Studies on Physiology of Some Plant Pathogenic Bacteria 
37 
of fermentation of any of the sugars. Analysis of sugar content at definite in¬ 
tervals would, no doubt, serve as the best means of determining whether or not 
a decrease was occurring and whether the products of fermentation were being 
utilized as rapidly as they were being formed. 
Attention might well be directed, at this point, to the fact that B. tabacum 
and B. angulatum are indistinguishable on the basis of their ability to ferment 
the four carbohydrates employed in the fermentation tests of the Descriptive 
Chart. The original description (24) of the former is in error as regards its 
ability to ferment glycerine and lactose, due largely to faulty preparation of 
these sugars. The organisms are, however, not identical. Aside from the 
fact that they produce diseases which are widely different in appearance, and 
that they differ in certain morphological features, such as size and flagella¬ 
tion, they are separable on the basis of their fermentative activity, since B. 
angulatum does not form acid from mannite and galactose as does B. tabacum. 
Little use has been made, up to the present time, in pliytopathological studies, 
of the rare sugars. Their value, will no doubt, be better appreciated and more 
emphasized proportional to their use in future investigations. 
Another fact of interest which appeared in these fermentation tests is the 
relation between carbohydrate concentration and pigment production. In plain 
bouillon, or bouillon plus 1 per cent or less of carbohydrate, B. glycineum de¬ 
velops brown pigment. With 2 per cent of these various sugars, there is an 
entire failure of the formation of brown pigment. The proximate cause of this 
inhibition of pigment production, as is generally accepted in investigations with 
animal pathogenes, is the concentration of hydrogen ions resultant from an 
optimum supply of fermentable carbohydrate. 
Experiment VI—The Influence of Buffer Upon Reaction in Bouillon Con¬ 
taining Varying Concentrations of Dextrose 
The bouillon used in this series contained 0.3 per cent Liebig’s beef extract, 
0.5 per cent NaCl and either 2 or 4 per cent Armour’s peptone. The determina¬ 
tions of pH were made at intervals of 48 hours with the results shown in 
Table 10. 
