TONUS 547 



The actual mechanism may possibly consist in the prevention of the spontaneous 

 disappearance of the products (lactic acid) caused by stimulation of the muscle 

 system, by which its potential energy is converted into that of tension. 



The "plastic tonus" of skeletal muscle, described by Sherrington in the 

 decerebrate animal, appears to be of similar nature, although the mechanism is 

 in the nerve centres in this case, instead of being peripheral. 



In this state the vasto-crureus, for example, may be maintained at different 

 lengths with the same load, or at the same length with different loads. Thus the 

 fibres may have a different tension with the same length. 



The phenomenon is a reflex from proprio-ceptors in the muscle itself. 



Decerebrate tonus behaves towards inhibitory stimuli in a manner different 

 from that shown by ordinary reflexes. 



There is some evidence to show that this decerebrate rigidity is not accompanied 

 with increase of metabolism, or with comparatively little. 



It is affected reflexly from muscle receptors of the neck and from the labyrinth. 



Certain facts described in the text indicate a relationship of tonus in skeletal 

 muscles to a sympathetic innervation of these muscles. 



The question as to the automatic activity of nerve centres is discussed briefly 

 in the text. 



LITERATURE 



Mechanism in Invertebrates. 

 Von Uexkiill (1912). 



Plastic Tonus. 



Sherrington (1909, 3). 



Relation to Position of Head. 



Magnus and De Kleijn (1912). 



