In the square scarificators, the top and two sides were detachable from the bottom and the other two sides. Turning the wing-tip nut on the top of the scarificator lowered, by means of a yoke, the bottom of the scarificator that was fitted by grooves into the top. By raising and lowering the bottom, one could regulate the length of blade protruding beyond the bottom, and hence the depth of cut. In the 1790s, the octagonal scarificator that was to become the standard English-American model began to appear in surgical texts. The early octagonal scarificator, as illustrated in Latta (1795) and Bell (1801), had sixteen rounded blades arranged as in the square scarificator, an iron triggering lever similar to that of the square scarificator, a button release on the side, and a flat key on top for regulating depth of cut.[117] Early in the nineteenth century the flat keys were replaced by round screws. Only the bottom or blade cover of the octagonal scarificator was detachable. In some of the octagonal scarificators, the round screw on top ran the height of the scarificator and screwed directly into an internally threaded post inside the blade cover. In other scarificators, the screw raised and lowered a yoke whose two sides were attached by additional screws to side projections of the blade cover. A notable improvement was made in the early nineteenth century when John Weiss, a London instrument maker, introduced a 12 blade octagonal scarificator whose blades, arranged on two rods or pinions, were made to cut in opposite directions. This advance was mentioned by Mapleson in 1813 and adopted by London professional cuppers thereafter. The advantage of the innovations was that the skin was thereby stretched, and a smoother, more regular cut could be made. Weiss's Improved Scarificator also featured blades that could easily be removed for cleaning and repair. In place of two rows of six blades, one could insert a single row of four blades to adopt the scarificator for cupping on small areas such as the temple.[118] The feature of inserting a pinion with clean and sharp blades permitted the cupper to own only two scarificators. For cleansing the blades the manufacturer supplied a thin piece of wood covered with wash leather or the pith of the elder tree.[119] Scarificators in which the blade rods turned in opposite directions (called "reversible" scarificators in trade catalogs) were more complicated to manufacture and therefore somewhat more expensive than unidirectional scarificators. The cocking lever meshed directly with only the first blade rod. To make the second blade rod turn in the opposite direction, an extra geared plate (or idler lever) was necessary to act as an intermediary between the cocking lever and the second blade pinion. The cocking lever turned the idler lever, which then turned the second pinion. Two support rods and two cantilever springs were needed in place of the one in unidirectional scarificators.