366 THE TISSUES. 



philis, gout, rickets, &c.; or from the presence of aneurism, abscesses, 

 sometimes from tumors, osteophytes, &c. The latter produce their 

 effect by cutting off the supply of blood to the bone, from compres- 

 sion of its nutrient vessels. 



If the circulation through the vessels of the medulla be inter- 

 rupted, a brownish-yellow pigment is formed in the medullary 

 canal, in the areolar tissue of the marrow. This is most common 

 in old persons. 



If the circulation through the periosteum be interrupted, it first 

 becomes atrophied itself, as is indicated by its shrinking, or by the 

 softening of its substance, together with the loss of its silvery lus- 

 tre, and its diminished adhesion to the bone. Simultaneously, also, 

 the bone becomes atrophied. In some cases of dropsy, the bone- 

 substance becomes lighter, it having undergone a partial resorp- 

 tion (as in senile atrophy, syphilis, cancerous cachexia, paralysis, 

 &c.) ; in others, it may disappear entirely (as in chronic diseases, 

 paralysis, and anchylosis). 



III. Fatty Degeneration of the Bones (Osteostearosis) may be re- 

 garded as one form of atrophy. It is most common in old persons 

 affected with apoplexy or cancer, and is indicated by the presence 

 of one or two, or even of entire groups of fat globules in the lacu- 

 nae, and sometimes even in the pores. (Fig. 196.) In the latter 

 case they are, however, isolated, wide apart, and far smaller. The 

 bone has a yellowish color, and a greasy feel, and a diminished 

 transparency when examined in thin plates. It has a greasy, lique- 

 fied medulla, and oil continues to exude in spite of repeated boiling. 

 This also constitutes one form of mollities ossium, while rachitis is 

 another. 



IV. Death of bone (necrosis), occurs sometimes from ostitis, and 

 always where the periosteum has been destroyed. There the lacu- 

 nae are but little changed; while the true osseous tissue is granular 

 and of a dark color. 



Y. Peculiar conditions exist in osteoporosis, osteomalacia, and 

 rachitis, and the chemical changes in the last disease have al- 

 ready been specified (p. 335). Osteoporosis consists in a dilata- 

 tion of the cancelli, and of the Haversian canals. In osteopsathyrosis, 

 the bone becomes extremely brittle from atrophy, with resorption 

 of the lamellae surrounding the Haversian canals. 



VI. Cancer and tubercle occur in bone, the former, however (espe- 

 cially the medullary form), far the most frequently. The latter is 

 believed by some to constitute the true pathological condition of 

 the bone in morbus coxarius. Here we find invading the bone 

 substance, the cancer-cells, and the tubercle- nuclei (pp. 139 and 117). 



VII. Pathological new -formations of bone (true ossification), occur 

 in a variety of parts and organs, especially in the periosteum and 

 dura mater, and in tendons and ligaments. Indeed, the possibility 

 must be admitted that true bone, distinguished by lacunae and pores, 

 may be developed in any part or organ consisting previously of 



