184 COOLING AGENCIES. 



permit the blood slowly to circulate, and so "barely to keep up the func- 

 tions of life. If, however, the stock of material available for combustion 

 is insufficient, the animal dies. 



Although we can not interfere with the rate of respiration, we can 

 Reduction of affect the quantity of air introduced into the system by arti- 

 temperatureby c i a l means, as in the operation of blood-letting ; for though, 



blood-letting ' r 



and in morbid alter Diooa nas been drawn, we may make the normal mini- 

 states. k er of respirations, 17 in a minute, and for each introduce 

 17 cubic inches of air, we have diminished the number of discs, which 

 are the carriers of oxygen ; and, as the experience of physicians in all 

 times has shown, there is no method so effectual in reducing any unusual 

 or febrile temperature. So, in like manner, in Asiatic cholera, the marble 

 coldness which the body presents is attributable to the loss of function 

 of the discs, and the consequent abatement in the quantity of oxygen in- 

 troduced. 



Thus far we have considered the means which the animal mechanism 

 ,, , . ' possesses for raising its own temperature ; it remains to show 

 reducing the how it can also regulate it. For any thing that has thus far 

 are * been said to the contrary, the combustions or oxidations 

 which are continually going forward should establish a constant rise, and 

 there must therefore be some principle of restraining such a rise within 

 due bounds. Considering also the incessant vicissitudes of atmospheric 

 temperature, a constant degree could not be maintained unless the sys- 

 tem possessed the means of depressing as well as elevating its heat. 



That the means of regulating the heat are purely physical, we should 

 Effect of cov- expect for many very obvious reasons. Economy of heat is 

 s'ecte^onduct- a ccomplished by non-conducting material. On this princi- 

 ibiiity. pie, hair, wool, and feathers act by excluding the contact of 



the atmosphere, their low conductibility being brought into operation. 

 In many cases, the manner in which this is done is clearly intentional. 

 Thus the down which is placed on the breast of a water-fowl is to screen 

 off the chilling influence of the water, which is there chiefly felt as the 

 bird swims on the surface. The deposits of fat in whales, their blubber, 

 at once affords a protection through its imperfect conductibility, and is 

 also a store of combustible material for the purpose of respiration. 



The chief cooling agencies in animals are, 1st. Radiation ; 2d. Loss 

 General cool- f neat by warming the expired air ; 3d. Loss by contact of 

 ing agencies, the cold external air ; 4th. Evaporation. The circulation of 

 the blood tends to establish an interior equalization, so that local varia- 

 tions are soon obliterated ; for, through whatever part the blood may flow, 

 it attains the temperature thereof, and, passing in succession from part to 

 part, equalizes the heat of all. 



It would be useless to offer any proof that a living being, like an in- 



