[Sidenote: _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].
[p] Optic, in sine Quest. 22.
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.
[Sidenote: _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].
[q] Animal Secret.
[r] _Marriote_'s Hydrostaticks.
Now if to this be added the increased Pressure of the Air, against the
internal Surfaces of the Vesicles in Expiration, the Force will be found
to be still greater. For supposing the Diameter of the _Larynx_ to be
equal to O.5 of an Inch; Supposing also the Pressure of the _Larynx_ in
an ordinary Expiration, by which the Force of the expired Air exceeds
the Pressure of the Atmosphere, to be two Ounces, as has been found by
Experiment[s], the Pressure of the Air in an ordinary Expiration upon
the Internal Surface of the Vesicles of the Lungs, will on this Account
only be equal to 1844736 Drams, or 19216 lib. _Troy_ weight, which added
to the Pressure on the Vesicles by the Weight of the Atmosphere, amounts
to 39444401.536 Drams, or 410879.182 + 64/96 Pounds _Troy_ weight. But
the Pressure of the Air on all the rest of the Surface of our Bodies
amounts but to 39900 lib. _Troy_, which is to the Pressure upon the
Internal Surface of the Lungs, as 1 to 10.297 + 28882/39900, and
consequently many more of the Contagious Particles will be communicated
this way, than thro' the whole Surface of the rest of the Body. The
Weights aforemention'd are indeed prodigious, but that is caused by the
great Increase of Surface by the Number of the Vesicles: For it is still
to be consider'd, that the Pressure upon each square Inch of the Surface
of these Vesicles, amounts to no more than the Pressure on every Inch
Square on the Surface of our Bodies, except that Increase which is made
by the Force of Expiration, otherwise these Vesicles cou'd in no wise
withstand so prodigious a Pressure. This Quantity _viz._ 75 Cubic Inches
or thereabouts seems to be emitted from the Lungs in an ordinary
Expiration, for I have found by Experiment, that the Lungs in a large
Expiration will emit above 160 Cubic Inches of Air. Having my self
fill'd an exhausted Receiver of that Size with Air at one Expiration, of
the same Density with that of the Atmosphere.
[s] _Kiel_'s Animal Secretion, _Edit. ult._
Now if we likewise consider the exceeding Smallness of the Pulmonary
Vessels, and also that the whole Quantity of Blood in the Body must
necessarily pass this Organ, in order to its being attenuated and made
fit for Circulation; It will necessarily follow, that the Alterations
made in the Texture of the Blood by the Poisonous _Effluvia_, are
communicated to it chiefly thro' this Organ. Besides, the Poisonous
Particles do not only Enter into the Blood in greater Quantities in this
Bowel, but when carried by these Passages, are capable of doing much
more Mischief, than if entring in at any other Part of the Body, in
Regard that they are more intimately mixt with it in its Comminution. I
have insisted the more largely on this Argument, because I find that
most who have wrote in this Subject, tho' they do suppose some of the
Contagious Particles may be communicated to the Blood this way, yet lay
the greatest Stress on the Mixture of these Particles with the _Saliva_,
which being swallowed carries them in common with our Nourishment. 'Tis
not Improbable indeed, that many of these Particles may be this way
communicated to the Blood; but it is as Probable, that many of them
which are by this way Communicated, lose much of their Force by their
Mixture with the _Bile_ and other Juices; As we see happens in the
Poison of the _Viper_, which taken at the Mouth is not deadly, but when
mixed immediately with the Blood produces the most violent Symptoms. The
same may be observed from many other Substances, which may be safely
taken into the Body by the common Passages, as most Acids, Spirit of
Wine, and other Substances, but when mixed immediately with the Blood,
by Injections into the Vessels of living Animals, produce Coagulations,
Convulsions, and Death: The principal Reason which has induced
Physicians to suppose, that the Poisonous _Effluvia_ are chiefly
communicated by these Passages, are those violent Vomitings which
frequently accompany it; But this happens equally in many other Fevers,
where there cannot be the least Suspicion of Contagion. The only
Objection to what I have here advanced seems to be, That if the
Contagion was communicated to the Blood chiefly by the Lungs, the
Coagulations wou'd be immediately form'd there, and this Bowel totally
obstructed. But if we consider, that the Chief Application of the Air to
the Pulmonary Vesicles is in Expiration, immediately after which the
Blood enters the _Vena Arteriosa_, whose Branches continually grow
wider, and give Space and Time for the Coagulating Particles to act with
their full Force, this Objection will of it self fall to the Ground.
The Contagious Particles being by these Means got into the Blood, do
there by Coagulating and Inspissating the more gross and tenacious
Parts, and highly Volatilising and Attenuating others of the most
Subtil, reduce the Blood into the above-mentioned State. Thus we see
that _Milk_, which is the Juice of an Animal, by the Addition of a small
Quantity of an Acid Spirit, changes from an equal Texture, to one of a
more gross and viscous, as well as more fluid and watry Substance. The
like may be observed in the White of an Egg and the Blood of an Animal
it self. Analogous to this is that Experiment of _Jo. Bapt. Alprunus_,
who examining the Matter of a Pestilential _Bubo_ by Distillation, found
at first a _Phlegm_, then a more fat and oily Matter, and lastly a Salt
ascending into the Neck of the _Retort_. But what was the most
Remarkable in this Experiment, was the prodigious Stench upon opening
the Vessels, exceeding as he expresses it a Thousand Wounds exposed to
the Summer's Heat, and likewise a Salt so exceedingly Acrid and Pungent,
as to equal, if not exceed _Aq. Regis_ it self[s].
[s] _Ph. Col._ No. II. p. 17.
I shall not from hence pretend to determine, that an Acid Salt is the
immediate Instrument of these Changes in the Animal Oeconomy, since the
same may be wrought by Spirit of Wine, and other Liquids[t]; and
Experience assures us, that the _Effluvia_, proceeding from the
putrifying Parts of Animal Bodies, abound with a Volatil Alcaline Salt,
as appears by Collecting them by the Bell, or in Distillation, by which
they afford some Phlegm, a most Fetid Oil, and exceedingly Pungent and
Volatil Salt; But this is sufficiently Evident from what has been said,
that whatever the determinate Nature of the particular Particles may be,
they do not only Coagulate the Animal Juices, and increase the Bulk of
the Particles of the Blood, but render the remaining Part exceedingly
Acrid and Pungent.
[t] _Boyl_'s Hist. Humani Sang. _Friend_'s Emonalogia in Fine.
Consonant to this Dr. _Hodges_ has observed a great Affinity between a
Pestilential and Scorbutic Habit of Body, and that those whose Blood
naturally abounded with Saline Particles, and had the rest Coagulated or
Inspissated, as happens in Scorbutic Constitutions, were more grievously
affected by the Pestilence; and also that most of those who Recover'd of
the late Plague, were very much subject to Scorbutic Diseases: The like
I have frequently observed, where the Small-Pox, Measles, _&c._ seizes
those of a Scorbutic Habit.
Nor is the Blood alone affected by its Mixture with these Saline
_Spiculæ_, but the rest of the Animal Juices also in Proportion, and
especially the Nervous Fluid, which consisting of the most fine Volatil
and Subtil Parts, will be render'd extreamly Acrid and Pungent: Whence
Pain, Sickness, Inflammations, _&c._ must necessarily succeed.
[Decoration]