18 THE ROYAL SOCIETY OF CANADA 



below the freezing point of their body-fluids for one hour without 

 being killed, the numerous observations of other investigators on 

 various insects quoted in earlier papers seem to indicate a possibility 

 that even in the case of the frog a very slow lowering of temperature 

 might produce a supercooling which would prevent death. A single 

 experiment was made to test this point. 



Twelve frogs were immersed in water in a large pail on February 2nd, 1921. 

 This was immersed in a much larger tank, also containing water, and placed in the 

 open. The frogs were thus exposed to slow cooling in the centre of a water mass of 

 about 20 inch side, exposed to an external temperature varying between —10° and 

 — 20°C. Immediately the frogs came in contact with the cold air at the water 

 surface they dived to the bottom of the pail, and as the temperature fell they gradu- 

 ally became completely motionless. A glass tube was immersed with the lower end 

 at the stratum of water in which the frogs lay, and a thermometer lowered into it 

 from time to time gave the approximate temperature to which they were submitted. 

 In 24 hours this fell to —1.5°, remained at about that point or slightly higher for 

 the next 30 hours and then sank to —3°. It remained between —2 and —4 for 

 three days, when it rose to freezing point, the external temperature having risen 

 to +2.5°. The pail was removed to room temperature, and the frogs allowed to 

 thaw gradually. They were all dead. Muscle failed to respond to electrical 

 stimulus. 



This experiment is not conclusive. It indicates, however, that 

 even if marked supercooling can take place — a very doubtful hypo- 

 thesis^ — ^any cooling slow enough to produce no fatal result must take 

 place at a considerable depth below earth or water, and thus is not in 

 disagreement with the assumption that frogs pass the winter in such 

 cold climates as Manitoba below water. 



The following observations by other investigators, not previously 

 mentioned in this series of papers, have a bearing on the problems 

 under consideration. 



Knauthe (1891) found that frogs could survive a 12 hours' 

 exposure to temperatures of — 1° to —5°, in which their body tempera- 

 tures sank from —0.2° to — 0.8°C. Few recovered when the body- 

 temperature reached —0.9°. 



Eleanor S. Brooks (1918) has made a series of observations 

 indicating that frogs can survive immersion in water for 75 minutes 

 at all temperatures between 0° and 35° without injurious effects. 



Professor A. Willey (1918) states: "In the summer time frogs 

 can survive a moderate duration of immersion; in winter they volun- 

 tarily submerge themselves and hibernate under water, becoming 

 inactive. A male frog {Rana virescens) was placed in a shallow dish 

 covered with a perforated zinc plate weighted down securely, the 

 whole being completely submerged in an aquarium on December 31st 



