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of a certain kind occur, and one just requires that particular kind, 
it ought not to be so much diluted, because the chance of getting 
cells at the edge is much too small. And then there is certainly the 
risk that in isolating one cell, one brings with it other cells which 
‘ause the experiment to fail. Therefore I still find the use of two 
needles necessary for difficult cases (also, for instance, in dealing 
with mucilaginous material). With the first needle the cell isolated 
is brought near to the culture-drop, with the second, which is then 
certainly still sterile, it is put into it. 
In my original apparatus the needles are always placed on either 
side of the microscope, on two separate stands; in my simplified 
arrangement with one needle stand, the first needle is in such cases 
replaced by the second. For this naturally the cover slip used for 
isolating must momentarily be placed on an ordinary moist chamber. 
One can however, without the microscope, also stretch the culture- 
drop with an ordinary platinum inoculation needle somewhat near 
to the edge of the isolated droplet; then also the isolated cell will 
come into it. 
There are still a few short remarks. 
Before Nisuwrnuuis lays the cover-slip, on which the isolation has 
taken place, on the moist chamber for the further development of 
the culture, he absorbs the drop of the material by means of a 
filter paper. With his method this is necessary, for the drops must 
for the purpose of being dragged lie close to another and this is 
very likely to give rise to contamination of the culture-drop by 
hyphae which grow out of the drop of the material. 
Whilst it remains doubtful whether after this absorption no cells 
are left behind, and germinate in the moist chamber, I here point 
out that by my method the distance can be so great that there can 
be no question of any such infection. I have never had any trouble 
from it. There are advantages in leaving the drop of material in its 
original place. The behaviour of the cells occurring in it (whether 
the spores develop, whether the bacteria remain mobile) sometimes 
enables important conclusions to be drawn. 
Nizuwennuis lays no drop on the floor of the moist chamber, 
because then the too considerable condensation on the cover slip is 
troublesome. 
This difficulty is avoided if the slips are cleaned in the way 
described above, and if the moist chamber is not — as in his method 
— placed on a fixed object in the incubator, so that the slide is 
the warmest, but is, for instance, placed in a small box on 2 strips 
of wood. NievweNHuis thinks that the slight evaporation from a large 
