282 THE INTERNAL SECRETIONS 1920 



filtration. Similarly, if stimulation of this structure 

 be continued in the same manner, the areas of normal 

 response presently will become irritable, flush markedly 

 and perhaps show beginning edema, while areas pre- 

 viously irritable will become temporarily incapable of 

 responding to vasodilator stimuli. 



As has been shown, vasoconstriction is an automatic 

 protective function, capable of operating under condi- 

 tions which temporarily disrupt peripheral vasodila- 

 tion. Areas whose vasodilator nerve end-plates from 

 any cause have become temporarily paralyzed or com- 

 pletely fatigued are immediately subject to automatic 

 vasoconstriction. Vasoconstrictors unopposed cause a 

 sharp vasoconstriction in exactly the same manner that 

 the muscles on the sound side of a face affected by facial 

 paralysis automatically contract and pull the mouth 

 toward the sound side, because of the loss of balancing 

 tonicity in the muscles of the paralyzed side. This auto- 

 matic localized vasoconstriction will continue until the 

 local vasoconstrictors in turn become fatigued or vaso- 

 dilating tonus returns. Thus a given urticaria-like 

 wheal may be assumed to develop because of localized 

 vasodilation with prompt fatigue-paralysis of the irri- 

 tated vasodilating end-plates thereafter; and to be 

 caused to persist through antagonistic vasoconstriction 

 of the same vessels, which condition prevents the 

 prompt reabsorption of serum locally exuded through 

 overpermeable vessel walls during dilation. 



Not always is such a relatively slow process required 

 to cause localized vasoconstriction. A powerful vaso- 

 constricting nervous impulse, such as fright, or the en- 

 trance into the general circulation of a potent foreign 

 protein, may suddenly overwhelm the vasodilating ap- 

 paratus and produce a sudden generalized vasoconstric- 

 tion, as in anapyhylactic shock, in which wheals do not 

 occur. Under such circumstances recovery is made by 

 all parts of the body with more or less facility except 



