THE RAT THEORY OF PLAGUE EPIDEMICS 7 



take no cognisance of the advances made by bacteriological research. 

 As may be gathered from the most recent works on such a subject, the 

 ways and means afforded to the B. pestis to produce infection, the course 

 of plague infection, and the exact problems underlying the spread of the 

 pest, must undergo remodelling upon the lines indicated by the results of 

 modern epidemiology. 



At the present time the general trend of opinion is against the 

 hitherto advanced causes of epidemic plague, namely, direct and indirect 

 mode of communication of the disease, and place infection. My own 

 experience of plague epidemics leads me to conclude that, apart from 

 cases of primary pneumonic plague, the dangers of one person infecting 

 another are over-estimated, and that place infection, apart from the 

 presence of plague-infected rats, is of no great significance. 



We know that rats are highly susceptible to plague, and they readily 

 communicate the infection to other rats. Rats, when suffering from 

 plague, are peculiar in their habits. They leave their holes. They are 

 apparently deprived of any sense of fear or danger when near human 

 beings. They progress with a drunken-like gait. Convulsive movements 

 cause them to make erratic springs into the air during ordinary 

 progression. They die suddenly, usually from convulsions. The natives 

 of Bombay are so frightened by the peculiar appearance of these animals, 

 and the finding of dead rats in their houses, that they flit at once. 

 According to Zupitza, the natives of Kisiba, in Ceatral Africa, have the 

 same dread of rats either suffering from this condition or dead in their 

 dwellings. 



These remarks bring me up to the general consideration of my own 

 results. Much evidence has been advanced in favour of the rat theory, 

 and that, when added to the conclusions drawn from my own researches, 

 ought to bring the epizootic and the epidemic into close relationship to 

 each other. 



Previous to my arrival in Hong-Kong, no attempt had been made to 

 thoroughly investigate the course of epizootic plague in rats. From 

 time to time a few rats had been examined for the presence of plague 

 infection, but these examinations, amounting to a few hundreds only, 

 cannot be regarded as of much value, beyond establishing the fact that 

 such a disease as " Rat Plague " existed in the Colony. 



(221) 



