196 THE BLOOD. 



the Blood. Proceedings of the Roy. Soc., vol. xiii. p. 355.] 

 The same facts can be demonstrated quite as advantageously, 

 and perhaps with greater ease, if the solution of the sulphhy- 

 drate of ammonium is substituted for the solution of sulphate 

 of iron used by Stokes. The change is, however, not so rapid: 

 it is accelerated by subjecting the liquid to a temperature of 

 40 C. 



19. Methaemoglobin. If a pure solution of ha3inaglobin 

 is left to itself at the ordinary temperature, it gradually loses 

 its brightness, and if it is then examined spectroscopically, it 

 is seen that a new band has appeared iu the orange at a point 

 where in ordinary blood there is least absorption. This band 

 is due to the presence of a new coloring matter, called by 

 Hoppe-Seyler methaemoglobin. The same change occurs under 

 other circumstances, e. (/., when carbonic acid gas is passed 

 through dilute solutions of hcemaglobin, or when glacial acetic 

 acid is added to dilute solution of defibrinated ox-blood, in ex- 

 tremely small quantity. [In larger proportions, acetic acid 

 determines the formation of hrematon. See 22.] Hemoglo- 

 bin undergoes the same transformation when acted on by per- 

 manganate of potash. If a crystal of pure permanganate is 

 dissolved in distilled water, and the solution added to very 

 dilute solution of blood, before the slit of the spectroscope, at 

 a temperature of about 25 C., the haemoglobin bands gradu- 

 ally disappear. In their place we have a spectrum, in which 

 there are not only the band mentioned above, but two others, 

 of which one nearly corresponds in position to the second hae- 

 moglobin band, while the other lies half way between the lines 

 E and F. Methaemoglobin is a substance of which the chemi- 

 cal constitution and relations are imperfectly ascertained. Its 

 presence is indicated spectroscopically in all collections of 

 blood which have been for some time extra vasated within the 

 body, e. (/., in thrombi, sanguinolent transudation liquids, etc. 



20. Preparation of the Crystalline Coloring Matters 

 which result from the Decomposition of Haemoglo- 

 bin, and Demonstration of their Absorption Spectra. 

 Hsemin. When dried blood is treated with glacial acetic acid 

 and warmed to the temperature of the body, a solution is ob- 

 tained which yields crystals of a new coloring matter, of re- 

 markable properties, which has been designated hamiin. The 

 crystals vary extremely in shape, sometimes occurring as 

 rhombic plates, sometimes as rods crossing each other at vari- 

 ous angles. They are not soluble without decomposition in 

 an}' liquid excepting hydrochloric acid, and are so little liable 

 to chemical change that they may be kept for years, exposed 

 to a moist atmosphere, without undergoing any change. Ilae- 

 min differs from haemal in ( 21) in containing an additional 

 equivalent of hydrochloric acid, on which account it is also 



