CHAPTER VIII 



REJUVENESCENCE OF MICROORGANISMS 

 WITHOUT SEXUAL REPRODUCTION 



1. The Microorganisms Parasitic on Insects 



If viruses can accomplish their rejuvenation in such a remarkable 

 way as above described, it should be expected that the secondary or- 

 ganisms evolved from viruses may apply the same tool for their 

 rejuvenation- 

 It is generally accepted that most of pathogenic Rickettsiae are 

 inherited in arthropod vectors from generation to generation. It is 

 unreasonable to consider that the secondary organisms choose the 

 virus-like rejuvenation mechanism only up to the stage of Rickettsiae, 

 and that the organisms evolved higher than Rickettsiae all abandon 

 the mechanism. According to the writer's view the microorganisms, 

 such as bacteria and protozoa, which perform no distinct sexual process 

 are still succeeding to this remarkable habitude of their ancestoi^s. 



This view is strongly supported by the fact that in a large number 

 of insect species, a special structure or organ is present, called my- 

 cetome, the principle function of Vv'hich appears to be that of housing 

 various microorganisms, some of which are of fungous nature while 

 others are called bacteroid. Most of these organisms cannot be culti- 

 vated outside the insect body, only capable of proliferating in the 

 host. 



These microorganisms are looked upon as symbiotes, and in some 

 cases the symbiotes apparently furnish their hosts with essential 

 substances, such as vitamines, which are lacking in their regular 

 diet ; in some other cases they supply hormone-like substances which 

 aid in the development of the ovaries. It appears quite possible that 

 the symbiotes of m.any insects are capable of fixing atmospheric 

 nitrogen. Certain insects cannot maintain their lives if the mjxetome 

 is mechanically removed, or the symbiotes are killed by drugs, such 

 as penicillin, or by maintaining the insects for a prolonged period at 

 higher temperatures (84). 



Thus the mycetome, an aggregate of microorganisms, is regarded 

 as an indispensable organ for the insects, and consequently the organ 

 together with the microorganism are inherited from generation to 



