BONE, NORMAL ANATOMY. 



407 



exhibit them, even if they existed in great 

 numbers. That they do so exist we have reason 

 to think from the phenomena of mollities, 

 exfoliation, and various other morbid actions, 

 as well as the changes which daily occur in 

 the growth of bone. 



3. Chemical composition. When bone is 

 heated to redness in an open fire, some of its 

 ingredients are consumed, and a white friable 

 earth is left behind. Again, if bone be ex- 

 posed for some time to the action of an acid, it 

 becomes soft and flexible. In both cases the 

 form and size of the original are retained, but 

 there is considerable loss of weight. These 

 facts were well known in the infancy of science ; 

 they were too obvious to escape notice ; but it 

 does not appear that they were explained before 

 the time of Nesbit in 1736,* nor very satis- 

 factorily then. The existence of an earthy and 

 an animal matter was afterwards proved by 

 Herissant, who showed, by experiment, that 

 acids did not soften the osseous substance as a 

 whole, but removed from it the earthy portion; 

 and that the soft animal matter was always 

 present, but concealed by an earthy " incrus- 

 tation" of its fibres.f The action of fire on 

 the animal portion was easily explained. Some 

 time after this Gahn discovered that the earth 

 was principally a phosphate of lime ; and later 

 chemists, especially Berzelius, have minutely 

 investigated the nature and proportions of these 

 different ingredients. It is now ascertained 

 that bones contain several earthy salts, varying 

 a little in different animals; that the earthy 

 and the animal parts do not always bear the 

 same proportion to each other in the different 

 classes; and that even in the same individual 

 age and situation give rise to varieties. 



It was long believed that fat formed an 

 essential part of bone, and that very important 

 properties depended on its mixture with the 

 osseous tissue; but this opinion was quite 

 erroneous. Fat is not always present, and 

 when it is, it invariably belongs to the medulla, 

 which may be looked upon as a distinct struc- 

 ture superadded to bone. It is, as it were, 

 an accidental deposit, and is not to be con- 

 sidered in the analysis. 



On removing the fat and periosteum, if we 

 suspend a bone for some days in diluted mu- 

 riatic acid, the earthy part is dissolved, whilst 

 nearly all the animal portion remains untouched. 

 This last is soft, translucent, and of a yellowish 

 white colour. It is called the cartilage of bone. 

 When washed and dried it contracts a little, 

 assumes a deeper colour, though still retaining 

 some translucency, becomes hard and tough, 

 and weighs about one-third of the original 

 bone. This substance yields, on being boiled, 

 a quantity of gelatine, which in young subjects 

 is very considerable, forming nearly all the 

 cartilage, but in the old a soft, white, elastic 

 substance still remains, possessing the figure of 

 the bone. According to Hatchet's experiments 



this last has the properties of coagulated albu- 

 men.* Berzelius,-|- however, shows that all 

 the cartilage may be resolved by boiling into a 

 clear colourless gelatine, which leaves on the 

 filter only a very small quantity of fibrous sub- 

 stance, the debris of vessels. He does not 

 admit the existence of any albuminous nidus, 

 and even looks upon the gelatine as the pro- 

 duct of a decomposition effected by coction on 

 the peculiar cellular basis of bone. 



The earth of bone is principally subphos- 

 phate of lime; it also contains carbonate of 

 lime and minute quantities of other salts. The 

 following is the analysis, as given by Berzelius, 

 of bone deprived of its oil, blood, and perios- 

 teum : 



Bones of man. 



Cartilage completely solu- 

 ble in water 32' 



Vessels 



Subphosphate of lime with 



a little fluate of lime. . .. 53*04 



Carbonate of lime 1 1*30 



Phosphate of magnesia .. T16 



Soda, and a very little mu- 

 riate of soda. 1-20 



in tuaii. 



12-17 V 

 M3J 



Of the ox. 



33-30 



100-00 



57-35 

 3-85 

 2-05 



3-45 

 100-00 



The proportion of earthy and animal matter 

 is the same generally in man and the other 

 mammalia. In birds there is more of the 

 animal part which does not perfectly dissolve 

 than in mammalia. In reptiles and osseous fishes 

 the cartilage of bones approaches in its nature 

 to the substance which, in cartilaginous fishes, 

 is the substitute for bone. This substance is 

 of a peculiar nature ; it yields neither gelatine 

 nor albumen, but is more analogous to inspis- 

 sated mucus than to any thing else. 



The earthy salts are not always in the same 

 proportion to each other in different animals. 

 We have seen that they are not the same in 

 man and the ox. Barros gives the following 

 table : 



Lion . 

 Sheep 

 Fowl 

 Frog , 

 Fish 



Phosphate of lime. Carbonate of lime. 



95-0 2-5 



830 19-3 



..... 88-9 10-4 



... .. 95-2 2-4 



91-9 5-3 



With respect to varieties depending on age 

 and situation, we have a table of the proportions 

 of animal matter and earth as found by Dr. 

 John Davy in several experiments, from which 

 it appears that old bones contain more earth 

 than young ones, and that the bones of the 

 head have a greater proportion than those of 

 the extremities.^ 



As to the exact nature of the earthy salts, 

 we have given the results obtained by Ber- 

 zelius as the latest and most accurate. But 

 it. may be right to state that differences of 



* Human Ostcogeny, by R. Nesbit, M.D. p. * Philosophical Transactions, 1800. 



Lond. 1736. t Traile de Chimie, Par. 1833. 



Memoires dc 1'Acadcmio Royalc des Science*, j See Monro's Elements of Anatomy, vol. i. 



1758. Edinb. 1825. 



