280 DR. 0. A. MAC MUNN ON MYOH2EMATIN' AND THE HISTOH2EMATINS. 
coloured constituent should be more useful than a colourless one is not clear, but in 
haemoglobin, hsemocyanin, and my echinochrome and Professor Lankester’s chloro- 
cruorin, as well as probably in Sorby’s aphidein, we have colouring matters which are 
respiratory pigments. 
II. Myoh^ematin. 
Until I had discovered the colouring matter which I have named myohaematin, it 
was believed by all physiologists that haemoglobin was the colouring matter to which 
the voluntary and cardiac muscles of animals owe their colour. The diaphragm of the 
rabbit after injection with salt solution being the muscle which has been used to 
demonstrate the presence of haemoglobin (Kuhne # ). While there is no doubt about 
the presence of haemoglobin in the plasma of the muscle of the heart, and in that of 
the voluntary muscles of most vertebrates, as Kuhne and others have shown, or in 
the muscular fibres of certain gasteropod molluscs, as Professor Lankester has shown, 
there is convincing evidence of the presence of myohaematin in the cardiac and 
voluntary muscles of invertebrates and vertebrates, which myohaematin either accom¬ 
panies, replaces, or is replaced by haemoglobin in individual cases. I will now give an 
account of the observations by which I have been led to this conclusion. I may, 
however, state here that Professor Kuhne has informed me that he has long “ sus¬ 
pected ” the presence of a yellow colouring matter in muscled 
Myohaematin in Arthropods. 
It is now about two and a half years since I discovered a new spectrum in the 
muscles of Ilydrophilus and Dyticus. In these beetles the muscles removed from the 
thorax, which have a reddish-yellow, or yellow colour, give a beautifully defined 
spectrum which is remarkable, in the first place, for the narrowness of its bands, and, in 
the second, from the fact that they differ totally from the bands of any decomposition 
product of haemoglobin. Neither acid nor alkaline haematin, acid or alkaline haemal o- 
porphyrin, nor methasmoglobin, nor hsemochromogen, has the remotest resemblance to 
this pigment with regard to the spectrum. I next found this spectrum in the alar 
muscles of every insect which I examined, and afterwards in the voluntary and heart 
muscles of every vertebrate, it was then systematically traced throughout the whole 
animal kingdom. 
To study the spectrum of myohaematin uninfluenced by the presence of other pig¬ 
ments one has only to open the thorax of the meat-fly (Musca vomitoria), place the 
reddish yellow muscle in the compressorium, throw a good light through the object 
and examine with the miscrospectroscope. On doing this, three bands, two of which 
are of great narrowness, and beautifully sharp, are seen ; the first is placed before the 
* Cf. Gamgee’s ‘ Physiological Chemistry,’ and Kuhne’s ‘ Lehrbnch der physiologischen Chemie.’ 
f It is more correct to describe it as yellowish-red, and a concentrated solution, obtained by a method 
•which I hope to describe shortly, is a red colour. 
