Law of separation of function of the spinal roots

Understanding of neural organization is expressed as a series of generalizations, one of which is the law of separation of function of the spinal roots. The importance of this law 'can harldy be overstated', and it is the basis for Sherrington's monumental studies on the reflex organization of the spinal cord. Cranefield states that this discovery is 'one of the most important in the history of biology,' putting it directly after Harvey's discovery of the circulation of the blood. Thus any data indicating that the generalization is incorrect or at leat oversimplified must be dealt with in detail. The law of separation of function of the spinal roots, often referred to as the law of Bell and Magendie, implies that each ventral root contains only motor axons and each dorsal root contains only sensory axons. Investigators who attack the generality of this law are proponents of the idea that there are significant numbers of afferent fibers in the ventral roots or efferent fibers in the dorsal roots. The authors discuss the various studies concerning ventral root afferent fibers and then the studies concerning dorsal root efferent fibers.