30 



Papers from the Marine Biological Laboratory at Torttigas. 



ing solution to cease two to three times more rapidly with every io° rise 

 in temperature, according to van't Hoff's empirical rule for the increase 

 in velocity of chemical reactions with rise of temperature. 



There is one possible source of error in an experiment of this kind. 

 We may not be able to distinguish between the time it takes for the ions 

 to diffuse into the nerve-muscle tissue and the time for them to stop 

 contraction, when present in sufficient concentration. It may be said, 

 however, that the diffusion time is very small. The nerve-muscle layer 

 of Cassia pea is thin, certainly less than 0.2 mm. A calculation of the 

 time required for a 0.375 molecular MgCl, solution to diffuse across a 

 distance of 0.3 mm. and reach 0.9 of the original (0.375 rnolecular) 

 concentration on the other side gave a value < i minute. The diffusion 

 constant for MgSO^ in pure water was used, as none other was available. 

 Acetic acid would diffuse through the same distance even more rapidly. 

 The above calculation is ver}^ rough and is only of value in showing how 

 short the diffusion time may be provided there is no resistance at the 

 cell boundary. 



There is positive evidence that considerable time is required for 

 MgCl2 and CH3COOH to stop conduction in the nervous network. This 

 network is epithelial in nature, external to the muscles, and directly in 

 contact with the sea-water, yet the muscles always cease to contract before 

 the nerves cease to conduct. Conduction continues about twice as long as 

 contraction. We see, then, that diffusion of the electrolyte must play 

 a very small part in the stoppage of nerve conduction in Cassiopea. 



This is also true for the muscles, as is shown below. Let us compare 

 the times required for different concentrations of CH3COOH to inhibit 

 contraction and conduction. The following is a table of inhibition times: 



•A correction must be made for the alkalinity of the sea-water, which is very high at Tortugas. 

 Red litmus paper is quickly turned blue. Phenolphtalein becomes faint pink. 



We assume that CH3COOH actually enters the muscle cells and that 

 the presence of a definite concentration within makes any further con- 

 traction an impossibility. The problem is, in what time would this 

 concentration be reached from varying concentrations on the outside. 

 It takes nine minutes for ^jj^ CH3COOH to stop contraction, yet less 

 than one minute for ^^^ CH3COOH. Velocity of diffusion is propor- 

 tional to the degree of concentration. The time values, one and nine, 

 could not possibly be accounted for by the above law, so that the differ- 

 ence in time must be attributed to the concentration of the acid in 

 affecting the tissue, and not to the diffusion rates for the respective 

 concentrations. 



