500 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
When arranged as shown in fig. 107, on the conductor plate, the binding 
screws of the first lie exactly on a pole-plate, and are by means of the 
metallic contact themselves electrified. The dimensions are so chosen 
that the pole-plate can be moved as much as 2 cm. without losing contact. 
In this way the electrified and yet independent object-holder can be 
moved sufficiently without hindrance, so that Microscope examination 
can be effectively carried out. 
On the upper side of the object-holder arrangements are made for the 
reception of the electrodes. 
Fig. 105 shows a form adapted for the smallest organisms and 
strongest objectives ; fig. 106, one for larger objects such as snails’ eggs. 
The former of these consists of an object-holder, as described above, 
with a shallow circular sinking, some 15 mm. in diameter, communicating 
on each side with a groove 2 mm. wide, in which lie the platinum thread 
poles of the electrodes. When this sinking and grooves are filled with 
Fig. 101. Fig. 105. 
water, and a cover-glass applied, the platinum poles can be placed at 
any desired distance, and can even be pushed under the cover-glass. 
This form of pole gives an ellipsoidal electric field ; platinum foil poles 
give a parallel electric field. 
The second object-holder is shown in fig. 106, and is of the same size 
as the former, but bears in addition a glass rectangular trough 11 mm. 
high. Its sides have an insertion 3 mm. deep, through which the copper 
wire electrodes project into the interior of the trough. The poles consist 
of small platinum shanks, and the adjoining jiarts of the wires are coated 
with an insulating varnish. Two glass slips 4 mm. high and 6 mm. 
apart are cemented on to the floor of the trough parallel to the electrodes, 
so as to fix the object better in the current. The trough contains a 
relatively large amount of water, which is very desirable for the larger 
organisms. A glass cover can be adapted to the trough. 
The above electrodes are naturally polarisable, but they answer well 
