58 THE BACTERIOPHAGE 



THE ULTRAMICR0BIAL BACTERIOPHAGE: AN ENDOPARASITE 



We have already considered the mode of action of the bacterio- 

 phage from the point of view of its macroscopic characteristics. 

 Various types of experiment allow us to penetrate somewhat further 

 into the more intimate nature of the phenomenon. 



Experiment has demonstrated that the bacteriophage is ca- 

 pable of development only at the expense of living bacteria, since 

 these provide its sole culture medium. This cultivation appar- 

 ently takes place within the interior of the bacterial cell, and 

 ultramicroscopic observation shows that this is indeed the case. 

 But first, let us consider some of the experiments which permit us 

 to recognize the manner in which the infection of the bacteria 

 is accomplished. 



Attempts have been made to effect a culture of the bacterio- 

 phage of the Shiga bacillus in a filtrate derived from Shiga or- 

 ganisms grown in bouillon for various lengths of time — 1, 7, 14, 

 and 21 days — but all have failed. Two counts of the number of 

 ultramicrobial elements, the one made immediately after the 

 inoculation, the other after incubation for a week at 37°C, 

 have given exactly the same number of germs. Thus, the bac- 

 teriophage is entirely incapable of multiplication in a medium 

 containing only the secretory products of the bacterium. The 

 bacterial body itself is essential. 



If the bacteriophage actually proliferates within the interior 

 of the bacterial cell, the ultramicrobes inoculated into a suspension 

 ought, before all multiplication, to disappear from the fluid. In 

 fact, each ultramicrobe ought first to penetrate a bacterial cell, 

 to multiply there and to reappear in the fluid only when this cell 

 is destroyed. It is easy to verify this hypothesis. 



Experiment XIV. The following suspensions are prepared : 



(1) 100 cc. of a suspension of the Shiga organisms containing 250,000,000 

 bacilli per cubic centimeter. This is inoculated with 0. 25 cc. of a culture 

 of the bacteriophage. 



(2) 100 cc. of a suspension of the cholera vibrio, containing 250,000,000 

 per cubic centimeter. This also is inoculated with 0.25 cc. of the same 

 culture of anti-Shiga bacteriophage. 



(3) 100 cc. of bouillon containing only 0.25 cc. of the same bacterio- 

 phage. 



