272 PHYSIOLOGY CHAP. 



and might fall within the limits of experimental error ; but if we 

 take into account the enormous quantity of blood that circulates 

 in the portal system during the whole period of digestion, we 

 cannot doubt that sugar can be absorbed by the capillaries of the 

 villi, however insignificant the amount present in 100 c.c. of portal 

 blood may be. 



It is only when the amount of sugar introduced into the 

 intestine is abnormally great that part of it is absorbed from the 

 lymphatics, and produces an increase in the sugar of the chyle 

 escaping by the fistula (Ginsberg, 1889). But in view of the slow 

 rate at which the chyle flows along the thoracic duct, it must be 

 remembered that even in this case of excessive dosage with sugar, 

 the quantity that traverses the lacteals is minute in comparison 

 with that absorbed by the blood capillaries and carried to the 

 liver. In the girl with a lymphatic fistula described by I. Munk 

 and Rosenstein, it was noted that at most one-half per cent of the 

 absorbed sugar passed through the lacteals. Since in this case 

 there was excessive absorption of water by the lacteals, it is 

 probable that the current of water carried off a part of the sugar 

 dissolved in it. Since the increased sugar content of the blood 

 during digestion can only be detected in the portal vein and not 

 in the hepatic veins, it follows that the sugar must be fixed and 

 stored up in the cells of the hepatic parenchyma. We shall see 

 the great importance of this fact in discussing the metabolism of 

 the liver. 



The experimental data which are to hand in regard to the 

 course of the proteins after absorption are less definite. Schniidt- 

 Miilheim, with Ludwig, found that ligation of the thoracic duct 

 did not hinder protein absorption. More precise observations 

 were made by I. Munk and Rosenstein (1890) in the case of the 

 girl of eighteen with a lymphatic fistula. After a copious flesh 

 meal, the effusion from the fistula showed no perceptible increase 

 either in percentage of proteins or in absolute quantity escaping 

 from the fistula during the twelve hours subsequent to the meal. 

 From this they concluded' that no amount of absorbed protein 

 worth noting passes by the lacteals ; it must therefore travel by 

 the blood capillaries of the mucous membrane of the intestine. 



Wurtz, however, prior to Munk, had observed that the chyle of 

 oxen before rumination contains only 3'97 per cent protein, while 

 after rumination the protein content was raised to 5'96 per cent. 



Possibly, as Foster rightly pointed out, all proteins do not take 

 the same path, and are not absorbed under identical conditions by 

 all animals. If in herbivora, where the diet contains little fat, the 

 whole of the carbohydrates and proteins were absorbed by the 

 blood-vessels of the intestinal mucous membrane, little would be 

 left to pass by the lacteals. The structure of the villi shows that 

 the central lacteal of guinea-pigs and rabbits is larger than in 



