378 Special Procedures II (chap. 23) 



With the handle of the scissors, break the shell at the air space end, 

 turn scissors and cut the shell around the long axis, being careful to 

 keep the tip of the scissors pressed against the inside of the shell while 

 cutting. This will prevent penetration of the yolk or the embryo. With 

 egg submerged in physiological saline at 37°C ^ in a finger bowl, re- 

 move top half of the shell. The chick will be found floating on the 

 upper surface of the yolk. It can be a waste of time to remove the lower 

 half of the shell, but many workers prefer to do so. This is a matter of 

 individual preference and ease of preparation. With small scissors, cut 

 quickly around the outside of the area vasculosa. Except for large em- 

 bryos, do not cut through the vascular area. Keep one edge gripped 

 by forceps, and slip a Syracuse watch glass under the chick. Withdraw 

 the watch glass and embryo with a little of the saline. Bring as little 

 yolk as possible with the chick. 



The vitelline membrane most likely will come with the embryo; 

 occasionally it will float free. If not, wave the embryo gently back and 

 forth in the saline until the membrane begins to float loose. Release 

 grip on embryo and remove the membrane. Make certain that the 

 embryo is wrong side up, that is, the side which was against the yolk 

 is now uppermost. Straighten out the chick, with no folds. Sometimes 

 washing with saline in a pipette across the top helps to clean and flatten 

 it. Pull off remaining saline and yolk, carefully, not just from one edge 

 but slowly and with gentle pressure on the pipette bulb around the 

 area vasculosa. Do not get so close that the embryo is drawn up into the 

 pipette. 



Have a circle of filter paper cut with the inside hole approximately 

 the size of the vascular area if it is to be retained, or a little larger than 

 the embryo if it only is to be used. Being careful not to disturb the 

 embryo, drop the circle of paper around it. Press gently around the 

 paper to make it adhere to the blastoderm. With a pipette apply fixative 

 (Gilson or Bouin's), carefully dropping it first directly on the embryo; 

 ease it on, do not squirt it on, and then work outward toward and over 

 the paper circle, finally adding enough fixative to completely immerse 

 embryo and paper. Leave overnight. The embryo should remain ad- 

 hering to the paper and can be transported in this fashion from solution 

 to solution. Fixation is followed by proper washing, depending upon 

 choice of fixative. Embryo is then stained in a carmine, hematoxylin 

 or hematein stain (see whole mounts) and dehydrated. Remove the 

 chick from the circle, clear and moiuit. The cover glass may have to be 



^ The author has found that with rapidity developed from experience, warm water serves 

 just as well as saline, with no ultimate harm to the chick if it is to be fixed immediately. 



