ii CHANGE OF FORM IN MUSCLE DURING ACTIVITY 107 



This brings forward the question, which anatomical constituents 

 of the cardiac apex are the first to be excited. Here, again, the 

 muscles seem to be of primary importance, the more so since 

 we have shown that curarised skeletal muscle is excited under 

 almost similar conditions into analogous rhythmical activity. It 

 seems to be an almost universal property of muscular substance to 

 fall under certain conditions, with all prolonged stimuli, into a 

 state of visible rhythmical excitation. Such a theory is not only 

 supported by the foregoing facts, but by further observations on 

 the rhythmical excitation of the sartorius and cardiac muscles 

 with the constant current. 



Apart from the " spontaneous " rhythmical phenomena of 

 excitation, called out in striated muscle by dilute solutions of 

 Xa 2 C0 2 , the specific action of this salt is also exhibited in a 

 striking increase of response to artificial stimuli. This is very 

 evident whenever a muscle that is not too thick, e.g. frog's 

 sartorius, is treated wholly or partly with correspondingly dilute 

 solutions. We shall presently refer to a very striking fact in 

 this connection, which bears on the alteration in the effect of the 

 constant current on a sartorius, half of which is treated with 

 Xa 2 C0 3 . But even with localised mechanical stimulation, as well 

 as with single induction shocks, or induced alternating currents, 

 the increase of excitability asserts itself in a conspicuous increase 

 in height of contraction, or tetanus curve, as well as by an aug- 

 mented tendency to contracture. 



The stronger solutions of Na. 2 S0 4 , as also very dilute solutions 

 of NaOH (in 0'5 % NaCl solution), act like Na. 2 C0 8 , only in a 

 less degree, so that seeing the identical action of these substances 

 upon cardiac muscle, we are justified in speaking of a specific 

 effect of the sodium salts in question, i.e. the contractile substance 

 of striated muscle is so altered by the presence of even small 

 quantities of these reagents, that it is excited more easily, and 

 with smaller stimuli, than under normal conditions. The much- 

 talked-of and frequently-tested action of veratrin an alkaloid 

 whose conspicuous effect upon striated muscle was first discovered 

 by Kolliker, and subsequently investigated by Bezold (71), Tick, 

 Bohm (72), and others is to some extent comparable. While in 

 the application of certain sodium salts, and of Na 2 C0 3 in parti- 

 cular, it is the increase of excitability towards all stimuli that 

 comes prominently forward, in veratrin- poisoning the extra- 



