INTRODUCTION 11 



it would be easy to demonstrate that it could not have been the bac- 

 teriophage which was involved, just as the bacteriophage could not 

 have been the cause of the phenomenon observed by Hankin. But in 

 the one case as in the other, making allowances for errors of com- 

 mission and for generahzations which may have been prematurely 

 drawn by the authors, over-enthusiastic concerning the facts acci- 

 dentally observed, I can see a possible explanation only in the bacterio- 

 phage. 



A third communication where the bacteriophage may have been the 

 cause of the facts observed, and here the probability is somewhat 

 greater, is that of Gildemeister.* In 1917, under the name of "Flat- 

 tenformen" he described irregular aberrant colonies of certain bacilH 

 (typhoid and coh). As a matter of fact it appears that what Gilde- 

 meister observed were simply bacterial colonies contaminated naturally 

 by the bacteriophage. I attribute the formation of these aberrant 

 colonies to bacterial mutations in the sense of deVries. 



I have found only these three communications in which the facts 

 disclosed might be explained as due to the action of the bacteriophage. 

 In view of the violence, as it might be termed, with which bacteriophagy 

 is often effected, it is indeed strange that it has not more often at- 

 tracted attention forcibly, especially in view of the ubiquity of the 

 bacteriophagous principle. I beUeve this can be explained in only one 

 way. There must have been many bacteriologists who have witnessed 

 the complete clearing of a broth culture which had been prepared with 

 material derived from the body of a man or sick animal, or who have 

 experienced the impossibility of subculturing to a sohd medium 

 an organism derived from the body, or again, who have observed on a 

 solid medium the presence of "plaques," the bare spots mentioned in 

 preceding paragraphs. Indeed, this is certain, since during the past 

 few years many bacteriologists have told me that they have encoun- 

 tered such things. 



In 1919, prior to my departure for Indo-China, that is, before I had 

 discovered that resistance to the plague bacillus, in man and in the 

 rat, was due to the presence in these animals of a bacteriophage viru- 

 lent for this bacillus, Nageotte told me that in the course of a con- 

 versation with Haffkine upon the subject of my studies, the latter 

 told him that he had observed repeatedly that bouillon tubes inoculated 



* Gildemeister, E. — Weitere Mitteilungen iiber Variabilitatserscheinungen 

 bei Bakterien, die bereits bei ihrer Isolierung aus dem Organismus zu beobachten 

 sind. Centralbl. f. Bakt., I. Orig., 1916/17, 79, 49. 



