Wool, the fleece of sheep, an animal fibre, whose function in nature has been two-fold, the protection from cold, and an aid to evaporation of cutaneous moisture, is admirably fitted as a material for clothing. It permits but slow radiation of heat, and absorbs moisture better than any other clothing material. It does this, according to Parkes, in two ways: 1st. By interposition between the fibres. 2d. By penetration into the central canal. His experiments led him to believe its hydroscopic powers double in proportion to its weight and quadruple for surface, as compared with cotton or linen. Perfectly dried wool has the power of absorbing 50 per centum, by weight, of water. Under ordinary conditions it contains 12 to 18 per centum. Other things being equal, then woolen fabrics will best prevent too rapid radiation of heat; silk next, cotton third, linen fourth. Wash-leather, buckskin and chamois-skin need not be considered, for one or all of the following reasons: Expense, poor provision for evaporation, poor washing qualities. As absorbers of moisture, rank, respectively: wool, silk, linen and cotton. _The advantages of cotton over wool lie in its cheapness and non-shrinking qualities. If properly constructed, however, the advantageous properties of wool can be utilized without the shrinking by using a cotton framework, into the meshes of which the loose, raw fleece is worked._ That fabric will be best adapted for health, which combined with greatest porosity, possesses the least (a) conductivity, (b) greatest hydroscopic power, and (c) best shape. By porosity is understood the freedom with which air can pass through the interstices of a fabric. Pettenkoffer's practical demonstrations with the following cloths, shows that if heavy flannel be taken as permitting 100 parts of air to pass, linen permitted 60.3 or 60 per centum; lambskin 50.7 or 50.7 per centum; silk fabric, heavy, 14.4 or 14.4 per centum; glove-leather 1.5 or 1.5 per centum. The conclusion follows that porosity does not injure the powers of preventing radiation (it even increases it) for flannel, admittedly the warmest clothing, permits the freest circulation of air. In consequence of the fact of a fabric's possessing great porosity, it contains in its interstices what might be called "residual air." Whether gases possess conductivity is open to discussion, but this is certain, that such power is very small. Could we by any means envelop the body in a layer of stationary air, we could reduce the heat-loss to a minimum. A striking example of the poor conductivity of _stationary air_ is related by Dr. Kane, the Arctic explorer, who found that on perfectly still days they could withstand, without suffering, a temperature of-70 F.,[A] with ears and hands exposed, but the moment a breeze sprung up it became necessary to seek immediate shelter. [A] 70° F, below Zero.