EFFECTS OF INANITION UPON ORGANS OF RAT 81 



somewhat too heavy for the normal at corresponding body 

 length. This might account for the result, even on the assump- 

 tion that the body length has remained constant during the 

 period of inanition. On the other hand, it is more probable that 

 there has been an actual slight decrease in the trunk length dur- 

 ing inanition (probably due to shrinkage of the intervertebral 

 disks), which would equally well account for the facts observed. 

 Individual variations must also be kept in mind, as well as the 

 possibility that the normal ratio of body weight to body length 

 in the strain of rats used may differ somewhat from the normal, 

 as determined by Donaldson. 



The theory of a decrease in the trunk length during inanition 

 is strengthened by the apparently changed ratio of tail length 

 to body length. In a separate paper (Jackson '15) I have shown 

 that the normal ratio of the tail length to body length in the 

 albino rat increases from an average of about 0.36 in the new- 

 born to 0.88 at 6 weeks (body weight 50 grams), decreasing 

 slowly to about 0.85 at a body weight of 200 grams and to about 

 0.80 at 300 grams. (The lower ratio found in the heavier rats 

 is partly due to the absence of females, in which the tail aver- 

 ages relatively longer than in the males.) Thus it appears that 

 in rats with body weights corresponding to the initial weights in 

 the inanition series, the normal average ratio of tail length to 

 body length should be between 0.80 and 0.85. It is impracti- 

 cable to nmke the actual measurements on the living animals, 

 although this might be done by the use of anesthetics. The 

 data given in table 3 show that at the end of the inanition period, 

 however, the average ratio in the acute inanition series is 0.93, 

 and in the chronic inanition series, 0.97. Thus it appears that 

 inanition in adult albino rats tends to produce relatively long- 

 tailed individuals, due probably to a shrinkage in the trunk length. 



Hatai ('08) reached the opposite conclusion, viz., that under- 

 feeding produces short-tailed individuals; but his observations 

 were upon younger, growing rats, in which the conditions might 

 be somewhat different. Morgulis ('11) in the salamander, Die- 

 myctylus, likewise found a greater shrinkage in the tail during 

 inanition, while Harms ('09) found the converse to be true in 



