186 HUMAN PHYSIOLOGY. 



beat of the heart ; the pathologic reflexes, which, on account 

 of the difficulty in explaining their production, are termed meta- 

 static e. g., ophthalmia, coryza, orchitis, which depend on a 

 reflex hyperemia; amaurosis, paralysis, paraplegia, etc., due to a 

 reflex anemia. 



3. Reflex movements in which the afferent impulse passes through 

 a sympathetic nerve, and the efferent 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 afferent and efferent 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 of the pupils from intestinal irritation 

 (worms), and many pathologic phenomena. 



Laws of Reflex Action (Pfliiger). 



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 the same side as the irritation. 



2. Law of Symmetry. If the irritation becomes sufficiently in- 

 tense, 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 in- 

 tense, it is propagated in the medulla oblongata ; motor reaction 

 then becomes general, and it 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 Reflex Movements. 



Among the reflexes connected with the more superficial portions 

 of the body there are some which are so frequently either exag- 

 gerated or diminished in pathologic lesions of the spinal cord that 



