840 PROTECTIVE INOCULATIONS. 
attack of the disease, and as many as four or five attacks have been 
known to occur in the same individual. 
In 1,100 cases collected by Wagner but 2 relapses occurred 
(=0.18 per cent). Ruge reports that in 440 cases treated at the 
Charité in Berlin there were but 2 relapses. The liability to sub- 
sequent attacks at a later period is shown by the following figures, 
which we copy from Ruge’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, 80.9 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 pheumonie croupose is a proteid substance, which they propose 
to call pneumotoxin. The substance produced in the body of an im- 
