BACTEKIOLYSIS 45 



It may be affirmed, therefore, that, aside from the matter of 

 alkalinity, the composition of the medium with respect to its 

 nutritive properties, exerts no influence on the development of 

 the bacteriophage. From the moment when it has at its disposi- 

 tion living and normal bacterial cells, against which it is active, 

 it multiplies — at the expense of these bacteria which constitute 

 its sole culture medium. 



CULTURE OF THE BACTERIOPHAGE ON SOLID MEDIA: ISOLATED 



COLONIES 



It has been stated that the bacteriophage sho ws the formation 

 of obvious colonies on agar, and that in order to obtain them it 

 is only necessary to inoculate a broth suspension of the Shiga 

 organism very lightly with a culture of the bacteriophage and to 

 distribute a drop of this suspension on agar. After incubation 

 the j3Cj^enn^_of_bacillary growth presents a number of areas free 

 of all apparent culture" If theThoculation of the bacteriophage 

 has been massive the surface of the agar appears sterile. Let us 

 consider the characters of these cultures. 



When the surface of the agar remains bare because of the large 

 numbeT^oT3acteriophagous organisms and maintains this appear- 

 ance indefinitely it has become unsuited for the cultivation of 

 the Shiga bacillus. When inoculated at such a time with a cul- 

 ture of this bacillus, even in a very abundant sowing, the slightest 

 development cannot be detected. The medium is, however, 

 normal for another bacterium. If inoculated with the cholera 

 vibrio, for example, the growth will be as luxuriant as if planted 

 upon fresh medium. Hence, if B. dysenteriae Shiga does not grow 

 it is only because the bacteriophagous organisms remain on the 

 surface of the agar and exercise their dissolving action on the 

 bacteria deposited thereon. This is readily confirmed. If we take 

 a tube of agar which has remained apparently sterile after having 

 been inoculated with a suspension of the bacteria containing a 

 bacteriophagous culture, and if the surface of the medium in such 

 a tube is washed with a few drops of sterile bouillon and to this 

 is added a fresh suspension of bacteria, this suspension will be 

 lysed within a few hours. 



