26 
tissues acquire the same tint, when the main object of colouring is 
defeated, namely, to isolate the individual cells and fibres by diffe- 
rent shades of colour. It sometimes happens, however, that the 
chromic acid is so permanently fixed in the tissue that logwood 
cannot displace it, however strong the solution you use may be. 
In this ease it is only necessary to soak the section for a few hours 
in very dilute solution of potash, say one per cent. of liquor po- 
tassce, or even less; then, after washing in spirit and water, again 
transfer to logwood, and they will stain rapidly and well. I may 
mention that I find the nests of palettes used by painters to be the 
most convenient and the cheapest articles for holding the staining 
fluid ; for, at the same time that they are a useful size and shape, 
by fitting one upon the other, they effectually preserve from dust. 
I procure mine at Mr. Stanley’s, opposite London Bridge Station, 
and I have brought a nest down for your inspection. When the 
sections appear to have received sufficient colour they are trans- 
ferred, on a needle, to a capsule containing water, and gently 
washed, then to methylated spirit, which must be changed in a few 
minutes, for deliquoration before they are transferred to the centre 
of a glass slip—one, two, or three aceording to size—and a drop of 
oil of cloves or oil of lavender is allowed to run under the sections, 
taking the place of the spirit as it evaporates, and permitting the 
chloroform balsam or dammar in which they should be mounted to 
thoroughly permeate the tissue. The sections should always be 
transferred from the spirit to the glass slip with a nice sized paint 
brush, since in this way large sections of the most delicate tissues, 
such as brain or lung, can be smoothly placed in the centre of the 
glass without any fear of breaking. ‘lhe spirit is then drained off 
before the drop of oil is allowed to run under. The oil of cloves 
is generally used, but I prefer the oil of lavender, since it seems to 
mix more readily with spirit, and so the section is not rendered 
quite so transparent, I think, as with oil of cloves. This, however, 
may only be fancy. Dammar also appears to be preferable to — 
chloroform balsam, since it is not so highly refractive, that is for 
stained sections. The balsam is as good, or better, for simple car- 
mine injections. I ought, perhaps, to mention glycerine jelly as a 
medium for mounting staimed sections in, but I believe that it is 
applied to better purposes, and that it is inferior to dammar. Still 
good specimens are so mounted, and it is a favourite with some. 
So much for cutting, staining, and mounting hardened animal 
tissues. A few words now in reference to tearing sections. The 
process is simple enough, but requires practice to accomplish it 
successfully. The tissues ‘arranged in longitudinal bundles are 
those to which it is most applicable, such as tendons, nerves, 
muscles, &c. A small piece is snipped off with a pair of scissors 
and placed in the centre of a glass slip with a drop of fluid, the 
half per cent. salt solution answers very well; then fixed at one 
