152 PREPARATION OF OBJECTS FOR THE MICROSCOPE. 



these troubles seem to be obviated by the minutest aperture 

 opening into the cell. 



I have on several occasions, both here and elsewhere, recom- 

 mended the shellac cement, which is now made by Mr. G. H. 

 Haass, the druggist, on East Main Street, as the best material for 

 building up cells for dry mounting. I have never yet seen 

 occasion to change my opinion in regard to it. The cells are 

 beautiful, durable and tough as horn when thoroughly dry. The 

 cement is so easily managed, can be so readily worked up into a 

 ring with the point of a knife blade on the turn table, that I 

 would think almost any one could easily acquire the skill or 

 knack of making the cells. I have made many hundreds of 

 them, and I know they cost me less labor and time than any 

 other cell that is made. I always carry along two dozen at a 

 time, first laying the foundation of the rings, making them of the 

 right size in diameter and breadth, then afterwards, with a day 

 or two of interval each time, making successive additions to them 

 until they are of the required depth. One hour's time is suffi- 

 cient for each operation with the whole two dozen ; and four 

 times going over them would make the deepest cells that one 

 would ever have occasion to use. Thus it takes me only ten 

 minutes in all, and at the most, for the making of each cell, and 

 it does not require any subsequent painting or fixing up. After 

 the mounting is completed however, I usually finish around the 

 outside with balsam, turning it up trim and true with the knife 

 point on the turn table. 



As I desire these remarks to be a pretty full expression of my 

 views and experience in the higher forms of mounting, I cannot 

 omit speaking a few words in regard to a certain cement which 

 has been recommended to you for cells for fluid mounting, on the 

 authority of Dr. Hunt, of Philadelphia. It is white zinc mixed 

 with gum dammar dissolved in benzole. Now every preparer of 

 slides would hail with delight a white cement that was safe to 

 use in all cases, but unfortunately no cement can be made white 

 without the mixture in it of solid particles, particles that do not 

 dissolve, that settle to the bottom of your vials. It is a mechan- 

 ical mixture, and no cement is safe to use in contact with liquids 



