CHEMICAL EXAMINATION OF THE BLOOD. 353 



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. 



Nitric Oxide Haemoglobin. This compound is more stable even 

 than carbon monoxide haemoglobin, and, like this, may be obtained 

 in crystalline form. Its spectrum is similar to that of carbon mon- 

 oxide haemoglobin. The bands, however, are less sharply denned 

 and paler than those of that compound, and, like these, do not dis- 

 appear on the addition of a reducing agent. The substance is met 

 with in poisoning by the gas in question. 



Cyanhsemoglobin. This has been obtained in crystalline form 

 by v. Zeynek ; it contains 1 molecule of hydrocyanic acid or the 

 univalent cyanogen radicle in firm combination. Its toxicity is 

 comparatively slight. 



Sulphohaemoglobin. This is met with in poisoning with hydro- 

 gen sulphide. The blood then becomes dark and of a dull-greenish 

 tint and on spectroscopic examination it shows one band in the green 

 portion and a second one in the orange between C and D. 



Kathaemoglobin. This term has been applied by Van Klaveren 

 to a decomposition-product of haemoglobin which results on boiling 

 a mixture of defibrinated blood with an alcoholic solution of sodium 

 hydrate. Unlike haematin, it is not a decomposition-product that 

 is free from albumin, but is a proteid which is still quite closely 

 related to haemoglobin. Arnold first described this substance as 

 neutral haematin. It contains somewhat less iron than haemoglobin, 

 a portion being split off during its formation as a water-soluble 

 organic compound which escapes on dialysis. 



Methsemoglobin. Methaemoglobin is a pigment which normally 

 does not occur in the blood, but is found after the ingestion of large 

 amounts of potassium chlorate, antifebrin, potassium permanganate, 

 turpentine, kairin, thallin, following the inhalation of nitrite of 

 amyl, ether, etc. It is encountered also in hemorrhagic transudates 

 and cystic fluids, and may occur in the urine when methsemoglobin- 

 aemia exists. 



The elementary composition of methaemoglobin is the same as 

 that of oxyhaemoglobin, but its molecular structure is manifestly 

 different, as in a vacuum it does not give up its oxygen. On 

 treating with reducing agents or on exposure to putrefactive organ- 

 isms, in the absence of oxygen, it is converted into haemoglobin. 

 When oxyhaemoglobin is decomposed with dilute acids or alkalies, 

 methaemoglobin is formed at some stage of the process, and precedes 

 the formation of haematin. During the preservation of oxyhaemo- 

 globin in the dry state, moreover, a partial transformation into 

 methaemoglobin is very likely to occur. The substance is crystal- 



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