I. TESTA OVI (
Putamen ovi, Egg-shell) is composed chiefly of calcium carbonate (89 to 97 per cent), calcium and magnesium phosphate (0.5 to 5 per cent), magnesium carbonate (0 to 2 per cent), and organic substance (2 to 5 per cent). The carbonate of calcium renders the shell absorbent and antacid. The albuminous membrane (
Pellicula ovi, Membrana putaminis) which lines the inner surface of the shell, is a keratin- (horn) like substance, soluble in alkalies, from which solution it is precipitated by acids. At the broad end of the egg it forms an air space, the
Follicula aëris .