INORGANIC SUBSTANCES. 39 



QUANTITY OF LIME PHOSPHATE IN 1000 PARTS IN THE 



Enamel of the teeth . 885 Milk .... 2.V2 



Dentine . . . .643 Blood .... 0.30 



Bone .... 576 Bile . 0.92 



Cartilage ... 40 Urine .... O.V5 



Notwithstanding the large quantity of lime phosphate in the body as 

 a whole, it is evident, from the preceding list, that most of it is deposited 

 in the solid tissues ; while it is present in but slender proportion in 

 the animal fluids. Of these fluids, milk alone contains lime phosphate 

 in notable quantity, where it is plainly subservient to the ossification 

 of the growing bones of the infant, by whom the milk is used as food. 

 In the circulating fluids, the internal secretions, and the urine, on the 

 other hand, the calcareous salt is in small amount. Its importance in 

 the body depends mainly upon its physical property of imparting rigidity 

 to the solid tissues, rather than upon its active qualities in the phe- 

 nomena of nutrition. 



In the solid tissues it is associated with other earthy anci alkaline 

 salts, but largely preponderates over them in amount. In the bones, the 

 quantity of lime phosphate is from five to six times greater than that of 

 all the other mineral ingredients together. 



In the bones, teeth, and cartilages, lime phosphate exists in a solid 

 form ; not deposited mechanically as a granular powder, but united 

 with the animal matter of the tissues, like coloring matter in colored 

 glass, the union of the two forming a homogeneous material. It is not, 

 on the other hand, so combined with the animal matter as to lose its 

 identity and constitute a new substance, as where hydrogen combines 

 with oxygen to form water ; but rather as salt unites with water in a 

 saline solution, both substances retaining their original character and 

 composition, though too intimately associated to be separated by 

 mechanical means. The lime phosphate, therefore, may be extracted 

 by maceration in dilute muriatic acid, leaving behind the animal sub- 

 stance, which still retains the original form of the bone or cartilage. 



In the solid tissues, lime phosphate is useful by giving to them 

 their due consistence and solidity. In the enamel of the teeth, the 

 hardest tissue of the body, it predominates exceedingly over the ani- 

 mal matter, and is present in greater proportion than in any other part 

 of the frame. In the dentine it is in somewhat smaller quantity, and 

 in the bones smaller still; though in the bones it continues to form 

 more than one-half their entire mass. The importance of this sub- 

 stance, in communicating to bones their natural stiffness and consist- 

 ency, is shown by the alteration which they suffer from its removal. 

 If a long bone be macerated in dilute muriatic acid, the earthy matter 

 is dissolved out, the bone loses its rigidity, and may be bent or twisted 

 in any direction without breaking. (Fig. 1.) 



In the formation of the bony skeleton during foetal life, infancy, and 

 childhood, the cartilaginous substance previously existing is replaced 



