IS THE BODY A MACHINE? 



41 



Absorption of food. The next function of this 

 machine to attract our attention is the absorption 

 of food from the intestine into the blood. The 

 digested food is carried down the alimentary 

 canal in a purely mechanical fashion by muscular 

 action, and when it reaches the intestine it begins 

 to pass through its walls into the blood. In this 

 absorption we find engaged another set of forces, 

 the chief of which appears to be the physical 

 force of osmosis. The force of osmosis has no 

 special connection with life. If a membrane 

 separates two 

 liquids of dif- 

 ferent composi- 

 tion (Fig. 1), a 

 force is exerted 

 on the liquids 

 which causes 

 them to pass 

 through the 

 membrane, each 

 passing through 

 the membrane 

 into the other 

 compartment. 

 The force which drives these liquids through 

 the membrane is considerable, and may some- 

 times be exerted against considerable pres- 

 sure. A simple experiment will illustrate 

 this force. In Fig. 2 is represented a mem- 

 branous bag tightly fastened to a glass tube. 

 The bag is filled with a strong solution of sugar, 

 and is immersed in a vessel containing pure 

 water. Under these conditions some of the sugar 



. To illustrate osmosis. In the vessel 

 A is a solution of sugar; in B, is pure 

 water. The two are separated by the 

 membrane C. The sugar passes through 

 the membrane into B. 



