(cameron] LOW TEMPERATURES ON THE FROG 265 



December after some severe weather had already been experienced. 

 By poking a stick a few feet down the narrow opening of a spring, and 

 stirring the surrounding mud, they were at once caused to rise to the 

 surface, and could be secured. Placed on the surface of the ground, 

 at a little distance from the spring, they immediately endeavoured to 

 return to it. 



Several observations have been made in the laboratory in line 

 with those just quoted. During the night of November 9th last, a 

 rather cold night, the window of our frog room was accidentally left 

 open. A flat tank contained Minnesota frogs. These were partially 

 frozen, but not killed, showing that a degree of cold below zero had 

 been reached for a short time. A second tank contained Illinois 

 frogs. This tank consisted of a sloping board, below which was a 

 small runnel filled with water. In the morning the surface of the 

 water in the runnel was frozen over, and beneath it was an almost 

 solid mass of frogs, all living. This observation led to the following 

 experiments. 



A pail was half filled with water, with a little mud at the bottom ; 

 boards were fixed across the pail above the water surface, and half a 

 dozen frogs placed on these. The pail was placed on the roof of the 

 University building during the whole of one night, in which the 

 minimum temperature reached was — 5-5°C. By morning, about 

 an inch of ice had formed on the surface of the water, and over the 

 interior surface of the pail. On breaking the surface of the ice two 

 frogs immediately rose to the surface of the water. On pouring away 

 the water, the remaining frogs were found in a more or less somnolent 

 condition, but perfectly normal, resting on the surface of the mud. 

 Similar experiments in which the water was replaced by thin muds 

 invariably gave fatal results. The frogs made no effort to burrow 

 or dive beneath the mud, even when it was only of the consistency 

 of a thin cream. 



The data given above led me to the following conclusions: 



(1) The death-temperature of R. pipiens from cold is —1-25° + 

 0-15°C. 



(2) There is no climatic adaptation, nor any periodic adaptation 

 due to hibernation, in R. pipiens. 



(3) The cause of death is a specific temperature effect on the co- 

 ordinating centres on the central nervous system. Those controlling 

 lung-respiration may be specially concerned. 



(4) Frogs surviving degrees of cold such as those occurring during 

 a Manitoban winter do so below the surface, near the margins of 



