188 Proceedings of Royal Society of Edinburgh. [sess. . 
Reduction of the two bands of Hb0 2 to the one of HbO is a 
striking demonstration upon a large scale, but it is not easy to hit 
upon the precise strength of the Hb0 2 solution that is most 
suitable. 
It must be remembered that (1) before reduction is attempted the 
two bands of the oxidised pigment must be clearly seen by all to be 
two, i.e., the intra-linear green must be well marked, and (2) the 
resulting single band must not be too faint when it does appear ; 
for it must be borne in mind that it is always fainter than either of 
the bands it replaces. 
To satisfy both these conditions, a percentage of '6 will be 
found most serviceable. Add to a nearly full hsematinometer of 
blood at this dilution a quarter of a test-tubeful of warm Am 2 S, 
in a few seconds the two bands will fade away into one. 
II . — Notes on Quantities of Materials used in preparing some of 
the HbO ^-derivatives for Large Scale Demonstration. 
1. Neutral Met-Hcemoglobin . — Of defibrinated sheep’s blood 
diluted 1*5 times its volume with water, 140 c.c. are taken and 
warmed to 35° C.; to this add 15 c.c. of a 10 per cent. sol. of potas- 
sium ferricyanide — the most reliable substance for preparing this 
pigment in quantity ; stir, filter. The band in red and that to the 
right of D are well seen ; the others are not to be expected in a 
wall-spectrum. 
2. Alkaline Met-Hcemoglobin . — To 140 c.c. of the pigment pre- 
pared as above, add 5 c.c. of hlH 4 IIO ; stir, filter; three of the four 
bands can be seen. It is misleading to describe either of these met- 
hsemoglobins as “ chocolate coloured ” ; in solution, as above pre- 
pared, the neutral one is of a dark port- wine colour, the alkaline 
of a ruby glow in transmitted light. Blood, when treated with 
several other substances which form a certain amount of met- 
hgemoglobin (e.g., KC10 3 , K-permanganate, Amyl nitrite, ^Formyl 
aldehyde), does, no doubt, look “ chocolate coloured,” but that is 
largely due to the fact that the pigment is present in the midst of 
various proteid precipitates from the blood itself. 
3. Acid Hcematin .— This has to be very carefully prepared, 
else there will be precipitation and opacity. Dilute defibrinated 
