476 THE GYPSY MOTH. 



of lead in the proportion of 2 lbs. to 150 gal. of water, from 

 July 9 to July 28, 1894, and which at the time of dissection 

 was full grown, normally active and healthy, yielded .025 

 milligrams of arsenic. If, for the purpose of illustration, 

 the weight of arsenic thus found be compared with the 

 weight of this caterpillar, and this ratio applied to the aver- 

 age weight of the adult human being, we obtain the rather 

 surprising result that such a caterpillar would withstand 

 uninjured an amount of arsenic, in proportion to its weight, 

 equivalent to twelve and one-half times the fatal dose for an 

 adult human l)eing, in proportion to the weight of the latter. 

 This illustrates the ability of this insect to resist arsenical 

 poisoning. 



Since the quantities of arsenic found were small in com- 

 parison with the amount the insect consumed, it is evident 

 that a considerable part of the poison must have been 

 eliminated from the body. The presence of arsenic in the 

 excrements of poisoned caterpillars indicates one source of 

 elimination. These investigations upon poisoned cater- 

 pillars show that an apparently large quantity of arsenic 

 may enter and even permeate all parts of the body of the 

 caterpillar without interfering with the vital processes, and 

 that a consideral^le part of the poison consumed with the 

 food is eliminated, chiefly in the excreta. 



One interesting result obtained from the analyses of the 

 diff'erent stages of the gypsy moth, made in 1893 and 1894, 

 is that pupae and imagoes from caterpillars which have been 

 reared on leaves sprayed with Paris green or arsenate of 

 lead may contain arsenic in recognizable quantities. Several 

 pupee and a few female imagoes, obtained under these con- 

 ditions, when subjected to chemical analysis gave ample 

 evidence of the presence of arsenic in their bodies. This 

 shows that the presence of arsenic in the pupa may not 

 materially interfere with the processes involved in the de- 

 velopment of the imago. 



Since, as has been repeatedly demonstrated, moths reared 

 from poisoned larvse are capable of reproduction, it is also 

 evident that the arsenic contained in their systems does not 

 injure the reproductive function. 



