486 OF NUTRITION. 



in which respect these formations correspond with the bones of the lower animals : but 

 in caries, the quantity of the carbonate is much smaller than usual. The proportion of 

 the earthy constituents of bones, to their organized basis, varies much in different parts 

 of the skeleton, and at different ages. Thus when the scapula contains 54 per cent, of 

 bone-earth, the temporal bone contains 63| per cent. According to Schreger,* in the 

 bones of a child, the earthy matter constitutes one-half; in those of an adult it amounts 

 to four-fifths, and in those of an old person to seven-eighths of the entire mass ; this is 

 probably too high an estimate, but it expresses sufficiently well the comparative state of 

 the bones at different periods.f The following are the results of the most recent and 

 careful analyses of Bone, by Marchand and Lehmann : those of the former were made 

 on the thigh-bones ; and those of the latter on the long bones of the arm and leg. 



MABCHAXD. LEHMANN. 



I Cartilage insoluble in H. cl."^ 



Organic matter < soluble - 33-26 32-56 



f Vessels j 



Phosphate of lime - 52-26 7 _, fi . 



Fluateoflime .... - 1-00 5 



Carbonate of lime ... . io-21 9-41 



Phosphate of Magnesia - - 1-05 1-07 



Soda - - ... 0-92 Ml 



Hydrochlorate of Soda - - - 0-25 0-38 



Oxides of iron and manganese and loss, - - 1-05 -86 



100-00 100-00 



The composition of the Phosphate of Lime in bones is peculiar; 8 proportions of the 

 base being united with 3 of the acid. According to Prof. Graham,t it is to be regarded 

 as a compound of two tribasic phosphates: namely, 2 Ca O, H 0, P O^ -f 2 (3 Ca O, P 

 O 5 ) ; with the addition of an atom of water, which is driven off" by calcination. It appears 

 to be united with the animal basis, as a definite chemical compound. The presence of 

 Fluoride of Calcium in bones has been denied ; according to the recent inquiries of Dr. 

 G. 0. Rees and M. Gerardin,|| it does not exist in recent bones; but is found in greater 

 or less proportion, in those which have become fossilized, having probably been intro- 

 duced by infiltration from without. If this be true, its presence may be regarded as a 

 sign that the bone is really fossilized. 



631. The Growth of Bone takes place, not merely by the addition of new 

 matter to its surface and extremities, but also by a proper interstitial change, 

 like that which takes place in the softer tissues. In this respect, its nutrition 

 differs from that which takes place in the skeletons of Invertebrated animals ; 

 for these, whether external or internal, grow only by additions to their surface. 

 One of the most remarkable changes which takes place during the growth of 

 long Bones, is the formation of the central medullary canal. In early life, the 

 internal cancelli are small, and the medullary canal does not exist ; but the 

 cancelli gradually enlarge, and those within the shaft coalesce with each other, 

 until a continuous tube is formed, around which the cancelli are very large, 

 open, and irregular. During this process, the shaft itself undergoes a great 

 increase in its diameter, the bony shell being, as it were, pushed outwards, so 

 as to form a larger circle than previously ; and this can be scarcely due to any 

 thing else than interstitial deposit. But the increase of long bones in length 

 is chiefly due to the progressive addition of ossific matter at their extremities, 

 by the transformation of the Cartilage which covers them. And their increase 

 in diameter, subsequently to the formation of the medullary canal, is for the 

 most part effected by the addition ^f new layers, with new systems of Haver- 

 sian canals and their concentric lamellae and radiating cavities. The difference 

 in the relations of the Bony substance to the vascular network, at different 



* Hildebrandt's Anatomy by Weber, vol. i. p. 316. 



f The proportion, however, is by no means constant; as Dr. Davy's experiments prove. 

 See his Anatomical and Physiological Researches. 



* Elements of Chemistry, [Am. Ed. p. 711.] Guy's Hospital Reports, vol. v. 

 1 Gazette Medicale, Oct. 15, 1842. 



