BACTERIOPHAGE AS AN ANTIGEN 409 



bacteria against which the opsonic effect is to be determined. The 

 mixture is aspirated in a capillary pipette which is sealed and placed 

 in the water-bath at 38°C. for fifteen minutes. The contents of the 

 pipette are then spread on a slide, stained, and examined. 



As reagents we have taken: Guinea pig leucocytes, a Shiga-bacterio- 

 phage suspension, and a suspension of Shiga bacilli. 



1. Control. 



Leucocytes, bacilli, ordinary bouillon 

 100 leucocytes phagocytize 36 bacilli 



Opsonic index = 1 



2. Leucocytes, bacilli, bacteriophage suspension two years old" 

 100 leucocytes phagocytize 692 bacilli 



Opsonic index = 19 . 2 



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



1:250 

 100 leucocytes phagocytize 156 bacilh 



Opsonic index = 4.3 



4. Leucocytes, bacilli, bacteriophage suspension six days old 

 100 leucocytes phagocytize 1510 bacilli 



Opsonic index = 41.9 



5. The same mixture, except the bacteriophage suspension is diluted 



1:250 

 100 leucocytes phagocytize 146 bacilH 



Opsonic index = 4.1 



6. The same mixture, except the bacteriophage suspension is heated at 



60°C. for 30 minutes 

 100 leucocytes phagocytize 728 bacilh 



Opsonic index = 20 . 2 



7. The same mixture, except the bacteriophage suspension is heated 



and diluted to 1:250 

 100 leucocytes phagocytize 101 bacilli 



Opsonic index = 2.7 



In the mixtures 2, 4, and 6, the indices recorded represent a mini- 

 mum. Many leucocytes contain so many phagocytized bacilli that 

 counting is impossible. Since in the above counts only those cells 

 which did not contain masses of bacteria have been included, the actual 

 index is therefore somewhat higher.* 



* It will be recognized that the opsonic indices obtained with sera are far below 

 these secured with the bacteriophage suspensions. With the former an index of 

 2 is exceptional. 



