vn INFECTION OF ANIMALS WITH PLAGUE 159 



recent gelatine and agar cultures, of broth cultures, of 

 milk cultures), as also with the various fresh plague 

 organs (lymph glands, spleen, liver, and lung 1 ), containing 

 abundance of B. pestis ; all of which experiments were 

 without positive results. Of these experiments it is 

 sufficient to mention the following : — 



Two rats and two mice were fed with milk cultures 

 (incubated five days at 37° C), which when tested by sub- 

 culture were crowded with living B. pestis. For feeding 

 purposes the milk culture was mixed with bread. After 

 the lapse of a week the same four animals and one 

 additional rat were fed with similar milk culture and 

 bread. All the animals, however, remained unaffected. 

 A fortnight later they were cutaneously inoculated with a 

 trace of a similar milk culture, and promptly succumbed 

 with plague between the third and fourth days. 



In the same way two guinea-pigs and two rats were 

 fed with the organs (minced and mixed with green food 

 and bread) of one of the above rats. No result followed. 

 After ten days these animals were inoculated (the guinea- 

 pigs subcutaneously, the rats cutaneously) with agar 

 culture derived from the spleen of one of the rats of the 

 above experiment. They all died of plague. 



In all experiments referred to here the rats used were, 

 unless otherwise stated, tame or white rats. As I have 

 explained in my reports to the M.O. of the L.G.B. for 

 1902-1903 and 1903-1904, tame white rats are highly 

 susceptible to plague infection in all the various ways. 

 Not so sewer rats. These rodents, although susceptible to 

 plague infection, are so to a lesser degree than tame rats, 



1 These were derived from guinea-pigs and rats that had died with acute viru- 

 lent plague. Such organs inoculated in minute doses into rodents produced acute 

 and typical plague. 



