The bacillus is a short, thickish rod, about two-thirds the length of the tubercle bacillus and somewhat broader (see Fig. 150). It is curved on its long axis so as to resemble a comma (but without the head of the printed comma). Sometimes there are two, end to end, with their curves in opposite directions, so as to resemble the letter S. They sometimes grow into longer spiral threads, from which they have been nuked as spirilla. As the spirals are not single cells, but made up of rows of commas, this conclusion is scarcely warranted, and the bacteria may still be regarded as curved bacilli. The bacillus is very actively motile by means of a single cilium which is at one end. The bacilli are readily stained by watery solutions of the aniline dyes, but the best is a strong watery solution of fuchsine. They require longer exposure than usual, not less than ten minutes for cover-glass preparations and twenty-four hours for sections. The fluid may be heated. Gram's method is not available as the bacilli are decolorized.

Cultures of the bacilli in gelatine show very characteristic appearances. The growing bacilli liquefy the gelatine slowly, producing a small funnel-shaped cup, the apex of which is occupied by the growing organism in the form of a granular whitish sediment. They also grow on potato, in milk, and even in water. They were found by Koch abundantly in the water of a tank in India. The presence of the cholera bacillus may be determined by a chemical colour test. Cultures made on media containing peptones (such as a simple 1 per cent, watery solution of peptone to which 1 per cent. NaCl has been added) give with chemically pure hydrochloric or sulphuric acid a red colour of varying intensity - the so-called Cholera red. This is due to the presence of nitroso-indol, a body formed by the addition of sulphuric acid to a mixture of indol and a nitrite - these latter substances being formed by the cholera organism during its growth. Other comma bacilli and the Vibrio Metchnikovi give similar reactions.

Cholera does not occur in animals, but Koch has succeeded by a special method in inducing the bacilli to grow in the intestinal canal of guinea-pigs. In order to this he overcomes the acidity of the stomach by an alkaline carbonate, and at the same time controls the peristaltic action of the intestine by opium, and then finds that cultures introduced into the stomach survive and propagate. The animal dies in about two days, and the intestine is found to contain large quantities of fluid faeces which teem with comma bacilli. An accidental contamination of one of Koch's pupils during a course of bacteriology resulted in an attack of cholera, thus affording a proof of the identity of the bacillus.

In cases of Asiatic cholera Koch has always found the comma bacillus in the rice-water evacuations and intestinal contents. The mucous membrane of the intestine is red and swollen, especially in the region above the ileo-ccecal valve. The bacilli are present not only in the contents, but in the tubular glands, sometimes penetrating between the epithelium and the basement membrane. The bacillus does not penetrate beyond the intestine, but it apparently produces a violent poison, which irritates the intestine and, being absorbed, leads to weakening of the heart, lowering of the temperature, muscular cramps, etc.

Fig. 150. - Comma bacillus from a culture, x about 1000.

If cholera organisms be introduced into the peritoneal cavity of an animal in which a high degree of immunity against cholera has been previously induced, their motility is impaired or lost, and they become gathered into little clumps, which after a short time disappear in the peritoneal fluid. This phenomenon, which constitutes Pfeiffer's Reaction, takes place outside of the animal body and may serve the purpose either of distinguishing the cholera organism from others resembling it, or of indicating the presence of " anti-microbic" substances in a special serum. A close analogy is offered by the bacillus of typhoid fever in which the reaction, applied in this latter sense, is used as a means of diagnosis.

A protective vaccine has been devised by M. Haffkine. An exalted virus is made by passing the bacillus through the peritoneal cavity of the guinea-pig a number of times in succession with intermediate culture. This virulent form is injected subcutaneously. As the vibrio does not survive in the subcutaneous tissue the cultures themselves may be injected, but it is safer to use carbolized cultures which can be preserved in sealed tubes for use. The injection of the strong vaccine is preceded by the use of a weakened form.

The bacillus is destroyed by drying, and is apparently transmitted by means of water, milk, etc.

Vibrio Metchnikovi

This is a comma bacillus of smaller size than the cholera bacillus, and more strongly curved. It was found by Gamaleia in an epidemic of gastro-enteritis in chickens. It is highly pathogenic in pigeons and young hens. When cultures are inoculated into the muscles of pigeons the animals die in about twenty hours, and the microbes are present not only in the neighbourhood of the inoculation, but also in enormous numbers in the blood. The microbe is also very pathogenic in guinea-pigs.

Guinea-pigs and pigeons may be immunized by injection of the sterilized culture containing the toxines, and the blood serum of such animals rapidly kills the bacillus.

Vibrio Of Finkler And Prior

This was obtained from cultures in a case of cholera nostras, but it has not been found in other cases, and has nothing to do with the causation of cholera. It is merely a laboratory culture. It resembles the cholera vibrio, but differs in its mode of growth in cultures. It is pathogenic in guinea-pigs, but less so than the cholera bacillus.

Vibrio Deneke

This also is a laboratory organism obtained first from old cheese. It is distinguished from cholera by cultural differences and is, in addition, very feebly pathogenic.

Literature

Anthrax - Bollinger, Ziemssen's Encycl., iii., 1875; Koch, Milz-brandimpfung, 1882; Chauveau, Comptes rendus, xc. to xcvi.; W. Koch, Deutsch. Chir., Lief. 9, 1886; Eppinger, Wien. med. Wochenschr., 1888; Paltauf, Wien. klin.Wochenschr., 1888. Typhoid fever - Eberth, Virch. Arch., lxxxi., 1880, and lxxxiii., 1883; Coats, Brit. Med. Jour., 1882, i., p. 421; Gaffky, Etiol. of enteric fever (Syd. Soc. transl.), 1886; Wright and Semple, Lancet, July, 1895. Relapsing fever - Obermeier, Berlin, klin. Wochenschr., 1873; Carter, Lancet, 1879, and, Spirillum as seen in Western India, 1882. Diphtheria - Loeffler, Mittheil. aus. d. k. Gesundheitsamte, ii., 1884; Roux and Yersin, Ann. de l'Inst. Pasteur, ii., 1888, iii., 1889, iv., 1890; Behring, Brieger, Kitasato, etc., Deutsch. med. Wochenschr. and Berlin, med. Wochenschr., 1890; Roux, Ann. de l'Inst. Pasteur, viii., 1894; Flexner and Anderson (Extension to lungs, etc.), Johns Hopkins Bulletin, 1898. Tetanus - Nicolaier, Deutsch. med. Wochenschr., 1884; Rosenbach, Langenb. Arch., Bd. 34, 1886; Brieger, Berlin, klin. Wochenschr., 1887, 1888; Kitasato, Zeitschr. f. Hygiene, 1889, 1891; Behring, ibid., 1892. Influenza - Pfeiffer, Deutsch. med. Wochenschr., 1892; Kitasato, ibid., 1892. Bubonic plague - Yersin, Ann. de l'Inst. Pasteur, vol. viii., 1894, p. 662. Cholera - Koch, Etiol. of cholera (Syd. Soc. transl.), 1886.