ACCLIMATION IN PLANARIA DOROTOCEPHALA. 287 



and are tested. For example, in No. I, the experimental worms 

 were kept three days in low temperature ; then their susceptibility 

 to KNC was tested at high temperature; and it was found that 

 in general they died an hour earlier than the controls which had 

 been living and were tested at high. 



These eleven experiments give results similar to those indicated 

 in the preceding graphs; worms tested immediately after they 

 have been put into a higher temperature than that at which they 

 have been living for a shorter or longer time show greater suscep- 

 tibility to cyanide than those which have been living indefinitely 

 at the higher temperature; those tested immediately after they 

 have been put into a lower temperature than that at which they 

 have been living for a shorter or longer time show a lower suscep- 

 tibility to cyanide than those which have been living indefinitely 

 at the lower temperature. In other words, worms brought into 

 a given temperature after a period of exposure to another tem- 

 perature show a difference in metabolic rate as indicated by 

 susceptibility from the animals which have been living indefinitely 

 at the given temperature. 



B. Short Time Acclimation. 



In the preceding section it has been shown that susceptibility 

 to cyanide is modified by exposure to given temperatures for as 

 short a time as three days. Further experiments were under- 

 taken to determine whether or not such modification can be 

 brought about in a still shorter period of time. 



A few experiments were performed with worms which had lived 

 but 36 hours at a particular temperature. These experiments 

 presented nothing new and were therefore soon discontinued. 

 Fig. 3 illustrates the general results of such experiments as were 

 made. It is the record of 10 worms acclimated to 30 for 36 

 hours (curve a-c), compared in KNC at 16 with worms which 

 had been living at 16 (curve a-b). This graph shows that worms 

 living at high temperature for 36 hours are less susceptible to 

 cyanide in low temperature than worms which have been living 

 at that low temperature; that is, that even so short a period as 

 36 hours is long enough to modify the metabolic rate, though 

 not to so marked a degree as longer time intervals. 



