Not long ago, eggs broken in a laboratory in Boston were found to be quite fresh, which, according to the memorandum made upon the vessel, were placed in the solution four years ago. [Illustration] The shell of the egg is lined upon its interior everywhere with a very thin but pretty tough membrane, which, dividing at or very near the obtuse end, forms a small bag which is filled with air. In new-laid eggs this follicle appears very little, but it becomes larger when the egg is kept. In breaking an egg, this membrane is removed with the shell to which it adheres, and therefore is regarded a part of it, which it is not. The shell proper is made up mostly of earthy materials, of which ninety-seven per cent is carbonate of lime. The remainder is composed of two per cent of animal matter and one of phosphate of lime and magnesia. Carbonate of lime is the same material of which our marble quarries and chalk beds are composed: it is lime, or oxide of calcium, combined with carbonic acid, and is a hard, insoluble mineral substance, which does not appear to form any portion of the food of fowls. Now, where does the hen procure this substance with which to form the shell? If we confine fowls in a room and feed them with any of the cereal grains, excluding all sand, dust or earthy matter, they will go on for a time and lay eggs, each one having a perfect shell made up of the same calcareous elements. Vanvuelin, the distinguished chemist, shut up a hen ten days and fed her exclusively upon oats, of which she consumed 7,474 grains in weight. During this time four eggs were laid, the shells of which weighed nearly 409 grains: of this amount 276 grains was carbonate of lime, 17-1/2 phosphate of lime, and 10 gluten. But there is only a little carbonate of lime in oats, and from whence could this 409 grains of the rocky material have been derived? The answer to this question opens up some of the most curious and wonderful facts connected with animal chemistry, and affords glimpses of many of the operations of organic life, which, to the common mind, seem in the highest degree paradoxical and perplexing. The body of a bird, like that of a man, is but a piece of chemical apparatus made capable of transforming hard and fixed substances into others of a very unlike nature. In oats there is contained phosphate of lime, with an abundance of silica; and the stomach and assimilating organs of the bird are made capable of decomposing or rending asunder the lime salts and forming with the silica a silicate of lime.