relation between the nervous and sanguiferous systems. 435 
of the nervous system which excite these muscles, not being 
sufficient to call them into action. It must bruise or lacerate to 
produce this effect. As the muscles of voluntary motion feel 
the impressions made on a very small part of the nervous sys- 
tem only, in proportion as this part is small, the impression 
must be great to affect them ; but the heart, which is in- 
fluenced through all parts of the nervous system, though not 
very powerfully through any one, feels all the impressions 
made on this system, provided they are made on a sufficiently 
extensive portion of it; thus, as long as the instrument re- 
mains in the brain, its stimulant effect on the heart continues. 
It is true, that although the heart is only influenced by 
agents applied to a large portion of the brain, we may con- 
ceive them so applied as to produce irregular action in it, and 
we find that certain irritations of the nervous system have 
this effect. But it is evident, that the heart not being subject 
to stimuli whose action is confined to a small portion of this 
system, and being equally affected through all parts of it, 
must render it much less subject to irregular action ; which 
may be one of the final causes of this organ, whose regular 
action is of such importance in the animal economy, being 
made subject to the whole, and not to any one part of the 
nervous system ; and readily accounts for our not being able 
to produce irregular action in it, in the above experiments. 
What has been said also explains why those, who have en- 
deavoured to influence the heart by stimulating its nerves or 
the parts of the brain from which they seem chiefly to origi- 
nate, have failed. When indeed the connection of the nerves 
of the heart is considered, it will be found to derive its nervous 
influence from every part of the nervous system, and not very 
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