x 111 ' ' 4 Shaw: Microtechnical Methods 247 



A clean slide is placed on a self-centering turntable, with care 

 that if it be slightly curved it shall rest on its ends and not on 

 its middle. With the table rotating slowly a ring of shellac 

 is applied to the slide. This ring is made of such width that 

 there are several millimeters of ring both within and without 

 the area of the circular cover glass to be used. The slide is 

 placed in a desiccator for the shellac to harden, after which 

 additional rings are added in the same manner until the ring 

 has been built up to the required thickness. Then, the ring 

 being dried to a suitable consistency, the slide is placed on the 

 turntable, rotated, preferably by means of a motor, and the 

 inner edge of the ring is trimmed away with a sharp instrument. 

 This leaves the inner side of the ring nearly perpendicular, 

 doing away with the sloping beach on which specimens would 

 be liable to get stranded and be crushed by the cover glass. It 

 is preferable that the thickest part of the ring be at or near 

 its inner edge, and therefore well within the periphery of the 

 cover. A clean, circular cover glass is then laid on the ring and, 

 if the consistency of the ring be just right, a slight pressure 

 on its center with a clean needle will cause it to stick sufficiently 

 to permit the application of a thin ring of shellac to the cover. 

 This ring is made with its inner diameter the same as that of 

 the slide ring and extends just to the outer edge of the cover. 

 The cover is then removed from the slide and placed in a desic- 

 cator for the shellac to harden. 



The specimens in glycerin are placed on the slide with suffi- 

 cient liquid to fill the space within the ring. The cover is placed 

 on the liquid with its ring lowermost and pressed gently upon 

 the slide ring. For continued pressure cylindrical metal weights, 

 a little smaller than the cover, are used. Superfluous glycerin 

 is removed from the upper surface of the slide ring with the 

 moistened end of a strip of filter paper. Then the slide is placed 

 on the turntable and shellac is applied so as to occupy all space 

 between the two shellac rings. Finally the slide is again placed 

 in a desiccator for hardening the shellac. 



Failures will be indicated, after a time, according to the con- 

 dition of the atmosphere to which the mounts are exposed. In 

 moist atmosphere there will be exudation of the liquid, and in 

 dry atmosphere bubbles will appear and grow. 



It is not desirable to use glass supports for regulating the 

 thickness of the chamber of these mounts unless such supports 

 are sealed in place, for they are very liable to get loose and 

 damage delicate specimens if the slides are not kept constantly 

 in a horizontal position. 



