1922] 



ROSEN — A BACTERIAL DISEASE OF FOXTAIL 



365 



anions, and the undissociated molecules, the last 2 often being 

 considered as important in the action of organic acids. The sub- 

 ject has received considerable attention and good summaries may- 

 be had in articles by Chambers (II, '20), Foster and Randall (II, 

 '21), Schoenholz and Meyer (II, '21), and Wolf and Shunk (II, 

 '21, pp. 14-20). It is of course clear that there is very little 

 significance in simply adding 0.05 or 0.1 per cent of the acids 

 employed without ascertaining what the active acidity of the 

 media has become. When this acidity is measured it is then pos- 

 sible to compare fairly accurately the effect of one anion with 

 another, at least at the same hydrogen-ion concentration. The 

 writer has endeavored to follow out the old methods by measur- 

 ing out 0.05 and 0.1 per cent of acid, adding this to nutrient 

 broth, and then ascertaining by colorimetric comparisons what 



the hydrogen-ion concentrations are. Comparatively equal 

 amounts of inoculum, 0.1 cc. of suspension from broth cultures 

 48 hours old, were used in the experiments made in Jena glass 

 tubes, having ascertained that these tubes had no appreciable 

 effect on the P H value after sterilization. Twenty cc. of medium 

 were used in each tube. The broth was rendered neutral, P H 7, 

 with sodium hydroxide before sterilization (tests after sterilizing 

 exhibiting the same P H ). The acids were added aseptically after 

 sterilization, the tubes being then incubated for 48 hours before 

 inoculation in order to make certain that contaminations had 

 not occurred. 



TABLE III 



EFFECT OF ACIDS ON GROWTH, MEDIUM NUTRIENT BROTH 



Acid 



Acetic 



Citric 



Hydrochloric 



Lactic 



Malic 



Phosphoric 85% 



Tartaric 



Per cent 



0.05 

 0.1 



0.05 

 0.1 



0.05 

 0.1 



0.05 

 0.1 



0.05 

 0.1 



0.05 

 0.1 



0.05 



0.1 



H-ion con- 

 centration 

 of medium 



4.9 



4.8 



fTo 



4.8 



5.5(f) 

 4.5 



5.0 



4.8 



5.0 

 4.7 



4.9 

 4.3 



4.9 



4.5 



Growth at 



end of 48 



hours 



None 

 None 



Good 

 None 



Very good 

 None 



Good 

 None 



None 

 None 



None 

 None 



Growth 



end of 



days 



at 

 6 



None 

 None 



None 



None 



None 



Fair 

 None 



None 

 None 



None 



None 



Fair (1 

 of 3) 

 None 



out 



Growth at 



end of 9 



days 



None 

 None 



None 



None 



None 



Good 

 None 



None 

 None 



None 



