9 6 



STUDY AND IDENTIFICATION OF BACTERIA. 



On gelatin stabs the liquefaction produces a turnip -like hollow 

 at the top of the puncture the air bubble appearance. It gives the 

 nitroso-indol reaction with sulphuric acid alone (cholera red). Kraus 

 attaches importance to the fact that cholera does not produce a 

 haemolytic ring on blood agar as do the pseudo- 

 cholera spirilla ; a difficulty is that many pseudo- 

 spirilla do not haemolize. It grows very rapidly on 

 peptone solution and this is the medium for the 

 enrichment test to be later described. On this it 

 may form a pellicle. On agar the colony is more 

 opalescent than the typhoid. It does not grow on 

 potato except at incubator temperature. It does 

 not coagulate or turn acid litmus milk. The spirilla 

 are found in myriads in the rice-water discharges, 

 these white flakes being desquamated epithelial cells. 

 They penetrate the crypts of Lieberkuhn, but rarely 

 extend to the submucosa. The symptoms are due 

 to an endotoxin. 



Cholera may be transmitted from water supplies, 

 when the outbreak is apt to be widespread and in 

 great numbers from the start. Also by indirect 

 contagion, as by flies or on lettuce, etc. A very 

 important point is that we have well persons whose 

 faeces contain virulent cholera spirilla (cholera carriers). To identify 

 such spirilla immunity reactions are necessary: 



1. Injected intraperitoneally into guinea-pigs, it produces a 

 peritonitis and subnormal temperature. This reaction 

 exists for spirilla other than the true cholera spirillum. 



2. Intramuscular injections into pigeons are only slightly 

 pathogenic, if at all. 



3. The agglutination test is the most practical. In this we 

 use serum from an immunized animal, in dilution of from 

 50 to 1000. Serum of cholera convalescents may show 

 agglutination as early as the tenth day; it is usually best 

 shown about the third week. Dunbar's quick method is 

 very practical. Make two hanging- drop preparations, 



FIG. 38. Spiril- 

 lum of cholera, 

 stub - culture in 

 gelatin, two days 

 old. (Frankel and 

 Pfeiffer.} 



