28 
mounted in glycerine and presents the appearance seen in the 
specimen under the microscope, with more or less clearness accord- 
ing to the success of the staining. This is a somewhat difficult 
preparation, and I believe rarely succeeds unless the frog’s cornea 
has been first inflamed. When you remember that the cornea 
examined fresh shows no structure at all, and by this method large 
cells with numerous processes ramifying in every direction, and 
bundles of nerve fibres crossing and recrossing fill the field of the 
microscope, you will, I am sure, have no hesitation in according to 
chloride of gold no mean position amongst your reagents. I have 
but a short space left at my command, and that I should like to 
occupy by a brief consideration of a very important aid to the 
study of animal tissues. I allude to injection of the blood vessels 
with some coloured material. It is impossible for me to go at all 
deeply into this process, and therefore I will only describe one 
variety—injection with the carmine gelatine mass, passing Over 
Beale’s glycerine fluids and numerous other preparations. I pre- 
pare the carmine mass after the manner recommended by Dr. 
Carter. Three drams of gelatine are dissolved in two ounces of 
water ; to one ounce and a half of this a solution of carmine is 
added, made by dissolving one ounce of pure carmine in two drams 
of strong liquor ammonia and diluted with an ounce and a half of ° 
water. To the remaining half ounce of gelatine solution one and a 
half drams of glacial acetic acid is added, and the two are mixed by 
gradually pouring gelatine solution with the acetic acid into that 
containing the carmine. The smell of ammonia should disappear, 
and the colour become lighter and redder. If this is not the case 
a little more acetic acid must be added, and its preparation is com- 
pleted. Let us suppose, then, that we are about to inject some 
small animal. An incision is first made in the skin over the front 
of the chest just to the left of the middle line. The left costal 
cartilages are then cut through to a sufficient extent to get at the 
heart, which is then drawn out of the opening, and kept out by @ 
thread passed through its apex, which may be held by an assistant 
or fixed. A hole is next made in the left side of the heart through 
which the nozzle is introduced, and passed up into the large vessel 
leading from the cavity on this side and called the aorta, in which 
it is fixed by a stout thread. The nozzle may or may not have a 
stop-cock attached. The syringe then having been first warmed by 
warm water, is filled with injection, which should be only just 
warm or it is sure to extravasate, and the process is steadily but 
rapidly completed. The body is then opened at once, and any ex- 
travasated injection washed out with ice-cold water, which sets at 
once the injection. Portions of transparent organs, as the intes- 
tines of a mouse or a frog, may be spread out at once on the centre 
of glass slips and allowed to dry on, and then mounted in balsam ; 
while the solid organs, first having ascertained those which are 
