294 DR. C. A. MAC MUNN ON MYOHSEMATIN AND THE HISTOHH3MATINS. 
derivative of the histohaematins, for in Uraster besides the lipoohromes and entei’o- 
chlorophyll, these are its only available source. This haematoporphyrin is nearly 
related to the urohse matin found in Addison’s disease, as I have already stated. 
Hasmatoporphyrin also occurs (as I have shown) in the integument of Limcix and 
Avion* and in their bodies again it is probably derived from the histohaematins and 
possibly from enterohsematin. Enterohsematin presents same remarkable resemblance 
to myohsematin. (1) Neither can be converted into all the decomposition products of 
haemoglobin. (2) Both are composed of a proteid and colouring matter united together. 
(3) In both acids cause the bands to disappear. (4) In both potassium hydroxide and 
sodium hydroxide intensify the bands. (5) In both the banded condition belongs to 
the reduced state and the bandless to the oxidised. Again myohsematin can be 
changed into a body which closely resembles (in its spectrum) enterohsematin. Hence 
in saying that enterohsematin may be the mother-substance of the integumental 
hsematoporphyrin, is practically the same as saying that it may be derived from the 
histohsematins. 
I have endeavoured to find out if anything like myohsematin could be prepared 
from any of the decomposition products of hsemoglobin, but without any definite 
result. In a solution of alkaline hsematoporphyrin (in rectified spirit and ammonia) a 
change took place spontaneously, after the solution had been shut up from air and 
light for some months; the four-banded spectrum disappeared and could not be 
regenerated, and in its place 1 observed some narrow bands closely resembling those 
of myohsematin, but placed much nearer the red end of the spectrum. They were 
narrower than those of any other decomposition product of hsemoglobin, but the 
solubility of the pigment and its refusal to be reduced, showed that it was not 
myohsematin. Acting on this hint, I tried the effect of various oxidising and reducing 
agents on hsematin and hsematoporphyrin, but no myohsematin-like spectrum could 
be obtained ; but it is probable that myohsematin is much nearer to hsemoglobin than 
to hsematoporphyrin, and the above may be an accidental resemblance. 
The Function of the Histohcematins and Myohcematin. 
I need not repeat the results obtained by the action of oxidising and reducing 
agents on these pigments, it will suffice to say that they are capable of oxidation and 
reduction, and are hence respiratory. Just as in Actinice —as I have shown in a former 
paper,—actiniohsematin is concerned in the respiration of the tissues, so these pigments 
are sdso concerned in it. They combine with the oxygen conveyed to them in the 
blood, and hold it for purposes of metabolism, parting with the carbon dioxide in ex¬ 
change for the oxygen. This is the only conclusion which anyone who has gone over 
the same ground can come to. These observations appear to me to point to the fact 
that the formation of C0 2 and the absorption of oxygen takes place in the tissues 
themselves (Peluger and Oertmann) and not in the blood. Hence these obser- 
*Proc. Birm. Phil. Soc., vol. iii., pp. 351-407; Journ. Physiol., vol. vi., pp. 22-39, and vol. vii., 
pp. 240 et seq. 
