ELEMENTS OF COMPOSITION. 51 



crystalline element of the blood. Dried blood, treated with warm acetic 

 acid, even when putrefaction has already set in, deposits regularly innu- 

 merable crystals of brown, dark-brown, or almost black colour, which 

 appear either in the form of rhombic pillars (when they resemble 

 hrematoidm), or in needles, single or arranged in stellate groups (fig. 33.) 

 The presence of chlorides of the alkalies 

 is, as Teichmann very properly remarks, 

 indispensable for the occurrence of this 

 crystallization. Ha3min crystals are 

 tolerably stable, do not decompose in 

 the air, and are neither soluble in water, 

 alcohol, ether, nor in acetic acid. They 

 may be dissolved, however, in boiling 

 nitric acid. Sulphuric acid likewise 

 reduces them readily to solution, as also 

 ammonia and weak potash. The latter, 

 when concentrated, changes the colour 



Of hsemin Crystals to black, Causing Fig. SS.-Crystals of hamiin. 



them at the same time to swell up. These crystals are of the greatest 

 importance in a forensic point of view, as a means of proving the presence 

 of small quantities of blood. Klihne obtained them from the colouring 

 matter of muscle. 



Until a few years ago, the chemical constitution of haemin was but 

 very imperfectly known. We are indebted to Hoppe for the first accu- 

 rate investigations of the subject. By him it was produced from pfce 

 haemoglobin (see above), besides which he demonstrated that it might be 

 again reconverted into ordinary hsematin. 



Hsematoidin, C 17 H 18 U,0 8 , or C 34 H 36 ^T 4 6 (?) 



Blood which has left the vessels, and is stagnating in the tissues, 

 undergoes gradually farther changes, by which a crystalline colour- 

 ing-matter is formed, nearly allied to hsematin, but destitute of iron. 

 This, which is known as hcematoidin, crys- 

 tallizes in rhombic prisms (fig. 34), but 

 also in acicular crystals (Robin). tinder 

 the microscope these appear red with trans- 

 mitted light ; with reflected, of a canthara- 

 dine green colour. Hsematoidin is very 

 soluble in chloroform, to which it communi- 

 cates a golden yellow tint, and also in sul- 

 phide of carbon, which acquires from its 

 presence a flame colour. Its crystals are 

 likewise dissolved by absolute ether, but not 

 by either absolute alcohol, water, ammonia, 

 solution of soda, or dilute acetic acid : in 

 concentrated acetic acid, however, they dis- Fi * 34 - H * matoidin r*"ta. 

 solve when warmed, communicating to the fluid a golden-yellow colour 

 (Holm). 



Staedeler obtained unusually large crystals of this pigment, measuring 

 as much as 0'45nim. from the ovary of the cow, by treatment with chloro- 

 form or sulphide of carbon (fig. 35). They appear under the micro- 

 scope, in the first place, in the form of acute-angled triangular tables with 

 one convex side, a. This curved border, however, may be replaced by 



