plant must be cut down, and the seeds beaten out, as is practised for other grain; but if it is not protected from birds, they will devour it as soon as it begins to ripen.

MILIUM (milium.) Grutum. In medicine, a very white and hard tubercle, in size and colour resembling a millet-seed. Its seat is immediately under the cuticle, so that when pressed it escapes, the contents appearing of an atheromatous nature.

MILIUM SOLIS. See LITHOSPERMUM. MILK (milch, Germ.; lait, Fr.) A fluid secreted by peculiar glands, and designed to nourish young animals in the early part of their life. It is of an opaque white colour, a mild saccharine taste, and a slightly aromatic smell. It is separated immediately from the blood in the breasts or udders of female animals. Man, quadrupeds, and cetaceous animals are the only creatures which afford milk. All other animals are destitute of the organs which secrete this fluid. Milk differs greatly in the several animals.

This fluid, the next in importance of all the animal liquids to blood, has been examined very largely by different chemists, and its analysis is curious and important. Scheele, Foureroy, and Vauquelin, Parmentier, Deyeux, and many others, have given particular attention to this subject, and from their united labours the following general account of its properties may be given.

Milk is a white opaque fluid, capable of moistening all substances that can be moistened by water: but its consistence is greater than that of water, and it is slightly unctuous: like water, it freezes when cooled down to about 30°; but Parmentier and Deyeux found that its freezing-point varies considerably in the milk of different cows, and even of the same cow at different times. Milk boils also when sufficiently heated; but the same variation takes place in the boiling-point of different milks, though it never deviates very far from the boiling-point of water. Milk is specifically heavier than water, and lighter than blood; but the precise degree cannot be ascertained, because almost every particular milk has a specific gravity peculiar to itself.

When milk is allowed to remain for some time at rest, there collects on its surface a thick unctuous yellowish-coloured substance, known by the name of cream. The cream appears sooner on milk in summer than in winter, evidently owing to the difference of temperature. In summer, about four days of repose are necessary before the whole of the cream collects on the surface of the liquid; but in winter it requires at least double the time.

After the cream it separated, the milk which remains is much thinner than before, and it has a blueish-white colour. If it is heated to the temperature of 1000, and a little rennet (which is water digested with the inner coat of a calf's stomach, and preserved with salt) is poured into it, coagulation ensues; and if the coagulum is broken, the milk very

soon separates into two substances; a solid white part known by the name of curd, and a fluid part called whey.

Thus we see that milk may be easily separated into three parts; namely, cream, curd, and whey.

1. Cream is of a yellow colour, and its consistence increases gradually by exposure to the atmosphere. In three or four days it becomes so thick that the vessel which contains it may be inverted without risking any loss. In eight or ten days more, its surface is covered over with mucors and byssi, and it has no longer the flavour of cream, but of very fat cheese. This is the process for making what in this country is called a cream-cheese.

Cream possesses many of the properties of an oil. It is specifically lighter than water; it has an unctuous feel; stains clothes precisely in the manner of oil; and if it is kept fluid, it contracts at last a taste which is very analogous to the rancidity of oils. When kept boiling for some time, a little oil makes its appearance, and floats upon its surface. Cream is neither soluble in alcohol nor in oils. These properties are sufficient to shew us that it contains a quantity of oil; but this oil is combined with a part of the curd, and mixed with some serum; cream, then, is composed of a peculiar oil, curd, and serum. The oil may be easily obtained separate by agitating the cream for a considerable time. This process, known to every body, is called churning. After a certain time, the cream separates into two portions; one fluid, and resembling creamed milk; the other solid, and called butter.

Butter is of a yellow colour, possesses the properties of an oil, and mixes readily with other oily bodies. When heated to the temperature of 960, it melts, and becomes transparent; if it is kept for some time melted, some curd and water, or whey, separates from it, and it assumes exactly the appearance of oil. But this process deprives it in a great measure of its peculiar flavour.

When butter is kept for a certain time, it becomes rancid, owing in a good measure to the presence of these foreign ingredients; for if butter is well washed, and a great portion of these matters separated, it does not become rancid nearly so soon as when it is not treated in this manner. It was formerly supposed that this rancidity was owing to the developement of a peculiar acid; but Parmentier and Deyeux have shewn that no acid is present in rancid butter. When butter is distilled, there comes over water an acid, and an oil, at first fluid, but afterwards concrete. The carbonaceous residuum is but small.

Butter may be obtained by agitating cream newly taken from milk, or even by agitating milk newly drawn from the cow: but it is usual to allow cream to remain for some time before it is churned. Now cream, by standing, acquires a sour taste; butter, therefore, is commonly made from sour cream.

Fresh

cream requires at least four times as much churning before it yields its butter as sour cream does; consequently cream acquires, by being kept for some time, new properties, in consequence of which it is more easily converted into butter. When very sour cream is churned, every one who has paid the smallest attention must have perceived, that the buttermilk, after the churning, is not nearly so sour as the cream had been. The butter, in all cases, is perfectly sweet; consequently the acid which had been evolved has in a great measure disappeared during the process of churning. It has been ascertained, that cream may be churned, and but ter obtained, though the contact of atmospheric air should be excluded. On the other hand, it has been affirmed, that when cream is churned in contact with air, it absorbs a considerable quantity of it.

In all cases, there is a considerable extrication of gas during the churning of butter. From the phenomena, it can scarcely be doubted that this gas is carbonic acid. Dr. Young affirms, that during the churning there is an increase of temperature amounting to four degrees.

These facts shew that considerable chemical changes go on during the process of churning. The agitation keeps the different substances in contact, and enables them to act upon each other. The expulsion of carbonic acid accounts for the diminution of acidity after churning; while the other phenomena would lead us to suppose, that the cream, before it becomes butter, unites to a new portion of oxygen.

The affinity of the oil of cream for the other ingredients is such, that it never separates completely from them. Not only are card and whey always found in the cream, but some of this oil is constantly found in creamed milk and whey; for it has been ascertained by actual experiment, that butter may be obtained by churning whey. 27 Scotch pints of whey yield at an average about a pound of butter. This accounts for a fact well known to those who superintend dairies, that a good deal more butter may be obtained from the same quantity of milk, provided it is churned as drawn from the cow, than when the cream alone is collected and churned.

The buttermilk, as Parmentier and Deyeux ascertained by experiment, possesses precisely the properties of milk deprived of cream.

2. Curd, which may be separated from creamed milk by rennet, has many of the properties of coagulated albumen. It is white and solid; and when all the moisture is squeezed oat, it has a good deal of brittleness. It is insoluble in water; but pure alkalies and lime dissolve it readily, especially when assisted by heat; and when fixed alkali is used, a great quantity of ammonia is emitted during the soJution. The solution of curd in soda is of a red colour, at least if heat is employed; owing probably to the separation of charcoal from the

curd by the action of the alkali. Indeed, when a strong heat has been used, charcoal precipitates as the solution cools. The matter dissolved by the alkali may be separated from it by means of an acid; but it has lost all the properties of curd. It is of a black colour, melts like tallow by the application of heat, leaves oily stains on paper, and never acquires the consistence of curd. Hence it appears that curd, by the action of a fixed alkali, is decomposed, and converted into two new substances; ammonia, and oil, or rather fat.

Curd is soluble also in acids. If, over curd newly precipitated from milk, and not dried, there are poured eight parts of water, containing as much of any of the mineral acids as gives it a sensibly acid taste, the whole is dissolved after a little boiling. Acetic acid and lactic acid do not dissolve curd, when very much diluted; but these acids, when concentrated, dissolve it readily, and in considerable quantity. It is remarkable enough, that concentrated vegetable acids dissolve curd readily, but have very little action on it when they are very much diluted; whereas, the mineral acids dissolve it when much diluted; but when concentrated, have either very little effect on it, as sulphuric acid, or decompose it, as nitric acid. By means of this last acid, as Berthollet discovered, a quantity of azotic gas may be obtained from curd.

Curd, as is well known, is used in making cheese; and the cheese is the better the more it contains of cream, or of that oily matter which constitutes cream. It is well known to cheesemakers, that the goodness of it depends in a great measure on the manner of separating the whey from the curd. If the milk is much heated, the coagulum broken in pieces, and the whey forcibly separated, as is the practice in many parts of Scotland, the cheese is scarcely good for any thing; but the whey is delicious, especially the whey last squeezed out, and butter may be obtained from it in considerable quantity. This is a full proof that nearly the whole creamy part of the milk has been separated with the whey. Whereas, if the milk is not too much heated (about 100 degrees is sufficient), if the coagulum is allowed to remain unbroken, and the whey separated by very slow and gentle pressure, the cheese is excellent; but the whey is almost transparent, and nearly colourless.

Good cheese melts at a moderate heat; but bad cheese, when heated, dries, curls, and exhibits all the phenomena of burning horn. Hence it is evident, that good cheese contains a quantity of the peculiar oil which constitutes the distinguishing characteristic of cream; whence its flavour and smell.

This resemblance of curd and albumen makes it probable that the coagulation of milk and albumen depends upon the same cause. Heat, indeed, does not coagulate milk, because the curd in it is diluted with too large a quantity of water; but if milk is boiled in contact with air, a pellicle soon forms

on its surface, which has the properties of curd. If this pellicle is removed, another suc ceeds; and by continuing the boiling, the whole of the curdy matter may be separated from milk. When this pellicle is allowed to remain, it falls at last to the bottom of the vessel; where being exposed to a greater heat, it becomes brown, and communicates to milk that disagreeable taste which, in this country, is called a singed taste. It happens more readily, when milk is boiled along with rice, flour, &c.

If to boiling milk there is added as much of any neutral salt as it is capable of dissolying, or of sugar or of gum arabic, the milk coagulates, and the curd separates. Alcohol also coagulates milk; as do all acids, rennet, and the infusion of the flowers of artichoke and of the thistle. If milk is diluted with ten times its weight of water, it cannot be made to coagulate at all.

3. Whey, after being filtered to separate a quantity of curd which still continues to float through it, is a thin pellucid fluid, of a yellowish-green colour and pleasant sweetish taste, in which the flavour of milk may be distinguished. It always contains some curd: nearly the whole may be separated by keep ing the whey for some time boiling; a thick white scum gathers on the surface, which is known by the name of skim-curd. When this seum, which consists of the curdy part, is carefully separated, the whey, after being allowed to remain at rest for some hours, to give the remainder of the curd time to precipitate, is decanted off almost as colourless as water, and scarcely any of the peculiar taste of milk can be distinguished in it. If it is now slowly evaporated, it deposits at last a number of white-coloured crystals, which are sugar of milk. Towards the end of the evaporation, some crystals of muriat of potass and of muriat of soda make their appearance. According to Scheele, it contains also a little phosphat of lime, which indeed may be precipitated by ammonia.

After the salts have been obtained from whey, what remains concretes into a jelly on cooling. Hence it follows, that whey also contains gelatine. Whey, then, is composed of water, sugar of milk, gelatine, muriat of potass, and phosphat of lime. The other salts which are sometimes found in it are only accidentally present.

If whey be allowed to remain for some time, it becomes sour, owing to the formation of a peculiar acid known by the name of lactic acid. It is to this property of whey that we are to ascribe the acidity which milk contracts; for neither curd nor cream, perfectly freed from serum, seems susceptible of acquiring acid properties. Hence the reason also that milk, after it becomes sour, always coagulates. Boiled milk has the property of continuing longer sweet; but it is singular enough that it runs sooner to putrefaction than ordinary milk.

The acid of milk differs considerably from

the acetic: yet vinegar may be obtained from milk by a very simple process. If to somewhat more than 8lbs. troy of milk six spoonfuls of alcohol are added, and the mixture well corked is exposed to a heat sufficient to support fermentation, provided attention is paid to allow the carbonic acid gas to escape from time to time, the whey, in about a month, will be found converted into vinegar.

Milk is almost the only animal substance which may be made to undergo the vinous fermentation, and to afford a liquor resembling wine or beer, from which alcohol may be separated by distillation. This singular fact seems to have been first discovered by the Tartars; they obtain all their spirituous liquors from mare's milk. It has been ascertained, that milk is incapable of being converted into wine till it has become sour; after this nothing is necessary but to place it in the proper temperature; the fermentation begins of its own accord, and continues till the formation of wine is completed. Scheele had shewed that milk was capable of fermenting, and that a great quantity of carbonic acid gas was extricated from it during this fermentation; but he did not suspect that the result of this fermentation was the formation of an intoxicating liquor similar to wine. The Tartars call the vinous liquid which they prepare kumiss. A very exact account of its preparation and medical uses has been published by Dr. Grieve. See the article KUMISS.

When milk is distilled by the heat of a water-bath, there comes over water having the peculiar odour of milk: which putrefies; and consequently contains, besides mere water, some of the other constituent parts of milk. After some time the milk coagulates, as always happens when hot albumen acquires a certain degree of concentration. There remains behind a thick unctuous yellowishwhite substance, to which Hoffman gave the name of franchippan. This substance, when the fire is increased, yields at first a transparent liquid, which becomes gradually more coloured; some very fluid oil comes over, then ammonia, an acid, and at last a very thick black oil. Towards the end of the process carbureted hydrogen gas is disengaged. There remains in the retort a coal which contains carbonat of potass, muriat of potass, and phosphat of lime; and sometimes magnesia, iron, and muriat of soda.

Thus we see that cow's milk is composed of the following ingredients:

Human Milk.-This is secreted by the glandular fabric of the breast in women. The secretory organ is constituted by the great conglomerate glands situated in the fat of both breasts, above the musculus pectoralis major. From each acinus composing a mammary gland, there arises a radicle of a lactiferous or galactiferous duct. All these canals gradually converging, are terminated without anastomosis in the papillae of the breasts by many orifices, which upon pressure pour forth milk. The smell of fresh drawn milk is peculiar, animal, fatuous, and not disagreeable. Its taste sweetish, soft, bland, agreeable. The specific gravity is greater than water, but lighter than blood; hence it swims on it. Its colour is white and opaque. In consistence it is oily and aqueous. A drop put on the nail flows slowly down, if the milk be good.

Time of Secretion.-The milk most frequent ly begins to be secreted in the last months of pregnancy; but on the third day after delivery, a serous milk called colostrum is separated: and at length pure milk is secreted very copiously into the breasts, that from its abundance, often spontaneously drops from the nipples.

If the secretion of milk be daily promoted by suckling an infant, it often continues many years, unless a fresh pregnancy supervene. The quantity usually secreted within twentyfour hours, by nurses, is various, according as the nourishment may be more or less chylous. It appears that not more than two pounds of milk are obtained from five or six pounds of meat. But there have been known nurses, who have given from their breasts two, or even more than three pounds, in addition to that which their child has sucked. That the origin of the milk is derived from chyle carried with the blood of the mammary arteries into the glandular fabric of the breasts, is evident from its more copious secretion a little after meals; its diminished secretion from fasting; from the smell and taste of food or medicines in the secreted milk and lastly, from its spontaneous acescence; for humours perfectly animal become putrid.

The milk of a woman differs: 1. In respect of food. The milk of a woman who suckles, living upon vegeto-animal food, never acesces nor coagulates spontaneously, although exposed for many weeks to the heat of a furnace. But it evaporates gradually in an open vessel, and the last drop continues thin, sweet, and bland, The reason appears to be, that the caseous and cremoraceous parts cohere together by means of the sugar, more intimately than in the milk of animals, and do not so easily separate; hence its acescence is prevented. It does acesce, if mixed or boiled with vinegar, juice of lemons, cremor tartar, spirit of vitriol, or with the human stomach. It is coagulated with the acid of salt or nitre, and by the acid gastric juice of the infant; for infants often vomit up the coagulated milk of the nurse. The milk of a sucking woman who lives upon vegetable food only, like cow's milk, easily and of its own

accord acesces, and is acted upon by all coagulating substances like the milk of animals.2. In respect of the time of digestion. During the first hours of digestion the chyle is crude, and the milk less subacted; but towards the twelfth hour after eating, the chyle is changed into blood, and then the milk becomes yellowish and nauseous, and is spit out by the infant. Hence the best time for giving suck is about the fourth or fifth hour after meals.-3. In re spect of the time after delivery. The milk secreted immediately after delivery is serous, purges the bowels of the infant, and is called colostrum. But in the following days it be comes thicker and more pure, and the longer a nurse suckles, the thicker the milk is secreted; thus new-born infants cannot retain the milk of a nurse who has given suck for a twelvemonth, on account of its spissitude.-4. In respect of food or medicines. Thus if a nurse eat garlic, the milk becomes highly impregnated with its odour, and is disagreeable. If she indulge too freely in the use of wine or beer, the infant becomes ill. From giving a purging medicine to a nurse, the child also is purged and lastly, children affected with tormina of the bowels, arising from acids, are often cured by giving the nurse animal food.5. In respect of the affections of the mind. There are frequent examples of infants being seized with convulsions from sucking mothers irritated by anger. An infant of one year old, while he sucked milk from his enraged mother, on a sudden was seized with a fatal hæmorrhage and died. Infants at the breast in a short time pine away, if the nurse be afflicted with grievous care; and there are also infants who after every coition of the mother, or even if she menstruate, are taken ill.

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The use of the mother's milk is, 1. It affords the native aliment to the new-born infant, in which respect milk differs little from chyle. Those children are the strongest who are nourished the longest by the mother's milk. 2. The colostrum should not be rejected; for it relaxes the bowels, which in new-born infants ought to be open, to clear their intestines of the meconium. 3. Lactation defends the mother from a dangerous reflux of the milk into the blood, whence lacteal metastasis and leucorrhæa are so frequent in lying-in women who do not give suck. The motion of the milk also being hastened through the breast by the sucking of the child, prevents the very common induration of the breast, which arises in consequence of the milk being stagnated. 4. Men may live upon milk, unless they have been accustomed to the drinking of wine. For all nations, the Japanese alone excepted, use milk, and many live upon it alone. Lastly, for many diseases, especially the gout, scurvy, dy sentery, and phthiscal tabes of the different viscera, a milk diet is reckoned amongst the most efficacious remedies.

Asses' milk. This more nearly resembles human milk than any other. The cream is in small quantity: by agitation it gives a butter,