58 THE BIOLOGY OF THE FROG chap. 



until it froze. As a film of ice began to form, the frog 

 attempted to keep up at the surface of the water, but it was 

 pushed down below and forced to remain there until frozen 

 in a solid cake of ice. Here it was kept for five hours, 

 while the surrounding temperature ranged from —6° to 

 — 8. 7° C. When the ice was then thawed, the frog was stiff 

 and showed no signs of life, but after an hour and a half it 

 had revived. 



Frogs from warm countries cannot endure so low a tem- 

 perature as those from higher latitudes. But the frogs in 

 northern regions are often killed by cold, especially during 

 severe winters. If they are prevented from burying deep 

 enough in the mud, the frost may overtake them. In some 

 localities the frogs may be largely exterminated during a 

 period of severe cold, so that few are found the next spring. 

 In regions of high latitude, where the ground is permanently 

 frozen below the surface, thawing out only for a few feet 

 during the summer, frogs do not occur, since no means are 

 afforded to escape from being solidly frozen during the 

 winter. 



It was observed by Knauthe that the color of frogs 

 exposed to the cold became very dark, even when they 

 were placed in sunlight, which under normal conditions 

 causes the skin to assume a lighter hue. 



Absorption of Water. — Frogs do not drink like the 

 higher animals, but absorb the water they require through 

 the skin. The meager and shriveled condition of a frog 

 which has been kept some time in dry air contrasts markedly 

 with its plump appearance after it has just been taken from 

 the water. The skin is loosely attached to the body, and 

 a considerable quantity of water may collect in the large 

 subcutaneous lymph spaces. Donaldson found that a group 

 of frogs after being kept in dry air for several hours lost 



