GENERAL STRUCTURE AND COMPOSITION 15 



greater part of the carbon taken into the Body ultimately leaves 

 it. United with calcium it is found in the bones and teeth in large 

 proportion. 



Formic, acetic, and butyric acids are also found in the Body; 

 stearic, palmitic, and oleic have been above mentioned as obtain- 

 able from fats. Lactic acid is often present in the digestive tract, 

 and when milk turns sour is formed from lactose. A substance of 

 the same percentage composition, C 3 H 6 O 3 (sarcolactic acid), is 

 formed in muscles when they work or die. 



Glycerin phosphoric acid (C 3 H 9 PO 6 ) is obtained on the decomposi- 

 tion of lecithin, a complex nitrogenous fat found in nervous tissue 

 and to some extent in all living cells. 



Inorganic Constituents. Of the simpler substances entering into 

 the structure of the Body the following are the most important : 



Water; in all the tissues in greater or less proportion and forming 

 about two-thirds of the weight of the whole Body. A man weighing 

 75 kilos (165 Ibs.), if completely dried would therefore lose about 

 50 kilos (110 Ibs.) from the evaporation of water. Of the con- 

 stituents of the Body the enamel of the teeth contains least water 

 (about 2 per cent), and 'the saliva most (about 99.5 per cent); 

 between these extremes are all intermediate steps bones con- 

 taining about 22 per cent, muscles 75, blood 79. 



Common salt Sodium chloride (NaCl) ; found in all the tissues 

 and liquids, and in many cases playing an important part in keep- 

 ing other substances in solution in water. 



Potassium chloride (KC1) ; in the blood, muscles, nerves and most 

 liquids. 



Calcium phosphate (Ca 3 2PO 4 ) ; in the bones and teeth in large 

 quantity. In less proportion in all the other tissues. 



Besides the above, ammonium chloride, sodium and potassium 

 phosphates, magnesium phosphate, sodium sulphate, potassium 

 sulphate, and calcium fluoride have been obtained from the Body. 



Uncombined hydrochloric acid (HC1) is found in the gastric juice. 



