Fuller v. Yentzer. Same v. Goodrich

Modifications or alterations in an invention consisting in a combination of old ingredients, which merely substitutes another old ingredient for one of the ingredients in the patented combination, is an infringement of the patent, if the substitute performs the same function and was well known at the date of the patent as a proper substitute for the one omitted from the patented invention; but the rule is otherwise if the ingredient substituted is a new one, or performs a substantially different function, or was not known at the date of the patent as a proper substitute for the one omitted…