AN ACCOUNT OF THE RATS OF CALCUTTA, WITH SOME 



REMARKS ON THE EXISTING CLASSIFICATION OF 



THE GENERA MUS AND NESOKIÄ. 



By Wm. C. Hossack, M.D., Plague Department, Calcutta. 



INTRODUCTORY. 



The present inquiry as to the rats occurring in Calcutta, their relative numbers 

 and habits, started originally in a very humble way, as the result of a suggestion made 

 by Colonel lycslie, Sanitary Commissioner to the Government of India. In a discus- 

 sion as to the part played by the fleas of rats in the dissemination of plague, he sug- 

 gested that the comparative mildness of the recent epidemics in Calcutta as compared 

 with Bombay, Poona and the towns and cities of Upper India, was due to the fact that 

 in these latter Mus rattus, the long-tailed Black Rat, was the predominant one, whereas 

 in Calcutta the predominant rat was Mus decumanus, the Brown or '' Norwegian " 

 Rat, a species which from its habits is brought into much less intimate contact with 

 man. The distinctions given as sufficient to separate the two varieties were as 

 follows : — 



Mus decumanus, a large, heavy-bodied rat with a blunt round head, tail shorter 

 than the head and body, and the ears small and round, so that when laid forward on 

 the head they fail to reach the eyes ; Mus rattus, a slender long-tailed rat with tail 

 longer than the head and body, long ears, so that when laid forward they cover the 

 eyes. At the time this suggestion was made conditions were extremely favourable for 

 collecting evidence on any point connected with rats, as rewards were being paid for 

 living rats, and large numbers, up to about two hundred a day, were being brought 

 into all the District Offices including District II, which is under my charge. A 

 few attempts at differential counts soon made it clear that the distinctions given 

 were quite insufficient, that tails were met with showing every gradation from 70 to 

 150 per cent, of the length of the head and body, and that the difference in the rela- 

 tion of ear to eye, though correct in a general way, was very unreliable. So I had 

 recourse to the authorities at the Indian Museum in the hope that a thorough 

 examination of a few type-specimens would enable me to settle the question in point ; 

 but my hopes were rudely dashed to the ground when I learned that the subject 

 of Indian rats was in a state of great confusion, that there were only two or three men 

 in the world who could tell with certainty the genus and variety of any given rat, and 

 these, only if they had before them skin, skull and spirit specimens, and then, only if 

 they had at hand existing types with which to compare their specimens. 



