BLOOD AND LYMPH. 561 



and has a more violet color. The shade of color naturally varies accord- 

 ing to the ratio of the oxyhemoglobin to the hemoglobin. Hemoglobin 

 is more readily soluble in water, and for this reason more difficult to prepare 

 and maintain in a crystalline form. It may be obtained easily from oxy- 

 hemoglobin by the withdrawal of oxygen, and this may be accomplished 

 by placing the oxyhemoglobin in vacuum, conducting an indifferent gas 

 through its solution, or by the use of a reducing agent. Beautiful crystals 

 of hemoglobin are also obtained by allowing a solution of oxyhemoglobin 

 to stand for some time in a sealed glass tube. 1 The oxygen of the oxy- 

 hemoglobin is gradually consumed, and hemoglobin is formed by the 

 reduction. 



Carbon monoxide 2 may take the place of oxygen in the oxyhemoglobin 

 molecule. It evidently is fastened at the same part of the molecule as the 

 oxygen, for it replaces the latter by its action upon oxyhemoglobin, and 

 makes it incapable of combining with oxygen except in the presence of a 

 large excess of the latter gas. It is herein that the poisonous action of 

 carbon monoxide lies. Carbon-monoxide-hemoglobin can be obtained in a 

 crystalline form, its crystals being isomorphous with those of oxyhemo- 

 globin. Its absorption spectrum is very similar. It also shows two absorp- 

 tion bands, which are, however, nearer the violet end of the spectrum. The. 

 action of reducing agents does not have the effect upon its spectrum that 

 is obtained with oxyhemoglobin. The two absorption bands do not dis- 

 solve into one band, or at least not within a short time. 



Hemoglobin is also capable of combining with nitric oxide, 3 NO, and 

 this last gas is even capable of driving carbon monoxide out of its combina- 

 tion in the blood. Nitric-oxide-hemoglobin is also crystalline and very 

 stable. It shows an absorption spectrum very similar to that of oxy- 

 hemoglobin except that the bands are paler. It is even less affected by 

 reducing agents than is the carbon-monoxide compound. 



The action of hydrogen sulphide 4 upon oxyhemoglobin gives rise first 

 of all to the formation of hemoglobin. Then, little by little, a greenish- 

 black coloration is formed, which reminds one of the appearance of a trace 

 of ferrous sulphide. This green shade is due to the formation of sulph- 

 hemoglobin, which, however, has never been prepared in a pure state. It 

 may be distinguished from hemoglobin by means of its spectral behavior. 



1 G. Hiifner: Z. physiol. 4, 382 (1880). If oxyhemoglobin is allowed to stand for 

 two weeks in a quiet place at 40 C., crystals from 1 to 2 centimeters long can be 

 obtained. 



2 G. Hiifner: Arch. Anat. Physiol. 1895, 209, 213. Hiifner and Kiister: ibid. 1904, 

 387. 



3 L. Hermann: Arch. Anat. Physiol. 1865, 469. Hufner and Reinbold: 1904, 

 Suppl. II, 391. 



4 Hoppe-Seyler: Zentr. Med. Wissensch. 1863, No. 28, p. 433. T. Araki: Z. 

 physiol. chem. 14, 405 (1890). E. Harnack: Ibid. 26, 558, (1898-99). 



