12<S 



The greatest liciuefaclion takes place at the central portion 

 l)ecausc of the many cells which are there already at the 

 be^innin}. ol" the cullivalion, therefore the cup-like impression 

 of (he eulliire imdiuin. 



The rate of speed al whic-h the epillielial cells grow. 

 comi)are(i with that of the fibroblasts, is slightly lower. — 



Hteeiilly Drew*'"' has tleveloped a method l)y whicli 

 he is able lo gel i)iire cultures of cpitheliuni By exposing 

 a eullurr wliieh contains as well epithelium as fibroblasts, 

 lo ullraviok'l rays, after first having covered Ihe areas of 

 the culluit wlurc Ihe epithelial cells are located witii 

 droi)lets of nu'rcury he is then able lo kill the fibro- 



blasts, and the epithelial cells, covered with mercury will 

 remain alive. 



Another difference which may be of considerable im- 

 portance is that the epithelial cells do nol change the 

 fibrin fibrillae into structures similar to the conneclivo 

 tissue fibrillae. \\ e know this already. Bui this fact seems 

 to have a vt-ry important bearing ujjon the |)hysiology of 

 these two tissue types. The epithelial cells seem lo have 

 a high proteolytic effect on the fibrin fibrillae. The con- 

 nective tissue cells have this ability also, in part, of lique- 

 fying the medium, but on Ihe other hand, it is able to 

 change the milieu exlerieure in such a way that 

 large, strong connective tissue fibres are produced. M the 

 present time there is still a discussion as to the oi'igin of 

 these fibres, whether they are of extra-cellular or intra- 

 ccllula]' origin. The relation of these connective tissue fibrils 

 to the composition of the culture medium is very interesting 

 and will be mentioned in the chapter on controlled oi' 

 somatic growth of complex tissues. 



As a supplement to these experiments. 1 attempted to 

 isolate and cultivate other kinds of epithelium than the 

 iris, especially epithelium with special functions. Although 

 these experiments are made quite recently and unpublisned, 

 I will briefly describe the technique. 



