202 ELECTRO-PHYSIOLOGY CHAP. 



muscle to a lever. The excitation-trough consists of a parallel- 

 epipedic ebonite box, the shorter walls of which are lined with 

 amalgamated zinc plates, which lead in the current. At some 

 distance from these are two other walls of baked porous clay, so 

 that a canal is formed on each side, bordering on the some- 

 what quadratic inner space of the trough. This contains 0'6 



NaCl solution, while the two canals are filled with con- 

 centrated solution of zinc sulphate. The muscle, conveniently 

 stretched by a weight, and quite uninjured, is plunged into the 

 centre space, so that the angle formed by the current in its pass- 

 age can obviously be altered in any direction by simply turning 

 the trough round. 



As might be expected with true longitudinal passage of 

 current (angle 0), the make twitch, or persistent make con- 

 traction, appeared, just as outside the fluid, but Leicher never 

 observed an effective opening excitation with the strength of 

 current employed (9 Dan.) If a current traverses the muscle 

 at an angle of 45, it still has a certain effect, but much less 

 than with true longitudinal passage. " Finally, if the muscle 

 is traversed at an angle of exactly 90, it usually remains 

 quiescent. More rarely with transverse passage a weak excita- 

 tion occurs, which, notwithstanding its inferior magnitude, varies 

 in response to any alteration of current." TJie total non- 

 excitability of striated muscle to electrical currents perpendicular to 

 the fibre-axis must after these simple demonstrations be accepted 

 as proven. It is easy to understand that the experiments in a 

 typical form could only be carried out on a muscle with 

 parallel fibres constructed as regularly as possible, and that any 

 preparation with a more complicated arrangement of fibres is a 

 priori excluded. There are no corresponding experiments on 

 smooth muscular parts, but it may be assumed that here also, in 

 so far as the contractile fibrils run parallel, they give no response 

 to the transverse passage of current. It is clear that the fact of 

 the dependence of excitation upon the magnitude of the angle at 

 which the contractile parts, lying in a definite direction, are 

 traversed by the lines of current, is of the greatest significance to 

 the theory of the action of the electrical current. Before enter- 

 ing upon this in detail another fundamental law of electrical 

 excitation must be considered, in regard to the question at 

 vital jinhit of the tract in f/ie muscle din-ell ij traversed an. 



