v SPINAL CORD AND NERVES 313 



respect, indicate " the extent to which the reactions of the visceral 

 musculature and some of the reactions of the skeletal musculature 

 accessory thereto are normally unconnected with higher conscient 



nervous organs. 



" i 



Sherrington's observations on monkeys, after cervical tran- 

 section, are very important. The motor root-cells that do not 

 respond to stimulation of the skin react perfectly to excitation by 

 the pyramidal paths at the cut end of the cord ; weak stimulation 

 of the central ends of the afferent root readily evokes reflex move- 

 ments, though far stronger stimuli fail absolutely when applied to 

 the skin and afferent nerve trunks. 



VII. When a stimulus applied to any sensory area of the body 

 evokes a reaction of the muscles belonging to the same or to 

 adjoining segments of the cord, the reaction is termed a short 

 spinal reflex; when, on the contrary, the stimulus evokes a 

 reaction on the musculature of a more or less distant uietauiere, 

 the spinal reflex is termed long. Short spinal reflexes are, as a 

 rule, more easily and readily elicited because they have less 

 resistance to overcome. 



Sherrington makes the following statements as to the intra- 

 spinal irradiation in short spinal reflexes : 



1. The degree of reflex spinal intimacy between afferent and 

 efferent spinal roots, i.e. the facility with which the reflex is dis- 

 charged, varies directly as their segrneutal proximity. The 

 excitation of a central end of a severed thoracic root evokes with 

 special ease contraction of muscles, or parts of muscles, innervated 

 by the corresponding motor roots, and next easily muscles inner- 

 vated by the next adjacent motor roots. The spread of short 

 spinal reflexes in many instances seems to be rather easier tail ward 

 than headward. 



2. Taken generally, for each afferent root there is in its own 

 segment a reflex motor path of as low resistance as any open to it 

 anywhere. In other words, each single afferent root, or a single 

 filament of it, evokes a special reflex movement with a minimal 

 stimulus. 



3. The different motor mechanisms for the skeletal musculature 

 lying in the same spinal segment exhibit markedly unequal 

 accessibility to the local afferent impulses. So that in many 

 animals it is easier to arouse reflex contraction of the flexors of the 

 homonymous knee and the extensors of the coutralateral than of 

 the extensors of the homonymous and the flexors of the contra- 

 lateral knee, although the respective motor fibres may be contained 

 in the same efferent root. 



4. When a spinal reflex discharge is prolonged, it usually 



1 Sherrington, Sc/tafcr's Text-Book of Physiology, 1900, vol. ii. p. 849. 



