SYMPATHETIC TRUNKS IN CHICK 337 



TECHNIQUE 



The operative technique employed does not differ essentially 

 from that which was described recently by Clark ('20). ^ The 

 destruction of tissue was accomplished by electrolysis. The 

 negative electrode, which was placed on the region to be de- 

 stroyed, consisted of a very fine metallic filament. 



The embryos were subjected to operation at the close of the 

 second day (48 hours) of incubation. At this time the spinal 

 ganglia are not yet differentiated, and in the posterior portion of 

 the trunk the neural tube is not yet closed. An attempt was 

 made to destroy just enough tissue along the dorsal aspect of 

 the embryo to insure the complete elimination of the neural 

 crest material, but to leave the ventral half of the neural tube 

 intact. It is quite mipossible at the time of operation to deter- 

 mine just how much tissue is destroyed. In some instances the 

 desired result was obtained; in others either the destruction of 

 tissue was not sufficiently extensive to insure the complete elim- 

 ination of the spinal ganglia, or it was so extensive that the neural 

 tube was ahnost or completely destroyed. Two of the embryos 

 which survived the operation and continued to develop were 

 killed at the close of the fourth day (96 hours) ; the others at the 

 close of the fifth day (120 hours) of incubation. 



DESCRIPTION OF MATERIAL 



A total of seven embryos in which the operation was effective 

 survived until thej'^ were killed to be prepared for study. In all 

 of these the portion of the trunk involved showed some distor- 

 tion, otherwise the embryos were quite normal in appearance. 

 Sections of these embryos indicate a marked degree of regenera- 

 tion of tissue in the effort to repair the injury caused by the op- 

 eration. Throughout the greater part of the region involved in 

 all of the embryos the neural canal is closed and the mesodermal 

 and ectodermal layers are completed dorsally. However, wher- 

 ever the neural crests and the dorsal portion of the neural tube 



2 Technique of operating on chick embryos. Science, N. S., vol. 51, pp. 

 371-373. 



