524 ROSS G. HARRISON 



indispensability is shown by the fact that no movement takes 

 place in its absence. 



The first experiments were made with tissues from embryos 

 of Rana palustris in the stage just after closure of the medullary 

 folds. These were followed by a series of experiments with 

 the tissues of chick embryos of various ages.'^ The fluid media 

 used were physiological sodium chloride, Locke's and Ringer's 

 solutions in varying degrees of concentration, blood plasma 

 and serum of the frog and the chicken respectively. The means 

 used to support the planted tissues were the fibrin net work 

 of the clotted plasma, spider web, the surface of the cover-glass, 

 and, in some accidental cases, the surface film of the fluid drop. 

 Control experiments were made in large drops of the fluid media, 

 in which the tissue was prevented by the size of the drop from 

 touching the cover-slip. 



At the time the experiments with frog tissues were made it 

 was not fully realized that the cover-slip might serve to support 

 moving cells, so that in respect to the solid support only cultures 

 upon spider web and in free hanging drops were made. In 

 some of the latter the pieces of tissue came into contact with the 

 cover-slip accidentally and cells began to wander out on the 

 glass. 



The technique used was in the main that employed in the study 

 of the development of nerve fibers, ''^ together with the modifi- 

 cations introduced by Burrows.^'' Sterihzed apparatus and fluids 

 were used throughout. The cultures were all made by the hang- 

 ing drop method, the cover-glass being placed over the hollow 

 of a deep depression slide, or upon a thin glass ring of about 20 

 mm. diameter and 2 nmi. height and sealed on with vaseline. 

 The frog tissues were kept at room temperature, while those 



^* A preliminary account of the experiments with frog embryo cells was pub- 

 lished in Science, vol. 34, 1911. The results upon chick tissues have been referred 

 to briefly in several general papers (see Anat. Rec, vol. 6, 1912; Trans. Am. 

 Cong. Phys. and Surg., 1913). The chick experiments were made with the assist- 

 ance of Mr. (now Dr.) Paul G. Shipley, to whom it gives me much pleasure to 

 express my thanks. 



i« Jour. Exp. Zool., vol. 9, 1910. 



1' Jour. Am. jNIed. Assoc, vol. 65, 1910; Jour. Exj). Zool., vol. 10, 1911. 



