DIETETICS. 939 



the metabolism in some part of the body. Thus it is stated that 

 the disease known as beriberi, which formerly in the Japanese 

 navy showed the high incidence of 325 cases out of 1000, has been 

 entirely eradicated by substituting for an exclusive diet of polished 

 rice one of equal quantities of barley and rice. Investigation has 

 shown that the material lost in the process of polishing the rice 

 is a relatively simple organic base (p. 904). In these respects the 

 science of dietetics has a wide field for investigation. In a general 

 way, however, the heat energy of a food expresses its value as a 

 means for supplying the energy needs of the living cells. In the 

 work that these cells perform, whether it is contraction, secretion, 

 or nervous activity, energy is needed, and this energy is carried 

 into the body in the potential chemical energy of the proteins, fats, 

 and carbohydrates, whatever may be the source from which these 

 foodstuffs are obtained. 



Dietetics. The subject of the proper nourishment of individ- 

 uals or collection of individuals in health and in sickness is treated 

 usually in works upon hygiene or dietetics. The practical details 

 of the preparation and composition of diets must be obtained 

 from such sources.* The general principles upon which practical 

 dieting depends have been obtained, however, from experimental 

 work upon the nutrition of man and the lower animals, some 

 account of which has been given in the foregoing pages. In a 

 healthy adult the main objects of a diet are to furnish sufficient 

 nitrogenous and non-nitrogenous foodstuffs, salts, and water to 

 maintain the body in an equilibrium of material and of energy 

 that is, the diet must furnish the material for the regeneration of 

 tissue and the material for the heat produced and the muscular 

 work and other work done. Nutritional experiments prove that 

 this object may be accomplished by protein food alone, together 

 with salts and water. It is doubtful, however, whether, in the 

 case of man, such a diet could be continued for long periods without 

 causing some nutritional disturbance, directly or indirectly. It 

 will be remembered that a pure meat diet is not entirely protein, 

 since all flesh contains some fats and carbohydrates (glycogen). 

 The functions of a diet are accomplished more easily and more 

 economically when it consists of proteins and fats, or proteins 

 and carbohydrates, or, as is almost universally the case, of proteins, 

 fats, and carbohydrates. The experience of mankind shows 

 that such a mixed diet is most beneficial to the body and most 

 satisfying to that valuable regulating mechanism of nutrition, 

 the appetite. Expressed in its most general form the cells of our 

 body need food for two purposes: First, to supply the energy 

 needs ; second, to furnish the material for the construction of their 



* For practical directions, see Gautier, "L'alimentation et les regimes," 

 1904; Blyth, "Foods: their Composition and Analysis." 



