IRRITABILITY. 



457 



move a boat by a rope, and before exerting any influence on the 

 boat was compelled to take up a considerable amount of slack. 



Muscular tone is a reflex action depending upon the reception 

 by the cord of afferent impulses, under which stimulation motor 

 impulses are sent out to the muscles ; and if the afferent nerve 

 are cut, the tone disappears. 



Peristalsis. The difference in the manner of contraction of 

 voluntary muscle, as the skeletal muscles, as compared with 

 that of involuntary muscle, as that of the intestines, is very 

 marked, for while the action of the former takes place rapidly 

 and throughout the entire muscle, the action of the latter is 

 slow, and moves from point to point as a wave, at a rate of 

 about 30 mm. per second, the contraction occurring at one part of 

 the intestines while it has disappeared at another, the circular coat 

 being especially active in the movement. It is called also vermicular 

 contraction. When the movement is in the direction opposite to 

 the normal, as in the intestine from below upward, or in the stomach 

 from the pylorus toward the cardia, it is reversed peristalsis. 



^ ^ 



\ 



FIG. 265. Schema to show the direction of currents to be obtained from 

 muscle. The schema represents a cylindric piece of muscle with normal 

 longitudinal surface (o c and 6 d), and two artificial cross sections (a 6 and c d). 

 The position of the equator is shown by line e. The unbroken lines connect points 

 of different potential, and the arrows show the direction which the currents would 

 take were these points connected with a galvanometer. The broken lines connect 

 points of equal potential from which no current would be obtained (Lombard). 



Rhythmicality. Involuntary muscular tissue exhibits the prop- 

 erty of contracting and relaxing with a certain degree of regu- 

 larity or rhythm, as in the spleen, where there are a true systole 

 and a diastole, recurring about once each minute, as demonstrated 

 by the oncometer (p. 338). 



Electric Phenomena (Fig. 265). A normal muscle in a condi- 

 tion of rest is iso-electric i. e., it is " equally electric throughout, 

 and hence has no electric current " ; the same is true of dead 

 muscle. If, however, the muscle is cut, the electrical condition 

 is changed, and if the part that is cut and the normal part are 

 connected to a galvanometer, the movement of the magnet at once 



