350 



[Vol. 9 



GARDEN 



acidity or alkalinity but its superiority over Fuller's method soon 

 became evident. Nutrient agar which gave a yellow or yellowish 

 green color with brom thymol blue (those covering the reaction 

 range of Pn 6.0-Pn 6.8 and therefore acid) when used as a sub- 

 strate always showed colonies producing a colorless region fol- 

 lowed by a dense precipitate, while agar which gave a blue color 

 with brom thymol blue (those having a reaction of Ph 7 or over, 

 hence neutral or alkaline) when used as the substrate showed col- 

 onies which never produced any precipitate. 



The presence or absence of a colorless zone plus precipitate 

 could then be controlled at will, depending on whether the me- 

 dium was rendered slightly acid or slightly alkaline as measured 

 by the hydrogen-ion concentration. Here then is a method of 

 measuring acidity and alkalinity which is just as simple as Ful- 

 ler's and much more accurate. By using this method the writer 

 was able to obtain a character which immediately distinguished 

 this bacterium from other similar-appearing organisms; in other 



of 



II 



hat other white 



might develop on a given plate, this organism could 



readily be recognized. (This power of prod 

 and a white Drecinitate was an excellent 



for differential 

 bring out this 



character as a quick 

 why Fuller's scale did 



A medium which 



-flO on Fuller's scale, and thus supposedly acid, is often 

 be shown later, reallv neutral or slisrhtlv alkaline. Besu 



this 



it has been found that a medium which is slightly acid when it 

 is prepared will change its reaction upon sterilization or upon 

 standing. In particular the writer has found that nutrient agar 

 kept in glass tubes of various "makes" will in time become al- 

 kaline. 2 This is especially true of much of the soft glassware ob- 

 tained during the war, so that media that tested P H 6 when made 

 would, after two weeks, test Ph 7, and moreover, the same degree 



'Miss Bryan (II, '21) has recently described a bacterial bud rot of cannas in 

 which she shows the pathogen producing a colorless zone surrounded by a white 

 precipitate on whey agar. Because of this similarity with the foxtail organism 

 it was thought desirable to compare Bacterium Cannae with the foxtail pathogen. 

 Miss Bryan very kindly furnished the writer with cultures of her organism. 

 Comparison between the two show numerous differences, morphological and 

 physiological, although as far as producing a precipitate is concerned they 

 behave alike. The interesting thing about B. Cannae is that it produces a color- 

 less area surrounded by a white precipitate not only on whey agar but also on 

 Ordinary nutrient agar possessing a slight acidity, as P 6.6. Furthermore, the 

 production of this character* can be controlled in the same manner as in the 

 foxtail organism. 



a Esty and Cathcart (II, '21) have recently given some interesting data on the 

 effect of different glassware on various solutions. 



