CARBONIC ACID. 849 



hours. On examination of the animal, the heart is found pulsating 

 violently, although the motion of the diaphragm is arrested. The 

 blood, after death, is of a bright color in the veins, as well as in the 

 arteries; the mucous membranes are red; the blood coagulates quickly ; 

 oxygen has evidently been absorbed in large quantity ; the blood in the 

 systemic capillaries is no longer properly changed to venous blood; 

 and, on the other hand, the presence of over-oxygenated blood in the 

 nervous centres which govern respiration, lessens their activity, which 

 is called into play apparently by the stimulus of a certain quantity of 

 carbonic acid in the blood. The symptoms produced by breathing 

 oxygen, are rapidly alleviated by respiration in atmospheric air. 



Of the three compound gases containing carbon, viz., carburetted 

 hydrogen CH 4 , carbonic oxide CO, and carbonic acid C0 2 , carbonic 

 oxide is the most poisonous. This gas, which is produced by the im- 

 perfect combustion of carbon, is given off, together with carbonic acid, 

 in the fumes of burning coke or charcoal. The addition of 5 per cent, 

 of this gas to air, is sufficient to make it irrespirable, and to cause 

 death ; and it is this gas, rather than the carbonic acid, which produces 

 fatal results in suicide by charcoal fumes. In these fumes, however, 

 besides the carbonic acid and the carbonic oxide, there are ammoniacal 

 salts, an empyreumatic oil, sometimes sulphurous acid, watery vapor, 

 nitrogen, and traces of free oxygen. The symptoms produced by 

 smaller quantities of carbonic oxide in air, are, giddiness, faintness, 

 headache, convulsions, and irregularity of the pulse ; the freest inspi- 

 rations, or insufflations of pure air, or of diluted oxygen, are essential 

 for recovery at such a crisis. When death ensues from the breathing 

 of carbonic oxide, the blood is not found dark, as in asphyxia from 

 carbonic acid, but even the venous blood is of a bright red hue, and 

 the properties of the corpuscles are permanently modified; for they 

 exhibit no further changes on exposure to oxygen or to carbonic acid. 



Carbonic acid being a natural product of the respiratory process, its 

 injurious effects upon animal life possess an interest greater than that 

 which attaches to those of other gases. The quantity of this gas in 

 ordinary air is about 4 parts in 10,000, g^^th part, or .04 per cent. 

 In air once breathed, the proportion rises to about 4 per cent, i. e., 

 2 J ^th part, or 400 parts in 10,000, a corresponding quantity of oxygen 

 being simultaneously removed. If this air be respired a second time, 

 a much smaller portion of carbonic acid is added to it, and still less at 

 each subsequent respiration. When air contains about 10 per cent., 

 or Jjjth its volume of carbonic acid, when one-half of the normal quan- 

 tity of oxygen has likewise disappeared, it is irrespirable, and fatal to 

 man. Warm-blooded animals have been found to die in an atmosphere 

 containing from 12 to 18 per cent. The symptoms of poisoning may 

 be said to begin with even a much smaller proportion in the air, even 

 with as little as one-third per cent. For a time no marked symptoms 

 are observed, but after a certain interval there occur headache, sense 

 of fulness in the temples and occiput, giddiness, muscular prostration, 

 oppression of the chest, difficult respiration, palpitation of the heart, 

 subjective, disturbed sensations, such as singing noises in the ears, and 

 flashes of light, faintness, delirium, then drowsiness, unconsciousness, 



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