xiii, c, 4 Shaw: Microtechnical Methods 249 
rangement is shown in fig. 1. The larger cover is placed on this 
holder slide and a small drop of Canada balsam is placed on it 
near each corner. A glass rodlet of the required size is placed 
on each droplet so as to project into the area of the smaller 
cover, and pressed into contact with the cover. The balsam is 
allowed to thicken or harden. Specimens in approximately the 
proper quantity of glycerin are placed on the center of the larger 
cover glass and covered with the smaller cover. Excess of 
glycerin is removed by use of a capillary pipette or a piece of 
slightly moistened filter paper, with care not to moisten the 
margin of the larger cover or the upper surface of the smaller 
cover. A deficiency of glycerin is supplied from a capillary 
pipette. The smaller cover should rest firmly on the glass rod- 
lets. The covers are then picked up with a pair of forceps, 
inverted, and placed, smaller cover lowermost, on a plain slide 
I 
Fig. 2. Sectional view of permanent mount. Slide, s; larger cover, b; smaller cover, k; 
glass rodlets, d; balsam, c; material, to. About 2£ times natural size. 
on which there has been placed, just previously, a drop of very 
thin balsam dissolved in xylene. As much balsam is added and 
allowed to run under the larger cover as is necessary to fill the 
marginal space. The arrangement is then as shown in fig. 2. 
Osterhout cautions that — 
The balsam should be quite fluid so that the weight of the preparation 
will force it out from beneath the lower cover glass, since it will not do to 
press down on it for this purpose on account of the danger of forcing the 
water out from between the covers. Neither will it do to heat to any 
great extent, since this may cause bubbles. The preparation is now set 
aside to dry and treated like any balsam preparation. 
A PLANKTON NET FOR LARGER ORGANISMS 
After using several unsatisfactory means of collecting Volvo- 
caceae I devised a plankton net which combines a number of 
advantages. The receptacle of this net is a sedimentation tube 
of 15 ec capacity with the bottom cut off and stopped with a 
cork. The bottom of the tube is removed by filing a nick near 
the closed end of the tube and pressing the tube firmly down 
on the end of a stick which fits inside the bottom. The cut 
end of the tube is then softened by heating in a flame and 
flared, by rotation on the conical tip of an arc lamp carbon, 
for the reception of the cork. 
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