DEVELOPMENT OF VESSELS WITHOUT HEART 179 



If a drop of warm water or Locke's solution is dropped upon the 

 opening at this time, it will help to loosen the membrane from 

 the shell, and will also prevent to some extent, long cracks and 

 the breaking off of large pieces of shell. The shell is removed 

 over an area about one centimeter or less in diameter and the shell 

 debris washed off with warm sterile Locke's solution. The shell 

 membrane is carefully stripped back with the forceps and the 

 blastoderm exposed and flooded with Locke's solution. If the 

 embryo is eccentrically placed, it may be necessary to rotate the 

 egg slightly or remove more of the shell. The heart, if not visi- 

 ble, may be brought into view by pulling on the covering mem- 

 brane with the forceps and turning the embryo slightly to one 

 side. 



The next procedure is cutting a small opening through the 

 vitelline membrane and lateral plate and, catching the heart with 

 the forceps, pulling it well out from the embryo and severiDg its 

 connections, both anteriorly and posteriorly, with the scalpel 

 or scissors. For this work I have used knives made from dis- 

 secting needles or by grinding down old scalpels, but I have found 

 the small iridectomy scissors much easier to handle and more 

 reliable. After removing the heart, the embryo is again covered 

 with the sterile Locke's solution warmed to about 100 degrees 

 Fahrenheit, the hole in the shell covered with a piece of isinglas ., 

 and sealed with a mixture of wax and resin (Rabaud). The 

 egg is now returned to the incubator and allowed to develop 

 further. 



The operation is carried out in the warm-box at incubator 

 temperature. If moderate aseptic precautions are observed 

 there is little danger of infecting the embryo. The work is done 

 under the binocular microscope, and is not difficult if the instru- 

 ments are sharp, but if they are dull, especially the forceps, it is 

 next to impossible to secure accurate results. 



On several occasions, at stages of from sixteen to twenty-four 

 hours incubation, I injured the embryo by burning with the 

 cautery or by cutting sufficiently to prevent its further develop- 

 ment. The extra-embryonic area, however, continued to grow 

 in a manner similar to that in the experiments in which the 



