Reactions of ^olosonia to Chemical Stimuli 55 



A control with distilled water preceded each experiment. I 

 found that the distilled water had to be particularly pure or of 

 itself it would afford a definite stimulus. The water finally used 

 was so prepared that the ^Eolosoma were practically indifferent 

 to its presence m the control expermient. There is always a 

 slight rheotactic stimulus to which .-Eolosoma will respond if the 

 flow from the capillary tube is rapid enough, I found, however, 

 that with the tube above mentioned there would be no characteris- 

 tic response under the conditions stated. The chemicals were 

 diluted in distilled water previously tested in the control. 



In order to obviate, as far as possible, differences in reaction 

 occasioned by such changes in the environmental conditions as 

 variations in temperature and light would produce, the major 

 experiments of this paper w"ere performed during the early hours 

 of the day, the culture jars being well protected from the light 

 during the hours preceding, and the room shaded during the course 

 of experiments. The temperature of the cultures and of the 

 materials used was maintained very close to 15° C. Even with 

 these precautions there is considerable variation in the behavior 

 of different individuals preventing a precise quantitative test of 

 stimuli. The qualitative reactions of many individuals, however, 

 show a close correlation with various strengths of stimuli, so that 

 we are able to analyze them with reasonable certainty. 



In the course of these investigations several hundred experi- 

 ments were made with each reagent. Only those, however, that 

 have a direct bearing on our problem will be reported this time. 

 I have therefore arbitrarily assorted the stimuli used into three 

 main groups as shown in Table I. 



TABLE I 



Threshold Normal Strong 



Mineral acids c. N/3000 c. n/iooo c. N/300 



Organic acids c. n/iooo c. n/6oo c. n/ioo 



Hydrates c. N/1500 c. n/Soo c. n/zoo 



Carbonates c. n/i2oo c. N/500 c. N/200 



Chlorides c. m/So c. M/40 c. m/io 



Bromides c. M/50 c. M/30 c. m/io 



FeSO^ c. m/ioooo c. m/8oo c. M/400 



CuSO^ c. m/Soooo c. m/ 20000 c. m/iooo 



ZnSO,, c. m/Soooo c. M/20000 c. M/2000 



