SUSCEPTIBILITY AND IMMUNITY. 261 



G. and F. Klemperer, in 1891, published an important memoir in 

 which they gave an account of their researches relating to the ques- 

 tion of immunity, etc., in animals subject to the form of septicaBmia 

 produced by the Micrococcus pneumonia crouposaB. They were able 

 to produce immunity in susceptible animals by introducing into their 

 bodies filtered cultures of this micrococcus, and proved by experiment 

 that this immunity had a duration of at least six months. They 

 arrived at the conclusion that the immunity induced by injecting fil- 

 tered cultures is not directly due to the toxic substances present in 

 these cultures, but that they cause the production in the tissues of an 

 antitoxin which has the power of neutralizing their pathogenic 

 action. The toxic substance present in cultures of the "diplococcus 

 of pneumonia" they call " pneumotoxin" ; the substance produced in 

 the body of an artificially immune animal, by which this pneumo- 

 toxin is destroyed if subsequently introduced, they call " anti -pneumo- 

 toxin." 



Emmerich, in a communication made at the meeting of the In- 

 ternational Congress for Hygiene and Demography, in London, re- 

 ported results which correspond with those of G. and F. Klemperer 

 so far as the production of immunity is concerned, and also gave an 

 account of experiments made by Donissen in which the injection of 

 twenty to twenty-five cubic centimetres of blood or expressed tissue 

 juices, filtered through porcelain, from an immune rabbit into an 

 unprotected rabbit, subsequently to infection with a bouillon culture 

 of "diplococcus pneumonise," prevented the development of fatal 

 septicremia. Even when the injection was made twelve to fifteen 

 hours after infection, by inhalation, the animal recovered. 



Emmerich and Mastraum had previously reported similar results 

 in experiments made upon mice with the Bacillus erysipelatos suis 

 (rothlauf bacillus). White mice are very susceptible to the patho- 

 genic action of this bacillus. But mice which, subsequently to in- 

 fection, were injected with the expressed and filtered tissue juices of 

 an immune rabbit, recovered, while the control animals succumbed. 

 According to Emmerich, the result in these experiments was due to 

 a destruction of the pathogenic bacilli in the bodies of the infected 

 animals ; and the statement is made that at the end of eight hours 

 after the injection of the expressed tissue juices all bacilli in the body 

 of the infected animal were dead. The same liquid did not, however, 

 kill the bacilli when added to cultures external to the body of an 

 animal. The inference, therefore, seems justified that the result de- 

 pends, not upon a substance present in the expressed juices of an 

 immune animal, but upon a substance formed in the body of the 

 animal into which these juices are injected. 



We have, however, an example of induced immunity in which 



