GROWTH OF TISSUES OF THE CHICK EMBRYO 71 



in thickness and the outgrowth of cells into the plasma can be 

 readily traced to this la>er. These cells are similar in every way 

 to interstitial cells growing from the heart and the myotomes. 



In 64 transplantations of whole neural tubes, only three prepa- 

 rations showed any activity of the nerve cells. The degeneration 

 of the tube as studied in seiial sections was commonly greatest in 

 the cells most distant from the surrounding medium. Poor nu- 

 trition was the probable cause of this eaily death. Injury of the 

 heart has most often been associated with the outgrowth of muscle 

 cells. Injury to the nervous system would possibly disturb an 

 equilibrium and stimulate activity. In the next series of prep- 

 arations hemisections of the tube were transplanted in the hope 

 of bringing plasma into close contact with both sides of the wall 

 as well as of disturbing the continuity of its cells. Of the thirty 

 preparations, 50 per cent formed long nerve fibies. In these prep- 

 arations, the form of the neural tube is lost after the third day 

 by an apparent separation of the cells. The mesenchyme layer 

 tends rather to move outward into the surrounding plasma that 

 to proliferate about the tube. 



The exuberant growth of the mesenchyme cells in all these prep- 

 arations covered the field of the growing nerves and hindered 

 decidedly in determining whether such cells were necessary for 

 nerve production. In the hope of obtaining pieces of the neural 

 tube uncontaminated by these cells, the later experiments were 

 made by teasing the tube into small pieces which were scattered 

 throughout the drop. Many of such pieces, free from mesenchyme, 

 sent out long nerve fibres into the clear plasma clot, fig. 8. The 

 activity of the tissue is also increased by division into small pieces, 

 when teasing is carefully done. The number of individual nerve 

 cells sending out processes stands in inverse ratio to the size of 

 the piece. Almost every cell in two pieces of ten and twelve cells 

 respectively sent out nerve processes. The study of growth of the 

 mesenchyme cells was also facilitated. One group of four cells 

 had grown to a mass of fifty cells after six days of cultivation. 



During the development of this technique for the study of nerve 

 fibres in culture, various forms of growing mesenchyme cells have 

 constantly been seen and some of the observations on the growth 

 of both of these tissues will be discussed below. 



