1G8 On the Genetics of the Ciliate Protozoa 



says that this ciliate will thrive in an infusion of hay in distilled water: 

 but in this medium conjugation cannot occur. Conjugation depends 

 upon the presence of salts. Addition of NaCl, NaBr, or Nal in certain 

 concentrations causes epidemics of conjugation — the efficacy of these 

 salts being in the order given. [That is, the order of efficacy corre- 

 sponds with the order of the halogens in the periodic sy.steni, and is 

 the reverse order of their toxicity.] The effects produced by CaClj and 

 FeoCls were surprising. One part (by weight) of either salt in one 

 million parts of medium was sufficient to inhibit conjugation: but 

 stronger doses (1 : 10,000) caused intense epidemics of conjugation. 

 Addition of iron to the cultures had the most pronounced effect. 



99. Similar but more extensive experiments have been made with 

 Paramecium caudatum by Zweibaum (1912). Stripped of detail, his 

 results are as follows. If a pure line oi Paramecium is richly nourished 

 in hay infusion, it will continue to multiply for an indefinite period 

 without conjugating. If organisms are from time to time tested by 

 placing them in solutions free from hay but containing (1) salts' in 

 strong or (2) salts in medium concentrations or (3) no salts, then still 

 no conjugations result. If however, the richly nourished culture is 

 changed — by removing the hay — into a " hunger culture," and if this 

 is similarly tested after the lapse of a considerable time (5 — 6 weeks), 

 then the trials result thus: in (1) and (3) no conjugations; in (2) 

 abundant conjugations. In other words, the conditions necessary for 

 conjugation in Paramecium, are — plentiful feeding, followed by starva- 

 tion, followed by treatment with salts in medium concentration. Con- 

 jugation can occur at temperatures from 9° C. to 29° C. (optimum 

 20° — 23°). There is an optimum concentration for each salt — which 

 was determined — and successful results can be obtained by substituting 

 glucose for salts. The most effective salt was found to be AICI3, which 

 in concentrations of N/24000 to N/48000 gave "always almost complete 

 epidemics" of conjugation. As they stand, these experiments appear 

 to be conclusive, though it is difficult to reconcile them with other 

 observations. It is to be hoped that the work of Ernnques and Zweibaum 

 will soon be repeated by independent investigators. 



100. Some additional evidence of the influence of external con- 

 ditions in causing conjugation is given by Baitsell (1912). He found 

 that two lines of Stylonychia, derived from the same original organism 

 but kept in different media, behaved differenti}' as regards conjugation. 



' Many different salts were tried, their several effects being described at length and 

 enumerated in 36 tables of experiments. 



