108 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
or any other liquid. The large model (fig. 7) is provided with grooves 
for the reception of slides of 76 X 26 mm., and the small model is in- 
tended for cover-glasses of 18 mm. in the side. 
Arsonval’s Thermostat modified for Benzin-heating.* — Mr. J. 
Ogmannikow has so modified Arsonval’s gas thermostat that it can now 
be heated with a benzin lamp of special construction, for the details of 
which the original must be consulted. 
The temperature maintained is said not to vary more than from 0 O- l 
-0 o, 4 and usually not more than 0 O- 2. Where gas is not obtainable a 
device of this sort is very useful. 
(4) Photomicrography. 
Photomicrography.! — For photomicrographical work the two 
requisites are a Microscope and a camera. The Microscope must possess 
an arrangement which allows the body-tube to be brought into a hori- 
zontal position while the foot rests firmly upon the table. The camera 
differs from the ordinary portrait camera in the greater length to which 
it can be drawn out. Such apparatus have been supplied for years by 
very many firms ; but they are either very expensive or, if cheap, are 
very defective, not possessing generally the length of bag which is 
indispensably necessary for taking bacteria, diatoms, &c. The institute 
of Klonne and Muller, of Berlin, has lately supplied a cheap and at 
the same time neatly constructed apparatus which answers every require- 
ment. Dr. B. Neuhaus, an authority on photomicrographical work, 
describes this apparatus in his ‘ Anleitung zur Mikrophotographie.’ 
The camera can be drawn out to 1 '80 in., and as there is light-proof con- 
nection of this with the body-tube there is no direct contact of the two. 
Sunlight reflected from a heliostat is the most convenient source of 
light. As the best substitute for sunlight, Neuhaus proposes the 
electric arc light, while other authors regarding this as too unsteady, 
recommend the magnesium, or still better the zircon light. But 
petroleum light is sufficient for almost all purposes. The proper 
method of illumination is by means of the condensing system to form 
an image of the source of light in the preparation. Most photomicro- 
grams have been hitherto obtained by the use of the Microscope 
objective without the eye-piece ; lately, however, very well made pro- 
jection eye-pieces have been recommended. The best safeguard from 
any shaking of the instrument during the exposure is afforded by a 
triple layer of thick felt under each leg of the table on which the 
apparatus stands. No precise directions can be given as to the time 
of exposure necessary for the production of a good negative. By direct 
sunlight, with the strongest magnifications and sufficient weakening of 
the light by the filter, a few seconds are sufficient. 
On the value of photomicrography the most contradictory opinions are 
held. Some think that in a short time it will quite drive drawing from 
the field, while others, taught by sad experience, are inclined to depreciate 
its importance. Both are wrong. Certain things will always remain to 
the draughtsman, while others belong exclusively to the photographer. 
* Wracz, 1890, pp. 725-6. See Centralbl. f. B.ikteriol. u. Parasitenk., x. (1891) 
p. 132. f Central-Ztg. f. Optik u. Mecliauik, xii. (1891) pp. 262-3. 
