PLAGUE AND BACILLUS PESTIS 813 



The curative plague serum prepared by Yersin and others by 

 the immunization of horses with plague cultures has been extensively 

 used in practice and though often disappointing, a definitely benefi- 

 cial influence on the milder cases has been noted. The sera are 

 standardized by their protective power as measured in white rats. 



The question of prophylactic vaccination and active immuniza- 

 tion will be taken up in connection with plague prevention below. 



Plague in Man. There are two chief methods by which the 

 disease is acquired by man. The first is by entrance of the bacilli 

 through the skin as a consequence of the bite of an infected flea. 

 During the act of biting, the flea may either regurgitate blood, or, 

 as is usually the case, deposit feces on the skin. The possibilities of 

 entrance of the plague bacillus through minor injuries in the skin 

 are so great that perhaps the infection may take place through the 

 lesion caused by the fleabite, but more likely is rubbed in by the 

 clothing or by scratching as the fleabite becomes inflamed and 

 irritated. 



The other method by which plague is transmitted to man is by 

 direct inhalation of sputum spray, a mode of infection which causes 

 pneumonic plague. According to Castellani and Chalmers 12 and 

 others, about 2.5 per cent of the cases occurring during epidemics 

 of bubonic plague are of the pneumonic variety, and there may be 

 special epidemics of pneumonic plague like the one described in 

 another section and studied by Strong, Teague and others 13 in 

 Manchuria and a more recent one which occurred in Northern China. 



The incubation time of the disease is usually less than ten days, 

 and may be no longer than two or three. The organisms entering 

 through the skin may cause a localized lesion at the point of 

 entrance. This may be of negligible size or may show a considerable 

 inflammatory reaction. The organisms enter the lymphatics and 

 cause the so-called bubo. The primary bubos are situated in the 

 glands into which the infected area drains and, for this reason, 

 the most common seat for these lesions is in the glands of the groin, 

 but they also may be first seen in the axillary, cervical or other 

 glands. Secondary bubos may arise in other parts of the body, 

 along the distribution of lymphatics, and the organisms rapidly enter 

 the blood stream, causing septicemia. 



12 Castellani and Chalmers, Manual of Tropical Medicine, W. Wood & Co., 

 N. Y., 1919. 



13 Teague and Strong, Philippine Jour, of Science, Sec. B, No. 7, 1912. 



