64 EVOLUTION OF THE INFECTIOUS DISEASES 



The theories of this condition cannot be demonstrated by 

 experiment but the result would be the same if in place of an 

 infection by living bacteria the organism had received an 

 injection or a series of injections of dead bacteria. At the 

 moment of the appearance of antibodies in excess it would 

 be immunized against the dose of living bacteria pathogenic 

 for controls and would be hypersusceptible (anaphylactic) 

 to a non-pathogenic dose of dead bacteria and finally hyper- 

 susceptible to a dose of living bacteria greater than its degree 

 of anti-infectious immunity. 



Whether the bacteria be living or dead at the end of the 

 incubation period, the organism will be exactly in the same 

 condition from the point of view of immunity and anaphylaxis. 

 If the results are different it is because living bacteria con- 

 tinue to multiply, but if the injections of dead bacteria in 

 considerable doses were continued after the time when the 

 organism became surcharged by an excess of antibodies the 

 picture of spontaneous infectious disease would be very 

 probably and almost certainly duplicated. In fact practical 

 antityphoid vaccination has shown that the subjects more or 

 less immunized by a previous healed typhoid infection are 

 infinitely more sensitive to the vaccine than normal subjects 

 and in the cases of alimentary poisoning caused by para- 

 typhoid swallowed in modified doses the crises are all the 

 more severe if the subjects are already strongly immunized. 1 



But then one may ask why does a spontaneous infection 

 not stop at the end of the incubation period since the patient 

 is at this moment more immunized than at the start of the 

 infection? This very thing happens much more often than 

 has been supposed at the present time not only in typhoid 

 but in every other infectious disease. In certain cases the 

 few mild symptoms permit the recognition of a disease which 

 aborts, but the great majority of these cases escape observa- 

 tion and acquired immunity can be revealed only by a study 

 of the serum, by vaccine reaction or by the opsonic index. 



1 A dozen persons, at least one of whom was immunized normally against 

 paratyphoid, swallowed by accident a heavy dose of paratyphoid bacilli 

 in milk. All of them were more or less indisposed, but only the immu- 

 nized individual was severely ill. 



