Front Page Titles (by Subject) LIII: A CONJECTURE AS TO THE CAUSE OF THE HEAT OF THE BLOOD IN HEALTH, AND OF THE COLD AND HOT FITS OF SOME FEVERS 1 - The Works of Benjamin Franklin, Vol. II Letters and Misc. Writings 1735-1753
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LIII: A CONJECTURE AS TO THE CAUSE OF THE HEAT OF THE BLOOD IN HEALTH, AND OF THE COLD AND HOT FITS OF SOME FEVERS 1 - Benjamin Franklin, The Works of Benjamin Franklin, Vol. II Letters and Misc. Writings 1735-1753 
The Works of Benjamin Franklin, including the Private as well as the Official and Scientific Correspondence, together with the Unmutilated and Correct Version of the Autobiography, compiled and edited by John Bigelow (New York: G.P. Putnam’s Sons, 1904). The Federal Edition in 12 volumes. Vol. II (Letters and Misc. Writings 1735-1753).
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A CONJECTURE AS TO THE CAUSE OF THE HEAT OF THE BLOOD IN HEALTH, AND OF THE COLD AND HOT FITS OF SOME FEVERS1
The parts of fluids are so smooth, and roll among one another with so little friction, that they will not by any (mechanical) agitation grow warmer. A phial half full of water shook with violence and long continued, the water neither heats itself nor warms the phial. Therefore the blood does not acquire its heat either from the motion and friction of its own parts, or its friction against the sides of its vessels.
But the parts of solids, by reason of their closer adhesion, cannot move among themselves without friction, and that produces heat. Thus, bend a plummet to and fro, and, in the place of bending, it shall soon grow hot. Friction on any part of our flesh heats it. Clapping of the hands warms them. Exercise warms the whole body.
The heart is a thick muscle, continually contracting and dilating nearly eighty times in a minute. By this motion there must be a constant interfrication of its constituent solid parts. That friction must produce a heat, and that heat must consequently be continually communicated to the perfluent blood.
To this may be added, that every propulsion of the blood by the contraction of the heart distends the arteries, which contract again in the intermission; and this distension and contraction of the arteries may occasion heat in them, which they must likewise communicate to the blood that flows through them.
That these causes of the heat of the blood are sufficient to produce the effect, may appear probable, if we consider that a fluid once warm requires no more heat to be applied to it in any part of time to keep it warm, than what it shall lose in an equal part of time. A smaller force will keep a pendulum going, than what first set it in motion.
The blood, thus warmed in the heart, carries warmth with it to the very extremities of the body, and communicates to them; but, as by this means its heat is gradually diminished, it is returned again to the heart by the veins for a fresh calefaction.
The blood communicates its heat, not only to the solids of our body, but to our clothes, and to a portion of the circumambient air. Every breath, though drawn in cold, is expired warm; and every particle of the materia perspirabilis carries off with it a portion of heat.
While the blood retains a due fluidity, it passes freely through the minutest vessels, and communicates a proper warmth to the extremities of the body. But when by any means it becomes so viscid as not to be capable of passing those minute vessels, the extremities, as the blood can bring no more heat to them, grow cold.
The same viscidity in the blood and juices checks or stops the perspiration, by clogging the perspiratory duct, or, perhaps, by not admitting the perspirable parts to separate. Paper wet with size and water will not dry so soon as if wet with water only.
A vessel of hot water, if the vapor can freely pass from it, soon cools. If there be just fire enough under it to add continually the heat it loses, it retains the same degree. If the vessel be closed, so that the vapor may be retained, there will from the same fire be a continual accession of heat to the water, till it rises to a great degree. Or, if no fire be under it, it will retain the heat it first had for a long time. I have experienced, that a bottle of hot water stopped, and put in my bed at night, has retained so much heat seven or eight hours, that I could not in the morning bear my foot against it, without some of the bedclothes intervening.
During the cold fit, then, perspiration being stopped, great part of the heat of the blood, that used to be dissipated, is confined and retained in the body; the heart continues its motion, and creates a constant accession to that heat; the inward parts grow very hot, and, by contact with the extremities, communicate that heat to them. The glue of the blood is by this heat dissolved, and the blood afterwards flows freely, as before the disorder.
TO CADWALLADER COLDEN
Philadelphia, 27 January, 1748.
I received your favor relating to the cannon. We have petitioned our Proprietors for some, and have besides wrote absolutely to London for a quantity, in case the application to the Proprietors should not succeed; so that, accidents excepted, we are sure of being supplied some time next summer. But, as we are extremely desirous of having some mounted early in the spring, and perhaps, if your engineer should propose to use all you have, the works he may intend will not very soon be ready to receive them, we should think ourselves exceedingly obliged to your government, if you would lend us a few for one year only. When you return to New York, I hope a great deal from your interest and influence.
Mr. Read, to whom Osborne consigned your books,1 did not open or offer them for sale till within these two weeks, being about to remove when he received them, and having till now no conveniency of shelves, &c. In our two last papers he has advertised generally, that he has a parcel of books to sell—Greek, Latin, French, and English,—but makes no particular mention of the Indian History; it is therefore no wonder that he has sold none of them, as he told me a few days since. I had one of them from London, which I sent you before any of my friends saw it. So, as no one here has read it but myself, I can only tell you my own opinion, that it is a well-written, entertaining, and instructive piece, and must be exceedingly useful to all those colonies which have any thing to do with Indian affairs.
You have reason to be pleased with the mathematician’s envious expression about your tract on gravitation. I long to see from Europe some of the deliberate and mature thoughts of their philosophers upon it.
To obtain some leisure I have taken a partner1 into the printing-house; but, though I am thereby a good deal disengaged from private business, I find myself still fully occupied. The association, lottery, and batteries fill up at present a great part of my time.2
I thank you for communicating the sheet on the first principles of morality, the continuation of which I shall be glad to see. I am, &c.,
[1 ]This piece I have found in Franklin’s handwriting among the papers of Cadwallader Colden. Its date is uncertain, but it was probably written before the year 1750.—Sparks.
[1 ]Mr. Colden’s History of the Five Indian Nations, which was published in London, and copies of which were sent over to be sold in Philadelphia.
[1 ]David Hall, a Scotchman by birth, and a friend of Mr. Strahan, who had worked in the same office with Franklin as a journeyman printer in London. His partnership with Franklin continued eighteen years, during which time he had the principal charge of the business. He conducted the Pennsylvania Gazette, and was likewise a bookseller and stationer. He died on the 17th of December, 1772, at the age of fifty-eight years. See Thomas’s History of Printing, vol. ii, p. 54.
[2 ]In his Autobiography Franklin says: “I proposed a Lottery to defray the expense of building a battery below the town, and furnishing it with cannon. It filled expeditiously, and the battery was soon erected.” “Mr. Logan put into my hands sixty pounds, to be laid out in lottery tickets for the battery, with directions to apply what prizes might be drawn wholly to that service.” The following memoranda, found in Franklin’s handwriting, show his manner of proceeding on this occasion: