110 ORIENTAL PLAGUE chap. 



necrosis, the affected portions being literally crammed 

 with B. pestis (see Fig. 7). Now, returning to the 

 rat, I think these experiments suggest that also under 

 natural conditions there may occur in rats cases of 

 pneumonic plague, due to a lesser susceptibility of 

 the individual rat ; cases, that is, which run a much 

 longer course, and in which the chief organs affected are 

 the lungs. Such animals would obviously be more 

 dangerous in an epidemiological sense, and for two 

 reasons : (1) they harbour plague for many days without 

 showing distinct signs of illness, and (2) their bronchial 

 secretion, pharyngeal and laryngeal mucus (see a former 

 page), being crowded with B. pestis, would represent 

 highly infective contagium, which by the breath, by the 

 saliva, or by a bite might, and probably would, be readily 

 aud widely spread amongst the surroundings. Moreover, 

 these observations would also suggest that the disease 

 may linger on for considerable periods amongst rats on 

 board ship or on land if one or the other of them, being 

 less susceptible, is afflicted with this pneumonic type of 

 plague. And it would further suggest that also as 

 regards pneumonic plague in man a "first" case of this 

 kind might in reality be a case in a person who was 

 naturally not endowed with the normal susceptibility, and 

 on account of such subnormal susceptibility became after 

 infection (cutaneously or by mucous membrane) affected 

 with the pneumonic type. Such a person, as is well 

 known, on account of the abundance of B. pestis in the 

 excretion from the lung, is highly infective for and readily 

 communicates plague to others, in whom, owing to the 

 easy access of the B. pestis to the air-passages (by the 

 breath), it is capable of causing pneumonic plague. 



