§ 5.311 BALANCE OF MONOVALENT ELECTROLYTES 209 



situation, are derived from the same source and are closely related 

 chemically (Fig. 5-15). 



There are indications of a similar type of hormone control 

 occurring in other vertebrates ; but the evidence is less conclusive, 

 and workers are not in full agreement. There is, as yet, practically 

 no evidence to show whether the same form of control occurs in 

 any invertebrates. 



The hormonal control of salts will be considered first (§ 5.31), 

 and that of water afterwards (§ 5.32), since the direction of move- 

 ment of the water is so often determined by that of the salts. 



5.31 BALANCE OF SODIUM IONS (Na+) AND OF 

 ASSOCIATED MONOVALENT ELECTROLYTES (K+ AND CI") 



5.311 Increase o/ Na"^ in the blood 



Active transport of ions across living membranes and especially 

 the so-called "sodium pump" are now well-known phenomena in 

 invertebrates as well as vertebrates. 



Invertebrates. Both crustaceans and insects living in fresh 

 water are known to take up sodium and chloride ions from the 

 surrounding water by active transport, through the gills in 

 Eriocheir^ and by the anal papillae in the larval Chironomus\ but, 

 as yet, there is no evidence of any hormonal control of these 

 activities. Although the isolated gills of Eriocheir make a beautiful 

 preparation for demonstrating active transport of sodium, they 

 have not apparently been examined for the effects of possible 

 hormones; drugs have, however, been shown to have closely 

 comparable actions here and on frog skin (Koch, 1954). 



Vertebrata. a number of cases now indicate some hormonal 

 control of active transport of ions across cell membranes in 

 vertebrates. This transport involves the use of metabolic energy, 

 derived from aerobic respiration, to overcome the osmotic gradient. 

 The action is stopped by lack of oxygen. Since among cold-blooded 

 vertebrates much more is known of the situation in Amphibia than 

 in Teleostei, they will be considered in that order. 



Concentration of the blood by inward passage of salts through the skin 



Amphibia. The skin of the frog plays an important part in 



maintaining the internal salt concentration well above that of 



