278 Absorption of Violet Rays by Hwmoglobin, §c. [Feb. 13, 



As Soret bad indicated, in the case of the compound of carbonic 

 oxide with haemoglobin, the absorption band is slightly displaced 

 towards the less refrangible end of the spectrum. The combination 

 of haemoglobin with nitric oxide presents an absorption band occupy- 

 ing precisely the position of that of the CO-compound. 



In the case of these two compounds, the mean ray absorbed corre- 

 sponds to A, 420' 5. 



II. When the molecule of dissociable oxygen is removed from oxy- 

 hemoglobin, either by the action of reducing agents, or by boiling 

 in vacuo, the absorption band in the extreme violet is remarkably dis- 

 placed towards the less refrangible end of the spectrum, the centre 

 of absorption corresponding to A, 426'0. When we reflect that the 

 addition of a molecule of oxygen to the enormous molecule of haemo- 

 globin cannot affect in an appreciable manner the mass of the mole- 

 cule, we must conclude that the displacement of the absorption band 

 towards the ultra-violet end when haemoglobin combines with oxygen 

 (all other conditions remaining the same), indicates that this com- 

 bination leads to a notable acceleration of the intra-molecular move- 

 ment, which is the cause of the absorption of the extreme violet rays 

 by haemoglobin. 



III. The absorption of the extreme violet depends on the iron-con- 

 taining moiety of the haemoglobin molecule, for, whereas it is not 

 presented by the albuminous product of the decomposition of the 

 blood- colouring matter, it is characteristic of the acid compounds of 

 haematin and of haemochromogen. 



IV. Solutions of alkaline haematin, even when enormously diluted 

 (1:30,000 of water), exert a general absorption of the ultra-violet 

 and extreme violet, but present no- trace of definite absorption, 

 either in the extreme violet or the adjacent ultra-violet region. 



The compounds of haematin with acids, e.g., haematin hydrochloride, 

 present even in solutions of great dilution (1 : 25,000 — 1 : 50,000) an 

 intense absorption band, which encroaches more and more on the 

 ultra-violet as the strength of the solution increases. In a solution 

 containing one part of crystallised haematin hydrochloride in 20,000 

 parts of glacial acetic acid the band extends between h and M, the 

 most intense absorption being between h and L. The less refrangible 

 border of this band is sharply defined, whilst the more refrangible 

 border is less definite. As the solution is diluted, the band becomes 

 narrower, through less and less of the ultra-violet being absorbed. 

 In highly dilute solutions the band which is still intense absorbs both 

 H and K. 



The acid compounds of haematin exhibit, therefore, an absorption 

 band, which is exactly on the boundary of the ultra-violet proper, 

 and which extends further and further into the ultra-violet as the 

 concentration of the solution increases. 



