6. Syncope by hemorrhage.—The functions of the brain are in man so dependent upon a regular supply of blood to the organ, that a sudden diminution of it is alone sufficient to occasion vertigo and unconsciousness ; and this occurrence often takes place when the action of the heart itself is little or not at all affected. _Every one is acquainted with the effect of a change in the relative quantity of the blood in the cerebral vessels, determined by suddenly rising from the recumbent posture. Now it has been often observed that vertigo in duced by other causes has been followed by suspension of the circulation ; that is to say, the state of the brain, which was attended by giddiness, arrested the motions of the heart. lt has therefore been inferred that loss of blood operates indirectly upon the heart through the affection of the brain. When two phenomena follow each other in such quick succession as to be all but simultaneous, it is difficult to determine which is cause and which is effect, or whether they may not be the common ef fects of some other event. Certain facts would seem to indicate that the latter is the true interpretation of the phenomena which we are considering. Thus hzemorrhage some times affects the nervous system in the manner alluded to, without presenting any cheek to the contractions of the heart; not to mention that it appears more consistent with analogy to conclude that the heart must be more directly influenced by the loss of that which is its natural stimulus, than by a change in a remote organ. Again, there are cases in which hwinorrhage makes a decided impres sion upon the organs of circulation before the brain has given signs of any material derange ment of its functions ; but in these the loss of blood is more gradual than in the former instances. " When hmorthage is very gra dual," says Dr. Alison, " all the indications of failure of the circulation may come on—the feebleness of muscular action,—the paleness and collapse of the countenance,—the cold ness beginning at the extremities,—the cold sweat beginning on the face,—and the pulse may become imperceptible ; without the senses or the intellect being impaired, and a slightly laborious or heaving respiration may be almost the only indication of injury of the nervous system up to the moment of death." From facts 4olf this description we should be willing to decide at once that it is a superfluous multiplication of causes to attribute the stop page of the circulation in any case of hzemor rhage to the influence of cerebral changes, when the direct operation of the cause upon the heart itself is adequate to the explanation ;—were it not for the important fact that beemorrhage alone often fails to produce syncope till some circumstance has intervened, the operation of which is manifestly upon the nervous system. Thus nothing is more common in bloodletting than to find tbe heart unaffected by the with drawal of a considerable quantity of its stimu lus, so long as the posture of' the body is horizontal ; but on raising the head, a change which for obvious reasons renders the brain more sensible of the loss of blood, the nervous symptoms, viz. vertigo and leipothymia, ap pear, and immediately afterwards the pulse falls and becomes imperceptible. In corro boration of this fact we might at first be inclined to mention that a diminution of the quantity of the blood, so far from depressing the circulation, often appears to excite it violently, as in what has been denominated heemorrhagic reaction ; but in such instances analogous effects have been also witnessed in the cerebral functions, namely, delirium and extreme sensibility, &c. On the whole we may conclude with regard to both these sys tems that the depressing effect of hmmorrhage depends rather upon the suddenness of the change, than upon the absolute diminution of the quantity of the fluid.
7. Syncope by poisons.—Some substances depress the action of the heart in the man ner to which we had occasion to refer when speaking of syncope by mechanical injuries of the tissues generally. Of this kind are the mineral acids, oxalic acid, and the pure alkalies. They produce death, when taken in certain quantities, by means of that de pression of the circulation which folloi,vs the destruction of the parts to which they are applied. In smaller quantities they may be more remotely fatal by exciting disease, gastro-enteritis for instance. One of the sub stances mentioned, viz. oxalic ; acid, may in duce direct depression of the circulation, un attended by cerebral affection, even when its chemical effect upon the stoinach is prevented by dilution. In this form it must be classed with a large collection of substances which in certain doses subdue the moving powers of the circulation, without any previous coma, without any alteration of the tissues, and without any g,astric irritation; such are arse nic in large quantities, tobacco, digitalis, and most of the animal poisons. To the same class belong those malarious and contagious poisons which occasionally induce fatal syn cope before any of their ordinary effects upon the general functions ; we scarcely need to mention cholera, malignant typhus, plague, scarlatina, &c. The narcotic substances mani festly act first upon the cerebro-spinal system ; syncope follows either with .or without as phyxia. Those which act rapidly appear to strike the circulation before asphyxia has had time to transpire ; we may instance hydro cyanic acid, essential oil of almonds, large doses of opium and of alcohol, certain gases, par ticularly sulphuretted hydrogen and cyanogen.
8. Syncope by cold and lightning.—It is not clear whether these outAvard agents arrest the circulation through their influence upon the nervous system, or by directly paralysing the irritability of the fibres of the heart.
9. Syncope by inanition.—In cases of this description it is probable that the failure of the heart's action is a compound result of the prostration of the nervous system, and of the diminution of the proper stimulus of the circulation.
10. Syncope by disease.—All fatal maladies must terminate in cessation of the heart'sa c tion, but we limit the present category to those cases in which this event is unpreceded by asphyxia. The others have been hinted at under the head of syncope by asphyxia. The diseases now under consideration may, we think, be conveniently arranged as follows :— I. Those which stop the motion of the heart
by obstructing its mechanism, e. g. collections of fluid in the pericardium, lesions of the val vular apparatus ; accumulation of fat, &c.; or by diminishing the contractility of the fibres, e. g. atrophy, or degeneration of the muscular substance ;4' or by perturbing in some unex plained manner the nervous influence, e. g. the functional form of angina pectoris. 2. Those which are attended with hmorrhage, e• g. aneurisms, and diseases of mucous surfaces. 3. Those which induce excessive and long-con tinued discharges. Thus fatal syncope has sud denly terminated a fit of diarrhoea; but it must be borne in mind that in such instances the power of the circulation had previously been greatly enfeebled either by deterioration of the blood, or by causes acting on the innervation of the heart, or by the existence of irritation in some part of the system. 4. Diseases implicating the cerebro-spinal organs. Some of these ope rate in the same manlier as those accidental injuries which produce concussion, and which have been already adverted to. Thus in that species of apoplexy which terminates instan taneously, (apoplexie foudroyante of French authors,) the sanguineous extravasation appears to have the same effect as a mechanical shock to the whole nervous mass. The more common form of apoplexy extinguishes life by impeding the respiratory movements. We have more than once known cases of structural disease of the brain terminate by sudden syncope, but have learned nothing from the necroscopy capable of explaining wby the fatal occurrence took place at the precise time when it did, rather than at any other moment in the period during which the disease had existed; though it was easy to conceive that a lesion of this description must have been competent at any time to produce such changes in the cere bral circulation as would induce the result in question. 5. Diseases attended with what has been vaguely called irritation, either short and intense, or modemte but long-continued. This irritation consists sometimes of inflam mation and its sequeloe, and sometimes of spe 'cific structural alterations. A good illustration of the former of these is afforded by peritonitis, which frequently cuts off the patient by sub duing the action of the heart, long before this effect could transpire from derangements of the organs contiguous to the seat of disease. Still more remarkable in this point of view are the effects of acute inflammation of a synovial capsule. • It is true that these affections are accompanied by violent pain, which might be said in common language to exhaust the powers of the system, or in stricter phrase, to produce a change in the nervous system in compatible with the continuance of the action of the heart; but mere pain will not account for the fact in question, since in other diseases it attains a more intense degree, and lasts longer, as in neuralgia, without inducing fatal consequences. The causation is probably analogous to that of syncope from mechanical injuries of tissues, to which we have already devoted some remarks. But why an inflam matory condition of serous membranes should exert a more depressing influence upon the circulation than that of many other tissues that might be named, is a subject wrapped in deep obscurity ; yet it is scarcely darker than the question, why such changes should in the first instance excite and perturb the heart, or why a similar excitement should ensue upon the soft ening of a cluster of tubercles, and to a degree inexplicable by the functional derangement of the part in which the tubercles exist. Dis eases in which the powers of the system are said to be worn out, are in reality such as have gradually enfeebled the action of the heart, partly perhaps through the intervention of changes affecting the blood, the respiration and the nervous system, but probably in a great measure by as direct a relation between the diseased part and the change in the circulation, as between violent lesions of tissue and syn cope. Under the present bead are included a host of chronic maladies. 6. Diseases caused by vitiation of the blood. Such are scorbutus, certain forms of marasmus, the cachexim revealed by dropsies, and certain fevers of a malignant character. We might also mention those depravations indicated by morbid secretions, such as tubercle, carcinoma, melanosis, &c. but that the solids are so much involved in these diseases, that it becomes difficult to determine whether the heart's action was weakened by the primary lesion of the blood, or by the secondary one of the tissues. 7. Diseases which produce vitiation of the blood. Such are that large class in which there is disorder of the cliylopoietic processes, and that smaller group in which the convey ance of the chyle is impeded. Derangements of the secernent and excernent organs must be arranged in this division, and particularly those of the liver, the skin, and the urinary apparatus. Diabetes is a state of the system in which the blood is probably deteriorated both by defective assimilation, and by faulty excretion. Upon the whole of this class of diseases it must be remarked that we seldom or never have opportunities of witnessing their uncombined influence in depressing the organs of circulation.
11. Syncope by old age.—We have, in a for mer article (AGE) endeavoured to trace the principal events in senile decay. The death which follows this gradual decline of the func tions presents the strongest possible contrast to that of sudden syncope. In the latter in stance the assault is made upon the very citadel of life, the conquest of which secures an im mediate surrender of the minor bulwarks and dependencies ; but in the former the fortress is reduced only after a long series of defections in the outworks, and a consequent loss of supplies, or, to quote the words of an illustrious author, " Voici done la grande difference qui dis tingue la mort de vieillesse, d'avec celle qui est l'effet d'un coup subit ; c'est que dans l'une, la vie commence a s'eteindre dans toutes les parties, et cesse ensuite dans le cceur; la mort exerce son empire de la circonference au centre. Dans l'autre, la vie s'eteint dans le cceur, et ensuite dans toutes les parties ; c'est du centre a la circonference que la mort en chaine ses phenomenes.""