SEC. 1. THE PHENOMENA OF MUSCLE AND NERVE. 

 Muscular and Nervous Irritability. 



The skeletal muscles of a frog, the brain and spinal cord of 

 which have been destroyed, do not exhibit any spontaneous move- 

 ments or contractions, even though the nerves be otherwise quite 

 intact. Left untouched the whole body may decompose without 

 any contraction of any of the muscles having been witnessed. 

 Neither the skeletal muscles nor the nerves distributed to them 

 possess any power of automatic action. 



If however a muscle be laid bare and be more or less violently 

 disturbed, if for instance it be pinched, or touched with a hot wire, 

 or brought in contact with certain chemical substances, or subjected" 

 to the action of galvanic currents, it will contract whenever it is 

 thus disturbed. Though not possessing any automatism, the 

 muscle is (and continues for some time after the general death ot 

 the animal to be) irritable. Though it remains quite quiescent 

 when left untouched, its powers are then dormant only, not absent. 

 These require to be roused or 'stimulated' by some change or 

 disturbance in order that they may manifest themselves. The 

 substances or agents which are thus able to evoke the activity of 

 an irritable muscle are spoken of as stimuli. 



But to produce a contraction in a muscle the stimulus need 

 not be applied directly to the muscle ; it may be applied indirectly 

 by means of the nerve. Thus, if the trunk of a nerve be pinched, \ 

 or subjected to sudden heat, or dipped in certain chemical *> 

 substances, or acted upon by various galvanic currents^ contrac- 

 tions are seen in the muscles to which branches of the nerve are 

 distributed. 



