224 
CORRESPONDENCE. 
In the second period an event presents itself, which induces 
us to divide this period into two subdivisions. In the year 1839, 
Scliwamm published his work on the foundation of all organic 
bodies—the cell. This was succeeded by a much needed, very 
valuable work, for instruction in the use of the microscope. The 
great and progressive improvement in the microscope, had made 
possible the works of Scliwamm and Yogel. 
The basis for this progress in the formation in the compound 
microscope was laid in France in 1824, through the discovery of 
the possibility of uniting several acromatic lenses to made an ob¬ 
jective system. Selligue and Chevalier were the first who worked 
with them. Amici obtained such favorable results that the work 
of perfecting went on, which led to the first histological work of 
value. 
We separate the second period of the German microscopy into 
two parts : The first extending from 1811 to 1839, and the second 
extending 1839 to the present day. 
As we do not intend to examine more fully the development 
of the German microscope, we shall not sketch its history further, 
but confine ourselves to mentioning the most important historical 
details, in order to understand rightly the position of microscopy 
in Germany. 
If we consider the progress of microscopy in Germany we shall 
see that it is identical with the development of the microscope 
itself. We shall examine first the simple and then the combined 
dioptric microscope. 
The oldest, simple, dioptric microscope known under the name 
Vitrum publicarum, was very little qualified for microscopial ob¬ 
servation, as the medium failed to regulate the distance between 
lens and object. It consisted of a short tube, with a lens which 
magnified about nine times, and on the other end, a flat glass 
plate upon which the object was glued—a flea or something of 
the kind. Other simple microscopes were constructed of lenses 
enclosed in a ring or cylinder, which rested upon an upright, the 
object being placed upon a second, which was- arranged so that 
the correct focus was obtainable. Still, more perfect instruments 
were made in 1673, by Leeuwenhoek, many of which were brought 
