388 



INDEX OF BACTERIAL MUTATION 



to be tested with equal volumes of buffer mixtures of varying Ch"^. 

 Two buffer series were employed, Na lactate-lactic acid and Na 

 acetate-acetic acid. The mixtures were made according to Tables 

 I and II. 



pH 



TABLE I. 

 Na Lactate-Laciic Acid Series. 



Na Lactate n/10 

 Lactic acid n/10 



Lactic acid n 



DistUled water. . 



2.4 



0.5 

 1.6 



pH 



TABLE II. 



Na Acetate-Acetic Acid Series. 



Na Acetate n/IO 

 Acetic acid n/10 

 Acetic acid n . . . 

 Distilled water. . 



Final vol- 

 ume, 2.1 cc. 



Preparation of Suspensions. 



Microbe G sediments rapidly in fluid media. It fails to remain 

 in even suspension when the sediment from a centrifuged culture is 

 taken up in 0.85 per cent NaCl. If, however, such sediments are 

 repeatedly washed in large volumes of distiUed water, very stable 

 suspensions can be obtained. In order to secure perfect compara- 

 bility, Microbe D was treated in a similar manner, although in this 

 case washing with distilled water is unnecessary and it yields stable 

 suspensions in 0.85 per cent NaCl. The technique of preparation of 

 suspensions was as follows. 



5 per cent rabbit serum broth cultures, 24 hours incubation, were 

 centrifuged, the supernatant fluids discarded, and the sediments 

 thoroughly shaken in a volume of distilled water equal to that of the 



