412 CHOLERA 



weaker and disappear in two or three months (Pfeiffer and 

 Issaeff). 



Specific agglutinative properties have, however, been detected 

 in the serum of cholera patients at a much earlier date, in some 

 cases even on the first day of the disease, though usually a day 

 or two later. The dilutions used were 1 : 15 to 1 : 120, and these 

 had no appreciable effect on organisms other than the cholera 

 spirillum (Achard and Bensande). Needless to say, such facts 

 supply strong additional evidence of the relation of Koch's 

 spirillum to cholera. 



Anti-Cholera Inoculation. Haffkine's method for inoculation 

 against cholera exemplifies the above principles. It depends 

 upon (a) attenuation of the virus that is, the cholera organism, 

 and (6) exaltation of the virus. The virulence of the organism 

 is diminished by passing a current of sterile air over the surface 

 of the cultures, or by various other methods. The virulence is 

 exalted by the method of passage that is, by growing the 

 organism in the peritoneum in a series of guinea-pigs. By the 

 latter method the virulence after a time is increased twenty-fold 

 that is, the fatal dose has been reduced to a twentieth of the 

 original. Cultures treated in this way constitute the virus exalte. 

 Subcutaneous injection of the virus exalte produces a local 

 necrosis, and may be followed Try the death of the animal, but if 

 the animal be treated first with the attenuated virus, the sub- 

 sequent injection of the virus exalte produces only a local oedema. 

 After inoculation first by attenuated and afterwards by exalted 

 virus, the guinea-pig has acquired a high degree of immunity, and 

 Haffkine believed that this immunity was effective in the case 

 of every method of inoculation that is, by the mouth as well as 

 by injection into the tissues. After trying his method on the 

 human subject and finding it free from risk, he extended it in 

 practice on a large scale in India in 1894, and these experiments 

 are still going on. So far the results are, on the whole, distinctly 

 encouraging. In the human subject two or sometimes three in- 

 oculations were formerly made with attenuated virus before the 

 virus exalte was used ; now, however, a single injection of the 

 latter is usually practised. Wassermann and Pfeiffer, and also 

 Klein, have found that guinea-pigs immunised by Haffkine's 

 method are not immunised against intestinal infection when the 

 animal is treated by Koch's method (vide p. 407). Notwith- 

 standing this fact Haffkine's method may still have a beneficial 

 effect, though it may not be preventive in all cases. 



Methods of Diagnosis. In the first place, the stools ought 

 to be examined microscopically. Dried film preparations should 



