268 VETERINARY PHYSIOLOGY 



The pig has sweat glands only on the snout ; the dog 

 only on the muzzle and foot pads. The sheep has few sweat 

 glands and perspires very little. Cattle also perspire little, 

 except on the muzzle. 



Moisture in the air increases the conductivity of the body 

 covering, and consequently the loss of heat by conduction 

 and radiation in a cold atmosphere is greater in proportion 

 to the humidity. On the other hand, moisture in the air 

 hinders the free evaporation of sweat, so that loss of heat 

 by evaporation is less rapid in a hot climate that is moist 

 than in one which is dry. Consequently in climates with 

 temperatures above that of the body the heat is better borne 

 by animals when the air is dry and moving. 



2. Respiratory Passages — Evaporation from the respiratory 

 passages and the heating of the respired air may account for 

 10 to 20 per cent, of the heat lost. In the dog the amount 

 of heat lost in this way may be considerably greater (p. 269). 



3. Urine and Faeces. — A certain amount of heat is lost 

 by raising the ingested food and water to body temperature, 

 at which the urine and fseces are voided. In the dog the 

 amount is small — something less than 2 per cent. Where 

 the food is bulky — as, for example, in ruminants on a heavy 

 root diet — the amount may be as much as 10 per cent, 

 of the total heat lost. 



Heat Production- 



A. Muscle. — As already indicated, muscle is the great heat 

 producer on account of its great bulk and constant activity. 

 Not only may it be demonstrated that (1) the temperature 

 of muscle in action rises, but (2) it has been found that the 

 temperature of blood coming from the muscles is slightly 

 higher than that of blood going to them. (3) Muscular 

 exercise raises the temperature of the bod3^ (4) Drugs 

 which interfere with muscular contraction, such as curare, 

 diminish the temperature, and (6) young animals, before 

 their muscular tissues become active, have a low temperature 

 unless kept in warm surroundings. 



B. Glands. — A certain amount of heat is produced in 



