CHAPTER 5 



GROWTH IN TOTAL BODY WEIGHT ACCORDING 



TO AGE 



1. Introduction. 2. Growth before birth. 3. Growth between birth and 

 maturity, 4. Weight-length ratio. 5. Modifications of growth in total body- 

 weight and organs. 6. Senescence. 



1. Introduction. Under the general caption of growth several 

 series of data are grouped in this chapter and in the four chapters 

 which follow it. The chapter heads explain the several group- 

 ings and show that some data are presented according to age 

 and other data according to some bodily measurement. 



The reasons for this procedure will be evident in each instance. 

 The effort has been made to gather as much of the data as pos- 

 sible under the caption of gi'owth as this seemed the best way 

 to make the records available for reference. 



The following tables present the size, weight and composition 

 of the albino rat and some of its parts, under conditions which 

 may be considered normal. 



As regards absolute measurements, it must be borne in mind 

 that the Albino is very responsive to external conditions as rep- 

 resented by food, housing, temperature, exercise, and incidental 

 disturbances, especially light and noises. 



No two colonies today are kept under more than approximately 

 similar conditions and it follows that the average size of the 

 animals from different colonies varies. The conditions just 

 noted also appear to influence the relative weights of some of 

 the viscera. For these reasons, each set of determinations will 

 be accompanied by a statement, as complete as possible, con- 

 cerning the special conditions surrounding the animals on which 

 the observations were made. 



2. Grotvth before birth. For the data on growth during the 

 first few days of fetal life, see Chapter 3, Embryology, early 

 stages, p. 38, Huber ('15 a) and other references there given. 



172 



