The Dilution Of Cows' Milk Reduces The Amount Of Sugar from 4.50 per cent to 1.50 per cent when two parts of water are added. Some additional sugar must therefore be added to bring it up to the necessary standard. Sugar of milk is the best for this purpose in that it is the same as exists in breast milk, but for common use it is too expensive. Maltose in the form of extract of malt may be used as it has stood the test of experience well. Malt extract contains about 50 per cent of maltose, and in addition soluble starch (10 to 15 per cent), proteins (about 5 per cent), ash (1 to 2 per cent), and an important diastatic ferment. It has a marked sweetening power, much more so than sugar of milk, and is easily digested and absorbed by an infant. It not only renders the milk very palatable but will convert any starch present, as when barley-water is added, and is believed to render the curd in the stomach less dense and indigestible. Honey contains from 74 to 78 per cent of invert sugar, which is really a predigested form of sugar and ready for immediate assimilation (Hutchison). It is well suited for infants, who relish it also as a "sweetener." Fresh honey is to be preferred, and those who keep bees as well as babies should not fail to employ this source of nutriment. Regarding the honey which is bought in shops, one has to exercise some care in securing a pure article, as adulteration is common. The price of honey, about 9d. a pound, compares favourably with that of malt extract, which is 3s. Cane sugar may also be employed with safety, and although not so digestible as the other forms of sugar, and more apt to produce fermentative disturbances, it usually acts well and has the advantage of being very cheap. The amount of sweetening matter to be added will vary with the age of the infant, but for the first month the addition of 1/2 oz. of sugar of milk or malt extract or honey, or of 3 drms. of cane sugar, to each 15 oz. of milk as prepared for use will be found sufficient.
The Risks Of Bacterial Contamination in connexion with cows' milk have led to certain precautions which are not called for in the case of breast-feeding. Those who keep their own cows or who can obtain the milk direct from the cows do not require to take any special measures. Some dairies also - very few in this country unfortunately - will deliver the milk under such conditions of purity and kept at such a low temperature, that the milk may be safely given to an infant without any treatment for the destruction of micro-organisms. Here it may be stated that in all probability fresh pure cows' milk, untouched by heating or preservatives, is the best artificial food for infants. Under the conditions of town life such milk is rarely to be obtained, and we have to consider what means may be safely taken to prevent the development of pathogenic and non-pathogenic organisms in milk. The use of preservatives such as salicylic acid, boric acid, formalin, etc., may be mentioned but only to be condemned. The ingestion of such chemicals, even in small quantities, over a prolonged period may affect the growing infant most injuriously and is certainly not indicated by nature's teaching. Further, the purpose of this method of preservation which is carried out by the milk dealer is not to maintain the purity and freshness of the milk but to prevent it from becoming noticeably bad. As to any weakening of its nutritive power he is entirely careless and is concerned only that the milk should be kept in a saleable condition by this means. The method then has many dangers and no advantages. What is preferable is that the milk should be delivered as fresh as possible and that the necessary treatment should be carried out at home. In this country the treatment takes the form of raising the temperature of the milk sufficiently high to destroy the micro-organisms present.
The heating must be carried out in such a way as to interfere as little as possible with the chemical composition and nutritive value of the milk. This is best secured by boiling the milk. The usual plan is to put the milk in a clean pan and boil it for one or two minutes. The drawback to this method is that it so alters the taste of the milk as to render it unpalatable for some infants. A better plan is to put the milk-containing pan into another containing water and to bring the water to the boil. The boiling should be continued for five minutes, at the end of which the milk will have been raised to the same temperature and should be removed and cooled rapidly. The milk itself has not been boiled because the boiling point of milk is higher than that of water, and thus the change in the taste is not induced. The milk should then be transferred to a clean glass vessel, fitted with a lid, or covered with fine muslin, or plugged with cotton wool, and placed in a cool place, for instance the outside ledge of a window. In hot weather the milk should always be kept on ice.
By this method of heating the pathogenic as well as the nonpathogenic organisms will be destroyed, although some spores may still remain untouched. Possibly some ferments in the milk have also been destroyed. Milk thus treated will undoubtedly "keep" better than unboiled milk, but should not on that account be kept for more than twelve hours, or else the quality of freshness will be lost. It must also be remembered that although boiled milk is sterile, it remains a suitable culture ground for bacteria if exposed to fresh contamination.
A considerable amount of controversy has taken place over the question of the relative digestibility of boiled and unboiled milk. Clinical experience seems to show that there is very little difference. Boiled milk is said to be more constipating than unboiled but this effect is by no means constant. On the whole it may be said that the boiling of milk, especially in hot weather, is a great safeguard and does not injuriously affect the nutritive properties of the food.