This is a complete food because the various foodstuffs exist in proportions and in quantities sufficient to sustain life for an indefinite period. While milk in Nature's plan is the sole food for young mammals, man has learned to use milk under all conditions and ages as a most wholesome and pleasing source of nutriment. While the milk of goats, and perhaps of other animals than the cow, is used in some countries, an overwhelming preponderance of milk used as human food is the milk of the cow. Cow's milk possesses only about thirteen per cent of nutriment while about eighty-seven per cent is water. However, when we remember that for young mammals the milk is both food and drink, we can easily understand why it should have these proportions. While milk is both food and drink for the young, it must not be looked upon as a proper agent for slaking thirst after the infantile stage. To take a glass of cold milk one or two hours before a meal to slake thirst would have the unfortunate result of failing to slake the thirst, besides introducing into the stomach a food whose presence would require all the digestive powers of the stomach, and as these would be in the midst of their activity at mealtime, there would be little or no appetite for further food. This interference with the regular digestive work of the stomach and disturbance of the appetite is sufficient reason for discouraging the use of milk between meals as a beverage. In the dietary for the well and sick, milk must be looked upon as food and not as drink, and it should never be given unless we wish to give food.

Table VIII - Milk And Milk Products

The thirteen per cent of organic food in milk is nearly equally divided between the butter fat, milk sugar and casein. The fat is emulsified, the minute fat droplets being each contained within a thin albuminous covering. When milk is allowed to cool and stand in receptacles free from any agitation, the milk fat will rise to the top in the form of cream. If this cream is skimmed off, and thoroughly shaken and beaten, the pellicles of the fat globules are broken; the fat globules than readily coalesce first into small masses, then into larger masses called butter, while the remaining portion of the cream representing the broken pellicles, together with milk sugar, and some casein, is called buttermilk. As a rule, the sugar has undergone partial fermentation and there is enough free lactic acid present in buttermilk to give it a definitely acid taste. Butter is one of the most easily digestible and at the same time most complex fats used in the dietary. While it is made up largely of a mixture of olein, palmitin, and stearin, these are not simple mixtures, such as we find the fat deposited in animal tissues, but they are so combined that one molecule of palmitic acid, a molecule of oleic acid, and a molecule of butyric acid, are joined as glycerids in a single fat molecule.

Milk, as found in the markets, is more likely to vary with respect to its fat contents than with respect to any other constituent. Therefore, in the inspection of milk the most important thing to determine is to find whether the proper proportion of butter fat is present. While the butter fat constitutes about 3.7 per cent of whole milk, or about 31 per cent of the total solids, it is more subject to variation than any of the other constituents. So that in fixing a standard the minimum of three per cent fat is usually allowed. However, this is greatly exceeded in milk that comes from certain breeds. The Jerseys and Alderneys, for example, produce a milk whose fat usually reaches five per cent or even more. In the inspection of milk the total solids are usually also determined. If these fall below twelve per cent there is ground for suspecting that water has been added to the milk. A not unusual method of modifying the milk is to add a little water or remove a little cream. As the removal of cream or the addition of water tends to make the milk less rich in color, a small amount of coloring matter is sometimes added. These adulterations, however, are not difficult of detection if they are repeated regularly by any dairyman.

Two facts make it difficult positively to detect adulteration of milk with water, or the removal of a small portion of the cream. These two facts are, first, that cows of different breeds produce milk that varies considerably in fat, as indicated above, and second, cows of a particular breed or individual cows will vary considerably from time to time in the composition of the milk, especially with reference to the fat. Illustrative of the first fact, we may cite the difference between the milk of Jerseys and Alderneys on the one hand, and Holsteins on the other. The former produce a very rich, yellowish milk, whose five per cent of cream rises rapidly, separating almost completely from the milk, which is left blue and thin. The milk of the Holstein is very much more voluminous in quantity, is so much poorer in fat that the dairymen, who have herds of Holsteins, frequently have difficulty in passing the lower limit prescribed in the inspection. In the milk of such breeds as Durhams, Holsteins, and others, the cream rises more slowly and less completely than in the case of Jersey milk. Of these two general types of milk, the Jersey type is better for butter making, while the Holstein type is better for all purposes where the milk is to be used as whole milk, being unseparated.

Reference was made above to variation in the milk of the individual herds of cows, this variation being due largely to a difference in the drink. Cows that are in dry pasture in hot August weather are likely to drink so freely of water to slake their thirst that they actually dilute the milk to where it may fall below the minimum required by inspection. Dairymen have learned that under such conditions cows should be kept in during the hot portion of the day and given a good feed of nourishing food.