CHEMICAL EXAMINATION OF THE BLOOD. 335 



matter is not described at this place. It is undoubtedly the most 

 exact, but necessitates the use of costly apparatus, which will be 

 found in only few laboratories. 



It has been pointed out that haemoglobin is characterized by the 

 readiness with which it combines with certain gases, and w r e have 

 just considered the most important of these compounds. Other 

 compounds of this character are carbon dioxide haemoglobin, carbon 

 monoxide haemoglobin, and nitric oxide haemoglobin. 



Carbon Dioxide Haemoglobin. Three different forms are said to 

 exist, which have been respectively termed , /9, and f carbohcemo- 

 globin, but they are comparatively little known. According to 

 Bohr, the carbon dioxide in these compounds is united with the 

 albuminous radicle of the haemoglobin, while the oxygen of oxy- 

 haemoglobin is combined with the pigmented group. He accordingly 

 finds that when a solution of haemoglobin is shaken with a mixture 

 of oxygen and carbon dioxide both of these gases are taken up inde- 

 pendently of each other. 



Carbon Monoxide Haemoglobin. This compound results from 

 the union of one molecule of haemoglobin with one molecule of carbon 

 monoxide, and is characterized by its greater stability as compared 

 with oxy haemoglobin. The carbon monoxide is in this case united 

 with the pigmented radicle of the haemoglobin, and may be split off 

 in this combination as carbon monoxide haemochromogen. Like the 

 native haemochromogen, the carbon monoxide compound can be 

 obtained in crystalline form, and on exposure to the air is likewise 

 transformed into haematin. Under the same conditions the haemo- 

 globin compound is gradually reconverted into oxyhaemoglobin. 



Blood containing carbon monoxide haemoglobin is characterized 

 by its cherry-red color, its resistance to putrefactive changes in the 

 absence of oxygen, and by its spectrum. This is similar to that of 

 oxyhaemoglobin, but its two bands of absorption, between D and E, 

 are placed rather nearer the violet end of the spectrum. Unlike the 

 spectrum of oxyhaemoglobin, however, that of the carbon monoxide 

 compound is not changed to the haemoglobin spectrum on treating 

 with reducing agents. Should oxyhaemoglobin be simultaneously 

 present, a mixed spectrum of the two substances is obtained. 



Such blood, moreover, when treated with double its volume of a 

 solution of sodium hydrate (sp. gr. 1.3), is not changed to a dirty 

 brownish mass, with a tint of green, as with normal blood, but 

 presents a beautiful red color, which changes to brown only on 

 standing. 



In its crystalline state carbon monoxide haemoglobin may be 

 obtained by saturating a sufficiently concentrated solution with car- 

 bon monoxide and cooling the mixture to C., when one-fourth of 

 its volume of cooled alcohol is added. On standing in the refrigera- 

 tor the substance separates out in the form of bluish-red crystals, 

 which are isomorphous with those of oxyhaemoglobin, but much 

 more stable. 



