292 
H. S. JENNINGS 
NO. 
MEASURED 
LENGTH IN MICRONS 
BREADTH 
[N MICRONS 
Old culture, no fresh food 
53 
132.30 ± 1 
59 
27.96 
± .43 
Same, three days after hay added; 
52 
139.42 =t 1 
16 
40.00 
± .52 
Same, one day later, in watch glass ; 
53 
131.92 ± 1 
10 
31.36 
± .35 
Here again conjugation followed upon a rapid decrease in the 
plumpness of the animals. But is is clear that starvation is not 
the cause of conjugation, for the animals that conjugated did not 
as a matter of fact (as the measurements show) become so thin 
as they were at the beginning of the experiment. Moreover, 
those left in the old infusion throughout the experiment (a and e, 
p. 290) continued to become steadily thinner, and at the end were 
much thinner than the specimens that conjugated. Yet these 
thinnest specimens never conjugated, because they were not 
subjected to the sudden change from rich to poor nutritive con- 
ditions. 
Indeed, we can say, looking at the general course of events, 
that it is the addition of fresh food that finally results in conjuga- 
tion; those parts of the culture to which fresh food is not added do 
not conjugate. The cause of conjugation is a decline in the nutri- 
tive conditions after a period of exceptional richness that has induced 
rapid growth and multiplication. To express this by saying that 
hunger induces conjugation is perhaps not incorrect, if we under- 
stand thereby relative hunger; hunger after satiety. 
After conjugation has ceased, the animals usually decrease in 
numbers and remain very thin. But they can continue to exist 
in this condition for long periods. I regularly kept them through 
the summer vacation in this condition, no fresh material being 
added to the culture sometimes for a period of four months. Dur- 
ing such times they existed in a sort of depressed condition, witt 
extremely slow multiplication. T never observed conjugatior 
in such periods, though it could readily be called forth by addin/ 
hay, as above described, or by placing them in a fresh infusic; 
made by boiling hay in water. 
