I STRUCTURE AND COMPOSITION. 13 



liver in ,'rnall quantities; also in the blood and lymph. It is 

 largely derived from glycogen, which is very readily Converted 

 into it. 



Lactose, or sugar of ntilJc (C ia H 3a O n -f H 2 0), found in 

 considerable quantity in milk. 



Inosit (C 6 H 12 6 -f 2H 2 0), also called muscle -sn gar aiv" 

 formerly classed in this group, is now known to be chf 

 cally not a real sugar or true carbohydrate. It exi^ 

 muscles, liver, spleen, kidneys, etc. 



Organic Non-Nitrogenous Acids. Of these the most im- 

 portant is carbon dioxide (C0 2 ), which is the form in which 

 by far the 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 obtainable from fats. Lactic acid is sometimes found in 

 the stomach, and when milk turns sour is formed from lactose.- 

 A body of the same percentage composition, C 3 H 6 3 (sarco- 

 lactic acid), is formed in muscles when they work or die. 



Glycerin phosphoric acid (C 3 H 9 P0 6 ) is obtained on the de- 

 composition of lecithin, a complex nitrogenous fat found in 

 nervous tissue. 



Inorganic Constituents. Of the simpler substances en- 

 tering 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 (1G5 Ibs.), if completely dried 

 would therefore lose about 50 kilos (110 Ibs.) from the evapo- 

 ration of water. Of the constituents 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 containing 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 keeping other substances in solution in water. 



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

 and most liquids. 



Calcium phosphate (Ca 3 2P0 4 ) ; in the bones and teeth in 

 large quantity. In less proportion in all the other tissues. 



