94 Dr. Parry on a Case of nervous Affection. 
versed together, I remarked to him, that if my theory of the 
usual cause of spasmodic or nervous affections were well 
founded, I should probably be able to suppress or restrain 
these muscular vibrations of the left arm, by compressing the 
carotid artery on the opposite or right side ; while little effect 
might perhaps be produced, by compressing the carotid of the 
side affected. The event was exactly conformable to my ex- 
pectation. Strong pressure on the right carotid uniformly 
stopped all the vibrations, while that on the left had no ap- 
parent influence. I may add that these experiments were 
afterwards, at my request, repeated on this lady in London by 
Dr. Baillie, and, as he informed me in a letter, with a similar 
result. 
It is perfectly well known to many of the learned Members 
of this Society, that irritations of the brain, when of moderate 
force, usually exhibit their effects on the nerves or muscles of 
the opposite side of the body ; and in the case before us, it is 
difficult to understand how the suspension of these automatic 
motions could have been produced by this pressure of the op- 
posite carotid, in any other way than by the interruption of 
the excessive flow of blood through a vessel morbidly dilated ; 
in consequence of which interruption, the undue irritation of 
the brain v/as removed, and the muscular fibres permitted to 
resume their usual state of rest. 
From these and many other similar facts, I am disposed to 
conclude, that irritation of the brain, from undue impulse of 
blood, is the common though not the only cause of spasmodic 
and nervous affections ; and I can with the most precise regard 
to truth add, that a mode of practice, conformable to this prin- 
ciple has enabled me, during more than twenty years, to cure 
