THE EFFECTS OF EXCESS OF CARBON DIOXIDE 303 



ness round the head. The forced breathing of oxygen is unaccom- 

 panied by such feelings. 



Probably a certain tension of C0 2 is required in the body fluids 

 for the proper carrying out of many bodily processes. If this be 

 lessened, such processes are impaired. 



Effects of Excess of Oxygen. Breathing an excess of oxygen under 

 normal conditions does not cause increased oxidation of the body. The 

 body cannot be fanned like a fire into rapid combustion. The nervous 

 system sets the rate of activity of the tissues. When, however, hard 



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;f.\ I fr 



y^i & K.V 



MQl f ^W|f\ 





t f^fVr J!l^;sc :;; 



M !(A. 'AA^gl^^^'j 



Wl L^'\ f&'/& 



h M&y 



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Fiu. 169. -SECTION OF Luxa SHOWING EXUDATION IN BRONCHIAL TUBE AND ALVEOLI 



OF LUNG PRODUCED BY THREE ATMOSPHERES OP OXYGEN. (Bulloch and Hill.) 



muscular work is being performed, an excess of oxygen in the alveolar 

 air enables more work to be done. This is because it prevents the 

 formation of lactic acid in the muscles, and thus lessens the hyperpncea, 

 which renders work inefficient, and maintains the force of the heart. 

 High percentages of 2 e.g., 3 atmospheres act as an irritant 

 to the lungs, induce pneumonia (Fig. 169), lower the metabolism, 

 and cause convulsions. Breathing of pure oxygen for several 

 hours at ordinary atmospheric pressure does not have any harmful 

 effect, but it causes pneumonia if breathed continuously for a day or 



