"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 close rooms and coaches, 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 frouzy, 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 occasions the colds observed upon sleeping in, wearing, and turning over such bedclothes 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 about one hundred and fifty years past, the English have called _colds_."
Much of this is true in a general way, for medical practitioners have long held that all colds do not arise from exposure or draughts; but they do not admit that colds can be taken from turning over old books and clothes, although the dust from these might make one sneeze.
John Adams and Franklin while travelling together through New Jersey to meet Lord Howe, in 1776, discussed the question of colds, and the former has left an amusing account of it. The taverns were so full at Brunswick that they had to sleep in the same bed. Franklin insisted on leaving the window wide open, and discoursed on the causes of colds until they both fell asleep.
"I have often asked him whether a person heated with exercise going suddenly into cold air, or standing still in a current of it, might not have his pores suddenly contracted, his perspiration stopped, and that matter thrown into the circulation, or cast upon the lungs, which he acknowledged was the cause of colds. To this he never could give me a satisfactory answer, and I have heard that in the opinion of his own able physician, Dr. Jones, he fell a sacrifice at last, not to the stone, but to his own theory, having caught the violent cold which finally choked him, by sitting for some hours at a window, with the cool air blowing upon him." (Adams's Works, vol. iii. p. 75.)