IS THE BODY A MACHINE? 



In the first place, most of the food when swal- 

 lowed is not soluble, and therefore not capable of 

 osmosis. But the process of digestion, as we have 

 seen, changes the chemical nature of the food. 

 The food, as the result of chemical change, has 

 become soluble, and after being 

 dissolved it is dialyzable i. e., 

 capable of osmosis. After di- 

 gestion, 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 

 dialysis. This can be under- 

 stood from Fig. 3, which repre- 

 sents diagrammatically a cross 

 section through the intestinal 

 wall. Within the intestinal wall, 

 at A, is the food mass in solu- 

 tion. At B are shown little 

 projections of the intestinal 

 wall, called villi, extending into 

 this food and covered by a mem- FlG< 2> _ In the bladder 

 brane. 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, C, and it 

 will be thus seen that the mem- 

 brane, B, separates two liquids, 

 one containing the dissolved food outside the villus, 

 and the other containing blood inside the villus. 

 Here are proper conditions for osmosis, and this 

 process of dialysis will take place whenever the 



- A 

 "B 



A is a sugar solu- 

 tion. In the vessel 

 B is pure water. 

 Sugar passes out 

 and water into the 

 bladder until it 

 rises in the tube 

 to a. 



