Raymond Pearl 
219 
obviously dififerent from what had been the prevailing type of non-conjugants in 
Series C and D, the most noticeable fact being that the individuals in Series E 
were unusually broad in proportion to their length. All conjugants, of course, 
had disappeared long before Series E was taken. After September 6th the 
growth of algae rapidly increased, and by September 8th Paramecia had com- 
pletely disappeared from the culture so far as I could determine. 
We have then, from this single culture, 1020 individuals included in four 
samples taken at intervals covering practically the whole course of a conjugation 
epidemic. 
Series B. This is a very short series, comprising only 12 pairs of conjugants 
and 24 non-conjugants. These came from another of my cultures at Leipzig, set 
like the one described above, with hay and pond-water and at the same date, 
July 25th. It, however, had developed in a somewhat different direction, probably 
largely as a result of having been placed in slightly dififerent conditions with 
respect to light. The dominant organisms in this culture were algae, various 
species of Euglena, hypotrichous infusoria, both large and small, and Para- 
mecium. Conjugating Paramecia were first found in this culture on the morning 
of August 22nd, and measurements on them were begun at once, on the same 
plan as that adopted in Series A, C, D, and E. During that day only 10 pairs 
of conjugants were found. From this it was concluded that an epidemic of 
conjugation was just starting ; but this was not the fact, for on the next day, 
with the most thorough searching, only two pairs of conjugants were found. After 
that none were found. It seems likely that in this instance there was no true 
conjugation epidemic at all, but that instead the fact was that in a restricted 
portion of the culture a limited number of individuals reached the physiological 
condition for conjugation at the same time. 
We may now discuss the methods used in killing and measuring the material, 
and in the calculation of the constants. The method used in killing and mounting 
the individuals of Series AA and F has already been described (p. 216). The 
measuring on these series was done with an ordinary ocular mici'ometer at a 
relatively low magnification, such that in Series AA one division of the micro- 
meter was equal to 13 microns, and in the F series to 8'6 microns. At the time 
these measurements were made no filar micrometer ocular was available. The 
units of measurement were really a half of 13 microns and 8"6 microns respec- 
tively, because at the low magnification it was possible to estimate accurately 
with the eye whether the points to be measured fell within the upper or lower 
half of a scale division. It was neither practicable nor, considering the objects 
in view, worth while to make any closer measurements on these series. 
The other series discussed in this paper, viz.. A, B, G, D and E, were killed 
and measured in a somewhat dififerent way. First as to the killing ; whenever, in 
examining a drop of culture fluid on a slide a pair of conjugants was seen, all the 
individuals on that slide were killed by dropping on it from a pipette eight to 
ten times as much killing fluid as there was water. The killing fluid used was 
