



1 36 CLINICAL BACTERIOLOGY AND H^EMATOLOGY 



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 con- 

 form 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 sul- 

 phuric acid will give a pink or crimson tint. This is the 

 "cholera-red" reaction, and is caused by the action of sul- 

 phuric 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 phenomena 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. 



The certain identification of the cholera vibrio is a matter of some 

 difficulty. Pure cultures can be obtained easily by successive inocu- 

 lations from one peptone-water culture to another at the earliest 

 possible moment (six to seven hours), followed by plating out. The 

 organism grows well on strongly alkaline medium, a fact which is 

 also of service, as most intestinal organisms grow very badly under 

 these conditions. 



The recognition of the organism depends on (i) the cultural 

 features, (2) agglutination with a standard anticholera serum issued 

 from a trustworthy laboratory, and (3) its pathogenic action on 

 animals. 



(i) Groivth in Stdb Cultures in Gelatin. It grows along the stab, 

 but most abundantly at the surface, where there is most air. Lique- 

 faction takes place in this region in a day or two, and a deep depres- 

 sion results, containing air, so that in about four days the whole 



