746 
Journal of Agricultural Research 
Vol. XXXI, No 8 
only the amount of material required to kill in 24 hours. Moore 
concluded that one-half pound of chloropicrin per 1,000 cubic feet 
was sufficient to kill most insects, and that 1 pound would give satis¬ 
factory results with all those tried. 
Since 1918 many papers have been published on this subject. In 
general, they are devoted to work on the various phases of toxicity 
on one hand and to use of the fumigant under practical conditions 
on the other. Notable among the papers of the first group are those 
by Bertrand and his associates in 1919, 1920, and 1921 (3-9). Those 
writers showed that as regards the toxicity of chloropicrin to insects, 
time and concentration bear an inverse ratio to each other. Bertrand 
also called attention to the fact that there was greater variation due to 
temperature than would be expected on the principle of Van t'Hoff 
and Arrhenius. He believed this to be due to the fact that much of 
the chloropicrin was retained in the tissues and continued to act 
after the insects had been removed from the gas, thus rendering the 
observation inaccurate so far as the time factor was concerned. It 
is interesting to note that when his results for toxicity with a concen¬ 
tration of 20 grams to the cubic meter are plotted against time and 
temperature, the results fall along a straight line continuing down 
to 0° C. This is noteworthy when one considers that'nearly all 
other fumigants have their toxicity so reduced at 12° or 15° C. that 
they are of little practical value at these temperatures. 
The results of other investigators are in accord with these of 
Bertrand and his associates, with regard to the toxicity of chloro¬ 
picrin, and there is agreement that the effect of the chloropicrin is 
probably due to action on enzymes. Remy (18) described paralysis 
of certain individuals of Argas rejlexus which survived fumigation; 
and Spencer (19) believed that the action was cumulative, resulting 
in the death of nearly all of the insects which at first gave evidence 
of having survived the fumigation. 
Regarding the practical use of chloropicrin we have the results 
of Burkhardt (10), Feytaud (13), Remy (18), Spencer (19), Wille 
(20, 21), Delassus (12), and others. Here we do not have the general 
agreement as to its promise that we have with regard to the labora¬ 
tory experiments on its toxicity. Delassus (12) and others advocate 
greater use of chloropicrin, and express the belief that the technique 
of using it needs improving. Burkhardt (10) reports poor results 
under conditions similar to those which gave good results with carbon 
disulphide and concludes that chloropicrin might be suitable for use 
in small receptacles which could be tightly sealed, but that it is not 
suitable for use on a large scale. 
TOXICITY EXPERIMENTS 
In the present writers 7 work, the first series of experiments was 
performed to determine the toxicity of chloropicrin under laboratory 
conditions. The chloropicrin was measured out. in a small cali¬ 
brated pipette and placed in a small stoppered vial until the insects 
had been introduced into glass jars of 8-liter capacity. The insects 
were placed in small bolting-cloth bags and suspended in the jars 
by means of threads, the ends of which hung over the edge of the 
mouth of the jars. The edges of the jars were greased with vaseline 
in order that there might be no leakage about the threads when the 
glass cover was in place. 
