194 Proceedings of Royal Society of Edinburgh. [sess, 
of haemochromogen, the whole of the green region being invaded 
by a considerable amount of absorption. This appearance of bands 
emerging from a haze is in marked contrast to the very sharply 
defined bands of hsemochromogen. 
4. Red Writing-Ink (not “ copying-ink ”). — An undiluted 
specimen cuts off all light from orange to violet, and thus resembles 
a solution of Hb0 2 , of strength greater than 1 per cent. Diluted 
with an equal volume of water, a little green to the left of the 
absorption-area is transmitted. A still more dilute solution resem- 
bles bilirubin, except that the left margin of the band is more hazy 
than is the case with the bile-pigment. 
5. Cochineal ( Tinctura cocci). — It differs from Hb0 2 thus : — 
(1) Both bands of coccus are broader than the correspond- 
ing blood-bands. 
(2) They thus invade more of the green region, of which 
there is much less than in the case of Hb0 2 , for the 
bands of coccus are far more ill-defined on their 
edges. 
(3) Compared with the blood-bands, there is not that rela- 
tive difference of depth that exists between the latter. 
(4) The bands of coccus, compared with each other, are, 
on a first glance, equally broad; if there is any 
difference of width between them (the haziness of 
their edges makes this very difficult of estimation),, 
it is the left-hand one that is the broader — the 
opposite of which holds good in the case of Hb0 2 . 
6. Hcematoxylin . — This spectrum somewhat resembles that of 
HbO ; it differs in that — 
(1) In the case of hematoxylin, all the blue light is? 
present ; this is notably not so with HbO. 
(2) The one broad band of hsematoxylin extends much 
farther into the green region than does that of HbO, 
which does not cut out all the green rays. 
(3) The hsematoxylin band extends farther into the orange- 
than is the case with HbO. Wave-lengths of 
hsematoxylin band are from A.608 to A474. To the? 
naked eye hsematoxylin is more purple than HbO. 
