THE COMMON OR BLACK RAT. 255 



above half of them were attacked by this disease. 

 He informs us that it is much more frequent in 

 males than females ; and that almost all Rats, when 

 they become old, have stones in their urinary 

 passages, and swellings and ulcers in the kidneys. 

 In one Rat, M. Morand found twelve stones, of 

 which nine had become of the size of a coriander 

 seed, and three were smaller. From others he 

 took out stones of the size of a grain of wheat. 

 The composition of these stones was very different 

 from that of stones found in other animals. Instead 

 of having, like those, a somewhat spherical nu- 

 cleus, serving as a basis to concretions which are 

 formed round it in an infinite number of ex- 

 tremely thin layers, the present had the same com- 

 position throughout. Their shape also was dif- 

 ferent, some of them being oval, and others 

 cubical : and the cubical ones, it was remarked, had 

 always a shining surface*. 



Like the former species, the Black Rats breed 

 frequently in the year ; and they commonly pro- 

 duce six or seven young ones at a litter. For these 

 the females form a comfortable nest, of wool, bits 

 of cloth, hay, or straw, in some dry and warm 

 place, about barns or other outhouses. It is said 

 that they do not suckle them long ; but that, as soon 



* Letter of M. Morand, Medecin de la Faculte" de Paris, inserted 

 in Melanges d'Histoire Naturelle, i. p. 138. 



as 



