19 



The follo-\ving facts may be added to the enumeration of the 

 cultural peculiarities of the plague bacillus : It does not liquefy 

 gelatin or blood serum^, does not ferment dextrose, levulose, lactose, 

 or mannit, grows sparingly on potato and on milk, which latter it 

 does not coagulate. 



In the preceding description of the morphology and of the 

 cultural properties of the plague bacillus no attempt has been made 

 to bring out all the details which have been reported in an extensive 

 literature, but merely to state clearly and emphasize those points 

 the knowledge of which is indispensable in the bacteriologic 

 diagnosis of plague. Staining of the plague bacilli in sections will 

 be referred to later. 



NOSOLOGY AND CLASSIFICATION. 



Bubonic plague of man is an acute, occasionally more subacute, 

 infectious disease, caused by a specific micro-organism, Bacillus 

 pestis, which generally first gains entrance through a trauma of 

 the skin or the mucous membranes and thence finds its way into 

 some of the peripheral lymph glands. In other cases it is inhaled 

 into the lungs, or in still others it enters directly into the general 

 blood circulation. These different methods of infection at once 

 suggest a classification into three main types — bubonic plague 

 proper, plague pneumonia, and plague septicaemia. Perhaps the 

 most prominent and most constant — certainly, even on superificial 

 examination, the most manifest — pathologic feature of all forms 

 of plague is the occurrence of hemorrhages both local at the site 

 or sites where the plague bacilli are colonized in great numbers, 

 as in the lymph glands and in the lungs, and general, subserous, 

 submucous, parenchymatous, and interstitial hemorrhages. The 

 great frequency and constancy of these hemorrhages in plague has 

 led to its classification as a hemorrhagic septicemia. Nothing, as 

 M'e expect to be able to demonstrate, could be more false than such 

 a definition of plague in man. It may be quite true that experi- 

 mental plague in certain of the lower animals is indeed generally 

 a hemorrhagic septicemia, but this, of course, a priori proves noth- 

 ing as to man. Anthrax, in some animals, is imdoubtedly a 

 septicemia, yet usually when contracted by man it is primarily 

 a local disease and frequently remains local. Diplococcus pneii- 

 monice, when introduced experimentally into mice, rabbits, or 



