Salinity 77 



Barnes (1932) studied the littoral terrestrial isopod Ligia baudi- 

 niana (Milne-Edwards) . He found that solutions of single ions 

 commonly present in sea water were toxic in the following order K, 

 Mg, Ca, Na. Rapid death in such a solution as KCl he believed to 

 be due to inhibition of respiratory movements. He concluded that 

 death in dilute sea water is due to the loss of essential salts rather 

 than injurious osmotic changes. Schlieper (1929) has shown that 

 certain marine animals are actively homoiosmotic in diluted sea 

 water, i.e., they work to maintain their body fluids at certain densi- 

 ties by excreting water. In the shore crab Carcinas maenas (Pen- 

 nant) the intensity of respiration is related to the salinity of the 

 surrounding medium and the crab is able to stand considerable dilu- 

 tion. The shore mussel Mytilus edulis L., on the other hand, can- 

 not keep up the molecular concentration of its blood in low dilu- 

 tions and dies, probably from the effects of asphyxiation. Fresh- 

 water clams have a low salt concentration in their body fluids, but 

 such salts as they have are essential, and their loss results in death 

 (Ellis, Merrick, and Ellis, 1930) . The oxygen consumption of 

 barnacles in air depends upon the salt concentration of their body 

 fluids (Borsuk and Kreps, 1929) . 



Schlieper (1929) maintains that in fresh-water animals, as well 

 as in marine, salinity of blood is related to rate of respiration. When 

 animals are not able to maintain their respiratory activities in 

 changed media they die. Keyes (1931) has studied the survival of 

 the minnow Fundulus heteroclitus (L.) in relation to salinity of 

 water and asphyxiation. He separated his fishes into two groups, 

 those that died quickly and those that lived longer, and found that 

 they differed in metabolic rate. A slow-living fish survives asphyxia- 

 tion better than one which has a rapid rate; a rapid-living marine 

 fish usually lives in fresh water better. The mechanism for the 

 regulation of such activities is probably concerned with electrolyte 

 equilibria. The oxygen consumption of a marine fish that has been 

 placed in fresh water decreases for a time, but gradually returns to 



