ANALYSES OF POTSOXED LARY.E. 475 



carefully washed in dilute acid and in distilled water, while 

 the purity of all chemical reagents employed in the analyti- 

 cal w^ork was demonstrated l)y a number of preliminary 

 tests. The method used in testing for the presence of 

 arsenic was the so-called Berzelius-Marsh process (Ameri- 

 can Chemical Journal, October, 1891), by means of which 

 a minute quantity of this poison can be readily recognized. 

 The results obtained from analyses of the organs and tissues 

 of a large number of caterpillars, Avhich were feeding un- 

 harmed on food treated with a liberal amount of Paris o-recn 

 or arsenate of lead (the only poisons used) , did not differ 

 materially from those of analyses of the same parts of cater- 

 pillars which had died from arsenical poisoning, while in 

 many caterpillars no arsenic was found. 



In l)oth cases arsenic was found chic^lly in the stomach, 

 intestinal and rectal contents, and throughout the walls of 

 the alimentary canal. It was also found in the excrements, 

 in the malpighian vessels, the dorsal vessel and blood and 

 in the muscular tissue, thus showing that the arsenic prob- 

 ably passes from the alimentary canal, where it is quite 

 equally distrilmted, into the blood, and is carried by the 

 circulation throughout the body, and thus eventually per- 

 meates all organs and tissues. Owing to the small size of 

 the parts subjected to analysis, some of them being of almost 

 microscopic dimensions, it was an extremely difficult process 

 to determine quantitatively the amount of arsenic present ; 

 yet this was accomplished by a comparison of the results 

 of the analyses with a series of finely graduated arsenic 

 "mirrors," for the use of which we are indebted to the 

 courtesy of Professor Hill of Harvard University. 



In some caterpillars, which had fed for a long time upon 

 food treated with the arsenical compounds previously men- 

 tioned, a considerable amount of arsenic was found ; while 

 those which had fed for a shorter time, as a rule, contained 

 smaller quantities of the poison. Many of those which had 

 thus fed for two or three weeks, when killed, were found to 

 contain more arsenic than caterpillars which had succumbed 

 to arsenical poisoning. One caterpillar, which had fed in 

 an out-door cage, upon willow leaves sprayed with arsenate 



