a well-known fluid, prepared by nature in the breasts of women, and the udders of other animals, for the nourishment of their young.

According to Dr Cullen, milk is a connecting and intermediate substance between animals and vegetables. It seems to be immediately secreted from the chylus, both being a white liquor of the same consistence; it is most copiously secreted after meals, and is of an accecent nature. In most animals which live on vegetables the milk is accecent; and it is uncertain whether it is not so likewise in carnivorous animals. But, whatever there be in this, it is certain that the milk of all animals which live on vegetables is aceseent. Milk being derived from the chyle, we thence infer its vegetable nature; for in those who live on both promiscuously, a greater quantity of milk is obtained, and more quickly, from the vegetable than from the animal food. Milk, however, is not purely vegetable, though we have a vegetable liquor which resembles it in taste, consistence, colour, aceseency, and the separability of the oily part, viz. an emulsion of the mucos olescer and farinaceous substances. But these want the coagulable part of milk, which seems to be of an animal nature, approaching to that of the coagulable lymph of the blood. Milk, then, appears to be of an intermediate nature between chyle taken up from the intestines and the fully elaborated animal fluid.

Its contents are of three kinds. First, there is an oily part, which, whatever may be said concerning the origin of other oils in the body, is certainly immediately derived from the oil of the vegetables taken into the stomach; for with these it agrees very exactly in its nature, and would do so entirely, if we could separate it fully from the coagulable part. Another mark of their agreement is the separability, which proves that the mixture has been lately attempted, but not fully performed. Secondly, besides this oily, there is a proper coagulable part. And, thirdly, much water accompanies both, in which there is dissolved a salino-saccharine substance. These three can be got separate in cheese, butter, and whey; but never perfectly so, a part of each being always blended with every other part.

Nothing is more common, from what has been said of its immediate nature, than to suppose that it requires no assimilation; and hence has been deduced the reason of its exhibition in the most weakly state of the human body. But wherever we can examine milk, we always find that it coagulates, suffers a decomposition, and becomes aceseent. Again, infants, who feed entirely on milk, are always troubled with eructations, which every body observes are not of the same quality with the food taken; and therefore it appears, that, like all other food, milk turns naturally aceseent in the stomach, and only enters the chyle and blood in consequence of a new recomposition. It approaches then to the nature of vegetable aliment, but is not capable of its noxious vinous fermentation, and therefore has an advantage over it. Neither, from this quality, is it like animal food, heating in the stomach, and productive of fever, though at the same time, from its quantity of coagulable matter, it is more nourishing than vegetables.

Milk is the food most universally suited to all ages and states of the body; but it seems chiefly designed by nature as the food of infants. When animals are in the foetal state, their solids are a perfect jelly, incapable of an assimilatory power. In such state nature has perfectly assimilated food, as the albumen ori in the oviparous, and in the viviparous animals certainly somewhat of the same kind, as it was necessary that the vessels should be filled with such a fluid as would make way for an after assimilation. When the infant has attained a considerable degree of firmness, as when it is separated from the mother, such a degree of weakness still remains as makes somewhat of the same indication necessary; it behoves the infant to have an alkaline food ready prepared, and, at the same time, its noxious tendency to be avoided. Milk then is given, which is alkaline, and, at the same time, has a sufficient quantity of acidity to correct the alkaline quality. As the body advances in growth, and the alkaline tendency is greater, the animal, to obviate that tendency, is led to take vegetable food, as more suited to its strength of assimilation.

Dr Cullen observes, that milk is suited to almost all temperaments; and it is so to stomachs disposed to aceseency, more than those substances which have undergone the vinous fermentation; nay, it even cures the heartburn, checks vinous fermentation, and precipitates the lees, when, by renewal of fermentation, the wine happens to be fouled. It, therefore, very properly accompanies a great deal of vegetable aliment; although sometimes its aceseency is troublesome, either from the large portion taken in, or from the degree of it; for, according to certain unaccountable circumstances, different acids are formed in the stomach in different states of the body, as in a healthy body a mild one, and in the hypochondriac disease one of a very acid quality. When the acidity of milk is carried to a great degree, it may prove remarkably refrigerant, and occasion cold crudities, and the recurrence of intermittent fevers. To take the common notion of its passing unchanged into the blood, it can undergo no solution. But if we admit its coagulum in the stomach, then it may be reckoned amongst soluble or insoluble foods, according as that coagulum is more or less tenacious. Formerly rennet, which is employed to coagulate milk, was thought an acid; but, from late observations, it appears, that, if it be an acid, it is very different from other acids, and that its coagulum is stronger than that produced by acids. It has been imagined that a rennet, which causes coagulation of milk, is to be found in the stomachs of all animals; but according to Dr Cullen, the coagulation of milk seems to be owing to a weak acid in the stomach, the relics of vegetable food, inducing, in healthy persons, a weak and soluble coagulum; but in different stomachs this may be very different, in some becoming heavy and less soluble food, and may even be evacuated in a coagulated undissolved state both by stomach and stool.

As milk is aceseent, it may be rendered purgative by mixture with the bile. Some examples of this have been remarked. But it is more commonly reckoned amongst those foods which occasion costiveness.

Hoffman, in his experiments upon milk, ascertained that all kinds of it contained much water; and when this was dissipated, he found the residuum very different in their solubility. But we must not thence conclude, that the same insolubility takes place in the stomach; for extracts made from vegetables with water are often very insoluble substances, and hardly diffusible through water itself. In Hoffman's extracts of milk, therefore, somewhat of the same kind might have appeared; and these substances, which in their natural state were not so, might appear very insoluble. However, we may allow that milk is always somehow insoluble in the intestines, as it is of a drying nature, and as cheese is very costive. And this effect shows that milk is always coagulated in the stomach; for if it remained fluid, no faces would be produced, whereas sometimes very hard ones are observed. In the blood-vessels it may, from its animal nature, be considered as nutritious; but when we consider its vegetable contents, and aceseency in the prime vis, we find that, like animal food, it does not excite that degree of fever in the time of digestion, and that from its aceseency it will resist putrefaction. Hence its use in hectic fevers, which, whatever be their cause, appear only to be exacerbations of natural feverish paroxysms, which occur twice every day, commonly after meals, and at night. To obviate these, therefore, we give such an aliment as produces the least exacerbation of these fevers; and of this nature is milk, on account of its aceseent vegetable nature.

There also appears something peculiar to milk, which requires only a small exertion of the animal powers in order to its assimilation; and besides, in hectic complaints, there is wanted an oily, bland food, approaching to the animal nature; so that upon all, these accounts milk is a diet peculiarly adapted to them, and, in general, to most convalescents, and to those of inflammatory temperaments.

The milks of women, mares, and asses, in a great measure agree in their qualities, being very dilute, having little solid contents, and these, when evaporated to dryness, being very soluble, and containing much saccharine matter of a very ready acescency, and their coagulum being tender and easily broken down. From this view they have less oil, and seem to have less coagulable matter than the rest.

The milks of cows, sheep, and goats, agree in possessing qualities opposite to those just mentioned; but here there is somewhat more of gradation. Cow's milk comes nearest to the former. Goat's milk is less fluid, less sweet, less glutinous, and has the largest proportion of insoluble part after coagulation, and indeed the largest proportion of coagulable part; its oily and coagulable parts are not spontaneously separable, and it never throws out a cream, or admits of butter to be readily extracted from it. Hence the virtues of these milks are obvious, being more nourishing, though at the same time less easily soluble in weak stomachs, than the three kinds above mentioned, less acetic, and more rarely laxative, and peculiarly fitted for the diet of convalescents without fever. The other kinds again are less nourishing, more soluble, more laxative, from being more acetic, and adapted to convalescents with fever.

These qualities in particular milks are considerably diversified by different circumstances. First, different animals living on the same diet give a considerably different milk; for there seems to be something in the constitution, abstracting from the aliment, which constitutes a considerable diversity of milk, not only in the same species of animals, but also in the same animal, at different ages, and at different intervals after delivery. This also applies to the choice of nurses. Secondly, milk follows the nature of the aliment more than any other juice in the human body, being more or less fluid and dilute, and more or less solid and nourishing, in proportion as these qualities are more or less in the aliment. The nature of the aliment differs according to its time of growth, old grass being always found more nourishing than young. Aliment, too, is always varied according to the season, as that is warm or dry, moist or cloudy.

The milk of each particular kind of animal is fitter for particular purposes, when fed on proper food. Thus the cow delights in the succulent herbage of the valley; if the sheep be fed there he certainly rots, but on the higher and more dry side of the mountain he feeds pleasantly and healthily; whilst the goat never stops near the bottom, but ascends to the craggy summit. The milks of these animals, therefore, are always best upon their proper soil; and that of goats is best in a mountainous country. In a dissertation of Linnaeus, we find many observations concerning the diversity of plants on which each animal chuses to feed. All the Swedish plants which could be collected together were presented alternately to domestic animals, and then it appeared that the goat lived on the greatest variety, and even on many which were poisonous to the rest; and that the cow chose the first succulent shoots of the plant, and neglected the fructification, which was preferred by the goat. Hence may be deduced rules concerning the pasturage of different animals. Thus farmers find, that, in a pasture which was only fit to feed a certain number of sheep, an equal number of goats may be introduced, whilst the sheep are no less nourished than before.

It is not easy to assign the difference between milk fresh drawn and that detained in the open air for some time; but certainly there is some material one, otherwise nature would not have directed infants universally to sucking; and indeed it seems better fitted for digestion and nourishment than the other. Physicians have supposed that this depended on the evaporation of some spirit; but Linnaeus cannot conceive anything except common water here; and besides, these volatile parts can hardly be nutritious. A more plausible account seems deducible from mixture.

Milk newly drawn and recently mixed is exposed to spontaneous separation, a circumstance hurtful to digestion; none of the parts being, by themselves, so easily assimilated as when they are all taken together. Hence milk newly drawn is more intimately blended, and therefore is most proper to weak persons and to infants.

Another difference in the use of milk exposed for some time to the air, is taking it boiled or unboiled. Physicians have generally recommended the former; but the reason is not easily assigned. Perhaps it may be that milk kept for some time exposed to the air has gone so far towards a spontaneous separation; whereas the heat thoroughly blends the whole, and hence its resolution is not so easy in the stomach; and thus boiled milk is more costly than raw, and gives more feces. Again, when milk is boiled, a considerable quantity of air is detached, as appears from the froth on the surface; and air is the chief instrument of fermentation in bodies; so that after this process it is not liable to acescency. For these reasons it is proper for the robust and vigorous.

Another difference of milk is, according as it is fluid or coagulated. The coagulated is of two kinds; either as induced by rennet, or occasioned by the natural acescency of the milk. The former preparation makes the firmer and less easily soluble coagulum; but, when taken with the whey unseparated, it is less difficult of solution, though more so than any other coagulum in the same case. Many nations use the latter form, which is more easily soluble, but very acetic, and therefore, in point of solution, should be confined to the vigorous, or to those who live on alkaline food; in fact, the Laplanders use it as their chief acetic condiment. From the same considerations it is more cooling, and in its other effects it is similar to all other acetic vegetables.

Milk by evaporation yields a sweet saline matter, of which Dr Lewis gives the following proportions:

| Twelve Ounces of | Left of Dry Matter. | From which Water extracted a Sweet Saline Substance amounting to | |-----------------|---------------------|--------------------------------------------------| | Cow's milk... | 13 drachms. | 11 drachm. | | Goat's milk... | 12½ | 1½ | | Human milk... | 8 | 6 | | Ass's milk... | 8 | 6 |

The saline substance extracted from ass's milk was white, and as sweet as sugar; that of the others was brown or yellow, and considerably less sweet; that from cow's milk had the least sweetness of any.

On distilling twelve quarts of milk in balne marie, at least nine quarts of pure phlegm were obtained. The liquor which afterwards arose was acidulous, and by degrees grew sensibly more and more acid as the distillation was continued. After this came over a little spirit, and at last the empyreumatic oil. The remaining solid matter adhered to the bottom of the retort, in the form of elegant shining black flowers, which being calcined and eluted, yielded a portion of fixed alkaline salt.

Milk set in a warm place throws up to the surface an unctuous cream, from which, by agitation, the butter is easily separated. The addition of alkaline salts prevents this separation, not, as some have supposed, by absorbing an acid from the milk, but by virtue of their property of intimately uniting oily bodies with watery substances. Sugar, another intermedium between oils and water, has this effect in a greater degree, though that concrete is by no means alkaline, nor an absorbent of acids.

The sweet saccharine part of the milk remains dissolved in the whey after the separation of the curd or fromaginous matter, and may be collected from it in a white crys- Milk talline form, by boiling the whey till all remains of the curdled substance have fallen to the bottom; then filtering, evaporating it to a due consistence, setting it to shoot, and purifying the crystals by solution in water and a second crystallization. Much has been said of the medicinal virtues of this sugar of milk, but it does not seem to have any that are considerable. It is from cow's milk that it has been generally prepared; and the crystals obtained from this kind have but little sweetness.

When milk is suffered to coagulate spontaneously, the whey proves acid, and on standing grows more and more so until the putrefactive state commences. Sour whey is used as an acid, preferable to the directly vegetable or the mineral acids, in some of the chemical arts, for dissolving iron in order to stain linen and leather. In the bleaching of linen this acid was commonly made use of for dissolving and extracting the earthy particles left in the cloth by the alkaline salts and lime employed for cleansing and whitening it. Butter milk is preferred to plain sour milk or sour whey, being supposed to give the cloth a yellow colour. Dr Home, in his treatise on this subject, recommends water acidulated with sulphuric acid, in the proportion of about half an ounce, or at most three quarters of an ounce, to a gallon, as preferable in many respects to the acid of milk, or that of any directly vegetable substance. He observes, that the latter are often difficult to be procured, abound with oleaginous particles, and hasten to corruption, whilst the vitriolic acid is cheap and pure, without any tendency to putrefy; that milk takes five days to perform its office, whilst the vitriolic acid does it in as many hours, perhaps in as many minutes; and that this acid contributes also to whiten the cloth, and does not make it weaker though the cloth be kept in it for months. He states, that acids, as well as alkalies, extract an oily matter from the cloth, and lose their acidity and alkalinity. Since this treatise appeared, the use of sour milk has been entirely superseded by sulphuric acid.

It is observable, that ass's milk has a great tendency, on standing for a little time, to become thick and ropy. In the Breslau collection for the year 1720, there is a remarkable account of milk which had grown so thick and tenacious as to be drawn out into long strings.

New cow's milk, suffered to stand for some days on the leaves of butterwort or sun-dew, becomes uniformly thick, slippery, and coherent, and of an agreeable sweet taste, without any separation of its parts. Fresh milk added to this is thickened in the same manner, and this successively. In some parts of Sweden, milk is thus prepared for food.

New milk has a certain glutinous quality, in consequence of which it is used for joining broken stone ware. There is a far greater tenacity in cheese properly prepared.

Milk, when examined by a microscope, appears composed of numerous globules swimming in a transparent fluid. It boils in nearly the same degree of heat with common water; some sorts rather sooner, and others a little later. After boiling it has less tendency to become sour than in its natural state. It is coagulated by acids both mineral and vegetable, and by alkalies both fixed and volatile. The coagulum produced by acids falls to the bottom of the serum; that made by alkalies swims on the surface, commonly forming a thick coriaceous skin, especially with volatile alkalies. The serum, with alkalies, proves green or sanguineous; with acids, it differs little in appearance from the whey which separates spontaneously. The coagulum formed by acids is dissolved by alkalies, and that formed by alkalies is redissolved by acids; but the milk does not in either case resume its original properties. It is coagulated by most of the middle salts, the basis of which is an earth or a metallic body, as solution of alum, fixed sal-ammoniac, sugar of lead, green and blue vitriol; but not by the chalybeate or purging mineral waters, nor by the bit- the whole, then," says he, "I am persuaded it will be found that human milk, in a healthy state, contains little or no curd, and that the general opinion of its nature and properties is founded upon fallacious analogy and superficial observations made on the matter vomited by infants. We may presume, that the cream of women's milk, by its inferior specific gravity, will swim on the surface of the contents of the stomach; and being of an oily nature, that it will be of more difficult digestion than any other constituent part of milk. When an infant, then, sucks very plentifully, so as to over-distend the stomach, or labours under any weakness in the powers of digestion, it cannot appear unreasonable to suppose that the cream shall be first rejected by vomiting. Analogous to this, we know that adults affected with dyspepsia often bring up greasy fluids from the stomach by eructation, and this especially after eating fat meat. We have, in some instances, known this to blaze, when thrown into the fire, like spirit of wine or oil." Of this opinion he derives a confirmation from the observation, that curds vomited by infants of a few days old are yellow, whilst in the course of a fortnight or three weeks they become white. This he accounts for from the yellow colour of the cream thrown up by the milk of women during the first four or five days after delivery.

Mr Clarke likewise controverts the common opinion, that human milk is so prone to acidity that a great number of the diseases of children are to be accounted for from that cause. "Whoever," says he, "takes the trouble of attentively comparing human milk with that of ruminant animals, will soon find it to be much less prone to run into the accecent or acid process. I have very often exposed equal quantities of human and cow's milk in degrees of temperature varying from the common summer heat, or 65°, to 100°; and I have constantly found that cow's milk acquires a greater degree of acidity in thirty-six hours than the human did in many days. Cow's milk becomes offensive-ly putrid in four or five days; a change which healthy human milk, exposed in the same manner, will not undergo in many weeks, nay, sometimes in many months. I once kept a few ounces of a nurse's milk, delivered about six or seven days, for more than two years in a bottle moderately corked. It stood on the chimney-piece, and was frequently opened to be examined. At the end of this period, it showed evident marks of moderate acidity, whether examined by the taste, smell, or paper stained with vegetable blues or purples; the latter it changed to a florid red colour; whereas cow's milk kept a few days changed the colour of the same paper to a green, thereby clearly showing its putrescent tendency."

He next proceeds to consider the probability there is of milk becoming so frequently and strongly acid as to occasion most of the diseases of infants. He begins with an attempt to show that the phenomena commonly regarded as indications of acrimony are by no means certain. Curdled milk has already been shown to be no sign of acidity; and the other appearance, which has commonly been thought to be so certain, namely, green faeces, is, in the opinion of Mr Clarke, equally fallacious. In support of this he quotes a letter from Dr Sydenham to Dr Cole, in which the former says, that the green matter vomited by hysterical women is not any proof of acid humours being the cause of that disease, for sea-sick people do the same. The opinion that green faeces are an effect of acidity, proceeds upon the supposition that a mixture of bile with an acid produces a green colour; but it is found that the vegetable acid, which only can exist in the human body, is unable to produce this change of colour, though it can be effected by the strong mineral acids. As nothing equivalent to any of these acids can be supposed to exist in the bowels of infants, we must therefore adopt some other method of accounting for the green faeces frequently eva-

cuated by them. "Why should sour milk, granting its existence, give rise to them in infants, and not in adults? Have butter-milk, summer fruits of the most accecent kind, lemon or orange juice, always this effect in adults by their admixture with bile? This is a question which, I believe, cannot be answered in the affirmative."

Upon the whole, Mr Clarke considers the disease of acidity in the bowels, though so frequently mentioned, as by no means common. He owns, indeed, that it may sometimes occur in infancy as well as in adult age, from weakness of the stomach, costiveness, or improper food; and an indubitable evidence is afforded by faeces which stain the blue or purple colour of vegetables to a red, though nothing can be inferred with certainty from the colour or smell.

He then proceeds to state several reasons for his opinion, that the greater number of infantile diseases are not owing to acidity. First, women's milk, in a healthy state, contains little or no coagulable matter or curd. Secondly, it shows less tendency out of the body to become accecent than many other kinds of milk. Thirdly, the appearances which have been generally supposed to characterize its acidity do not afford satisfactory evidence of such a morbid cause. Fourthly, granting this to be the case, we have plenty of mild absorbents, capable of destroying all the acid which can be supposed to be generated in the bowels of an infant; yet many children are observed to die in consequence of these diseases, which are supposed to arise from acidity. Fifthly, though the milk of all ruminant animals is of a much more accecent nature than that of the human species, yet the young of these animals never suffer anything like the diseases attributed to acidity in infants. Sixthly, history informs us that whole nations use sour curdled milk as a considerable part of their food, without feeling any inconvenience; which, however, must have been the case if acidity in the stomach were productive of such deleterious effect as has been supposed. This reasoning appears to be very plausible, and nothing has as yet been offered to contradict it.

In a memoir by MM. Parmentier and Deyeux, members of the Royal College of Pharmacy in Paris, we have an account of a great number of experiments on the milk of asses, cows, goats, sheep, and mares, as well as women. The experiments on cow's milk were made with a view to determine whether any change was produced in the milk by the different kinds of food eaten by the animal. For this purpose some were fed with the leaves of maize, others with cabbage, others with small potatoes, and others with common grass. The milk of those fed with the maize was extremely sweet; that from the potatoes and common grass was much more serous and insipid; and that from the cabbages proved the most disagreeable of all. By distillation only eight ounces of a colourless fluid were obtained from as many pounds of each of these milks; that obtained from those which fed upon grass had an aromatic flavour; whilst a disagreeable one resulted from cabbage, and none at all from the potatoes and maize. This liquid became fetid in the space of a month, whatever substance the animal had been fed with, acquiring at the same time a viscidity, and becoming turbid; that from cabbage generally, but not always, becoming first putrid. All of them separated a filamentous matter, and became clear on being exposed to the heat of 25° of Reaumur's thermometer. In the residuum of distillation no difference whatever could be perceived. As the only difference therefore existing in cow's milk consists in the volatile part, our authors conclude that it is improper to boil milk either for common or medicinal purposes. They observed also that any sudden change of food, even from a worse to a better kind, was attended by a very remarkable diminution in the quantity of milk. The residuum of the distillation yielded, in a strong fire, a yellow oil and acid, a thick and black em- pyreumatic oil, a volatile alkali, and towards the end a quantity of inflammable air, and at last a coal remained containing some fixed alkali with muriatic acid.

On agitating in long bottles the cream from the milk of cows fed with different substances, all of them were formed into a kind of half-made butter, of which that formed from the milk of maize was white, firm, and insipid, that from potatoes was softer and more pinguedinous, and that from common grass was the best of all. Cabbage, as in other cases, gave a strong taste.

In the course of these experiments, an endeavour was made to determine whether butter is actually contained in the cream, or whether it be a chemical production of the operation of churning. They could not find any reason absolutely satisfactory on either side, but incline to the latter opinion; because when cream has been allowed to remain amongst the milk, and the whole curdled promiscuously, fat cheese, without any butter, is produced. The oily parts cannot be separated into butter either by acids or any other means than churning; even the artificial mixture of oil with the cream is insufficient for the purpose.

The serum of milk was reduced by filtration to a clear and pellucid liquor; and, by mixture with fixed alkali, it deposited a portion of fromaginous matter which had been dissolved in the whey. The sugar of milk was also found in this liquor.

In these experiments upon the milk of various animals, it was found that that of asses yielded by distillation an insipid liquor, and deposited a liquor similar to the lymph of cow's milk. This kind is coagulated by all the acids, but not into an uniform mass, exhibiting only the appearance of distinct floeculi. It affords but little cream, which is with difficulty converted into a soft butter, that soon becomes rancid. It has but a small quantity of saccharine particles, and these are often mixed with muriatic selenite and common salt. Goat's milk has a thick cream, which is agreeable to the taste; and the milk itself may be preserved longer in a sound state than any other species, the serum on its surface being naturally convertible into palatable cheese. It is easily made into firm butter, which does not soon become rancid, and has a good flavour. The butter-milk contains a large quantity of fromaginous matter, which readily coagulates; but it has still less saccharine matter than that of asses. Sheep's milk can scarcely be distinguished from that of a cow, and easily parts with its cream by standing. It is of a yellow colour, of an agreeable flavour, and yields a great proportion of butter; but this is not solid, and soon becomes rancid. Mare's milk is the most insipid and least nutritious of any, notwithstanding which it has been much recommended for weak and consumptive patients. It is probable that, in such cases, it proves efficacious by being more consonant than any other to the debilitated powers of digestion. It boils with a smaller fire than any other kind of milk, is easily coagulated, and the distilled water does not so soon change its nature. It has but a small quantity of fromaginous matter, and very few oily particles. The cream cannot be made into butter; and the whey contains about as much sugar as cow's or goat's milk.

It has also been remarked, that in order to augment the quantity, as well as to improve the quality, of the milk of animals, they should be well fed, their stalls kept clean, and their litter frequently renewed. They should be milked at stated hours, but not drained; and great attention should be paid to the breed, because inferior cattle are maintained at as great expense as the most valuable kinds. No change ought to be made in the food; although, if the milk be employed for medicinal purposes, it may be improved by a proper mixture of herbs.

In their experiments on women's milk, MM. Parmenier and Deycux differ somewhat from Mr Clarke. They first tried the milk of a woman who had been delivered four months before, and observed that, after the cream had been separated, the other part appeared of a more perfect white, and that it could not be coagulated either by vinegar or mineral acids, a circumstance which they attributed to a superabundance of serum. But they found that in proportion to the age of the milk it was more easily coagulable; and this was confirmed by experiments made upon the milk of twenty nurses. Its coagulability was not increased by heat. The cream, by agitation, formed a viscid unctuous matter, which, however, could not be changed into perfect butter; but they found it extremely difficult to determine the proportions of the various component parts of human milk, as it differs remarkably, not only in different subjects, but in the same subject at different times. In a nurse aged about thirty-two years, who was extremely subject to nervous affections, the milk was one day found almost quite colourless and transparent; in two hours afterwards, a second quantity drawn from the breast was viscid like the white of an egg; and in a short time it became whiter, but did not recover its natural colour until the evening. It was afterwards found that these changes were occasioned by the woman having in the mean time had some violent hysterical fits.

Milk of Vegetables. For the same reason that the milk of animals may be considered as a true animal emulsion, the liquors of vegetables may be termed vegetable milks. Accordingly emulsions made with almonds are commonly called milk of almonds. But besides this vegetable milk, which is in some measure artificial, many plants and trees contain naturally a large quantity of emulsive or milky juices. Of this kind are lettuce, spurge, fig-tree, and the tree which furnishes the elastic American resin. The milky juices obtained from all these vegetables derive their whiteness from an oily matter, mixed and undissolved in a watery or mucilaginous liquor. Most resinous gums are originally such milky juices, which afterwards become solid by the evaporation of their more fluid and volatile parts.

Milky Way, or Via Lactea. See Astronomy.