214 THE MOSAIC STAGE OF DIFFERENTIATION 



a greater or lesser extent, and these transformations are accom- 

 panied by irreversible physiological changes, as a result of which 

 the tumour cell becomes capable of glycolysis (or fermentative in- 





t 



\M^^:^ 



'^i.'\ 



' '^ •• 



^ t 







Fig. 1 02 

 Microphotographs of living cultures of chick fibroblast tissue. Above, typical 

 fibroblasts (after 103 days' cultivation and 13 passages). Below, macrophages 

 derived by metaplasia from a pure culture of fibroblasts (12 passages as pure 

 fibroblast culture in optimum medium, then 29 days' growth in an unfavourable 

 medium containing no embryonic tissue juice). (From R. C. Parker, Joiirn. Exp. 

 Med. LViii, 1932.) 



tramolecular respiration) and is less dependent on normal aerobic 

 respiration.^ 



These examples will be sufficient to demonstrate the real exist- 

 ^ See Warburg, 1926. 



