PROTOPLASM 19 



There are very minute quantities of several other elements in the bodies 

 of higher animals, including fluorine in the enamel of the teeth and also 

 sihcon and iodine, but these are found only in certain tissues and are 

 not considered normal constituents of protoplasm. Minute amounts of 

 copper, manganese, zinc, and bromine have been found in marine inverte- 

 brates. The first five elements named in the table above are always 

 present and a certain number of the last group are also, but some of them 

 may be lacking. 



Though some elements are present in small amount, this small amount 

 is none the less vital to the performance of the functions of living matter. 

 Certain of these elements are especially abundant in particular forms of 

 protoplasm, such as iron in the protoplasm of red blood corpuscles and 

 phosphorus in the protoplasm of the nerve and reproductive cells. 



2. These elements are in combination in a variety of compounds which 

 may be classified as follows: 



Organic Compounds Inorganic Compounds 

 Proteins Salts 



Fats Water 



Carbohydrates 



Proteins are, vso to speak, foundation substances; about them is built 

 up the complex aggregate called protoplasm. They contain four ele- 

 ments — carbon, oxygen, hydrogen, and nitrogen — together with sulphur 

 and in some cases phosphorus, and have certain pecuhar properties. 

 They are colloidal and have a tendency to coagulate on heating. The 

 protein molecule is very large and is built up of many amino acids, which 

 are acids containing the amino group NH2. The number of different 

 proteins in different forms of protoplasm is very great ; different species of 

 animals have different types of protein, and particular tissues in one 

 animal contain proteins which are not found in the other tissues of the 

 same animal. 



Fats are also colloids and consist of carbon, hydrogen, and oxygen, 

 the oxygen being very small in amount as compared with the carbon 

 and hydrogen. This fact makes them susceptible of a great amount of 

 oxidation, with the consequent production of a large amount of heat. 

 There are three different types of fats: (1) true fats, which include com- 

 pounds of glycerin and fatty acids, mostly oleic, palmitic, and stearic; 

 (2) lipoids, including the phosphorus-containing fats, an example of which 

 is lecithin, and the sugar-containing fats, or cerebrosides, found in 

 nervous tissue; and (3) sterols, including cholesterol, which seems to 

 occur in every animal cell. 



Carbohydrates, which include sugars and starches, may also be in 

 a colloidal condition, although neither they nor fats show any tendency 

 to coagulate with heat. They also consist of carbon, hydrogen, and 

 oxygen, but there is relatively a much greater amount of oxygen than 



