PHYSIOLOGY FOR BEGINNERS 



Iron (Fe). Cast iron and steel consist almost entirely of 

 the element iron. The element occurs abundantly in com- 

 bination with earthy substances, as ores of iron. It is also 

 present in the blood in combination with certain substances. 



Compound substances are either organic or inorganic. 

 The compounds which carbon forms with hydrogen, and 

 generally with oxygen and nitrogen in addition to hydrogen, 

 and occasionally with a few other elements also, are called 

 organic compounds. They are so called because they were 

 formerly supposed to be formed only by the agency of animal 

 and plant life. All other compounds are called inorganic. 

 These are said to be mineral in nature, and in a very large 

 number of them a metallic element is present. 



Water (H<,O) is a compound consisting of two parts by 

 volume of hydrogen united with one of oxygen. A large 

 amount of water occurs in all tissues of the body ; in fact, the 

 water present accounts for two-thirds of the body weight. 



Ammonia (NH 3 ) is a compound gas consistingof three parts 

 by volume of hydrogen united with one of nitrogen. It is com- 

 monly formed by the decay of animal and vegetable matter. 



Carbonic acid gas (carbon dioxide) (CO 2 ) is a com- 

 pound gas consisting of one part by volume of carbon united 

 with two of oxygen. It is formed when carbon, or any 

 substance containing carbon, such as coal, wood, oil, is burnt 

 in air. It exists in the air, and is evolved from the earth 

 by volcanoes. Carbonic acid is formed by living animals, and 

 is present in the blood and tissues. 



Carbon monoxide (CO) is a combustible gas formed by 

 the incomplete combustion of carbon. It consists of one part of 

 carbon united with only one part of oxygen. When it burns it 

 forms carbonic acid gas. It is not found in the animal body. 



The other inorganic compounds found in the body are 

 those compounds called acids and salts. 



Acids are compounds which hydrogen forms with certain 

 other elements, most commonly non-metallic elements, and 

 often with oxygen as well. Examples of acids are hydrochloric 

 acid (HC1), formed by the union of hydrogen and chlorine, 

 sulphuric acid (H 2 SO 4 ), and phosphoric acid (H 3 PO 4 ). Car- 

 bonic acid (H.>C6.^) is formed by the union of carbonic acid 

 gas (CO.,) with water. Carbonic acid gas is generally called 



