igo Mr . Brodie on the different Modes 
into actual contact with its fibres, there is no evident reason 
why, the removal of the brain, and the employment of artifi- 
cial respiration, should occasion so material a difference in its 
effects. If the contractions of the voluntary muscles had de- 
pended on the infusion circulating with the blood, it is reason- 
able to suppose that the pressure on the aorta would have 
occasioned some diminution of them, and that the complete 
obstruction of the circulation would have caused them to cease 
altogether. 
From these considerations, I am induced, on the whole, to 
believe that the infusion of tobacco, when injected into the in- 
testines, influences the heart through the medium of the ner- 
vous system ; but I have not been able to devise any experi- 
ment, by which the truth or fallacy of this opinion might be 
put beyond the reach of doubt. 
It appears remarkable, that the brain and nervous system, 
although not necessary to the action of the heart, should, when 
under the influence of the infusion of tobacco, be capable of 
influencing this organ so as to stop its action ; but this is ana- 
logous to what we see occur in consequence of violent emotions 
of the mind. Those states of the nervous system, which ac- 
company the passions of joy, fear, or anger, when existing in 
a moderate degree, render the heart more sensible to the 
stimulus of the blood, and increase the frequency of its con- 
tractions ; while, when the same passions exist in a greater 
degree, the heart is rendered altogether insensible to the 
stimulus of the blood, and syncope ensues. 
