RATE OF REXEWAL OF THE FISH SKELETON 205 



regulating the j)lu)sphate concentration of tlie plasma, hut possihly 

 also in a more direct way, as suggested by Robison's (1912) earl\ 

 studies on bone formation. More recent work by Roche and Mourgue 

 (1939) leads to Ihc result thai a fracture of the rat's femur involves 

 a loss of appreciable^ amounts of the mineral constituents of the femur 

 followed by an opposite process after the lapse of about one month. 

 In the first weeks, phosphatase activity of the bone is also enhanced. 

 Roche and Mourgue made the very interesting observation that the 

 fracture of the left femur leads not only to an initial decrease in the 

 mineral content of the fractured left bone, followed later by a reversal 

 of this process, but a similar ])ehaviour is also shown by the intact 

 right femur. The enchanced phosphatase activity of the bone tissue 

 may be due to an increased magnesium concentration produced ])y 

 osteolysis following the fracture. Thus, even a fluctuation in the magne- 

 sium content of the plasma may promote the rate of renewal of the ske- 

 leton. 



Fluctuations in the phosphate, calcium, magnesium, and phosphatase 

 contents of the plasma thus make possible a biological recrystallization 

 of bone apatite and, corespondingly, a renewal of the skeleton. That 

 this process, which can be followed by making use of isotopic indicators, 

 was found to be a slow one is easy to understand. The bone apatite 

 contains a very appreciable part of the body's calcium and phosphorus 

 contents, anfl these constituents are present in a crystalline state. 

 Dissolution and formation of such crystallites may be expected to \)v 

 a slow process. Furthermore, we must envisage the probability that a 

 partial dissolution of a crystallite may be followed by a new formation 

 of some molecular layers which protect the underlying part of the crystal 

 from further changes. This process can often be repeated and leads to a 

 repeated renewal of a fraction of the crystallites, while the remaining 

 part of the crystal remains unchanged. The pronounced difference in the 

 rate of renewal of epiphysial and diaphysial tissues found by various 

 workers is due mainly to the better circulation taking place in the soft 

 epiphysial bones but, possibly, to some extent to the smaller size of the 

 crystals of the epiphysial tissue which favours an interchange between 

 lymph (plasma) and bone phosphate. 



In this paper are communicated the results of experiments carried 

 out with the aim of measuring the rate of renewal of the mineral consti- 

 tuents of the fish skeleton. However, a short survey of the results 

 hitherto obtained for the rate of renewal of the skeleton of mammalia 

 will first be given. 



