480 PREPARATION AND MOUNTING 
15. For blue injection, which is not, however, much use: 
with reflected light, as before stated, take— 
Prussian Wiley... .\0c02 -ksagudeeeans 73 grains, 
nallie BOI, wea; ockeokaaeeeeeeeeeee j ss 
PIES WE ccGyeiescuckdncunbaeetbec- bese 4 ounces. 
The oxalic acid is first finely powdered in a mortar, the 
Prussian blue and a little water added, and the whole then 
thoroughly mixed with the size. 
16. It may here be repeated, that it is only when the 
capillaries are to be filled that there is any need to be at the 
trouble to. prepare the colours by this double decomposition; 
and, indeed, colours ground so finely may be procured that 
the above instructions would have been omitted, had it not 
been supposed that some students might find a double plea- 
sure in performing as much of the work as possible by their 
own unaided labours. 
17. The process of injection may now be considered; but 
it is impossible for written instructions to supply the place 
of experience. I will do my best, however, to set the novice 
at least in the right way. There are two kinds of injection 
—one where the object and colours are opaque, and conse- 
quently fit for examination by reflected light only; the 
other, where the vessels are filled with transparent colours, 
and must be viewed by transmitted light. The first of these 
is most frequently employed, so we will begin with it. In 
the object which is to be injected, a vessel of the kind which 
we wish to be filled must be found; an opening must then 
be made in it to allow one of the small pipes before men- 
tioned to be thrust some distance within it. When this is 
accomplished, thread the curved needle with a piece of silk 
thread; or very fine string, which some operators rub well 
with beeswax. This thread must not be too thin, else there 
is danger of cutting the vessel. The cord is then carried 
ander the inserted pipe, and the vessel bound tightly upon 
it, the ends being brought up round the transverse arms, 
