the persistence of porosity. The fibers of wool, even when moistened, lose but little of their elasticity and do not allow the pores to close, while the filaments of linen, cotton, and silk become quite soft under the influence of moisture, and do not resist the invasion of the water. For this reason damp wool cools us much less than damp linen. A linen or silken shirt is cooler than a woolen one, because it more completely sponges off the sweat and exposes it to evaporation. These facts illustrate clearly the capital influence which space between the fibers exercises on the physical properties of cloths. A cloth must evidently be considered as a tissue formed of textile matter and air. The properties of the fibers themselves can give us only the most incomplete ideas of the physical effects which their assemblage would bring about. The arrangement of the fibers and the manner in which they are prepared are most frequently the important points. There is reason to believe that by looking along this road, still so little explored, we shall reach results that will permit us to make a better use of some of the innumerable textile materials which Nature has put at the disposition of our industry.
Hygienists, in speaking of different cloths, are generally contented with classifying them vaguely in the order of conductibility, and of designating by that word the greater or less facility they offer to the passage of heat. It is agreed that conductibility decreases in the following order: linen or hemp cloth, cotton, silk, and wool. Cloths made of linen, hemp, and cotton, are considered the coolest. They are readily moistened and cool the skin by both conductibility and evaporation. Linen, whether made of hemp or flax, is, says M. Bouchardat, of all substances destined for clothing, the one that most favors the affections resulting from the impression of moisture on the skin. But with many persons the coolness and pleasant feeling of linen are very highly appreciated as advantages.
Cotton cloth lets less heat escape, absorbs and retains a part of the perspiration, and cools less rapidly by evaporation; its use is generally more advantageous than that of linen. An opinion or prejudice prevails widely that cotton is less healthful than linen, based on the fact that, being a less perfect conductor and rougher, cotton irritates the skin more than linen does. Examined with the microscope, the fibers of cotton appear angular and stiff, while those of linen are round and supple. Cotton is not agreeable in cutaneous affections, but wool, in such cases being more hairy and warmer, would be still more disagreeable. This is the only condition, says M. Bouchardat, in which any other substance than very fine, well-washed, and well-worn linen can be worse than it. Aside from this, cotton cloth has the advantage over linen of being warmer in winter, and, in summer, of not exposing the body to the dangers of too rapid cooling. It should be used in preference to linen by inhabitants of cold and moist countries. Wool is still more irritating than cotton, on account of the stiffness of the