BACTERIOLYSIS 35 



If, immediately after the inoculation, and at regular intervals 

 for six hours, a loopful of the liquid is planted on agar, all the 

 tubes remain sterile. One would readily think that the absence 

 of colonies of Shiga means that they have been killed with the 

 first contact with the inoculated bacteriophage. But this is 

 not the case for if instead of planting agar with the suspension 

 as such, it is previously diluted to 1 : 1000 with bouillon, and then 

 this dilution is planted on agar numerous colonies of B. dysenteriae 

 develop. The bacilli have by no means been killed. If the 

 transfer of the undiluted suspension to agar remains sterile it is 

 simply because the agar has been planted simultaneously with 

 many living Shiga bacilli and also with a large number of the 

 ultramicrobes. Indeed, the bacilli have commenced to multiply 

 in the nutritive medium but the bacteriophage has not been 

 inactive. Finding the bacilli which they parasitize within reach, 

 the ultramicrobes act upon them, reproduce, and inhibit the 

 bacillary growth. In the other case, with the suspension diluted 

 to 1 : 1000, the bacilli and the bacteriophagous germ, a thousand 

 times less numerous, are separated by spaces sufficiently great 

 so that immediate interaction is less readily accomplished. This 

 allows the bacilli which are outside of the immediate neighborhood 

 of an ultramicrobe to multiply and to form colonies. 



A second dilution (1:1000) of the suspension, made after the 

 latter has been incubated for an hour, more often remains sterile 

 when transferred to agar and only rare colonies develop. After 

 two hours of incubation, cultures on agar always remain sterile. 

 At this time all the bacilli contained in the suspension have been 

 attacked and none of them are able to reproduce. 



2. Inoculation with few anti-microbial elements. Six tubes of 

 the Shiga bacillus suspension are inoculated with the bacteriopha- 

 gous culture (containing 3000 million per cubic centimeter) in 

 such a way that each tube receives one six-millionth of a cubic 

 centimeter. When incubated, four give normal cultures of 

 B. dysenteriae and all subcultures on agar give normal growths. 

 They are therefore without interest to us. The other two, how- 

 ever, which have each received probably one, certainly not more 

 than two ultramicrobes, show the following picture: The sus- 

 pension becomes more and more turbid. After two hours at 



