ANIMAL HEAT 377 



ently, causing the animal any inconvenience. Heat centres 

 have also been located in other portions of the brain, such as the 

 optic thalamus, septum lucidum, etc., and in the spinal cord. 

 By some it is supposed that this extra heat production takes 

 place in the liver, but the balance of opinion inclines to locating 

 it in the muscles. No special set of thermogenic nerves is 

 known to exist, and no special heat-regulating centre has ever 

 been discovered ; but there is good reason for believing that 

 through the nervous system the physiological oxidations in the 

 muscles are reflexly regulated, and heat produced according to 

 requirements. Rubner, who has specially studied the question 

 of animal heat, considers that chemical regulation does not 

 perform the same important function with man as with animals, 

 in consequence of his custom of protecting the surface of the 

 body with clothing. 



Heat Loss. — Unless some conditions exist in the body for the 

 regulation of the temperature, the heat resulting from metabolic 

 activity would continue to rise steadily until it accomplished the 

 destruction of the animal, and that this is no mere figure of 

 speech is evident from the fact that a horse produces sufficient 

 heat during idleness to raise the body to boiling-point in less 

 than two days. In order to maintain the temperature at a 

 constant point, heat production and heat loss must balance. 

 This balance may be struck either by heat production being 

 diminished, or as the result of increased loss of heat. The 

 temperature of the body may rise either in consequence of an 

 actual increase in metabolism, or through difficulties in getting 

 rid of heat. The processes by which, within narrow limits, 

 accurate and prompt adjustment is made is known as heat 

 regulation, or thermotaxis. 



If cold water be poured on a hot body, the body is cooled ; 

 if the surface of a heated body be wetted and the water allowed 

 to evaporate, the body is cooled. If a cold body be placed in 

 contact with one which is hot, heat is lost. And processes some- 

 what similar to these are occurring in the animal body. 



1. By Radiation and Conduction heat is lost to surrounding 

 bodies, provided, of course, that they are at a lower temperature 

 than that of the animal ; if the surrounding medium is hotter 

 than the animal's body, then heat is gained instead of being 

 lost. The natural or artificial covering, be it hair, wool, or 

 clothing, checks the loss by radiation and conduction, as in a 

 dry condition they are bad conductors of heat. When wet, 

 however, they are good conductors, and a considerable amount 

 of heat is lost from sweating or rain. Clothing acts by im- 

 prisoning a larger amount of warm air, the air so confined being 

 a bad conductor. 



