BACTERIAL VACCINES 259 



As early as 1880 Touissant proposed the use of dead cul- 

 tures of bacteria to produce immunity. But because injec- 

 tions of such cultures were so frequently followed by abscess 

 formation, doubtless due to the high temperatures used to 

 kill the bacteria, the method was abandoned. Further, Pas- 

 teur and the French school persistently denied the possi- 

 bility of success with such a procedure, and some of them 

 even maintain this attitude at the present time. The suc- 

 cesses of Wright and the English school which are being 

 repeated so generally wherever properly attempted, leave 

 no doubt in the unprejudiced of the very great value of the 

 method and have unquestionably opened a most promising 

 field both for preventive inoculation and for treatment in 

 many infectious diseases. That the practice is no more 

 universally applicable than are immune serums and that it 

 has been and is still being grossly overexploited is undoubted. 



The use of a vaccine is based on two fundamental prin- 

 ciples. The first of these is that the cell introduced must not 

 be in a condition to cause serious injury to the animal by its 

 multiplication and consequent elaboration of injurious sub- 

 stances. The second is that, on the other hand, it must con- 

 tain antigens in such condition that they will act as stimuli 

 to the body cells to produce the necessary antibodies, 

 whether these be opsonins, bactericidal substances, or anti- 

 endotoxins. In the introduction of living organisms there 

 is always more or less risk of the organism not being suffi- 

 ciently attenuated and hence of the possibility of its pro- 

 ducing too severe an infection. In using killed cultures, 

 great care must be exercised in destroying the organisms, 

 so that the antigens are not at the same time rendered inactive. 

 Hence in the preparation of bacterial vaccines by Wright's 

 method the temperature and the length of time used to kill the 

 bacteria are most important factors. This method is in gen- 

 eral, to grow the organisms on an agar medium, rub off the 

 culture and emulsify in sterile normal salt solution (0.85 

 per cent. NaCl). The number of bacteria per c.c. is deter- 

 mined by staining a slide made from a small volume of the 

 emulsion mixed with an equal volume of human blood drawn 

 from the finger and counting the relative number of bac- 



