NUTRITION IN SENESCENCE AND REJUVENESCENCE i6i 



production in different individuals and pieces or tissues of small 

 animals. The agreement between the results obtained with this 

 apparatus and those of the susceptibility method has already been 

 mentioned (pp. 73, 74). 



A number of estimations of carbon-dioxide production in starved, 

 reduced animals, as compared with well-fed, growing animals of 

 the same size, have been made with the aid of this apparatus.' 

 The worms used for the estimation of carbon-dioxide production 

 were taken from a starvation stock after ninety-four days of star- 

 vation. The animals were twenty to twenty-four millimeters 

 long at the beginning of the starvation period, and after ninety- 

 four days without food had undergone reduction to a length of 

 seven millimeters. In each estimation the carbon-dioxide pro- 

 duction of one of these starved animals was compared with that 

 of a young, well-fed animal of the same size. 



Two estimations were made with normal uninjured animals and 

 in both cases the carbon-dioxide production of the starved animal 

 in a given length of time was slightly greater than that of the fed 

 animal. But since the animals moved about to some extent, and 

 since the apparatus is so sensitive that differences in carbon- 

 dioxide production resulting from differences in motor activity 

 might be a serious source of error, it was thought desirable to elimi- 

 nate movement as far as possible. This was accomplished by re- 

 moving the heads of the two animals to be compared and making 

 the estimation after they had become quiet. These headless 

 animals remained quiet in the chambers of the biometer, but gave 

 essentially the same result as those with heads. In the two esti- 

 mations made with such animals the carbon-dioxide production of 

 the starved animal was practically the same as that of the fed 

 animal. In other words, the rate of production of carbon dioxide 

 in the starved, reduced animal is practically equal to that in the 

 young, growing animal of the same size, and this rate is much 

 higher per unit of body weight than that in large, old animals. The 

 results obtained by the direct susceptibility method are thus fully 



' These estimates were made at my request by Dr. Tashiro before the biometer 

 was available for general use, and I take this opportunity of acknowledging my obliga- 

 tion to him, both for conducting the experiments and for permitting me to use the 

 results. 



