The study of the fatal changes in asphyxia is also of peculiar importance as illustrating the manner in which the circulation, and the organic functions maintained by it, are con nected with the nervous system. It will be observed, that as the vitality of hybernating animals, during the state of torpor, is inde pendent of respiration, so it is also, in a great measure at least, independent of the larger masses of the nervous system ; and Dr. M. Hall found, by experiment in a hedgehog in this state, that the circulation went on regu larly for ten hours after the gradual but com plete destruction of the brain and spinal cord.
Indeed, the maintenance of the circulation. after the head of an animal has been cut off,, by the artificial respiration, i. e. by inflating its , lungs in a manner resembling its natural breathing, (which has been so often practised by Fontana, Cruikshanks, Bichat, Brodie, Le Gallois, Wilson Philip, and others ) is in it self a clear proof that the circulation, and other functions of organic life* in animals, are necessarily and immediately dependent on the animal life, only inasmuch as the natural respiration of animals, and the arterialization of their blood, are dependent on sensation. And ac cordingly we know, that in that stage of animal existence, where the supply of sufficiently arterialized blood is provided fOr without the intervention of sensation, i. e. in the foetus in utero, the whole organic life is altogether in dependent of the animal, and goes on perfectly, not only before sensation is felt, but even in cases where the essential organs of sensation and of voluntary motion, the brain and spinal cord, do not exist. It is not until the moment of birth, when the arterialization of the blood is put in dependence on sensation,—that the brain and spinal cord become essential for the maintenance of organic life ; or that we possess any proof of influence being exercised by the nervous system, over that part of the animal ceconomy.
It seems probable, that if we possessed the means of making the artificial respiration ex actly similar to the natural, and neither injuring the structure of the lungs, nor introducing more air into them than is useful, in practising it, the circulation, and perhaps all the func tions of organic life, might be maintained, after the head of an animal is cut off, until nearly the time when it must fail for want of nourish ment; but it must also be remembered, that in the adult animal, as the experiments of Le Gallois, Dr. Wilson Philip, Flourens, and others have shewn, injuries of the brain and spinal cord, (particularly injuries suddenly in flicted on any large portions of these organs,) may directly influence, or even wholly sup press, vital actions belonging to the head of organic life, for the performance of which we have no evidence of their furnishing any ne cessary condition.
As the function of respiration thus appears to be the only link by which the organic life is immediately and necessarily connected with animal life, it is naturally to be expected that the extinction of animal life should affect the organic functions just in the same way as the suspension of respiration does, and therefore that in the case of death beginning at the brain, as Bichat expressed it, (i. e. of death consequent on the extinction of sensation and voluntary motion,) the circulation and other organic functions should be brought to a stand just in the same manner as in death by as phyxia. And in what is strictly called death by coma, this is really the case; the sensations being gradually more and more impaired, the sense of anxiety in the chest, which prompts to the acts of. respiration, is ultimately extinguished ; but even after the last breath has been drawn, the pulsations -of the heart still continue, and the blood then gradually stagnates in the lungs, the circulation comes to a stand, and the blood is found after death congested on the right side of the heart, just as in the case of asphyxia already described.
That this is truly the mode of fatal termina tion in cases where death takes place strictly in the way of coma, was first unequivocally proved by Sir B. Brodie,'* who found, by experi ment, that animals poisoned by opium or other narcotics, and in which the acts of re spiration had ceased, in consequence of the impression made on the brain and the gradu ally increasing insensibility, might be recovered by the artificial respiration, just as asphyxiated animals may be. Indeed the same expedient had been previously employed with success (although not suggested by an equally accurate view of its mode of action) by Mr. Whately.-1 The reason why the same expedient cannot be expected to avail in cases of disease termi nating by coma is simply that in these cases the cause of the coma is not temporary, like the effect of a narcotic poison, but permanent. It seems possible that it may yet be found successful in some cases of insensibility with convulsion, in children, unconnected with or ganic lesion.