July 23. 1917 Toxic V allies and Killing Efficiency of Arsenates 207 



(3) All of the arsenic devoured by the insects in feeding upon sprayed 

 foliage is not assimilated, but a portion passes through the intestinal 

 tract in the excrement. The percentage amount of the arsenic assimi- 

 lated depends upon the arsenate used; lead hydrogen arsenate was 

 assimilated readily and most of the arsenic was retained in the tissue, 

 while much of the basic lead arsenate was found in the excrement. 



(4) It requires approximately 0.1595 mgm. of arsenic pentoxid to kill 

 1,000 small tent caterpillars, and approximately 1.84 mgm, of arsenic 

 pentoxid to kill 1,000 nearly mature tent caterpillars, irrespective of 

 the particular arsenate used as a spray. 



(5) Preliminary experiments on the burning effects of calcium arsenate 

 indicate too severe injury to warrant the practical use of this spray. 



