It has been asserted by _Bichat_[11] that the immediate cause of death, when it takes place suddenly, must be the cessation of the functions of the heart, brain, or lungs; although it is sometimes difficult to determine which of these organs is the first to fail in its action; this may be well exemplified by the poisonous operation of Arsenic upon the animal economy, which when introduced into the circulating system will, according to the valuable experiments of _Mr. Brodie_, occasion stupor and paralysis, a feeble and intermitting contraction of the heart, and slow and laborious respiration; but it is found that in some cases, one order of symptoms will predominate, and be the first to display themselves, whilst in others, the very contrary will obtain, without perhaps our being able to assign the immediate cause of such deviations. There are, moreover, cases of sudden death, in which the principle of animation would seem to be at once annihilated in every part of the animal machine, and when every organ appears to be simultaneously affected, as in that occasioned by the agency of intense cold, and sometimes, for it is not in every instance, by that of lightning, or electricity; still, as a general proposition, the aphorism of _Bichat_ must be admitted; and we shall proceed to investigate the subject of sudden death, as connected with medico-judicial inquiry, upon principles deduced from the enlightened views of this distinguished philosopher. To the able and satisfactory researches of our English physiologist, _Mr. Brodie_, we are also greatly indebted for a correct notion of the nature and order of succession, of those events by which life is quickly extinguished; his attention was many years ago directed to one important branch of this subject,—to the investigation of that series of changes produced on living bodies by the operation of poisons, the results of which were published in the _Philosophical Transactions_,[12] to which we shall have frequent occasion to refer in the following pages. Since that period he has diligently pursued the subject in its more extensive ramifications, and in his lectures, delivered from the anatomical chair of the College of Surgeons during the last year, he presented a condensed and philosophical history of the phenomena of death, in general, in which he elucidated many leading points that were before obscure, established several propositions that have long been considered doubtful, and rejected a mass of popular error, which, under the sanction of authority, has continued to retard our inquiries, and to embarrass and misguide our practice. The author of the present section of this work has to acknowledge the kindness and liberality by which he is enabled to avail himself of these luminous researches, having been furnished by his friend _Mr. Brodie_ with the manuscript notes from which the lectures were delivered.