108 



PHYSIOLOGY 



CHAP. 



FIG. 33. Haeiuiu crystals. (Preyer.) 



permanganate of potash, potassium ferricyanide, active oxygen, 

 hydrogen peroxide, etc., haemoglobin is converted into methaemo- 

 globin, which is an isomer of oxy haemoglobin, but in which the 

 oxygen is more closely combined, so that it cannot be driven out 

 by the unaided vacuum. Methaemoglobin can also be formed jn 



circulating blood by the excessive 

 use of chlorate of potash and 

 other substances used in medicine 

 in recent years as antipyretics. 



Haemoglobin undergoes spon- 

 taneous decomposition slowly 

 under the influence of air and 

 water, rapidly as the effect of 

 acids or alkalies, or of heating. 

 Another iron -containing pigment 

 is thus formed, haemochromogen, 

 which oxidises readily in the 

 presence of oxygen and is con- 

 verted into haematin, which gives 

 a brownish colour to the solution. 

 Along with haernochrornogen and 

 haematin, the decomposition of haemoglobin gives rise to con- 

 siderable quantities of acid or alkali albumin, according as acids 

 or alkalies are used to break up the blood pigment. From these 

 facts Hoppe-Seyler regards haemoglobin as a protein, which con- 

 sists of an albumin, associated 

 with an iron-containing pigment, 

 haemochromogen. One hundred 

 parts of haemoglobin contain 

 ninety-six parts albumin and four 

 parts pigment. Haemin must 

 be noted among the decomposi- 

 tion products of blood pigment on 

 account of its great practical im- 

 portance ; it crystallises in the 

 form of small rhombic plates or 

 rods, of a shining brown colour 

 (Pig. 33). Haemin crystals are 

 of great importance in forensic 



medicine, in the detection Of FK , 3 4.-Haematoidin crystals. (V. Frey.) 



blood-stains. A trace of dried 



blood suffices to obtain them. A grain of sodium chloride is- 

 added, dissolved in a few drops of glacial acetic acid, and cautiously 

 heated over a spirit lamp until gas bubbles are formed. 



Haemin is haematin hydrochloride, and to obtain pure haematin 

 it is necessary to start from this combination. It is a sulphur-free 

 compound, but is richer in iron than haemoglobin. When treated 



