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cuss a few of the habits of rats that had an important bearing on the spread 

 of plague. He considered, first, the species of domestic rats. There were two 

 very distinct species : Mus decumanus, the common rat found in Europe ; it 

 was a burrowing rodent and lived in drains and cellars. Mus rattus was the 

 common rat of Bombay and the Bast generally ; it lived in the roofs of houses 

 and even trees ; it was a truly domestic rat. Plague might rage as an epizootic 

 among rats of the species of Mus decumanus and man would have little 

 chance of infection, but an epizootic of this disease among rat of the species 

 Mus rattus was very liable to be communicated to man. The species 

 of rat affected with plague had an important bearing on the spread of 

 the disease in man, not from any inherent difference in the susceptibility 

 to the disease in the particular species, but because of the habits of 

 the species. The disappearance of plague from Europe was coincident 

 with the invasion of that Continent by the brown rat and the displacement of 

 the black rat by that species. While the habits of the black rat played an 

 important part in the spread of plague, the habits of men encouraged or dis- 

 couraged the prevalence of this species of rat. In Europe the brown rat dis- 

 placed the black rat as pucca buildings became erected, as drainage systems 

 were developed, as stables were separated from dwelling-houses, as shops, 

 warehouses and granaries were no longer used as human habitation. As stone 

 and wooden floors displaced mud and rush-covered ground, as beds became 

 used in place of heaps of straw, so the black rat was driven from his haunts 

 and the brown rat had it all his own way. man and rats were separated from 

 one another and plague ceased to trouble, for man played an important part 

 in spreading the diseases among rats. Rats like men were gregarious in their 

 habits, they had their maharwaras and buniapuras, some rats lived on the 

 refuse of the people and others installed themselves in the granaries of the rich. 

 There was little communication between these communities in the same 

 village or town, and there could be still less communication between the rats 

 of one town and those of another except through human agency. Ships, rail- 

 ways, and roads, the means of conveyance of merchandise, were also the means 

 of communication between rats of one town and those of another ; the rats as 

 " stowaways" were conveyed with human merchandise. As this was a chance 

 means of communication, the larger the means of transport the chances were 

 greater : hence ships transferred rats in this way more frequently than 

 railway trains. Seaport towns, therefore, were specially liable to be infected 

 by this method, viz., from rat to rat through merchandise conveyed by man. 

 Another habit of rats that had an important bearing on the spread of plague 

 was their habit of migrating as a community when scared by an unusual mortal- 

 ity among them In this habit they resembled man. Plague could under 

 these circumstances be spread from one rat community to another rat com- 

 munity in the same town where fresh focus of infection might be set up. 

 This habit also increised the chances of infected rats being conveyed by 

 merchandise. Again, the breeding season of rats played an important part 



