346 HOYT S. HOPKINS 



part of distilled water. These were allowed to stand for several 

 weeks as 'dormant cultures/ with very little nutriment, at the 

 end of which time hay infusion was added. Such cultures to 

 which hay infusion has been added to induce rapid multiplication 

 will be referred to as 'renewed cultures.' After about the fifth 

 day portions of these cultures were treated with salt solutions 

 in small Stender dishes. 



The renewed cultures of P. aurelia often yielded about as 

 many conjugating pairs as the smaller (experimental) cultures 

 derived from them, and treated with salt solutions. It was found 

 further that certain inorganic salts added to the renewed cultures 

 directly, i.e., immediately following the period of dormancy, 

 at the time of renewal, made these organisms (P. aurelia) more 

 susceptible to conjugation after the preliminary period of multi- 

 plication of about five days. Small watch-glass cultures derived 

 from these usually yielded conjugants earlier — after the third 

 or fourth day following renewal of the main culture — but the 

 renewed cultures themselves often yielded just as many pairs 

 after the fifth day, showing that the sudden change brought 

 about through such 'isolation experiments' is not an essential 

 condition for the appearance of conjugation. 



In general it may be said that large cultures of Paramecium, 

 of either species, give fewer conjugating pairs than small cultures 

 of the same race when treated in a similar manner. This condi- 

 tion may perhaps be attributed to the greater accumulation 

 of organic matter (excretion products) in large cultures than in 

 small and in part to the more uniform conditions. 



The experimental procedure will be described in greater detail 

 in connection with the experiments themselves. The culture 

 medium used throughout during the course of this work on 

 Paramecium consisted of hay infusion. 'Tap-water' was used 

 to maintain the stock cultures, which were contained in battery 

 jars and kept at room temperature. Cultures intended for use 

 in future experiments were diluted with distilled water just before 

 being subjected to their period of dormancy, and at the end of 

 this period were renewed with an equal part of hay infusion in 

 distilled water, changed subsequently every three to four days. 



