BACTERIOPHAGE AS AN ANTIGEN 411 



suspension, still moist, are dissolved in 10 cc. of physiological saline. 

 A mixture is made containing this solution, a suspension of Shiga 

 bacilli, and a leucocytic suspension in equal parts. The mixture is 

 held at a temperature of 38°C. Microscopic examination of stained 

 preparations, made after 15 minutes, shows that 100 leucocytes have 

 taken up 536 bacilli (this count is a minimum, since some of the leuco- 

 cytes had taken up so many bacilli that they could not be counted). 

 The index is 14.9. 



It is interesting to determine whether the active principle, causing 

 such a marked stimulation in opsonic action, is also operative upon 

 bacteria which have developed an acquired resistance to bacteriophagy. 

 The following experiments bear on this point. 



Mix equal parts of a suspension of Shiga bacilli resistant to the 

 action of the bacteriophage, a Shiga-bacteriophage suspension two 

 years old, and a suspension of leucocytes. After fifteen minutes, 100 

 leucocytes have ingested 8 bacteria. The index is thus 0.22, or 90 times 

 less than with normal bacilli. 



Prepare a similar mixture, but with a bacteriophage suspension 

 six days old. Here, 100 leucocytes have phagocytized 13 bacilli. 

 The index is 0.38, or 108 times less than with normal bacilli. 



Another mixture is made, using the solution of the alcoholic pre- 

 cipitate. 100 leucocytes have phagocytized 19 bacilh. The index is 

 0.53, or, 28 times less than with normal bacilli. 



From this it is clear that bacteria which resist the bacteriophage 

 also resist phagocytosis. 



The same experiment has been performed with a race of the Barbone- 

 bacteriophage and the bacterium of barbone. The results were com- 

 parable, as follows: 



(A) 1. Control. Mixture of equal parts of leucocyte suspension, 

 bouillon, and suspension of the bacterium of barbone. 



After fifteen minutes at 38°C. there are no bacteria in 100 leucocytes. 



2. Mixture of equal parts of leucocyte suspension, the suspension of 

 the bacterium of barbone, and a Barbone-bacteriophage, 8 months old. 



After fifteen minutes 100 leucocytes have ingested 109 bacteria. 



3. The same mixture, except that the bacteriophage suspension is 

 diluted 1:250. 



One hundred leucocytes have phagocytized 52 bacteria. 



4. Mixture of one-third leucocyte suspension, one-third bacterial sus- 

 pension, and one-third solution of the alcohol precipitate of a recent suspen- 

 sion of the Barbone-bacteriophage (2 mgm . of precipitate in 10 cc .of saline) . 



One hundred leucocytes have phagocytized 239 bacteria. 



