27 



porting material, and it is impoiiant to notice how 

 determining the stroma is for the morpliology of cells. It 

 is absolutely essential for Ihc lite of tissue cells to have a 

 solid, or in some way solid support for their outgrowth. 



This phenomenon of the nccessily for the tissue cells 

 to have a support or a frame work for retaining the life 

 has been discussed by Harrison 2^1). The support may 

 be the fibrin in clotted plasma, the surface of the covei'' 

 alass, the surface of the fluid film, the framework of 

 spider-webs, silk gauze or cotton threads or the like. In 

 cultures in which the tissue floats free in a fluid medium 

 no outgrowth occurs and the cells succumb. The cells, cul- 

 tivated in a fluid with the cover glass as the only support 

 tend to be much more flattened because there are only 

 2 dimensions to the support; when cultivated in the fibrin 

 clot the cells are fusiform and more tubular because of 

 the three-dimension support. 



Leo Loeb called this dependency of the cells to the 

 solid phase, stereotropism. If cells are permitted to live in 

 a fluid medium they will succumb very rapidly. It is tho 

 solid supporting apparatus which determines the form of 

 the tissue cells, and without supi)ort the cells contract 

 themselves, become round and seem to be unable to assimi- 

 late and multiply. This phenomenon that the cells become 

 round as soon as the culture medium liquefies or when 

 the supporting apparatus is removed has probably been 

 observed by several investigators, but was first described 

 by U h 1 e n h u t h ^^s), later by Rous 4^^) and then by m>'- 

 self 19*). It is probably a phenomenon which can be ex- 

 plained by surface tension, as B ii t s c h 1 i *') and Quincke 

 *^'') have explained similar ])henomena. 



Under the conditions of experiments generally used, we 

 do not actually find morphological changes, transformation 

 or differentiations in the cells cultivated in vitro. The che- 

 mical and mechanical environments are usually the same 

 all the time in the cultures. The age phenomena of the 



