76 Causes of Emigrations 



pies of these are: (1) marine invertebrates in which the salt content 

 of the body fluids is much like that of sea water in which they live, 

 i.e., they are isotonic and isohalin with the surrounding medium; 

 (2) the elasmobranchs (in which body fluids have the same osmotic 

 pressure as sea water, but contain different salts, and in which the 

 density of the blood is maintained by large amounts of urea) and 

 such animals as earthworms, fishes, and frogs which contain body 

 fluids that differ more or less in concentration and composition 

 from the surrounding medium but are influenced by changes in it; 

 and (3) reptiles, birds, and mammals which differ markedly from 

 the surrounding medium and are little influenced by changes in it 

 (Adolph, 1925). 



Death in an unsuitable medium may be due to lack of ability to 

 adjust the body fluids so that they are in equilibrium with the me- 

 dium, to the toxic action of solutes, to the loss of essential salts, to 

 inability to carry on processes such as respiration which are essential 

 for metabolism, or to other causes. Hayes (1930) found that Para- 

 mecium reared in culture media did not flourish when salinity pro- 

 duced by adding sea water reached Vc or more. "The animals re- 

 acted to changes in salinity in at least four ways: alteration in body 

 shape, change in volume, variation in proportion of water, and 

 deviation from normal rate of respiration. The rate of consumption 

 decreased witfi increasing salinity to the point of isotonicity, after 

 which respiration increased; the curve was thus U-shaped." Quigley 

 (1928) tested the effects of various substances on a shark, Squalus 

 suckleyi (Girard) , chiefly by varying the proportion of salts present 

 in sea water. He found that the addition of NaCl, KCl, or CaCl to 

 sea water was not very toxic but that "the most toxic solution was 

 sea water with added salts." Cessation of respiration usually oc- 

 curred before the heart stopped beating. Koidsumi (1928) investi- 

 gated the effects of sea water on certain fresh-water chironomid 

 larvae and found that sea water was rapidly fatal, though there are 

 other species of chironomids which regularly live in the ocean. 



