INORGANIC SUBSTANCES OF THE BODY 103 



Cellulose forms a large portion of the cell wall or the woody structure 

 of plants. It is extremely insoluble. Chemically, it is more complex than 

 the common starch molecule. The hydrochloric and hydrofluoric acid 

 extracted (ash-free) filter-papers and absorbent cotton are examples of prac- 

 tically pure cellulose. 



INORGANIC SUBSTANCES OF THE BODY. 



Salt. The inorganic principles of the human body are numerous. 

 They are derived, for the most part, directly from food and drink and pass 

 through the system unaltered. Some radicals are newly formed by oxi- 

 dation within the body, as, for example, a part of the sulphates and car- 

 bonates from the sulphur of the proteins and the carbon of protein, fat, and 

 carbohydrate. 



Much of the inorganic saline matter found in the body is a necessary 

 constituent of its structure, as necessary in its way as protein or any other 

 organic principle. Another part is important in regulating or modifying 

 various physical processes, as absorption, solution, and the like. A part 

 must be reckoned only as matter which is, so to speak, accidentally present, 

 whether derived from the food or the tissues, and which will, at the first 

 opportunity, be excreted from the body. The principal salts present in 

 the body are: 



Sodium and Potassium Chlorides. These salts are present in nearly all 

 parts of the body. The former seems to be especially necessary, judging 

 from the instinctive craving for it on the part of animals in whose food it 

 is deficient, and from the condition which is consequent on its withdrawal. 

 The quantity of sodium chloride in the blood is greater than that of all its 

 other saline ingredients taken together, but it is present chiefly in the fluids 

 of the body. In the tissues, the muscles for example, the quantity of sodium 

 chloride is less than that of the chloride of potassium, which forms a constant 

 ingredient of protoplasm. 



Calcium Fluoride. It is present in minute amount in the bones and 

 teeth, and traces have been found in the blood and some other fluids. 



Calcium, Potassium, Sodium, and Magnesium Phosphates. These phos- 

 phates are found in nearly every tissue and fluid. In some tissues the bones 

 and teeth the phosphate of calcium exists in very large amount. The phos- 

 phate of calcium is intimately incorporated with the organic basis or matrix, 

 but it can be removed by acids without destroying the general shape of the 

 bone. After the removal of its inorganic salts, a bone is left soft, tough, 

 and flexible. 



Potassium and sodium phosphates, with the carbonates, maintain the 

 alkalinity of the blood. 



Calcium Carbonate. It occurs in bones and teeth, but in much smaller 



