| EDUCATIONAL VALUE OF PHOTOMICROGRAPHY. |
By ARTHUR CURTIS SCOTT,
MADISON, WISCONSIN.
THE part of the universe which the penetrating power of the microscope reveals to the student of nature, though concerned with the infinitesimal, equals the macroscopic portion in magnitude and significance.
Modern scientific consideration recognizes the fact that no more accurate method of research can be concentrated on the question of origin, cyclic changes in development and existing structure of various forms of matter, both organic and inorganic, than that of their minute examination under the microscope. It is a familiar fact that early investigators with this instrument, as well as many at the present time, exhibit as results of their work drawings of the objects examined. While these pictures made with the camera lucida may be reasonably exact when drawn by a careful investigator under the best conditions, it is true that they are frequently inaccurate under ordinary circumstances, and when numerous reproductions are desired the photomicrograph is largely superseding the laborious work of the draftsman.
It is probable that the application of photography to the reproduction of microscopic structure has largely been due to the demand for unmodified and unprejudiced exactness of detail. Again the photographic plate is more sensitive and more efficient than the retina, for not only is the human eye easily fatigued, but it is quite unable to regard slight differences of illumination, or to differentiate the most minute characteristics of specimens. While it is a fact that the plate is most sensitive to light of a certain color and intensity, it is also true that the requirements can be readily obtained, and that the silver salt is able to indicate the action of light that fails to stimulate the sense of vision. The existence of funiculi in the coma-bacilli of Asiatic cholera, for example, was proved by the aid of photography after repeated failures to discover them by other means.
The middle of the nineteenth century marks the beginning of attention to photomicrography when Mayer of Frankfort devised apparatus for this work. Since that time wonderful advance has been made both in photography and microscopy, and we now may obtain not only extremely rapid and color sensitive plates, with readily modified developers that allow a considerable latitude of exposure, but micro-
