252 THE BACTERIOPHAGE AND ITS BEHAVIOR 



A bacteriophage virulent for this organism may be isolated under the 

 same conditions as was the case for B. typhosus. I have found it, 

 possessing a very high virulence, in the stools of patients convalescent 

 from paratyphoid fever. In normal individuals it is found less fre- 

 quently than are races virulent for B. typhosus and especially for B. 

 paratyphosus B. The last is the most frequently encountered of the 

 three (d'Herelle). 



Bachmann and de la Barrera*"^ have reported that extremely interest- 

 ing mutations of this bacillus occur through the action of the bacterio- 

 phage. 



Aside from colonies showing a strongly modified morphology, they 

 say, others are to be found which are small and transparent, and which 

 are very different from the normal type.* The bacilli composing 

 these colonies showed an outspoken increase in agglutinability by an 

 anti-typhoid serum and this agglutinabihty increased during the course 

 of successive transfers. With the anti-typhoid serum used by these 

 authors the following agglutinations were obtained : 



With the homologous B. typhosus 1 : 6000 



With the original B. paratyphosus A 1 : 1000 



With B. paratyphosus A, mutant (Fi) 1 :2000 



With the same after the 4th generation (F4) 1 : 6000 



With the same after the 6th generation (Fe) 1 : 6000 



This by no means represents an increase in the general agglutinability 

 of the original para A organisms, for while this original para A bacillus 

 was agglutinated by its homologous serum in a dilution of 1:3200 

 the para A mutant of the 6th generation (Fe) was agglutinated only in a 

 dilution of 1 : 1600. 



But here is a fact which is still more strange. The anti-F4 serum, 

 that is to say, the serum of an animal prepared by injections of the mu- 

 tant form in the 4th generation, agglutinated the homologous F4 organ- 

 ism at a titre of 1 : 3200, agglutinated B. typhosus, 1 : 800, and aggluti- 

 nated the original para A bacillus, 1:800. 



The anti-serum to the Fe generation agglutinated its homologous or- 

 ganism, as well as B. typhosus and the F4 strain, to the limit, but it 

 did not agglutinate to any degree the original B. paratijphosus A from 

 which the mutants F4 and Fe were derived. 



To summarize this, Bachmann and de la Barrera have observed with 



* Unfortunately these authors did not show whether they were working with 

 mixed colonies or not, or if ultrapure, whether the colonies were resistant or 

 susceptible. According to their description, however, it would appear that they 

 were dealing with partially resistant, ultrapure colonies. 



