568 MICROSCOPY. 
tically as good as the more difficult and expensive plan of rotating 
the stage only; though for objects illuminated from above it is _ 
less convenient. It is also made binocular. 
Mountine Diatoms.—It is due to Dr. Christopher Johnston of 
Baltimore, to say that I am indebted to his very valuable papet, 
on the “ Preparation of Diatomacez” for the method of retaining 
the diatoms in place, mentioned in my note. If dry mounting is 
preferred, I have found by experiment, that the diatoms may be 
arranged as before stated on the cover, without the gelatine coat, 
and fixed in place by moistening with vapor as before stated. 
This plan has some advantages for real study. — W. W. RINER. 
Bioop Crrsrats.— The detection of blood by finding eo | 
tals is a much easier process than has been thought, and is ae 
much more generally applicable. In blood decomposed, or that 
has been treated by acids or caustic alkali, hæmoglobin is changed $ 
into a new substance; hematin is formed, whicb, combined ue 
hydrochloric acid, gives characteristic crystals. In order to obtain 
them we must proceed thus: A small fragment of dried blood we 
placed on a slide; it is dissolved in a drop of water, and ae gc 
portion of sea-salt is added. It is covered with a thin slide, atf 
pure acetic acid is made to pass between the two slides, and it R l 
heated over a spirit-lamp to boiling point. Acetic acid 18 si! | 
added, and it is heated afresh; this is repeated till the cry 5 
are obtained. They are rhomboidal, of a dirty brown color, qa 
characteristic, and require to be seen with a magnifying Pri “ 
three hundred or four hundred diameters. With the pies a 
quantity of blood this reaction can always be produced.— 40" 
Science Review. oh 
TOLLES NEW IMMERSION J7H.— About three weeks d 
ceived from Mr. R. B. Tolles a th immersion ora m 
to the one purchased by Mr. Crisp of London (see D eet 
March 1874). Mr. Tolles claims for this objective es a ny 
160. The performances of this new {th are at once 
markable, on Amphipleura pellucida (dry) it shows 
