Notes. 
229 
off by the triangular prolongation of the blotting paper already men- 
tioned. An inverted flask, F, filled with water, has its mouth just 
touching the surface of the water in the tumbler, E, and keeps the level 
of the water in the tumbler constant, thus ensuring the regular escape 
of drops from the capillary tube, D. The capillary tube has a 
thickened portion in the middle, which I find convenient to keep the 
tube steady. To be quite sure that the tube will work properly it is 
well to empty and refill it every 24 or 48 hours. 
The object to be observed is placed on the slide within the central 
hole, C, cut in the blotting paper. It is covered with a coverslip 
slightly larger than the hole. The coverslip must not be put on in the 
usual manner, for in this way it is difficult to avoid having air-bubbles 
under it ; but, when the paper is thoroughly saturated with water, the 
coverslip is placed beside the hole ; it is then slid slowly over it, and 
the space between it and the slide is gradually filled with water. 
Fig. 13, copied from a photograph taken by Mr. J. B. Farmer, and 
for which I am very much indebted to him, represents the apparatus 
in use. I may here state that the apparatus does not interfere with 
the drawing of an object, as the large vessel which receives the water 
dropping down from the blotting paper may be replaced by a very 
small one for some time, and thus the space on the right-hand side of 
the microscope is almost entirely left free. 
As the water between the coverslip and the slide is in direct com- 
munication with the water in the blotting paper, which is constantly 
being renewed, it cannot become foul. I have never yet observed in 
my cultures (some of which lasted over a month) a strong growth of 
Bacteria, such as one would be sure to find in foul water. But in 
certain cases it may become desirable to have the water more rapidly 
renewed than is possible in the way above described. This is easily 
done by cutting a narrow channel (either straight or curved) from the 
central hole in the blotting paper to the place where the water drops 
down on the slide from the capillary tube. The strength of the current 
of water which one gets in this way may be regulated by a small 
piece of blotting paper which has been teased out with a needle. 
With the arrangement described above it is only possible to use 
moderate powers (up to the combination of Zeiss’ Ocular 5, Objective 
D). For many purposes this is quite sufficient. If higher powers are 
required, the paper may be removed and the object observed in the 
usual way, but of course it is then very difficult to continue the culture 
