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



succession of phenomena ; for it is evident that when you have to do 

 with a number of events which appear to be simultaneous, the most 

 effectual way to determine their causal relations is to ascertain the 

 order of their occurrence. For, inasmuch as one event which follows 

 another cannot be its cause, the proof of their sequence which accurate 

 time-measurement affords may be of infinite value in indicating where 

 the starting point in a complex series of changes is to be sought for. 



The inquiry as to the relation between functional activity and the 

 electrical phenomena accompanying it, can only be entered upon by 

 finding instances in which both processes can be observed together. 

 Amongst these, those are to be preferred in which the question presents 

 itself in its simplest form, the experimental conditions can be most 

 easily controlled, and the observations can be made with the greatest 

 exactitude. 



It might at first sight seem desirable to begin by describing the 

 electrical manifestations of functional activity in the simplest organisms 

 and organs. There are, however, important reasons for following the 

 reverse order. To do so is in conformity with the general rule that a 

 problem can be most easily solved when it presents itself in its simplest 

 form. In the lowest organisms the relation of function to structure, 

 so far from being simple, is necessarily very complex, for functions 

 of the most varied kind have to be discharged by one and the same 

 mechanism, and often in default of any mechanism at all that we can 

 discover; whereas in the higher plants and animals we find for the 

 most part that every kind of work has its instrument, every action its 

 agent. It is in the highest organisms therefore that elementary physio- 

 logical questions must be studied, and it is in them that they have been 

 most studied. 



Of the elementary vital functions, motion was the one fixed upon as 

 the subject of this lecture by its founder. Its fitness for our purpose 

 is pre-eminent. Motion, in the physiological sense, is simple, control- 

 lable, measurable. It is, moreover, a function of paramount import- 

 ance as the means by which the animal organism maintains its relation 

 to the external world. In the higher animals, muscle is the instrument 

 of motion, and therefore claims our consideration. It has, in addition, 

 the advantage of being a structure of which the chemical, thermal, 

 and mechanical properties are better known than those of any other. 

 This advantage applies particularly to the muscles of the frog, which 

 on that account, as well as on the grounds which have been the occa- 

 sion of their being most studied, are to be preferred for our present 

 investigation. What we have first to do therefore this afternoon is to 

 determine the relation between the electrical concomitants of muscular 

 action and muscular action itself ; but before entering upon it, I must 

 occupy you for a few minutes in stating what is at present most cer- 

 tainly known as to the nature of that action. 



