46 BULLETIN 1147, U. S. DEPARTMENT OE AGRICULTURE. 
(b) Sample 45 is least soluble and sample 10 is most soluble in the 
bodies of insects. Samples 10 and 25 were totally water soluble 
before they were eaten, but after being eaten only about three- 
fourths of the arsenic was obtained as soluble arsenic. 
(c) While no general deductions can be made as to the average 
percentages of arsenic found soluble in the bodies of insects, when 
the figures under " control results" are subtracted from these aver- 
ages, as a general rule, the higher the percentages of arsenic made 
soluble by the juices of the insects, the higher are the rates of toxicity. 
Using lead arsenate (sample 39) as a standard, the last statement is 
strongly supported by the results obtained with the first seven 
arsenicals (samples 39, 28, 57, 27, 71, 45, and 64), but it is not so 
strongly supported bv the following five samples (64C, 62, 90, 23, 
and 74). 
(d) The percentages of water-soluble arsenic in the original samples 
of arsenicals bear no relation to the toxicity of those arsenicals, 
except in the case of those which are totally water soluble. 
(e) As a general rule, the larger the average amount of arsenic 
in the insects analyzed, the higher is the rate of toxicity of that 
arsenical. Using average weights of the undried insects fed on all 
14 of the arsenicals and average amounts of arsenic per insect, a 
bee weighing 98 milligrams contained 0.0119 milligram of arsenic, 
a silkworm weighing 1,370 milligrams contained 0.1063 milligram, 
and a Ceratomia weighing 1,620 milligrams contained 0.0219 milligram 
of arsenic. Thus, although a silkworm is 14 times as large and a 
Ceratomia is 16 times as large as a bee, the silkworm contained 9 
times as much arsenic as did the bee and 5 times as much as did 
the Ceratomia. This difference in amount of arsenic probably may 
be explained by the fact that for bees and silkworms the spray mix- 
tures were used five times the usual strength, while for the Cera- 
tomia the usual strength (1 pound to 50 gallons of water) was suffi- 
cient to kill the insects within 24 hours. 
(/") None of the water extracts of the bodies of the insects fed 
on the various arsenicals showed an alkaline reaction, and the 
highest acid reaction was 5.8 (pH value). As an average pH value 
for the 14 arsenicals, the bees gave a value of 6; the silkworms, 5.7; 
and the Ceratomia, 6.1; and as an average pH value for any arsen- 
ical against all three insects, the only figures obtained are 5.8, 5.9, 
and 6. Again it is shown that the pH value has nothing to do with 
the percentage of arsenic rendered soluble by the insect juices. 
Experiments like those performed on the three foregoing species 
of insects were also performed on another large but easily killed 
caterpillar (Datana integerrima G. & R.). As trie number of these 
caterpillars was limited, only samples 39, 57, and 64 were used against 
this species, so that the results obtained could not be easily incor- 
porated in Table 21. They are, however, similar in all respects 
to those already discussed. 
MINIMUM DOSAGE OF LEAD ARSENATE REQUIRED TO KILL SILKWORMS. 
By means of a needle-pointed pipette, an acid lead arsenate (sample 
39) was dropped upon fresh mulberry leaves. Upon evaporation 
of the water from these drops, the portions of leaves bearing the 
white spots were fed to large hungry silkworms in the last instar. 
