1922] 



ROSEN — A BACTERIAL DISEASE OF FOXTAIL 361 



Since Fuller's scale has had such common usage it seems de- 

 sirable to present actual comparisons of this scale with the deter- 

 mination of hydrogen ions. Various investigators have given 

 comparative figures, the table given by Norton ('19) and repro- 

 duced above, is one illustration of such comparison in bacterio- 

 logical culture media. 



The titrations were made by the ordinary methods using phe- 

 nolphthalein as indicator. Attention should be called to the fact 

 that figures under titration represent parts per thousand as rec- 

 ommended originally by Fuller instead of parts per hundred as is 

 used by Norton. 1 It will be noted that while the total acidity 

 titration (Fuller's scale) shows the media to be markedly acid, 

 the acidity in terms of hydrogen-ion concentration is very nearly 

 neutral or even alkaline. Figures obtained by me show the same 

 thing. A few are here listed : 



P H Fuller 's scale 



Nutrient beef broth acidulated with 0.1% citric acid 4.8 +24.0 



Nutrient beef broth acidulated with 0.05% hydro- 

 chloric acid . 5.5 +12.0 



Nutrient beef broth neutralized with sodium hydroxide™ .7.0 + 10.0 



Nutrient beef broth rendered alkaline with sodium hy- 

 droxide 7.2 + 6.0 



Here also a medium which is neutral or even alkaline with ref- 

 erence to hydrogen-ion concentration appears acid in Fuller's 

 scale. This of course is not surprising since, as is now well known, 

 the color change of phenolphthalein instead of being at the neu- 

 tral point, is actually on the alkaline side, between P H 8 and 

 Ph 9.6, so that media below P H 8 would appear acid if this indica- 

 tor is used. It is necessary to emphasize the fact that these com- 

 parisons are merely indications of what differences may be ex- 

 pected. Any changes, such as the amount or kind of peptone or 

 of beef extract, will change the value on Fuller's scale even in the 

 presence of the same amount of acid. In these comparisons the 

 medium used consisted of 3 grams of Liebig's beef extract, 10 

 grams of "Bacto" peptone, and 1000 cc. of distilled water. 



GEOWTH OF THE FOXTAIL ORGANISM ON VARIOUS MEDIA 



Two different kinds of agar were used, the Difco powdered 

 agar and a shredded agar of unknown make. No difference in 

 growth was noted but the first is to be preferred since it is more 

 readily soluble. Difco peptone was used and two different kinds 



*A discussion of the difference in interpretation of Fuller's scale is given by 

 the writer in another publication (Rosen, II, '22). 



