IS THE BODY A MACHINE 1 ? 



49 



which passed into the blood in the intestine 

 through the influence of the osmotic force, now 

 pass out into the lymph under the influence of 

 the same force. The food is thus brought into 

 the lymph ; and since the lymph lies in actual 

 contact with the living muscle fibres, these fibres 

 are now able to take directly from the lymph 

 the material needed for their use. The power 

 which enables the muscle fibre to take the 

 material it needs, discard- 

 ing the rest, is, again, one 

 of the vital processes which 

 we defer for a moment. 



Respiration. Pursuing 

 the same line of study, we 

 turn for a moment to the 

 relation of the circulatory 

 system to the function of 

 supplying the body with 

 oxygen gas. Oxygen is 

 absolutely needed to carry 

 on the functions of life; 

 for these, like those of 

 the engine, are based upon 

 the oxidation of the fuel. 

 The oxygen is derived 

 from the air in the sim- 

 plest manner. During its 

 circulation the blood is 

 brought for a fraction of a second into practical 

 contact with air. This occurs in the lungs, where 

 there are great numbers of air cells, in the walls 

 of which the blood-vessels are distributed in great 

 profusion. While the blood is in these vessels 



FIG. 6 A bit of muscle with 

 its blood-vessels: a, the 

 muscle fibres ; 6, the 

 minute blood - vessels. 

 The fibres and vessels are 

 bathed in lymph (not 

 shown in the figure), 

 and food material passes 

 through the walls of the 

 blood - vessels into this 

 lymph. 



