DIETETICS. 947 



For a person in health and leading an active, normal life, appetite 

 and experience seem to be safe and sufficient guides by which to 

 control the diet; they may be relied upon, at least, to protect the 

 body from undernutrition. The opposite danger of overeating 

 is a real one, particularly among those who do not lead an active 

 life. It is, however, a hygienic offence that is usually committed 

 knowingly and may consequently be controlled by those who have 

 sufficient wisdom. Physiological knowledge emphasizes clearly 

 enough the great fact that the mechanisms of nutrition and 

 digestion, like the other mechanisms of the body, should not be 

 subjected to unnecessary strain. For those who are in health, 

 the important rule to follow in the matter of diet is to avoid an 

 excess in eating. In conditions of disease, in regulating the diet 

 of children or of collections of individuals, as in the army, navy, 

 etc., it is necessary for purposes of hygiene or for purposes of 

 economy to arrange the diet in accordance with the knowledge 

 obtained from experience and from scientific investigations. 

 In this direction much has already been accomplished, but more 

 remains to be done, particularly in the selection of a properly 

 balanced diet and in the adaptation of the diet to special conditions. 

 The principles governing the selection of a diet adequate to meet 

 the energy needs of an individual or group of individuals are simple, 

 and in recent years they have been followed successfully by those 

 charged with the feeding of groups of people, schools, hospitals, 

 armies, etc. But the energy needs, while important and indeed 

 essential, are not the only object to be borne in mind in selecting 

 dietaries. Outside such obvious considerations as the palatable- 

 ness and digestibility of the food selected, it has become increas- 

 ingly evident from experimental studies that attention must be 

 paid to the proportions of the various foodstuffs and, indeed, even 

 to the particular kinds of energy-jdelding foodstuffs that are 

 selected. To use a current phrase the diet must be properly bal- 

 anced. It is possible to select a diet which yields the requisite 

 amount of energy and yet may induce a condition of malnutrition. 

 This possibility seems to be illustrated in the disease known as 

 pellagra. The prevalent view in regard to this condition seems to 

 be that it is due to a maladjustment in the elements of the diet- 

 ary, rather than, as in the case of beriberi, to a lack of some special 

 vitamin. The various general ways in which a diet may be ill- 

 balanced or maladjusted are indicated by McCollum* as follows: 



1. An inadequate supply of the necessary inorganic constituents. 



2. Inadequate amounts of protein, or the use of proteins of poor 

 quality, that is to say, of proteins not containing all the necessary 



* McCollum, Harvey Lecture, "Jour. Amer. Med. Assoc," May 12, 1917. 



