ANGIONEUROTIC EDEMA 283 



those areas whose vasodilators previously have been 

 irritable and near fatigue, or whose vasoconstrictors 

 have been irritable and respond to stimuli in an exag- 

 gerated manner before giving way to fatigue. Under 

 such circumstances the formation of a wheal could not 

 occur, as no increased permeability of the vessel walls 

 has occurred. Where localized vasodilation has pre- 

 ceded fatigue, wheal formation may be expected, due 

 to localized vessel-wall permeability. Once established, 

 whether preceding or following wheal formation, local 

 areas of vasoconstriction persist, if undisturbed by 

 treatment, until the local vasoconstrictors in turn be- 

 come fatigued, when relaxation supervenes and the 

 lesion disappears. That the disappearance of the local 

 vasoconstriction and wheal is due to fatigue paralysis 

 of the local vasoconstricting nerve end-plates would 

 seem to be proven by the fact that local anesthesia 

 produced by sponging the affected surface lightly with 

 chloroform will cause much more rapid disappearance 

 of wheals. 



The part played by the posterior lobe of the pituitary 

 body in this series of phenomena does not become ap- 

 parent in the milder varieties of urticaria, but in the 

 severer forms is often plainly evident in the severe 

 diarrhea, colic, and other gastrointestinal manifesta- 

 tions related to unusual peristaltic action or an ex- 

 cessive contractility of the non-striated musculature. 



Vasoconstrictor fatigue necessarily would be swift 

 and the disappearance of wheals prompt, were the af- 

 fected vasoconstrictors not supported and sustained in 

 their contraction by some agency external to them- 

 selves. As previously pointed out, that agency in the 

 body which possesses this ability to the most marked 

 degree, i. e., selective contractile effect upon the muscle 

 fibres of the circulatory system, is adrenin, the product 

 of the adrenal medulla. It would appear, therefore, 

 that long-persisting urticarial wheals, like those of 



