THE METABOLISM OF CARBOHYDRATES 907 



requirements as much as possible at the expense of protein and fat. 

 The administration of meat will diminish the fat metabolism to a 

 certain extent, but since it does not alter the D : N ratio it would appear 

 that the latter does not depend in any way on the quantity of fat 

 undergoing oxidation. This is shown in the following respiration 

 experiment (Mandel and Lusk) on a dog with phloridzin glycosuria, in 

 which the metabolism during starvation and after ingestion of meat 

 was determined : 



The enormous waste of energy involved in such a constant loss of 

 sugar will be apparent if we consider that a D : N ration of 3-65 means 

 that 52-5 per cent, of the energy in the protein taken as food or set 

 free from the tissues is lost to the organism in the form of glucose. 

 According to Rubner 28-5 of the energy of meat protein is not utilised 

 in the body, but is liberated simply as heat. This stimulating effect 

 of protein on metabolism or on the processes of oxidation in the body 

 is described by Rubner as the ' specific dynamic action ' of proteins. 

 If we accept this view and add this 28-5 per cent, lost as heat to the 

 52-5 per cent, lost as sugar there would remain a balance of only 

 19 per cent, actually available for the vital activities of the tissues. It 

 is not to be wondered at that the nitrogenous metabolism may be 

 increased three to five fold as a result of the artificial induction of 

 the diabetic condition. 



The carbohydrate starvation has other deleterious effects, since 

 we have evidence that a certain amount of carbohydrate food is a 

 necessary condition for both fat and protein metabolism. The 

 necessity of carbohydrate for the assimilation of protein is brought 

 out in an experiment by Cathcart. It has long been known 

 that carbohydrate administration has a sparing effect on protein 

 metabolism. If an animal or man be starved, the nitrogenous output 

 sinks to a certain level and there remains practically stationary. If 

 now pure carbohydrate food be administered sufficent to meet the 

 energy requirements of the animal or man (about 35 calories per kilo), 

 there is at once a rapid drop in the output of nitrogen and therefore 

 in the protein waste of the tissues. Fat has a much slighter or no 

 sparing effect on the nitrogenous metabolism. Indeed in certain 

 experiments by Cathcart the administration of fat caused an actual 

 rise in the nitrogenous output. The same contrast between carbo- 



