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acids, and the form of growth on broth will vary; there will be varieties which grow luxuriantly in given media, and others which do not grow there at all; some will be phosphorescent in the dark and others not; some will give the indol reaction, and others will be deprived of this property, and so on ” (Haffkine).

(3) The specificity of the cholera spirillum has also been seriously called into question by the fact that vibrios closely resembling it have been detected in the drinking supplies of communities which were not suffering from cholera at the time. Thus, Sanarelli isolated thirty-two such vibrios from the drinking water at Versailles. They were of extreme variability; a few gave indol reaction, others did so after a few days, and the remainder not at all.

The differential diagnosis of these organisms is a matter of considerable difficulty, but Pfeiffer has proposed a test which is satisfactory in most cases. This test depends on the fact that the serum of an animal immunised against cholera is protective against this organism, but not against any other species. Thus, if the mixture of an organism and the immunised serum be injected into the peritoneal cavity of a healthy guinea-pig, and a drop of the peritoneal fluid microscopically examined, the organism will be found swollen and disintegrated, if it belongs to the same species as that employed for immunising the animal. As a result it has been found that the majority of Sanarelli's vibrios are the degenerate descendants of true cholera germs, which, perhaps, existed in the course of a former epidemic. What is the precise origin of those organisms which, while giving all the reactions of the cholera vibrio, exist in localities where this disease has never appeared, is a question which cannot be satisfactorily answered.

Of the numerous organisms more or less resembling the cholera spirillum, there are two vibrios, which, on

account of their historic importance, deserve a passing notice. They are the spirillum of Finkler and Prior and the spirillum Metschnikovi. The former, obtained from the dejecta of patients suffering with cholera nostras, liquefies gelatine much more quickly than the cholera spirillum, and, unlike the cholera germ, grows upon potato at the room temperature. The spirillum Metschnikovi obtained from the intestinal contents of chickens also liquefies gelatine more rapidly than the cholera spirillum, and is fatal to pigeons, even in minute doses.

Protective inoculation against cholera by Haffkine's method has yielded very promising results in India. For this purpose Haffkine prepares two vaccines or prophylactic fluids—one, a strengthened vaccine obtained by growing the virus in the peritoneal cavities of a series of guinea-pigs; and the other, a mild vaccine obtained by passing a current of air over the strengthened virus, so as to weaken its pathogenic powers. The ordinary laboratory cultures are usually attenuated, but cannot be employed for inoculation, as they vary widely as regards their virulence. Haffkine’s vaccines, on the contrary, are absolutely fixed in their value, and herein lies the secret of the success of this treatment.

The weakened vaccine is first inoculated, and is then followed by the strengthened vaccine. A slight reaction occurs after each inoculation, but in no case is there any danger to life.

TYPHOID.

The organism of typhoid fever was demonstrated in the spleen by Eberth in 1881, and subsequently isolated and studied by Gaffky. It is, therefore, sometimes called the Eberth-Gaffky bacillus. Although it has not hitherto been possible to exactly reproduce the disease in animals, this

Fig. 13.-Bacillus Typhosus.
[From Curtis's Essentials of Practical Bacteriology.]

organism is nevertheless recognised as the veritable germ of typhoid fever.

The B. typhosus occurs as a short fat rod, about 2 u long, and with rounded ends. It is actively motile, and possesses about ten to twenty flagella arranged round the entire periphery of the organism. It does not form spores, and is stained with aniline dyes, but not by Gram’s method.

In gelatine plate cultures small white colonies appear in two or three days, the surface of which are covered with lines and grooves not unlike " the veining of a vine leaf”. A uniform turbidity is produced in bouillon, but the growth is most luxuriant in agar and glycerine-agar. On potatoes, having an acid reaction, there is an “invisible growth,” which is said to be highly distinctive. Milk is not coagulated, but a slight acidity is produced.

[graphic]

Fig. 14.—Bacillus Typhosus. Gelatine plate culture.

[From Curtis's Essentials of Practical Bacteriology.]

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The typhoid bacillus is peculiarly resistant, and may linger a long time upon clothing, in stools, and in the soil. It resists the action of gastric juice for several hours, but is rapidly killed by sunlight and various disinfectants.

As animals do not suffer from typhoid fever it is not easy to reproduce this disease by inoculation. However, by increasing the virulence of germs by various means, it is possible to obtain cultures which are truly pathogenic for animals. On the other hand, attenuated cultures of typhoid bacilli may suffice to produce the disease if the resistance of the animals has been previously lowered by making them inhale sewer gas.

The bacillus occurs constantly in typhoid stools, in the intestinal lesions, as well as in the spleen and liver. It is rarely found in the blood. Locating itself in the intestine it produces poisonous substances, which give rise to fever and the other specific lesions. During the existence of the disease the system reacts in a peculiar manner, the exact significance of which is not sufficiently known. The reaction has been studied by Widal, who showed that the serum of typhoid patients causes the bacilli to lose their motility and aggregate into clumps. This is the principle of the serum diagnosis of typhoid, which is now extensively employed for the differentiation of this disease.

Protective inoculation against typhoid with the serum of immunised animals has been largely practised by Wright. The subject is still in the experimental stage, but the results hitherto obtained are certainly encouraging.

Relation to Bacillus Coli Communis.- The B. coli communis, or the “colon bacillus,” is an organism almost identical with the B. typhosus in its general appearance, and it becomes important to distinguish the one from the other. The colon bacillus, however, is shorter, has fewer flagella, forms a thick yellow layer on potato, produces gas, and gives the indol reaction.

It is a normal inhabitant of the human intestine, and is usually harmless. But it becomes significantly abundant in cholera and various forms of enteritis. It sometimes

Agglutination is also well seen in cholera, plague, and dysentery. The phenomenon may be studied under the microscope or in a test tube, in which case the clumps settle in the fluid in the form of sediment (“ sedimentation).

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