472 MOVEMENTS VOICE AND SPEECH. 



cnt upon the action of the motor nerves. If, for example, a muscle be cut 

 across in a surgical operation, the divided extremities become permanently 

 retracted ; or if the muscles of one side of the face be paralyzed, the muscles 

 upon the opposite side insensibly distort the features. It is difficult to 

 explain these phenomena by assuming that tonicity is due to reflex action, 

 for there is no evidence that the contraction takes place as the consequence 

 of a stimulus. All that can be said is that a muscle, not excessively fatigued, 

 and with its nervous connections intact, is constantly in a state of insensible 

 contraction, more or less marked. 



Sensibility of the Muscles. The muscles possess that kind of sensibility 

 which gives an appreciation of the power of resistance, immobility, and elas- 

 ticity of substances that are grasped, or which, by their weight, are opposed 

 to the exertion of muscular power. It is by the appreciation of weight and 

 resistance that the force required to accomplish muscular acts is regulated. 

 These properties refer chiefly to simple muscular efforts. After long-con- 

 tinued exertion there is a sense of fatigue that is peculiar to the muscles. 

 It is difficult to separate this entirely from the sense of nervous exhaustion, 

 but it seems to be to a certain extent distinct ; for when suffering from the 

 fatigue that follows over-exertion, it seems as though a nervous stimulus 

 could be sent to the muscles, to which they are for the time unable to respond. 



When the muscles are thrown into tetanic contraction, a peculiar sensa- 

 tion is produced, which is entirely different from painful impressions made 

 upon the ordinary sensory nerves. In the cramps of cholera, tetanus, or the 

 convulsions from strychnine, these distressing sensations are very marked. 



If the muscles possess'any general sensibility, it is very slight. A muscle 

 may be lacerated or irritated without producing actual pain, although con- 

 traction produced by irritants and the sense of tension when the muscles are 

 drawn upon can always be appreciated. 



Muscular Contractility, or Excitability. During life and under normal 

 conditions, the muscles will always contract in obedience to a proper stimulus 

 applied either directly or through the nerves. In the natural action of the 

 organism, this contraction is induced by nervous influence either through voli- 

 tion or reflex action. Still, a muscle may be living and yet have lost its con- 

 tractility. For example, after a muscle has been for a long time paralyzed 

 and disused, the application of the most powerful stimulus will fail to induce 

 contraction ; but when examined with the microscope, it is found that the 

 nutrition of the muscle has become profoundly affected, and that the con- 

 tractile substance has disappeared. Muscular contractility persists for a cer- 

 tain time after death and in muscles separated from the body ; and this fact 

 has been taken advantage of by physiologists in the study of the properties 

 of the muscular tissue. A muscle detached from the living body continues 

 for a time to respire, and it undergoes some of the changes of disassimilation 

 observed in the organism. So long as these changes are restricted within 

 the limits of physical and chemical integrity of the fibre, contractility re- 

 mains. As these processes are very slow in the cold-blooded animals, the 

 excitability of all the parts persists for a considerable time after death. 



