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 
