834 PHYSIOLOGY 



fat which is absorbed takes this path by way of the lymphatics and 

 the thoracic duct. Ligature of the thoracic duct, if effective, certainly 

 impedes the absorption of fat, but does not abolish it. If the thoracic 

 duct lymph be collected during the absorption of a given quantity of 

 fat from the intestine, not more than 60 per cent, of the fat which has 

 disappeared from the gut can be recovered from the lymph. What 

 happens to the remainder we do not know. Apparently it does not 

 reach the blood in a finely divided condition. If the thoracic duct 

 be ligatured the percentage of fat in the blood rapidly falls to a 

 minimum which remains constant, even during starvation. If now 

 fat be administered, although a considerable proportion of it may 



A B 



'.V 



PIG. 348. Columnar epithelium from small intestine of frog [stained with 



osmic acid to show fat-absorption. 



A, five hours after a meal of olive oil ; B, three hours later. It should 

 be noticed that the fat globules first formed grow in size in the course of 

 digestion, pointing to a gradual deposition of fat on the globules from 

 solution in the protoplasm. (SCHAFER.) 



be absorbed, the percentage of fat in the blood is not raised. If 

 therefore the fat is absorbed directly into the blood it cannot be in 

 the particulate condition, and it must be in such small quantities 

 at a time that it is at once removed from the blood by the tissues 

 through which this fluid flows. It is difficult to imagine that any 

 large proportion of this lost fraction of the fat is absorbed into the 

 blood stream in the form of soaps, since, as Munk has shown, soaps 

 injected into the blood stream act as potent poisons and give rise 

 to a great fall of blood pressure, incoagulability of the blood, and 

 a condition of coma. We must therefore leave out of account for 

 the present the mechanism of absorption of this lost fraction and 

 endeavour to trace the course of the absorption of that part of the 

 fat which makes its way into the lymphatics. 



Microscopic examination of a section of the villus during fat 

 absorption shows that the absorption occurs for the most part through 

 the epithelial cells. These are found closely packed with fat granules 

 (Fig. 348), which, small at the beginning of the process of absorption, 



