282 PHAGOCYTOSIS— OPSONINS 



in this connection, bearing in mind that the idea of a vaccine 

 is that it contains the causative organism of the infection, 

 as indicated on page 249. 



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

 tures of bacteria to produce immunity. But because 

 injections 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, Pasteur and the French school persistently denied 

 the possibility of success with such a procedure, and some 

 of them even maintain this attitude at the present time. 

 The successes 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 treat- 

 ment 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 

 substances. The second is that, on the other hand, it must 

 contain antigens in such condition that they will act as 

 stimuli to the body cells to produce the necessary anti- 

 bodies, whether these be opsonins, bactericidal substances 

 or antiendotoxins. In the introduction of living organisms 

 there is always more or less risk of the organisms not being 

 sufficiently attenuated and hence of the possibility of its 

 producing 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 

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

 the culture and suspend in sterile normal salt solution (0.85 



