The arguments which have been advanced in excuse of the use of preservatives when used in minute quantities have, perhaps, been more vigorously urged for salicylic acid than for almost any other substance. This argument has been urged with such vigor and such ingenuity that a further reference may not be out of place here. The principle which is laid down is that a substance which is injurious to health when added to foods, if not a natural constituent thereof, or if not added for condimental purposes, does not lose its power of injury to health because it is diluted or given in small quantities. The only change which is made is to mask the injurious effects produced--to make them more difficult of ascertainment and impossible of measurement. The fallacy of the argument that small quantities of an injurious substance are not injurious may, perhaps, be best represented graphically. The accompanying chart (Fig. 7) shows theoretically the normal and lethal dose of a food and a drug or, as in this case, a chemical preservative. The chart shows two curves, one representing a chemical preservative and one representing a food. The normal dose of a food is that quantity of food which maintains a healthy adult body in equilibrium. It is represented in the chart on the right by the number 100. If the quantity of food necessary to maintain the equilibrium in a healthy adult body is slightly diminished, no apparent change is at first experienced and possibly even no discomfort. If, however, the quantity of food be still further diminished progressively, as indicated by following the curve down to the left, the point is finally reached when no food is given at all and death ensues, represented by 0 on the left hand of the diagram designated “Lethal dose.” As the curve begins to deviate from the perpendicular on the right the degree of injury is very readily noticed and starvation or symptoms of starvation are set up. Thus if you follow the perpendicular on the right downward to the point 80 the divergence of the corresponding point of the curve is already measurable. As you descend to 0 the magnitude of the measurement increases. It requires but very little further illustration to show how easily the effect of diminishing the normal dose of a food can be measured immediately after the curve begins to vary appreciably from the perpendicular on the right. [Illustration: FIG. 7.--GRAPHIC CHART REPRESENTING THE COMPARATIVE INFLUENCES OF FOODS AND PRESERVATIVES.]