430 M. H. JACOBS 



is perhaps possible also that the absence of appreciable amounts 

 of 'buffer substances' may have been another of the factors con- 

 cerned, since there is some evidence of the production of abnormal 

 amounts of acids at elevated temperatures. At any rate, it was 

 found that apparently the most reliable results could be ob- 

 tained when normal culture fluid was used, although very similar 

 results were also secured in some cases with pond-water when 

 the animals had been kept in it for at least twelve hours previous 

 to the experiments. 



The apparatus employed was of a simple nature. It consisted 

 of a 2-liter beaker, used as a water-bath, supported on a stand 

 and heated from below by an alcohol lamp whose position could 

 be altered to furnish much or little heat as desired. In the 

 beaker were placed a number of test-tubes containing enough 

 water or culture fluid to make them float upright. The trans- 

 parency of the whole apparatus was found to be of advantage, 

 not only in favoring such, manipulations of the material as were 

 necessary, but in making it possible to observe the visible effects 

 of the high temperature on, for example, the movements of the 

 animals. 



When a sudden exposure was desired, the water in the water- 

 bath and in the test-tubes was first allowed to assume the proper 

 temperature, and then a considerable number of the organisms 

 were taken in the smallest possible quantity of water in a capillary 

 pipette (this being very easy in the case of both of the animals 

 used on account of their habit of collecting in a dense ring around 

 the edges of the culture jar) and suddenly forced into one of the 

 test-tubes in such a way as to insure thorough mixing. The 

 quantity of water used was so small as practically not to affect 

 the temperature of the water in the test-tube, calculation showing 

 that the momentary lowering of its temperature, which was not 

 even indicated on an ordinary mercurial thermometer, could not 

 have been, as a rule, more than 0.1 °C. After this sudden intro- 

 duction to the temperature of the experiment the organisms were 

 either all allowed to remain in the test-tube for the required 

 length of time and then suddenly poured into sufficient cool 

 water to bring them back immediately to within their normal 



