214 PHOTOGRAPHING WITH THE MICROSCOPE [Ch. VII 



streak cultures may be arranged so that the sloping surface will all 

 be in focus at once by inclining the test-tube. 



§ 337. Recording and storing negatives. — Each negative should 

 have a record upon it w T ritten on the film side with India ink; then it 

 will never get mixed up. For ease in finding them there should be 

 a record on the containing envelope also. Finally, it is a good plan 

 to have a card catalogue of one's negatives. For a form see § 358. 



For storing negatives a good method, where one does not have 

 too many, is to put them in envelopes and store in boxes or drawers 

 like book catalogue cards. 



Photographing with the Microscope 



§ 338. The first pictures made on white paper and white leather, 

 sensitized by silver nitrate, were made by the aid of a solar microscope 

 (1802). The pictures were made by Wedgewood and Davy, and Davy 

 says: "I have found that images of small objects produced by means 

 of the solar microscope may be copied without difficulty on prepared 

 paper" (§ 338a). 



Thus among the very first of the experiments in photography the 

 microscope was called into requisition. And naturally plants and 

 motionless objects were photographed in the beginnings of the art 

 when the time of exposure required was very great. 



Although first in the field, photo-micrography has been least 

 successful of the branches of photography. This is due to several 

 causes. In the first place, microscope objectives have been naturally 

 constructed to give the clearest image to the eye ; that is, the visual 

 image, as it is sometimes called, is for microscopic observation of 

 prime importance. The actinic or photographic image, on the other 

 hand, is of prime importance for photography. For the majority 

 of microscopic objects transmitted light (§ 85) must be used, not 

 reflected light as in ordinary vision. Finally, from the shortness of 

 focus and the smallness of the lenses, the proper illumination of the 

 object is accomplished with some difficulty, and the fact of the lack 

 of sharpness over the whole field with any but the lower powers 

 have combined to make photo-micrography less successful than ordi- 

 nary macro-photography. So tireless, however, have been the efforts 



