650 ACTIVE IMMUNIZATION 



The Indian Plague Commission a few years ago reported as follows : 



1. Inoculation sensibly diminishes the incidence of attacks of plague. 

 It is, however, not an absolute protection against the disease. 



2. The death-rate is markedly diminished by its means, not only 

 the incidence of the disease, but also the fatality, being reduced. 



3. The protection is not conferred on those inoculated for the first 

 few days after the injection. 



4. The duration of the immunity is uncertain, but it seems to last 

 for a number of weeks, if not for months. 



After the disease has once developed, vaccination is of no avail. 

 When there is eminent danger of infection, vaccine and antiserum should 

 be given together. 



CHOLERA 



Protective inoculation against cholera was first practised by Ferran, 

 a Spaniard, in 1884, although little definite knowledge as to the value 

 of the procedure resulted from his work. He is said to have used impure 

 cultures of bacilli isolated from the feces of cholera patients. Broth 

 cultures were prepared, and the living organisms injected subcutane- 

 ously, using eight drops for the first and 0.5 c.c. for the second and third 

 doses, the injections being given at intervals of six or eight days. While 

 his method and results have been questioned, he was, however, the 

 first to use a method employed later, with some modifications, by Haff- 

 kine in India with good results. 



Preparation of Cholera Vaccine. Haffkine, following Pasteur's 

 method with anthrax, uses two vaccines, a weaker and a stronger, 

 living microorganisms being used in both and injected subcutaneously. 

 Vaccine No. 1 is weaker, and is obtained by growing the bacilli on agar 

 at a temperature of 39 C. Vaccine No. 2 is composed of more virulent 

 organisms, prepared by passing the vibrios through a series of guinea- 

 pigs until a strain is obtained which is invariably fatal to these animals 

 within twelve, or at least twenty-four, hours. Cultures are grown on 

 agar, washed off with 8 c.c. of sterile bouillon or saline solution, and 

 administered hi doses of 1 c.c., which is equivalent to about two loopsful 

 (4 mm.) or 4 mg. of living bacilli. 



Kolle has shown, however, both by animal experimentation and in 

 the human being, that heat-killed cultures are equally good, and that 

 living cultures are unnecessary and may be undesirable. 



By this method the vaccine is prepared by cultivating a virulent 

 strain on flasks of agar for twenty-four hours, as described in the pre- 



