193 



mcnces suddenly lo differentiate, when a portion of connec- 

 tive tissue is added. By differentiation the formation of 

 rudimentary tubules is meant liere. These are found to be 

 formed in normal as well as in cancerous epithelium. — It 

 is, in other words, the formative ability of the epithelium, 

 which is meant by differentiation here. Drew ^^'"'j describes, 

 however, the growth of epithelium as -sheets of undifferenti- 

 ated tissue". C h a m p y !-•') describes the d e d i f f e r e n I i - 

 ation of the epithelial cells, going on in vitro, as a 

 transformation of the epithelium into an indifferent em- 

 bryonic tissue, not unlike fibroblasts. From this, it is not 

 quite correct of D r e w i^^) to call the epithelium growing in 

 sheets, undifferentiated tissue. The question of dedifferen- 

 tiation according to C h a m p y can now be considered as 

 settled. Fischer ^^-) and E b e 1 i n g and Fischer ^'•') have 

 proved that epithelium cultivated in vitro does not dedif- 

 ferentiate in the sense of C h a m p y, but can be cultivated 

 indefinitely and behave as epithelium, morphologically and 

 biochemically all the time. 



D r e w^ 1^') describes also, that keratinization is a conse- 

 cutive process on epithelium under the direct influence of 

 fibroblasts in vitro. 



Our experiments have shown that both phenomena desc- 

 ribed by Drew i"), generally take place without the pre- 

 sence of fibroblasts or connective tissue cells at all. (Fig. 12.) 

 The strain of epithelium of our own, is a pure culture — 

 and there had not been the slightest contamination with 

 fibroblasts during the cultivation; nevertheless, the epithelium 

 has "differentiated" in the sense of D r e w to primitive 

 tubules. (Fig. 15.) These kinds of "differentiations" we have 

 observed now^ and then in up to 3 months old strains of 

 epithelium which had not been in contact with fibroblasts 

 all that time. 



The same can be said about the keratinization: this is 

 also described by -Drew as a process which originates 

 under the influence of fibroblasts. 



13 



