Scheme (After Glucksmann) Illustrating the Relationship Between Cell 

 Division and Cell Differentiation in Different Types of Normal Tissue 



DIVIDING 

 CELL 



)IFFEREN- 

 TIATING 

 CELL 



FIG. 4. Irradiated tissue culture showing generalized destruction. 



FIG. 5. Eye of 2-day rat (left) showing degeneration only in the undiiferenti- 

 ated layers of the retina; eye of 10-day rat (right) showing differentiated retina and 

 absence of degeneration after exposure to radiation. 



FIG. 6. Part of the eye of the frog tadpole showing degenerate cells restricted 

 to the germinative zone. 



CiExetic Effects of Radiation 



(c) 



''A 



FIG. 7. Photoiniciosraphs of chromosomes in Tradcscantia pollen-grains that 

 have been X-rayed. (<;) A dicentric chromosome, arisen by sister chromatid-union in 

 a chromosome-break, forms a bridge at anaphase joining the two polar groups of 

 chromosomes, (fe) An acentric fragment-chromosome lags at the equator of the 

 spindle at anaphase, (c) Asymmetrical chromatid-interchange and a chromosome- 

 break at metaphase. 



105 



