1. The colour of milk is affected by various substances ingested by the cow; thus madder turns it saffron, rhubarb makes it red or yellow (Mosler), and it is coloured blue by some drugs. The colour is then uniform throughout the milk, and not superficial as in the case of the blue imparted by the growth of fungi, as described below. If milk be made blue by addition of litmus the solution will be reddened by action of such bacilli as the lactic-acid bacillus, the bacillus typhosus, and the streptococcus pyogenes.

Cows fed on brewers' swill or refuse of glucose factories, or cows allowed to eat decaying autumn leaves, garlic, certain injurious meadow plants, or strong-smelling plants like cabbages, turnips, and onions, will give unhealthy, strong-smelling, bad-tasting, or deteriorated milk. Beets tend to make cow's milk acid. Cows should not be given unclean water to drink. Offensive odours and tastes imparted to milk through the cow, or by absorption from surrounding substances, are most intense while the milk is fresh; whereas if due to bacteriological influences, they only become apparent after some hours, and go on increasing. H. Weller found nearly i per cent of alcohol in milk from cows fed on distillery slops which contained 6 per cent of it.

2. The milk first secreted after calving (colostrum) contains more albumin than casein. It is viscid, turbid, frothy, yellow, slightly acid, and coagulates on boiling. In the cow colostrum has a sickly odour, and is purgative even when cooked. It remains so for about a month after parturition. Colostrum corpuscles may be easily detected by microscopic examination.

The bulling cow may be highly nervous during ovulation, and, as a reflex consequence, her milk becomes acid.

Cows which are teased and worried by dogs or otherwise, or made to exercise too much, give milk which sours easily and disagrees with infants. Underfeeding makes the animal give inferior, watery milk.

3. Cows suffering from certain diseases may transmit them through their milk to man, although this method of infection is less common than that through milk to which germs have had access in process of handling or transportation. The principal diseases which may be derived from the cow through her milk are tuberculosis and diphtheria.

The Massachusetts Society for Promoting Agriculture, in a report upon "The Infectiousness of Milk," confirms the fact that milk from cows having tubercular udders is infectious to man. (This statement is contradicted by Koch, who, in common with several other observers, has claimed that human and bovine tuberculosis are non-interchangeable.) Tubercle bacilli were also demonstrated in the milk of twelve out of thirty-six cows having tuberculosis, but whose udders were not affected. The inference is drawn from the report that 3 per cent of the milk furnished to Boston is infected. It is estimated that 6 per cent of all cows are tubercular.

Tubercular milk is of poorer quality, thinner, and bluer than normal milk.

Cases have been reported of infection of a nursing infant through a tubercular mother's milk, and calves are undoubtedly so infected through cows; but it must be remembered that the infant is much exposed to infection by its mother's sputum, and may inhale dried sputum from beneath her bedclothing or within the room.

However, the presence of tubercle bacilli has been indubitably demonstrated at least a half dozen times in human breast milk. Tabes mesenterica and tubercular meningitis in children have been caused by infected milk.

The foot-and-mouth disease of cattle is transmitted to man if the milk of cows so affected be drunk without boiling, which destroys the germs (Bollinger). This disease is transmitted even when the milk is diluted ten times or taken in coffee or tea, but adults must drink a good deal of it in order to become affected. Butter and cheese made from such milk also carry the infection (Schneider). The foot-and-mouth disease diminishes the quantity of milk given by the cow by one half, and the milk coagulates too quickly and has a yellowish colostrum-like appearance. If the disease be severe the milk separates into slimy coagulae and whey, and, on boiling, curdles in stringy masses. In other cases the taste is acid, and on standing twelve hours a yellow sediment is precipitated with a nauseous, rancid odour. The milk becomes infected from sores upon the nipples.

4. 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.

Soxhlet says that if mother's milk were sold like cow's milk after as much careless handling, it would produce as much disease. Calves have been known to acquire diarrhoea when fed milk from unclean pails, and the animals were cured by allowing them to suck the very cows that had been milked into the pails. According to Sedgwick, milk may contain a million bacteria to the cubic centimetre after its journey from cow to table.

Cow's milk is too often tainted with excrementitious matter from the stable or cow yard. The cows lie upon foul bedding, or bespatter their udders continually in barnyard filth. Soxhlet has said that in judging the quality of milk one should consider "not so much what the cow fed on, as rather what kind of cow dung the milk contains".

The following data from the report of a commission of disinterested physicians upon the "Walker-Gordon guaranteed milk " from the dairy at Plainsboro, N. J., exhibit an ideal system of cleanliness. 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. Pine shavings are used for bedding. The milk is drawn into pails with small openings, to 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.