No. 4.] GYPSY MOTH APPENDIX. 479 



No. 1, no glucose. 



No. 2, 4 quarts glucose to 100 gallons of water. 

 No. 3, 6 quarts glucose to 100 gallons of water. 

 No. 4, 8 quarts glucose to 100 gallons of water. 

 No. 5, 10 quarts glucose to 100 gallons of water. 



The sprayed bushes were suitably tagged (not in the order 

 given above), and, after passing through several showers, were 

 examined on June 23 at my request by Mr. Forbush and Professor 

 Fernald, who were unable to decide, so far as the apparent amount 

 of poison was concerned, which area was sprayed Avithout glucose 

 and which ones were treated with glucose solutions. Other exam- 

 inations by some of our most experienced employees at later inter- 

 vals gave the same result. This method of investigation, how- 

 ever, is an indirect one, since all that is obtained is a consensus 

 of opinion. Greater weight may be attached to the results of the 

 tests to be detailed. 



2. Chemical Tests. 



On August 4, fifty-one days after the time of spraying, fail- 

 samples of foliage, eight leaves each, were gathered from the 

 bushes sprayed without glucose and from those sprayed with glu- 

 cose at the rate of 4 quarts to 100 gallons of water. These 

 samples were submitted to our chemist, Mr. F. J. Smith, who ex- 

 amined equal weights of the ground foliage for arsenic. From the 

 sample where no glucose was used, 2 grams of pulverized foliage 

 yielded 5.3 mgms. of arsenate of lead. The sample of foliage 

 treated with glucose yielded .72 mgm. arsenate of lead front 2 

 gms. foliage. In other words, the glucose-treated foliage retained 

 less arsenic than that sprayed with a normal mixture. The unex- 

 pected wide difference in the results of these two analyses led Mr. 

 Smith to analyze later in the season (September 1) two entire 

 bushes from the experimental plots. One of these bushes had 

 been sprayed without the use of glucose, the other with glucose at 

 the rate of 6 quarts to 100 gallons of water. The results of these 

 later analyses are much more satisfactory, because of the increased 

 amount of material used. From Mr. Smith's report I take as 

 follows : — 



Analyses of foliage sprayed with arsenate of lead ; leaves dried at 

 100° C. : — 



No. 1, no glucose : 31.5 grms. leaves give 41.5 mgs. arsenate of lead 

 (Pb 8 (As0 4 ) 2 , or 9.17 gr. per pound. 



No. 2, with glucose: 31.05 grms. leaves give 52.3 mgs. arsenate of 

 lead (Pb ;! (As0 4 ) 2 , or 11.76 gr. per pound. 



The difference of 2.59 gr. per pound is infinitesimal. 



