WEIGHTS OF ORGANS IN UNDERFED YOUNG RATS 



113 



nearly the normal above cited, so it is doubtful whether there is 

 any actual increase in the head-weight (either relative or absolute) 

 during the experiment. The larger ten weeks group, however, 

 is nearly equal to the controls in average body-weight, and shows 

 an apparent increase in head-weight from an average of 5.01 

 to 5.34 grams, or from 20.6 per cent to 22.7 per cent (table 4; 

 fig. 3). In any event, however, the increase in the head-weight 

 is slight, and is not apparent in the two rats held constant from 

 three to thirteen and sixteen weeks (average of the two is 20.6 

 per cent). On the other hand, there appears to be a slight 

 increase in the weight of the head in the rats held constant from 

 six to thirty-two weeks (15.2 to 17.7 per cent), and from ten to 

 thirty-five (12 to 14.0 per cent). 



On the whole, therefore, the evidence would appear to indicate 

 that in young rats held at constant body-weight for considerable 

 periods of time there is a slight increase in the weight of the head. 

 This is probably due to the increase in skeletal weight, which in 

 the head probably overbalances the decrease in the weight of the 



The head; average absolute weight, average percentage of net budy-weight and range 



indicated 



DESCRIPTION' or RATS 



Normal head at 3 weeks (Jackson '13) 



Controls at 3 weeks 



Body-weight constant 3 weeks (age of 3 to 6 weeks) 

 Body-weight constant 5 weeks (age ot 3 to 8 weeks) 

 Body-weight constant 7 weeks (age oi 3 to 10 weeks) 

 Hody-weightconstantlO weeks (age of 3 to 13 weeks) 

 Body-weight constant 13 weeks (age of 3 to 16 weeks) 



Normal at 6 weeks (Jackson '13) 



Controls at 6 weeks 



Body-weight constant 26 weeks (age of 6 to 32 weeks) 



Controls at 10 weeks 



Body-weight constant 25 weeks (ageof 10to35 weeks 

 (normal head for corresponding body-weight of 



1)5 grams forms about 12.0 per cent 



Controls at 32 and 35 weeks 



ABSOLUTE WEIGHT 

 (and R.*.NGE) : GRAMS 



4.60 

 5.01 

 4.83 

 4.73 

 5.34 

 5.00 

 5.50 

 7.40 

 6.40 



(3.44- 5.85) 

 (4.70- 5.90) 

 (4.50- 5.10) 

 (4.60- 4.90) 

 (4.60- 6.50) 



(6.30-9.40) 

 (6.20- 6.60) 

 8.30 r8.20- 8.50) 

 13.30 (11.10-14.70) 



12.10 



20.30 (17.40-26.30) 



RELATIVE WEIGHT 



(AND range; 



PER CENT 



22.5 



20.6 

 21.6 

 23.9 

 22.7 

 19.6 

 21.6 

 15.2 

 15.0 

 17.7 

 10.1 



(16.3-27.3) 

 (18.3-23.0) 

 (19.9-23.3) 

 (19.9-26.0) 

 (20.4-26.2) 



(11.3-18.0) 

 (14.6-15.5) 

 (16.8-18.6) 

 ( 8.6-11.7) 



14.0 



10.7 ( 9.8-11.4) 



