AN

ESSAY

ON

Contagious Diseases.

THE
PREFACE.

The Design of this small Treatise being to deduce the Causes, and explain the Phœnomena of some of the most Fatal Diseases which afflict Mankind, can stand in Need of no Excuse, whatever the Performance it self may; and especially at a Time, when not only several of them Rage amongst us with uncommon Violence, but we are Daily threatned with the dreadful Calamity of a Raging Pestilence. I have endeavour'd to reduce these Diseases to the same Simplicity with Others, to speak Intelligibly of them, and show the real Changes in the Animal Oeconomy, from the Principles of the Modern Philosophy.

The Learned Authors who have already wrote on this Subject, have rejected this Part of it, as being so easie and obvious as to need no Explanation. I doubt not indeed but this is their Case: But how easie soever it may be to explain these Phœnomena, 'tis not every one, conversant in the Practice of Physick, that will give himself the trouble to deduce them; and 'tis for such chiefly that this small Tract is designed; to whom if it prove any way serviceable, I shall gain the End I proposed by it.

ERRATA.

Page 8. Line 20. before Contagion insert a Pestilential. Page 52. Line 17. read Buboes.

OF

Contagious Diseases.

CHAP. I.

Contagious Diseases are generally defin'd by Physicians to be such, as are capable of being communicated to us by the Air, or the Effluvia of Morbid Bodies. When the Cause producing these Diseases is general, and not occasioned by the peculiar Qualities of particular Places, but brought from Abroad, they are stiled Epidemic.

The Causes therefore of these Diseases must either be generated in the Air, or produced from the Effluvia of Animal, Vegetable, or Mineral Substances floating in it. And consequently the Effects of the Contagious Particles must be extreamly various, according to the Qualities of the Bodies from which they are produced.

When any of these Causes is of so deleterious a Nature, as not only to be Infectious, but to destroy all or most of those that are affected by it, That Disease is called a Pestilence.

But before I proceed to examine the particular Properties and Effects of the Contagious Particles, it will be Necessary to Demonstrate the following Propositions.

Prop. I.

The Magnitude of the Particles of the Blood being increased, Obstructions will be formed in the Ramifications of the smaller Vessels, which will happen sooner or later, in Proportion to the increased Magnitude of the Particles, and the smallness of the Vessels.

Demonstration.

Let the Canal A be an Artery of a middle Size, sending out the Branches C, D, E, F, G, H; Let the Dotts represent the increased Moleculæ of the Blood, it is evident that these must be stopt some where or other in the Ramifications of the Vessels C, D, E, F, G, H, whenever the Diameters of the Moleculæ exceed those of the containing Vessels.

Prop. II.

The Magnitude of the Particles of the Blood being increased, those Capillary Vessels nearest the Heart will be soonest obstructed, and vice versa; The rest in Proportion to the Velocity of the Blood, Diameters of the Canals, and their Distance from the Heart.

Demonstration.

This is sufficiently evident from the foregoing; For the sooner those Moleculæ arrive at the Capillary Vessels, the sooner those Vessels will be obstructed, and vice versa, and consequently cæteris paribus the Capillaries of the Branches C, H, in the preceeding Figure, which are nearest the Heart, will be sooner obstructed than those of E, F.

Prop. III.

The Magnitude of the Particles of the Blood must be increased either by the Union of a greater Number of them than in a Natural State; Or by the Alteration of their Figure, by which their Surfaces become larger than before.

Demonstration.

This is evident from the Observations of Lewenhoeck and Malpighius on the perspirable and other ultimate Vessels, which are visible by the Microscope, and consequently larger than the Orifices of the Lacteals, which the best Glasses will not discover. Whence it will follow, that no Particle can pass this way into the Blood, which single can obstruct the Vessels, and consequently this Effect can only be produced by the Action of the Particles upon each other, viz. either by the Union of a greater Number, or some Alteration in their Figures, whereby their Surfaces become larger than before. Thus the Globules of the Blood as appears by the Microscope, are nearly of a Spherical Figure, which being the most capacious, as well as most apt to constitute a Fluid Body, by touching in the fewest Points The farther any Particles deviate from this Figure, the more likely they will be to obstruct the Vessels, and vice versa.

Prop. IV.

The Contagious Particles being admitted into the Blood, do there coagulate its Parts, and form Moleculæ of a larger Size than ordinary.

Demonstration

The Force of the Heart and Cavities of the Canals being the same, when the Infection is first taken, as before, the Blood would pass with the same Facility thro' the Vessels as at other Times, and Obstructions could not be formed, were not the Moleculæ thus increased; as our Senses show they are by the Eruption of Pustules in the Small-Pox, by the great Inflammations, Mortifications, Buboes, and Carbuncles in Malignant and Pestilential Fevers; and consequently the Contagious Particles do increase the Bulk of several of the constituent Parts of the Blood, by altering the Figures of its Particles, and forming Moleculæ of a larger Size than in a Natural State.

CHAP. II.

It has been the constant Observation of Physicians, as well ancient as modern, and confirm'd by numerous Instances, that a hot and moist Constitution of the Air, joyn'd with southerly Winds, was generally a Fore-runner of malignant and Pestilential Fevers. Thus Hippocrates observes, that the Constitution of the Air preceeding that malignant Fever describ'd in the 3d Book of his Epidemics, 'was calm, moist, and southerly, and succeeded a hot, and dry Season; the Winter, calm, cloudy, rainy, warm, southerly; some Showers, and Northerly Winds about the Equinox; the Spring, calm and southerly, with great Rains; the Summer very hot, with little Wind, and much Rain about the Dog-days [a]. Some Authors led by the Title of this Book of his Epidemics, viz. Κατάστασις Λοιμώδης or the Pestilential Constitution, have imagin'd the Diseases here spoken of, to be the same with that terrible Plague describ'd by Thucydides, which taking its Rise in Æthiopia, and passing thence thro' Lybia and Ægypt, miserably harass'd all Persia, Phœnicia, Judea, Greece, and Cœle Syria, and was one of the most dreadful Calamities of this kind that ever appeared in the World. But whosoever will give himself the Trouble to compare the Symptoms of the Fevers here described by Hippocrates, with those related by that accurate Historian [b], who both had it himself, and visited many others in it, will find that there is not the least Similitude between them. The one being highly infectious, and not the least Appearance of Contagion in the other: Galen also the best Interpreter of Hippocrates, in his Comment on this Book of his Epidemic's suspects, this Title to be spurious, tho' both he and others observe much the same Constitution of the Air to be the Fore-runner of these Diseases.

What Places most Subject.

Pestilential and Malignant Fevers, are likewise observ'd to be the most frequent in those Places where the Climate is hot and scorching, and especially when Rains fall in such Seasons of the Year. Thus in Ægypt and some other Parts of Africa, if Rains fall during the Months of July and August, the Plague usually breaks out the September following [c].

This is still more remarkable in such Places, as not only are Situated in the forementioned Climate, but are likewise deprived of a constant Succession of pure and clear Air. An Instance of this we have in Grand Caire, which besides being subject to the common Disadvantages of the Country, (as are a Climate hot and scorching, a Situation low and flat, exposed chiefly to the warm Winds, their Water fetid and stagnating, being reserv'd in Vaults and Canals, which are Annually fill'd by the Overflowing of the River, the Air abounding with putrid Steams and Exhalations, arising from the Parts of Animals, Vegetables, and other Substances brought down and there deposited by the River), lies close under the Hill of the Castle, by which all Wind and Air is intercepted, which causes such a stifling Heat there, as ingenders many Diseases. [d]

That these may justly be esteem'd the Causes of the greater Frequency of these Diseases in this Place, than others in the same Climate, appears from their being so rarely known in those Places, which tho' equally hot, enjoy an Air free from Vapours. [e] Thus in Numidia and some other Parts of Africa, the Plague is scarce to be found once in a hundred Years, and hardly at all in the Land of Negroe. [f]

Several Causes of the Plague.

The other Observations of the Causes of these Fevers, may be reduced to such as arise from the Stinks of stagnating Waters in hot and close Weather, to some putrid Exhalations of the Earth, to the Parts of Animals and Vegetables putrifying in the open Air, or the taking of corrupt & unwholsome Nourishment.

Of the first kind was that at Selinis, occasioned by the stinking Exhalations of the stagnating Waters adjacent, which the discerning Empedocles removed by scouring its Ditches from their Filth, by a fresh Current of Water drawn from two Rivers in the neighbouring Country [g].

To the second Class may be reduced that Pestilential Fever, which the same great Philosopher check'd at Agrigentum, by stopping the Mouths of some neighbouring Mountains, whose pernicious Fumes had infected the adjacent Country [h]; As also that mentioned by Ammianus Marcellinus, which broke out in Seleucia, and over-ran a great Part of Greece, Italy, and Parthia, and took its Rise from the opening of an old Vault in the Temple of Apollo.

To the Third belong, such as are occasioned by the Parts of Vegetables and Animals, especially those of Men, putrifying in the open Air. As was that mention'd by Livy, which over-ran a great Part of Italy, and owed its Rise to the dead Bodies of the Romans and Fidenates left unburied in the Field of Battle [i]. Analogous to this was that which from the same Cause appeared in Germany, Anno 1630; And likewise that mentioned by Ambrose Parree from the same Cause; as also that mentioned by Diodorus Siculus, occasioned by great Quantities of Locusts driven by Winds into the Sea, and thence cast up in Heaps on the Shore. To this likewise must be reduced those Malignant and Pestilential Fevers, which so frequently attend Camps and Seiges, especially in the hot Eastern Countries, whose numerous Armies frequently feel the dismal Effects of these stinking Fumes: As do likewise the vast Caravans of the Mahometans in their Annual Pilgrimages to Mecca.

To the last belong those Pestilential Fevers, which take their Rise from a preceeding Famine, as was that in Judea in the time of Herod [k], in which the Product of the Ground being consumed by the great Heat, and long Drought of the preceeding Summer, the poorest sort of People were obliged, thro' the Scarcity of Provisions, to make use of such Food as afforded unwholesome and putrifying Juices.

CHAP. III.

The Changes wrought in the Animal Oeconomy from the above-mention'd Causes, may be reduced to such as depend either on the Increased Heat of the Air join'd with its Humidity; Or to such as are produced from the particular Qualities of the putrid and Contagious Particles floating in it; Or to the united and complicated Effects of all together.

Effects of a hot and moist Air.

The Alterations produced in the Body from a greater Heat continually surrounding it, provided it be not Excessive, are a Rarefaction of the Juices, and Relaxation of the Fibres on the Surface of the Body, and greater Derivation of the Fluids that way. Whence proceeds a large Evacuation of the perspirable Matter. This being continued in a greater Proportion than in a Natural State, will gradually deprive the Blood of its Aqueous and Spirituous Parts, and leave the remaining serous Part more stock'd with acrid and pungent Salts, and the Gross, Terrestrious, Oleaginous, and Viscous Particles more firmly united by their nearer Approach, and stronger Cohesion to each other. This greater Heat or Quantity of Fiery Particles, continually surrounding the Body, will necessarily insinuate it self into, and unite with the Saline, Sulphureous, and other Particles, in the same manner as we see it does with other Substances, both Solid and Liquid [l]; And likewise by increasing the Velocity of the Circulation and Attrition of the Particles against each other, render them on these Accounts also more Volatile, Pungent and Stimulating, and consequently the Blood will consist of Particles more gross and inspissated or coagulated, and likewise of those of a more acrid and pungent Disposition than in a natural State.

The Blood being in this depraved Condition, the rest of the Animal Juices must degenerate in Proportion thereto, and the Nervous Fluid, as it consists of the most volatil and subtil Parts, be extreamly acrid and pungent, as well as unequal in its Texture and Fluidity, from the more viscous Parts contain'd in it.

Putrid Fevers how produced.

This then being the State of the Blood and other juices of the Body, it is easy to perceive how from very Slight, and otherwise trivial Occasions, a Fever of a very Malignant Nature may be produced. Thus the perspirable Matter from a slight Cold taken being retained, or the Vessels any otherwise filled by Irregularities in Diet, or others of the Non-naturals, the Weight of the moving Fluid will be increased, and the Circulation be more languid and slow. Whence the intestine Motion of the Particles of the Blood being diminished, the viscous Parts will cohere more strongly and in greater Quantities than before, and obstruct the Capillary Arteries, especially in the Extremities, and a Coldness, Stretching, Yawning, Torpor, &c. necessarily succeed, the constant Attendants of a beginning Fever; All which will bear a Proportion to the Quantity retain'd, and the Viscosity of the moving Fluid.

These Disorders will necessarily be increased on account of the Air's Spring being weakned by its Heat, the Vessels of the Lungs being less inflated, and the Globules of the Blood less broken and divided, and the more especially in a humid Air, Heat and Moisture necessarily relaxing the Tone of the Fibres and Vessels, and rendring them less Springy and Elastic. Hence then the Quantity of Spirits being diminish'd, and their Motion more slow, the Contraction of the Heart and other Muscles will be more weak and languid, and being stimulated by the Acrimony of the Circulating Liquors, must contract more frequently than in a Natural State; The Consequence of which is Weakness, Faintness, Thirst, and Dejection of Spirits.

These and the preceeding Symptoms will necessarily continue, 'til such time as the gross and viscous Matter, being shook and loosen'd by the Action of the Capillary Vessels, is washed away into the Veins by the force of the Circulating Fluids, and there continues its Course with the rest, 'til it be either attenuated and secreted, or lodged again in the Capillaries to excite new Disorders.

Malignant Fevers.

Now if to this evil Disposition of the Air be added a number of pungent stimulating Particles, whether bred in the Body or floating in the Air, and thereby communicated to the Blood, which are apt to coagulate the Animal Juices, so as to form Moleculæ of such Shapes and Sizes as more firmly obstruct the Capillary Vessels, and at the same time stimulate and corrode the nervous Parts; It will necessarily happen, that the preceeding Symptoms must be highly exasperated, and a Fever of a much worse Nature produc'd.

Hence then must follow a violent Hurry and Colluctation of the Fluids, the Viscid and coagulated Parts of the Blood in some Parts obstructing the Circulation of the Juices, and the Acrid, Volatil, and Fiery Parts, rarefying and dissolving others of the more Liquid, to the greatest degree of Pungency and Volatility imaginable.

Hence it is easy to perceive how the Motion of the Blood must necessarily be in some Parts more languid, by the Cohesion of the more Viscous parts, in others quicker, join'd with a pungent and stimulating heat, from the increased Velocity and Acrimony of the moving Fluid, and the various Actions of the Particles upon each other, and their Impulses on the containing Vessels; As also how these are capable of almost infinite Variations, in Proportion to the different Quantities and Qualities of the constituent Particles. Hence then appears the Reason of that wandering and uncertain Heat and Coldness, in different Parts of the Body at the same time. Hence appears the Reason of that great Inquietude and Anxiety, of those uncertain and partial Sweats, Watchings, Tremors, stretching Pains of the head, and the like, as will be more fully shown hereafter.

But before I proceed to explain the Nature of a Fever truly Pestilential, it will be necessary to observe, that notwithstanding the foremention'd putrid Disposition be generally a Prelude to a Pestilential Constitution of the Air, yet it has never that I know of been observ'd, that these Causes alone at their first Onset, produced a real Plague or Pestilential Contagion, without the Concurrence of some preceeding Infection, either brought from abroad, or gradually augmented from the increased Putrifaction of the Air, and Poisonous Steams of Morbid Bodies.

Thus the putrid Air of Camps in hot Countries is frequently found to produce Pestilential Fevers, but this never happens at their first Onset; The Diseases first appearing being Fluxes, Putrid, and afterwards Malignant Fevers; which being exasperated and propagated by the Virulent Effluvia of Diseased Bodies, and the increased Putrifaction of the Air, grow up gradually to those of a Pestilential, and exceedingly infectious Disposition.

Of Putrifaction & Fermentation.

Now Putrifaction being only a kind of Fermentation, wherein the Particles of a putrifying Body are put into an intestine Motion, and by their Action and Attrition broken and divided, and since all fermenting Substances do emit vast Quantities of small separable Parts, it will necessarily follow, that the most subtil and active Particles of the Purifying Body will be elevated into the Air, and float in it.

Effluvia from putrified Bodies what.

These Effluvia consist of the finest and most volatil saline and oleaginous Particles, highly attenuated and set at Liberty from the gross Oil and Terrestrious Part, as appears from the Distillation of such Substances, all which afford great Quantities of a pungent and volatil Salt. It is likewise observable, that the subtil Oleaginous Particles being specifically lighter, as well as more easily attenuated and divided than those of a Saline Nature, will be thrown off in greater Proportion in the beginning of the Fermentation or Putrifaction than the heavier Salts will be, which must either be more attenuated and volatilised, or require a greater force to raise them into, and sustain them in the Air than the former, and consequently the greatest Emission of these saline Particles will be after the Fermentation has been for some time continued; As we find it happens in all fermenting Liquors, as Wine, Beer, Cyder, and the like. All which emit, during the Fermentation, greater Quantities of Particles of an active attenuated Oil or Spirit for some time, than of a Saline Nature, which requiring a longer time in order to attenuate them, are not raised till the former are in a manner quite exhaled, as appears from collecting the Steams of fermenting Liquors, and of those which are turn'd sower by Distillation, and consequently the Exhalations arising from putrifying Bodies will after some time consist mostly of Saline Particles highly attenuated and volatilised, and those not wrapt up and sheathed in the Oily ones, and thereby render'd innocuous, and often useful to the Body, but naked and exceedingly acrid and poignant.

How unfit an Air stock'd with these kind of Particles is for Respiration, appears from several of Mr. Boyl's Experiments on Animals, shut up with putrified Air in the Receiver, most of which with incredible Inquietude die sooner than in Vacuo, as also from the pernicious Effects of the Steams of Vaults, Mines, the Grotto de Cane, and such like. But besides this Inaptitude of such Air to expand the Pulmonary Vessels, these minute and pungent Particles may be considered as so many Stimuli or Lancets, acting upon and penetrating the Coats of the Stomach, Lungs, and other Vessels. On which Account they are not only capable of creating great Disordes, as Inflamation, Pain, Sickness, Anxiety, Vomiting, &c. in the Stomach and Nervous Parts; But likewise being carried immediately into the Blood, will there stimulate the ultimate Vessels, ferment, dissolve, or coagulate the circulating Juices according to the particular Qualities and Quantity of the Contagious Particles. Nor is it unlikely, that from the various Action of the Particles upon each other, and their different Combinations in a stagnating Air, Particles may be formed of Qualities vastly differing from, and in their Force almost infinitely exceeding those of their Primogenial Salts and first Principles, as in Sublimate, some Preparations of Antimony, &c. Instances of which those versed in Chymistry are no Strangers to.

Infectious Particles how produced.

Now supposing the Blood Saturated with these kind of Particles, and a Malignant Fever produced by their means, we all know that the Blood in this State throws off vast Quantities of subtil and active Particles thro' the Perspirable, Salival, and other Excretory Ducts of the Body, which not only must load the adjoining Air with great Quantities of them, and render it capable of producing more dismal Effects than the preceeding, but also the Particles thus thrown off must be endued with a more acrid and pungent Disposition than the former, inasmuch as they are more subtily divided and attenuated by the Force of the Fever, than those in the preceeding Disposition of the Air, where so powerful an Agent was wanting, And consequently produce a Fever of a most infectious and deleterious Nature; And especially when the Infection is taken toward the latter end of the Disease, at which time the Saline Particles will be more exalted and volatilised, as well as thrown off in greater Quantities, and thereby made more capable of producing an infectious Contagion.

For the Blood in these Circumstances may not unaptly be compared, as was before hinted, to a fermenting Liquor, whose Parts being constantly in Motion, are continually throwing off great Quantities of subtil and active Spirits, capable of exciting the same Fermentation, and producing the same Qualities in those of the like Species, as appears from our manner of fermenting Ale, Beer, &c. with Yeast, which is a Spirituous Ferment, and also from the Sower Ferments used in making Vinegar, &c.

Analogous to this we may observe, that the Blood in different Diseases, as well as different Animals, throws off great Quantities of active Particles, which when mixed with the Blood of a Healthful Person, are capable of exciting the same Fermentation and Disorder in the Animal Juices, with those of the Morbid Animal from which they exhale, as we find in the Small-Pox, Measles, Saliva of a Mad-dog, and the like.

This then being the Disposition of the Blood and other Juices, in those Fevers which we call Pestilential, it is evident, that whatever the particular Substance of the Contagious Particles may be, they must be endued with such Qualities as will Coagulate the Animal Juices, Stimulate the Fibres to frequent Vibrations, cause Obstructions in the Capillary Vessels, and render the Blood and other Juices of the Body exceedingly Acrid and Pungent, as appears from hence and the foregoing Propositions; The Symptoms and Consequences (cæteris paribus) being the same, whether the Disease has gradually grown up to this Height, or took its Rise only from Contagious Particles brought from abroad.

How propagated.

This is the Method by which I suppose these Contagious and Pestilential Particles to be first generated and produced, in those places which are most subject to them, and thence propagated first into the Neighbourhood, and afterwards to greater Distances by way of Intercourse and Commerce. The Pestilential Effluvia being pack'd up and conveyed in Goods of a soft and loose Texture, as Silk, Wool, Cotton, and the like; And so much the more easily, as the Air into which these infested Materials are brought, is predisposed to act in full Concert with them; as happens in all Places at some times more than others; At which time if these infectious Particles be communicated, they exert their Rage with the utmost Violence, but frequently are either dissipated and lost, or produce Diseases of less fatal Consequence, in an opposite Disposition of the Air.

Why the Plague ceases.

Thus hard Frost, strong cold and Northerly Winds, are found frequently to put an End to, or at least bridle the Fury of Contagious Diseases, and render them more mild and curable, as was observable in the Beginning of the last great Plague in London [m], and frequently taken Notice of in other places by the Writers on this Subject. Consonant to this we find in Ægypt, that the Rising of the Nile by giving a fresh Motion to, and altering the Disposition of their stagnating and putrid Air, by the mild Vapours and Nitrous Exhalations [n] issuing from it, immediately checks the Raging of the Plague, and reduces it to a Fever of a more mild and curable Nature; insomuch that as Purchas and others inform us, if there die in Grand Caire 500 Persons of the Plague the Day before, yet upon the Increase of the River it ceases to be Pestilential, and none die of it [o]. And indeed it can hardly be imagin'd, how the Plague when it has once got establish'd in any Place, shou'd cease but with the Destruction of all or most of the Inhabitants, was it not checked by some Alteration in the Disposition of the Air, and gradually reduced to a Fever of a more mild and curable Disposition.

It will I think be needless to show, that the Distempers here treated on are propagated by Contagion; But it may not be altogether unnecessary to explain by what Methods these Alterations in the Animal Oeconomy are brought about, and especially as the Means by which they are chiefly communicated, have not that I know of been fully examin'd.

CHAP. IV.

Of a Pestilence by Contagion.

The Contagious Particles whether they be generated in the Air, or produced by the Effluvia of Morbid Bodies, being sustain'd in it, are thereby applied to the Surface of our Bodies, with a Force equal to the Pressure of the Incumbent Atmosphere. This Pressure upon the External Superficies of a human Body of a middle Size, has been demonstrated to be equal to 39900 Pounds Troy-weight, and consequently supposing the Body in every Part encompassed with these Particles, the whole Force with which all these Particles are on this Account propell'd into the Body, will amount to the aforesaid Sum. But every single Particle is only applied with the Force of a Column of Air of the Height of the Atmosphere, and whose Base is equal to the Surface of that Side of the intruding Particle, opposite to the cutting Angle. Now the Contagious Particles from their extream Smallness and pungent Angles, may not only be consider'd as Bodies applied to us with the preceeding Force, but likewise as so many small Knives or Lancets, acting upon and penetrating the Coats of the Lungs and Surface of our Bodies, with a Force proportional to the Smallness of their cutting Angles. This appears not only from several Propositions in Mechanics, but even to our Senses, by the strong Contraction of a Cord or Fiddle-string in moist Weather. The Particles of Water from their exceeding Smallness, being protruded into the Cord, with a Force capable of Raising the greatest Weights. Now if to these be likewise added the strong attractive force of these small Volatil Particles, occasioned from their Exiguity, it will be no difficult matter to conceive, that they are capable of penetrating the Vessels of our Bodies. Thus the Attractive Force of the Magnet is greater in Proportion to its Bulk, in Small ones, than in those of a larger Size, from the greater Proximity of all its Particles to each other. And 'tis on this Account that Sir Isaac Newton computes the Attractive Force of the Particles of Light, to be to that of other Bodies, as 1000000000000000 to 1, in Proportion to the Quantity of Matter contained in them [p].

This I think is sufficient to shew, that these Acrid and Pungent Particles are able to penetrate the Surface of our Bodies, and get into the Blood that way; And indeed Experience it self confirms it in all other Pungent and Acrid Substances, as Garlic, Cantharides, Arsenic, and all Pungent and Corroding Bodies.

The Pressure of the Air on the Internal Surface of the Lungs in Breathing determined.

But tho' the whole Superficies of our Bodies are Penetrable by these Poisonous Particles, yet the principal Mischief is communicated to the Blood in its Passage thro' the Lungs. For considering the prodigious Number of the Pulmonary Vesicles, into all which the Air enters in Respiration, and likewise the vast Increase of their Surfaces on that Account, and also the greater Force by which these Particles are applied to the Internal Surfaces of the Vesicles in Expiration, in Proportion to that whereby they are applied to other Parts of the Body of equal Superficies; it will evidently appear, that the Contagion is chiefly communicated by these Vessels to the Blood. For it appears by the Barometer, that every Inch Square upon the Surface of our Bodies is pressed upon by a Weight nearly equal to 1800 Drams, when the Mercury stands highest in the Barometer. Now supposing with Dr. Kiel [q] that both the Lobes of our Lungs contain 226 solid Inches, of which only 1/3 or 75 Inches are Vesicles. Supposing also the Diameter of a Vesicle to be 1/50 Part of an Inch, the Surface of the Vesicle will be .001256 and the Solidity .0000043, by which if we divide 75 the Space fill'd by the Vesicles, the Quotient, viz. 17441860 X .001256 the Surface of a Vesicle, gives the Sum of the Surfaces of all the Vesicles, = 21906.976 square Inches. Which Sum being multiplied by 1800, the Number of Drams which every square Inch of the Surface of our Bodies sustains, gives the Weight which the whole Internal Surface of the Lungs sustains by the sole Pressure of the Atmosphere, when the Mercury stands highest in the Barometer, equal to 39442556.800 Drams, equal to 410859.966 + 64/96 lib. Troy weight, as appears from the known Laws of Hydrostaticks [r].