SECT. 12] GYCLOSES, PHOSPHORUS, SULPHUR 1205 



initial value, or rather below it. This must surely be due to the fact 

 that, in the water-soluble phosphorus, we have the principal form 

 in which phosphorus is transported from place to place. It would 

 never be likely to make up a great part of the total phosphorus, for 

 its concentration would always be kept low owing to its destruction 

 as soon as it was formed, but yet a slight rise might be expected to 

 hint at a more intense transport of phosphorus. The water-soluble 

 organic phosphorus is perhaps especially associated with ossification, 

 as an intermediate stage in the transformation of ether-soluble into in- 

 organic phosphorus. In this fraction would be included hexosephos- 

 phates, glycerophosphates, inositolphosphates (phy tin-like bodies), 

 etc. From the point of view of bone formation great interest attaches 

 to these effects. Robison in 1923 discovered an enzyme in calcifying 

 bone which had the power of breaking down hexosemonophosphoric 

 acid to inorganic phosphate, and also attacked the glycerophosphoric 

 esters, but no cyclose phosphorus compounds. It was not present 

 in other tissues besides bone, except to a slight degree in the intestine 

 and kidney (Robison & Soames; Robison & Kay; Robison & Good- 

 win), and Robison & Martland showed that there was concurrence 

 between the onset of calcification and the appearance of the bone 

 phosphatase. Subsequent work indicated that the bone phosphatase 

 was exclusively concerned with calcification in growth, while the 

 kidney phosphatase was concerned with normal functioning. Kay 

 found that on the 12th day of development in the chick there was 

 three times as much phosphatase in the leg bones as on the 21st day, 

 and that on the 12th day the water-soluble organic substrate was 

 present to a much greater extent than in the unincubated egg. Now 

 in the curves for the embryo only (Fig. 375) it is noticeable that 

 just during the period of most vigorous bone formation, i.e. from 

 the 1 2th to the 21st day the water-soluble organic phosphorus is 

 steadily decreasing. It is as if the water-soluble organic phosphorus 

 was concentrated to a high level in the embryonic body during the 

 first half of incubation, only to be transferred into the inorganic form 

 by the activity of the bone phosphatase during the last half. Thus the 

 lipoid phosphorus is transformed into a suitable substrate for the 

 bone phosphatase, reinforcing the small amount of the substrate 

 initially present, and then, as calcification proceeds, is deposited in 

 inorganic form. Kay made some observations on rabbit embryos and 

 young animals, from which the graph in Fig. 377 {a) has been con- 



