66. I distribute the sympathies of mucous membranes, like those of most of the other organs, into three general classes. In the first class are ranked the sympathies in which irritation, on one part of the mucous surface, produces a sensation in a distant part. A stone in the bladder occasions pain at the end of glans; worms in the intestines excite an itching at the nose. Whytt has seen a painful affection induced over the whole side of the head by a foreign body in the ear; an ulcer in the bladder produces a pain in the superior parts of the thighs every time that the patient passes his urine. 67. I refer to the second class those sympathies in which the irritation of one point on mucous surfaces produces irritability in a different structure; thus, too lively an impression on the pituitary membrane occasions sneezing; the irritation of the bronchi coughing; biliary concretions produce spasmodic vomiting; stones in the bladder occasion retraction of the testicle towards the ring. In all these cases there is contraction of the muscles produced by the irritation of the mucous surface, distant from the place in which that contraction occurs. 68. The last class of the sympathies of mucous membranes embraces those in which the irritation of any part of their extension determines elsewhere the exercise of their tonicity. Here we must refer to what we have said upon glandular action being augmented by the irritation of the extremities of the excretory ducts. Thus it is evident, that the increase of the tonic power of the parotid for the secretion of the saliva, and of its excretory duct in order to transmit it, when the extremity of this duct is irritated by food, sialogogue medicines, &c.,--it is evident, I say, that this augmentation is a phenomenon purely sympathetic. We may designate each of these three classes by the name of the vital power which they bring into action, calling the first sympathy of sensibility; the second, sympathy of irritability; and the third, sympathy of tonicity. 69. This manner of classing the sympathies is entirely borrowed from the state of the vital powers, of which they are but irregular modifications, and only aberrations, still unknown in their nature. Nevertheless it is subject to very great inconveniences: yet it appears to me to be preferable to that of Whytt, who simply follows the order of the regions; and even to that of Barthy, who, more methodical, examines them successively in the organs connected by systems, in those which are insulated, and in those situated in symmetrical halves of the body. SECTION IX. OF THE FUNCTIONS OF MUCOUS MEMBRANES.