Evening star., 1939-09-19
Of Stars, Men
And Atoms
Notebook Of Science Progress
In Field, Laboratory
And Study
BIZ Thomas r. Henri.

By Thomas r. Henry.
Most of the bacteria, yeasts, moulds
and protozoa significant in medicine,
agriculture and industry now are in
cluded In the American Type Culture
Collection maintained at Georgetown
University Medical School.
The collection was started by the
American Museum of Natural History in
1911. It soon overburdened its hous-
ing facilities there and finally was trans
ferred to Washington. Nearly 5000 sep
crate families now are maintained in
living condition under the supervision
of DR.. Mario Mollari, the curator.
The original function of the collec-
ton was ito collect and preserve authen-
tic cultures of bacteria and other
microorganisms. "Its facilities are avail
able for the study and identification OF
strains of microorganisms submitted by
individuals. The collection serves as q
depository for the cultures OF micro
organisms which have been studied and
described but which cannot be main
tanned longer by those who have studied
them. BY means of special apparatus
the bacteria can be preserved by means
of q freezing g-drying technique.
Strains of the bacteria are available
both in the -and-dried condition
and in the active, growing state. The
growing icro-organisms are fed on
nutrient medium and kept in a large
refrigerator. The warmer the tempera-
ture the faster they live and the faster
they die. Almost all of them, however,
can live for weeks at room temperature.
The collection depends for support
upon bacteriologists the world over who
have given collections and who pay small
fees for occasional shipments OF needed
species. A printed catalogue lists $500
cultures now available.
Growth of cell masses now has been
observed for the first time through the
development of a new technique by
botanists at Columbia University. This
has resulted in the solution of several
mysteries which hitherto have sur
rounded living tissues.
1t was found that the final fate OF q
cell or the service which it will perform
in life, is determined at the time of
its birth, according to Prof. Edmund
w. Snnott. New cell walls are formed
in the position which they will occupy
permanently and it was discovered that
these walls do not grow at equal rates
but that some parts increase IN size
much more repidly than others.
Through planting a certain species OF
small seeded grass between two thin
sheets of moist, translucent paper on
microscopic slide the manner in which
cells in root tips divide and expand,
causing the root to grow, was recorded.
The slides, with the seedlings growing on
them, were placed under microscope
| and examined at intervals OF several
hours. Drawings were made by means
of an apparatus which cast an outline
of the cells on sheet of paper, en-
abling the observer to trace accurately
the exact changes In the number and
size of the cells that had occurred.
Several facts have been established
by this new study of living plant tissue, .
DR.. Sinnott says. by comparing each
cell with its neighboring cell we deter
mined that new cell walls are formed IN
| the exact position which they occupy
permanently There is no Sliding
growth of one cell over another. This
has long been a subject OF controversy
| among students of plant life.
New cell walls are sometimes straight
but they are often curved and In their
formation and position follow approx
mately the behavior which liquid f1lm,
like that of a soap bubble, would fol-
low under similar conditions.
Previous to the discovery OF this
new technique studies Of the growth OF
cells were accomplished mainly by OBJ
serving material which had been killed,
| stained and cut into thin slices for
microscopic examination. 1t Is difh-
cult to see the process taking place In
4 living tissues in this manner because in
order to be seen under a microscope
material must be thin enough to allow
light to pass through 1t. Growth by cell
division in the living tissues has been
studied in cell filaments and other small
groups of cells but a typical growing
point, such as the tip of stem or root
where cell division chiefly takes place,
is usually so Opaque that the details
cannot be observed.
"This difficulty was overcome by .
choice of appropriate material and meth
DDS. Plants with very small seeds pro-
duce roots which are very delicate and
thin enough to be studied directly un-
der the microscope. In most cases
however, the sheathing root cap, which
covers and protects the tip of the root
makes it impossible to see what Is
going on. In some of the small seeded
grasses a root cap is almost entirely alb
sent and the region can be. clearly OBJ
served.
Entire cell pedigrees can be studied
in detail. The outermost layer of cells
is. of course, the easiest to see but the
second and sometimes the third layer
can be studied by careful focusing. The
frequency of cell division in the material
studied varied from about one in II
hours to one in SO hours. Changes II
the cell wall were also observed and II
was found that all parts Of the wal
do not grow at equal rates, as has COM