ACCLIMATION IN PLANARIA DOROTOCEPHALA. 2Q5 



to twenty-four hours after decapitation there is almost complete 

 inactivity in all the different temperatures, and the time between 

 decapitation and experiment was always within these limits. 

 That the animals do not excrete any appreciable amount of any 

 non-volatile acid was shown by the fact that after the color 

 change was produced by the worms the indicator solution could 

 be brought back to the original color by shaking thoroughly with 

 air; and there is no good reason to believe that they excrete any 

 other volatile acid than CO 2 . 



The results obtained by this method are briefly as follows: 

 first, worms brought from a low to a higher temperature show in 

 the higher temperature a higher rate of metabolism as indicated 

 by CO 2 production than that of the worms which have lived at 

 the higher temperature ; second, so far as the evidence goes worms 

 brought from a higher to a lower temperature show a lower rate 

 of CO 2 production than those which have been living at the lower 

 temperature. Table IV. gives the results of 24 experiments in 

 which worms acclimated to low and tested at medium tempera- 

 ture (experimental) are compared with worms which have been 

 living indefinitely and are tested at medium temperature (con- 

 trol). 



As can be seen at a glance the majority of these experiments 

 gave very consistent results, extensive and beautiful evidence 

 that worms acclimated to cold showed higher CO 2 production in 

 medium temperature than worms acclimated to and tested at 

 the medium temperature. Of the twenty-four experiments per- 

 formed, seventeen, that is, 83 per cent., gave this result. The 

 possibilities of experimental error here are: Observations over 

 too short a period of time ; too great a discrepancy in the weights 

 of the two lots of worms; the inaccuracy of judgment due to 

 the use of an unsatisfactory indicator. Of the four exceptions 

 to the majority rule in this table, three, nos. 2, 6 and 21, can all 

 be explained on one or the other of these grounds. No. 5 is 

 explicable only as the result of individual variations in rate of 

 CO 2 production, which are sometimes considerable. 



The other two possible "raised-temperature" series medium- 

 high and low-high gave results in the main like that of Table 

 IV.; worms acclimated to a lower temperature than the one at 



