Acidum Carbonicum. CO2. Fixed Air. Aerial Acid. Spiritus Lethialis of the ancients. Is at ordinary temperatures a gas. By pressure it is condensed into a liquid, and by intense cold it is solidified. Sp. gr. 1.5245. Eq. Wt. 22. It exists extensively both in the organic and inorganic kingdoms.

Med. Prop. and Action. The pure gas when inhaled acts as an irritant, causing spasmodic contraction of the glottis and consequent asphyxia. On mixing the gas with about twice its volume of air. Sir H. Davy found that he could breathe it, though it soon produced vertigo and somnolency. The first symptom usually experienced on breathing an atmosphere containing Carbonic Acid gas is throbbing headache, with a fulness and tightness across the temples, giddiness, loss of muscular power, a sensation of tightness at the chest, increased action of the Heart, and often palpitations; the ideas become confused, and memory partially fails. Buzzing in the ears, impaired vision, and a strong tendency to sleep succeed, or syncope ensues. Convulsions, sometimes accompanied with delirium, foaming at the mouth, and vomiting, precede death. Dissection shows engorgements of the cerebral vessels, and sometimes serous or even sanguineous effusions. The treatment of poisoning by this gas is free exposure to the air; artificial respiration by the Marshall Hall or Sylvester methods; galvanism of the phrenic nerve; cold affusion; moderate blood-letting, especially by cupping at the nape of the neck; and the employment of stimulants, either given internally, or applied externally in the form of frictions. As an ansthetic, its properties have been examined by M. Herpin. * He states that the gas, when diluted with 80 or 90 per cent. of air, causes none of the toxic effects of the pure gas, but produces gradual anaesthesia, without any signs of suffocation, without pain or any apparent disturbance of the system; its action, he considers, is chiefly directed on the brain and nervous system. He considers that it is particularly adapted for maintaining an anaesthesia previously induced by Chloroform, as its action may be kept up for an almost indefinite period without danger to the patient. As a local anaesthetic, it will be considered more fully presently. When taken into the stomach in small quantities, in the form of an effervescing draught, this gas checks nausea and allays gastric irritability. Water charged with it is a good vehicle for the exhibition of many saline remedies. Locally applied to ulcerated surfaces, its primary action is that of a stimulant.

* Ann. de Therap., 1859, p. 59.

735. Therapeutic Uses

In Phthisis, the inhalation of Carbonic Acid was first employed by Dr. Percival, in 1774. He found it palliate the febrile symptoms; and this result was confirmed by the observations of Drs. Hulme, Withering, and Beddoes. It has more recently been employed by the Russian physicians to arrest the progress of Phthisis; and their views are supported by the observation of Guillot,* that the deposit of carbonaceous matter in the lungs operates as a check to the further deposit of tuberculous matter. Girtanner, however, found it produce only momentary relief; and in the hands of Muhry.it entirely failed.

736. In Gastric Irritability, Nausea, and Vomiting, Carbonic Acid given in the form of an effervescing draught has a most soothing and sedative effect. If acidity of the stomach exist, the draught may contain an excess of alkali. It is very useful in the gastric irritability of fever.

737. In Calculous Disease, when the urine contains a white or phosphatic deposit, Carbonic Acid water (bottled soda-water, or water aerated in a gasogene apparatus) may be given with advantage. In Irritability of the Bladder, Dr. Churchill found the local application of this gas of great service. It may be used as advised in the next section.

738. In Painful Affections of the Uterus, the local application of this gas, by its local anaesthetic action, often exercises the most beneficial effect. Its value in Cancer of the Uterus was first pointed out by Dr. Dewees;§ and in 1840, Dr. Clutterbuck || employed it with success in allaying great irritability of that organ. Prof. Simpson ¶ has recently brought the subject prominently forward, pronouncing it, in these cases, a good and powerful local anaesthetic. He directs a tablespoonful of crystallized Tartaric Acid, mixed with a tablespoonful of crystallized Bicarbonate of Soda, to be put into an ordinary wine-bottle, and three or four wine-glassfuls of water to be added: the gas which is evolved is to be carried off through a caoutchouc tube, and applied to the womb by means of a gum elastic nozzle attached to the extremity of the tube. The first evolution of gas within the vagina is attended with a slight feeling of heat; but this is soon followed by a soothing effect. In addition to its local anaesthetic property, the gas is one of the best local applications which can be made to an ulcerated surface. If the Acid fail to afford relief, a teaspoonful of Chloroform may be added to the contents of the bottle before introducing the cork. For the relief of uterine pains, perhaps no measure is so productive of relief. As a means of inducing premature labour, the use of the Carbonic Acid douche has proved effectual in the hands of Prof. Simpson,* Scanzoni,t and others. In Dysmenorrha, Prof. Mojon found Carbonic Acid fumes of the greatest service.

* Encyclograph Med., Dec. 1848. Hufeland's Journ., i. p. 197, and ii. p. 60. Dublin Quart. Journ. of Med.,

Aug. 1857. § On Diseases of Females, p. 269 || Lancet. Oct. 10, 1840. ¶ Edin. Med. Journ., July 1856.

739. In Tic Douloureux, Sciatica, and other Neuralgic Affections, in Atonic Rheumatism and Gout, the local application of Carbonic Acid baths, and especially of the douche, has been productive of great benefit.