BLACK RAT AND BROWN RAT 29 



If one of them be set free in a room, it will be " all 

 over the place " at once, climbing up the curtains, 

 springing on bookshelves. A brown rat under the same 

 conditions keeps to the floor, seeking some dark hole 

 or retreat, for it is above all things a ground animal, 

 a burrower. 



There is certainly a difference in disposition, but 

 this does not agree with the popular idea. Mus rattus 

 is wild and shy and extremely difficult to tame. Mus 

 decumanus quite readily becomes tame. The white 

 rat is not an albino Mus rattus, as is usually stated, 

 but the characters of its ears, tail, teeth and skull 

 show that it belongs to the decumanus species, and 

 this relationship has recently been confirmed by one 

 of the most subtle tests of affinity, the form of the 

 blood crystals. 



Black rats and brown rats appear to have been 

 originally natives of Asia, but the brown rat is the 

 more northerly form, hardier and more adapted to 

 live in fields and drains and the open air of northern 

 Europe. Both species have extended their range 

 through the agency of man. The black rat came here 

 probably from Mediterranean ports, and finding 

 suitable conditions, spread over Great Britain and 

 Ireland, not only occupying ports and harbours and 

 granaries, but taking to the open country for 

 which it was less suitable. Records of it have been 

 found in literature back to the sixth century, but it 

 had not become notorious until the fourteenth cen- 

 tury. The brown rat was a later arrival, probably 

 beginning to come in numbers with the Baltic trade 

 in the seventeenth and eighteenth centuries. It has 

 rapidly spread over the country, and has become the 



