432 ELECTRO-PHYSIOLOGY CHAP. 



standing the undoubted difference of water-content in the super- 

 ficial and deeper layers of fibres in the muscle, the transfer of 

 excitation does not seem to be confined to the former, although 

 the direct excitation of the moister, non-fasciculated inner side 

 is less certain to produce secondary excitation of the muscle than 

 stimulation of the dry outer surface. This seems to indicate that 

 the dry layers of fibres, which are the most excitable, may 

 perhaps be distinct from the others in yet another characteristic 

 (i.e. more pronounced electromotive activity). In any case many 

 factors combine to produce this response of desiccated, or com- 

 pressed, muscle. 



Langendorff (59) has recently made some interesting observa- 

 tions, in the frog, on phenomena analogous to those of drying 

 muscle, after subcutaneous injection of glycerin ; these effects 

 seem equally to be due to a secondary excitation from muscle to 

 muscle caused by dehydration. If 1/5 2 cc. glycerin is in- 

 jected under the skin of the back of a curarised frog, vigorous 

 and sustained contractions appear after some time at each excita- 

 tion, not merely in the same, but also in adjacent muscles, similar 

 to those which may be observed in desiccated preparations, and 

 doubtless to be interpreted in the same manner. 



III. POSITIVE VARIATION OF THE MUSCLE CUERENT 



Hering distinguishes, in addition to the " action current " of 

 Hermann, due to a " down " change at a led-off part, a second 

 kind of action current caused by an " up " change of a led-off 

 point, without any necessary " down " change at the other lead- 

 off. If this should happen in the case of a muscle, it would 

 obviously give rise during tetanisation to a positive instead of a 

 negative variation of the demarcation current, due to increased 

 positivity of the uninjured longitudinal surface, associated with 

 upward modification. And in point of fact, certain recent 

 observations seem to substantiate this theoretically possible 

 event. Gaskell (60), in the first place, observed a pronounced 

 positive variation upon the cardiac muscle of the tortoise during 

 excitation of the vagus nerve. We subsequently succeeded in 

 demonstrating a similar effect upon the adductor muscle of the 

 crab's claw during indirect electrical tetanisation. As a result 

 of a prolonged series of experiments upon the innervation and 



