THE BLOOD. 163 



Hcematin in acid solution. If an excess of acetic acid is added to 

 blood, and the solution is boiled, the color alters to brown from decom- 

 position of haemoglobin and the setting free of haematin ; by shaking 

 this solution with ether, a solution of haematin in acid solution is obtained. 

 The spectrum of the ethereal solution (colored plate) shows no less than 

 four absorption bands, viz., one in the red between c and D, one faint 

 and narrow close to D and then two broader bands, one between D and 

 E, and another nearly midway between b and F. The first band is by 

 far the most distinct, and the acid aqueous solution of haematin shows 

 it plainly. 



Hcematin in alkaline solution. If a caustic alkali is added to blood 

 and the solution is boiled, alkaline haematin is produced, and the solu- 

 tion becomes olive green in color. The absorption band of the new 

 compound is in the red, near to D, and the blue end of the spectrum is 



* 



* 



Fig. 139. Haematoidin crystals. (Frey.) Fig. 140. Hsemin crystals. (Frey.) 



absorbed to a considerable extent. If a reducing agent be added, two 

 bands resembling those of oxy-haemoglobin, but nearer to the blue, ap- 

 pear; this is the spectrum of reduced hcematin, or haemochromogen. 

 On violently shaking the reduced hasmatin with air or oxygen the two 

 bands are replaced by the single band of alkaline haematin. 



Hsematoidin. This substance is found in the form of yellowish 

 crystals (fig. 139) in old blood extravasations and is derived from the 

 haemoglobin. Their crystalline form and the reaction they give with 

 fuming nitric acid seem to show them to be closely allied to BiliruUn, 

 the chief coloring matter of the bile, and in composition they are prob- 

 ably either identical or isomeric with it. 



Haemin. One of the most important derivatives of haematin is 

 haemin. It is usually called Hydrochlorate of Hwmatin (or hydrochlor- 

 ide), but its exact chemical composition is uncertain. Its formula is 

 said to be C 32 H 30 N.Fe0 3 HCl, and it contains 5.18 per cent of chlorine, 

 but by some it is looked upon as simply crystallized haematin. Al- 

 though difficult to obtain in bulk, a specimen may be easily made for 

 the microscope in the following way: A small drop of dried blood 'is 

 finely powdered with a few crystals of common salt on a glass slide and 



