THE METABOLISM DURING STARVATION 629 



carbon dioxide is derived from oxidation of glycogen and how much from the 

 oxidation of fat. A very efficient check on this calculation is furnished 

 if the individual or animal can be placed at the same time in an accurate 

 calorimeter, as in Benedict's experiments, owing to the fact that a gramme 

 of fat when converted into carbon dioxide and water produces more than 

 double the amount of heat which would be evolved by the complete oxidation 

 of glycogen. In Benedict's experiments the heat-value of the metabolism 

 calculated by the above method agreed with the heat as actually measured 

 by the calorimeter within 0-5 per cent., whereas if the total carbon of the 

 first day had been reckoned as fat, the discrepancy would have been as high 

 as 5 per cent, in many cases. The influence of glycogen metabolism on that 

 of protein during the first and second days of fasting is shown in the following 

 experiments (Benedict) : 



The total metabolism per kilo body weight very soon attains a constant 

 level. The relative part taken in the production of the total energy by fats 

 and proteins respectively may vary from animal to animal according to the 

 amount of fat available in the body. If the animal has been receiving 

 previous to the experiment a diet rich in protein the excretion of nitrogen 

 and urea in the urine diminishes rapidly during the first days of starvation. 

 During the first two days therefore a considerable proportion of the necessary 

 energy is obtained at the expense of protein. Between the third and 

 fifth day, however, the nitrogenous excretion reaches a minimum, at which 

 point it remains approximately constant to within a day or two before death. 

 If the animal has been receiving a diet very poor in protein the excretion 

 of nitrogen may be low throughout the whole course of the experiment. 

 These facts are illustrated by the curves in Fig. 320, which show the output 

 of urea in three experiments on a dog under different conditions of nutrition. 

 In the first experiment the dog, before the experimental period, had. been 

 receiving 2500 grm. of meat daily ; in the second it had been receiving 

 1500 grm. of meat, and in the third only a small quantity, which was not 

 accurately measured. Although there is a great difference between the 

 urea output during the first day of the experiments, the urea output during 

 the sixth to eighth days is identical. In many cases for a few days before 



