PLAGUE AND BACILLUS PESTIS 819 



infection, however, according to McCoy, form very few cases, not more 

 than about seventeen in all having been found since the squirrel origin 

 was first studied. The squirrel flea can carry plague from squirrel 

 to squirrel and from squirrel to other rodents. 



Such transmission does not hold good, however, for the pneumonic 

 form of the disease. Careful studies have been made on the pneumonic 

 form by Strong, Teague, Crowell and Barber 23 who observed the 

 Manchurian epidemic which occurred during the winter of 1910 to 

 1911, and during which, within three months, 50,000 people died 

 of the disease. According to these writers the infection here is not 

 as formerly supposed primarily a septicemic condition, during 

 which the lungs become secondarily involved, but occurs by direct 

 inhalation into the bronchi. The organisms either pass along the 

 bronchioles into the alveoli, or through the walls of the bronchioles 

 into the lungs, giving rise first to peribronchial inflammations and 

 later to more diffuse processes, followed by pneumonic changes of 

 the lobar or lobular type. After this, the blood becomes quickly 

 infected and bacteriemia is, therefore, secondary to pneumonia. 

 As mentioned above, the organisms are coughed out with the drop- 

 lets of sputum, and thus sprayed into the atmosphere. If the 

 atmosphere is dry, they will rapidly die out. If, however, the 

 weather is cold and the atmosphere charged with moisture the 

 organisms may remain alive for considerable periods and inhalation 

 of virulent organisms may take place easily. Acording to the same 

 writers, the organisms are not usually exhaled by the expired air 

 during ordinary respiration or even during the labored respirations 

 of the pneumonic case, but only during coughs when they may 

 be sprayed out in enormous numbers even when the naked eye 

 can detect no visible spray. In this form of plague, then, the 

 transmission is very largely direct. 



McCoy states that pneumonic plague rarely occurs from rat 

 infection, and states that it is an interesting and perhaps "significant 

 fact" that in plague squirrels there seems to be a definite tendency 

 to localize in the lungs, a thing which rarely happens in rats. From 

 a study of the plague cases in the United States, he states that 

 except for one single focus of thirteen cases, this form of the disease 

 has not occurred. This pneumonic outbreak originated from a 

 bubonic case of squirrel origin which developed secondary pneu- 



23 Strong, Teague, Crowell and Barber, Philippine Jour. Science, Sec. B, 7, 1912. 



