50 PHYSIOLOGY OF MUSCLES AND NERVES. 



the quiescent muscle when unweighted. If an experi- 

 ment is successfully arranged so that an inactive muscle 

 is not extended by the weight h — by fastening the latter 

 to the muscle, but immediately supporting it, so that 

 it does not extend the muscle — and if the muscle is 

 then irritated, it is evident that the muscle is incapable 

 of raising this weight from its support. By finding the 

 weight which is exactly sufficient to effect this, it is 

 evident that we shall find an expression for the magni- 

 tude of the energy with which the muscle strives to 

 pass from its natural into a contracted condition. This 

 energy is called the force, of the muscle. A method of 

 accurately determining this will presently be explained. 



2. As far as it is possible to examine the matter, 

 the condition of muscles during their distinct pulsations 

 is exactly as in tetanus. All that has been said of the 

 height of elevation, and of the accomplishment of la- 

 bour dependent on this, and of the alteration in the 

 elasticity, is as true of distinct pulsations as of the 

 tetanic condition. But it is very hard to observe the 

 alteration in form during the very short time which is 

 occupied by one of these pulsations. Means of drawing 

 very accurate conclusions even on this point have, how- 

 ever, been found, especially since Helmholtz turned his 

 attention to the matter, in 1852. 



Various methods are employed in experimental re- 

 search to measure very short periods of. time acciuately, 

 and to study processes which occur even within the 

 shortest periods. Not only has the speed of the cannon- 

 ball during the various periods of its passage from the 

 mouth of the cannon to its arrival at its destination 

 been measured, but this has also been done in the case 

 of the yet shorter time occupied by the explosion of 



