Mechanical wood pulp which enters so largely into the manufacture of paper is easily recognised by those who have given a fair amount of attention to the microscopical examination of plant life. Wood pulp is always used in conjunction with some binding material such as cotton or flax fibres. Many different kinds of wood are converted into pulp and of course it requires a considerable amount of experience to say exactly what kind of wood has been used in a certain paper. Some of the woods are poplars of various kinds, others spruces and firs. It is easy to distinguish the conifers as spruces and firs are called, for the reason that the trees bear cones. The little fragments of wood, scattered throughout the paper, have minute circular perforations upon them, resembling miniature quoits, if they belong to the conifers; none of the other woods possess these “pits” as they are called. Very many other plant remains may be found in paper, for instance hop fibres are used sometimes and their presence is usually shown by remnants of the climbing hooks which, during life, studded the climbing stem of the hop. Some of the important animal hairs, used in the manufacture of clothing, may now claim our attention. Wool and silk are of course the most important. The best wool is all obtained from the domestic sheep so let us examine one or two of the easily obtained hairs from this animal. As with the vegetable fibres we may examine them in a drop of water but, in this case, we shall find that we cannot make the water go near the wool for the reason that the latter is covered with a film of grease, called wool fat. Our first care, therefore, it to get rid of the wool fat and this may be done by shaking the specimen with a little ether or chloroform. Having cleaned the wool fibres we may proceed to examine them under a high magnification and, to see their structure fully, we must move the fine adjustment to and fro, for it is not possible to obtain a true idea of its structure without doing so. We shall see that the hair consists of two layers, an outer skin and an inner core. The latter consists of a number of cells, whilst the former is composed of scales, of which the lower edges are arranged beneath the upper edges of the previous scales, like tiles on a roof. The free edges of the scales project outwards a little so that the wool, when not so highly magnified, appears to have a toothed margin. Further examination will show us that no single scale completely envelops the strand of wool, usually two scales make the complete circuit. It is a curious and easily tested phenomenon that in say an inch of wool from the same kind of sheep there are always the same number or very nearly the same number of scales. By counting the scales, experts can tell from what animal the wool is derived.