264 MANUAL OF BACTERIOLOGY. 



Staining; by Gram's method it is decolorized. It is aerobic. 

 It grows at ordinary temperatures, but better in the incubator. 

 It grows on most media. The growths are grayish- white. 

 Gelatin and blood-serum are not Uquefied. In bouillon, 

 the medium remains clear, while a granular deposit forms on 

 the sides and bottom of the tube. In bouillon to which a few 

 minute drops of sterile oil, as cocoanut oil, have been added, 

 a growth takes place from the under side of the oil drops. 

 Such growths extend down, and are called stalactite growths. 

 The stalactites break off, with the slightest disturbance. 



Remarkable involution forms appear on agar containing 

 3 per cent, of common salt. The stalactite growths and the 

 forms occurring on salt-agar are considered the most charac- 

 teristic cultural peculiarities.* 



It is sometimes sensitive to drying, but may sometimes 

 survive prolonged drying. When spread in thin layers, it is 

 killed in three to four hours by direct sunlight; in a few minutes 

 by steam at 100° C., and in one hour by one per cent, carbolic 

 acid.f It is pathogenic for rats, mice, guinea-pigs, rabbits 

 and a number of other animals. 



In man it appears usually to enter through wounds of the 

 skin. Other possible avenues of infection are the air-passages, 

 the mouth and the gastro-intestinal tract. In plague three 

 different clinical forms are to be recognized — the bubonic, 

 the pneumonic and the septicemic. The bubonic form is com- 

 monest. The point in the skin at which the inoculation takes 

 place seems generally to exhibit no inflammatory reaction. 

 The lymph-nodes are generally swollen, especially the deep in- 

 guinal and axillary nodes. The swollen lymph-nodes may 

 suppurate. The suppurating nodes are often infected simul- 



* Wilson. Journal Medical Research. Vol. VI. 1901. 



t See Rosenau. Viability of BaciUus pestis. Marine Hospital Service. 

 Hygienic Laboratory Bulletin. No. 4. 1901. 



