XXI.] THE COLOUR OF BLOOD. RESPIRATION. 223 



of the wave-lengths of these lines expressed 

 (roughly) in millionths of a millimetre, B = 687, 

 (7=657, D = 589, .# = 527, ^ = 486. If prac- 

 ticable these lines should be observed in the 

 solar spectrum. 



Introduce between the flame and the spectro- 

 scope a much diluted solution of haemoglobin. 

 Note 



a. The two absorption bands, both between the 

 lines D and E\ the one (a) near D being 

 narrower and darker than the one (/3) near E 

 (if the solution is very dilute, (a) may be the 

 only band seen). 



6. The middle of (a) is about w.L. 578 *, that 

 of () about w. L. 5-iO. 



5. Increase gradually the strength of the solution. 



a. The spectrum is more and more cut off both 

 at the blue and at the red end, but especi- 

 ally at the former. The absorption bands 

 are both blacker and broader. 



b. As the solution becomes stronger, the two 

 bands run together, the ends of the spectrum 

 also suffering absorption, so that light passes 

 through only in a space in the green (middle 

 about w. L. 507) and a broader space in the 

 red (middle about w. L. 650). 



c. With a still stronger solution, the green light 



1 The mid-lines of the bands given here varies somewhat with the 

 strength of the solution. 



