4G() STATE BOARD OF AGRICULTURES. 



sarily imply or prove the presence of oxidase nclivity, and no entirely 

 satisfactory method of visibly donoiuslrafiiif/ oxidase activity in the 

 tissues of living uninjured insects was found. Upon studying the case, 

 however, tJiere -was nevertheless found to l>e visible evidence of almost 

 positive oxidase activily nalnrally i)resent in certain living cells of 

 most insects. The facts which set forth this evidence follow: — 



The wing covers of newly emerged adults of P. coniiitus were almost 

 without color — pure white. They gradually began to brown, becoming 

 darker and darker until they finally appeared jet black — and by that 

 time, they were entirely dry and hard. When the (\vv, black wing covers 

 were crushed and tested they were found to contain catalase and an 

 (almost) insoluble tyrosin-oxidase (see Fig. 3, Plate I) ; reductase ac- 

 tivity was practically absent. The dark coloring matter of the crushed 

 wing-covers appeared to be identical with the dark pigment which 

 formed when the insect-extract or blood was exposed to air. Moreover, 

 this melanic pigment in both cases was like the melanic pigment ob- 

 tained when tyrosin, in solution, ^^as oxidized by insect tissue-extract. 

 (Tyrosin is a protein derivative). The Aving-cover pigment, as well as 

 both the other pigments just mentioned, could be reduced by confining 

 it in the absence of oxygen with fresh tissue-extract which was rich in 

 reductase activity. The coloration of newly emerged insects could be 

 entirely stop]>ed at any stage by dropping the insecls into boiling water 

 and keeping them at that temperature for about 20 minutes. Again, if 

 white, newly moulted insects {Pcriplancta Americana was used) were 

 submerged in CSo and ke])t there, almost no dark coloration developed. 

 Also (as has been generally found by experience) in order to i)reserve 

 white grubs and pupae in alcoliol widiout darkening or discoloring, they 

 first had to be treated with boiling water. That is to say, some means, 

 (such as heat) appeared to be necessary to destroy the oxidase activity 

 before placing the white adults, grubs or pupae in alcohol; otherwise, the 

 inhibiting action of the strong reductase, present in the living body, 

 rapidly passed after death, and the oxidase (which is injured but not 

 entirely destroyed by alcohol) then brought about oxidation and blacken- 

 ing of the tissues. Likewise, since an oxidase Avhich could oxidize ty- 

 rosin was present in the wing-covers and outer integument of P. cornutus 

 and the cockroach {Periplaneia Americana) it appeared that the cutic- 

 ular excretion poured out from the hypodermal cells beneath the old 

 integument before it became moulted-— the excretion which loent to form 

 the integument of the newly moulted insect — contained not only the ty- 

 rosin-oxidase but also a tyrosin-like derivative (i. e. some similar organic 

 derivative) which oxidized, under the influence of the oxidase, to form 

 the brown or melanic coloration of the integument. These added in- 

 stances of the activity of an oxidase did not, so far. prove its presence 

 in living cells. The evidence showed, however, that in blood exposed to 

 the air, in extract of the tissues exposed to air, in the cuticular integument 

 of the newly moulted adult beetle and in the tissues of the dead grub 

 and pupae (killed by some means that does not destroy an oxidase) a 

 very similar, if not an absolutely identical, melanic pigment developed 

 under the influence of an oxidase in every case — and more rapidly as the 

 reductase activity passed. Moreover, these instances of melanic pigment 

 formation served to call to mind the fact that in certain cells of the 



