706 REFLEX ACTIONS. [BOOK m. 



influenced, in the way of augmentation or depression, by ner- 

 vous impulses reaching it from other parts of the nervous 

 system. 



When we turn to the teaching of disease, we again find that 

 reflex movements carried out by the cord or by parts of the 

 cord are, on the whole, scanty and simple. 



In some stages of certain diseases of the spinal cord exten- 

 sive reflex movements it is true are witnessed ; but these are 

 not purposeful coordinated movements, such as have been 

 described above as occurring in frogs and mammals after ex- 

 perimental interference, but rather mere exaggerations of the 

 simpler reflex movements witnessed when the nervous system 

 is intact. In cases of paraplegia (such being the term gener- 

 ally used when disease or injury has cut off the cord, generally 

 the lower part of the cord, from the brain so that the will can- 

 not bring about movements in, and the mind derives no sensa- 

 tions from, the parts below the lesion, the legs for instance), 

 it sometimes happens that contact with the bedclothes, or 

 other external objects, sets up from time to time rhythmically 

 repeated movements, the legs being alternately drawn up and 

 thrust out again. And an exaggeration of the ' knee-jerk ' or 

 other ' tendon reflexes ' is a very common symptom in certain 

 spinal diseases. It is rarely if ever that reflex movements of a 

 really complicated character are observed. Moreover clinical 

 experience shews that in man, when a portion of the cord is 

 isolated, reflex actions carried out by means of that portion so 

 far from being exaggerated are much more commonly exceed- 

 ing feeble or absent altogether. In the cases in which the 

 physiological continuity of the lower with the upper part of 

 the cord has been broken by disease, by some growth invading 

 the nervous structures or by some changes of the nervous 

 structures themselves, we may attempt to explain the absence 

 from the lower part of coordinate reflex activity, such as is 

 seen in the lower animals, as due to the disease not only affect- 

 ing the powers of the actually diseased part, but influencing 

 the whole cord below, and either by inhibition, of which we 

 shall speak presently, or in some other way depressing its func- 

 tions. But the same absence of complex reflex movements is 

 also often observed in cases in which the cord has been severed 

 by accident, and indeed, though accidental injuries to the 

 human cord generally produce more profound and extensive 

 mischief than that which results in animals from skilful experi- 

 mental interference, clinical experience tends, on the whole, to 

 support the view that in man the more complete subordination 

 of the spinal cord to the brain has led to the dying out of the 

 complex reflex actions which are so conspicuous in the lower an- 

 imals. This however cannot be regarded as distinctly proved. 



465. We have dwelt above chiefly on reflex actions, 



