476 J. A. DAWSON 



subcultures carried during the work the animals have been iso- 

 lated daily by means of a capillar}^ pipette and a Zeiss binocular, 

 oculars 2 and objectives F55. Separate pipettes have been used 

 for each culture, and these have been carefully sterilized before 

 using by thorough boiling or by heating in a small gas flame. 

 'Stock' cultures of the animals remaining in each line after the 

 daily isolation have been kept on the depression slides for a day 

 or two, so that an animal could be replaced in case of accident. 

 Both line and stock cultures have been kept in moist chambers. 

 For special purposes animals have been allowed to multiply on 

 these stock slides, thus forming small mass cultures. Small 

 Petri dishes (35 cc. capacity) have been used for growing mass 

 cultures, and this method has been found to have several advan- 

 tages, since a Petri dish of this size may be quickly and accu- 

 rately examined with the binocular microscope, while the cover, 

 although fitting loosely, prevents contamination and permits 

 but very slow evaporation. 



The culture medium used was varied as much as possible. The 

 basis of the medium was hay boiled thoroughly in tap-water. 

 To this was added from time to time various decaying vegetable 

 and animal material from laboratory aquaria and ponds. Occa- 

 sionally living snails were finely chopped and added to the medium. 

 In all cases contamination was prevented by thorough boiling — 

 the medium being usually allowed to stand overnight before 

 using. Thus an attempt was made to supply the animals with 

 as varied an environment as possible, since such a Varied envi- 

 ronment' (Woodruff, '08, '11) has been used for the continued 

 maintenance of Paramecium aurelia in pedigreed cultures. 



Attempts to obtain conjugation were made, following in general 

 the methods used by Maupas ('89), Calkins and Cull ('07), 

 Jennings ('10), and Woodruff ('14), and others. Stock cultures 

 were also frequently allowed to multiply on depression slides 

 and in small Petri dishes for the same purpose. In all cases the 

 result was the same, i.e., invariably animals were obtained 

 which made what have been interpreted as abortive attempts to 

 conjugate. 



