WEIGHTS OF UNDERFED YOUNG ALBINO RATS 349 
rats underfed to three weeks, and also to a slight extent at later 
periods. 
The spinal cord shows a marked increase in weight in the test 
rats up to ten’weeks of age, and also to a lesser degree in the 
longer periods. 
There is a marked increase in the weight of the eyeballs in the 
test rats during both the short and the very long fasts. 
The thyroid gland apparently remains practically unchanged 
in weight in the test rats at three, six, and ten weeks, but usually + 
suffers a loss later. 
The thymus shows a progressive decrease to about 80 per cent:- 
loss in weight in the test rats at ten weeks, with still greater loss 
(up to 94 per cent) at later periods. 
There is little change in the weight of the heart in the test rats 
at three weeks. At six and ten weeks there is an apparent in- 
crease of 13 and 27 per cent respectively. During the longer 
fasting periods the heart apparently loses weight. 
At three, six and ten weeks the lungs show a loss of about 29 
per cent in the test rats. At the later periods there is an apparent 
increase which is of questionable significance. 
The liver shows an apparent increase of 16, 70 and 64 per cent 
in weight in the test rats at three, six and ten weeks, respectively. 
During the very long fasts it is variable, with a tendency to de- 
crease considerably in the majority of cases. 
There is an apparent loss of 49 per cent in the weight of the spleen 
in the test rats at three weeks, while at six and ten weeks there is 
an apparent increase of about 27 per cent. During the later 
periods the spleen is variable, showing a tendency to decrease in 
most instances. 
The alimentary canal, including contents, shows a loss in the 
test rats at three weeks of age, whereas at six and ten weeks there 
is an apparent increase. The changes are variable in the longer 
periods. 
There is a marked increase in the weight of the empty alimen- 
tary canal in the test rats up to ten weeks. A reduction in 
weight, however, usually occurs during the very prolonged 
fasts. 
THE JOURNAL OF EXPERIMENTAL ZOOLOGY, VOL. 25, NO. 2 
