When milk is allowed to remain exposed to the air in a cool place, the "bonny clobber," or sour milk, is produced in this wise. Some clot or cream collects on the top, and a mycelium, or membrane of delicate fungi, also forms on the uppermost surface of the milk, which now acquires an acidulous taste, and is sometimes a little effervescent, whilst curdling in the same way as it would by rennet; though this present curdling is caused by lactic acid, developed from the sugar of milk by a living low fungus and ferment termed the "bacillus of sour milk." Although generally rejected, yet sour milk is an agreeable, nutritious fluid, easily digested. It should be well stirred before use, and perhaps have some cream added; the taste can be heightened by white sugar and powdered cinnamon, with dice of bread, or bread crumb, to give it body. Lactic acid, when neutralized with an alkali, such as carbonate of soda, makes a useful hypnotic for sleepless patients with nervous indigestion. To a tumblerful of curds, and whey, add a tea-spoonful of carbonate of soda in powder, or enough to neutralize the acid. Sweeten to the taste, and add a grating of nutmeg, if liked. This is best when taken hot at bedtime.

It is likewise helpful against the sleeplessness of Bright's disease (of the kidneys), or albuminuria. Again, a tumblerful of new milk with a table-spoonful of sound old ram mixed in it, and sweetening the draught if wished, will often answer the sustaining purpose of cod-liver oil as an early morning dose, whilst far more palatable and stomachic. Still nicer food is the delicate sweetmeat which is called "junket," (being actually a cream cheese which bears this name, because brought in or served on rushes, giunca, a rush), as curds mixed with cream, sweetened, and spiced, exquisite food for the little people. Thus Milton relates in his beautiful L' Allegro: -

"With stories told of many a feat How faery Mab the junkets eat".

A mixture of milk and eggs, especially if sugar is added, inevitably curdles if heated to a high temperature, when the clear liquid which escapes is whey, and not merely water. This liquid may be given as a nutritious and safe drink in typhoid fever, as well as milk diluted with barley water, or butter milk, or the eau albumineuse (unboiled white of egg mixed with cold water). During convalescence the best beverage is toast-water.

In new milk, by churning, the oil globules which have already risen to the surface through standing (and which consist mainly of fat, mixed with some curd, and retaining some whey) unite to form Butter; whilst the liquid residue is butter-milk, which is essentially a solution of milk sugar, with the mineral salts, principally phosphates, retained therein, also some wandering butter elements. "Those persons," says Professor Koch admonitorily, "who are nervous lest the milk they drink should contain elements of typhoid fever, or other mischief, should remember that these bacilli may just as probably lurk in the butter, (which cannot be boiled as a preventive)." Freshly made dairy butter, uncooked, may be eaten freely against chronic constipation, especially by persons in years, and by thin persons of active habits. The chief point in which butter-milk differs from new milk is thus shown to be its poverty of fat, whilst otherwise it is nutritious, digestible, and refreshing, though to some patients the taste is disagreeable. Butter-milk is used largely in Holland for the healthy, as well as for weakly invalids. It differs totally from human milk, yet frequently proves curative to infants when this latter fails.

As obtained from the dairy, it should be a sour fluid full of finely suspended flocculent curd. It must be boiled at once; but to prevent wholesale curdling, a level tablespoonful of ground rice, or flour, to each thirty-five ounces, should be previously mixed with it. The boiling should be done over a slow fire, in an emamelled pot, whilst constantly stirring it until it has boiled up two or three times; also two or three tablespoonfuls of sugar should be added to each litre (thirty-five ounces), using cane, or beet sugar for the purpose, but not milk sugar. Metal spoons are not to be employed in the process, else the lactic acid will act on them chemically. When prepared after this manner, the butter-milk food, for infants, has a yellowish colour, and a sourish taste, and it is not more curdled than it was before being boiled. In cases of slight diarrhoea, the motions change thereby immediately; they become less in amount, consistent, and homogeneous; from being sour, their reaction becomes alkaline. The lactic acid, though present only in quite small quantity, produces an anti-fermentive action, which is of definite use. Moreover, ammonia is generated by the bacillus of butter-milk, and is helpful.

For such curative objects a reliable butter-milk can be made at home, the necessary small outlay for a hand-churn being then incurred. New milk must be left to ripen for twenty-four hours before it is churned, a little sour milk being previously added, so as to turn it. But it will not answer to make use of sweet butter-milk, which does not contain any suspended curd. Infants under four weeks of age will need some cream in addition to the butter-milk. Soured milk will prevent or arrest noxious fermentative changes of the food when reaching the large bowels. Lactic acid bacteria, which become present in considerable numbers, are hostile to the growth of the putrefactive bacteria.

For making sour milk soup: half a pint of sour milk is mixed with a small dessertspoonful of fine flour, which must be whipped into it; thin with cold water, and add half a pint of scalding water, boiling the while, and stirring well all the time. If the soup becomes too thick, add hot water in order to thin it. Before dishing up, boil a little powdered or bruised caraway seeds. Add small squares of toast neatly to the soup, and pour the decoction over it. When stomach disorder is present, the milk should be skimmed.