IRRITABILITY AND CONDUCTIVITY 169 



The Independent Irritability of Muscle. The 

 stimulus that causes the contraction of a muscle 

 may be applied either to the nerve or- to the 

 muscle itself. If to the nerve, the muscle will 

 be thrown into the active state not by the origi- 

 nal stimulus, but by a nerve impulse. If to the 

 muscle, the nerve will still be stimulated, for 

 examination shows terminal fibres distributed, in 

 skeletal muscle at least, probably to every fibre, 

 and with few exceptions to all parts of the 

 muscle. The fact that muscles may contract 

 when an electric current flows through them, or 

 when otherwise stimulated, does not therefore of 

 itself indicate that electricity is a stimulus to 

 muscle protoplasm. Before this can be estab- 

 lished, it will be necessary to demonstrate con- 

 traction in parts of muscle not provided with 

 nerves ; for example, the distal part of the sar- 

 torius, or in muscles in which the nerves have 

 been destroyed by curare or by degeneration. 



Nerve- free, Muscle. Kemove the sartorius 

 muscle, together with the portion of the pelvis 

 and the tibia to which the muscle is attached, 

 and lay it on a glass plate. Stimulate the distal 

 (tibial) fifth, in which examination with the 

 microscope would show the absence of nerve 

 fibres, with a strong break induction current. 



The nerve-free muscle will contract. 



