396 APPLICATION OF METHODS OF BACTERIOLOGY 



tinued cultivation under artificial conditions, and it is said 

 that from slowly developing, chronic buboes non-virulent 

 or feebly virulent cultures are often obtained. Variations 

 in the degree of virulence have been observed in different 

 colonies from the same source. Virulence is said to be 

 accentuated by passing the organism through a series of 

 susceptible animals. 



It has been observed that in the suppurating lymphatic 

 glands of man a variety of organisms may be present, but 

 among them are always the plague bacilli. 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 micrococci that are present. Also, in this event, 

 the streptococci retain the Gram stain, while the pest bacilli 

 do not and the staphylococci may or may not. 



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. He does not regard either the air- 

 passages or the alimentary tract as frequent portals of infec- 

 tion. Wilm, on the contrary, is inclined to regard the 

 alimentary tract as a frequent portal of infection; 1 and there 

 are numerous opinions that in the pulmonic type of plague, 

 its most fatal manifestation, infection is always by way 

 of the respiratory tract. 



The order in which the lymphatics manifest disease ap- 

 pears to depend upon the location of the primary infection. 

 That is to say, if it is upon the lower extremities, the super- 

 ficial and deep inguinal glands are the first to show signs 



1 Wilm, Hyg. Rundschau, 1897, p. 217. 



