1290 HEMOGLOBIN. 



THE COLOURING MATTERS AND PIGMENTS OF 

 THE ANIMAL BODY. 



HEMOGLOBIN AND ITS DERIVATIVES. 1 



1. Haemoglobin. 2 This is the well-known constituent of 

 the red corpuscles to which the dark colour of the blood from 

 an asphyxiated animal is due. It is also present to a less and 

 somewhat variable amount in ordinary venous blood, in pres- 

 ence of correspondingly variable amounts of the compound 

 which it forms with oxygen, namely ox}'-haemoglobin. In 

 normal arterial blood it is probably present in mere traces, if at 

 all, since here its affinities for oxygen are completely satisfied 

 to form oxy-haemoglobin. 



Owing to the ease and avidity with which haemoglobin 

 unites with oxygen to form the distinct and stable compound 

 known as oxy-haemoglobin, its investigation is attended with 

 considerable experimental difficulties, hence our knowledge of 

 it as a chemical substance is on the whole less complete than 

 is that of oxy-haemoglobin. Haemoglobin may be obtained 

 in a crystalline form, but with some considerable difficulty 

 owing to its extreme solubility in water. The crystals may 

 be prepared by sealing up a concentrated aqueous solution of 

 oxy-ha3inoglobin in glass tubes from which, if necessaiy, all 

 remaining air is displaced by hydrogen : on prolonged standing 

 all the oxygen disappears during the putrefactive reduction 

 which ensues, and finally, more readily on exposure to a low 

 temperature, crystals of haemoglobin make their appearance in 

 the fluid. A similar production and formation of crystals is 

 frequently observed when crystals of oxy-haemoglobin are sealed 

 up with Canada balsam under a cover-slip and kept for some 

 time. The form of the crystals obtained from the blood of 

 different animals has not yet been fully investigated. 



As ordinarily seen the crystals of haemoglobin have a dark 

 red appearance, unlike the bright scarlet of oxy-haemoglobin, 

 with a strong purple or bluish tint. They are extremely soluble 

 in water, much more so than the crystals of oxy-haemoglobin. 



In addition to the absorption band ordinarily described for 

 haemoglobin, it also shows one in the extreme violet end of 

 the spectrum between Cr and I£, its centre corresponding to 

 w. L. 426. 



1 The more important characteristics and properties of these substances have 

 been previously described in some detail (§ 275 to § 282) and may therefore be 

 here dealt with very briefly. 



2 The single name haemoglobin is used here to denote what is more fre- 

 quently and usually called ' reduced ' haemoglobin, as distinct from oxy-hsemo- 

 globin. The adoption of the name as here used is both simpler and more logical. 



