FUNCTIONS OF ftiE SPINAL CORD 911 



to stimuli by reflex movements more readily after the medulla 

 oblongata has been divided from the spinal cord or the brain re- 

 moved. In the dog the scratch reflex is elicited more easily after 

 removal of the cerebral cortex or its elimination by cerebral 

 anaemia. In the guinea-pig, after extirpation of the cortex of one 

 hemisphere, the scratch reflex is more readily evoked on the side 

 of the lesion (Brown). 



That the brain exerts more than a merely inhibitory influence on 

 the production of reflex movements is suggested by many facts. 

 The knee-jerk, for example, is increased or ' reinforced ' if an instant 

 before the tendon is struck the patient makes a voluntary movement 

 or is acted on by a sensory stimulus (Bowditch and Warren). In 

 health it varies in strength with many circumstances which affect 

 the activity of the central nervous system as a whole (Lombard, 

 etc.). It often disppears in pathological lesions, situated high up 

 in the cord in man, and is markedly impaired after high section of 

 the cord in dogs. In hemiplegia (paralysis of one side of the body, 

 caused by disease in the brain) the cutaneous reflexes on the para- 

 lyzed side may sometimes be absent for years. Some observers 

 have even gone so far as to say that under normal conditions the 

 so-called spinal reflexes are really cerebral in other words, that 

 the afferent impulses run up to the brain and there discharge efferent 

 impulses, which pass down to the motor cells of the anterior horn 

 and cause their discharge. It may be admitted that there is no 

 physiological ground for supposing that the afferent impulses which 

 have to do with the reflex contraction of the muscles of the leg 

 when the sole is tickled, stop short at the motor cells of those spinal 

 segments from which the efferent nerves come off, while the af- 

 ferent impulses which have to do with the sensation of tickling pass 

 up to the brain. The probability is that under ordinary circum- 

 stances such afferent impulses pass up the cord in long afferent 

 paths, as well as directly towards the motor cells along those fibres 

 of the posterior roots and their collaterals which bend forward into 

 the anterior horn at the level of their entrance into the cord. And 

 the only question is whether, as a matter of fact, the spinal motor 

 cells are most easily discharged by the impulses that reach them 

 directly, or by the impulses that come down to them by the round- 

 about way of the brain, and the efferent fibres tiiat connect it with 

 the cord. It is evident that the answer to this question need not 

 be the same for all kinds of animals. It may well be that in the 

 higher animals, in which the cortex has undergone a relatively great 

 development, the spinal motor mechanisms are more easily dis- 

 charged from above than from below, while in lower animals the 

 opposite may be the case. When the cord is cut off from the brain 

 the afferent impulses may overflow more easily into the spinal motor 

 cells since their alternative path is blocked. In the frog, where 



