BONES. 237 



parallel to that of the marrow tubes. They are rather more 

 opaque than the concentric plates which surround the marrow 

 tubes. Whether they be solid or perforated has not been de- 

 termined. In the cartilages of the ribs these particles are very 

 irregular in their position. 



The weight of cartilage in the long bones varies from 28 to 

 33 J per cent. It is very difficult to prevent a portion of it from 

 being dissolved by the muriatic acid employed to remove the 

 earthy salts of the bone. The best way is to take care that the 

 acid be very dilute . When the cartilages of bones are boiled a 

 sufficient time in water they are converted into collin, while the 

 permanent cartilages of the body by the same treatment become 

 chondrin. It is obvious from this that there is a difference be- 

 tween the cartilages of bones and the permanent cartilages, 

 though in what that difference consists we cannot at present spe- 

 cify. It has been already stated, on the authority of Berzelius, 

 that when the cartilage is thus converted into collin or chondrin 

 the blood-vessels of the bones remain undissolved, and fall to the 

 bottom of the liquid under the form of delicate fibres. 



2. The other constituent of bone is the earthy salts, which are 

 gradually deposited in the cartilage as the age of the animal ad- 

 vances. The bones of the foetus, at a certain interval before 

 birth, are all cartilage. At birth they are partly bone and part- 

 ly cartilage. The ossification goes on progressively, and in old 

 age only those permanent cartilages retain their nature which 

 are necessary for the maintenance of life and motion ; as the 

 cartilages of the ribs and those that tip the articulating bones. 



The earthy salts are held in solution by the muriatic acid. 

 From the effervescence which attends the action of muriatic acid 

 on bones, it is obvious that one of these salts is a carbonate. 

 And as calcined bones contain carbonate of lime, there is no 

 reason to doubt that carbonate of lime constitutes one of the 

 earthy salts which exists in bones. 



If we saturate the muriatic acid solution with caustic ammo- 

 nia, adding an excess of that alkali, the phosphate of lime 

 precipitates and may be collected on the filter. It constitutes 

 more than one-half of the weight of the bone subjected to ana- 

 lysis. 



If we now add carbonate of ammonia to the liquid which has 



