150 
Proceedings of the Royal Society of Edinburgh. [Sess. 
For the purpose Htifner’s spectrophotometer was employed. After 
plotting the curves of absorption of diluted blood and the product obtained 
by the action of sodium nitrite, it was decided to observe the effect in 
the neighbourhood of X 574. Under the influence of sodium nitrite the 
absorption band of oxyhsemoglobin present in this region becomes much 
lighter. The appearance of the band in the red was found to be much less 
suitable for the purposes of the investigation owing to the low intensity 
of the absorption band of met haemoglobin. The source of light was an 
incandescent burner. The collimator and ocular slits were made as narrow 
Conc. 
Na.N0,, 
M 
/ 
700 
N 
BOO 
N' 
500 
N 
400 
_N_ 
500 
N 
/ 
/k 
y 
/ 
Z 
A 
/ 
7 
200 
N 
/ 
100 
1 
Mins. 2 4 6 8 10 12 14 16 
Fig. 1. — Curves showing time of appearance of absorption band in 
red (methsemoglobin) on adding different strengths of sodium 
nitrite solution to a solution of defibrinated blood and of 
washed blood corpuscles. 
A, solution of defibrinated blood ; B, solution of washed corpuscles ; Ordinates, 
strengths of sodium nitrite in final product; Abscissce , time in minutes 
as was possible for accurate observation. The collimator slit, measured 
with a microscope, was OOl mm. ; the ocular slit was 0T mm. The region 
of the spectrum observed was X 571-577. The solution of ox blood (ox 
blood was used throughout the experiments in this paper) was put into one 
test-tube and the solution of sodium nitrite into another test-tube. At a 
definite time the two solutions were mixed by pouring from one test-tube 
to the other, at least three times, and then filling the Schulz absorption 
vessel. The first observation of the absorption could be made within twenty 
seconds of the commencement of the mixing. Further observations were 
taken at definite intervals, at first usually at half-minute intervals. The 
shortest time in which two observations could be made and recorded, with 
reasonable accuracy, was ten seconds. The extinction coefficient was then 
