Of recent years it has been discovered that a very large proportion of infant mortality is traceable to the use of impure milk, and that many diseases, especially diarrhoeal disorders of summer, are preventable when proper care is exercised to protect the milk supply. The subject is rapidly claiming public attention, and suitable controlling legislation has been already adopted in most civilised countries.

The prevention of adulteration and contamination of milk is a matter of vital importance from both an economic and hygienic standpoint. Children, who are so largely dependent upon milk, do not well tolerate its adulteration, and milk is so much used as a raw food - perhaps more than any other one article of diet - that its careful inspection in regard to contamination by disease germs or adulterants is imperative, and the constant vigilance of the health boards of large cities is required to protect the public from imposition. According to H. D. Chapin and G. B. Fowler, of the Milk Commission appointed by the Medical Society of the County of New York to investigate the milk supply of that city in 1900, "over 6,000 children under five years died in New York city from diar-rhceal diseases largely due to drinking old and contaminated milk".

It is better and simpler, however, for much of the inspection to be done at the dairy farms, and in many parts of this country the State boards of health appreciate the importance of this matter, and the sale of milk from diseased cows is prevented at first hand. When a cream separator at a creamery is cleaned it is often found to contain a residue of manure, hairs, dirt, and perhaps pus and blood from inflamed udders.

The examination of milk requires the adoption of a legal standard of quality. In New York city the Health Board depends chiefly upon the use of the lactometer above described. (See Estimation of Solids in Milk, page 59.) In States such as Massachusetts, Rhode Island, and Maine a chemical analysis is required by law. The normal specific gravity established is 1.030 (in New York 1.029), and the normal average amount of cream is 8 per cent by volume.

The inspection of milk in all large cities and towns is made at the railway stations or ferries where the cans are received. The examination is under the direction of expert officers, usually members of the local health board. It is impossible and unnecessary to examine all the milk brought in, but the officers make frequent seizures and destroy at once all milk found below the legal standard. Milk sold in shops and otherwise must also be occasionally examined, for its dilution and adulteration is very easy and profitable to the unscrupulous. Gross impurities in milk, such as dirt, hair, etc., may be removed by filtration through absorbent cotton. A few germs are also removed in this manner. A noted milk dealer of Berlin, who dispenses 60,000 quarts of milk daily, forces it through gravel filters from below upward, thereby removing the gross impurities.

Milk may be altered by -

1. Addition of water, pure or impure. 2. Addition of colouring matter. 3. Addition of preservatives. 4. Addition of substances used for thickening after dilution.

1. The commonest method of adulterating milk, and the one often most difficult of detection, is by dilution with water. If the water thus used is pure it does no harm other than to defraud the consumer; but if impure, as it often is when drawn from wells near manure heaps, in barnyards, or country privies, it may prove fatal.

2. The normal whiteness and opacity of milk is due to its fat globules. If milk has been much diluted it becomes pale and bluish, and both milk and cream are sometimes artificially coloured with anilines or other pigments. This form of fraud is less injurious to health than the others, for but very minute quantities of colouring matters are employed. Annotto is the commonest dye used to impart a yellow colour to milk, cream, and butter. It is prepared from the seeds of a tropical American tree (Bixa orellana). It is detected by allowing the milk to stand in a tall glass, when the lower stratum will contain the pigment associated with the casein instead of remaining colourless, while the naturally yellower cream floats on top (Hird). The cow's food may sometimes colour the milk red or pink, and it may be so stained by traces of blood, in which latter case the lower layers are of deeper hue than the upper.

3. Various substances are added to milk and its products - condensed milk, butter, cheese, and koumiss - to keep them from souring. These are usually sodium bicarbonate, borax, or boric acid. Salicylic acid and formaldehyde are less often used. In small quantities they do not affect its taste or hurt the digestion of adults, but they may be injurious and even fatal to infants, and their use should never be tolerated. Salicylic acid is sometimes put into beer for a similar purpose, although this is prohibited by law. The presence of boric acid is detected by mixing one part of milk with two parts each of hydrochloric acid and saturated turmeric tincture. After drying on a water bath and adding a little ammonia, a dark-blue colour appears which changes to green.

4. Both milk and cream, after dilution with water, are sometimes thickened again with such substances as flour, arrowroot, farina, whiting, chalk, tragacanth, or carbonate of magnesia, which disguise the natural blueness of the attenuated fluid. Effervescence in milk produced by addition of a strong mineral acid shows the presence of carbonates. Sugar is added to raise the specific gravity of diluted skimmed milk.

Milk is contaminated or rendered unlit for use by - 1. Improper or poisonous foods eaten by the animal. 2. Poor condition of the animal, due to nursing, worrying, etc. 3. Contamination by disease germs from the cow. 4. Contamination by extraneous disease germs. 5. Souring and decomposition. 6. Absorption of bad odours.