THE RED BLOOD-CORPUSCLES 935 



solutions diluted so that there is only one part of the pigment in 

 25,000 parts of water, so that the formation of reduced alkaline 

 haematin is an even more delicate test for blood than the spectrum of 

 oxyhaemoglobin itself. When CO -haemoglobin is treated in the same 

 way with alkali in the absence of oxygen, a body CO -haemochromogen 

 is formed which contains exactly the same volume of CO in combina- 

 tion as the original CO-haemoglobin. This fact, combined with the 

 possibility of reducing ordinary alkaline haematin by the action of 

 ammonium sulphide or Stokes's fluid, indicates that the group of 

 atoms which in haemoglobin is responsible for taking up oxygen or 

 carbon monoxide gas passes unchanged into the haemochromogen 

 molecule. Haemochromogen therefore represents an iron-containing 

 coloured radical which can combine with protein bodies to form 

 haemoglobin, and is responsible for the oxygen-combining powers of 

 the latter. We may assume therefore that oxy haemoglobin and 

 CO -haemoglobin contain oxyhaemochromogen and CO -haemochromogen 

 respectively. 



Hcematoporphyrin. If haemoglobin, haematin, or haemin be mixed 

 with concentrated sulphuric acid, it dissolves forming a purple-red 

 solution. On pouring this solution into a large quantity of water, 

 haematoporphyrin is thrown down in the form of a brown precipitate. 

 In order to prepare haematoporphyrin, pure crystallised haemin is added 

 to a saturated solution of hydrobromic acid in glacial acetic acid. The 

 whole is allowed to stand for three or four days and then thrown down 

 into distilled water. The resulting mixture is filtered and the haemato- 

 porphyrin thrown down by careful neutralisation of the hydrobromic 

 acid with caustic soda. Haematoporphyrin is easily soluble in alkalies 

 and somewhat less readily so in acids, forming alkaline and acid 

 haematoporphyrin respectively. The formula of haematoporphyrin has 

 been given by Nencki and Sieber as C 16 H 18 N 2 3 , and is according to 

 them isomeric with the chief bile-pigment, bilirubin. According to 

 Zaleski its formula is C 34 H 38 N 4 6 = 2C 17 H 19 N 2 3 . An alcoholic 

 solution of haematoporphyrin acidulated with hydrochloric acid shows 

 two absorption bands : one, the fainter, between C and D, and the 

 other, broader and more defined, midway between D and E. Solutions 

 of alkaline haematoporphyrin show four absorption bands : a weak 

 band between C and D, another between D and E, a more strongly 

 marked band nearer to E, and a fourth band, darkest of all, between 

 band F. It will be observed that in the formation of haematoporphyrin 

 from haematin the iron of the latter has been split off by the action of 

 the strong acid. Laidlaw has found that the splitting off of iron occurs 

 much more readily in the absence of oxygen. If reduced haemoglobin 

 be taken, or defibrinated blood which has been allowed to stand until 

 it is thoroughly reduced, it is sufficient to add 15 per cent, hydrochloric 



