32 ACTIVE IMMUNIZATION 



which will be referred to under proteid immunization, seem to prove that 

 they are not alike. For laboratory work it is advisable to use living 

 cultures only in cases of absolute necessity. 



In heating bacteria to destroy their virulence and thus be suitable for 

 inoculation, we must be very careful not to raise the tempera- 

 Death of ture to such a degree that not only the toxicity but also the 

 Bacteria immunization power is destroyed. It is best to employ the 

 by Heat, minimum amount of heat which will kill the respective bacteria. 

 For most of these as Typhoid, Paratyphoid, Colon, and Dysen- 

 tery bacilli, Cholera Vibrios, Meningo-, Staphylo-, Strepto- and Pneumo- 

 cocci, one hour at 60 C. is sufficient. 



The bacteria are grown upon agar cultures and the required amount 

 is removed and suspended in sterile physiological salt solution or bouillon. 

 This suspension is then placed into a hot water bath or thermostat regu- 

 lated at 60 C., for one hour.' 



If the bacteria employed are highly infectious, one must be sure that 

 all bacteria have been killed. This must especially be noted when giving 

 prophylactic inoculations in man. Several drops of the emulsion are 

 therefore transferred to agar tubes and incubated for a day or two. If 

 a growth appears, the emulsion is to be reheated; if not it can be considered 

 sterile. 



The mode of immunization with dead bacteria is the same as has 

 been described for the living ones. In general the dosage to be used may 

 be larger. 



Small doses are injected at first, followed later on by increasing quanti- 

 ties at intervals of five to eight days, e.g. 



Intravenous inoculation of a rabbit with dead typhoid bacilli. 



Result. Protection against living virulent bacteria, appearance of 

 agglutinins, bacteriolysins, bacteriotropins and complement binding 

 substances in the serum. 



i ./I. 1909. Rabbit No. i. i loopful of a typhoid agar slant culture killed at 60 C. 



and injected intravenously. 

 6./I. 4 loopfuls of typhoid culture killed at 60 C. and injected 



intravenously. 



I2./I. i culture of typhoid killed at 60 C. and injected intra- 



venously. 

 20./I. Infection with i culture of the living typhoid bacilli 



injected intravenously. Animal remains alive. 

 Rabbit No. 2. Control. 



20./I. Infection: 1/4 loopful of living typhoid bacteria intra- 



venously. 

 22./I. f(death). 



The use of killed typhoid bacteria for prophylactic immunization has 

 recently been widely adopted. This has been stimulated to a great degree 

 by the successful experiments of Wright, and Pfeiffer and Kolle. 



