REFLEX ACTION 59 



15. Inject one drop of a 1 p.c. solution of sulphate of 

 strychnine under the skin of the back. In a few minutes 

 the slightest stimulus applied to any part of the animal 

 will produce violent tetanic spasms of the whole body. 

 A preliminary stage of increased reflex action may also 

 be observed. 



16. With a straight seeker or a piece of stout wire 

 destroy the whole of the spinal cord. The spasms im- 

 mediately cease. 



17. Repeat any of the above observations ( 3 12). 

 No reflex actions will now be produced. The lymph- 

 hearts have ceased to beat. 



B. Innervation of the muscles of the leg by the 

 roots of the lumbar plexus and by its branches. 



The spinal nerves which form the roots of the limb 

 plexuses intermix in the plexus, and the branches from 

 the plexus contain fibres from two or more spinal nerves. 

 The branches of the plexus run to separate muscles or 

 groups of muscles ; thus most muscles (and each part of 

 the skin) receive nerve fibres from more than one spinal 

 nerve. This can be observed in the frog's leg; the move- 

 ments caused by stimulating the several nerves can at 

 the same time be noticed. 



a. Pithed frog. On one side, tie and cut the 7th, 8th 

 and 9th spinal nerves close to their exit from the spinal 

 cord, stimulate them separately with weak faradic cur- 

 rents for a few seconds at a time. The movements pro- 

 duced vary in different frogs, but it will be seen that the 



