REACTION OF EMBRYONIC CELLS TO SOLIDS 523 



from his studies on the growth of epithehum and carcinoma, was 

 hkewise led to the view that these tissues are stereotropic. 



Nevertheless, none of these cases established the occurrence of 

 this phenomenon beyond doubt. It seemed to be only a probable 

 explanation of certain scattered facts. The experiments described 

 in the present paper were designed to put the hypothesis to a 

 more rigorous test. 



Examples of stereotropism (thigmotaxis) have long been known 

 in plants and there is a wide range of reactions in animals that 

 may be gathered under this head, some of which have been 

 considered by J. Loeb^^ and by Verworn.^^ These reactions, 

 are however carried out mostly by complex mechanisms and 

 have but little direct resemblance to the cellular phenomena 

 here considered. The best known case of positive stereotropism 

 in single cells is that of the spermatozoa of Periplaneta, originally 

 described by Dewitz,'^ who called attention to its significance 

 in the act of fertilization. Jennings's^^ description of the move- 

 ments of amoeba indicate that here also reaction to solids plays 

 an important part in locomotion. 



METHOD OF EXPERIMENTATION 



The plan of experimentation in the present work consisted in 

 varying the three principal factors involved in the cultivation 

 of tissues, viz., the tissue itself, the fluid medium, and the solid 

 support. The results have shown that all three of these factors 

 have some determining relation to the movement observed. 

 Each tissue has certain characteristics, as seen especially in the 

 differences manifested by epithelium, connective tissue and 

 nervous tissue ; the constitution of the fluid medium has a marked 

 effect upon the vigor of the movement ; the solid support influences 

 the form and arrangement assumed by the moving cells, and its 



" Heliotropism der Tiere. Wtirzburg, 1889; Studies in general physiology, 

 Chicago, 1905; Dynamics of living matter, New York, 1906; Winterstein, Ver- 

 gleichende Physiologie, Bd. 4, article on Tropisms. 



1- Bewegung der lebendigen Substanz, Jena 1892; AUgemeine Physiologie. 



13 Pfliiger's Archiv., Bd. 38, 1886. 



^* Behavior of the lower organisms. New York, 1906. 



