Inorganic Ions 



TABLE 8 (continued) 

 CONCENTRATIONS OF IONS IN TISSUES AND BODY FLUIDS 



77 



Numerous analyses of body tissues in a variety of animals show the tendency 

 to concentrate potassium and calcium and to Hmit chloride and sodium (Table 

 8). In sixteen marine gastropods the concentration of potassium and calcium 

 in the whole snail is uniformly higher than that of these elements in sea water, 

 that of sodium is about the same, and that of magnesium is similar to or lower 

 than that in sea water. ^^ The ability of cells to accumulate certain elements 

 and to exclude others is general. In marine algae the vacuolar sap differs from 

 the protoplasm, and both differ from the sea water. The mechanisms of ionic 

 selection constitute important cellular problems and have been frequently 

 reviewed. ■^^' ^'^ Our present concern, however, is with the ionic correspond- 

 ence between the body fluids of animals and their medium. 



IONS IN BODY FLUIDS AND IN EXTERNAL MEDIA 



Concentration of Ions. Table 9 presents representative analyses of ions in 

 millimols per liter of body fluids of a variety of animals.- In a general way the 

 similarities are more striking than the differences among phyla and classes. 

 Usually the total sum of cations exceeds the sum of all anions, the anion deficit 

 being made up by proteins and amino acids. 



The concentrations of different ions in the body fluids of an animal in a 

 given medium may vary with the season and temperature, with physiological 

 state, and with sex, age, and other conditions. The blood of crayfish, for 

 example, taken in May and June, has a higher concentration of Na+ and a 

 lower concentration of Ca++ than that of crayfish taken in January and 

 February. ^^ The blood of butterflies in the larval stage contains more Mg+ + 

 and CI- but less K+ and phosphate than does that in the pupal stage. -^ 



Insects are remarkable in the high potassium and low sodium in the serum, 

 the ratio of Na to K being consistently lower than that in frogs and mammals. 

 A silkworm has in its body fluids about the same sodium concentration as the 

 mulberry leaves on which it feeds, but on pupation it loses practically all of 

 its sodium and the pupal tissues contain much potassium but negligible 

 sodium. ^" A series of carnivorous insects showed an Na to K ratio greater 

 than 1, and a series of herbivorous insects showed an Na to K ratio of less 

 than 1. 24. 25 However, diet per se does not determine the Na/K ratio, at 



