242 STRONG AND TEAGUE. 



not swollen, nor was there any CBdema of the cervical tissues, 

 as was practically always seen in the control guinea pigs. In 

 a number of cases, the tonsils were examined and found to be 

 normal. There was frequently (edematous fluid in the trachea. 

 The larynx and vocal cords were, as a rule, not injected. In a 

 few cases the trachea was slightly reddened. There were not 

 such marked evidences of a septicaemia as seen in the control 

 guinea pigs. No haemorrhages were noted in the intestines and 

 omentum. The spleen and liver showed no miliary abscesses. 



There were no cervical, axillary, nor inguinal buboes. The 

 lungs showed primary pneumonia in every case. There was 

 always much oedema of the lung. The pneumonia was either 

 in the stage of engorgement or of red or early gray hepatiza- 

 tion. In a number of the cases, a pleuritic exudate was ob- 

 served over the hepatized areas. The plague bacilli were always 

 most numerous in the lungs. 



From these observations, it is obvious that the infection in 

 monkeys occurred by inhalation and resulted in primary plague 

 pneumonia. It also is evident that in some instances, in which 

 monkeys are exposed to infection by inhalation, the primary 

 point of infection may not only be the lungs but also the mucous 

 membranes of the mouth and throat. That plague infection 

 may occur through the mucous membranes of the mouth and 

 throat in monkeys was demonstrated by placing a small quan- 

 tity of plague bacilli, by means of a glass rod, on the posterior 

 portion of the throat.' 



These animals all died of plague septicaemia, with or with- 

 out infection of the glands of the neck. That is, in the cases 

 in which the infection was severe and the susceptibility of the 

 animals more marked, the animals succumbed to septicaemia 

 before cervical buboes developed. In none of these instances 

 was pneumonia present. Primary plague pneumonia only results 

 when infection by inhalation has in addition taken place. 



Therefore, experiments performed with monkeys in the vac- 

 cination and subsequent infection of the animals by inhalation 

 give us much more valuable information in regard to the pro- 

 tection afforded by vaccination against pneumonic plague than 

 do those performed with the guinea pigs. In the instances 

 where the infection was severe and all of the control unvac- 

 cinated monkeys succumbed to pneumonic-plague infection, only 

 9 per cent of the vaccinated monkeys survived. 



' See IV, p. 176 of this report. 



