88 THE BACTERIOPHAGE 



bacteria (their morphology will be discussed shortly) are sur- 

 rounded by a mucous material. They are actual zoogleic colonies. 



As has been said above, there can be no doubt as to the nature 

 of these bacteria, since all biologic reactions show that they react 

 as did the bacteria of the same species which were used to prepare 

 the original suspension. Moreover, in every instance, they revert 

 to normal form. It is only necessary to eliminate the bacterio- 

 phage, the cause of the transformation. 



It is thus very obvious that the resistance of the bacterium to 

 the action of the bacteriophage profoundly modifies its form. 

 Resistance accompanies a transformation into the coccus form, 

 and when the bacterium, having to defend itself against an 

 extremely virulent bacteriophage increases its resistance, there is 

 formed a mucous capsule which certainly functions by hindering 

 the penetration of the ultramicrobes into the bacterial body. 

 Encapsulated bacteria thus enjoy a refractory state. 



The transformation is accompanied by modifications in the 

 properties of the bacterium; increase in viability, enhanced viru- 

 lence, and inagglutinability by specific sera. 



The resistance persists only as long as the bacterium must 

 needs resist the action of the bacteriophage. In the absence of 

 ultramicrobes 6 the resistance gradually falls, somewhat more 

 rapidly when it was not very marked. In extreme cases it disap- 

 pears after about thirty transfers on agar. This represents a 

 very considerable number of generations. 



We have seen that it is experimentally possible to render a 

 bacterium resistant to the action of the bacteriophage and we 

 have indicated different methods which enable us to reproduce 

 this phenomenon at will. It is not an artificial phenomenon but 

 is a reproduction of a natural process which takes place within the 

 organism. 



Each strain of a species of a pathogenic bacterium, recently 

 isolated from the body of an individual, offers a different resistance 

 to the action of the bacteriophage, and this resistance, as we know, 

 may extend to an absolutely refractory state. These differences 

 of resistance arise, as will be demonstrated later, in hereditary 



6 Suitable means have been indicated for purifying a mixed culture by 

 eliminating the bacteriophage. 



