EMORY L. ELLIS AND MAX DELBRUCK 



369 



TABLE I 



Independence of Plaque Count on Plating Method 



Agar concentration 



Plates were prepared in which the agar strength varied, and all spread with 0.1 cc. 

 of the same dilution of a phage preparation. There is no significant difference in the 

 numbers of plaques obtained. 



Agar concentration, per cent. 

 Plaque counts 



Average 



Plaque size, mm . 



Concentration of plating coli 



A broth suspension of bacteria (10' bacteria/cc.) was prepared from a 24 hour agar 

 slant and used at various dilutions, as the plating suspension for a single phage dilution. 

 There are no significant differences in the plaque counts except at the highest dilution of 

 the bacterial suspension, where the count is about 15 per cent lower. 



Temperature of plate incubation 



Twelve plates were spread with 0.1 cc. of the same suspension of phage and bacteria, 

 divided into three groups, and incubated at different temperatures. There were no sig- 

 nificant differences in the plaque counts obtained. 



Temperature, °C . 

 Plaque count. . . . 



Average . 



37 

 352 

 343 

 386 

 422 



376 



24 

 384 

 405 

 403 

 479 



418 



10 



405 

 377 

 400 

 406 



397 



41 



