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and half sweet oil should be melted in a porcelain dish. 
A small portion of the wax should always remain unmelted 
in the dish to provide against overheating. The tray should 
be half filled with the melted mixture, and its contents blown 
upon so as to cool them as rapidly as possible. One of the 
prepared ova which has been just before placed on blotting- 
paper to remove the superabundant moisture, should then be 
placed on the surface of the cooled wax, near one end of the 
tray, in such a position that it has the plane through which 
it is desired to cut sections of it parallel to thatend. As the 
wax in the tray was rapidly cooled by being blown upon, that 
in the dish will still remain fluid. With this the tray 
should now be filled up to the brim, and the whole allowed to 
cool. . 
There is considerable difficulty in imbedding an embryo or 
ege so as to cut it exactly in the desired direction. I think 
that this tray plan will be found most conducive to success in 
this particular. The ova should be lifted from place to place 
by means of a thin substance inserted under them. The best 
thing for the purpose is what the Germans call a loffel or spoon; 
it consists of a handle of tolerably stout wire, about five inches 
long, with the end beaten out flat and turned up, till it is 
nearly at right angles with the handle. This instrument is 
most useful for moving all kinds of fine microscopic sections 
from one reagent to another, &c. It is impossible to lift a 
prepared ovum with forceps or needles, as it is very brittle and 
easily crushed. ‘The wax in the tray being set, the paper 
should be removed, and the end of the block at which the 
ovum rests should be sliced away with a razor till the ovum 
comes into view. A section as thin as possible should then 
be made of the ovum, as little wax being taken with it as 
possible. The razor must be thoroughly wetted with alcohol, 
and it will be found that in all cases much finer sections can 
be cut when absolute alcohol is used ; absolute alcohol adheres 
so much more closely to the razor than weaker spirit, and 
thus allows the section to slide over its surface without 
wrinkling, which in the case of the frog’s egg means break- 
ing to pieces. The section must be washed carefully down 
to the extremity of the razor, which must be inclined down- 
wards, by means of absolute alcohol applied behind it with a 
brush. It must then be washed off on to the centre of a clean 
side! Decently thin sections of the frog’s egg during the 
1 T have not found it necessary to use carmine staining for sections of 
frog’s ova or early embryos, as the cell structure is sufficiently defined by 
the natural pigment which the cells contain. If in later embryos this be 
found necessary, the staining should be done at this stage. 
