Raymond Pearl 
217 
From the above account it will be seen that the conjugation was between 
individuals from the same culture. Regarding the general character of this 
material, I can only say that the preparations are by far the finest I have ever 
seen of fixed and mounted infusoria, in point of giving a true representation of the 
condition of the living orgauisms in respect of shape and size of body. This I may 
say has been the comment of all who have seen the slides. Unfortunately the 
staia has now faded somewhat, so that the nuclear conditions are not shown as 
clearly as was formerly the case. 
Series A, C, D and E. The individuals included in these series all came from 
a single culture in the Zoologisches Institut at Leipzig. This culture was set with 
dry hay and pond water in an aquarium jar holding about three litres, July 25th, 
1905. In about a week there was an abundance of infusorian forms in the 
culture, the dominant species in point of numbers being Chilumonas parameciimi, 
Paraviecium candatum, and an unidentified species of the common hypotrichan 
genus Oxytricha, together with immense numbers of a large form of the bacterium 
Spirillum. Very soon the Oxytrichae began to diminish in numbers, while at the 
same time the Paramecia rapidly increased until finally there was a very tiourishing 
culture of this form. At this time I was measuring for another purpose specimens 
of Ghilomonas from this culture, and on Tuesday, August 15th, 1 noticed on a slide 
which had been mounted during the afternoon of the Saturday before a single pair 
of conjugating Paramecia. A careful search through samples taken from the 
culture was at once instituted, with the result that during the remainder of that 
day I succeeded in finding eight pairs of conjugants. The next day in seven 
hours of continuous searching I found 22 pairs, the next day 54 pairs, and from 
that time on the numbers continued to increase until the height of the epidemic 
was passed. From these facts it will be evident that the epidemic was only just 
at its beginning on August 15th. It should be stated that from the time all of the 
cultures were started regular routine examinations were made to see whether 
conjugation was occurring in any of them. No conjugating individuals were 
found before this first pair on August 15th. 
The plan which it seemed wisest to follow in handling this material was to take 
samples at somewhat widely separated intervals during the course of the conjuga- 
tion epidemic. It was deemed best to follow this plan because I had strong 
reasons to expect, from an experimental study* on variation in Paramecium 
which has been going on for some two years, that there would be a marked cj'clic 
change in the variation constants during the course of the epidemic, due to 
environmental influences. It seemed desirable to detect and measure such a 
progressive change if it should occur. Now it is evident that the simplest way 
to attain this end would be to make bulk killings of large samples of the culture 
at suitable intervals, and then measure the preserved individuals at leisure. This 
method, however, I did not dare to adopt for the reason that the conjugants 
* For a preliminary report see Pearl, K., and Dunbar, F. J., " Some Kesults of a Statistical Study of 
Variation in Paramecium." Seventh Report, Michigan Academy of Science, pp. 77 — 86. 
