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 
