animals in which the parts round the place of inoculation present the same edematous exudations as we find in human beings.
I shall now give a few short notes about the Bacillus. The Bacilli are to be found in the blood, in the buboes, in the spleen and in all other internal organs of the victims of plague. The Bacilli are rods with rounded ends which are readily stained by the ordinary aniline dyes; the poles being stained darker than the middle part, especially in blood preparations, and presenting a capsule sometimes well marked, sometimes indistinct. The Bacilli found in the spleen are best stained by a solution of methyl blue. I am at present unable to say whether or no Gram's double-staining method can be employed. I shall report upon this on a future occasion.
The Bacilli show very little movement, and those grown in the incubator, in beef tea, make the medium somewhat cloudy. The growth of the Bacilli is strongest on blood serum at the normal temperature of the human body (37° C)—under these conditions they develop luxuriantly and are moist in consistence and of a yellowish grey colour; they do not liquify the serum. On Agar-Agar jelly (the best is good glycerine agar) they also grow freely. The different colonies are of a whitish grey colour, and by a reflected light show a bluish glance; under the microscope they appear moist and in rounded patches with uneven edges—at first they appear everywhere as if piled up with 'glass wool,' later on as if having dense, large centres. cover-glass preparation is made from a cultivation on agar-agar, and, after having been stained, is observed under the microscope; long threads of Bacilli are seen, which might, by careless inspection, be mistaken for a coccus chain, but are recognised with certainty as threads of Bacilli under closer observation. The growth on agar-gelatine is similar to that on agar-agar; in a puncture cultivation, at the ordinary temperature after a few days, they are found growing as a fine dust, in little points alongside the puncture, but with very little growth on the surface. Whether these Bacilli are able to liquify ordinary gelatine or not, I am at present unable to decide, as the temperature of Hongkong ranges so high that the employment of simple nutritive gelatine is out of the question. I shall give further information on this question later.
On potatoes at a temperature of from 28° C. to 30° C. there was no growth after ten days' observation, but at a temperature of 37° C. the Bacilli developed sparingly after a few days—they were whitish grey in colour and exsiccated.
As mentioned before the Bacilli grow best at a temperature of from 36° C. to 39° C.—at how low a temperature growth is possible, I am unable at present to state.
So far I have been unable to observe the formation of spores.
Experiments on Animals. Mice, rats, guinea-pigs, and rabbits are susceptible to inoculation. If these animals are inoculated with pure cultivations, or with the blood of a plague patient in which the Bacilli have been observed, or with the contents of a bubo, or with pieces of internal organs, or even with the contents of the intestine, they begin to become ill in from one to two days, according to the size of the animal. Their eyes become watery, they begin to show disinclination for any effort, later on avoid their food and hide quietly in a corner of the cage. The temperature rises to 41.5° C., and with convulsive symptoms they die in from two to five days.
I must observe that in Hongkong I could only obtain small guinea-pigs (weight from 100 to 150 grammes) and small rabbits (from 200 to 250 grammes). If I could have experimented upon larger animals it is possible life would have been somewhat prolonged beyond the periods mentioned above.
The parts around the point of inoculation are infiltrated with a reddish gelatinous exudation, the spleen is enlarged, sometimes there is a swelling of the lymphatic glands, and in all the organs the Bacilli are found. The results found after death
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