CHEMICAL CONSTITUENTS OF BODY AND FOOD. 27 



Somewhat more water is excreted daily than is ingested, since 

 some water is formed in the tissues by the oxidation of hydrogen. 



SALTS. 



The most important salts found are the sulphates and chlorides 

 of sodium; the phosphates of sodium, potassium, calcium, and mag- 

 nesium; and the carbonates of sodium and calcium. 



Of these various salts, sodium chloride is the most important 

 and "the most common one found. In the fluids blood, serum, 

 lymph,, and urine this salt is high in percentage. While in the 

 body it favors absorption by increasing the endosmosis of the tissues 

 and so aids metabolic processes, the absence of sodium chloride for 

 an extended time causes disturbances and disorders in the constitu- 

 tion. There are about 3000 grains of common salt present in the 

 body. About 180 grains are excreted daily in the urine, while some 

 finds its exit as a component of the faeces, sweat, and tears. 



A practical illustration of its value to animal life may be gained 

 by noticing how wild animals repair to the so-called "salt licks" at 

 various times, traveling for many miles to procure it. 



The Africans in the interior of their country do not have NaCl, 

 but use the ashes of certain plants. These ashes chiefly contain KC1 

 and K 2 S0 4 and one-twentieth per cent, of sodium salts. 



Calcium phosphate is a very prominent factor of the mineral 

 solids of the body. It forms about one-half of the bony skeleton, 

 where it is most abundant, although it occurs to some extent in all 

 other solids and fluids. This salt is particularly conspicuous in milk. 



Iron is an important element of haemoglobin. It is this iron 

 in the red blood-corpuscles that is the means of holding the oxygen 

 without being itself oxidized. A want of it causes the pathological 

 condition called anaemia. In the blood of an adult are found forty- 

 five grains. In small proportions it is found in the liquids of the 

 body, as the chyle, lymph, bile, urine, etc., in the faeces, and traces 

 in the liver and spleen. 



i. CARBOHYDRATES. 



The carbohydrates are found principally in the vegetable king- 

 dom. They are, however, not indigenous to the vegetable kingdom, 

 but are found and formed in animal tissues; notably, glycogen, or 

 animal starch; dextrose; and lactose, or milk-sugar. 



For the sake of a clearer conception of the term carbohydrate the 

 components of the name are used when it is defined as a compound of 



