Tench (Provencal and Humboldt) -370 = 1 Frog (Marchand) 1.342 — Man ( Sch aril ng) 4.506= 12 Pigeon (Boussingault) 42.317=114 Quantity of oxygen absorbed at the lungs. — That a quantity of oxygen gas greater than what is necessary to form the carbonic acid gas in the expired air disappears from the inspired air, is now placed beyond a doubt. The quantity of oxygen gas that disappears from the inspired air by absorption at the lungs is not uniform, even in the same indi vidual, for any length of time, and the varia tions in this respect are in all probability determined by the same circumstances which affect the evolution of carbonic acid gas, the absorption of oxygen being increased when the evolution of carbonic acid is increased, and vice versa. Dalton calculated that he himself respired 500 cubic feet of atmospheric air, containing 105 cubic feet of oxygen, in the 24 hours, and that 25 cubic feet of the oxygen, weighing 15,120 grains, or 2.6 lbs. Troy, were absorbed at the lungs. Valentin and Brunner, in 34 analyses of the air expired by 3 individuals between 33 and 54 years of age, found the average quantity of oxygen gas to be 16.033, the maximum 17.216, and the minimum 14.968 parts by volume in the 100 parts of the expired air. Proceeding on these results of Valentin and Brunner, we may esti mate the average amount of oxygen that dis appears from the inspired air at 4.78 by volume in the 100 parts.
While the experiments upon the relation of the quantity' of oxygen absorbed at the lungs to that of the carbonic acid gas evolved, made by Lavoisier, Sir II. Davy, and Dalton on the human species, by Legallois, Dulong, Despretz, and Dr.W. F. Edwards upon the warm-blooded animals, by Treviranns upon several cold blooded animals, and by Marchand upon frogs, all concur in making the oxygen absorbed greater than what is necessary to form the carbonic acid exhaled, they exhibit very con siderable differences in the relative propor tions of the absorbed oxygen and exhaled carbonic acid gas. In some of these experi ments, the oxygen absorbed was considerably greater than what is necessary to form the carbonic acid gas. In Marchand's experiments on frogs subjected to prolonged fasting, the relation of the oxygen absorbed to the car bonic acid evolved-constantly increased, until it amounted to between 410-130 : 100.* Valentin and Brunner, in their experiments on the human species, found the relative proportions of these two gases to approximate so closely to their diffusive volumes, that they believed the small difference between the results obtained by actual experiment and when calculated according to the law of the diffusion of gas, discovered by Graham, arose from incidental circumstances ; and as the diffusive volume of carbonic acid gas is to oxygen gas as 1 : P1742, they maintain that for every 1 volume of carbonic 'acid gas evolved from the blood, 1.1742 voluine of oxygen gas is aborbed. Valentin has given the following table, constructed from facts furnished by Quetelet, Andra], and Gavarret, conjoined with calculations of the relative quantities of oxygen absorbed and carbonic acid evolved according to the law of the diffiision of gases, to exhibit the weight of the body, the quantity of carbon consumed in respiration, and the probable amount of oxy gen absorbed and carbon consumed .at the different periods of life in the human spe cies t : — Prom the details given above we may ob tain information of considerable importancn on several practical points. A consideratioe of the large quantity of atmospheric air pass ing through the lungs in the 24 hours, and the extent to which it is vitiated by this in the removal of a part of its oxygen and the sub stitution of a quantity of carbonic acid gas, will assist us in acquiring definite information regarding the amount of ventilation required in the apartments of our private and public buildings. It appears that between 400 and
600 cubic feet of atmospheric air pass daily through the lungs of an adult enjoying mode rate exercise; and the estimate of Dalton, that 23 cubic feet of oxygen gas are, during the same period, aborbed at the lungs, is pro bably not far from the average. The same air cannot be breathed twice without in ducing prejudicial effects, so that at each in spiration entirely fresh air ought to be sup plied, or the air already breathed ought to be so largely diluted by the admission of fresh air as to be restored very nearly to its original composition. Leblanc informs us, that in the Chamber of Deputies in Paris, where the system of ventilation is based upon the prin ciple of furnishing to each individual from 10 to 20 metres cubes (353'316 to 706.331 English cubic feet) of air per hour, the air issuing from the apartment contained from 2 to 4 of carbonic acid gas in the 1000 parts by weight.* The quantity of pure atmospheric air here furnished is probably somewhat insuf ficient, if the presence of 1 part of carbonic acid in the 100 of atmospheric air be likely to act prejudicially when breathed for a long time continuously. From Dr. Snow's experiments, it appears that the prejudicial effects of breath ing air deteriorated by respiration, is not en tirely due to the presence of an incrcased quantity of carbonic acid gas, but also in a considerable degree to the diminution of the oxygen. He found that birds and mammalia introduced into an atmosphere containing only from 16 to 101 per cent. of oxygen soon died, though means were adopted for remov ing the carbonic acid formed by respiration.* The increase of the carbonic acid gas to 12 and 20 per cent., provided the oxygen gas was still as high as 21 per cent., did not appear to enfeeble the vital actions more rapidly than the diminution of the oxygen to the extent above stated. Any notable diminution in the percentage of the oxygen gas, even when no carbonic acid is present, cannot take place without danger to the warm-blooded ani mals t, and the carbonic acid in the air respired acts more or less energetically in destroying life, as it has been produced at the expense of the oxygen of the air, or been added to it already formed.t The experiments on the effects of dimi nished frequency of the respirations in re ducing the aniount of carbonic acid gas evolved from the blood in a given time, are in accordance with observations made on the state of the blood and its circulation, when this condition has been induced in man or in the other warm-blooded animals. A diminu tion in the frequency of the respiratory move ments occasionally occurs to a notable extent in the course of sorne diseases. and this de serves the careful attention of the practitioner, as it is likely' to lead to very serious conse quences.* The greater length of time that the respi rations may be suspended without inducing insensibility', when a deep expiration followed by a deep inspiration has immediately pre ceded, affords additional illustration of the procedure which a person ought to adopt when he wishes to suspend, during diving, &c., the respirations for the longest period consistent with his safety. The manner and the order in which the vital actions are brought to a stand when the chemical changes between the blood and the atmospheric air are arrested, have been discussed under the article AsPHYxfa.t Experiments have been made by Nysten*, by Mr. Macgregor-1-, Dr. MalcolmI, and by Hannover§, upon the quantity of carbonic acid gas evolved from the lungs in some diseases, but these have not yet been carried sufficiently far to furnish us with any practical or theoretical conclusions of importance.