CONDITIONS OF EXISTENCE 



species showing a distinct avoidance of neutrality. In a number 

 of species the number of individuals on either side of neutrality 

 was greater than at the neutral region (Table VII). 



TABLE VII 



SHOWING CORRELATION BETWEEN DISTRIBUTION AND ALKALINITY AND ACIDITY 



TO PHENOLPHTHALEIN (AFTER WELLS) 

 (Figures show numbers of individuals in a cubic meter of water) 



R = Rotifer, C = Cladoceran, P = Protozoan, Co = Copepod, n. c. = no collection. 



The amount of salt in parts per million which ranges from 50- 

 500 in water occupied by numerous fresh-water species is of com- 

 paratively little significance to animals but of much importance to 

 plants. The effect of most salts upon organisms is due to the 

 character of the ions, valence, electrical charges, etc. The effect 

 of any combination of salts is due to their combined action. For 

 example, marine animals will not live in NaCl alone even when 

 the osmotic pressure is the same as in sea water; it is very toxic. 

 They will not live in NaCl and KC1 or NaCl and CaCl 2 ; all three 



cators is also very important. Methyl orange is unaffected by CO 2 and other organic 

 acids because of their small ionization. Thus Marsh's conclusion, based upon methyl 

 orange, that if water becomes acid it kills fishes is incorrect for this reason and because 



. Phenolphthalein is color- 

 H+io~ 7 N 



it turns red at 



OH-io- 10 N 



and remains yellow at _ 



less at 



H+io- 



, j 



and turns red at 



H+io^N 



Rosalie acid is rose at 



OH- 10-^ N OH- lo- 6 N ' "" OH- io~ 7 N 



which is true neutrality. In the table above true neutrality probably falls in the first 

 column to the right of the center. CO 2 production may be sufficient to neutralize 

 this slight alkalinity in the layer of water next to the animal. The terms alkalinity 

 and acidity are used in this chapter in the sense of concentration of H+ and OH~ ions. 



