498 STATE BOARD OF AGRICULTUUM 



PLATE I. 



Fig. 1. Sample of thick creamy extract in the left slender dish was 

 treated strongly with CS, and ~Yo hydroqninone was added later in 

 the presence of the CSg. 



Check extract to the right (not treated) had the same amount of jy 



hydroqninone added, at the same time as the treated extract. 



The darker color of the check shows the greater oxidation of the hydro- 

 qninone to quinone. 



Fig. 2. Shows the form of sealed tube in which the reducing action 

 of insect-tissue extract toward methylene blue, indigo carmine, etc., was 

 studied. 



Fig. 3. First cup to the left shows the darkened solution of tyrosin, 

 oxidized under the influence of a crushed elytra (thoroughly cleaned 

 with alcohol) of an old adult P. coniutus. 



Middle cup contains clear unoxidized solution of tyrosin with crush- 

 ed elytra which had been healed to boiling for 10 minutes. 



Cup to the right — check, containing only tyrosin solution which re- 

 mained clear during the 7 days of the test. 



Fig. 4. Cockroach (P. americaiia) , showing the head and arrange- 

 ment of the white bristol-board collar to prevent the insecticide powder, 

 with which the body was treated, from reaching the insect's mouth. 



