40 CHESTER A. STEWART. 



limits of normal variability, and show no indications of any 

 persistent effects of the earlier maintenance period. 



13. Thymus (Table F). 



The weight of the thymus at the end of the maintenance 

 period was from 87.7 to 93.9 per cent, below Donaldson's norm. 

 This agrees closely with Jackson's ('15) observation of 90 per cent, 

 loss in the weight of the thymus due to "hunger involution" 

 during maintenance in young rats from the age of 3 to 10 weeks. 

 At the end of two weeks of refeeding, the thymus was still 

 somewhat below Donaldson's norm (9.0 to 32.5 per cent.); 

 but at the end of the fourth week it exceeded the norm 70.4 and 

 52.5 per cent, in the male and female test rats respectively, while 

 the controls averaged 14.6 per cent, below. It is therefore 

 evident that the thymus returned to the normal proportion 

 between the second and fourth weeks of refeeding. The weight 

 of the thymus in the test rats refed four weeks was remarkably 

 high, indicating a marked over-compensation of the loss during 

 "hunger involution." 



In the adult rats the thymus was relatively heavier in the 

 female controls than in the female test rats, whereas the converse 

 was true of the males. This inconsistency, together with the 

 known variability in the normal weight of the thymus (average 

 coefficient of variation is 34, according to Jackson, '13) makes it 

 doubtful whether the result is due to the experimental conditions 

 or is due merely to normal variation. Further observations will 

 be necessary to determine this question. 



The results in general therefore indicate that in the stunted 

 rats, the thymus returns to the normal proportion shortly after 

 the second week of refeeding, and greatly exceeds the normal at 

 the end of the fourth week. The data for rats refed to the adult 

 stage indicate the possibility of a permanent over-compensation 

 in the growth of the thymus upon refeeding after a period of 

 maintenance. 



Jonson ('09) subjected a rabbit (age 6 weeks) to inanition for 

 31 days, during which time the body weight increased from 553 

 to 655 grams. The animal was then refed for three weeks, at 

 the end of which time the weight of the thymus was found 



