Variations in the Sex Ratio of Mus rattus. 335 



of function to take place after nerve anastomosis is not due to a simple 

 re-education process, as there is no evidence of this during recovery, but is 

 probably due to an alteration in the centres under the influence of altered 

 afferent impulses from the muscles, the brain thus having the capacity 

 quickly to adapt itself to such alteration. 



Variations in the Sex Ratio of Mus rattus Associated ivith an 

 Unusual Mortality of Adult Females. 

 By F. Norman White, M.D. (Lond.), Capt. I.M.S. 



(Communicated by Prof. C. J. Martin, F.R.S. Eeceived November 28, 1913, — 

 Read January 22, 1914.) 



At the commencement of June, 1911, whilst engaged on plague epidemio- 

 logical observations in the United Provinces my attention was drawn to the 

 fact that nearly all the young Mus rattus that were being trapped and 

 examined by our staff in Lucknow were females. It was this strange 

 phenomenon, the parallel of which I had never encountered during a five 

 years' experience of plague research in India, that prompted the inquiry, 

 the results of which are briefly set forth in this paper. 



A few words explanatory of the methods employed in the daily routine 

 examination of rats will show the nature of the material at my disposal. The 

 prime object in trapping and examining large numbers of rats was, of course, 

 to ascertain how far facts thus collected would assist us in solving the plague 

 epidemiological problems with which we were faced. The species, sex, and 

 weight in grammes of each rat caught were noted ; the address of the house in 

 which the rat was trapped and the number and species of fleas found on it 

 were recorded. The sex of each rat was noted after dissection of the animal, 

 and if it were female a further note was made as to the existence of 

 pregnancy. If pregnant the number of foetuses was likewise written down. 

 Finally, any pathological or other condition calling for comment was fully 

 described. 



All this information, which was in the first place recorded on cards, 

 one card for each rat, was at the end of the day's work entered in a 

 register. Weighing the rat was done in a specially constructed spring 

 balance, by means of which the weight in grammes to the nearest multiple 

 of 10 could be readily and accurately ascertained. I wish to emphasise 

 the fact that the sex of the animal was noted only after dissection, so that 



