44 



THE STORY OF LIFE'S MECHANISM. 



than the blood. Under these conditions, which 

 will always occur after food has been digested 

 by the digestive juices, the food will begin to 

 pass through this membranous wall of the in- 

 testine into the blood under the influence of the 



physical force 

 of osmosis. 

 Thus the prim- 

 ary factor in 

 food absorption 

 is a physical 

 one. 



We must 

 notice, how- 

 ever, that the 

 physical force 

 of osmosis is 

 not the only 

 factor con- 

 cerned in ab- 

 sorption. In 

 the first place, 

 it is found that 

 the food dur- 

 ing its passage 



FIG. 4. Diagram of a single villus enlarged. , , \i 



B represents the membranous surface UllOUgU Llie 



covering the villus ; C, the blood vessels festinal Wall Or 

 within the villus. - ~ . . , ' 



FIG. 5. An enlarged figure of four cells of Shortly aiter- 



the membrane B in Fig. 4. The free sur- wnr J Q nnrlpr 



face is at a; / shows fat droplets in pro- WdlUb, Uliuei 



cess of passage through the cells. goes a further 



change, so that 



by the time it has fairly reached the blood it 

 has again changed its chemical nature. These 

 changes are, however, of a chemical nature, and, 



FIG. 5. 



FIG. 4. 



