EFFECT OF RAREFIED AIR. 183 



If there be an abstinence from food, since the introduction of air by 

 respiration goes on without abatement, the body itself must A starvin 

 undergo oxidation, lose weight, and emaciation occur. Its imai dies of 

 tendency to follow the diurnal variations of temperature be- c 

 come more and more strikingly marked as the process of starvation goes 

 on, and finally a rapid and unchecked decline of the heat ensues. Yet 

 even then life may be preserved by the application of sufficient external 

 warmth, and from an extreme condition of attenuation an animal may be 

 rescued by the use of food ; but for such a recovery the external warmth 

 must be continued until there has been time for digestion and absorption 

 to take place. If, however, such an extraneous aid be not duly applied, 

 the temperature of the starving animal goes on diminishing, and he dies 

 of cold. 



The doctrine we are here inculcating, that animal heat is due to oxida- 

 tion in the system, is still further strikingly illustrated by Effectofre . 

 what might be termed starving the respiration. As cold is spiring rarefied 

 felt from want of food, so also it is from want of air. In as- air ' 

 cending high mountains, the effect upon the system has been graphically 

 expressed as " a cold to the marrow of the bones ;" a difficulty of making 

 muscular exertion is experienced ; the strongest man can scarcely take a 

 few steps without resting; the operations of the brain are interfered with ; 

 there is a propensity to sleep. The explanation of all this is very clear. 

 In the accustomed volume of air received at each inspiration, there is a 

 less quantity of oxygen in proportion as the altitude gained is higher. 

 Fires can scarce be made to burn on such mountain-tops ; the air is too 

 thin and rare to support them ; and so those combustions, which should 

 go on at a measured rate in the interior of the body, are greatly re- 

 duced in intensity, and hence the sense of a penetrating cold. Such 

 journeys, moreover, illustrate how completely the action of the muscular 

 system, and also of the brain, is dependent on the introduction of air ; 

 and under the opposite condition of things, where men descend in diving- 

 bells, though surrounded by the chilly influences of the water, they ex- 

 perience no corresponding sensation of cold, because they are breathing a 

 compressed and condensed atmosphere. 



The respiratory apparatus of certain animals permits a reduction in the 

 amount of air introduced under exposure to a due degree of _,, 



. fo Phenomena of 



cold. Such animals are said to hybernate. At the com- hybemating 

 ing on of winter their adipose tissues are engorged with fat. animals - 

 As they pass into their annual sleep, the rate of their respiration falls. 

 The marmot, which in activity will make 140 respirations in a minute, 

 makes now but 3 or 4; the temperature of the body descends, and combus- 

 tion of the store of fat goes on more slowly. Yet it does go on, for, toward 

 spring, the animal has become very lean ; sufficient heat is disengaged to 



