MOTION IN ANIMALS AND PLANTS. 331 



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 mus- 

 cular 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 

 certainly known as to the nature of that action. 



When a muscle is roused to activity by the presence of an exciting 

 cause, its mechanical properties suddenly change. It shortens, and if 

 the shortening is resisted becomes tight. If the resistence is such as 

 can not be overcome it tightens without shortening. With reference 

 to this mechanical change, we know that it is dependent on chemical 

 change, and that that change is oxidation. Admitting these proposi- 

 tions, we must necessarily believe that the oxidation is sudden, i. e., 

 explosive, because its mechanical effect (the tension or tautness I have 

 mentioned) attains its maximum at a very short period after the 

 moment at which the process begins. 



At ordinar}^ temperature we find that in a whole muscle the tension 

 which is induced by an excitation attains its maximum in about three 

 one-hundredths second. But if we fix our attention on a single mus- 

 cular element, i. e., on one of the infinite number of molecular mech- 

 anisms by the cooperation of which the mechanical change consequent 

 on excitation is brought about, it can be shown that in each taken 

 separately a much shorter duration than three one-hundredths second 

 must be assigned to the process of transition. According to Bern- 

 stein, less than one one-hundredth second must be assigned to the 

 chemical process which takes place in a muscular element in response 

 to a single stimulus.^ 



This chemical process of extreme suddenness is followed without 

 measurable loss of time by the conversion of chemical energy of 

 the oxidizable material into mechanical energy, which immediately 

 manifests itself either in shortening or in the effort to shorten. The 

 way in which this transference takes place must for the present be 

 left an open question, for, as Professor Engelmann explained in the 

 Croonian lecture for 1895, the transformation of chemical into mechan- 



^ See Pfliiger's Archiv, vol. 67, p. 211, 1897, where Bernstein describes his method 

 of measuring the period of latency. As in the method described by me in the Jour- 

 nal of Physiology in 1895, a magnified image of the moving surface of a muscle 

 excited directly is received on a slit, behind which a sensitive plate passes. From 

 the curve so obtained Bernstein determines the moment at which the rate of expan- 

 sion increases most rapidly, and regards this as the moment at which the moving 

 force is at its maximum. This conclusion, of course, applies to the part of the muscle 

 immediatelv excited. 



