72 GEORGE ALFRED BAITSELL 



In the cultures kept on the. beef medium, the results of the ex- 

 periments show that a condition different from that in the hay cul- 

 ture was present. The cultures died out quite abruptly following 

 the epidemics of conjugation. A study of both the living and the 

 prepared material previous to the occurrence of conjugation en- 

 tirely failed to reveal any pathological conditions present in the 

 animals and indicated that the beef medium furnished a favorable 

 environment for this race of S. pustulata. However, since in both 

 the beef cultures all of the animals reached a physiological state in 

 which conjugation was a necessity, as shown by the death and 

 degeneration of the non-conjugants, it cannot be said that the 

 beef medium was one which was suitable for the indefinite exist- 

 ence of this species without conjugation and therefore, in this 

 sense, the medium was an unfavorable one for this species, since, 

 as shown by Woodruff in his work with Paramaecium aurelia, 

 conjugation is not a necessity for the continued and indefinite 

 existence of protozoan protoplasm when a medium which is 

 entirely suitable is supplied. 



In brief, then, it is believed that the death of the cultures whether 

 kept on a hay or a beef medium was not due to the ending of any 

 definite life cycle but rather to the failure of either of these media 

 to furnish an environment which was exactly suitable for the 

 unlimited reproduction of this race of Stylonychia pustulata. 



VIII. SUMMARY 



1. The objects of these experiments were (1) to observe the effect 

 of the different culture media upon the life history of Stylonychia 

 pustulata, and (2) in case conjugation occurred to study its 

 effect upon the progeny under the influence of the different media. 



2. Two media were used in this work, viz., a 'constant' medium 

 consisting of a 0.025 per cent solution of Liebig's extract of meat 

 and a hay infusion medium. 



3. Three cultures of S. pustulata have been under observation, all 

 of which were started from descendants of an original individual 

 isolated from a laboratory culture September 21, 1910. Cul- 

 ture Sb was started October 2, 1910, and was carried on a beef ex- 



