258 SPIRILLUM CHOLERA ASIATICS. 



bactericidal action. This substance is not found in the blood 

 until after the first week of convalescence, and disappears 

 within four weeks. There is no natural immunity to cholera. 

 Koch believes that one attack conveys a permanent immunity* 

 The blood-serum of immunized animals confers immunity. 



Immunity in man is produced by a form of vaccination 

 which was first proposed by Haff kine. He begins by inject- 

 ing a dead culture, and five days afterward he follows it with 

 an injection of a virulent culture, which is repeated on the 

 tenth day. The immunity obtained in this way is not perma- 

 nent, but serves merely as a prophylactic measure or a 

 protective during epidemics of cholera. The production of 

 immunity to cholera by means of an antitoxin which causes 



FIG. 112. 



Contact smear of colony of cholera spirilla from agar. X 700. (Dunham.) 



the formation of lysogenic bodies in the blood is as yet a 

 matter of dispute, although Haffkine's results have been very 

 good. It is at best only a protective, the efficacy of which 

 cannot be depended upon at all times. 



Diagnosis : A flake of intestinal mucus is spread on a slide 

 and stained with a hot carbol-fuchsin solution. A positive 

 diagnosis can be made in about 50 per cent, of all cases. On 

 the whole, it is preferable to cultivate the organism, as the 

 results obtained in this manner are positive in each case. 

 Pure cultures are made as already described. The distinc- 

 tive appearance of the plate culture, the gelatin stab culture, 

 and the cholera-red reaction are sufficiently characteristic to 

 be of diagnostic value. Animal experimentation may also 



