﻿44 BULLETIN 1147, U. S. DEPARTMENT OF AGRICULTURE. 



with acid load arsenate (sample 39). After having been dried by an 

 electric fan, the leaves were led to 50 large hungry silkworms. When 

 the silkworms had ceased eating, they were removed to clean cages 

 where the feces, contaminated as little as possible, were collected and 

 subsequently analyzed. The next morning a sample of 34 dead and 

 dying silkworms was thoroughly washed for five minutes in running 

 tap water, then, one worm at a time, in six different washes, the first 

 four consisting of hydrochloric acid (2 per cent) and distilled water 

 and the last two of distilled water alone. A pencil brush was used for 

 scrubbing them. Analysis of the sixth wash showed the presence of no 

 arsenic. These experiments were repeated five times. To determine 

 how much of the arsenic had passed through the intestinal walls, the 

 alimentary canals of three sets were removed by careful dissections. 



The results of the analyses of these samples were as follows: 84 

 entire silkworms yielded 2.66 milligrams of arsenic oxid, being 54 

 per cent water-soluble; 72 silkworms with alimentary canals removed 

 yielded 0.89 milligram of arsenic oxid, being 36.7 per cent water- 

 soluble; the alimentary canals of these 72 silkworms yielded 1.03 

 milligrams of arsenic oxid, being 55.9 per cent water-soluble; and the 

 2.18 grams of dried feces from these 72 silkworms yielded 0.45 milli- 

 gram of arsenic oxid. According to the figures obtained from these 

 72 silkworms, 37.6 per cent of the total arsenic eaten had passed 

 through the walls of the alimentary canals, 43.4 per cent of it was 

 retained inside these canals, and 19 per cent of it was voided with the 

 feces. Reaction (pH) of water extract from the larvae was neutral 

 (7); from the alimentary canals, slightly alkaline (7.1); from the 

 larvae with the alimentary canals removed, slightly acid (6.2) ; and 

 from the feces, acid. 



The foregoing experiments were repeated on a larger scale by feed- 

 ing 13 arsenicals sprayed on leaves to caterpillars of the catalpa- 

 sphinx moth {Ceratomia catalpse Bdv.). The results obtained in- 

 dicate the following: (a) As a general rule, the higher the percentages 

 of water-soluble arsenic in the larvae and feces, the higher the rates of 

 toxicity of those arsenicals; (6) the percentage of water-soluble 

 arsenic in the arsenical ingested usually has little to do with the rate 

 of toxicity; (c) the amount of arsenic found per caterpillar is fairly 

 constant for all the arsenicals used ; (d) the higher the ratio of total 

 arsenic (per 100 grams of larval material or feces) found in the larvae 

 to that found in the feces, the higher the rate of toxicity; (e) the 

 reaction (pH) of water extracts from the larvae fed various arsenicals 

 seems to bear no relation to the rate of toxicity. 



In 1920 the preceding experiments were repeated on a much larger 

 scale, using the following insects: Honeybees, 2 sets (each of 100); 

 silkworms, 3 sets (each of about 25) ; Ceratomia, 2 sets (each of about 

 25) . The procedure followed was the same as that in the preliminary 

 tests, but, in order to determine the percentage of arsenic actually 

 made soluble by the juices of the insects, the percentage under 

 "control results" in Table 21 was subtracted from the percentage of 

 arsenic found soluble in the bodies of insects. Since the solubility of 

 a minute quantity of arsenic in 500 cubic centimeters of water 

 proved to be greater than that of a larger quantity, an amount of 

 arsenic approximating the average amount found in a sample of the 

 insects analyzed was employed as a control. 



