NOT DESCRIBED IN PREVIOUS SECTIONS. 521 



stain more intensely than the centre, so that they often present a 

 clear space in the middle. Sometimes the bacilli appear to be sur- 

 rounded by a capsule. ... In bouillon the bacillus has a very char- 

 acteristic appearance, resembling the cultures of the streptococcus of 

 erysipelas a clear liquid with grumous deposits on the walls and at 

 the bottom of the tube. These cultures examined under the micro- 

 scope show veritable chains of short bacilli, presenting in places a 

 considerable spherical enlargement." 



Biological Characters. We quote from Kitasato's preliminary 

 report as follows : 



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 

 (34 C.) ; under these conditions they develop luxuriantly and form a col- 

 ony moist in consistence and of a yellowish-gray color ; they do not liquefy 

 the serum. On agar-agar jelly (the best is good glycerin agar) they also 

 grow freely. The different colonies are of a whitish-gray color and by re- 

 flected light have a bluish appearance ; under the microscope they appear 

 moist and in rounded patches with uneven edges ; at first they appear every- 

 where as if piled up with "glass-wool," later as if haying dense, large cen- 

 tres. If a cover-glass preparation is made from a cultivation on agar-agar, 

 and, after haying 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 recognized with certainty as " threads of bacilli " 

 under closer observation. The growth on agar-gelatin 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 ba- 

 cilli are able to liquefy ordinary gelatin or not I am at present unable to de- 

 cide, as the temperature of Hong-Kong ranges so high that the employment 

 of simple nutritive gelatin is out of the question. I shall give further infor- 

 mation on this question later. On potatoes at a temperature of from 28 

 to 30 C., there was no growth after ten days' observation, but at a tempera- 

 ture of 37 C. the bacilli developed sparingly after a few days ; the growth 

 was whitish-gray in color and exsiccated. As mentioned before, the bacilli 

 grow best at a temperature of from 38 to 39 C. ; at how low a temperature 

 growth is possible I am unable at present to state. So far I have been un- 

 able to observe the formation of spores. 



Experiments on Animals. Mice, rats, guinea-pigs, and rabbits are sus- 

 ceptible to inoculation. If these animals are inoculated with pure culti- 

 vations, 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 wa- 

 tery, they begin to show disinclination for any effort, later they 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 Hong-Kong I could only obtain small guinea-pigs 

 . (weight from one hundred to one hundred and fifty grammes) and small 

 rabbits (from two hundred to two hundred and fifty grammes). If I could 

 have experimented upon larger animals it is possible that life would have 

 been prolonged somewhat 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 lym- 

 phatic glands, and in all the organs the bacilli are found. The results found 



