Financial losses from egg breakage have increased over the years. To seek any relation with shell strength, the structure of eggshell and shell membranes were examined by light microscope, transmission electron microscope and scanning electron microscope. They were taken from eggs laid by laying hens, from eggs removed from the oviduct and from eggs laid prematurely, and occasionally from incubated hen eggs and eggs of guinea-fowl, duck, turkey, emu and ostrich. The results with different methods of measurement showed how shell membranes vary in thickness, how some structural properties of shell may influence shell strength, how the shell and shell membranes form and how they are destroyed during incubation and what factors influence the cuticular surface of the eggs.

Ultrastructure of the hen eggshell and its physiological interpretation

Booth, V. H. (1956). Carotene, its Determination in Biological Materials. Cambridge: W. Heffer and Sons Ltd. (In the Press.) Fisher, R. A. (1950). Statistical Methodsfor Research Workers, I Ith ed. Section 21.1. London: Oliver and Boyd. Fraps, G. S. (1946). Arch. Biochem. 10, 485. Goodwin, T. W. (1955). In Modern Methods of Plant Analysis. Vol. 3 , p. 272. [K. Paech and M. V. Tracey, editors.] Berlin: Springer. Paul, M. F., Ells, V. R. & Paul, H. E. (1951). Amer. J. dig. Dis. 18, 278. Ramasarma, G. B. & Hakim, D. N. (1942). Ann. Biochem. 2, 181. Sexton, E. L., Mehl, J . W. & Deuel, H. J . Jr. (1946). J. Nutr. 31, 299. Sherman, W. C. (1941). J . Nutr. 22, 153. Wagner, K. H., Gunther, L. & Schulze, L. (1941). Vitam. u. Horm. I, 455. With, T. K. (1940). Absorption, Metabolism and Storage of Vitamin A and Carotene. Copenhagen: Munksgaard.

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The effect of calcium depletion on the chemical composition of bone minerals in laying hens.

1. Four experiments were carried out with Warren laying hens to elucidate the changes in plasma inorganic phosphorus (Pi) concentration during egg formation. 2. In hens receiving a normal diet containing a calcium supplement in a powdery form Pi increased from 25 to 42 mg/1 during an entire shell formation cycle (from 10 to 22 h after oviposition of the previous egg), while in cockerels Pi decreased slightly during the night. 3. This increase in Pi in hens, was not related to cessation of feeding at the onset of darkness but was specifically connected with the beginning of shell secretion. 4. When hens received calcium as crushed sea‐shells separately from the diet, the nocturnal peak in Pi virtually disappeared and only a temporary increase of 4 mg/1 between 10 and 14 h after oviposition remained. 5. These results indicate that the beginning of shell secretion is always accompanied by an increase in Pi and that a separate presentation of dietary calcium reduces the bone mobilisation at night.

Plasma inorganic phosphorus concentration during egg‐shell formation: Effect of the physical form of the dietary calcium

1. A series of balance experiments to compare calcium carbonate, calcium sulphate and calcium gluconate as sources of calcium for laying hens is described. 2. Not one of the three supplements showed all-round superiority, but calcium sulphate was the worst. 3. The main results indicate that: (a) Calcium sulphate and gluconate cause scouring but carbonate does not. (b) The best retention of calcium occurs with gluconate and the worst with sulphate. (c) Calcium carbonate gives the best shells and calcium sulphate the worst. 4. The experiments also throw fresh light on some more general aspects of calcium and phosphorus metabolism. 5. On the basis of these general results and a review of the literature of blood calcium and phosphorus in laying hens a theory dealing with certain aspects of egg-shell formation is presented.

Calcium and phosphorus balances with laying birds.

PEARSON, TERRY W., AND ANDREW M. GOLDNER. Calcium transport across avian uterus. I. E$Ects of electro&e substitution. Am. J. Physiol. 225(6) : 1508-l 5 12. 1973.-Unidirectional calcium fluxes from serosa to mucosa (JS,, ) and mucosa to serosa (Jmds ) were determined across the isolated quail uterus. When the tissue was bathed with normal bicarbonate buffer, the spontaneous electrical potential difierence was approximately 8 mv, mucosal surface negative. Tissue conductance was 27 mmho cm-2. The short-circuit current could not be explained by the net flux of sodium ion, calcium ion, or the sum of these fluxes. When the electrochemical gradient across the tissue was maintained at zero, there was a net flux of 0.164 PEq cm-2hr-1 in the secretory direction, serosa to mucosa. Removal of sodium ion did not alter net calcium flux; however, individual removal of the anions reduced the net flux primarily by reducing the serosa to mucosa flux. Bicarbonate removal reduced net calcium flux to 0.069 PEq cm-2hr? These results indicate that calcium transport across the avian uterus can occur against an electrochemical gradient and that the net flux is dependent in part on bicarbonate ion.

J. G. Feinberg

Papers

Fluctuations of Calcium and Inorganic Phosphorus in the Blood of the Laying Hen During the Cycle of One Egg