C. F. ROUSSELET ON SOME MICRO-CEMENTS FOR FLUID CELLS. 95 



good enough to send me an old slide, an anatomical preparation, 

 mounted in a deep glass cell in some watery fluid with a small 

 bubble in it, which he said was at least forty-five years old. Mr. 

 Hughes could give me no further information, except that the 

 bubble had always been there, and had most probably been left 

 in the mount intentionally to act as a safety valve against the 

 expansion of the fluid. Here, then, is a fluid mount which can 

 be called permanent, and I therefore tried to find out who the 

 mounter was and how it was closed. It has two coats of cement, 

 first a yellow cement like gold size, and over that some black 

 alcohol cement. Mr. W. T. Suffolk, the treasurer of the E. M. S., 

 with his great experience in such matters, was able to give me full 

 information on this slide, and such valuable suggestions regarding 

 fluid mounts in general, that I cannot do better than give here 

 long extracts of his letters. 



In reply to my inquiries Mr. Suffolk wrote the following : — 

 " The slide you send me is by Hett, a well-known mounter. 

 The period you name is correct ; I have a few of his slides pur- 

 chased 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 replaced it with distilled water + 5 per cent, carbolic 

 acid -f 5 per cent, glycerine ; this mixes freely with any of the 

 above fluids and gets rid of the volatile alcohol — which I think it 

 well to do. The inclosed air bubble I consider good, and when a 

 cell contains any quantity of fluid I always 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 bvibble 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, there- 

 fore think you have done right in using gold size. I have rather 



