The importance of securing a full amount of fat in the dietary, and especially in the natural form of gravity cream, has led to the adoption of top milk mixtures by many. The upper portion of the milk after standing is separated from the lower and used for the infant. This is done by using a glass vessel with a large opening and syphoning off the lower portion of the milk, which is to be used for puddings, etc., or the upper half or third of the milk, as may be considered best for the infant, may be ladled off. Chapin's dipper may be used for this purpose.
Dr. Ashby's plan is as follows : Thirty ounces of fresh milk are placed in a glass bottle and allowed to stand for four or five hours in a cool place, the opening of the bottle being closed with cotton wool. At the end of this time the upper 10 oz. will contain an average of 10 per cent. fat while the upper 15 oz. will contain 7 1/2 per cent fat. The lower two-thirds (20 oz.), or the lower half (15 oz.) should then be syphoned off, according to the strength required, and replaced by water with 1 oz. of sugar-of-milk dissolved in it.
The mixture is pasteurized and then cooled rapidly in running water or ice. The weaker mixture will contain protein 1-1.3 per cent, fat 3-3.5 per cent, and milk sugar 6 per cent, while the stronger will contain protein 1.75 per cent, fat 3.35 per cent and sugar 6 per cent, i.e. a slightly larger amount of protein. Infants at the age of three weeks should be able to take top milk containing 10 per cent fat diluted with two parts of sugar-water, and at the age of three or four months, top milk with 7 per cent cream, diluted with an equal quantity of sugar-water. The strength of the cream mixture can be diminished for weakly infants, or those suffering from digestive disturbances.
Dr. Cautley gives the following details. Fresh cows' milk is allowed to stand for three hours, and the top half is separated. This contains about 8 per cent of fat and the usual percentages of protein and sugar. For an infant under three months he takes 5 oz. of this top milk, and adds 1 oz. of lime-water, 6 1/2 drachms of sugar and 14 oz. of water. The mixture will then have the following composition : protein 1 per cent, fat 2 per cent and sugar 5 per cent. If the mixture is well digested, the strength can be gradually increased by adding 1 oz. of top milk and subtracting 1 oz. of water, once or twice a week, until the mixture consists of top milk 10 oz., lime-water 1 oz. and water 9 oz. (or a percentage of the solids given above, 2-4-6). If more fat is required in the food, all that is necessary is to use the top third or the top fourth, in making the mixture. He finds that by this method with very little trouble and with sufficient accuracy the diet can be altered in details in any particular case, provided that a milk of fairly steady average composition is used and that the details are carefully carried out.
More elaborate variations in the use of top milk have been described, but the above methods are simple and efficient. The advantage in maintaining a full amount of fat in the dietary in the form of natural cream is evident. In families where time and brain power are available for carrying out the details this method will be found most useful. The quality of the milk is not interfered with in any way and it may be boiled or not according to the conditions previously discussed. There are no drawbacks associated with this method which might prove prejudicial to the infant's health at a later period. At the same time the strength of the milk in cream must be regulated by the physician. Experience has shown that the natural instinct of the mother is to make the mixture as strong as possible and that fat indigestion is apt to follow. A mixture containing from 6 to 8 per cent of fat is not readily tolerated for long, and such mixtures will often be made by the use of top milk unless the precise directions of the physician are correctly carried out. Owing to the varying strength of cows' milk in cream, it is advisable to take rather less top milk than the above mathematical calculations would suggest, so as to avoid indigestion from excess of fat.