SALT ABSORPTION AND METABOLISM 



77 



and to combine electrostatically with ions, but no specific mechanism 

 is proposed for subsequent decomposition of the complex so formed. 

 The view that the cation carrier is acidic is based on the observation 

 that hydrogen ions compete with other cations for the absorption 

 mechanism (see p. 55). Comparable competition between hydroxyl 

 and other anions has also been claimed. 



2. Electro-chemical Hypotheses 



a. The Lundegdrdh hypothesis. Some of the early investigators, 

 notably Hoagland and Steward, while recognizing a general 



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 1-234 



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Fig. 27. Ion absorption and respiration. Bromide absorption (shaded 



rectangles) and carbon dioxide production in 4 days by slices of various 



storage tissues (Berry and Steward, 1934). 



dependence of salt uptake on respiration, could not demonstrate a 

 quantitative relationship between the two processes. The rate at 

 which a storage tissue respires, for example, is a poor guide to the rate 

 at which it absorbs salts (Fig. 27). Lundegardh and Burstrom (1933) 

 contended, however, that an exact quantitative correlation exists 

 between anion absorption and a particular component of respiration 

 which is stimulated by sah, and is called "anion" or "salt" respir- 

 ation, in contrast to a basal or "ground" respiration which is 

 unrelated to uptake of salt (Fig. 28, a, b). In the presence of cyanide 

 at an appropriate concentration (0-0001 M HCN), salt uptake and 

 salt respiration are completely inhibited, without any apparent effect 

 on "ground" respiration (Fig. 28b). This fact led Lundegardh (1939) 

 to propose that anion respiration is mediated through cytochrome 



