88 SOLUTIONS AND PROTOPLASM [Cn. Ill 



If we take as our unit in Table X the concentration repre- 

 sented by v p, and in Table XI the concentration represented 

 by v, we may conclude that the subjection for 22 hours to a 

 1.8 MW % or to a 3 MW % solution of the salt has given a 

 resistance capacity of between 2 and 3 times the normal.* 



The question now arises, what is the cause of this increased 

 resistance capacity ? It is not merely apparent, resulting from 

 the selection of the more resistant individuals, thus elevating 

 the mean. It is clearly due to a diminution in the intensity of 

 osmosis; and this must be due to the establishment of an equi- 

 librium between internal and external osmotic pressures. 



Now, this equilibrium can only be brought about by the 

 density of the internal fluids becoming equal to that of the 

 external medium; and this requires that the salt held in solu- 

 tion shall traverse the bounding protoplasmic films, gaining 

 the interior. That such a traversing occurs has been argued 

 by M ASSART ('89), who has himself produced new evidence for 

 this conclusion. As is well known numerous pigments in 

 solution penetrate to the nucleus of the living protist. Potassic 

 nitrate (JANSE, '87, p. 22), glycerine, and urea (DE VRIES, 

 '88 and '89) have been observed to penetrate protoplasm. f 

 That NaCl does the same thing has been shown by many 

 observers. Thus, EMERY ('69) found that when a frog is 

 placed in a salt solution and is left there for some time, then 

 rinsed in water until no salt appears in the washings, and, 

 finally, put into pure water, salt is given forth from the epider- 

 mis (precipitation on adding silver nitrate). Likewise PLATEAU 

 ('71, p. 20) found that various fresh-water Arthropods reared 

 in a salt solution excreted an unusual amount of salt ; and 

 FREDERIC ('85) has determined that the quantity of salt in the 

 blood of Carcinus varies from 3.1% to 1.5%, according to the 



* A few data concerning proper acclimatization cultures to NaCl may be 

 found useful. To acclimate bacteria O.OOo to 0.009 MW % may be added daily ; 

 OscSllaria, 0.01 MW %, added monthly ; Anabsena and Tetraspora, 0.018 M W %, 

 added monthly ; Ciliata, 0.003 MW %, daily ; Hydra viridis, 0.001 MW %, daily 

 for 6 days ; Tubifex, 0.02 MW %, daily ; tadpoles, 0.004 to 0.014 MW %, daily. 



t A fact observed by BERT ('71) suggests that some solids are taken into the 

 body in acclimatization ; for, he says, fresh-water fishes acclimatized to sea 

 water gain in weight, and when placed in fresh water fall to the bottom. The 

 fact that they fall to the bottom indicates that their specific gravity is increased. 



