EXPERIMENTAL RESULTS 101 



In another species of amoebae (A. sphaeronucleus) , the effects of 

 enucleation are similar. The interesting and delicate experiments of 

 Comandon and De Fonbrune (1939) have shown that motility {i.e. 

 pseudopod formation) is resumed in a truly dramatic manner when 

 a nucleus is reintroduced into a cytoplasmic fragment which has 

 been severed from the nucleus 2 or 3 days previously. If, however, 

 the enucleate half comes from an amoeba which has been operated 

 on 6 days before, the graft of a nucleus no longer has a favourable 

 effect. Apparently, irreversible changes occur, sooner or later, in 

 enucleated cytoplasm. 



Very interesting also are the nuclear transfer experiments of 

 Lorch and Danielii (1950) and DanieUi et al. (1955) (see also Da- 

 nielli, 1955, 1959). These workers have succeeded in exchanging 

 nuclei between two distinct, but closely related, species of amoebae, 

 A.proteus and A. discoides. The result is the production of "hybrids" 

 in organisms in which no sexual reproduction is known to take 

 place. They found that the nucleus of either species is capable of 

 restoring locomotion activity in enucleated cytoplasm. The mor- 

 phological characters of the "hybrids" {e.g. shape, size of the nu- 

 cleus) show strong cytoplasmic dominance. The shape and locomo- 

 tion are intermediate between those of the "parent" strains. As we 

 shall see later, however, the nucleus exerts specific effects on the 

 production of certain proteins. It is the belief of Danielii (1955, 1959) 

 that the nucleus determines the specific character of the macro- 

 molecules, while the cytoplasm is more important in the organiza- 

 tion of these macromolecules into functional units. One thing is 

 clearly proved by these elegant experiments: there exist mutual 

 interactions and exchanges between nucleus and cytoplasm. We 

 shall soon find other instances in which the nucleus lies under cyto- 

 plasmic control. It would thus obviously be a mistake to believe 

 that the control exerted by the nucleus on the cytoplasm is the only 

 type of control in the cell. 



After these introductory remarks on the biological effects of 

 enucleation in amoebae, we shall now deal with the RNA and pro- 

 tein metabolism of nucleate and enucleate fragments. 



Cytochemical observations with Unna staining show that the 



References p. 133/135 



