CHAPTER VI. 



PRODUCTION OF HEAT AND WORK. 



Science teaches that no energy is ever lost. The various forms 

 of energy, whether latent energy or that of electricity, light, heat, 

 or motion, may all be changed one into the other, but no loss of 

 total energy ever occurs. Food consumed by the animal contains 

 latent energy derived from the sun. When complex food nutrients 

 or body tissues are decomposed or broken down in the body into 

 simple compounds, this latent energy is released as active muscular 

 energy or as heat. Thus all the energy used by the animal in main- 

 taining its body temperature, and in the performance both of the 

 internal work of the body and of all external work, is derived in- 

 directly from the energy of the sun. 



I. Heat. 



103. Body temperature. — Cold-blooded animals maintain their 

 bodies at but little above the temperature of the surrounding air or 

 water. With warm-blooded animals the body temperature is usually 

 above that of the surrounding air and quite independent of it. The 

 normal body temperature of the principal farm animals is as fol- 

 lows •} 



Beg. Cent. Deg-. Fahr. 



Horse 36.9-38.2 98.4-100.8 



Ox 38.0-39.3 100.4-102.8 



Sheep 38.4-41.0 lOl.a-105.8 



Pig 38.2-40.7 100.9-105.4 



The wide difference between the normal temperatures of differ- 

 ent animals of the same species is remarkable, and is especially 

 noticeable in the case of the sheep. The temperature of the indi- 

 vidual animal may vary Avithin narrow limits even when the animal 

 is perfectly healthy, but a variation of even 1 degree from normal 

 with any farm animal generally indicates some bodily derangement. 



A high stable temperature for animals increases the amount of 

 water drank, induces sweating, and leads to loss of appetite. Too 

 low a temperature is likewise objectionable, since more food is 

 needed to maintain the heat of the body. Animals that are being 

 wintered over and are merely holding their own, dairy cows, young 



' Smith, Man. Vet. Physiol., p. 339. 



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