382 



Annals New York Academy of Sciences 



equal halves suggests that the particles may reproduce by longitudinal divi- 

 sion; occasionally they appear to be vacuolated. 



Particle reproduction is synchronized with the division of the protozoan.'^ 

 Further evidence in support of this view is given in figure 1. Animals re- 



SYNCHRONOUS DIVISION 



7-- 



& 5 



CL 



o 



CL 



(3 4 



o 



3-- 



LAMBDA PARTICLES 



Growth Medium 



Resting Medium 



PARAMECIUM 



'Growth Medium 



Resting Medium 







3 4 5 6 

 DAYS 



Figure 1. Growth medium: see table 1. 

 jjhosphate buffer, pH 7.0. 



7 8 9 



Resting medium: isotonic saline, 0.01 M 



moved during the log phase of growth, washed to remove all traces of the 

 original medium and resuspended in a buffered salt solution, "resting medium," 

 failed to multiply. Estimates of the particle population revealed that they, 

 too, did not increase in number. Synchronous division may account for the 

 ability of the particles to keep pace with the host, although it seems likely that 

 this may be only a partial answer to the phenomenon. It has been observed 

 that occasionally one or more of the animals loses all its particles. Clones 



