption 

 than in the blood of the rest of the body, and even this is not 

 increased if the contents of the thoracic duct are not permitted 

 to enter the venous circulation. Just what becomes of the 40 

 per cent, unaccounted for is not known. It was long regarded 

 as impossible for the absorbed fat to be deposited in the tissues 

 unaltered, and it was supposed that it all underwent such changes as 

 to destroy its integrity, and that the fat which existed in adipose 

 tissue and elsewhere was entirely a new formation. In reference 

 to this Liebig said : " In hay or the other fodder of oxen no beef- 

 suet exists, and no hog's lard can be found in the potato-refuse 

 given to swine." While it is true that some of the fat of the 

 body is produced from other substances than the absorbed fat, 

 still, the evidence is conclusive that under certain circumstances 

 this is deposited in the tissues without undergoing any change 

 whatsoever. If a dog is starved until the reserve supply of fat 

 has been exhausted, and it is then fed with rape-seed or linseed 

 oil or mutton tallow, fat will be again deposited in the tissues 

 and in it some of the fat given as food will be recognizable. It 

 is, however, a question whether this occurs except under the 

 exceptional conditions here mentioned, although some of the best 

 authorities state that the fat in the blood after a meal is eventually 

 stored up in the connective-tissue cells of adipose tissue. Others 

 claim that the fat of the food is completely oxidized, and that 

 the body-fat is formed from proteids or carbohydrates, or both. 

 The probabilities are that proteids and carbohydrates are the 

 principal sources of the body-fat, and that fat itself is sometimes 

 a contributory factor, although its main office is to supply the 

 body with heat or other form of energy. 



Absorption by the I<arge Intestine. Although destitute 

 of digestive power, this portion of the alimentary canaUplays an im- 

 portant part in the process of absorption. The food undergoes diges- 

 tion in the stomach and small intestine, staying in the former from 

 one and a half to five hours, and in the latter also a variable time. 

 In one case, in which by reason of the existence of a fistula at the 

 end of the small intestine it was possible to investigate this ques- 

 tion^ it was found that food began to enter the large intestine from 



