522 



THE ABSORPTION OF FOOD 



[CH. XXXIV. 



brates) ; moreover, fat particles have never been seen in the striated 

 border of the cells. 



Eecent research has shown that particles may be present in the 

 epithelium and lymphoid cells while no fat is being absorbed. These 

 particles are apparently protoplasmic in nature, as they stain with 

 reagents that stain protoplasmic granules ; they, however, also stain 

 darkly with osmic acid, and so are apt to be mistaken for fat. There 

 is, however, no doubt that the particles found during fat absorption 

 are composed of fat. There is also no doubt that the epithelial cells 

 have the power of forming fat out of the fatty acids and glycerin into 

 which fats have been broken up in the intestine. Munk, who has 

 performed a large number of experiments on the subject, showed that 

 the splitting of fats into glycerin and fatty acids occurs to a much 

 greater extent than was formerly supposed ; these substances, being 

 soluble, pass readily into the epithelium cells ; and these cells per- 

 form the synthetic act of building 

 them into fat once more, the fat so 

 formed appearing in the form of small 

 globules, surrounding or becoming 

 mixed with the protoplasmic granules 

 that are ordinarily present. Another 

 remarkable fact which he made out 

 is that after feeding an animal on 

 fatty acids the chyle contains fat. 

 The necessary glycerin must have 

 been formed by protoplasmic activity 

 during absorption. The more recent 

 work of Moore and Rock wood has 

 shown that fat is absorbed entirely 



as fatty acid or soap; and that preliminary emulsification, though 

 advantageous for the formation of these substances, is not essential. 



We thus see how with increase of knowledge due to improved 

 methods of research, a complete change has come in the ideas physio- 

 logists hold regarding this subject. It is not so many years ago, that 

 the physical change emulsification which fats undergo in the 

 intestine was considered to be more important than the chemical 

 changes fat-splitting and saponification. In fact, the small amount 

 of chemical change which was supposed to occur was regarded as 

 quite subordinate, and of value merely in assisting the process of 

 emulsitication. We now know that the exact converse is the truth ; 

 the chemical change is the important process, and emulsification the 

 subordinate one. 



Bile aids the digestion of fat, in virtue of its being a solvent of 

 fatty acids, and it probably assists fat absorption by reducing the 

 surface tension of the intestinal contents; membraries moistened 



FIG. 411. Mucous membrane of frog's intes- 

 tine during fat absorption, ep, epithe- 

 lium ; sir, striated border; C, lymph 

 corpuscles ; I, lacteal. (B. A. Schiifer.) 



