Associated with an Unusual Mortality of Adult Females. 337 



the city had almost completely escaped plague, though in the more remote 

 past its epidemics had been extremely severe. Our very high catches 

 indicated a very large rat population and a complete recovery from the 

 onslaughts of plague. In Cawnpore of 51,181 M. rattus examined in one 

 year 25,838 were females, i.e., 98 males for every 100 females (see Table II). 



(4) Banda Town has never suffered from epidemic plague. M. rattus was 

 present in very large numbers. In Banda of 10,127 rats caught during 

 11 months 5174 were females, i.e., 96 males for every 100 females (see 

 Table III). 



In Lucknow, in which city the very abnormal conditions, fully described 

 below, were present, of 34,908 M. rattus caught during the course of one 

 year 18,396 were females, i.e., 89 males for every 100 females (see Table I). 



Disturbance in the Sex Ratio of M. rattus in Lucknow and its Readjustment. 



A reference to Table I will indicate the nature of the phenomenon in 

 Lucknow to which reference has been made. The table sets forth the 

 weight frequency distribution of male and female M. rattus respectively 

 for each of the 12 months from February, 1911, to January, 1912. There 

 appears to have been some influence at work destroying adult females and 

 sparing the males. This " influence " began its manifestations in March 

 and produced its maximum effect in May and June. 



As if to compensate for the apparently wholesale destruction of adult 

 females, females only appear to have been born. These two processes, the 

 destruction of females and the suppression of male births, proceeded 

 pari passu. In June not a single male rat below the weight of 80 grm. 

 was trapped, whereas 610 females of less weight than 80 grm. were caught. 

 As the numbers of adults of the two sexes began to approximate more closely 

 the one to the other, young male rats were again trapped in increasing 

 numbers. In November, December, and January, the sex ratio approximated 

 to that normally pertaining. 



Such, in brief, are the facts ; satisfactory explanations of the phenomenon 

 are difficult to come by. It may possibly be advanced that in the above brief 

 recapitulation of observed facts I have assumed more than the facts warrant. 

 The objection that is most likely to be raised is to the assumption that failure 

 to catch adult females signifies destruction of females. The shyness of the 

 female might account for the phenomenon. This point has been referred to, and 

 it was partly to meet this objection that I studied similar facts concerning 

 95,629 rats caught in various places. A reference to the tables of Cawnpore, 

 Banda, Coimbatore, and Ballia rats will show that in no place other than 

 Lucknow was such a circumstance observed. Female rats are not shyer or 



