258 JOURNAL, BOMBAY NATURAL HISTORY SOCIETY, Vol. XVI, 



communication between the rats of one town with those of another ; 

 stray individuals are carried along with merchandise ; stowaways, as they 

 might be called, are taken from one town to another. This is only a 

 chance means of communication between rats of one place and those of 

 another ; and the chances are, of course, greater where the means of 

 conveyance is larger. Ships transport rats, therefore, in this way much 

 more frequently than railway trains, and railway trains more frequently 

 than carts. 



Another habit of rats must here be considered, a habit too in which 

 they resemble uneducated men. On the occurrence of any unusual 

 mortality, from any cause, among a community of rats, they quit the 

 place where the mortality has occurred ; — they migrate as a community. 

 In this way infection is often communicated from one community of rats 

 in a village or town to another in the same village or town. Here a 

 fresh focus of infection may in consequence be set up. Occasionally 

 some individuals of such a migrating community may seek refuge in a 

 ship or railway train or cart, and may carry this infection through 

 human agency to another town. This is one important way in which 

 plague may be spread from one place to another by human agency. Sea- 

 port towns, as will be understood from what has been said above, are 

 most frequently infected in this way. I would instance Sydney, Port 

 Elizabeth, Durban, Lisbon, Glasgow, etc. 



But there is another means of communicating the disease by means 

 of human agency from rats of one town to those of another town, which 

 will be discussed later when the part played by fleas in the spread of the 

 disease is considered. I mention this fact here because it becomes 

 possible only in connection with the migrating tendency of rats. I need 

 hardly discuss at length this migrating instinct (shall I call it 7) 

 which impels rats to shun places which are associated with their death or 

 destruction. Who has not set a trap for rats and found, that after two 

 or three have been taken, the rats will not look near the trap again ? 

 Who has not noticed, that if a good dog or cat is introduced upon rat- 

 infected premises, after a few of the animals have been destroyed the 

 others disappear ? Who has not noticed, that poison placed for rats will 

 cause the disappearance of far larger numbers of them than are actually 

 destroyed by the poison? This habit of migration, due to fear of destruc- 

 tion, is a very important habit of rats in the spread of plague. I should 

 like, however, to emphasize the fact that the extent of the migration is 



