422 CHOLERA. 



oculations are made with attenuated virus before the virus exalte 

 is used. Wassermann and Pfeiffer, and also Klein, have found, 

 however, that guinea-pigs immunised by Haffkine's method are 

 not immunised against intestinal infection when the animal is 

 treated by Koch's method (that is, by paralysing the intestines 

 with opium, vide p. 416). Notwithstanding this fact Haffkine's 

 method may still have a beneficial effect, though it may not be 

 preventive in all cases. 



Means of distinguishing the Cholera Organism. — According 

 to Koch the most important points in the diagnosis of cholera 

 are : — 



(«) Microscopical characters of the dejecta. (<5) Appearance 

 of the colonies in gelatin plates, (c) Their appearance on agar 

 plates. ((3?) The growth in peptone solution. (^) 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 in identifying the 

 cholera organism. In addition, however, the various properties 

 of an anti-cholera serum may be employed ; of these the most 

 easily applied is the agglutinative reaction. The following is an 

 account of Pfeiffer's reaction, which was the first to be intro- 

 duced. 



Pfeiffer's Reaction. — A loopful (2 mgrm.) of recent agar culture of the 

 organism to be tested is added to i c.c. of ordinary bouillon containing .00 1 

 c.c. of anti-cholera serum. The mixture is then injected into the peritoneal 

 cavity of a young guinea-pig (about 200 grm. in weight), and the peritoneal 

 fluid of this animal (conveniently obtained by means of capillary glass tubes 

 inserted into the peritoneum) is examined microscopically after a few minutes. 

 If the spirilla injected have been cholera spirilla, it will be found that they 

 become motionless, swell up into globules, and ultimately break down and 

 disappear — positive result. If they are found active and motile, then the pos- 

 sibility of their being true cholera spirilla may be excluded — negative result. 

 In the former case (positive result) there is, however, still the possibility that 

 the organism is devoid of pathogenic properties and has been destroyed by 

 the normal peritoneal fluid. A control experiment should accordingly be 

 made with .001 c.c. of normal serum in place of the anti-cholera serum. If 

 no alteration of the organism occurs with its use, then it is to be concluded 

 that the organism in question has been demonstrated by the specific reaction 

 to be the cholera spirillum (see Chapter XX.). 



Properties of the Serum of Cholera Patients and Conva- 

 lescents. — Lazarus was the first to show that the serum of 



