170 PRACTICAL PHOTOMICROGRAPHY. 



shown. If a one inch o. g. has sufficient aperture to show 

 muscle striation, it is folly to use a one-eighth o. g.; if magnifi- 

 cation alone is wanted, in suck a case we should decidedly 

 recommend camera enlargement. 



Isolated histological subjects are sometimes very difficult, 

 the difficulties coming under various heads already touched in 

 this chapter or about to be touched. We allude to such things 

 as epithelium cells, red and white blood corpuscles, sperma- 

 tozoa, etc., spread on a slide. These objects do not, as a rule, 

 take kindly to stains, and they are not only more or less 

 rounded but require considerable magnification to make their 

 morphology visible. Here again we must look to color-correct 

 photography to give us contrast, and to accurate correction 

 objectives, both for the actinic focus, and by careful collar 

 or tube adjustment. We usually meet the pale red or blue 

 of such staining by the yellow screens and yellow-sensitive 

 plates. Slow development carefully restrained is indicated, 

 and sometimes intensification necessitated. As a sample of 

 this class we may cite the task of reproducing ciliated epithe- 

 lium cells, to show which well, cilia, nuclei, and protoplasm, is 

 not easy. 



The ease or difficulty of photographing cover glass prepara- 

 tions of bacteria depends chiefly on their staining. The stains 

 most frequently used for such preparations are either violet 

 (gentian) or red (fuchsine). Few things are more difficult to 

 photograph than a microbe lightly stained with gentian violet, 

 or very lightly with fuchsine. If the stain in either case be 

 pale, the only hopeful method is to use yellow screens and 

 color- correct plates, no more angle than necessary being 

 brought into play. Some organisms badly stained with 

 Bismarck brown have completely baffled all our attempts to 

 photograph them. In the case of pale pink staining, some- 

 times the result of faded or abortive fuchsine or eosine stain- 

 ing, the signal green glass screen has more than once helped 

 us, but in most cases the yellow screen, theory to the contrary, 

 has proved more useful. If organisms are well stained, the 

 colors vigorous, the ground clear, the material evenly and 

 thinly spread, the difficulties of this class of works are great 



