462 THE PLAGUE BACILLUS 



[Plague may also possibly be transmitted from man to man through the agency of 

 bugs. Nuttall found plague bacilli in the intestinal canal of bugs and has shown that 

 they can convey the infection of plague from infected to healthy animals. Verjbitski 

 showed that the ordinary domestic bug, Cimex lectularius, will bite mice, rats, and 

 guinea-pigs, and that plague bacilli can be recovered from these insects for periods 

 varying from 1-8 days after they have been fed on septicsemic animals. Jordansky 

 and Kladnitsky find that the plague bacillus retains its virulence in the bodies of 

 bugs for 10 days and more.] 



Flies may also play a part in the dissemination of plague. They die in large 

 numbers during an epidemic of plague and the bacillus can be found in their bodies 

 (Yersin). [Jordansky and Kladnitsky are however of opinion that neither flies, 

 cockroaches nor ants play an important part in plague. 



[Ogata has suggested that mosquitoes may convey the infection from the diseased 

 to the healthy subject.] 



Infection by feeding. Man only very rarely becomes infected through the ali- 

 mentary canal (Wilm has recorded one case in which the most prominent symptoms 

 were intestinal and in which the bubo was found to be in the mesenteric glands). 

 [With regard to animals the Advisory Committee find that " in nature intestinal 

 infection rarely or never takes place and that in consequence rats do not become 

 infected by eating the carcases of their comrades " ; cf. experimental feeding 

 experiments (p. 464).] 



[" The position of knowledge on the question of the importance of alimentary 

 infection in the spread of plague may be summarized as follows : 



[1. Contamination of aliments may conceivably lead to the infection of human 

 beings on occasion, but the chance of bacilli reaching foodstuffs destined for con- 

 sumption uncooked, and in which they would multiply greatly, are slight. 



[2. The alimentary canal is not an easy method of infecting animals, large quan- 

 tities of virulent bacilli being usually necessary. 



[3. There is absolutely no epidemiological evidence pointing to alimentary infec- 

 tion being anything but uncommon, and in about 75 per cent of human cases, 

 the situation of buboes indicates skin infection " (C. J. Martin).] 



Infection by the respiratory passages is easily effected in animals, and is not 

 of rare occurrence in man : "it would appear to be the only channel of infection 

 in pneumonic cases " (Balzaroff). [" Pneumonic plague may arise by the inhalation 

 of bacilli into the lungs, where they rapidly multiply and early gain access to the 

 blood stream, or bacilli which have gained entrance through any other channel 

 and have become generalized may subsequently establish themselves in the lungs 

 and occasion a secondary pneumonia. Some degree of secondary pneumonia is not 

 uncommon in man and animals suffering from bubonic plague. A case of bubonic 

 plague may therefore become a potential source of a pneumonic outbreak. The 

 spread of the pneumonic form of the disease offers no difficulties, since it was shown 

 by Childe that the sputum of these cases contains innumerable bacilli, and by Martini 

 that plague pneumonia is readily produced in animals exposed to an atmosphere 

 containing droplets of an emulsion of plague culture. Pneumonic plague is obviously 

 spread by man-to-man infection " (C. J. Martin). 



[In the recent epidemic of pneumonic plague in Manchuria, rats were not attacked 

 by the disease, but the tarbagan (Arctomys bobax 1 ) was held to be responsible for 

 the presence of endemic plague in Mongolia and in the Russian provinces adjacent. 

 The connexion between the tarbagan and plague has not been satisfactorily worked 

 out, but all the evidence available seems to show that there might be truth in the 

 belief of the infective power of the marmot in this connexion. The origin, how- 

 ever, of the pneumonic plague in Manchuria has yet to be discovered (Petrie). 



[However probable it may seem on the evidence at present available it cannot 

 be said to be proved that contact alone is the only factor concerned in the spread 

 of pneumonic plague. Though " some degree of secondary pneumonia is not un- 

 common in man and animals suffering from plague " (Martin) yet the experience 

 in plague hospitals in India is opposed to the view that infection takes place by 

 direct contact with a patient suffering from plague and in the laboratory the Advisory 

 Committee found that " fleas and fleas alone were the transmitting agent in the 

 experimental production of plague epidemics among animals." Since then contact 



[ J The Bobac or Polish marmot.] 



