EXPERIMENT STATION BULLETINS. 467 



compound ejes of insects, and of the ocelli of insects and spiders, and 

 in the hypodermal cells forming the circular boundary of ocelli, there 

 was to be quite commonly found a melanic pigment which had its origin 

 ill the cells during ontogenic development, in view of the proven cases 

 of melanic pigment formation through oxidase action cited above, the 

 inference that the development of melanic pigment in certain eye and 

 hypodermal cells was an example of a similar oxidase acting upon some 

 constituent of the cells, themselves, seemed to have justification. Other 

 similar evidence might be given all tending to show that melanic pigment, 

 in animal tissues, develops through the oxidation of some organic con- 

 stituent of the tissues — under the influence of an oxidase* acting after 

 the tissue-reductase has been either weakened or destroyed by some 

 means. 



In order, then, to learn something finally concerning the effect of a few 

 contact insecticides (when used only in such amounts as were necessary 

 to kill) upon oxidases, catalases and reductases in the living tissues of 

 P. cornutus, the method of study was varied as follows: 



Insects were killed by the insecticide agent to be studied, using various 

 amounts of the agent for the length of time necessary to kill. The bodies 

 were then extracted by the method already described, as soon as the 

 insects were considered dead or beyond recovery, and the strengtli of the 

 oxidase, catalase and reductase activities in tliis extract was compared 

 with that in a fresh extract similarly prepared from the same number of 

 untreated insects. Tests were made in this manner using heat, hydro- 

 cyanic acid gas, chloroform anci carbon disulphide. It will be appre- 

 ciated that it was impossible to check the factors of time, original 

 strengths of catalase, oxidase and reductase in the extracts, etc. by this 

 method as accurately as they could be checked in the former method 

 where samples were taken at the same time, from a single extract, for 

 stud}'. Nevertheless, the results showed certain things very satisfactorily. 



The extract from gasoline-vapor-killod beetles was always much weaker 

 in reductase activity than the check, while the catalase and oxidase 

 activity remained much the same. For example, when two beetles were 

 treated with about 3% gasoline vapor for 20 hours, it required 4 hours 

 for the treated extract to reduce a certain amount of methylene blue 

 — the check accomplishing the same reduction in 10 minutes. Prac- 

 tically no difference could be seen in the rapidity with which alcoholic 

 guaiac was oxidized; and a check-extract-sample liberated only 2 c. c. 

 more of oxygen from the standard hydrogen peroxide than a similar 

 sample-extract of the insects killed by gasoline. 



The extract from beetles killed with carbon disulphide was ahvays 

 quite white or very light straw color at first and it remained so for two 

 or three hours, usually, before it began to darken. That is, oxidase 

 action always appeared to be almost entirely absent, at first. After a 

 few hours, however, this activity became partly recovered. Catalase- 

 action was usually injured one-half or more, and the reductase much less, 

 so that it was relatively strong, at first, as compared with the oxidase 

 activity. 



Keductase in the extract of beetles treated 2^2 hours with strong 



♦Hammarsten (Mandel) in bis "Physiological Chemistry" quotes Fttrth -with Schneider and 

 Prisbram, Gessard, Neuberg and Dewitz as having shown the presence of tyrosinases in 

 Insect-tissue and sepia, in melanotic tumors and in pigmented skin. 



