502 THE CHOLERA GROUP 



Blood serum is liquefied. Broth is densely clouded and in plain 

 broth or in Dunham's solution a pellicle is usually formed after twelve 

 to twenty-four hours' growth. A pellicle does not ordinarily develop 

 in sugar-containing broth. 



Milk is acidified, the degree of acid produced varying greatly with 

 the strain of organism. Some cultures produce enough acid to cause 

 acid coagulation of the milk. No peptonization takes place. Litmus 

 milk is not coagulated. 



The production of hemolysis (erythrocytolysis) by cholera vibrios 

 is a subject of controversy. It was formerly maintained that vibrios 

 which agglutinate at high dilution with specific cholera sera of high 



FIG. 72. Cholera vibrios from feces. 



potency were non-hemolytic. The consensus of opinion at the present 

 time concedes that a moderate proportion of typical cholera vibrios 

 are hemolytic, although the active hemolysin can not always be 

 obtained in a soluble form. This property is shared by many cholera- 

 like organisms. A group of vibrios, of which two strains, Vibrio Nasik, 

 and Vibrio El Tor, are the best known, are so closely related to the 

 cholera vibrio that they have caused much study and speculation. 

 The former fails to agglutinate with a specific cholera serum, but is 

 strongly hemolytic; the latter also fails to agglutinate at high dilution, 

 although it acts as an antigen with cholera serum in the complement- 

 fixation test. It produces a thermostabile soluble toxin. 1 



The organisms are aerobic, facultatively anaerobic. They were 

 formerly considered to be strongly aerobic; it is doubtful, however, 

 if they are markedly more aerobic than other intestinal bacteria. The 



1 See Kraus and Pribram, Wien. klin. Wchnschr., 1905, No. 39. 



