WEIGHTS OF ORGANS IN UNDERFED YOUNG RATS 141 



weeks being probably too high, on account of the inclusion of a 

 litter with abnormally large spleens) ; while in the rats at eight 

 and ten weeks there is a considerable decrease. In the case 

 of the three to ten weeks series, the decrease would be from 

 0.091 gram (0.37 per cent of the net body-weight) to 0.053 gram 

 (0.22 per cent of the body-weight), or a decrease of nearly 42 

 per cent in absolute weight. (No correction has been made 

 for the difference in body-weight, which is 0.5 gram lower at 

 ten weeks). If the normal relative weight of the spleen at three 

 weeks (0.28 per cent, Jackson '13) be taken as a basis of esti- 

 mate, however, the loss would appear considerably less. 



In the rats held at constant body-weight at later and longer 

 periods (six to thirty-two weeks and ten to thirty-five weeks) 

 there appears to be no appreciable change in the average weight 

 of the spleen. It may be concluded therefore that in young 

 rats held at constant body-weight beginning at the age of three 

 weeks there is a marked tendency to a reduction in the weight 

 of the spleen; while at later (and longer) periods the spleen ap- 

 pears to undergo no material change in weight. It must be 

 remembered, however, that the spleen is normally one of the most 

 variable organs in the body (Jackson '13), and final conclusions 

 should be correspondingly guarded. 



In adult albino rats during chronic inanition the average loss 

 in weight is nearly proportional to that of the entire body, while 

 in acute inanition the loss appears very much greater (Jackson 

 '15 a, '15 c). 



STOMACH AND INTESTINES 



The stomach and intestines, including mesentery and pan- 

 creas, are considered both with contents (table 19 a) and empty 

 (table 19 b). Considering first the empty canal, it appears in 

 rats held at constant body-weight from the age of three weeks 

 to increase from about 4.8 per cent of the body-weight to 8.0 

 per cent at six and eight weeks, decreasing to 6.0 per cent at 

 ten weeks. In absolute weight the increase would be from about 

 1.13 grams (1.20 grams less correction on account of difference 

 in body-weight) at three weeks to 1.45 grams at ten weeks, an 



