1 2 o THE INVOL UNTAR Y NER VO US S YS TEM 



network. This is a proposition which is to my mind highly 

 unlikely. All muscular tissue possesses the power of rhythmic 

 contraction to a greater or less degree. Ordinary striated muscle, 

 with its more rapid contraction, has lost this power to a much 

 larger extent than unstriped or cardiac muscles. The more em- 

 bryonic the muscle the greater is its rhythmic power. 



The power of manifesting rhythm depends upon the condition 

 of the muscle, upon what is often called a condition of tone ; this 

 condition does not necessarily imply contraction but rather a 

 readiness to contract, owing to the muscle having attained a 

 condition of unstable equilibrium. This condition of tone is de- 

 pendent upon both nervous and chemical factors. As long as 

 the muscle is in continuity with the nerve cell, which nourishes 

 its nerve, the action of that nerve cell keeps the muscle in a con- 

 dition of tone, so that it can manifest rhythmic contractions. 

 When it is separated from its nerve cell it loses its tone, but 

 that condition can be restored by the action on the muscle of 

 certain chemical substances, especially salts of sodium, so that 

 the rhythmic activity again becomes evident. This seems to me 

 yet another instance of the condition of a tissue not being de- 

 pendent solely on its connexion with the nervous system, but 

 also upon chemical substances brought to it in its nutrient fluid. 

 The nervous action upon which the tone of the muscle depends 

 is ultimately conveyed to the muscle by the network of fibres on 

 it. It is said to be a true network, not an interlacing of fibres, 

 and in many cases it is formed from the axons of both sym- 

 pathetic and enteral nerve cells. According to Fletcher's ob- 

 servations on the retractor penis muscle, it will not degenerate 

 until separated from both systems of nerve cells. 



It is, however, universally accepted that the separation of 

 either nerve cell profoundly modifies any rhythmic activity 

 present at the moment of separation, though later a readjust- 

 ment may take place with the return to a condition very near or 

 identical with the original ; the permanent removal of the cells of 

 one of the two systems, which are in connexion with the network, 

 need not necessarily prevent an effectual control of tone by the 

 peripheral network ; that is to say, the integrity on the nervous 

 side of one system only is sufficient to maintain a nervous con- 

 trol of tone. Thus the tone of the heart can be maintained by 

 the intrinsic nerve cells alone, although they belong entirely to 



