DEGENERATION AND DEATH IN ENTAM@BA RANARUM. 719 
the cytoplasm—increases with lowering of temperature.! This 
at once suggests that the events preceding encystation in 
EK. ranarum are somewhat as follows: In winter the lower- 
ing of the temperature leads to an acceleration in the growth 
of the nucleus. In the ordinary course of events the nucleus 
then regulates its size by extruding a quantity of nuclear 
matter into the cytoplasm. ‘This act then calls forth in the 
organism those changes which bring about encystation. 
The occurrence of physiological degeneration could thus 
be explained as follows: When the lowering of temperature 
occurs, some unknown factor acting upon the amoeba prevents 
the elimination of the excess of nuclear material produced. 
This, therefore, would lead to considerable increase in the 
size of the nucleus—which, as I have shown, actually occurs. 
As the nuclear material is not given up to the cytoplasm the 
factor which determines encystation does not come into play, 
so that the animal does not encyst. The excess of nuclear 
material is gradually turned into pigment, etc., and the un- 
encysted animal finds itself in a highly abnormal condition, 
from which it is unable to recover. It therefore undergoes 
degeneration and death. 
This gives us, I think, a plausible explanation of the 
phenomena which I have observed. There yet remains, 
however, the question—at present unanswerable—W hat is the 
factor which, ex hypothesi, prevents the regulation, by 
elimination of nuclear matter, of the size of the nucleus, and 
in consequence, prevents encystation and causes death? It 
is conceivably some toxic body—e. g. a secretion of the host, 
or the metabolites of the amcebe themselves, or a toxin pro- 
duced by the large numbers of bacteria in the host’s gut. On 
the other hand, it may be a factor whichlies within the ameeba? 
' See, for example, Popoff, ‘“ Experimentelle Zellstudien,” ‘Arch. f. 
Zellforschung,’ Bd. 1, 1908. Lowering of temperature caused both an 
absolute and a relative increase in the size of the nucleus in the Infusoria 
studied. 
* That the overgrowth of the nucleus is itself the primary cause of 
degeneration and death appears to me highly improbable. I would as 
soon argue that grey hairs are the cause of old age in man. 
