REVIEWS. i 231 
recommended for the same purpose. Wenham’s binocular arrange- 
ment, notoriously consisting of a single prism, is mentioned as an 
arrangement of prisms. The use of unground glass slips is men- 
tioned with indifference, though the student should never use them, 
unless they are to be covered with paper, without rubbing off the 
cutting edges on a grind-stone or on any wet piece of soft sand- 
stone. As a convenient substitute for the mounted needles whose 
preparation is directed by the author, crochet needles may be 
bought of suitable size and style, deprived of their hooked ends 
and sharpened on an oil-stone or hone; or the form may be pur- 
chased in which the needle is removable and easily replaced by a 
common needle, being clamped into the handle by a screw-move- 
ment. Likewise the conical glasses, scratched with a file, for esti- 
mating the bulk of sediments, may be replaced by 4 oz. grad- 
uated measuring glasses, which, sold by the dealers in druggists’ 
glassware, can often be obtained of exactly the desired shape. 
“ Healthy blood,” on page 39, should read hene human blood. 
Such objects as the “various species of acari” should not be 
mounted in the dry way, much less received as typical of a class of 
specimens peculiarly adapted for such -preparation ; nor should a 
book of the present day reproduce from the old authorities the 
abominable direction to place a dry object upon the slide and pro- 
tect it by a cover carefully laid upon it and fastened down by 
gummed paper. Glycerine is, perhaps wisely, recommended to 
the beginner in mounting wet specimens, although a more difficult 
medium to manage than Farrant’s Gum and Glycerine or Walms- 
ley’s Glycerine Jelly. 
The use of blue glass (spectacles, etc.) is casually noticed as a 
means of correcting the yellow glare of artificial light; but the 
position of the blue glass is not so unimportant a consideration as 
would reasonably be inferred from the text; in the writer’s experi- 
ence the best results are obtained by a flat piece of glass lying 
upon the diaphragm or below the achromatic condenser; a curved 
plate (deep-blue chimney) near the flame, or flat plate in the cone 
of light over the achromatic condenser, or over the eye-piece, 
being much less satisfactory : a very pale-blue chimney, just tinted, 
may be used to take off the glare without whitening the light ; and 
the white, translucent ‘ porcelain ” chimneys, recently introduced, 
may, if quite thin, often be used to advantage. The author, in 
his enthusiasm for high powers, scarcely urges with sufficient dis- 
