66 STUDIES ON ALKALINE PHOSPHATASE 



waves of alkaline phosphatase occurred at different sites, includ- 

 ing a wave of intracellular phosphatase during the formation of 

 cartilage. But there was no calcification of the cartilage until 

 extracellular phosphatase appeared in the cartilage. 



In the calcification of fish scales and of teeth there is a similar 

 development of phosphatase prior to calcification (Thorell and 

 Wilton, 1945; Greep et ah, 1948; Lorch, unpublished). It thus 

 appears that the process of calcification, where the calcium is 

 laid down as calcium phosphate, is invariably produced by the 

 formation of extracellular phosphatase. The converse of this, 

 however, is not necessarily true. There are probably many sites 

 in which extracellular phosphatase is laid down in which no calci- 

 fication occurs. These sites normally include healing wounds, 

 though occasionally calcification will occur in a healing wound. 

 It also appears that failure to form bone in the dogfish is not 

 due to any deficiency in the calcification mechanism, but is due 

 to a lack of the reorganization of amorphous calcium phosphatase 

 into organized bone. This conclusion is, of course, readily com- 

 patible with the view that the cartilaginous skeleton of the dog- 

 fish is not primitive but has evolved by loss of one of the vital 

 processes of bone formation. On the other hand, this state of 

 affairs certainly does not prove that the cartilaginous fishes are 

 not primitive, since the state of affairs found in their skeletons 

 could represent either a loss of ability to reorganize calcium phos- 

 phate into bone, or a system in which this capacity has never 

 been evolved. 



It should perhaps be mentioned that it is not by any means 

 clear by what mechanism a sufficient concentration of phosphate 

 esters is produced in the calcifying regions to secure liberation 

 of an adequate supply of phosphate by enzyme activity. It may 

 be that a sufficient quantity of phosphate esters is normally pres- 

 ent in the intercellular fluid. Some authorities have suggested 

 that, since the cells in the calcifying regions are commonly rich 

 in glycogen, what occurs is that sugar is stored in these cells and 

 released as glucose phosphate or some other phosphate ester at 

 the time of formation of calcium phosphate. This, however, can- 

 not be the whole story, since, in order to form the phosphate ester, 

 phosphate is also required. If, therefore, the function of glyco- 

 gen found in calcifying regions is to provide a store of glucose for 

 the formation of phosphate esters, it is also necessary that the 



