ASPHYXIA. (Gr. Acrptica. Fr. Asphixie. Ger. Scheintod, Asphyxie. Ital. Asfssia.) The word Asphyxia, according to its derivation (from a and ovvb.), pulsus,) ought to signify what is usually expressed by the term Syncope, i. e. failure of the heart's action ; but it is now always used to express failure of the process of respiration.
It is hardly necessary to say, that there is no more general law of vital action, in all classes of organized beings, than its dependence on oxygen, i. e. on a certain chemical action taking place between the nourishing fluids of that living body (whether animal or vegetable) and the oxygen of the atmosphere. This law is, indeed, as general as the dependence of vital action on heat, and in like manner as a certain elevation of temperature (short of what acts chemically on the organized textures) is destructive to life, so a certain concentration of oxygen in the air inhaled, at least by the higher orders of animals, affects them as a poison." Many organized substances, as the seeds, roots, and stems of vegetables, the pupae of insects, eggs, even perfect animals of some of the lower classes, may retain their vitality, as is commonly said, i. e. remain susceptible vital action, for very various periods of time, at low temperatures, without exercising any action on the oxygen of the atmosphere ; but whenever the phenomena indicating vital ac tion take place in them, exposure to oxygen, and a certain alteration of the air surrounding them, very soon become necessary conditions of the continuance of vitality.
The alterations which take place in the air in contact with different living bodies are some what various. Water is exhaled probably in every instance. In the case of some animals, particularly fishes, there is certainly an absorp tion of azote ; and in that of vegetables growing under the influence of light, there is a decided absorption of carbon from the carbonic acid of the atmosphere, and an evolution of pure oxygen. But it is now generally agreed, that, in all cases, the action between the atmosphere and the nourishing fluid which is essential to the motion and vivifying power of the latter, is that which is denoted by the disappearance of part of the oxygen from the air that comes in contact with that fluid, and the substitution of a quantity of carbonic acid.
Some time since it was the prevalent opinion, that the nature of that action was merely an excretion of carbon, which immediately on its being evolved from the nourishing fluid, en tered into combination with the oxygen of the air,- and was carried off; and the chief reason for this opinion was, that the volume of oxy gen which disappeared in the process, was believed to be just equal, in all cases, to that of the carbonic acid that appeared. As it is known that the volume of any quantity of carbonic acid is just the same as that of the oxygen contained in that quantity of acid, if the fact had been as above stated, the coinci dence could hardly have been accidental, and the inference would have been nearly inevitable, that the oxygen of the atmosphere did not enter the nourishing fluids, but merely dissolved and carried off the excreted carbon.
But the numerous experiments of Dr. Ed wards* and of M. Du Long,t seem to have nearly established the proposition, that in the respiration of by far the greater number of animals, the volume of oxygen that disappears from, is somewhat greater than that of the carbonic acid that appears in, the air employed: the same result was obtained in experiments by Allen and Pepys on birds and if this be so, it is certain that the respiration of these animals is attended with an actual absorption of oxygen, at least to a certain extent.
This conclusion authorizes us to inquire far ther, whether it is not more probable, that the whole of the oxygen which disappears from air in contact with the nourishing fluid of living beings, is absorbed into that fluid, and that the carbonic acid which appears is exhaled, ready formed, in its place. And several facts spew that this is by far the more probable suppo sition; and that oxygen is essential to vital action, not merely as a means of carrying off superfluous carbon, which has become noxious; but as itself' an ingredient in the nourishing fluids, necessary for the maintenance of their motion and vivAing power.