EDUCATIONAL VALUE OF PHOTOMICROGRAPHY. 143 



EDUCATIONAL VALUE OF PHOTOMICROGRAPHY. 



By ARTHUR CURTIS SCOTT, 



MADISON, WISCONSIN. 



THE part of the universe which the penetrating power of the micro- 

 scope reveals to the student of nature, though concerned with the 

 infinitesimal, equals the macroscopic portion in magnitude and signifi- 

 cance. 



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 examina- 

 tion 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 reproduc- 

 tion of microscopic structure has largely been due to the demand for 

 unmodified and unprejudiced exactness of detail. Again the photo- 

 graphic 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- 



