INFECTION AND METHOD OF DEVELOPMENT. 175 



deposited largely upon the mucous membranes of the mouth and 

 throat. 



The experiments performed on monkeys seem to throw much 

 more light upon the mode of pneumonic-plague infection in man. 

 The lesions in 55 monkeys infected by spraying were studied at 

 necropsy. There was a marked similarity in general in the 

 pathological changes encountered. In practically all of the 

 animals there was absence of any sign of plague infection about 

 the cervical tissues. The submaxillary and cervical lymphatic 

 glands and those about the trachea were not swollen, nor was 

 there any oedema of the cervical tissues, as was practically always 

 seen in the experiments with guinea pigs. In none of the cases 

 examined did the tonsils show evidence of primary disease, though 

 in a number of instances they were sectioned and stained. In 

 some instances they were moderately congested. Plague bacilli 

 were scanty in them and when present were not more numerous 

 than in the heart's blood and never so numerous as they were 

 in the lungs or spleen. 



There was frequently oedematous fluid in the trachea, and in a 

 few cases the trachea was slightly reddened. The larynx and 

 vocal cords were not as a rule injected. There was not such 

 marked evidence of septicaemia as seen in the experiments with 

 guinea pigs, but plague bacilli could always be recovered from the 

 heart's blood by culture. 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 pneumonic changes in every case. 

 There was always much oedema. In those animals which suc- 

 cumbed a shorter time after infection, the lobular type of pneu- 

 monia was much more frequently encountered. In those which 

 survived a longer period, whole lobes of the lung usually showed 

 pneumonia. The progress of the lesions is well shown in Plate 

 VII, figs. 2 and 3. The process evidently begins as a lobular 

 bronchial pneumonia. By the fusion of a number of the areas 

 of lobular pneumonia, the whole lung may become involved. 

 The large pneumonic areas were either in the stage of engorge- 

 ment or of red or early gray hepatization. In a number of 

 cases a pleuritic exudate was observed over the hepatized areas. 

 In no case were miliary abscesses observed in the lungs. In 

 the cases with the early lesions, the plague bacilli were always 

 most numerous in the lungs, and in section were found in greatest 

 profusion about the bronchioles, in the peribronchial lymph spaces 

 and alveoli, and beneath the pleura. In some instances the cells 



