380 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
may be heated with the hot wire so as to saturate the whole of the paper 
disc, except the central moistened spot, which must be left unsaturated, 
with paraffin. The next step is to prepare a discoidal pad about 1 in. in 
diameter composed of ten to twenty superposed thicknesses of filter- 
paper ; upon this a disc of filter-paper is superposed. Fig. 70 shows 
the arrangement of the parts. The cap-ring 0 of a large-sized live-box 
holds a perforated mica cover m m in place. The perforation of the mica 
should be a little larger than the disc of paper e, immediately below which 
lies a disc of filter-paper /, which is saturated with paraffin, except at its 
centre. Then follows the pad of several thicknesses of filter-paper P. 
Fig. 70. 
The mode of preparation is as follows : — Place P upon the glass disc g 
of the live-box or compressor, then lay / upon P, then put the cap C in 
place and slip it close down over the drum D, so as to hold / firmly down 
upon P. Next moisten the central exposed part of /, that is the part 
not saturated with paraffin, with a little water, pick up one of the little 
discs of filter-pith by one edge with a fine forceps, and lay it down on 
the moist centre of /, when it will at once flatten out and adhere to /, 
and just neatly cover the central area not saturated with paraffin. On 
the apparatus so prepared place a drop of water D swarming with 
animalcules from a vigorous culture on e, when it will be found that the 
water will be drawn rapidly through e and / into P, in the direction of 
the arrows. In this way several drops of water may have a large part 
of their population separated out and caught upon the surface of e. To 
kill the contents of D it is only necessary to add a little saturated 
corrosive solution or 1 per cent, osmic acid. The animalcules are at 
once precipitated by the killing agents upon the upper surface of e , 
where they are caught and held in the meshes formed by the pith-cells. 
The filter e should now be gently removed by means of a needle and 
forceps. With gentle handling Mr. Ryder finds that Ciliates will 
remain attached to e, and may be passed through a dozen reagents 
without becoming detached, and that the pith-disc may be imbedded in 
paraffin very readily by the watch-glass method. The pith-discs may 
also be mounted entire, and in this way most instructive preparations 
may be prepared. Staining is also entirely under control, and with this 
method it has been found possible to cut 18 longitudinal serial sections 
and 50 transverse serial sections of Paramsecium with a thickness of 
