GROWTH OF PARTS 



183 



2. Systems. The relative growth of the various systems is 

 also given for the integument, ligamentous skeleton, musculature 

 and viscera. The method of preparing each system and the 

 series of organs here comprising the viscera have been pre- 

 viously noted (p. 182). The following table 124 is based on table 

 4 (loc. cit., p. 460) to which has been added the average values 

 of the net body weights. 



It is to be noted that the percentages in tables 123 and 124 are 

 based on the "net body weight" of the rats. According to 

 Jackson and Lowrey this is about 95 per cent of the gross weight, 



TABLE 123 



Albino rat Average percentage weight of head, trunk and extremities all with skin, 

 at various ages sexes combined (Jackson and Lowrey, '12) 



and this factor can be used therefore to transform net into gross 

 weight. 



Jackson and Lowrey conclude (p. 472) that their data indicate 

 no noteworthy differences between the sexes in the relative 

 weights of the various parts and systems, and that the body of the 

 albino rat has practically reached the adult proportions in 

 several of its component parts and systems at the age of ten weeks. 



Corresponding observations, though less extensive, made on 

 the Norway rat are given in chapter 13. 



The Skeleton, (a) Ligamentous Skeleton. Since the values for 

 the skeleton as given in table 124 were obtained by the dis- 

 section of the soft parts from the bones it is evident that the 

 "ligamentous skeleton" thus prepared would have a greater 

 weight than the "cartilaginous skeleton" prepared by maceration. 



