INVERTEBRATA, CRYPTOGAMIA, MICROSCOPYj ETC. 861 



The centre can be turned out with a penknife or other convenient 

 tool on a turntable. The cell can be cleaned with a rag moistened 

 with benzine, or to avoid the difficulty of this the glass slip may be 

 covered with a solution of gum tragacanth, to which a small quantity 

 of sugar has been added, allowing it to dry before the application of 

 the wax, when the marks of the knife left in turning out the cell can 

 be removed by washing in water only. These cells would not, how- 

 ever, do for mounting in glycerine, water, &c., and the adhesion of the 

 wax to the slide would be destroyed ; but if the pi-ocess is carried a 

 little further and the slide with the cell on is soaked in w^ater, the 

 cell will be freed, and when washed and dried can be apjdied to 

 another slide. By this use of gum any number of cells can be made 

 and kept ready, like glass and vulcanite cells. 



Dry "Mounts" for the Microscope— Wax and Gutta-percha 

 Cells.* — The following is by Professor Hamilton L. Smith (in the 

 new American weekly periodical ' Science,' w'hich is intended to be 

 conducted on a similar plan to ' Nature '). 



" What shall we use to preserve dry mounts effectually ? 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 

 disposed of. The writer has, within the last five years, mounted, or 

 has had mounted under his siqjervision, some 15,000 slides of various 

 microscopical 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 Euleustein series of diatoms, e. g., 

 which I have seen, are spoiled ; and my cabinet is full of such prepa- 

 rations. Even Moller's do not escape, though they are, u2)on the 

 whole, the most durable. I have abundance of amateur works that 

 no doubt looked very beautiful just as they issued from the hands of 

 the enthusiastic 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 for foraminifera and other opaque objects, 

 and of wax rings for diatoms and other transjiarent objcjcts. The 

 number of spoiled specimens, especially of diatoms and delicate 

 transparent objects which I can now show, proves that this method of 

 mounting is decidedly bad. I have lived to see the day when I shall 

 be quite glad if the responsibility of suggesting sucli 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 



♦ 'Science,' i. (ISSO) p. 'J(J. 



