And as too gross, so too rare an Air is unfit for Respiration. Not to mention the forced Rarefactions made by the Air-Pump, in [the following Note]; it is found, that even the extraordinary natural Rarefactions, upon the tops of very high Hills, much affect Respiration. An Ecclesiastical Person, who had visited the high Mountains of Armenia, (on which some fancy the Ark rested) told Mr. Boyl, that whilst he was on the upper part of them, he was forced to fetch his Breath oftner than he was wont. And taking notice of it when he came down, the People told him, that it was what happen’d to them when they were so high above the Plane, and that it was a common Observation among them. The like Observation the same Ecclesiastick made upon the top of a Mountain in the Cevennes. So a learned Traveller, and curious Person, on one of the highest Ridges of the Pyrenees, call’d Pic de Midi, found the Air not so fit for Respiration, as the common Air, but he and his Company were fain to breath shorter and oftner than in the lower Air. Vid. Phil. Transact. No. 63, or Lowthorp’s Abridg. Vol. 2. p. 226.
Such another Relation the learned Joseph Acosta gives of himself and his Company, that, when they passed the high Mountains of Peru, which they call Periacaca, (to which he saith, the Alps themselves seemed to them but as ordinary Houses, in regard of high Towers,) He and his Companions were surprized with such extreme Pangs of Straining and Vomiting, (not without casting up of Blood too,) and with so violent a Distemper, that he concludes he should undoubtedly have died; but that this lasted not above three or four Hours, before they came into a more convenient and natural Temperature of the Air. All which he concludes proceeded from the too great Subtilty and Delicacy of the Air, which is not proportionable to humane Respiration, which requires a more gross and temperate Air, Vid. Boyl, ubi supra.
Thus it appears, that an Air too Subtile, Rare and Light, is unfit for Respiration: But the Cause is not the Subtilty or too great Delicacy, as Mr. Boyl thinks, but the too great Lightness thereof, which renders it unable to be a Counterbalance, or an Antagonist to the Heart, and all the Muscles ministring to Respiration, and the Diastole of the Heart. Of which see [Book 4. Chap. 7. Note 1.]
And as our Inability to live in too rare and light an Air may discourage those vain Attempts of Flying and Whimsies of passing to the Moon, &c. so our being able to bear an heavier State of the Air is an excellent Provision for Mens Occasions in Mines, and other great Depths of the Earth; and those other greater Pressures made upon the Air, in the Diving-Bell, when we descend into great Depths of the Waters.
[d] That the Inhabitants of the Air, (Birds and Insects,) need the Air as well as Man and other Animals, is manifest from their speedy dying in too feculent, or too much rarefied Air; of which see the preceding and following [Note (f).] But yet Birds and Insects (some Birds at least) can live in a rarer Air than Man. Thus Eagles, Kites, Herons, and divers other Birds, that delight in high Flights, are not affected with the Rarity of the Medium, as those Persons were in [the preceding Note]. So Insects bear the Air-Pump long, as in the following [Note (f).]
[e] Creatures inhabiting the Waters need the Air, as well as other Animals, yea, and fresh Air too. The Hydrocanthari of all Sorts, the Nymphæ of Gnats, and many other Water-Insects, have a singular Faculty, and an admirable Apparatus, to raise their back Parts to the top of the Waters, and take in fresh Air. It is pretty to see, for Instance, the Hydrocanthari come and thrust their Tails out of the Water, and take in a Bubble of Air, at the tip of their Vaginæ and Tails, and then nimbly carry it down with them into the Waters; and, when that is spent, or fouled, to ascend again and recruit it.
So Fishes also are well known to use Respiration, by passing the Water through their Mouths and Gills. But Carps will live out of the Water, only in the Air; as is manifest by the Experiment of their way of Fatting them in Holland, and which hath been practised herein England, viz. they hang them up in a Cellar, or some cool Place, in wet Moss in a small Net, with their Heads out, and feed them with white Bread soaked in Milk for many Days. This was told me by a Person very curious, and of great Honour and Eminence, whose Word (if I had leave to name him) no Body would question: And it being an Instance of the Respiration of Fishes very singular, and somewhat out of the way, I have for the Reader’s Diversion taken notice of it.
[f] By Experiments I made my self in the Air Pump, in September and October, 1704; I observed that Animals whose Hearts have two Ventricles, and no Foramen Ovale, as Birds, Dogs, Cats, Rats, Mice, &c. die in less than half a Minute counting from the very first Exsuction; especially in a small Receiver.
A Mole (which I suspected might have born more than other Quadrupeds) died in one Minute (without Recovery) in a large Receiver; and doubtless would hardly have survived half a Minute in a small Receiver. A Bat (although wounded) sustained the Pump two Minutes, and revived upon the re-admission of the Air. After that, he remained four Minutes and a half and revived. Lastly, After he had been five Minutes, he continued gasping for a time, and after twenty Minutes I re-admitted the Air, but the Bat never revived.
As for Insects: Wasps, Bats, Hornets, Grashoppers, and Lady-Cows seemed dead in appearance in two Minutes, but revived in the open Air in two or three Hours time, notwithstanding they had been in Vacuo twenty four Hours.