II HABITS AND NATURAL HISTORY OF THE FROG 57 



cover, although they may at first appear as if dead. The 

 cause of death is probably the coagulation of certain albumi- 

 nous compounds in the blood and tissues. 



Frogs have little power of withstanding extreme cold, for 

 the reason that they have no means of keeping their tem- 

 perature very much above that of their surroundings, and 

 their tissues consequently become frozen. On the other 

 hand, they can withstand a reduction of their own bodily 

 temperature far below the point which would be quickly 

 fatal to any warm-blooded animal. They may be even 

 frozen in ice for a short time and subsequently recover 

 if gradually thawed out. Knauthe ^ found that frogs which 

 were exposed to a temperature of from —1° to —5" C. for 

 twelve hours became stiff and the limbs lost their pliability. 

 The animals were then laid in wet moss and kept for several 

 days slightly above the freezing point (.2° to .5° C), under 

 which condition they gradually came back to activity. The 

 bodily temperature of the frogs in the experiment sank to 

 from —.2° to —.8° C. Examination of the web of the 

 foot and the tongue revealed no signs of circulation of the 

 blood, which seemed to be no longer in a fluid state. 



The bodies of some specimens were cut open and the 

 heart was found to have entirely stopped beating. Accord- 

 ing to Knauthe, — and other observers have obtained the 

 same results, — if the tissues of the frog become entirely 

 frozen, the animal will not recover. The bodily temperature 

 cannot be lowered much below —1° C. without producing 

 a fatal result. The animal may, perhaps, be frozen and then 

 recover, but it cannot be frozen hard. 



Miiller-Erzbach ^ performed the experiment of placing 

 the frog in a dish of water, which was gradually cooled off 



1 Knautiie, 7.ool. Atiz., Bd. 14. 



2 Miiller-Erzbach, Zool. Anz., Bd. 14. 



