Worcester, [MA?]: Self published 1856. Single sheet, 4 3/4 x 7 5/8 inches. Blank corner torn off, minor soiling. Folded for mailing. A printed letter from Agent O. F. Harris, noting that Dr. Nye of Weymouth [MA?] "has just concluded a series of successful experiments in the manufacture of Colored Gutta Percha, for Dental purposes...fully equal to that of Dr. Slayton's..." Near Fine. 
A 2019 review "Gutta-percha in endodontics - A comprehensive review of material science" by Vijetha Vishwanath and H Murali Rao includes a section called "EVOLUTION OF GUTTA-PERCHA IN DENTISTRY" It establishes the following early milestones: 1846 - Alexander Cabriol surgical uses; 1847 - Edwin Truman-GP-Temporary filling material; 1847 - Hill-Hill's stopping restorative material-Mixture of bleached GP, carbonate of lime and silica ; 1849 - Chevalier, Poiseuille and Robert-GP tissue (laminated sheets)-Academy of Medicine, Paris; 1864 - First patent by Alexander, Cabriot, and Duclos; 1867 - Bowman-root filling material-St Louis Dental Society; 1883 - Perry-Softened GP with gold wire; 1887 - S. S. White Co.-Manufacture of GP.
There was much experimentation at the time, with "Slayton's work described in Dental News Letter A Quarterly Publication Devoted... " By Volume 8, Issue 2 (1856) several dentists had written into the journal noting other uses for Slayton's Gutta Percha. It was the wild west of dentistry fillings, with some of the preparations noting wax must be applied before the preparations so that arsenic doesn't kill the nerve!
This letter shows just how fast the new material was being exposed to the "public" which in this case are other dentists we presume. Not only could you get instructions for use, but also for manufacture - or buy it yourself "the ready Article" for $25. Not cheap in 1856.