EFFECT OF LOW TEMPERATURES ON HYDRA. 85 



this manner when the temperature is lowered, it is probable that 

 the loss of cell boundaries is due to some other condition than 

 change of temperature. An entirely similar effect may be pro- 

 duced by keeping the Hydra in water that is not frequently 

 renewed. It is possible that the reversal of vital phenomena 

 described by Greely may have been merely a degeneration brought 

 about by some such unfavorable condition. That he was able to 

 get such Hydra to return to normal after bringing them to the 

 room temperature for several days is no indication that they had 

 been only in a resting condition. If after the temperature was 

 raised the adverse conditions were at the same time removed, 

 then any intact cells which may have escaped degeneration, might 

 quickly regenerate the entire body. The ability of Hydra to re- 

 generate from a few cells is well known. 



Greely' s statement that Hydra when kept at low temperature 

 are resolved into undifferentiated protoplasm is misleading. It 

 is impossible to tell whether he meant merely that the cell 

 boundaries are destroyed, the nuclei remaining intact ; or 

 whether the nuclei too, are broken down so that the body is 

 made up of a simple protoplasmic mass entirely devoid of differ- 

 entiation. The former is probably what he meant. In such 

 event it is possible that after all cell boundaries are destroyed 

 regeneration may take place, but in this series of experiments no 

 evidence of this has been seen. It is most likely that in all his 

 Hydra that passed from his so-called resting stage to a normal 

 condition, there had been only a partial destruction of cells, and 

 that the few remaining cells regenerated the body. 



Though Greely's results were not corroborated by these exper- 

 iments yet his statement that reduction of temperature does bring 

 about a loss of water is substantiated. All the effects due to 

 lowering the temperature I think can be ascribed to this cause. 



In concluding, it may be repeated that reduction of tempera- 

 ture for the length of time mentioned by Greely does not cause 

 Hydra to be resolved into undifferentiated protoplasm. When 

 this does take place it is due to unfavorable conditions and is a 

 degeneration effect and not a temperature effect. 



This work was done in the Zoological Laboratory of the 

 University of Missouri under the direction of Professor Lefevre, 

 to whom I am indebted for many valuable suggestions. 



