PLAGUE 171 



Cold dead rats are harmless, as the flea has forsaken them for 

 another warm host. 



The Indian Musk Rat, Crocidura coerulea, is highly resistant to 

 plague. Only one rat was found to be naturally infected witTi plague 

 by the Indian Plague Commission (Kerandel). 



THE CARRIER. 



The flea most common in rats is Zenopsylla cheopis, but others, as 

 Ceratophyllus fasciatus and Pulex irritans, are capable. 



Infection by the flea is due to faecal infection of the proboscis or 

 of the wound made by it, which transmits the bacilli to the skin. 



Humans are infected by the Z. cheopis from the Epimys rattus. 



It is found on humans after cases of plague in man. 



Plague infection may persist in fleas for one or two months in the 

 cool weather, and subsequently give rise to an epizootic (Bacot). 



P. vestimenti is capable of transmitting plague infection also 

 (Swellengrebel). 



Air, however, does carry the bacillus in the pneumonic type from 

 the sputum. The bubonic or septicaemia is not spread from man to 

 man, but from rats to man. 



Bugs can also act as carriers, C. rotundatus. 



In California the ground squirrel, Citellus beecheyi, is subject to 

 plague, and its common flea, C. acutus, spreads it from one to another 

 and will bite man. In ^Manchuria plague started among those who 

 handled the Tarahagan (Arctomys bol^e) ; no infected rats were found. 

 The epidemic was pneumonic. 



PATHOLOGY. 



The site of the flea bite is sometimes marked by a vesicle, the con- 

 tents containing B. pestis in large numbers; the bacilli travel by the 

 lymphatics to the nearest glands ; some pass to the thoracic duct, 

 thence to the blood-stream, and so cause a septicaemia. More often 

 they remain and multiply in the lymph glands and the peripheral 

 lymph sinuses. Their toxins cause cell degeneration, periglandular 

 serous infiltration, and later, degeneration of the walls of blood-vessels 

 and haemorrhage. The l^^mphatics are matted by the exudation, 

 femoral, inguinal, axillary, iliac and cervical. The groin glands are 

 infected most, as they drain the largest skin area. The bacilli may 

 get direct to the blood-stream by injuring the veins in the primary 

 bubo. Lymphatic glands also become affected after the infection has 

 become a septicemia. Also the lung causing bronchitis and secondary 

 pneumonia, spleen, liver, kidneys, skin and other organs. 



The sputum and saliva can be infected forty-eight days after the 



