744 THE BONES AND JOINTS. 



OSTEOMALACIA. 



This lesion consists in the softening of fully formed hard bon> tissue 

 by the removal of its inorganic salts. It is to be distinguished from 

 rickets, whose lesions are due to a faulty development of bone, although 

 in certain external characters the two diseases sometimes present consid- 

 erable similarity. Osteornalacia usually occurs in adults, most fre- 

 quently in females during pregnancy and after parturition ; more rarely 

 it occurs in males, and in females uuassociated with the above conditions. 

 Its cause is not known. 



Microscopical examination shows that the decalcification occurs first in 

 the periphery of the Haversian canals and in the inner layers of the walls 

 of the marrow spaces. As the salts of lime are removed the basement 

 substance at first remains as a finely fibrillated material, still preserving 

 the original lamellation. The bone cells may be changed in shape or 

 degenerated. After a time the decalcified tissue may disintegrate and 

 be absorbed, and its place occupied by new-formed marrow or granula- 

 tion tissue. As the disease goes on the marrow tissue is congested and 

 red, the fat absorbed, and there is a great accumulation of small sphe- 

 roidal cells ; or the marrow may assume a gelatinous appearance. The 

 decalcification and absorption of the bone from within may proceed so 

 far that the bony substance in the cancellous tissue almost entirely dis- 

 appears, and the compact bone is reduced to a thin, soft, decalcified tis- 

 sue. The disease is not always continuously progressive, but may be 

 subject to temporary cessation. 



As a result of this softened condition of the bones, the weight of the 

 body and the actions of the muscles may induce a series of deformities 

 which are sometimes excessive ; curvatures of the spine, complete and 

 incomplete fractures of the bone, distortions of the pelvis, sternum, etc. 

 There is a tendency in this disease to a general involvement of the bones, 

 but the changes are sometimes confined to single bones or groups of 

 bones. The cranium is rarely much affected. 



ALTERATIONS OF THE BONE MARROW IN LEUKEMIA AND 

 ANEMIA. 



In certain forms of leukaemia the marrow of the bones is very 

 markedly altered. The change consists mainly in an accumulation in 

 the marrow tissue of spheroidal cells, often in a condition of fatty degen- 

 eration, which lie in the meshes of reticular connective tissue and in and 

 along the walls of the blood-vessels. There may also be absorption of 

 the fat, and sometimes enlargement of the marrow cavity from absorp- 

 tion of the bone. These alterations seem to be primarily due to an 

 hyperplasia of the marrow cells. The new cells which accumulate in the 

 marrow under these conditions are of various forms. Most characteristic 

 are colorless, spheroidal cells which considerably resemble the large 



