MICROSCOPY. 315 
from the objective ; wlien on the other hand the greatest possible 
amplification was desired, then both objective and ocular were 
used. In this way by the use of Hartnack’s immersion lenses the 
finest test objects were exhibited, and the six sided spaces of the 
Pleurosigma shown as four to five millimetres in diameter. For 
such times as sunlight is not available he recommends the Drum- 
mond light, and promises to give the results of his experience 
in its use. 
In place of the expensive heliostat, no doubt the simple arrange- 
ment often used by lecturers on Natural Philosophy might be 
adopted. It consists of a mirror outside the window movable in 
two directions by means of screws whose heads come within the 
room.— T. D. B. 
ANGULAR ÅPERTURE.— Dr. Pigott revives the subject of dia- 
phragms behind the objective, and reports some very remarkable 
results somewhat similar, of course, to those resulting from the 
use of an achromatic condenser of very small angular aperture. 
He does not demonstrate the advantages of using a diaphragm 
Over the objective as compared with the other and more usual 
method. 
PREPARATION AND Preservation or TissvEs.— Dr. J. J. Wood- 
ward commences, in “ The Lens,” a summary of the various meth- 
ods employed for this purpose. He prefers to harden the tissue by 
gradual dehydration by means of alcohol, and to cut it (imbedded 
if small, in paraffine) either off-hand or in a common section 
machine. By the latter means sections less than one-two-hun- 
dredth of an inch thick are easily obtained. He covers the top of 
the section machine with a glass plate suitably perforated and ce- 
mented fast by means of marine glue; and advises that the 
alcohol used to dehydrate the specimens be saved and filtered for 
the preservation of large anatomical specimens. 
Dr. I. N. Danforth gives, in the same Journal, his methods of 
Preparation, the main object of which is simplification of the 
usual procedures. He makes the pithy assertion that success — 
€pends more upon tact than upon tools. He cuts the sections 
and preserves them in slightly acidulated glycerine. He very | 
