234 
HAEMOGLOBIN. 
But these total reflections do go on in the case of the actual coloured 
corpuscles in a precisely similar manner to that which would occur in 
the hypothetical case just discussed ; and the light reflected by them 
is conditioned by, and corresponds to, the absorption of the spectral 
colours exerted by the haemoglobin and the oxyhemoglobin respectively. 
The visible spectrum of reduced haemoglobin. — It has already 
been stated that, when a solution of oxyhemoglobin is reduced, the 
two absorption-bands a and /3 disappear and are replaced by a single 
one (7) situated between I) and E, which is less deeply shaded and 
possesses less sharply-defined edges (see Plate I., Spectrum 5). This 
summary description must now be supplemented. 
The right-hand diagram on p. 233 exhibits fairly accurately the 
absorption of light by solutions of reduced hemoglobin of varying con- 
centrations. The single absorption-band (7), though occupying in solutions 
of from 0"2 to 0"4 per cent, and 1 cm. in thickness, the greater part of 
the space between Frauenhofer's lines D and E, has its centre or darkest 
region rather nearer D than E. According to my own measurements, 
the darkest part of the band corresponds approximately to A 550. 
It is to be noted that solutions of reduced hemoglobin have a much 
greater absorptive power for the rays between A and B, and a smaller 
absorptive power for those between F and G, than corresponding solu- 
tions of oxyhemoglobin. 
The Spectrophotometeic Constants of Reduced Haemoglobin. 
In his most recent researches, Hiifner has determined the spectro- 
photometric constants of haemoglobin for the same spectral regions as 
were selected by him, in the same researches, for the determination of 
the constants of oxyhemoglobin. 
In the case of reduced hemoglobin the respective extinction-co- 
efficients are distinguished as s r and s' r , and the corresponding absorp- 
tion relations as A r and A' r . 
The following are the results of Hiifner's determination ■} — 
A r 
A' r 
(A 551-A 556) 
(A 531 -5-A 542-5) 
0-001354 
0-001778 
The quotient -- is a constant of special importance; it is 07617. 
The value of the quotient - has also been determined by Hiifner ; 1 it 
is 0-6541. 
The determination of the amount of oxy- and reduced haemo- 
globin when both are present. — A'ierordt pointed out that the absorption 
1 G. Hiifner, "Neue Versuche zur Bestimmung der Sauerstoffcapacitat des Blutfarb- 
stoffs," Arch./. Physiol., Leipzig, 1894, S. 140. 
