life, without which conftant discharge there could be no circulation, motion, or life in any body.

41. Accordingly the animal machine is compofed of three general diftinct principles; the firft is the folids, ferving to give ftrength, ftability and motion to the whole machine, and to the fluids contained therein; the fecond, is the internal fluids contained in the folids, namely, the blood, the principles whereof are elementary water, with a certain proportion of earth, oil, falt, fpirit, elementary fire, and air, diffolved therein. The third principle is an external, elaftic, heavy fluid, the air, containing and enveloping the whole fyftem of the animal folids, as within a fluid mould, matrix, or bandage.

42. In confequence of what has been remark'd, the whole system of the animal folids is to be confidered as an elaftic, vafcular, compreffible machine, fuftain'd between two oppofite antagonist powers, acting continually thereon, with variable forces, and contrary directions; one of which powers is the blood, &c. contained in the folids, ferving both to repair them, and to keep their spring duly distended from the axis outwards to the circumference of the veffels; the other antagonist power is the air, containing and strongly encompaffing the folids, which acting by its preffure and elafticity outwardly, and with a contrary direction thereupon, ferves to fupport the folids againft the diftending impetus of the contain'd fluids,, by compreffing and bending their spring inwards from the surface to the axis of the veffels. So that the whole fyftem of the folids may be properly confidered as a lever acted upon by two oppofite powers, namely, the internal contain'd fluids, the blood, and the external containing fluid, the air; when therefore the folids have their fpring and elasticity duly balanced and counterpoized, both outwardly and inwardly, by the contrary actions and preffures of the faid two antagonist powers, all the movements and functions both of body and mind will be regularly executed; and in fuch a state only confifts the idea of perfect health. But when any one of the said two powers prevails, and gains the afcendent over the other, whereby the fpring and moving force of the folids, either of the whole body, or any of its parts becomes too much augmented or diminished, the balance of health, with all the movements and operations of the animal machine, will be difturbed and difconcerted proportionally. And altho all difeafes proceed from this one caufe alone, of too great, or too fmall a moving force in the folids, yet will they appear greatly diverfified in their phenomena, fymptoms, and degrees, according as the change made in the moving force is greater or lefs, and as it affects the folids of the whole body, or fome of its organs only.

43. As the conftriction and relaxation of the folids, with the properties and qualitics of the fluids, and confequently both health and difeafes, depend in a manner abfolutely upon the preffure, and other qualities of the air, had we a power to change the preffure, and other properties of the air, at all times and places, and cause them to operate upon the body in any degrees requir'd, we should then be furnifhed with the true natural method of effecting this great intention as to the conftriction and relaxation of the folids, which we might render more or lefs denfe, compact and elastic, and thereby augment or diminish their moving force proportionally (No. 26); how this may be effected will be fhewn hereafter.

44. The

44. The organization and mechanism of animal bodies neceffarily require that the system of the folids be duly counterbalanced, and have their fpring equally comprefs'd and diftended by the preffure of fluids, acting both inwardly and outwardly, with contrary directions, thereon. As to the first cafe, that the folids require to have their fpring bent outwardly by the preffure of their contain'd fluids, the blood, is manifeft from what happens upon any great evacuation or hemorrhage, whereby, if the quantity of the fluids be by any cause whatever fo much diminished, that the veffels, especially the aorta, or great artery, in its fyftole and state of contraction, can't fufficiently comprefs the blood, in that cafe a total ceffation of all motion and life immediately enfue; fecondly, that it is as neceflary that the folids have their spring comprefs'd and bent inwards, by an external elaftic fluid, as the air, acting outwardly thereon, is equally evident from what would follow fuppofing the air immediately encompaffing a perfon's body to be either annihilated, or kept from acting thereon, the confequence whereof would be, that the folids, for want of air to fupport them outwardly, would be over, powered, and give way to the diftending force of the contain'd rarefying fluids, whereupon the person that very moment would be deprived of all motion, fenfation and life, as effectually as if all his vital organs the heart, brain, lungs, or his whole mass of blood had been annihilated. 45. From the foregoing obfervations, and confidering that it is impoffible for any animal to be produced, live, or grow, without air, as being the great univerfal principle of all degrees of life, it follows that the external air encompaffing our body, with what is inclosed in its cavities, and within the interftices of the fluids, is to be confidered as an effential part in the compofition of all animal bodies, as much, and for the very fame reason, as the blood itself, one fluid being as abfolutely and conftantly neceffary as the other, to the very being, motion, life and exercise of all the faculties both of body and mind. Neither can this pofition be invalidated by faying, that in confequence of this new doctrine, if the air is an effential part of our bodies, the fame becomes chang'd every time we move out of one place into another, inasmuch as this objection is of equal force as to the folids and blood, both which are in a perpetual fluxion and change, neither the fyftem of the folids nor fluids being the fame to day, as yesterday, or to morrow, and much less what they will be at the end of a month or year, when it is probable not one particle of the old stock of blood will be remaining. the blood by which the folids are repaired being fucceffively chang'd and supply'd by the food we take in daily at different times and places, as much as the air which forms the external part of our bodies requires to be continually and fucceffively chang'd.

46. Having fhewn the air to be an effential part of the animal machine, as much as the blood, let us next take a general view of the terreftrial atmosphere, with the changes it is fubject to, by which we shall better conceive the changes animals muft fuffer by being continually and neceffarily immerg'd therein, and communicating therewith.

47. The atmosphere encompaffing the earth is a general chaos and receptacle, between which and the earth (which may be confider'd as a body under digeftion by the action both of the folar and fubterraneous fire) there is a conftant reciprocal circulation of vapours, exhaling from

all

all bodies animal, vegetable and foffil; and as the air is more or less impregnated therewith, it operates with very different qualities and forces, and produces very different and contrary effects in animal bodies.

48. The atmofphere being ever impregnated with ethereal fire and light, and the exhalations of all bodies, ferves as the general laboratory of nature for fubliming, preparing, and difpenfing that univerfal vegetative, vivifying fpirit, to render the earth prolific; and the atmosphere, thus conftituted, ferves alfo as a univerfal menftruum, by the continual ofcillatory motion whereof the parts of all bodies are kept in a perpetual agitation and ferment, and by which the feveral progreffive ftates refpecting the generation, accretion, and corruption of all bodies, animate and inanimate, are brought about.

49. The atmosphere, being a fluid eminently endow'd with elasticity and gravity, is subject to a state of ebbing and flowing alternately, by the mutual gravitation between it and the fun and moon, and that at the fame time, and by the fame causes, as the tides are produced in the ocean; by which alternate ebbing and flowing of the atmosphere twice each day, and twice each month with an accumulated force (at the fame time with the fpring tides) the bodies of animals immerg'd therein must be fubject to the like periodical changes alfo, as is evident in the cafes of lunatics, epileptics, maniacs, &c. all animals being fubject more or less to some extraordinary menftrual crifis and evacuation, &c.

50. Befides the alterations produced in the atmosphere by the joynt attraction of the fun and moon, its gravity is much alter'd by the winds, as alfo by heat, cold, humidity, &c. in fuch wife that the air in the fame place fhall often differ one tenth part in denfity and weight, in which cafe the difference of its preffure upon a perfon of an ordinary fize will be equal to about 40000 pounds weight, which great variety of preffure must produce great difference in the ftricture and tenfion of the folids, and expanfion of the fluids in the human body; in cafe of a greater weight the fibres become more strongly braced, and the fluids condens'd.

51. Moreover heat and cold being two powerful general inftruments of nature, and as the atmosphere admits of great variations as to both thefe qualities, and that often fuddenly from one extream to another, upon thefe accounts it becomes capable of producing very great and fudden alterations in the animal folids and fluids, which fudden tranflations from one extream to the other are generally the productive cause of moft of the capital epidemical diftempers.

52. The atmosphere being alfo fubject to fréquent great changes as to the degrees of humidity and drynefs, upon this account it is capable of producing very great alterations in the animal folids, as to their conftriction and relaxation, as alfo in the fluids, as to their rarefaction and condenfation.

53. Moreover as the atmosphere becomes agitated by winds, tempefts, earthquakes, thunder, lightning, fubterraneous fires, exhalations, &c. from all thefe caufes it becomes the inftrument of producing many and great morbid affections in animal bodies.

54. From the idea which the foregoing obfervations give us of the animal body, as being an elaftic, vafcular, compreffible machine, composed of contractile veffels, filled with fluids fubject to great de

grees

grees of rarifaction and condenfation, and encompaffed every way by the air outwardly, as within a fluid, elaftic mould or bandage, we readily learn from thence, that as the outer tabernacle and part of our bodies confifts of air, and as this particular atmosphere or shell of air immediately enveloping the body of every animal is neceffarily fubject to the like alterations as the general terrestrial atmosphere, as communicating therewith, we need no longer wonder, nor want a reason why our bodies, being immerg'd continually in this turbulent, restless element, the air, fubject to fuch frequent, fudden, great mutations from fo many caufes, fhould at the fame time participate and be affected with the like changes, either for the better or worse, in fuch wife that every the leaft alteration in the gravity, heat, cold, elafticity, preffure, moisture, drynefs, motion, vapours, &c. of the atmosphere, produces a proportional change in the body, as in a barometer, thermometer, and hygrometer, by which perpetual changes of the air, our bodies are kept In a continual variable state of motion, the folids being always either contracting, or dilating, and the fluids expanding and condenfing, heating or cooling, &c.

55. All phyficians, antient and modern, allow the air, and its different conftitutions, to be the great catholic remedy and inftrument of nature, by which all that relates to the prefervation of health, with the production and cure of diseases, is in a manner wholly govern'd and regulated; of which there needs no proof, it being a truth obvious to every common obferver, as well as the philofopher and phyfician, that certain diseases keep time exactly as to their appearance, paroxyfms, remiffions, intermiffions, periods, and difappearance, &c. revolving periodically with the seasons of the year; and thus we find the spring, fummer, autumn, and winter, each productive of fuch diseases as may be naturally accounted for, from the predominant conftitutions of the air at those seasons, as to its greater or lefs gravity, elafticity, heat, cold, moisture, drynefs, motion, exhalations, &c. and the diftempers which reign about the intermediate feasons, are the very fame specific difeafes, only differing in degrees, with thofe that prevail about the four cardinal seasons, and from which they derive their diftinguishing fymptoms; fo that we may juftly fay with Hippocrates (Febrium omni

Aer faber et medicus eft,) "That the feveral feasons of the year, "or the feveral conftitutions and qualities of the air at those seasons, are "the true parent and general productive cause both of health and dif" eases."

56. Phyfic is in nothing so defective as in this one great point, of all the moft neceffary, relating to the knowledge and phyfiology of the air, and in the manner how to change and apply its mechanical properties and qualities, and cause them to operate in fuch degrees and combinations, as fuits beft with the conftitutional ftructure and indications of the body, and organs of refpiration; and had the fame pains and charge been bestowed in difcovering, by fuch mechanical experimental methods, the mighty alterations that may be produced by applying the properties of the air, thus duly regulated, to the human body, with the phyfiology of its effects, all faithfully register'd, with a view to the improvement of phyfic, as hath been vainly spent int fearch of its principles and properties in a philofophical, metaphyfical

way,

way, we fhould long ago have had a more perfect knowledge of the air, and been made fenfible, from experience, of its univerfal efficacy in preserving health, and curing diseases. This appears to be a neglect the moft amazing and aftonishing poffible, to obferve that the philofophers, mathematicians, chemifts, the profeffors of botany, agriculture, gardening, &c. have all given more attention to the influence and effects of the air upon the fubjects of their feveral arts, than the phyficians, who are infinitely more interested therein, and ought of all perfons to be the most ready to promote and encourage fuch experimental enquiries into a fubject hitherto unattempted, and which promises infinite good to mankind.

57. Nature, univerfal reason, and the experience of all ages, have established the following maxims; firft, that the air, and its different conftitutions in the feveral feasons of the year, is the principal caufe both of health and difeafes, as its properties are well or ill proportioned to the conftitutional ftructure of the body, and organs of relpiration; Secondly, No disease can be cured, unless its caufe is taken away, or made to operate in a contrary manner; or, which comes to the same thing, difeafes are only to be cured by caufes contrary to those by which they were produced. From whence follows this third aphorifm, That all diseases, produced by the properties and qualities of the air, acting with a force relatively difproportionate and improper either for the body or refpiring organs (to which most diseases, and thofe of the capital epidemic kind, are owing) admit of no poffible cure by any other means but by changing those very properties and qualities of the air, by which the difeafes are produced and fupported, and caufing them to operate with contrary degrees and forces. Thus, for example, if a perfon becomes diseased by the air's acting with a degree of gravity, relatively difproportionate, and improper either for his body or refpiring organs, or both, it neceffarily follows, that if the air could, be chang'd, and made to operate with a weight and preffure relatively proper, and well proportion'd to his body and organs of respiration, he will thereby receive a certain, safe, perfect cure; which would be impoffible to effect by any other means. And the fame reafoning holds equally true as to all the other properties and qualities of the air, namely, its elafticity, heat, cold, moisture, drynefs, motion, reft, exhalations, &c. any of which, when they become the cause of diseases, by their acting with forces relatively improper to the body, or refpiring organs, in all fuch cafes thefe very properties of the air, which are the cause of the disease, must neceffarily be chang'd, and made to operate with forces relatively proper, upon which alone the cure of all diseases produced by the different conftitutions of the air abfolutely depends.

58. As the new methods described in this treatise for preferving health, and curing difeafes, are grounded on the invincible demonftration and argument of the foregoing article, hence is deduced and propofed the following great and most useful phyfical problem :

PROBLEM.

59. To find a method whereby the air, that univerfal principle of life, health, and diseases, may have all its properties and qualities of gravity, elasticity, preffure, heat, cold, humidity, drynefs, motion,

effluvia,