PATHOLOGICAL STATES OF BO^'E. 365 



merit, fracture of the olecranon process, and that of the patella. It 

 is also common in fracture of the spongy bones, and may occur in 

 fracture of any bone under unfavorable circumstances ; of which a 

 want of rest at the point of fracture is the most common, though 

 by no means the only one. In some cases a want of plasma or of 

 plasticity in it, is the cause of non-union by bone. 



The question whether the plasma from which the new osseous 

 tissue is developed is exuded by the periosteum alone, or by the 

 other soft parts also, is not so important as some authors seem to 

 have held. Obviously it can make no difference whether it be 

 poured out by the vessels of the periosteum alone (as it certainly is 

 in part), or not. Whencesoever derived, however, it can be organ- 

 ized into bone only while in contact with either bone or periosteum; 

 and hence the importance of leaving all the spiculae of bone in 

 place, in cases of comminuted fracture, as centres of ossification for 

 repairing the injury provided they are not so detached as to cause 

 irritation as foreign bodies. 



Finally, cases occur in which entire bones have been reproduced 

 after removal, provided the periosteum had been preserved. This 

 has occurred with the lower jaw-bone, the ribs, the scapulae, and the 

 clavicle in a case known to the author. A rudiment of bone has 

 sometimes been reproduced in the lower animals, when the whole 

 periosteum, as well as the bone, had been excised. (Heine?) 



Pathological Conditions and New Formations of Bone. 



The changes in the chemical composition of bone in its various 

 pathological states have already been noticed on pages 334 5. 



I. Hypertrophy of bone assumes various forms, which may, how- 

 ever, be reduced to two classes: (1), external deposits (hyperostoses), 

 formed chiefly from the periosteum ; and (2), internal deposits, or 

 sclerosis. 



1. In regard to the hyperostoses (exostoses and osteophytes), 

 Virchow shows that those of the cranium are formed directly from 

 white fibrous tissue, without the intervention of cartilage. Some- 

 times the new bone-structure is perfectly normal ; sometimes not so. 

 They appear from periostitis, and in arthritis, syphilis, &c. 



2. In sclerosis (osteosclerosis), the substance of the bone is more 

 dense and harder than usual, and the term eburnation has been here 

 applied. Here the Haversian rods are increased at the expense of 

 the cancelli and the medullary canal. The lacunas also appear to 

 contain calcareous salts, and are more opaque than usual. 



II. Atrophy of bone manifests itself in old age (senile atrophy of 

 the bones), and a similar condition may occur in tuberculosis, sy- 



