VIII REJUVENESCENCE OF MICROORGANISMS 283 



killed. It has actually been known that the mammary cancer of mice 

 is induced by a virus-like agent which can be transmitted from parent 

 to offspring through germ cells ; that is, the predisposition to the 

 cancer is inheritable. 



The writer is of the firm opinion that at least the majority of the 

 primitive secondary organisms can accomplish their rejuvenation by 

 becoming thus patterns of the gene of their hosts, but it seems reason- 

 able to suppose that they must abandon such means as they advance 

 higher in the course of the evolution. As above considered, primitive 

 secondary organisms such as bacteria, fungi, and perhaps protozoa 

 can apparently invade the germ cells, but when they evolved into 

 higher multicellular organisms, their structure might become too 

 complicated to be reduced into a virus state with the result that 

 they would become unable to make use of the host germ cells. 



