208 Histology of Minute Blood-vessels. [9 ee ei 
fully conducted, are not stained at all. For this purpose I have 
most frequently employed, at the Museum, a solution made by dis- 
solving one part of crystallized nitrate of silver in four hundred 
parts of distilled water, but considerable variation on either side of 
this strength does not much modify the result, provided the solution 
is well washed off before the tissue is exposed to the light. 
If the same solution is injected into the blood-vessels, the lining 
epithelium is handsomely mapped out in all those membranous and 
superficial parts in which a ready exposure to the action of light is 
practicable, and although in the parenchymatous organs, such as 
the liver, the spleen, the kidneys, &., the juices of the tissues are 
apt to interfere with the reaction, yet even here occasional success 
may be attained. In practice it is often found advantageous to 
combine the silver solution, intended for injection, with a certain 
amount of gelatine, by which the blood-vessels are kept handsomely 
distended, and the beauty of the preparation is much increased. 
This plan was proposed by Chrzonszczewsky in the paper already 
quoted. His formula, which I have found to work well, is as 
follows :—Half an ounce of fine gelatine is dissolved in four ounces 
of distilled water, and to this is added a solution of one scruple of 
nitrate of silver in two fluid drachms of distilled water. After in- 
jecting with this fluid, the tissue is exposed to the light precisely as 
after the use of the simple silver solution. 
There are preserved in the Microscopical Section of the Museum 
a number of silver stainings in which the epithelium has been thus 
mapped out on the skin, the peritoneum, the lymphatic sacs of frogs, 
and the blood-vessels. These preparations, after the action of the 
silver, have been mounted in Canada balsam with or without the 
previous staining of the nuclei with carmine. The detailed steps of 
the process may prove useful to some readers. ‘The silver staiming 
haying been successfully accomplished, the nuclei are tinted prefer- 
ably by the solution of carmine in borax, described by Thiersch in 
his work on epithelial cancer.* It is prepared as follows :—Four 
parts of borax are dissolved in fifty-six parts of distilled water, and 
one part of carmine added to the solution; one volume of this fluid 
is mixed with two volumes of absolute alcohol, and after crystals 
have formed the mixture is filtered. The filtrate may be used for 
staining, but if the crystals of carmine and borax which remain on 
the filter are dissolved in a small quantity of distilled water, I find 
the solution thus obtained answers a still better. purpose. The 
portion of tissue to be studied is soaked in this solution until 
coloured deep red. It is afterwards treated with a saturated solu- 
tion of oxalic acid in alcohol, by which all colour is gradually 
remoyed except from the nuclei. So soon as this is accomplished 
* «Der Epithelialkrebs, Leipsic, 1865, 8. 92. 
