Keith Lucas. 



xxxix 



time. Keith Lucas brought forward convincing evidence that Gotch's 

 contention was correct, in that the number of degrees of contractile stress 

 possible for a muscle to manifest is not greater than the number of nerve 

 fibres supplied to it. In a subsequent paper, description is given of 

 experiments on a muscle whose nerve contains only eight or nine fibres. In 

 this case, the nerve itself was stimulated. Thus the contraction of voluntary 

 muscle was brought into line with that of the heart and Bowditch's " all or 

 nothing " law showai to apply. Still later, Adrian, a pupil of Keith Lucas, 

 was able to extend the law to the nerve fibre itself, by the use of an ingenious 

 method to be referred to below. 



The next step in the theory of contraction was to show that the wave 

 does not change in magnitude during its passage, so far as normal muscle is 

 concerned, although it may suffer diminution in fatigued muscle. 



An important series of papers claims our attention at this stage, a series 

 which may be said to have their starting point in the observations of Waller 

 that the amount of energy required to stimulate a nerA^e varies with the 

 rate at which this energy is applied. Different nerves have a different 

 *' characteristic," due to the natural rate of movement possessed by some 

 constituent, which rate controls the effective taking up of the incident energy. 

 Keith Lucas' first experiments were made, as were those of Waller, by the 

 use of condensers of adjustable capacity, charged to different potentials. 

 Subsequently, it was found better to use as index the potential required with 

 currents of varying durations, a factor related to the former in a definite way, 

 since the energy is expressed by vH, where v is the potential and t the 

 duration of a current. Similar results were obtained with a simple apparatus 

 designed to vary the rate of increase of an applied current. The methods 

 described were utilised in the analysis of complex excitable systems, such as 

 the sartorius muscle with its nerve. It was found that the muscle has two 

 distinct optimal rates of incidence of energy, one of a very much greater 

 magnitude than the other. This statement still held after sufficient curare 

 had been given to abolish the effect of stimulation of the nerve trunk, so that 

 there must be some additional excitable substance situated between the nerve 

 and the muscle. By testing a part of the muscle free from nerve endings, it 

 was found that the low rate belonged to the muscle fibre itself. The nerve 

 trunk was found to have an optimal rate rather higher than that of muscle, 

 while the intermediate substance had an extremely high rate. The form of 

 the curve expressing the time-course of the relationship between duration of 

 current and potential required to excite, as the muscle changes after excision, 

 was shown to be altered by the presence or absence of calcium. Tliis fact 

 was brought into relationship with Nernst's theory of excitation, to which 

 more attention was given later. 



Another property of excitable tissues which is connected with the time- 

 factor in question is the summation of two stimuli, each just below 

 effective strength. If the excitatory process set up by the first stimulus 

 has not disappeared when the second arrives, there is summation. So 



VOL. xc. — B. h 



