Diplococcus of Neisser
6. Micrococcus gonorrhœæ (Neisser, 1879). This organism is more frequently spoken of as a diplococcus. It occurs at the acute stage of the disease, but is not readily differentiated from other similar diplococci except by technical laboratory methods. Each element presents a straight or concave surface to its fellow. A very marked concavity indicates commencing fission. The position which these diplococci take up in pus is intracellular, and arranged more or less definitely around the nucleus. Difficulty has often been found in cultivating this organism in artificial media outside the body. Wertheim and others have suggested special formulæ for the preparation of suitable media, but it is a very simple matter to secure cultures on agar plates smeared with human blood from a pricked finger. The plate is incubated at 37° C. At the end of twenty-four hours small raised grey colonies appear, which at the end of about four days show adult growth. The margin is uneven, and the centre more opaque than the rest of the colony. This diplococcus is readily killed, and sub-cultures must be frequently made to retain vitality and virulence. Light, desiccation, and a temperature of 55° C. all act germicidally. The organism stains readily in Löffler's blue, but is decolourised by Gram's method. It is more or less strictly parasitic to man. Its shape, size, character of growth, and staining properties assist in differentiating it from various similar diplococci.[98]
Anthrax. This disease was one of the first in which the causal agency of bacteria was proved. In 1849 Pollender found an innumerable number of small rods in the blood of animals suffering from anthrax. In 1863 Davaine described these, and attributed the disease to them. But it was not till 1876 that Koch finally settled the matter by isolating the bacilli in pure culture and describing their biological characters.
It is owing in part to its interesting bacterial history, which opened up so much new ground in this comparatively new science, that anthrax has assumed such an important place in pathology. But for other reasons, too, it claims attention. It appears to have been known in the time of Moses, and was perhaps the disease described by Homer in the First Book of the Iliad. Rome was visited by it in 740 B.C.
Anthrax is an acute disease, affecting sheep, cattle, horses, goats, deer, and man. Cats, white rats, and Algerian sheep are immune. Swine become infected by feeding on the offal of diseased cattle (Crookshank).
The post-mortem signs are mainly three: The spleen is greatly enlarged and congested, is friable to the touch, and contains enormous numbers of bacilli; the skin may show exudations forming dark gelatinous tumours; and the blood remains fluid for some time after death, is black, tar-like, contains bubbles of air, and shows other degenerative changes in the red corpuscles, whilst the small blood-vessels contain such vast quantities of bacilli that they may be ruptured by them. Particularly is this true in the peripheral arteries. Many of the organs of the body show marked congestion.
| Bacillus of Anthrax and Blood Corpuscles | Threads of Bacillus Anthracis, Showing Spores |
Clinically there is rise of temperature and rapid loss of muscular power. The bacilli of anthrax are square-ended rods 1 µ broad and 4–5 µ long. In the tissues of the body they follow the lines of the capillaries, and are irregularly situated. In places they are so densely packed as to form obstructions to the onward flow of blood. In cultures they are in chains end to end, having as a rule equal interbacillary spaces. In cultures long filaments and threads occur. The exact shape of the bacillus depends, however, upon two things: the staining and spore formation. Both these factors may very materially modify the normal shape. The spores of anthrax are oval endospores, produced only in the presence of free oxygen, and at any temperature between 18 and 41° C. On account of requiring free oxygen, they are formed only outside the body. The homogeneous protoplasm of the bacillus becomes granular; the granules coalesce, and we have spores. Each spore possesses a thick capsule, which enables it to resist many physical conditions which kill the bacillus. When the spore is ripe or has exhausted the parent bacillus, it may take on a resting stage, or under favourable circumstances commence germination, very much after the manner of a seed. The spores may infect a farm for many months; indeed, cases are on record which appear to prove that the disease on a farm in the autumn may by means of the spores be carried on by the hay of the following summer into a second winter. Thus, by means of the spores, the infection of anthrax may cling to the land for very long periods, even for years. Spores of anthrax can withstand 5 per cent. carbolic acid or 1–1000 corrosive sublimate for more than an hour; even boiling does not kill them at once, whilst the bacilli without their spores are killed at 54° C. in ten minutes. When the spores are dry they are much more resistant than when moist. Hence the persistence of the anthrax bacillus is due to its spores.
The bacillus is aërobic, non-motile, and liquefying. Broth cultures become turbid in thirty-six hours, with nebulous masses of threads matted together. The pellicle which forms on the surface affords an ideal place for spore formation.
Cultures in the depth of gelatine show a most characteristic growth. From the line of inoculation delicate threads and fibrillæ extend outwards horizontally into the medium. Liquefaction commences at the top, and eventually extends throughout the tube. On gelatine plates small colonies appear in thirty-six hours, and on the second or third day they look, under a low power of the microscope, like matted hair. The colonies after a time sink in the gelatine, owing to liquefaction. On potato, agar, and blood serum anthrax grows well.