RESISTANCE OF BACTERIA 227 



for a given organism are introduced into a suspension of these bacteria. 

 A double phenomenon occurs. The corpuscles, as the result of the 

 passages from bacterium to bacterium increase in virulence, but certain 

 particularly apt bacteria resist and serve as the origin of resistant lines. 

 The elimination of such organisms is what makes it necessary to filter 

 through a candle between each of the passages from suspension to 

 suspension of susceptible organisms. One may observe very frequently, 

 however, that the virulence of the corpuscles, after starting to increase, 

 becomes fixed in spite of multiple passages and Tomaselli has shown 

 that in these cases precisely, a production of filterable forms of ultra- 

 bacteria leads to the development of normal resistant forms. From this 

 one can see that filtration through a candle is of no avail. Both the 

 bacteriophage corpuscles and the ultrabacteria pass through, and the 

 latter, developing in the following passage yield resistant bacteria. 



The importance of this phenomenon warrants inserting here a sum- 

 mary of the experiments of Tomaselli. He worked with a Coli-bacterio- 

 phage in combination with 5 strains of B. coli. He showed that at the 

 beginning, before any passages were made, the virulence of this race for 

 these different strains was as follows: — weak (+) for strains 1, 2, and 3; 

 moderate ( + +) for strains 4 and 5. Invariably the filtrates obtained 

 after the bacteriophagy of strains 3 and 4 again became turbid, while on 

 the contrary, the filtrates from 1, 2, and 5 remained clear indefinitely. 



With this bacteriophage he carried out serial passages with each of 

 these 5 strains, following the usual method, that is to say, inoculation 

 of the filtrate into a suspension of normal bacteria and filtration through 

 a candle after 24 hours. The passages were continued without inter- 

 ruption up to a point where the virulence ceased to increase. He 

 obtained thus a maximal increase (+ + + + ) for strains 1 and 2; a 

 moderate virulence (++) for strains 3 and 5; while the virulence re- 

 mained weak (+) for strain 4. 



After each passage the filtrates obtained with strains 3 and 4 became 

 turbid after some time, meaning that with these two strains ultra- 

 bacteria formed. 



In further experiments Tomaselli sought to determine whether the 

 formation of ultrabacteria was limited as to time. He found that they 

 no longer formed when the corpuscles and the bacteria had remained 

 in contact for about 20 days. As a matter of fact, if, instead of filtering 

 the suspension where bacteriophagy had taken place 24 hours after the 

 inoculation of the bacteriophage, he permitted the contact to be pro- 



