PRACTICAL PHOTO-MICROGRAPHY. 169 



potash.) And though as a rule we consider intensification of 

 negatives after fixing, by mercury or otherwise, an operation 

 little commendable, we must confess that for this particular 

 class of object it has frequently proved vastly useful to us. 

 A fine sample of this class of subject is a " plate" split off, 

 usually by accident in cleaning, a diatom. 



Physio-and Pathological Preparations are easy, difficult, or 

 impossible to reproduce well according to their cutting and 

 mounting. Assuming that the points to be portrayed by pho- 

 tography are well seen by the eye, it is our business to over- 

 come difficulties of staining ; but difficulties of uneven mount- 

 ing, bad sectioning and the like are beyond our control. We 

 would protest here both for our own sake and for the sake of 

 pathological and physiological science, against the mania, 

 apparently spreading, for gossamer sections. Granted that 

 there are cases where no instrument we have can cut a section 

 too thin, it is none the less true that those cases are exceed- 

 ingly rare. A section cut to show the more minute bacteria, 

 or for histological purposes in general, can perhaps not be 

 too thinly cut, but for ordinary physiological and patho- 

 logical research, sections are often cut too thin to be of any 

 real use ; and they are most obnoxious to the photo-microg- 

 rapher. On the other hand tissues imperfectly or improperly 

 prepared for cutting cannot be cut thin enough for any useful 

 purpose, and the mischief of thick cutting is made all the 

 more apparent when staining that would be good for ordinary 

 sections, is used on these " slabs " of tissue.* 



Given, however, a good section of the class of subject now 

 under notice, we ought to produce by photography a repre- 

 sentation far beyond the best that manual dexterity can 

 accomplish. The question resolves itself into one of color- 

 correct photography with careful and skillful correction of 

 the objective specially if the work be histological. If " cells " 

 are to be shown in the characteristic state of health or disease, 

 the optical adjustment of all apparatus must be perfect. 

 Epithelial cells, for instance, may be horribly travestied by 

 improper lens correction or false lighting. The lowest power 

 should be used that will show the formation required to be 



* There are those who maintain, with some reason, that a section can 

 hardly be too thin, provided it is sufficiently stained. 



