The Life-History of Hypotrichous Infusoria. 615 



The results obtained with beef-extract as a stimulant for worn- 

 out Protozoa led me to test the effect of some of the more common 

 salts on the fission-rate, since, as Liebig claimed, the stimulating 

 property of beef-tea is probably due to the extractives and not 

 to the small amount of proteid which it contains. For this work 

 potassium phosphate (monobasic and dibasic), potassium chlorid, 

 potassium bromid, and potassium sulphate; sodium chlorid, and 

 magnesium sulphate were chosen. The series of experiments with 

 these seven salts extended from the early partof July to the middle 

 of September, 1904. Thework with each salt extended over twenty 

 days. The salts were made up into equivalent normal solutions^ 

 and these were then diluted as indicated in the descriptions of 

 the individual experiments. In each case tw^o solutions of dif- 

 ferent strength were employed, and each of these was applied 

 both as an initial and as a daily stimulus. The culture of Gas- 

 trostyla steinii was used in this work {cf. Diagrams V and VI). 



I. Experiments with Potassium Phosphate {Monobasic and 



Dibasic). 



On July 6, 1904, eight cultures (each consisting of four lines) 

 of Gastrostyla were started w^ith individuals isolated from my 

 culture A of this species, which had been under observation since 

 May 28. Four of these cultures w^ere used for experiments with 

 the monobasic and four with the dibasic salt. Of these cultures, 

 half were used for initial stimulation and half for daily stimulation; 

 and of each half, one was used for y^ solutions and the other for 

 yyW solutions of the salt in question. 



The method of applying the salt was, briefly, as follows: In 

 the case of initial stimulation, one individual was placed on a slide 

 with as little of the culture-medium as possible. To this was 

 added the solution of the salt to be tested and this was removed 

 again immediately and fresh salt solution put on. Each trans- 

 ference was performed with a pipet used only for this purpose. 

 The length of each initial stimulus was thirty minutes and when 

 this had expired the specimen was transferred back to the grass- 

 infusion. In the case of daily stimulation the method of procedure 



^The solutions were made according to the definition of "normal'' solutions as given in Sutton's 

 Volumetric Analysis, Eighth edition, 1900. 



