"irurS.Strim'] Microscopical Preparations. 155 
on tlie accurate balance used for the National Assays, to weigh 
exactly 48 milligrammes, I made twenty dots of fresh blood from 
my finger, which, when dry, added '4 of a milligramme to the 
original weight, and consequently were each on an average equiva- 
lent to about • 02 of a milligramme, or ^^Vir of a troy grain nearly. 
The fourth part of one of these spots, weighing of course in round 
numbers YiriwiT of a grain, was detached with the point of a cataract 
needle, and when moistened under the showed many hundred 
well-defined red blood corpuscles ; ten circular ones among these 
measured with the micrometer averaged ^^-§^th. of an inch in 
diameter, and could therefore, by this criterion of superior size 
alone, be diagnosticated from the corpuscles of an ox, sheep, or pig, 
with the same feeling of certainty with which any surgeon could 
testify that a perforation of the skull only half an inch across could 
not possibly have been made by a bullet measuring an inch in 
diameter. — Paper read he/ore the Microscopical Section of the 
Academy of Natural Sciences, Philadelphia, and communicated to 
the * Monthly Microscopical Journal ' by the author. 
V. — On the Staining of Microscopical Preparations. 
By Dr. W. K. M'Nab. 
1. Staining with Acetate of Mauvine. 
A. This can be used with very good effect in staining thin sec- 
tions of wood. If these are preserved in Canada balsam they seem 
to be permanently stained, as a few specimens put up in January, 
1866, are now quite as brightly coloured as they were at first. By 
means of the colouring the high powers of the microscope can be 
used, bringing out points of structure not easily demonstrated 
without being so treated. Sections (transverse) of coniferous 
woods show beautifully .the structure of the punctated tissue, as 
well as the junctions of the cell- walls and the thickening layers of 
ligneous matter. 
B. Sections of the young stems of ivy were last year (February, 
1868) successfully stained with acetate of mauvine and glycerine.* 
Since then most of the specimens have faded. The contents of the 
cells have lost colour entirely, but the cuticular layer of the epidermis 
retains its colour, as well as the young ligneous cells. In a speci- 
men now before us, the pith and the enclosed cell-contents are now 
colourless, but the zone of cells in which a deposit of ligneous 
matter has been formed are brightly coloured. The very small 
* See ' Botanical Society Transactions.' 
M 2 
