152 PROTOPLASMIC ACTION AND NERVOUS ACTION 



solution prevents the loss of irritability; the inference is 

 therefore justified that the effect depends upon a with- 

 drawal of electrolytes, especially sodium chloride, from 

 the tissue. That the electrolytes thus removed come 

 almost entirely from the interstitial spaces of the tissue, 

 and not from the interior of the cells, was later proved 

 by Urano and Fahr.^ The important conclusion follows 

 that the presence of electrolytes (salts) in the external 

 medium is essential to the normal irritability of the cell. 



Overton discusses the question whether the removal 

 of sodium salts acts by preventing the conduction of 

 stimulation or by deranging the contractile mechanism 

 of the cell. Biedermann had previously shown that 

 after incorporation of sufficient water in hypotonic salt 

 solution, a muscle may lose the power of contraction 

 without losing that of conducting stimuli.^ By immers- 

 ing a portion of a sartorius in isotonic sugar solution, 

 Overton showed that stimuli are not transmitted through 

 the salt-free muscle. It is known that a muscle deprived 

 of irritability in sugar solution will shorten in solutions 

 of chloroform or other cytolytic substances; presumably, 

 therefore, the contractile mechanism is structurally 

 intact, but fails to act in the absence of electrolytes 

 because of the failure of conduction. Without the power 

 of transmitting stimuli, the muscle is unable to contract 

 as a whole. 



The least concentration of NaCl required for the 

 maintenance of irritability was determined by using 

 mixtures of isotonic sugar solution (6 per cent) and 



'Urano, Z. BioL, L (1907), 212; LI (1908), 483; Fahr, Z. Biol., 

 LII, 72. 



» Biedermann, Ber. Akad. Wiss. Wien, XCVII (1888), loi. 



