230 
Notes. 
in the case of very minute objects. In some cases I have, however, 
succeeded in carrying the culture a little further by proceeding in the 
following manner : — The hole in the blotting paper was made slightly 
larger than the coverslip. The latter was thus allowed to come closer 
down on the slide than when it was supported by the paper. The 
portions of the paper surrounding the hole were then teased out by 
means of a needle, and the teased parts were made to touch the 
margin of the coverslip. This was sufficient to prevent the water 
under the coverslip from becoming foul, and at the same time it pre- 
vented drying up. After some days, however, the water usually flooded 
the coverslip more or less. 
When the paper has been used for about 20 days it does not allow 
the water to pass through very freely, and it has therefore to be 
renewed. This is not very easily done, but I have almost invariably 
succeeded by proceeding in the following manner : — First of all an 
excess of water is brought on the paper. As soon as the coverslip 
begins to float it is removed. When this is done, as much water as 
possible is removed from around the object with a piece of fresh 
blotting paper, and then the blotting paper which has been used the 
whole time is carefully lifted and taken off, and a new piece of exactly 
the same size is put down in its place. When this has become 
thoroughly soaked with water, the hole is again covered with a cover- 
slip in the manner already described. During this whole process the 
object is almost constantly kept under observation with a low power, 
so that it may not be lost even if it be slightly moved. As this process 
may be repeated any number of Limes, it is obvious that a culture may 
be kept in operation any length of time. 
To make a culture successful, it is of course necessary to adapt it 
as much as possible to the needs of the organism which one wants to 
grow. It is not my purpose to discuss this point here in detail. I 
wish only to point out that the supply of light and of heat has to be 
carefully regulated. One ought, for instance, never to forget to turn 
away the mirror of the microscope after observation, so that concen- 
trated light may not fall on the object for any length of time. Special 
attention has also to be paid to the fact that certain organisms will 
only grow in certain kinds of water, &c. 
In order to show what results can be attained with this arrange- 
ment, I will shortly describe my last culture, which is still in progress 
to-day (July 5th). On the 2nd of June a culture of Pediastrum Bory- 
