Of the number of respirations in a given time. — The ordinary respirations should be counted without the individual being con scious of the observation ; otherwise they be come disturbed in number, and sometimes in character.
Out of 1897 cases, 1731 of them breathed from sixteen to twenty-four times, and nearly one-third of them twenty times a minute.
The mean relative velocity of the breatking and the pulse is about one respiration to four pulsations of the heart (twenty to eighty), and the variation in health in the number of respirations is from sixteen to twenty-four, and of the pulse from sixty-four to eighty eight per minute.
From TABLE I I, phthisis pulmonalis in creases the velocity of the breathing move ments from twenty (the healthy mean) to twenty-eight, and cases are numerous up to thirty-six respirations per minute.
A sudden change in atmospheric pressure affects the number of breathing movements in a given time. We found the following limited but sudden increase of atmospheric pressure increase them as follows. In South Hetton coal-mine in the county of Durham, — Depth of the mine 1488 feet.
The additional pressure of_the of an atmosphere increased the ordinary breathing from one to three times per minute.
This difference was purely the effect of pressure, and not that of fatigue or mental emotion. It, might only be temporary. Aeronauts inform us that diminished pres sure increases the number or respirations ; but with them there is this difference, that with diminished pressure there is a sensation of a want of air. When the barometer is low
we feel lassitude, and call the "day heavy," when in truth the air is lighter, and we ourselves are heavier ; when the barometer is high, we generally experience an indescribable sensation of pleasure—the vital energies seem doubled. With a sudden and considerable fall of the barometer there is a transient plethora. The blood-vessels become distended, owing to which, together with certain hygrometric changes in the air, we feel listless, and the least exertion produces perspiration. Du hamel observed that, in the month of De cember, 1747, the barometer in less than two days fell in., producing a change of pressure on the body of a man, of 14001bs. ; this he ob serves was accompanied with many sudden deaths. It is evident that with an increased pressure we get more air into the lungs with a given mobility; for, cceteris paribus, air, with the barometer at 30 in. must be more dense than the same air with the barometer at 29 in. In the mine in question, we experienced a sensa tion of lightness and vigour. The number of respirations are always increased when there is a preternatural increase in the temperature of the body.