CO129-275 - Governor Sir Robinson - 1897 [1-5] — Page 192

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Experiments on the inoculability of bubonic plague were made on all kinds of animals, both with cultures and with fragments of the organs of patients that had died of the plague. They were rats and house mice, which died in great numbers during the epidemic; next in order of susceptibility came white mice, guinea-pigs, rabbits, pigs, monkeys, and fowls. Cats became feverish after inoculation, but did not die. Pigeons were non-inoculable.

In the albuminous urine of 40 patients suffering from plague, plague bacilli were found in over ... of the cases. They could usually be detected by simple microscopical examination; frequently also in fragments of the organs and with pure cultures of the bacillus. Sometimes the urine contained also pus-cocci.

The bacillus was never detected in the sweat.

B.—The Bacillus of Bubonic Plague.

The plague bacillus is a short, thick rod with rounded ends, about 1 μ in length and 0.3 μ in breadth. The bacillus is non-motile. It is stained by all basic aniline dyes, but is not stained by Gram's method. In simple stained cover-glass preparations of the blood and the organs, the ends of the bacillus stain much more deeply than the middle. Often the ends of the bacillus remain entirely unstained, so that it has the appearance of a diplococcus. Sometimes the bacillus is surrounded by a clear area. Very frequently the bacillus is found in the interior of the white blood corpuscles.

The bacillus grows in artificial nutritive media, both at the temperature of the blood and at the ordinary temperature of the room. The optimum temperature is 37° C. Below 25° C, a decline in the rapidity of growth becomes noticeable. The bacillus thrives better on nutritive media containing glycerine than on those made without the admixture of this substance. Spore-formation was never observed.

On gelatine plates, the bacillus grows without liquefying the medium and produces in 48 hours small, round, greyish-white colonies. When these are examined microscopically, they have at first the appearance of ground glass, and later a darker, granulated appearance, sometimes with notched borders.

In gelatine puncture and streak cultivation, the bacillus grows slowly to form grey or greyish-white cultures, without liquefying the gelatine.

On agar plates, the bacillus forms within 24 hours small, round, greyish-white colonies, of the size of a pin's head, which by reflected light show a bluish sheen with iridescent borders. The colonies usually reach the size of a lentil only and remain isolated. Frequently, however, some of the colonies increase considerably in size after a few days and outgrow the others. Old colonies on agar plates have usually a ragged appearance.

If from the colonies just described, puncture and streak cultivations upon agar are made, it is found that tubes inoculated from the smaller colonies show a scantier growth than those inoculated from the larger colonies. The streak cultivations on agar appear white or greyish-white and show by reflected light a bluish sheen. The puncture cultivations have a whitish appearance along the depth of the insertion and extend but little superficially from the point of inoculation.

Subcutaneous inoculation of rats, house-mice, white mice, guinea-pigs, and rabbits with fragments of organs of patients that had died of the plague killed the animals in from one to six days. Mice died usually in from one to three days, rats in from two to four days, guinea-pigs according to their size in from two to five days, rabbits in from four to seven days. Soon after the inoculation, the animals' temperature rose to 40° C (104° F); they sat with ruffled fur in a corner of the cage; they lost appetite; shortly before death, they fell suddenly on their side and died in convulsions, which sometimes lasted two or three hours.

On post-mortem examination, there was found at the site of inoculation a hæmorrhagic, gelatinous exudation; there was inflammation of the lymphatics leading to the nearest lymphatic glands; these glands were red and swollen and often imbedded in a yellow, gelatinous exudation. The lungs were usually congested; the right side of the heart was usually distended with bluish-black blood; the liver was red and swollen; the spleen was bluish, much swollen, and frequently studded with small follicles. The kidneys and the adrenals were congested and usually swollen. The intestine was often congested, and the mesenteric glands were sometimes moderately swollen and congested. In the various organs, especially in the lymph-glands, the liver, the kidneys, the spleen, and the blood, the plague bacillus was present; it was usually found also in the urine and in the fæces.

When subcutaneous inoculations of pure cultures were made in animals, it was found that the virulence of the cultures was very variable. Cultures of the third and fourth generations proved much less virulent than those of the first and second generations; and cultures derived from the larger, over-grown colonies on agar plates were much less virulent than cultures derived from the smaller colonies on the same plates.

If fresh cultures of the first generation were used for subcutaneous inoculations, the bacilli being those growing in the smaller colonies on agar plates, which colonies had been directly derived from the organs, blood, or urine of plague patients, the inoculated mice, rats, guinea-pigs, and rabbits died according to their size in from one to twelve days. Mice died as a rule in from two to seven days; rats from four to five days; small guinea-pigs weighing from 150 to 200 grammes within five days; large guinea-pigs weighing from 400 to 500 grammes in from five to nine days; and rabbits in from seven to twelve days. The appearances on post-mortem examination were identical with those seen in animals inoculated with fragments of the organs.

The less virulent cultures always gave rise to fever on inoculation and were fatal to mice; they were seldom, however, fatal to rats; still more rarely fatal to guinea-pigs. When fatal, the duration of the illness was longer than in animals of the same species inoculated with the more virulent cultures. Rabbits inoculated with the less virulent cultures suffered from fever but were not killed.

The growth of the bacillus on bouillon is very characteristic in this respect, that it resembles that of "the streptococcus pyogenes." The growth forms at the bottom and along the sides of the test-tube as a granular or flocculent precipitate, while the bouillon itself remains clear. If it is shaken, the precipitate is distributed throughout the fluid. The cultures do not give the indol reaction.

On potato, the growth is very scanty. At blood-heat, in from 36 to 48 hours, very delicate greyish-white or white crusts are formed. At the temperature of the room, the growth is not apparent until after three or four days.

Sterilised milk is curdled by the bacillus.

The most favourable culture medium for the bacillus is a 2‰ alkaline solution of peptone containing 1% of gelatine.

In stained cover-glass preparations from artificial cultures, the bacillus has usually the appearance of a diplococcus. Very frequently, four to six of such bacilli lie joined together in a chain, and they then resemble streptococci. Such appearances are seen most often in cultures in bouillon and in hanging-drop cultivations. Frequently, especially in old cultures, bulging, oval, almost spherical forms are seen. In old cultures, the bacilli stained less readily.

Intra-peritoneal inoculations caused great swelling of the intestinal follicles and of the mesenteric glands, but otherwise the symptoms were the same as those produced by subcutaneous inoculation. The intra-peritoneal inoculations were as a rule more rapidly fatal. The less virulent cultures more often proved fatal when inoculated intraperitoneally than when inoculated subcutaneously.

The introduction of fragments of the organs or of pure cultures into the stomach, either by mixing them with the food or through the stomach-tube, was usually fatal to mice and almost always fatal to rats and to small young guinea-pigs and rabbits. The post-mortem appearances were generally speaking the same as those found after subcutaneous and intra-peritoneal inoculations. There was more swelling of the intestine, the intestinal follicles, and the mesenteric glands than in animals killed by subcutaneous inoculation; on the other hand, the external lymphatic glands were usually less swollen than in animals killed by subcutaneous or by intra-peritoneal inoculation.

In post-mortem examinations on animals, the inguinal and the cervical glands were nearly always found to be much more severely affected than the axillary glands.