456 TOKUYASU KUDO 



average weight (26.7 to 34.8 per cent) in the two longest tests. 

 Its change in weight therefore appears quite different from that 

 of the ovaries. 



THYROID GLAND 



The thyroid gland shows an apparent loss in average weight 

 in all but the last test group (table 2) . In most cases the differ- 

 ence is too small to be significant, however, especially when the 

 individual variation in the weight of the thyroid gland and also 

 the great difficulty in dissecting it out in a uniform manner are 

 considered. Jackson ('15 a), however, found an apparent loss of 

 about 24 per cent in the thyroid of rats underfed from three weeks 

 of age. 



In adult albino rats during thirst, both acute and chronic, the 

 thyroid glands lose markedly in weight (Kudo, '21). 



THYMUS 



The loss of 68.9 to 91.3 per cent in the average weight of the 

 thymus in the various test groups (table 2) is greater than that in 

 any other organ. According to Hatai ('14), the thymus should 

 reach its maximum absolute weight (0.29 gram) at about eighty- 

 five days of age, after which it normally undergoes a slow age 

 involution. As is well known, the thymus is especially liable to 

 a rapid involution under various unfavorable circumstances 

 ('accidental involution' of Hammar). This was found by Jack- 

 son ('15 a) in rats underfed at three weeks of age and later, and 

 also by Stewart ('19) in newborn rats. In adult rats during 

 thirst the involution of thymus is likewise very marked, with 

 loss of about 90 per cent in weight (Kudo, '21). 



SUPRARENAL GLANDS 



In the suprarenal glands of the rat there is normally a sexual 

 difference in weight, observable from the age of about six weeks 

 (Jackson, '13, Hatai, '13). Before this age the sexes may safely 

 be grouped together, as in my controls. In the test groups the 

 sexes are separated, although on account of the small numbers 

 and the irregularity of the data they are combined into only two 



