32 APPLIED PHYSIOLOGY 



upon various circumstances. If the intake be greatly in 

 excess of the minimum required for the maintenance of 

 nitrogenous equilibrium, the larger part is devoted to 

 early denitrification and utilized for energy produc- 

 tion. Much heat may be liberated in consequence of 

 this, which may, indeed, be harmful in cases in which 

 heat regulation is defective. Hence the importance of 

 avoiding large protein meals in fever. If, on the other 

 hand, but little protein is consumed, a large proportion 

 finds its way to the tissues. The amount and nature of 

 the other food constituents also exert a determining 

 influence in the matter. The gelatin, carbohydrates, 

 and fats of the food exert a shielding influence on the 

 protein, preventing it from undergoing the ' denitrifica- 

 tion ' process, and enabling a larger proportion to take 

 part in tissue metabolism than would otherwise be the 

 case. This shielding process is known to physiologists 

 as the doctrine of the ' protein-sparers.' The exact 

 mechanism of the sparing process is unknown to us, but 

 some idea of its possible modus operandi may be arrived at 

 by the use of a somewhat anthropomorphic simile. Let 

 us assume that into the neighbourhood of a cell there is 

 brought in solution an equal number of molecules of 

 protein, carbohydrate, and fat respectively, ^ir would 

 appear that the cell has least difficulty in ' tackling ' 

 (to use an expressive colloquialism) the molecules of 

 protein, possibly because they are most like itself, and 

 therefore least foreign to it, and in consequence more 

 molecules of protein are broken up than of either carbo- 

 hydrate or fat. If, however, instead of an equal number 

 of molecules of each kind reaching the neighbourhood of 



