ABSORPTION 371 



built up in the epithelial cells from the absorbed glycerine 

 and the fatty acids or soaps. Now, it has been shown that 

 when an animal is fed with fatty acids they are not only 

 absorbed, but appear as neutral fats in the chyle of the 

 thoracic duct, having combined with glycerine in the in- 

 testinal wall; and the epithelial cells contain globules of fat, 

 just as they do when the animal is fed with neutral fat. 

 Further, it is known that fat-splitting goes on in the 

 alimentary canal to a much greater extent than would be 

 necessary merely for the formation of a quantity of soap 

 sufficient to emulsify the whole of the fat in the food ; indeed, 

 at certain stages of digestion most of the fatty material, both 

 in the small and large intestine, has been found to consist 

 of fatty acids. To clinch the matter, it has been proved 

 that fatty substances which are not easily split up and 

 saponified (for example, lanolin, the fat of sheep's wool, a 

 mixture of compounds of fatty acids with cholesterin and 

 allied bodies) are not absorbed even when they are easily 

 emulsified. 



Leucocytes have been asserted to be the active agents in 

 the absorption of fat. They have been described as pushing 

 their way between the epithelial cells, fishing, as it were, 

 for fatty particles in the juices of the intestine, and then 

 travelling back to discharge their cargo into the lymph. 

 This view, however, is erroneous. But although the leuco- 

 cytes do not aid in the absorption of fat from the intestine, 

 they appear to take it up from the epithelial cells, conveying 

 it through the spaces of the network of adenoid tissue that 

 occupies the interior of the villus, to discharge it into the 

 central lacteal, where it mingles with the lymph and forms 

 the so-called molecular basis of the chyle. A part of the fat 

 reaches the lacteal in some other way, without being carried 

 by the leucocytes. The contraction of the smooth muscular 

 'fibres of the villus and the peristaltic movements of the 

 intestinal walls alter the capacity of the lacteal chamber, 

 ^and so alternately fill it from the lymph of the adenoid 

 reticulum, and empty it into the lymphatic vessel with which 

 it is connected. By this kind of pumping action the passage 

 of fat and other substances into the lymphatics is aided. In 



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