256 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
that is taken off, the elasticity of the specimen causes the latter to lift 
the cover up again, and what naturally happens ? Why, of course the 
air runs in, because “ nature abhors a vacuum.” 
Nor is this the only fault of spring-clips, for even a moderate amount 
of pressure is sufficient to damage many delicate specimens. Take the 
case of sections of stems of plants ; the effect of squashing very fre- 
quently makes the cells and vessels in parts turn on one side, and where 
each cell should by rights be in its natural place, nothing is seen 
but a jumbled mass of tissue. Yet spring-clips are still frequently used 
in balsam mounting, the reason being that they fulfil a twofold purpose. 
One use of them is to produce pressure. This, as we have seen, is a 
bad purpose. Not but what a certain small class of specimens require 
flattening out, but this must be done before mounting them ; it is too 
late to make the attempt when they are in the balsam. Their other use 
is to keep the cover in place while the balsam is hardening, and it is for 
this alone that they are usually used. They do not accomplish this end 
practically, for as a general rule, in applying the clip, the cover gets 
slightly shifted to begin with ; moreover, they are almost certain to tilt 
the cover on one side or the other unless supports have been placed 
round its edges. 
Nearly two years ago the idea occurred to the author that what was 
wanted was an arrangement that would hold the cover in its proper 
position by firmly gripping the edges instead of pressing down on the 
top of the glass. Since then he has mounted a number of slides, using 
these “ pressureless edge clips ” until the balsam has hardened, and with 
such success that now he “ uses no other.” 
Fig. 29 shows one of the pressureless clips of the natural size, and 
how they are used for keeping the cover of a slide in its proper position. 
Fig. 29. 
It will be noticed that two clips are necessary, and when in use they 
firmly clip the slide only, their four points resting against the edges, 
not on the top of the cover-glass. In this way the cover is perfectly 
firmly held in position ; it is impossible for it to slip out of place, while 
no pressure is applied to the object. In applying them to the slide, 
they are first clipped on anywhere, and then pushed up until their points 
touch the edges of the thin glass circle ; this can generally be accom- 
