468 CHEMISTRY OF THE PROTEIDS CHAP. 



are converted into coloured compounds by the haemoglobin. This 

 test in the absence of other indirectly oxidising media is better than 

 is the guaicum test. 



For blood pigment Eiegler l has devised the following hydrazin- 

 reagent : 



Dissolve NaOH . . .10 grammes 



In water. . . 100 cc. 



Add hydrazin-sulphate . . 5 grammes 



Alcohol 96-97 per cent . . 100 cc. 



Shake vigorously and filter after 2 hours. 



0'05 grs. commercial haemoglobin or J cc. of blood + 30 cc. of 

 reagent when shaken and allowed to stand shows the beautiful purple 

 colour of haemochromogen. When shaken with air the solution turns 

 green owing to the formation of haematin ; on standing a reconversion 

 into haemochromogen takes place. 



Haemoglobin is composed of a histone-like, basic, albuminous radical 

 called globin, and a non-albuminous, acid moiety, containing iron, which 

 is termed haematin. See chart on p. 465. Haemoglobin is character- 

 ised by combining with oxygen, carbon dioxide, carbon monoxide, and 

 perhaps with other gases, to form the loose, chemical compounds of 

 oxy haemoglobin, carbonic acid haemoglobin, carbonic oxide haemoglobin, 

 etc. Amongst these the most important is oxyhaemoglobin, as respira- 

 tion depends on it. According to Cohnheim oxyhaemoglobin is called 

 in Germany simply ' haemoglobin,' while in this country the reduced 

 haemoglobin is called haemoglobin. Most of the chemical investigations 

 and most of the analyses have been made with oxyhaemoglobin, as this 

 compound crystallises more readily than does reduced haemoglobin, and 

 as the latter by absorption of oxygen is constantly changed into the 

 former. Owing to the gigantic size of the haemoglobin molecule, no 

 difference in the analyses of oxy- and reduced haemoglobin can be 

 made out. The double method of estimating the molecular weight of 

 haemoglobin has already been discussed on p. 328. Jaquet's 2 calcula- 

 tions based on the figures yielded by analysis have led to the same 

 conclusion as have those of Hiifner, 3 who estimated the power haemo- 

 globin possesses of binding gases : the molecular weight of haemoglobin 

 is 16669. 



1 E. Eiegler, Zeitschr. f. analyt. Chem. 43. 539 (1904). 



2 A. Jaquet, Zeitschr. f. physiol Chem. 14. 289 (1889). 



3 G. Hiifner, Arch.f. (Anat. und) Physiol 1894, p. 130. 



