Even if already immersed during carriage in various preservative fluids, it still contains much water, and, if so, neither will it keep for an indefinite length of time, nor could it be satisfactorily examined under the microscope. It must be soaked in one of various chemical solutions, to harden and preserve it. If very small indeed, a mere speck, it perhaps only needs to be transferred to a fluid in which it can be "mounted" and placed under the microscope. But with the vast majority of specimens, an immense amount of labour is needed before they are ready for inspection under the microscope. This will easily be understood if we reflect for a moment on the way in which objects are examined under the microscope. For purposes of scientific investigation, they are rarely looked at under light that falls upon their surfaces, that is to say, by reflected light; for this method can show nothing but details which are external and comparatively unimportant. They are seen by light placed behind them so as to shine through them, _i.e._ by transmitted light. If the object is not extremely thin, it will shut out too much light, and thus it cannot be clearly seen, therefore all objects, except the most minute, must be divided into thin slices, technically known as "sections." If we want to know not only the microscopic structure of organs, but also their shape and position in the body, and their relations with other parts, we must have every successive section carefully preserved, and the whole row arranged in correct successive order; the physiologist may often content himself with single sections; the zoologist must have rows and rows of them. What a task this was, a quarter of a century ago, for scientists who cut their sections by hand!