720 SUMMARY OF CURRENT RESEARCHES RELATING TO 



sumption, the cement will always bo more or less dark. Perfectly 

 clear, sherry-coloured varnish can only be obtained by going through 

 a series of solutions which are only suitable for the preparation of 

 large quantities. 



Amber-lac for closing Microscopical Preparations.*— Dr. W. 

 Bchrens recommends amber-lac for ringing round cover-glasses, clos- 

 ing preparations, &c. The first kind, a commercial preparation, ho 

 used was probably made from broken up amber-refuse;, but it must 

 have contained other constituents as it was of a dark olive-brown 

 colour. In bulk it was opaque, but in thin layers on glass had a 

 beautiful amber tint. Tho solvent, judging from the smell, was, 

 principally at least, linseed oil. Two other kinds marked J and O 

 were also examined. O was a fluid of a bright cognac colour. J was 

 a brownish black liquid quite non-tiansparcnt. 



Specimens closed with this medium were found to be perfectly 

 hard in about a week, and when submitted to severe tests gave evidence 

 of tenacity. The specimens used were vegetable preparations mounted 

 in glycerin. 



Why do Dry Mounts Fail?! — ^ ss M. A. Booth, in looking over 

 her collection of slides, representing the work of European and 

 American preparers, with a view to noting their keeping qualities, has 

 been so surprised at tho number of failures as to query whether 

 permanence in microscopical work is possible. Why is it that so 

 large a proportion of dry mounts fail ? Obviously because that 

 motto which should emphatically be the microscopist's motto, 

 festina lente, is not heeded by all workers. The advances in the 

 merely mechanical portions of mounting have evidently not kept 

 pace with those in its purely scientific departments, or else micro- 

 scopists sometimes forget to take counsel of their good common sense 

 in the use of cements. In her collection are slides which have cost 

 hours of skilful manipulation and yet are utterly ruined because of 

 inattention to the details of the proper use of a cement. How do we 

 sometimes apply balsam to a mount ? By running it under the cover 

 and trusting to capillary attraction to fill the field. But why should 

 this law of capillary action be operative in the case of the balsam and 

 suspended in that of the cement ? From careful observation and a 

 not limited experience — speaking of dry mounts of diatoms and the 

 like — Mips Booth is convinced that success or failure depends not so 

 much upon the kind of cement used, as upon the care with which it 

 is used. 



In her own work, however, she has fixed upon white zinc as the 

 most reliable cement, and has sent out hundreds of slides made with 

 this cement, accompanied with the request that all failures be 

 returned, so that she might replace them with perfect slides ; but not 

 a slide has ever been returned. It has been her experience that 

 white zinc properly prepared and properly used never fails. The 

 secret of success with good white zinc is, that the rings shall be 



* Zcitschr. f. Wiss. Mikr., ii. (1885) pp. 54-7. 

 t Micr. Bulletin (Queen's), ii. (1885) pp. 17-8. 



