Jan, 15,1917 
Blackleg Disease of Potato 
119 
all three organisms. In the case of the mercuric-chlorid test one 2-mm. 
loop of a deeply clouded, 24-hour broth culture was transferred to 
check tubes of sterile distilled water and to others containing varying 
dilutions of the poison, the weakest being 1 to 50,000. After one hour 
transfers were made from these to fresh broth tubes. In no case was 
growth obtained except from the inoculated check tubes of pure water. 
Where mercuric chlorid was added directly to broth tubes it was found 
that it required a concentration of 1 to 10,000 to produce the same results. 
With formaldehyde no attempt was made to determine how weak a 
solution would be effective. It was simply tested and found that one 
part in 250 in distilled water or beef broth was sufficient to kill all or¬ 
ganisms in an hour's exposure. This was somewhat weaker than is 
usually used for disinfecting potato tubers and the time one-half as long. 
PATHOGENICITY 
As has already been stated, all of the strains studied were tested at 
various times to determine their ability tq produce the characteristic 
blackleg disease of the stem and softrot of the tuber. From the beginning 
to the close of the work B. solanisaprus , B. melanogenes , and the three 
strains from Maine were found to be pathogenic to potato stems, leaf 
stalks, and tubers. 
When first received in March, 1910, the culture of B.atrosepticus either 
failed to attack or caused a slow decay of pieces of potato tubers pro¬ 
duced the season before, which had been cut under aseptic conditions and 
placed in tubes of sterile water. However, after several repeated trans¬ 
fers from one 24-hour-old potato-broth culture to another it was found to 
produce a fairly rapid decay when inoculated into potato tubers, especially 
those which were immature and recently dug. This strain has continued 
to rot tubers, provided they were not too mature and care was taken not 
to allow the inoculated portion to dry out too rapidly.. 
It has been the custom whenever the pathogens were tested on growing 
stems of potato plants to inoculate a plant each time with each of the 
nonpathogenic strains. B. atrosepticus was repeatedly used in this way, 
but the results were negative previous to June 15, 1916. A plant inoc¬ 
ulated on this date by puncturing the young, growing stem near the 
base with the needle of a hypodermic syringe and inserting a small 
amount of a 24-hour-old culture in the tissues of the pith, was observed 
five days later to be showing slight blackening around the point of inoc¬ 
ulation. Closer examination showed that the pith had been softened and 
decayed for a short distance above the puncture. This diseased condi¬ 
tion did not progress much farther, however. About a month later 
several other young stems were inoculated with transfers of the stock 
strain of B. atrosepticus and this time the positive results were more 
marked. The inoculated stems were blackened on the surface for a dis- 
