492 WILBUET C. DAVISON 



was covered with typical round dysentery colonies. This 

 "bare" area was subcultured on another agar plate. After 

 twenty-four hours at 37°C. this plate contained in equal pro- 

 portions, small, regular, round, typical dysentery colonies and 

 large mucoid colonies with very irregular outhnes and a "moth 

 eaten" appearance. Some were crescentic in shape, others 

 triangular, and still others somewhat round with deep indenta- 

 tions in the edges. The edges of many of these colonies were 

 more dense and refractiie than their centers and appeared white 

 and opaque in contrast to the gray translucency of the center. 

 They resembled in every way, the photographs of "sensitive" 

 colonies that WoUstein (Davison, 1922) has published. Forty- 

 two successive subcultures of these "moth eaten" colonies, each 

 gave rise to 10 to 100 per cent of the "moth eaten" colonies and 

 to 90 per cent of the small regular round colonies. Press of 

 work prevented carrjdng these subcultures to more than forty- 

 two generations. 



Occasionally subcultures of the "moth eaten" colonies failed 

 to grow in peptone water or on agar and reinoculation with several 

 "moth eaten" colonies was necessary. '^Tien a "moth eaten" 

 colony was subcultured in peptone water for one or two transfers, 

 and then plated on agar, the plates frequently remained sterile 

 or else contained nothing but regular colonies indicating the 

 influence that a change in media might play in the multiplication 

 of one or the other of these types. Gram-stained smears of these 

 "moth eaten" colonies were largely composed of short fat Gram- 

 negative bacilli with very few long forms. They were decolorized 

 with more difficulty than smears of normal colonies. The 

 "moth eaten" colonies represent the "sensitive" or "lysogenic" 

 strain and the small, regular, round colonies the "resistant" 

 strain described by others (Davison, 1922), 



FILTRATES OF PEPTONE "WATER CULTURES OF A "SENSITIVE" 

 STRAIN OF BACT. DYSENTERIAE (fLEXNER) 



The growth from twelve "moth eaten" colonies of the eighth 

 generation of the "sensitive" strain of Flexner baciUi described 

 above was inoculated into 500 cc. of peptone water (table 10). 



