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CHAPTER II.

MILK.

ILK is correctly stated to be the only food complete in itself. Not only is milk furnished with every requisite of nutrition, but for a certain period of life, that of early infancy, it is the only food required in a condition of health, and in many instances the addition of any other description of food besides milk is absolutely injurious.

The natural secretion which is provided for all young animals, varying only in the proportion of its constituents, is curiously enough adapted to the necessities of the younger carnivora whose future diet is flesh alone, and for the little lambs who will ultimately browse upon herbage. Milk is therefore the universal food, as well as the perfect food, for the whole range of mammalia.

It must not be supposed that milk contains, either in the principles of its composition, or in their relative proportions, the strong meat fit for the sustentation of mature life.

The great divergence before alluded to, between

flesh on the one hand and vegetable food on the other, is quite sufficient to prove that milk by itself cannot replace the diet suited to the instincts of animal life after the earlier portion of its existence. If this be granted with regard to the carnivora and herbivora, the analogy will hold good when the natural instincts predispose to an omnivorous diet, whether these be exhibited among four-footed mammals or by human bipeds. It is therefore necessary to clear away the oft-repeated error that the milk diet, however essential in infancy, is a proper and judicious food to place entire dependence on in after life.

Regarding milk in its very essence as a food, it must be taken from the standpoint of its use as nourishment from the moment of birth. When the first natural secretion of milk is obtained, whether from the human mother or the cow, it is composed of ingredients very different in proportion and quality from that of the milk intended for the subsistence of the young animal. Its first peculiarity is that it contains a large excess of solid matters generally, and particularly an excess of mineral matters or salts, which cause it to assume a purgative action.

The first milk of the cow is termed beastings by the dairymen, and its extra richness and yellow colour is sometimes shown in the milk retailed by

them. It cannot, however, be considered advisable to distribute this mixed up with the later milk of other cows. In the human subject the peculiarity of the first milk is of a like nature, and is termed colostrum.

Human milk contains about eleven per cent. of solids, in which the sugar greatly preponderates. Neither the casein or cheesy matter nor the butter is nearly so abundant as in the milk of the cow; nor are the salts contained in the human milk present to the extent of much more than a third of those found in cows' milk. From this it is evident that in all attempts to feed infants upon cows' milk, it must be reduced by the addition of water to such an extent as will somewhat approximate it to the milk derivable from a healthy natural source.

This may be roughly stated to be accomplished by the addition of one-third water, and a little sugar. The reason for this dilution of cows' milk when employed for infant feeding will be better shown by contrasting the amount of solids and their composition; and to render this comparison more complete it may be as well to subjoin particulars of the components of the milk of asses and goats. Both of these have been frequently prescribed and used as substitutes for human milk when cows' milk has been found to disagree. The milk of the cow averages about thirteen to four

teen per cent. of solids, of which the casein forms about one-third part. This, however, varies to some extent inversely with the amount of butter present. The quantity of sugar of milk is perhaps more constant, but in all really good dairy milk the amount of salts, composed of phosphoric acid, lime, and magnesia, almost invariably reaches as much as seven parts in a thousand. The solids of asses' milk more nearly approximate to those of the human mother, being about ten per cent. Of these the cheesy matters and butter bear but a small proportion, while the sugar is present to the extent of about half the total solids. The salts or mineral matters are about half those in cows' milk, and therefore more nearly resemble the human secretion in this respect. Goats' milk, on the other hand, bears a closer similarity to that of cows, the casein or cheesy matter predominating in this instance; and goats' milk can only be considered as more closely approaching the natural food of the infant inasmuch as there is less butter, and considerably less salts.

In alluding to the difference of proportion in the composition of different milks, a much greater attention might have been accorded to the amount, small as it is, of albumin, or the equivalent of the white of egg, which is to be found in milk of all kinds.

The albumin present is at first in a highly soluble form, and is therefore particularly easy of digestion in that condition. It is, however, very prone to decomposition, and not only to decompose of itself, but also to excite fermentation in the other constituents of the milk. To such an extent is this the case, that in warm weather a distinct change can be detected within a few hours of milking, if the milk has not been rapidly and efficiently cooled directly it is obtained.

When examined under the microscope, milk which has been carelessly treated or allowed to retain too high a temperature, commences to exhibit the peculiar germs of lactous fermentation. These germs are distinct evidence of an acid change long before any acidity can be detected by the palate; and among other reasons for the early development of this very undesirable fermentation, one must be particularly, alluded to. Any neglect of the most scrupulous cleanliness in the milking sheds, or vessels into which the milk is drawn, or in the coolers or cans, or any other utensils with which the milk may come in contact or even a close or unhealthy atmosphere, may prove sufficient not only to set up this process of lactous fermentation, but as the milk is highly absorbent of the minutest particles which are carried by air bad flavour may be communicated, and noxious