76 



SCIENCE 



[Vol. LV, Ko. 1412 



It is believed that the forms here described 

 and interpreted are unique in inorganic na- 



*'"®' Alan W. C. Menzies 



Ralph Beebe 

 Princeton, N. J. 



UNLIKE INTERPRETATIONS OF FULLER'S 

 SCALE IN DETERMINING DEGREE 

 OF ACIDITY 

 In following directions for making up bac- 

 teriological culture media the writer has been 

 impressed by the marked differences in acidity 

 as recommended by different bacteriologists. 

 Tor example, "The Standard Methods of Water 

 Analysis," adopted by the American Public 

 Health Association, 1917, and commonly used 

 by bacteriologists, recommends the use of cul- 

 ture media of a + 1.0 acidty.^ Smith (4, 

 p. 69), however, apparently recommends a 

 + 15.0 agar and a + 10.0 gelatin, and these 

 figures are frequently used by plant patholo- 

 gists in designating the acidity of culture 

 media. 



The question which naturally arises is, do 

 bacterial pathogens of plants require in general 

 a much higher degree of acidity than bacteria 

 of milk, sewage, water, animal pathogens, etc., 

 or is it possible to explain this difference by 

 assuming unlike interpretations of Fuller's 

 scale. The writer with the hope of clarifying 

 the situation has compared the descriptions of 

 Fuller's method as given by Smith, whose texts 

 are universally used by plant pathologists, 

 with the description usually presented by bac- 

 teriologists, particularly animal pathologists, 

 and also with the description originally pre- 

 sented by Fuller. He finds that Fuller's scale 

 is interpreted differently. 



Smith's (1. c.) description follows: "The 

 plus and minus on Fuller's scale denotes, 

 respectively, acid and alkaline media. The 

 + 10, for example, means that exactly 10 cubic 

 centimeters of normal alkali must be added to 

 a liter (wiiter's italics) of the culture medium 

 to render it exactly neutral to phenolphthalein, 

 and, correspondingly — 10 means that the fluid 



1 Since Fuller 's scheme has several decided dis- 

 advantages it is being supplanted by more accu- 

 rate methods. (See Report of the Committee on 

 the Descriptive Chart for 1919. Jour. Bad., 

 5: 127-143. 1920). 



is alkaline to phenolphthalein and that 10 cc. 

 of normal acid would need to be added to 

 bring 1 liter back to the neutral point." He 

 follows this interpretation of FuUer's scale, as 

 amount per liter, in his very recent work 

 (5, p. 106): "Our standard agar is +15 and 

 our standard gelatin + 10 on Fuller's scale, or 

 1.5 per cent, and 1 per cent, respectively, if 

 reckoned on 100 c. c. portions. It is best to 

 keep to Fuller's scale since we make up media 

 in liters, not in 100 c. c. portions." 



The following description of Fuller's scale, 

 taken from Park and Williams' (3, p. 102), is 

 typical of the interpretations placed upon this 

 scale by various texts on animal pathogens : 

 "Calculation — Five c. c. of medium require 2.4 

 c. c. of N/20 NaOH, therefore 100 c. c. 

 (writer's italics) — ^would require 2.4 e. c. of 

 N/1 NaOH — ; in other words, the medium is 

 2.4 per cent, acid to phenolphthalein or + 2.4 

 if expressed according to Fuller's method or 

 scale." It will be noted that in this interpreta- 

 tion Fuller's scale is used as degree of acidity 

 in 100 c. c. of medium in contrast to those 

 interpretations in which the scale denotes de- 

 gree of acidity in 1,000 c. c. of medium. 



Fuller's (1, p. 388) own description reads 

 as follows : "For accuracy and convenience, 

 the expression of acidity or alkalinity of cul- 

 ture media in numbers of cubic centimeters of a 

 normal solution per liter (writer's italics) is by 

 far the best, and I recommend its universal 

 adoption as a standard method." Concerning 

 degree of acidity with reference to optimum 

 growth, he says (p. 391) : "Speaking in gen- 

 eral terms the available data appear to war- 

 rant the placement of the optimum degree of 

 reaction within narrower limits, between 10 

 and 20 of our scale," and (p. 394) he adds, 

 "As it is very urgent that some fixed point be 

 adopted I venture to suggest that for quantita- 

 tive water analysis .... 18 on our scale be 

 taken as a standard. This means, of course, 

 that such a solution would require 18 cubic 

 centimeters per liter of normal alkali to render 

 it neutral to phenolphthalein." This usage, as 

 amount per liter, has been generally adopted by 

 plant pathologists, while the animal patholo- 

 gists, in general, use the scale as denoting 

 amount per 100 c. c. 



It should be pointed out that Fuller does not 



