318 



ABSORPTION. 



fats are taken up by the lacteals and may be absorbed in small quantity by the blood- 

 vessels. Although it is now pretty well understood how endosmotic liquids pass through 

 the walls of the blood-vessels and absorbents, the mechanism of the penetration of fatty 

 particles, which is no less constant, is still somewhat obscure. 



There can be no question with regard to the actual penetration of the minute parti- 

 cles of the chyle into the lacteals and even into the blood-vessels. In birds, indeed, ac- 

 cording to Bernard, all the fat which is absorbed is taken up by the blood-vessels, the 

 lymphatics of the intestine never containing a milky fluid. Confining our discussion to 

 the mechanism of the absorption of fatty emulsion in mammals, it must be admitted that 

 the assumption of the existence of orifices in the walls of the lacteals, even if we deny the 

 actual anatomical demonstration of these openings, becomes almost necessary ; for the 

 experiments upon the passage of fatty particles through closed membranes are certainly 

 very unsatisfactory. Taking into consideration all of the facts bearing upon the question, 

 it seems more probable that orifices exist in the vessels than that the fatty particles pene- 

 trate by endosmosis; but it must be remembered that this idea rests upon the un- 

 doubted physiological fact of the absorption of emulsions rather than upon anatomical 

 grounds ; and, if we were not called upon to explain the absorption of fatty particles, it 

 is doubtful whether the stomata of the vessels would be so generally admitted. It is not 

 infrequently the case that we are forced to assume the existence of certain anatomical 

 arrangements as the only reasonable explanation of physiological phenomena, when act- 

 ual demonstrations are unsatisfactory. With regard to the lacteals, when we remember 

 the excessive tenuity of the vessels of origin, the close adhesion of their walls to the 

 surrounding tissues, the novelty and uncertainty of the staining processes, and the fact 

 that some anatomists deny that the finest so-called lymphatic plexuses of origin have any 

 distinct walls, it is readily understood how, as physiologists, we must regard the exist- 

 ence of stomata in the lymphatics as an idea based upon the necessity of explaining well- 

 established physiological phenomena, rather than a clearly-demonstrable anatomical fact. 

 In studying the mechanism of the penetration of fatty particles into the intestinal villi, 



it has been ascertained that the epithelial cells 

 covering the villi play an important part in this 

 process. It was first ascertained by Goodsir that, 

 during the digestion of fat, these cells became 

 filled with fatty granules. This fact has been 

 confirmed by Gruby and Delafond, Kolliker, 

 Funke, and others. Funke, in his atlas of physi- 

 ological chemistry, figures the appearances of the 

 intestinal epithelium during the digestion of fat, 

 as contrasted with the epithelium observed dur- 

 ing the intervals of digestion, showing the cells, 

 during absorption, filled with fatty granules. 



It is true, as a general law, that insoluble sub- 

 stances, with the exception of the fats, are never 

 regularly absorbed, no matter how finely they 

 may be divided. The apparent exceptions to this 



^ mercury ^ & ^ of mmute subdivision like 



an emulsion, and carbonaceous particles. In the 



case of mercury, it is well known that minute particles in the form of unguents may be 

 introduced into the system by prolonged frictions ; but this cannot be regarded as an 

 instance of physiological absorption. The passage of small carbonaceous particles 

 through the pulmonary membrane seems to be purely mechanical. The same thing may 

 possibly occur when fine, sharp particles of carbon are introduced into the alimentary 

 canal ; but the experiments of Mialhe with pulverized charcoal, and particularly those 

 of Berard, Robin, and Bernard with lamp-black introduced into the intestinal canal of 



intestine of the 



