Jan. 15,1917 
Blackleg Disease of Potato 
101 
B . melanogenes was received from Dr. Pethybridge in 1911. This has 
also shown a good degree of virulence and like B. solanisaprus has re¬ 
peatedly produced on inoculation from pure cultures a rapid and com¬ 
plete softrot of potato tubers and a typical decay of the stem resembling 
in every particular the blackleg as it occurs in the field. 
methods used 
In the present investigation the writer has endeavored to follow as 
closely as possible the procedures outlined by the Committee on Standard 
Methods of Water Analyses 1 and those recommended by Smith (32, v. 1). 
For what seemed good and sufficient reasons, certain deviations were 
made from the procedures recommended above; but wherever this has 
been done, mention has been made of the fact and each named organism 
or cultural strain has been treated exactly like all others. The most 
important change has been the substitution of Liebig's extract of meat 
for infusion of lean beef as a basis for ordinary bouillon, gelatin, agar, 
and bouillon containing carbohydrates for fermentation purposes. 
The reasons for this are that the meat extract is a standard product, 
compounded on a large scale by a reliable concern, and can be purchased 
the world over, while, on the other hand, no two lots of lean beef obtained 
from the market have exactly the same composition with regard to 
amount of fat or fiber present, or decomposition products developed 
from the different periods of storage before use. The chief objection to 
the use of lean beef as a basis of fermentation broths is that it is first 
necessary to remove the muscle sugar from the meat infusion by inocula¬ 
tion with Bacillus coli Consequently the test for fermentation which 
follows is made, not in a culture medium most favorable to the growth 
of the organism to be tested, but in one containing the various metabolic 
by-products of another. Each lot of meat-extract bouillon before being 
used for fermentation purposes was first tested for fermentable carbo¬ 
hydrates by filling a fermentation tube with it and inoculating it with 
B. coli In no case was any gas produced. Moreover, in many tests of 
bouillon made from Liebig’s extract during the last 15 years, in only one 
instance did any gas develop and then only a small bubble in the end of a 
fermentation tube, the closed arm of which contained approximately 25 
c. c. of medium. 
However, a careful comparison was made as to the rate of develop¬ 
ment and vigor of growth of the various organisms in bouillon made 
from an infusion of lean beef, and in that made from Liebig’s extract. 
In ordinary bouillon no difference was observed between the two in this 
respect. In fermentation broth made from the meat extract a better 
1 Report of Committee on Standard Methods of Water Analysis to the laboratory section of the Ameri¬ 
can Public Health Association, presented at the Havana meeting, Jan. 9,1905. 141 p. Chicago, Ill., 1905. 
Reprinted from Jour. Infect. Diseases; Suppl. 1, 1905. 
