298 ELLINOR HELENE BEHRE. 



time acclimation we would suppose that the lot given a number 

 of hours' start would have begun a second acclimation to the 

 new temperature and would consequently show a new lower 

 rate, producing less CO 2 in the same length of time than the lot 

 which was subjected to change of temperature simultaneously 

 with the beginning of the experiment. As a matter of fact such 

 was the case in a few experiments tried in the way described 

 above, at any rate up to the sixth hour after setting up the experi- 

 ment, and in one case for as long as twenty-four hours at least. 

 With other combinations of temperature in the same direction, 

 the results were consistent with the above. "Medium-high" 

 and "low-high" lots showed slower CO 2 production if given 

 twelve hours' start at the second temperature than if the CO 2 

 production was estimated at once upon change of temperature. 

 Thus even these few tentative experiments give further evidence 

 of an acclimation after only 12-24 hours. 



B. The Biometer Method. 



The findings as to carbon dioxide production by the colori- 

 metric method are further confirmed by the results of experi- 

 ments with worms in the biometer, an apparatus devised by 

 Tashiro (1914) to show very minute amounts of CO 2 by the 

 formation of crystals of barium carbonate on the surface of a 

 drop of the hydrate, and used extensively by him in the study 

 of nerve metabolism and to some extent by him and Child ('136) 

 in experiments on this same form, Planaria dorotocephala. The 

 biometer can be used for comparative estimation of CO 2 pro- 

 duction in Planaria, but the method is so delicate that the best 

 results are obtained with single individuals except when the 

 worms are very small. With larger numbers the barium car- 

 bonate forms too rapidly to permit of accurate comparison, 

 accordingly all the experiments reported here are the results of 

 testing one worm against another. The worms to be tested were 

 decapitated to decrease motor activity, were weighed (in all 

 cases except the first one), then dried for a moment on filter 

 paper and put into the biometer on small cover slips. The 

 method of weighing was the same as that for the colorimetric 

 CO 2 determination (see above, p. 293) ; as often as possible the 



