PREFACE 



The preliminary notes upon the phenomenon of bacteriophagy, 

 beginning with those published in 1917, attracted the attention of 

 scientists to but a moderate degree, despite the fact that the facts 

 presented appeared to be contrary to all of that which had been de- 

 scribed up to that time. Only after the publication of the first collected 

 work in 1921 did investigators on all sides really undertake the study 

 of this phenomenon, as interesting as it is complex. Four years have 

 elapsed since then and during this time more than six hundred memoirs 

 and notes have appeared, to what purpose the reader of the following 

 pages will see. 



The present text is divided into three parts. 



It is evident, a priori, that by virtue of the principle that "there can 

 be no effect without a cause" the phenomenon of bacteriophagy is 

 induced by a "something" — by a "principle." This is necessarily 

 true whatever may be the hypothesis advanced as to the state or 

 nature of the causative agency. 



A study of bacteriophagy in vitro is the first aspect of the problem 

 which we will consider. In reality, this is simply a study of the re- 

 spective behaviors of the unknown "principle, "the cause of the phenom- 

 enon, and of the bacterium which is subject to the phenomenon. 

 Before studying the nature of a principle we must know something 

 of how that principle behaves. 



From the broader point of view all of the studies carried out on the 

 phenomenon of bacteriophagy itself have confirmed my first observa- 

 tions. Thanks to the experiments of a great many authors certain 

 details of the process have been more clearly defi^ned, and it may be 

 said that today the phenomenon itself is well understood. There 

 remains, however, still another side to the question, a phase which 

 opens a field of the greatest theoretical and practical importance, 

 namely, the problems associated with the resistant forms of bacteria, 

 with the infravisible forms in particular. 



What are the properties of this "principle" which causes the phenom- 

 enon? What is its physical state? And more important yet, what 

 is its biological state? These are the things that it is important for 

 us to discover. These are the points which it is particularly important 

 to bring to the attention of the trained scientific mind. 



