POSTNATAL GROWTH IN THE ALBINO RAT 3 



MATERIAL AND METHODS 



The following data are utilized in the present paper. For the 

 weight of the whole body of the albino rat (Mus norvegicus 

 albinus) at various ages a series of 570 original observations is 

 given in table 1. For the individual organs, 344 animals were 

 killed and dissected at various ages, and the weights of the organs 

 were observed (tables 3 to 15). 



Of data available for comparison, there should be mentioned 

 first the extensive series of observations by Donaldson on the 

 growth of the whole body ('06) and of the brain and spinal cord 

 ('08) of the albino rat. I am furthermore indebted to Professor 

 Donaldson and Dr. Hatai, of The Wistar Institute of Anatomy, 

 for unpublished observations upon the weight of the principal 

 viscera in about 200 albino rats. With the exception of the 

 central nervous system, however, these data are not included 

 with my own, but were utilized merely for comparison. 

 . The albino rats used by me (table 1) were reared from stock 

 obtained partly from M. Cattell, Garrison-on-Hudson, New York, 

 and partly from B. F. McCurdy, a dealer in Chicago. The litters 

 from each source were kept separate, but no constant difference 

 in growth and variability was noticeable between them. The 68 

 litters included in table 1 are for the most part not closely related 

 (although in a few cases observations upon the body weight of 

 the same litter are repeated at successive ages). 



The albino rats were kept in stationary cages in an animal 

 house and were well cared for. A supply of chopped corn was 

 kept constantly in the cages. A liberal amount of wheat bread 

 soaked in whole milk was supplied daily, and fresh meat (beef) 

 once a week. Water in abundance was provided. 



From the age of about six weeks onward, the cexes of each 

 litter were kept separate, and (with the exception of a part of 

 the females at one year) therefore represent unmated animals. 

 Watson ('05) has shown that weights of the body and of the 

 central nervous system are somewhat increased in the female 

 through bearing young. It is probable that other organs, also, 

 may be thereby more or less affected (especially the reproductive 



