ACCLIMATION IN PLANARIA DOROTOCEPHALA. 279 



may even endure 39 if the rise is gradual. This acquired 

 resistance to high temperature persists through four weeks' 

 subsequent exposure to very low temperature. In these two 

 cases an alteration of temperature has evidently produced a 

 persistent effect on the protoplasm. 



All the observations and experiments quoted show that organ- 

 isms have the capacity to acclimate to considerable changes of 

 temperature if these are brought about gradually; but very 

 slight attempts have been made to give an explanation of the 

 physiological significance of the acclimation process. The only 

 noteworthy attempt to analyze the processes involved in acclima- 

 tion is that of Davenport (1897). In regard to the Confervse 

 that live in hot springs, he suggests the following: Since it is 

 known that the coagulation point of at least one protein, egg 

 albumin, rises in proportion as it is dried, and since a number of 

 investigators have held that death from high temperature is 

 due to coagulation of proteins, the increased resistance to ex- 

 treme heat is probably due to loss of water. However, there is 

 some evidence at present that death from high temperature is 

 due rather to accumulation of acids in the tissues (Mayer, '17), 

 which throws some doubt upon Davenport's interpretation of 

 acclimation in hot springs. Further, acclimation to extreme 

 cold is, according to Davenport, a loss of irritability. The 

 process of acclimation, then, consists in the modification of 

 protoplasm through excessive heat or cold in such a way that 



% 



it is not so strongly irritated by these extreme temperatures, 

 and that the coagulation and freezing points are shifted, possibly 

 through loss of water (1897, p. 258). This conception of the 

 process of acclimation is inadequate in that it regards proto- 

 plasm as a static mass, which alters its condition through suc- 

 cessive stages, rather than as a continually changing dynamic 

 system. 



The studies reported in this paper were undertaken to deter- 

 mine the effect of temperature changes upon the metabolism of 

 Planaria dorotocephala and to discover if possible a physiological 

 basis for the phenomenon of acclimation to temperature changes. 



The work was carried on at the University of Chicago, 1915- 

 1918, at the suggestion and under the direction of Prof. C. M. 



