"A constant galvanic action is kept up in the mouth when more than one kind of metal is used in filling teeth, and galvanism is often the cause of extensive injury to the teeth. The most remarkable case I ever saw was that of a lady for whom I filled several teeth with tin. After a time decay took place around some of the fillings. I removed them and began to refill, but there was so much pain I could not proceed. I found that by holding a steel plugger an inch from the tooth I could give her a violent galvanic shock. I observed that the exhalation of the breath increased the evolution of galvanism." (Dr. L. Mackall, _American Journal of Dental Science_, 1839.) "When a faulty tooth in the upper jaw had been stopped from its side with tin, the interstice between it and the adjoining tooth being quite inconsiderable, while the upper surface of a tooth not immediately beneath it in the lower jaw was stopped with the same metal, I have known a galvanic shock regularly communicated from one tooth to the other when by the movement of jaws or cheeks they were brought near together." (Dr. E. Parmly, _American Journal of Dental Science_, 1839.) "An interesting debate here sprung up on the action where two metals are used in one filling, such as gold and tin, the saliva acting as a medium, and where the baser metal is oxidized by exhalents and by imbibition through the bony tooth-structure." (Pennsylvania Society of Dental Surgeons, 1848.) "A patient came to me and complained of pain in the teeth. Upon examination I found an amalgam filling next to one of tin. With a file I made a V-shaped separation, when they experienced immediate relief from pain." (Dr. Nevill, _American Journal of Dental Science_, 1867.) In regard to the decay of teeth being dependent on galvanic action present in the mouth, Dr. Chase, in 1880, claimed that a tooth filled with gold would necessarily become carious again at the margin of the cavity, wherever the acid secretions constantly bathe the filling and tooth-substance. A tooth filled with amalgam succumbs to this electro-chemical process less rapidly, while one filled with tin still longer escapes destruction. The comparative rapidity with which teeth filled with gold, amalgam, or tin, are destroyed is expressed by the numbers 100, 67, 50. He prepared pieces of ivory of equal shape and size, bored a hole in each, and filled them. After they had been exposed to the action of an acid for one week, they had decreased in weight,--viz, piece filled with gold, 0.06; amalgam, 0.04; tin, 0.03.