THE BACILLUS OF BUBONIC PLAGUE. 275 



have been observed in different colonies from the same 

 source. 



In man the bacilli are most numerous in the en- 

 larged, suppurating lymphatics. They are present, but 

 in smaller numbers, in the blood and the internal organs. 



It has been observed that in the suppurating lym- 

 phatic glands of man a variety of organisms may be 

 present, conspicuous among them being the so-called 

 plague bacillus. Occasionally, micrococci predominate. 



In these cases of mixed infection the pest bacilli are 

 said to stain less intensely with alkaline methylene-blue 

 than do the streptococci, and more intensely than do the 

 staphylococci that are present. Also, in this event, the 

 streptococci retain the Gram stain, while the pest bacilli 

 and the staphylococci do not. It has been suggested 

 that possibly the organisms found by Kitasato in the 

 blood, and which he describes as pest bacilli, that re- 

 tained the color when treated by the method of Gram, 

 were pairs of micrococci and not bacilli at all. 



It is the opinion of Aoyama that the suppuration of 

 the glands is not caused by the plague bacillus, but is 

 rather the result of the action of the pyogenic cocci 

 with which it is so often associated. 



Again, according to Aoyama, the most important and 

 frequent mode of infection in man is through wounds 

 of the skin. He does not regard either the air-pas- 

 sages or the alimentary tract as frequent portals of 

 infection. 



The order in which the lymphatics manifest disease 

 appears to depend upon the location of the primary 

 infection. That is to say, if it is upon the feet, as of 

 persons who go barefooted, the superficial and deep 

 inguinal glands are the first to show signs of the dis- 



