In how many branches of commerce, we wonder, does the microscope play its part. It is used in several departments of engineering for examining steels and many other metals not only for defects but to see how they are made up. It is used in brewing for studying the various yeasts and other substances, including the hops which go to the making of beer. All manufactures which depend upon fermentation, such as wine and vinegar making, are largely dependent upon the work of the microscope. In dairy work the microscope is invaluable. In the examination of various fabrics the assistance of the microscope is always summoned. Paper manufacture and paper testing give work for the microscopist but it would, we think, be easier to give a list of the branches of commerce in which the microscope is not used than to attempt to enumerate those which make use of the instrument. We cannot possibly describe all the uses to which the microscope is put, so we will confine ourselves to one or two of the more important and, at the same time, to those which can, for the most part be repeated at home. The two most important commodities for mankind are food and clothing; we cannot live without food and those of us who take but little pride in our appearance, must have clothing of some sort. We have said a little about food in another chapter and there we have also mentioned the impurities which find their way, by accident or design, into some of the commoner foods. In this chapter we will deal first of all with clothing describing how many of the raw materials may be recognised under the microscope and showing very briefly how fraud in connection with the manufacture of wearing apparel is detected. Practically all clothing is made from animal or vegetable fibres, some, however, is made of artificial fibres and these we shall mention. The vegetable fibres used in the manufacture of wearing apparel are all either hairs or what are called bast fibres and the latter, in non-scientific language, may be described as the strands which run through the roots and stems of most plants. The chief requirements of vegetable fibres, destined to be woven into fabrics, are strength, it is obvious that a weak fibre would be useless; length, the longer the fibre the better and as we shall see later, short fibres are often made up into inferior material; pliability, a stiff fibre would make an uncomfortable fabric; firmness and durability. Animal fibres used in the manufacture are either hairs or silk.