84 THE BACTERIOPHAGE 



The cultures secured by the inoculation of the mucous colonies on differ- 

 ent media show the following reactions: 



In agar stabs: small lenticular colonies about the needle track. 



In gelatine : as in agar, the resistant bacteria remain alive and cultivable 

 for at least eleven months. In the case of the Shiga dysentery organisms 

 this represents a viability at least ten times as great as that of the normal 

 bacillus. 



In gelatine stabs: large opaque colonies with opaque centers. 



On glycerine potato (prepared as for the cultivation of B. tuberculosis}'. 

 very rare colonies on the potato, very abundant growth in the fluid at the 

 bottom of the tube. 



In milk: not coagulated in ten days. 



In litmus milk: turns to mauve after two months. 



On coagulated serum: no growth. 



In neutral red: no change in two months, either on agar or in bouillon. 



In litmus milk (Petruschky) : acid after ten days and remains acid. 



When the mucous colonies are suspended and heated to 60C. 

 they are not cultivable, for then the culture contains only the 

 living very virulent ultramicrobe which is not killed until a tem- 

 perature of about 75C. is reached. Reinoculated into bouillon, 

 the refractile, mucous, mixed colonies yield two types of culture, 

 (a) mixed cultures showing changes in turbidity, and (6) aggluti- 

 nated cultures, which, as we know, always depend upon the degree 

 of virulence of the bacteriophage and the capacity of resistance of 

 the bacterium, factors which regulate the appearance of the 

 culture. 



We have seen that if an agglutinate, taken from a mixed culture 

 in stable equilibrium, is introduced into a suspension, a lysis of the 

 suspension is followed by a growth of the agglutinate. The same 

 thing transpires if an abundant seeding is made on tubes of slant 

 agar having a growth of the Shiga bacillus. First, plaques appear, 

 and then after three or four days a mucous colony develops in the 

 center of each plaque. In both instances the bacteriophage acts 

 upon the normal non-resisting bacteria and dissolves them, then 

 the refractory bacilli multiply as they would have done on a 

 sterile agar or in bouillon. 



THE RESISTANT BACTERIUM 



From that which has preceded it may be deduced that the 

 acquisition of resistance by a bacterium is reflected in a marked 



