544 
SUMMARY OP CURRENT RESEARCHES RELATING TO 
The apparatus for mechanical movement is essentially the ordi- 
nary mechanical stage, but working directly by hand instead of by 
rack and pinion, the especial advantage being the free long movement 
thus permitted. It is in two parts. A rectangular frame (a) showing 
front margin (</), as seen from behind, the lateral bar of which is 
bevelled to fit into the triangular groove in the side of the stage-plate, 
in which it slides forward and backward; and a thin plate (b and /) 
longer than the preceding and a little narrower, its bevelled edges 
sliding laterally in a V-shaped groove on the inner edges of the 
anterior and posterior bar of the frame just mentioned. The project- 
ing ends of this plate serve as hand-rests in dissecting. Three small 
screws are set in it as stops for the slide, and the knobs by which it 
is moved are bored in the centre as sockets for the stage forceps. Its 
central opening is of the same size as the larger opening in the 
stage-plate, and in this rests loosely a circular piece of glass (c) 
with a central opening (d), on which a dish may be set in 
examining small alcoholics. This apparatus, when well fitted and 
smoothly ground, works with a nicety and precision scarcely, if at all, 
inferior to that of the geared movement. An ordinary slide in position 
is shown at e. 
This stage was made October, 1890, to my order and from my 
drawings, by the McIntosh Optical Company of Chicago, from whom I 
learn that it is now furnished with many of their own instruments, being 
adapted to the round stage-plate of their Microscopes by placing under 
it a thin false stage-plate which bears beneath a socket that slips into 
the central opening of the stage.” 
Introduction to the use of the Polarization Microscope in Histo- 
logical Investigations.* — This little book is intended by Dr. H. Ambronn 
to assist those who do not possess the physical and mathematical training 
necessary for understanding the more advanced works on the same subject 
such as those of Valentin f and Nageli.f To the mineralogist and petro- 
logist the polarization Microscope has become an indispensable requisite, 
but even at the present time it is very little used by histologists. This is 
mainly due to the wide-spread idea that a very thorough knowledge of 
physical and mathematical optics is necessary in order to be able to work 
with this instrument. The author’s aim in the present work is to give 
quite an elementary treatment of the subject with the hope of turning the 
attention of histologists to these methods of investigation. The book is 
thus only intended to be an introduction to the larger manuals, and accord- 
ingly only the simplest explanations are given and all mathematical 
formulae are avoided. 
The first four chapters of the book are devoted to an elementary dis- 
cussion of the undulatory theory, the phenomena of polarization, double 
refraction, the interference colours between crossed nicols, and the use of 
the gypsum plate in determining the position of the axes of elasticity. 
* ‘ Anleitung zur Benutzung ties Polarisationsruikroskops bei liistologischen 
Untersuchuugen,’ Leipzig, 1892, 59 pp., 27 figs., and 1 coloured plate. 
f ‘ Die Untersuchung der Pflanzen und Tkiergewebe in PolarLierten Lichte,’ 
Leipzig, 1861. 
X ‘ Die Anwendung des Polarisation s-apparates auf die Untersuchung vegeta- 
bilisclier Elemeutartheile,’ Leipzig, 1863. 
