THE CHARACTER OF THE CONTRACTION OF MUSCLE 75 



strontium and calcium. It is frequently associated with lesions of the 

 central nervous system, such as give rise to hemiplegia. It may also 

 appear as a functional disorder in somnambulism and hysteria; in 

 fact, if these conditions have persisted for sometime, it may happen 

 that entire groups of muscles remain permanently in an exaggerated 

 tonic or contractured state. Unless degenerated, muscles of this kind 

 may still be made to give either short twitches or tetani. This fact 

 tends to show that an ordinary contracture is different from a tetanus. 

 It represents rnerely a tonic setting or contraction of the muscle in 

 consequence of an intrinsic or extrinsic excitation and may be classi- 

 fied either as functional or organic, in accordance with its cause and 

 duration. 



Explanations of this phenomenon have been submitted by Fick, 

 Grlitzner and von Frey. More recently Botazzi^ has stated that a 

 contracture represents merely an exaggerated condition of tonus 



Mrscc 



Fig. 41. — Contra ctube of Muscle. 

 A, contracture; B, tonic contracture; C, clonic contracture. 



which serves as an ''internal support" to the muscle. It is a well 

 known fact that tonus varies negatively as well as positively. Hence, 

 if a muscle is stimulated while maintaining its shortened condition, the 

 resulting contraction rises above the level of the contracture, but the 

 quick shortening observed at this time is independent of the slow 

 persistent shortening causing the contracture. It is believed by 

 Botazzi that the former is made possible by the activity of the aniso- 

 tropic substance, and the latter by that of the isotropic substance. 



Under certain conditions, and especially during irritations of the 

 central nervous system, these prolonged tonic contractions frequently 

 assume a rhythmic character. They are then designated as clonic 

 contractions. A brief clonus of certain muscles is often obtained 

 in neurasthenia and hysteria. A very typical one may be produced 

 in certain cases of organic disease of the spiaal cord by suddenly 

 flexing the foot upon the leg. This abrupt stretching of the calf 

 muscles causes them to contract rhythmically for some time, thus 

 giving rise to the so-called ankle-clonus. 



^ Jour, of Physiol., xxi, 1897, 1. 



