42 THE BACTERIOPHAGE AND ITS BEHAVIOR 



These two basic conditions being satisfied, it may be said that, as a 

 general rule, the most favorable medimn, that in which bacteriophagy 

 will take place in the most perfect fashion, is that which, because of its 

 composition, provides best for the development of the particular type 

 of bacteria selected to undergo the dissolution. This is not strange, 

 for it is not in fact in the medium itseK that the bacteriophage acts 

 and multipHes, it is within the bacteria themselves. The interior of 

 the bacterial cell is the true and sole medium for the multiplication of 

 the bacteriophage (d'Herelle^^"). This is by no means equivalent to 

 saying that the composition of the medium is of no consequence, for 

 all conditions which modify the state of the bacteria are reflected in 

 the phenomenon, one of whose manifestations and indeed the most 

 obvious one, is the dissolution of these bacteria. For example, it is 

 shown by many experiments that the "critical period" in the life 

 history of the bacterial cell in the presence of the bacteriophage is the 

 moment of its division. But it must not be assumed that only those 

 bacteria in the process of division are subject to attack. It is then, 

 because of its influence upon the development of the bacteria that the 

 composition of the medium has a reflected effect upon the phenomenon 

 of bacteriophagy. 



All of the experiments presented in the first edition of this text* 

 were carried out, except where stated to the contrary, with cultures or 

 suspensions of bacteria prepared with the ordinary bouillon used in the 

 Vaccine Laboratories of the Pasteur Institute. This is the so-called 

 Martin's bouillon, made by mixing in equal parts a beef infusion (400 

 grams per liter) and a peptone solution, prepared in the laboratory by 

 acid autodigestion at 50°C. of pig stomach (200 grams of minced gas- 

 tric mucosa per liter). The adjustment of the reaction was effected 

 by the old method, using phenolphthalein as indicator, the final reac- 

 tion being -6 to -8, which corresponds very closely to a pH of 7.6 

 to 7.8. Preliminary control experiments had shown me that such a 

 degree of alkahnity was best suited to the reaction (d'Herelle^^^), as the 

 following indicates. 



Peptone water (containing 25 grams of Chassaing peptone and 5 

 grams of NaCl per Uter) is neutralized to phenolphthalein. The 

 medium is then frankly alkaline to litmus. It is then distributed into 

 tubes, 10 cc. to each. Hydrochloric acid is added to each tube in dilu- 

 tions to form an increasing degree of acidity. All of the tubes are 



* The Bacteriophage; Its Role in Immunity. Williams & Wilkins Co., Balti- 

 more, 1922. 



