414 FIRST CLASS OF MINERAL CONSTITUENTS. 



induration (or eburneation) the bones often do not regain their 

 normal quantity of phosphate of lime. 



Von Bibra has very fully investigated the composition of the 

 different bones of the same individual, and has made the beautiful 

 observation that those bones which are the most exposed to mecha- 

 nical influences contain the largest amount of earthy constituents. 

 The action of this law is manifested even in different families of 

 the same class of animals ; thus, for instance, in the rasores or 

 scraping birds, the femur contains the largest quantity of phos- 

 phate of lime, in the grallatores or waders, the tibia, and in all 

 other birds, the humerus. 



That the phosphate of lime and the earths generally are only 

 mechanically deposited in the bones, is obvious from the circum- 

 stance that we can so thoroughly deprive them of all mineral con- 

 stituents by dilute hydrochloric acid, that they leave scarcely a trace 

 of ash. 



It has for a long time been a matter of discussion whether the 

 phosphate of lime is, or is not, chiefly deposited in the bone-cor- 

 puscles and the canalicula chalicophorce. I am however now con- 

 vinced that the dark colour of these parts in refracted light, and 

 their white colour in reflected light, essentially depends on their 

 containing air. Any one may readily convince himself that this is 

 the case, by treating one thin section of bone with dilute hydro- 

 chloric acid, so as to remove the earths, and another with a dilute 

 solution of potash, so as to remove the cartilaginous substance, 

 and comparing the two under the microscope. Frerichs* attempted 

 to demonstrate that the earths were uniformly distributed through- 

 out the bone by showing that osseous laminae from which the car- 

 tilaginous substance had been removed by a dilute solution of pot- 

 ash received an uniform yellow tint on the addition of nitrate of 

 silver, and that the bone-corpuscles were not distinguished by any 

 special depth of colour. 



Phosphate of lime also occurs in many other parts of the 

 animal body, although in far less quantity than in the bones ; 

 indeed there is no animal tissue, in whose ash, on incineration, we 

 do not find phosphate of lime. 



Liebigf regards the insolubility of certain tissues, as for 

 instance, muscular fibre and cellular tissue, as partially due to 

 the bone-earth which they contain. In the transition of the 



* Ann. d. Ch. u. Pharm. Bd. 43, S. 251. 

 t Ibid. Bd. 50, S. 170. 



