144 RESPIRATION. 



veloped lungs ; these animals are cold to the touch, that is, 

 they have relatively a lower temperature than man, and 

 their positive temperature is but little above that of the 

 external air. Accordingly, zoologists have so arranged the 

 animal kingdom that warm-Hooded animals, including 

 man, the Ijff ds, and the quadrupeds, are classified together ; 

 while the cold-blooded animals, such as the fish, tortoise, 

 frog, and all that have no vertebral column, are classed 

 by themselves. 



47. The temperature of the human body is about 100 

 Fahrenheit, and remains about the same through winter 

 and summer, in the tropics as well as in the frozen regions 

 of the north. It may change temporarily within the range 

 of about twelve degrees; but any considerable, or long-con- 

 tinued elevation or diminution of the bodily heat is certain 

 to result disastrously. 



48. Man is able to adapt himself to all extremes of 

 climate; and, in fact, by means of clothing, shelter, and 

 food, is able to create for himself an artificial climate where- 

 ever he choses to reside. The power to resist cold consists 

 chiefly in preventing the heat which is generated by the 

 vital processes of the body from being lost by radiation. 

 Warm clothing, such as we wear in winter, has, in reality, 

 the same temperature as that which is worn in summer ; 

 but, by reason of being thick and porous, it is a bad con- 

 ductor of heat, and thus prevents the escape of that 

 produced by the body. If woollen fabrics were intrinsically 

 warm, no one would wrap a piece of flannel, or blanket, 

 around a block of ice to prevent its melting in summer. 



49. The faculty of generating heat explains how it is 

 that we are enabled to resist the effects of cold; but how 

 does the body withstand a temperature higher than its 



47. State what is said respecting the temperature of the human body. 



48 1 Ability of man to adapt himself to different climates ? In what does the 

 power to resist cold consist ? What is said about warm clothing ? 



49 Men in an atmosphere above the boiling-point ? In foundries and glass 

 works ? 



