CONDITIONS FOR CONJUGATION 341 



conjugation is probably not essential to the continued life of the 

 race. For, although a nuclear reorganization process occurs 

 only within the cyst, animals can be derived from the cysts 

 which develop with the same renewed vigor as characterizes 

 exconjugants. 



The direct effect of altered environmental conditions in deter- 

 mining conjugation was more strongly emphasized by Enriques 

 ('09), who employed solutions of electrolytes to induce epidemics 

 of conjugation in Cryptochilum nigricans. His studies led him 

 to believe that the process is in no way bound up with an inferred 

 'life-cycle,' and so is not dependent primarily upon internal 

 factors. This same general method was adopted later by 

 Zweibaum ('12) in a careful study of a race of Paramecium 

 caudatum. During the early history of this race conjugation 

 could be induced at times simply by subjecting samples of the 

 flourishing cultures to the action of certain salt solutions. Later 

 it was found necessary to subject the cultures to a preliminary 

 period of partial starvation ('disette') lasting from five to six 

 weeks. Cultures which had been maintained under conditions 

 of steady growth ('cultures continuatives') no longer gave 

 conjugants when treated with salts, except in rare instances, 

 and then in very small numbers. From the 'dormant' cultures, 

 however, conjugants were readily obtained after allowing the 

 organisms to multiply rapidly in a rich culture medium, changed 

 every three or four days during a period of about one week, then 

 subjecting them to the action of the salt solutions in optimal 

 concentrations (as determined previously by experiment). This 

 last process is to be carried out with large numbers of paramecia, 

 in a small culture dish, the organisms being thus limited to a small 

 amount of nutriment. The solutions of salts are then added 

 in the ratio of three parts of salt solution to one part of culture 

 (15 cc: 5 cc). The essential steps in the procedure are seen 

 to be those laid down by Maupas — with an added factor, namely, 

 the treatment with a chemical reagent. In general the chlorides 

 of aluminium, gold and ferric iron, and the salts of sodium, 

 were found to be most effective. Just what role the electrolytes 

 may serve, whether as an additional stimulant or in some other 



