FUNCTIONS OF THE SPINAL CORD. 123 



The reflex excitability of the cord may be 



1. Increased by disease of the lateral columns, the administration of 

 strychnia, and in frogs, by a separation of the cord from the brain, the latter 

 apparently exerting an inhibitory influence over the former and depressing 

 its reflex activity. 



2. Inhibited \yy destructive lesions of the cord, e.g., locomotor ataxia, 

 atrophy of the anterior cornuae, the administration of various drugs, and, in 

 the frog, by irritation of certain regions of the brain. When the cerebrum 

 alone is removed and the optic lobes stimulated, the time elapsing between 

 the application of an irritant to a sensory surface and the resulting movement 

 will be considerably prolonged. The optic lobes (Setchenow's centre) 

 apparently generating impulses which, descending the cord, retard its reflex 

 movements. 



All movements taking place through the nervous system, are of this reflex 

 character, and may be divided into excito-motor, sensori-motor, and idea- 

 motor. 



Classification of Reflex Movements. (Kiiss ) They may be divided 

 into four groups, according to the route through which the centripetal and 

 centrifugal impulses pass. 



1. Those normal reflex acts, e.g., deglutition, coughing, sneezing, walk- 

 ing, etc., pathological reflex acts, e. g., tetanus, vomiting, epilepsy, which 

 take place both centripetally and centrifugally, through spinal nerves. 



2. Reflex acts which take place in a centripetal direction through a 

 cerebro spinal sensory nerve, and in a centrifugal direction through a sym- 

 pathetic motor nerve, usually a vasomotor nerve, e.g., the normal reflex 

 acts, which give rise to most of the secretions, pallor and blushing of the 

 skin, certain movements of the iris, certain modifications in the beat of the 

 heart; the pathological, which, on account of the difficulty in explaining 

 their production, are termed metaslatic ', e.g., ophthalmia, coryza, orchitis, 

 which depend on a reflex hypersemia; amaurosis, paralysis, paraplegia, etc., 

 due to a reflex anaemia. 



3. Reflex movements, in which the centripetal impulse passes through a 

 sympathetic nerve, and the centrifugal through a cerebro-spinal nerve; 

 most of these phenomena are pathological, e. g., convulsions from 

 intestinal irritation produced by the presence of worms, eclampsia, hysteria, 

 etc. 



4. Reflex actions, in which both the centripetal and centrifugal impulses 

 pass through filaments of the sympathetic nervous system, e.g., those 

 obscure reflex actions which preside over the secretions of the intestinal 

 fluids, which unite the phenomena of the generative organs, the dilatation 



