THE NEURO-MUSCULAR JUNCTION 279 



ascribe this action to a stimulation of the sympathetic nerve-endings, since 

 adrenalin is equally effective if applied after the whole of these nerve-endings 

 have been made to degenerate by section of the post-ganglionic sympathetic 

 nerve-trunks. Its action therefore must lie at the junction between nerve 

 and muscle, and must be on some intermediate or receptor substance de- 

 veloped at the myoneural junction, and having for its function the trans- 

 ference of the excitatory process from the nerve fibre to the contractile 

 substance of the muscle fibre. Similar receptor substances may act as 

 intermediaries in every case of propagation of an impulse across a synapse 

 of whatever description, and may by their properties determine the peculiar 

 qualities of the synapse. We may compare them to the fulminating cap 

 which in a shell is used to transfer the process of combustion from the slow- 

 match to the bursting charge. Their existence is of especial importance 

 when we endeavour to investigate the mode of action of drugs. It is probable 

 that they will be found to play a great part in determining the differential 

 action of drugs on various tissues in the body. 



