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Although the general proposition seems to be established, that the brain is not immediately necessary to the action of the heart, yet it must not lead us to the conclusion that the heart is therefore incapable of being affected by violent impressions on the nervous system; the fact is quite otherwise, for although the brain may be removed, and the circulation be nevertheless maintained by artificial respiration, yet an injury of another kind inflicted on the brain, may be followed by those immediately fatal consequences which decapitation itself would not produce; thus is a blow on the head commonly followed by syncope, and there are certain poisons that would seem to act in the same manner, such is the Infusion of Tobacco,^[224] which suspends the action of the heart long before the animal ceases to respire, and kills by producing syncope, although in this latter case it has been questioned whether the spinal marrow may not be primarily affected, which has been shewn by recent experiments to have an intimate relation with the action of the heart. Be this as it may, it is sufficiently obvious, that the second division of the first class is sanctioned by theory, and confirmed by experiment.