Both gravity cream and skimmed milk contain 4.50% milk sugar. Twenty ounces of gravity and skimmed milk are required to furnish the desired percentages of fat and protein. These twenty ounces in a thirty-two-ounce mixture must add 20/32 or 4.50% of sugar to the mixture. Twenty thirty-seconds of 4-1/2 or 20/32 of 9/2 = 180/64, or practically 3% of milk sugar. It is, however, desired to have 6% of milk sugar in the mixture. That is, 3% more of milk sugar is required. This additional sugar must be added in the form of dry milk sugar. Three per cent of thirty-two ounces is 3/100 of thirty-two. This will give the amount of sugar desired in ounces. The sugar is to be measured in rounded tablespoonfuls, or half ounces. If the figures given above are multiplied by two, the result will be the number of rounded tablespoonfuls needed. That is, 3/100 of 32 x 2 = 192/100 rounded tablespoonfuls, or for all practical purposes, two rounded tablespoonfuls. It is also desired to have the amount of lime water in the mixture equal to 25% of the cream and milk in the mixture. There are twenty ounces of cream and milk in the mixture. Twenty-five per cent of twenty ounces is five ounces. Five ounces of lime water must therefore be added. The total quantity of the mixture is to be thirty-two ounces. The milk sugar goes into solution and, therefore, does not add to this quantity. The difference between thirty-two and twenty-five ounces is seven ounces. Seven ounces of water must, therefore, be added to make up the quantity desired. ~Changing the Formula.~--It is often found necessary to change the formula when using artificial feeding for infants, and under these circumstances it is necessary to know the percentages of the food constituents contained in the formula already in use. For this purpose the following method, quoted from "Diseases of Nutrition and Infant Feeding,"[75] is included: ~Morse and Talbot's Method.~--Suppose that a baby is taking a food made up of-- Gravity cream 12 ounces Skimmed milk 18 ounces Limewater 6 ounces Barley water 12 ounces Milk sugar 4 rounded tablespoonfuls