GENERAL DISCUSSION 333 



bacq: In many cells the synthesis of protein and nucleic acids is con- 

 tinned and at the same time no mitosis takes place. Such giant cells 

 have been described by a gi'eat many authors, for examjile, Pnck on 

 cultures of Erhlich's carcinoma. The presence of giant cells is revealed 

 inider the microscope. These observations confirm the formulation as 

 I have already expressed it. 



BARENDSEN : I would like to draw attention to the fact that chromo- 

 some replication is necessary for the beginning of mitosis, but if only 

 one of the chromosomes is not replicated mitosis can be inhibited. In 

 contra-distinction to this, in order to inhibit the synthesis of DNA, a 

 considerable amount of it must be damaged. I have shown that if only 

 one a-particle penetrates into a nucleus, then reduplication of the 

 chromosomes is inhibited. 



The inhibition of DNA synthesis in these conditions does not occur 

 because only an insignificant part of the DNA is affected by one a- 

 particle. 



May one regard these two processes as a single jihenomenon? The 

 mitosis delay process is much more sensitive. 



bacq: We must not allow any kind of confusion to arise during the 

 discussion. The reduplication of chromosomes and the synthesis of DNA 

 are two quite different matters. Moreover, Gray has said that it is 

 necessary to pursue the distinction between the time delay of mitosis 

 and the constant inhibition of mitosis. The giant cells about which I 

 spoke are an example of a constant, long inhibition of mitosis. 



ALEXANDER : Is it ill fact true that the doubling of each chromosome 

 is necessary in order that a cell may divide? In many cancerous cells 

 chromosome abnormalities are observed with almost every division. 

 But nevertheless these tumours grow very well. This has been demon- 

 strated by the cytologist, P. C. Roller. 



hollaender: I pointed out in my paper that a hypotonic medium 

 may cause mitotic delay and even in general stop mitosis. This means 

 that at the basis of the inhibition there may lie a very simple physical 

 process. And I think that physical chemists and scientists interested 

 in the permeability problem could take part in the solution of this pro- 

 blem. Such a simple process as mitosis delay in a hypotonic medium has 

 not yet been investigated from the physico-chemical i3oint of view. 



ERRERA : The difficulties of studying the primary causes that delay 

 mitosis are connected with the fact that most biochemical processes are 

 inhibited much earlier than the time of discoverv of mitotic inhibition. 



