188 General Notes. 
key-piece, except that it has no glass disk. It serves to steady as 
well as guide the trepan during the process of cutting. 
The fork has two notches at the ends of its prongs, fitted to 
receive the two bars of the mounting-ring. When adjusted to the 
bars, the fork serves as a means of holding the embryoscope 
securely, while screwing or unscrewing the key-piece. ° 
The wrench, the use of which has already been explained, is similar 
in construction to the wrench used for mathematical instruments. 
e mounting-ring is fastened to the egg by means of a cement 
consisting of two parts of wax and three parts of colophonium. The 
cement is hard and brittle at the ordinary room-temperature, but 
becomes soft and kneadable when held in the hand for a few 
moments. After warming the mounting-ring over a gas or a 
spirit lamp, a roll of the softened cement is pressed into the space 
which must be completely filled between the lower face of the 
diaphragm and the lower edge of the ring. As soon as the ring 
becomes sufficiently cool, it is pressed firmly to the equatorial 
surface of the egg, and the excess of the still soft cement, which is 
thus forced outward and inward beneath the ring, should be 
removed before it becomes brittle, by the aid of a small, sharp- 
pointed blade. In order to avoid injuring the blastoderm, which 
might occur if the hot ring were fastened to the shell directly over 
it, it is best to fix the ring to the side rather than the top of the egg- 
After the ring has been securely fixed and the superfluous cement 
‘removed, the exposed edges of the remaining cement, seen beneath 
the lower edge of the ring and the inner edge of the diaphragm, 
must be covered with a coat of an alcoholic solution of yellow 
shellac. This may be applied with a small brush, care being taken 
to cover the cement completely, and as little of the egg-shell as: 
possible. 
After the shellac has dried, a process which is completed in 
twelve to fourteen hours in the open air and in six hours in the 
incubator, the shell may be trepanned. 
Antiseptic precautions are required in opening the _ An 
oblong porcelain trough or glass dish is first filled with a 3% 
solution of carbolic acid, and in this are placed the instru- 
ments to be used in the operation: a glass rod, a medium-sized 
brush, small shears, forceps, the trepan, and the guide-ring. Before 
using, these instruments are dried with carbolized cotton, and after 
using returned to the dish of carbolic acid. 
r washing the hands in dilute sublimate or carbolic acid, & 
perfectly fresh egg is painted with the three per cent, solution 
carbolic acid, and then dried with carbolized cotton. The small 
end of the egg-shell is then cut out with the shears, and the thick 
white poured with the aid of the glass rod into a clean dish, leaving 
the yolk and the thinner white in the shell. The white is to be 
