284 DK, C. A. MAC MUNN ON" MYOHAEMATIN AND THE HISTOH^MATINS. 
third myohsematin bands having partially coalesced, and the second band being as dark 
as the third, the band before I) being, however, well marked. Hence this change is 
not the same as that effected by acids. I have tried the effect of a current of oxygen 
passed over insect muscle placed in a suitable gas chamber placed beneath the micro¬ 
spectroscope ; but, although the gas was passed for ten minutes, and the experiment 
several times repeated, the myohsematin bands persisted. The reason, of course, may be 
that the gas did not penetrate the substance of the muscle, but merely passed over its 
surface.* Still the fact remains that exposure to air diminishes the intensity of the 
bands, that as I have found repeatedly the bands are less distinct when the insect is 
killed in flight, that when thus invisible, or nearly so, they can be brought back by the 
use of Stokes’s fluid or ammonium sulphide. Hence, then, myohsematin can be oxidised 
and reduced in the case of insects ; its fully oxidised state is denoted by the absence 
of bands, its reduced state by their presence. The same was found to be the case with 
the histohsematins, so that one may safely conclude that these 'pigments are concerned 
in the respiration of the tissues in which they occur. 
Myohsematin also occurs in spiders. It is present in the muscle of the eephalo- 
thorax of Epeira diadema, Tegenaria civilis, and other spiders ; in these the muscles 
are pale, and, therefore, contain but little myohmmatin, but its bands can generally 
be brought into view by treatment with reducing agents (spectrum 16 , Chart III.). 
In Crustaceans the distribution of myohsematin is confined apparently to the 
cardiac muscle. 
In all the specimens of Astacus fluviatilis examined the heart muscle showed the 
spectrum of myohsematin, all five bands being visible. In the voluntary muscle it 
could not be found (spectrum 17, Chart III.). 
In the heart of Cancer pagurus it is found, and it is absent from the other muscles 
(spectrum 18, Chart III.). 
In the heart of Idomarus vulgaris the myohsematin bands could be measured in 
the large spectroscope and gave the following readings :— 
1st band ... X 613 to X 593, 
2nd band . . . X569 „X563 (about), 
3rd band . . . X556 „X550 (spectrum 1, Chart IV.). 
It was absent in the voluntary muscle. 
In Pagurus bernhardus it is present in the heart muscle, but as in the others 
absent from the voluntary muscle. 
In Carcinus mcenas the heart musclet shows myohsematin bands. 
In all these cases the bands are made more distinct by the use of reducing agents 
and fainter by exposure to the air. 
* It is well known that the O in the O-haamoglobin of vertebrate muscle is not given off in vacuo. 
f But not the voluntary muscles. 
