Pasteurizing the Milk.—The corks are then adjusted, the bottles placed in the pasteurizer[73] and pasteurized for the desired number of minutes. The water in the pasteurizer must be cold in the beginning and the rise of temperature recorded on the thermometer, which is adjusted at a convenient place in the pasteurizer where the scale can be read easily. If the temperature of the water is too high, add cold water and lower the flame beneath the pasteurizer. When the desired number of minutes has elapsed, lift the bottle rack above the water for a few minutes and allow a stream of cold water to flow into the pasteurizer, taking care not to chill the bottles too suddenly or they will crack. Cool the bottles as quickly as possible and place on ice until needed, warming the bottle of milk as needed in warm water.
Amount Given at Each Feeding.—At birth a baby will usually take from one half to one ounce at each feeding, this amount is increased at the rate of a quarter of an ounce each week until the baby is receiving eight ounces at each feeding. Or the food is measured to allow of from one ounce to an ounce and a half more than the child’s age in months. For example a baby six months old would receive from seven to seven and a half ounces at each feeding. Some babies are bigger and stronger than others and require the maximum amount, while others are less vigorous and the amount of food which they can handle at a feeding may fall slightly short of the above amounts, but the quantities indicated above will serve as a guide in measuring the formula.
Method of Calculation of Formula.—The calculation of a formula consists in determining the amount (in grams or ounces), of the various constituents contained in the formula when the percentage of each is known. Or, in determining its percentage composition when the amount of fat, protein, carbohydrate and diluent is given. There are certain inaccuracies in all simple methods of calculation and the use of the Babcock tester to determine the fat content in the milk to be used, is advised in all milk or formula rooms. The following method of calculation has been found satisfactory, and the nurse must master it in order to intelligently carry out the directions of the pediatrist.
Determining the Composition of Formula.[74]—Gravity cream and skimmed milk are used in this method, the cream is estimated as containing 16% fat, and consists of the entire cream layer from a quart bottle of milk which has been allowed to stand without being disturbed for six hours or longer. The cream must be dipped off with a cream dipper, or poured off. If there is not a sufficient number of ounces in one bottle of milk, a second must be used, the entire cream layer taken, then mixed with that obtained from first bottle, before the required number of ounces are measured off. Skimmed milk is estimated as being fat-free (although this is not entirely accurate). Both gravity cream and skimmed milk are estimated as containing 3.2% protein, and 4.5% sugar. In this method, one rounded tablespoonful of milk sugar is estimated as weighing one half ounce (dextri-maltose may be estimated in the same way). With this brief explanation of the terms used we will proceed with the method itself.
It is always essential before beginning the calculation of the formula, to know what percentages of fat, sugar, and protein it is to contain, and the amount to be given in twenty-four hours; it is also necessary to know how much lime water is to be added if this substance is to form a part of the formula.
Suppose a thirty-two-ounce mixture is to be made containing 3% of fat, 6% of sugar, 2% of protein, and lime water sufficient to equal 25% of the cream and skimmed milk in the mixture. The fat in the food must be derived from cream, since it is the only substance containing fat to be used in the formula. If the food was composed entirely of gravity cream it would contain 16% of fat. Since it is to contain but 3% of fat it is evident that only 3/16 of the mixture must be gravity cream, 3/16 of thirty-two ounces is six ounces. Six ounces of gravity cream will, therefore, provide the 3% of fat desired in the mixture. The gravity cream contains protein as well as fat. There are six ounces of gravity cream in the thirty-two-ounce mixture. The protein content of gravity cream is 3.2%. The protein content of a thirty-two-ounce mixture containing six ounces of gravity cream is evidently 6/32 of 3.2% or 0.60%. Two per cent protein is, however, desired in the mixture. The gravity cream has provided only 0.60%. One and forty hundredths per cent of protein, the difference between the percentage of protein desired and that furnished by the gravity cream, must be obtained in some other way. It must be obtained, moreover, from some substance which does not contain fat. Skimmed milk is such a substance. Skimmed milk contains 3.2% protein. In order to get 1.40 per cent in the mixture by the use of skimmed milk, it is evident that 140/320 of the mixture must be skimmed milk. 140/320 of thirty-two ounces is fourteen ounces. Fourteen ounces of skimmed milk will, therefore, provide the additional 1.40% of protein desired.
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 4½ 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 × 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—