330 MOTION IN ANIMALS AND PLANTS. 



depends on the circumstance that all animal organisms and certain 

 parts of plants possess the faculty of being awakened from a state of 

 rest to normal activity. 



Even under the most favorable conditions the observation of this 

 transition is attended with difficulties which arise from the complexity 

 of the chemical and mechanical changes, and the shortness of the time 

 spent in their accomplishment. It is this crowding together of chemi- 

 cal, thermal, and electrical phenomena into a very brief period which 

 determines the method for their elucidation, a method consisting to a 

 large extent of a determination of time relations, i. e., of the order of 

 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 can not be its cause, the pro6f of their sequence which accurate 

 time measurement affords ma}^ 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. 

 Among these, those are to be preferred in which the question pre- 

 sents 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 organ- 

 isms and organs. There are, however, important reasons for follow- 

 ing 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 ele- 

 mentary physiological 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 preeminent. Motion, in the physiological sense, is simple, control- 

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

 tance 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, 



