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microscope; with one the cell was isolated, and set down close to 
the culture-drop, and with the other, i.e. always the pointed needle, 
the cell was placed in the culture-drop. 
The original intention of this was as follows: if it should happen 
that sometimes a second cell is introduced into the eye of the needle 
in addition to the one that is to be isolated, this one perhaps might 
be released unnoticed and could enter the drop together with the 
cell to be isolated. This mistake can however be avoided if the 
latter transference to the culture-drop is effected by means of the 
second needle, which is known to be sterile. 
In the meantime I have learnt from experience that in many cases 
the whole operation can very well be carried out with one needle, 
in which case the cells of the material must occur so isolated from 
each other that one cell can easily be taken up without another 
accompanying it. 
On that account the simplified apparatus has only one needle- 
holder, to the left of the microscope. No general rule can however 
be made, and I intend to return to this later. 
In the other arrangement the microscope stands on a plate which 
can be moved in 4 directions by means of 2 screws: one always 
begins with the microscope so placed that the needle, when it 
touches the glass, comes into the middle of the field of vision. 
In the simplified apparatus this plate, although convenient in 
practice, is left out, on account of expense; therefore the miscroscope 
is adjusted by hand and by tapping with the finger-tip (by which 
means very slight displacements are obtained). 
The needle-holders can be adjusted for microscope stages of 
various heights. 
In the years since my last publication I have gained much other 
experience which I may add. 
Firstly, with special regard to bacteria: one should isolate from 
material which is as young as possible. Recent experiments have 
clearly shown that bacteria in a culture very quickly die. The curve 
of growth which is obtained with the times as abscissae and the 
bacteria ag ordinates, rises quickly and then falls quickly. In cholera, 
at 37° for example it already reaches a maximum after 12 hours. 
In older cultures therefore there is a greater chance of isolating 
weak individuals, which then produce no colony. 
Further, at the time of isolating unnecessarily long illuminations 
must be avoided. Since however in this method the light must 
be fairly strong, particularly in a power of 1000 times, it is 
best to work with artificial light, for instance with incandescent 
