IMMUNITY 77 



cannot possibh^ be made until after the toxin has had 

 abundant time to combine with the body cells. In the 

 treatment of epidemic cerebrospinal meningitis spinal 

 injections of specific antimeningococcus serum have 

 reduced the mortality to about one-half that of cases not 

 so treated. 



So far as the bacteriolysins are concerned the clinical 

 results have not been very satisfactory. Investigation 

 has disclosed many difficulties which must still be over- 

 come. In speaking of these sera it is better to use the 

 term "antibacterial/' because, after all, when we im- 

 munize an animal against a certain bacterium we do not 

 produce merely a bacteriolysin, but a serum which 

 contains also agglutinins, precipitins, opsonins, and, 

 perhaps, still other antibodies. 



Because of the non-success attending the use of the 

 antibacterial sera, attention has been turned to treatment 

 of bacterial infections by means of active immunization. 

 Thus, when we inject a horse with diphtheria toxin in 

 order to produce antito^rin we actively immunize; when we 

 inject the antitoxin into a child in order to protect the 

 child against diphtheria we passively immunize. (See 

 page 99.) 



Bacterial Vaccines. — Acti^^e Immunization consists usu- 

 ally in injecting the patient with dead bacteria, thus caus- 

 ing the production on his part of the various antibodies 

 already described, and thus bringing about a condition of 

 immunity. The bacteria are usually grown on agar, in 

 the ordinary way, and, after being washed off into a 

 test-tube containing a little salt solution, are heated for 

 about half an hour to 60° C in order to kill all the bac- 

 teria. Sterility is insured by suitable tests. The suspen- 



