SEC. 4. THE AUTOMATIC ACTIONS OF THE 

 SPINAL CORD. 



595. We speak of an action of an organ or of a living body 

 as being spontaneous or automatic when it appears to be not 

 immediately due to any changes in the circumstances in which the 

 organ or body is placed, but to be the result of changes arising in 

 the organ or body itself and determined by causes other than the 

 influences of the circumstances of the moment. Some automatic 

 actions are of a continued character ; others, like the beat of the 

 heart, are repeated in regular rhythm ; but the most striking 

 automatic actions of the living body, those which we attribute to 

 the working of the will and which we call voluntary or volitional, 

 are characterized* by their apparent irregularity and variableness. 

 Such variable automatic actions form the most striking features 

 of an intact nervous system, but are conspicuously absent from a 

 spinal cord when the brain has been removed. 



A brainless frog placed in a condition of complete equilibrium 

 in which no stimulus is brought to bear on it, protected for in- 

 stance from sudden passing changes in temperature, from a too 

 rapid evaporation by the skin and the like, remains perfectly 

 motionless until it dies. Such apparently spontaneous movements 

 as are occasionally witnessed are so few and seldom, that we can 

 hardly do otherwise than attribute them to some stimulus, internal 

 or external, which has escaped observation. In the mammal (dog) 

 after division of the spinal cord in the dorsal region regular and 

 apparently spontaneous movements may be observed in the parts 

 governed by the lumbar cord. When the animal has thoroughly 

 recovered from the operation the hind limbs rarely remain quiet 

 for any long period ; they move restlessly in various ways ; and 

 when the animal is suspended by the upper part of the body, the 

 pendent hind limbs are continually being drawn up and let down 

 again with a monotonous rhythmic regularity, suggestive of 

 automatic rhythmic discharges from the central mechanisms of 

 the cord. In the newly born mammal too, after removal of the 



