Since a man takes into his lungs 480 cubic inches of air per minute, in walking four miles an hour he draws in 2400 cubic inches, and if six miles 3260 cubic inches a minute.[289]
[289] Parkes.
Dr Smith estimated the amount of carbonic anhydride evolved under differing conditions, and found that—
| Carbonic acid exhaled per minute in grains. | |
| During sleep | 4·99 |
| Lying down, and almost asleep (average of three observations) | 5·91 |
| Walking at the rate of 2 miles an hour | 18·10 |
| Walking at the rate of 3 miles an hour | 25·83 |
| Working at the treadmill, ascending at the rate of 26·65 feet per minute (average of three observations) | 44·97 |
The relative amounts of carbonic anhydride eliminated from the lungs during periods of rest and exercise have also been investigated by Pettenkofer and Voit. The following table, which gives the results of their experiments, also records the quantities of oxygen absorbed, and of water and urea excreted at the same time:—
| Absorption of Oxygen in Grammes. | Elimination in Grammes of— | |||
| Carbonic Acid. | Water. | Urea. | ||
| Rest-day. | 708·9 | 911·5 | 828·0 | 37·2 |
| Work-day. | 954·5 | 1284·2 | 2042·1 | 37·0 |
| Excess on work-day (with exception of urea) | 246·6 | 372·7 | 1214·1 | 0·2 |
If the quantities in the above table be converted into ounces it will be found that nearly 83⁄4 oz. more oxygen were absorbed and 13 oz. more of carbonic anhydride eliminated by the lungs during a work-day than during a rest-day.[290] It must be stated that during the work-day an interval of rest was taken, and that the labour was by no means excessive.
[290] Parkes.
Hirn and Speck appear to have conclusively proved that the formation of the carbonic anhydride occurs in the muscles, and that it is rapidly carried off from them. In short, this latter result seems essential for the development of muscular energy. At any rate it is found that if the respiratory movements be in any way interfered with during exercise, and the elimination of carbonic anhydride in any degree checked, the muscular power rapidly diminishes.
An examination of Pettenkofer and Voit’s table shows that exercise gives rise to the escape of a large amount of water from the body, and to a slightly diminished quantity of urea.