practice of phyfic, as the second does, in a great measure, that of furgery,

26. As to the manner and mechanism whereby the animal folids have their force augmented or diminished, or how their constriction and relaxation are effected, of this we can form no other rational idea, than that the more the original stamina or machinula of the folids approach each other, or are brought into clofer union and contact, the attraction of cohefion between them being thereby increas'd, their elafticity, Spring, and moving force become augmented proportionally, which is what is understood by the conftriction of the folids; and the more their compounding fibrilla are fet afunder, whereby their mutual cohefion. is leffen'd, their elafticity and force are diminish'd in proportion; which is what is meant by their relaxation. This reasoning we have confirm'd from experience, from obferving, that our bodies are more ftrong and active, the more compact, denfe, and lefs their dimensions are, which we find to be the ftate of our bodies in the winter, when they are every way of lefs dimenfions, than in the fummer; or after ufing the cold and hot bath; or when the atmosphere changes from heavy to light, from cold to hot, from dry to moift, &c.

27. It is impoffible to conceive the idea of any difeafe but what must proceed either from too great conftriction or relaxation of the nervous mufcular folids, either of the whole body, or fome of its parts; and in all diseases, there are certain infeparable fymptoms, which clearly indicate the folids either of the whole body, or fome of its organs, to be in a state of too great conftriction or relaxation; for as all the phenomena, and alterations of the body, are only effects refulting from, and ever proportion'd to the moving force of the folids, (No. 16, 17, 20, 21, 22.) which is always in proportion to the degrees of their conftriction or relaxation; and as all the internal motions and alterations are ever accompany'd with, and difcoverable only by certain external, obvious, fenfible qualities, which come under the cognizance of our fenfes, confequently it is from these external, fenfible, evident qualities only, that we can form a true judgment of the state of the folids of the body and its parts, as to the degrees of their conflriction and relaxation, and of the proper indications for reftoring the difaffected organs.

28. However the animal folids can't receive from human art a greater degree of ftrength and force than what they received at their first formation (No 14,) yet nevertheless the fame may occafionally, from the influence of extrinfic causes, and mostly from errors in the non-naturals, have their moving force rais'd or lower'd, beyond what is confident with longevity, and a continued state of health; and in this refpect only it is that they come properly under the direction of the phyfician, whofe principal business is to make a right judgment as to the degrees of the constriction and relaxation of the folids of the body and its parts, and to know how to regulate the fame, fo as to keep the force of the folids within due bounds, and in a fit ftate for circulating the fluids, which for that end must be kept of a proper quantity, that is, fuch as is proportioned to the moving power of the folids.

29. It is manifeft from (No. 19, 20, 22.) That all the operations, phenomena, and difeafes of the body are purely the effects of its motion only, and do all vary in proportion as the quantity of motion varies in the whole body or its parts; and as the whole motion of the body is entirely

entirely owing to the nervous muscular folids, it follows that all the alterations in the body, tending either to health or ficknefs, proceed primarily from the different degrees of force in the folids, from which alone they receive all their distinguishing symptoms and characteristics; from whence it follows that there is but one general intention to be taken for preferving health, and the cure of all diseases, and that is, in keeping the moving force of the folids rais'd or lower'd, as fuits beft with their conftitutional ftructure, and for attaining the indications wanting.

30. As a conclufion from the foregoing obfervations, the following general propofition is deduced, namely, The beft method for effecting this cardinal intention, relating to the regulating the conftriction and relaxation of the folids, with the qualities of the fluids depending thereon, is by fubmiting the body, or its parts, at proper times, to a greater or lefs quantity of preffure, by means either of air or water, taking care that their other properties, of elafticity, heat, cold, humidity, drynefs, &c. be duly proportioned in fuch degrees as fuits best with the prefent conftitutional state of the body, and organs of refpiration, &c. The truth of this capital propofition is demonftrable from the mechanism of the animal folids (No. 26.) and structure of the body, and refpiring organs, which being compofed of claftic tubes, when the preffure upon the body or its parts is augmented or diminish'd (whether the preffure be produced by air, water, or both,) the effects thereof will be communicated and propagated inftantaneoufly throughout the whole animal fyftem, fo that every the fmalleft evanefcent capillary tube, with its contain'd fluids, will be fenfibly affected and moved thereby. Thus if an additional preffure be laid on the body, the whole fyftem of the folids being thereby contracted, and their moving force increased, the fluids will be attenuated, and circulated with greater velocity, whereby obftructions will be removed, and the fecretions promoted. But if the external preffure on the body be diminished, the internal prefiure from the contain'd fluids, as the blood, becoming thereupon increas'd, will caufe the whole fyftem of the veffels to dilate, whereby the folids becoming relax'd, and their moving force diminish'd, the fluids will have their motion, fecretion, &c. diminish'd proportionally.

31. That preffure, when apply'd, in proper times and quantities, to an elaftic, vafcular, compreffible machine, as the human body, is capable of producing in the moft perfect manner all the alterations in the folids and fluids, neceflary for preferving health, and curing diseases, is demonftrable from the principles of hydraulics, and the preffure of fluids moving in elaftic veffels, with the laws relating to the communication of motion by preffure, percuffion, &c. as will be more particularly fhown in the feveral parts of this treatise.

32.

CHA P. I.

HE author, in this chapter, demonftrates the prefent practice of bathing to be very imperfect, often injurious, and its falutary effects in a great-measure loft; and propofes a new method, whereby it may be greatly improved, and freed from the imperfections and ill effects to which it is fubject; to which end he obferves as follows.

33. The

33. The univerfal efficacy of the cold and hot baths, for preferving health, and curing difeafes, is too well establish'd from experience to require any proof; it is alfo demonftrable, from the laws of motion and animal mechanism, that the falutary effects of both baths are owing to two principles, namely, preffure and ftimulation; as to which it may be remark'd, that the water, by its preffure, acts alike in both baths, but its qualities of cold and heat produce different and contrary effects, the former ferving to conftringe, and thereby increase the moving force of the folids, and at the fame time to condense the fluids; whilft the latter relaxes the folids, and rarefies the fluids. It may be further observed, as to the hot bath, that the preffure and heat of the water act with oppofite forces and directions, and thereby weaken each other's effects, the preffure tending to contract and condenfe, whilft the heat, by its ftimulus, relaxes and rarefies the folids and fluids. But in the cold bath, the preffure of the water, with the stimulus arifing from its cold, co-operate with joynt forces and directions, both tending to contract the folids, and condense the fluids; which renders the cold bath of more general use and benefit, as its preffure and ftimulus both confpire with one direction, and to one end, without deftroying the effects of each other. And as the human body is an elaftic, vafcular, compreffible machine, the whole fyftem of the folids becomes fubject to a fudden and general contraction upon going into the cold bath, and during its operation is made to ofcillate and vibrate with great celerity and force, from the furface inwards to the axis of the body, and from thence outwards to the furface, by which reciprocal action and reaction between the folids and fluids, the former will be ftrengthned, and the latter attenuated, and circulated with greater velocity; and if a vifcidity prevails in the fluids, it will be diffolved, and the whole series of veffels and glands fqueez'd and scoured, obftructions remov'd, and the fecretions increas'd, efpecially by the cutaneous and renal glands. So that all the intentions and alterations, that can be produced by conftringing and bracing the folids, with the motion, digeftion, fanguification, heat, fluidity, derivation and revulfion of the fluids, may be most certainly effected by a judicious ufe of the cold bath.

34. But as the efficacy of the bath is allow'd to confift chiefly in its preffure, this being always of one definite quantity, the alterations produced thereby must be of one determin'd quantity alfo, effects being, ever proportion'd to their caufes. Thus fuppofe the external area of a person's body equal to fifteen feet, and taking one part with another to be immerg'd two feet under water, which is rather more than what it is in ordinary bathing or fwimming, the additional preffure which he will fuftain is equal to about 2280 pounds weight, fo that this is both the very greateft, as alfo the very leaft preffure he can receive in bathing; and if his cafe required either a greater or lefs degree of preffure, he can't poffibly have the benefit thereof; whence it is manifeft that, as the preffure of the water in bathing operates always with one unalterable quantity and force, its falutary effects, depending chiefly upon its preffure, muft neceffarily be limited and proportioned to that quantity only. So that let a perfon's ftrength, age, conftitution, indications, and other circumftances be what they will, he must in bathing the common way always fuftain the fame degree of preffure without variation,

M m

which

which renders bathing, as now practised, exactly the fame with a medicine, as fuppofe an emetic, to be administered always in one invariable dofe to all perfons alike, men, children, ftrong and weak, without diftinétion; this all phyficians would condemn as a moft pernicious practice, well knowing that not only different perfons, but the very fame perfon at different times, and for different indications, require the quantities of medicines, be what they will, to be varied from lefs to greater, and the contrary, as answers beft with the prefent intentions; and it is for the fame reafon, that in fome obftinate diftempers, as the hydrophobia, &c. plunging or immerging the body deep in falt water is of more service than ordinary bathing in frefh water, by reafon both of the greater preffure, and furprize, which operates as a ftimulus, whereby greater effects are produced in the body. But this practice of fudden deep immerfion, being often attended with fatal effects, when any of the internal vifcera are weak and unfound, can never be reduced into common practice, being only to be used in defperate cafes, and befides being but of fhort duration can't effect any notable lafting change in the folids and fluids, which is the reafon it proves often ineffectual, tho' no remedy or means can compare with it for efficacy in fuch obftinate cafes, could the aforefaid objections be removed.

35. From what hath been faid it is manifeft that the great imperfection in the practice of bathing is, that the preffure is always of one invariable quantity; and this ferves to fhew at the fame time how greatly it may be improved, could the preffure be apply'd in all degrees required. From this fhort rationale upon the mechanical operation and effects of bathing, with the imperfections attending the prefent ufe thereof, and the great improvements that may be made therein, all which are invincibly demonftrable from the principles of hydroftatics and hydraulics, with the laws relating to the communication of motion by preffure, applyed to an elaftic, vafcular machine, as is the human body, is deduced and propofed the following capital phyfical problem,

PROBLEM.

36. To find a method whereby the preffure of the water in bathing may be increas'd to any quantity required, and adjufted in all degrees as fuits beft with the conftitution, ftrength, age, fymptoms, ftructure and indications of every perfon; and that the preffure be laid on, and taken off the body gradually, and the perfon put in a condition to continue under the preffure, as long as is neceffary for attaining the intentions proposed thereby, &c.

37. The author hath given a mechanical folution of this cardinal problem, with the draught and defcription of a machine and apparatus for bathing, either in cold or hot water, whereby a perfon, tho' no deeper under water than in a common bath, may be made to fuftain a preffure from the water of any qnantity required, from that of one perpendicular foot of water, extending through all the intermediate degrees of preffure, to that of a hundred or a thousand feet; by which means the preffure upon the body may be regulated to any degree as will fuit best with the prefent conftitutional ftate and indications, whereby the practice of bathing will be retrived from its prefent imperfect state, and from being a particular remedy, as operating with one definite force,

and

and as fuch properly applicable to one cafe only, will be render'd by this new method a univerfal remedy of general efficacy, in all cafes, wherein bathing of any fort, or the application of preffure in any degree to the body, is proper; fo that where bathing proved useful in one cafe before, it will now be of use in many different cafes; and as the fame is thus improved, will be one of the moft efficacious univerfal remedies, and, when judiciously applyed, will produce all the primary intentions wanting in the animal folids and fluids, either for preserving health, or curing difeafes. This he exemplifies and demonftrates in fome of the moft obftinate diftempers, as, agues, cachexies, droplies, relaxed folids, cutaneous diseases, venereal distempers, and the bite of a mad dog, or any other animal, with its laft fatal diftinguishing fymptoms, the hydrophobia, &c.

38. Here alfo is fhewn how the practice of pump-bathing, with the method of fumigating the body with vapour baths, either humid or dry, may be greatly improved by this bathing machine, and apparatus. The author explodes the receiv'd opinion, that the water, during the time of bathing, enters the body by certain cutaneous inhaling veffels; all which, with many ufeful obfervations, together with the draughts and defcription of the machinery thereto relating, may be found explained more fully in the original treatise.

39.

CHA P. II.

39. HE author, in this chapter, difcourfes of the mechanical operations of the air, confider'd as operating with all its changeable properties upon the whole external human body, with its univerfal great influence upon animal life, health, and diseases; to which purpose he obferves as follows:

40. An animal body confifts of various organs, both internal and external, compofed of an infinite number of contractile-distractile veffels, fo framed and put together as to conftitute one compound pneumatico-hydraulic machine, all the organs and parts whereof require to be moved, warm'd, moiftned and nourish'd, by fome fluid fubftance, as the blood, conftantly circulating and permeating the whole fyftem. Now fuppofing the animal machine to have all its folids and veffels form'd in the most perfect manner, and fill'd with their proper fluids, yet it could never be put in motion, or exert any one vital function, without being continually furrounded with an elaftic, heavy fluid, as the air, to fupport the fpring of the folids outwardly, against the diftending force of their contained fluids. And thus we find no animal or vegetable can ever be produced, live, grow, or expand its fibres in their natural form and figure, unless they are at all times inclosed within a fluid element, as the air, which by its preffure refifts equaily the elongation of its fibres. The atmosphere, by its variable preffure, &c. ferves as a fluid mould, or matrix, to keep both animal and vegetable bodies in conftant motion, and likewife fets limits and bounds to their growth, which they cannot exceed. And befides the air is neceffary to all degrees of life in animals, vegetables, fire, &c. as it is an absorbing, exhaling medium, ferving to carry off the fulphureous and humid vapours continually iffuing from all bodies endow'd with any degree of

life,