IN recent years, the attention of control engineers has been attracted to the communication characteristics of nerves, particularly in regard to their function in the feedback control of muscle. Muscles are highly non-linear power amplifiers, which require complex nervous control circuitry to permit smooth and continuous movement of the limbs. This control circuitry consists of multiple feedback loops, and the problem is to determine experimentally the function of individual loops. One approach is to open circuit specific peripheral neural paths and observe the effect on over-all performance.