37 8 THE PROPERTIES OE STRIPED MUSCLE. 



cavity of the ventricle and the tube are filled with salt solution, which, 

 when the tube is fixed in an upright position, stands in it at the height 

 of a few centimetres. The heart thereupon begins to beat, but eventually 

 stops in systole. By a suitable arrangement, a voltaic current is led 

 through the ventricle from base to apex, or the reverse. On closing the 

 current the ventricle relaxes at the anode, and the wave of relaxation is 

 propagated towards the cathode. If the closure is of short duration, the 

 ventricle returns, when the current is opened, to its previous state of 

 tonus, and the observation may be repeated. Here again it is seen that 

 the effect of the current is to annul an existing state of excitation, rather 

 than to bring into existence a new state. 



The fact that, in these instances, the elements of muscular structure 

 lengthen when subjected to mechanical or electrical disturbance, is difficult 

 to understand, chiefly because it appears to be against the purpose to 

 which those elements are adapted in the organism, i.e., against their 

 function. If, therefore, stimulation is the equivalent of Auslosung — the 

 discharge of function — we cannot designate as stimulation an action by 

 which activity is quelled. A living organism cannot be waked into 

 inactivity. 



Yet the fact remains that the agents which we are in the habit of 

 regarding as stimuli may, by their direct action, quell function. Since 

 Pfluger discovered that by the voltaic current we can at will modify the 

 vital condition of a motor nerve in either of the two possible directions, 

 — augmentation and diminution, — we have recognised in nerve and in 

 other excitable structures, an up and a down state. The essence of what 

 we know about these states is, first, that the down state is a concomitant 

 of activity, the up state is similarly associated with rest ; and, secondly, 

 that the latter is the antecedent condition of restitution or repair, the 

 former of capacity for function {Functionsfahigkeit). Hence the two 

 states constitute one cyclical process, in which each state is alike the 

 consequence and cause of the other. But no sooner have we expressed 

 this intimate relation, than again the essential difference between the 

 two presents itself — the contrast between functional activity and repose. 

 The contrast consists mainly in this, that while in the former the thermo- 

 genetic and electrical changes are sudden, easily recognised, and 

 are so conspicuous that they constitute the most characteristic pheno- 

 mena of animal life, those of assimilation or restitution are so little 

 obvious that their existence is rather a matter of inference than of 

 observation. 



Summation of a series of mechanical responses — Genesis of 

 tetanus. — Tetanus has already been defined as the response to a succes- 

 sion of instantaneous stimuli. The typical form of this response (complete 

 tetanus) is obtained when the frequency of the excitations is such that 

 the intervals between them are each equal to the time required for the 

 muscle, excited by a single instantaneous stimulus under isometric 

 conditions, to attain its greatest tension. A muscle, so tetanised, has an 

 equilibrium length a, which, as we have already seen, is considerably 

 less than >., the length which it strives to attain (and may overshoot) in 

 response to a single instantaneous excitation; in other words, the distance 

 l-\ is considerably greater than 1-7,. When an " unloaded " muscle, i.e. 

 one with a load say of 0-5 grm., is tetanised, its actual length and its 

 equilibrium Length (a) are identical. The same unloaded muscle 

 .shortens nearly to the same extent when excited by an instantaneous 



