104 



in Iho hh)()(l-c()M<^iiliini in vivo. Later Loeb "^) also advanced 

 the ojiinion. that Ihisc cells do nol dedilTerentiale. 



C h a Ml ]) y ' '"^ cnllivalcd kidnc.x (issue and found. IhaL 

 its strnctnre chanf^ed; indilTerent lui)ules were loi-uied. which 

 later on lost their renal and Tinnlly Iheii- epilhelial character. 



l" hlenh u t h '•'■'! showed. Ili;d Inpeluni ceils from the 

 retina changed Iheir ty|)ical epithelial character with modi- 

 fications in the consistency of the culture medium. 



('. hlopin I ■' . in his recent paper was not able to sup- 

 port llie assumption of (Ihampy. I have ali'eady observed 

 myself (Fischer) ''■'-) that epithelial cells cultivated i)n the 

 free surface of the coagulum did nol change morphologi- 

 cally after more llian four months cultivation in vitro. This 

 has been entirely confirmed by labeling '•''), as he had a 

 strain of epithelial cells for more than bS months. As soon 

 as the epithelial cells were allowed to grow embedded in the 

 plasma clot, the individual cells changed from polygonal 

 to fusiform cells. In order to find out truly what happens 

 to the different tissue cells when grown in vitro, it is absolu- 

 tely necessary to be certain of the kind of cells we are 

 operating with. \{ the present time no method is known by 

 which it is possible to isolate single cells for obtaining pure 

 strains, as it is known from the bacteriological leclini([ue. As 

 described in another chajjler. a tecliui(pie was worked out 

 to isolate cells; bid single cells do nol seem to develop and 

 multiply unless they are in contact with several other in- 

 dividuals This method can, therefore, not be a|)plied. 



There are two nu'thods by which it is possible to obtain 

 pure cultures of tissue cells the one, by which the ! issue 

 cells for cultivation are obtained pure from the very begin- 

 ning, i. e. an anatomical m e I h o d. the other, more 

 generally ap})lied, to be used only For certain cells, 

 may be called a p h y s i o 1 o g i c a I el e c live m e t h o d. 

 If a i)iece of heai't. for instance, is exj)ianled in a certain 

 medium, the muscle cells and a few ollui- cell types die 

 out rathei' I'apidly and the fibroblasts will conlinue to grow 



