NOTES AND MEMORANDA. 
277 
pletely and in such a way that the incident and emerging rays are 
parallel, which, as far as we know, was never accomplished before. 
In connection with the microscope, as it was shown, it interfered very 
little with the definition, and, although the light is twice refracted 
and reflected, the loss of light is much less than one would expect. 
With the microscope, the prism is placed right above the objective, 
and the instrument may be used in any inclined position. A pair of 
such prisms might be used also for an erecting binocular microscope, 
of which the two bodies have the same inclination to the stage. The 
projection of the front is a square, that of the profile an isosceles 
triangle. The angles at the base of the triangle are 27° • 19 for crown 
glass of a refracting index of 1 • 53, in order to obtain the greatest 
aperture combined with the smallest prism. 
Logwood Staining of Tissues. — I wish now, says Dr. Arnold, in 
the ‘ Lens,’ to describe a process that seems to do away with the two 
objections raised against carmine. This method I have made use of 
for nearly two years, and the excellent results it gives can be vouched 
for not only by myself, but by many students who have worked under 
my directions. In fact, it has taken the place of carmine in my labo- 
ratory to a considerable extent. The colouring matter of logwood 
( Hcematoxylon Campecliianum ) is one of the most valuable staining 
materials known to me. This substance was, I believe, first used by 
C. F. Muller, in his investigations on the cornea. The method which 
is recommended by Muller can be found in the works devoted to micro- 
technology. I wish to give merely the manner in which the staining 
solution is made and used in my own laboratory. The ordinary log- 
wood extract is finely pulverized in a mortar and about three times 
its bulk of alum (in powder) added ; the two ingredients are well 
rubbed up together and mixed with a small quantity of distilled water. 
The complete admixture of the alum and hfematoxylin is necessary, and 
this will require fifteen to twenty minutes’ vigorous stirring. More 
water may now be poured on, and the solution, after filtration, should 
present a clear, somewhat dark-violet colour. If a dirty red is ob- 
tained, more alum must be incorporated, and the mixture again fil- 
tered. By always having an excess of both alum and hfematoxylin in 
the mortar, a saturated solution can be obtained, which, after filtration, 
may be combined with alcohol, — one ounce of the logwood fluid with 
two drachms of seventy-five per cent, alcohol. I have found that a 
much better colour can be had by allowing the mixture, after thorough 
trituration, to stand for several days before filtering and adding the 
alcohol. Should a scum form on the surface of the liquid after it has 
been some time made, a few drops of alcohol and careful filtering will 
be all that is required. With a strong solution, such as has been de- 
scribed, the colouring is very rapid, requiring but a few minutes ; 
whereas if a slower tinting be desired, the fluid may be diluted with a 
mixture of one part alcohol and three parts water. Whether the 
tissue has been previously hardened in alcohol or any of the chrome 
compounds, it is coloured equally well, — the nucleus of a most bril- 
liant purple, the cell-body of a distinct neutral tint. An overstaining 
causes an almost perfect blackening of the nucleus, while the pro- 
