72 CONTRACTILE ELEMENTS. 



tonicity is only its tendency to assume that form. Neither 

 is the so-called tonicity of the sphincters a property inde- 

 pendent of their elasticity. These muscles, under their 

 natural form, No. 1, are arranged in order to completely 

 close the openings which they circumscribe, so that these 

 openings really do not exist, and are only formed when 

 dilated by a body animated by a certain force, which brings 

 into play the elasticity of the sphincters (tonicity of authors). 

 This tonicity or perfect elasticity of living muscle is under 

 the dependence of the nervous system. When the nerves 

 that belong to these muscles are cut, the tonicity disappears, 

 the muscles become flaccid, and the sphincters are relaxed. 1 

 The origin of tonicity is not yet demonstrated. It has a 

 reflex character. Brondgeest has shown that if the sensory 

 nerves, coming from a part where the muscles are in a per- 

 fect condition of tonicity, be cut, this tonicity will immedi- 

 ately disappear (vide p. 108). 



These considerations concerning the elasticity and the nat- 

 ural form, No. 1, of the muscle, help us to solve a question 

 which is differently answered by other writers: Are the flex- 

 ors of the extremities superior in force to the extensors, or 

 vice versa? From the fact that in repose, or after death, the 

 limbs are generally found to be in a state of semi-flexion, 

 it has been supposed that there is a predominance of force 

 on the part of the flexors ; but where there is repose there 

 is no struggle, and without a struggle there can be no pre- 

 dominance of force. This position only proves that the 

 flexors are shorter than the extensors, and that extension, 

 under these conditions, brings into play the elasticity of 

 the flexors. But suppose the state of repose to cease, and 

 the struggle begin, as, for instance, in tetanus, when all the 

 muscles are contracted, and we shall find all the extremities, 

 and the trunk itself, extended ; whence we conclude, con- 

 trary to the majority of writers, that the extensors are more 

 powerful than their antagonists. 



Chemical Phenomena. The muscle, in its natural form, No. 

 1, lives and receives nourishment, that is to say, its chemical 

 composition is constantly changing : it also breathes ; a muscle, 

 even though detached from the body, as long as it lives con- 

 tinues to absorb oxygen, and give out carbonic acid ; and the 

 longer it can breathe, the longer it lives, as, for instance, when 



1 See Cl. Bernard. " Proprietes des Tissus Vivants." When 

 the nerve of a muscle is cut, the venous blood which flows from the 

 muscle closely resembles arterial blood. 



