MODES OF DISTINGUISHING THE SPIRILLUM. 393 



Metchnikoff has prepared a true antitoxic cholera serum by 

 injections of repeated and gradually increased doses of the 

 toxine, and has found that this antitoxic serum has a distinct 

 effect against the choleraic affection of rabbits. 



For Haffkine's method of preventive inoculation vide 

 chapter on Immunity. 



Means of Distinguishing the Cholera Organism. 

 According to Koch the most important points in the dia- 

 gnosis of cholera are : 



(a) Microscopical characters of the dejecta, (b) Ap- 

 pearance of the colonies in gelatine plates, (c) Their 

 appearance on agar plates, (d) The growth in peptone 

 solution, (e) The cholera -red reaction. (/) The effect 

 of intraperitoneal inoculation of guinea-pigs with pure 

 cultures. 



There can be no doubt that in the great majority of 

 cases these points taken collectively are sufficient, but 

 difficulties have arisen, as in some cases of apparently true 

 cholera the cultures obtained have shown variations, and 

 on the other hand, there have been cultivated from other 

 sources spirilla which only differ from the cholera spirillum 

 in a few minor points. Pfeiffer has accordingly introduced 

 the method of diagnosis referred to above, which depends on 

 the principle that the serum of an animal highly immunised 

 against the cholera spirillum (anti-cholera serum) will pro- 

 tect another animal against that organism only. Further, 

 he has found that a striking change is observed micro- 

 scopically in the vibrios when injected along with the pro- 

 tective serum into the peritoneal cavity of another guinea- 

 pig Pfeiffer's reaction. Pfeiffer's principle so far may be 

 said to involve an assumption, though there is a consider- 

 able amount of evidence that the assumption is correct. 

 The method is as follows : A loopful (2 mgrm.) of recent 

 agar culture of the organism to be tested is added to 

 i c.c. of ordinary bouillon containing .001 c.c. of anti- 

 cholera serum. The mixture is then injected into the peri- 

 toneal cavity of a young guinea-pig (about 200 grm. in 

 weight), and the peritoneal fluid of this animal (conveniently 



