VIII REJUVENESCENCE OF MICROORGANISMS 279 



has meanwhile shown the tendency to increase steadily with the 

 decline of tuberculosis. This very important and interesting problem 

 will be discussed in most detail also in the next Part. 



3. The Significance of Filtrable Forms of Bacteria 



It seems probable that almost all the parasitic bacteria are being 

 rejuvenated in the same way as tubercle bacilli, although the degree 

 of the connection with the host may vary greatly with the species of 

 bacteria. For example, the connection appears to be particularly firm 

 in lepra as well as in tuberculosis, while in other diseases such as 

 typhoid and dysentery it may be loose. 



The filtrable form has been known and discussed for the longest 

 time with tubercle bacillus. But the presence of related forms appears 

 to be universal with bacteria, supporting the above idea that bacteria 

 are generally inherited through germ cells of the host. It has long 

 been known that dysentery bacillus can restore its full form even 

 after decomposed into filtrable particles ; that is, viable dysentery 

 bacillus can be formed from lysed filtrate of the bacteria by phage 

 (90). It is said that newly generated bacteria are phage resistant, 

 which must be expected from the theory of the writer as already 

 referred to. Again, Kasahara et al. (91) have found with many kinds 

 of bacteria that original forms are actually produced from the filtrate 

 of bacteria decomposed by ultra-sonic vibration. 



On the other hand, Klieneberger (92) isolated from cultures of 

 StYepto-bacillus milifofmis a minute organism which she designated as 

 L-form. This resembles the virus-like organism of bovine pleuropneu- 

 monia. They are isolated from many other bacterial species, and 

 transformation into this virus-like forms is brought about apparently 

 always by an injury to the bacteria, especially when treated with 

 penicillin. Diens (93) is of the opinion that these virus-like organisms 

 are part of a life-cycle not only in the streptobacillus, but in other 

 bacterial species. In fact, he has succeeded in causing their appear- 

 ance in cultures of E. colt, Haemophilis influenzae, Flavobaeterium, the 

 gonococcus and F. funduliformis. Some workers believed at least some 

 of these L-forms to be analogous to the so-called fitrable forms, but 

 some others appear to hold the opinion that these two forms are 

 different (94) (95). It has been reported that in penicillin-containing 

 media P. vulgaris showed L-type growth. It is a note-worthy fact 

 that L-forms thus produced could be changed into bacillary forms 

 when transplanted to penicillin-free media or passed intraperitoneally 

 through mice ; the L-form appeared to be anaerobic and non-pathogenic 



