We have so far discussed the nutritive values of various foods; we shall now consider a class of foods in which the nutritive value is not the principal factor, but which are endowed with another peculiarity, namely : the refreshing properties of their juices. Providence has so arranged that just in the very hottest regions the most juicy fruits are to be found, so that the faint and thirsty man may be refreshed by them. This is not only accomplished by the quantity of water contained in such fruits, but also by a series of organic acids and important salts which are represented in considerable amounts in their juices. Some fruits are richer in iron and lime than are many other foods. The refreshing action is not only the result of the organic acids above mentioned, but is also induced by the large quantities of sugar contained in some fruits. This makes them valuable foods, and dried figs, dates, and bananas are so nutritious because of the sugar contained in them that some vegetarians live only upon fruits. Such a diet might, it is true, contain much more of the carbohydrates than is required for our daily ration, but a corresponding amount of the important nutrient substance, albumin, is missing, without which we cannot really thrive. The majority of fruits are very poor in albumin, and the quantity which is contained in them, as is also the case with the carbohydrates, cannot be well assimilated by our digestive organs, since the cellulose prevents the action of the digestive fluids. It is for this reason that some kinds of fruits are more digestible and better assimilated when they are cooked, since this process softens the cellulose. Unfortunately, however, considerable of the important nutrient salts are thus lost, much being contained in the skins of the fruits. We have here an analogy to the cereals, in which important salts are also lost by the removal of the outer portions. When in peeling fruits the upper layer of the fruit-meat is removed, flavoring substances are lost, in which just this portion of the fruit is very rich. True vegetarians, there-fore, and especially those living upon fruits alone, do not pare the fruits, and eat them raw. Since for such a diet a very healthy stomach is required, it can certainly not become a general habit. As we have already said in referring to a vegetable diet, a diet of this sort followed for a time may undoubtedly present great advantages, but to adopt it for a permanent use would give rise to great dangers for our health. On the other hand, the taking of a large quantity of easily digested fruit during several weeks, as a fruit or grape cure, may be very beneficial, since, as we shall show later on, it has a very favorable influence upon many conditions. A healthy person should always eat fruit in the raw state. For those who are ill or delicate, and particularly for those whose stomachs and intestines do not properly carry on their functions, the fruit should be stewed. When cooked, fruit, to be sure, loses not only a portion of the nutrient salts, but also of the carbohydrates, as a considerable part o,f the sugar is cooked out into the sauce. When diabetics eat stewed fruit they should never eat the juice, which contains much sugar. In the cases in which the juice is eaten, the carbohydrates which have been lost are again replaced. The rather large quantity of acid has, like the fiber content, a very unfavorable action upon the digestion, particularly when the fruit is unripe; consequently only such as is fully ripe should be eaten.
Negligence in this respect, particularly in the case of children, will give rise to serious intestinal disturbances. When the fruit ripens, the quantity of acid and cellulose is materially lessened. In some fruits which are gathered in an unripe condition and kept for some time, the sugar content is increased owing to a ferment contained in them; thus, very ripe bananas contain a great deal o,f sugar. In dried fruits such as bananas, figs, dates, etc., the sugar content is sometimes exceedingly great.
The fine aroma, the perfume of the fruit, is caused by ethereal oils which are principally contained in the cells of the skins. Just as rice, as has already been explained, loses its taste when transported without the skin, so apples and pears lose all of their delicate aroma and flavor when they are left for a time without their skins. The organic acids are principally malic, tartaric, citric, and tannic. When too much of these is present the digestion suffers, and when too little the taste suffers. A small quantity of acid in some fruits may have a stimulating effect upon the appetite, thus starting the process of digestion.