It may be thought that the space devoted to a discussion of the anatomical structure of the skin is disproportionately large; but there can be no doubt that, in order to make improvements, nothing is of more importance than a clear conception, even to the smallest details, of the materials and causes to be dealt with. The illustrations are from actual specimens, and enable the various parts of the hide to be identified under the microscope. As this instrument is a most useful means of investigation in the tanning industry, and one likely to be of increasing importance, it will be well, before proceeding further, to say a few words, both on the selection of a suitable instrument, and on its manipulation in general. To do useful work, it is not necessary to possess a very elaborate or expensive instrument, but it is essential that the microscope be well made and good of its kind. As high powers are often required in the examination, both of hide sections and of ferments, which are the principal objects of investigation in a tannery, it is of the first importance that the fine adjustment should be perfectly steady, without vibration or backlash. This, in the writer's experience, is never the case with cheap microscopes, in which the fine adjustment is made by a screw at the side of the tube moving the nose by means of a lever. A much more satisfactory arrangement is that in which the whole body of the microscope is raised or lowered by a screw in a pillar at the back of the stand on which it slides. A rack for the coarse adjustment is useful, but not essential. If a sliding tube only is provided, it must be tight enough not to slip, but must move easily up and down with a sort of screwing movement. A mechanical stage is not at all necessary, and for most purposes one of black glass is better as well as cheaper. The diaphragm for regulating the light should be as near level with the surface of the stage as possible, and when examined with a low power should appear in the centre of the field. For research work on the minuter ferments, an achromatic condenser and the finest oil- or water-immersion lenses are necessary, but directions for this are beyond the scope of the present work. It may, however, be mentioned that Prof. Flügge,[A] a first-class authority on the subject, especially recommends Abbé's illuminating apparatus as made by Zeiss. [Footnote A: "Fermente und Mikroparasiten," Leipzig, 1883.] A frequent defect in cheap English microscopes is that the mirror for substage illumination does not bring the rays of a lamp to a focus exactly on the slide, but frequently some inches above it. This may be to a great extent overcome by the use of a bulls'-eye condenser between the lamp and the microscope. Another defect is that sometimes the centre of the mirror is not in a line with that of the microscope body.