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taneous tissue. It may appear as one or more firm papules 3 or 4 

 millimeters in diameter. The most frequent appearance is a brawny 

 oedematous and blood-stained reaction which extends over an area 

 perhaps an inch in diameter; at times purulent change may be well 

 advanced. Very rarely one finds so extensive an oedema as to cause 

 the lesion to somewhat resemble the widespread gelatinous reaction 

 seen so commonly in the guinea pig. On one or two occasions we 

 have seen an extensive slough at the site of inoculation. 



BUBO. 



It is very exceptional that one finds in cases of induced plague the 

 typical, firm, caseous bubo surrounded by an infiltrated area, as is 

 so commonly seen in natural infection in rats. The glands are some- 

 times enlarged and injected without other changes. The commonest 

 lesion, however, is a markedly enlarged gland which upon close inspec- 

 tion is seen to have a number of yellowish points just under the cap- 

 sule. These points are especially well seen when a section is made 

 through the gland. The gland may be squeezed out of the capsule 

 and it breaks down readily enough when pressure is made upon it; 

 but the uniform necrotic process that one sees so often in natural rat 

 plague is absent. 



LIVER. 



Granular lesions precisely like those found in natural infections 

 are very common. If the rat has died on the sixth day or later, the 

 ordinary lesions are apt to be replaced by necrotic foci that may be 

 as much as 2 millimeters in diameter. 



SPLEEN. 



This organ is found mottled more frequently than in natural plague 

 infection, and large granules are much more common. 



The subcutaneous injection is rarely so well marked as it is in 

 natural infections. 



Pleural effusion of the same nature as that found in natural plague 

 is common. Hemorrhagic foci are not rare in the lungs, and occa- 

 sionally the organs are partty consolidated. 



CHRONIC PLAGUE DUE TO ARTIFICIAL INOCULATION. 



Occasionally a rat that has been inoculated but has survived a 

 week or longer, will show, when killed, only an abcess at the site of 

 the injection. Stained smear preparations may show a large variety 

 of bacterial forms. We have not been able to demonstrate the 

 presence of B. pestis in these lesions, yet there is no doubt but that 

 the lesion is the result of the inoculation. 



A lesion more frequently found is a caseous or a purulent lymphatic 

 gland. If the inoculated rat has been killed about ten days after 

 the inoculation, in some cases one or more of the peripheral lymph 



