188 CLINICAL BACTERIOLOGY. 



this phenomenon does not take place, the vibrio in question 

 is not the cholera-organism. One source of error must, 

 however, always be borne in mind, if Pfeiffer's reaction 

 proves positive : It is possible that the organisms present are 

 attenuated, to a certain degree saprophytic, vibrios, that 

 are dissolved in consequence of the normal bactericidal 

 activity of the organism of the guinea-pig, in the absence 

 of any specific serum. To avoid this error, a platinum 

 loopful of the culture in question added to one cubic centi- 

 meter of normal serum-bouillon mixture (i : 100) is in- 

 jected into the peritoneal cavity of a control guinea-pig. If, 

 after the lapse of twenty minutes, the vibrios are found 

 living and motile in the control-animal, whereas those 

 treated with cholera-serum are destroyed, then the diagnosis 

 of Asiatic cholera may be made with certainty. 



The second test, that of Gruber, is more readily per- 

 formed, as experiment on an animal is not required. The 

 suspected vibrios* may be added to the serum of an 

 animal rendered immune to cholera in the proportions 

 of I to 50, i to 100, and above ; and the mixture is studied 

 at once with high powers of the microscope. If the 

 vibrios lose their motility ; if they collect in groups ; 

 if, thus, agglutination takes place then the suspected 

 microorganisms are true cholera-vibrios. One of the 

 macroscopic agglutination-tests (p. 64) may be made e. g., 

 bouillon is inoculated with the suspected vibrios and the 

 serum of an animal immune to cholera is added in the pro- 

 portion named. If, after the lapse of from sixteen to 

 twenty-four hours, the vibrios have formed a flocculent pre- 

 cipitate at the bottom of the test-tube, while the overlying 

 fluid has become clear, then again the suspected organisms 

 are true cholera-bacilli. Gruber's reaction has the advan- 

 tage of being independent of the virulence of the micro- 

 organisms, and, besides, it renders unnecessary the induc- 

 tion of a high degree of immunity in the animals yielding 

 the blood-serum. 



The Development of Cholera. Infection takes place 

 invariably by way of the moutli, the bacilli being taken up 

 with articles of food, and principally with drinking-water. 

 Infection through the air is possible only in the immediate 

 neighborhood of the source of infection. The rapid death 

 of the germs on drying renders improbable the transmission 

 of the disease for long distances by means of dust, etc. 



