355. There are a great many methods of printing photographic pictures by mechanical means. A negative is made in about the usual way, and if the prints are to appear right and left as in nature, it must be reversed, either in the camera or transferred after it is made. A print is made from the negative upon a gelatin film sensitized with a bichromate. This film-print is affixed to lithographic stone, metal, glass, or some other hard, even surface, and then the impressions, or prints, are pulled from it much the same as the common lithograph is printed. The process is not practical for the every-day work of the photographer whose patronage demands only small lots of prints from any one negative; but for trade purposes it is well adapted, and is largely practised, especially in Europe.