342 PROTECTIVE INOCULATIONS. 
twenty-four hours and then passed through a Chamberland filter. 
Ten cubic centimetres of this filtrate was injected into the ear vein of 
rabbits. Some of the animals so treated proved to be immune against 
general infection when inoculated with a virulent culture of the micro- 
coccus, but they had a localized inflammation and cedema about the 
point of inoculation. After recovering from this they proved to be 
entirely refractory against subsequent inoculations. 
Foa and Scabia (1892) have reported success in producing immu- 
nity with filtered cultures, and also with a glycerin extract from the 
blood of an infected rabbit. This, after filtration, was injected sub- 
cutaneously in doses of two cubic centimetres at intervals of five days. 
The authors named have also produced immunity in rabbits by the 
use of “pneumo-protein.” This is an extract from the bacterial cells 
obtained by first collecting these from the surface of a Chamberland 
filter through which the cultures have been passed; then digesting 
them for three hours at 55° C. in a five-per-cent solution of glycerin. 
According to Foa and Scabia immunity produced in this way is more 
decided and of longer duration than that resulting from the other 
methods tested by them. 
Mosny (1892) has also made numerous experiments which show 
that rabbits may be immunized by means of filtered cultures, or by 
the juices from the tissues of an immune animal obtained by macer- 
ation and filtration. When sterilized cultures were employed the best 
results were obtained by first heating very virulent cultures for three 
hours at 60° C. The dose employed was ten cubic centimetres, and 
immunity was not established immediately but required a period of 
at least four days for its development. 
The blood serum of immune rabbits was not found to have any 
bactericidal power, and the micrococcus of pneumonia preserved its 
vitality longer in the blood serum of immune rabbits than in that of 
other animals of the same species. 
G. and F. Klemperer had previously reported that the blood of 
immune rabbits does not destroy the micrococcus of pneumonia or re- 
strict its development. 
Issaeff (1893) also reports his success in immunizing rabbits by 
means of sterilized cultures or filtered blood from infected animals 
recently dead. A single intravenous injection of ten cubic centi- 
metres of filtered blood, prepared as heretofore indicated (p. 340), 
sufficed to confer immunity. To test immunity the animals were 
subsequently inoculated with two to four drops of virulent blood; and 
to maintain it the inoculations (0.5 cubic centimetre) were repeated 
every four weeks. Although immune against infection these animals 
