At the instigation of Rotch, elaborate tables have been prepared by George E. Gordon and J. H. Waterhouse, by means of which the amounts of cream, skimmed milk, and sugars needed to furnish all kinds of percentage combinations of the proximate principles of milk can be determined at a glance.

The percentage of each ingredient should be modified to suit the needs of children suffering from digestive disorders, and to suit the needs of healthy, growing children. It is surprising what a transformation can be wrought in a suffering child by properly adapting its food to its digestive capacity. In most cases too high a percentage of protein has produced indigestion. Sometimes too little fat and sugar have caused malnutrition; or 'infants' foods' rich in starch and cane-sugar have not been digested, have fermented in the child's stomach or intestine, and have produced illness. A milk mixture made of pure ingredients and uniform at all times in its composition frequency restores such children to health as if by magic. While pure milk and percentage modification of milk are the two great needs of most infants who must be reared upon a bottle, a few are found who will do better upon other preparations.

Rotch advises the following percentage modifications of milk according to the varying age of the child:

More than the required amount of mineral matter is found in the cream and milk that is ordinarily used. The percentage mixtures are made slightly alkaline by using lime-water in part to dilute the milk. Sometimes it is necessary to change the percentage of protein more slowly than is indicated in the foregoing table. A tew infants will be affected by a sudden change of 1/2 of 1 per cent., and adapt themselves to it slowly. The changes may have to be made by sixths or quarters of 1 per cent.

A percentage modification may be made at home as well as in the laboratory. If, however, it is left to nurse-maids or to mothers who do not appreciate the need of accuracy and absolute cleanliness, results as good as are obtained from milk procured at milk laboratories cannot be expected.

When milk modification must be made at home, the greatest pains should be taken to procure pure, fresh milk of uniform composition. (See p. 73.) As soon as it is received, it should be put into a two-quart fruit-jar to which the top should be fastened tightly. The full jar must be kept for the next six hours constantly at a temperature of approximately 350 F. At the end of this time the cream will be at the top of the jar. If the upper fourth is now separated from the rest, the needed cream and skimmed milk will be had. This separation is best accomplished by siphoning off twenty-four ounces, or three-fourths, from the bottom of the jar. The upper fourth, amounting to eight ounces, is left in it. Then the following table of

Rotch's will enable any intelligent and trustworthy person to prepare the needed mixtures:

These proportions give twenty ounces of each mixture. Enough should be prepared to last twenty-four hours. It should be divided into as many feeding-bottles as there are feedings to be given. These should be stoppered with aseptic cotton, and placed into a clean refrigerator. One bottle should be taken at a time, as it is needed. The greatest care must be exercised to insure cleanliness of the bottles. When one is emptied, it should be rinsed immediately. Later it should be sterilized by boiling in water. It should be allowed to drip and to dry with its mouth downward in a clean room.

To find the necessary amounts of cream, milk, water, and milk-sugar to furnish any given percentage of each in a milk mixture, Baurer recommends the use of the following formulas; in them Q means the total quantity of modified milk needed for twenty-four hours; F means the percentage of fat; S, the percentage of sugar; P, the percentage of protein; C, the amount of cream required; M, the amount of milk; W, the amount of water; S', the amount of milk-sugar. To find the amount of cream needed the following formula must be employed:

(Q/12)(F-P)=C.

To satisfy this formula, cream that contains 16 per cent, of fat must be used. This is the percentage richness of gravity cream. If cream containing 12 per cent, of fat is used, Q must be divided by 8 instead of by 12. To find the amount of milk needed, this formula must be used:

(QxP)/4-C=M

To find the amount of water needed, this formula must be employed:

Q-(C + M)=W.

To find the amount of dry milk-sugar, this formula is needed:

(S-P)XQ_= S' 100

To illustrate the working of these formulas, let us suppose that we desired twenty ounces of modified milk containing 4 per cent, of fat, 6 per cent, of sugar, and 1 per cent, of protein.

If we substitute these figures in the first formula, we will have:

20/12 x (4 - 1) = 5 of cream.

Substituting in the second, third, and fourth formulas, we get:

(20x1)/4 - 5 = 0 of milk.

20 - (5 +0) = 15 of water.

((6-1)x20)100 =1 of sugar.

1 The measure for sugar holds 33/8 drams.

Thus we find that five ounces of cream, no milk, fifteen ounces of distilled water, and one ounce of sugar will give twenty ounces of modified milk of the desired composition.