[cameron-brownlee] low temperatures ON THE FROG 109 



depends on the most different conditions, as rapidity of freezing, dura- 

 tion of cooling, water content of tissues, and especially on the super- 

 cooling of the body-fluids. He states that the body-size of the cooled 

 insect is of influence in so far as supercooling will be slighter the larger 

 the body, since with this increases the probability of formation of the 

 first ice crystals. 



In the case of the frog Gadow * takes a distinctly conservative view. 

 "Many Amphibia and Reptiles can endure a surprising amount of cold, 

 and during hibernation their temperature may sink to freezing-point. 

 This power of endurance does not apply to all alike; tropical species 

 can stand less than those which live in temperate and cold regions. In 

 spite of many assertions to the contrary, it may safely be asserted that 

 none of our European frogs, toads, and newts survive being frozen hard. 

 They may be cooled down to nearly — PC, and they may be partially 

 frozen into the ice. Circulation of the blood is suspended in such 

 cooled-down frogs; their limbs may become so hard that they break 

 like a piece of wood, but the citadel of life, the heart, must not sink much 

 below freezing-point, and must itself not be frozen, if the animal is to 

 have a chance of recovering. The protoplasm resists a long time, and 

 so long as some of it is left unfrozen the rest will recover. Hibernating 

 frogs are lost if they are reached by prolonged frost during exceptionally 

 severe winters. Every frog will be killed in an artificial pond with a 

 clean concrete bottom, but if there is sufficient mud, with decaying 

 vegetable matter, the creatures survive, simply because they are not 

 absolutely frozen. A severe winter not infrequently kills off all the 

 younger creatures, while the older and more experienced hide them- 

 selves more carefully and live to propagate the race." 



Amongst the most recent experiments are those of Fraser Harris f 

 who has carried out experiments on the pithed and normal frog. His 

 pithed animals did not survive an internal temperature of -2°C., or 

 even a prolonged lowering of the internal temperature to 0°C., while 

 normal frogs frozen in water survived external temperatures of an hour's 

 duration or longer varying from -6° to -11°C. He thinks that the 

 minimal temperature is above -2°. 



In view of the apparent indefiniteness of many of the above state- 

 ments, and their lack of agreement, it seemed to be very desirable to 

 carry out further experiments on the frog. Accordingly, Mr. W. L. 

 Mann, B.A., working in this laboratory two winters ago, subjected 

 frogs to external temperatures varying between— 10° and— 15°C. for 

 short periods. He found that they would survive exposure to a temp- 



* "Amphibia and Reptiles" (The Cambridge Natural History), 1901, p. 68. 

 t "Observations on Frogs at Temperature below Zero," Proc. Physiol. Soc, 

 liii-iv, J. Physiol., 40, 1910. 



