500 WILBXJRT C. DAVISON 



subcultures of some of these spontaneously "irregular" colonies 

 contained "irregular" colonies for as long as ten generations. 

 Subcultures of others contained nothing but regular colonies. 

 The "irregular" colonies did not appear to be as viable as normal 

 colonies and subcultures occasionally failed to grow. Inasmuch 

 as these "irregular" colonies occurred more frequently in sub- 

 cultiu-es of old laboratory strains than of freshly isolated strains, 

 it is possible that aging may influence their development. 

 Growth in media containing lactose also appeared to favor their 

 development. Filtrates of cultures of these "irregular" colonies 

 were somewhat more lytic than filtrates of normal cultures 

 (table 13). It is possible that these "irregular" colonies of 

 normal strains and the "moth eaten" colonies of "sensitive" 

 strains are related or even perhaps identical. 



The different degrees of lysis produced in different cultures 

 by the same filtrate (part I) apparently did not depend altogether 

 on the presence or absence of "irregular" colonies in these cul- 

 tures as only in six strains were "irregular" colonies noted. 



FILTRATES OF PEPTONE "WATER CULTURES OF NORMAL STRAINS OF 

 BACT. DYSENTERIAE (fLEXNER) 



Inasmuch as the bacteriolytic activity of stool filtrates, which 

 had become contaminated with stool or air organisms and had 

 then been refiltered, was sometimes increased, it seemed possible 

 that filtrates of normal cultures theinselves might be bacteriolytic. 

 I therefore inoculated regular and "irregular" colonies of several 

 strains of normal Flexner bacilli into peptone water and filtered 

 these cultures after various periods of incubation at 37°C. 

 (table 13). Eleven of the twenty filtrates (55 per cent) of pep- 

 tone water cultures of regular colonies of five normal strains of 

 Flexner bacilU and all of the six filtrates (100 per cent) of "irreg- 

 ular" colonies were slightly bacteriolytic. The degree of bacter- 

 iolysis was much less than that of stool filtrates and of filtrates 

 of cultures of "sensitive" strains. In none of the instances in 

 which subcultures were made of dysentery bacilU which had been 

 incubated with these filtrates of normal cultures were "sensitive" 

 colonies found. It is therefore probable that although filtrates 



