1080 SUMMARY OF CURRENT RESEARCHES RELATING; TO 



sufficient numbor of tho cleaned diatoms with water upon it to form 

 a perfectly oven layer of tho diatoms over tho central part of tho 

 covor. As tho water ovaporates tho frustules will gather closo 

 togcthor and form a compact mass in a single, uniform layer, perfectly 

 adapted for a display slido. An exceedingly thin and clear solution 

 of gum may be used in this operation to attach the frustules more 

 securely. When thoroughly dry, cement tho cover-glass over a ring, 

 just deep enough to protoct the diatoms, preferably with a dead black 

 bottom. 



This particular diatom, howovcr, is a far moro brilliant object 

 when mountod in balsam and viewed with a dark field. It is likewise 

 one of the most difficult to mount in balsam, owing to the persistence 

 with which the air is retained within tho frustules. A mount in 

 balsam of the diatoms attached to the seaweed as they grow can bo 

 made by the method devised by the late Charles Stodder. Selecting 

 a perfectly dry specimen, place it in chloroform for a short time, 

 and, if necessary in order to remove all the air, heat tho latter gently. 

 In this way tho frustules become filled with the liquid. Then place 

 some drops of chloroform on a slide, transfer the specimen selected 

 for mounting to this, and keep it covered with the liquid. It is well 

 to put on a cover-glass to prevent rapid evaporation of the liquid. 

 Then add chloroform balsam and let it run under the covor and follow 

 the chloroform as it evaporates from tho frustules, aiding the opera- 

 tion with gentle heat. In this way the hollow frustules can be com- 

 pletely filled with balsam without difficulty, and tho mounts thus 

 obtained are very fine. 



In mounting the free frustules in balsam we have adopted a plan 

 somewhat different in detail, in order to obtain a perfectly flat and 

 even layer of frustules against the cover-glass. The cleaned speci- 

 mens in considerable abundanco were first placed in chloroform in a 

 small vial, and raw, hard balsam added until a not very thick solution 

 was obtained, which thoroughly permeated the cells. The solution 

 was poured upon a cover-glass resting on a mounting table, with a 

 spirit-lamp beneath. In a short time the frustules settled down upon 

 the cover- glass and formed an even layer. The closer they are the 

 more effective the result. Heating now, very gently indeed, the 

 balsam becomes slowly hardened without distributing the diatoms. 

 If necessary, more balsam can be added, but if possible, a sufficient 

 quantity should be put on at first, as the addition of more is likely to 

 disarrange the specimens. The balsam must be thoroughly hardened, 

 without heating enough to discolour it. We now have the frustules 

 nicely mounted in the balsam on the cover-glass, and the latter may 

 now be turned over and attached to a ring on a slide, and the mount 

 thus finished. It will be greatly improved, however, by the well- 

 known process of backing with black varnish. First put on a layer 

 of shellac over the balsam to protect it from the action of turpentine, 

 and then apply an opaque layer of black varnish. When this is 

 thoroughly dry, mount the cover-glass on a ring, and it will make one 

 of the finest objects in any cabinet. 



