Franklin’s penchant for air baths were part of his theory about the cause of the common cold. Although germs and viruses had yet to be discovered, Franklin was one of the first to argue that colds and flu “may possibly be spread by contagion” rather than cold air. The best defense was good ventilation. Throughout his life, Franklin liked open windows, even in the midst of winter.
TO BENJAMIN RUSH, JULY 14, 1773
Dear Sir,
…I shall communicate your judicious remark relating to air transpired by patients in putrid diseases to my friend Dr. Priestley. I hope that after having discovered the benefit of fresh and cool air applied to the sick, people will begin to suspect that possibly it may do no harm to the well. I have not seen Dr. Cullen’s book, but am glad to hear that he speaks of catarrhs or colds by contagion. I have long been satisfied from observation, that besides the general colds now termed influenzas, which may possibly spread by contagion as well as by a particular quality of the air, people often catch cold from one another when shut up together in small close rooms, coaches, &c. and when sitting near and conversing so as to breathe in each other’s transpiration, the disorder being in a certain state. I think too that it is the frowzy corrupt air from animal substances, and the perspired matter from our bodies, which, being long confined in beds not lately used, and clothes not lately worn, and books long shut up in close rooms, obtains that kind of putridity which infects us, and occasions the colds observed upon sleeping in, wearing, or turning over, such beds, clothes or books, and not their coldness or dampness. From these causes, but more from too full living with too little exercise, proceed in my opinion most of the disorders which for 100 years past the English have called colds. As to Dr. Cullen’s cold or catarrh frigore, I question whether such an one ever existed.
Traveling in our severe winters, I have suffered cold sometimes to an extremity only short of freezing, but this did not make me catch cold. And for moisture, I have been in the river every evening two or three hours for a fortnight together, when one would suppose I might imbibe enough of it to take cold if humidity could give it; but no such effect followed: boys never get cold by swimming. Nor are people at sea, or who live at Bermudas, or St. Helena, where the air must be ever moist, from the dashing and breaking of waves against their rocks on all sides, more subject to colds than those who inhabit parts of a continent where the air is driest. Dampness may indeed assist in producing putridity, and those miasmas which infect us with the disorder we call a cold, but of itself can never by a little addition of moisture hurt a body filled with watery fluids from head to foot…
With great esteem and sincere wishes for your welfare, I am, sir, your most obedient humble servant,