﻿ARSENIC ALS. 



47 



One drop would occasionally kill a large worm but more often two 

 drops were fatal. In almost every case three drops proved fatal 

 within 24 hours. Therefore, for these larvae three drops ma 

 regarded as a minimum fatal dosage of acid lead arsenate. An 

 analysis of 100 drops (4 sets) from the same pipette gave 0.0001 

 milligram of metallic arsenic as an average per drop, making 0.027."'> 

 milligram of arsenic a minimum fatal dosage for fully grown silk- 

 worms. 



An analysis of 59 of the dead silkworms, each of which had eaten 

 three drops of the arsenical, gave 0.0027 milligram of arsenic, per 

 larva, indicating that 90 per cent of the arsenic eaten had been 

 voided in the feces before the larvae died. Silkworms which had 

 received a maximum dosage of the same arsenical voided in the feces 

 only 19 per cent of the arsenic eaten, and Ceratomia, which had 

 received an average dosage of the same poison, voided G4 per cent of 

 the arsenic with the feces. 



QUANTITY OP ARSENIC EATEN BY INSECTS IN FEEDING TESTS. 



During the feeding tests many samples of dead larvae were pre- 

 pared for analyses, but only those of webworms (E. textor) and those 

 of potato-beetle larvae were finally analyzed. The webworm is one 

 of the most difficult to kill by arsenic, while the potato-beetle larva 

 is one of the most easily killed. Some of the webworms were washed 

 as described on page 44, but most of them were not washed. Also 

 several samples of feces (more or less contaminated) were analyzed. 

 The percentage of toxicity, as shown in Table 22, is the average of 

 the mortalities recorded on the third, sixth, and tenth days for the 

 one species concerned. 



Table 22. — Arsenic consumed by insects in feeding tests, 1919. 



Species of insects 



Arsenicals and controls. 



Condition of 



larvas before 



being analyzed. 



Num- 

 ber of 

 larvae 

 ana- 

 lyzed. 



Arsenic 



per 

 larva. 



Arsenic (parts 



per million) 



in— 



Tox- 

 icity 

 after de- 

 ducting 



and sample No. 



Larvas. 



Feces. 



mor- 

 tality 



of 

 control. 



Webworms (E. tex- 

 tor): 

 39 



Commercial acid lead 



arsenate. 

 do 



Washed 

 dried. 



and 



163 



400 

 200 



400 

 200 



180 



130 



160 



200 



200 



200 

 200 

 200 



200 



Milli- 

 grams. 

 0.0017 



.0025 

 .0014 



.0024 

 .0040 



.0033 



.0040 



.0027 



.0050 



.0016 



.0055 

 .0050 

 .0028 



.0053 



359 



385 

 303 



4S1 

 691 



436 



674 



399 



747 



303 



917 

 911 

 383 



613 



527 



1,114 

 746 



1,125 

 330 



851 



355 



365 



539 



SIS 



903 

 946 

 840 



306 



15 





39 



6S.6 



5 



Commercial calcium ar- 

 senate. 

 do 



Washed 

 dried. 



and 





5 



59.1 



28 



Commercial basic lead 

 arsenate. 



Laboratory calcium arse- 

 nate. 



Sample 69 plus 1 gram 

 lime per 418 cc. 



Laboratory barium arse- 

 nate. 



Commercial magnesium 

 arsenate. 



Laboratory sodium arse- 

 nate plus Bordeaux 

 mixture. 



Commercialzinc arsenite. 



Commercial Paris green . 



Laboratory aluminum 

 arsenate. 



Laboratory copper 

 barium arsenate. 



do 



4S.9 



69 



do 



15.1 



69B 



do 



6.3 



71 



do 



31.5 



62 



do 



36.5 



55 



do 



59.3 



23 



do 



63.6 



64 



do 



62.6 



73 



do 



32.0 



74 



do 



41. S 









