vii INFECTION OF ANIMALS WITH PLAGUE 155 



a flea taken from a plague rat may contain the B. pestis ; 

 it is far from justifying the proposition that such a con- 

 dition indicates one of the general modes of the trans- 

 mission of plague, and affords no warrant at all for 

 supposing that the flea represents a real intermediary host 

 in which the B. pestis multiplies and acquires virulence. 

 Nevertheless, Hankin attempts to explain in the latter 

 way certain epidemics of plague in man which have 

 appeared in particular localities some considerable time 

 after the introduction of a case of plague into them. 



So far we have left out of consideration one possible 

 channel of transmission of plague which must be, and has 

 always been, in the mind of every one acquainted with 

 plague as it occurs in nature. This is transmission of 

 infection by means of food, i.e. infection by way of the 

 alimentary canal. 



First of all, what are the epidemiological facts observed 

 hitherto ? It is an occurrence of no uncommon kind for 

 rats to die of plague in places where fodder and food-stuffs 

 are accessible to them, e.g. fodder, grain, rice, and flour 

 stores, larders on ships, etc., and in circumstances con- 

 sistent with such rats having contracted the disease by 

 eating food-stuffs previously specifically contaminated by 

 plague rats. For instance, a plague rat living in stores 

 would most probably be capable of polluting these food- 

 stuffs by its intestinal discharges, by its urine, possibly also 

 after death by dispersal of plague bacilli previously stored 

 in its tissues. 



In the second place, there is no theoretical reason why 

 both in the rat, as also in the human subject, the mucous 

 membrane of the digestive tract, including that of the 

 mouth and fauces, should not be as amenable (perhaps 



