114 



PHYSIOLOGY 



about it. We can neither 

 aid nor interfere with it. 

 This is called a reflex 

 movement. 



The Value of the 

 Nerves.— The value of the 

 nerves to the body lies in 

 their extreme sensitiveness 

 and in the rapidity with 

 which a stimulus passes 

 through them. Many ex- 

 periments have been 

 tried with lower animals 

 to ascertain whether nerves 

 are responsible for their 

 various reactions or 

 whether the reactions are 

 dependent upon muscles. 

 By removing the nerves 

 from these animals so that 

 they can play no possible 

 part and by stimulating 

 the muscles directly, it 

 was found in every case 

 that the animal showed its 

 usual reaction and that 

 this reaction depended 



Fig. 71.— Diagrammatic front view of the spinal cord and bulb, showing spinal 

 nerves, one side chain of sympathetic ganglia, and some of cranial nerves. 

 Ce.p., cervical plexus ; «.*., branch to sympathetic system ; Br.p„ brachial 

 plexus; S.g., sympathetic ganglia; L.p., lumbar plexus; S.c, sciatic nerve ; 

 S.p.i sacral plexus ; C.p., coccygeal plexus. (From Fitz.) 



