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 1 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 -.S D 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. 



Mtiller-Erzbach 2 performed the experiment of placing 

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



1 Knauthe, Zoo I. A/iz., Bd. 14. 



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



