CHOLERA VIBRIO 507 



Immunity. As a rule one attack confers lasting immunity. 



Artificial Immunity. Attempts have been made to induce artificial 

 active immunity: 



1. By subcutaneous inoculation of virulent cholera vibrios in man, 

 either directly or after exaltation of their virulence for guinea-pigs 

 or rabbits. 1 (2) By the injection of autolyzed cultures of cholera 

 vibrios, heated at 60 C. for an hour to kill them, then suspended in 

 distilled water at 37 C. for three to four days, and filtered through 

 porcelain. 2 (3) Vaccines, (a) Killed cultures (Kolle); (b) sensitized 

 cultures (Besredka); (c) bacterial extractives. 



The only method thus far which has yielded encouraging results 

 is that of HarTkine. 3 This consists in the injection of from 0.25 to 0.5 

 c.c. of a suspension of an agar culture of cholera vibrios suspended 

 in 5 c.c. of sterile saline solution. This is introduced subcutaneously. 

 The results reported from India are claimed to be favorable. 



Bacteriological Diagnosis. Isolation and identification of the cholera 

 vibrio. 



1. Microscopic. The feces may be examined directly for cholera 

 vibrios. Large numbers of slightly curved or S-shaped actively motile 

 vibrios, which when stained with dilute carbolfuchsin exhibit slightly 

 tapered ends, are very suggestive. A bit of mucus (a "grain of rice" 

 from a rice-water stool) is particularly good for microscopical exam- 

 ination. The organisms frequently exhibit a marked parallelism of 

 their long axes, resembling a school of fish in their arrangement if 

 the material is not roughly handled during the preparation of the 

 smear. 



2. Culture. (a) Schottelius' method. The principle involved: 

 The cholera vibrio grows particularly well in alkaline peptone solu- 

 tion (Dunham solution). Bacillus coli and other intestinal organisms 

 grow less readily. 



Technic. A loopful of feces, 4 or preferably a small piece of mucus 

 is emulsified in a tube of Dunham's peptone solution and incubated 

 at 37 C. for six to eight hours. The cholera organisms are very 

 aerobic and actively motile, and collect in large numbers at the 

 surface of the medium, therefore two or three loopfuls of material 

 from the surface of the Dunham tube are inoculated into a second 



1 Haffkine. 2 Haffkine and Ferran. 3 Bull. Inst. Past., iv, 697, 737. 



4 If the preliminary microscopical examination fails to reveal a preponderance of 

 vibrios of characteristic morphology, a larger amount of fecal material must be taken. 

 Several grams of feces emulsified in 100 to 500 c.c. Dunham solution may give positive 

 results in exceptional cases when smaller samples are negative. 



