ORIGIN AND FATE OF OSTEOCLASTS 333 



"the osteoblasts are constructive osseus elements; the osteoclasts 

 are destructive elements. The former elaborate bone; the latter 

 resorb it." 



There is no direct evidence as to how bone matrix (inorganic 

 and organic) is resorbed. One might assume it is essentially a 

 double process of decalcification and of digestion of the organic 

 substrate; conditions such as osteomalacia, in which the lime 

 salts are removed leaving the organic framework, perhaps sup- 

 port such a view. In the absence of more appropriate evidence, 

 therefore, the activity of an acid (carbon dioxide or lactic acid?) 

 and an enzyme can be tentatively suggested. 



According to Morpurgo and Satta ('08 a, '08 b), there is asso- 

 ciated with bone a thermolabile entity, an enzyme they believe, 

 responsible for calcium removal during experimental autolysis 

 of bone. The provisional nature of these two communications 

 renders their evaluation difficult. 



In his Harvey Lecture, Wells ('10-' 11) marshals numerous 

 facts to support the view that bone resorption is accomplished 

 through the agency of carbon dioxide. It is demonstrable that 

 calcium is normally contained in the blood in amounts approx- 

 imating saturation and that this content is from two to four 

 times that soluble in water. This amount of calcium in the blood 

 is held in solution by the colloids and the carbon dioxide. "In 

 normal ossification, and in most instances of pathological calci- 

 fication, the deposition is probably initiated by a process of col- 

 loidal adsorption .... Reduction in the amount of 

 carbon dioxide in such areas, or some unknown agency, causes 

 a precipitation in this colloid matrix, . . . ."It is well 

 known "that, no matter how sclerotic the walls of the veins may 

 become, they rarely, if ever, calcify so long as there is venous 

 blood rich in C0 2 flowing through them. As soon as they are 

 occluded, however, calcification occurs readily enough (e.g., 

 phleboliths)." It has been long established that carbon dioxide 

 in solution will dissolve calcium from bone but that NaHC0 3 

 cannot so act. Furthermore, studies on this solubility in vitro 

 and in vivo show "that pieces of ivory are absorbed most rapidly 

 in tissues whose metabolism is the most active, and where, by 



