Microscopy. 189 
used in screwing in the key-piece, and must therefore always be 
prepared beforehand. 
After these preparations, the egg to which the mounting-ring has 
been cemented is disinfected in the manner above described, and 
placed in an egg-carrier with the ring uppermost. The inside of 
the ring is then brushed with carbolic acid, which is shaken out 
after one or two minutes and replaced by a 4% solution 
of common salt, which is also allowed to remain from one to 
two minutes, and then completely removed by means of carbolized 
cotton. The guide-ring is now screwed in, and the egg trepanned 
from the side, in order to avoid injuring the blastoderm. The egg 
is next plaeed with its opening upward, and the guide-ring removed. 
When the trepan is withdrawn, the excised piece of shell often 
comes with it, and sometimes the underlying shell-membrane. If 
this is not the case, the two pieces must be removed separately by 
the aid of the pincers. Care must, of course, be taken not to 
injure the blastoderm and the zona pellucida. . 
The thin white, which was left with the yolk in the shell, is 
allowed to flow over the glass rod upon the exposed blastoderm 
until the ring is filled, care being taken to avoid air bubbles. The 
wax-cloth diaphragm is next taken from the dish of carbolic acid, 
dried in blotting-paper, drawn through the thick white, and inserted 
in the ring in close contact with the metallic diaphragm ; and then 
the key-piece, previously washed with carbolic acid and dried with 
carbolized cotton, is slowly screwed down. The superfluous white 
18 thus slowly forced out through the vent (Vo), until the key-piece 
reaches the diaphragm and closes the vent. Finally, when the 
Strength of the hand is no longer sufficient, the egg with its embryo- 
mN is placed in the metallic fork, and the wrench applied until 
ka. this means it is no longer possible to turn the key-piece 
er. 
Th 
What more complicated in the case of eggs that have already been 
water, and provided with covered apartments for the reception of 
the egg, the thin white, the carbolic acid, and the salt solution, 
The key-piece may be removed as often as desired, provided the 
_ Seve precautions are taken each time in inserting it. If the key- 
- Plece is unscrewed by means of the fork and wrench, it must, of 
Course, be washed in’ the warm carbolic acid, and the vent cleared 
by the introduction of a wire. , 
egg must be placed in the incubator with the embryoscope 
* 
