Carbohydrates (general formula, CmH2nOn) are bodies in which the hydrogen and oxygen exist in the same proportion as in water, the carbon being variable. The following examples of this group are met with in the textures of the body: -
Grape Sugar (Dextrose), C6H1206, occurs in minute quantities in the blood, chyle and lymph. It forms crystals which readily dissolve in their own weight of water. The watery solution has a dextro-rotatory power on the ray of polarized light. When mixed with yeast, the fungus (Saccharomyces cerevisice) of the yeast causes alcoholic fermentation of the sugar, whereby alcohol and carbon dioxide are formed.
C6H1206 = 2C2H60 + 2C02.
Moderate heat (25° C.) aids the process, and cold below 50 C. checks it; an excess of either sugar or alcohol stops it.
The presence of casein or other proteid material, when decomposing, gives rise to lactic fermentation, producing first lactic acid, then butyric acid, carbon dioxide and hydrogen.
C6H12 06 = 2C3H603 = C4H802 + 2C02 + H1.
Milk Sugar (Lactose), C12H22On + H20, metameric with cane sugar (sucrose). It is the characteristic sugar found in milk. It is not so soluble as dextrose, and does not undergo direct alcoholic fermentation, but under the influence of certain organisms it readily gives rise to lactic acid by lactic fermentation in the same way as dextrose. (See page 102).
Inosit, C6H1206 + 2H20, is an isomer of grape sugar, which is incapable of undergoing alcoholic fermentation. It is crystal-lizable, and easily soluble in water. It has no effect on the polarized ray. It is found in the muscles, and also in the lungs, spleen, liver and brain.
Glycogen, C6H10O5, a body like dextrin, first found in the liver. It gives an opalescent solution in water, and is readily converted into dextrose by an amylolytic ferment, or weak acids. It has a strong dextro-rotatory power. It can be found in most rapidly growing tissues. (See Glycogenic Function of the Liver).