_Sheep's wool_ does absorb (see Knowledge 191) the aqueous vapor. Loosely distributed fibres of wool in a suitable fabric take hold of the vapor of the insensible perspiration in the gaseous form, and by virtue of gaseous diffusion continually exchange this with the gasses of the outer atmosphere. The conclusion, therefore, is that such a material is best suited for clothing, both in winter and summer. Sir John Billingall (lecturer on Military Surgery) mentions his experience in India, and the proof of the utility of wool in checking the progress of a most aggravated form of dysentery in the Second Battalion of the Royals. The result of this has led to the enforcement of the use of belts for tropical service. Mr. Sage of the Army Clothing Depot at Pemlico, tells me many thousands have lately been made there. My experience and subsequent observations have proven that, although loosely woven flannels may advantageously prevent the sudden chills from the evaporations of accumulated perspiration, this is better _done by a knitted fleecy wool fabric worn next the skin_. JAROS HYGIENIC MATERIAL, WOOL FLEECE KNIT. HYGIENIC UNDERWEAR BY L. D. RODGERS, A. M., M. D. (From Peoples' Health Journal, October, 1885.) Considerable scientific attention has recently been very profitably devoted to the question of fabrics for underwear most conducive to health. Interesting experiments have been made developing facts which will surprise almost everyone on learning them for the first time. One of the simplest and most readily understood of these experiments was that of filling tin cans with hot water and wrapping each one with a different fabric, and then observing with thermometers the varying rapidity in the loss of heat. Thus showing accurately the relative heat preserving value of each fabric. Of two cans surrounded with the same amount of common cotton batting, in one case the cotton being compressed, and the other not, the loss of heat was found to be much more rapid in the former than in the latter. Showing, therefore, conclusively, that loose open fabrics are warmer than those which contain less air in their interstices. This accords with the well-known fact that the new flannel is warmer than old which has undergone the felting or fulling processes. Assuming that flannel contains 100 units of air in its interstices, the permeability of other substances have been found to be as follows: Linen, 58; silk, 40; buckskin, 58; kid, 1; chamois, 51. Doubling the layers of any given material does not diminish the loss of heat in the same proportion. Assuming the loss of heat through a single layer to be 100, through a double layer of the same material it is found to be as follows: Thin silk, 97; gutta percha, 96; shirtings, 95; stout silk, 94; thick home-spun linen, 91; chamois leather, 88-90; flannel, 86; summer buckskin, 88; winter buckskin, 86. Thus we see that the loss of heat through two layers of thin silk is only three per cent.