1298 H^MATIN — HISTOH^MATIK 



blood or a strong solution of oxy-haemoglobin be made strongly 

 acid by the addition of acetic acid the haemoglobin is decom- 

 posed, haematin is set free, and if the solution be shaken up 

 with ether and allowed to stand, the ether rises to the surface 

 and is more or less coloured owing to the presence of haematin 

 held in solution in the acid ether. This acid ethereal solution 

 shews, in addition to the one band already described as char- 

 acteristic of hsematin in an acid solution, three other bands 

 whose positions and relative intensities are sufficiently shewn 

 in Fig. 90, No. 6. Solutions of hsematin in an alkali shew no 

 definite absorption band in the extreme violet. In acids, or 

 with its acid compounds, a strongly marked band may be seen 

 between h and L. 



Pure hsematin is a scaly but not crystalline mass of bluish- 

 black colour and 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 sub- 

 stance ; may be heated to 180° without decomposition, but by 

 stronger heating, if 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 benzene. 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 solu- 

 tions 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. 



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 hsematolin, to which the formula CesHygXgO; is 

 assigned. 



If potassium cyanide be added to an alkaline solution of haema- 

 tin, this now shews one broad absorption band extending from D to 

 E. By the action of reducing agents, this band is replaced by two 

 other bands. The substance to which these appearances are due is 

 known as cyan-haematin, but all further information is still wanting. 



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 

 \)ccur the same part that haemoglobin does to the tissues gen- 

 erally. Our knowledge of these pigments is however as yet 



