v INTERNAL EESTITUTIVE SECRETIONS 271 



latter is more milky than that of the portal vein, showing it to be 

 fat absorbed from the lacteals and not from the blood capillaries of 

 the intestinal villi. This is proved by the fact that during the flow 

 of chyle from the fistula of the thoracic duct the portal blood 

 contains a very small amount of fat. The deficit of absorbed fat 

 can, therefore, only be explained, according to Foster, on the 

 assumption that, as it passes through the lymph glands of the 

 mesentery, part of it escapes from the chyle and the blood torrent 

 by unknown ways, and by a process of which we have as yet no 

 conception. 



Foster's view was opposed as long ago as 1901 by Munk and 

 Friedenthal, and in 1907 by D'Errico, who more particularly con- 

 tested the data on which Foster founded his theory. D'Errico 

 calculated the fat content of the blood collected from the portal 

 and jugular veins, and proved that under normal conditions, after 

 a meal rich in fats, the former contained more fat than the latter 

 (0412-0-385 per cent in the portal blood, 0'280-0'212 per cent in the 

 blood of the jugular). This difference was not less in the samples 

 of blood collected after deflecting the mouth of the thoracic duct to 

 the exterior (0412-0'315 per cent of fat in the portal, 0-205-0'208 

 per cent in the jugular). 



If this larger fat content of the portal blood is to be ascribed 

 to the fat absorbed by way of the blood-vessels, we must conclude 

 that absorption by this path is considerable, seeing the large 

 amount of blood that circulates in the portal system during the 

 period of digestion. It must, however, be remembered that the 

 work so far carried out on the fat content of the blood is unreliable 

 because, as Kumagawa and Suto showed (even if they are taken 

 comparatively), the methods employed may lead to grave errors 

 which make any interpretation of the results questionable. It is 

 advisable to regard the subject of the paths of fat absorption as an 

 open question, which has not been decided by Foster's theory. 



While the question whether part of the fat is absorbed by the 

 capillaries of the villi, and passes by the venous paths of the portal 

 system, is thus under discussion, it is indisputable that the sugar 

 introduced with the food, as well as that formed during the 

 digestion of carbohydrates, under conditions of normal alimenta- 

 tion traverses the portal system exclusively, and is carried by it to 

 the liver. Von Mering's accurate researches (1877) show that the 

 percentage sugar content of the chyle collected from the thoracic 

 duct is not perceptibly greater than that of the lymph collected 

 before a meal, and that of the arterial blood, which never exceeds 

 0'06-0'16 per cent. On the other hand, on comparing the percentage 

 amount of sugar from the blood of the portal vein with that of the 

 hepatic veins, it is found that while the difference is negligible 

 in the fasting state, it is increased during digestion in the former 

 (up to 0'4 per cent), and not in the latter. This is no great increment, 



