36 JOURNAL OF THE [April^ 



preservation of the fresh-water algae, this is the main objection to 

 the use of pure or diluted glycerin, glycerin and camphor water, 

 camphor water and alcohol, glycerin jelly, Farrant's and Bul- 

 loch's media [i.e., mixtures of gum arabic and glycerin), etc. 

 The same objection may probably hold to the more complicated 

 mixtures, such as Heintzch's preservative for desmids, algse, etc. 

 (alcohol, glycerin, and distilled water), Hervey's preservative for 

 marine algae (glycerin and sea-water), etc 



4. Contraction, or, it may be. Irregular Expansion, produced by 

 Osmotic Actiofi through the Cell Wall. — A most efficient cause of 

 alteration in shape of the colloidal masses inside of the wall must 

 probably lie in this interchange of liquid and soluble matters 

 with the medium outside. The greater the difference in density 

 (commonly aimed at for the sake of contrast in refractive index, 

 with corresponding improvement in definition), as when the ex- 

 ternal preservative is nearly pure water {c-g., camphor water), or 

 in solubility, as when the preservative is a strong saline solution, 

 the more active the osmosis and the more speedy the deforma- 

 tion. We may consequently expect that solutions of common 

 salt, potassium acetate, aluminum acetate, calcium chloride, etc., 

 and the large number of preservatives made up of complex com- 

 binations of sundry salts, must be specially objectionable in this 

 way, where protoplasm forms are concerned; so also, perhaps, 

 even syrup, honey, dextrin, and solutions of gums, to some degree. 



5. Contraction by Heat. — The more delicate forms of proto- 

 plasm, even after death, are commonly sensitive to very slight 

 elevations of temperature. This presents one serious objection 

 to the use of hot glycerin jelly, aside from that founded on the 

 absorption of water by its content of glycerin. 



It is, of course, still more efficient for harm in the resinous 

 media, like balsam and dammir, and many others of higher re- 

 fractive index in which heat is used, such as sulphur and arse- 

 nious acid, realgar, etc. 



We may, therefore, conclude that any medium requiring a 

 temperature much above 30° C. (say 85° F.) for sufficient fluidity is 

 unfitted for the preservation of protoplasm. 



6. Disintegration by Bacteria and Minute Infusorians. — In 

 many or most cases a living object, plant or animal, when about 

 to be immersed in the fixing or hardening solution and the pre- 



