There is no food which has been the subject of more investigation as to its sanitary relations, or concerning which there has been more regulative legislation in order to insure healthful quality, than is the case with cow's milk. This is justified by the importance of this milk as human food. Not only is it quite generally consumed by adults, but it constitutes the entire food of many infants, and forms a generous share of the diet of thousands of young children. The fact that this article of food may exert a determinative influence upon the health of the young, and therefore upon the physical status of the adult, raises it to a position of supreme importance. It is essential, therefore, that those who control the milk supply for the family and for institutions shall be able to exercise an intelligent judgment concerning its quality.

305. Ways In Which Quality Of Milk Is Modified

There are several ways in which the sanitary or other qualities of normal milk may be modified, of which the following are the principal:

1. Adulteration by the addition of water, causing a reduction of food value.

2. The removal of a portion of the milk solids.

3. The introduction of non-pathogenic germ life after it is drawn from the cow, causing, under certain conditions, undesirable fermentations.

4. The introduction of pathogenic germ life after the milk is drawn from the cow, rendering the milk a means of communicating infectious diseases.

5. The introduction of disease germs through the udder of the cow.

6. The introduction of compounds known as preservatives, having for their purpose the prevention of fermentations in milk that must be kept a long time before consumption.

306. What Is Normal Milk?

Before discussing the various ways in which milk may be harmed for human consumption, it is well to form a clear idea of what normal milk is. It is, in brief, such milk as the child draws from the breast of a perfectly healthy mother, or the calf from the udder of the healthy cow. It is fresh milk from a healthy mammal, to which nothing whatever has been added, even of invisible germ life, from which nothing has been taken, and in which no changes have occurred. It is milk that would keep sound for a long time, and which might be given to infants with the assurance that it is wholesome and free from any form of infectious disease.

It is such milk as is found in the village or city supply only when it is drawn and handled by expensive and elaborate methods that are rigidly controlled. Only a minute percentage of commercial milk can be considered as normal when it reaches the consumer. Even that which is found on the tables of farm homes is far from normal, for it must be confessed that much milk used for home consumption is badly managed.

307. The Adulteration Of Milk With Water

As will be seen elsewhere in this volume, the normal milk of all species of animals contains a large percentage of water, that of the cow varying from 84 to 89 per cent as nearly extreme limits. It is evident, therefore, that cow's milk has no standard composition; for it varies with breed, period of lactation, and from other less definite causes. Because milk intended for domestic consumption has been mostly sold by volume without much opportunity on the part of the purchaser to know its composition, producers and middlemen have not always resisted the temptation to increase their profits by adding water. The milkman and the pump handle have long been associated in the minds of consumers of " blue " milk. It is possible to add a certain proportion of water to the milk of one breed of cows without reducing its quality below that of some other breed, and even the thinnest normal milk may be rendered more dilute without the consumer being able to detect the fraud. Nothing short of an examination of the original milk in comparison with the suspected sample is competent to detect all degrees of adulteration with water, though the grosser dilutions may be established on other grounds.