86 SOLUTIONS AND PROTOPLASM [Ch. Ill 



Turbo, Area, Cardium edule, Mytilus edulus, etc.) bringing 

 them to live in fresh water by gradually diluting the medium. 



Plateau ('71) gradually accustomed the fresh-water Asel- 

 lus aquaticus to pure sea water, so that even in mixtures con- 

 taining between 20% and 80%. of sea water tlaey laid eggs and 

 produced a second generation. The second generation lived 

 108 hours in pure sea water, while Asellus freshly taken and 

 plunged into sea water live only about 5 hours. 



Not only the larger organisms, but also tissues and Protozoa 

 may become acclimated. Roth observed in '66 (p. 190) that 

 cilia become " accommodated " to gradually increasing densi- 

 ties ; Engelmann ('68, p. 343), however, denied, though with- 

 out critical experiments, the validity of this conclusion for the 

 case of the ciliated epithelium of the frog's throat. Later, 

 CzERNY ('69, p. 161) succeeded in acclimating Amceba to a 4% 

 solution of NaCl, although Amoeba rarely resists 1% when sud- 

 denly subjected to it. 



These early experiments have since been greatly extended, 

 observations having been made upon nearly all groups of organ- 

 isms — upon algae, by Richtek ('92) ; upon Myxomycetes, by 

 Stahl ('84); upon Actinospherium, by Vekworn ('89, p. 10); 

 upon bacteria, Flagellata, Ciliata, and Hydra, by Massart 

 ('89); upon Ciliata, by Fabre-Domergue ('88); upon Crus- 

 tacea, by Plateau ('71), Schmankewitsch ('75 and '77), 

 and Bert ('83); upon the tadpoles of frogs, by Yung ('85, 

 p. 520) ; and upon representatives of almost all of the principal 

 groups, by DE Varigny ('88) and Gogorza ('91). 



The aims and methods of these experimenters have been 

 very diverse. Some have sought merely to illustrate how 

 marine organisms may have come to live in fresh water, or the 

 reverse. Such have usually made mixtures of fresh and salt 

 water, the proportions of the one gradually increasing (de 

 Vakigny, Schmankewitsch, Gogorza), or they have added 

 sea salt, dry or in solution, to the normal fresh-water medium 

 of the organism (Yung). Massart, on the other hand, having 

 in mind the more fundamental problem of the action of density 

 upon protoplasm, has employed solutions of a single salt at a 

 time — solutions, moreover, based usually upon the osmotic 

 index of the salt as a unit of concentration. 



