122 



COLLECTED STUDIES IN IMMUNITY. 



with vibrio Metchnikoff. This serum was inactivated by heating 

 to 57 C. for half an hour. Normal active rabbit serum served as 

 complement. 



TABLE I. 



Three drops of bouillon to each tube. All the tubes filled to the same volume 

 with 0.85% salt solution, then placed into the thermostat at 37 C. for three 

 hours. Finally, five drops of each plated on agar. 



This experiment shows that the inactive immune serum alone 

 is innocuous to vibrio Metchnikoff (Control II); also that 0.3 cc. of 

 the active normal rabbit serum alone is innocuous. However when, 

 for example, 0.01 cc. immune serum is mixed with 0.3 cc. normal 

 active rabbit serum, the many thousand germs inoculated are killed. 

 In the same way 0.005 cc. immune serum plus 0.3 cc. normal active 

 rabbit serum also causes the death of all the organisms. With 

 smaller amounts of immune serum (but with the same amount of 

 the complementing serum as before) the destruction of the germs is 

 incomplete, while with still smaller amounts there is no destruction 

 whatever. But the destructive effect also becomes less when more than 

 0.01 cc. immune serum is used, so that with 0.5 cc. immune serum 

 no destructive at all can be observed. Hence if we had tested only 

 the mixture of 0.5 cc. of this immune serum plus 0.3 cc. normal 

 active rabbit serum we should certainly not have supposed that 

 ^we were dealing with a powerful immune serum. That this action 



