UNICITY OF BACTERIOPHAGE PROTOBE 373 



While the following experiments can be very readily interpreted by 

 the hypothesis of a lytic ferment secreted by the bacteriophage I hasten 

 to add that they may also be interpreted in other ways, a fact which 

 naturally deprives them of the character of proof. 



Divide a suspension of staphylococci (125 million cocci per cubic 

 centimeter) into two portions. Inoculate the first with 0.05 cc. of a 

 Coli-bacteriophage, the second with 0.05 cc. of the same bacteriophage 

 together with some susceptible B. coli. Both tubes are placed in a 

 water-bath at 45°C. After 3| hours the opacity of the second sus- 

 pension is about half of that of the first. Spreadings on agar show, 

 after incubation, for the staphylococcus suspension a layer of growth 

 extending over the entire surface of the agar, for the mixed staphylococ- 

 cus-coli suspension, isolated colonies. 



Results of the same nature have been secured in another experiment 

 where a Coli-bacteriophage was combined, in one tube with Vibrio 

 metchnikovii, and in another, with a mixture of the vibrio and B. coli. 



The results are the same if a suspension of streptococci is used with 

 the Coli-bacteriophage. Spreadings on agar of a drop of a suspension 

 of streptococci inoculated with a Coli-bacteriophage give innumerable 

 colonies; a spreading of a mixed streptococcus-coli suspension yields 

 only a dozen colonies. 



Here are some experiments of another type, carried out in physiologi- 

 cal saline. A suspension of staphylococci, 250 million per cubic centi- 

 meter, is heated for a half hour at 70°C., and tests show that the fluid is 

 sterile. Each of three tubes receives this suspension. To the first 

 of these add 1 cc. of a very potent Staphylo-bacteriophage, to the second 

 0.25 cc, and to the third 0.1 cc. After 48 hours at laboratory tem- 

 perature the first suspension is hardly cloudy (the turbidity is about 

 equal to that of a suspension containing 40 million cocci per cubic centi- 

 meter), the second tube is about half as cloudy as at the beginning, 

 while the third is unchanged, showing no evidence of clearing. 



Obviously, these experiments are open to the criticism that they give 

 no proof that the dissolving ferments are produced by the bacteriophage. 

 This I realize perfectly, and the experiments are to be taken only at 

 their face value. 



As a matter of fact, up to the present time, no experiment has been 

 performed which allows us to select between the three possible hypothe- 

 ses of which I have spoken. The second, especially, is as probable as 

 the third. 



