284 SPECIAL HISTOLOGY. 



theless, tlie fibres themselves contract to a certain extent, in 

 consequence of which the Avhole muscle becomes tense. This 

 tension must be carefully distinguished from that dependent 

 upon the muscular elasticity, which is generally much less 

 considerable. What has been termed the " tone" — tonus — of 

 muscles, does not in most cases depend upon contraction, but is 

 an elastic tension; I therefore hold, that the posture of the body 

 and the occlusion of the transversely striated sphincters during 

 sleep, has nothing to do with a contraction of the muscles, 

 although such contraction is indubitably requisite to bring the 

 body into this posture. In my opinion, during sleep, all the 

 muscles (of course, with the exception of the respiratory) are 

 at rest, being held in a state of tension, and of antagonism to 

 their opponents merely by their elastic force, and are con- 

 sequently in the condition of a muscle when supported, in a 

 person in the waking state. As for instance, a biceps, when 

 the arm is bent, may immediately lose its tension if the 

 arm be supported, so in the same way may all other voluntary 

 muscles ; only it must not be forgotten, that such a condition 

 of muscular rest may ensue upon all conceivable degrees of 

 contraction. Even the orbicularis oris, when contracted, may 

 be at rest and lose its vital tension. The mouth, nevertheless, 

 will remain closed, for this reason, that although the elastic 

 force, as always after a contraction, will not fail to exert a 

 certain degree of extension upon it, it is unable to open 

 the mouth, owing to its limited amount and inability to 

 overcome the weight of the lips. I do not believe in any 

 muscular " tone," if under that term be understood a long- 

 continued involuntary contraction (though at first excited by 

 the will) ; but am of opinion, that what has been most gene- 

 rally described under this name, is merely an elastic tension, 

 which has been confounded with the contraction upon which 

 it has ensued. From all we know, the nerves are incapable 

 of exciting a long persistent contraction in the striped muscles, 

 but very capable of producing great effects, when the states 

 of contraction and of rest are duly alternated, as for instance 

 in walking, running, &c, and in the heart and respiratory 

 muscles. 



The importance of this view of the nature of the muscular 

 " tone," as regards the physiology of the nerves, is sufficiently 



