4 ORGANISM AND ENVIRONMENT 



process does not occur to any appreciable extent in 

 the lungs, but in the living tissues of the body gener- 

 ally. Oxygen is taken up by the blood in the lungs, 

 and thence carried by the circulation to every part of 

 the body, the blood yielding its oxygen to the tissues 

 in passing. Similarly the carbon dioxide formed is 

 carried by the blood from the tissues to the lungs, 

 where it is given off to the air breathed. 



But another still more important point, often 

 entirely missed in popular accounts of physiology, has 

 appeared clearly. Within wide limits the oxidation 

 process is practically independent of the abundance in 

 supply of either oxygen or food material to the body. 

 The amount of oxygen in the air breathed, or carried 

 by the blood to the tissues, may be increased greatly 

 without increasing the rate of oxidation; and even 

 after long starvation the consumption of oxygen per 

 unit of body weight remains about the same. The 

 oxidation process is thus evidently very closely regu- 

 lated, in the burning of a fire there is no such regu- 

 lation unless it is artificially brought about. Although 

 increase in the breathing does not cause increase in the 

 rate of oxidation, yet it is evident that increase in 

 breathing and in the rate of circulation accompanies 

 increase in the rate of oxidation, as for instance during 

 muscular exertion. Here again we have regulation 

 coming in, but this time it is regulation of the air 

 supply. 



To account for the regulation the vitalistic theory 

 presupposes the activity of the "vital principle" as a 

 regulating agent which controls the consumption of 



