THE ABSORPTION AND USE OF FOODS 451 



composed fat is quite soluble in water and is doubtless absorbed 

 readily. 



After the absorbing cells of the intestinal wall have taken up 

 the fatty acid and glycerin, these are recombined within the cells 

 into fat. The presence of fat droplets in the absorbing cells can be 

 demonstrated microscopically. We know that the fat droplets are 

 not absorbed as such, but are formed after their constituents have 

 been separately taken up, because these fat droplets are always 

 observed in the part of the cells away from the intestinal cavity, 

 and never in the part next to it; also because we know that the 

 digestive splitting to acid and glycerin takes place, a meaning- 

 less process if not necessary to absorption. 



The fat finds its way into the circulation by way of the lymph- 

 channels of the villi, the lacteals, and the thoracic duct, entering 

 the blood stream at the point of emptying of the thoracic duct in 

 the large vein of the shoulder. The fats alone, of all the food- 

 stuffs, take this course, and we may suppose the difference to 

 mean that the liver has no special function to carry out in con- 

 nection with the fats as it has for carbohydrates and proteins. 

 Therefore the fats are shunted into another course which carries 

 them into the blood stream without having first to traverse the 

 liver. 



Absorption from the Large Intestine. The chyle that passes 

 through the ileocolic valve into the large intestine contains com- 

 paratively little absorbable food material. The carbohydrates and 

 fats are very completely removed during the passage of the small 

 intestine, and fully ninety per cent of the proteins as well. There 

 remains for the large intestine, then, only the absorption of the 

 protein residue and the absorption of water. It is probable that 

 this latter function, that of absorbing water, is in reality the chief 

 one possessed by the large intestine. There is virtually no ab- 

 sorption of water in the small intestine ; the chyle passes the ileo- 

 colic valve as liquid as it is when leaving the stomach. Thia 

 maintenance of a liquid consistency is, of course, essential to the 

 absorptive processes, and it is only after all absorbable food has 

 been removed that the water, which is also needed by the Body, 

 is taken up. 



The Food Requirement of the Body. If we know how much 

 energy the Body liberates in a day, and how much tissue break- 



