INORGANIC SUBSTANCES OF THE BODY 103 



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 tricalcium phosphate 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 

 quantity than the phosphate. It is found also in some other parts. The 

 small concretions of the internal ear of some fishes (otoliths) are composed 

 of crystalline calcium carbonate, and form the only example of inorganic 

 crystalline matter existing as such in the body. 



Potassium and Sodium Carbonates and Sulphates. These are found in 

 the blood and most of the secretions and tissues. 



Silicon. A very minute quantity of silica exists in the urine and in 

 the blood. Traces of it have been found also in bones, hair, and some 

 other parts. 



Iron. The especial place of iron is in hemoglobin, the coloring- matter 

 of the blood, of which a full account will be given with the chemistry of the 

 blood. Iron is found, in very small quantities, in the ashes of bones, mus- 

 cles, and many tissues, and in lymph and chyle, albumin of serum, fibrin, 

 bile, milk, and other fluids. 



Iodine occurs as an iodized protein in the thyroid gland. Biologically, 

 it is found as a tri-iodotyrosin in sponges and the Gorgonian corals. 



Water. Water forms a large proportion, more than two-thirds, of 

 the weight of the whole body. Its relative amount in some of the principal 

 solids and fluids of the body is shown in the following table (from Robin 

 and Verdeil) : 



