Evening star., 1915-09-12

history and the weak places where
they may be attacked; food materials
are tried on them to see which are
Ihealthful or stimulating and which are
poisonous; they are subjected to dlf-
ferent temperatures and conditions: IN
short, the habits of these minute
thieves of plant health are determined
through study of the nature of their
associates and their environment.
One cannot pick up diseased lear.
| however, and reach any definite con
| clusions about it's parasites by SIMPLY
i observing it carefully The scientific
process of making a pure culture mast
! be followed. This process separates
| and multiplies the organisms present
| until they exist each by ltseif in great
| enough quantities to be studied on Spe-
cial foods under the microscope. Her e
| their reactions are perfectly revealed.
| Making pure culture of plant hac.
| terra is identical with the process or
| bacteria. The bacteria from the dis
| eased portion of the plant are placed
in a test tube of liquefied gelatin and
evenly distributed by shaking.
| Then the bacteria are poured from
| the test tubes along with the melted
gelatin into shallow glass dishes which
have close-fittng glass covers. Here
| the gelatin soon hardens making a
! firm. moist surface. on which the COLI
| onies multiply, each according to its
| own kind each one being the product
of a single germ. intintesimally small.
! The colonies are then ready to be
| transferred to other media.
These media are steriliZed prepara-
tions of bacterial food. and may be
made of any number of ordinary food
products. such as beef, potatoes. vari-
Gus sugars. milk or cornmeal.
In studying any species of bacteria
they must be put through these cul-
ture processes not less than nineteen
| times. 1t is not sufficient to observe
! the bacteria nurtured on beef bouillon
| alone; the reaction of the organism to
al al of the culture media on or, the seien- en-
| tific menu is noted also. Thus, all OBJ
| servation of the cultural features of
! the bacteria is standardized, and it is
possible to tell from a scientists rec
| ord how every colony of bacteria re-
Sponded to every test.
This. the first step in the study, COW
! ers a long period, for many tests are
| made Test tubes of bacteria are sub
| Jected to: heat and cold, in the heat
! and ice ther&nostats. to find out the
| temperature in which they grow best
| and the maximum and minimum tenn
| peratures under which they can exist.
Another step is that which determines
! what kind of plant tissue the bacteria
i've IN. This process calls for exact
and careful treatment. In a small
oven. plant cells. taken from the dis
eased area containing the bacteria, are
| 1nhltrated in paraffn. This preserves
scope.
When the time comes to study the re-
! lation of the parasite to the plant cell
tiny sections are sliced off by the mi
crotome, an instrument which may be
| regulated to cut thinnest shavings from
| the parafiin block. These shavings are
stained after removal of the paraffin,
| mounted under glass cover and placed
under the microscope. where they are
| studied TO give light on the morpholog-
| ical features of the bacteria and their
action on the plant. Hundreds of these
| little paraff1n blocks are stored away in
| the laboratory, numbered and recorded,
| to be easily consulted for reference
| whenever they may be asked for
| To any laymap the most wonderful
| feature of this work lies in this OBJ
| servation of bacteria through the mi
croscope. To look through this instru
| ment and see clearly a mass of moving
| organisms which do not exist for the
naked eye is to understand partially
| the wonder and delicacy of the work
performed by the woman pathologists.
Moreover, when one realizes that path
illogical discoveries which are relieving
| disease all over the world are made
| through just such cautious and precise
| labor. then does the marvel of modern
| science find its symbol and the spirit of
| the age its embodiment.
| But this is only one element of the
| work. Another branch takes the pa
| thologist away from the laboratory to
| the greenhouse. Here, with solutions
containing pure cultures of the various
! bacteria under observation, they inocu-
| late fresh, healthy plants either by
needle puncture by spraying. This
| procedure gives opportunity to
, study the action of the bacteria on the
plant and to determine which, If any,
| of the various ones are the actual
! cause of the disease as it progresses
| through it's various stages. For it
| often happens that the commonest Or
ganism found in connection with the
disease is not the cause of it.
| Plants vary in their receptivity to
disease. Even individuals of the same
| variety differ, so they must be studied
| as to their behavior to find a resistant
/ variety. 1t may be that valuable SEN
| sitive varieties of plants by cross
hybridization with strong but inferior
plants will yield resistant desira BILE
plants. In this manner the ravages of
a disease may be offset and stamped
out of locality.
1t has been learned that certain spe-
cies of bacteria which affect only
|