740 PHYSIOLOGY 



leaving the blood stream in a manner which at present has not been deter- 

 mined. Not all the 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 disap- 

 peared 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 per- 

 centage of fat in the blood rapidly falls to a minimum which remains con- 

 stant, even during starvation. If now fat be administered, although a 

 considerable proportion of it may be absorbed, the percentage of fat in the 



FIG. 350. 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.) 



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 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. 350), which, 

 small at the beginning of the process of absorption, rapidly enlarge till they 

 occupy the greater part of the cell lying between the nucleus and the basilar 

 striated border. Most observers are agreed that no fat globules are to be 

 seen within the border itself. 



