27 
end with one needle, while with the other the fibres are separated 
longitudinally into as fine a fasciculi as possible. A drop of the 
fluid in which it is to be mounted is then placed on the under side 
of the cover glass, which is then allowed to quietly settle over the 
specimen. The process of tearing is much facilitated by first ma- 
cerating the tissue in a very weak solution of bichromate of potash 
for a few days ; or even in half per cent. solution of common salt. 
Next, in reference to some of the uses of gold and silver for stain- 
ing purposes ; let us take the latter first. Its great feature is, that 
it first stains the crevices or interspaces of the tissue, and it is for 
this that it is so useful. For instance, let us take a piece of 
peritoneum, the transparent membrane which lines the abdominal 
cavity, and is reflected over all the organs it contains, and stain one 
portion with nitrate of silver, another with carmine or logwood, 
and examine a third portion in its fresh state. The fresh will show 
no appearance of cells or nuclei on the surface of the membrane ; 
that stained with logwood will show nuclei only: and that with 
nitrate of silver a flat layer of cells only; while if the silver and 
logwood stainings have been combined, a perfect layer of nucleated 
cells will be found covering the internal layer of the membrane. 
The method of staining with silver is as follows :—Take a piece, 
say of the mesentery of a cat, that portion of the peritoneum which 
retains the intestines in place, and steep it in a solution of nitrate 
of silver for a few minutes ; then remove it and wash it thoroughly 
in repeated changes of common water until it ceases to cause a 
white precipitate of chloride of silver. Then expose it in a capsule 
of water to light until it assumes a bronze tint. Mount in glycerine 
—the best medium for silver and gold stainings—and a perfect 
layer of flat cells will be seen, by focussing, to line both sides, for 
the membrane here is double. The preparation is more beautiful 
and valuable if, before mounting it, it is placed for a few hours in 
the logwood staining fluid, since not only are the nuclei rendered 
visible, but also the other structures of the peritoneum, such as the 
connective tissue, cells, vessels, &c. The omentum, mesentery, 
parietal peritoneum, centrum tendineum, and cornea, form excellent 
subjects for staining with nitrate of silver. The half per cent. 
chloride of gold solution is very useful and often yields good 
_ results. But time will only permit me to draw your attention to 
one instance of its value, and that is for bringing out the corneal 
corpuscles and nerves. This specimen is best obtained by procur- 
- ing a fresh frog's cornea, and, having scraped off the epithelium 
_ which lines the upper and under surfaces, by placing it in a half 
_ per cent. solution of gold until it assumes a straw colour. This 
usually takes from a quarter to half-an-hour. It is then washed 
and exposed to light in a capsule containing slightly acidulated 
_ water for one, two, or three days according to the light, until the 
_ yellow colour has changed into a reddish purple; it is then 
