158 HYDROGEN OXYGEN. 



proportion, or in excess, and in another it is in a less proportion than 

 in water. 



The first class of alimentary principles in which these two elements 

 are in the same ratio as in water, are called hydrates of carbon, con- 

 sisting of carbon and the two elements of water, hydrogen and oxygen, 

 as with starch, sugar, gum, vinegar, &c. These, therefore, afford 

 carbon for oxydation in the system, while the hydrogen remains united 

 with the oxygen in the water. Gramnivorous animals expire a vol- 

 ume of carbonic acid equal to that of the oxygen they inspire ; hence 

 there is no loss of oxygen. A large proportion of the food of these 

 animals consists of principles containing hydrogen in the proportion 

 of water, or at the point of its saturation with oxygen. The affinity 

 of hydrogen at the temperature of the body is greater than for carbon, 

 hence a volume of carbonic acid is expired corresponding with that 

 inspired, as little hydrogen is afforded to combine with the oxygen. 



The second class or group of principles, in which hydrogen is in ex- 

 cess, includes nitrogenized and non-nitrogenized food. These princi- 

 ples are lard, alcohol, protein, albumen, fibrine, &c. These constitu- 

 ents of food are ultimately changed in the system by the conversion of 

 their carbon into carbonic acid, and the hydrogen into water. The 

 hydrogen of food unassimilated with the unoxydized carbon is expel- 

 led in urine and the faeces. The union of hydrogen and oxygen causes 

 the evolution of heat ; and in the combustion of equal weights of hy- 

 drogen and oxygen the former gives out more heat than the latter. 



The third class or group contains hydrogen in a less proportion than 

 in water, as in pectine, or vegetable jelly, and some vegetable 

 acids ; their hydrogen is therefore combined with carbon and oxygen. 



Oxygen. This is the most important element of food and of organ- 

 ized beings, and is said to constitute 3-4ths of the solid globe. It con- 

 stitutes 23-100ths, by weight of the atmosphere, and 8-9ths, by weight of 

 the water and mineral portion of the world, and 16-22ds of the car- 

 bonic acid of the atmosphere. The three most abundant constituents 

 of the earth, silica, carbonate of lime and alumina, are composed of 

 about 45 per cent, of oxygen. It is the most active agent in all nat- 

 ural phenomena; and without its ceaseless influence, all life would 

 cease. It is an essential element of food, such as starch, fats, sugar, 

 gum, &c. It is thrown out of the animal system in the form of car- 

 bonic acid and water ; so that such food as contains oxygen in a small 

 quantity, consumes a larger portion of atmospheric oxygen than that 

 in which it is deficient ; the quality of food, consequently, greatly af- 

 fects respiration. Vegetable diet greatly reduces and animal food 

 equally augments the consumption of oxygen. Some of the vegetable 

 salts, as acetate, tartrate, citrate, &c. when swallowed, are partially de- 

 composed in the system, the acid disappears and carbonic acid is sub- 

 stituted. In taking these salts in a state of effervescence, this change 

 is obvious. 



