PATHOGENIC BACTERIA. 32! 



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 ex- 

 tend 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.* 



*-r 



FIG. 76. Bacillus of bubonic plague. (Yersin.) 



It is sometimes sensitive to drying, but may sometimes sur- 

 vive prolonged drying. When spread in thin layers, it is killed 

 in three to four hours by direct sunlight. Dried out on cotton 

 and linen cloth the bacilli were found to be still alive after 18 

 hours exposure to sunlight. The action of sunlight is in direct 

 proportion to the thinness of the layer into which the cultures 

 are spread, being seriously hindered when the layer is thick, 

 in a few minutes by steam at 100 C. Rosenau states that it 

 is killed in one hour by one per cent, carbolic acid, but others 



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

 21 



