MUSCULAR CONTRACTION. 471 



or tetanic action. While the electric current is not identi- 

 cal with the nervous force, it is the best substitute we can 

 employ in experiments on muscular contractility, and has 

 the advantage of not affecting the physical and chemical 

 integrity of the nervous and muscular tissue. In studying 

 this subject, we will first follow some of the experiments 

 upon muscular contraction excited artificially, and then 

 apply them, as far as possible, to the strictly physiological 

 actions of muscles. 



There are two classes of phenomena that may be pro- 

 duced by electrical excitation of motor nerves: 1. When 

 the stimulus is applied in the form of a single discharge, it 

 is followed by a single muscular contraction. 2. Under a 

 rapid succession of discharges, the muscle is thrown into a 

 state of permanent, or tetanic contraction. It will greatly 

 facilitate our comprehension of the subject to study these 

 phenomena separately and successively. 



The muscular contraction produced by a single stimulus 

 applied to the nerve is called, by the French, secousse (shock), 

 and by the Germans, Zilckung (convulsion). It will be con- 

 venient for us to employ some term that will express this 

 sudden action of the muscular fibres, as distinguished from 

 the contraction that takes place on repeated stimulation, or 

 in continued muscular effort ; and we will designate a single 

 muscular contraction, then, as spasm, applying the term 

 tetanus, to continued action. 



Spasm Produced ~by Artificial Excitation. If an elec- 

 tric discharge, even very feeble, be applied to a motor nerve 

 connected with a fresh muscle, it is followed by a sudden 

 contraction, succeeded by a rapid relaxation. Under this 

 stimulation, the muscle shortens by about three-tenths of its 

 entire length. 1 The form of the contraction, as registered 

 by the apparatus of Helmholtz, Marey, and others who have 

 applied the so-called graphic method to the study of muscu- 



1 BECLARD, Traite elemental de physiologic, Paris, 1859, p. 507. 



