m 



CHEMISTRY. 



[AtlilZ.VTAKY PRINCIPLES. 



period. M science has endeavoured to prove; yet we 

 know tht all nutriment psisns only through the body. 

 By this, however, U not meant, that wh.it ha* be< 

 eeived by the mouth U immediately voided. On the 

 contrary, the different ingredients of which our d uiy 

 aliment it composed, become, in reality, essential con- 

 LmU of the body iUelf. We may, therefore, con- 

 aider that which U rejected to be only the dross which 

 has gradually became unfitted for the function* of life 



I!i ! .. .; !, :. :it LM ::. ' iv. 



The eeaenoe of the iugostod nutriment passes from the 

 digestive canal into the circulation, during which pro- 

 cess it U tranafortnwl into blood, and thus conveyed to 

 the Mveral organs of the body. There it undergoes 

 certain alterations, and returns at waste material into 

 the venous blood, from which certain organs secrete and 

 discharge it externally. 



2. The first change, therefore, which nutriment under- 

 goes, after leaving the alimentary canal, U sanguilic.i 

 The aggregate of the changes which solid ami liquid 

 foods undergo u]> to sanguification, is called digestion. 

 The various organs of the body which unitedly produce 

 these changes, are termed by physiologists, the digestive 

 on >;.- 



From the mouth, into which the saliva is poured by 

 a number of glands through corresponding ducts, the 

 aliment descends into the stomach. In the coats of the 

 stomach are glands, smaller and simpler in construction, 

 but far more numerous than the salivary glands, and 

 which, during the process of digestion, secrete a peculiar 

 fluid, termed gastric juice. Next after the stomach 

 come the small intestines, into which the liver ami 

 pancreas, two large glandular organs, pour their 

 secretions the former the bile, the latter a fluid some- 

 what similar to saliva. In the coats of the intestines. 

 also, are numerous small glands supplying the intestinal 

 juice. The Urge intestines follow ; the lowermost, a 

 tenth p.\rt of which is called the rectum, terminating in 

 the anus. 



Besides the secretions enumerated above, there is 

 found considerable quantity of mucus throughout the 

 whole intestinal canal This mucus is materially dif- 

 ferent in different places, owing to the admixtures which 

 it receives in the several parts of the canal. 



Saliva, gastric juice, bile, pancreatic and intestinal 

 juice, combined with mucus, are themselves products of 

 the blood ; from which, having been elaborated by 

 various glandular organs-they flow, as before stated, 

 into the digestive canal. Thus do the fluid combinations, 

 which have themselves been furnished by the blood, 

 contribute, in return, to the accomplishment of all those 

 transformations of the nutriment, which are necessary 

 for sanguification. 



3. The Alimentary Pritxiples. In order to under- 

 stand these various alterations, it is necessary to make 

 ourselves acquainted with the constituent parts of the 

 nutriment we employ. Let us imagine, for instauc , a 

 kind of aliment so compounded that it alone shall be 

 sufficient to maintain life. Nature furnishes such an 

 example in milk. This article contains salts, sugar, fat, 

 and a substance very nearly resembling albumen or the 

 white of egg, which is the principal constituent of 

 cheese, and is hence called caseine. 



Tiieitu four prm.-ij.li-* constitute by far the greater 

 proportion of all nutritious aliment. We say the greater 

 pro]x>rtion, not the whole ; for either fat or sugar may 

 be absent singly in nutritious food, but not both toge- 

 ther. Salts, fat, and albumen, or salts, sugar, and 

 albumen, are three components which, together, are abso- 

 lutely necessary for the nutrition of the body. Thi-y 

 are examples of three groups of alimentary substances, 

 which represent the essential part of all solid and liquid 

 food. To express these groups in more general terms, 

 we have 



1- The inorganic. 



2. The organic destitute of nitrogen. 

 ' The organic possessing nitrogen. 



The easeutial distinction between these three classes, 

 lias iii tho particular nature of their composition. 



IB. 



Nitrogen. 



Tim more important elements f nutriment 

 Potassium. Iron. phorus. Hydrogen. 



S.>dimu. fine. Sulphur. 



Calcium. Chlorine. Oxygen. 



Magnesium. 



The seven elements, from 

 principally to the mineral kingdom; they compose the 

 inorganic aliments that is to say, those which exist 

 without any mediate or immediate intervention of living 

 boings ; as, for instance, common salt. Tho instruments 

 <>f living beings are called organs; and all those sub- 

 stances are called organic, the production of which 

 depends upon the mediate or immediate activity of 

 plants or animals ; for example, sugar and alcohol are 

 organic substances. 



:<m, carbon, and hydrogen are to be found in all 

 living bodies, whilst entirely absent in many minerals. 

 Therefore they may be denominated, in a stricter sense, 

 organic elements. It is true they appear also in the 

 inorganic world, just as inorganic elements appear also 

 in the organic. 



Intermediate between these two groups are oxygen, 

 phosphorus, and sulphur, being nearly as much organic 

 as in >rganio elements. 



4. There are combinations of two inorganic elements 

 in our nutriment ; amongst these common salt, which 

 consists of sodium and chlorine, holds the principal 

 place. A combination very similar to common salt is 

 that of chlorine and potassium, the latter of which re- 

 pivsouts the chief element of potash. We shall hereafter 

 speak of common salt and chloride of potassium, under 

 the appellation of compounds of chlorine. Both are dis- 

 tinguished by their free solubility in water. 



To these combinations, each consisting of two elements, 

 fluoride of calcium may be added, which is to be found 

 in very minute quantities in wheat, in milk, and in 

 blood, and is known to most readers as fluor spar. It is 

 composed of fluorine and calcium. Water dissolves 

 it only at a high temperature, and even then very 

 sparingly. 



It may seem strange that common salt is not called a 

 salt by chemists ; the salts of chemists are even not 

 similar to common salt in taste. Therefore, as we men- 

 tioned before, salts are only an example of the class of 

 inorganic elements. In chemical language, a salt is a 

 combination which does not consist of two elements, but 

 of a combination of two parts, each containing two 

 elements.* 



The number of salts is exceedingly large. In treating 

 on the subject of food, it will only be important to refer 

 to the oxy-salts ; these consist of different elements of a 

 metal forming, with a little oxygen, a base called an 

 alkali, and of a non-metallic substance, with a large 

 quantity of oxygen, forming an acid. 



Almost all bases have a corrosive taste, like lime ; 

 almost all acids a sour one, as sulphuric acid ; but this 

 is not an essential quality either of bases or acids. A 

 really significant characteristic of bases is their attraction 

 for acids ; and of acids, their tendency to unite with 

 bases. These duplex combinations of bases with I 

 constitute salts. The matter which is commonly em- 

 ployed as a test of both acids and alkalies, is litmus, 

 which is a blue pigment, prepared from a hard, granu- 

 lated, grayish-white plant, belonging to the class of 

 lichens, which, under the name of Swedish moss, is 

 imported principally from Sweden. Acids turn the 

 litmus red ; while bases or alkalies restore its natural 

 colour. The general reader may at any time aid his 

 imagination by thinking of lime as the representative of 

 the bases, sulphuric acid of the acids, f 



If. in the combination of a base and an acid, the base 

 predominate in quantity, therefore communicating to 

 the compound its peculiar properties, the salt is called 

 basic, and acid if the acid nave the preponderance ; if 

 neither predominate, the salt is called neutral salt. 



The bases of the salts of our nutriment are constituted 

 out of the first four elements, which are called above, in 

 a stricter sense, the inorganic. They arc all metals, and, 



See unif, p. 30*. t Ante, p. tuft. 



