190 



ous Iraiisplanls (k-lorioi'ales al'lcr slioj'icr or loiiffer periods, 

 may hv Ihc iiH[)ossil)ility ol' cslablisliijig a pliysioloj^i- 

 cal link ol Iho Iransplanled cell-individiiais willi Ihc 

 cells ol" llie new host, (cf. Ihc (•xj)erimenl (jn duck and 

 chicken Iieart p. 185). Many ol' Ihc Uiinor IraiisplaJils wliicli 

 will nol lake, may also be Ine rcsidl ol' a missing cslahlish- 

 mcnl ol' a physiological conlacl willi Ihc new (organism. 

 Ill' alhreplic theory of Ehrlich may l)e explained 

 in the same way. The mouse carcinoma, when trans- 

 planted to a rat, will grow and ]>ersisl Tor a lime and will 

 then progressively disappear. It lives and grows at the ex- 

 l)ensc of the transplanted tumor cells themselves and Ihc 

 humors from the new host do not perhaps even inhihil 

 the growth of the lumor cells, bill the unknown, the specific 

 slimulalion for the mulliplication of the tumor cells cannot 

 be obtained in the new host. It is, of course, a more or less 

 theoretical conclusion, which has yet to be proved. 



In a former chapter of this book 1 have mentioned some 

 ex]K'rimcnls undertaken in order to settle definitely, thai 

 epithelium, cultivated for a long period of time in vitro, 

 still remains epithelium and behaves as such. — The in- 

 teraction of fibroblasts belonging to a ten years old strain 

 and epithelium of a three months old strain was studied 

 in vitro. Epithelium and fibroblasts were placed side by 

 side in a culture, and allowed to grow in close proximity 

 for several passages. — After the first 48 hours, a dislinct 

 difference was observed in the character of the two frag- 

 ments. The epithelium grew as a compact mass with the in- 

 dividual epithelial cells in close contact. The fibroblasts 

 migrated into the culture medium and formed a network. 

 Afler a few passages the fibroblasts overgrew the epithe- 

 lial fragment entirely. The combined culture showed a peri- 

 pheral growth mainly composed of fibroblasts, and the only 

 ap])arcnt indication of the presence of epithelium was that 

 the central ])orli()n of the culture appeared semi-transparent 

 and homogeneous and not as dense and opaque as a typical 



