1000 
Journal of Agricultural Research 
Vol. XXXI, No. 10 
from two to four weeks. The cowpea, lima-bean, and soy-bean 
cultures did not form a serum zone. The rate of serum-zone forma¬ 
tion is influenced greatly by the amount of inoculum. 
The behavior of the various cultures of nodule-forming bacteria in 
litmus milk was of considerable value in separating strains. Dif¬ 
ferences were noted in rate of serum-zone formation, depth of zone, 
amount of reduction, and in change of reaction aipong organisms of 
a single cross-inoculating group. Probably the ability of these 
organisms to change the reaction of the medium in which they grow 
is an adaptation to their natural environment and has some relation 
to their life functions. 
CONCLUSIONS 
The litmus milk brings out characteristics of the nodule bacteria 
not shown by plain milk. On the basis of reaction and reduction, it 
separates these organisms into two groups. This separation is more 
marked with freshly isolated cultures than with cultures carried in 
the laboratory for a long time. 
o 
