330 THE BLOOD. 



hcemochromogen (see below), while the albuminous substance is 

 known as globin. These two substances are apparently united in 

 the haemoglobin molecule, through an additional radicle, which is as 

 vet unknown. 



d'lobin, is closely related to histon, and, like it, presents the fol- 

 lowing characteristic reactions : it is precipitated by ammonia from 

 its solutions in dilute hydrochloric acid, and is insoluble in an excess 

 of the reagent. With concentrated nitric acid it is thrown down in 

 the cold, but not from its heated solutions. Under certain condi- 

 tions it can be coagulated on boiling, but, unlike the other coagula- 

 ble albumins, its coagulate is readily soluble in acids. It contains 

 54.97 per cent, of carbon, 7.2 per cent, of hydrogen, 16.89 per cent, 

 of nitrogen, and 0.42 per cent, of sulphur. The amount of globin 

 which can be obtained from the haemoglobin molecule is quite large, 

 and according to Schultz amounts to 86.5 per cent., while 4.2 per 

 cent, only is represented by the pigment itself. 



Isolation. A solution of oxyhaemoglobin in water, prepared at 

 a temperature of 40 C., is treated with dilute hydrochloric acid 

 until the red color changes to brown. This mixture is extracted 

 with 80 per cent, alcohol (one-fifth volume) and ether (one-half 

 volume) until the ether takes up no more coloring-matter. The 

 resulting aqueous-alcoholic solution is precipitated with ammonia, 

 filtered, and the precipitate dissolved in very dilute acetic acid. On 

 filtering, the globin is again precipitated with ammonia and col- 

 lected on a silk filter. After washing with absolute alcohol, then 

 with water, again with alcohol, and finally with ether, the substance 

 is dried first in the air and then at a temperature of 100 C. The 

 resulting material constitutes pure globin, as a yellowish loose 

 powder, which is not especially hygroscopic. 



Hsemochromogen. The isolation of haemochromogen is rather 

 difficult, owing to the avidity with which it combines with oxygen to 

 form hcematin in alkaline solution. Hoppe-Seyler, however, suc- 

 ceeded in obtaining the substance in crystalline form, by heating 

 hemoglobin with sodium hydrate solution in an atmosphere of hy- 

 drogen. In acid solutions haemochromogen gradually loses its iron 

 and is converted into hcematoporphyrin. In alkaline solution it 

 presents a beautiful cherry-red color, and on spectroscopic examina- 

 tion gives two bands of absorption. One of these is very intense, 

 and located between D and E, nearer D, while the other is not so 

 dark, but wider, and found about E and extending beyond b. To 

 demonstrate the spectrum of haemochromogen, bloody fluid is mixed 

 with a solution of sodium hydrate, when the resulting haematin is 

 reduced with ammonium sulphide, or Stokes reagent, viz., an am- 

 moniacal solution of ferrous tartrate, or stannous chloride. 



The haemochromogen radicle, as has been stated, represents the 

 pigmented group of the haemoglobin molecule, and to its presence 

 the power of haemoglobin to combine with oxygen, carbon dioxide, 

 and other gases, is unquestionably due. 



