182 T. G. Taylor, A. Williams, J. Kirkley 



Acknowledgements 

 We are indebted to Miss Judith Metcalfe and Miss Janet Stanley for their 

 assistance; and to Messrs Sandoz Products Ltd for their help. The work was sup- 

 ported by grants from the Medical Research Council to P. Fourman and to C. G. 

 Woods. 



References 



Clark, C. G., J. Crooks, A. A. Dawson, and P. E. G. Mitchell: Disordered calcium meta- 

 bolism after Polya gastrectomy. Lancet i, 734 (1964). 



Jones, C. T., J. A. Williams, E. V. Cox, M. J. Meynell, W. T. Cooke, and F. A. R. Stam- 

 mers: Peptic ulceration: some haematologlcal and metabolic consequences of gastric 

 surgery. Lancet ii, 425 (1962). 



NoRDiN, B. E. C, and R. Eraser: The indirect assessment of parathyroid function. In Ciba 

 Foundation Symposium on Bone Structure and Metabolism. Wolstenholme, G. E. W., 

 and C. M. O'Connor (eds.). London: Churchill 1956, p. 222. 



Changes in the Activities of Plasma Acid and Alkaline 

 Phosphatases during Egg Shell Calcification in the Domestic Fowl 



T. G. Taylor, A. Williams, J. Kirkley 

 Department of Physiological Chemistry, The University, Reading, England 



The calcium metabolism of the laying bird is probably more intense than that of 

 any other organism. The laying hen, for example, secretes on the egg shell 1.6 — 2.4 g 

 calcium, in the form of the carbonate, in a period of 20 hours or so, most of it during 

 the last 16 hours of the shell-calcification process. The total plasma volume of an 

 average hen is 100 ml and the average level of total plasma calcium is 25 mg/100 ml 

 and it may thus be calculated that a weight of calcium equal to the total amount in 

 circulation at any one instant is removed from the blood every 10 — 15 minutes 

 during the main period of the formation of the egg shell. When the rate of calcium 

 absorption from the gut is less than the rate at which calcium is deposited on the 

 shell the balance is derived from the skeleton, and during the early hours of the 

 morning the bulk of calcium is supplied from the latter source. 



During the laying period the marrow cavities of the majority of the bones of 

 female birds contains a system of secondary bone which grows out from the endosteal 

 surface in the form of fine interlacing spicules, and it is this bone (known as 

 medullary bone) which is mobilized during the process of shell formation, and re- 

 built when shell calcification is not in progress. The phase of bone-destruction is 

 characterized by the presence of large numbers of osteoclasts and in the bone-forming 

 phase osteoblasts predominate, and the cell population thus undergoes cyclic changes 

 during the formation of the egg. 



Because of the rapid changes in cellular activity which the medullary bone under- 

 goes, the laying hen is a most useful species for the study of bone metabolism and in 

 the present work the changes in the activities of acid and alkaline phosphatases in 

 the plasma during critical stages of laying cycle have been studied. The overall 



