454 STATE BOARD OF AGRICULTURE. 



This is illustrated in table III by No. 2, where in the first five hours, 

 the fresh extract used 0.9 c. c. more 0, iu the gasoline chamber than was 

 used by its duplicate sample in pure air. When Ihe same samples had 

 then run undisturbed for nineteen hours, it was found on the other hand, 

 ihat the pure air sample had taken up the most oxygen by 0.4 c. c. In 

 No. 4 the stock extract was about five ho\irs old when the samples were 

 taken for the tests. Note that in this case, while the first test period of 

 six hours showed more oxygen used in pure air, the longer second period 

 gave an increased excess of oxygen used by the pure air sample. These 

 results, taken with those obtained by the former method, seem to justify 

 the conclusion that carbon disulphide and gasoline inhibit or lessen the 

 rate of oxidation of hydroquinone in solution in the tissue extract of 

 Passalus cornutus. Furthermore, iu the case of gasoline, the effects on 

 the rate of oxidation arc not marked, unless the extract is a few hours 

 old at the beginning of the test; and if perfectly fresh extract is used 

 for a short period the results may be contradictory — apparently. As 

 has already been mentioned, however, the series of experiments, results 

 of which are recorded in Table III, were run after a study had been 

 made of insect tissue reductase and of tlie effect of gasoline upon the 

 reductase. This latter study, it is believed, afi'ords an explanation of 

 the apparantely contradictory results obtained when gasoline-vapor acts 

 for short intervals upon freshly made "insect-tissue extract plus hydro- 

 quinone" solution. (See page 28.) 



(b) INFLUENCE UPON THE REDUCING ACTIVITY. 



Some evidence has already been given of the existence of a strong 

 reducing power in the fresh extract of Passalus cornutus; namely, the 

 reduction (when air is excluded) of the dark molaulc pigment which 

 develops in the extract through the influence of the oxidasic enzyjues 

 when tissue-extract has been exposed to the air for a while, and the 

 reduction of methylene blue to leuco-methylene blue Avhen air is ex- 

 cluded from extract to which a little methylene blue has been added. 

 Still other evidence may be given. If comparatively fresh ''extract plus 

 hydroquinone" which has already oxidized enough of the hydroquinone 

 to quinone to give the solution a reddish-brown hue, is then confined in 

 the absence of air or free oxygen for a few hours, the reddish-brown 

 quinone will all be reduced; and if a little perfectly fresh extract is 

 added before excluding the air, the reduction takes place more rapidly. 

 Fresh extract stained blue with a little indigo carmine will reduce the 

 stain to leuco-indigo carmine in the absence of free oxygen; and then, 

 the reduced color body will oxidize and turn the extract solution blue 

 again, if air is admitted — just as happens also Avhen confined extract, 

 holding leuco-methylene blue, is once more exposed to the air. After 

 fresh extract has caused alcoholic guaiac to be oxidized to guaiac blue, 

 if the entire mixture is then confined from free oxygen, the reducing 

 bodies show their presence by reducing all guaiac-blue back to its former 

 condition. Likewise, after tyrosin has been oxidized to the black melanic 

 pigment, the latter can then be reduced by the extract, if air is excluded. 

 In every case after reduction, oxidation may again be brought about if 

 the confined extract containing the reduced body is once more exposed 

 to air. 



