500 THE CHOLERA VIBRIO 



has been emulsified. Ten minutes afterwards withdraw, with a very fine-pointed 

 pipette, a few drops of the peritoneal fluid and examine it under the microscope 

 (either stained or unstained). If the vibrios are motile and have retained their 

 characteristic shape, the reaction is negative, and the vibrio is not a cholera vibrio. 

 If on the other hand only non-motile spherical dots are seen, then the vibrio may 

 be regarded as a true cholera vibrio (vide also p. 227). 



If there be no immunized guinea-pig at hand, inoculate a normal guinea- 

 pig intra-peritoneally with an emulsion of the vibrio mixed with a little tested 

 anticholera serum. The same granular change will be seen as in the fore- 

 going case, and in addition the organisms will be agglutinated into small 

 clumps. 



2. The vibrios are equally agglutinated and disintegrated by an anti- 

 cholera serum in vitro (Metchnikoff, Bordet). 



To demonstrate this phenomenon rub up a small quantity of an agar culture in a 

 little sterile broth and examine under the microscope to make sure there are no 

 clumps : then add 5 to 10 per cent, of the serum and in a few minutes agglutina- 

 tion followed by granulation of the bacilli will occur, the result being most marked 

 when the mixture has been incubated for 2 hours at 37 C. 



An agglutinating serum can be easily obtained by inoculating cultures 

 killed by heat into the peritoneal cavity or into the veins of a guinea-pig 

 or rabbit. 



Applications. The phenomenon of agglutination furnishes a means of 

 identifying the vibrio : as a rule, Pfeiffer's phenomenon on the one hand and 

 agglutination in vitro on the other occur only with cholera vibrios and not 

 with closely related species. In practice it will be sufficient to perform one 

 of these tests because no vibrio has yet been encountered which gives one and 

 not the other and vice versa. Unfortunately the value of the method is not 

 absolute since it sometimes fails with vibrios isolated from the stools of cholera 

 patients and may be produced with vibrios devoid of all pathogenic properties. 



Serum diagnosis. The serum of persons suffering from cholera will agglu- 

 tinate an emulsion of the cholera vibrio in 5-60 minutes in a dilution of 1 in 

 20 (Achard and Bensaude). This reaction furnishes a rapid method of 

 diagnosis, but it has to be remembered that normal human serum may 

 agglutinate the vibrio in a dilution of 1 in 10 (Pfeiffer and Kolle). 



7. Complement fixation. 



Cholera serum contains immune bodies (sensibilisatnces] specific for the 

 vibrio. The complement fixation reaction applied according to the method 

 of Bordet and Gengou (p. 232) gives very accurate results in differentiating 

 the cholera vibrio from organisms allied to it (de Besche and Kon). 



SECTION IV.- DETECTION, ISOLATION AND IDENTIFICATION 

 OF THE CHOLERA VIBRIO. 



The detection and isolation of vibrios in general is easy, but identification 

 of the cholera vibrio in particular presents considerable difficulties. 



1. Detection and isolation. 

 A. Microscopical examination. 



This method of investigation is applicable only to the examination of stools, 

 or of the exudates and tissues of animals. 



Detection in the excreta. Take one of the small mucous or riziform particles, 

 spread it on a slide and stain with dilute carbol-fuchsin. In typical cases 

 this is a conclusive test the vibrios are found in almost pure culture arranged 



