vii INFECTION OF ANIMALS WITH PLAGUE 153 



which pass on into the subacute or even chronic stage ; 

 rats, that is, which, though affected with plague, do not 

 succumb within five or six days. I have pointed out that 

 under these conditions the lungs are profoundly and 

 intensively affected; that they show extensive consoli- 

 dation, the bronchi being filled with inflammatory products 

 containing crowds of plague bacilli ; * and I have described 

 experiments showing that the oral, pharyngeal, and laryn- 

 geal purulent exudation of a rat so affected produces on 

 cutaneous inoculation typical acute plague. 2 From this 

 it was inferred by me that a rat of this kind would by its 

 bite of another rat be capable of communicating plague 

 (by cutaneous inoculation) to such other rat. A chronically 

 affected rat would, I noted, have many chances of doing 

 this, seeing that such rat is generally drowsy and sulky, 

 and that when disturbed by other animals it generally 

 bites them, a method of positive inoculation actually 

 observed under experimental conditions. 



[It may be added that the German Plague Commission 

 have produced plague in rats by simply placing plague 

 material into their conjunctival sacs ; and further, it has 

 been observed that rubbing in plague material (taken 

 from a plague animal or from culture) into the skin of the 

 nostrils or mucous membrane of the nasal cavity of 

 guinea-pigs was sufficient, in a majority of instances, to 

 produce plague.] 



Ways and opportunities of experimentally infecting 

 rats with plague with materials derived from plague rats 

 are in fact so many and various that it is probable that 



1 See Plate II. in Report of the Medical Officer of the Local Government Board 

 for 1902-1903. 



2 Loc. tit., see Fig. 9, Plate III. p. 690, Report of the Medical Officer for 1902- 

 1903. 



