42 
ZOOLOGY: L. L. WOODRUFF 
Proc. N. A. S. 
The culture has been maintained by 
the isolation of a specimen from each 
of these lines practically every day, 
with the exception noted below. The 
number of divisions in each line has 
been recorded at the time of isolation 
and the average rate of these four lines 
has again been averaged for varying 
numbers of days (5, 10, or 30 days) as 
the exigencies of the different experi- 
ments demanded. These data have 
afforded the graphs of the division rate. 
Permanent preparations have been pre- 
served from time to time for the study 
of the cytological changes during the life 
history. During the first eight months 
of the work the culture medium con- 
sisted of infusions of hay and fresh grass, 
but from February, 1908, to the present 
time various materials collected from 
ponds, swamps, etc., have been em- 
ployed. The infusions were thoroughly 
boiled to prevent the contamination 
of the pure culture with foreign strains 
of Paramecium. In short, the cells of 
the four lines of the culture to-day are 
direct lineal descendants by division of 
the single animal isolated in 1907. 
The object of starting the culture was 
to determine whether Paramecium can 
reproduce by division indefinitely with- 
out recourse to conjugation. Through- 
out the work the possibility of conjuga- 
tion in the four lines of the culture has 
been precluded by the almost daily iso- 
lation of the products of division. 
Accordingly its continued life and health 
has long since justified the conclusion 
that conjugation, involving syncaryon 
formation, is not, as previously gener- 
ally maintained, a sine qua non for the 
continued life of Paramecium, in par- 
ticular, and, presumably, of Infusoria 
in general. At the completion of the 
CO CQ tH 
