With adults the demand for food is of two kinds. First, there is the temporary demand which is determined in large part by idiosyncrasy, by appetite, the season, the variety of the supply, and the environment. This is in large part psychological and has fully as much to do with the quality of the food and manner of serving as with the amounts actually eaten. Second, in comparison with this we have the permanent demand as represented by the total amount and energy content of the food eaten rather than by any transitory changes resulting from whims of appetite or individual caprice.

The body requires food to meet its needs for repair and maintenance and to keep the weight at the normal level. When there is a persistent loss in body-weight, this is an index that too little food is being taken. When there is a persistent gain, too much food is eaten. Just what is the best weight for the normal adult will be discussed subsequently, but with any weight, deviations are produced by either too much or too little food.

Food is also required by the body to maintain its usual state or plane of nutrition. When the body has been educated to living upon a high nutritional level, there is a distinct demand for food to maintain this level. When it has been educated by necessity or otherwise to a lower level for a long time, the question arises: will the return of a plethora of food supply affect the food habits or will there be a tendency to maintain the low level?

Finally, the dietetic habits reflect in large part the state of euphoria or well-being of the individual. If he does not feel well, he usually eats less. With free selection of food, man usually eats until he feels satisfied and is quite disinclined to eat less than will produce this feeling. Frequently to secure this he eats a larger amount than he needs.

Undernutrition, as commonly interpreted, implies not only loss of weight, but frequently emaciation to such a degree that it is visible, even to an alarming extent. Pathologists, on the other hand, state that undernutrition may exist without ocular evidence of waste. This is not so conflicting as may at first appear, for it is increasingly evident that by undernutrition must be understood not merely the loss of a visible proportion of fat to body-structure, but also a disturbance of the state of well-being of the neuro-muscular organism, thus affecting the effi-eiency. Any dietetic regime which produces this disturbance may, in the absence of an obvious pathological lesion, for purposes of discussion At least, be termed undernutrition.