SPRAYING. 137 



leim used for the gypsy-moth work, although the best of it 

 remained in good condition from one to three months ; yet 

 in some cases it became necessary to make two or three ap- 

 plications during a season. During windy weather bands 

 upon dusty streets require frequent attention and occasional 

 renewal. Dr. Smith says that in no case has he ever ob- 

 served any injurious effect of dendrolene upon the trees. 



Dendrolene is supplied by Prof. F. L. Nason, New Bruns- 

 wick, N. J. Insect lime can be obtained of the Bowker 

 Fertilizer Company, Boston, Mass., and of Wm. Menzel & 

 Son, New York. 



Spraying with Paris Green. 



When the second commission began work in the spring 

 of 1891, it was learned that the efficacy of Paris green as an 

 insecticide for the gypsy moth was doubted by many people 

 in Medford. Experiments were therefore immediately begun 

 to determine whether spraying with Paris green would kill 

 the caterpillars. In April young caterpillars were hatched 

 by artificial means in the office of the commission and fed 

 upon leaves which had been carefully sprayed with a solution 

 consisting of one pound of Paris green to one hundred and 

 fifty gallons of water. Not only was the ordinary Paris 

 green experimented with, but samples of finely bolted poison 

 were secured. The experiments showed that the use of 

 either quality of Paris green caused death. It was noticed, 

 however, that the caterpillars which ate the leaves sprayed 

 with the pulverized poison died soon after beginning to feed, 

 or within twenty-four hours ; while those which ate of the 

 leaves sprayed with the ordinary Paris green lived for several 

 days, very few dying within twenty-four hours. The ma- 

 jority lived three or four days and some even a longer 

 time. Samples of both the pulverized and ordinary Paris 

 green were analyzed and the analyses gave substantially the 

 same amount of arsenic in each. From this it would appear 

 that both were equally poisonous. Why they were not 

 equally effective has not been fully determined. But as the 

 ordinary Paris green was made up of fine crystals which were 

 more or less insoluble, while a larger proportion of the finely 

 powdered Paris green was apparently soluble in water, the 



