GROWTH OF SYSTEMS 



75 



The authors call attention to the relative increase in the weight 

 of the head during the first week — as peculiar in the rat — and 

 also point out that the maximum relative weight is shown by the 

 head at one week — by the forelimbs at three weeks, by the hind 

 limbs at five months and by the trunk at a year — the wave of 

 most active growth thus passing from the head caudad with ad- 

 vancing age. 



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

 also given for the integument, ligamentous skeleton, musculature 

 and viscera. The method of preparing each system has been 

 previously noted. The following table 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 49 and 50 are 

 based on the 'net body weight' of the rats. According to Jack- 

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

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

 weight. 



TABLE 50 

 Average percentage weights of integument, ligamentous skeleton, musculature, 

 viscera and remainder. Based on Jackson and Lowrey ('12), table 4. For the 

 corresponding absolute weights see table 51 



