Studies on Physiology of Some Plant Pathogenic Bacteria 
45 
Adjustment of Reaction. —In the routine preparation of media accord¬ 
ing to usual methods, the medium is rendered neutral after the materials have 
been dissolved, is then boiled, after which it is adjusted to the desired pH con¬ 
centration and is finally sterilized. In objection to this procedure, as Clark (4) 
has shown, it makes considerable difference whether alkali is added to bring 
the medium to the neutral point, and it is then adjusted to the desired acidity 
from this point or whether adjustment is made by introducing only a frac¬ 
tion of the alkali. Then, too, if adjustment is made as in the present studies 
only after the media have been cooled, flocculation, such as occurs in meat in¬ 
fusion and peptone broths with consequent change in buffer content, is pre¬ 
vented. Strongly acid or alkaline solutions and the employment of aseptic 
precautions will best serve for the adjustment of reactions. If finally media 
are not reheated after adjustment, changes in hydrogen ion concentration are 
avoided. 
FERMENTATION 
% Preparation of carbohydrates. It is easily conceivable that a sufficient 
amount of reducing sugar could be formed from di- and polysaccharides when 
sterilized in a complex solvent like bouillon, so that an organism known to 
form acid from reducing sugars, but not from di- and polysaccharides could, 
in fermentation tests with these carbohydrates, produce an increase in acidity 
and thus lead to erroneous conclusions. In order to avoid this hydrolysis of 
carbohydrates, especially as occurs during sterilization in such complex sol¬ 
vents as culture media with its weakly acidic or basic properties, various in¬ 
vestigations have employed concentrated carbohydrate solutions, prepared sep¬ 
arately. They may be dissolved in distilled water, autoclaved at 10 pounds 
for 10 minutes and added aseptically to cooled sterile media in flasks. If then, 
the media are tubed or plated in sterile containers, the process of preparation 
of media containing sugars is both simplified and is in conformity with the 
best practice as determined by the laws of physical chemistry. 
Concentration of carbohydrates. An optimum concentration of sugar, 
which can only be determined by experimentation, appears to be one of the 
factors involved in fermentation studies. One per cent of carbohydrate, the 
amount recommended by the Committee’, (5) is manifestly insufficient for many 
plant pathogenes to permit acidification to proceed until the characteristic final 
hydrogen ion concentration is attained. If tests for changes in reaction are 
made at frequent intervals, a procedure which is very desirable, the production 
of small amounts of acids can then be detected and a reversal of the reaction, 
such as may occur in the presence of insufficient fermentable sugar, will not be 
the cause of error. The results of fermentation tests would, it is believed, be 
very much enhanced in value if data on duration of fermentation and amount 
of change in reaction were included. In connection with studies on concentra¬ 
tion of carbohydrates, it has been noted that a governing influence is exerted by 
concentration of buffer and by initial reaction. In short, then, such data should 
be accompanied by a statement of the exact composition of the experimental 
media. 
Kind of carbohydrates. Medical bacteriologists long ago realized that 
fermentation studies which involved only the four carbon compounds of the 
Descriptive Chart are very incomplete. They have, accordingly, made use of 
the “rare sugars” as shown in the routine separation of such closely related 
