THE BLOOD. 



159 



This change may be also effected by passing through the solution of 

 blood or of oxy-haemoglobin, hydrogen or nitrogen gas, or by the action 

 of reducing agents, of which Stokes's fluid * or ammonium sulphide are 

 the most convenient. 



With the spectroscope, a solution of deoxidized or reduced hcemogloUn 

 is found to give an entirely different appearance from that of oxidized 

 haemoglobin. Instead of the two bands at D and E we find a single 

 broader but fainter band occupying a position midway between the two, 

 and at the same time less of the blue end of the spectrum is absorbed. 

 Even in strong solutions this latter appearance is found, thereby differ- 

 ing from the strong solution of oxidized haemoglobin which lets through 

 only the red and orange rays; accordingly to the naked eye the one 

 (reduced haemoglobin solution) appears purple, the other (oxy-haemoglo- 



Fig. 137. Hexagonal oxy-hsemoglobin crystals, from blood of squirrel. On these hexagonal platea 

 prismatic crystals grouped in a stellate manner not unfrequently occur (after Funke). 



bin solution) red. The deoxidized crystals or their solutions quickly 

 absorb oxygen on exposure to the air, becoming scarlet. If solutions 

 of blood be taken instead of solutions of haemoglobin, results similar to 

 the whole of the foregoing can be obtained. 



Venous blood never, except in the last stages of asphyxia, fails to 

 show the oxy-haemogiobin bands, inasmuch as the greater part of the 

 haemoglobin even in venous blood exists in the more highly oxidized con- 

 dition. 



Action of Gases on Haemoglobin. Carbonic oxide gas, passed 

 through a solution of haemoglobin, causes it to assume a cherry-red color, 



* Stokes' s Fluid consists of a solution of ferrous sulphate, to which ammonia 

 has been added and sufficient tartaric acid to prevent precipitation. Another 

 reducing agent is a solution of stannous chloride, treated in a way similar to 

 the ferrous sulphate, and a third reagent of like nature is an aqueous solution 

 of yellow ammonium sulphide, NH 4 HS, 



