L 



MAINTENANCE OF UNIFORM TEMPERATURE. 435 



As has been said, the exact income of heat is uncertain and 

 variable, because the data upon which the absolute amount can 

 be calculated are not scientifically free from error. According 

 to the most careful estimates an adult weighing 82 kilo, produces 

 2,700,000 units of heat in the twenty-four hours, which are ex- 

 pended in the following way : 



In warming ingesta, 70,157 units of heat. 



In warming tidal air, 140,064 " 



By the evaporation of 656 grm. water 



from the air passages, 397.536 " 



By surface loss 2,092,243 " 



From this it appears that more than three-quarters of our heat 

 are lost by the skin (77.5 per cent.) ; by pulmonary evaporation, 

 14.7 per cent. ; in heating the air breathed, 5.2 per cent. ; in 

 heating ingesta, 2.6 per cent. 



MAINTENANCE OF UNIFORM TEMPERATURE. 



In order that the vital processes of man and the other homceo- 

 thermic animals should go on in a normal manner, it is necessary 

 that their mean temperature remain nearly the same, and we 

 have seen that under ordinary circumstances it varies only about 

 one degree below or above the standard, 37 C., notwithstanding 

 the changes taking place in the temperature around us. Thus 

 we can live in any climate, however cold or warm, and so long as 

 our body temperature remains unaltered we suffer no immediate 

 injury. 



There is a limit, however, to this power of maintaining a uni- 

 form standard temperature. If a mammal be kept for some time 

 in a moist medium, where evaporation cannot take place, at a 

 temperature but little higher than its body, say over 45 C., its 

 temperature soon begins to rise, and it dies with the signs of 

 dyspnoea and convulsions (probably from the nervous centres 

 being affected) when its temperature arrives at 43-45. If 

 placed in water at freezing point an animal loses its heat 

 quickly, and when its body temperature has fallen to about 20 

 C., it dies in a condition resembling somnolence, the circulation 

 and respiration gradually failing. 



