240 PHYSIOLOGICAL CHEMISTRY. 



and has found an essential difference. The quantity of water in 

 the fresh bones varies between 138 and 443 p. m. The bones of 

 the extremities and the skull contain 138-222, the vertebrae 168- 

 443, and the ribs 324-356 p. m. water. The quantity of fat varies 

 between 13 and 269 p. m. The largest amount of fat, 256-269 

 p. m., is found in the long tubular bones, while only 13-175 p. m. 

 fat is found in the small short bones. The quantity of organic 

 substance, calculated from fresh bones, was 150-300 p. m., and 

 the quantity of mineral substances 290-563 p. m. Contrary to 

 the general supposition the greatest amount of bone-earths was not 

 found in the femur, but in the three first cervical vertebrae. In 

 geese the largest amount of bone-earth was found in the humerus 



(HlLLER). 



We do not possess trustworthy statements in regard to the com- 

 position of bones at different ages. There is no question, however, 

 that the mineral constituents increase until a certain age is reached, 

 at which time the bones attain their necessary solidity. On the 

 other hand, it is not certainly known whether this increase stops 

 at a certain point or whether, as was formerly thought, it con- 

 tinues, even if slowly, uninterrupted from childhood to old age. 



The composition of bones of animals of different species is but little 

 known. The bones of birds contain, as a rule, somewhat more water than 

 those of mammalia, and the bones of fishes contain the largest quantity of 

 water. The bones of fishes and amphibians contain a greater amount of 

 organic substance. The bones of pachydermata and cetaceae contain a large 

 proportion of calcium carbonate ; those of granivorous birds always contain 

 silicic acid. The bone-ash of amphibians and fishes contains sodium sulphate. 

 The bones of fishes seem to contain more soluble salts than the bones of other 

 animals. 



A great many tests have been made to determine the exchange 

 of material in the bones for instance, with food rich in lime and 

 with food deficient in lime but the results have always been 

 doubtful or contradictory. The attempts, also, to substitute other 

 alkaline earths or clay for the lime of the bones have given contra- 

 dictory results. KEAPP found that the bones of the animals under 

 experimentation were tinged with red after a few days or weeks ; 

 but these tests have not led to any positive conclusion in regard to 

 the growth or exchange of material in the bones. 



Under pathological conditions, as in rachitis and softening of 

 the bones, an ossein has been found which does not give any 



