Many systems for percentage feeding of infants have been evolved. One of the simplest is the top milk method. The cream is allowed to rise. The upper third of the bottle containing practically all the fat, will contain approximately 10 per cent. of fat; the upper half 7 per cent. of fat. In the upper third, the ratio of fat to protein is 3.1; in the upper half, 2.1; in whole milk, 1.1 (approximately).

Top Milk Method I. Emmet Holt

Top-Milk

To secure a milk for infant feeding which is fresh and at the same time one which contains an extra amount of fat, the practice has come largely into vogue of using the upper portion - a third, fourth, or fifth from milk purchased and delivered in bottles - after it has stood only a few hours. To this the term "top-milk" or "upper-milk" has been given. Different percentages of fat may be obtained by varying the amount removed and the length of time the milk has been allowed to stand. Top-milk and thin cream are practically identical in composition, although they may differ in freshness.

If cow's milk from a mixed herd is put into bottles soon after it is drawn and rapidly cooled, it will be found that after four hours the upper fourth will contain nearly all the fat that will rise as cream, and that the upper layers will have nearly the same percentage of fat whether the milk has stood for four hours, for eight hours, or over night. This has been demonstrated in a series of experiments made for me by Messrs. Upton & Jeffers, at the Walker-Gordon Farm at Plainsboro. After the milk had been standing under the conditions mentioned, fat-tests were made with the Babcock apparatus of the different four-ounce layers of bottled milk which contained originally 4 per cent. of fat. The different layers were carefully removed with a siphon, with the following results:

1L. Emmett Holt, M.D.: "The Diseases of Infancy and Childhood." Fifth Edition, Copyright, 1897, 1902, 190S, 1907, 1909. D. Appleton & Co.

Each of these percentages represents the averages, each test having been repeated many times, 110 different tests in all having been made. It will be seen that after four hours the composition of the separate layers does not change very much with the period of standing. With this knowledge, it becomes a comparatively simple matter to secure almost any desired percentage of fat by simply varying the number of ounces removed from the upper part of the quart.

This will of course not be the same with all milks, but will vary considerably according as the supply is from a good herd of selected cattle of mixed breeds (average 4 per cent. fat), a Jersey or Alderney herd (5.25 to 5.50 fat), or from widely scattered farms such as make up the general supply of any large town or city (3.25 to 3.50). It is therefore absolutely necessary for the physician to know with which one of these he is dealing, if the milk for infant feeding is to be modified at home from the different layers of top-milk. More mistakes are made just here than at any other step in this method of feeding.