CHAPTER XII. 



THE BONES AND JOINTS. 

 The Bones. 

 ATROPHY. 



IN old age or in senile conditions the bones may become atrophied by 

 the absorption of the hard tissue ; the medullary spaces are enlarged, the 

 marrow tissue contains less fat and is often gelatinous in appearance. 

 As the result of the lack of use, or from any cause which interferes with 

 the nutrition of the bone, such as paralysis of the muscles or diseases of 

 the joints, the bones may atrophy. In connection with atrophy there 

 may be an ossifying periostitis, which results in making the bone look 

 even larger than normal-< Many of the conditions commonly called 

 atrophy, such as the Erosions of bones from tumors, etc., pressing upon 

 them, are really due to a rarefying osteitis. 



The bones, sometimes as the result of atrophy and sometimes from 

 causes which we do not understand, are unusually brittle and liable to 

 fracture. This disposition is sometimes hereditary. 



DISTURBANCES OF CIRCULATION. 



Hyperaemia. The evidences of this condition are most marked to the 

 naked eye in the periosteum and marrow, particularly the latter. It 

 should be remembered that the color of the marrow varies considerably 

 under normal conditions, depending upon age and situation. In the 

 bones of the foetus and new-born, and near the areas of ossification in the 

 young, the marrow is normally red in color. In adults the marrow of 

 the sternum, vertebrae, and to a certain degree that of the ribs, pelvic 

 and cranial bones, and the cancellous tissue of the ends of the long bones, 

 is red or reddish in color. But most of the marrow, particularly in long 

 bones of the extremities, is of a yellowish color from the presence of fat 

 cells. In old age the marrow of all the bones is apt to become pale, and 

 to assume a more or less translucent or gelatinous appearance. 



Hypersemia usually occurs as an accompaniment of inflammatory proc- 

 esses in the bone, and, when marked, the periosteum is swollen and red ; 

 the compact bone tissue may appear of a pink color, while the marrow, 

 either by an increase in the amount of blood or absorption of its fat, or 

 both, may be of a uniform dark red color or mottled with red and red- 

 dish-yellow. 



Haemorrhage. This may be due to wounds and injuries, to inflamma- 

 tory and uecrotic processes; and small haemorrhages often accompany 



