X. ON THE EXISTENCE OF SENSITIZING SUB- 

 STANCES IN THE MAJORITY OF 

 ANTIMICROBIAL SERA * 



By DRS. JULES BORDET AND OCTAVE GENGOU. 



(From Professor Metchnikoff's Laboratory.) 



The serum of many animals contains alexin, that ill-defined, 

 chemically unknown substance to which is due the property of 

 sera in general of producing a harmful effect on various cells and on 

 certain bacteria. The activity of the alexin is destroyed on heating 

 serum to 55 degrees. Alexin is found, in relatively similar amounts, 

 in the serum of normal and of vaccinated animals' artificial im- 

 munization changes neither its amount nor its properties. 



When an animal is vaccinated against the cholera vibrio there is 

 formed in the body a particular substance, the preventive or sen- 

 sitizing substance, that resists heating to relatively high tempera- 

 tures. This substance is not in itself in any way destructive for 

 the vibrio. It does, however, faciliate in a specific manner the 

 destructive action of the alexin on this micro-organism. It may 

 further be said that the specific bactericidal property of cholera 

 serum, although primarily due to the alexin, properly speaking, 

 depends on the collaboration of two substances, the alexin and the 

 favoring or sensitizing substance. This conception, offered by one 

 of us in 1895, explains the various properties of cholera serum. It 

 is closely applicable also to the specific hemolytic sera between 

 which and cholera serum most evident analogies exist. In brief, 

 the intense destructive power in bacteriolytic or cytolytic serum is 

 due to the presence of a specific antibody, the sensitizer, in addi- 

 tion to the ordinary alexin. 



In the preceding description, in referring to sera specific for bac- 

 teria, we have mentioned cholera serum only. As a matter of fact 



* Sur l'existence de substances sensibilisatrices dans la plupart des scrums 

 antimicrobiens. Annales de l'lnstitut Pasteur, XV, 1901, 290. 



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