56 TEXTBOOK OF ZOOLOGY 



upon the surfaces of the colloidal particles, they acquire an electric 

 charge. Protoplasm exhibits these several phenomena because of 

 its colloidal nature. 



Chemical Nature of Protoplasm 



Up to the present time, protoplasm has eluded complete and 

 exact chemical analysis. Nevertheless the compounds of living 

 matter are composed of several elements, many of them the most 

 ordinary and abundant in the world. The list of elements necessary 

 to make human protoplasm could be gathered in almost any locality 

 on the face of the earth. As a rule the elements found in protoplasm 

 are oxygen, carbon, hydrogen, nitrogen, sulphur, phosphorus, cal- 

 cium, sodium, chlorine, magnesium, iron, potassium, iodine, and fre- 

 quently others like silicon, aluminum, copper, manganese, bromine, 

 and fluorine. The most abundant of these are found named in the 

 first part of the list. A few of them are usually given as constitut- 

 ing approximately the following percentages of protoplasm : oxy- 

 gen 65 per cent, carbon 18 per cent, hydrogen 10 per cent, nitrogen 

 3 per cent, calcium 2 per cent, phosphorus 1 per cent, and all others 

 makijig up the remaining 1 per cent. These elements are found 

 combined to form compounds. The organic compounds include car- 

 hohydratcs, fats, proteins, and also enzymes. The inorganic com- 

 povmds consist of several inorganic salts and water. 



The carbohydrates, which include starches and sugars, are com- 

 pounds of carbon, oxygen, and hydrogen. The proportion of the 

 hydrogen to oxygen in the molecule is the same as found in water, 

 two to one. The principal carbohydrate found in protoplasm is the 

 monosaccharid, or simple sugar, glucose, whose formula is CeHioOe- 

 This is actually built into some parts of the cell, but its chief func- 

 tion is to furnish the most available source of energy by its ready 

 oxidation. When a molecule of glucose is burned, the potential 

 energy is released as kinetic or mechanical energy, and there are 

 formed six molecules of v.'ater (H2O) and six molecules of carbon 

 dioxide (CO2). Glucose is converted to a starchlike substance, 

 glycogen, for storage in the various animal tissues. This substance 

 must be reconverted to glucose before it is available for production 

 of energy. 



Fats, like carbohydrates, are composed of carbon, hydrogen, and 

 oxygen but in more complex molecular arrangement. There is much 

 more carbon and hydrogen with less oxygen, which allows the fats 



