The microscope stands in the forefront among the instruments which have proved of value as weapons of scientific and technical investigation. Although it is a very old instrument, before the invention of photography the only way in which a permanent record could be made of what the observer saw in his microscope was by making a drawing. This procedure, while giving very elegant results, could not be considered to give an infallible record of all the details observed, nor of their respective tone values. It was not until photography was invented that a true record of the image in the microscope could be made in permanent form, and it is not surprising that practically the first use of photography in the scientific field was to record this image. In 1802 Wedgwood and Davy made photomicrographs on white leather soaked in silver nitrate, using the so-called solar microscope, but they could not fix them. The first permanent photomicrographs were made in 1837 by Reade, who had discovered fixation by hypo.
By skilful understanding of the use of the microscope, and a knowledge of the properties of photographic plates and films, photomicrographers are able to obtain results showing fine details with the utmost clarity. They understand fully the conditions necessary to obtain these results, and by the use of light filters they can control the contrasts of differently colored parts of their subjects to any desired extent.
In 1926 in a discourse at the Franklin Institute in Philadelphia on the color sensitivity of photographic materials Mees19 made the following prophecy concerning photomicrography: "Until quite recently, the microscope has remained a visual instrument, the photomicrographic methods being employed only to depict what had already been seen. It seems likely that before long the microscope in its turn will become a photographic instrument, the