92 PHOTO-MICROGRAPHS. 
reference to photography, as upon the optical 
apparatus used and the technical skill of the 
operator as a microscopist and photographer. 
In the present section, the writer proposes to 
indicate the kind of objects most suitable for 
making photo-micrographs, and the methods of 
preparation which have given him the best 
results. 
In giving this account, special reference will be 
had to the objects which have furnished the illus- 
trations for the present volume, and these will be 
taken up in the order in which they appear in the 
plates. 
Micrococci. (PLate II. Fie. 2.) 
These minute vegetable organisms require a 
high power for their detection. When properly 
stained, they may be photographed with a good 
one-tenth-inch objective; but a higher power is 
better. The writer has obtained his best results 
by the use of the one-eighteenth-inch homogene- 
ous immersion objective of Zeiss. 
Tt is well to adopt a standard amplification for 
each class of objects, so that they may be readily 
compared as to dimensions by a simple inspection 
of photo-micrographs, made at different times 
and places. The standard adopted by the writer 
for bacterial organisms, — Bacteria, — the class to 
which our Micrococci belong, is one thousand diam- 
eters. A less amplification than this will not show 
the smallest Micrococci in a satisfactory manner, 
and a greater is not necessary for a majority of 
the Bacteria. 
