108 



On Mounting Media so far as they Relate to Diatoms. 



By H. Morland. 



(Read April 22nd, 1887.) 



The object of my paper this evening is not only to give some 

 information and to offer some hints relative to the various 

 media in which the Diatomacess are mounted, but also to 

 solicit such information and hints in return from those members 

 who have paid special attention to this subject. I have myself 

 worked at several of the media to which I shall refer, but 

 others have never yet come into my hands ; but having seen 

 slides prepared with them, added to remarks I have heard 

 made relative thereto, I venture to treat this subject as a 

 whole. With this explanation, it can be readily understood 

 that this paper is by no means exhaustive of the subject taken 

 in hand. 



Mounting media, for convenience sake, may be divided into 

 four classes, viz., Air, Fluids, Resins, and Chemicals. I will 

 treat of these classes in the order in which I have named them. 

 Air. — This medium, in consequence of the introduction of 

 immersion lenses, is now almost out of date ; still, for ordinary 

 dry lenses, it is as useful now as ever it was, and even for 

 immersion lenses it answers for those parts of the diatom valve 

 which touch or are adherent to the covering-glass. Diatoms 

 mounted in this medium (or in any other) should, as a rule, be 

 on the underside of the covering-glass. They should be 

 perfectly dry, and the system of sealing them up by means of 

 damp cements cannot be too strongly condemned, as in such 

 case the cover-glasses are certain to get " dewed " in course of 

 time, the " dew-drops ' in many instances surrounding the 

 diatoms, and interfering with their due examination; to over- 

 come this difficulty, 1 always attach my covers by means of 

 heat to rings of perfectly hard and dry cement on the slide. 

 Slides with air-mounted diatoms ought to be carefully handled 

 w lien being cleaned, for if too much pressure be applied to the 



