REPRODUCTION OF THE HYPOTRICHOUS INFUSORIA 53 



late various species of Infusoria during periods of depression, it 

 appeared probable that if a solution of the proper strength was 

 used that a beef extract solution would provide a ' constant ' med- 

 ium in which the organisms would thrive. In order to determine 

 the proper strength of solution to be used a series of preliminary 

 experiments was undertaken. As a result it was found that a 

 solution of 0.025 per cent gave the best results. Accordingly a 

 large quantity of the solution was made at the beginning of the 

 work, and placed in test tubes (25-50cc. in each), and these were 

 then plugged with cotton and sterilized. The solutions in the test 

 tubes remained sterile until placed on the slides.^ The hay infusion 

 was ma'de by placing about one gram of hay in 85cc. of tap water 

 and then raising the temperature of the mixture to the boiling point. 

 The infusion thus made was used for three or four days afterwards. 

 No attempt was made to use the same kind of hay at all times or to 

 have the infusion of exactly the same strength. 



The graphs in this paper showing the rate of division were com- 

 puted from the sum of all the divisions in the four lines of a 

 culture for the period stated, e.g., a total of 80 divisions in ten days 

 for the four lines of a culture is 20 divisions in ten days for one line, 

 or exactly two divisions per day. In such a graph we get the av- 

 erage rate of four lines again averaged for ten or thirty-day per- 

 iods as the case may be. By such a method individual peculiari- 

 ties and tendencies are largely eliminated and the curve of the 

 graph shows the average division rate of the animals in the four 

 lines of a culture. 



III. MATERIAL 



A specimen of Stylonychia pustulata was found in a laboratory 

 hay infusion, September 21st, 1910. It was isolated on a regular 

 depression slide and a few drops of hay infusion added. Within 

 the next twenty-four hours two divisions occurred producing four 

 individuals. Each of these was isolated on a separate slide and 

 the four lines of the culture were thus started. After the culture 



' For further information in regard to the use of beef extract as a culture med- 

 ium and the effect of its use in a culture of Paramaecium aurelia, the reader is re- 

 ferred to the paper by Woodruff and Baitsell ('11). 



