THE BIOLOGY OF THE CELL SURFACE 



known that a certain complex of physical and chemical 

 conditions in the cytoplasm is necessary for the initiation 

 and completion of mitosis. The rhythm of nuclear division 

 is itself parallel with the rhythm of structural and physico- 

 chemical changes in the cytoplasm. Abundant evidence 

 indicates that parallelling the rhythm of mitosis is a rhythm 

 of susceptibility and resistance of the cytoplasm to many 

 and diverse experimental means. In some cases, notably 

 that of the egg of Nereis, the experimental means including 

 radiations are as effective on the egg in the condition of the 

 resting nucleus as in stages of mitosis. The susceptibility 

 displayed by a nucleus is to be correlated with changes 

 in the cytoplasm; and since radiations are not alone among 

 means which may be more effective on cells in stages of 

 mitosis than on those with the so-called resting nuclei, we 

 can not denominate Roentgen or radium rays as specific 

 chromosome-affecting means. 



What is true is rather this: radiations are far nicer means 

 than, for example, hypotonic and hypertonic solutions, 

 heat and cold — all of which give effects similar to those of 

 radiations. Radiations produce effects which are more 

 rapid, more exactly measurable and more widespread in a 

 given population of cells. This, in my judgment, is the 

 chief value of radiations as experimental means. ^ Failure 

 to appreciate that in experiments with radiations the cyto- 

 plasm is affected and that radiations belong to a large class 

 of experimental means has given birth to the fertile error 

 that Roentgen, radium and other rays are causative factors 

 for inducing directly profound changes in chromosomes. 

 The offsprings of this notion, nursed by the gene-theory 

 of heredity, are theories concerning the origin not 

 only of species but also of the whole realm of living 

 things. 



1 Just, ic/^6c. 



34S 



