WEIGHTS OF ORGANS IN UNDERFED YOUNG RATS 117 



cerning the head and extremities, it follows that there cannot be 

 much change in the trunk-weight, since the probable slight in- 

 crease in the weight of the head is off-set by a slight decrease in 

 the extremities. In the largest group, however, held at constant 

 body-weight from three to ten weeks of age (fig. 3), the trunk 

 would apparently decrease from an average of 54.1 per cent to 

 53.4 per cent. This apparent change is so slight as to be (prob- 

 ably) insignificant. 



The results concerning the parts of the body therefore fail 

 to indicate ^ny decided change of proportional weights in young 

 animals held for considerable periods at constant body-weight. 

 There is apparently a very small increase in the head, counter- 

 balanced by a corresponding decrease in the trunk and extremi- 

 ties, but the change is so slight as to be of doubtful significance. 

 During inanition in adult rats, there is apparently a relative 

 increase in both head and extremities, counterbalanced by a 

 relative decrease in the trunk (Jackson '15 a, ' 15c). 



INTEGUMENT 



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

 weeks to six, eight, ten, thirteen and sixteen weeks, there is a 

 very marked loss in the weight of the integument (including 

 hair and nails; table 6; fig. 4). In the case of the largest (three 

 to ten weeks) group, the decrease is from an average of 21.9 

 per cent to 14.5 per cent of the body-weight. In terms of abso- 

 lute weight, the decrease is from 5.30 grams (5.59 grams, less 

 correction on account of difference in body-weight, which aver- 

 ages 25.1 grams at three weeks and 23.8 grams at ten weeks) 

 to 3.41 grams, a decrease of about 36 per cent. The decrease 

 would appear slightly greater if the difference in relative weight 

 of the integument for different initial body-weights were taken into 

 account. There is apparently even greater loss at the other 

 ages. It would appear that this loss (which is perhaps chiefly 

 a loss of fat) occurs rather early, as at six weeks (body-weight 

 held constant three weeks) the loss is as great as at subsequent 

 and longer periods. 



