Studies on Physiology of Some Plant Pathogenic Bacteria 9 
No. 269. Isolated August 31, 1918. Young leaf lesions were placed in 95 per 
cent alcohol for an instant, then for one minute in 1-1000 solu¬ 
tion of biclilorid of mercury and washed through six sterile water 
blanks. Dilution plates on potato agar were made from macer¬ 
ated lesions. Pathogenicity proved from inoculations in the 
field in 1918 and in the greenhouse during the winter of 1918- 
1919. Brown’s peptone media. 
No. 270. Isolated January 17, 1919, from naturally ififected leaf collected in 
the greenhouse. Surface sterilization was effected as in the case 
of No. 269 and dilution plates made. Does not brown peptone 
media. Pathogenicity proven by inoculation of plants in the 
greenhouse. 
No. 211. This is the first strain isolated in the study of the disease, and was 
the strain used in all cultural and much of the inoculation work 
in comparison with the type strain No. 268. Isolated September 
25, 1915. Does not brown peptone media. 
The strain from North Carolina, herein designated No. 19, was isolated June 
12, 1919, agrees culturally with a strain isolated during July of the previous 
year, has several times been proven to be pathogenic and is the type strain of 
Bacterium sojae. 
CULTURAL STUDIES 
Method. Since it was early found to be impossible to verify the reac¬ 
tion of the strains toward carbohydrates by use of media prepared according 
to methods which have previously been employed, other methods which in¬ 
cluded a more accurate adjustment of initial reaction and a more careful prep¬ 
aration of sugars were adopted. These methods take advantage of recent re¬ 
finements in methods of adjusting the reaction of culture media colorimetri- 
cally and electrometrically to supplant the inaccurate and illogical titration 
method which employed phenolphtlialein as an indicator. They also take into 
account the well known fact that not only acid or alkali but also heat, can 
hydrolyze sugars and therefore interfere with the proper preparation of sugar 
media.* 
As is indicated in the preparation of Krumweide’s brilliant green agar, su¬ 
gars in distilled water, and therefore apart from the influence of a complex 
solvent like culture media with its acid or alkali content, can be sterilized 
*Physiological chemists have long recognized that hydrogen ion concentra¬ 
tion and temperature are important factors which influence the decomposition 
of carbohydrates. In alkaline solution, all of the monosaccharides and some of 
the disaccharides are unstable. In acid solution the decomposition of mono¬ 
saccharides proceeds more slowly and is less complete than in alkaline, and 
in any case, the reaction is hastened by boiling. Further, the di-and polysac¬ 
charides are less stable in acid than in alkaline solutions. (See Matthews, 
A. P. Physiological Chemistry 2d edit. 1915, N. Y.) 
The application of these facts is made the basis of an investigation by 
Mudge (1) who pointed out that maltose and lactose in water solution or in 
peptone broth seem to be hydrolyzed more by heating for three successive days 
in an Arnold than by autoclaving at 15 pounds for 15 minutes, while sucrose 
and raffinose in water solution did not break down. 
Advantage has been taken of these facts by a considerable number of bac¬ 
teriologists, not only in their published investigations but in routine work as 
well. The preparation of stock solutions of sterile carbohydrates in distilled 
water will no doubt in time become a generally adopted laboratory practice. 
References : 
(1) Mudge, C. S. The effect of sterilization upon sugars in culture media. 
Jour. Bact. 2 :403-415, 1917. F. A. W. 
o 
