[2]. Respiratio. Respiration is immediately caused by the sensorial power of sensation in consequence of the baneful want of vital air; and not from the accumulation of blood in the lungs, as that might be carried on by inhaling azote alone, without the oxygenous part of the atmosphere. The action of respiration is thus similar to that of swallowing our food to appease the pain of hunger; but the lungs being surrounded with air, their proper pabulum, no intermediate voluntary exertions are required, as in hunger, to obtain and prepare the wanted material.
Respiration is similar to slow combustion; the oxygenous part of the atmosphere is received through the moist membranes, which line the air-cells of the lungs, and uniting with the inflammable part of the blood generates an acid, probably the phosphoric acid; a portion of carbonic acid is likewise produced in this process; as appears by repeatedly breathing over lime-water, which then becomes turbid. See Botanic Garden, P. I. Canto I. l. 401. note.
[3]. Sternutatio. Sneezing consists of muscular actions produced by the sensorial faculty of sensation; and is an effort to dislodge, by means of air forcibly impelled through the nostrils, some material; which stimulates the membrane, which lines them, into too great action, and might thence injure the sense of smell which is diffused on it.
In this operation the too great action of the vessels of the membrane of the nostrils is the remote cause; the sensation thence induced is the proximate cause; and the muscular actions are the proximate effect.
This action of sneezing frequently precedes common respiration in new-born children, but I believe not always; as like the latter it cannot have been previously acquired in the uterus.
It is produced in some people by sudden light, as by looking up at the sky in a morning, when they come out of a gloomy bed-chamber. It then becomes an associate action, and belongs to Class [IV. 1. 2. 2].
M. M. When it is exerted to excess it may be cured by snuffing starch up the nostrils. See Class [I. 1. 2. 13].
[4]. Anhelitus. Panting. The quick and laborious breathing of running people, who are not accustomed to violent exercise, is occasioned by the too great conflux of blood to the lungs. As the sanguiferous system, as well as the absorbent system, is furnished in many parts of its course with valves, which in general prevent the retrograde movement of their contained fluids; and as all these vessels, in some part of their course, lie in contact with the muscles, which are brought into action in running, it follows that the blood must be accelerated by the intermitted swelling of the bellies of the muscles moving over them.
The difficulty of breathing, with which, very fat people are immediately affected on exercise, is owing to the pressure of the accumulated fat on the veins, arteries, and lymphatics; and which, by distending the skin, occasions it to act as a tight bandage on the whole surface of the body. Hence when the muscles are excited into quicker action, the progress of the blood in the veins, and of the lymph and chyle in the absorbent system, is urged on with much greater force, as under an artificial bandage on a limb, explained in Art. [IV. 2. 10]. and in Sect. XXXIII. 3. 2. Hence the circulation is instantly quickened to a great degree, and the difficulty of breathing is the consequence of a more rapid circulation through the lungs. The increased secretion of the perspirable matter is another consequence of this rapid circulation; fat people, when at rest, are believed to perspire less than others, which may be gathered from their generally having more liquid stools, more and paler urine, and to their frequently taking less food than many thin people; and lastly, from the perspiration of fat people being generally more inodorous than that of lean ones; but when corpulent people are put in motion, the sweat stands in drops on their skins, and they "lard the ground" as they run. The increase of heat of corpulent people on exercise, is another consequence of their more rapid circulation, and greater secretion. See Class [I. 2. 3. 17].
Other causes of difficult or quick respiration will be treated of under Asthma, Pertussis, Peripneumony, Tonsillitis.