X \- I T I . THE R li I. A T 1 O N BETWEEN F E R - 



T I L T T Y AND N O R M A L I T Y 



IN RATS. 



By R. E. IyLoyd, D.Sc, Offg. Professor of Biolooy^ Medical 

 College, Calcutta. 



During a recent visit to the west of India I had an oppor- 

 tunity of seeing the work which was being carried on by 

 the Plague Commission at Poona and Belgaum ; at both of these 

 places large numbers of rats were being caught dail}^ each rat 

 being the subject of careful observation. The results of these obser- 

 vations were recorded as a matter of routine, so that no detail, 

 which might have a bearing on the questions before the Commis- 

 sion, might be lost. While watching the progress of the work, and 

 admiring the thoroughness with which it was executed, I received 

 the idea that some of the statistics which were being accumulated 

 might be of great value to Biology. Among the facts recorded was 

 that of the number of young contained in each pregnant female. 

 It is well known that among mammals which produce a number of 

 young at a birth there is an individuality as regards that number. 

 It is the common experience among dog fanciers, that certain 

 bitches will always produce four or five pups at a time, while 

 others will always produce one or two. It very rarely happens 

 that a bitch will produce a large litter at one time and a small 

 one at another time. Therefore we may assume that the number 

 of young produced by a rat at any one time is a fair measure 

 of the fertility of that rat ; though imperfect it would be diffi- 

 cult to devise a better means of measuring this itnportant charac- 

 ter. From both Poona and Belgaum, I obtained the records 

 of the fertility- of one thousand rats as measured in this way. 

 It occurred to me that a definite relation had been established 

 between fertility and normalit}^ in the case of certain organ- 

 isms. Among such organisms it had been found that those which 

 were most normal or true to the type of their race were also 

 the most fertile. I am indebted for this information to a book 

 entitled " Variation in Animals and Plants " by H. M. Vernon. This 

 book quotes the observations of Professor Karl Pearson, who 

 counted the number of stigmatic bands on a large number of poppy 

 capsules and the number of the seeds which ripened in each capsule. 

 The number of the seeds was regarded as a measure of the fertility 

 of the poppies. It was found that those plants which were abnor- 

 mal as regards the number of their stigmatic bands always con- 

 tained a smaller number of seeds than those which were normal. 



