FOOD. 



difficulty, and are apt to irritate and derange the 

 stomach and its functions. The fat of different 

 animals, however, differs in point of digestibility ; 

 and, what is more curious still, differs also accord- 

 ing to the part of the animal from which it is taken. 

 The digestibility of fat is much affected by modes 

 of cooking ; it is also greatly modified by the action 

 of vegetable acids and of common culinary salt. 



MINERAL FOOD. 



It has been already mentioned that man derives 

 little of his food directly from the mineral world, 

 and that the greater number of saline and earthy 

 substances indispensable to healthy aliment are 

 obtained indirectly from the vegetable and animal 

 products used by him as food. In fact, the only 

 substances obtained directly from the inorganic 

 kingdom, and consumed in large quantities, are 

 water and salt two substances as necessary to 

 existence as the air we breathe. The former, as 

 has been seen, enters largely into the composition 

 of every species of food ; it acts as a solvent and 

 diluent in all cases, and permeates everywhere the 

 tissues to whose subsistence and growth it admin- 

 isters. The latter, though usually taken as a 

 palatable condiment, is really essential to the 

 maintenance of health and vitality, and accord- 

 ingly appears as a constituent of the blood and 

 the tissues elaborated therefrom. 



Water, as consumed by man either as a bever- 

 age or as a constituent of his food, is generally in 

 a fresh state ; that is, contaminated as little as 

 possible by foreign ingredients. The nature and 

 constitution of water have been already detailed 

 under the heads CHEMISTRY and SUPPLY OF 

 WATER : all that is necessary to be here observed 

 is, that the supply for dietetic uses should be freed 

 from all mechanical impurities, and from all 

 chemical impregnations, which may render it 

 unpalatable, unsuitable for culinary purposes, or 

 detrimental to the system of the consumer. Abso- 

 lutely pure water is not found in nature, nor does 

 it indeed seem to be required by the animal 

 economy. It is only pure when distilled, and even 

 if wholesome in this state, it is not palatable until 

 it has reabsorbed more or less of the gaseous con- 

 stituents separated from it by the process of dis- 

 tillation. The purest waters always contain some 

 amount, however small, of common salt, lime, 

 magnesia, iron, and other saline matters ; as also 

 organic matter. It is only when these foreign 

 substances exist in large amount that water 

 becomes objectionable. 



Respecting the alimentary functions of water, 

 Dr Pereira, after remarking that it is the natural 

 drink of all adults, observes : ' It serves several 

 important purposes in the animal economy: 

 Firstly, It repairs the loss of the aqueous part 

 of the blood, caused by evaporation and the 

 action of the secreting and exhaling organs ; 

 Secondly, It is a solvent of various alimentary 

 substances, and therefore assists the stomach 

 in the act of digestion, though, if taken in very 

 large quantities, it may have an opposite effect, 

 by diluting the gastric juice ; Thirdly, It is prob- 

 ably a nutritive agent assisting in the forma- 

 tion of the solid parts of the body. It has not, 

 indeed, been actually demonstrated that water is 

 decomposed in the animal system ; or, in other 

 words, that it yields up its elements to assist in 



the formation of organised tissues ; yet Such an 

 occurrence is by no means improbable. It appears 

 from Liebig's observations, that the hydrogen of 

 vegetable tissues is derived from water ; and it is 

 not probable that the higher orders of the organ- 

 ised kingdom should be deficient in a power 

 possessed by the lower orders. Dr Prout appears 

 to admit the existence of this power, but thinks 

 that it is rarely exercised by animals. The water 

 which constitutes an essential part of the blood 

 and of the living tissues, assists in several ways in 

 carrying on the vital processes. " In the blood," 

 says Prout, "the solid organised particles are trans- 

 ported from one place to another ; are arranged 

 in the place desired ; and are again finally removed 

 and expelled from the body, chiefly by the agency 

 of the water present." It is from water that the 

 tissues derive their properties of extensibility and 

 flexibility. Lastly, This fluid contributes to most 

 of the transformations which occur within the 

 body.' 



Salt. Referring the reader to our article on 

 USEFUL MINERALS for an account of the 

 modes of procuring and preparing this indispens- 

 able article, we shall here strictly confine our 

 remarks to its dietetic or alimentary importance. 

 This substance occurs in all vegetable and animal 

 organisms, and hence a certain quantity is present 

 in every article of food. In the human body, it 

 constitutes one-half by weight of the total salines 

 of the blood ; but it is unequally distributed 

 throughout the fluids and structures, very little 

 being present in the bones and teeth, and so 

 much as 13 parts in every icoo in the tears. 

 It is a remarkable fact that the proportion 

 in the blood does not seem to vary, for even after 

 large quantities have been taken, the excess which 

 for a time occurs in the blood, is quickly got rid 

 of by increased elimination ; while the proportion 

 in the blood cannot be diminished to any marked 

 extent by giving food from which salt has been 

 altogether removed. Salt has the property of 

 increasing tissue-changes, as judged by the aug- 

 mented excretion of urea and the elevation of 

 temperature ; under its influence, animals consume 

 more food, and become stronger and more active ; 

 but they do not, to a corresponding extent, gain in 

 weight, on account of the simultaneous increase of 

 tissue-change, and therefore of tissue-waste, which 

 occurs. In virtue of the chlorine it contains, salt 

 renders the gastric juice more abundant and more 

 icid, and in this way also it improves digestion. 

 [t appears to have a beneficial influence on various 

 other secretions, and markedly upon that of the 

 nammary glands, the quantity of milk secreted 

 during lactation being increased, and its quality 

 often improved. The necessity that a certain 

 quantity should be supplied with the food, is shewn 

 jy the instinct of animals, the promptings of 

 appetite, and the result of numerous observa- 

 tions in which the health has suffered from its 

 deprivation. The amount of salt consumed by 

 a full-grown person has been estimated at 16 

 bs. a year, or about 5 oz. a week, or threc- 

 "ourths of an ounce a day ; but of course this 

 estimate will vary exceedingly according to the 

 tastes and habits of individuals. 



All the varieties of salt, whether small-grained, 

 like the basket or table salt, or in large crystals, 

 like the bay andJisAery salts, consist essentially of 

 chloride of sodium, which is composed of 60 per 



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