-40 Prof. J. Burdon-Sanderson. Relation of Motion in Animals 



muscle strives against a resistance which it cannot overcome, or 

 shortens without resistance, or does both simultaneously, the change of 

 tension in the one case, of form in the other, or of both, are measurable 

 processes of which the time-relations can be ascertained with great 

 accuracy. We are on safe ground therefore in using either change of 

 tension or change of form as a means of estimating the vital activity of 

 muscle, and in fact both are required. 



For every investigation in which muscular function is in question, 

 three points come prominently forward : (1) The moment at which 

 mechanical energy comes into play ; (2) the maximum energy dis- 

 played ; and (3) the time at which that display culminates. As 

 regards the first point, the time occupied before the mechanical 

 response begins was, for many years, believed to be 1/100 second. 

 This estimate was accepted as though on the authority of Helmholtz, 

 but was really based on a misunderstanding of his experimental data. 

 But we now know that the change of form resulting from the action of 

 a single instantaneous stimulus begins in the muscle element not later 

 than 4/1000 second after the moment of excitation, and I may be per 

 mittecl to show you how this result can be arrived at with absolute 

 certainty by the photographic method. (Photograph shown.) 



As regards the second and third points, we find it better to measure 

 contractile activity by change of tension rather than by change of form, 

 firstly, because the method of measuring tension is less liable to error, 

 and, secondly, because the process of development of tension is more 

 rapid than the development of change of form. For, although with 

 the exquisite methods we now possess of getting rid of inertia in our 

 recording apparatus, it is possible to measure the shortening with great 

 exactitude, yet it is easier to guard against errors of observation when 

 the other (isometric) method is used. 



Having seen how functional activity can be measured, we may 

 advert to the question that principally concerns us this afternoon 

 ■ — the question, namely, whether the electrical phenomena may also 

 be regarded as expressions of functional activity. Assuming for the 

 moment the question to be answered in the affirmative, with what 

 part cf our tension curve should we expect the electrical concomitant 

 to coincide 1 Assuredly with the first and second hundredths of a 

 second after excitation, i.e., with the period of greatest activity of the 

 unknown process by which chemical is replaced by mechanical energy, 

 and, for a reason which I will at once explain, with the very begin- 

 ning of that process. For, as I have already indicated, the transition 

 does not occur at the same moment everywhere, and inasmuch as the 

 method which we use for the investigation of electrical change takes 

 cognisance only of what happens within an area of a couple of milli- 

 metres, we should expect it to occur not at a moment corresponding 

 to the maximum development of tension in the whole muscle, but at 



