352 THE BLOOD. 



ometer of Sahli. 1 In the first the color of the blood is compared 

 with that of a glass wedge that has been stained with the golden 

 purple of Cassius. The same principle holds good for the second. 

 In the third a standard solution of hsematin hydrochlorate is 

 employed. 



The spectro-photometric determination of the blood coloring- 

 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 we have 

 just considered the most important of these compounds. Others 

 are carbohsemoglobin, carbon monoxide haemoglobin, nitric oxide 

 haemoglobin, sulphohaemoglobin, and cyanhaemoglobin. 



Carbohaemoglobin. Three different forms are said to exist, 

 which have been respectively termed a, /5, and 7- carbohcemoglobin, 

 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 oxyhaemoglobin 

 is combined with the pigmented group. He accordingly finds that 

 when a solution of haemoglobin is shaken with a mixture of oxy- 

 gen and carbon dioxide both of these gases are taken up indepen- 

 dently of each other. 



Carbon Monoxide Haemoglobin. This compound results from 

 the union of one molecule haemoglobin with one molecule of carbon 

 monoxide, and is characterized by its greater stability as compared 

 with oxyhaemoglobin. The carbon monoxide is in this case united 

 with the pigment radicle of the haemoglobin at the same point 

 where oxygen usually enters, and may be split off in this combina- 

 tion as carbon monoxide haemochromogen. Like the native haemo- 

 chromogen, 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 haemoglobin com- 

 pound 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. 



1 For a description of these, see Simon's Clinical Diagnosis, Lea Bros., 6th edition. 



