294 



consciousness may be lost before the hyperpncea develops. For 

 this reason the effects of want of oxygen are particularly insidious. 

 Hence the great danger of entering deoxygenated air which collects in 

 wells, sewers, and unventilated parts of coal-mines men are over- 

 come without warning. Thus a man exploring a cavity in the roof 

 of a mine breathed the deoxj'genated air therein, and fell unconscious 

 off a short ladder. Breathing the purer air on the floor, he quickly 

 recovered, and, jumping up, knocked down the man who held the 

 ladder '' for making him tumble off the ladder !" 



FIG. 159. ANESTHETIZED DOG. 



Injection of 15 c.c. CO blood into peripheral carotid. Upper tracing, respiration; 

 lower tracing, blood -pressure. Time in seconds. 



To effect rescues from deoxygenated air, a suitable breathing 

 apparatus must be worn. The presence of such air can be tested by 

 the use of a cage-bird. Owing to its rapid metabolism, the bird is 

 affected much more rapidly than a man. 



In animals, it has been shown that the respiratory centre responds 

 to changes in the temperature of blood going to the centre. Warming 

 the blood in the carotics causes increased breathing; cooling it tends 

 to diminish breathing. This mechanism probably plays a great 

 part in those animals who regulate their heat loss mainly by respira- 

 tion, and not by the skin. The short, sharp panting of the dog is 

 characteristic. Such respiration is very frequent and shallow. 



The respiratory centre is co-ordinated by impulses which reach it 

 through afferent nervous channels, but considerable divergence of 

 opinion exists as to the amount these play in the regulation of 

 respiration in man. Special acts are undoubtedly due to nervous 



