Page:The Scientific Monthly vol. 3.djvu/566

560 upon which the body depends for its fuel, nor for the great bulk of its building materials. These latter materials—proteins, fats or oils, and carbohydrates (i. e., sugars and starches), when chemically pure, have little or no taste or smell. (Sugars and various mineral salts are of course exceptions to this statement.) But so long as flavor bodies accompany nutritive substances, as is the case in most of the animal and vegetable tissues which man has appropriated for his food, the facts just stated are without much practical significance. When these tissues have undergone manipulation which divorces flavor bodies from nutritive substances, the case is quite different. For instance, in the use of boiled meat, appetite leads us to prefer the broth, which contains most of the flavor bodies (except those which may have escaped into the air with the steam), but which has practically no nutritive value, unless quite greasy; and to reject the tasteless meat, which contains 96 per cent. of the protein; very likely we also skim the soup to remove most of the fat, which is a highly concentrated form of fuel.

The preference for thin and crisp rather than greasy bacon is another illustration of the same thing. In a recent experiment it was found that of the 129 calories which represented the fuel value of a very thin 20 gram (three fourths ounce) slice, only 9 calories remained when the slice was sent to the table; 120 calories being represented by the fat which "fried out" into the pan. In this case a considerable amount of flavor body also goes into the fat, yet most persons would not consider eating it unless it has been skilfully blended with large quantities of other foods; whereas the scrap of skeleton tissue which has lost 93 per cent. of its food value is a dainty morsel.

Many more illustrations might be given to show the great and often inordinate changes in food value of our dietaries, due to some special, sometimes even erratic demand for what the individual has been led to consider a satisfactory flavor or an agreeable texture. These demands are apt to be particularly conspicuous and variable with individuals who are sedentary workers of the middle and upper classes, who live mostly in stagnant indoor air, whose muscular tone is usually low, with relatively feeble hunger contractions. For their appetite sensations, through the development of keen discrimination made possible by the wide choice of foods now offered, even to those of very moderate means, may be exceedingly acute, though their actual food requirement is relatively low.

Let us enumerate several instances of the lack of correspondence between popular demand and actual food value. The sauce made from dried fruits is usually much higher in fuel and even in protein than are the fresh fruits, but the latter are commonly preferred for their more delicate flavor; whether they have any further advantages over the dried fruits (possibly in the presence of the still mysterious