Front Page Titles (by Subject) XXXII: TO JOSIAH AND ABIAH FRANKLIN - The Works of Benjamin Franklin, Vol. II Letters and Misc. Writings 1735-1753
Return to Title Page for The Works of Benjamin Franklin, Vol. II Letters and Misc. Writings 1735-1753
The Online Library of Liberty
A project of Liberty Fund, Inc.
XXXII: TO JOSIAH AND ABIAH FRANKLIN - 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).
About Liberty Fund:
Liberty Fund, Inc. is a private, educational foundation established to encourage the study of the ideal of a society of free and responsible individuals.
The text is in the public domain.
Fair use statement:
This material is put online to further the educational goals of Liberty Fund, Inc. Unless otherwise stated in the Copyright Information section above, this material may be used freely for educational and academic purposes. It may not be used in any way for profit.
TO JOSIAH AND ABIAH FRANKLIN
Philadelphia, 6 September, 1744.
Honored Father and Mother:
I apprehend I am too busy in prescribing and meddling in the doctor’s sphere, when any of you complain of ails in your letters. But as I always employ a physician myself when any disorder arises in my family, and submit implicitly to his orders in every thing, so I hope you consider my advice, when I give any, only as a mark of my good will, and put no more of it in practice than happens to agree with what your doctor directs.
Your notion of the use of strong lye I suppose may have a good deal in it. The salt of tartar, or salt of wormwood, frequently prescribed for cutting, opening, and cleansing, is nothing more than the salt of lye procured by evaporation. Mrs. Stevens’s medicine for the stone and gravel, the secret of which was lately purchased at a great price by the Parliament, has for its principal ingredient salt, which Boerhaave calls the most universal remedy. The same salt intimately mixed with oil of turpentine, which you also mentioned, makes the sapo philosophorum, wonderfully extolled by some chemists for like purposes. It is highly probable, as your doctor says, that medicines are much altered in passing between the stomach and bladder; but such salts seem well fitted in their nature to pass with the least alteration of almost any thing we know; and, if they will not dissolve gravel and stone, yet I am half persuaded that a moderate use of them may go a great way towards preventing these disorders, as they assist a weaker digestion in the stomach, and powerfully dissolve crudities such as those which I have frequently experienced. As to honey and molasses, I did not mention them merely as openers and looseners, but also from conjecture that, as they are heavier in themselves than our common drink, they might when dissolved in our bodies increase the gravity of our fluids, the urine in particular, and by that means keep separate and suspended therein those particles which, when unused, form gravel, &c.
I will inquire after the herb you mention. We have a botanist here, an intimate friend of mine, who knows all the plants in the country. He would be glad of the correspondence of some gentlemen of the same taste with you, and has twice, through my hands, sent specimens of the famous Chinese ginseng, found here, to persons who desired it in Boston, neither of whom has had the civility to write him a word in answer, or even to acknowledge the receipt of it, of which please to give a hint to brother John.
We have had a very healthy summer and a fine harvest; the country is filled with bread; but as trade declines since the war began, I know not what our farmers will do for a market. I am your affectionate and dutiful son,
TO CADWALLADER COLDEN
Philadelphia, 15 August, 1745.
I received your favor of the 20th past, which your medical piece enclosed, the reading of which gave me a great deal of pleasure. I showed it to our friend Mr. Bartram, who carried it home, and, as he since tells me, is taking a copy of it. His keeping of it for that end has prevented my showing it to any other gentleman as you desired, and hitherto prevented my writing to you upon it, as I intended. But, lest you should conclude me the very worst correspondent in the world, I shall delay no longer giving you some thoughts that occurred to me in reading of it, choosing rather to be blamed for not writing to the purpose than for not writing at all.
I am extremely pleased with your doctrine of the absorbent vessels intermixed with the perspiratory ducts, both on the external and internal superficies of the body. After I had read Sanctorius, I imagined a constant stream of the perspirable matter issuing at every pore in the skin. But then I was puzzled to account for the effects of mercurial unctions for the strangury, sometimes occasioned by an outward application of the flies, and the like; since whatever virtue or quality might be in a medicine laid upon the skin, if it would enter the body it must go against wind and tide, as one may say. Dr. Hales helped me a little when he informed me, in his Vegetable Statics, that the body is not always in a perspirable, but sometimes in an imbibing, state, as he expresses it, and will at times actually grow heavier by being exposed to moist air. But this did not quite remove my difficulty, since, as these fits of imbibing did not appear to be regular or frequent, a blistering plaster might lie on the body a week, or a mercurial unguent be used a month, to no purpose, if the body should so long continue in a perspirable state. Your doctrine, which was quite new to me, makes all easy, since the body may perspire and absorb at the same time, through the different ducts destined to those different ends.
I must own, however, that I have one objection to the explanation you give of the operation of these absorbents. That they should communicate with the veins, and the perspirants with the arteries only, seems natural enough; but as all fluids by the hydrostatical law pass equally in all directions, I question whether the mere direction of one of those minute vessels, where it joins with a vein or artery, with or against the stream of blood in the larger vessel, would be sufficient to produce such contrary effects as perspiring and absorbing. If it would, both perspirants and absorbents might proceed from the arteries only, or from the veins only, or from both indifferently; as, by the figure in the margin, whether the vessel a b is an artery or a vein, if the stream moves from a to b, the minute communicating vessel c shall be a perspirant, and d an absorbent; and the contrary, if it moves from b to a. Yet I cannot say I am certain the mere direction of the vessel will have no effect; I only suspect it, and am making a little machine to try an experiment with for satisfaction.
It is a siphon made of two large joints of Carolina cane united at e, into which two small glass tubes, f and g, are to be inserted, one on the descending and the other on the ascending side. I propose to fill the siphon and the two glass tubes with water, and, when it is playing, unstop at the same instant the tops of both glass tubes, observing in which the water sinks fastest. You shall know the success. I conceive the pressure of the atmosphere on the apertures of the two glass tubes to be no way different from the pressure of the same on the mouths of the perspirants and absorbents, and if the water sinks equally in the two tubes, notwithstanding the direction of one against and the other with the stream, I shall be ready to think we must look out for another solution. You will say, perhaps, that it will then be time enough when the experiment is tried, and succeeds as I suspect; yet I cannot forbear attempting at one beforehand while some thoughts are present in my mind. If a new solution should be found necessary, this may be ready for consideration.
I do not remember that any anatomist that has fallen in my way has assigned any other cause of the motion of the blood through its whole circle than the contractile force of the heart, by which that fluid is driven with violence into the arteries, and so continually propelled by repetitions of the same force till it arrives at the heart again. May we for our present purpose suppose another cause producing half the effect, and say that the ventricles of the heart, like syringes, draw when they dilate as well as force when they contract? That this is not unlikely may be judged from the valves nature has placed in the arteries to prevent the drawing back of the blood in those vessels when the heart dilates, while no such obstacles prevent its sucking (to use the vulgar expression) from the veins. If this be allowed, and the insertion of the absorbents into the veins and of the perspirants into the arteries be agreed to, it will be of no importance in what direction they are inserted. For, as the branches of the arteries are continually lessening in their diameters, and the motion of the blood decreasing by means of the increased resistance, there must, as more is constantly pressed on behind, arise a kind of crowding in the extremities of those vessels, which will naturally force out what is contained in the perspirants that communicate with them. This lessens the quantity of blood, so that the heart cannot receive again by the veins all it had discharged into the arteries, which occasions it to draw strongly upon the absorbents that communicate with them. And thus the body is continually perspiring and imbibing. Hence after long fasting the body is more liable to receive infection from bad air, and food, before it is sufficiently chylified, is drawn crude into the blood by the absorbents that open into the bowels.
To confirm this position, that the heart draws as well as drives the blood, let me add this particular. If you sit or lean long in such a manner as to compress the principal artery that supplies a limb with blood, so that it does not furnish a due quantity, you will be sensible of a pricking pain in the extremities like that of a thousand needles, and the veins, which used to raise your skin in ridges, will be (with the skin) sunk in channels, the blood being drawn out of them, and their sides pressed so closely together that it is with difficulty and slowly that the blood afterwards enters them when the compressed artery is relieved. If the blood was not drawn by the heart, the compression of an artery would not empty a vein, and I conjecture that the pricking pain is occasioned by the sides of the small vessels being pressed together.
I am not without apprehension that this hypothesis is either not new, or, if it is new, not good for any thing. It may, however, in this letter, with the enclosed paper on a kindred subject, serve to show the great confidence I place in your candor, since to you I so freely hazard myself (ultra crepidam) in meddling with matters directly pertaining to your profession, and entirely out of the way of my own. If you give yourself the trouble of reading them, it is all I can modestly expect. Your silence about them afterwards will be sufficient to convince me that I am in the wrong, and that I ought to study the sciences I dabble in before I presume to set pen to paper. I will endeavour, however, to make you some amends by procuring you from better judges some better remarks on the rest of your piece, and shall observe your caution not to let them know from whom I had it.
The piece on Fluxions I purpose shortly to read again, and that on the several species of matter, when you shall have what little I shall be able to say about them.
The members of our Society here are very idle gentlemen. They will take no pains. I must, I believe, alter the scheme and proceed with the papers I have, and may receive, in the manner you advise in one of your former letters. The mention of your former letter puts me in mind how much I am in arrear with you. Like some honest insolvent debtors, I must resolve to pay ready money for what I have hereafter, and discharge the old debt by little and little as I am able.
The impertinence of these mosquitos to me (now I am in the humor of writing) prevents a great deal of mine to you, so that, for once, they are of some use in the world. I am, Sir,
Your most humble servant,