Ii8 
Journal of Agricultural Research 
Vol. VIII, No. 3 
always prevent later clouding of the inoculated and heated tubes of broth. 
In no case, except with a single tube of B. melanogenes , did growth occur 
after heating at 47 0 and above, but clouding always appeared after an 
exposure to 46° C. and below. Transfers from well-clouded broth 
cultures 36 to 48 hours old appeared more resistant than those a few 
days older. The strains carried under the name of B . phytophthorus 
showed a much higher thermal death point. For the culture received 
from Dr. Appel it was between 51 0 and 52 0 , while that from Dr. Schuster 
was killed at 54 0 but not at 53 0 . 
In making the thermal-death-point determinations thin-walled test 
tubes of 16 to 17 mm. internal diameter and approximately 16 cm. long 
were employed. Each tube contained 10 c. c. of meat-extract broth, 
+ 15 Fuller’s scale. 
Immediately after inoculation they were transferred to a specially 
constructed water bath, provided with a stirring apparatus and an accu¬ 
rate, certified thermometer, and immersed nearly their entire length in 
the heated, constantly moving water. The period of immersion was 10 
minutes and the bath during this time was maintained within one-tenth- 
of 1 degree C. of the required temperature. 
Effects of drying. —The effect of drying was tested as follows: A 
2-mm. loop of a 24-hour broth culture was removed to and spread upon 
small, sterilized, cover glasses in sterile petri dishes. These were allowed 
to dry at the same temperature as incubation for varying periods after 
the last trace of moisture had disappeared from the cover glasses. Then 
the latter were picked up with flamed forceps and dropped into tubes of 
sterile bouillon. Only B . solanisaprus , IIIA, and SE were tested in this 
way. The results were somewhat variable. Usually one or two minutes’ 
drying were sufficient to produce sterility, although in one or two cases 
growth appeared after 10 and 15 minutes’ drying. However, in each 
case like this the growth was much retarded. 
Effect of sunlight. —The effect of sunlight was tested only in the 
case of the three organisms mentioned in the preceding paragraph. The 
usual method was followed: The freshly inoculated and half-covered 
petri-dish cultures were exposed on blocks of ice to bright sunlight at 
midday in a greenhouse. There was no diminution of resulting colonies 
on the exposed side in 10-and 20-minute exposures, slight diminution at 
30 minutes, while at 60 minutes all the organisms on the exposed side were 
killed, and no colonies developed. This test was made in November 
and consequently the conditions were not favorable. Doubtless the 
same exposure outdoors in midsummer would have shown sunlight to 
be more effective in killing the organisms. 
Effect of germicides. —In testing the effect of germicides, only 
mercuric chlorid and formaldehyde were employed, and only B . solan¬ 
isaprus, IIIA, and SE were tested. The results were the same with 
