234 HISTOHyEMATINS. 



fineness of the powder. It is a remarkably stable substance ; 

 may be heated to 180 without decomposition, but by stronger 

 heating is finally decomposed, liberates an odour of hydrocyanic 

 acid, and leaves a residue (12'5 p. c.) of pure oxide of iron. It is 

 quite insoluble in either water, alcohol, ether, chloroform, or ben- 

 zol. It is somewhat soluble in strong acetic acid, especially if 

 warm, also in alcohol (not water) to which some acid has been 

 added, and readily soluble in alkaline solutions or in alcohol con- 

 taining alkalis. It is not affected either by strong caustic alkalis 

 even when heated, or by hydrochloric or nitric acids. It may be 

 dissolved in strong sulphuric acid, but is now found to have un- 

 dergone a change during solution which results in the removal of 

 iron and the production of hsematoporphyrin or iron-free hsema- 

 tin J (see below). 



If the decomposition of hsematin by sulphuric acid be brought about 

 in the absence of oxygen an iron-free insoluble substance is obtained 

 known as haematolin, to which the formula C 68 H 78 N 8 7 is assigned. 2 



If potassium cyanide be added to an alkaline solution of hsematin, 

 this now shows one broad absorption band extending from D to E 

 (Hoppe-Seyler). By the action of reducing agents, this band is re- 

 placed by two other bands. 3 The substance to which these appear- 

 ances are due is known as cyan-haematin, but all further information 

 is still wanting. 



Some more recent observers (Nencki and Sieber) have assigned 

 to hsematin the formula CsoHsaN^FeO^ the validity of which as 

 against the views of Hoppe-Seyler is not as yet generally accepted. 

 It will be referred to again under haemin. 



10. Histohaematins. This is the name assigned to a class of 

 pigments which are stated to be of wide-spread occurrence in the 

 tissues of both vertebrates and invertebrates, and to be related to 

 though quite distinct from haemoglobin and haematin. They are 

 regarded as respiratory pigments, playing towards the muscles or 

 other tissues in which they more particularly occur the same part 

 that haemoglobin does to the tissues generally. Our knowledge of 

 these pigments is however as yet limited to the spectroscopic ap- 

 pearances which they present either in situ in the mother-tissue 

 or in solutions obtained by the action of ether, while their respi 

 ratory function is assumed from the changes which they exhibit 

 under the influence of reducing agents and subsequent exposure 

 to oxygen. Of these histohsematins the one most fully de- 

 scribed is known as myohaematin from its characteristic presence 

 in muscles. 



1 The haematoin of Preyer. See " Die Blutkrystalle," 1871, S. 178. 



2 Hoppe-Seyler, Med.-chem. Unters. 1871, Hf. 4, S. 533. Cf. Nencki u. Sieber, 

 Bar. d. d. chem. Gesell. Bd. xvii. (1884), S. 2272. 



3 See Gamgee, Physiol. Chem. Vol. i. p. 115. 



