92 CLINICAL BACTERIOLOGY AND HEMATOLOGY 



in opposite directions, giving the whole the appearance of a 

 very elongated spiral. In the stools (but not usually in cultures) 

 the individual rods have frequently a parallel arrangement, pre- 

 senting the appearance of " shoals of fish swimming up stream." 



If you see these appearances examine the Gram specimen. 

 Very few organisms will be visible, as the cholera vibrio does 

 not retain the stain when treated in this way. 



If vibrios having the above characters are present, proceed as 

 follows : 



Take two or three small flasks (preferably sterilized by heat), 

 and add to each loo c.c, of water, i gramme of peptone, and 

 ^ gramme of common salt ; boil thoroughly, and allow to cool. 

 This forms a culture medium in which the cholera vibrio will 

 grow very rapidly, and other organisms far more slowly. 



Inoculate each flask with a loopful or two of dejecta, plug 

 each with cotton-wool, and incubate for eight to twelve hours at 

 37° C. If cholera vibrios are present the cultures will conform to 

 the following tests : 



(a) There will be a film on the surface. This will be more 

 marked after a few hours longer. 



(b) This scum will present the microscopic appearances 

 described above, except that the vibrios are usually somewhat 

 straighter than those which occur in the stools, and the " fish-in- 

 stream" arrangement is not marked. They will not stain by 

 Gram's method. 



(c) The addition of a small quantity of pure strong sulphuric 

 acid will give a pink or crimson tint. This is the " cholera-red " 

 reaction, and is caused by the action of sulphuric acid on indol 

 in the presence of a minute quantity of a nitrite ; many other 

 organisms {e.g. , the B. coli) produce this colour after the addition 

 of a nitrite, very few without it. The cholera vibrio produces 

 nitrites as well as indol. 



Interpretation of Results. 



In a case in which the above p>henomena are observed, the 

 inference that the patient is suffering from true Asiatic cholera is 

 so strong that the authorities should be notified and the fullest 

 precautions taken. 



A case in which they are absent is almost certainly not one of 

 true cholera. 



