WEIGHTS OF UNDERFED YOUNG ALBINO RATS dao 
shows a marked decrease in the test rats when compared with 
either my controls or with the Wistar norm tables. For example, 
in the case of the eight test rats weighing about 50 grams after 
very long underfeeding the thyroid has apparently suffered a 
loss of approximately 50 per cent in the males, although there is 
apparently no change in the females. 
These latter results therefore agree in general with those ob- 
tained by Jackson (’15 b) in rats held at maintenance from the 
age of three to six, eight and ten weeks. In my younger rats, 
however, subjected to inanition for various periods starting at 
birth, the weight of the thyroid apparently remains practically 
unchanged. The power of maintenance in the thyroid therefore 
appears stronger in the very young rats. Considerable allow- 
ance should be made for experimental error due to the difficulty 
in dissecting the thyroid gland in an accurate manner. 
During acute inanition in adult rats, Jackson (15 a) reports 
that the thyroid gland apparently loses little or no weight, while 
in chronic inanition with an average loss in body weight of 36 
per cent, the thyroid gland loses only about 22 per cent in weight. 
THYMUS 
As is evident from table 2, the weight of the thymus is, without 
exception, much lighter in the test rats than in the controls. At 
three, six and ten weeks of age the loss in weight amounts to 
approximately 30, 60 and 80 per cent respectively. The decrease 
in weight of the thymus in the test rats, while very marked in ~ 
all groups, is especially striking in the four test males underfed 
412 days. From an average of 0.207 gram in the controls, the 
weight in the test rats has decreased to 0.011 gram, a loss of 
approximately 94 per cent. This decrease is not so remarkable, 
however, when the normal involution with age is taken into ac- 
count. According to the Wistar tables, the normal weight of the 
thymus at 400 days is only 0.03) gram. 
Thus it is evident, as was observed by Jackson (’15 b) that the 
thymus loses markedly in weight in young rats underfed for 
various periods. He found a loss of about 90 per cent for the 
THE JOURNAL OF EXPERIMENTAL ZOOLOGY. VOL. 25, NO 2 
