I/O CHARLES PACKARD. 



to exactly 2 cc. of w/i28o XH 4 OH solution. The amount of 

 liquid thus added reduces the strength of the ammonia to W/I3OO. 

 The stained Paramcecia when put into this solution give first 

 the avoiding reaction and quickly begin to lose color. The pro- 

 toplasm, and later the gastric vacuoles, turn yellow, and finally 

 become colorless. There is a wide variation in the rate at which 

 the color fades in individual cells, some destaining in three or 

 four minutes while others retain some pink color as long as ten 

 minutes. In order to determine the average time for destaining 

 the usual number of cells (about 40), I used the following method. 

 The cells were observed, during their destaining, under a bin- 

 ocular microscope and each one, as soon as it lost color, \vas re- 

 moved and the time which had elapsed since its first entrance into 

 the ammonia solution recorded. The following measurements, 

 typical of many, indicate the rate of destaining. 



PARAMCECIUM DESTAINED IN n/i28o NHjOH. 

 Minutes Elapsed. No. of Cells Destained. 



i o 



2 o 



3 



4 3 



5 2 



6 4 



7 5 



8 8 



9 6 



10 6 



ii 6 



12 5 



Total 45 Ave. 8.5 min. 



By this method the personal equation is greatly reduced since 

 the observer cannot form any idea of what the average will be 

 until the entire number of cells has been destained. Many tests 

 on the same pure culture of Paramcecium gave very constant 

 results, the average time of destaining in tests carried out on the 

 same day varying less than one half minute. Other lines of 

 Paramcecia showed somewhat different averages but even here 

 they differed from each other by not more than one and one half 

 minutes. 



A study of Paramcecium cells at different phases of their life 

 cycle shows that the permeability varies, being much greater at 

 the time of conjugation than at any other period. Thus among 

 four lines of cells in which conjugation did not occur, the de- 



