ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
135 
in bouillon. After an incubation of four weeks a microscopical examina- 
tion showed that tubercle bacilli wore as constantly present in the agar 
and as constantly absent from the bouillon. 
(5) Mounting-, including Slides, Preservative Fluids, &c. 
Formalin as a Hardening and Preservative Medium.* — Prof. F. 
Hermann writes very enthusiastically on the fixative and preservative 
properties of formaldehyde, known commercially as formalin. Used in 
0*5 to 1*0 per cent, solution it is found to thoroughly fix and harden 
not only pieces but whole organs (e. g. a calf’s heart) in from 12 to 24 
hours. Its particular advantage is that the transparency of living 
tissues is almost perfectly retained, the best examples of which are those 
of the eyes of small animals. Formalin also preserves the natural 
colours of the skin, though it rapidly extracts blood-pigment, and thus 
bleaches portions of the preparation, yet its fixative property, coupled 
with the advantages of preserving the transparency of tissues and 
structure, and its conservation of the natural colours of integuments 
indicate that it is especially adapted for museum purposes. As a fixa- 
tive for microscopical preparations formalin has no advantage over the 
ordinary fixative media. It fixes as well but not better, and its use 
is associated with the inconvenience that tissues previously treated 
with formalin are not suited for after hardening with alcohol. It is 
obvious, therefore, that until this inconvenience has been surmounted, 
the use of formalin cannot be recommended when microscopical sections 
are required. 
Cleaning Hew Cover-glasses.f — Prof. Zettnow finds that the best 
way to remove all traces of grease, which prevents the regular distri- 
bution of fluids, from new cover-glasses is to barn it off, and for this 
purpose he uses a piece of sheet iron 8-10 cm. square. The imperfectly 
cleaned cover-glass placed on the iron is held in the flame of a Bunsen’s 
burner for several minutes. The glasses never crack, and twelve to fifteen 
can be cleaned at a time. 
Dr. M. Kuster’s Hollow Spheres for Microscopic Objects.^ — Ur. A. 
Zimmermann gives the result of his examination of Ur. Max Kuster’s 
hollow spheres. They are made of thin glass, and have a diameter of 
about 15 mm., with a circular opening about 3 mm. wide, through which 
the objects to be observed are introduced. For observation, the spheres 
can be brought directly under the Microscope, and serve at once as 
object-holder and cover-glass. The use of the spheres is naturally 
confined to small objects suspended in liquids ; they are therefore espe- 
cially recommended for preparations of bacilli. 
A further advantage claimed for them is that the reagents, which 
are simply introduced into the hollow space, in this way act much more 
uniformly and intensely, while no air-bubbles or displacements are pro- 
duced as when a cover-glass has to be raised. 
A disadvantage in the new method consists in the difficulty expe- 
rienced in the observation and in the displacement of the preparation. 
* Anat. Anzeig., ix. (1893) pp. 112-5. 
t Centralbl. f. Bakteriol. u. Parasitenk., xiv. (1893) pp. 63-4. 
j Zeitschr. f. wise. Mikr., x. (1893) pp. 164-6. 
