1893.] NEW-VORK MICROSCOPICAL SOCIETY, 39 



B. Organisms with endoplasm of oj-dinary density {e.g., most of 

 the filamentous algse). — This is a solution founded on experience 

 with Petit's preservative : 



Copper chloride o.i gm. 



Copper nitrate o. i " 



Cliloral hydrate o. 5 " 



Distilled water, just boiled 100 c.c. 



From this solution, however, the trace of acidity must be 

 removed in this way: Another solution is prepared of a few 

 grammes of any soluble copper salt ; to this a weak solution of caus- 

 tic potassa is added in slight excess ; the precipitate of hydrated 

 copper oxide (CuH^Oj) thus obtained is washed thoroughly, first 

 by decantation and then upon a filter. This purified residue is then 

 thrown into the one hundred cubic centimetres of preservative 

 first prepared, and the whole frequently shaken at intervals un- 

 til a neutral reaction is shown by test papers, and then filtered. 



C. Organisms ivith Apparently Dense Endoplasm. — To one 

 hundred cubic centimetres of Solution B add ten grammes of 

 gum arabic, in selected white grains, shake until solution, and 

 filter. Possibly gelatin may be found preferable to gum arabic. 

 The object of thickening the solution is to prevent any ten- 

 dency to osmosis ; though, of course, the approximation of 

 refractive index within and without the organism may tend to 

 decrease the definition. 



VI [. Balsam- Paraffin for Cells. 



The materials commonly used for cell construction, though of 

 excellent application, particularly shellac varnish, gold size. 

 Bell's cement, copal varnish, and zinc cement, are open to two 

 objections. 



1. The freshly spun cells can only be used after baking or dry- 

 ing, which may require considerable length of time. This some- 

 times stretches into weeks or months in the case of gold size, 

 where the process of ripening is mainly one of oxidation. 



2. The material, even after thorough drying, is gradually solu- 

 ble or liable to softening under the action of some of the con- 

 stituents of common preservatives, ]3articularly alcohol and inor- 

 ganic acids. 



Id 1880 we began the use of paraffin for spun cells, and it has 



