CONDITIONS OF EXISTENCE 



41 



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) 



Name of animal 



Alkalinity in cc. per liter 

 of CO2 to make neutral 



Pleosoma R 



Asplanchna R. 



Diaphanosoma C. 



Diaptomus Co 



Anuraea P. 



Cyclops Co. 



Notholca R. 



Daphnia C. 



Ceratium P. 



Polyarthra R. 



Triarthra R. 



3.925 

 11,320 



2,885 

 7,850 

 4,000 



13,775 



625 



1,260 



52,330 



12,350 



o 



o 



400 



2,750 



6,660 



1,250 



7,620 



685 



650 



104,500 



1,620 



n. c. 



o 



o 



n. c. 



17,350 



200 



7,620 



65 



400 



85,160 



2,350 



o 



Neu- 

 trality 



O 



O 



260 



2,220 



30 



25 



o 



130 

 2,025 



160 

 n. c. 



Acidity in cc. of CO2 

 per liter 



0.25-0.5 0.75-1 



o 

 o 

 o 



1,440 

 20 



30 



65 



1,145 



11,760 



1,190 



1,050 



o 

 o 

 o 



390 



20 

 o 

 o 



25 

 750 



,240 

 ,110 



o 



o 



o 



100 



20 



5 

 o 

 o 



1,670 

 40 



2,425 



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 KCl or NaCl and CaCl2; all three 



cators is also very important. Methyl orange is unafifected by CO2 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 



H+ 10^ N H+ 10-* N 



it turns red at ,=r^ -—-^ and remains yellow at prz^ r-rr . Phenolphthalein is color- 



OH-io-i^N -^ OH-io-»N 



less at ^^z^ ^:^^^ and turns red at pr^- — — - . Rosalie acid is rose at ^r^j —i-^r 



OH- 10-6 N OH- 10-6 N OH- 10^ N 



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



column to the right of the center. CO2 production may be sufl'icient 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. 



