6Q 



VETERINARY PHYSIOLOGY 



greater distance than is A from the cathode. Similarly, the 

 anodal closing contraction has the better pole, the cathode as 

 the stimalating pole, but in the worst position D, far 

 from the cathode. The anodal opening contraction has 

 the less effective pole — the anode as the origin of excita- 

 tion, but in the better position C, close to the stimulating 

 pole. 



Cathode, Closing A \p p. 

 Anode, Closing D /'-•'-• 

 Anode, Oldening C t a n 

 Cathode, Opening B j^-^- 



Pole. 



Better 

 Better 

 Worse 

 Worse 



Position. 



Better 

 Worse 

 Better 

 Worse 



Strength of Current 

 necessary to stimulate. 



Weakest 

 Medium 

 Medium 

 Strongest 



The strength of the current required to stimulate is 

 measured in milliamperes. The effective strength varies 

 o-reatly, even in normal individuals of the same 

 species. 



Changes in Disease and Injury. — In tetany in children, 

 and after the removal of the parathyreoids in man and 

 animals (p. 603), a condition of increased excitability of 

 the nerves to mechanical and galvanic stimulation occurs, 

 and this is used in the diagnosis of these conditions when 

 other symptoms are latent. 



When the nerve to a muscle is cut it rapidly loses its power 

 of responding to electrical stimulation (p. 76), but the muscle 

 continues to respond, and its response, although at first it 

 may be decreased, is afterwards increased and becomes 

 peculiarly slow. Some neurologists have maintained that 

 there is a qualitative change in the response, that the 

 response to anodal closing — A.C. becomes greater than that 

 to cathodal closing — C.C. With fine electrodes applied to ex- 

 posed muscle this does not occur. It is probably due to the 

 fact that in normal muscle it is the nerve endings which are 

 stimulated, but that in degeneration the response depends 

 upon the number of muscular fibres stimulated rather than 

 upon the pole applied. Hence in anodal closing the worst 



