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GLANDERS occurs chiefly among horses and asses, but may be communicated to persons associated with the infected animals, such as stablemen and grooms. The infective material is present in the discharges from the nostrils and in the pus from the nodules.
The exciting cause is a bacillus somewhat shorter and thicker than the tubercle bacillus. The bacillus mallei stains readily with the ordinary dyes and frequently shows a “beaded” appearance on staining. It is decolorised by Gram's method of staining. It is a strict parasite and does not form spores.
The B. mallei does not grow in infusions of hay or horse manure, but can be cultivated in glycerine-agar and blood serum. The growth on potato is very characteristic. On this medium, at incubation temperature, the growth readily appears as a honey-like layer, which later changes to a brownish or chocolate colour.
Glanders can be easily communicated to laboratory animals, and accidental infection in man has frequently been recorded. It is said that lions and tigers in menageries have contracted the disease from being fed on the flesh of infected animals.
Drying, high temperature, and antiseptics quickly kill the glanders bacillus. The organism has never been found outside the body.
A toxic substance (mallein) has been obtained from cultures of the bacillus. This, when injected into infected animals, acts like tuberculin when used for the detection of tuberculosis.
The bacillus of influenza was discovered by Pfeiffer, in 1892, in the purulent bronchial secretions of infected patients. It is the shortest of all known bacilli, and on account of its minute size may be mistaken for a coccus.
Fig. 21.-Influenza Bacillus. From a film prepared from
[From Curtis's Essentials of Practical Bacteriology.] The bacilli are usually arranged in chains. They are ærobic and do not form spores.
Artificial cultures are made with difficulty. The best medium is blood-agar, which, after inoculation with the sputum, shows characteristic colonies at the end of twentyfour hours. These, when observed with a lens, are seen
to consist of minute transparent dots, like drops of dew, which always remain separate from each other. “This feature is so characteristic that the influenza bacilli can be thereby with certainty distinguished from other bacteria” (Kitasato).
The influenza bacillus is quickly destroyed by antiseptics and drying, although in the moist sputum it may remain alive for two to three weeks.
Although the disease cannot be reproduced in animals, there can be little doubt that Pfeiffer's bacillus is the essential cause of influenza. The bacilli are mainly localised in the respiratory tract, where they produce their toxic metabolic products which, as in the case of B. diphtheriæ, have a selective affinity for the nervous tissue.
The bacteriology of this disease has been worked out only within the last few years. The specific organism was discovered in 1894 by Kitasato and Yersin, being constantly met with in the enlarged glands, blood, and internal organs. In the pneumonic form of the disease it is present in the sputum.
In form the bacillus pestis (Frontispiece, Fig. VI.) is a short oval rod, rounded at both extremities. In specimens from blood it is usually arranged in pairs, giving rise to the appearance of diplococci. But in artificial cultivations it frequently forms chains of varied lengths.
It is readily stained by aniline dyes, but the extremities take on a deeper hue than the intervening portion (“polar staining”). It does not form spores, and, according to Kitasato, is actively motile.
In cultivations the organism is especially prone to undergo degenerative changes and give rise to various involution forms. It, however, grows well on ordinary media. In broth it gives rise to a granular deposit on the sides and bottom of the tube. On agar-agar (and better still, on glycerine-agar) it forms an abundant cream-coloured growth which, when viewed from behind, presents a dull, silvery appearance. Haffkine has found that if broth cultures, containing a little ghi or cocoanut oil, are kept absolutely at rest, the organisms grow in a most charac