EFFECTS OF INBREEDING ON BODY WEIGHT 9 



individuals, of which the majority were the progeny of brother 

 and sister matings, the others were the offspring of inbred fe- 

 males and stock males. The number of animals for which 

 weight records were taken is, it is hoped, large enough to be 

 fairly representative of the inbred colony as a whole and to give 

 results that have some statistical value. 



No animals belonging to the first six inbred generations were 

 weighed at regular intervals, but fortunately a series of weight 

 records is available that will give some idea of the size of these 

 rats after they became adult. In order to ascertain the effects 

 of close inbreeding on the weight of the central nervous system, 

 one of my colleagues, Dr. S. Hatai, made careful autopsies of 

 the four rats used in starting the experiment and he also exam- 

 ined a large number of their descendants. From the record 

 cards for these animals I was able to obtain the body weights 

 of a considerable number of rats belonging to the first six gen- 

 erations of the two inbred series. The body weight data for 

 only the best of the animals reared during this period were 

 used in the present case; records for all individuals that were 

 noted as having deformed teeth or other malformations were 

 excluded, as well as the records for those animals that were ob- 

 viously runts. 



Table 1 shows the body weight records for 92 males and for 

 73 females belonging in the first six generations of the A series 

 of inbreds: table 2 gives similar data for 85 males and for 64 

 females of the B series. Only one record for each individual was 

 obtained, i.e., the body weight at the time that the animal was 

 killed. 



. The 'mean age in days,' as given in the first column of table 1 

 and of table 2, shows the median points in thirty periods that 

 correspond to the ages at which the rats of the later inbred 

 generations were weighed. For example, under the mean age 

 '151 days' are grouped the body weights of all of the animals 

 that were killed when they were from 136 to 165 days of age. 

 As no records were taken of animals that were less than 105 

 daj^s old the first age group given is that for 120 days. 



