[Reprint from The Microscope for Ffrbtkry 
A METHOD OF USING WITH EASE OBJECTIVES OF 
SHORTEST WORKING DISTANCE IN THE 
CLINICAL STUDY OF BACTERIA. 
C 
A. CLIFFORD MERCER, M. D., F. R. M. S. 
z I XHE working distance of homogeneous immersion objectives of 
A short focus and great numerical aperture is little. In the 
clinical study of bacteria, sputa and other more or less fluid material 
are generally prepared on the under surface of cover-glasses, com- 
monly, when not measured and assorted, so thick as to make 
examination with the above most suitable objectives impossible. 
To avoid this difficulty I dry and stain the material on the 
slide, drop homogeneous immersion fluid upon the preparation and 
lower the objective into the drop. Homogeneous fluid replaces the 
cover-glass with optical propriety. A 
A twenty-fifth, which has been nearly useless over ordinary 
cover-glass preparations, is now used with gratifying freedom in 
manipulation over uncovered, but homogeneously immersed, slide 
preparations.