SS a ee 
1905] SCHN EIDER—CULTIVATION OF RHIZOBIA 301 
evenly by inclining the dish slightly from side to side and set aside 
to cool. Pour contents of tube no. 3 into Petri dish no. 2, and con- 
tents of tube no. 4 into dish no. 3, spread medium and set aside. 
After the media in the Petri dishes are well coagulated, place the 
dishes where they will not be interfered with. They may be placed 
in an incubator provided the temperature is kept well below the 
melting point of the culture medium. I have obtained the most 
uniform results by keeping the plate cultures at the normal tempera- 
ture of the laboratory. 
About the third day the growths will begin to appear as very 
small light grayish specks; several hundred, more or less, in dish 
no. 1; twenty-five to thirty in dish no. 2; and perhaps only five to 
ten in dish no. 3. These are rhizobia cultures, and if the work was 
well done there will in all probability be no foreign microbes present. 
The cultures on the upper surface of the medium will be circular in 
outline, while those within the medium will be spindle-shaped. 
Growth of cultures is comparatively slow, thus giving ample time for 
study and to make tube cultures, plate cultures, etc. Tube cultures 
have been quite fully described in previous papers, likewise the 
morphology of the rhizobia grown in various artificial media. 
Various other methods of isolating rhizobia have been tried suc- 
cessfully, but the method just described is recommended as giving the 
best Tesults. It is somewhat lengthy in detail, but nevertheless simple 
iD operation. It will be found that the isolation and cultivation of 
thizobia is indeed simple, and even the beginner in the study of bac- 
teriology will wonder what might have been the cause of the diffi- 
Culties encountered by the earlier (1886 and later) investigators of 
— the root nodule organisms. The difficulties however will become 
somewhat evident on examining the cultures microscopically. The 
morphological characteristics are found to be entirely changed, so 
t there is no similarity between the organism as it appears in the 
nodule and the organism as it appears in the artificial culture media. 
CALIFORNIA CoLLEcE oF PHARMACY, : 
San Francisco. 
