720 SUMMABY OF CURRENT RESEARCHES RELATING TO 



on the cover in the dry mounts, and possibly that process would be 

 sufficient for the balsam mounts without the film of isinglass, as stated 

 on p. 68 of Davies' « Manual of Mounting.' " 



Mr. Sharp has tried several kinds of mechanical finger, but 

 declares he " can do the work quite as well and in less than half the 

 time " by the method described above. 



Mr. W. M. Bale also discusses * the subject of mounting diatoms 

 in symmetrical groups in continuation of a previous paper | in which 

 he described the process for valves which are very small and flat, and 

 are to be mounted dry. Large or uneven diatoms are, however, liable 

 to leave the slide at the least jar, and must therefore be attached with 

 some cement ; while any diatoms which are to be mounted in balsam 

 must be fixed to the slide or cover with a cement not soluble in the 

 turpentine contained therein. In these cases, a minute drop of clear 

 gum may be deposited near the centre of a clean slide, and thinned 

 with a drop or two of water, the whole being spread backwards and 

 forwards over the slide with the blade of a knife till none appears to 

 be left in the centre where the objects are to be placed. The diatoms 

 are then arranged on the slide in the usual manner after breathing 

 on it, and when dry they will adhere to its surface, after which they 

 may be covered in the ordinary way. With dry mounts especial care 

 must be taken that the merest invisible film of gum remains on the 

 slide, the appearance of the diatoms being spoiled if they are saturated 

 with gum or any similar material. 



For transferring valves from one slide to another mounted bristles 

 are best, one rather stout for large diatoms, and another not thicker 

 than a human hair, and somewhat curved for lifting small valves and 

 remaining particles of dust. Bristles are, however, too elastic for 

 moving the diatoms into the exact position, for which a fine needle is 

 almost indispensable. 



When the objects are to be mounted in balsam, the slide should 

 be allowed to dry, and a small drop of carbolic acid placed on the 

 diatoms, which are then to be examined with the Microscope, as it 

 frequently happens that the gum, if not thin enough, seals up the 

 minute cells in the valve, or even the whole cavity beneath it, pre- 

 venting the entrance of the acid. In this case a drop of spirits of 

 wine placed on the diatoms will usually find speedy entrance and 

 dispel all bubbles, and while the diatoms are still wet with the spirit 

 the carbolic acid may be placed upon them. Gentle warmth will 

 then evaporate the spirit, leaving the acid, and it only remains to 

 apply a small drop of balsam and a cover, taking care, if any of the 

 valves are very convex, to provide rests to prevent the cover from 

 crushing them. It is better to let the balsam fall on the diatoms 

 than to apply the cover first, and let it run in, as it very often carries 

 in with it particles of dust, cotton fibres, &c, which may be on the 

 slide or the edge of the cover, and which are apt to come in contact 

 with the diatoms and remain there. The running-in process is only 

 necessary when the valves are not cemented to the slide, and when, 



* Journ. Micr. Soc. Victoria, i. (1882) pp. 97-9. 

 f Ibid., i. (1881). 



