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considered as of secondary importance. The cover-slips must be fairly 
new, at any rate not so old as to show signs of weathering (micro- 
scopically to be recognised as small scratches, — an appearance 
also given, however, by some impurities). Crark and DuGear describe 
in detail their method of cleaning; | myself boil them about 10 min. 
in a soap-solution, then they are well rinsed in plenty of ordinary 
water, preferably separately, and are stored dry. Other methods of 
cleansing, such as in the well-known mixture of potassium dichromate 
or in aether, can of course precede, if necessary, this boiling in a 
soap-solution. 
Only by using good cover-slips can sharply defined drops be 
obtained. Further the slips must a short time before isolation be 
smeared with vaseline; if this is done some days before, then the 
drops are not so good. The diluting of the material is an important 
factor. The best and simplest method 1 found to consist in placing 
a very large drop of fluid on an ordinary cover-slip which has been 
prepared with vaseline. 
This can be done much better than with the eye of a 
needle, by using a strip of platinum foil + 5 ¢.m. in length, 
Ei wim. EN breadth, which is bent longitudinally at right 
angles into a small gutter and which is further treated as an ordinary 
inoculation needle. About this drop one need not be so particular, 
as it is a large one; some material is introduced into it, and 
there distributed. If too much has been introduced some may be 
removed by the gutter-needle and then liquid is again added. The 
material drops are taken out for the purpose of isolation, and it is 
preserved, when necessary, in a moist chamber. 
In my last publication I stated that the material drops should 
always consist of physiological sodium chloride solution, because then 
the isolated droplet separates most readily from the large drop. In 
my later experiments I found that some other fluid may also be 
used for the purpose, although they are slightly less suitable ; such 
are meat broth, glucose-peptone for yeast and moulds, etc. 
Finally a few hints and improvements may be mentioned. 
By capillarity particles of vaseline and bacteria may sometimes 
dry on the ends of the isolating needles, especially if they are not 
cleaned immediately after use. In this case mere dipping into sulphuric 
acid is not enough; it is best first to wash the ends with ether, 
then to keep them for a quarter of an hour in concentrated sulphuric 
acid heated to 100° on a water bath. 
The slit in the isolated chamber, through which the needle projects, 
is closed with liquid paraffin, thickened with a little finely divided 
