cotton, diaphanous, cylindrical, and presenting little swellings at tolerably regular intervals. The elementary fibres (of which the main fibre is composed) can be often seen in these swellings, and also at the end of broken threads which have been much used. The hemp fibre is something like

this, but much coarser, and at the knots it separates often into a number of smaller fibres. Silk is a little like linen, but finer, and with much fewer knots.

As an Article of Clothing.-Linen conducts heat and absorbs water

FIG. 96.-Jute-United and single elongated Cellular Tissues. Resinous (?) matter adhering more or less to

all the fibres.

slightly better than cotton. It is a little smoother than cotton. As an article of clothing it may be classed with it. In choosing linen regard is had to the evenness of the threads, and to the fineness and closeness of the

texture. The color should be white, and the surface glossy. Starch is often used to give glossiness. This is detected by iodine, and removed by the first washing.

Jute.-Jute is now very largely used, and appears to enter into the adulteration of most fabrics. Jute is obtained from the Corchorus capsularis, and comes to England from Russia and India. The fibres are of considerable length, are hollow, thickened, and with narrowings and constrictions in the tubular portions; sometimes an air-bubble may be in the fibre, as shown in the drawing. The drawing, by Dr. Maddox, shows the differences between the jute and cotton or linen.

Wool-Microscopic Characters.-Round fibres, transparent or a little hazy, colorless, except when artificially dyed. The fibre is made up of a number of little cornets, which have become united. There are very evident slightly oblique cross markings, which indicate the bases of the cornets; and at these points the fibre is very slightly larger. There are also fine longitudinal markings. There is a canal, but it is often obliterated. When old and worn, the fibre breaks up into fibrilla; and, at the same time, the slight prominence at the cross markings disappear, and even the markings become indistinct. By these characters old wool can be recognized. Size of fibres varies, but an

average is given by the figure. The finest wools have the smallest fibres.

As an Article of Clothing.-Wool is a bad conductor of heat and a great absorber of water. The water penetrates into the fibres themselves and distends them (hygroscopic water), and also lies between them (water of interposition). In these respects it is greatly superior to either cotton or linen, its power of hygroscopic absorption being at least double in proportion to its weight, and quadruple in proportion to its surface.

This property of hygroscopically absorbing water is a most important one. During perspiration the evaporation from the surface of the body is necessary to reduce the heat which is generated by the exercise. When the exercise is finished, the evaporation still goes on, and, as already noticed, to such an extent as to chill the frame. When dry woollen clothing is put on after exertion, the vapor from the surface of the body is condensed in the wool, and gives out again the large amount of heat which had become latent when the water was vaporized. Therefore a woollen covering, from this cause alone, at once feels warm when used during sweating. In the case of cotton and linen the perspiration passes through them, and evaporates from the external surface without condensation; the loss of heat then continues. These facts make it plain why dry woollen clothes are so useful after exertion.'

FIG. 97.--Wool x 285.

1 Pettenkofer gives (Zt. für Biol., Band i., p. 185) some experiments showing the hygroscopic power of wool as compared with linen. He shows that linen not only absorbs much less water, but parts with it much more quickly; thus, to cite one experiment,,

In addition to this, the texture of wool is warmer, from its bad conducting power, and it is less easily penetrated by cold winds. The disadvantage of wool is the way in which its soft fibre shrinks in washing, and after a time becomes smaller, harder, and probably less absorbent.'

In the choice of woollen underclothing the touch is a great guide. There should be smoothness and great softness of texture; to the eye the texture should be close; the hairs standing out from the surface of equal length, not long and straggling. The heavier the substance is, in a given bulk, the better. In the case of blankets, the softness, thickness, and closeness of the pile, the closeness of the texture, and the weight of the blanket, are the best guides.

In woollen cloth the rules are the same. When held against the light, the cloth should be of uniform texture, without holes; when folded and suddenly stretched, it should give a clear ringing note; it should be very resistent when stretched with violence; the "tearing power" is the best way of judging if "shoddy" (old used and worked-up wool and cloth) has been mixed with fresh wool. A certain weight must be borne by every piece of cloth. At the Government Clothing Establishment at Pimlico, a machine is used which marks the exact weight necessary to tear across a piece of cloth. Schlesinger recommends the following plan for the examination of a mixed fabric containing shoddy:-Examine it with a microscope, and recognize if it contains cotton, or silk, or linen, besides wool. If so, dissolve them by ammoniacal solution of copper. In this way a qualitative examination is first made. Then fix attention on the wool. In shoddy both colored and colorless wool-fibres are often seen, as the fibres have been derived from different cloths which have been partially bleached; the coloring matter, if it remains, is different-indigo, purpurin, or madder. The diameter of the wool is never so regular as in fresh wool, and it changes suddenly or gradually in diameter, and suddenly widens again with a little swelling, and then thins off again; the cross marking or scales are also almost obliterated. When liquor potassæ is applied the shoddy wool is attacked much more quickly than fresh wool.

The dye also must be good, and of the kind named in the contract, and tests must be applied.

Leather.-Choice of leather; it should be well tanned, and without any marks of corrosion, or attacks of insects. The thinner kind should be perfectly supple.

Leather is not only used for shoes, leggings, and accoutrements; it is employed occasionally for coats and trousers. It is an extremely warm clothing, as no wind blows through it, and is therefore well adapted for cold, windy climates. Leather or sheepskin coats are very common in

equal surface of linen and flannel being exposed to the air after being placed in equal conditions of absorption, the linen lost in 75 minutes 5.993 grammes, and the flannel only 4.858 grammes of water. Subsequently the evaporation from the linen lessened, as was to be expected, as it was becoming drier; that from the flannel continued to pass off moderately. The much greater cooling effect of linen is seen.

The porosity of clothing, i.e., the rapidity with which air is driven through, is a point to be noted. By an equal pressure equivalent to a column of water 4.5 centimetres high, an area of 1 centimetre diameter forced air through as follows:-Through linen, 6.03 litres; flannel, 10.41; lambskin, 5.07; glove-leather, .15; wash-leather, 5.37; silk-fabric, 4.14.

It thus appears that the warmest clothing (flannel) may be the most porous; mere porosity, in fact, is only one element in the consideration.

In washing woollen articles, they should never be rubbed or wrung. They should be placed in a hot solution of soap, moved about, and then plunged into cold water; when the soap is got rid of they should be hung up to dry without wringing.

Turkey, Tartary, Persia, the Danubian Provinces, and everywhere where the cold north winds are felt. In Canada, coats of sheepskin or buffalohide have been found very useful, and are commonly used by sentries.

Waterproof Clothing,—Like leather articles, the india-rubber is an exceedingly hot dress, owing to the same causes, viz., impermeability to wind, and condensation and retention of perspiration. It is objected to by many on these grounds, and especially the latter; and Lévy informs us that the Council of Health of the French Army have persistently refused (and, in his opinion, very properly) the introduction of waterproof garments into the army. If, however, woollen underthings are worn, the perspiration is sufficiently absorbed by those during the comparatively short time waterproof clothing is worn, and the objection is properly not valid, unless the waterproof is continually worn.

The great use of waterproof is, of course, its protection against rain, and in this respect it is invaluable to the soldier, and should be largely used. By the side of this great use, all its defects appear to be minor evils.

India-rubber cloth loses in part its distensibility in very cold countries, and becomes too distensible in the tropics. It is also apt to rot by absorption of oxygen. Paraffined cloth is equally good, and the paraffin does not rot the fibre like common oil.

General Conclusions.

Protection against Cold.-For equal thicknesses, wool is much superior to either cotton or linen, and should be worn for all underclothing. In case of extreme cold, besides wool, leather, or waterproof clothing is useful. Cotton and linen are nearly equal.

Protection against Heat.-Texture has nothing to do with protection from the direct solar rays; this depends entirely on color. White is the best color; then gray, yellow, pink, blue, black. In hot countries, there

fore, white or light gray clothing should be chosen.

In the shade, the effect of color is not marked. The thickness, and the conducting power of the material, are the conditions (especially the former) which influence heat.

Protection against Cold Winds.-For equal thicknesses, leather and indiarubber take the first rank; wool the second; cotton and linen about equal. Absorption of Perspiration.-Wool has more than double the power of cotton and linen.

Absorption of Odors.-This partly depends on color; and Stark's observations show that the power of absorption is in this order—black, blue, red, green, yellow, white. As far as texture is concerned, the absorption is in proportion to the hygroscopic absorption, and wool therefore absorbs more than cotton or linen.

Protection against Malaria.-It has been supposed that wearing flannel next the skin lessens the risk of malaria. As it is generally supposed that the poison of malaria enters either by the lungs or stomach, it is difficult to see how protection to the skin can prevent its action; except indirectly, by preventing chill in persons who have already suffered from ague. But the very great authority of Andrew Combe, drawn from experience at Rome, is in favor of its having some influence; and it has been used on the west coast of Africa for this purpose, with apparently good results.

CHAPTER XIV.

CLIMATE.

It is not easy to give a proper definition of climate.

The effect of climate on the human body is the sum of the influences which are connected either with the solar agencies, the soil, the air, or the water of a place, and as these influences are in the highest degree complex, it is not at present possible to trace out their effects with any certainty.

With regard generally to the effect of climate on human life, it would seem certain that the facility of obtaining food (which is itself influenced by climate), rather than any of the immediate effects of climate, regulates the location of men and the amount of population. The human frame seems to acquire in time a wonderful power of adaptation; the Eskimos, when they can obtain plenty of food, are large strong men (though nothing is known of their average length of life), and the dwellers in the hottest parts of the world (provided there is no malaria, and that their food is nutritious) show a stature as lofty, and a strength as great, as any dwellers in temperate climates. Peculiarities of race, indeed, arising no one knows how, but probably from the combined influences of climate, food, and customs, acting through many ages, appear to have more effect on stature, health, and duration of life, than climate alone. Still, it would seem probable that, in climatic conditions so diverse, there arise some special differences of structure which are most marked in the skin, but may possibly involve other organs.

How soon the body, when it has become accustomed by length of residence for successive generations to one climate, can accommodate itself to, or bear the conditions of, the climate of another widely different place, is a question which can only be answered when the influences of climate are better known. The hypothesis of "acclimatization" implies that there is at first an injurious effect produced, and then an accommodation of the body to the new conditions within a very limited time; that, for example, the dweller in northern zones passing into the tropics, although he at first suffers, acquires in a few years some special constitution which relieves him from the injurious consequences which, it is supposed, the change at first brought with it. There are, therefore, two assumptions, viz., of an injurious effect, and of a relief from it. Are either correct?

It may seem a bold thing to question the commonly received opinion, that a tropical climate is injurious to a northern constitution, but there are some striking facts which it is difficult to reconcile with such an opinion. The army experience shows that, both in the West Indies and in India, the mortality of the soldier has been gradually decreasing, until, in some stations in the West Indies (as, for example, Trinidad and Barbadoes), the sickness and mortality among the European soldiers are actually less than on home service in years which have no yellow fever. In India, a century