A STUDY OF BLOOD MANUFACTURE 



95 



covered with tiny hairlike processes that give a velvety 

 appearance to the surface. Each of these minute elevations 

 is called a vil'lus (Latin vittus = a tuft of hair). The villi are 

 exceedingly numerous in the small intestine of man, the total 

 number being estimated at about four millions. 



Each villus, when highly magnified, is found to be a com- 

 plicated structure. Up through its center pass one or more 

 hollow tubes, the closed ends 

 of which lie just beneath the 

 cells that cover the top of 

 the villus. The tubes of the 

 different villi connect with 

 one another and are of great 

 importance in carrying away 

 from the intestine the fats 

 that are absorbed. If a cat 

 is fed with milk and after 

 three or four hours is killed, 

 one can see that these minute 

 vessels in the villi and the 

 larger tubes in the mesentery 

 into which they empty are 

 filled with a milky stream of 

 the absorbed fat droplets. 

 For this reason the tubes are 

 called lac'teals (Latin lac, 

 foc&'s = milk). 



Around the lacteal of each 

 villus is a network of minute 

 blood vessels. Since they lie close to the single layer of 

 cylindrical cells which cover the outer surface of the villus, 

 the liquefied food is readily absorbed by the blood current. 

 One may therefore compare the absorbent action of the villi 

 with the absorption that takes place through the walls of the 

 root hairs of plants. In structure, however, a villus is very 

 much more complicated than is a root hair. 



FIG. 



35. Diagram of Two Villi, 

 highly magnified. 



b.v = blood vessels. 

 e = cells covering villi. 

 I = lacteals for absorbing fat. 



