264 BACTERIOLOGY 



cholera and plague by means of cultures that had been 

 killed by heating to -a moderate temperature. Such dead 

 organisms when injected bring about a reaction in the body 

 which is manifested by a marked increase in the specific 

 agglutinative and bactericidal properties of the blood- 

 serum. 



Wright introduced a similar method of vaccination against 

 typhoid fever. The prophylactic treatment consists of one 

 or more injections of dead cultures of bacillus typhosus.^ 



Metchinkoff and Besredka maintain that immunity is 

 less complete and is accompanied by more severe reactions 

 when induced by dead bacterial vaccines than when a small 

 quantity of "sensitized" living culture is employed. 



With this in mind they prepare vaccines by subjecting 

 living cultures to the action of specific immune serum that 

 has been heated sufficiently to destroy its disintegrating 

 power. By this plan the haptophore side chains of the bac- 

 teria are saturated with specific immune bodies, manifested 

 by the agglutination of the bacteria. The agglutinated mass 

 is then washed to remove the serum, centrifuged and the 

 sediment used for vaccination. The subcutaneous injection 

 of vaccines so prepared is said to be followed by little or 

 no local pain and almost no constitutional reactions. These 

 advantages are attributed to the sensitization in vitro, 

 which would otherwise go on within the tissues and account 

 for the undesirable reactions. 



The method of Gay differs from the foregoing in that the 

 sensitized living bacteria are killed by heating before they 

 are injected. 



' See Chapter on Typhoid Fever. 



