INORGANIC BODIES. 81 



the exact salts that are present in the body. They doubtless 

 form chemical combinations with the complex organic com- 

 pounds, which we do not understand, and probably have im- 

 portant functions to perform, such as rendering certain materials 

 (globulins) soluble, or otherwise facilitating tissue change. 

 The salts pass out of the body in many secretions, notably 

 in the urine, where they have great influence on the elimination 

 of urea, and therefore form an important constituent of that 

 secretion. 



Common Salt (Sodium Chloride}, NaCl, is the most widely 

 spread, and is present in greater quantity than any other salt in 

 all fluids and tissues, except in bones, teeth, red blood corpuscles 

 and red muscle. 



Potassium Chloride commonly accompanies sodium chloride in 

 small quantity. In the red blood corpuscles and in muscle it 

 occurs in greater amount than the sodium salt, while in the blood 

 plasma but little is found in comparison with the soda salts, and 

 any excess seems to act as a poison to the heart. 



Carbonates and phosphates of calcium, sodium, potassium and 

 magnesium occur in small quantities in most tissues. The earthy 

 part of bone is chiefly composed of calcium and magnesium phos- 

 phate and calcium carbonate, together with some calcium 

 fluoride. 



Sulphate of sodium and potassium, probably formed in the 

 body from the oxidization of the sulphur in the complex proteid 

 materials, occur in most tissues, and are removed from the body 

 by the kidneys. 



Finally, we find two of the elements free in the textures. Of 

 these Oxygen plays by far the most important part. It is widely 

 distributed among the fluids of the body, from which it can be 

 removed by reducing the pressure of the oxygen of the atmos- 

 phere by means of an air pump. Oxygen is introduced into the 

 body by the lungs, where the blood takes it from the air. In the 

 blood only a small quantity of that which can be removed by the 

 air pump is really free, the remainder is chemically combined 

 with the coloring matter of the blood. It is absolutely necessary 

 for life, as it alone can enable the chemical changes of the tissues, 



