26 



SCIENCE. 



DRY "MOUNTS" FOR THE MICROSCOPE. 



BY PROFESSOR H. L. SMITH, HOBART COLLEGE, N. Y. 



What shall we use to preserve dry mounts effect, 

 ually? Many may think that nothing is easier; a 

 cell of Brunswick black ; a wax ring, or one of 

 balsam ; but the question is not thus easily to be dis- 

 posed of. The writer has, .within the last five 

 years, mounted, or has had mounted under his 

 supervision, some 15,000 slides of various micros- 

 copical objects, chiefly, however, foraminifera and 

 diatoms; half of these were dry mounts. 



Two things are important — the cell should be 

 quickly and easily made, and the object when 

 mounted in it should remain unchanged. There 

 are very few cells as now made which will fulfil 

 both these conditions, especially the latter. The 

 deterioration of delicate dry mounts, and especially 

 of test objects, sometimes within a few months after 

 their preparation, but more or less certain in nearly 

 every case, is well enough known. 



All of the dry mounts of the Eulenstein series of 

 diatoms, e. g., which I have seen, are spoiled ; and 

 my cabinet is full of such preparations. Even 

 Moller's do not escape, though they are, upon the 

 whole, the most durable. I have abundance of 

 amateur works that no doubt looked very beauti- 

 ful just as they issued from the hands of the en- 

 thusiastic preparers, which are now, alas, mere 

 wrecks ; and worse than this, many choice and 

 rare specimens, which I cannot replace, hopelessly 

 ruined. 



I believe that I was the first one to suggest the 

 use of sheet wax for the bottoms of cells tor foram- 

 inifera and other opaque objects, and of wax rings 

 for diatoms and other transparent objects. (See 

 Journal Quekett Club.) 



The number of spoiled specimens, especially of 

 diatoms and delicate transparent objects which I can 

 now show, proves that this method ot mounting is de- 

 cidedly bad. I have lived to see the day when 1 shall 

 be quite glad if the responsibility of suggesting such 

 a nuisance as the wax ring can be transferred to 

 some one else. For large opaque objects like most 

 of the foraminifera, seeds, pollens, &c. the object 

 itself is not so much injured, but the covering glass 

 will, sooner or later, become covered (inside the 

 cell), on the under surface, with a dew like deposit, 

 which, when illuminated, will glisten almost like 

 so many minute points of quicksilver, and though out 

 of focus when the object is viewed, will show very 

 disagreeably, like a thin gauze between ; and with 

 transparent objects these minute globules will not 

 only dot the entire field, as so manv dark or light 

 points, but the object itself will appear as though 

 it had been wetted. 



Not long ago a well-known optician showed to 

 me a spoiled slide " podura." The scales were 

 very good and large — in fact, it was a slide which 

 I had given to him, and it had been selected by 

 myselt in Beck's establishment in London as 1111- 

 exceptionably line. This slide began slowly to show 

 symptoms of " sweating." One scale alter another 



appeared as though moisture had, in some mysteri- 

 ous way, penetrated to the objects ; it was not water, 

 however, for when the cover, after much trouble, 

 had been removed, and warmed sufficiently 

 to evaporate anything like water, the scales still 

 exhibited the same appearance, and, in fact, the 

 heat required to get rid of this apparent moisture 

 was so great, that the scales were charred. When 

 wax rings are used, this apparent wetting or 

 " sweating " occurs quickly, and more disagreeable 

 than this, innumerable elongated specks, possibly 

 crystalline, appear all over the under surface of the 

 cover-glass. The same trouble occurs when any of 

 the ordinary asphalt preparations are used, and the 

 only cement which I have thus far found to be toler- 

 ably successful is shell-lac thoroughly incorporated 

 with the finest carbon (diamond black) such as is 

 used in the preparation of the best printing inks ; 

 the solvent being alcohol, these rings dry rapidly, 

 and the cover is attached by heating. Even these 

 rings cannot be trusted, unless thoroughly dry, and 

 spontaneous drying is better than baking. I have 

 had preparations spoiled after mounting on asphalt 

 rings, which had been made for over a year, and 

 which had been subjected for several hours to the 

 heat of a steam bath. With large, somewhat course 

 objects, the defect is not so marked, but with deli- 

 cate ones, and especially test objects, it is simply a 

 nuisance. With care 1 think the shell-lac rings may 

 answer pretty well. I have not tried the aneline 

 colored rings. The moisture (whatever it is), and 

 the crystalline specks, appear to be derived from the 

 vaporizable parts of the wax, or cement, given off 

 under conditions where one would suppose such a 

 tiling impossible; it is however a fact; I have 

 the proof of it, and I dare say hundreds of others 

 have, too plainly evident. 



There is another mode of making cells which 

 promises well for permanence. My attention was 

 first called to this method by Dr. Tulk, of London, 

 who suggested for this purpose the thin gutta-percha 

 tissue, used by surgeons in the place of oiled silk, I 

 have had special punches made, which cut neat 

 rings from this tissue, and I have used these rings 

 with the greatest satisfaction. I have no prepara- 

 tions of my own more than about two years old ; 

 these so far, show no signs of change. Dr. Tulk in- 

 forms me that he has them ten years old, and still 

 good as when new. I have noticed that in some re- 

 cent papers in the mineralogical journals the 

 writers, who with little experience, have so lauded 

 wax rings, speak of " thin rubber" for rings, evi- 

 dently they have seen somewhere the gutta-percha 

 mount, and supposed it rubber — the latter will not 

 answer, melted rubber will not become hard. One 

 beauty of the gutta percha ring is the very moderate 

 heat required ; it is thus available lor many objects 

 which might be injured by the greater heat neces- 

 ary for the asphalt or shellac rings. As these rings in 

 the arrangement which I have spoken of, can be rap- 

 idly made, and as they can be kept for any length of 

 time (shut away from the dust), they are at any 

 moment ready as well as convenient lor use. The 

 preparation is first arranged, dried or burnt on the 

 cover, the slide cleaned, a ring laid on the centre 

 and on this the cover is placed ; the whole is now 



