CII. XXXIV.] 



ABSORPTION OF FATS 



521 



Absorption of Pats. Tho fats undergo in the intestine two 

 changes : one a physical change (emulsification), the other a chemical 

 change (saponification). The lymphatic vessels are the great channels 

 for fat absorption, and their name lacteals is derived from the milk- 

 like appearance of their contents (chyle) during the absorption of fat. 



The course which the minute fat-globules take may be studied by 

 killing animals at varying periods after a meal of fat, and making 

 osmic acid microscopic preparations of the villi. Figs. 410 and 411 

 illustrate the appearances 

 observed by Schafer. 



The columnar epithelium 

 cells become first filled with 

 fatty globules of varying 

 size, which are generally 

 larger near the free border. 

 The globules pass down the 

 cells, the larger ones break- 

 ing up into smaller ones 

 during the journey; they 

 are then transferred to the 

 amoeboid cells of the lym- 

 phoid tissue beneath : these 

 ultimately penetrate into 

 the central lacteal, where 

 they either disintegrate or 

 discharge their cargo into 

 the lymph - stream. The 

 globules are by this time 

 divided into immeasurably 

 small ones, the molecular 

 basis of chyle. The chyle 

 enters the blood-stream by 

 the thoracic duct, and after 

 an abundant fatty meal the blood-plasma is quite milky; the fat 

 droplets are so small that they circulate without hindrance through 

 the capillaries. The fat in the blood after a meal is eventually 

 stored up especially in the cells of adipose tissue. It must, 

 however, be borne in mind that the fat of the body is not exclusively 

 derived from the fat of the food, but it may originate also both from 

 proteid and from carbohydrate. 



The great difficulty in fat absorption was to explain how the fat 

 first gets into the columnar epithelium : these cells will not take up 

 other particles, and it appears certain that the epithelial cells do not 

 in the higher animals protrude pseudopodia from their borders (this, 

 however, does occur in the endoderm of some of the lower inverte- 



FIG. 410. Section of the villus of a rat killed during fat 

 absorption, ep, epithelium; sir, striated border; 

 c, lymph-cells ; d, lymph-cells in the epithelium ; 

 I, o ntral lacteal containing disintegrating lymph- 

 corpuscles. (E. A. Schafer.) 



