CHOLERA VIBRIO 565 
aiice. After twenty to twenty-four hours' incubation the organisms 
have produced a slight licjuefaction which gives the surface of the 
medium a "ground-glass" appearance when the plate is viewed at an 
acute angle. Liquefaction proceeds rai)idly. The cultures which have 
been grown on artificial media for a long time liquefy gelatin more 
slowly and eventually may lose this property. In sugar-free gelatin 
stab cultures an "air bubble," so-called, frequently forms just below 
the surface of the medium. This probably is the result of the evapora- 
tion of water from the liquefied medium. No liquefaction takes place 
in sugar gelatin. 
Blood serum is liquefied. liroth 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 de\elop 
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 
an acid coagulation of the milk. No peptonization takes place. Litmus 
milk is not coagulated. 
Fig. 77. — Cholera vibrios from feces. 
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 
potency were non-hemol\'tic. The consensus of opinion at the ])resent 
time concedes that a moderate proportion of typical cholera vibrios 
are hemolytic, although the active hemolysin cannot always be obtained 
in a soluble form. Greig^ has found that a majority of cholera-like 
vibrios induce hemolysis of goat's erythrocytes, differing in this 
respect from standard strains of the cholera vibrio. This property 
is shared by many cholera-like organisms. A group of vibrios, of 
which two strains. Vibrio Nasik, and Vibrio YA Tor, are the best known, 
are so closely related to the cholera vibrio that they have caused much 
1 Indian Jour. Med. Research, 1917, 2, No. 2. 
