382 PHILOSOPHY OF ZOOLOGY. 
in many instances, parts of animals which had been frozen 
recovered their functions when thawed, yet in no case did 
_ recovery take place when the whole body had been frozen. 
The efforts of the body to generate heat, when thus ex- 
posed to a cold medium, rapidly exhaust the vital energy, 
and when these cease to be made, or have become too weak 
to accomplish their object, the temperature sinks, and freez- 
ing and death simultaneously take place. 
Dr Hunrer found, that even eggs possessed this power 
of generating heat, when exposed toa cooling medium. An 
egg which had been frozen and thawed, was put into a cold 
mixture along with one newly laid. The fresh one was seven 
minutes and a half longer im freezimg than the other. In ano- 
ther experiment, a fresh laid egg, and one which had been 
frozen and thawed, were put into a cold mixture at 15° ; 
the thawed one soon came to 32°, and began to swell and 
congeal ; the fresh one sunk to 293°, and in twenty-five 
minutes after the dead one, it rose to 2°, and began to 
swell and freeze *. During these twenty-five minutes, it 
must have generated a very great deal of heat, before it 
yielded to the influence of the cold mixture. 
In what manner, it may now be asked, are these extraor- 
dinary capabilities of varying the temperature, maintained 
and regulated in the animal frame ? 
The influence of the cutaneous system in modifying the 
heat of the body, is very considerable. The skin is, a bad 
conductor of caloric, and consequently protects the inter- 
nal organs from the sudden influence of heat or cold. In 
the performance of this function, the cuticle and its appen- 
dices act a conspicuous part. In the warm-blooded ani- 
mals, we observe their bodies covered with hair or feathers, 
and these in the greatest abundance, where the parts stand 
most in need of protection. Among these animals, the 

“ Phil. Trans. 1778, p. 29, 30. 
