MUSCULAR CONTRACTION 21 



of calcium to the sodium chloride solution prevents the 

 untoward effects of the latter alone and maintains the normal 

 impermeability of the egg-membrane. The work of Osterhout 

 on the electrical conductivity of plant tissues affords interesting 

 parallels. 



Clowes has in fact constructed a model in which the inter- 

 stices of a partition of filter-paper fixed by rubber rings in a 

 U-tube are filled with an emulsion consisting of oil and a 

 saline medium containing sodium, potassium, and calcium 

 chlorides in roughly the same proportions as they occur in 

 living tissues. The conductivity of the artificial membrane 

 varies in the presence of electrolytes in the medium in a manner 

 closely analogous with the conductivity of protoplasmic sur- 

 faces in plant cells, as in Osterhout 's experiments. In pure 

 NaCl conductivity increases ; in pure CaCl2 it decreases, owing 

 presumably to reversible changes of phase in the interstices 

 of the filter paper. 



Some light is thrown on the relation of electrolytes to the 

 contraction of muscle by a study of the concomitant electrical 

 phenomena. Thus in vertebrate heart- muscle the absence 

 of calcium does not prevent electrical changes after mechanical 

 response has ceased. To have a clear appreciation of the 

 relation of muscle to electrolytes it is essential to recognise 

 not only that muscle is the seat of a state of tension which in 

 appropriate circumstances results in mechanical work being 

 done, but that it is also the seat of a propagated disturbance 

 leading up to the events which condition this state of tension. 

 The foregoing treatment of the contractile mechanism has been 

 focussed on the events which succeed the explosive breakdown 

 of some substance intermediate between glycogen and lactic 

 acid ; but, as we have seen, the electrical phenomena must be 

 referred to phenomena independent of the nature of the 

 contraction process itself. The disturbance which travels 

 along the muscle initiating the breakdown of glycogen has so 

 many points in common with excitation and conduction in 

 nerve that there is excellent justification for extending to the 

 action-current of muscle an interpretation analogous to that 

 suggested for the corresponding phenomenon of nerve discussed 



