COMPOSITION OF BONES. 57 



withstanding the great lapse of years since it was in a living 

 state : and a repetition here of the same experiments on the 

 teeth and bones of the same animal has exhibited the same 

 result. I was also informed by the late Mr. Say, a distin- 

 guished naturalist, that animal matter has been detected in 

 fossil shells, the existence of which was probably anterior to 

 that of the human family. 



The phosphoric acid of bones gives them a luminous appear- 

 ance at night. Bichat says, that in these cases he has found 

 an oily exudation on the luminous points, probably from the 

 marrow or contiguous soft parts. This phenomenon will 

 account for many of the superstitions which in all ages have 

 affected ignorant minds, on the subject of burying grounds. 



The immersion of a bone in diluted muriatic acid is the best 

 method of demonstrating the animal part in a separate state. 

 The strong affinity of the acid for the earthy part, and the 

 soluble nature of the salt thus formed, leave the animal matter 

 insulated. In this state it preserves the original form of the 

 bone, is cartilaginous, flexible, and elastic. The action of hot 

 water alone, upon a bone, by continued boiling, will, from the 

 soluble nature of the cartilage, separate the latter from the 

 earthy part, and convert it into gelatine. " The gelatine may 

 be precipitated afterwards from the water by tannin. The 

 mode of this combination of animal and of earthy matter is 

 not understood, but it is generally supposed to exist by the ex- 

 tremely small cavities of the former receiving earthy particles, 

 in the same way that sponge holds water.* 



There are no means for investigating the minute anatomy 

 of the bones more favourable than the removal of the earthy 



* If we conceive the phosphate of lime and the other earthy materials of bone 

 to be in a state of solution in the blood and serum with which the cartilaginous 

 rudiment of the bone is impregnated, any action which would precipitate the 

 earthy materials, would also, of course, impregnate the cartilage with them, and 

 this process may be considered as completed when the bone acquires its proper 

 consistence. 



Considering cellular substance as the parenchyma or primordium of all other 

 parts, it is probably a speculation not entirely groundless, that every peculiar 

 tissue or glandular texture has its elements precipitated from the circulating 

 fluid in a manner analagous to that of the calcareous part of bone. This idea 

 also affords a clue to a result almost uniform in protracted macerations of all 

 tissues, to wit, the parts being brought back to the primordial state, by the pe, 

 puliar depositee in them being dissolved in the water and removed, 



