538 



MOVEMENTS. 



Muscular Contraction. 



The stimulus of the will, conveyed through the conductors of motor influences from 

 the brain to a muscle or set of muscles, produces an impression upon the muscular fibres 

 and causes them to contract. In parts where the muscles have been exercised and edu- 

 cated, this action is regulated with exquisite nicety, so that the most delicate and rapid, 

 as well as powerful contractions may be produced. Certain movements, not under the 

 control of the will, are produced as the result of unconscious reflection from a nervous 

 centre, along the motor conductors, of an impression made upon sensitive nerves. During 

 this action, certain important phenomena are observed in the muscles themselves. They 

 change in form, consistence, and, to a certain extent, in their constitution ; the different 

 periods of their stimulation, contraction, and relaxation are positive and well-marked ; 

 their nutrition is for the time modified ; they develop galvanic currents ; and, in short, 

 they present a number of general phenomena, distinct from the results of their action, 

 that are more or less interesting and important to the physiologist. 



The most striking of the phenomena accompanying muscular action is shortening and 

 hardening of the fibres. It is only necessary to observe the action of any well-developed 

 muscle to appreciate these changes. The active shortening is shown by the approxima- 

 tion of the points of attachment, and the hardening is sufficiently palpable. The latter 



phenomenon is marked in proportion to 

 the development of the true muscular 

 tissue and its freedom from inert mat- 

 ter, such as fat. We have already seen 

 that it is the muscular substance alone 

 which has the property of contraction ; 

 and we have shown that this action in- 

 creases the consumption of oxygen and 

 probably of other matters, the produc- 

 tion of carbonic acid and some other 

 excrernentitious principles, and that it 

 develops heat. 



Notwithstanding the marked and 

 constant changes in the form and con- 

 sistence of the muscles during contrac- 

 tion, their actual volume is unchanged, 

 or it undergoes modifications so slight 

 that they may practically be disre- 

 garded. Experiments upon this point 

 have been so uniform in their results, 

 that it is hardly necessary to refer to 

 them in detail. All modern observers 

 accept the results of the older experi- 

 ments, in which muscles have been made 

 to contract in a vessel of water con- 

 nected with a small upright tube, show- 

 ing that, when the muscles are in active 

 contraction as the result of a galvanic 

 stimulus, the elevation of the liquid in 

 the tube is unchanged. It is evident, 

 therefore, that a muscle, while it hard- 

 ens and changes in form during contraction, does not sensibly change in its actual volume. 



Changes in the Form of the Muscular Fibres during Contraction. It has been found 

 exceedingly difficult to determine a question apparently so simple as that of the change 



to show that muxcles do not increase 

 in volume during contraction. (Marey.) 

 A, vessel of water, provided with a tube (C) ; B, galvanic ap- 

 paratus ; D, nerve, to which the stimulus is applied. 



