HEAT AND LIFE. 149 
sations of life in all beings become more rapid; but this 
stimulus is only fleeting, and soon, when it reaches a cer- 
tain degree, this heat gives place to the cold of death. 
Bernard carefully examined animals dying under these con- 
ditions, and the first phenomenon that struck him was the 
rapidity with which corpse-like rigidity came on. The 
heart grew suddenly insensible to any stimulus; effused 
spots appeared at several points on the skin. The heat 
fixed in coagulation the soft matter that composes the mus- 
cular fibres. These had the look of being struck with light- 
ning. On the other hand, the arterial blood of the animal 
grew black, ill-supplied with oxygen, overloaded with car- 
bonic acid, and assumed the look of venous blood. Yet in 
this state the blood has not lost its physiological properties, 
and under the influence of a new supply of oxygen can re- 
gain its normal state, and grow ruddy again. The heat, 
provided the degree be not too elevated, only promotes 
activity in sanguine combustion, without changing the blood. 
Nor does the nervous system either appear to suffer much. 
The element most deeply affected is muscle ; heat 7s a pot- 
son of the muscular system, like sulpho-cyanuret of potas- 
sium, and the upas-antiar. It is the loss of the vital proper- 
ties of this system which, by bringing about rigidity of the 
muscles, then the stoppage of circulation, and consequently 
of respiration, is a necessary cause of death. This destruc- 
tion of the contractile muscular fibre occurs toward 37° or 
39° in cold-blooded animals, toward 43° or 44° in mammals, 
toward 46° or 48° in birds, that is, speaking generally, at 
a temperature five or six degrees higher than the natural 
temperature of the animal. Bernard calls attention to the 
fact that in no case is it allowable to suppose that life op- 
poses a kind of resistance to the excessive heating; on the 
contrary, vital movement tends to quicken it,.and that may 
be readily understood. The internal heat produced by the 
animal unites with the acquired heat, and the renewal of 
