788 THE POPULAR SCIENCE MONTHLY. 



acid. This combustion raises the temperature of the blood, and the 

 warm liquid, which penetrates everywhere, warms the organism almost 

 in the same way that a house is heated by hot-water pipes. The ac- 

 tivity of respiration and the consumption of oxygen are diminished 

 during sleep, but increased in taking exercise, when a part of the heat 

 produced is transformed into mechanical work ; but, from birth to 

 death, man continues, without ever wholly resting, to draw the breath 

 that keeps up the fire of life. 



Notwithstanding this incessant production of heat, which may be 

 increased or diminished, according to circumstances, by as much as 

 fifty per cent, the temperature of the body continues almost invariable. 

 In health it is always about 98, and seldom varies as much as 2 ; 

 and yet we know that in some regions of the globe the monthly 

 means of external temperature present variations rising to more than 

 115, with much wider divergences in extreme cases. In parts of 

 Siberia the extremes range from 70 or 80 below zero to 80 or 90 

 above ; temperatures of from 120 to 130 have been remarked in hot 

 regions in Australia and Asia ; and men have been able to support 

 much higher temperatures than these for a short time Blagden 

 259 for seven minutes, and a certain Martinez, by wrapping his head 

 in cloth, 338 for a quarter of an hour. Under such excessive heats, 

 the temperature of the blood may rise a few degrees higher than its 

 ordinary extreme ; but such cases are abnormal. 



Constancy of bodily temperature is an indispensable condition of 

 health to warm-blooded animals. By what means does Nature sup- 

 ply deficiencies of internal heat and eliminate an injurious excess, 

 and, in either case, restore the organs to the temperature which is most 

 agreeable to the regular performance of the functions of life? The 

 means are various. When food becomes insufficient, calorification is 

 effected at the expense of the tissues of the animal, and it grows 

 lean. When heat is produced in excess, the organism rids itself of it 

 speedily by several outlets. The body may be cooled by radiation, 

 by evaporation, or by conduction or convection. It is estimated that 

 radiation generally carries off half, and the other two ways a quarter 

 each, of the surplus heat. These ratios are, however, far from being 

 constant ; they vary with external circumstances. Evaporation is the 

 valve that regulates the loss of heat, by completing, at a given point, 

 the action of conduction and radiation. 



The intensity of radiation, by which heat is dissipated from the 

 body around, is proportional to the difference between the normal 

 temperature of the body and that of the surrounding medium, and 

 increases in the neighborhood of a very cold body. We may in this 

 way explain the chilly sensation we feel and which persists in a room 

 that has not been used for a long time, after the fire has been kindled, 

 and even after the air in the room has become quite warm ; while, 

 after the room has been well warmed up, we may feel quite comfort- 



