ii2 Immunity 



The occasional variations in immunity of different in- 

 dividuals also determine that having been vaccinated once 

 an individual may not again become susceptible to vaccina- 

 tion, though he may become susceptible to the more actively 

 invasive organisms of variola, or that he may soon become 

 again susceptible to both diseases, or that in very rare cases 

 no immunity against variola will result from vaccination. 

 In most cases successful vaccination can be repeated once 

 or twice at intervals of seven or ten years, and experience 

 shows that the immunity against smallpox conferred by 

 vaccination is of longer duration and usually becomes per- 

 manent after vaccination has been repeated once or twice. 



Sanitarians are accustomed to speak of efficient and 

 inefficient vaccination. These are vague terms and do not 

 seem to be understood by the laity. Efficient vaccination 

 is vaccination repeated as often as is necessary. It has 

 already been shown that individual variations determine 

 that a few individuals never become immune, hence never 

 can be efficiently vaccinated. Other persons are efficiently 

 vaccinated by a single operation. The term is usually inter- 

 preted to indicate that which experience has shown to be 

 efficient in average cases. 



Failures not uncommonly result from causes having 

 nothing to do with the problems of immunity. That an 

 operation of scarification has been performed upon a child, 

 and that a scar has remained thereafter may mean nothing. 

 It is not the operation but the disease that achieves the 

 result, and if the operation be improperly done, poor i. e., 

 old or inert matter introduced, or if after introduction it 

 be destroyed by the application of antiseptics, no effect can 

 be expected. Hence all persons that have been vaccinated 

 may not have had vaccinia, the essential condition leading 

 to immunity. Nor does the occurrence of a local lesion act 

 as a guarantee that vaccinia has been induced. Careful 

 examination of the resulting lesions should always be made, 

 that the type of the infection may be studied. It is the 

 disease, vaccinia, that must occur three days incubation, 

 three days vesiculation, three days pustulation, and subse- 

 quent cicatrization with the formation of a punctate scar. 



An arm may be never so sore, may suppurate or even 

 become gangrenous, without vaccinia having occurred or 

 the desired benefit attained. 



The accidents of vaccination were formerly numerous and 



