808 CONTRACTION-WAVE IN MUSCLE 



dependent principally upon the specific constitution of the tissue, 

 the temperature, and the composition of the surrounding medium. 

 What part the medium plays in the transmission of the contraction 

 wave is not fully known. 



Mayer^ found that the rate of nerve conduction in the marine 

 medusa Cassiopea was closely proportional to the total concentration 

 of the cations Na, Ca, and K in the medium. When the sea water 

 was diluted with distilled water a decline in the rate of nerve conduc- 

 tion was observed with increasing dilution. He attributed these 

 results to the change in the adsorption of the above cations by the 

 tissue; but it may also indicate, as Lillie pointed out^ a direct correla- 

 tion of the rate of physiological conduction with the electrical con- 

 ductivity of the medium. In fact, the decline in propagation-rate 

 runs closely parallel with the decline in the electrical conductivity 

 of the sea water when similarly diluted. Mayer, however, found 

 that under some conditions the propagation-rate may be indepen- 

 dent of the electrical conductivity; thus a dilution of sea water with 

 0.4 molar magnesium chloride solution causes a decrease in the 

 velocity of the nerve conduction to a degree closely proportional to 

 the degree of dilution, although the electrical conductivity remains 

 essentially unchanged.^ The addition of magnesium however, must 

 disturb the balance of the salts in the medium and introduce other 

 factors of a special kind; and the possibility remains that in physio- 

 logically balanced media the rate of transmission of the excitation 

 state may be determined, other conditions being equal, by the elec- 

 trical conductivity of the solution. 



In the light of these and other facts and of general theoretical 

 considerations, Lillie advocates the theory "that the transmission 

 of the excitation-state from the immediate site of activity to the 

 adjoining resting areas is dependent on an electrical local action of the 

 same essential nature as that which is responsible for the etching or 

 corrosion of non-homogeneous metallic surfaces {e.g., of iron) in con- 



2 Mayer, A. G., Am. J. Physiol, 1915-16, xxxix, 375; 1916-17, xlii, 469; 1917 

 xliv, 591. 



3 Lillie, R. S., Am. J. Physiol, 1916, xli, 133. 



" Mayer. A. G., Am. J. Physiol. 1915-16, xxxix, 381. 



