THE EXISTENCE OF SENSITIZING SUBSTANCES. 225 



vaccinated guinea-pig). After 1J hours in the thermostat stained 

 preparations were made from each tube. 



In tube "a" we found that the cholera vibrios kept their normal 

 appearance, but all the Proteus rods showed granular degeneration. 

 In tube "b," on the contrary, numerous Proteus rods were found 

 but the vibrios had all lost their normal appearance and become 

 completely metamorphosed. In tubes "c" and "d," containing 

 no Proteus, as might be expected, the vibrios were completely 

 transformed.* It is obvious, then, that in tube "a" the sensitized 

 proteus bacilli have absorbed the alexin and so protected the sub- 

 sequently added vibrios. 



The mixtures were left at room temperature overnight and the 

 next day placed in the incubator for 6 hours. When stained prepa- 

 rations were then made the results were striking. 



In tube "a," in which the proteus bacilli were destroyed, the 

 cholera vibrio has undergone marked multiplication. In tube 

 "b," containing non-sensitized Proteus, the reverse is true; the Pro- 

 teus has grown out, but no vibrios are found. Therefore in these 

 two tubes containing the same amount of alexin the bactericidal 

 power has been directed, in one, against one organism, in the other, 

 against another. Although the vibrios in each mixture were equally 

 sensitized, they have grown in tube "a," because the harmful in- 

 fluence of the alexin was diverted by the properly sensitized Pro- 

 teus vulgaris; this bacillus has acted, in a way, as a shield for the 

 vibrio.f 



The data considered in the present article, when added to those 

 we already have, give the conception, that under immunization an 

 animal forms an appropriate sensitizer capable of causing the bac- 

 terium it affects to absorb alexin, the appearance of a general 

 law. 



We shall not here consider how far the presence of a sensitizer in 



* In controls of both the vibrio and Proteus made each with its heated specific 

 serum alone there is agglutination, but no metamorphosis. 



f This is a correct demonstration of the principle established by one of us in 

 1895: "That the bactericidal substance is the same in normal as in vaccinated 

 animals. In the case of animals vaccinated against certain diseases the energy of 

 the bactericidal substance acts particularly against a given microbe owing to the 

 specific preventive substance (sensitizer), which varies according to the bacterium 

 used for immunization. It is by means of this peculiar preventive substance that 

 the animal body directs its destructive power against a particular infection." 



