TONUS 



539 



substance which increases surface energy or osmotic energy, it disappears again 

 spontaneously, under the usual conditions. The permanent tonic state of the 

 smooth muscle, which we have been discussing, might be explained by supposing 

 that the internal changes in the muscle cell, which result in the increase of tension, 

 are prevented from disappearing. The mechanism which is responsible for the 

 bringing about of this 

 temporary irreversibility 

 of the contractile process, 

 may be put into action, 

 or inhibited, by the inter- 

 vention of special nerve 

 fibres. The state of ten- 

 sion into which excitation 

 puts the muscle thus 

 remains until the external 

 inhibitory influence comes 

 into play and sets going 

 the opposite process 

 associated with relaxa- 

 tion, in which the pro- 

 ducts of the contractile 

 process disappear. 



We have, in fact, in- 

 dications of something of 

 this sort in the "con- 

 tracture," associated with 

 fatigue, in the skeletal 

 muscle, as well as in the 

 action of veratriiie (page 

 417) and of certain 

 electrolytes (Mines, 1912). 

 Moreover, we shall see 

 presently that the tonic 

 contraction of decerebrate 

 rigidity presents some 

 peculiarities of this 

 nature, when compared 

 with ordinary reflex or 



voluntary tetanus. 



If we suppose the 

 actual state of contrac- 

 tion of the muscle, as well 

 as the excitatory process 

 which precedes the con- 

 traction, to be associated 

 with some degree of 

 electrical negativity, and 

 this seems to be the case, 

 at all events, in the heart 

 (see Figs. 172 and 173) 

 and in the voluntary 

 muscle under veratrine 



FIG. 172. ELECTRICAL CHANGE WITHOUT CONTRACTION. The 

 uppermost curve in each of the three tracings is the move- 

 ment of a lever connected to the auricles of the frog's heart. 

 The middle one is the record of the string galvanometer. 

 The lowest one, the beat of the ventricle. The iipper 

 tracing is a normal one, the perfusion fluid containing 

 calcium. The middle tracing shows the effect of omitting 

 calcium. The electrical change persists, but there is no 

 change of form of the muscle. The lowest tracing was 

 obtained after adding strontium in amount equivalent to 

 the calcium of the upper tracing. The beats return, as 

 Ringer showed, but are considerably increased in dura- 

 tion. Note, especially in the last curve, that the electrical 

 change begins and ends rather earlier than the mechanical 

 one, but that the total duration is the same. 



(Mines, 1913, 3, p. 230.) 



(de Boer, 1913, 2), then 



the observations of W. F. Ewald (1910) are to the point here. Examining 

 the adductor muscle of Anodonta, he found two states of electrical negativity, 

 one, the " twitch " current, which appears at the beginning of a reflex closing 

 of the shell, probably the contraction of the motor muscle, and another one 

 following this, a slow one, and apparently proceeding pari passu with the degree 

 of tonus of the catch muscle. This latter is, according to the investigator, steady 



