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46 THe MIcROSCOPE. 
A METHOD OF USING WITH EASE OBJECTIVES OF 
SHORTEST WORKING DISTANCE IN THE 
CLINICAL STUDY OF BACTERIA. 
A. CLIFFORD MERCER, M.D., F. R. M. 8. 
HE working distance of homogeneous immersion objectives of 
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 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. ; 
INTESTINAL PARASITIC INFUSORIA OF FROGS. 
PROF, D. 8. KELLICOT. 
VERY teacher of biology knows that the patient frog is a highly 
useful animal. It is as widely known, and almost as widely 
practiced,that to demonstrate the action of cilia, a bit of mucous scraped 
from the roof of the mouth and covered in a drop of 6 per cent. solu- 
tion of common salt, is excellent. It may not be so generally known that 
the frog carries in the small intestine a host of parasitic infusoria 
which demonstrate this phenomenon very finely, in some regards 
better than the epithelium referred to above. The interesting form 
appears to be Nyctotherius cordiformis, Stein. It may be found by 
snipping off a short piece of the small intestine, laying it open and 
scraping the mucous into water on a slide. The species is relatively 
large, and in the artificial medium soon loses vitality, moves slowly 
and the long cilia may be seen in action to advantage. Perhaps the 
normal salt solution of the laboratory is better than water in which 
to study them. By the way, this Nyctotherius I have called 
cordiformis, since it has the same habitat, agrees in form and other 
specific details, except that, so far as I can make out with careful 
manipulation, there is no seta rising from the widened entrance to 
the pharynx, as represented by Stein’s figure. It is true that the 
