XIIIC - 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 



C 



Fig. 2. Sectional view of permanent mount. Slide, s; larger cover, 6; smaller cover, it; 

 glass rodlets, d; balsam, c; material, m. About 2i 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 cc 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. 



156153 4 



