NERVE 



87 



upon as the private path of the special reflex it produces. 

 In acting upon the muscles the special incoming impulse 

 has to get command of the common outgoing path. 



Fig. 36 shows how one set of outgoing neurons is played 

 upon by a whole series of ingoing neurons from different 

 parts of the body. 



When any muscle is made to contract, its antagonist 

 is inhibited or relaxed. This has been demonstrated by 

 takino: a simultaneous record from flexors and extensors. 



Under the influence of strychnine the inhibitory effects 



Fig. 37. — To show the way in which the different Reflex Arcs react ou one 

 another. S., skin; M., muscle; V., viscus ; C, spinal cord with 

 synapses. (M'Dougall. ) 



may be converted into excitor effects, and when this occurs 

 havoc is played with the co-ordination of the reflex. 



A study of the familiar "scratch reflex" which can 

 often be produced by rubbing the shoulder of a normal 

 dog, and which can much more inevitably be produced 

 in the spinal animal, has demonstrated that, whatever 

 be the character of the stimulus producing it, the scratch- 

 ing movements occur at a perfectly definite rate of four 

 or five per second, and that the movements consist of a 

 perfectly rhythmical alternation of contraction and relaxation 

 of the flexor and extensor muscles by which the leg is first 



