282 
H. S. JENNINGS 
Most of these twenty epidemics of conjugation occurred a few 
days after new hay had been added to the culture, though 
this procedure had no effect in producing conjugation in D, nor 
in many other strains. 
The small strain c, likewise extensively used in the work reported 
in 1909, has been in the laboratory for the same length of time as 
D (two years and ten months) . During this time it has shown two 
epidemics of conjugation, September 25, 1907, and March 8, 1909. 
Long continued systematic and varied experimentation with the 
object of getting it to conjugate at other times has been quite 
unsuccessful, although k, under precisely the same conditioas, 
showed epidemics of conjugation every few weeks, or even at 
intervals of but a few days, as we have seen. 
The very small race ^, described in my paper of 1909, has 
shown, since it has been in the laboratory (two years and six 
months), on two occasions a few scattering conj ugants. Attempts 
to produce epidemics of conjugation have been unsuccessful. 
The very large race L2 (two years in the laboratory) has shown 
two epidemics of conjugation. 
The two races g and C2, of my paper of 1909, have resembled 
k in their readiness to conjugaie, though the tendency is not 
quite so marked in these cases. But each has conjugated several 
times during the period (somewhat more than two years) that 
they have been in the laboratory. Both g and C2 were derived 
from single individuals, the former taken November 13, 1907, 
the latter January 29, 1908. 
In practical work in the laboratory the difference between the 
diverse races in respect to conjugation was most striking. Certain 
of the races could be depended on to give conj ugants at short 
notice whenever such were desired, and epidemics of conjugation 
often occurred when there was no intention of producing them. 
With other races it was impossible to get conj ugants, though they 
were much desired for other purposes. 
These general observations were supplemented by precise ex- 
periments. Many of these experiments were undertaken for other 
purposes, but gave results on our present subject. 
