$8 JOURNAL OF THE [April, 



Copper chloride (crystallized) 0.2 gm. 



Copper nitrate " 0.2 " 



Glacial acetic acid , 0.5 '• 



Camphor water 50 c c. 



Distilled water 50 c.c. 



Shake up until solution, and filter. 



After some time, however, we found it advisable not to use this 

 ■solution in its full strength, but with the addition of an equal bulk 

 of boiled distilled water. More recently two further modifica- 

 tions of the formula have suggested themselves. First, the glacial 

 acetic acid should be omitted. Secondly, as the two copper 

 salts, even in the chemically pure form supplied in commerce, 

 have ordinarily an acid reaction, the free acids should be neutral- 

 ized in some way. 



It should also be remarked that the nature of protoplasm itself 

 varies so greatly, as to constitution, density, color, transparency, 

 contractility, and other properties, that it is not at all probable 

 that a single preservative of universal application can ever be 

 devised, even for the forms of vegetable protoplasm. 



The desirable qualities, in a mounting medium suited to pre- 

 serve aggregates of protoplasm in their original form, size, and 

 color, as seen within the organic cell, are the following : 



Neutral reaction ; absence of dehydrating power ; density ap- 

 proaching that of protoplasm; fluidity below 30° C. ; content of 

 ■efficient germicide ; and very low or very high refractive index. 

 Where, then, can we find this ideal preservative medium for 

 protoplasm? Only hitherto, 1 think, in the dreams of the hope- 

 ful naturalist. 



In my own Laboratory our attention has been largely given to 

 the preservation of the fresh-water algae and water fungi. From 

 former experience we have hopes of success from the following 

 preservatives, now on trial. 



A. Organisms with delicate walls and rather thin and watery en- 

 doplasm {e.g., desmids, beggiatoa, etc.). — A tiny grain of naptha- 

 lin is inserted, part way but firmly, into the inner side of the 

 cell-wall (paraffin or wax), and only the filtered native or mother 

 water of the organism (or boiled and cooled distilled water) is 

 used to fill the cell. In this we hope to have a substitute for 

 camphor water, with a more efficient and permanent germicide. 



