Journal of Agricultural Research 
Vol. VIII, No. 3 
116 
At the end of 12 to 18 hours the cultures in the —10 bouillon were as 
heavily clouded as the neutral; those at —20 were well clouded but 
plainly less than at —10. At this time B . atrosepticus , B . solanisaprus, 
B . melanogenes , IIIA, SE, and IIP were practically identical in the 
amount of cloudiness they produced on the different media, but showed 
no growth beyond — 20, B. phytophthorus from Appel and B. phytoph - 
thorns from Schuster showed a decreasing amount of cloudiness up to 
and including —40, but they showed no growth in the tubes of media 
with a reaction of — 50. 
In 48 hours the last two named had produced a faint but evident 
growth in the medium having a reaction of —30. At the end of two 
weeks all showed growth at — 40 and all but B . atrosepticus and SE at 
- 50 - 
Optimum reaction for growth in bouillon. —This is approxi¬ 
mately the same for all of the organisms studied. It lies very close to 
the neutral point of phenolphthalein, but is apparently on the alkaline 
side. Observations to determine this must be made with these organ¬ 
isms during the first 12 to 18 hours of growth. Broth cultures with a 
reaction of +10 with hydrochloric acid and —10 with sodium hydrate, 
Fuller’s scale, were practically equally well clouded in 24 hours, but the 
add cultures in the early stages of growth were observed to cloud slightly 
more slowly. Sodium hydrate restrains the growth much less than does 
hydrochloric add, but in both alkaline and add media of stronger reaction 
than that first mentioned there was a very dedded falling off in the cloud¬ 
ing during the first 24 hours as compared with that obtained with media 
of neutral reaction. 
Vitality on culture media. —Cultures of B. solanisaprus and the 
three organisms from Maine in neutral beef-extract bouillon, stored at a 
temperature of from 15 0 to 18 0 C., were found to be alive at the end of 8 
to 10 months, provided the moisture had not entirely evaporated. Tests 
were made with the other organisms, but with somewhat younger cul¬ 
tures and in each case they were found to be alive in the bouillon. Cul¬ 
tures in liquefied gelatin were also found to possess long vitality, but upon 
agar slants* milk, and the various carbohydrate broths, the organisms 
were killed out much more readily. Those in milk were frequently found 
to be entirely dead at the end of three months. 
Temperature relations. —The optimum temperature for growth in 
the six pathogens studied is not far from 25 0 C., although no attempt 
was made to determine this within a variation of 5 0 C. above and below. 
Numerous tests were made of all the strains at the same-time in seven 
different incubator chambers, running from 5 0 to 35 0 C. Considerable 
differences were noted in the rates of growth at lower temperatures, even 
in different tests of the same strain, but as the optimum was approached 
a striking uniformity was obtained. This is well illustrated by Table III, 
which gives the results secured from a single series. In the temperature 
