355 
spectrum No. 3, the narrow bands being due to one and the 
greater part of the broad absorption of the blue end to the 
other. ‘These two narrow bands are at once removed by 
citric acid. The addition of the ferrous salt to an alkaline 
solution also removes the bands, and they are restored if re- 
oxidised in a short time. When the solution is kept for a 
day or two deoxidised, and then rapidly reoxidised, no bands 
make their appearance ; but if, after having been thus kept 
deoxidised, the cell be exposed uncovered to the air, so as to 
reoxidise slowly, another compound is formed, which gives a 
spectrum with an absorption-band nearer the red end than 
that shown in No. 3, made much more faint by citric acid, 
removed at once by deoxidising the alkaline solution, and 
reappearing when reoxidised. Since some of these solutions 
are often turbid, it is requisite to use strong concentrated sun- 
light to penetrate through them. 
It will thus be seen that by exposing the solution to the 
air Aphideine passes successively into four different coloured 
products, and by deoxidisation and by subsequent exposure 
two others are formed. These complicated changes do not 
thus rapidly occur in the comparatively pure solution 
obtained by boiling the insects in water. It seems requisite 
that it should contain some of the (perhaps albuminous) sub- 
stances present when the insects are crushed up in cold 
water, which by their rapid decomposition seem to induce the 
above-named changes in the Aphideine itself. 
In my paper on some compounds derived from the colour- 
ing matter of blood,! I briefly described some of the products 
of the oxidisation of hemoglobin. Of these there are at least 
four, three of which are characterised by the presence of 
absorption-bands at the red end of their spectra when the 
solutions are deoxidised. The products of the change of 
Aphideine are in some respects analogous to these, only that 
except in one the bands are characteristic of the oxidised 
state. ‘The physical and optical properties of Aphideine and 
its products differ completely from those of the colouring 
matter of the cochineal insects of commerce. Whether this 
is a normal constituent of the living insects or a product can 
only be decided by examining them when alive, which 
hitherto I have not been able to do. I have met with 
Aphideine only in several dark-coloured species of Aphides, 
but at the same time I must confess that my acquaintance 
with the colouring matters of insects is very limited. 
When carefully selected living Aphides of the apple tree 
are quickly crushed up in ether, and the clear solution agi- 
? ‘Quart. Journ. of Micros. Science,’ x, 1870, pp. 400—402. 
VOL. XI.—NEW SER. AA 
