Regulation of ganglion cell production by Sonic hedghog

A viscometer, particularly suited for blood viscometry. The inventive viscometer is circularly symmetrical and comprises a cylindrical channel for housing an unknown fluid and a ring-shaped channel, concentric with the cylindrical channel, for housing a known Newtonian fluid. A floatable cover element is provided with a cylindrical projection adapted to associate with the cylindrical channel and the fluid housed therein, and is further provided with a ring-shaped projection adapted to associate with the ring-shaped channel and the Newtonian fluid housed therein. The cover element floats in the known Newtonian fluid with a fluid bearing action, the ring-shaped projection being coated with a material which is non-wettable, and the channel being coated with a material wettable by the known fluid. The block in which is defined the cylindrical channel and the block in which is defined the ring-shaped channel are rotated in opposite directions, and the relative velocity of rotation therebetween is adjusted until the floating cover element is stationary. The relative rotation between the cylindrical channel block and the ring-shaped channel block is proportional to the viscosity of the unknown sample.