50 THE BACTERIOPHAGE 



Number of bacilli Lysis is complete 



per cc. in 



50,000,000 14* hours 



100,000,000 14* hours 



200,000,000 14* hours 



250,000,000 14* hours 



300,000,000 16 hours 



400,000,000 16 hours 



500,000,000 18 hours 



These results are readily understood. In the first case the 

 number of ultramicrobes is very great from the start, all of the 

 bacteria, or by far the greater part of them, are immediately 

 attacked, and this quickly arrests the development of the bac- 

 terial culture. In the second case, as a result of the small num- 

 ber of ultramicrobes inoculated, very few of the bacteria are at 

 once attacked, and those which remain unharmed are free to 

 develop, so much the more as the suspension is the more dilute. 

 To be convinced of this it is only necessary to observe the sus- 

 pensions and to compare their relative opacity from time to time. 

 All become more and more turbid during the first few hours after 

 the inoculation, and in five or six hours after the inoculation they 

 all present a comparable opacity, corresponding to approximately 

 650,000,000 bacilli per cubic centimeter. In a word, whatever 

 may be the original titre of the suspension at the time when it 

 is inoculated with a limited number of the bacteriophagous or- 

 ganisms, the latter must always operate on a suspension of about 

 650,000,000 bacilli per cubic centimeter, since in all cases the 

 bacteria reproduce until they attain this number. Hence, 

 lysis will always take place within very nearly the same length 

 of time. 



A suspension of young bacilli, containing about 500,000,000 

 bacilli per cubic centimeter is completely lysed by the action of 

 a bacteriophage of maximum activity. Beyond this figure the 

 medium never entirely clears, and remains the more cloudy the 

 more concentrated the suspension, regardless of the number of 

 ultramicrobes inoculated. A suspension containing 1,000,000,000 

 bacilli per cubic centimeter, for example, will never be completely 

 lysed, whether it is inoculated with a few individual bacteriophag- 

 ous organisms or whether it is inoculated with some thousands of 

 millions. However, in working with suspensions which are ex- 



