Experiments with Treponema pallidum. 257 



indurated lesions which were difficult to distinguish from primary 

 lesions produced by this mode of inoculation. The differences 

 noted were a more rapid growth and a tendency to early and wide- 

 spread necrosis with central softening — reactions which in the 

 rabbit are indicative of a malignant turn of the infection. 



The gradations in the reactions described (omitting Type 1) 

 may all be observed with a first infection in any considerable series 

 of animals inoculated with well adapted strains of Treponema 

 pallidum and the more characteristic ones furnish conclusive 

 evidence that a local infection together with the usual manifesta- 

 tions of disease may be produced by the reinoculation of animals 

 already infected. Further than this, it is by no means certain that 

 infection may not occur also in instances where no lesion is pro- 

 duced at the site of inoculation since the immediate production 

 of a lesion cannot be regarded as an essential criterion of infection. 



The character of the results obtained could be definitely re- 

 lated to a number of factors, among which may be mentioned the 

 relative virulence of the organisms used for the primary and for 

 the secondary inoculation, the progress of the original infection 

 (acquired resistance), the presence of actively developing lesions 

 (inhibition), and individual animal variation (native resistance). 

 Finally, reactions of Type 4 which include all of the essential 

 features of the local reaction to a primary infection were obtained 

 with ease in certain animals by the superinoculation of the two 

 older strains of Treponema pallidum upon the more recently 

 isolated ones, even after the original lesions had practically re- 

 solved. It is thus clear that in given instances, the resistance 

 acquired as a result of infection with an organism of low virulence 

 may never reach the point of an effectual protection against one 

 of high virulence. However, the crucial test of the possibilities 

 presented by the problem of superinfection rests more upon the 

 demonstration of a definite influence upon the course of the disease 

 than upon any form of local reaction which may be produced. 

 This phase of the subject is reserved for a separate communication. 



