WEIGHTS OF UNDERFED YOUNG ALBINO RATS 345 
Considerable allowance must be made for experimental error; 
and for variability (the extent of which is unknown). 
The data for the control rats indicate no sexual difference in 
the weight of the gland at the ages observed. Hoskins (’16) 
likewise found no significant difference according to sex. 
DISCUSSION 
In general, the results of the present investigation concerning 
the effects of underfeeding upon very young rats and upon slightly 
older rats underfed for very long periods agree fairly well with 
those obtained by Jackson (’15 b) in rats held at maintenance for 
various periods beginning at three weeks of age. There are, how- 
ever, certain differences found in my rats in which the underfeed- 
ing began shortly after birth, or was prolonged for very consider- 
able periods. These differences are probably due chiefly to the 
varying tendencies to growth and maintenance among the various 
organs at different periods. 
With reference to their growth tendency in young rats held at 
constant body weight, the organs are divided by Jackson (’15 b) 
into three classes: (1) those having a growth tendency so strong 
that they continue to increase, even when the body weight is held 
constant; (2) those which approximately hold their weight con- 
stant (variation within 10 per cent) under these conditions; and 
(3) those which are unable to maintain themselves and lose in 
weight. 
The distribution of the organs according to this scheme for my 
rats underfed from birth to ten weeks, also for those weighing 
about 50 grams after very long periods of fasting, together with 
Jackson’s ('15 b) results for rats underfed from three to ten weeks 
are shown in table 4. 
On comparing my results with Jackson’s it appears that in very 
young rats underfed from birth to ten weeks of age a larger num- 
ber of organs show a tendency to increase than in rats underfed 
from three to ten weeks. On the other hand, very long fasting 
apparently adds to the number of organs which fall into the 
group showing approximate maintenance or a tendency toward 
loss in weight. 
