Andral and Gavarret have drawn the fol lowing conclusions from their experiments: 1. The quantity of carbonic acid gas ex haled from the lungs, in a given time, varies according to the age, the sex, and the consti tution of individuals ; and that, independently of the weight of the body. 2. At all periods of life extending from 8 years (the earliest age subjected to experiments) up to the most advanced old age, the quantity of carbonic acid evolved from the lungs differs in the two sexes, but, cceferis paribus, the male exhales a considerably larger quantity than the female. This difference is most marked between 16 and 40 years of age, during which period the male generally evolves nearly twice as much as the female. 3, In the male, the quantity of carbonic acid exhaled goes on conti nually increasing from 8 to 30 years of age, and becomes suddenly very great at the age of puberty. After 30 years of age it begins to decrease, and this so much the more de cidedly as the person approaches extreme old age, at which period it may be reduced to the quantity evolved at 10 years of age. 4. In the female also, the evolution of carbonic acid increases from infancy up to puberty ; but at this period, contrary to what takes place in the male, it remains stationary, so long as the menstrual secretion continues natural. At the time the menses cease, the evolution of carbonic acid gas from the lungs undergoes a marked augmentation ; but after a while it begins to decrease, as in the male, and pro portionally as she advances towards old age. 5. In the female, during gestation, the exhala tion of carbonic acid from the lungs equals the quantity exhaled at the period of the ces sation of the menses. 6. In both sexes, and at all ages, the quantity of carbonic acid is so much the greater, as the constitution is stronaer and the muscular force more deve loped°.
The most important of the data upon which the above inferences are founded are as follows :— In the male child, in his progress upwards from his 8th to his 15th years, the quantity of carbon given off by the lunas was raised, on an average, from 5 grammes°(77.165 Troy grains) to 8.7 grammes (134.267 Troy grains) per hour ; while in the female at the same age it was on an average 1 gramme (15.433 Troy grains) less per hour. In the male at 16 years of age, or soon after puberty, it sud denly increased to 157.416 Troy grains, on an average, per hour ; and from this period up to the age of 20 and 25 it gradually increased, on an average, to 172'849 and 191.369 Troy grains per hour. At this point it remained nearly stationary until about 40 years of age, when it began to undergo a slight diminution, but not to any great extent until 60 years of age. Adult females, who menstruated regu larly, lost, on an average, 98.771 grains only of carbon, by the lungs, in an hour,—a quan tity not greater than that lost by girls. Take the average loss of carbon, by the lungs, in the male at 174.392 grains between the ages of 15 and 20 years, it is, on an average,1.55.873 grains between 40 and 60 years; and 141.953 grains between 60 and 80 years. In the fe male, at the period of the cessation of the menses, the loss of carbon is suddenly ele vated from an average of 98.771 to 129.637 grains per hour ; and a similar elevation, and nearly to the same extent, was observed in four females during pregnancy. In females between 50 and 60 years of age, the loss was 112.660 grains, and between 60 and 80 it was, on an average, 104.944 grains in an hour. In one female of 82 years, it was 92.595 grains, and in a male of 102, but remarkably hale for his years, it was 91.590 grains. In a male, aged 26, and remarkable for his muscular de velopment, the loss was as high as 217.105 grains, while in another male, aged 45, of mo derate height, but extremely feeble muscular development, it amounted on an average only to 132.723 grains an hour.* Scharling, after allowing seven hours for sleep to an adult, and nine for a child, calculates, from his experiments on six individuals, the amount of tbe loss of carbon from the body as follows :— In these experiments of Scharling the evo lution of carbonic acid by the skin was in cluded, with that evolved through the mouth and nostrils ; and the quantity is calculated for the twenty-four hours. But in some sub
sequent experiments, by uniting the use of the mask used by Andral and Gavarret with the box, he has been enabled to ascertain the relative amount of the loss by these two dif ferent channels in an hour. In other respects, he has endeavoured to assimilate his experi ments, in regard to the hour of the day, &c., to those of Andral and Gavarret, and has given the following comparative view of the results :— Influence of the respiratory movenzents upon the evolution of carbonic acid from the lungs.—This point has been particularly ex amined by Vierordt in 171 experiments upon himself, and he has ascertained that the fre quency, extent, and duration of the respiratory movements have a marked effect, not only upon the relative proportion of the carbonic acid gas in the expired air, but also upon the absolute quantity evolved from the lungs in a given time. t We shall afterwards find, when we come to describe the theory of respiration, that the results obtained by Vierordt are of considerable importance in a theoretical point of view.
Frequency of the respiratory movements.— When the -number of respirations is less than usual, the percentage of the carbonic acid in the expired air is increased, while its absolute quantity is diminished ; on the other hand, when the respirations are more frequent than usual, the percentage of carbonic acid in the expired air is diminished, while its absolute quantity is increased. Vierordt endeavours to point out that the diminution in the per centage of the carbonic acid gas in the ex pired air when the respirations are more fre quent, probably bears a certain proportion to their frequency or length per minute, sup posing their bulk to be the same. The operation of this law, according to Vierordt, may be illustrated as follows. Let us take the average number of respirations in a state of rest as 12, and suppose these to be doubled or increased to 21, the relative percentage of carbonic acid will be dimi nished by 0-8 ; if the number of respirations be again doubled, or increased to 48, the carbonic acid will suffer a still further dimi nution of 0.4 per cent. ; and if the respira tion be again doubled, and increased to 96 per minute, the carbonic acid will suffer a farther reduction of 0.2 per cent. On the other hand, if the number of respirations be less than 12 (here taken as the normal number of respirations by Vierordt) by one half or reduced to 6 in the minute, the re lative percentage of carbonic acid will be in creased above what it is in the normal fre quency by 1.6. If the percentage of carbonic acid in the expired air be 4.1, when the re spirations are 12 in the minute, it will be 5.7 per cent. when the respirations are 6, and 2.7 per cent. when they are 96 in the minute. Proceeding upon the existence of this law, he supposes that if the respirations were increased from 96 to twice that number, or 192, the percentage of the expired air would suffer a farther reduction of only 0.1 per cent. ; in other words, it would be reduced from 2.7 to 2.6 per cent. This last ratio, viz. 2'6, he believes to be the smallest percentage of carbonic acid gas that the expired air can present. If Vierordt be correct in supposing that the percentage of carbonic acid in the expired air has a fixed arithmetical proportion to the frequency or length of the respiratory movements, we could, after determining the normal number of respirations, the bulk of air expired, and the percentage of carbonic acid gas, when the body is in a state of rest, be able to determine both the relative and the absolute quantity of carbonic acid gas in the expired air from the number of respirations alone, when these are either increased above, or diminished below the normal number, provided the bulk of each respiration continues equal. He has constructed the following table to illustrate the variations in the absolute quan tity of carbonic acid gas occasioned by altera tions in the frequency of the respiratory move ments. The normal number of respirations is supposed to be 12, the average bulk of each respiration to be 500 cubic centimetres (30.5 English cubic inches), and the percentage of carbonic acid to be 4.1.