.NOTES AND MEMORANDA. 
85 
of different hardening reagents, such as alcohol, chromic acid, 
bichromate of potash, &c. 
Microscopical preparations obtained by these processes may be pre- 
served like others in fluids or balsam. It should be observed, however, 
that picric acid, being, as I have said, soluble in water and in alcohol, 
might easily be removed from the preparations upon which it has been 
made to act. To prevent this inconvenience it is important that the 
glycerine used to preserve the preparations should be slightly tinged 
with picric acid, and if balsam is used it is necessary to dehydrate the 
preparations in alcohol containing also a small quantity of the same 
acid in solution. In the latter case, after this treatment, the prepara- 
tion may at once be placed in oil of cloves or turpentine without 
fear of the staining suffering from it. I would likewise observe hero 
that if it is intended from the flrst to mount the preparation in balsam, 
the operation may be abridged by transferring the preparation 
immediately from the solution of aniline blue, in which it has acquired 
the tint I have indicated above, to a bath of alcohol to dehydrate it, the 
alcohol containing ^ per cent, of picric acid in solution. 
With the picro-aniline solution not only may different tissues be 
stained according to the ordinary process, i. e. by plunging the pre- 
paration into it, but interstitial injections may be made with it, and 
small artificial oedemata produced with Pravaz’s syringe. By operating 
thus, for example, on a lymphatic gland, the colouring matter can bo 
made to penetrate into the cavernous system where the endothelial 
cellules may be recognized lightly coloured with green, the character- 
istics of which, already well described by Professor Bizzorero, are 
seen with more clearness than with any other reagent. If a small 
oedema be produced under the skin of the groin in a rabbit or guinea- 
pig, the connective cellules and the fibres between which they are 
situated may be studied to perfection, as Kenaut has done, by means of 
cosine, which is soluble in water. The picro-aniline solution, finally, 
may be very well employed in interstitial injections intended to show 
the relation between the cellule connectives, especially when the 
picric acid instead of being dissolved in water is dissolved in one-tliird 
part of alcohol. 
The preparations thus obtained are not affected by the weak acids, 
I acetic phenic, diluted chlorohydric &c., whilst alkaline solutions rapidly 
I destroy their beautiful outline. The preparations, mounted in fluids 
or dry, wdth the precautions mentioned, preserve their stain for a very 
I long time, for I have some which have undergone no alteration for 
more than a year. 
I The picro-aniline solution (which is specially to be recommended 
i for the study of the lymphatic glandular system and for the retina) 
I does also very well for other normal or pathological tissues. Thus I 
j have preserved some complete sections of the medulla oblongata stained 
by this method, which for clearness and elegance leave nothing to be 
envied in those produced by carmine. 
! Amplifiers . — In an article on the “ Amplifier,” by Dr. Devron, in the 
!f ‘ American Journal of Microscoj)y,’ he says : — “ The Tolies’ amplifier 
' used on a large compound microscope, with lenses of various makers, of 
