340 PROTECTIVE INOCULATIONS. 



attack of the disease, and as many as four or five attacks Lave been 

 known to occur in the same individual. 



In 1,100 cases collected by Wagner but 2 relapses occurred 

 (=0.18 per cent). Huge reports that in 440 cases treated at the 

 Oharite in Berlin there were but 2 relapses. The liability to sub- 

 sec juent attacks at a later period is shown by the following figures, 

 which we copy from Euge's paper: In 280 cases reported by Stortz, 

 26.4 per cent had previously suffered an attack of the disease; in 

 133 cases reported by Morhart the proportion of previous attacks was 

 41.3 per cent; in 157 cases by Pohlmann, 34.4 per cent; in 166 cases 

 by Schapira, 31.3 per cent; in 128 cases by Keller, 36.9 per cent; in 

 175 cases by Grisolle, 30.9 per cent. 



The writer, in a series of experiments made during the winter of 

 1880-81, obtained experimental evidence which showed that suscep- 

 tible animals (rabbits) acquire immunity from the pathogenic action 

 of this micrococcus as a result of inoculations with an attenuated 

 virus. The experiments referred to had as their object the determi- 

 nation of the comparative value of various germicidal agents, as tested 

 upon this micrococcus ; incidentally it was found " that a protective 

 influence has been shown to result from the injection " (into rabbits) 

 " of virus, the virulence of which has been modified, without being 

 entirely destroyed, by the agent used as a disinfectant." (Quoted 

 from the writer's report of the experiments referred to, "Studies 

 from Biological Laboratory," Johns Hopkins University, Balti- 

 more, 1882.) 



In 1891 G. and F. Klemperer published an important memoir re- 

 lating to the pathogenic action of this micrococcus and the production 

 of immunity in susceptible animals by means of filtered cultures. In 

 some cases this immunity was found to last as long as six months. A 

 curious fact developed in their researches was that the potency of the 

 substance contained in the filtered cultures was increased by subject- 

 ing these to a temperature of 41 to 42 C. for three or four days, or 

 to a higher temperature (60 C. ) for an hour or two. When injected 

 into a vein after being subjected to such a temperature, immunity was 

 complete at the end of three or four days ; but the same material, not 

 so heated, required larger doses and a considerably longer time (four- 

 teen days) to confer immunity upon a susceptible animal. The un- 

 warmed material caused a considerable elevation of temperature, last- 

 ing for some days. The authors mentioned conclude from their 

 investigations that the toxic substance present in cultures of Micro- 

 coccus pneumoniae crouposse is a proteid substance, which they propose 

 to call pneumotoxin. The substance produced in the body of an im- 



