It is advisable to refer very briefly to some of the more common defects in milk as an article of food. The most commonly encountered adulteration is dilution with water. When the dilution is made with pure water it is a fraud, and when, as sometimes happens, the water is from an impure source, it is a crime. Milk is sometimes artificially coloured by the addition of minute quantities of colouring matter, a little special pigment being added to impart the yellow colour characteristic of good cream. A pinkish or reddish coloration of the milk may arise from the ingestion by the animals of food rich in pigment. Various preservatives are frequently added to the milk, notably borax, boric acid, salicylic acid, and formaldehyde, and these may be very prejudicial to the digestion of milk in the case of infants and delicate children. The milk, after a preliminary dilution, is frequently fortified by the addition of flour, farina, whiting, tragacanth, or magnesium carbonate; the addition of one or other of these substances gets rid of the thin colour of diluted milk. Sugar may also be added to the diluted milk to raise its specific gravity to a satisfactory standard.

Milk Contamination

Milk may be contaminated by the cow's disease germs, e.g., tuberculosis and diphtheria. Extraneous disease germs may find their way into milk through contact with unclean hands, or from polluted water used for dilution or for washing cans and pans. Examples of diseases so induced are typhoid fever, scarlet fever, gastro-enteritis, diarrhoea, etc. The milk is often tainted with excrementi-tious matter from the cowshed. Professor Silvanus Thompson describes the ideal system of cleanliness which provides a "guaranteed milk ": -

"Each milkman, before milking, is required to cleanse his hands in hot water with soap and a nail-brush; he then dons a clean white linen suit from the sterilising chamber, and takes a clean towel and milking stool; he is not allowed to moisten his hands with the milk in milking, and he must wash his hands each time before milking another cow. All cows must have given a negative tuberculin test, and all are groomed twice a day before milking. The milk is drawn into pails with small openings, and exclude droppings from the animal's belly. The milk is strained through sterilised absorbent cotton, and placed in a cooler, which reduces the temperature to 400 F. within twenty minutes after leaving the udder. It is then bottled and stored in ice water ready for shipment".

Good, clean, uncontaminatcd milk should keep fresh, exposed in a clean room at ordinary temperature of 68° F., for forty-eight hours, without souring and coagulating. But if the air is warmer, or if the milk be in any way contaminated, it will sour in a few hours. Boiled milk will keep fresh about half as long again as fresh milk. A large number of bacteria are capable of inducing lactic acid fermentation of the milk sugar, and some of them carry the decomposition further, to the development of carbonic acid and alcohol. This latter interferes with the normal digestion of milk. Lastly, it is important to bear in mind the absorbent power of milk: it may acquire a flavour or odour from substances in its vicinity. It should not, therefore, be kept in a pantry beside such foodstuffs as stale cheese or onions, and it should not be left exposed in a sick-room or anywhere near a waste-pipe.