174 STRONG AND TEAGUE. 



fection with miliary abscesses. Distinct evidences of pneumonia 

 were present in only about 23 per cent of the guinea pigs. 

 Plague bacilli were frequently not very abundant in the lungs, 

 unless pneumonic areas were encountered, but were always 

 present in the heart's blood. The lungs were sometimes red- 

 dened, congested, and oedematous, and sometimes contained 

 hsemorrhagic infarcts. Small areas of primary bronchial 

 pneumonia were encountered in some of the cases, and in one a 

 whole lobe of the lung showed pneumonic engorgement. In two 

 instances either red or early gray hepatization was present. 

 Numerous miliary abscesses were occasionally encountered in 

 the lungs. (See Plate VII.) The areas of bronchial pneumonia 

 were firm, contained no air, and were usually irregular in outline 

 and red, reddish yellow, or yellow in color. On cut section they 

 were sometimes wedge-shaped. In those instances in which 

 hsemorrhagic infarcts, .miliary abscesses, and in addition reddish- 

 yellow or yellow areas of lobular pneumonia are present (see 

 Plate VII), we must conclude that the infection of the lung is 

 secondary, and that in these instances we are not dealing with 

 primary pneumonic plague, in which infection enters through 

 the bronchi, but with secondary infection of hsemotogenous 

 origin. Such a conclusion is supported by the microscopical 

 study of these lesions. A section of the lung in the vicinity of 

 one of the hepatized areas, pictured in Plate VII, shows the 

 bacteria in very large numbers both about and within the small 

 blood vessels, and in places infarctions have occurred ; numerous 

 haemorrhages from the vessels have also taken place; in the 

 neighborhood of the pneumonic areas the bacteria are also plenti- 

 ful in the lung alveoli and in the perivascular spaces. 



Therefore, these changes suggest that the primary point of 

 infection did not always occur in the bronchi or alveoli of the 

 lung. From a study of all the lesions in guinea pigs, it would 

 appear that these animals, under the conditions of the experi- 

 ments in which the spraying was carried on, did not frequently 

 develop primary plague pneumonia, but that infection occurred 

 through the mucous membranes of the mouth and throat, result- 

 ing in a general septicaemia generally preceded by the formation 

 of early buboes of the cervical glands and sometimes followed 

 by the development of secondary areas of plague pneumonia. 

 It would appear that in guinea pigs, either on account of too 

 shallow respiration or the small size of the larynx and trachea, 

 the bacteria are not so likely to penetrate to the smaller bronchi 

 by means of the inspired air. Instead, they are apparently 



