5O THE A B C OF PHOTO MICROGRAPHY 



the classes of subjects included in this group. 

 Low powers are exemplified by photographs 

 of insect eggs, and parts of their anatomy, 

 sections of stems, seeds, woods, leaves, min- 

 erals, etc. Animal tissues, both normal and 

 diseased, are usually photographed under 

 medium powers, which really embrace a large 

 portion of the most important work in photo- 

 micrography. High powers are necessary for 

 germs, bacteria, cell structure, diatoms, blood- 

 and pus-corpuscles, etc. I have endeavored 

 in the present chapter to carry my readers 

 through the various processes involved in mak- 

 ing negatives in each group named; also to 

 give them practical examples in illumination 

 by polarized and transmitted light or on a 

 dark field, of transparent objects, and by 

 reflected light of opaque ones. 



Low powers, transmitted light. It is more than 

 probable that the beginner's first attempt at 

 photo-micrography will be made with one of 

 the various students' microscopes now in such 

 general use. Supposing this to be the case, we 

 will utilize such an outfit in my first demon- 

 stration. The microscope which happens to 

 be available at the moment is one of Spencer's 

 stands, furnished with two object-glasses, 

 f and i, two eyepieces of the usual Huyghe- 



