Studies on Physiology of Some Plant Pathogenic Bacteria 
5 
ever. All of the tubes containing media which had remained solid were placed 
in boiling water until the media had liquified, whereupon they were again 
cooled to 7.5°C. The alkaline gelatin again solidified, but 1.5 cc. of HC1 in 10 
per cent gelatin and 1.7 cc. in 15 per cent gelatin were now the limits of the 
jellifying power. 
Tarle 2.—Effect of Acid and Alkali on Solidification of Gelatin 
10 Per Cent Gelatin 
15 Per Cent Gelatin 
Gela¬ 
tin 
HC1 
NaOH 
Physical 
State, 
7.5° C. 
Gela¬ 
tin 
HC1 
NaOH 
Physical 
State, 
7.5° C. 
Per 
Per 
Per 
Per 
cc. 
cc. 
Cent 
cc. 
Cent 
cc. 
cc. 
Cent. 
cc. 
Cent 
10 
3.5 
10.15 
Liquid 
10 
3.0 
9.02 
Semisolid 
10 
3.0 
9.02 
Semisolid 
10 
2.5 
7.82 
Solid 
10 
2.5 
7. 82 
Solid 
10 
2.0 
6.51 
Solid 
10 
2.0 
6.51 
Solid 
10 
1.7 
5.68 
Solid 
10 
1.7 
5.68 
Solid 
10 
1.5 
5.11 
Solid 
10 
1.5 
5.11 
Solid 
10 
1.2 
4.19 
Solid 
10 
1.2 
4.19 
Solid 
10 
1.0 
3.55 
Solid 
10 
1.0 
3.55 
Solid 
10 
0.5 
1.86 
Solid 
10 
0.5 
1.86 
Solid 
10 
0.5 
0.95 
Solid 
10 
0. 5 
0.95 
Solid 
10 
1.0 
1.82 
Solid 
10 
1.0 
1.82 
Solid 
10 
1.2 
2.14 
Solid 
10 
1.2 
2.14 
Solid 
10 
1.5 
2.61 
Solid 
10 
1.5 
2.61 
Solid 
10 
1.7 
2.90 
Solid 
10 
1.7 
2.90 
Solid 
10 
2.0 
3.33 
Solid 
10 
2.0 
3.33 
Solid 
10 
2.h 
4.00 
Liquid 
10 
2.5 
4.00 
Semisolid 
DISCUSSION 
Manifestly, in the case of both agar and gelatin, strong acid or alkali in the 
presence of high temperatures is capable of destroying the jellifying power. 
Everyone who has made culture media according to accepted methods, i. e., 
sterilized them after the adjustment of reaction, has found that an acidity of 
2 to 2.5 per cent normal HC1 or a pH concentration of approximately 4 to 3.5 
is the limit of solidification of agar. Alkalis in related proportions in the 
presence of heat have been found to exert a similar action on the jellifying 
power of agar. Fellers (1917) however, found that this range of jellifying 
power for 2 per cent agar could he extended to 5 per cent normal HC1 or 5 
per cent KOH if the acid or alkali were added while the agar was boiling hot 
and it was not subsequently sterilized. These highly acid or alkaline media 
were furthermore employed by him (1916) in studies on soil flora, since appro¬ 
priate quantities could he transferred by means of a sterile pipette to sterile 
Petri dishes. When one permits the media to cool before adding the acid or 
alkali as was done in our studies, and as is indicated in Fellers’ work, the 
range of solidification may be extended very much farther. The application of 
the principles involved herein are believed to make it possible both to simplify 
the making of media and to improve methods for investigation on the influence 
of hydrogen ion concentration on microorganisms. Reference to two recent 
papers, one by Webb (1919) on the influence of reaction on the germination 
of fungous spores and the other by Fred and Davenport (1918) on the growth 
