MAK0AL OF CATTLE- JFEEBIHO. 23 1 



Conduction and Radiation from tlie Skin. — Tliis is 

 one of the principal sources of loss of heat by the body, and 

 also the one which is most susceptible to regulation. Henne- 

 berg,* in his respiration experiments on sheep, already 

 cited, estimates that the total amount of heat produced by 

 the animals experimented on was applied as follows : 



To warming the ingesta 4.0 per cent. 



** **• '* inspixed air 4.^ *' 



* * evaporation of water 26.7 " 



^' supply loss by radiation, etc 05.1 *' 



Experiments on man have given very similar results. 



Plainly, the greater the amount of blood passing through 

 the \ essels of the skin, the more heat will be lost, while, 

 on the other hand, a diminution in the current of blood 

 will check the loss of heat. 



IsTow when the skin is exposed to cold, as, for example, 

 to cold air or to the water of a cold bath, the capillaries of 

 the skin are contracted and the blood-vessels of the vis- 

 cera expanded, thus diverting a portion of the blood from 

 the former to the latter and sometimes causing a rise of 

 temperature in the interior of the body. 



Conversely, under the influence of warmth the capillaries 

 of the skin dilate, admitting more blood, and thus eiBfecting 

 a cooling of the latter. To this is to be added the loss of 

 heat by the evaporation of the perspiration, to which atten- 

 tion will be called on subsequent pages. 



In this manner the loss of heat from the surface of the 

 body is regulated in accordance with the external tem- 

 perature, but there are numerous experiments wdiich show 

 that under such circumstances the produetmi of heat 

 also varies, though we have but little knowledge of the 



* Heue Beitrj^e, etc., 1871, p S27. 



