CHEMICAL BASIS OF THE ANIMAL BODY. 235 



metallic lustre, strongly resembling iodine. When finely powdered it 

 appears dark or light brown according to the 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 benzol. 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 

 containing 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 undergone 

 a change during solution which results in the removal of iron and 

 the production of haematoporphyrin or iron-free haematin 1 (see below). 



If the decomposition of haematin 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 hasmatin, this now shows 

 one broad absorption band extending from D to E (Hoppe-Seyler). By the action 

 of reducing agents, this band is replaced by two other bands 3 . The substance to 

 which these appearances are due is known as cyan-hasmatin, but all further 

 information is still wanting. 



Some more recent observers (Nencki and Sieber) have assigned to 

 haematin the formula C 32 H 32 N 4 Fe04., 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 re- 

 spiratory 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 appearances which they present either 

 in situ in the mother-tissue or in solutions obtained by the action of 

 ether, while their respiratory function is assumed from the changes 

 which they exhibit under the influence of reducing agents and 

 subsequent exposure to oxygen. Of these histohaematins the one 

 most fully described is known as myohaematin from its characteristic 

 presence in muscles. 



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



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

 Ber. d. d. chem. GeselL Bd. xvn. (1884), S. 2272. 



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



