Digestion. Seguin and Lavoisier **, in their experiments upon Seguin found that when he was in a state of repose and fasting he vitiated only 1210 cubic inches of oxygen gas in an hour, while, during digestion, this was raised to between 1800 and 1900 cubic inches. Spallanzani if observed that snails, after a redundant repast, exhaled considerably more carbonic acid gas than when fasting. Similar observations have been made upon insects by Sorg + and Newport :r., upon the Mammalia by Zimmermann §, and upon the human species by Scharling II, Valentirlf, and Vierordt. The most complete experiments on this point are those of Vierordt, performed on himself, the results of which are contained in the following tables. His dinner lasted from 30 minutes past 12 to 1 o'clock : — To ascertain that this increase in the quan tity of carbonic acid evolved from the lungs was really dependent upon digestion, and not upon any other cause, the experiment was repeated at the same period of the day when he had not dined, and had eaten nothing since his breakfast at 7 o'clock, and the following results were obtained : — Notwithstanding, therefore, that Prout failed to observe any decided increase in the quantity of carbonic acid gas throvvn off by the lungs during digestion, and that Mr. Coa thupe maintains from his experitnents that the carbonic acid in the expired air increases with increased abstinence from food, and that its maximum quantity is before breakfast and imme diately before dinner *, we must consider the evidence detailed above perfectly conclusive in proving that the quantity of carbonic acid evolved in respiration is considerably in creased after a full meal.
Fasting.— In describing the effects of di gestion upon the quantity of carbonic acid evolved from the lungs, we were led. to refer to the manner in which the opposite condition of the body, or that of fasting,' operates. That fasting diminishes the quantity of carbonic acid in the expired air is not only proved by the facts already mentioned, but also by the experiments of Scharling upon the human species, of Boussingault upon the turtle dove, and of Marchand upon frogs. The two last experimenters found that in very prolonged fasting the quantity of carbonic acid was greatly diminished.
Alcohol. — Dr. Prout states that alcohol, and all liquors containing it which he had tried, have the remarkable property of diminishing the quantity of carbonic acid gas in the expired air much more than any thing else he had made the subject of experiment, and its effects were most remarkable when taken on an empty stomach. Vierordt mentions, in confirmation of Prout's observations on this point, that in four experiments, after having taken from one half to a bottle of wine, the percentage of carbonic acid had fallen, a quarter of an hour after this, from 4.54 to 4.01, and it continued to exercise this effect from one to two hours.f A strong infusion of tea has, according to Prout, an effect similar to alcohol.
According to Dr. Fyfe, vvhen a person has taken rnercury or nitric acid for some time, the quantity of carbonic acid is diminished.
Conditions of the mind.—Prout found that anxiety and the depressing passions diminish the percentage of carbonic acid in the expired air ; and Vierordt, on two occasions, observed this effect, for a short time at least, from mental emotions, both of a joyful and of an opposite nature. Scharling remarked that in those persons who felt very anxious on being enclosed in the box used by him in his expe riments, the evolution of carbonic acid gas from the body was much diminished.
Exercise.— Front states that moderate ex ercise, as walking, seems always at first to increase the evolution of carbonic acid, but when continued it ceases to produce this effect, and when carried the length of fa tigue the quantity is diminished : that violent exercise appears to lessen the quantity from the first, or if any increase occurs, this is trifling and transitory ; and that, after violent exercise, the quantity is much lessened. In Prout's mode of experimenting, the percen tage of carbonic acid having been alone ascer tained, we have no certain means of judging of the changes in the absolute quantity of carbonic acid evolved, as the increase in the number of respirations and in the bulk of the air respired, occasioned by exercise, was not taken into account. In the experiments of Seguin and Lavoisier already referred to, it was found that Seguin, when fasting and at rest, vitiated in the hour 1210 cubic inches of oxygen gas: by an amount of exercise equal to raising 15 lbs. to a height of 613 feet, this was increased to 3200 while still fasting, and to 4600 cubic inches, while digesting food. In Scharling,'s experiments, where the absolute quantity of carbonic acid gas evolved from the whole body in a given time was ascertained, the quantity of carbonic acid was increased during exercise. Vierordt ascertained that during the increased respiratory movements occasioned by moderate exercise, that on an average there was an increase per minute of 18.978 English cubic inches in the expired air, containing an increase of 1.197 cubic inch of carbonic acid gas, giving, however, an in crease of carbonic acid gas in the expired air of only 0.140 per cent. There can, therefore, be no doubt that the evolution of carbonic acid gas from the lungs can be considerably increased by exercise.* Temperature.— The effects of low tempera tures upon the respiratory process, as ascer tained by Spallanzani and Treviranus upon snails and insects, by Marchand upon frogs, and by different observers upon the hyber nating warm-blooded animals, are not appli cable to the human species, since the re duction of the temperature to a certain extent induces in these animals a lethargic condition, well known under the term hy bernation, altogether different from its effects upon man and the other warni-blooded animals. Seguin and Lavoisier state that in their ex periments, Seguin, in a temperature of 82° Fahr., fa.sting and at rest, consumed, in the space of an hour, 1210 French cubic inches of oxygen ; while in a temperature of 57° Fahr., he consumed in the same time 1344 cubic inches.* Crawford -I-, in experiments upon guinea-pigs, ascertained that these animals, in a given time, deteriorate a greater quantity of air in a cold than in a warm medium. The most perfect experiments on this point, at least on the human species, are those of Vierordt.$ He ascertained, by numerous trials upon himself, the effects of temperature from 37°,4 to 75°-2 Fahr. From a table, showing the results obtained, both upon the respiration and the pulse, at each degree of the centigrade thermometer within the limits mentioned, he has constructed the following shorter table, where the first table is arranged in two divisions,—the one containing the aver age of all the lower, and the other the average of all the higher temperatures. In the follow. ing table the measures of the expired air and carbonic acid have been reduced to English cubic inches.