IS THE BODY A MACHINE ? 



43 



After digestion, therefore, the food is dissolved 



in the liquids in the stomach and intestine, and 



is in proper condition for dialysis. Furthermore, 



the structure of the intestine is such as to pro- 



duce conditions 



adapted for dialy- 



sis. This can be 



understood from 



Fig. 3, which re- 



pre^sents diagram- 



matically a cross 



section through 



the intestinal wall. 



Within the in- 



testinal wall, at 



A, is the food 



mass in solution. 



At B are shown 



little projections 



of the intestinal 



n ,, i . 77 . 



Wall, Called Wilt, 



pvtpTirh'no- into 

 thlS lOOQ and 



covered by a 



membrane. One of these villi is shown more 

 highly magnified in Fig. 4, in which B shows 

 this membrane. Inside of these villi are blood- 

 vessels, (7, and it will be thus seen that the 

 membrane, B, separates two liquids, one contain- 

 ing the dissolved food outside the villus, and the 

 other containing blood inside the villus. Here 

 are proper conditions for osmosis, and this pro- 

 cess of dialysis will take place whenever the in- 

 testinal contents holds more dialyzable material 



- 3. Diagram of the intestinal walls. 

 A, lumen of intestine filled with 

 digested food. B, villi, containing 

 blood-vessels. C, larger blood-vessel, 

 which carries blood with absorbed 

 food away from the intestine. 



