EPITHELIAL MOVEMENT 547 



Though all precautions were taken to keep the cultures free 

 from bacteria, it was sometimes necessary to throw away a 

 whole series as a result of infection. This was due obviously to 

 the difficulty of perfect sterilization of the tissue. 



In the aggregate, more than 1800 cultures were made, and in 

 nearly all of the experiments two kinds of culture medium (plasma 

 and serum) were used. The following descriptions are the results 

 of the study of about 1500 cultures which were free from faulty 

 technique. 



Fig. 1. Diaji;rain showing various types of movement of corneal epithelium 

 cultivated in plasma, g, cover-glass; c, tissue of cornea cultivated; ep, corneal 

 epithelium; ed, endothelial surface; m, culture medium; t, cut end of the piece of 

 cornea. Cell movement into the plasma (M), along the endothelial surface 

 {E), on the epithelial surface {E'), along the cover-glass {G), and along the lower 

 surface of plasma (.S). 



1. Description of the types of epithelial movement in plasma 



(fig- 1) 



The cornea of the frog was very suitable for this purpose. 

 For the observance of the intimate cell structure and a closer 

 study of the mechanism of cell movement, high powers could be 

 used. It was, of course, necessary to supplement the study of 

 the living tissue by fixed and stained preparations of whole cul- 

 tures and b}' serial sections. The observation of the living 

 cultures was limited to the first week. 



