ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 493 



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 riug 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 egg. An oblong 

 porcelain trough or glass dish is first filled with a 3 per cent, solution of 

 carbolic acid, and in this are placed the instruments 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. 



After washing the hands in dilute sublimate, or carbolic acid, a 

 perfectly fresh egg is painted with the 3 per cent, solution of 

 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 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 1/2 per cent, 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 placed 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 pellacida. 



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 is 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 embryoscope is placed in the metallic fork, and the 

 wrench applied, until with this means it is no longer possible to turn 

 the key-piece farther. 



