Latent Heat. C3 



Th:;t the evaporation of water from a body docs lower iU 

 temperature may be easily proved by covering the bulb of 

 a thermometer with a close fitting layer of dry muslin, not- 

 ing the temperature. If the muslin be now wet, with 

 water having the temperature noted, and the thermometer 

 rapidly whirled in a drying atmosphere its temperature 

 will quickly fall, owing to the withdrawal of heat from the 

 bulb by the evaporation of water from the muslin. 



45. Regulation of Animal Temperatures. All of our do- 

 mestic animals require the internal temperature of their 

 bodies to be maintained constantly at a point varying only 

 a little from 100 F., and this necessity requires provi- 

 sions both for heating the body and cooling it. The cool- 

 ing of the body is accomplished by the evaporation of per- 

 spiration from the skin, and the amount of perspiration Is 

 under the control of the nervous system. When the tem- 

 perature becomes too high, because of increased action on 

 the part of the animal, or in consequence of a high ex- 

 ternal temperature, the sweat glands are stimulated to 

 greater action and water is poured out upon the evaporat- 

 ing surfaces and the surplus heat is rapidly carried away; 

 each pound evaporated by heat from the animal withdraw- 

 ing about 9G6.6 heat units. 



46. Bad Effects of Cold Kains and Wet Snows on Domestic 

 Animals. When cattle, horses and sheep are left out in the 

 cold rains of our climate the evaporation of the large 

 amount of water which lodges upon the bodies, and espe- 

 cially in the long wool of sheep, creates a great demand 

 upon the animals to evaporate this water. The theoretical 

 fuel value of one pound of beef fat is 16,331 heat units, 

 and that of average milk is 1,148 heat units. A pound of 

 beef fat may therefore evaporate 



and a pound of average cow's milk 



= 1.18 Ibs. of water 



