EFFECTS ON THE THYMUS 297 



periods, Stewart ('18, '19) found a smaller loss (30-80 per cent); and in the 

 stunted offspring of severely underfed pregnant rats, Barry ('20, '21) found 

 the thymus only 21 per cent subnormal in weight. 



The reduction in the thymus of underfed young albino rats is shown by 

 Figs. 80 and 81. 



Upon refeeding rats underfed from 3 to 12 weeks of age, Stewart ('16) 

 found the thymus still somewhat subnormal after 2 weeks; but after 4 weeks 

 it appeared 50-70 per cent above normal, possibly indicating an over-com- 

 pensatory growth. In rats underfed from birth to 3, 6 or 10 weeks of age, 

 and subsequently refed to 25, 50 or 75 g. body weight, Jackson and Stewart 

 ('19) found the thymus variable, but in most cases still slightly subnormal in 

 weight (Table 7). In rats similarly refed to maximum (adult) weight, after 

 earlier periods of underfeeding, Jackson and Stewart ('20) found the thymus 

 still subnormal in weight in 3 of the 4 groups (Table 8). The evidence would 

 seem to indicate a permanent dwarfing of the thymus in most cases, although 

 the great normal variability renders the results uncertain. 



Trowbridge, Moulton and Haigh ('18) and Moulton, Trowbridge and Haigh 

 ('22a), in steers on different planes of nutrition, found that the thymus ("heart 

 sweetbread") averages higher in weight in fat animals, but the reduction in 

 the poorly nourished is much less than might be expected from the results of 

 of inanition in other species. 



McCarrison ('19b, '21) gave organ weights indicating a great loss in the 

 weight of the thymus in pigeons during starvation as well as on various deficient 

 diets. Findlay ('21) found total disappearance of the thymus in starved 

 pigeons and fowls (Table 13). 



Ikeda ('22) in fasting rabbits found that the thymus atrophies more rapidly 

 than the other viscera, due chiefly to emigration of lymphocytes, but also to 

 degeneration of the parenchyma. Okuneff ('22) observed large amounts of 

 isotropic, and especially of anisotropic, lipoids in the thymus of rabbits starved 

 until the ordinary reserve fat was assumed to be exhausted. 



Several observations indicate that the thymus undergoes a typical involution 

 during hibernation. A winter-atrophy of the thymus was noted by Ver Eecke 

 ('99) in the frog (species?) ; and by Schaffer ('08) in the mole. A similar process, 

 with the typical involution changes during hibernation, was described by Aime 

 ('12, '12a) for chelonians {Emys vittata, Clemnys leprosa, Testudo mauritanica) . 

 The annual regeneration is apparently by a process of budding, the epithelioid 

 buds being later invaded secondarily by small thymic cells, which form the 

 cortex (as in normal development). Dustin ('13) observed a seasonal 

 involution in adult amphibia, Rana fusca and Bufo vulgaris. Mann ('16), 

 however, found apparently no uniform change in the thymus of hibernating 

 spermophiles (Spermophilus tridecemlineatus) . 



(B) Effects of Partial Inanition 



These will include changes in the thymus during various partial dietary 

 deficiencies, especially in rickets, beriberi, scurvy, and thirst (aqueous inanition). 



