ANIMAL FLUIDS AND TISSUES. 363 



tinal secretions. The quantity passed depends on the nature of 

 the food taken, and on the energy of the digestive powers. A 

 grown person, in normal condition, discharges from 7 to 9 

 ounces daily. An approximate analysis of the feces of a 

 healthy adult shows : 



"Water, 77.3 per cent. 



Mucin, 2.3 



Proteids, 5.4 



Extractives, 1.8 



Fats, 1.5 



Salts, 1.8 

 Eesinous, biliary, and -> 

 coloring matters, J 



Insoluble residue of food, 4.7 " 



Bone is chemically distinguished from other tissues by the 

 large quantity of inorganic salts which it contains. Bones con- 

 tain about 35 per cent, of organic matter combined with 65 per 

 cent, of mineral matter. Different bones (and even different 

 parts of the same bone) of the same person differ somewhat in 

 composition ; moreover, the bones of a child contain somewhat 

 more of organic matter than those of a grown person, as may 

 be shown by the following analyses of the corresponding bone 

 in children and a grown person: 



Child one year. Child five years. Man twenty-five year*. 



Organic matter, 43.42 per cent. 32.29 per cent. 31.17 per cent. 



Tricalcium phosphate, 48.55 " 59.74 " 58.95 " 



Magnesium phosphate, 1.00 " 1.34 " 1.30 " 



Calcium carbonate, 5.79 " 6.00 7.08 " 



Soluble salts, 1.24 " 0.63 " 1.50 " 



Frequently human bones contain calcium fluoride, which sub- 

 stance, to the amount of 1 to 2 per cent., is a normal constituent 

 of the bones of many animals. The organic matter of bone is 

 called ossein, and is a mixture of collagen, elastin, and an albu- 

 minoid existing in the bone-cells. Collagen is a nitrogenous 

 substance, insoluble in water, but forming when treated with it 

 under the influence of heat and pressure, gelatine, an amorphous, 

 tasteless, translucent substance, which swells up in boiling 

 water, forming on cooling a soft jell} 7 ; an impure form of gela- 

 tine is common glue. 



