CHEMICAL EXAMINATION OF THE BLOOD. 331 



Haemoglobin itself can be obtained in crystalline form, and is 

 characterized by the great resistance which it offers to putrefaction 

 and tryptic decomposition. It is stated that even after the lapse of 

 years decomposed blood contains its haemoglobin as such, and that 

 on shaking with air it may again be transformed into pure oxy- 

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

 and on spectroscopic examination gives 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 Oxyhaemoglobin, 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 haemoglobin, and in arterial blood its oxy-compound is 

 almost exclusively encountered. 



The amount of haemoglobin 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 haemoglobin 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. Oxyhaemoglobin is the oxy-compound of haemo- 

 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 haemochromogen radicle. In this manner, 

 however, the haemochromogen is converted into haematin, and we 

 may therefore say that Oxyhaemoglobin, in contradistinction to 

 haemoglobin, consists of the globin radicle united by some unknown 

 group to a haematin radicle (see also page 333). 



Haematin. In accordance with the above considerations, we 

 find that on decomposition of Oxyhaemoglobin haematin is obtained 

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

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

 the haematin is correspondingly reconverted into haemochromogen by 

 treating with reducing agents. The decomposition of Oxyhaemo- 

 globin with the formation of haematin can be readily effected by 

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



