July 15,1925 Eff ect of Low Temperatures on Bruchus obtectus 
167 
stage (and therefore also probable differences in the colloidal character 
of the lymph) have been considered, as well as the influence of the rate 
at which the insect was cooled. 
GENERAL DISCUSSION 
The typical graph of an insect's reaction to temperature, both high 
and low, is given in great detail in Bachmetjew's second volume (#). 
Knight (10) gives a simplified graph, which includes the essential 
features with which the writer is concerned. 
There is first a gradual lowering of the insect's temperature to a 
point designated by Bachmetjew as the “critical point." It is pre¬ 
sumed that the freezing of the body fluids causes the typical rebound 
to a point which the same author calls the “freezing point of the 
lymph." Bachmetjew concluded that it was necessary to again cool 
the insect to its supercooling temperature, or “critical point," after 
the rebound had taken place, before death ensued. It has been the 
experience of the writer that one rebound was sufficient to cause 
death. This was also the experience of Pirsch (IS) and Knight (9). 
Careful examination of the data on which Bachmetjew based his con¬ 
clusions shows considerable discrepancy. If the freezing was hurried 
or incomplete it is possible that muscular contractions after the insect 
thawed out again might have given the impression that life still 
remained. The data presented in this paper show that there is also 
a distinct ante-mortem zone of muscular activity. From the purely 
physical standpoint it seems reasonable to conclude that crystalliza¬ 
tion results in a disruption of cell tissue which, while not necessarily 
fatal to a plant, is fatal to an insect. There is a possibility, however, 
that when a fairly large insect is frozen the disruption oi cell tissue 
may be only local and not sufficient to cause death. This would be 
most likely in the case of an insect which has been impaled on a 
thermocouple point. 
FREEZING EXPERIMENTS WITH BRUCHUS OBTECTUS 
Table I gives the results obtained by freezing 25 individuals in each 
stage—adults, pupae, and larvae. The adults were taken out of the 
bean just previous to emergence. This stage was the most satis¬ 
factory from the experimental standpoint, since variables due to the 
more active metabolism, histolysis, and histogenesis, encountered 
in the more immature stages, were absent. The criterion of color 
was used to determine approximately the age of the pupae; the age 
of the larvae was determined by size. 
