120 THE ROYAL SOCIETY OF CANADA 



Experiment 15. Jan. 22nd. A frog was exposed to an external temperature 

 of between —5° and — 9°C. for four hours. The internal temperature remained 

 between —5° and — 7°C. for two hours. There was no recovery, and all muscular 

 tissues were killed. 



Experiment 16. Feb. 5th. A frog was exposed to an external temperature of 

 between —10° and — 5°C. for 6 hours. The internal temperature sank to —0-5°, 

 remained constant at that temperature for two hours, and then fell slowly to — 6 • 5°C. 

 There was no recovery. 



Experiment 14. (q.v.) shows that frogs do not survive a temperature of 

 -2-75°C. 



Experiment 17. Feb. 4th. A frog was kept in an external temperature varying 

 between — 8° and — 12°C. for three hours. The internal temperature varied between 

 — 1° and — 2°C. for If hours. The frog was then removed from the cooling chamber 

 and slowly regained room temperature. It did not recover co-ordinate movement. 

 After two hours external stimulation gave the usual response throughout. After 

 4^ hours the thorax was opened, and the heart found to be beating strongly. Stim- 

 ulation of the sciatic nerve evoked no response (Cp. experiment 1). 



Experiment 18. Mar. 18th. A frog was exposed to an external temperature 

 varying between — 12° and — 13°C. for 1^ hours. The internal temperature varied 

 between —0-8° and — 1-3°C. for one hour. The animal was allowed to warm up 

 slowlj^ and completely recovered. 



E. Exacter experiments on the normal intact frog. 



In order to carry out very exact experiments, it is necessary to eliminate as 

 far as possible a temperature gradient in the animal, and therefore it is essential 

 to obtain some self-regulating apparatus in which a temperature constant to at least 

 0-2° and varj-ing at wUl between —1° and — 4°C. can be maintained for several 

 days if necessary. We have made repeated attempts to devise such an apparatus 

 using a modified form of the ordinary thermostat, with supplies of warm and 

 cold air, but we have not yet succeeded in devising an instrument sufficiently 

 delicate. 



A constant low temperature apparatus has been constructed by Cotton* buc 

 this is not only very large, but is also very costly to construct. 



We have had to content ourselves with an arrangement regulated by hand 

 The frog was enclosed in a thin copper cylinder, and protected from the metal by a 

 paper sheet. The cylinder was enclosed in a glass bottle, just fitting through the 

 constricted neck of the bottle, so that around it was considerable air-space. The 

 bottle was immersed to the lip in a jar containing strong brine, and this again in a 

 freezing mixture. The brine was usually kept at a temperature between —8° and 

 12°C., under which condition the temperature of the air adjacent to the copper 

 cylinder varied Ijetween —2° and — 4°C. Slight variations in this could be produced 

 by adding warm brine. Round the bottle was tightly coiled a copper spiral tube, 

 through which warm air could be aspirated at will, and this also produced a very 

 rapid, though slight effect on the interior temperature of the bottle. 



The temperatures of the frog's interior and exterior were measured by iron- 

 constantan thermo-needles, placed, the one in the frog's stomach (with a glass 

 protecting sheath) the other in contact with the skin. The thermo-currents were 



*J. Econ. Entomol., 3, 140, 1910. 



