1893.] NEW- YORK MICROSCOPICAL SOCIETY. 21 



tention of the naturalist are constituted, in by far the largest 

 number of cases, of formed, non-contractile material. Even deli- 

 cate tissues consist, in large part, of sacs, sheaths, or other enve- 

 lopes enclosing protoplasm or sarcode, but themselves constituted 

 of formed material, such as cellulose, chitin, etc., able to resist 

 heat or partial desiccation or dehydration without much distor- 

 tion. For the numerous objects of this vastly predominant class- 

 many good mounting media have been found. Their sheaths, 

 carapaces, and skeletons being tough and stout enough to resist 

 most of the tendency to distortion produced by the contraction 

 of the minutely divided protoplasm they contain, the processes 

 and the preservatives employed answer a useful purpose. By 

 selective absorption of stains, or by exceedingly delicate contrac- 

 tions or expansions effected by treatment with acids, absorbents 

 of water, etc., particular details of organic structure become pe- 

 culiarly colored, swollen, or shrunk, and so rendered prominent 

 by contrast and more easily distinguishable. Most histological 

 preparations, for example, by their vari-colored tissues, intensified 

 nuclei, etc., serve to convey supposed or established facts from' 

 one observer to others. For such purpose, these methods are 

 legitimate and most useful, but may be, and generally are, just as 

 artificial as those of drawing and photography for the true repre- 

 sentation of structure. 



But, on the other hand, for the permanent preservation of liv- 

 ing contractile matter, without immediate or ultimate contraction 

 and distortion, such as the protoplasmic contents of thin walled 

 cells of fresh-water algse, water fungi, bacteria, rhizopods, infu- 

 sorians, etc., no satisfactory medium has yet been found. This 

 is an entirely different problem from that above considered, and 

 for its solution the elements of the higher tissues, with their mi- 

 nute subdivision of contractile matter in granules and cylinders 

 often less than ten microns in diameter, afford too diminutive a 

 field for exact microscopic discrimination of effects produced by 

 various processes and reagents. 



But he who attempts to preserve an object like amoeba, the 

 cell contents of a desmid or spirogyra, bacteria in zoogloea, etc., 

 cannot deceive himself in regard to his limited degree of success,, 

 as he notices the contracting contour of the comparatively huge 

 mass of protoplasm. Only an object of this class, however, cani 



