ACCLIMATIZATION 



85 



3. ACCLIMATIZATION TO SOLUTIONS OF GREATER OR LESS 

 DENSITY THAN THE NORMAL 



In the preceding section we saw that different organisms had 

 diverse resistance period to the same density of solution. In 



rt, this may be accounted for, as we have seen, on the ground 



a difference in the rapidity of osmotic action thick-skinned 

 inimals resisting longer than thin-skinned ones. All diversity 



the effect of solutions, cannot, however, be accounted for on 

 is ground. Thus, the molluscs of the sea and those of fresh 

 ater appear to have an equally pervious epidermis, yet the 

 rruer will, of course, withstand a much stronger solution of 

 lt than the latter. This difference in resistance capacity 

 ems closely correlated with the conditions of the medium in 

 hich the organism has been reared. Thus, BEUDANT ('16) 

 und that littoral species (living, therefore, in a part of the sea 

 here the water is much diluted by rivers), e.g. Ostrea, Mytilus, 

 atella vulgata, resist fresh water better than deep-sea species; 



d this discovery has been abundantly confirmed by DE 



AKIGNY ('88).* 



That the conditions of density of the culture medium deter- 

 ine the resistance capacity is proven by experiment, for, by 

 rying the density of the culture solution, we may vary the 



istance period of the individuals experimented on. BEUDANT 

 16) was the first to show this. He used Lymnea, Physa, 

 lanorbis, Ancylus, Paludina, and some other fresh-water Mol- 

 sca. He began in April by putting these organisms into a 

 XaCl solution, and, continuing to add salt slowly, by Sep- 

 mber many of these withstood a 4% solution a solution 

 kills animals suddenly subjected to it. He performed 



ewise the reverse experiment upon marine Mollusca (Patella, 



extremes of density in which organisms are capable of living are often 

 nsiderable. On the one hand, the individuals of some species, especially fish, 

 able to migrate from fresh to salt water and back, with impunity. On the 

 er hand, many species of a family, the other members of which are marine, 

 ve become accustomed to fresh water. Examples of this last case are the 

 droid Cordylophora lacustris, the mollusc Dreissena, and the endoproctan 

 ozoan Urnatella. Likewise, some marine species have come to live in exces- 

 ively salt water. Such, for example, is the case with Artemia salina which 

 ives in Salt Lake, Utah, containing over 22% of salts. (LEIDY, '72, p. 165.) 



