BACILLUS PESTIS 413 



are very great. Death usually intervenes in less than a week. The 

 marked cardiac depression which is a feature of this type of plague 

 is of some differential diagnostic value. One or more lobes are infected, 

 the inflammation being catarrhal in nature. Enormous numbers of 

 plague bacilli are coughed up with the sanguinoserous exudate, which 

 are readily transmitted to doctors, nurses and attendants by droplet 

 infection. Very frequently a generalized invasion of the blood stream 

 occurs. 



Bubonic plague, the most common type of the disease in man, is 

 essentially a localization of plague bacilli which have gained entrance 

 to the tissues through the skin in the regional lymph glands. The 

 inguinal glands are more commonly invaded; next in order of fre- 

 quency are the axillary, then the cervical glands. The glands 

 are violently inflamed, and not infrequently soften and caseate. A 

 generalized blood infection septicemic plague may occur either 

 secondarily following the development of a bubo or of pneumonic 

 plague, or, less commonly, as an initial generalized invasion following 

 very shortly after infection and before the bubo becomes conspicuous. 

 In such cases the organisms may be obtained in pure culture from the 

 blood stream, and in about 20 per cent, of cases may be actually 

 demonstrated in stained preparations of the blood by microscopical 

 examination. 



Immunity and Immunization. Recovery from one attack of plague 

 in man almost always confers lasting immunity. Immunity has been 

 induced in animals monkeys, rats and guinea-pigs by inoculation 

 with living avirulent cultures. Usually a moderate reaction is noticed, 

 and a bubo may even form, but the animal recovers, and even after 

 months successfully resists several times the fatal dose of virulent 

 organisms. This method is far too dangerous for human practice. 

 Bacillus pseudotuberculosis rodentium, an organism that occasionally 

 is found in diseased rats producing lesions superficially not unlike 

 plague, will immunize rats against Bacillus pestis and vice versa. This 

 bacillus must be sharply differentiated from the plague bacillus in 

 the microscopic diagnosis of plague in rodents. It fails to infect guinea- 

 pigs by the cutaneous method, however, and is less virulent for labora- 

 tory animals. Cultures of plague bacilli heated to 50 C., or killed 

 with chemicals, as phenol or alcohol, have also been employed success- 

 fully, but the degree of resistance to subsequent infection is less. 1 

 Specific bacteriolysins and agglutinins develop during the immunizing 

 process. 



1 Kolle and Otto, Ztschr. f. Hyg., 1903, xlv, 507. 



