i2o6 METABOLISM OF LIPOIDS, STEROLS, [pt. iii 



structed. The kidney phosphatase increases in activity before birth, 

 and afterwards attains a constant level — the bone phosphatase de- 

 creases to a constant level. 



Fig. 377 (b) shows the admirable experiments of Fell & Robison 

 who studied the phosphatase in chick embryo bones, developing both 

 in vivo and in vitro. It is evident that the activity of the enzyme (as 

 measured by the phosphorus hydrolysed in 24 hours from sodium 

 glycerophosphate) increases in the bones from chicks incubated 

 normally. The same increase is seen in bone fragments differentiating 



O mgms. P hydrolysed in 24 hrs.from sodium glycero-phosphate 



i> » per mgm. dry weight of bone 



'Femurs /'"''^"^-ph^ (Fell S^ Robison) 



» -> 5 10 



E(>5r- Days of development 



(a) 



6 18 20 22 24 26 



Fig- 377- 



'ij '\j I ^ zu 25 30 



Days culture of 6 -day femurs in vitro 



in vitro although it is slower. In both cases, a peaked curve is seen 

 when the units of activity are referred to unit dry weight, no doubt 

 because after a time the ash is laid down more rapidly than the phos- 

 phatase is formed. The almost perfect self-differentiation of the bones 

 in these experiments was very striking; it was shown by 6th-day but 

 not by 4th or 5th-day bones. In this connection the finding of 

 phosphatase by Martland & Robison only in centres of active 

 ossification in human foetal bones should be remembered. 



It is worth remarking in connection with ossification that Hatchett 

 in i8oo made the curious observation that "in the ova of those 

 tribes of animals, the embryos of which have bones, there is 

 a portion of oily matter, and in those ova whose embryos consist 



