1899] MICROSCOPICAL JOURNAL. 13 



mounter. The period you name is correct; I have a few 

 of his slides purchased about 1854-5. All I have are 

 still in good condition ; the included air bubble is in all 

 of them. I consider the yellow varnish to be gold size, 

 which was much in use by the best of the early mounters ; 

 the black finish is probably a mixture of shellac and lamp 

 black, added merely for ornament and harmless under 

 the circumstances; the bare gold size would not have been 

 sightly enough for sale purposes. The usual mounting 

 fluid for such preparations (thick injected organs) was 

 dilute alcohol ; sometimes a saline solution, sometimes a 

 little creosote has been used with the alcohol, with or 

 without glycerine. In remounts I have successfully re- 

 placed it with distilled water plus 5 per cent carbolic acid 

 plus 5 per cent glycerine ; this mixes freeiy with any of the 

 above fluids and gets rid of the volatile alcohol — which 

 I think it well to do. The enclosed air bubble I consider 

 good, and when a cell contains any quantity of fluid I al- 

 ways use it : it acts as a spring, the expansion of the fluid 

 in a perfectly filled cell sooner or later forcing the 

 weakest point of the cell when it expands from increased 

 temperature. The included air bubble is a very different 

 thing from an intruded one, which always means mischief. 



"I have had no experience of formalin, but from its 

 composition should consider that, like alcohol, it would 

 attack shellac, therefore think you have done right in us- 

 ing gold size. I have rather a dislike to varnishes and 

 cements of which the composition is unknown, as, how- 

 ever well they may be spoken of, you are quite in the 

 dark as to their action on mounting fluids. 



"My varnishes are practically two : gold size, — this is 

 composed principally of boiled linseed oil, possibly com- 

 bined with a resin dissolved in turpentine, in fact a first- 

 rate oil varnish. It should be obtained at a good shop 

 and be of the best quality. My other varnish is shellac, 

 which I always make myself ; it is almost as easy to make 



