The feathers of birds owe their bright colors to an oily secretion corresponding to the pigment in hair, and microscopical observation has revealed the fact that when these colors fade the oily secretion disappears, and is replaced by air. That extreme terror may blanch feathers as well as hair is shown in the case of a poor little starling, which upon being rescued from the claws of a cat became suddenly white. THE NAILS (p. 54).--The nails are mere modifications of the scarfskin, their horny appearance and feeling being due to the fact that the scales or plates of which they are composed are much harder and more closely packed. The root of the nail lies embedded, to the extent of about the twelfth part of an inch, in a fold of the sensitive skin, and, as may be observed from an inspection of the part, the scarfskin is not exactly continuous with the nail, but projects a little above it, forming a narrow margin. The nail, like the scarfskin, rests upon, and is intimately connected with, a structure almost identical with the sensitive skin; this is, however, thrown into ridges, which run parallel to one another, except at the back part, where they radiate from the center of the root. On examining the surface of the nail, a semicircular whitish portion is detected near its root; its color is dependent upon the fact that the ridges there contain fewer blood vessels, and therefore less blood, and on account of its half-moon shape it is called the _lunula_. The nail is constantly increasing in length, owing to the formation of new cells at the root, which push it forward, while the increase in its thickness is due to the secretion of new cells from the sensitive layer beneath, so that the farther the nail grows from the root, the thicker it becomes. Its nutrition, and consequently its growth, suffers in disease, the portion growing during disease being thinner than that growing in health; and accordingly a transverse groove is seen upon the nail, corresponding to the time of an illness. It will thus be seen that by a mere examination of the nail we can astonish our friends by telling them when they have been ill; and it has been estimated that the nail of the thumb grows from its root to its free extremity in five months, that of the great toe in twenty months, so that a transverse groove in the middle of the former indicates an illness about two and a half months before, and in the middle of the latter, about ten months.