339 



Troja. This membrane has no more to do with the formation of the 

 new bone, in necrosis, than with that of the callus in fracture*. The pe- 

 riosteum, covering a bone affected with necrosis, does not become thick- 

 er, and does not acquire more consistence ; nor is there formed around 

 the ends of a fractured bone, a ring to keep them cemented, as was the 

 opinion of Duhamel ; an opinion recently brought forward in a work in 

 which the author seems to delight in reviving errors that have been aban- 

 doned for ages. Destitute of nourishment, (lead and dried up in this ar- 

 tifical necrosis, the sequestra moves in the centre of the new osseous 

 production, from which it may be extracted by a perforation made for 

 that purpose. It is owing to the same sympathy, that the dull noc- 

 turnal pains which are occasioned by the warmth of the bed, in patients 

 in the last stages of the venereal affection, and which appear to have their 

 seat in the centre of the long bones, occasion a swelling of these bones 

 and of the periosteum. 



The use of the periosteum is to regulate the distribution of the nutri- 

 tious juices of bones, since, whenever it is removed, granulations arise, 

 in an irregular manner, on the spot that is bared. This quality is, be- 

 sides, common to all fibrous membranes whose destruction is followed by 

 excrescences from the organs which they cover. The same take place, 

 whenever trees are partially stripped of their bark. It has been errone- 

 ously believed, that the periosteum, in the same way as the bark of plants, 

 contributes to the growth of the bones, by the successive induration of 

 its internal lamina. 



The marrow which tills the central cavity of the long bones ; and the 

 medullary fluid contained in the cells of the spongy substance, bear the 

 greatest analogy to adeps, both in their chemical composition and in their 

 uses (CVI.) The proportion of these two fluids is uniformly relative.^ 

 In very thin people, the bones contain a marVow that is thin and watery, 

 and though this fluid always fills the internal cavities of these .organs, 

 whose solid parietes cannot collapse, it contains much fewer particles in 

 the same bulk ; and its quantity like that of the fat, is in fact diminished. 

 It is the product of arterial exhalation, and does not serve to the imme- 

 diate nutrition of the bone, as was thought by the ancients ; at least, it 

 does not answer the purpose solely, for, in the numerous class of birds, 

 the bones contain cavities for air, and are destitute of this fluid. It is dif- 

 ficult to determine the use of the marrow and of the medullary fluid : 

 may they not answer the purpose of filling the cavities which Nature has 

 formed in the bones, so as to render them lighter ? Does a part of these 

 fluids exude through the cartilages of the joints, and mix with the syno- 

 via to increase its quantity: and to lessen the friction of the articulating 

 surfaces ? If this transudation may take place after death, why might it 

 not take place, when all the parts are in a state of vital warmth and ex- 

 pansion! ? 



* The manner in which the new bone acquires a periosteum, in cases of the regene- 

 ration of this texture, is a matter of much interest and doubt. In the examination of 

 some specimens, Dr. Knox observed a thin membrane covering 1 the osseous granulations; 

 but he knew of no facts to decide whence the membrane proceeds. " It is not unlike- 

 ly," he remarks, "that it is supplied by the cellular texture either of the new bone, or 

 of the surrounding- parts ; and that in some instances it may be merely a prolongation of 

 the old. New skin on ulcers does not always grow from the surrounding 1 healthy edg- 

 es : which fact may be applied to the formation of new periosteum." Copland. 



f The marrow of the bones is contained in the medullary membrane. This latter sub- 



