The calcium content of the serum of sexually immature White Leghorn pullets is about 11·4 mg. per 100 c.c. A maximum variation of ± 1·5 mg. was recorded. 2. The calcium content of the serum of laying hens during the interval between oviposition and the next ovulation is about 17 mg. The maximum variation recorded was ± 2·5 mg. 3. When an egg is present in the oviduct the calcium content of the serum was found to vary between 10·5 and 28·5 mg. 4. It is suggested that the functionally active ovary maintains the blood calcium at a higher level than that of the sexually immature bird, and that the presence of an egg in the oviduct is accompanied by the mobilisation of calcium in the tissue during shell secretion, producing a transitory rise in blood calcium. 5. Some evidence for a transitory rise in the magnesium content of the serum during shell secretion was also obtained. The expenses of this research were defrayed by a grant from the Sex Hormones Committee of the Medical Research Council.
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Charles et al. (1933) studied this question.