82 CM. JACKSON 



Triton. This question is discussed more fully in the paper above 

 referred to (Jackson '15), the conclusion being that inanition in 

 young rats also tends to produce relatively long-tailed individuals. 



HEAD 



The head (fig. 1; table 3) in acute inanition averages about 

 11.2 per cent of the body weight, varying from 10 per cent in 

 the larger rats to 13.9 per cent in the smaller. Normally (Jack- 

 son '13; Jackson and Lowrey '12) in rats corresponding to the 

 body weight at the beginning of the experiment, the head should 

 range from about 8 per cent in the larger rats to 10 per cent in 

 the smaller, the average for the group being about 9 per cent. 

 Thus we may assume that during the period of acute inanition 

 the head has increased from an average of about 9 per cent to 

 about 11.2 per cent of the body. This is an increase of about 

 one-fourth in the relative size of the head. 



Since the whole body has lost an average of one-third in ab- 

 solute weight, it might appear at first glance that the head 

 has remained nearly constant in absolute weight. This, how- 

 ever, is not true. If the body weight decreased one-third while 

 the head remained constant in absolute weight, the relative 

 (percentage) weight of the head would increase in the ratio of 

 2: 3 or from 9 to 13| per cent. A study of the absolute weights 

 of the head, compared with the normal, at the beginning of the 

 experiment shows that the head has actually lost weight, but in 

 much smaller proportion than the body as a whole. This is what is 

 to be expected since, as will be shown later, the brain, eyeballs 

 and skeleton in general lose but little or none in absolute weight 

 during inanition; while the loss in fat (some of which is on the 

 head) is great, and the loss in the integument and musculature is 

 in nearly the same proportion as in the body as a whole. 



The head of the 6 rats subjected to chronic inanition averages 

 11.4 per cent of the body weight, slightly higher than in acute 

 inanition. The rats used in chronic inanition averaged smaller 

 in body weight (table 3), and the normal relative initial weight 

 of thsir heads should therefore be slightly higher, about 10 

 per cent (instead of 9 per cent, as in the acute inanition group). 



