x, B,4 Crowell: Pathologic Anatomy of Bubonic Plague 258 
a 
tion of rats in cargo from China, since China at the time had 
infected ports from which vessels were constantly arriving. 
CLASSIFICATION OF PLAGUE CASES 
BUBONIC AND PNEUMONIC PLAGUE 
It is known that Bacillus pestis may produce two types of 
disease which differ in their epidemiologic, symptomatologic, 
and pathologic aspects. This difference in the type of disease 
caused by the same microorganism is dependent on the portal 
of entry into the host and on the condition of the atmosphere 
in regard to temperature and humidity. When infection occurs 
through the skin or exposed mucous membranes, the bubonic 
type of the disease occurs and is manifested usually by enlarge- 
ment of the superficial lymphatic glands draining the area in- 
oculated, by fever and prostration, sometimes by extensive 
eutaneous symptoms, sometimes by marked pulmonary symp- 
toms, and frequently by marked cerebral symptoms. When the 
infection takes place through the respiratory tract, the primary 
pneumonic type of the disease occurs with symptoms chiefly 
referable to the lungs. The bubonic type is said to be trans- 
mitted chiefly from infected rats to the human being through 
the agency of the rat flea (Loemopsylla cheopis). Attention 
has been drawn to the possibility of its transmission by the 
cat,°> as well as by direct contact with either plague patients 
having open cutaneous lesions, or with material infected by 
such patients, or by those with pulmonary or pharyngeal lesions 
from which the sputum may be infective. 
In the primary pneumonic form infection occurs by the inhala- 
tion of droplets of infective material produced in the acts of 
coughing or sneezing by patients with the pneumonic type of the 
disease. It is known that this method of transmission is com- 
mon during an epidemic of primary pneumonic plague, and it 
is a possibility that, under suitable conditions of temperature 
and humidity, the primary pneumonic type may be similarly 
contracted from a patient with bubonic plague who has a sec- 
ondary plague pneumonia. In these cases the infection is said 
by some to occur in the upper respiratory tract and extend 
secondarily to the lungs through the blood stream. Others main- 
tain that a primary infection of the lung occurs by direct inhala- 
tion of the infective material into the finer bronchioles and 
air sacs. 
“Teague and Barber, Ibid. (1912), 7, 172. 
* Schobl, Ibid. (1918), 8, 426. 
