xvi] VIBRIO AND SPIRILLUM 447 



case from the observations recorded. This harmonises well 

 with R. Pfeiffer's discovery of the germicidal action of the 

 serum of actively immunised guinea-pigs against fatal doses 

 of the cholera vibrio. By itself this link of the evidence is 

 not very strong, but it proves this that the blood-serum of 

 an individual after an attack of cholera possesses a specific 

 immunising action against the cholera vibrio, and it is per- 

 missible to conclude that this power of the serum was 

 brought about by the action of the cholera vibrio just as is 

 the case in Pfeiffer's active immunisation of guinea-pigs. Not 

 that it proves that the disease produced in the guinea-pig 

 by intraperitoneal injection is a process comparable to cholera 

 in man, but it shows that within the blood of the living body 

 the cholera vibrio is capable of creating specific immunising 

 substances, and taken together with the analogous observa- 

 tions with the bacillus of diphtheria, the bacillus of tetanus, 

 the pneumococcus, the bacillus of septicemia, and other 

 specific microbes it becomes extremely probable that also 

 in cholera of man the production of immunising serum, is 

 due to a like cause, i.e. to the cholera vibrio. 



Haffkine in a long continued series of observations has 

 estabhshed that by transmission of the peritoneal exudation 

 of a guinea-pig, dead after intraperitoneal injection of living 

 cholera culture, through a large number of successive guinea- 

 pigs ultimately the vibrios present in such exudation (see a 

 former page) assume increasingly greater virulence, so much 

 so that cultures made from the peritoneal exudation of the 

 last animal of the series (twenty to thirty transmissions) 

 yield extremely virulent vibrios, a tenth or a twentieth or 

 less of the dose of that with which the series was started, 

 being now sufficient to produce fatal results in sixteen to 

 twenty hours when injected intraperitoneally. Such cul- 

 tures of "exalted virulence' injected subcutaneously into 



