414 A MANUAL OF PHYSIOLOGY 



a mixture of compounds of fatty acids with cholesterin and allied 

 bodies) are not absorbed even when they are easily emulsified. 

 Even fats with a melting-point far above the temperature of the 

 body can be absorbed after being split up. The palmitate of 

 cetyl alcohol, the chief constituent of spermaceti, melting at 

 53 C., was absorbed to the extent of 15 per cent., 85 per cent, 

 being excreted in the faeces. It appeared as palmitin in the chyle 

 of a human being flowing from a fistula, the palmitic acid having 

 been absorbed as such, or as a sodium soap, and having then 

 united with glycerin to form the neutral fat, palmitin. 



Some observers have endeavoured to show that the fat is 

 absorbed without change by introducing into the intestine fat 

 stained with dyes, such as alkanna red or Sudan III., which are 

 insoluble in water. The stained fat was found in the epithelial cells 

 of the villi, in the lacteals, and, in the case of a patient suffering 

 from chyluria, in the urine. But this evidence is not conclusive, 

 for it has been shown that the pigments might easily have been 

 absorbed after decomposition of the fat, since, although insoluble 

 in water, they are soluble in fatty acids, and therefore to some 

 extent in the intestinal contents, and readily pass into the lymph. 

 As already pointed out, the bile plays an important part in 

 the solution of the fatty acids, which may form loose compounds 

 with the amide group of the bile-acids. In these loose combina- 

 tions, soluble in water, the fatty acids can -be absorbed from the 

 intestinal contents (Pfliiger). 



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 leucocytes 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 another way. The con- 

 traction 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 lym- 

 phatics is aided. In the dog most of the fat goes into the lacteals, 

 and thence by the general lymph-stream through the thoracic 

 duct into the blood. And in man the chyle collected from a 



