402 ACCOMMODATION TO VARIATIONS IN TEMPERATURE. 



The organism is superior to the engine in the fact that more work in 

 proportion to heat is transformed from the same measure of potential 

 energy. While the best gas-engine is capable of converting 10.82 per 

 cent, of the potential energy of illuminating gas into work and the 

 remainder into heat, the human being is capable of furnishing 35 per 

 cent, of work in making ascents and in doing work of other character 

 only 25.4 per cent. from the chemical transformation in its muscular 

 tissue, Pfluger's experimental dog as much as 48.7 per cent., and an 

 excised bit of frog's muscle even 50 per cent. Work alone, without 

 simultaneous production of heat, can never be transformed from chem- 

 ical potential energy in an inanimate or animate motor. 



ACCOMMODATION TO VARIATIONS IN TEMPERATURE. 



All bodies possessing great heat-conductivity, when brought in contact 

 with the skin, appear much cooler or warmer respectively than poor 

 conductors. The reason for this lies in the fact that they abstract more 

 heat from the body or supply more heat to the body than the latter. 

 Thus the water of a cold bath will always feel colder than the air at 

 the same temperature, because it is a better conductor of heat. In the 

 temperate zone, for example: 



AIR WATER 



At 1 8 C. feels moderately warm, Up to 18 C. appears cold, 



From 25 to 28 C., hot, From 18 to 29 C., cool, 



Above 28 C., extremely hot. From 34 to 35 C., indifferent, 



Above 35.5 C., warm, 

 At 37.5 C. and above, hot. 



So long as the temperature of the body is higher than that of the 

 surrounding medium, the body gives off heat, and in greater amount 

 and more rapidly the better the conductivity of the surrounding medium. 

 As soon, however, as the surrounding temperature becomes higher than 

 that of the body, the latter takes up heat and in greater amount and 

 more rapidly as the medium is a better conductor. Therefore, hot 

 water appears to be of a higher temperature than air at the same tem- 

 perature. 



A human being may remain for eight minutes in a bath at a tempera- 

 ture of 4 5 . 5 C . , but not without risk to life . The hands tolerate immersion 

 in water of a temperature of 5 o . 5 C . , but not of a temperature of5i.65C. 

 At a temperature of 60 C. intense pain is felt in the integument. On 

 the other hand, a human being may tolerate air at a temperature of 

 127 C. for eight minutes. Girls have remained for as long as twenty 

 minutes in air at a temperature of 132 C. Under these circumstances 

 the bodily temperature rises but little, namely, to 38.7 or 38.9 C. 

 This depends upon the fact that the air, acting as a poorer conductor 

 of heat, does not convey so much heat to the body as does water. Fur- 

 ther, and this is the most important fact, the body exposed to hot air 

 is capable of losing heat at its surface through abundant sweating 

 and evaporation, and to this end the increased evaporation of water due 

 to the increased activity of the lungs contributes. The enormous accel- 

 eration of the heart-beat up to above 160 causes constantly renewed 

 volumes of blood to be sent to the skin through its greatly dilated blood- 

 vessels, for the secretion of sweat and evaporation. In the degree in 



