112 HUMAN PHYSIOLOGY. 



which depend on a reflex hyperaemia; 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 ob- 

 scure reflex actions which preside over the secretions of the intestinal 

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

 of the pupils from intestinal irritation (worms), and many pathological 

 phenomena. 



Laws of Reflex Action. (Pfluger.) 



1. Law of Unilaterality. If a feeble irritation be applied to one or 

 more sensory nerves, movement takes place usually on one side only, and 

 that upon the same side as the irritation. 



2. Law of Symmetry. If the irritation becomes sufficiently intense, 

 motor reaction is manifested, in addition, in corresponding muscles of the 

 opposite side of the body. 



3. Law of Intensity. Reflex movements are usually more intense on 

 the side of the irritation ; at times the movements of the opposite side 

 equal them in intensity, but they are usually less pronounced. 



4. Law of Radiation. If the excitation still continues to increase, it is 

 propagated upward, and motor reaction takes place through centrifugal 

 nerves coming from segments of the cord higher up. 



5. Law of Generalization. When the irritation becomes very intense, 

 it is propagated to the medulla oblongata; motor reaction then becomes 

 general, and is propagated up and down the cord, so that all the muscles 

 of the body are thrown into action, the medulla oblongata acting as a focus 

 whence radiate all reflex movements. 



Special Centres in the Spinal Cord. 



Genito-spinal centre. In the lower portion of the spinal cord are 

 located the centres which control the sphincter muscles of the rectum and 

 bladder, the erection of the penis, the emission of the semen, the action of 

 the uterus during parturition, etc. 



Cilio-spinal centre. Situated in the spinal cord between the 6th cervical 

 and 2d dorsal nerves ; stimulation of the cord in this situation produces a 

 dilatation of both pupils through filaments of the sympathetic, which take 

 their origin from this region of the cord. 



