ihe' dctian of Cold on Animals. 1 1 5 



from my experiments and his, that the total suspension of res- 

 piration is a phenomenon as incontestible as it is curious. 



The circulation is nearly in the same state as the respirat'"' 

 lion. At first there is no pulse in the arteries of the limbs. 

 If we open a vein or an artery, there is either discharged no 

 blood at all, or only a few drops of a blackish blood. If we 

 touch the heart we feel only occasional and uncertain move- 

 ments, ji' 



It is known that animals have the power of producing a cer- 

 tain degree of heat which constitutes their proper temperaturey 

 and that this temperature is nearly 38° Centigrade (100°,4 

 Fahr.) among the Mammalia, and varies very little in them, 

 at least within the limits of the temperature which corresponds 

 to different regions of the globe. 



Among the hybernating Mammalia, the animal heat is also 

 t58° in the waking state, but in the lethargic state falls quite 

 suddenly to 5°, (41° Fahr.) 4°, (39° Fahr.) or even 3°, (37° 

 Fahr.) ; and next to the almost complete extinction of circu- 

 lation and respiration, nothing is more astonishing than th6 

 variations of this animal heat, whose uniformity and regularity 

 appears to be one of the most general laws of the entire class 

 to which these animals belong. 



I come now to the external conditions of lethargy. 



Cold is, at least in our climates, the first of these conditions. 

 While the warm season, indeed, lasts, these animals do not be- 

 come lethargic ; when the cold season begins, then lethargy 

 commences. 



During their lethargy, too, we see them alternately torpid 

 or awake, according as the temperature sinks or rises ; and it 

 is not the rise of temperature only which awakes them. A 

 sudden diminution of temperature, which, if it had found them 

 awake, would have made them torpid, awakes them when it 

 finds them torpid. 



It requires, therefore, a certain and constant degree of co^ld, 

 in order that lethargy be produced and maintained. Next to 

 cold, the most favourable condition is rest, or a freedom from 

 excitation, and, if we consider the faculty of the animal to 

 produce heat, and also, that it is chiefly by motion that it is 

 produced, we shall then see that these two conditions, riz. the 



