CHAPTER 11 



THE BACTERIOPHAGE 



In 1915, Twort described a curious degenerative change that he had observed in 

 cultures of a staphylococcus derived from calf-lymph. He was able to transmit 

 this change from one culture of the susceptible organism to another, by placing 

 on the surface of an inoculated agar slope a drop of a highly diluted filtrate from a 

 suspension of an earlier growth that had undergone the degenerative change. In 

 1917 d'Herelle recorded his first series of observations on the lytic properties of 

 filtrates of mixed cultures obtained from the faeces of patients suffering from bacillary 

 dysentery. In these preliminary studies, he was able to demonstrate the occurrence 

 of rapid and generalized lysis in a growing broth culture of a dysentery bacillus to 

 which some of the filtrate from the original mixed culture had been added, and the 

 transmission of the lytic agent in a prolonged series of cultures of the susceptible 

 bacterium, by the addition to each new culture of a filtrate obtained from the 

 preceding one after lysis had occurred. 



There can be no doubt, though d'Herelle has strenuously opposed this view, 

 that these two descriptions afford different examples of the same essential process. 

 With our present knowledge, we are, indeed, able to identify earlier records of 

 curious happenings and appearances in bacterial cultures as instances of this lytic 

 change ; but in none of these cases was the nature of the process studied in any 

 detail, nor was its transmission by bacteria-free filtrates demonstrated. Twort's 

 original paper, on the other hand, contains a complete demonstration of all the 

 essential features of this important and significant reaction ; and it has hence come 

 to be generally known as the " Twort-d'Herelle phenomenon." 



D'Herelle's observations, which he has recorded in numerous papers from 1917 

 onwards and collected in three monographs (d'Herelle 1921, 1926, 1930^, have, 

 however, been far more detailed and extensive, and have played a major part in the 

 development of our present conceptions. The name that he applied to the lytic 

 agent, Bacteriophage, has come into general use, familiarly shortened to the diminu- 

 tive phage ; and the view, consistently maintained by him, that this agent is a 

 filtrable virus, parasitic on bacterial cells, has won increasing support, particularly 

 within recent years. 



An extensive literature has grown around this subject ; but we can here do 

 no more than summarize certain of the more important observations, and the 

 conclusions that have been drawn from them. The results obtained in recent 

 studies have, indeed, deprived many of the earlier records of all save historical 

 interest. 



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