62 



CLINICAL BACTERIOLOGY AND 



Method. — Take a mixture of the bacterial emulsion 

 and mix with it a small quantity of serum from an 

 animal immune to the bacterium in question, and inject 

 into the peritoneal cavity of a healthy guinea-pig. After 

 half an hour the peritoneal fluid and exudate is micro- 

 scopically examined; and if the reaction is a positive one 

 the organisms will be found to have undergone degenera- 

 tion, in which case the organism will be found to belong to 

 the same species as the one which the already immunized 

 animal was invaded by. On the other hand, if the reaction 



Fig, 30. — A, Micro-organism ; B, Immune Body or Amboceptor; 

 C, Complement (Ehrlich). 



is a negative one the organism belongs to a different species 

 to that by which the animal was immunized. 



Opsonins. 



Wright has shown there exists in blood-serum an anti- 

 body which possesses the specific virtue of sensitizing the 

 bacteria present, and in this manner prepares them for 

 the devouring activities of the leucocytes. He calls this 

 antibody " opsonin," or " feast-preparer." It appears this 

 opsonic power which the serum exerts upon each kind of 

 bacterium is a specific one, for we find if an animal is 



