94 Immunity 



various spontaneous cases of cow-pox observed in places remote 

 from one another. Experts are undecided whether cow-pox is 

 variola modified by passage through the cow so that the transplanted 

 micro-organisms are only capable of inducing a local instead of a 

 general disease, or whether it is an independent affection natural to 

 the cow. 



In reality the matter is unimportant, so long as the desired effect 

 is accomplished, and the true lineage of the virus is only a matter 

 of scientific curiosity. As immunity is almost invariably a specific 

 effect resulting from infection, it would seem most likely that cow- 

 pox and smallpox were originally identical. 



The advantage of "vaccination" over " inoculation " is that the 

 induced disease is local and not dangerous except in rare cases, 

 and that it is not contagious. The natural variations in the sus- 

 ceptibility of different vaccinated individuals determine that a few 

 persons cannot be successfully vaccinated, being immune to the 

 mildly invasive organisms of vaccinia, though perhaps susceptible 

 to the actively invasive organisms of variola; that a few individuals 

 shall prove abnormally susceptible to vaccinia so that the disease 

 departs from its usual local type and generalizes, but that in nearly 

 all cases the disease will follow the well-known type of a local lesion 

 characterized by definite periods of incubation, vesiculation, 

 pustulation, and cicatrization. 



The occasional variations in immunity of different individuals 

 also determine that having been vaccinated once an individual 

 may not again become susceptible to vaccination, 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 permanent 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 under- 

 stood 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 

 interpreted 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 scarifica- 

 tion has "been performed upon a child, and that a scar has remained 

 thereafter may mean nothing. It is not the operation but the dis- 



