The Life-History of Hypotrichous Infusoria. 



619 



was due to the series becoming accustomed to it, and accordingly 

 I started a new series from the control and stimulated both this 

 and the old series at the same time. From the results (see 

 Diagram IX) it was evident that this hypothesis was not sub- 

 stantiated, for the new series showed even a greater drop in the 

 fission-rate than did the old. Instead, it was apparent that the 

 difference in effect of the salt at these later periods must be sought 

 in the change in the general vitality of the culture itself. When 

 the salt was first used the vitality of the series was considerably 



Potassium Chlorid and Sodium Chlorid. 

 KCl NaCl 



Diagram X. 

 Effect of initial and daily stimulation with KCI, "^j and ^?^, and NaCl, P- and ^^j^, on the division- 

 rate of Gastrostyla. Averages are for five-day periods. The eight experiments plotted in this diagram 

 were carried on simultaneously from July 26, to August 15, 1904. Method of plotting is the same as 

 in Diagram VIII. 



greater than toward the end of the experiment, as is indicated by 

 the comparative fission-rates of the two times; and the conclusion 

 seems to be justified that a given stimulus produces different effects 

 at different periods in the life-cycle. This result shows how com- 

 plicated is the whole problem of the effect of stimuli on protoplasm, 

 and the great amount of work that will have to be done before it 

 will be possible to attain any satisfactory knowledge of the part 

 played by a particular salt in the economy of the protozoon. 



