CHEMICAL EXAMINATION OF THE BLOOD. 347 



haemoglobin. Its solutions present a beautiful purplish-red color, 

 and on spectroscopic examination give rise to a single band of 

 absorption, which lies between D and E and extends slightly to the 

 left beyond D. This is most conveniently shown by taking a solu- 

 tion of oxyhemoglobin, and reducing this with ammonium sulphide 

 or Stokes' fluid, as directed above. 



Most important is the avidity with which haemoglobin combines 

 with various gases, and upon this characteristic indeed its chief 

 function, as a respiratory pigment, is based. This property, as has 

 been stated, is referable to the chromogen radicle, and more partic- 

 ularly to the iron, which it contains. Every atom of this is capable 

 of combining with one molecule of oxygen or of carbon dioxide, 

 and in this form largely the oxygen of the air is carried to the vari- 

 ous tissues of the body, and the carbon dioxide removed. In the 

 circulating blood we accordingly find only relatively small amounts 

 of free hemoglobin, and in arterial blood its oxy-compound is 

 almost exclusively encountered. 



The amount of hemoglobin which is contained in human blood, 

 either as such or in combination with oxygen or carbon dioxide, is 

 about 14 per cent., but subject to certain variations, even in health, 

 while in disease still greater deviations from the average normal 

 amount are observed. A great diminution may here occur, and is 

 most marked in chlorosis and pernicious anaemia, in which the per- 

 centage may fall as low as 2.35. 



As the isolation of the hemoglobin from the blood resolves 

 itself into the isolation of its oxy-compound, this will be considered 

 together with its quantitative estimation under that heading. 



Oxyhaemoglobin. Oxyhemoglobin is the oxy-compound of hemo- 

 globin, and differs from its mother-substance in containing two 

 atoms more of oxygen, which are bound to the one atom of iron, 

 than are present in the hemochromogen radicle. In this manner, 

 however, the hemochromogen is converted into hematin, and we 

 may therefore say that oxyhemoglobin, in contradistinction to 

 hemoglobin, consists of the globin radicle united by some unknown 

 group to a hematin radicle. 



Hsematin. In accordance with the above considerations, we 

 find that on decomposition of oxyhemoglobin hematin is obtained 

 instead of hemochromogen. This latter, indeed, is at once trans- 

 formed into hematin on exposure to oxygen, and, as we have seen, 

 the hematin is correspondingly reconverted into hemochromogen by 

 treating with reducing agents. The decomposition of oxyhemo- 

 globin with the formation of hematin can be readily effected by 

 heating its solutions to a temperature of 80 C., by treating with 

 dilute mineral acids, or with stronger solutions of the alkaline 

 hydrates, as also by peptic or tryptic digestion. To obtain the 

 substance in a pure state, however, it is best to start with hcemin 

 (see below), which can be readily obtained in crystalline form. 

 To this end, oxyhemoglobin is treated with a trace of sodium 



