316 IV. THE PRINCIPLES OF LIFE PHENOMENA 



It is known that the mitotic spindle is birefringent and that the 

 birefringency decreases when the chromosomes are separating (158). 

 This demonstrates that the protoplasm threads between the two cent- 

 rioles are pulled extensively so that they are arranged quite regularly 

 in a parallel alignment, thus the birefringency revealing in the spindle, 

 but that when the contraction of the threads takes place causing the 

 separation of the chromosomes, the regular alignment is to be lost 

 followed by the disappearance of the birefringency. 



The fact that mitosis is the general, fundamental feature of or- 

 ganisms must depend upon that it is the mechanism easiest and most 

 favorable for the organism to achieve the cell division. Thus the 

 division of chromosomes without the preliminary fission of centriole 

 may tend to cause only the increase of chromosomes without the cell 

 division, because the divided centrioles only can produce the space 

 where the essential protoplasm substance is absent, making the cell 

 division possible. As is well known colchicine prevents the formation 

 of the mitotic spindle, but do not affect the chromosomes, so that in the 

 presence of colchicine chromosomes are increased without cell division, 

 a fact suggesting that colchicine inhibits the growth or the division 

 of the centriole. 



The reason why the division of centrioles and chromosome is initi- 

 ated normally is not clear. It may depend upon some basic property 

 of proteins. Protoplasm-like masses prepared in vitro by the writer 

 also cannot grow unlimitedly, suggesting that the fusion of elementary 

 bodies can occur only to a certain limit. Both centrioles and chromo- 

 some may be the aggregates of elementary bodies, so that if they grow 

 over a certain limit they may be bound to split. Colchicine may exert 

 some influence on physicochemical property of the protein composing 

 the centrioles to make the centrioles unable to grow or to divide if 

 the growth is not inhibited. 



An interesting phenomenon associated with neutron- or r-irradiation 

 of maize seeds has been found by Schwartz (159). The seedling irradi- 

 ated at the higher dose levels were not only taller but also much 

 healthier in appearance than those at the lower levels. These seedlings 

 could not be differentiated from normal unirradiated young seedlings 

 except that there was a cessation of farther growth after approximately 

 5 days. The finding concerning the phenomenon which must be noted 

 here is that cytological examination of the root tips from plants whitth 

 received high doses of irradiation revealed a complete absence of cell 

 division. In other words, the growth was due entirely to cell elon- 

 gation in these seedlings. Thus the conclusion drawn by Schwartz 

 was that at high radiation levels the seeds were killed in the sense 

 that no farther cell divisions occurred. According to the writer's view 



