42 INTRODUCTION. 



rent. Its existence, in suitable proportion, is necessary to the 

 mechanical office of these parts, giving them their power of 

 resistance, without rendering them too brittle. It is more 

 abundant in the bones of the lower extremities, which 

 have to sustain the weight of the body, than in those of the 

 upper extremities ; and in the ribs, which are elastic rather 

 than resisting, it exists in less quantity than in the bones of 

 the arm. 



The necessity of a proper proportion of phosphate of lime 

 in the bones is made evident by cases of disease. In rachi- 

 tis, where, as is seen by the table, its quantity is very much 

 diminished, the bones are unable to sustain the weight of the 

 body, and become deformed. Finally, when the phosphate of 

 lime is deposited, they retain their distorted shape. The 

 phosphate of lime may be extracted from the bones by ma- 

 ceration in dilute hydrochloric acid, which dissolves it, leav- 

 ing only the organic substance. Bones treated in this way, 

 though they retain their form, become very pliable ; and a 

 long slender one, like the fibula, may be actually tied into 

 a knot. 



Origin and Discharge of Phosphate of Lime. The ori- 

 gin of this principle is exclusively from the external world. 

 It enters into the constitution of our food, and is discharged 

 with the feces, urine, and other matters thrown off by the 

 body. Its quantity in the urine is exceedingly variable. Le- 

 canu found from G'43^ to 29*250 grains thrown off by the 

 kidneys during the twenty-four hours. 1 



Carbonate of Lime, CaO, CO 2 . 



Carbonate of lime exists in the Bones, Teeth, Cartilage, In- 

 ternal Ear, Blood, Sebaceous Matter, and sometimes in the 

 Urine. It exists as a normal constituent in the urine of some 

 herbivora, but not in the carnivora, nor in man. It is most 



1 LEHMAKN, Physiological Chcm,istry, American Edition, vol. ii., p. 161. 



