740 



THE BOXES AND JOINTS. 



masses of detritus. Sometimes the lime salts are removed from the base- 

 ment substance, which is converted into atypical fibrillar tissue and fatty 



and granular detritus. Very ex- 

 tensive suppurations and necrosis 

 may be associated with caries. 



Long-continued caries, especial- 

 ly in badly nourished individuals, is 

 apt to become complicated with tu- 

 berculous inflammation. 



There is very little tendency to 

 spontaneous healing in caries, but it 

 may occur, and the defects produced 

 may be more or less supplied by 

 means of new-formed bone. 



RACHITIS. (Rickets.) 



Eickets is a developmental dis- 

 ease of bone, in which the proper 

 ossification does not take place. The 

 disease usually occurs during the 

 first two years of life, but may be 

 congenital, 1 or may occur as late as 

 the twelfth year. 



The physiological growth of 

 bones presents three phases. They 

 grow in length by the production of 

 bone in the cartilage between the 

 epiphysis and diaphysis; in thick- 

 ness, by the growth of bone from 

 the inner layers of the periosteum. 

 At the same time the medullary 

 canal is enlarged, in proportion to 

 the growth of the bone, by the disap- 

 pearance of the inner layers of bone. 



In rickets these three phases of growth are abnormal. The carti- 

 laginous and subperiosteal cell growth, which precedes ossification, goes 

 on with increased rapidity and exuberance and in an irregular manner, 

 both between the epiphyses and diaphyses and beneath the periosteum, 

 while the actual ossification is imperfect, irregular, or wanting. At the 

 same time the dilatation of the medullary cavity goes on irregularly 

 and often to an excessive degree. 



If one examine microscopically in a rachitic bone the region between 

 the epiphysis and diaphysis (Fig. 490), he finds that the cartilage cells 

 are not regularly arranged in rows along a definite zone in advance of the 

 line of ossification, as in normal development, but that there is an irreg- 

 ular heaping-up of cartilage cells, sometimes in rows, sometimes not, 



1 Salvetti, Ziegler's Beitrage z. path. Anat., etc., Bd. xvi., p. 29, 1894, bibliography. 



FIG. 489. CARIES OF THE VERTEBRAE. 



