Croonian Lecture.―The messages in sensory nerve fibres and their interpretation

Abstract

The nervous apparatus which intervenes between stimulus and sensation has been the subject of more than one Croonian lecture. It may claim to be a suitable topic for a discourse on the “Causes and reasons of the phenomena of local motion,” but it is a dangerous topic as well, since it forces us to consider the mind as well as the body and to attempt the measurement of phenomena which lie outside the framework of the physical sciences. But in spite of its many difficulties the field is one in which mental and material changes are brought into the closest possible relation, and it should be worth exploring if for this reason alone. The sensory apparatus is most often studied by comparing stimulus and sensation. The method discussed in this lecture is a recent introduction scarcely assimilated to the older lines of work; it deals with an intermediate link in the chain, for it attempts to compare both stimulus and sensation with the messages which pass up the sensory nerve fibres. It has depended on an improvement in the technique of nerve physiology and it is sad to recall that this improvement followed closely on the death of the investigator who was most fitted to profit by it. Nineteen years ago Keith Lucas, then only 33 years of age, delivered the Croonian lecture on the "Process of Excitation in Nerve and Muscle.” His lecture is a characteristic example of the rigid analytic method which he used in formulating the problems of nervous activity, but it does not reveal the mastery of experimental technique which enabled him to solve them. Much of his later work dealt with the action currents of nerve, the brief electric changes which are our main clue in the study of nervous conduction. He used the capillary electrometer to record them and his design of the electrometer system and of the machine for analysing its records showed his remarkable gifts on the instrumental side; it is quite certain that our knowledge of all that takes place in the nervous system would have advanced much further by now had he lived to make use of the newer methods of electrical measurement.