ASIATIC CHOLERA AND THE CHOLERA ORGANISM 833 



Coagulated blood serum is liquefied by the cholera vibrio. On 

 potato, growth is profuse and appears as a brownish coarse layer. In 

 milk, growth is rapid and without coagulation. In broth, general 

 clouding and the formation of a pellicle result. The rapidity and 

 luxuriance of growth of the cholera spirillum upon alkaline pepton 

 solutions render such solutions peculiarly useful as enriching media 

 in isolating this microorganism from the stools of patients. In 

 pepton solution, too, the cholera spirillum gives rise to abundant 

 indol, demonstrated in the so-called " cholera-red" reaction. This 

 reaction has a distinct diagnostic value, but is by no means specific. 

 In the case of the cholera spirillum the mere addition of strong 

 sulphuric acid suffices to bring out the color reaction. This is due 



FIQ. 88. FIG. 89. 



FIG. 88. CHOLERA SPIRILLUM. Stab Culture in Gelatin, three days old. 

 FIG. 89. CHOLERA SPIRILLUM. Stab Culture in Gelatin, six days old. (After 

 Frankel and Pfeiffer.) 



to the fact that, unlike some other indol-producing bacteria, the 

 cholera organism is able to reduce the nitrates present in the medium 

 to nitrites, thus itself furnishing the nitrite necessary for the color 

 reaction. The medium which is most suitable for this test is that 

 proposed by Dunham, 2 consisting of a solution of 1 per cent of 

 pure pepton and .5 per cent NaCl in water. 



Dieudonne has recommended a selective medium upon which 

 cholera spirilla will grow well, but upon which the colon bacillus 

 will grow either very sparsely or not at all. Cocci will produce 

 minute pin-point colonies only and other common bacilli like those 

 of the proteus group will grow hardly more easily than bacillus 

 coli. Its preparation is very simple. 



2 Dunham, Zeit. f. Hyg., ii, 1887. 

 'Dieudonne A., Cent. Bakt., 1., orig., 1909, 



