28 



cells arc sup|)i'cssc(l owinj^ lo the Incl. Ih;il Ihc ciillurc 

 incdiuni always conlains siii)s(aiiccs tVom ;in or-faiiisin in 

 early einbryonie slaj^e. A<fe and (lilTereiilialion are prol)- 

 ahly related |)lieni»inena. very complex, due to co-operation 

 bclwccn all the or^an systems. .Much discussion has ap- 

 peared as to whether ci-lls from the \arious tissues dediffc- 

 rcnliate when culti\ate(l in \itro to priudti\c end)i'yonic, 

 indiflerent cells, as staled, for instance, by (Ihanipy '-•') 

 and later by I'hlenhuth '■'' . () p |) e I "-j mentions in his 

 book that tissue culti\;dion is a disappointment owiii^' lo 

 the fad. Ihal the ()nl<fr()wing cells are indifferenl and can- 

 not be (pialified. All investigators agreed with him at Ihal 

 lime. It is, however, not true Ihat tissue cells dedifferen- 

 tiate in vitro; I lunc demonstrated that epithelial cells, 

 when they are obtained j)urc. free from oilier cells, grow 

 in vitro indefinitely, in a manner characteristic for epithe- 

 lium, and no transformation oi- dedifferentiation takes jjUico. 

 In these experiments it is important to gel from the very 

 beginning the pnrc tissue for cultivation, ecpially as impor- 

 tant as it is when cultivating bacteria. In obtaining pure 

 cultures of the various tissues for culti\ation. unfoi'tunatv-ly 

 the method used in bacteriology' can not very well be ap- 

 plied here. Tlie safest and best method is lo slart out with 

 tissues which arc pure when taken out of the body; or 

 take advantage of the fact that certain tissues grow belter 

 in vitro than certain others; this physiological elective me- 

 thod can with success be employed in gelling epithelium 

 fi'om the iris attached to the lens or as \\ . 11. Lewis*, has 

 indicated to cultivate |)ieces of amnion which consist only 

 of smooth muscle and e|)ilhelium. Xeithei" the lens nor 

 the smooth muscle grow for any length of time and pro- 

 gressively the epithelium is obtained pure. Hut the \-ery 

 best and most reliable method is lo gel the tissue pure 

 from the very beginning from certain loci elecli. (larlilage 

 has been obtained pure in a like mannei-. 

 *) personal communication. 



