20O METHODS OF SERO-DIAGNOSIS. 



be said, however, to date from the discoveries by Pfeiffer and 

 Bordet in connection with bacteriolysis and haemolysis. 



It was in 1894 that Pfeiffer found that, on introducing large 

 numbers of living cholera vibrios into the peritoneal cavity of 

 guinea-pigs actively immunized against these organisms, the 

 vibrios underwent a granular degeneration, succeeded eventually 

 by solution of their bodies. Further, he noted that the same 

 effect on the vibrios could be produced in normal guinea-pigs by 

 introducing into their peritoneal cavity, at the same time as the 

 organisms, a small quantity of peritoneal exudate or serum from 

 an actively-immunized animal. This constitutes the well-known 

 " Pfeiffer's phenomenon." Then Metchnikoff showed that this 

 bacteriolysis occurred not alone in vivo, but also in vitro, on the 

 addition of a mixture of normal peritoneal fluid and serum from 

 an animal immunized against cholera, to a suspension of cholera 

 vibrios in a test tube. Then Bordet, having demonstrated the 

 fact that fresh, normal serum could replace the normal peritoneal 

 fluid of the guinea-pig, proved further that if the serum from 

 the cholera-immune animal was fresh, and not heated to 6o° C, 

 as it had been in Metchnikoff's experiments, that, by itself, when 

 added to a suspension of cholera vibrios, it could produce their 

 lysis. Then, going further, he showed that this serum from the 

 cholera-immune guinea-pigs, though producing bacteriolysis when 

 fiesh, lost this power, or became inactivated, on heating to 55 ° C, 

 but the lytic power could be restored to the heated serum, or, in 

 other words, it could be reactivated, by the addition to it of fresh 

 normal serum. Thus, he directly conceived the idea that there 

 were two bodies, whose presence was necessary for the produc- 

 tion of bacteriolysis, one a thermolabile body, destroyed by heat- 

 ing the serum to 55 ° C, and the other a thermostable one, which 

 resisted the effect of heating even to 70 ° C for one hour To 

 the first he gave the name alexin, and to the second the name 

 of substance sensibilisatrice. 



Now, as the bacteriolytic property of the serum from the 

 cholera-immune guinea-pig was specific, only acting on the cholera 

 vibrio, but, on the other hand, " reactivation " of this serum, 

 after inactivation by heating it to 55 ° C could be brought about 

 by the addition of normal serum obtained from animals of other 

 species, it came to be believed, firstly, that whilst the alexin was 

 a body normally present in blood serum, the substance sensibilisa- 

 trice or sensitizing substance was only formed in the serum fol- 

 lowing immunization ; and, secondly, that whilst the sensitizing 

 body would increase in quantity during immunization, the 

 amount of alexin present remained practically unaltered. Later 

 on, Bordet, in 1898, showed that the formation of lysins could be 

 produced in response to the injection into the animal body of 

 cells other than bacterial, and showed that by the injection into 

 an animal, say, for instance, a rabbit, of blood of an animal of 

 different species, say. a sheep, there was produced, after a certain 

 time, in the serum of the rabbit, the power of dissolving .the . 

 corpuscles of the sheep. The action of this hcemolytic serum 



