ABSORPTION. 171 



known. They are, at all events, so altered in the blood, while 

 passing through the lungs, that they lose the form of a fatty emul- 

 sion, and are no longer to be recognized by the usual tests for 

 oleaginous substances. 



The absorption of fat from the intestine is not, however, exclu- 

 sively performed by the lacteals. Some of it is also taken up, 

 under the same form, by the bloodvessels. It has been ascertained 

 by the experiments of Bernard 1 that the blood of the mesenteric 

 veins, in the carnivorous animals, contains, during intestinal diges- 

 tion, a considerable amount of fatty matter in a state of minute 

 subdivision. Other observers, also (Lehmann, Schultz, Simon), have 

 found the blood of the portal vein to be considerably richer in fat 

 than that of other veins, particularly while intestinal digestion is 

 going on with activity. In birds, reptiles, and fish, furthermore, 

 according to Bernard, the intestinal lymphatics are never filled 

 with opaque chyle, but only with a transparent lymph ; so that these 

 animals may be said to be destitute of lacteals, and in them the fatty 

 substances, like other alimentary materials, are taken up altogether 

 by the bloodvessels. In quadrupeds, on the other hand, and in 

 the human subject, the absorption of fat is accomplished both by 

 the bloodvessels and the lacteals. A certain portion is taken up 

 by the former, while the superabundance of the fatty emulsion is 

 absorbed by the latter. 



A difficulty has long been experienced in accounting for the ab- 

 sorption of fat from the intestine, owing to its being considered as a 

 non-endosmotic substance ; that is, as incapable, in its free or undis- 

 solved condition, of penetrating and passing through an animal 

 membrane by endosmosis. It is stated, indeed, that if a fine oily 

 emulsion be placed on one side of an animal membrane in an endos- 

 mometer, and pure water on the other, the water will readily pene- 

 trate the substance of the membrane, while the oily particles cannot 

 be made to pass, even under a high pressure. Though this be true, 

 however, for pure water, it is not true for slightly alkaline fluids, 

 like the serum of the blood and the lymph. This has been de- 

 monstrated by the experiments of Matteucci, in which he made 

 an emulsion with an alkaline fluid containing 43 parts per thou- 

 sand of caustic potassa. Such a solution has no perceptible alkaline 

 taste, and its action on reddened litmus paper is about equal to 

 that of the lymph and chyle. If this emulsion were placed in an 



1 Leqons de Physiologie Experimentale. Paris, 1?5<3, p. 325. 



