84 THE AMERICAN MONTHLY [May, 
proof than 95 per cent., whzch cannot be used as a substitute for 100 per 
cent. alcohol in this process of tmbedding. 
7. The time during which the piece must remain in the chloroform will 
depend upon the size of the specimen. The worker can, however, tell when to 
make the next transfer by these indications :—(z) At first currents may be seen 
in the chloroform, as the alcohol leaves the piece and the chloroform replaces 
it; these will cease, even after shaking, at the end of the process. (zz) The 
specimen, at first opaque, will gradually become very translucent, and close 
watching will tell when there is no further change in this direction. (zzz) The 
specimen when first placed in the chloroform will float at its surface, but as 
saturation with chloroform goes on it becomes heavier, and finally gravitates 
to the bottom of the vessel. It is very essential that all traces of alcohol be 
removed before the next process is initiated. 
8. A saturated solution of the pure paraffine in chloroform provides a step 
between the pure chloroform and the pure paraffine, by which a part of the 
chloroform is gotten rid of before the piece is subjected to a temperature 
higher than that of the atmosphere of the room. 
9. The paraffine used for imbedding must be chosen in accordance with 
the temperature of the room where the sections are to be cut. If too soft a 
paraffine be used the sections will be crushed by the razor ; if too hard, then 
the thin slice will roll up, and cause great vexation, and make the ‘ ribbon’ 
a failure. It is only after experience with various grades that one can 
select the best to use upon a particular occasion. Paraffines of various 
grades, soft, medium, and hard, can be bought of the chemists, who can 
_ also usually supply the other reagents in pure state. In immersion in 
melted paraffine care must be taken to prevent the temperature of the 
steam or water surrounding the cup holding the paraffine from rising far be- 
yond the melting point of the paraffine. This is ordinarily about 55° C. 
The temperature must never be allowed to rise to or beyond 60° C.* 
10. The precise steps in the imbedding process are these :—A small paper 
box is made, by folding, from a piece of writing-paper, or two L-shaped pieces 
of lead are used upon a glass slide, and thus an oblong mould is formed, into 
which the melted paraffine is poured. Its outer surfaces begin at once to cool, 
but the centre remains liquid for some time. The piece, carefully lifted from 
beneath upon a ‘ section-lifter’ (which may be made by hammering flat the 
end of a piece of copper wire four inches long), is now deposited in the 
melted paraffine in the mould, and, with a warm needle, adjusted so that sec- 
tions cut across the block will pass through it in the desired plane; the 
section is now held thus a second or two, till the paraffine has hardened sufh- 
ciently to prevent its displacement, and then the mass is allowed to cool. 
There is no hurry about cutting the sections after imbedding ; it may be done 
whenever convenient, for the piece will now undergo no change. 
11. In cutting sections after this method of imbedding has been employed, 
the razor should be pushed straight ahead without any lateral movement. 
To do this the razor at the part used must be perfectly free from any breaks 
in its edge, however slight ; it should look entire, even to microscopic exam- 
ination, and be very sharp indeed. Before cutting the sections the parafhiine 
block, with the imbedded piece, must be fixed in the microtome, care being 
exercised that the surface presented to the knife be the one prepared for in 
adjusting the piece in melted paraffine. After the block is mounted in the 
microtome in position, the paraffine should be pared down by four vertical 
cuts around the piece at right angles to each other, thus enclosing the piece 
in a four-sided prism of paraffine. The edge of the prism which the knife 
* On water-bath apparatus consult this Yournad/, vol. vii, p. 203, 1886, 
