474 CHOLEEA 



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

 and (b) 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 twentyfold 

 — 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 by 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. In the human 

 subject two or sometimes three inoculations were formerly made 

 with attenuated virus before the virus exalte' was used ; now, 

 however, a single injection of the latter is usually practised. 

 The results of preventive inoculation in India and in Russia 

 have been such as to establish its efficiency, both the case in- 

 cidence and the mortality being reduced. 



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

 to be examined microscopically. Dried film preparations should 

 be made and stained by any ordinary stains, though carbol-fuchsin 

 diluted four times with water is specially to be recommended. 

 Hanging-drop preparations, with Or without the addition of a 

 weak watery solution of gentian-violet or other stain, should also 

 be made, by which method the motility of the organism can be 

 readily seen. By microscopic examination the presence of spiril la 

 will be ascertained, and an idea as to their number obtained. 

 In some cases the cholera spirilla are so numerous in the stools 

 that a picture is presented which is obtained in no other con- 

 dition, and a microscopic examination may be sufficient for 

 practical purposes. According to Koch, a diagnosis was made 

 ,in 50 per cent, of the cases during the Hamburg epidemic by 

 microscopic examination alone. In the case of the first appear- 

 ance of a cholera-like disease, however, all the other tests 

 should be applied before a definite diagnosis of cholera is 

 made. 



