Let us, however, describe first the way in which objects are prepared for section-cutting--whether by hand or by machine. It has already been noticed that animal substances contain a quantity of water, and therefore will not keep. The same circumstance renders them soft and squashy, so that the sharpest razor in the world, in cutting a section, must necessarily do more or less damage to the structure of the delicate tissues. The water is held in the meshes of the tissues just as it is held, for example, in the meshes of a sponge. Now, if we were dealing with the sponge, we could get it to absorb any other fluid substance besides water; we might choose one that would prevent decomposition; we might choose one that would go harder by cooling; so as to change the sponge into a strong solid block that could be knocked about without sustaining any damage. This is exactly what we must do with our animal tissue to prepare it for section-cutting; and the most convenient fluid for the purpose is melted wax. But whereas we might take our sponge out of water, squeeze it dry, and dip it straight into melted wax, we can by no means do so with our animal tissues. For one thing they usually cannot be squeezed, and where they can, they would of course be irretrievably ruined by such a rough process. Even the transference of the specimen from one fluid to another of very different qualities and density, would deface the tissues. Cells would burst, or be squeezed out of shape, and organs would be loosed from their right position by the currents set up in all parts of the specimen, under such circumstances. We must, therefore, try to get rid of the water by degrees. This may be done by gradually adding alcohol, a fluid which may be diluted with water in any proportion. We begin with a comparatively weak solution of alcohol, say about fifty per cent., and immerse the specimen in this for some little time. The time required depends somewhat upon the size of the specimen; if a large one, a new fluid will take longer to filter through it. Then we must change this solution of alcohol for stronger ones, say seventy per cent. and ninety per cent. successively, and finally to absolute alcohol. By this time the alcohol will have removed almost nearly all trace of water from the specimen. The latter is now nearly but not quite ready to be imbedded in melted wax; but first we must soak it for a while in a fluid intermediate in thickness between the alcohol and the wax, and capable of mixing in a friendly manner with both. Then it goes into a bath of melted wax, and is kept for hours at a stated temperature until the wax permeates it thoroughly. Then the melted wax and the specimen along with it is poured into a little mould and left to cool. The block of wax containing the specimen is cut down to a quadrangular shape, and is now ready for section cutting. In old days the block was placed in a stand, and successive sections were cut from it by hand with a razor.