MOLECULAR DEATH.
Molecular life is constituted by two func tions, Nutrition and Contraction, for which certain conditions are requisite. The former demands a mechanism or tissue of pores or in finitely minute tubes, the ingress and egress of fluid, and a certain quality of this fluid ; the latter, a fibrous arrangement of particles, in most animals and in all a peculiar property called irritability or contractility. The viola tions of these conditions are necessarily fol lowed by molecular death. We shall consider them in detail.
Destruction of the tissues.—It is all but a truism to assert that the function of a tissue must cease when its mechanism is broken up, though mere integrity of the mechanism is insufficient to maintain the function. The changes which ensue are as follows. The sub stance is no longer capable of receiving and transmitting fluid in the same manner as for merly ; the fluid which it contained is either confused with the disorganized solid particles, or is altogether eliminated ; the fibres are unfitted for contraction ; and the nervous filaments are paralysed. In this condition the part has ob viously no kind of connection with the rest of the system, by the exchange either of fluid, or of nervous influence; it is dead both abso lutely and relatively. If the other organs sur vive its death, certain processes commence in its immediate vicinity, by means of which a mechanical as well as a vital separation is effected ; while the mortified part, as it is technically called, is abandoned to the play of various chemical affinities among its particles, and between these and surrounding agents. According as these changes are less or more ad vanced, there is gangrene or sphacelus. It may happen however that the other parts of the frame may lose their vitality soon after the local injury ; but their dissolution will depend upon the violation of other conditions than that which we are at present discussing. Thus the part disorganized may be essential to the distribution of blood throughout the system, and the other parts may die from the want of this supply, their mechanism remain ing entire. Or the injury, notwithstanding that the part may not be thus functionally es sential to the circulation, may exert a no less certain opemtion, either indirectly by an im pression made upon the central organs of in nervation, and reflected upon those of circu lation and respiration, or immediately by an impression upon the latter. (See the remarks upon Systemic Death.) The propagation of the dissolution will depend much upon the peculiar organization of the animal ; but in all cases, as we have already intimated, text ural death in one part has no immediate in fluence in producing the same kind of death in other parts ; the latter event will be found attributable to the impediment offered by the former to some important function of the whole system. The textural lesion which we
have been considering may be caused either by mechanical violence, or by chemical action, such as that of' corrosive substances and of heat. It is possible that solid tissue may un dergo spontaneous decomposition, but we are unable to ascertain the fact, because in ulti mate structure, where fluids and solids are so intimately intermixed, we have no means of distinguishing the priority of changes.
Arrest of the fluid of nutrition.—The access of this fluid is variously provided for in the different classes of animals. The capillary cir culation in the higher species resembles that which suffices for the whole system in the lower species, inasmuch as the blood in the capillaries of a tissue bears the same relation to that tissue, as the water in the stomach of one of the Radiata to the whole animal. The consequences of abstracting the fluid in the one case, or of cutting off the supply of blood in the other by obstructing its vessels, will be pre cisely analogous. The polype will desiccate, lose its proper form, and decay ; the medusa will shrivel and putrefy ; while in man the tissue dies, and is decomposed, as in senile gangrene, or in the sloughing of a hannorrhoid to which a ligature has been applied. Sup pression of the action of the heart violates throughout the body the condition of vitality under discussion, and consequently all the tissues die, but the phenomena which they exhibit are not the same as in more partial obstruction of the circulation, because the chemical agencies are different, particularly that of surrounding heat. A gangrenous spot is under the influence of an atmosphere of 98° at the lowest ; while the dead or dying organs of animals which have been simultaneously deprived of their circulation, are submitted only to the temperature of the media in which they may chance to be placed. The higher this may be within certain limits, the more closely will the putrefactive changes resemble those of gangrene. It must be remembered, however, that in the latter case other chemical agents are probably presented in the fluids effused by those contiguous parts which still maintain their vitality.