ANIMAL FLUIDS AND TISSUES. 663 



bone) of the same person differ somewhat in composition ; more- 

 over, 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 years. 



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 " 



Ferric phosphate, Traces. Traces. Traces. 



Frequently human bones contain calcium fluoride, which substance, 

 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 ossein, a 

 collagen, yielding gelatin on boiling with dilute hydrochloric acid. 



Experiment 76. Pour upon 3 grammes of bone 10 c.c. of water, and then 

 10 c.c. of hydrochloric acid. (Notice that carbon dioxide is liberated.) The 

 dilute acid dissolves the mineral constituents of the bone, leaving the organic 

 matter (ossein) as a swollen mass, which retains the shape of the bone. 



Decant the acid solution, and to part of it add an excess of ammonia, then 

 acidify with acetic acid. The greater part of the precipitate formed by am- 

 monia will dissolve. The insoluble part contains traces of silica, but is chiefly 

 ferric phosphate, most of which is derived from the blood in the bone. Filter 

 and test portions of filtrate for phosphoric acid with ammonium molybdate 

 and for calcium with ammonium oxalate. Dissolve the washed precipitate on 

 the filter with a little hydrochloric acid, and test for phosphoric acid as above, 

 and for iron with potassium ferrocyanide. (The detection of the mineral con- 

 stituents of bone may be carried out with the ash left from incinerating bone.) 



Wash the ossein, obtained above, first with water, then with dilute solution 

 of sodium carbonate, and finally with water again. Put the washed ossein in 

 a beaker with a little water and boil until most of the ossein has been dissolved. 

 Neutralize, if necessary, with sodium carbonate, and filter while hot into a test- 

 tube. On standing, the solution gelatinizes more or less completely. Ossein 

 is converted into gelatin by this treatment. 



Gelatin. The purest commercial form of gelatin is known as 

 isinglass, prepared from the sounds or air-bladders of certain fishes ; 

 it is much used as an article of food in creams and jellies. An 

 impure gelatin, prepared from animal refuse (hoofs, bones, hides, etc.), 

 forms common glue, and its solution in acetic acid is sold as liquid 

 glue. In a pure state gelatin is a colorless or slightly yellowish, 

 transparent, tasteless mass. The presence of gelatin often prevents 

 the formation of precipitates by holding them in suspension in a 

 finely divided state, so that they may pass through filter-paper. 



