THE BACTERIOPHAGE CORPUSCLE 79 



wise, as they first appeared ; the plaques once formed undergo no modi- 

 fication, they never increase in size and they are never overgrown by 

 the surrounding bacterial culture. 



As for the cultures presenting a normal bacterial growth (tubes 8, 

 9, 10 and 11, and, of course, tube 12), they also undergo no further modi- 

 fication and if they be further examined by subculture it is found that 

 they will yield indefinitely normal cultures of the dysentery bacillus. 



If we observe the nature of the reaction which takes place in the sus- 

 pensions themselves, that is, the tubes from which the agar slants were 

 implanted we will find that after incubation for 24 hours bacteriophagy 

 is complete in the tubes containing dilutions 10~^ to 10~^. After 48 

 hours it is also complete in tubes 6 to 10, that is, in those containing 

 dilutions lO"" to 10-^°, while the tube with the 10"^^ dilution remains 

 turbid. This last tube may be subcultured indefinitely with the result 

 that the successive cultures are as normal as are those of the control 

 tube (tube 12). 



This experiment has been repeated a great many times with bacteria 

 of different species: the staphylococcus, B. pestis, B. typhosus, B. 

 gallinarum, etc., and has always given, from the broad point of view of 

 the principle involved, analogous results. The course of the phenome- 

 non is always the same. The only point subject to variation is the 

 extent of the dilution, and such a quantitative difference is, of course, 

 compatible with what we know of bacteriophagy. For example, in 

 working with another race of bacteriophage, also active against the 

 dysentery bacillus, the last active dilution may be 10"^, and in this case 

 the agar tubes corresponding to dilutions 10~^ and 10"^ will be bare. 

 The agar tube representing the dilution 10~^ will show shreds of 

 growth. The tube representing 10~^ will be covered by a layer of cul- 

 ture studded with about 100 plaques, the one corresponding to 10"^ 

 will present but 12 plaques, and those tubes corresponding to the remain- 

 ing dilutions of the series will be covered with normal cultures of 

 dysentery bacilli. 



In another experiment carried out with Staphylococcus aureus and with 

 a race of the bacteriophage active for this organism, the last active 

 dilution may be 10-^^ The agar tube corresponding to the dilution 



place with races of the bacteriophage which are extremely potent, races which 

 cause in a liquid medium a total and permanent dissolution of a normal suspension, 

 the medium remaining limpid indefinitely. If there are any who have not been 

 able to isolate such a race I will gladly send them one upon request. These races 

 will permit them to carry out all of the experiments described in this text. 



