The principal virtue of grapes is contained in their sugar, which differs chemically from cane sugar, and passes more quickly into the bodily system, with speedy combustion as a food. The amount of this grape sugar varies according to the greater or less warmth of the climate in which the different grapes are grown. Tokay grapes are the sweetest; next are those of Southern France; then of Moselle, Bohemia, and Heidelberg, whilst the fruit of the vine in Spain, Italy, and Madeira, is not so well adapted for curative purposes. The grape fruit consists of pulp, stones, and skin. Within the pulp is contained the grape sugar, together with a certain quantity of fruit sugar, which is identical with cane sugar. The grape sugar warms (and fattens) speedily, being taken up straightway into the circulation without waiting to be changed slowly by the saliva; therefore this grape sugar serves to repair the waste of burning fever quickly, and to recruit the strength promptly when thereby consumed, grapes being at such times most grateful to the sufferer. But for the same reason they do not suit inflammatory, or gouty persons under ordinary circumstances, as well as foods sweetened with cane sugar which has to undergo slower chemical conversion into heat, and sustenance.

The chief ingredients of grape fruit are tannin, gum, bitartrate of potash, sulphate of potash, tartrate of lime, magnesia, alum, iron, chlorides of potassium, and sodium, tartaric, citric, racemic, and malic acids, some albumin, and azotized matters, with water. Grapes can supply but little nutritious matter for building up the solid structures of the body. Sweet grapes act as gentle laxatives, though the stones, if crushed are astringent. When taken in any quantity grapes act freely on the kidneys, and promote a flow of urine. The acids of the fruit are burnt off from their alkaline bases which remain behind, and help to neutralise such other gouty acids as they may encounter. But for a person in good health, and with sound digestion, grapes are excellent to furnish bodily warmth by their ready-made sugar, whilst the essential flavours of the aromatic fruit are cordial and refreshing.

Besides being useful against gout by its alkaline base, the bitartrate of Potash salt (cream of tartar) in grapes proves of remedial use for other affections. It is reputed to have been of signal curative service in, or against small-pox. Mr. Rose, of Dorking, first gave it in 1826, and with remarkable success, losing only one case in over a thousand, and that one complicated with whooping cough. Likewise the son, Mr. Charles Rose, later on gave the remedy against small-pox with equally satisfactory effects. In 1863 it was tried by the authorities of the Highgate Small-pox Hospital, with the result that they reported "it does not seem to do the least good." Yet during the same time it was being given at Dorking with a result that the mortality there among unvaccinated patients was only 11 per cent as against 47 in the Highgate Small-pox Hospital. The usual mixture was a quarter of an ounce of the bitartrate of potash to a pint of water, taking a wineglassful of this at frequent intervals. Later on the same remedy was supplied in the form of whey; half, or three-quarters of an ounce of cream of tartar being administered in half a pint of hot, almost boiling milk.

Mr. Rose came to the conclusion that this was essential in some cases, which the other form of the potash salt taken with Turkey Rhubarb, failed to benefit. "I am willing," wrote Edward Hume to the Liverpool Mercury, 1875, "to forfeit my reputation as a public man if the worst cases of small-pox cannot be cured in three days simply by the use of an ounce of cream of tartar dissolved in a pint of water, and drunk at intervals, when cold, as a certain never-failing remedy. It has cured thousands, never leaves a mark, never causes blindness, and avoids tedious lingering illness".

A limited diet of sweet grapes taken almost exclusively will sometimes work wonders for the feeble digestive powers of persons rendered weak and bloodless by over-work, or worry; to eat a grape each minute for an hour at a time, three or four times in the day, while taking very little else beyond dry bread, will often prove highly beneficial in such cases.

What is known as the Grape Cure is pursued in the Tyrol, Bavaria, on the banks of the Rhine, and elsewhere, with two objects in view according to the respective class of patients. Those weakly bloodless persons who are labouring under wasting disease, as in chronic catarrh of the lungs, requiring quick supplies of animal warmth, and adipose repair, gain special help from sweet ripe grapes, being ordered to take these almost exclusively, from three to six pounds a day. On the other hand, sufferers from torpid biliary functions, sluggish liver, or passive local congestions, benefit rather by taking the grapes not fully ripe, and not sweet, in moderate allowance; these latter grapes have a diuretic, and somewhat laxative effect, being eaten four or five times a day during the promenade; their reaction is alkaline, as aforesaid, therefore suitable for persons troubled with gravel, or acid gout.

For consumptive persons the ripe, luscious, sweet grapes, besides affording an exceptionally large quantity of warming, fattening glucose (i.e. grape sugar), specifically stimulate the lung substance to healthier action, and help it to throw off effete matters by thus encouraging the formation of new tissue. During the grape cure the fruit if taken on an empty stomach would act as a laxative: so that eating them does not begin until after breakfast. A hundred pounds weight of ripe, sweet grapes include within their pulp as much as thirteen pounds, full weight, of the purest glucose; and because of this abundance the said glucose has received, wherever obtained, the comprehensive name of grape sugar. Furthermore, the tartaric acid which sweet grapes contain plentifully is the basis of several so-called "blood-purifying" medicines. Neuralgia and the sleeplessness of debility may be materially improved by the sweet grape cure, because nutrition is thereby stimulated, and the needful quality of good blood restored.