THE SMALL-MAMMAL PROBLEM 743 



progress, finding congenial surroundings in the cellars and 

 drains of the towns, and along the banks of the rivers and 

 canals. As described above (p. 583), the coming of R. nor- 

 vegicus to Britain led to the almost complete extinction of 

 R. rattus as an inland inhabitant of this country during the 

 eighteenth and nineteenth centuries. Quite recently, however, 

 R. rattus has been recovering its lost ground — a fact of import- 

 ance in connection with the argument now being presented. 



When R. norvegicus arrived in Britain, in the early part 

 of the eighteenth century, it found R. rattus in complete 

 possession. At that date rat-proofing was not attempted, and 

 the rat population in the towns was kept in control by the 

 ratcatcher. So far as human intervention was concerned, both 

 species were upon terms of equality. In these conditions, 

 favoured by its own constitution and character, R. norvegicus 

 triumphed and R. rattus was defeated. In the later part of 

 the Victorian period it was difficult to procure any example 

 of the latter species away from the vicinity of the docks. 

 Towards the end of the nineteenth century, and in later years 

 down to 1 91 5, great changes took place in many of our cities. 

 Many of the older houses were demolished, and upon their 

 sites were erected buildings of stone, characterised by a lavish 

 use of cement in ^their foundations, as well as by the possession 

 of perfect sanitary appliances and well-guarded drains. These 

 buildings, particularly the most modern examples, are for the 

 most part proof against rats seeking entrance through base- 

 ments, and therefore they remain free from infestation by 

 R. norvegicus. But R. rattus is primitively an arboreal species ; 

 and telephone wires and cables now extend from building to 

 building, bridging the streets. The chief waterside colonies 

 of R. rattus to be found in our ports are situated for the 

 most part in lofty, solidly-built warehouses. These rats 

 issue from the upper floors of the dockside premises, and 

 pass along the telephone wires to the roofs of other buildings. 

 Roof kitchens are among the improvements of the modern 

 structures, and R. rattus soon invades them, effecting an 

 entrance from the roof through skylight, window, or ventilator. 

 In this way new colonies are formed at increasing distances 

 from the docks, and in many towns, as in London, the species 



