BACILLUS PESTIS 239 



are enlarged and show a characteristic granular or mottled appear- 

 ance, sometimes with abscess formation and necrosis. Rats and 

 mice may also be infected by feeding them with pure cultures or 

 the dead carcasses of their infected comrades. In such cases it 

 is thought that infection takes place through the mucous mem- 

 branes of the mouth rather than by the intestinal canal. The 

 fact that infection may take place through slight abrasions of the 

 skin serves a useful purpose in diagnosis. Often rats submitted 

 for examination are decidedly decomposed. If, however, the sus- 

 pected material is rubbed on to the freshly shaved abdomen of a 

 guinea pig the plague bacilli enter through the slight scarification 

 due to shaving and give rise to a general infection, whereas the other 

 organisms present are not able to penetrate the skin. 



In man three clinical types of plague are recognized : (1) bubonic, 

 (2) pneumonic, and (3) septicemic. In the bubonic form the 

 lymphatic glands become intensely inflamed and swollen, ending 

 in necrotic softening if the patient lives long enough . The surround- 

 ing connective tissue is similarly affected, and often subcutaneous 

 hemorrhages occur, causing the dark colored spots which originated 

 in the middle ages the popular name of " black death." Usually 

 one group of glands is first affected, and from this primary " bubo " 

 the swelling and necrosis extends to other groups. Hemorrhage 

 and necrosis may also occur in the lungs, liver, and spleen. 



In the pulmonary form the disease appears as a broncho-pneu- 

 monia often attended by hemorrhages; there is usually a large 

 amount of frothy, blood-tinted sputum in which the bacilli are 

 present in enormous numbers. In this form the disease is ex- 

 tremely infective and almost always fatal. The mortality is esti- 

 mated to be 90 per cent or more. 



In plague septicemia there is a slight general enlargement of 

 the lymphatic glands, but no primary bubo is discoverable. A case 

 commencing in the bubonic form may, however, terminate with 

 septicemia. In the bubonic and the septicemic types the bacillus 

 remains in the diseased organs and the blood stream and is not 

 eliminated in the excretions. These forms of the disease therefore 

 are not contagious in the usual sense of the word, but are spread 



