Numerous methods are employed for the preparation, hardening, staining, and section cutting of animal and vegetable tissues for the microscope, the details of which are modified, or varied as may be found needful, from time to time, by those whose intimate acquaintance with the subject entitles them to make innovations and changes in this very important department of microscopy. In the hands of the original worker, formulæ and methods will only be regarded as finger-posts pointing out a means of saving time in turning over pages to find this or that special method of staining. For this particular reason I have collected all the most accredited formulæ together in an Appendix at the end of the book, and arranged them alphabetically for ready reference. As to section cutting, the student will do well to practise himself in making dissections, thick and thin sections, of vegetable and animal substances. The medical student will require no advice on this point, as the use of the scalpel, and those instruments needed for microscopical work, form an important part of his education. Of all the instruments contrived for delicate dissections, none are more serviceable than those which the student may make for himself out of ordinary needles. These may be fixed in handles as represented in Fig. 229, in addition to which, a pair of scissors and forceps, and a few small knives, such as those used in eye-operations, will prove most suitable. The double-bladed scissors represented in Fig. 227, with curved blades, are brought into use for cutting vegetable and other soft structures, the disadvantage attendant upon the use of which is owing to the curvature of the blades; when dealing with flat surfaces, the middle of the section is left too thick to exhibit structure. The double-bladed knife of Professor Valentin was formerly held in high estimation by the microscopist, but this has been almost superseded by the microtome, which has taken the place of all other instruments, since by its aid uniform series of nearly all substances can be cut. The standard unit of a perfect section cutter, of any kind, has been fixed by the Royal Microscopical Society at the one-thousandth of a millimetre. [Illustration: Fig. 227.--Section Scissors and Forceps.] The use of the razor for cutting sections has not been wholly abandoned, the method of using which is as follows:--Take the tissue between the thumb and finger of the left hand, hold the finger horizontally, so that its upper surface may form a rest for the razor to glide upon, take the razor firmly, and keep the handle in a line with the blade, then draw it through the tissue from heel to point and towards yourself. While cutting keep the razor well wetted with diluted methylated spirit. [Illustration: Fig. 228.--Dissecting Knives.]