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Rh containing the dejecta from cnolfera cases, although cases arc recorded in which " artificial " infection of the human subject has undoubtedly taken place, whilst, as Metchnikoff demonstrated, very young rabbits, deriving milk from mothers whose mammary glands have been smeared with a culture of the cholera vibrio, soon succumbed, suffering from the classical symptoms of this disease.

If, however, previous to the injection of the cholera bacillus the acidity of the stomach be neutralized by an alkaline fluid, especially if at the same time the peristaltic action of the intestine be paralysed by an injection of morphia, a characteristic attack of cholera is developed, the animal is poisoned, and in the large intestine a considerable quantity of fluid faeces containing numerous cholera bacilli may be found. There appear to be slight differences in the cholera organisms found in connexion with different outbreaks, but the main character■ istics are preserved throughout, and are sufficiently distinctive to mark out all these organisms as belonging to the cholera group. Amongst the known predisposing causes of cholera are the incautious use of purgative medicines, the use of unripe fruit, insufficient food and intemperance. These may be all looked upon as playing the part of the alkaKne solution in altering the composition of the gastric juices, and especially as setting up alkaline fermentation in the stomach and small intestine; beyond this, however, the irritation Set up may bring about an accumulation of inflammatory serous fluid, from the albumens of which, as we have seen, the cholera organism has the power of producing very active toxins.

The part played by want of personal cleanliness, overcrowding and unfavourable hygienic conditions may be readily understood if it be remembered that the cholera bacillus may grow outside the body. The number of cases in which epidemics of cholera have been traced to the use of drinking-water contaminated with the discharges from cholera patients is now considerable. The more organic matter present the greater is the virulence of water so contaminated; and the addition of such water to milk has, in one instance at least, led to an outbreak. If cholera dejecta be sprinkled on moist soil or damp linen, and kept at blood-heat, the bacillus multiplies at an enormous rate in the first twenty-four or thirty-six hours; but, as seen in the Dunbar-Schottehus method, at the end of three or four days it is gradually overcome by the other bacteria present, which, growing strongly and asserting themselves, cause it to die out. The importance of this saprophytic growth in the propagation of the disease can scarcely be over-estimated. Water which contains an ordinary amount of organic and inorganic matter in solution does not allow of the multiplication of this organism, which may soon die out; but when organic matter is present in excess, as at the margin of stagnant pools and tanks, development Occurs, especially on the floating solid particles. This bacillus grows at a temperature of 30° C. on meat, eggs, vegetables and moistened bread; also on cheese, coffee, chocolate and dilute sugar solutions. In some experiments carried out by Cartwright Wood and the writer in connexion with the passage of the cholera organism through filters it remained alive in the charcoal filtering medium for a period of at least forty-two days, and probably for a couple of months. It must be remembered that cholera bacilli are gradually overcome or overgrown by other organisms, as only on this supposition can the immunity enjoyed by certain regions, even after the water and soil have been contaminated, provided that no fresh supply is brought in " to relight the torch, " be explained. In most of the regions in which cholera remains endemic the wells are merely dug-out pits beneath the slightly raised houses, and are open for the reception of sewage and excreta at all times. These dejecta contain organic material which serves as a nutriment on which infective organisms, derived from the soil and ground-water, may flourish. Not only dejecta, but also the rinsings from soiled linen and utensils used by cholera patients should be removed as soon as possible, "without allowing them to come into contact with the surface of the soil, with wells, " or with vegetables and the like. The discovery of Koch's comma bacillus has so

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altered our conceptions of the aetiology of this disease that we now study the conditions under which the bacillus can multiply and be disseminated, instead of concerning ourselves with the cholera itself as some definite entity. Telluric agencies become merely secondary factors, the dissemination of the disease by winds from country to country is no longer regarded as being possible, whilst the spread of cholera epidemics along the lines of human intercourse and travel is now recognized. The virulent bacillus requires the human organism to carry it from those localities in which it is endemic to those in which epidemics occur. The epidemiologist has come to look upon the study of the cholera organism and the conditions under which it exists as of more importance than mere local conditions, which are only important in so far as they contribute to the propagation and distribution of the cholera bacillus, and he knows that the only means of preventing its spread is the careful inspection of everything coming from cholera-stricken regions. He also recognizes that the herding together of people of depressed vitality, under unhygienic and often filthy conditions, in quarantine stations or ships, is one of the surest means of promoting an epidemic of the disease; that attention should be confined to the careful isolation of all patients, and to the disinfection of articles of clothing, feeding utensils, and the like; that the comma bacillus can only be driven out of rooms by means of light and fresh air; that thorough personal, cuhnary and household cleanliness is necessary; that all water except that known to be pure should be carefully boiled; and that all excess, both in eating and drinking, should be avoided. The object of the physician in such cases must be first to isolate as completely as possible all his cholera patients, and then to get rid of all predisposing causes in the patients themselves, causes which have already been indicated in connexion with the aetiology of the disease.

Attention has frequently been drawn to the fact that patients who have lived for some time in a cholera region, or who have already suffered from an attack of cholera, appear to enjoy a partial immunity against the disease. Haffkine, working on the assumption that the symptoms of cholera are produced by a toxin formed by the cholera organism, came to the conclusion that, by introducing first a modified and then a more virulent poison directly into the tissues under the skin, and not into the alimentary canal, it would be possible to obtain a certain in susceptibility to the action of this poison. He found that for this purpose the cholera bacillus, as ordinarily obtained in pure culture from the intestinal canal, is too potent for the preliminary inoculation, but is not sufficiently active for the second, if any marked protection is to be obtained. By allowing the organism to grow in a well-aerated culture the virulence is gradually diminished, and this virulence, once abolished, does not return even when numerous successive cultures are made on agar or other nutrient media. On the other hand, by passing the cholera bacillus successively through the peritoneal cavities of a series of about thirty guinea-pigs, he obtains a virus of great activity; this activity is soon lost on agar cultivations, and ii is necessary, from time to time, again to pass the bacillus through guinea-pigs, three or four passages now being sufficient to reinforce the activity.

From these two cultures the vaccines are prepared as follows: The surface of a slant agar tube is smeared with the modified cholera organism. After this has been allowed to grow for twenty four hours, a small quantity of sterile water is poured into the tube, and the surface-growth is carefully scraped off and made into an emulsion in the water; this is then poured off, and the process is repeated until the whole of the growth has been removed. The mixture is made up with water to a bulk of 8 c.c, so that if I c.c. is injected the patient receives 5 of a surface-growth; it is found that this quantity, when injected subcutaneously into a guinea-pig, gives a distinct reaction, but does not cause necrosis of the tissues. If the vaccine is to be kept for any length of time, the emulsion is made with 0-5 % carbolic acid solution, prepared with carefully sterilized water, and the mixture is made up to 6 c.c. instead of 8 c.c, since the carbolic acid appears tc interfere slightly with the activity of the virus. The stronger virus is prepared in cxaclly the same way. The preliminary' injection, which is made in the left flank, is followed by a rise in temperature and by local reaction.