298 SENESCENCE AND REJUVENESCENCE 



general agreement that the rate of metabolism falls rapidly during 

 the early stages of starvation to a more or less constant level. In 

 the later stages of starvation the well-known premortal increase 

 in nitrogen elimination occurs, which most authors believe to be 

 due to increased breakdown of tissue substance after the reserves 

 of fat have largely disappeared. In Benedict's latest study of 

 starvation-metabolism, covering a fasting period of thirty-one days 

 in the human subject, the oxygen consumption, carbon-dioxide pro- 

 duction, and heat production per kilo of body-weight show a slight 

 increase toward the end of the period, and other investigators men- 

 tion slight changes of the same sort, but whether these facts have 

 any significance in connection with rejuvenescence is not yet clear. 

 While considerable loss of weight occurs before death, in no case 

 is there a degree of reduction comparable to that observed in the 

 lower invertebrates. Apparently the higher animals are unable 

 for some reason to use their own tissues as a source of nutrition to 

 any such extent as the lower forms. Probably this inability is due 

 in large part to the relatively high physiological stability of the 

 tissue components, but other factors may also be concerned. 



While there is no distinct indication of any rejuvenescence 

 during the starvation period, it has often been noted that the body- 

 weight after starvation becomes greater than before. Von Seeland 

 ('87) found this to be the case in fowls with periodic starvation. The 

 increase in weight was due primarily to increase in proteids and 

 not to deposition of fat. Noe ('oo) obtained similar results by 

 periodic starvation of rabbits and mice. In man also a starvation 

 period is often followed by an increase in vigor and body-weight, 

 and starvation, properly controlled, is believed by many to possess 

 a certain therapeutic significance. 



The injurious effects of overnutrition in man are commonly 

 supposed to be due in large measure to the accumulation of fat or 

 to intoxications. The possibility must, however, be admitted that 

 overnutrition may actually increase the rate of senescence to some 

 slight extent by increasing the deposition in the cellular substratum, 

 not only of fat, but of other substances which aid in decreasing the 

 general rate of metabolism. Instances of longevity in man on a 

 low diet are not lacking, and much has been written during recent 

 years of the perils of overeating. 



